REGULATORY IMPACT ANALYSIS
For The
National Emissions Standards for Hazardous Air Pollutants
for Source Categories: Organic Hazardous Air Pollutants from the
Synthetic Organic Chemical Manufacturing Industry and
Other Processes Subject to the Negotiated Regulation
for Equipment Leaks
EPA Document Number EPA-453/R-94-019
March 1994
Emission Standards Division
U.S. Environmental Protection Agency
Office of Air and Radiation
Office of Air Quality Planning and Standards
MD-13, Research Triangle Park, North Carolina 27711
March 1994
This report has been reviewed by the Emission Standards Division of the Office of Air Quality Planning and
Standards, EPA, and approved for publication. Mention of trade names or commercial products is not intended to
constitute endorsement or recommendation for use. Copies of this report are available through the Library
Services Office (MD-35), U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, or from
National Technical Information Services, 5285 Port Royal Road, Springfield, VA 22161.
ii
FOREWORD
This Regulatory Impact Analysis (RIA) was initiated under the
authority of Executive Order 12291. On October 1, 1993, the Order was
rescinded and replaced by Executive Order 12866. The Hazardous Organic
NESHAP RIA at present does not explicitly reflect this change. This is
necessary due to the tight court-ordered schedule for this regulation.
EXECUTIVE SUMMARY
The Environmental Protection Agency (EPA) plans to
promulgate regulations to reduce air pollutant emissions from
synthetic organic chemical manufacturing industry (SOCMI)
facilities in eight source categories, and facilities in seven
non-SOCMI equipment leak source categories. Both new and
existing facilities that meet the Clean Air Act definition of
major sources will be regulated under the authority of sections
112(c) and (d). This decision is based on evidence that SOCMI
facilities release air pollutants that have adverse effects on
both public health and welfare, and the need for additional
control of air pollutants already covered by the Act before the
1990 Amendments.
Section 112(b) lists 189 hazardous air pollutants (HAP's).
The proposed regulation will reduce the emissions of
approximately 150 of the organic chemicals on the list. The
proposed regulation requires sources to achieve emissions limits
reflecting the application of the maximum achievable control
technology (MACT).
The HON regulation covers five types of emission points:
process vents, wastewater, transfer operations, storage vessels,
and equipment leaks. The regulation is made up of two standards,
one covering the first four emission points, and the second
covering equipment leaks. The standard for the first four
emission points was arrived at by the usual regulatory process,
while the equipment leaks standard was developed by regulatory
negotiation.
This regulation is unusual in that the regulation of the
emissions occurring from production of an extremely large number
of chemicals is being targeted at one time. Facilities in
virtually every state shall be affected by the HON. In
determining the regulatory options, the Agency evaluated methods
of determining what technologies should be applied for particular
types of emissions, what would be the minimum level of stringency
for pollutant control, and strategies for obtaining control at
the lowest cost (emission averaging).
The standards will require reductions of emissions of HAP's,
which are a subset of VOC's (volatile organic compounds). The
level of control provided by the regulatory options chosen ranges
from no control for existing small storage tanks (i.e, storage
tanks with less than 10,000 gallon capacity) to 95 percent
control for new process vents. The total amount of emission
reduction for HAP's will be 456,000 Mg (megagrams), and for all
VOC's (including HAP's) approximately 949,000 Mg.
iii
These standards, based on the regulatory options chosen,
will cost the nation $230 million annually by the fifth year
after all affected sources have complied with the regulation
(i.e., 1999), and will require $450 million in capital
investment. The economic impacts for the regulatory options
chosen are expected to be small. Price increases for a large
majority (83 percent) of affected chemicals are expected to be
under 2 percent, and decreases in production for a very large
majority (87 percent) of affected chemicals are expected to be
under 2 percent. Due to the flexible nature of the SOCMI, and
the several process routes possible for production of most SOCMI
chemicals, significant closures for SOCMI facilities are quite
unlikely.
The regulatory alternatives under consideration will not
affect a substantial number of small entities, so a Regulatory
Flexibility Analysis is not required.
The absence of valuation and sufficient exposure-response
information precludes a quantitative benefits analysis at this
time.
iv
Table of Contents
Acronyms, Definitions, Units and Conversions
Chapter 1- Background
1.1 Introduction
1.2 Legal History
1.3 Retrospective on Section 111 and 112 Standards affecting
the SOCMI
1.4 Executive Order 12291
1.5 Guide to the References
Chapter 2- The Proposed HON Emission Standards in Brief
2.1 Subpart F: Applicability of the HON
2.2 Subpart G: Provisions for Process Vents, Wastewater
Operations, Storage Vessels, and Transfer Operations
2.3 Subpart H: Provisions for Equipment Leaks
Chapter 3- The Need for and Consequences of Regulatory Action
3.1 The Problems
3.2 Need for Regulation
3.2.1 Market Failure
3.2.1.1 Air Pollution as an Externality
3.2.1.2 Natural Monopoly
3.2.1.3 Inadequate Information
3.2.2 Insufficient Political and Judicial Forces
3.2.3 Harmful Effects of Hazardous Organic Air Pollutants
3.3 Consequences of Regulation
3.3.1 Consequences if EPA's Emission Reduction Objectives
are Met
3.3.1.1 Allocation of Resources
3.3.1.2 Emissions Reductions and Air Quality
3.3.1.3 Costs
v 3.3.1.4 Energy Impacts
3.3.1.5 Solid Waste and Water Quality Impacts
3.3.1.6 Technological Innovation
3.3.1.7 State Regulation and New Source Review
3.3.1.8 Other Federal Programs
3.3.2 Consequences if EPA's Emission Reduction Objectives
are not Met
Chapter 4- Control Techniques
4.1 Combustion Technology
4.1.1 Incinerators
4.1.1.1 Thermal
4.1.1.1.1 Applicability
4.1.1.1.2 Types of Thermal Incinerators
4.1.1.2 Catalytic
4.1.1.2.1 Applicability
4.1.1.2.2 Types of Catalytic Incinerators
4.1.2 Flares
4.1.2.1 Applicability
4.1.2.2 Efficiency
4.1.2.3 Types of Flares
4.1.2.3.1 Steam-Assisted Flares
4.1.2.3.2 Air-Assisted Flares
4.1.2.3.3 Non-Assisted Flares
4.1.2.3.4 Pressure-Assisted Flares
4.1.2.3.5 Enclosed Ground Flares
4.1.3 Boilers and Process Heaters
4.1.3.1 Description of Boilers
4.1.3.2 Description of Process Heaters
4.1.3.3 Efficiency of Boilers and Process Heaters
4.1.3.4 Applicability of Boilers and Process Heaters
4.2 Product Recovery Devices
4.2.1 Absorbers
4.2.1.1 Absorber Efficiency
4.2.1.2 Applicability of Absorbers
4.2.2 Steam Stripping
4.2.2.1 Description
4.2.2.2 Collecting, Conditioning, and Recovery
4.2.2.3 Efficiency of Control
4.2.2.4 Applicability
vi
4.2.3 Carbon adsorbers
4.2.3.1 Types of Adsorbers
4.2.3.2 Control Efficiency
4.2.3.3 Applicability
4.2.4 Condensers
4.2.4.1 Description
4.2.4.2 Control Efficiency
4.2.4.3 Applicability
4.2.5 Vapor Collection Systems for Loading Racks
4.2.5.1 Description of Vapor Collection Systems
4.2.5.2 Efficiency
4.2.5.3 Applicability
4.3 LDAR
4.3.1 Equipment Description and Controls
4.3.1.1 Pumps
4.3.1.1.1 Seals for Pumps
4.3.1.1.2 Sealless Pumps
4.3.1.2 Compressors
4.3.1.3 Agitators
4.3.1.4 Pressure Relief Devices
4.3.1.5 Open-Ended Lines
4.3.1.6 Sampling Connections
4.3.1.7 Process Valves
4.3.1.7.1 Seals for Valves
4.3.1.7.2 Sealless Valves
4.3.1.8 Connectors
4.3.1.9 Instrumentation Systems
4.3.2 Closed Vent Systems
4.3.3 Work Practices
4.3.3.1 Leak Detection Methods
4.3.3.1.1 Individual Component Survey
4.3.3.1.2 Area Survey
4.3.3.1.3 Fixed Point Monitors
4.3.3.2 Repair Methods
vii
4.4 Internal Floating Roofs
4.4.1 Types of Losses and How They are Controlled
4.4.1.1 Control of Seal Losses
4.4.1.2 Control of Fitting Losses
4.4.1.3 Control of Deck Seam Losses
4.4.2 Applicability
Chapter 5- Regulatory Options
5.1 Introduction
5.2 No Additional EPA Regulation
5.2.1 Judicial System
5.2.2 State and Local Action
5.3 EPA Regulation
5.3.1 Categories, Emission Points, and Floors
5.3.2 Development of MACT and Regulatory Alternatives
5.3.3 Description of MACT and the Regulatory Alternatives
5.3.4 Role of Cost Effectiveness
5.3.5 Economic Incentives: Subsidies, Fees, and Marketable
Permits
Chapter 6- Control Cost and Cost Effectiveness Analysis
6.1 Cost Impacts of Control Technologies
6.2 Cumulative Cost Control Analysis
6.2.1 Building Chemical Trees
6.2.2 Cumulative Control Cost Methodology
6.2.3 Cumulative Control Cost Results
6.3 Costs and Regulatory Options
6.4 National Costs
6.4.1 Monitoring, Recordkeeping, and Reporting Costs
6.4.2 Summary
Chapter 7- Economic Impact Analysis
7.1 Industry Profile
7.1.1 Introduction
7.1.2 Production, Shipments, and Capacity Utilization
7.1.3 Demand and End-Use Markets
7.1.4 Foreign Trade
7.1.5 Pricing
7.1.6 Financial Profile
7.2 Studies of 20 Selected Chemicals
7.2.1 Selection Rationale
viii
7.2.1.1 HON Compliance Costs
7.2.1.2 Volume of Production
7.2.1.3 Basic Feedstock Chemicals
7.2.1.4 Selected Chemicals
7.2.2 Methodology for Selected Studies
7.2.2.1 Profiles
7.2.2.2 Economic Impacts
7.2.2.2.1 The Model
7.2.2.2.2 Compliance
7.2.2.2.3 Pricing
7.2.2.2.4 Elasticities
7.2.2.2.5 Estimating Market Adjustments
7.2.2.2.6 Market Structure
7.2.3 Results of Studies
7.3 Distribution of Cumulative Costs
7.4 Implications for the Rest of the Affected Chemical Industry
7.4.1 Low Cost Impacts
7.4.2 Immediate Cost Impacts
7.4.3 High Cost Impacts
7.5 Small Business Impacts
7.6 Control Device Manufacturing Industry
7.7 Conclusions
Chapter 8- Benefits
8.1 Introduction
8.2 Hazardous Air Pollutant Benefits
8.2.1 Health Benefits of Reduction in Hazardous Air
Pollutants
8.2.2 Welfare Benefits of Reduction in Hazardous Air
Pollutants
8.3 Ozone Benefits
8.3.1 Health Benefits of Reduction in Ambient Ozone
Concentration
8.3.2 Welfare Benefits of Reduction in Ambient Ozone
Concentration
8.4 Particulate Matter Benefits
8.5 Additional Benefits
8.6 Conclusion
ix
Chapter 9- Weighing the Benefits and the Costs
9.1 Introduction
9.2 Economic Efficiency Considerations
9.3 Cost-Effectiveness of HON Induced VOC Emission Reductions
In Ozone Nonattainment Areas
9.4 Conclusions
x
List of Tables Page No.
3-1 HON Chemicals by Classification . . . . . . . . 3-7
5-1 Regulatory Options . . . . . . . . . . . . . . . 5-8
5-2 Floor Elements . . . . . . . . . . . . . . . . . 5-9
6-1 Annualized Control Cost Estimates . . . . . . . 6-3
6-2 Cost Effectiveness for Model Units (Quarterly
Valve Monitoring) . . . . . . . . . . . . . . . 6-4
6-3 Cost Effectiveness for Model Units (Monthly
Valve Monitoring) . . . . . . . . . . . . . . . 6-5
6-4 Annualized Control Cost Estimates for Example
Model Tank . . . . . . . . . . . . . . . . . . . 6-7
6-5 Cost Effectiveness for Wastewater Model Streams . 6-9
6-6 Annual Control Cost Estimates . . . . . . . . . . 6-11
6-7 Cumulative Control Cost Analysis Results for
Total Industry Control (TIC) Options . . . . . . 6-14
6-8 Control Options for Process Vents - Existing
Sources . . . . . . . . . . . . . . . . . . . . . 6-15
6-9 Control Options for Process Vents - New Sources . 6-16
6-10 Control Options for Wastewater - Existing Sources 6-17
6-11 Control Options for Wastewater - New Sources . . .6-18
6-12 Control Options for Transfer Operations - Existing
Sources . . . . . . . . . . . . . . . . . . . . . 6-19
6-13 Control Options for Transfer Operations - New
Sources . . . . . . . . . . . . . . . . . . . . . 6-20
6-14 Control Options for Storage Vessels: Existing
Sources 10,000 to 20,000 Gallon Capacity . . . . 6-21
6-15 Control Options for Storage Vessels: New Sources
10,000 to 20,000 Gallon Capacity . . . . . . . . 6-22
6-16 Control Options for Storage Vessels: Existing
Sources 20,000 to 40,000 Gallon Capacity . . . . 6-23
xi
6-17 Control Options for Storage Vessels: New Sources
20,000 to 40,000 Gallon Capacity . . . . . . . . 6-24
6-18 Control Options for Storage Vessels: Existing
Sources 40,000 Gallon Capacity and Greater . . . 6-25
6-19 Control Options for Storage Vessels: New Sources
40,000 Gallon Capacity and Greater . . . . . . . 6-26
6-20 Annualized Costs of Monitoring, Recordkeeping, and
Reporting from HON Compliance . . . . . . . . . 6-27
6-21 National Control Cost Impacts in the Fifth Year . 6-28
7-1 SIC Codes for the SOCMI . . . . . . . . . . . . . 7-4
7-2 Selection of Twenty SOCMI Chemicals . . . . . . . 7-11
7-3 Summary of Market Adjustments . . . . . . . . . . 7-20
7-4 Likelihood of Closure and Process Change Under TIC
Controls . . . . . . . . . . . . . . . . . . . . 7-22
7-5 Distribution of HON Chemicals by Percentage Cost
Increase and Annual Production (106 kg): TIC
Option . . . . . . . . . . . . . . . . . . . . . 7-25
7-6 Summary of Percentage Price Increases for Selected
Chemicals . . . . . . . . . . . . . . . . . . . . 7-26
7-7 1990 Sales and Employment of Selected SOCMI
Members . . . . . . . . . . . . . . . . . . . . . 7-29
xii
Acronyms, Definitions, and Conversions
Acronyms
BID Background Information Document
CAA Clean Air Act
CAAA Clean Air Act Amendments of 1990
CPP Chemical Production Processes
EPA Environmental Protection Agency
HAP Hazardous Air Pollutant
HON Hazardous Organic NESHAP (NESHAP is defined
below)
LDAR Leak Detection and Repair
LEL Lower Explosive Limit
MACT Maximum Achievable Control Technology
NAAQS National Ambient Air Quality Standards
NESHAP National Emission Standards for Hazardous Air
Pollutants
NPDES National Pollutant Discharge Elimination
System
OAQPS Office of Air Quality Planning and Standards
OSHA Occupational Safety and Health Administration
POTW Publicly Owned Treatment Works
RACT Reasonably Available Control Technology
RFA Regulatory Flexibility Act; also Regulatory
Flexibility Analysis
SIC Standard Industrial Classification
SIP State Implementation Plan
SOCMI Synthetic Organic Chemical Manufacturing
Industry
xiii
TLV Threshold Limit Value
TRE Total Resource Effectiveness
VOC Volatile Organic Compound
VHAP Volatile Hazardous Air Pollutant
VOHAP Volatile Organic Hazardous Air Pollutant
VVHAP Very Volatile Hazardous Air Pollutant
Chemical Symbols
CO2 Carbon dioxide
CO Carbon monoxide
HCl Hydrochloric acid
NH3 Ammonia
NOx Nitrogen oxide
O3 Ozone
SO2 Sulfur dioxide
Economic, Regulatory, and Scientific Terms
Annual Cost Annualized capital plus annual operating
costs
Area Source Any emission source emitting less than
10 tons per year of a single HAP or 25
tons or more per year of two or more
HAPs, unless EPA establishes a lesser
quantity cutoff
bbl One barrel; equal to 42 gallons
Btu One British thermal unit
C/E Cost effectiveness, which is the net
present value of cost of emission
control divided by the present value of
emission reductions in megagrams
(defined below)
xiv
Gg One gigagram, or 1,000,000 kilograms
Gm One gram
kw One kilowatt, or 1,000 watts
lpm One liter per minute
Major Source Any emission source emitting 10 tons
or more a year of a single HAP or 25
tons or more a year of two or more HAPs
Mg One megagram, or 1,000 kilograms
MJ One megajoule, or .949 Btu
MW One megawatt, or .949 Btu per second
ppmv parts per million by volume (air)
ppmw parts per million in water
psia Pounds per square inch absolute
112(b) Section of Title III in the CAAA that
requires the EPA to promulgate
regulations establishing emission
standards for new and existing sources
of HAPs on the list of 189 HAPs in the
title
scfm One standard cubic foot per minute
Title I The first title of the CAAA; this title
classifies nonattainment areas, sets
attainment schedules, and prescribes
control measures for O3, CO, PM-10, and
for SOx, NOx, and Lead
Title III The third title of the CAAA; this title
lists the 189 HAPs to be controlled with
MACT, as well as the control of major
and area sources, incinerator air
emissions, accidental releases, and
special studies
TIC Total Industry Control; the most
stringent regulatory option for each
source type
xv
Units and Conversions
This report uses metric units, some of which may not be
familiar to all readers. The EPA is required by Congress to use
metric measurements. The following is a short guide to the units
and their conversions.
Conversions
To Approximate As Multiply by
_________________________________________________________________
Mg (megagram) Ton (2,000 lb) 1.1
scm (standard scf(standard
cubic meter) cubic foot) 35.3
MJ (megajoule) Btu (British 949
thermal unit)
MW (megawatt) Btu/second 949
kg (kilogram) lb (pound) 2.2
_________________________________________________________________
xvi
CHAPTER 1
BACKGROUND
1.1 Introduction
The NESHAP being promulgated is commonly known as the
hazardous organic NESHAP, or HON. The HON would regulate
emissions of certain organic hazardous air pollutants from SOCMI
process units. A SOCMI process unit is defined as a unit
producing one or more of a list of SOCMI chemicals. A SOCMI
process unit is only covered by the HON if it either 1) produces
a HAP as a product, by-product, co-product, or intermediate; or
2) uses a HAP as a reactant or raw material to produce a SOCMI
chemical. Seven non-SOCMI source categories would also be
regulated under the proposed equipment leaks standard (see
Section 2.1): styrene/butadiene rubber production; polybutadiene
production; chlorine production; pesticide production;
chlorinated hydrocarbon use; pharmaceutical production; and
miscellaneous butadiene use.
1.2 Legal History
On November 15, 1990, the Clean Air Act was amended
significantly. Section 112 was substantially revised at that
time altering the basic framework for regulating emissions of
toxic air pollutants from stationary sources.
Prior to the amendments passed in 1990, Section 112 required
the Administrator to list air pollutants for which he intended to
establish NESHAPs. Within 180 days after the listing of such air
pollutants, regulations were to be proposed. Final regulations
were to be issued in another 180 days. Thus, once the
Administrator added a pollutant to the Section 112 list, a final
NESHAP for that pollutant had to be issued within one year. The
statute itself did not contain a list of hazardous air
pollutants.
The amendments enacted in 1990 altered the preexisting
scheme of Section 112 fundamentally. Instead of requiring the
Administrator to determine which air pollutants ought to be
listed and regulated as hazardous air pollutants, Congress
provided a list of 189 hazardous air pollutants in the statute
itself. EPA may revise that list only in conformance with clear
statutory guidelines. The Agency is now required to develop a
list of all categories and subcategories of sources emitting any
of the listed pollutants, and develop technology-based standards
to control such emissions. Thus, these standards are to be based
on the sources of the emissions rather than being set pollutant
by pollutant as in the past and are no longer to be risk based.
Regulations for all source categories must be promulgated within
10 years of enactment of the amendments. Generally, assessment
and control of any remaining unacceptable health risk is to occur
8 years after the technology-based standards are promulgated.
However, for the HON the residual risk assessment is to be
conducted 9 years after promulgation.
1.3 Retrospective on Section 111 and 112 Standards Affecting the
SOCMI
The provisions of the promulgated standards incorporate
data, information, and experience gained by EPA through previous
rulemaking efforts involving similar sources. Information on
control technology applicability, performance, and cost were
available from previous NSPS and NESHAP regulatory development
efforts. This information was considered in selecting MACT and
in developing the proposed standards.
Under the NSPS program, EPA has promulgated NSPS for SOCMI
air oxidation and distillation process vents; SOCMI emissions
from equipment leaks; petroleum refinery equipment leaks; and VOC
emissions from volatile organic liquid storage vessels.
Similarly, under the NESHAP program, regulations were promulgated
for benzene storage tanks, transfer racks and wastewater
emissions , and for vinyl chlorine and benzene equipment leaks.
In the development of the HON, this previously collected array of
information was carefully reconsidered in light of the provisions
of the CAA of 1990. This technical information is presented in
detail in the HON BID.
Each of these previous efforts regulates some sources or
chemicals that would be subject to the HON, but none of them
comprehensively regulate emissions of all of the organic HAP's
emitted from new and existing SOCMI process units from all
emission points. The HON would regulate all five of the emission
points at each affected SOCMI source (see Section 2.1), and would
regulate emissions of any of the listed organic HAP's. The first
of the HON standards (Subpart G) was developed through usual
regulatory procedures, and covers four of the five emission
points. An analysis of various regulatory alternatives was
conducted for this standard. The second, the equipment leaks
NESHAPs (Subpart H), was developed through the regulatory
negotiation process, and, as a result, a formal analysis of
regulatory alternatives was not conducted.
The negotiators in this process originally were to develop
standards for equipment leaks for 13 source categories that would
be affected by standards already under development. The
standards under development would have applied to only eight
organic chemicals. However, during negotiation of the
amendments to the CAA, EPA expanded the scope of the standards to
include all SOCMI processes that produce or use as a reactant one
of the 149 organics listed in the CAA list of 189 HAP's (55 FR
8984, March 9, 1990; 55 FR 14349, April 17, 1990). Petroleum
refinery processes were not to be covered, however.
1.4 Executive Order 12291
The President issued Executive Order 12291 on February 17,
1981. It requires EPA to prepare regulatory impact analyses
(RIAs) for all regulations having "major" impacts. An impact is
considered "major" if the annual effect on the economy is $100
million or more, and/or may result in a "significant" increase in
prices. The EPA considers the HON regulations to be major and
thus is issuing this RIA.
Along with requiring an analysis of benefits and costs, E.O.
12291 specifies that EPA, to the extent allowed by the Clean Air
Act and court orders, demonstrate 1) that the benefits of the HON
regulations will outweigh the costs and 2) that the maximum level
of net benefits will be reached. Chapter 8 describes the
benefits in detail. As explained in that chapter, EPA cannot
quantify some of the benefits. Thus, EPA cannot show
quantitatively that the benefits of the regulations will outweigh
the costs. Despite this problem of quantifying benefits, EPA has
determined that CAA Sec. 112 requires issuance of the HON
regulations at the stringency level described in Chapter 2. For
more information, refer to Chapter 9 and the Federal Register
preambles to the HON.
1.5 Guide to the References
Most of this RIA is a summary of research reports, analyses,
correspondence, minutes of various meetings and hearings, policy
directives, legal notices, laws, regulations, and other documents
relating to the development of CAA Sec. 112 regulations for SOCMI
(and certain non-SOCMI) facilities. The principal references are
listed in the back of the chapter on the subject of interest to
you. Consult these references, as well as the preambles that
accompany proposal of the HON in the Federal Register, for more
detailed information. References are held in public dockets and
are available for inspection and copying-the latter may require a
fee-during normal business hours. For more information on the
docket, contact:
Air and Radiation Docket
and Information Center (LE-131)
Room M-1500,
Waterside Mall
401 M Street, SW
Washington, DC 20460
Hours: 8:00 a.m. to 4:00 p.m.
Phone No.: (202) 382-7549
FAX: (202) 260-4000
CHAPTER 2
THE PROPOSED HON EMISSION STANDARDS IN BRIEF
The HON is organized in four subparts. Subpart F provides a
description of the applicability of the standards. Subparts G,
H, and I provide the control, monitoring, recordkeeping and
reporting requirements for the standard.
2.1 Subpart F: Applicability of the HON
The HON will regulate certain components of new and existing
major sources, as defined by Section 112(a), in the SOCMI and 7
non-SOCMI equipment leak source categories.
To define the SOCMI source category, Subpart F includes a
list of organic HAP's and a list of approximately 400 synthetic
organic chemicals produced by the SOCMI as commercial products.
The "chemical manufacturing processes" used to produce these 400
chemicals can, but do not always, result in organic HAP
emissions. Only those processes resulting in HAP emissions are
subject to the standard.
As proposed, Subpart F defines "source" for the SOCMI source
category as all process vents, storage vessels, transfer racks,
wastewater streams, and equipment leaks in the organic HAP
emitting chemical manufacturing processes that are subject to the
HON. To be subject to the HON, a chemical manufacturing process
must be used to produce one or more of the approximately 400
SOCMI chemicals listed in Subpart F, and have an organic HAP as
either 1) a product, by-product, co-product, or intermediate; or
2) a raw material in the production of another SOCMI chemical
product.
To be part of the same source, chemical manufacturing
processes that are subject to the HON must also be located within
a contiguous plant site under common control.
Subpart G will apply to the following kinds of emission
points in SOCMI chemical manufacturing processes: process vents,
wastewater operations, storage vessels and transfer operations.
Subpart H will apply to the equipment leaks in SOCMI
chemical manufacturing processes, while Subpart I will apply to
these non-SOCMI equipment leak source categories:
styrene/butadiene rubber production; polybutadiene production;
chlorine production; pesticide production; chlorinated
hydrocarbon use; pharmaceutical production; and miscellaneous
butadiene use.
2.2 Subpart G: Provisions for Process Vents, Wastewater
Operations, Storage Vessels and Transfer Operations
Subpart G of the proposed rule would require the owner or
operator of a source to limit source-wide emissions of HAP's.
Subpart G provides specific instructions for determining how much
emissions must be reduced at each source. The required emissions
reduction is determined by how much emissions would be reduced if
a "reference control technology" were applied to all the
"Group 1" emission points in the source.
The proposed standard specifies the reference control
technology for each kind of point. Group 1 points are those
points that meet the applicability criteria included in the
control requirements for the proposed standard. The reference
control technologies and applicability criteria for Group 1
points are specified in Subpart G of the standard as well as the
definition list in the HON preamble.
The owner or operator of a source can use two methods to
comply with the emissions reduction requirement. Either method
can be used exclusively, or the two can be combined.
The first method is to apply the reference control
technology, or an equivalent technology, to Group 1 emission
points; thereby achieving some part of the required emission
reduction at each Group 1 point that is controlled.
The second method is to average emissions from two or more
emission points such that the overall required emission reduction
is achieved. With the second method, emissions averaging, the
owner or operator does not have to apply the reference control
technology to each Group 1 point, as long as an equivalent or
greater emissions reduction is achieved elsewhere in the source.
The proposal provides specific procedures that must be followed
to utilize emissions averaging as a means of compliance with the
HON. These procedures are summarized in Section III.B.6 of this
notice.
Although equipment leaks are included in the definition of
source for the SOCMI source category, equipment leaks can not be
included in the emissions averages because: 1) the equipment
leaks standard has no fixed performance level; and 2) no method
currently exists for determining the magnitude of allowable
emissions to assign equipment leaks for purposes of emissions
averaging. When this methodology is developed, EPA will consider
allowing equipment leak emissions to be included in emissions
averages.
2.3 Subpart H: Provisions for Equipment Leaks in SOCMI
Processes
The provisions in Subpart H of the proposed rule were
developed using regulatory negotiation and represent an extension
of existing equipment leak control techniques to the eight source
categories regulated by this final rule.
Subpart H proposes work practice requirements to reduce
emissions from equipment leaks for equipment in volatile HAP
service for 300 or more hours per year. To be in volatile HAP
service is to be in contact with or containing fluid that is 5
percent or more HAP.
The following types of equipment are subject to the proposed
standards in Subpart H: valves, pumps, connectors, compressors,
pressure relief devices, open-ended lines, sampling connection
systems, instrumentation systems, agitators, product accumulator
vessels, and closed-vent systems and control devices.
2.4 Subpart I: Provisions for Equipment Leaks in non-SOCMI
Processes
In contrast to the sources in the SOCMI source category,
sources in the non-SOCMI processes would be covered by this
subpart and subpart H. For these processes, the source would
include every type of equipment subject to the proposed standards
in Subpart H except product accumulator vessels and closed-vent
systems and control devices. The Agency is also considering
regulating the other kinds of emission points in these processes
in future section 112 standards.
CHAPTER 3
THE NEED FOR AND CONSEQUENCES OF REGULATORY ACTION
3.1 The Problems
One of the concerns about potential threats to human health
and the environment from chemical manufacturing plants is air
emissions of hazardous organics. Hazardous chemicals can also
find their way into underground water supplies, and in the solid
waste stream. Health risks from emissions of hazardous organics
into the air include increases in cancer incidences and other
toxic effects. This chapter discusses the need for and
consequences of regulating of hazardous air emissions from
chemical plants. Section 3.2.3 provides more detail on the
health risks of these pollutants.
3.2 Need for Regulation
3.2.1 Market Failure
The U.S. Office of Management and Budget (OMB) directs
regulatory agencies to demonstrate the need for a major rule.1
The regulatory impact analysis must show that a market failure
exists and that it cannot be resolved by measures other than
Federal regulation. Market failures are categorized by OMB as
externalities, natural monopolies, or inadequate information.
The following paragraphs address the three categories of market
failure. Chapter 5 discusses the regulatory options and makes a
case for the necessity of a Federal regulation.
3.2.1.1 Air Pollution as an Externality
Air pollution is an example of a negative externality. This
means that, in the absence of government regulation, the
decisions of generators of air pollution do not fully reflect the
costs associated with that pollution. For a chemical plant
operator, air pollution from the plant is a product or by-product
that can be disposed of cheaply by venting it to the atmosphere.
Left to their own devices, many plant operators treat air as a
free good and do not fully "internalize" the damage caused by
emissions. This damage is born by society, and the receptors---
the people who are the ones adversely affected by the pollution--
-are not able to collect compensation to offset their costs.
They cannot collect compensation because the adverse effects,
like increased risks of morbidity and mortality, are by and
large, non-market goods, that is, goods that are not explicitly
and routinely traded in organized free markets.
Consider an example. It may be somewhat unreal, but it
illustrates why air pollution is a market externality. A young
man estimates that over his remaining lifetime he has a risk of
getting cancer of, let's say, 4 chances in 10. A new chemical
plant is being constructed in his neighborhood, and he
pessimistically calculates that the added pollution to his own
environment will boost his odds of getting cancer to, say, 5
chances in 10. He walks up to the people owning the chemical
plant and offers to "sell his exposure" to the plant's air
pollution for a bargain basement price of just $5 a day. For his
efforts he gets no more than a laugh. What's wrong? Most young
men either would be unwilling to even consider such a
transaction, or, if they were willing, they would not know enough
about their futures and about the effects of the pollution to set
such a precise price. Furthermore, even if they were willing and
did have a price, they would not have any good way of coming to
terms with the plant owners. The plant owners would ordinarily
not attempt such a transaction for many of the same reasons the
young man would not attempt it. Given that the plant owners and
the young man could accept such a transaction, if transactions
costs were low enough and all others parties' concerns were
negligible, a transaction which would internalize the air
pollution externality could occur, as explained in Coase's
theorem. However, it is unusual for this type of externality to
be eliminated by this route.
How would it help to force chemical firms either to
compensate the people suffering the consequences of the
pollution, or simply to reduce the pollution? Where there are
negative externalities like air pollution, the market price of
goods and services does not reflect the costs, borne by receptors
of air pollution, generated in the course of producing the goods
and services. Government regulation can be used to improve the
situation. The NESHAP's will force chemical plant owners and
operators to reduce the quantity hazardous organic air pollutants
they emit. With the NESHAP's in effect, what chemical plant
owners and operators must spend to produce chemicals will more
closely approximate the full social costs of production. In the
long run, chemical firms will be forced to increase prices of the
products sold in order to cover total production costs. Thus,
prices will rise, consumers accordingly will reduce their demand
for chemical products, and hence less chemicals will be provided.
The more the costs of pollution are internalized by the chemical
plants, the greater the improvement in the way the market
functions. If we could internalize all negative externalities---
including, of course, those from chemical plants---society's
allocation of resources would be improved.
3.2.1.2 Natural Monopoly
In some respects, chemical firms can tend toward "natural"
monopolies. There are large economies of scale in chemical
manufacturing; the heavy up-front capital needed to construct a
plant acts as a barrier to entry. Due to the necessity for heavy
up-front capital, most chemical markets are oligopolies (i.e.,
dominated by a few firms). Thus, each firm in this type of
market possesses more monopoly power than if each firm were
operating in a more competitive market. The NESHAP's are not
designed to address this circumstance, and will not reduce the
tendency of chemical production markets toward monopoly or
oligopoly.
3.2.1.3 Inadequate Information
The third category of potential market failure that
sometimes is used to justify government regulation is inadequate
information.
Some chemical manufacturing facilities can reduce costs by
installing air pollution control devices, reducing leaks or
recycling hazardous organic chemicals. Due to lack of
information, some of these facilities do not install such
systems. The NESHAP's would require the collection of
information that may give a chemical plant owner enough data to
make an informed decision on whether or not control devices are
the best option.
3.2.2 Insufficient Political and Judicial Forces
There are a variety of reasons why many emission sources, in
EPA's judgment, should be subject to reasonably uniform national
standards. The principal reasons:
* Air pollution crosses jurisdictional lines.
* The people who breathe the air pollution travel freely,
sometimes coming in contact with air pollution outside their
home jurisdiction.
* Harmful effects of air pollution detract from the nation's
health and welfare regardless of whether the air pollution
and harmful effects are localized.
* Uniform national standards, unlike potentially piecemeal
local standards, are not likely to create artificial
incentives or artificial disincentives for economic
development in any particular locality.
* One uniform set of requirements and procedures can reduce
paperwork and frustration for firms that must comply with
emission regulations across the country.
None of these reasons, by itself, provides overriding justi-
fication for Federal action in the case at hand. Collectively,
however, the reasons argue against reliance on state and local
action to control hazardous organic air emissions from chemical
plants.
Citizens, as well as EPA, may sue state and local
governments to force them to control hazardous organic air
emissions from chemical plants. Litigation under both the CAA
and RCRA is possible. However, EPA has not explored ways of
improving the judicial route so that it might serve as a
substitute for action under Section 111 of the CAA.
3.2.3 Harmful Effects of Hazardous Organic Air Emissions
Only health effects associated with hazardous organic air
emissions are addressed in these NESHAP's. Direct exposure to
air emissions can occur through inhalation, soil ingestion, the
food chain, and dermal contact.
Out of the 189 hazardous air pollutants identified in the
Clean Air Act Amendments, 149 chemicals are being regulated by
the HON; however, of these 149, only 110 are regulated by
Subpart G of the HON. Of these 110 chemicals, half are known or
suspected carcinogens and approximately half are not known to
cancer in either humans or animals. The EPA has devised a
system, which was adapted from one developed by the International
Agency for Research on Cancer (IARC), for classifying chemicals
based on the weight-of-evidence.2 Three of the carcinogens,
benzene, vinyl chloride, and bis(chloromethyl)ether, are
classified as group A or known human carcinogens. This means
that there is sufficient evidence to support that the chemical
causes an increased risk of cancer in humans. One of these known
human carcinogens, benzene, is a concern to the EPA because long
term exposure to this chemical has been known to cause leukemia
in humans. While this is the most well known effect, benzene
exposure is also associated with aplastic anemia, multiple
myeloma, lymphomas, pancytopenia, chromosomal breakages, and
weakening of bone marrow (53 FR 28504; July 28, 1988).
Vinyl chloride is another known human carcinogen. Exposure
to vinyl chloride has been known to cause angiosarcoma of the
liver. It has also been associated with other forms of cancer as
well as noncancerous effects. The noncancerous effects include
liver damage and, potentially, chemical mutagenicity and
teratogenicity (40 FR 59533; Dec. 24, 1975).
Most of the carcinogenic chemicals on the list are
classified as group B or probable human carcinogens. This means
that there is limited or no data on human carcinogenicity, but
sufficient data on animal carcinogenicity to suggest possible
increased human risks as well. Some examples of the twenty-five
probable human carcinogens on the list are 1,3-butadiene, carbon
tetrachloride, acetaldehyde, benzyl chloride, and
tetrachloroethylene. In several rat studies, 1,3-butadiene
caused several tumors on different organs (50 FR,
pp. 41466-41468, Oct. 10, 1985). In addition, at high concen-
trations, it can cause coughing, fatigue, sleepiness, headache,
giddiness, unconsciousness, respiratory paralysis, and death.3
Carbon tetrachloride is known to cause cancer in animals and is
thus suspected to cause cancer in humans. It may also increase
stratospheric ozone depletion, which can cause a rise in the
incidence of skin cancer and possibly various other effects (50
FR 32621; Aug. 13, 1985).
Twelve of the HON chemicals are considered to be group C or
possible human carcinogens. A few of these are acrolein,
vinylidene chloride, allyl chloride, and 1,1,2,2-
tetrachloroethane. For these chemicals, there is either
inadequate data or no data on human carcinogenicity, and there is
limited data on animal carcinogenicity.
The remaining 70 HON chemicals do not show evidence of
carcinogenicity. However, they are considered hazardous because
of the other significant adverse health effects with which they
are associated. Some examples of these chemicals include methyl
chloroform, and triethylamine. One of these chemicals,
chloroprene, causes various effects at different lengths of
exposure. Possible effects from acute exposure range from
vertigo and nausea at very short exposure periods to liver damage
and death after a few hours. Subchronic toxicity effects
observed in human studies include fatigue, pressure and chest
pain, dermatitis and hair loss. Subchronic animal studies at
higher concentrations and for longer periods of time revealed
effects ranging from small increases in underdevelopment and
behavioral effects to lung and liver tissue damage and death (50
FR 39632; Sept. 27, 1985).
Methyl chloroform is another noncarcinogen that is a concern
to the EPA. Acute exposure to this chemical may result in small
changes in perception, while subchronic effects of slight
histological and biochemical alterations have been observed in
mice livers. At high concentrations, liver necrosis has been
reported.
The following table lists the HON chemicals by CAS number
and their classification by their carcinogenic effect, if any.
Table 3-1. HON Chemicals by Classification
CAS Chemical Classification*
Number Name
_________________________________________________________________
71432 Benzene A
542811 Bis(chloromethyl)ether A
75014 Vinyl chloride A
107131 Acrylonitrile B1
75218 Ethylene oxide B1
50000 Formaldehyde B1
75070 Acetaldehyde B2
79107 Acrylic acid B2
62533 Aniline B2
98077 Benzotrichloride B2
100447 Benzyl chloride B2
75252 Bromoform B2
106990 1,3-Butadiene B2
56235 Carbon tetrachloride B2
67663 Chloroform B2
111444 Dichloroethyl ether B2
542756 1,3-Dichloropropene B2
77781 Dimethyl sulfate B2
123911 1,4-Dioxane B2
122667 1,2-Diphenylhydrazine B2
106898 Epichlorohydrin B2
106934 Ethylene dibromide B2
107062 Ethylene dichloride B2
118741 Hexachlorobenzene B2
75092 Methylene chloride B2
75569 Propylene oxide B2
127184 Tetrachloroethylene B2/C
79016 Trichloroethylene B2/C
107028 Acrolein C
107051 Allyl chloride C
75343 Ethylidene dichloride C
87683 Hexachlorobutadiene C
67721 Hexachloroethane C
78591 Isophorone C
79345 1,1,2,2-Tetrachloroethane C
79005 1,1,2-Trichloroethane C
75354 Vinylidene chloride C
60355 Acetamide B2
75058 Acetonitrile NC
98862 Acetophenone NC
79061 Acrylamide NC
90040 o-Anisidine 2B (IARC)
92524 Biphenyl NC
HON Chemicals by Classification (Continued)
CAS Chemical Classification*
Number Name
_________________________________________________________________
105602 Caprolactam NC
75150 Carbon disulfide NC
79118 Chloroacetic acid NC
532274 2-Chloroacetophenone NC
108907 Chlorobenzene NC
126998 Chloroprene Under EPA review
1319773 Cresols/Cresylic acid (isomers and
mixture) C
95487 o-Cresols/Cresylic acid (isomers and
mixture) C
108394 m-Cresols/Cresylic acid (isomers and
mixture) C
106445 p-Cresols/Cresylic acid (isomers and
mixture) C
98828 Cumene NC
106467 1,4-Dichlorobenzene B2
111422 Diethanolamine NC
121697 N,N-Dimethylaniline NC
64675 Diethyl sulfate 2A (IARC)
119937 3,3'-Dimethylbenzidine B2
68122 N,N-Dimethylformamide 2B (IARC)
57147 1,1-Dimethylhydrazine B2
131113 Dimethyl phthalate NC
51285 2,4-Dinitrophenol NC
121142 2,4-Dinitrotoluene B2
140885 Ethyl acrylate B2
100414 Ethylbenzene NC
75003 Ethyl chloride NC
107211 Ethylene glycol NC
0 Glycol ethers NC
123319 Hydroquinone Under EPA Review
108316 Maleic anhydride NC
67561 Methanol NC
74839 Methyl bromide NC
74873 Methyl chloride NC
71556 Methyl chloroform NC
78933 Methyl ethyl ketone NC
60344 Methylhydrazine B2
108101 Methyl isobutyl ketone NC
624839 Methyl isocyanate NC
80626 Methyl methacrylate NC
1634044 Methyl tert-butyl ether NC
101688 Methylenediphenyl diisocyanate (MDI) NC
HON Chemicals by Classification (Continued)
CAS Chemical Classification*
Number Name
_________________________________________________________________
101779 4,4-Methylenedianiline 2B (IARC)
91203 Naphthalene NC
98953 Nitrobenzene NC
100027 4-Nitrophenol NC
79469 4-Nitropropane B2
108952 Phenol NC
106503 p-Phenylenediamine NC
75445 Phosgene NC
85449 Phthalic anhydride NC
0 Polycyclic organic matter B2
(depending on
specific constituents)
57578 beta-propiolactone B2
123386 Propionaldehyde NC
78875 Propylene dichloride B2
106514 Quinone NC
100425 Styrene C
108883 Toluene NC
95807 2,4-Toluenediamine B2
584849 2,4-Toluene diisocyanate B2
95534 o-Toluidine B2
120821 1,2,4-Trichlorobenzene NC
95954 2,4,5-Trichlorophenol Under EPA Review
121448 Triethylamine NC
540841 2,2,4-Trimethylpentane NC
108054 Vinyl acetate C
1330207 Xylenes NC
95476 o-Xylene NC
108383 m-Xylene NC
106423 p-Xylene NC
*The carcinogens included in this list are chemicals which have
been designated as group A, B1, B2, C, 2A, or 2B by IRIS, CRAVE
verification, IARC, or a Health Assessment Document. NC stands
for without evidence of carcinogenicity.
3.3 Consequences of Regulation
3.3.1 Consequences if EPA's Emission Reduction Objectives are
Met
3.3.1.1 Allocation of Resources
There will be improved allocation of resources associated
with chemical manufacturing. Specifically, more of the costs of
the harmful effects of chemical production will be internalized
by chemical plants. This, in turn, will affect consumers'
decisions on whether, where, how, and how much chemicals to use.
To the extent these newly-internalized costs are then passed
along to the people who use the chemical products, and to the
extent these people are free to buy as much or as little products
as they wish, they will purchase less (relative to their
purchases of other competing services). If this same process of
internalizing negative externalities occurs throughout the entire
chemical manufacturing industry, an economically optimal
situation is approached. This is the situation when the marginal
cost of resources devoted to chemical production equals the
marginal value of the products to the people who are using the
chemical products. There are many "ifs" in this chain of events.
It is easy to cite situations where the air pollution control
costs will not ripple through as suggested here and affect
decisions by the consumers of chemical products. Nevertheless,
in the aggregate and in the long run, the NESHAP's will move
society toward this economically optimal situation.
3.3.1.2 Emissions Reductions and Air Quality
Under the proposed standard, it is estimated that emissions
of HAP's will be reduced by 460,000 megagrams annually by 1997
and emissions of VOC's (which includes HAP's) will be reduced by
950,000 megagrams annually by 1997. (For more information refer
to Chapter 8 of this document.) Air quality will improve. (This
analysis does not translate emission reductions into ambient air
quality improvements.)
There will be a slight increase in emissions of carbon
monoxide and nitrogen oxides resulting from the on-site
combustion of fossil fuels as part of control device operations.
These estimates are 1,650 megagrams per year of carbon monoxide
and 16,600 megagrams per year of nitrogen oxides.
3.3.1.3 Costs and Benefits
The national annual cost of emission control, including
monitoring, recordkeeping, and reporting will increase by about
$226 million by 1997. Expected benefits include reduced risks
for certain adverse health and welfare effects from lower levels
of HAP's and VOC's emissions. (See Chapters 8 and 9.)
3.3.1.4 Energy Impacts
Increases in energy use were estimated for steam, natural
gas, and electricity. These three types of energy were compared
and totaled on a barrels of energy (BOE) basis. Under the
standard, estimates for increases in total energy use are 2.69
billion J/yr (470,000 BOE/yr) of electricity, 6.56 billion J/yr
(1,150,000 BOE/yr) of natural gas, and 2.85 billion J/yr (500,000
BOE/yr) of steam. This equates to 2.12 million BOE/yr (15.5
billion J/yr).
3.3.1.5 Solid Waste and Water Quality
Impacts for water pollution and solid waste were judged to
be negligible and were not quantified. The required controls do
not generate any solid waste. However, in time, as collection
and control equipment is replaced, the components themselves may
become part of the solid waste stream.
3.3.1.6 Technological Innovation
Section 112 of the CAA regulations serve to disseminate both
pollution control and chemical manufacturing technology, and to
stimulate further technological development. Chemical facility
constructors have the freedom to seek the most economical way to
comply with standards. The NESHAP's may promote the sharing of
technology with other countries, and probably will open new
directions of research in chemical manufacturing technology.
3.3.1.7 State Regulation and New Source Review
State regulatory programs will be strengthened. The
NESHAP's will be delegated to the states for enforcement as part
of their operating permitting programs if they are approved the
EPA. Assuming states do not pull resources from other programs
to handle their enlarged responsibilities, there will be a
natural strengthening of state air pollution control staffs.
Recognition that the NESHAP's are effectively reducing emissions
will expedite the state process of reviewing applications for new
chemical plants and issuing permits for their construction and
operation. There will be less controversy involved. Finally,
state regulations will be uniform, and the disadvantages of the
piecemeal approach to emission regulation will be avoided.
3.3.1.8 Other Federal Programs
The effects of the NESHAP's on other Federal regulatory
programs have not been thoroughly investigated. Under Title I
there are CTGs (control technology guidelines) that specify
levels of control for VOC's in nonattainment areas. Any NESHAP
shall require control in attainment and nonattainment areas.
While the baseline for the HON incorporates present CTGs, the
effect from new CTGs is not incorporated. There is possible
overlap between these new CTGs and HON for facilities in
nonattainment areas. The extent of this overlap has not been
defined.
3.3.2 Consequences if EPA's Emission Reduction Objectives are
not Met
The most obvious consequence of failure to meet EPA's
emission reduction objectives would be emissions reductions and
benefits that are not as large as EPA is projecting. However,
costs are not likely to be as large either. Whether it is
noncompliance from ignorance or error, or from willful intent, or
simply slow compliance due to owners and/or operators exercising
legal delays, poor compliance can save some facilities money.
Unless states respond by pouring more resources into enforcement,
then poor compliance could bring with it smaller aggregate
nationwide control costs. EPA has not included an allowance for
poor compliance in its estimates of emissions reductions. This
is because poor compliance is unlikely.
If the emission control devices degraded rapidly over time
or in some other way did not function as expected, there could be
a misallocation of resources. This situation is very unlikely
because the NESHAP's are based on demonstrated technology. Other
ways the regulations could fail are conceivable.
References
1. U.S. Office of Management and Budget. Regulatory Impact
Guidance, Appendix V of Regulatory Program of the United
States Government, April 1, 1991 - - March 31, 1992.
2. U.S. Environmental Protection Agency. The Risk Assessment
Guidelines of 1986, Office of Health and Environmental
Assessment, Washington, D.C. August 1987.
3. Sittig, Marshall. Handbook of Toxic and Hazardous Chemicals
and Carcinogens, Second Edition. New Jersey: Noyes
Publication, 1985. pp. 153-154.
CHAPTER 4
CONTROL TECHNIQUES
The scope of the HON is broad. The control technology and
techniques involved are extensive. Combustion technology,
product recovery devices, steam strippers, and vapor recovery
tanks are all part of the technology requirements for the HON,
and leak detection and repair (LDAR) programs will be used to
control fugitive emissions. This chapter does not attempt to be
comprehensive in explaining the technology and techniques used to
control air toxics emissions under the HON; it does attempt to
survey what technologies and techniques are being used and how
effective they are.
4.1 Combustion Technology
Combustion control devices, unlike noncombustion control
devices, alter the chemical structure of the VOC. Destruction of
the VOC by combustion is complete if all VOC's are converted to
CO2 and water. Incomplete combustion results in some of the VOC
remaining unaltered or being converted to other organic compounds
such as aldehydes or acids. If chlorinated or sulfur-containing
compounds are present in the mixture, the products of complete
combustion include the acid components HCl or SO2, respectively,
in addition to water and carbon dioxide.
4.1.1 Incinerators
Incineration is one of the best known methods of industrial
gas waste disposal. It is a method of ultimate disposal, that
is, the constituents to be controlled in the waste gas stream are
converted rather than collected. Provided proper engineering
design is used, incineration can eliminate the desired organic
chemicals in a gas stream safely and cleanly.
The heart of an incinerator is a combustion chamber in which
the VOC-containing waste stream is burned. The temperature
required for combustion is much higher than the temperature of
the inlet gas, so energy is usually supplied to the incinerator
to raise the waste gas temperature. This is accomplished by
adding auxiliary fuel (usually natural gas).
The amount of auxiliary fuel required can be decreased and
energy efficiency increased by providing heat exchange between
the inlet stream and the effluent stream. The effluent stream
containing the products of combustion, along with any inerts that
may have been present in or added to the inlet stream, can be
used to preheat the incoming waste stream, auxiliary air, or both
via a "primary", or recuperative, heat exchanger.
Auxiliary air may be required for combustion if the
requisite oxygen is not available in the inlet gas stream. Most
industrial gases that contain VOC's are dilute mixtures of
combustible gases in air. With air oxidation reactor and
distillation processes, the waste gas stream is deficient in air.
Important in the design and operation of incinerators is the
concentration of combustible gas in the waste gas stream. Having
a large amount of excess air (i.e., in excess of the required
stoichiometric amounts) may be costly, but any mixture within the
flammability limits, on either the fuel-rich or fuel-lean side of
the stoichiometric mixture is considered a fire hazard as a feed
stream to the incinerator. Therefore, some waste gas streams
are diluted with air before incineration, even though this
requires more fuel in the incinerator.
There are two types of incinerators: thermal and catalytic.
While much of what was discussed above applies to both, there are
important differences in their design and operation.
4.1.1.1 Thermal Incinerators
As is true of other combustion control devices, thermal
incinerators operate on the principle that any VOC heated to a
high enough temperature in the presence of sufficient oxygen will
be oxidized to CO2 and water. The theoretical temperature for
thermal oxidation depends on the properties of the VOC to be
combusted. There is great variation in theoretical combustion
temperatures between different VOC's.
There are three requirements that must be met for a thermal
incinerator to be considered efficient: 1) a high enough
combustion chamber to enable oxidation of the organic compounds
to proceed rapidly to completion; 2) enough turbulence for good
mixing of the hot combustion products from the burner, the
combustion air, and the organic compounds; and 3) sufficient
residence time for oxidation to reach completion.1
A typical thermal incinerator is a refractory-lined chamber
containing a burner or set of burners at one end. Entering gases
are mixed with the process vent streams and the inlet air in a
premixing chamber. Then the stream of gases passes into the main
combustion chamber. This chamber is designed to allow the
mixture enough time at the required combustion temperature for
complete oxidation (usually from 0.3 to 1.0 second). A heat
recovery section is often added to increase energy efficiency.2
Oftentimes inlet combustion air is preheated; if this occurs,
insurance regulations require the VOC concentration must be
maintained below 25 percent of the lower explosive limit (LEL) to
minimize the possibility of explosions. Concentrations from 25
to 50 percent are permitted given continuous monitoring by LEL
monitors.
The required level of VOC control of the waste gas that must
be achieved within the time it spends in the thermal combustion
chamber dictates the reactor temperature. The shorter the
residence time, the higher the reactor temperature must be. Once
the unit is designed and built, the residence time is not easily
changed, so that the required reaction temperature becomes a
function of the particular gaseous species and the desired level
of control. These required combustion reaction temperatures
cannot be calculated a priori, although incinerator vendors can
provide guidelines based on their extensive experience.
Predictions of these temperatures are further complicated by the
fact that most process vent streams are mixtures of compounds.3
Good mixing is also important, particularly in determining
destruction efficiency. Even though it cannot be measured,
mixing is a factor of equal or even greater importance than other
parameters such as temperature. The most feasible and efficient
way to improve the mixing in an incinerator is to adjust it after
start-up.4
Other parameters affecting thermal incinerator performance
are the heat content of the vent stream, the water content of the
stream, and the amount of excess combustion air (the amount of
air above the stoichiometric air needed for combustion).
Combustion of a vent stream with a heat content less than 1.9
MJ/m3 (52 BTU/scf) usually requires burning supplemental fuel to
maintain the desired combustion temperature.
The maximum achievable VOC destruction efficiency decreases
with decreasing inlet VOC concentration because combustion is
slower at lower inlet concentrations. Therefore, a VOC weight
percentage reduction based on the mass rate of VOC exiting the
control device versus the mass rate of VOC entering the device is
appropriate for vent streams with VOC concentrations above
approximately 2,000 ppmv (which corresponds to 1,000 ppmv VOC in
the incinerator inlet stream since air dilution is typically
1:1).5
4.1.1.1.1 Applicability
Thermal incinerators are technically feasible control
devices for most vent streams. They are not recommended,
however, for vent streams with potentially excessive fluctuations
in flow rate (process upsets, for example), and for vent streams
containing halogens. The former case would require a flare (see
Section 4.2) and the latter case would require additional
equipment such as acid gas scrubbers (see Section 4.1.3).
4.1.1.1.2 Types of Thermal Incinerators
The very simplest type of thermal incinerator is the direct
flame incinerator, which is made up of only the combustion
chamber. Energy recovery devices such as a waste gas preheater
and a heat exchanger are not included with this type of
incinerator.
A second type of thermal incinerator is the recuperative
model. Recuperative incinerators use the exit (product) gas to
preheat the incoming feed stream, combustion air, or both via a
heat exchanger. These heat exchangers can recover up to 70
percent of the energy (or enthalpy) in the product gas. The two
types of heat exchangers commonly used for this purpose and many
others are plate-to-plate and shell-and-tube. Plate-to-plate
exchangers can be built to achieve a variety of efficiencies and
offer high efficiency energy recovery at lower cost than shell-
and-tube designs. But when gas temperatures exceed 520 degrees
Celsius, shell-and-tube exchangers usually have lower purchase
costs than plate-to-plate designs. Moreover, shell-and-tube
exchangers offer better long-term structural reliability than
plate-to-plate units.6
Occasionally it is desired to recover some of the energy
added by auxiliary fuel in the traditional thermal units (but not
recovered in preheating the feed stream). Additional heat
exchangers can be added to provide process heat in the form of
low pressure steam or hot water for on-site application. The
need for this higher level of energy recovery will be dependent
upon the plant site. The additional heat exchanger is often
provided by the incineration unit vendor.
A third type of thermal incinerator is the regenerative
incinerator. This type of incinerator use direct contact heat
exchangers constructed of a ceramic material that can tolerate
the high temperatures needed to achieve ignition of the waste
stream. The concept behind this incinerator type is that the
traditional approach to energy recovery in thermal units still
requires a significant amount of auxiliary fuel to be burned in
the combustion chamber when waste gas heating values are too low
to sustain the desired reaction temperature at the moderate
preheat temperature employed. Under these conditions, additional
fuel savings can be realized in units with more complete transfer
of exit stream energy. Hence the regenerative incinerator.
In this type of incinerator, the inlet gas first passes
through a hot ceramic bed thereby heating the steam to its
ignition temperature. The hot gases then react and release
energy in the combustion chamber and while passing through
another ceramic bed, thereby heating it to the combustion chamber
outlet temperature. The process flows are then switched, now
feeding the inlet stream to the hot bed. This cyclic process
affords very high energy recovery (up to 95 percent).7
4.1.1.2 Catalytic Incinerators
A catalyst promotes oxidation of some VOC's at a lower
temperature than that required for thermal incineration. The
catalyst increases the rate of the chemical reaction without
becoming permanently altered itself. Catalysts typically used
for VOC incineration include platinum and palladium. These
catalysts work well for most organic streams, but are not
tolerant of compounds containing halogens such as chlorine and
sulfur. Among the catalysts that have been developed that are
effective in the presence of these halogens are chromia/alumina,
cobalt oxide, and copper oxide/manganese oxide.8 Inert
substrates are coated with thin layers of these materials to
provide maximum surface area for contact with the VOC in the vent
stream. Compounds containing elements such as lead, arsenic, and
phosphorus should, in general, be considered poisons for most
oxidation catalysts. In addition, particulate matter, including
dissolved minerals in aerosols, can rapidly blind (deactivate)
the pores of catalysts and deactivate them over time. Because
essentially all the active surface of the catalyst is contained
in relatively small pores, the particulate matter need not be
large to blind the catalyst.
For optimal operation, the volumetric gas flow rate and the
concentration of combustibles (in this case, VOC's) should be
constant. Large fluctuations in the flow rate will cause the
conversion of the VOC's to fluctuate also. Changes in the
concentration or type of organic compounds in the gas stream can
also affect the overall conversion of the VOC contaminants. Most
changes in flow rate, organic concentration, and chemical
composition are generally the result of upsets in the
manufacturing process generating the waste gas stream.
4.1.1.2.1 Applicability
Applicability of catalytic incinerators for control of VOC's
is limited by the catalyst deactivation sensitivity to the
characteristics of the inlet gas stream. The vent stream to be
combusted should not contain materials that can poison the
catalyst or deposit on and block the reactive sites on the
catalyst surface. In addition, catalytic incinerators are unable
to handle high inlet concentrations of VOC or very high flow
rates. Catalytic incineration is generally useful for
concentrations of 50 to 10,000 ppmv, if the total concentration
is less than 25 percent of the LEL and for flow rates of less
than 2,820 m3/min (100,000 scfm).9 Catalytic units are also
typically used for vent streams with stable flow rates and
concentrations (refer to Section 4.1.1.2).
4.1.1.2.2 Types of Catalytic Incinerators
One type of catalytic incinerator is fixed-bed. Fixed-bed
incinerators themselves come in two varieties, depending on the
type of catalyst used: the monolith and packed-bed. The
monolith catalyst is the most widespread method of contacting the
VOC-containing stream with the catalyst. In this scheme the
catalyst is a porous solid block containing parallel, non-
intersecting channels aligned in the direction of the gas flow.
Monolith catalysts offer the advantages of minimal attrition due
to thermal expansion/contraction during startup/shutdown and low
overall pressure drop.
A second contacting scheme is a simple packed-bed in which
catalyst particles are supported either in a tube or in shallow
trays through which the gases pass. The tray type arrangement is
the more common packed-bed scheme due to the use of pelletized
catalysts. This tray arrangement is preferred because pelletized
catalysts can handle inlet streams containing contaminants such
as phosphorus or silicon.10 The tube arrangement is not used
widely due to its inherently high pressure drop compared to a
monolith, and the breaking of catalyst particles due to thermal
expansion when the confined catalyst bed is heated/cooled during
startup/shutdown.
A third contacting pattern between the gas and catalyst is a
fluid-bed. Fluid-beds have the advantage of very high mass
transfer rates, although the overall pressure drop is somewhat
higher than for a monolith. Fluid-beds also possess the
advantage of high bed-side heat transfer compared to a normal gas
heat transfer coefficient. This higher heat transfer rate to
heat transfer tubes immersed in the bed allows higher heat
release rates per unit volume of gas processed and therefore may
allow waste gases with higher heating values to be processed
without exceeding maximum permissible temperatures in the
catalyst bed. The catalyst temperatures depend on the rate of
reaction occurring at the catalyst surface and the rate of heat
exchange between the catalyst and imbedded heat transfer
surfaces.
In general, fluid-bed systems are more tolerant of
particulates in the gas stream than fixed-bed or packed-bed
systems. This results from the constant abrasion of the
fluidized catalyst pellets, which helps remove these particulates
from the exterior of the catalysts in a continuous manner.
4.1.2 Flares
Flaring is an open combustion process in which the oxygen
necessary for combustion is provided by the air around the flame.
The organic compounds to be combusted are piped to a remote,
usually elevated, location and burned in an open flame in the
open air using a specially designed burner tip, auxiliary fuel,
and sometimes steam or air to promote mixing for nearly complete
(98 percent minimum) destruction of combustibles. Good
combustion in a flare is governed by flame temperature, residence
time of organic species in the combustion zone, turbulent mixing
of the organic species to complete the oxidation reaction, and
the amount of oxygen available for free radical formation.
Combustion is complete if all combustibles (i.e., VOC's) are
converted to CO2 and water, while incomplete combustion results
in some of the VOC's being unaltered or converted to other
organic compounds such as aldehydes or acids.
Flares are generally categorized in two ways: 1) by the
height of the flare tip (i.e., ground-level or elevated), and 2)
by the method of enhancing mixing at the flare tip (i.e., steam-
assisted, air-assisted, pressure-assisted, or unassisted).
Elevating the flare can prevent potentially dangerous conditions
at ground level where the open flame is located near a process
unit. Further, the products of combustion can be dispersed above
working areas to reduce the effects of noise, heat radiation,
smoke, and objectionable odors.
In most flares, combustion occurs by means of a diffusion
flame. A diffusion flame is one in which air diffuses across the
boundary of the fuel/combustion product stream toward the center
of the fuel flow, forming the envelope of a combustible gas
mixture around a core of fuel gas. This mixture, on ignition,
establishes a stable flame zone around the gas core above the
burner tip. This inner gas core is heated by diffusion of hot
combustion products from the flame zone.
Cracking can occur with the formation of small hot particles
of carbon that give the flame its characteristic luminosity.11 If
there is an oxygen deficiency and if the carbon particles are
cooled to below their ignition temperature, smoking occurs. In
large diffusion flames, combustion product vortices can form
around burning portions of the gas and shut off the supply of
oxygen. This localized instability causes flame flickering,
which can be accompanied by soot formation.
4.1.2.1 Applicability
Flares can be dedicated to almost any VOC stream, and can
handle fluctuations in VOC concentration, flow rate, heating
value, and inerts content. Flaring is appropriate for
continuous, batch, and variable flow vent stream applications.
Some streams, such as those containing halogenated or
sulfur-containing compounds, are usually not flared because they
corrode the flare tip or cause formation of secondary pollutants
(such as acid gases or sulfur dioxide). If these vent types are
to be controlled by combustion, thermal incineration, followed by
scrubbing to remove the acid gases, is the preferred method.12
The majority of chemical plants and refineries have existing
flare systems designed to relieve emergency process upsets that
require release of large volumes of gas. Often, large diameter
flares designed to handle emergency releases are also used to
control continuous vent streams from various process operations.
Typically in refineries, many vent streams are combined in a
common gas header to fuel boilers and process heaters. However,
excess gases, fluctuations in flow rate in the fuel gas line, and
emergency releases are sometimes sent to a flare.
4.1.2.2 Efficiency
Five factors affecting flare combustion efficiency are vent
gas flammability, auto-ignition temperature, heat content of the
vent stream, density, and flame zone mixing.
The flammability limits of the vent stream influence
ignition stability and flame extinction. Flammability limits are
the stoichiometric composition limits (maximum and minimum) of an
oxygen-fuel mixture that will burn indefinitely at given
conditions of temperature and pressure without further ignition.
In other words, gases must be within their flammability limits to
burn. If these limits are narrow, the interior of the flame may
have insufficient air for the mixture to burn. Fuels, such as
hydrogen, with wide limits of flammability are therefore easier
to combust.
The auto-ignition temperature of a vent stream affects
combustion because gas mixtures must be at a sufficient
temperature and concentration to burn. A gas with a low auto-
ignition temperature will ignite more easily than a gas with a
high auto-ignition temperature.
The heat content of the vent stream is a measure of the heat
available from the combustion of the VOC in the vent stream. The
heat content of the vent stream affects the flame structure and
stability. A gas with a lower heat content produces a cooler
flame that does not favor combustion kinetics and is more easily
extinguished. The lower flame temperature will also reduce
buoyant forces, which reduces mixing.
The density of the vent stream also affects the structure
and stability of the flame through the effect on buoyancy and
mixing. By design, the velocity in many flares is very low;
therefore, most of the flame structure is developed through
buoyant forces as a result of combustion. Lighter gases
therefore tend to burn better. In addition to burner tip design,
the density also affects the minimum purge gas required to
prevent flashback, with lighter gases requiring more purge.13
Poor mixing at the flare tip or poor flare maintenance can
cause smoking (particulate matter release). Vent streams with
high carbon-to-hydrogen ratios (> 0.35) have a greater tendency
to smoke and require better mixing to burn smokelessly.14 For
this reason, one generic steam-to-vent-stream ratio is not
appropriate for all vent streams. The steam required depends on
the vent stream carbon-to-hydrogen ratio. A high ratio requires
more steam to prevent a smoking flare.
The efficiency of a flare in reducing VOC emissions can be
variable. For example, smoking flares are far less efficient
than properly operated and maintained flares. Flares have been
shown to have high VOC destruction efficiencies, under proper
operating conditions. Up to 99.7 percent combustion efficiency
can be achieved.
4.1.2.3 Types of Flares
4.1.2.3.1 Steam-Assisted Flares
Steam-assisted flares are single burner tips, elevated above
ground level for safety reasons, that burn the vented gas in
essentially a diffusion flame. They reportedly account for the
majority of the flames installed and are the predominant flare
type found in refineries and chemical plants.15 To ensure an
adequate air supply and good mixing, this type of flare system
injects steam into the combustion zone to promote turbulence for
mixing and to induce air into the flame.
4.1.2.3.2 Air-Assisted Flares
Air-assisted flares use forced air to provide the combustion
air and the mixing required for smokeless operation. These
flares are built with a spider-shaped burner (with many small gas
orifices) located inside but near the top of a steel cylinder two
feet or more in diameter. Combustion air is provided by a fan in
the bottom of the cylinder, and the amount of combustion air can
be varied by varying the fan speed. The primary advantage air-
assisted flares provide is that they can be used in the absence
of steam.
4.1.2.3.3 Non-Assisted Flares
The non-assisted flare is just a flare tip without any
auxiliary provision for enhancing the mixing of air into its
flame. Its use is limited essentially to gas streams that have a
low heat content and a low carbon/hydrogen ratio that burn
readily without producing smoke.16 These streams require less air
for complete combustion, have lower combustion temperatures that
minimize cracking reactions, and are more resistant to cracking.
4.1.2.3.4 Pressure-Assisted Flares
This type of flare use vent stream pressure to promote
mixing at the burner tip. If sufficient vent stream pressure is
available, these flares can be applied to streams previously
requiring steam or air assist for smokeless operation. Pressure-
assisted flares generally have the burner arrangement at ground
level, and consequently, must be located in a remote area of the
plant where there is plenty of space available. They have
multiple burner heads that are staged to operate based on the
quantity of gas being released. The size, design, number, and
group arrangement of the burner heads depend on the vent gas
characteristics.
4.1.2.3.5 Enclosed Ground Flares
The burner heads of an enclosed flare are inside a shell
that is insulated. This shell reduces noise, luminosity, and
heat radiation and provides wind protection. A high nozzle
pressure drop is usually adequate to provide the mixing necessary
for smokeless operation and air or steam assist is not required.
In this context, enclosed flares can be considered a special
class of pressure-assisted or non-assisted flares. Enclosed
flares are always at ground level.
Enclosed flares generally have less capacity than open
flares and are used to combust continuous, constant flow vent
streams, although reliable and efficient operation can be
attained over a wide range of design capacity. Stable combustion
can be obtained with lower heat content vent gases than is
possible with open flare designs, probably due to their isolation
from wind effects.17
4.1.3 Boilers and Process Heaters
4.1.3.1 Description of Boilers
Industrial boilers are combustion units that boil water to
produce high and low pressure steam. Industrial boilers can also
combust various vent streams containing VOC's, including vent
streams from distillation operations, reactor processes, and
other general operations.
The majority of industrial boilers used in the chemical
industry are of watertube design, and over half of these boilers
use natural gas as a fuel.18 In a watertube boiler, hot
combustion gases contact the outside of heat transfer tubes which
contain hot water and steam. These tubes are interconnected by a
set of drums that collect and store the heated water and steam.
Energy transfer from the hot flue gases to the water in the
furnace watertube and drum system can be better than 85 percent
efficient.19 Additional energy can be recovered from the flue gas
by preheating combustion air in an air preheater or by preheating
incoming boiler feed water in an economizer unit.
When firing natural gas, forced- or natural-draft burners
throughly mix the incoming fuel and combustion air. A VOC-
containing vent stream can be added to this mixture or it can be
fed into the boiler through a seperate burner. In general,
burner design depends on the characteristics of the fuel-- either
the combined VOC-containing vent stream and fuel or the vent
stream alone (when a separate burner is used).
4.1.3.2 Description of Process Heaters
A process heater is similar to an industrial boiler in that
heat liberated by the combustion of fuels is transferred by
radiation and convection to fluids contained in tubular coils.
It is different from an industrial boiler in that process heaters
raise the temperature of process streams instead of producing
high temperature steam. Process heaters are used in many
chemical manufacturing operations to drive endothermic reactions.
They are also used as feed preheaters and as reboilers for some
distillation operations. The fuels used in process heaters
include natural gas, refinery offgases, and various grades of
fuel oil.
A typical process heater design consists of the burner(s),
the firebox, and a row of tubular coils containing the process
fluid. Most heaters also contain a convective section in which
heat is recovered from hot combustion gases by convective heat
transfer to the process fluid.
4.1.3.3 Efficiency of Boilers and Process Heaters
Average furnace temperature and residence time determine the
combustion efficiency of boilers and process heaters, just as
they do for incinerators. When a vent gas is injected as a fuel
into the flame zone of a boiler or process heater, the required
residence time is reduced because of the relatively high
temperature and turbulence of the flame zone.
Residence time and temperature profiles in boilers and
process heaters are determined by factors such as overall
configuration, fuel type, heat input, and excess air level.20 A
mathematical model developed to estimate furnace residence time
and temperature profiles for a variety of industrial boilers
predicts mean furnace residence times ranging 0.25 to 0.83 second
for natural gas-fired watertube boilers that range in size from
4.4 to 44 MW (15 to 150 x 106 Btu/hr).21 Boilers with a 44-MW
capacity or greater generally have residence times and operating
temperatures that would ensure a 98 percent VOC destruction
efficiency. The required temperatures for these size boilers are
at least 1,200 degrees Celsius.
Firebox temperatures for process heaters can show wide
variations depending on the application. Firebox temperatures
can range from 400 degrees Celsius for preheaters and reboilers
to 1,260 degrees Celsius for pyrolysis furnaces. Tests conducted
by EPA on process heaters using a mixture of benzene offgas and
natural gas showed greater than 98 percent destruction efficiency
for C1 to C6 hydrocarbons.22
4.1.3.4 Applicability of Boilers and Process Heaters
Both of these devices are used throughout the chemical
industry to provide steam and heat input essential to chemical
processing. Most of these devices possess sufficient size to
provide the necesary temperature and residence time for VOC
destruction. Furthermore, boilers and process heaters have
proved effective in destroying compounds that are difficult to
combust, such as PCBs (polychlorinated biphenyls). Boilers and
process heaters are thus effective in reducing VOC emissions from
any vent streams that are certain not to reduce the performance
or reliability of the boiler or process heater.
Ducting some vent streams to a boiler or process heater can
present potential safety and operating problems. The varying
flow rate and organic content of some vent streams can lead to
explosive mixtures or flame instability within the furnace. In
addition, vent streams with halogenated or sulfur-containing
compounds are usually not combusted in boilers or process heaters
due to the possibility of corrosion.
Boilers and process heaters are most applicable where the
potential exists for heat recovery from the combustion of the
vent stream. Vent streams with a high enough VOC concentration
and high flow rate can provide enough equivalent heat value to
act as a substitute for fuel that would otherwise be needed.
Because boilers and process heaters cannot tolerate wide
fluctuations or interruptions in the fuel supply, they are not
widely used to reduce VOC emissions from batch operations or
other noncontinuous vent streams.
4.2 Product Recovery Devices
4.2.1 Absorbers
In absorption, a soluble vapor is absorbed from its mixture
with an inert gas by means of a liquid in which the solute gas is
more or less soluble. For any given solvent, solute, and
operating conditions, there exists an equilibrium ratio of solute
concentration in the gas mixture to solute concentration in the
solvent. The driving force for mass transfer at a given point in
an operating absorber is the difference between the concentration
of solute in the gas and the equilibrium concentration of solute
in the liquid.
Devices based on absorption principles include spray towers,
venturi and wet impingement scrubbers, acid gas scrubbers, packed
columns, and plate columns. Spray towers have the least
effective mass transfer capability due to their high atomization
pressure requirement, and are generally restricted to particulate
matter removal and control of high-solubility gases such as SO2
and NH3 (ammonia).23 Venturi scrubbers have a high degree of
gas/liquid mixing and provide high particulate matter removal
efficiency. They also require high pressure drops (i.e. high
energy requirements) and have relatively short contact times.
Their use is also restricted to high-solubility gases. Acid gas
scrubbers are used with thermal incinerators to remove corrosive
combustion products. Acid gas is formed upon the contact of
halogenated or sulfur-containing VOCs with intense heat during
incineration. This gas is quenched to lower its temperature and
is then scrubbed in an absorber. In most cases, the type of
absorber used is packed or plate columns, the two most commonly
used absorbers for VOC control.
Packed towers are vertical columns containing inert packing,
manufactured from materials such as porcelain, metal, or plastic,
that provides the surface area for contact between the liquid and
gas phases in the absorber. Packed towers are used mainly for
corrosive materials and liquids with tendencies to foam or plug.
They are less expensive than plate columns for small-scale or
pilot plant operations where the column diameter is less than
0.6 m. They are also suitable where the use of plate columns
would result in excessive pressure drops.
Plate columns contain a series of trays on which contact
between the gas and liquid phases in a stepwise fashion. The
liquid phase flows down tray to tray as the gas phase moves up
through openings in the tray (usually perforations or bubble
caps), passing through the liquid on the way.
The major design parameters for absorbing any substance are
column diameter and height, system pressure drop, and required
liquid flow rate. Deriving these parameters is accomplished by
considering the solubility, viscosity, density, and concentration
of the VOC in the inlet vent stream (all of which depend on
column temperature); the total surface area provided by the
packing material; and the mass flow rate of the gases to be
treated.
4.2.1.1 Absorber Efficiency
Control efficiencies for absorbers can vary widely depending
on the solvent selected, design parameters, and operating
practices. Solvents are chosen for high solubility for the
specific VOC and include liquids such as water, mineral oils,
kerosenes, nonvolatile hydrocarbon oils, and aqueous solutions of
oxidizing agents, sodium carbonate, and sodium carbonate.24 An
increase in absorber size (i.e., contact surface area) or a
decrease in the operating temperature can increase the VOC
removal efficiency of the system for a given solvent and solute.
It is sometimes possible to increase VOC removal efficiency by
changing the solvent.
4.2.1.2 Applicability of Absorbers
The primary determinant of absorption applicability for
controlling VOC emissions is the availability of a suitable
solvent.25 Water is a suitable solvent for absorption of organic
chemicals with relatively high water solubilities (e.g., most
alcohols, organic acids, aldehydes, glycols). For organic
compounds with low water solubilities, other solvents (usually
organic liquids with low vapor pressures) are used.
Other important factors influencing absorption applicability
include absorptive capacity and strippability of VOC in the
solvent. Absorptive capacity is a measure of the solubility of
VOC in the solvent. The solubility limits the total quantity of
VOC that could be absorbed in the system, while strippability
describes the ease with which the VOC can be removed from the
solvent. If strippability is low, then absorption is less viable
as a VOC control technique.26
The concentration of VOC in the inlet vent stream also
determines the applicability of absorption. Absorption is
usually considered only when the VOC concentration is above 200
to 300 ppm.27 Below these gas-phase concentrations, the rate of
mass transfer of VOC to solvent is decreased enough to make
reasonable designs infeasible.
4.2.2 Steam Stripping
Steam stripping can be used as initial treatment of a
process wastewater stream to reduce the VOC loading of that steam
before it is sent to the facility-wide wastewater treatment
system. There are several components in a steam stripping
system: a feed tank, heat exchanger, steam stripping column,
condenser, overhead receiver, and a destruction device (if
necessary).
4.2.2.1 Description
Steam stripping involves the fractional distillation of
wastewater to remove VOC's. The basic operating principle of
steam stripping is the direct transfer of heat through contact of
steam with wastewater. This heat transfer vaporizes the more
volatile organic compounds. The overhead vapor contains water
and organic compounds, and it is condensed and separated to
recover the organic fraction. Recovered organic compounds are
either recycled for reuse in the process or incinerated in an on-
site combustion device for heat recovery.
Steam stripper systems may be operated in batch or
continuous mode. Batch steam strippers are more prevalent when
the wastewater feed is generated by batch processes, when feed
characteristics are highly variable, or when small volumes of
wastewater are generated. They may also be used if wastewater
contains relatively high concentrations of solids, resins, or
tars. In batch stripping, wastewater is charged to the receiver,
or pot, and brought to the boiling temperature of the mixture.
Solids and other residues remaining in the bottom of the pot
(hence the term "bottoms") at the completion of the batch are
nonvolatile, heavy compounds that are removed for disposal. By
varying the heat input and fraction of the initial charge boiled
overhead, a batch stripper can be used to treat wastewater
mixtures with widely varying characteristics.28
In contrast to batch strippers, continuous steam strippers
are designed to treat wastewater streams with relatively
consistent characteristics. Continuous strippers can have
several stages and achieve greater efficiencies of VOC removal
than batch strippers. Other advantages offered by continuous
strippers include more consistent effluent quality, more
automated operation, and lower annual operating costs.
Typically, wastewater steams continuously discharged from
process equipment are usually consistent in composition. A
continuous steam stripper system would thus be indicated for
treating the wastewater. However, batch wastewater streams can
also be controlled by continuous steam strippers by incorporating
a feed tank with adequate residence time to provide a consistent
outlet composition.
4.2.2.2 Collecting, Conditioning, and Recovery
The controlled sewer system or hard piping from the point of
wastewater generation to the feed tank controls emissions before
steam stripping. The feed tank collects and conditions the
wastewater fed to the steam stripper. If the feed tank is
adequately designed, a continuous steam stripper can treat
wastewater generated by some batch processes. In these cases,
the feed tank serves as a buffer between the batch process and
the continuous steam stripper. During periods of no wastewater
flow from the batch process, wastewater stored in the feed tank
is fed to the stripper at a relatively constant rate.
Often present in the feed tank are aqueous and organic
phases. The feed tank provides the retention time necessary for
these phases to separate. The organic phase is recycled to the
process for recovery of organic compounds or disposed by
incineration. The water phase is fed to the stripper to remove
the soluble organic compounds. Solids are also separated in the
stripper feed tank; the separation efficiency depends on the
density of the solids dissolved in the process wastewater. The
more dense solids, which settle to the bottom of the tank, are
removed periodically from the feed tank and are usually
landfilled or landfarmed.
After this conditioning of the wastewater, it is pumped
through the feed/bottoms heat exchanger where it is preheated and
then pumped into the steam stripping column. Steam is sparged
into the stripper at the bottom of the column, and the wastewater
feed enters at the top. The wastewater flowing down the column
contacts the flowing countercurrently up the column. Both latent
and sensible heat is transferred from the steam to the organic
compounds in the wastewater, vaporizing them into the vapor
stream. These constituents flow out the top of the column with
any uncondensed steam.
The wastewater effluent leaving the bottom of the stripper
is pumped through the feed/bottoms heat exchanger which heats the
feed stream and cools the bottoms before discharge. After
leaving the exchanger, the bottoms stream is usually either
routed to an on-site wastewater treatment plant and discharged to
an NPDES-permitted outfall, or sent to a publicly owned treatment
works (POTW).
Recovery of both VOC's and water vapors from the gaseous
overheads stream from the steam stripper is usually accomplished
with a condenser. The condensed stream is fed to an overhead
receiver, and the recovered VOC's are usually either pumped to
storage and recycled to the process unit or combusted for their
fuel value in an incinerator, boiler, or process heater (all
discussed earlier in this chapter). If an aqueous phase is
generated, it is returned to the feed tank and recycled through
the steam stripper system.
4.2.2.3 Efficiency of Control
The degree of contact between the steam and the wastewater
is the primary variable affecting the ability of a steam stripper
to remove VOC's. In turn, this variable is affected by five
factors: 1) column dimensions (height and diameter); 2) the
contacting media (packing or trays); and 3) operating parameters
such as the steam-to-feed ratio, column temperature, and
wastewater pH.
Control efficiency increases as column height increases
since there is greater opportunity for contact between the steam
and the wastewater. The column height is determined by the
number of theoretical stages required to achieve the desired
removal efficiency. The number of theoretical stages is a
function of the equilibrium coefficient of the pollutants and the
efficiency of mass transfer in the column, and this number can be
computed by either the McCabe-Thiele graphical method or the
Kremser analytical method.
The column diameter determines the required cross-sectional
area for liquid and vapor flow through the column. The smaller
the cross-sectional area, the higher the superficial gas
velocity, which increase turbulence and mixing resulting in high
column efficiencies. However, the column cross-sectional area
must be sufficient to prevent flooding from excessive liquid
loading or liquid entrainment. This area also affects the liquid
retention time, with higher retention times resulting in higher
efficiencies. These factors have to be weighed in selecting the
column diameter and the design velocities.
The contacting media in the column also play an important
role in determining the mass transfer efficiency. Packing or
trays are used to provide contact between liquid and vapor
phases. Packing provides for continuous contact while trays
provide staged contact. Trays are usually more effective for
wastewater containing dispersed solids because of the plugging
and cleaning problems encountered with packing. Tray towers can
also operate over a wider range of liquid flow rates than packed
towers. Packed towers, on the other hand, are often more cost
effective to install and operate when treating highly corrosive
wastewater since corrosion resistant ceramic packing can be used.
Also, the pressure drop through packed towers may be less than
through tray towers.29
The steam-to-feed ratio required for high removal
efficiencies is affected by the wastewater temperature as it
enters the column. If the feed temperature is lower than the
operating temperature at the top of the column, part of the steam
is required to heat the feed. With good column design,
sufficient steam flow is provided to heat the feed as well as
volatilize the organic constituents. Any steam in excess of this
flow rate helps carry VOC's out of the top of the column with the
overheads stream. Also, increasing the steam-to-feed ratio will
increase the ratio of the vapor to liquid flow through the
column, which increases the stripping of VOC's into the vapor
phase.
Two other influences on VOC removal are the column
temperature and wastewater pH. Temperature influences the
solubility and equilibrium coefficients of the organic compounds.
pH has an effect on the vapor liquid equilibrium characteristics
of VOC's. To ensure steam stripping is successful, columns are
operated at pressures slightly exceeding atmospheric, and
operating temperatures are usually slightly higher than the
normal boiling point of water. Wastewater pH is controlled by
adding caustic to the feed.30
4.2.2.4 Applicability
Steam stripping is most applicable to treating wastewaters
with organic compounds that are highly volatile and have a low
solubility in water. The VOC's that have low volatility tend not
to volatilize and thus are not easily stripped out of the
wastewater by the steam. Similarly, VOC's that are very soluble
in water tend to remain in the wastewater and are not easily
stripped by steam. Oil, grease, solids content and pH of
wastewater also affect applicability. High oil, grease, and
solids levels can cause operating problems for steam strippers,
and extremes in pH may prove to be corrosive to equipment.
Design or wastewater preconditioning techniques can be used to
mitigate these problems.
4.2.3 Carbon Adsorbers
Adsorption is a mass-transfer operation involving
interaction between gas- or liquid-phase components and solid-
phase components. In this operation, certain components of a
gas- or liquid-phase (or adsorbate) are transferred to the
surface of a solid adsorbent. The transfer is accomplished by
physical or chemical adsorption mechanisms. Physical adsorption
takes place when intermolecular (van der Waals) forces attract
and hold the gas molecules to the solid surface. Chemisorption
occurs when a chemical bond forms between the gaseous- and solid-
phase molecules. A physically adsorbed molecule can be removed
readily from the adsorbent (under suitable temperature and
pressure conditions); the removal of a chemisorbed component is
much more difficult.
Most industrial adsorption systems use activated carbon as
the adsorbent. Activated carbon effectively captures certain
organic vapors by physical adsorption. The vapors can then be
released for recovery by regenerating the adsorption bed with
steam or nitrogen. Oxygenated adsorbents such as silica gels or
diatomaceous earth exhibit a greater selectivity for capturing
water vapor than organic gases compared to activated carbon.
They thus are of little use for high-moisture vent streams
characteristic of some VOC-containing vent streams.31
Among the factors influencing the design of a carbon
adsorption system are the chemical characteristics of the VOC
being recovered, the physical properties of the inlet stream
(temperature, pressure, and volumetric flow rate), and the
physical properties of the adsorbent. The mass of VOC that
adheres to the adsorbent surface is directly proportional to the
difference in VOC concentration between the gas phase and the
solid surface. In addition, the quantity of VOC adsorbed depends
on the adsorbent bed volume, the surface area of adsorbent
available to capture VOC, and the rate of diffusion of VOC
through the gas film at the gas- and solid-phase interface (the
mass transfer coefficient). It should be noted that physical
adsorption is an exothermic operation that is most efficient
within a narrow range of temperature and pressure.32
4.2.3.1 Types of Adsorbers
There are five types of adsorption equipment used in gas
collection: 1) fixed regenerable beds;
2) disposable/rechargeable cannisters; 3) traveling bed
adsorbers; 4) fluid bed adsorbers; and 5) chromatographic
baghouses. The fixed-bed type is the one most commonly used for
control of VOC's,33 so this section addresses this type only.
Fixed-bed units can be sized for controlling continuous,
VOC-containing streams over a wide range of flow rates, ranging
up to several thousand cubic meters per minute (100,000 scfm).
VOC concentrations in streams that can be treated by fixed-bed
units can range from several parts per billion by volume (ppbv)
to 10,000 ppmv.
Fixed-bed adsorbers can be operated in two modes:
intermittent or continuous. In intermittent mode, the adsorber
removes VOC's for a specified time (called "the adsorption
time"), which corresponds to the time during which the controlled
source is emitting VOC's. In continuous mode, a regenerated
carbon bed is always available for adsorption, so that the
controlled source can operate continuously without shutting down.
While continuous operation allows for more adsorption over the
same period of time because it does not need to be shut down,
more carbon must be provided. This is necessary since a bed for
desorbing must be provided along with the adsorbing bed in order
to recover the captured VOC from the carbon.34
4.2.3.2 Control Efficiency
Well designed and operated carbon adsorption systems can
achieve control efficiencies of 95 to 99 percent for a variety of
solvents including ketones such as methyl ethyl ketone and
cyclohexanone. The VOC control efficiency depends on factors
such as inlet vent stream characteristics (temperature, pressure,
and velocity), the physical properties of the compounds present
in the vent stream, the physical properties of the adsorbent, and
the condition of the regenerated carbon bed.
The adsorption capacity of the carbon and the resulting
outlet concentration are dependent upon the temperature of the
inlet vent stream. High vent stream temperatures increase the
kinetic energy of the gas molecules, causing them to overcome van
der Waals forces and release from the surface of the carbon. At
vent stream temperatures above 38 degrees Celsius, both
adsorption capacity and outlet concentration may be adversely
affected.35
Increasing vent stream pressure improves VOC removal
efficiency. Increased stream pressure results in higher VOC
concentrations in the vapor phase and increased driving force for
mass transfer to the carbon surface. Decreased stream pressure,
on the other hand, is often used to regenerate carbon beds.
Reduced pressure in the carbon bed effectively lowers the
concentration of VOCs in the vapor phase, desorbing the VOCs from
the carbon surface to the vapor phase.
Vent stream velocity entering the carbon bed must be quite
low to allow time for diffusion and adsorption. Typical inlet
vent stream velocities range from 15 to 30 meters per minute
(50 to 100 feet per minute). If inlet VOC concentrations are low,
as is expected in the SOCMI, the bed area required for the volume
needed usually permits a velocity at the high end of this range.36
The required depth of the bed for a given compound is
directly proportional to the carbon granule size and porosity and
to the inlet vent stream velocity. For a given carbon type, bed
depth must increase as the vent stream velocity increases.
Generally, carbon adsorber bed depths range from 0.40 to 0.95
meter (1.5 to 3.0 feet).
The condition of the regenerated carbon bed will change with
use. After repeated regeneration, the carbon bed loses activity,
resulting in reduced VOC removal efficiency.
4.2.3.3 Applicability
Carbon adsorption cannot be used universally for
distillation or process vent streams. It is not recommended
under the following conditions, common with many VOC-containing
vent streams: 1) high VOC concentrations, 2) very high or low
molecular weight compounds, 3) mixtures of high and low boiling
point VOC's, and 4) high moisture content.
Absorbing vent streams with VOC concentrations above 10,000
ppmv may result in excessive temperature rise in the carbon bed
due to the accumulated heat of adsorption resulting from the VOC
loading. If flammable vapors are present, insurance company
requirements may limit inlet concentrations to less than 25
percent of the LEL.37
The molecular weight of the compounds to be adsorbed should
be in the range of 45 to 130 gm/gm-mole for effective adsorption.
High molecular weight compounds that are characterized by low
volatility are strongly adsorbed on carbon. The affinity of
carbon for these compounds makes it difficult to remove them
during regeneration of the carbon bed. Conversely, highly
volative materials (i.e, molecular weight less than about 45 gm)
do not adsorb readily on carbon, thus adsorption is not typically
used for controlling streams containing such compounds.
Adsorption systems can be very effective with homogeneous
vent streams but much less so with streams containing a mixture
of light and heavy hydrocarbons. The lighter organic compounds
tend to be displaced by the heavier compounds, greatly reducing
system efficiency.
Humidity is not a factor in adsorption at adsorbate
concentrations above 1,000 ppmv. Below this level, however,
water vapor competes with VOC's in the vent stream for adsorption
sites on the carbon surface. In these cases, vent stream
humidity levels exceeding 50 percent (relative humidity) are not
desirable.38
4.2.4 Condensers
Condensation is a separation technique in which one or more
volatile components of a vapor mixture are separated from the
remaining vapors through saturation followed by a phase change.
The phase change from gas to liquid can be achieved in two ways:
1) by increasing the system pressure at a given temperature or 2)
by lowering the temperature at a constant pressure. The latter
method is the more common to achieve the specified phase change,
and it alone is addressed here.
4.2.4.1 Description
The basic equipment includes a condenser, refrigeration
unit(s), and auxiliary equipment such as a precooler,
recovery/storage tank, pump/blower, and piping.
The two most commonly used condenser types are surface
condensers and direct contact condensers.39 In surface
condensers, the coolant fluid does not contact the vent stream;
heat transfer occurs through the tubes or plates in the
condenser. As the vapor condenses, a film forms on the cooled
surface and drains away to a collection tank for storage, reuse,
or disposal. Because the coolant from surface condensers does
not contact the vapor stream, it is not contaminated and can be
recycled in a closed loop. Surface condensers also allow for
direct recovery of VOC's from the gas stream.
Most refrigerated surface condensers are the shell-and-tube
type, which circulates the coolant fluid on the tube side. The
VOC's condense on the outside of the tube (the shell side).
Plate-type heat exchangers are also used as surface condensers in
refrigerated systems. Plate condensers operate under the same
principles as the shell-and-tube systems, for there is no contact
between the coolant and vent stream), but the two streams are
separated by thin, flat plates instead of cylindrical tubes.
In contrast to surface condensers, direct contact condensers
cool the vapor stream by spraying a liquid at ambient or lower
temperature directly into the vent stream. Spent coolant
containing VOC's from direct contact condensers usually cannot be
reused directly. Additionally, VOC's in the spent coolant cannot
be recovered without further processing. The combined stream
could present a potential waste disposal problem, depending upon
the coolant and the specific VOC's.
A refrigeration unit generates the low-temperature medium
necessary for heat transfer for recovery of VOC's. Typically in
refrigerated condenser systems two kinds of refrigerants are
used, primary and secondary. Primary refrigerants such as
ammonia and chlorofluorocarbons (e.g., chlorodifluoromethane) are
those that undergo a phase change from liquid to gas after
absorbing heat. Secondary refrigerants, such as brine solutions,
have higher boiling points and thus act only as heat carriers and
remain in the liquid phase.
There are some applications that require auxilary equipment.
If the vent stream contains water vapor or if the VOC has a high
freezing point (e.g., benzene or toluene), ice or frozen
hydrocarbons may form on the condenser tubes or plates. This
will reduce the heat transfer efficiency of the condenser and
thereby reduce the removal efficiency. Formation of ice will
also increase the pressure drop across the condenser. In such
cases, a precooler may be used to remove the moisture before the
vent stream enters the condenser. Alternatively, ice can be
melted during an intermittent heating cycle by circulating
ambient temperature brine through the condenser or using radiant
heating coils.
It is necessary in some cases to provide a recovery tank for
temporary storage of condensed VOC before its reuse,
reprocessing, or transfer to a large storage tank. Pumps and
blowers are typically used to transfer liquid (e.g., coolant and
recovered VOC) and gas streams, respectively, within the system.
4.2.4.2 Control Efficiency
The major parameters that affect the removal efficiency of
refrigerated surface condensers designed to control air/VOC
mixtures are: 1) Volumetric flow rate of the VOC-containing vent
stream; 2) Inlet temperature of the vent stream; 3)
Concentrations of the VOC's in the vent stream; 4) Absolute
pressure of the vent stream; 5) Moisture content of the vent
stream; and 6) properties of the VOC's in the vent stream, such
as dew points, heats of condensation, heat capacities, and vapor
pressures.40
Any operator of a condenser should remember that a condenser
cannot lower the VOC concentration to levels below the saturation
concentration at the coolant temperature. Removal efficiencies
above 90 percent can be achieved with coolants such as chilled
water, brine solutions, ammonia, or chlorofluorocarbons.
4.2.4.3 Applicability
Condensers are widely used as product recovery devices.
They may be used to recover VOC's upstream of other control
devices or they may be used alone for controlling vent streams
containing relatively high VOC concentrations (usually greater
than 5,000 ppmv). In these cases, the removal efficiencies of
condensers can range widely, from 50 to 95 percent.
Since the temperature necessary for condensation depends on
the properties and concentration of VOC's in the vent stream,
streams having either low VOC concentrations or more volatile
compounds require lower condensation temperatures. Also,
depending on the type of condenser used, disposal of the spent
coolant can be a problem. If cross-media impacts are a concern,
surface condensers would be preferable to direct contact
condensers.
Condensers used as emission control devices can process flow
rates as high as about 57 m3/min (120,000 scfm). Condensers for
vent streams with greater volumetric flow rates and having high
concentrations of noncondensibles will require significantly
larger heat transfer areas.
4.2.5 Vapor Collection Systems for Loading Racks
When liquids are transferred into a transport vessel, vapors
in the head space of that vessel can be lost to the atmosphere.
The principal factors affecting emissions from transfer
operations are the vapor pressure of the chemical being
transferred. Other factors that influence emissions from
transfer operations include the transfer rate and the purge rate
of nitrogen (or other inert gas) through the vessel during
transfer.
The vapor pressure of the chemical being transferred has the
greatest influence on emissions from transfer operations. For
pure materials, the vapor pressure gives a measure of the amount
of organic compound lost during transfer. The total potential
emissions from any transfer is related to the void volume of the
transport vessel and the concentration of the VOC in the head
space.
The mode of transfer is also an important factor in
determining emissions from transfer operations. Top splash
loading creates the most emissions because it enhances the
agitation of the liquid being transferred, creating a higher
concentration of the compound in the vapor space. With alternate
loading techniques, such as submerged fill or bottom loading, the
organic liquid is loaded under the surface of the liquid, which
reduces the amount of agitation and suppresses the generation of
excess vapor in the head space of the transport vessel.
The rate of transfer has a more subtle influence on
emissions; its greatest effect is on air quality. Transfer rate
will dictate the short-term emission rate of the compound being
transferred, thereby influencing exposure to the worker or
public.
A nitrogen purge is used to reduce the potential for
explosion of some chemicals in air or to keep some chemicals
moisture-free. Using an inert gas purge increases the emission
rate of VOC lost to the atmosphere because it creates a turnover
rate of gas through the transport vessel, increasing the total
volume of vapor discharged to the atmosphere.
Most vapor collection systems collect the vapors generated
during transfer operations and transport them to either a
recovery device for return to the process or a combustion device
for destruction. In vapor balancing systems, vapors generated
during transfer operations are returned directly to the storage
facility for the material, and the system requires no additional
controls.
4.2.5.1 Description of Vapor Collection Systems
Vapor collection systems consist of piping that captures and
transports to a control device VOC's in the vapor space of
transport vessels that are displaced when liquids are loaded.
These systems may use existing piping normally used to transport
liquids under pressure into the transport vessel or piping
separate from that for transfer. Collection systems comprise
very few pieces of equipment and minimal piping. The principal
piece of equipment in a collection system is a vacuum pump or
blower, used to induce the flow of vapors from the transport
vessel to the recovery or combustion system.
Blowers can also be used to remove vapors from the head
space of the tank car as liquid is transferred into the tank car.
Standard recovery techniques such as condensation or
refrigeration/condensation systems, or combustion can be applied
to the captured vapors.
Vapor balancing is another means of collecting vapors and
reducing emissions from transfer operations. Vapor balancing is
most commonly used where storage facilities are adjacent to the
loading facility. In this collection system, an additional line
is connected from the transport vessel to the storage tank to
return any vapor i