United States
Environmental Protection
Agency
Office of Information
Analysis & Access
Washington, DC 20460
EPA-745-B-99-014
December 1999
EMERGENCY PLANNING AND
COMMUNITY RIGHT-TO-KNOW
ACT - SECTION 313
Guidance for Reporting Hydrochloric Acid (acid
aerosols including mists, vapors, gas, fog, and other
airborne forms of any particle size)
Section 313 of the Emergency Planning and Community Right-to-Know Act of 1986
(EPCRA) requires certain facilities manufacturing, processing, or otherwise using listed toxic
chemicals to report their environmental releases of such chemicals annually. Beginning with the
1991 reporting year, such facilities also must report pollution prevention and recycling data for
such chemicals, pursuant to section 6607 of the Pollution Prevention Act, 42 U.S.C. 13106.
When enacted, EPCRA section 313 established an initial list of toxic chemicals that was
comprised of more than 300 chemicals and 20 chemical categories. EPCRA section 313(d)
authorizes EPA to add chemicals to or delete chemicals from the list, and sets forth criteria for
these actions.
CONTENTS
Section 1.0 Introduction 3
1.1 Who Must Report 3
1.2 Thresholds 4
1.3 What Constitutes Aerosol Forms of Hydrochloric Acid and Their
Manufacture, Processing, or Otherwise Use 4
Section 2.0 Guidance On Hydrochloric Acid Aerosols For Certain Specific Activities
That Generate Aerosols Forms 6
2.1 Hydrochloric Acid Aerosols Generated In Acid Reuse Systems .. 6
2.2 Hydrochloric Acid Aerosols Removed By Scrubbers 7
2.3 Hydrochloric Acid Aerosols Generated In Storage Tanks 7
Section 3.0 Properties of Hydrochloric Acid 8
3.1 Industrial Sources of Hydrochloric Acid Aerosols 10
U.S. Environmental Protection Agency
Region 5, Library (PL-12J)
77 West Jackson Boulevard, 12th Flo*
Chicago, ft 60604-3590
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CONTENTS cont.
3.1.1 Pulp and Paper Mills 11
3.1.2 Acid Aerosols From Hydrochloric Acid Manufacture 14
3.1.3 Secondary Metal Production 16
3.1.4 Steel Pickling 17
3.1.5 Stone, Clay, and Glass Products 20
3.1.6 Hydrochloric Acid Aerosol Formation From Combustion
Processes 21
3.1.6.1 Coal Combustion 21
Section 4.0 Measurement Methods 22
References 23
Appendix 1 26
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Section 1. Introduction
On July 25, 1996 (61 FR 38600), EPA modified the listing for hydrochloric acid (HC1)
(Chemical Abstracts Service Registry Number 7647-01-0) on the list of toxic chemicals subject
to the reporting requirements under section 313 of the Emergency Planning and Community
Right-to-Know Act of 1986 (EPCRA) (17). EPA modified the listing by deleting non-aerosol
forms of hydrochloric acid from the section 313 list based on the conclusion that they cannot
reasonably be anticipated to cause adverse effects on human health or the environment. EPA
added a modifier to the listing for hydrochloric acid to exclude the non-aerosol forms. The listing
now reads "Hydrochloric acid (acid aerosols including mists, vapors, gas, fog, and other airborne
forms of any particle size)." Therefore, beginning with the 1995 reporting year, facilities are no
longer required to include non-aerosol forms of hydrochloric acid in threshold and release
determinations. In this document we will use the term "hydrochloric acid aerosols" to indicate
airborne forms of hydrochloric acid as listed under section 313 of EPCRA.
The purpose of this document is to assist facilities in determining the sources and
amounts of hydrochloric acid aerosols that are to be included in threshold and release
determinations under EPCRA section 313. This document is not meant to be exhaustive, but
rather provides some guidance to help facilities in their determination of threshold and release
quantities. Threshold and release determinations for hydrochloric acid aerosols are highly
dependent on site specific conditions and equipment. Therefore, this document can only provide
general information concerning the possible formation and release of hydrochloric acid aerosols.
Guidance documents are available for some industry sectors subject to EPCRA section 313 and
these documents should be consulted for additional information (see http://www.epa.gov/tri).
Section 1.1. Who Must Report
A plant, factory, or other facility is subject to the provisions of EPCRA section 313, if it
meets all three of the following criteria:
• It is included in the primary Standard Industrial Classification (SIC) codes 20
through 39 or is in one of the following industries: Metal Mining, SIC code 10
(except SIC codes 1011, 1081, and 1094); Coal Mining, SIC code 12 (except SIC
code 1241); Electric Utilities, SIC codes 4911, 4931, or 4939 (each limited to
facilities that combust coal and/or oil for the purpose of generating power for
distribution in commerce); Commercial Hazardous Waste Treatment, SIC code
4953 (limited to facilities regulated under the Resource Conservation and Recovery
Act, subtitle C, 42 U.S.C. section 6921 et seq.); Chemicals and Allied Products-
Wholesale, SIC code 5169; Petroleum Bulk Terminals and Plants, SIC code 5171;
and, Solvent Recovery Services, SIC code 7389 (limited to facilities primarily
engaged in solvent recovery services on a contract or fee basis); and
• It has 10 or more full-time employees (or the equivalent of 20,000 hours per year);
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and
• It manufactures (includes imports), processes or otherwise uses any of the toxic
chemicals listed on the EPCRA section 313 list in amounts greater than the
threshold quantities specified below.
In addition, pursuant to Executive Order 12856 entitled "Federal Compliance with Right-
to-Know Laws and Pollutant Prevention Requirements," federal facilities are required to comply
with the reporting requirements of EPCRA Section 313 beginning with calendar year 1994. This
requirement is mandated regardless of the facility's SIC code.
Section 1.2. Thresholds
Thresholds are specified amounts of toxic chemicals manufactured, processed, or
otherwise used during the calendar year that trigger reporting requirements. Reporting is
required for hydrochloric acid aerosols if the following thresholds are exceeded.
• If a facility manufactures or imports 25,000 pounds of hydrochloric acid aerosols
over the calendar year.
• If a facility processes 25,000 pounds of hydrochloric acid aerosols over the calendar
year.
• If a facility otherwise uses 10,000 pounds of hydrochloric acid aerosols over the
calendar year.
The quantities of hydrochloric acid aerosols included in threshold determinations are not
limited to the amounts of hydrochloric acid aerosols released to the environment. All
hydrochloric acid aerosols manufactured, processed, or otherwise used are to be counted toward
threshold determinations. This includes any amount of hydrochloric acid aerosols that may be
generated in closed systems, storage tanks, or that are generated in stacks prior to or after being
treated by scrubbers.
Section 1.3. What Constitutes Aerosol Forms of Hydrochloric Acid and Their
Manufacture, Processing, or Otherwise Use
For the purposes of the reporting requirements under EPCRA section 313, hydrochloric
acid aerosols include mists, vapors, gas, fog, and other airborne forms of any particle size. Since
hydrochloric acid is a gas under ordinary conditions, it should be especially noted that the
gaseous form of hydrochloric acid, commonly referred to as hydrogen chloride, is included under
the EPCRA section 313 hydrochloric acid aerosols listing. Also note that there is no size limit
for particles that must be included under the EPCRA section 313 hydrochloric acid aerosols
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listing. Although the qualifier includes the terms mists, vapors, gas, and fog these terms are not
specifically defined for EPCRA section 313 since the last part of the qualifier "other airborne
forms of any particle size" makes it clear that any airborne form is covered by the listing. The
specific terms mists, vapors, gas, and fog are included to make it clear that hydrochloric acid that
is identified as being in one of these forms would be covered by the hydrochloric acid aerosols
listing.
If hydrochloric acid is present in the form of a gas, fog, vapor, mist or any other airborne
form, then hydrochloric acid is considered to be in the aerosol form and is covered by the
EPCRA section 313 hydrochloric acid aerosols listing. Solutions of hydrochloric acid which do
not become airborne are not covered by the EPCRA section 313 hydrochloric acid aerosols
listing but such solutions may generate hydrochloric acid aerosols during their manufacture,
processing or use. In general, hydrochloric acid aerosols are manufactured any time a solution
of hydrochloric acid is made to become airborne such as when it evaporates, is sprayed or
distilled. However if gaseous HC1 is absorbed into atmospheric water forming a mist, fog or
aerosol, no additional aerosol hydrochloric acid is produced since the gas is already considered a
reportable aerosol form. If the generation of hydrochloric acid aerosols through spraying or other
means is intentional (i.e., it is intended that the hydrochloric acid aerosol be generated for a
particular use activity) then, in addition to manufacturing the hydrochloric acid aerosol, such
aerosols are also being otherwise used. Thus, spraying of hydrochloric acid aerosols on to an
item for cleaning, etching, or other purposes constitutes the manufacture and otherwise use of
hydrochloric acid aerosols. Similarly, during pickling or cleaning of metals, if hydrogen gas is
liberated and sweeps hydrochloric acid into the air, then hydrochloric acid aerosols are generated.
If hydrochloric acid aerosols are used in a process in which any part of the hydrochloric acid
becomes incorporated into a product which is then distributed in commerce then, under EPCRA
section 313, the hydrochloric acid aerosols are considered to have been processed. Examples of
processes in which hydrochloric acid aerosols are manufactured, processed or otherwise used are
given below.
Hydrochloric acid aerosols are generally manufactured when:
• evaporation of HC1 occurs from a tank containing hydrochloric acid solution;
• volatilization of HC1 occurs during loading and unloading;
• when HC1 is entrained in hydrogen emanating from a metal cleaning or pickling
tank;
• when HC1 is distilled (including distillation for reclamation);
• when material containing chlorine is burned;
• when HC1 gas is formed as a result of a chemical reaction; or
• when solutions of hydrochloric acid are sprayed into the air.
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Hydrochloric acid aerosols are generally processed when:
• any part of the hydrochloric acid aerosol becomes incorporated into a product that is
distributed in commerce.
Hydrochloric acid aerosols are generally otherwise used when:
• HC1 is applied as a spray for surface treatment.
Section 2.0. Guidance On Hydrochloric Acid Aerosols For Certain Specific Activities That
Generate Aerosols Forms
EPA has provided the following guidance for specific activities that generate
hydrochloric acid aerosols. The guidance in sections 2.1, 2.2, and 2.3 is intended to apply only to
the specific situations discussed in these sections. If you are not sure whether this guidance
applies to the situation at your facility, then EPA should be consulted before using this guidance.
Section 2.1. Hydrochloric Acid Aerosols Generated In Acid Reuse Systems
When solutions of hydrochloric acid volatilize, the "manufacture" of a listed chemical
(hydrochloric acid aerosols as defined in section 1.3) has occurred. This is a result of the
qualifier to the hydrochloric acid listing, which excludes non-aerosol forms and limits the
reporting to aerosol forms only. The addition of the acid aerosol qualifier has an impact on
certain processes that, prior to the addition of the qualifier, would not have been considered to be
"manufacturing" a listed chemical. Acid reuse systems that use aqueous solutions of
hydrochloric acid to generate acid aerosols, use the acid aerosols, condense them back into
solution, and then reuse the acid solution again and again are impacted by the addition of the acid
aerosol qualifier. In such processes, the continuous reuse of the acid solutions generates very
large quantities of acid aerosols that technically should be counted towards the "manufacture"
[the generation of the acid aerosol is the "manufacture" of hydrochloric acid (acid aerosol)] and
"otherwise use" thresholds. This may result in many facilities greatly exceeding the
"manufacture" and "otherwise use" reporting thresholds that, prior to the addition of the
qualifier, would not have exceeded thresholds.
While it is technically correct to apply all of the quantities of acid aerosols generated in
such systems towards the "manufacture" and "otherwise use" reporting thresholds, EPA did not
intend to increase the reporting burden as a result of addition of the hydrochloric acid aerosol
qualifier. In addition, under EPA's general approach to reuse systems, a toxic chemical is not
counted toward thresholds each time it is reused but only once per reporting period, and that
approach would apply to hydrochloric acid reuse systems were it not for the aerosol qualifier.
Therefore, EPA is providing the following guidance to reduce the reporting burden for facilities
that operate such processes and to bring the treatment of such systems into alignment with EPA's
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general approach to reuse.
Rather than having facilities count all quantities of acid aerosol generated in such systems
towards the "manufacture" and "otherwise use" thresholds, EPA will allow facilities to apply the
total quantity of acid in these systems only once to these thresholds. For example, if an acid
reuse system starts the year with 2000 pounds of acid and 500 pounds is added during the year
then the total amount applied towards acid aerosol thresholds would be 2500 pounds. This
reflects a one time per year counting of all of the acid molecules as being in the acid aerosol form
rather than counting them over and over again each time the acid aerosol form is generated and
subsequently used. Since in these acid reuse systems the acid aerosols are "manufactured" and
then "otherwise used" the 10,000 pound "otherwise use" threshold would be the threshold that
would first trigger reporting from such systems.
The guidance in this section applies only to acid reuse systems and the reporting of
hydrochloric acid aerosols and sulfuric acid aerosols under EPCRA section 313. This guidance
does not apply to any other types of processes or to any other listed chemical.
Section 2.2. Hydrochloric Acid Aerosols Removed By Scrubbers
When a scrubber is used to remove hydrochloric acid aerosols prior to or in a stack, the
acid aerosols are usually converted to the non-aerosol form. The non-aerosol forms of
hydrochloric acid are not reportable under EPCRA section 313 because the qualifier to the
hydrochloric acid listing includes only acid aerosol forms. Hydrochloric acid as a discrete
chemical has not actually been destroyed by the scrubber, but the form of hydrochloric acid
reportable under EPCRA section 313 has been destroyed. Therefore, since hydrochloric acid
aerosols removed by scrubbers are converted to a non-reportable form, the quantity removed by
the scrubber can be reported as having been treated for destruction.
Section 2.3. Hydrochloric Acid Aerosols Generated In Storage Tanks
Hydrochloric acid aerosols are generated in the empty space (head space) above
hydrochloric acid solutions contained in storage tanks. The amounts of acid aerosols generated
in such storage tanks are to be applied towards the "manufacture" threshold for hydrochloric acid
aerosols. In such storage tanks the hydrochloric acid molecules are constantly moving between
the atmosphere and the solution. EPA does not intend for facilities to count such movement of
the acid molecules in and out of the stored acid solution as continuous "manufacture" of
hydrochloric acid aerosols. For such storage tanks the amount of acid aerosol to be applied
towards the "manufacture" threshold is the average amount that existed in the atmosphere above
the acid solution during the year.
Each facility should determine the average conditions for their specific storage tank (i.e.,
the capacity of the tank, the average amount in the tank, the average head space in the tank, the
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concentration of the acid solution stored, the temperature, and other information that may have
an impact on aerosol calculations) and make the appropriate calculation of the amount of acid
aerosol to apply towards the "manufacture" threshold. Any amounts of hydrochloric acid
aerosols that may be released from the storage tank through venting or fugitive releases must also
be included in the threshold determination. If the storage tank is refilled and drawn down several
times during the year then the calculations should be based on all of the acid that was stored in
the tank. For example, if a 10,000 pound capacity tank is refilled and drawn down 6 times during
the year (such that 60,000 pounds of acid were stored in the tank during the year) then the tank
calculations, based on the average condition for one 10,000 pound tank of acid, should be
multiplied by 6.
EPA has an AP-42 document that presents models for estimating air emissions for
organic liquid storage tanks (26). These models can be adapted to estimate emissions of
hydrochloric acid aerosols. EPA also has software programs for estimating the losses of volatile
organic chemicals (VOCs) from storage and treatment facilities which can be adapted to
hydrochloric acid aerosols. TANKS, a DOS-based computer software program, is useful for
estimating emissions from fixed- and floating-roof storage tanks. WATERS (Wastewater
Treatment Compound Property Processor and Air Emissions Estimator program) is another
DOS-based computer software program that is useful for estimating chemical-specific emissions
from wastewater collection and treatment systems.
The TANKS 3.0 program requires certain information about a storage tank and the liquid
it contains to calculate the tank's air emissions. This information is entered and stored in tank
records. There are four categories of information in a tank record: tank information (e.g.,
construction type, and physical characteristics); fitting information (for floating roof tanks only);
site information (e.g., ambient temperature, wind speed); and liquid information. Information on
the chemical composition and vapor pressure of the stored hydrochloric acid must be provided.
Information has been provided in Appendix 1 to assist in such calculations.
WATERS is an analytical model for estimating chemical-specific emissions from
wastewater collection and treatment systems. It can be used for estimating emissions from open
tanks and agitated systems. Both of the above software estimation programs can be downloaded
from the EPA web site at http://www.epa.gov/ttn/chief/software.html
Section 3.0. Properties of Hydrochloric Acid
HC1 is a gas at normal temperature and pressure with a normal boiling point of -85 °C.
The gas is generally referred to as hydrogen chloride, while the solution is more commonly
referred to as hydrochloric acid, however the terms are often used interchangeably. HC1 gas is
readily absorbed by water. Therefore, gaseous HC1 will partition into atmospheric water such as
fog, mist, and cloud water (the very small aerosol droplets of water of which clouds are
composed).
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The solubility of HC1 in water at atmospheric pressure is 42% by weight at 20 °C. It is
essentially totally ionized in solution. Hydrochloric acid solutions deviate widely from Henry's
law1 at all concentrations. Concentrated hydrochloric acid solutions (-37%) fume readily in
moist air.
Under EPCRA section 313, hydrochloric acid aerosols are reported as 100% HC1 so the
amount of releases reported is independent of whether HC1 is present as a gas or in atmospheric
water (e.g., mist or fog) containing fractional amounts of HC1.
Hydrogen chloride and water form a constant boiling mixture (azeotropic mixture or
azeotrope); at atmospheric pressure, 101 kiloPascals (kPa), the mixture boils at 108.584 °C and
has a composition of 20.222 wt % HC1 (2). As the pressure increases, the boiling point increases
and the azeotropic composition decreases (see Appendix 1). At HC1 concentrations below the
azeotropic concentration, the vapor has a higher water concentration than the solution with which
it is in equilibrium. At concentrations higher than the azeotropic concentration, the vapor is
enriched in HC1 relative to the liquid. Above 35 wt % HC1, the vapor has very little water
content.
An equation of state for hydrochloric acid for mole fractions (x) up to 0.23 at
temperatures up to 780 K and pressures up to 150 bar has been developed and describes the
behavior in the single phase (vapor) region to about ± 1% (20). In the equation below the
pressure (p) is in kPa2 and the temperature (T) in degrees Kelvin.
log]0 p = 7.515 - 2056 T1 + xna (2.064 - 888 T1)
Commercial reagent grade hydrochloric acid normally contains 36.5 to 38.0 wt % hydrochloric
acid with the remainder being water. A vapor-liquid phase diagram (Figure Al), vapor
composition data (Figure A3 and Table Al), and vapor pressure data (Table A2) as a function of
temperature and composition for aqueous hydrochloric acid appear in Appendix 1. Conversion
factors for pressure and concentration units appear in Tables A3 and A4 of Appendix 1.
Nomograms3 are available which allow you to determine the partial pressure of HC1, the partial
pressure of water, the total pressure, and the vapor composition of the vapor as a function of
concentration of aqueous hydrochloric acid and temperature (19). The information in Appendix
1 and the guidance in sections 2.3 can be used to assist in determining if significant amounts of
hydrochloric acid aerosols are present in storage tanks.
'Henry's law states that the partial pressure of a component becomes proportional to its mole fraction in the
limit of zero concentration.
To obtain the pressure in other units, add the following constant to the right hand side of the equation:
bars, -2.000; torr, 0.875; atm, -2.006; psi, -0.839.
3 A nomogram is a graphic representation that consists of several lines marked off to scale and arranged in
such a way that by using a straightedge to connect known values on two lines an unknown value can be read at the
point of intersection with another line.
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Section 3.1. Industrial Sources of Hydrochloric Acid Aerosols
In 1995 there were 1976 facilities that reported for hydrochloric acid aerosols under
EPCRA section 313(18). In order to analyze the more significant industrial sources of
hydrochloric acid aerosols, this document focuses on the 326 facilities that reported releases of
25,000 pounds or more to air. The number of these facilities in each of the covered 2-digit SIC
codes is shown in Table 1, as well as the prominent types of industries within each SIC code that
have reported hydrochloric acid emissions to air. The industries shown in italics include 50
facilities that are in the 97.4th percentile (over 326,000 pounds per year) for hydrochloric acid
releases to air. These 50 facilities' air emissions are almost entirely from point sources, and 34
of them report producing hydrochloric acid as a byproduct.
Table 1. Industrial Categories of 326 Facilities Emitting over 25,000 Ibs/yr of Hydrochloric
Acid Aerosols in 1995 and Top 50 Emitters.
2-Digit
SIC Code
26
28
33
37
32
20
24
30
29
34
22
49
21
35
36
38
27
Category
Paper and Allied Products
Chemicals and Allied Products
Primary Metal Industries
Transportation Equipment
Stone, Clay, and Glass Products
Food and Kindred Products
Lumber and Wood Products
Rubber and Misc. Plastics Products
Petroleum and Coal Products
Fabricated Metal Products
Textile Mill Products
Electric, Gas, and Sanitary Services
Tobacco Products
Industrial Machinery and Equipment
Electronic & Other Electric Equipment
Instruments and Related Products
No. Sites*
(326)
236
161
54
20
19
12
11
8
7
7
5
4
4
4
3
1
1
(50)
46
30
6
1
3
1
1
1
1
1
3
1
1
Major Industries in Category"
Paper, pulp and paper board mills
Plastics and resins, industrial inorganic chemicals,
organic fibers; pharmaceuticals; alkalies and
chlorine
Blast furnaces and steel mills; aluminum sheet,
secondary nonferrous metals; cold finishing of
steel; steel wire; aluminum rolling and drawing
Motor vehicle bodies; motor vehicle parts; space
propulsion units and parts
Cement, hydraulic; minerals, ground or treated;
glass; lime; bricks
Malt beverages, wet corn milling, soybean oil mills
Sawmills and planing mills; reconstituted wood
products; softwood veneer and plywood
Plastic products
Petroleum refining; petroleum and coal products
Metal coatings
Non-woven fabrics
Electric services, combination utilities, refuse
systems
Cigarettes
Construction machinery
Photographic equipment and supplies
*A site may list more than one SIC code.
**The industries shown in italics are among the top 50 facilities for hydrochloric acid releases to air. Other industries are those
more frequently occurring among the 326 facilities emitting more than 25,000 pounds of HC1 to air.
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The industrial breakdown does not necessarily indicate that emissions result from
processes unique to the industry. For example, combustion of chlorine-containing organic waste
or fuels may result in emissions of hydrochloric acid aerosols. This may occur at Electric
Utilities burning coal (SIC codes 4911) or at a Commercial Hazardous Waste Treatment facility
(SIC code 4953) burning chlorine-containing waste.
Section 3.1.1 Pulp and Paper Mills
The kraft pulping process involves the digesting of wood chips at elevated temperature in
"white liquor", an aqueous solution of sodium sulfide and sodium hydroxide, to dissolve the
lignin that binds the cellulose fibers of the wood together. The spent liquor used to digest wood
chips, called "black liquor", is combusted in recovery furnaces to recover heat and cooking
chemicals. Black liquors can contain significant levels of chlorides which during combustion
undergo both transformation and partitioning. A small fraction of the chlorides can be converted
to hydrochloric acid and be released to the atmosphere in stack gases. Kraft recovery furnace
flue gas is the largest source of hydrochloric acid emissions from pulp and paper mills. It is
released from recovery furnaces of both the direct contact evaporator (DCE) and non-direct
contact evaporator (NDCE) types. In a DCE, the flue gas comes in contact with the black liquor,
whereas in a NDCE, it does not. Chlorides in black liquor originate primarily from the wood
chips used for pulping and the caustic used as makeup during white liquor preparation. Mill
process water may also contribute significant chloride. The chloride component of black liquor
may end up either in the smelt or deposited particulate phase as inorganic alkali salts or in the
emitted gas phase as mostly hydrochloric acid. The smelt is dissolved in water to form "green
liquor", which is transferred to a causticizing tank where quicklime is added to convert the
solution back to white liquor for return to the digester. A lime mud precipitates from the
causticizing tank. This is calcined in a lime kiln to regenerate quicklime. HC1 aerosols are
emitted from the causticizing area/lime kilns. However in most studies, these emissions are
included with those from the recovery furnaces.
In developing National Emission Standards for Hazardous Air Pollutants (NESHAP),
EPA analyzed data from their 5 Mill Study, a Texas Mill Study, and International Paper reports
(24). The Agency looked at emissions from processes connected with kraft pulp mills and
derived average HC1 emission factors for these processes. No HC1 emissions were indicated for
acid sulfite, and neutral sulfite semi-chemical (NSSC) pulping and soda mills. EPA emission
data and emission factors for kraft pulp mills appear in Table 2.
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Table 2. Emissions and Emission Factors from Kraft Pulp Mills*
Process Unit
Causticizing area
DCE Recovery furnaces
NDCE Recovery furnaces
Bleach plant air vents
Boilers
Example Kraft Mill Emission Estimates (Mg/yr)
(based on 1000 TODP per day)
Range
0,81-6.6
9.2-85
NA
NA
NA
Typical Emissions
2.5
58
(59)
0.63
C3.0)
Typical HCI
Emission Factors
(Ib/TODP)
0.0159
0.362
0.365
0.0396
0.0192
"Source: Reference 24. Emissions and emissions factors based on tons of oven-dried pulp (TODP) arc derived from data on
methanol and HCI to methanol ratios. Boiler data is based on average of industry test data reports. NA = not available
While the formation of HCI in the combustion of coal, municipal solid waste, and other
chloride-containing fuels is due to the direct conversion of organic chlorides to HCI during
combustion, HCI formed in a kraft recovery furnace, where the bulk of the chlorides are in the
inorganic form, is believed to result from an entirely different mechanism involving SO2, namely
4NaCl + 2SO
2H2O
O2 -> HCI + 2Na2SO4.
The reaction may involve KC1 in addition to NaCl shown above. The discovery of this
reaction mechanism followed the observation that the mole percent chlorine in the gas phase
increased with the sulfur content of the liquor.
The National Council of the Paper Industry for Air and Stream Improvement (NCASI)
tested fourteen recovery furnaces, 10 of the non-direct contact type and 4 of the direct contact
type for HCI emissions (5). In the study, emissions of SO2 and pertinent information on furnace
operating conditions was collected to ascertain whether there was a relation between HCI
emissions and other factors. Stack emissions were measured according to EPA Method 26. A
prototype continuous monitoring system for HCI gave unacceptably low results compared with
the standard method. HCI emissions for the mills were very variable. The results of the study
appear in Table 3. NCASI also compiled results of recent HCI emission tests for 17 kraft
recovery furnaces (1 1 NDCE and 6 DCE) from other mills. These data also appear in Table 3.
Results are reported in Ibs of HCI per ton of black liquor solids (BLS) or Ibs of HCI per ton of
air-dried pulp (ADTP).
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Table 3. Kraft Mill Emission Factors from NCASI Study and 17 Individual Mill Study*
Study/Mill Type/Number
NCASI- 10NDCE
NCASI - 4 DCE
NCASI - 14 Mill SUMMARY
17 Mill Study- 11NDCE
17 Mill Study - 6 DCE
17 Mill Study - SUMMARY
2 1 NDCE Recovery Furnaces
1 0 DCE Recovery Furnaces
HC1 Emissions in Ib/ton BLS
Range
0.00 to 0.84
0.06 - 0.52
8x 10'4-0.84
ND- 1.23
ND - 0.36
ND-1.23
ND- 1.23
ND - 0.52
Average
0.29
0.25
0.28
0.24
0.14
0.20
0.26
0.18
HC1 Emissions in Ib/ADTP
Range
1 x 10J- 1.36
ND - 2.00
Average
0.47
0.37
0.44
0.33
* Source Reference 5 Abbreviations BLS = black liquor solids, ND = not detected, DCE = direct contact evaporator, NDCE = non-direct
contact evaporator
The chlorine content of the as-fired black liquor solids averaged 0.85% (range 0.36 to
1.35%). Material balances showed that only a very small amount of the chloride present in the
as-fired black liquor solids (1.4% on the average) is released through the stack as HC1; the rest is
captured in the precipitated dust (24-34%) or retained in the smelt (64-75%). The results showed
that stack HC1 concentrations correlated strongly only with SO2 concentrations in kraft recovery
stacks. In the case of NDCE furnaces for stack SO2 concentrations ranging from 0-500 parts per
million (ppm), the stack HC1 concentration could be best expressed as a Langmuir-type
absorption isotherm
[HCl]
1.28x[SO2]
1 + 0.017 x [SO]
where the concentrations of HCl and SO2 are expressed as ppm dry stack O2. The rate-
controlling step involved the adsorption of SO2 by the salt. For DCE furnaces, there was no clear
correlation between stack HCl and stack SO2 levels. However, NCASI data and recent tests at
individual mills showed HCl emissions from DCE furnaces to be significantly lower than for
NDCE furnaces.
NCASI also analyzed the chloride inputs to kraft liquor cycles for 8 of the mills because it
might shed some light on the emission behavior of HCl. They found that the average chloride
input for mills that used reagent grade caustic was 0.48 Ib Cl/ADTP whereas those that used
diaphragm-grade caustic was 0.94 Ib/ADTP. Similarly, NCASI found that the chloride content
of the wood chips ranged from 12 to 93 ppm, averaging 35.5 ppm (45.7 and 29.8 for hard and
13
-------
soft woods, respectively) dry basis. However, emission factors were not developed that reflected
these differences in chloride inputs.
The average hydrochloric acid emissions from the direct contact and non-direct contact
evaporator recovery furnaces can be used to estimate hydrochloric acid emissions. For example,
a kraft mill using 1100 tons of air dried pulp (ADTP) per day and generating 0.62 tons of BLS
per ADTP while operating two DCE furnaces for 365 days per year has determined that an
appropriate HC1 emission factor for their furnaces is 0.18 Ib/ton BLS. Therefore, the pounds of
HC1, H, emitted during the year will be:
H = 1100 ADTP/day x 365 days/year x 0.62 ton BLS/ADTP x 0.18 Ib HCl/ton BLS = 44,800
HC1 emission factors for recovery furnaces vary widely as the data provided in Tables 2 and 3
indicates. In the absence of site-specific emission factors, use an emission factor from these
tables that best approximates your facility.
The pounds of hydrochloric acid aerosols produced in recovery furnaces on site should be
combined with that produced from the bleach plant and from waste wood combustion and coal
combustion in boilers which are used for steam and power generation. Generally, bark is the
major type of waste burned in pulp mills and either a mixture of wood and bark waste or wood
waste alone is burned most frequently in the lumber and plywood industries. An average
emission factor for 'chlorine' from wood waste combustion is 7.8 x 10"3 Ib/ton (7). Assuming the
emissions to be HC1, this emission factor is equivalent to 8.0 x 10"3 Ib of HCl/ton. However the
factor was based on data from one source test. Guidance on the production of HC1 in coal-fired
boilers is given in Section 3.1.6.1.
Sludge from the waste water treatment plant where bleaching waste water is sent may be
burned and release HC1 to air. Hydrochloric acid emissions may also occur from the bleach plant
where SO2 is used to treat vent gas for controlling C12 and C1O2 emissions (6). The following
reactions indicate that HC1 is released in the process.
2C1O2 + 5SO2 + 6H2O -> 2HC1 + 5H2SO4
Cl, + SO, + 2H,0 -+ 2HC1 + H,SO,
Section 3.1.2 Acid Aerosols from Hydrochloric Acid Manufacture
Over 90% of hydrochloric acid is produced as a byproduct from the production of
chlorinated solvents, fluorocarbons, isocyanates, organics, magnesium, and vinyl chloride
monomer (2,13,14). Examples of these include (15):
• Vinyl chloride from dehydrochlorination of 1,2-dichloroethane
C1CH2CH2C1 -> CH2=CHC1 + HC1;
14
-------
Isocyanates from amine phosgenation
RNH2 + COC12 -+RNCO + 2HC1;
Chlorination of aliphatic hydrocarbons
CH3C1 + 2C12 -> CHC13 + 2HC1; and
Fluorocarbons from alkyl chlorides
CC14 + 3HF -» CC1F3 + 3HC1.
Much of the vinyl chloride monomer and chlorinated solvents byproduct acid is recycled into the
production process. If HC1 is recycled in a closed system no HC1 aerosol emissions are likely to
occur. After the chlorination process, the HCl-containing gas stream goes to an absorption tower
where concentrated hydrochloric acid is produced by absorption of HC1 gas into a weak solution
of hydrochloric acid. The final gas stream may be sent through a scrubber to remove any
remaining HC1 before it is vented to the atmosphere.
Another process for producing byproduct HC1 is from magnesium metal recovery using
electrolytic reduction of magnesium chloride from seawater to form magnesium and chlorine.
The magnesium chloride hexahydrate is dehydrated stepwise; the further dehydration of the
dihydrate results in some hydrolysis with the concurrent formation of hydrogen chloride (16).
Less than 10% of U.S. HC1 production is made by the direct reaction of hydrogen and
chlorine,
H2 + C12 -+2HC1,
generally referred to as the thermal method. This reaction is highly exothermic and when a
stoichiometric mixture is used produces a very pure product after cooling. The 'burner gas' that is
produced is sent into an absorber to produce hydrochloric acid solutions.
Hydrochloric acid is also recovered from the disposal of chlorinated hydrocarbons by
incineration (1). The combustion of these wastes ideally produce hydrogen chloride, water, and
carbon dioxide. Excess oxygen must be present to insure complete combustion. However, the
hydrogen chloride gas formed can also react with this oxygen to form chlorine and water,
4HC1 + O2 -+2C12 + 2H2O.
The reaction has a negative enthalpy and entropy of reaction. With increasing temperature, the
equilibrium shifts to the left, favoring the formation of HC1. A temperature greater than 1000 °C
is necessary to keep the chlorine at an acceptable level. For this reason and to prevent nitrogen
oxides from forming, incineration is carried out between 1000 and 1200 °C.
15
-------
Anhydrous hydrochloric acid may be recovered from aqueous acid. If the aqueous acid is
more concentrated than the azeotropic concentration, simple distillation is adequate. Any
recovery or manufacturing process in which vapor phase hydrochloric acid is produced from the
aqueous acid is considered as the production of hydrochloric acid aerosols according to section
313 of EPCRA. An old method of HC1 production based on the reaction of a metal chloride,
particularly sodium chloride, with sulfuric acid or a hydrogen sulfate salt is not used presently in
the United States.
Nearly all the hydrochloric acid aerosols emitted from hydrochloric acid manufacturing
plants come from the exit gases of the absorber or the purification system (12). The purification
system for byproduct anhydrous HC1 is dictated by the level and type of contaminants originating
from the primary process and the end use of the acid. Common methods of purification include
absorption, adsorption, distillation, or chemical reactions. In many cases the HC1 can be utilized
internally without further purification. An example is in vinyl chloride manufacturing where
byproduct HC1 from the 1,2-dichloroethane cracking step can be used directly in the
oxychlorination unit. According to a 1985 emission inventory, less than one percent of HC1
emissions came from direct production of HC1 (12). EPA analyzed emission data and estimated
emission factors for byproduct HC1 manufacture of 0.15 Ib/ton (0.08 kg/Mg) HC1 produced with
a final scrubber and 1.8 Ib/ton (0.90 kg/Mg) HC1 without a scrubber. However the data are weak,
being based on few and relatively old data, and at best provide only an estimate of emissions
from this industry.
Section 3.1.3. Secondary Metal Production
Hydrochloric acid emissions from secondary metal production and foundries arise from
chlorine-containing components in the feed (e.g., lacquer) or flux. Therefore, HC1 emissions
would be highly dependent on the feed, the type and amount of fluxing agent required, as well as
the type and efficiency of pollution control equipment used. In secondary lead production, the
feed is primarily spent lead acid batteries. HC1 emissions in secondary lead production arise
from the PVC cell separators used in the batteries. However, PVC is being replaced by a
material that does not contain chlorine and the proportion of batteries containing PVC separators
will decline as these batteries are removed from service (25). In 1994, less than 0.1% of batteries
contained PVC. Therefore, secondary lead production would no longer be a major source of HC1
emissions in the future and EPA withdrew proposed C12/HC1 emission standards for the industry
(25).
In secondary aluminum operations, chlorine or other chlorinating agents (e.g., anhydrous
aluminum chloride, chlorinated organics) may also be introduced as fluxes in demagging
operations. Excess chloride combines with aluminum to form aluminum chloride which is a
vapor at furnace temperatures and readily combines with water vapor to form hydrochloric acid.
A few emission factors, reported in the FIRE database (9), are listed for reference in Table 4.
16
-------
Table 4. Emission Factors for Secondary Metal Production.
Source
Secondary lead production
Secondary lead production
Secondary aluminum
production
Feed
spent lead batteries
spent lead batteries
aluminum cans, de-
laauerine olant
Emission Factor
2.5x 10-3lb/tonlead
produced
2.7 Ib/ton lead
produced
1.6x 10-3lb/lbcans
Pollution Control
Device
Afterburner, baghouse,
ammonia scrubber
Afterburner, baghouse
Multiple cyclones
Reference
Date
1994
1994
1991
Section 3.1.4. Steel Pickling
During the hot forming or heat treating of steel, oxygen from the air reacts with the iron
to form iron oxides or scale on the surface of the steel. This scale must be removed before the
iron is subsequently shaped or coated. One method of removing this scale is pickling with
hydrochloric acid. Pickling is conducted by continuous, semi-continuous or batch modes
depending on the form of metal processed. In developing a National Emission Standard for the
Steel Pickling industry, EPA recently surveyed the industry and produced a background
information document containing detailed information concerning the various processes in the
industry, pollution control devices, and emissions (21).
When iron oxides dissolve in hydrochloric acid, ferrous chloride is formed according to
the following reactions:
Fe2O3 + Fe + 6HC1 -> 3FeCl2 + 3H2O
FeO + 2HCl ->FeCl2 + H2O
Since Fe3O4 is Fe2O3'FeO, the reaction for Fe3O4 is the sum of the two reactions. Some of the
base metal is consumed in the first reaction as well as in the following reaction:
Fe + 2HCl
An inhibitor is usually added to lessen the acid's attack on the base metal while permitting it to
act on the iron oxides. The rate of pickling increases with temperature and concentration of HCI.
As pickling continues, HCI is depleted and ferrous chloride builds up in the pickling liquid to a
point where pickling is no longer effective. At this point, the old liquid is discharged and the
pickling tank replenished with fresh acid. Typical HCI concentrations in a batch pickling process
are 12 wt % for a fresh solution and 4 wt % before acid replenishment. At these concentrations,
the concentration of HCI in the vapor phase increases rapidly with temperature.
Hydrochloric acid aerosols are produced and released into the air during the pickling
process as HCI volatilizes and steam and hydrogen gas with entrained acid fumes rise from the
surface of the pickling tank and from the pickled material as it is transferred from the pickling
17
-------
tank to the rinse tank. Pickling and rinse tanks are covered and the acid fumes are generally
collected and treated by control devises ( e.g., packed tower scrubbers) to remove HC1.
Emissions from many batch operations are uncontrolled. Pickling is sometimes accomplished in
vertical spray towers. In this process, all the HC1 in the pickling solution produces hydrochloric
acid aerosols that is also used. Acid storage tanks and loading and unloading operations are also
potential sources of HC1 emissions. Uncontrolled HC1 emissions from a storage tank may be on
the order of 0.07 to 0.4 tons per year (tpy) of HC1 per tank, depending on tank size and usage.
For each million tons of steel processed at continuous coil or push-pull coil model facilities,
storage tank losses are estimated to amount to 0.39 tpy. For other types of pickling facilities,
storage tank losses are estimated to be about 11.19 tpy of HC1 per million tons of steel processed.
The guidance for acid storage tanks in section 2.3 is applicable to storage tanks used in
conjunction with the pickling process and may be extended to apply to the pickling process itself.
For storage tanks, one applies the amount of hydrochloric acid aerosol generated from a tank
under average capacity and other conditions to the manufacturing threshold and multiplies that by
the number of times the tank has been drawn down and refilled. The amount of acid aerosol
manufactured during the picking process can be similarly determined by the amount of HC1
generated from the pickling tanks during the processing of a certain amount of material and
scaling that figure up to apply to all the material processed by the same process and under the
same conditions. The amount of hydrochloric acid aerosols lost from the pickling tanks are
counted towards the material released to air unless the aerosol is collected and removed before
exiting the stack. The hydrochloric acid aerosol collected in a scrubber is converted to the non-
aerosol form, not reportable under EPCRA section 313; the hydrochloric acid aerosol removed
by the scrubber is considered to have been treated for destruction (see Section 2.2).
Hydrochloric acid may be recovered from the waste pickling liquid (WPL) in an acid
regeneration process. This process has the potential of emitting significant amounts of
hydrochloric acid aerosols. Often acid regeneration plants surveyed by EPA (21), annual
capacities ranged from 3.2 to 39.8 million gallons per year for a single facility. The spray
roasting acid regeneration process is the dominant one presently employed. One older facility
used a fluidized bed roasting process.
In the spray roasting acid regeneration process, WPL at 2-4% HC1 comes into contact
with hot flue gas from the spray roaster which vaporizes some of the water in the WPL. The
WPL then becomes concentrated pickling liquor (CPL). The CPL is then sprayed on the spray
roaster where ferrous chloride in the droplets falling through the rising hot gases react with
oxygen and water to form ferric oxide and HC1,
FeCl2 + O2 + H2O -» Fe2O3 + HCl.
Flue gas containing HC1 goes to a venturi preconcentrator and an absorption column. The
regenerated acid contains approximately 18% HC1 by weight. Emissions from acid regeneration
plants range from about 1 to more than 10 tpy from existing facilities with and without pollution
control devises (controlled and uncontrolled facilities). The amount of hydrochloric acid
regenerated as an aerosol should be applied towards the EPCRA section 313 "manufacturing"
18
-------
threshold.
Acid regeneration plants have storage tanks for spent and regenerated acid and these
tanks are potential sources of HC1 emissions. Emission estimates for uncontrolled and controlled
storage tanks at acid regeneration facilities are 0.0126 and 0.008 tpy per 1,000 gallons of storage
capacity, respectively.
Acid recovery systems are used to recover the free acid in the WPL. They are not
employed in larger facilities because they recover only the 2-4% free HC1 in the spent acid, but
leave the FeCl2 in the solution which must be processed or disposed of separately. These acid
recovery systems are generally closed-loop processes that do not emit HC1. However, any acid
aerosols generated in these types of recovery systems should be applied towards the EPCRA
section 313 "manufacturing" threshold.
In their survey, EPA compiled data from different types of pickling operations and their
estimated emissions (21). This information is reproduced in the Table 5.
Table 5. Annual Emission Estimates from Steel Pickling Operations
Type of Facility
Continuous coil
Push-pull coil
Continuous rod/wire
Continuous tube
Batch
Acid regeneration
Storage tanks
No. of
Facilities
36
19
20
4
26
10
99
No. of
Operations
64
22
55
11
59
13
369 (est)
Uncontrolled emission
(Mg/yr)
22,820
815
6,524
100
2,632
5,662
41
Controlled emissions
(Mg/yr)
2,640
29
4,252
52
1,943
393
24
Source: Reference 21, page 3-32.
In order to estimate emissions from pickling facilities, EPA developed seventeen model
plants to represent five types of pickling operations and one acid regeneration process (21). The
model plants include one or more size variation for each process model. The model plants were
developed from information obtained from a survey of steel pickling operations and control
technologies. EPA estimated emissions rates for model facilities. Using these emission rates and
the production and hours of operation for the model pickling plants, emission factors were
calculated. These appear in Table 6.
19
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Table 6. Emissions and Emission Factors for Model Pickling Plants
Production Hours of Uncontrolled Control
Type Facility Operation HCI Emissions Efficiency
(tpy)* (hr) (Ib/hr) %
Continuous Coil (S)
Continuous Coil (M)
Continuous Coil (L)
3ush-pull coil (S)
•Mash-pull coil (M)
•Mash-pull coil (L)
Continuous rod/wire (S)
Continuous rod/wire (M)
Continuous rod/wire (L)
Continuous tube (S)
Continuous tube (L)
Batch (S)
Batch (M)
Batch (L)
\cid Regeneration (S)
\cid Regeneration (M)
\cid Regeneration (L)
450,000
1,000,000
2,700,000
300,000
550,000
1,300,000
10,000
55,000
215,000
80,000
420,000
15,000
75,000
170,000
4
13.5
30
6,300
6,300
7,000
5,000
4,400
8,760
5,100
7,800
7,200
6,400
6,700
4,400
4,600
5,700
8,200
7,700
8,760
111
179
347
12
27
42
46
119
413
73
312
16
65
147
7
28
1064
93
92
92
98
98
95
98
84
—
95
95
94
90
81
98
98
98.5
Emission Factor
Ibs HCI/tons processed**
(U) (Q
1.6
1.1
0.9
0.2
0.2
0.3
23.5
169
13.8
5.8
5.0
47
4.0
4.9
14350.0
15970.4
310688.0
0.1
0.1
0.1
0.0
0.0
0.0
0.5
2.7
—
0.3
0.2
03
0.4
0.9
287.0
319.4
4660.3
Source: Based on information in Reference 21.
Abbreviations: S = small; M = medium; S = large; U = uncontrolled; C = controlled.
*Units of production for acid regeneration facilities are in millions of gallons/yr.
**Emission factor units for acid regeneration facilities are in Ibs of HCI per million gallons of HCI produced.
A National Emission Standard for Hazardous Air Pollutants (NESHAP) for new and
existing hydrochloric acid process steel pickling lines and HCI regeneration plants pursuant to
section 112 of the Clean Air Act as amended in November 1990 has been proposed (62 FR
49051, September 18, 1997). The purpose of this rulemaking is to reduce emissions of HCI by
about 8360 megagrams per year.
Section 3.1.5. Stone, Clay, and Glass Products
Mineral products invariably contain chloride impurities which may be emitted as
hydrochloric acid aerosols during processing. Some chloride may also be retained in condensed
phases and therefore a mass balance approach to determining the amount of HCI emissions
would not be expected to yield accurate results. As with any high-temperature, energy-intensive
industrial processes, combustion of fuels to generate process energy may release substantial
amounts of HCI. Therefore, emissions from the fuel may contribute to those measured for the
process. EPA has reviewed data from emission tests and developed emission factors for brick
manufacture, cement kilns, and glass manufacture.
An emission factor (EF) of 0.17 Ib/ton (0.65 kilogram per Megagram (kg/Mg)) was
estimated for uncontrolled HCI emissions from natural gas-fired kilns used in brick manufacture
20
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(11). The EFs were developed using A-rated (excellent) data from one test, B-rated (above
average) data from two tests, and C-rated (average) data from 2 tests, but because of the wide
range of the data, 0.018 Ib/ton to 0.41 Ib/ton, the average emission factor developed is D-rated
(below average).
Emission factors of 0.049 Ib/ton (0.025 kg/Mg) and 0.14 Ib/ton (0.073 kg/Mg) of clinker
production have been developed for portland cement kilns using electrostatic precipitators and
fabric filters, respectively. The ratings for these EFs are E (poor) and D (below average),
respectively, in part because the small number of facilities used in developing the factors may not
be representative of the industry. All emission tests used were for coal-fired kilns. Hazardous
wastes are often added to cement kilns both as a subsidiary fuel or to dispose of the waste.
Emission factors cannot be developed for such kilns because emission characteristics would be a
function of the amount and chemical constitution of the waste used and therefore could not be
used in estimating emissions from other kilns in the industry.
For container and pressed and blown glass, hydrogen chloride is reported to be emitted
during surface treatment process at a rate of < 0.2 Ib/ton (8).
The emission factors for stone, clay and glass products are summarized in Table 7.
Table 7. Emission Factors for Stone, Clay and Glass Products
Industry
Brick Manufacture
Portland Cement
Portland Cement
Container, Pressed and Blown Glass
Pollution Control
uncontrolled
electrostatic precipitator
fabric filter
not reoorted
Emission Factors
Ibs/ton product
0.17
0.049
0.14
<0.2
kg/Mg product
0.65
0.025
0.073
Section 3.1.6. Hydrochloric Acid Aerosol Formation from Combustion Processes
EPCRA section 313-covered facilities that combust chlorine-containing fuel or other
material have the potential for manufacturing and releasing hydrochloric acid aerosols. Facilities
that combust coal and/or oil for the purpose of generating power for distribution in commerce
and facilities that combust or incinerate solid waste and that are regulated under RCRA subtitle C
are examples of such facilities.
Section 3.1.6.1 Coal Combustion
Hydrochloric acid aerosols are produced in boilers during coal combustion. According to
a 1985 inventory, over 89% of all HC1 emitted to the atmosphere resulted from coal combustion
(12). While most of the chlorine contained in the coal is released in the form of hydrogen
chloride, lesser amounts of chlorine gas may also be emitted and a portion of the chlorine content
21
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of the fuel may be absorbed onto fly ash or bottom ash (10). If HC1 aerosols are produced during
or after combustion, the amount must be applied to the manufacturing threshold. In the absence
of better data, facilities can use the HC1 emission factors presented in Table 8. These factors are
more appropriate than those AP-42 factors, which are averages of factors for each type of coal
(10). Use the emission factor that corresponds to the type of coal being combusted. If a facility
combusts a mixture of coal types, and knows the mixture ratio, it may apply this ratio to the
emission factors in Table 8. Facilities that do not know the type of coal they use should assume
the coal is bituminous or subbituminous, since these types are commonly used. Hydrochloric
acid aerosols may also be manufactured during plant maintenance from the evaporation of boiler
cleaning wastes.
Table 8. Emission Factors for HC1 Manufactured during the Combustion of Coal
Source
Anthracite Coal
Bituminous Coal
Subbituminous Coal
Lignite
Emission Factor
(Ibs/ton coal)
0.91
1.9
1.9
0.01
If a facility combusts 1 million tons of bituminous coal the amount of HC1 manufactured
can be calculated will be:
1.9 Ib HCl/ton coal x 1,000,000 tons coal = 1,900,000 Ibs HC1
This exceeds the 25,000 Ib manufacturing threshold and Form R reporting for HC1 aerosols is
required. The amount of HC1 aerosols released to air from the stack will be the amount
manufactured minus amounts removed by air control devises and will depend of the efficiency of
the devise for removing HC1. (See also, EPCRA section 313 Industry Guidance for Electric
Generating Facilities, January 1999, EPA 745-B-99-003)
Section 4. Measurement Methods
For source sampling, EPA has specified extractive sampling trains and analytical
procedures for the determination of hydrogen chloride emissions from stationary sources (3).
An error was noticed in the procedure for Method 26, for which changes were promulgated on
April 22, 1994. In section 4.1.2, the word "not" should be removed from the phrase .... "but not
greater than 120 °C." to read "but greater than 120 °C" (4).
22
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References
(1) Austin S, Glowacki, A. 1989. Hydrochloric Acid. Ullmann's Encyclopedia of Industrial
Chemistry, Vol A13,pp. 283-296.
(2) Hisham MWM, Bommaraju TV. 1995. Hydrogen Chloride. Kirk Othmer Encyclopedia of
Chemical Technology, 4th ed. Vol 13, pp. 894-925.
(3) EPA. 1995. 40 CFR Part 60 - Standards of Performance for New Stationary Sources;
Appendix A - Test Method 26 - Determination of Hydrogen Chloride Emissions from Stationary
Sources; Test Method 26A - Determination of Hydrogen Halide and Halogen Emissions from
Stationary Sources - Isokinetic Method.
(4) 59 FR 19306-19323, April 22, 1994. Standards of Performance for New Stationary Sources;
Appendix A - Test Methods; Revisions to Methods 18 and 26 and Additions of Methods 25D
and 26A to Appendix A.
(5) National Council for Air and Stream Improvement (NCASI). 1994. A study of kraft recovery
furnace hydrochloric acid emissions. Technical Bulletin No. 674, National Council for Air and
Stream Improvement, New York, NY. August 1994.
(6) National Council for Air and Stream Improvement (NCASI). 1991. Bleach plant Cl and
C1O2 emissions and their control. Technical Bulletin No. 616, National Council for Air and
Stream Improvement, New York, NY. September 1991. p. 7.
(7) EPA. 1995. Compilation of Air Pollutant Emission Factors (AP-42). Wood Waste
Combustion in Boilers, pp. 1.6-1 to 1.6-18. October 1996. Research Triangle Park, NC: U.S.
EPA, OAQPS.
(8) EPA. 1986. Compilation of Air Pollutant Emission Factors (AP-42). Glass Manufacturing.
pp. 1.15-1 to 1.15-10. October 1986. Research Triangle Park, NC: U.S. EPA, OAQPS.
(9) EPA. Factor Information Retrieval Data System (FIRE). Version 5.IB (December 1996).
Research Triangle Park, NC: U.S. EPA, OAQPS.
(10) EPA. 1996. Compilation of Air Pollutant Emission Factors (AP-42). Bituminous and
Subbituminous Coal. pp. 1.1-1 to 1.1-46. October 1996. Research Triangle Park, NC: U.S. EPA,
OAQPS.
(11) EPA. 1997. Compilation of Air Pollutant Emission Factors (AP-42). Brick and Structural
Clay Product Manufacture, pp. 11.3-1 to 11.3-68. August 1997. Research Triangle Park, NC:
U.S. EPA, OAQPS.
23
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(12) EPA. 1997. Background Report. AP-42 Section 8.6. Hydrochloric Acid Manufacture, pp.
8.6-1 to 11.3-68. October 1997. Research Triangle Park, NC: U.S. EPA, OAQPS.
(13) SRI International. 1996. 1996 Directory of Chemical Producers. United States of America.
pp. 660-662. Menlo Park. CA: SRI International.
(14) Chemical Manufacturing Reporter. Chemical Profile. Hydrochloric Acid. September 25,
1995.
(15) Buice JE, Bowlin RL, Mall KW, Wilkinson JA. 1987. Hydrochloric Acid. Encyclopedia of
Chemical Processing and Design, Vol 26, pp. 396-417.
(16) Wilson CB, Claus KG, Earlam MR, and Hillis JE. 1995. Magnesium and Magnesium
Alloys. Kirk Othmer Encyclopedia of Chemical Technology, 4th ed. Vol 15, pp. 622-674.
(17) EPA. 1995. Hydrochloric acid: Toxic chemical release reporting: Community right-to-
know. Final rule. 61 FR 38600. July 25, 1996.
(18) EPA. 1995. Toxic Release Inventory.
(19) Othmer DF, Naphtali LM. 1956. Correlating pressures and vapor compositions of aqueous
hydrochloric acid. Industrial and Engineering Chemistry 1: 6-10.
(20) Kindler W, Wiister G. 1978. Equation of state for the vapour of concentrated and diluted
hydrochloric acid. Ber. Bunsenges. Phys. Chem. 82: 543-545.
(21) EPA. 1997. National Emission Standard for Hazardous Air Pollutants (NESHAP) for Steel
Pickling - HC1 Process - Background Information for Proposed Standards. EPA-453/R-97-012.
June 1997. Research Triangle Park, NC: U.S. EPA, OAQPS.
(22) Rosenberg, DS. 1980. Hydrogen Chloride. Kirk Othmer Encyclopedia of Chemical
Technology, 3rd ed. Vol 12, pp. 983-1014.
(23) Fritz JJ, Fuget CR. 1956. Vapor pressure of aqueous hydrogen chloride solutions, 0 to
50 °C. Industrial and Engineering Chemistry 1: 10-12.
(24) EPA. 1997. Chemical Pulping Emission Factor Development Document (Revised Draft).
1997. July 8,'1997. Research Triangle Park, NC: U.S. EPA, OAQPS.
(25) EPA. 1995. National Emission Standards for Hazardous Air Pollutants from Secondary
Lead Smelting. 60 FR 32587, June 23, 1995.
(26) EPA. 1997. Compilation of Air Pollutant Emission Factors (AP-42). Organic Liquid
Storage Tanks, pp. 7.1-1 to 7.1-101. February 1996. Research Triangle Park, NC: U.S. EPA,
OAQPS.
24
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(27) EPA. 1997. Emergency Planning and Community Right-to-Know Act Section 313.
Guidance for Electricity Generating Facilities. EPA-745-B-97-016. September 26, 1997.
Washington, DC: Office of Pollution Prevention and Toxics.
25
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APPENDIX 1
100
Q-
S
o.oi -—•~—
0.001 -
0.0001
20
40 60
HCI content, wt %
100
Figure Al. Vapor-liquid phase diagram for the HC1-H2O
system (Reference 2, p. 901). Pressure is in MegaPascals
(MPa).
In the vapor-liquid phase diagram for the hydrogen chloride-water system shown in Figure Al,
the solid lines separate the two-phase region from the liquid phase and the dashed lines separate
the two-phase region from the gas phase. The numbers associated with the curves correspond to
the temperature in °C. Line A-A connects the azeotropic points and B-B1 represents the critical
segregation curve above the critical point of water. Figure A2 illustrates the use of this diagram.
26
-------
100
10
30
CL
2
0.1
-1
0.01 -
-2
30,,.
0001 -
-3
00001
20
40 60
HCI content, wt %
80
100
97%
Figure A2. Vapor—liquid phase diagram for HC1-H2O
system at 30 °C.
Figure A2 contains the vapor-liquid phase diagram for 30 °C and has been drawn to illustrate the
use of Figure Al. To find the composition of the vapor in equilibrium with a 40 wt % solution of
hydrochloric acid, construct a vertical line from 40 wt % on the abscissa. Where this line
intersects the solid (liquid) line, construct a horizontal line. Where the horizontal line intersects
the dashed (gas) line, read the HCI content of the gas phase off the abscissa (roughly 97 wt %
HCI). The total pressure of the solution is found from where the horizontal line intersects the
ordinate (roughly 0.1 Mpa).
The composition of the vapor as a function of HCI concentration in the liquid and temperature is
shown in Table Al and Figure A3. They show that for a dilute solution the vapor is essentially
water and for solutions above 20 mole % HCI the vapor is over 90 mole % HCI. Table A2
contains the HCI partial pressure and total vapor pressure of the solution (in parenthesis) in the
concentration range of 1.0 to 15.88 molal.
27
-------
Liquid
TABLE Al. Vapor Composition of HC1-H2O Systems
Vapor, Mole % HCI
Molality
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
15.88
Weight %
3.51
6.80
9.86
12.73
15.42
17.95
20.34
22.58
24.70
26.72
28.63
30.43
32.16
33.79
35.35
36.63
Source: Reference 19
Mole % 0 °C
1.77 4.09x10""
3.48 2.84x1 0'3
5.14 11.72xlQ-3
6.72 0.04
8.26 0.15
9.75 0.464
11.19 1.394
12.59 3.822
13.94 10.12
15.27 23.49
16.54 43.6
17.77 65.6
18.97 82.2
20.12 91.0
21.28 95.4
24.11 97.8
too
M
BO
SO
40
30
20
10
*
5
4
3
2
5 '.a
a a*
5 0.6
C 0.5
Z 0-*
I °-3
# 0.2
"o
5
aw
0.06
0.05
004
ao
0.01
OOOB
0006
0.005
0.004
0.00
a oo
= I I I
= /
= ///
— 1 II
~ Ill
///
II
1 1
— II
— HI
III
\- III
III
=
— Ill
— Ill
- Ill
- ill
JJ
— II
- II
- II
~20"C/
™ /
- o°c
1 1 1
0 5 10 15
10 °C
6.01x10-"
4.09x1 0'3
16.51xlO'3
0.0592
0.194
0.597
1.735
4.79
11.94
25.70
46.62
67.05
82.4
91.03
95.7
97.6
f '
1 1
20 25
20 °C 30 °C 40 °C 50 °C
8.88x10-" 12.9x10-" 19.0x10'" 27.5x10-"
5.87xlO'3 S.llxlO'3 11.9xlO'3 16.3xlO'3
23.12xlO'3 32.1xlO'3 4.32xlO'2 .0616
0.0808 0.109 0145 .198
0.257 0.335 0.437 .574
0.767 0.968 1.215 1.552
2.152 2.631 3.198 3.931
5.68 6.72 7.86 9.29
13.55 15.00 17.29 19.72
28.15 30.41 32.85 35.75
48.29 50.5 52.55 55.3
68.35 69.55 70.6 71.9
82.4 83.0 83.4 83.4
90.9 90.4 91.0 91.0
95.4 95.4 94.9 95.1
97.3 97.4 97.1
1 =
—
~
=
__
"""
~*
—
1
30 35
Mol % HCI in solution
Figure A3. Vapor composition of
hydrogen chloride-water systems
(Reference 22, p. 988).
28
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TABLE A2. Partial Pressure of HC1 And Total Vapor Pressure of HC1-H2O Systems
Liquid
HCI Partial Pressure (Total Vapor Pressure) (torr)
Molality
1.0
20
30
40
50
60
7.0
80
90
100
11.0
120
13.0
140
150
15.88
Wt%
3 51
680
986
1273
15.42
1795
20.34
22.58
2470
2672
2863
3043
32.16
33.79
35.35
3663
Mole %
1 77
348
5 14
6.72
8.26
975
11.19
12.59
1394
1527
16.54
1777
18.97
20 12
21.28
24.11
0°C
l.SlxlO'5
(442)
1.20x10'"
(4.22)
4.68x10-"
(399)
1 59x1 0-1
(3.69)
4 89x1 0'1
(337)
0.0141
(304)
00382
(2.74)
0.0987
(2.58)
0.240
(2.37)
0.552
(235)
I 229
(282)
255
(389)
5 II
(6.22)
999
(1 097)
18 56
(1939)
31 0
(31.7)
10 CC
5 33xlO'5
(8.87)
3 45x10-"
(844)
1 32x1 0'1
(7.95)
4.36x10"'
(738)
0.0131
(676)
00366
(6.13)
00964
(5.55)
0242
(505)
0571
(478)
1278
(497)
2.77
(5.94)
5.60
(8.35)
11 00
(1336)
20.75
(22.8)
380
(397)
61.2
(62.7)
20 °C
149x10-"
(1678)
944x10'"
(1608)
3 SlxlO'1
(1517)
0.0114
(14 10)
00333
(12.94)
00903
(11 80)
0.231
(1072)
0563
(991)
1 295
(956)
283
(1005)
586
(12 14)
1175
(1720)
22.25
(27.0)
41 1
(452)
72.2
(757)
114 8
(118)
30 °C
396x10'"
(30.70)
243x10"'
(29 96)
888x10''
(27 54)
00279
(25.73)
00794
(237)
0210
(217)
0521
(198)
1236
(184)
276
(18.4)
5.87
(193)
11 97
(237
23 14
(333
436
(525
768
(845)
1325
(139)
201 4
(207)
40 °C
1 01x10''
(53 27)
605X10-1
(508)
00211
(488)
00659
(453)
0 183
(419)
0468
(385)
1 132
(354)
261
(332)
569
(329)
11 73
(357)
2328
(443)
44 1
(625)
795
(957)
1374
(152)
232
(235)
360
(371)
50 °C
245x10"'
(89 18)
00143
(87 64)
00497
(8065
0 149
(754
0401
(699
1 001
(645
2354
(599)
527
(56.8)
11 20
(568)
226
(63.2)
439
(794)
809
(1125)
140
(168)
242
(266)
400
(421)
Source: Reference 23.
The above table contains the partial pressure of hydrochloric acid and total vapor
pressure of the solution (in parentheses) over aqueous hydrochloric acid solutions in the
concentration range of 1 to 15.88 molality (23). The partial pressure of hydrochloric acid above
a hydrochloric acid solution is very low compared to the total vapor pressure at low
concentrations; the bulk of the vapor being composed of water. Consequently, when a dilute
solution of hydrochloric acid boils, more water than hydrochloric acid is volatilized so that the
concentration of the remaining acid increases, and the boiling point of the solution rises. This
process continues until the acid concentration reaches 20.222 weight % HCI, when an azeotrope
(a mixture of two liquids that boils at constant composition; i.e., the composition of the vapor is
the same as that of the liquid) is formed and the concentration of hydrochloric acid in the vapor is
the same as that of the solution. Above the azeotropic concentration, the partial pressure of
hydrochloric acid increases rapidly with concentration and hydrochloric acid aerosol production
will be substantial.
29
-------
TABLE A3. Pressure Conversion Factors*
IkPa
Ibar
1 torr
1 atm
1 psi
kPa
1.0000
100.00
0.1332
101.33
6.895
bar
l.OOOOxlQ-2
1.0000
1.333X10'4
1.0133
6.895 xlO'2
torr
5.501
750.1
1.0000
760.0
51.71
atm
9.869x1 Q-3
0.9869
1.316xlO-2
1.0000
6.805xlO-2
psi
0.1450
14.50
1.934xlO-2
14.70
1.0000
* To use the table to convert from atm to kPa use the entry in the atm row and the kPa column to obtain 1 atm
101.33 kPa.
TABLE A4. HC1 Concentration Conversion Factors**
molal (m) mole fraction (x) weight fraction (w)
m 1 55.5x/(l-x) 27.4w/(l-w)
x m/(m + 55.5) 1 18.02 w/(36.45 +18.43 w)
w 36.45 m / (36.45 m + 1000) 36.45 x 7(18.02 + 18.43 x ) 1
* To convert, for example, x = 0.l to molality: m = 55.5 (O.I)/(1-0.1) = 6.17.
30
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