Emission Calculations
Introduction...4
Calculating Emissions for Air Permitting ...4
Qualifying Emissions ...4
Quantifying Emissions...5
Calculations and Emission Limits from MDEQ Rules...5
Particulate Matter ...6
Sulfur-Bearing Compounds...6
Volatile Organic Compounds (VOCs) ...7
Air Toxics...8
Emissions Inventory for the Renewable (Title V) Operating Permit ...10
Potential and Actual Emissions...11
Point and Fugitive Emissions ...12
Completing Your Emissions Inventory ...12
Compile Plant-Wide Information ...13
Identify Emission Units...14
Identify Regulated Pollutants ...15
Calculating Emissions for MAERS...17
What Pollutants Must Be Reported?...17
Reporting Toxic Pollutants ...17
Toxic Chemical Release Inventory (TRI) and MAERS ...18
Approaches to Emission Estimation ...20
Direct Measurement...21
Stack Tests...21
Continuous Emission Monitoring Systems...21
Step 1 – Calculating the Hourly Emission Rate ...22
Concentration of Air Pollutant in the Stack ...22
Stack Gas Flow Rate...25
Calculating Hourly Mass Emission Rate ...28
Step 2 – Calculating the Source Specific Emission Factor...29
Step 3 – Determining the Annual Mass Emission Rate...31
Mass Balance...32
Mass Balances Examples ...33
Surface Coating Operations...33
Considerations When Calculating VOC Emissions ...37
Laboratory Hoods...37
Emission Calculations 2002 Page 2
Emission Factors and Emission Models ...39
What are Emission Factors?...39
Emission Factor Examples...40
Grinding Operations ...40
Foundry Emissions...41
Fuel Burning ...43
NOxEmissions Calculation for an Incinerator ...44
Open Top Vapor Cleaners ...45
Limitations of Emission Factors ...48
Emission Factors Provided with MAERS ...49
Emission Factor Resources ...49
Emission Factor and Inventory Group ...49
Emission Inventory Improvement Program...50
Clearinghouse for Inventories and Emission Factors (CHIEF)...50
Emission Factor Publications ...53
Compilation of Air Pollutant Emission Factors...54
Pollutant Terminology and Conventions in AP-42 ...55
Particulate Matter ...55
Organic Compounds ...56
Toxic, Hazardous, and Other Noncriteria Pollutants...57
Emission Factor Ratings ...57
Other Ways to Obtain AP-42 Information and Updates ...60
Emission Inventory Improvement Program (EIIP) Preferred and Alternative Methods for Estimating Air Emissions ...60
Others Ways to Obtain Information and Updates...62
Locating and Estimating(L&E) Document Series...63
CHIEF Software and Computer Models ...63
Factor Information Retrieval (Fire) Data System ...64
How MAERS Look-up Emission Factor Table and Fire Differ ...65
TANKS ...66
Storage Tank Standing and Working Storage Losses...66
Landfill Gas Emissions Model...71
SPECIATE 3.2 ...71
WATER 9 ...71
Wastewater Treatment Plants...71
MDI Emissions Estimator Software... 72
MOBILE 6...74
AIR CHIEF...74
Version 9.0 System Requirements ...75
How to Order Air CHIEF...75
Where to Go for Help on CHIEFS...76
Source-Specific Emission Factors ...76
Industry-Specific Guidance ...77
References ...78
Appendix A. Federal Listed Air Toxics (Hazardous Air Pollutants)...79
Appendix B. List of Federal Regulated Air Pollutants ...84
Appendix C. Source Categories for Fugitive Emissions ...88
Appendix D. AP-42 Contents, Fifth Edition...90
Emission Calculations 2002 Page 4
Emission Calculations
Introduction
There are at least three activities that require a facility to calculate the emissions of air contaminants: applying for and complying with an air permit, determining applicability to the Renewable Operating Permit program, and complying with the Michigan Air Emissions Reporting System (MAERS). The methods of calculating emissions are common to all three activities. Therefore, the emission calculation examples and discussions found under the MAERS section of this tab are pertinent to air permitting and ROP applicability.
Calculating Emissions for Air Permitting
An estimate of actual emissions is the first step in evaluating the impact of the proposed installation or modification of a process. A source must first qualify and quantify the emissions to determine which federal and/or state regulations might apply. When emissions are characterized, control and pollution prevention techniques can be planned for compliance with the appropriate emission standards. The permitting agency, the Michigan Department of Environmental Quality (MDEQ), establishes the allowable limits for air emissions in the special conditions of the permit to install.
Qualifying Emissions
Qualifying emissions means identifying what compounds, elements or particles are being released from the given source or process. The emitted materials are process or industry specific. A reference for understanding various types of sources is the Air Pollution Engineering Manual (AP-40). Frequently, industry-specific trade organizations can provide information about sources.
Steps in qualifying emissions for a specific processes include: • Making an inventory of raw materials used in the process.
• Outlining the physical, chemical or biological changes that occur to those raw materials.
• Determining which of the raw materials pass through unchanged and also have the potential to be emitted to the atmosphere.
• Determining what by-products are produced as a result of the process and have the potential to be emitted to the atmosphere.
• Combining the raw materials and by-products for an overall list of the type of emissions which could be released from the source.
From the list of materials emitted to the atmosphere, determine which are subject to regulation. Are any criteria pollutants (sulfur dioxide, particulates, carbon monoxide, oxides of nitrogen, ozone precursors, haze precursors, or lead) emitted? Are toxic air contaminants, hazardous air pollutants (HAPs), or other similar compounds present? This will give an indication of which federal and state regulations need to be consulted for further information.
Quantifying Emissions
Once the emissions have been identified, the next step is quantifying them. This means determining how much of each chemical is being released to the atmosphere. Regulations are based on quantified emissions expressed in units such as pounds per hour and tons per year. Emissions are quantified based on one or a combination of several factors. These include sampling, emission factors, equipment data and information from chemical MSDS sheets, and the mass balance approach.
An explanation and examples of each emission estimation technique is found under “Calculating Emissions for MAERS” beginning on page 17.
The present Michigan Permit to Install application package requires supporting information that includes an emissions summary. Each process needs a one-page emissions summary covering amounts of all pollutants in pounds per hour and tons per year. Emissions from each vent or stack need to be quantified with each toxic air contaminant listed individually as maximum pounds per hour, stack concentration in micrograms per cubic meter (µg/m3), and predicted ambient impact in µg/m3. Emission estimates need to provide a reasonable margin of safety to ensure that the process can operate within the levels quantified.
Calculations and Emission Limits from MDEQ Rules
Specific guidance for calculation of air releases and information regarding emission limits can be found in the Michigan Administrative Rules for Air Pollution Control. Certain sources and pollutants are also specifically addressed in federal regulations for National Emission Standards for Hazardous Air Pollutants (NESHAPs), New Source Performance Standards (NSPS) provisions, and the Prevention of Significant Deterioration (PSD) program.
Some of the major sections of the Rules are devoted to provisions for sources of Particulate Matter (Part 3), Sulfur-bearing compounds (Parts 4 and 5), and Volatile
Emission Calculations 2002 Page 6 Organic Compounds (Parts 6 and 7). Other pollutants are addressed within the context of other sections. Specific applicability of some of the rules is dependent upon whether a source is located in an area where air quality meets standards (attainment) or not (nonattainment).
In some cases, specific methods for source emission testing are referenced in the Rules. These methods which are based largely on the provisions of 40 CFR part 60 (1989) are listed in Part 10, Intermittent Testing and Sampling, Rule 1004 (R 336.2004). A complete copy of Part 10 is available from the MDEQ Air Quality Division.
Particulate Matter
Emissions of particulate matter are discussed in Part 3, Emission Limitations and Prohibitions--Particulate Matter of the Rules. Table 31 lists maximum allowable emissions at operating conditions for fuel burning equipment, incinerators, steel manufacturing, ferrous cupola foundry operations, chemical and mineral kilns, asphalt paving plants, cement manufacture, iron ore pelletizing, fertilizer plants, and various exhaust systems. Coke ovens are addressed in Rules 349-357 and 360; steel manufacturing in Rules 358-359, 361-363, 365-366; basic oxygen furnaces in Rule 364; and sintering operations in Rule 367. Figure 31 presents a chart relating emissions to steam capacity rating and Table 32 provides information on allowable rate of emission based on process weight rate.
Sulfur-Bearing Compounds
Parts 4 and 5 of the Rules provide information on emission limitations and prohibitions for sulfur-bearing compounds. Part 5 rules are essentially obsolete at this point. Power plants are the subject of Rule 401. Table 41 presents the amount of sulfur in fuel limitations for fuel-burning equipment and Table 42 lists equivalent emission rates. Guidance for fuel burning sources other than power plants is found in Rule 402. Oil- and natural gas-producing or transporting facilities and natural gas-processing facilities are regulated under Rule 403. Sulfuric acid plants are addressed in Rule 404.
Emission Calculations March 1999 Page 7
Volatile Organic Compounds (VOCs)
Emission limitations for existing volatile organic compound (VOC) sources are found in Part 6 of the Rules with VOC limitations for new sources in Part 7. However, new sources will need to reference Part 6 Rules for emission rates. There are presently revisions and additions to these rules that may come into effect in the future.
The purpose of the Part 6 and 7 Rules is to reduce emissions of VOCs, specifically in ozone nonattainment areas so that attainment with National Ambient Air Quality Standards can be achieved. Table 1 lists the current Part 6 rules.
Reference to the Rules for your specific industry prior to performing calculations can provide guidance as to the type of calculation that needs to be done. For instance, surface coating emission rates are frequently expressed in pounds of volatile organic compounds minus water as applied or pounds of VOCs per gallon of applied coating solids (Tables 62, 63, 65, 66, 67 of the Rules). Applications such as graphic arts may express limits in pounds VOC per pound of solids (Table 64), and flat wood paneling coating line VOCs are given in pounds per 1,000 square feet of product.
Emission Calculations March 1999 Page 8
Air Toxics
The current Michigan air toxics program applies to new or modified sources of toxic air contaminants. A discussion of the Michigan air toxics program is found in Part 2, Rules 224 through 232. The Michigan toxic air contaminants go beyond the 188 hazardous air pollutants listed in the Clean Air Act Amendments of 1990. All known substances can be regulated as toxic air contaminants with the exception of some specifically listed substances. Amounts of toxic air contaminants (TACs) are calculated on a pound per hour basis for maximum allowable emission rates. Information is also needed to calculate micrograms of TAC per cubic meter for various screening levels.
EXAMPLE #1: Automobile and Light Duty Truck Painting
For Automobile and Light Duty Truck painting, you may have to calculate VOC emissions for surface coating operations in units of pounds of VOC per gallon of applied coating solids (lb VOC/gal coating applied). To complete this calculation, additional information is needed on the solids content by volume of the coating and the application equipment transfer efficiency.
Coating A
VOC Content of Coating = 3.2 lbs. VOC/gal of coating Solids Content (by volume) = 54%
Transfer Efficiency = 55% (i.e., solids applied; varies with spray gun type) lb VOC
gal. of applied coating solids =
lb VOC gal. coating x
gal. coating gal. coating solids x
gal. coating solids gal. applied coating solids
= 3.2 lb VOC gal. coating x
gal. coating
0.54 gal. coating solids x
gal coating solids
0.55 gal. of applied coating solids
lb VOC
gal. of applied coating solids =
10.7 lb VOC
Table 1.
Air Part 6 Rules, Emission Limitations and Prohibitions -- Existing Sources of Volatile Compound Emissions
[Promulgated as of January 1994] 601 Definitions.
602 General provisions for existing sources of volatile organic compound emissions. 603 Rescinded.
604 Storage of organic compounds having a true vapor pressure of more than 1.5 psia, but less than 11 psia, in existing fixed roof stationary vessels of more than 40,000-gallon capacity. 605 Storage of organic compounds having a true vapor pressure of 11 or more psia in existing
stationary vessels of more than 40,000-gallon capacity.
606 Loading gasoline into existing stationary vessels of more than 2,000-gallon capacity at dispensing facilities handling 250,000 or more gallons per year.
607 Loading gasoline into existing stationary vessels of more than 2,000-gallon capacity at loading facilities.
608 Loading gasoline into delivery vessels at existing loading facilities handling less than 5,000,000 gallons per year.
609 Loading delivery vessels with organic compounds having true vapor pressure of more than
1.5 psia at existing loading facilities handling 5,000,000 or more gallons of such compounds per year.
610 Existing coating lines; emission of volatile organic compounds from existing automobile, light-duty truck, and other product and material coatings.
611 Existing cold cleaners.
612 Existing open top vapor degreasers. 613 Existing conveyorized cold cleaners. 614 Existing conveyorized vapor degreasers.
615 Existing vacuum-producing systems at petroleum refineries. 616 Process unit turnarounds at petroleum refineries.
Emission Calculations March 1999 Page 10 Table 1.
(continued)
617 Existing organic compound-water separators at petroleum refineries. 618 Use of cutback paving asphalt
619 Perchloroethylene; emission from existing dry cleaning equipment.
620 Emission of volatile organic compounds from existing flat wood paneling coating lines. 621 Emission of volatile organic compounds from existing metallic surface coating lines.
622 Emission of volatile organic compounds from existing components petroleum refineries; refinery monitoring program.
623 Storage of petroleum liquids having a true vapor pressure of more than 1.0 psia, but less than 11.0 psia, in existing external floating roof stationary vessels of more than 40,000-gallon capacity. 624 Emission of volatile organic compound from an existing graphic arts line.
625 Emission of volatile organic compound from existing equipment utilized in the manufacturing of synthesized pharmaceutical products.
626 Rescinded
627 Delivery vessels; vapor collection systems.
628 Emission of volatile organic compounds from components of existing process equipment used in manufacturing synthetic organic chemicals and polymers; monitoring program.
629 Emission of volatile organic compounds from components of existing process equipment used in processing natural gas; monitoring program.
630 Emission of volatile organic compounds from existing paint manufacturing processes.
631 Emission of volatile organic compounds from existing process equipment utilized in manufacture of polystyrene or other organic resins.
632 Emission of volatile organic compounds from existing automobile, truck, and business machine plastic part coating lines.
651 Standards for degreasers.
Emissions Inventory for the Renewable Operating Permit
One of the first steps in evaluating the potential impacts of the Clean Air Act (CAA) Amendments of 1990 is to develop an accurate inventory of all actual and potential
air emissions from emission units at your facility. Individual pieces of equipment or processes with the potential to emit pollutants used to be referred to as "sources." Under the CAA Amendments, individual pieces of equipment or processes are referred to as "emissions units," while a "source" now represents the entire facility.
The primary purpose for conducting an air emissions inventory is to allow your facility to quantify actual and potential emissions of all regulated air pollutants to then determine your major source status under the CAA. This section provides guidance on completing inventories of criteria pollutants, newly regulated hazardous air pollutants (HAPs) as found in Appendix A, and other regulated pollutants in Appendix B. The inventory is used in determining whether your facility is subject to specific regulatory requirements, including Title V of the CAAA. Keep in mind that if your are subject to Title V, you will be asked to gather information beyond emissions estimates. This section describes this "emissions-related" information.
Potential and Actual Emissions
An emissions inventory containing potential and actual emissions is essential because the determination of the applicability of many aspects of the CAA, and hence what needs to be included in the renewable (Title V) operating permit application, depends on a facility’s "potential to emit" a pollutant. Potential to emit is formally defined as...
the maximum capacity of a stationary source to emit a pollutant under its physical and operational design. Any physical or operational limitation on the capacity of the source to emit a pollutant, including air pollution control equipment and restrictions on hours of operation or on the type or amount of material combusted, stored, or processed, shall be treated as part of its design only if the limitation or the effect it would have on emissions is federally enforceable (emphasis added) (40 CFR part 70).
Potential emissions differ from actual emissions in the following two ways:
• Potential emissions are calculated using maximum allowable hourly emissions, based on an enforceable permit or regulatory limit, whereas actual emissions use average hourly emissions. If no maximum allowable hourly emissions limit exists, then potential emissions must be calculated using maximum hourly emissions. The maximum hourly emission rates will either be 1) maximum allowable hourly emission rates or 2) the maximum hourly capacity or design rate of the unit.
• Potential emissions must take into account potential hours of operation, assumed to be 24 hours per day, 365 days per year (equal to 8,760 hours per year), unless a facility's federally enforceable permit constrains it to some lesser number of annual hours of operation. Actual emissions are calculated according to the hours an emissions unit was actually emitting over a given year.
Emission Calculations March 1999 Page 12 If permit limitations exist for an operation at your facility, such as a pollution control device or limits on hours of operation, those may be considered in determining your facility’s potential to emit, it is imperative that these limitations be federally enforceable. State construction or preconstruction permits were historically the prevalent means for obtaining a federally enforceable limit on an emissions unit. Existing (pre-Title V) state operating permit programs have varying degrees of federal enforceability.
Point and Fugitive Emissions
A complete emission inventory will include actual and potential emissions from all emissions units, including point sources and fugitive emissions at your facility. Point sources are emissions units with a discrete emission point, such as stacks, chimneys, vents, or other functionally-equivalent openings. Fugitive emissions are those that do not arise from a discrete emission point, such as solvent releases in a paint mix room, or oil mist emissions from metal working equipment released into the building and then eventually into the atmosphere through plant windows and doors. Most facilities are more familiar with point source emissions.
The role of fugitive emissions in major source applicability determinations varies depending upon the relevant major source definition (see Table 2). For nonattainment pollutants and hazardous air pollutants (HAPs), fugitives always count toward the applicability thresholds. However, for the 100 tons per year (tpy) general threshold, fugitives only count if the facility may be considered one of the 27 source categories listed in the permit rule (See Appendix C).
Table 2. Role of Fugitive Emissions in Applicability Determination
CAA Program Includes Fugitive Emissions?
Nonattainment pollutants Yes
HAPs Yes 100 tpy general threshold Only for 27 named source categories
Completing Your Emission Inventory
The rest of this section provides step-by-step guidance on completing a facility-wide emissions inventory. Some of the steps involve techniques to estimate emissions of pollutants. However, an emissions inventory for Title V application purposes requires much more information than simply pound per hour or ton per
Emission Calculations March 1999 Page 13 year emission rates.
The steps for conducting an emissions inventory are: • Compiling emissions data
• Identifying applicable requirements • Quantifying emissions
• Assembling the inventory
Compile Plant-Wide Information
The first step in conducting an emissions inventory is to identify and gather background data and information that will be used throughout the inventory process. Sources of information, such as those listed below, should be assembled from plant and corporate files to help identify and characterize the facility's air emissions:
• Emissions reports, test results, ventilation surveys, stack inventories • Air permit applications and air permits
• Toxic chemical release reporting forms prepared for SARA Title III, Section 313 • Production, raw material usage rates
• Emission composition and product information found in Material Safety Data Sheets (MSDSs), inventory reports
• Process or block flow diagrams, or roof drawings
• Michigan air quality regulations to define allowable emissions
• Potential hours of operation for the calendar year (8,760 or as constrained by permit or design) and actual hours of operation for each emissions unit
Emission Calculations March 1999 Page 14 • State Implementation Plan (SIP) emission inventory descriptions for your facility,
or similar facilities
Identify Emissions Units
The next step in the emissions inventory process involves the systematic identification of all emissions units (both point and fugitive) at your facility. For the inventory to be complete, we recommend that you include any piece of equipment involved in operations or support of operations that could release pollutants to the atmosphere. You should include units even if they have been exempt from state permitting or are considered "grandfathered" from permitting requirements. You generally do not need to include equipment associated with office activities (such as "white out" fluid, paint spray cans for office use, or cleaners for office lavatories). You should include seemingly insignificant activities, such as use of paint spray cans for marking items being manufactured at your facility, if the equipment or activity is part of, or supports operations. Some items that should be included, but that are often overlooked include:
• product, raw material, and waste material storage and handling operations • storm water run-off, sewage and process wastewater treatment plants • laboratories
• cooling towers • CFC sources
Point and fugitive emission units can be initially identified by reviewing plant flow and design drawings, prior or current air pollution and other environmental permits, emission reports made to regulatory agencies, and other information describing the plant that has been collected. In addition, emission units can be identified through discussions with plant operations and maintenance personnel.
Your list of identified emissions units should be visually verified during a plant through by personnel that are familiar with the plant and its operations. This plant walk-through should be thorough to identify any emissions units that have not previously been included in existing inventories. Care should be taken to identify emissions units that are not operating at the time of the walk-through, but may be operated at other times during the year.
All identified emissions units should be given a unique designation or identification number to facilitate record keeping and data entry into a database. This designation can be as simple as a unit number or a code that designates the building, facility, or process. The designations should be consistent with any other designations that may
have been assigned in current air pollution permits or in any reports submitted to regulatory authorities.
In addition to identifying emissions units, we recommend that you also identify personnel responsible for design, operations, and maintenance of each identified unit. These personnel will be able to provide important information for each unit that will be useful during the preparation of the inventory.
Note again that you need to address emissions from units that may seem insignificant and that you may not have had to address in the past. It may eventually turn out that you will not need to address these units in your Title V permit beyond identifying them; however, you cannot adequately calculate your facility-wide potential to emit regulated pollutants unless you include all emissions units in your inventory.
Identify Regulated Pollutants
After identifying emissions units at your facility, you will need to identify the regulated pollutants emitted from each unit. These pollutants can be identified from the information sources mentioned previously, as well as from your general knowledge of the manufacturing processes and operations that take place at your facility.
Compounds regulated under the CAA are: the six criteria pollutants for which the USEPA has promulgated National Ambient Air Quality Standard (NAAQS), the 188 chemicals to be regulated as HAPs, Title VI stratospheric ozone depletion pollutants, and pollutants regulated under the NESHAP and NSPS regulations.
These compounds constitute the universe of federally regulated air pollutants, and are the pollutants you must address under the Title V operating permit program.
Emission Calculations March 1999 Page 16 Table 3. Facility Emissions Summary
Table from the Title V Operating Permit Workbook prepared for the American Automobile Manufacturers Association is an example of
how to organize emission inventory information Plant:
Date:
Criteria Pollutants Potential Emissions Actual Emissions SO2 PM-10 VOC CO NOx Lead Hazardous Air Pollutants
(HAPs) List each HAP*:
Potential Emissions (tpy)
Actual Emissions (tpy)
Other Regulated Pollutants List those Applicable*:
Potential Emissions (tpy)
Actual Emissions (tpy)
*
Calculating Emissions for MAERS
Facilities, under Rule 2 (R336.202) of the Michigan Administrative Rules for Air Pollution Control are required to report their annual emissions of air pollutants to the Air Quality Division of the MDEQ. Operational Memorandum No. 13 (see Tab 16 – AQD Guidance) provides information on which facilities must report. The AQD has a set of forms and instructions facilities must use and follow to report their emissions. In 1999, AQD replaced the Michigan Air Pollution Reporting (MAPR) forms with an entirely new set, including an electronic version. This new reporting mechanism is referred to as the Michigan Air Emissions Reporting System (MAERS). For more information about MAERS, see Tab 10 – Complying with Permit and Reporting Requirements.
Some of the information contained in this section was taken from the emission factor publications found in the USEPA, Office of Air Quality Planning & Standards’ Technology Transfer Network (TTN). The TTN is a collection of technical Web sites containing information about many areas of air pollution, including emission estimation. The TTN can be accessed directly from the Internet via the World Wide Web. The Internet address is www.epa.gov/ttn.
What Pollutants Must Be Reported?
Emissions for the following pollutants must be reported: • Ammonia
• Carbon monoxide (CO);
• Nitrogen oxides (NOx) expressed as NO2; • Particulate matter (PM);
• Particulate matter less than 10 microns (PM-10); • Particulate matter less than 2.5 microns (PM-2.5) • Sulfur oxides (SOx) expressed as SO2
• Volatile organic compounds (VOC); and • Lead (Pb).
However, if the emission of one of the above pollutants from a source classification code (SCC) is less than 0.01 tons (20 pounds) per year, the emission does not have to be reported. Additional discussion of pollutant terminology and conventions begins on page 55.
Reporting Toxic Pollutants
Under MAERS, the reporting of approximately 240 toxic pollutants is optional. MDEQ, AQD will analyze the emissions data submitted by each company and estimate the toxic air pollutant emissions from the information provided for the criteria pollutants. This includes activity information such as source classification codes and material throughput. Facilities submitting their MAERS report electronically will be able to view the estimation of toxics prior to submitting their report. The MAERS software is
Emission Calculations 2004 Page 18 equipped with an emission calculator. If the emission estimates are in error, the AQD would appreciate the facility’s help in correcting those estimates of toxic emissions.
Toxic Chemical Release Inventory (TRI) and MAERS
Section 313 of the federal Emergency Planning and Community Right-to-Know Act (EPCRA) of 1986, also known as Title III of the Superfund Amendments and Reauthorization Act, requires certain facilities to report Toxic Chemical Release Inventory (TRI) information for any listed chemicals manufactured, processed, or otherwise used by the facility above specific thresholds.
Manufacture - production, preparation, import, or compound of an EPCRA Section 313 chemical. Example: manufacturing benzene on-site for distribution and sale.
Process - preparation or process of a listed toxic chemical for distribution in commerce. This is usually the incorporation of a toxic chemical into a product. An EPCRA Section 313 chemical is processed as a reactant, as a formulation or article component, repackaged, or as an impurity. Example: process paint containing certain glycol ethers.
Otherwise use - use of a listed toxic chemical that is not covered by the terms “manufacture” or process.” EPCRA Section 313 chemicals are otherwise used as chemical processing or manufacturing aids, or for ancillary or other use. Example: using Freon 113 as a coolant in a closed-loop refrigerant system to cool process streams.
There are about 650 toxic chemical categories covered by Section 313. A small number of these are identified as persistent, bioaccumulative and toxic (PBT). Activity thresholds for non-PBT chemicals are more than 25,000 pounds manufactured, or more than 25,000 pounds processed, or more than 10,000 pounds otherwise used. PBT chemical thresholds are significantly lower regardless of the activity - more than 10 pounds or 100 pounds, depending on the chemical; for dioxin and dioxin-like compounds the activity threshold is more than 0.1 grams.
The USEPA can add, remove, or modify the list of toxic chemicals that must be reported. Facilities should check each year for any changes to the Section 313 chemicals and chemical categories and reporting requirements.
Michigan has over 900 TRI facilities and almost 2,000 MAERS facilities. Although the MDEQ does not have an exact knowledge of how many facilities are filing both reports, it is estimated that well over half of the TRI facilities report under MAERS.
Facilities that report toxic pollutants under MAERS and are subject to EPCRA Section 313 TRI reporting requirements should develop a system that could satisfy both. This would eliminate the redundancy of calculations. The following outlines MAERS and TRI requirements.
y The reporting period for both MAERS and TRI is the calendar year. The initial submittal dates of the reports differ. MAERS forms are due March 15. TRI forms are due July 1.
y Under MAERS, facilities must estimate and report their releases of seven criteria air contaminants and may report an additional 240 toxic pollutants (80 requested by the Great Lakes Commission and 160 requested by the Toxics Unit of the Air Quality Division). All 188 Hazardous Air Pollutants (HAPs) are included in the list of 240 toxic pollutants. A majority of the MAERS toxic pollutants are included in one form or another on the list of TRI chemicals. Under EPCRA Section 313, facilities must estimate and report releases (including disposal) and other waste management activities for approximately 650 chemicals and chemical compound categories.
y The submittal of emission data collected by MAERS to EPA must be made on a process-by-process basis, as defined by EPA source classification codes (SCCs). In addition to emission estimates, several other parameters such as material throughput, operating schedules, stack parameters, and emission factors must be reported at the process level. EPCRA Section 313 TRI requires facilities to report at the facility level.
y Under MAERS, facilities do not have to report an emission if it is less than 20 pounds per year for each activity (SCC process). EPCRA Section 313 has no minimum threshold for quantity released; once a facility meets the reporting threshold for chemical use mentioned above, it must submit a report, even if there are no releases.
A facility should consider developing an effective emission estimation system that can adequately address MAERS and EPCRA Section 313 TRI reporting requirements.
Emission Calculations 2002 Page 20
Approaches to Emission Estimation
There are numerous approaches to estimating emissions of air contaminants. Figure 1 depicts the various approaches to emission estimation that should be considered when analyzing the tradeoffs between the cost and quality of the resulting estimates. In this section, three approaches will be discussed including some examples on how to use them: direct measurement, mass balance, and emission factors and models. Most of the following examples are calculations of actual yearly emissions as required by MAERS. However, a few potential emission calculations, as required by the Renewable Operating Permit program, will also be included.
Figure 1. Approach to Emission Estimation
Source: Air Pollutant Emission Factors (AP-42) Fifth Edition, Volume 1: Stationary Point and Area Sources, U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, Research Triangle Park, North Carolina.
Emission Calculations March 1999 Page 21
Direct Measurement
The most accurate way of estimating emissions from a source is directly measuring the concentration of air pollutants in the stack gas. Stack tests and continuous emission monitoring systems (CEMS) are two methods of collecting actual emission data. This section explains how source testing data from stack tests and CEMS can be used in the completion of a facility’s Michigan Air Emission Reporting System (MAERS) submittal. The discussion will focus on the methodology to follow in converting data collected during source testing into a pollutant mass emission rate, i.e., tons of pollutant emitted per year. Albeit very important for compliance demonstration purposes, this discussion will not include comparison of stack testing and CEMS results, or all of the various air pollutant concentration limits contained within the state and federal air quality regulations.
The use of source test data reduces the number of assumptions regarding the applicability of emissions data to a source (a common consideration when emission factors are used); as well as the control device efficiency, equipment variations, and fuel characteristics. Even then, the results will be applicable only to the conditions existing at the time of the testing or monitoring. To provide the best estimate of longer-term (e.g., yearly or typical day) emissions, these operating conditions should be representative of the source's routine operations.
Stack Tests
Stack tests provide a means to determine the concentration of emissions of an air pollutant at the point of release. These tests are conducted according to established procedures. Stack tests provide a snapshot of emissions during the period of the test. Samples are collected using probes inserted into the stack, then pollutants are collected in or on various media and sent to a laboratory for analysis or analyzed on-site by continuous analysis. Pollutant concentrations are obtained by dividing the amount of pollutant collected during the test by the volume of the air sampled. Only trained stack testers should perform the stack tests.
Continuous Emission Monitoring Systems
Continuous emission monitoring systems (CEMS) involve the installation of monitoring equipment that accumulates data on a pre-determined time schedule in a stack or duct. The continuous measurements provide data under all operating conditions. Use of CEMS requires attention to detail and strict adherence to state and federal guidelines. Emissions data are available through direct measurement using continuous emissions monitors, usually located in the exhaust downstream of a combustion device. Information obtained from CEMS is considered reliable,
Emission Calculations 2004 Page 22 provided the devices are subject to a quality control/quality assurance (QA/QC) program that includes appropriate calibration. A CEMS provides a continuous record of emissions over an extended and uninterrupted period of time. Various principles are employed to measure the concentration of pollutants in the gas stream. These principles are usually based upon photometric measurements. Instrument calibration drift can be problematic for CEMS. The owner is responsible for proper calibration, operation, and validation of the monitoring equipment and emission data.
Stack tests and CEMS directly measure two important values: the concentration of a specific air pollutant ([air pollutant]) in the stack gas and stack gas flow rate. Multiplying these two values together will equal a mass emission rate typically expressed as
pounds of air pollutant per hour (see Equation 1 and Step 1). Once the hourly mass emission rate is calculated, it can be easily converted to a source specific emission factor by dividing the hourly mass emission rate by the hourly activity (i.e., hourly material throughput during the stack test or CEMS measurement, such as ton of coal combusted per hour [see Equation 2 and Step 2]). The annual emission rate of the air contaminant is simply the product of the source specific emission factor and annual activity (i.e., annual material throughput, such as tons of coal combusted during the year) (see Equation 3 and Step 3).
Eq (1) [air pollutant] * stack gas flow rate = hourly mass emission rate
Eq (2) hourly mass emission rate / hourly activity = source specific emission factor Eq (3) source specific emission factor * annual activity = annual emission rate of
air pollutant
Step 1 - Calculating the Hourly Emission Rate
According to Equation 1, the hourly mass emission rate is the concentration of air pollutant multiplied by the stack gas flow rate. The concentration of air pollutants and stack gas flow rate can be reported in a number of different ways or units, such as milligrams per cubic meter (mg/m3) or pounds per standard cubic foot (lbs/scf). To correctly calculate the hourly emission rate, the concentration and gas flow rate must be in units that are compatible with each other.
Concentration of Air Pollutant in the Stack
The concentration of an air pollutant is calculated by dividing the mass of the air pollutant collected by the volume or mass of stack gas sampled (see Equation 4). During a stack test, most air pollutants are collected on some type of media. The
Emission Calculations March 1999 Page 23 type of media depends on the type of air contaminant being measured. For example, particulate matter and metals, which are solids, are collected on a filter. Benzene, which is in a gaseous state, is collected on a solid sorbent, such as charcoal. The total volume of stack gas sampled is typically measured by a dry gas meter. Continuous emission monitoring systems (CEMS) measure gaseous air pollutants directly by fluorescence (SO2), infrared spectroscopy (CO), chemiluminescence (NOx), and flame ionization detection (VOCs). Table 4 identifies the concentrations of the criteria air pollutants typically found in stack test and CEMS results. Concentrations can be reported on a mass or volume basis.
mass of air pollutant collected
Eq (4) ________________________ = concentration volume or mass of air sampled
Table 4 - Source Testing Results
Pollutant Mass of Pollutant Collected Volume of Stack Gas Sampled Concentration of Pollutant in Stack Gas
Concentration Units VOCs, SO2, NOx, CO, HCL ppmvd PM, TOXICS M(grams) Vd(m3@ dry standard conditions) M * 1000mg/g Vd mg/m3 PM M(grams) Vdw(scf) M * 1 lb/453.59 grams Vdw lbs/scf PM M(grams) Vd(dscf) M * 1 lb/453.59 grams Vd lbs/dscf PM M(grams) Vd(dscf) M * 15.432 grains/gram Vd grains/dscf PM M(grams) Vdw(acf) M * 1 lb/453.59 grams*1000 Vdw * pdw lbs/1000 lbs (actual) PM M(grams) Vd(dscf) M * 1 lb/453.59 grams*1000 Vd* pd lbs/1000 lbs (dry)
Emission Calculations March 1999 Page 24
Table 5 - Nomenclature
acf actual cubic feet
acfm actual cubic feet per minute
C concentration (mass of air pollutant/mass or volume of air) dscf dry standard cubic feet
dscfm dry standard cubic feet per minute Fd fuel factor (dscfm/MMBtu)
ft3 cubic feet
Hin heat input rate (MMBtu/hr)
HHV higher heating value (Btu/lb, Btu/gallon, or Btu/cubic feet)
M mass of air pollutant
m3 cubic meters @ dry standard conditions mg milligrams
MW molecular weight of the pollutant. The molecular weight of the air pollutant is the sum of the atomic weights of all atoms in the molecule. One mole of molecules contains 6.022 x 1023 molecules. The mass of one mole of pollutant is its molecular weight * lb/lb-mole.
P pressure
pdw density of all sampled gas at standard conditions pd density of dry gas at standard conditions
ppmvd pollutant concentration expressed in units of parts per million volume dry. 1 ppmvd = 1 lb-mole of pollutant/106 lb-moles of air at dry conditions. Since ppmvd is a volume to volume ratio, it is independent of temperature and pressure.
Q stack gas flow rate
R mass fuel rate (lbs/hr)
scf standard cubic feet
scfm standard cubic feet per minute
STP Standard temperature (70oF) and pressure (29.92 inches of Hg absolute) as defined in Michigan Rule 119(M).
T temperature
Vd volume of dry gas @ STP
Vw volume of water vapor @ STP
Vdw volume of all sampled gas @ STP
Videal volume occupied by one lb-mole of ideal gas will occupy a volume of 386.5 ft3 @ 70oF and 29.92 inches of Hg
Emission Calculations March 1999 Page 25
Combustion Sources: The stack gas leaving a combustion device (e.g. incinerator or
boiler) contains certain levels of air pollutants which can be made to appear smaller if the total stack gas quantity is increased by adding non-pollutant gas to the stream. The volume fraction of any gas present in the stack gas can be reduced by dilution, i.e., adding air. It is for this reason that combustion equipment concentration emission standards are written with a specified amount of excess air (e.g., 0.08 grains/dscf corrected to 12% carbon dioxide). These excess air corrections are important when comparing stack test results to the emission standards but not when calculating the mass emission rate. No matter how much the stack gas is diluted, the mass emission rate will not change because the decrease in concentration will be offset by the increase in stack gas flow rate.
If concentrations from stack tests are corrected to 50% excess air, 7% CO2, or 7% O2, make sure the stack flow rate is in the same units when calculating the mass emission rate.
Stack Gas Flow Rate
The second piece of information needed to calculate the hourly mass emission rate is the stack gas flow rate (see Equation 1). As one can see in Table 4, the concentrations are based upon volumes of air at actual or standard pressure and temperature, and dry or wet conditions. Therefore, it is necessary to know how to convert acfm to scfm and scfm to dscfm.
Flow rates can be determined using continuous volume flow rate monitor, stack sampling data or, for combustion sources, can be estimated based on heat input using fuel factors.
Converting ACFM to SCFM
The volume of a gas varies with changes in pressure and temperature. In order to simplify comparison of gases, chemists adopted a set of standard conditions of temperature and pressure. Accordingly, Rule 119(m) of the Michigan Administrative Rule for Air Pollution Control defines standard conditions as a gas temperature of 70o Fahrenheit (460 + 70oF = 530oR) and a gas pressure of 1 atmosphere (29.92 inches of mercury absolute).
Table 6 - Conversion Factors
1 gram/1000 milligram 60 minutes/hour 0.02832 m3/ft3 1 gram/15.432 grains 1 lb/453.59 grams 1 lb/7000 grains
Emission Calculations Spring 2000 Page 26 The volume of a gas or volume flow rate of a gas at one temperature and pressure can be converted to its volume or volume flow rate at standard conditions by using the ideal gas equation which relates pressure, volume, and temperature.
According to the ideal gas law:
Eq (5) Qstd = Qo(Tstd/To) (Po/Pstd)
Where:
Qstd = gas flow rate at standard temperature and pressure Qo = gas flow rate at actual conditions
Pstd = pressure at standard conditions is 29.92 inches Hg or 1 atmosphere Tstd = temperature at standard conditions is 70oF
Po = pressure at actual conditions (inches Hg) To = temperature at actual conditions (oF)
Eq (6) Qscfm = Qacfm * (460 + 70oF ) * Po (460 + To) * Ps
Converting SCFM to DSCFM
Certain processes will generate moisture in the stack gas Eq (7) Qdscfm = Qscfm * (100 -% moisture)
100
This approach can only be used for exhaust flows < 5% moisture
For Combustion Sources: When direct measurements of stack gas flow rate are not
available, Q can be calculated using fuel factors (Fdfactors):
Eq (8) Qdscfm = Fd * 20.9 * Hin
(20.9 - %O2) * 60 min/hr
Where:
Fd = fuel factor, dry basis
%O2 = measured oxygen concentration, dry basis expressed as a percentage Hin = heat input rate in MMBtu/hr
Eq (9) Hin = R * HHV 106
Where:
R = mass fuel rate in lbs/hr
HHV = higher heating value of the fuel in Btu/lb
The average Fd factors are provided in EPA Reference Test Method 19 for different fuels and are shown in Table 7. Also in Table 7 are the higher heating values (HHV) of fuel.
Table 7- Fuel Factors and Higher Heating Values
Fuel Type Fd (dscf/MMBtu) HHV(Btu)
Coal anthracite 10,100 12,300/lb bituminous 9,780 13,000/lb lignite 9,860 7,200/lb Oil residual 9,190 150,000/gal distillate 9,190 140,000/gal Gas natural 8,710 1,050/scf Wood 9,240/lb 5,200/lb Wood Bark 9,600/lb 4,500/lb EXAMPLE #2:
Company A operates a distillate oil-fired boiler. The fuel rate is 20 gallons of oil per hour. The percent O2 in their exhaust gas is 2.1%. Determine the stack gas flow rate Qdscfm.
Step 1 - Calculate the heat input rate (Hin) MMBtu/hr Hin = (R * HHV)/ 106
Hin = (20 gal/hr * 140,000 Btu/gal * 1MM)/10 6
Hin = 2.8 MMBtu/hr
Step 2 - Calculate the stack gas flow rate Qdscfm
From Table 7, the Fdfactor for distillate oil is 9,190 dscf/MMBtu Q = Fd* ((20.9)/(20.9 - %O2)) * (Hin /60)
Q = 9,190 * ((20.9)/(20.9 - 2.1)) * (2.8/60) Qdscfm = 477
Emission Calculations 2004 Page 28
Calculating the Hourly Mass Emission Rate
According to Equation 1 (see page 22), calculating the mass emission rate might appear to be quite simple; just multiply the stack gas concentration of air pollutant by the stack gas flow rate to get a mass emission rate. The trick in making this calculation is being sure the units of concentration of air pollutants are compatible with the units of the stack gas flow rate. The following equations will explain how the air pollutant concentrations reported in stack tests and CEMS data (see Table 4) can be converted to the hourly mass emission rate expressed in units of pounds per hour (lbs/hr).
Converting ppmvd to lbs/hr
Eq (10) Cppmvd* MW * Q dscfm * 60 min/hr = lbs/hr Videal * 106
lb-mole pollutant lb pollutant lb-mole air ft3air 60 min = lb/hr MM lb-mole air lb-mole pollutant 386.5 ft3air min hr
EXAMPLE #3:
Company B operates a boiler equipped with a CEMS for SO2. According to the CEMS, the in-stack concentration of SO2 is 33 ppmvd. The stack gas flow rate Qdscfm is 155,087. What is the emission rate of SO2in lbs/hr?
Using Equation (10) and the molecular weight of SO2is 64 (i.e., 32+(16 * 2)):
33 * 64 * 155,087 * 60 = 51 lbs of SO2/hr 386.5 * 106
Converting mg/m3 to lbs/hr
The mass of air pollutant per volume of stack gas (mg/m3) is corrected to dry standard conditions. Thus, to calculate the mass emission rate, the concentration of air pollutant is multiplied by the stack gas flow rate, in units of dscfm.
Eq (11) C mg/m3* Vdscfm * 60 min/hr * 0.02832 m 3 /ft3= lbs/hr 453.6 gram/lb * 1000 mg/gram mg ft3 lb min m3 gram = lbs/hr m3 min gram hr ft3 mg
Converting lbs/scf to lbs/hr Eq (12) C lb/scf * Q scfm * 60 min/hr = lbs/hr lb * ft3 * min = lbs/hr ft3 min hr Converting lbs/dscf to lbs/hr Eq (13) C lb/dscf * Q dscfm * 60 min/hr = lbs/hr lb * ft3 * min = lbs/hr ft3 min hr Converting grains/dscf to lbs/hr
Eq (14) C grains/dscf * 1 lb/7000 grains * Q dscfm * 60 min/hr = lbs/hr
grains * lb * ft3 * min = lbs/hr ft3 * grains * min * hr
Converting lb/1,000 lbs (actual) to lbs/hr
Eq (15) lb pollutant * Q acfm * 60 min/hr * paw = lbs/hr 1000 lb air
lb pollutant ft3 min lb air = lbs/hr
lb air min hr ft3
Converting lb/1,000 lbs (dry) to lbs/hr
The density of air at dry standard conditions is 0.075 lbs/ft3
Eq (16) lb pollutant * Q dscfm * 60 min/hr * 0.075 lb/ft3= lbs/hr 1000 lb air
lb pollutant * ft3 * min * lb air = lbs/hr lb air * min * hr * ft3
Step 2 - Calculating the Source Specific Emission Factor
The hourly mass emission rate determined from CEMS or stack test data (see Step 1) can be converted into a source specific emission factor. An emission factor is the amount of pollutant emitted per activity. Activities are typically expressed in
Emission Calculations 2004 Page 30 terms of material usage, e.g., tons of coal or gallons of oil fired. The basic equation used in emission factor calculations is:
Eq (17) Emission Factor (EF) = Emission Rate (ERhourly) Activity (Ahourly)
lb of pollutant emitted = lb pollutant emitted hr ton of material ton of material/hr
See page 76 for additional discussion on source specific emission factors. EXAMPLE #4:
Company B operates a boiler that has an SO2emission rate (ER) of 51 lbs/hr. During the stack test, the coal firing rate (A) was 6.7 tons/hr. Calculate the SO2emission factor (EF).
Using Equation 17:
EFSO2 = 51 lbs SO2/hr . 6.7 tons coal combusted/hr EFSO2 = 7.612 lbs SO2/ton of coal
For Combustion Sources: Often a stack test may report emissions in units of
lbs/MMBtu. This is calculated by taking the lbs of pollutant/hr emission rate from the test and dividing by the heat input rate Hin (see Step 1 below). To convert lbs/MMBtu to an annual emission rate, use the fuel throughput and heating value of fuel (see Step 2 below).
Eq (18) lbs pollutant/MMBtu * MMBtu/year * ton/2000 lb = tons pollutant/yr
Step 1 - Converting lbs/hr to lbs/MMBtu:
(lbs pollutant/hr ) / Hin = lbs pollutant/MMBtu
Where: Hin = R * HHV 106
lbs pollutant * hr * lbs fuel * 106 = lbs pollutant hr * lbs fuel * Btu * 1MM MMBtu
Step 2 - Calculating MMbtu/year
HHV * lbs fuel used/year = MMBtu/year
Btu * lbs fuel * MM = MMBtu
lbs fuel * year * 106 year
Step 3 - Converting lbs/MMBtu to tons/year
lbs pollutant* MMBtu * 1 ton = tons pollutant
MMBtu * year * 2000 lbs year
Step 3 - Determining the Annual Mass Emission Rate
The annual emission rate is the product of the source specific emission factor (determined in Step 2) multiplied by an annual activity rate. Some examples of an annual activity rate are tons of coal combusted per year or gallons of paint applied per year.
EQ (19) Annual Emission (ERannual) = Emission Factor (EF) * Activity (Aannual)
lb of pollutant emitted = lb pollutant emitted * ton of material yr ton of material * yr
EXAMPLE #5:
Company B burns 41,000 tons of coal during the year. What is the annual mass emission rate (ER) of SO2?
Using Equation 19:
ER annual = 7.612 lbs SO2/ton of coal * 41,000 tons coal/yr * 1 ton/2000 lbs ER annual = 156 tons of SO2/yr
One final key point to consider when deriving an annual mass emission rate from source test data: stack tests are generally only conducted over several hours or days at most. It’s a snap shot of the emission unit’s emissions. Over time, changes to the emission unit may occur that could result in emission rates that are different than those taken during the stack test. The facility may then have to conduct a new test to reflect these new operating conditions.
Emission Calculations March 1999 Page 32
Mass Balance
Mass balance is a method that estimates emissions by analyzing inputs of raw materials to an emission unit and accounting for all of the various possible outputs of the raw materials in the form of air emissions, wastewater, hazardous waste, and/or the final product. As the term implies, one needs to account for all the materials going into and coming out of the process for such an emission estimation to be credible.
M A S S B A L A N C E A P P R O A C H
a ir e m is s io n s ra w m a te ria ls p ro d u c t h a z a rd o u s w a s te w a s te w a te r E M IS S IO N U N ITFigure 2. Mass Balance
A mass balance approach can provide reliable average emission estimates for specific emission units. For some emission units, a mass balance may provide a better estimate of emissions than an emission test would. In general, mass balances are appropriate for use in situations where a high percentage of material is lost to the atmosphere (e. g., sulfur in fuel, or solvent loss in an uncontrolled coating process). The use of mass balance involves the examination of a process to determine whether emissions can be estimated solely on knowledge of operating parameters, material compositions, and total material usage. The simplest mass balance assumes that all solvent used in a process will evaporate to become air emissions somewhere at the facility. For instance, for many surface coating operations, it can be assumed that all of the solvent in the coating evaporates to the atmosphere during the application and drying processes. In such cases, emissions equal the amount of solvent contained in the surface coating plus any added thinners.
Mass balances are greatly simplified and very accurate in cases where all of the consumed solvent is emitted to the atmosphere. But many situations exist where a portion of the evaporated solvent is captured and routed to a control device such as an afterburner (incinerator) or condenser. In these cases, the captured portion must be measured or estimated by other means, and the disposition of any recovered material must be accounted for. As a second example, in degreasing operations, emissions will not equal solvent consumption if waste solvent is removed from the unit for recycling or incineration. A third example is where some fraction of the diluent (which is used to liquefy cutback asphalt, for example) is believed to be retained in the substrate (pavement) rather than evaporated after application. In these examples, a method of accounting for the non-emitted solvent is required to avoid an overestimation of emissions.
Mass balances may be inappropriate where material is consumed or chemically combined in the process, or where losses to the atmosphere are a small portion of the total process throughput. As an example, applying mass balances to petroleum product storage tanks is not generally feasible because the losses are too small relative to the uncertainty of any metering devices. In these cases, emission factors can be used.
Mass Balance Examples
Below are some examples of using the mass balance approach of estimating emissions. The processes included in the examples are surface coating operations, laboratory hoods, and combustion sources.
Surface Coating Operations
Surface coating operations, including preparation of the articles to be coated, can involve a variety of emissions such as volatile organic compounds (VOCs) and particulates from painting, metals from grinding, metals and VOCs from foundry operations, and other criteria pollutants from fuel. Emissions of volatile organic compounds (VOCs) from surface coating operations are a result of evaporation of thinners and solvents found in the coating. The main factor affecting VOC emission rates is the percent of volatile matter in the coating being applied. Most Material Safety Data Sheets (MSDSs) indicate the percent weight or volume of volatile matter in the coating. The MSDS may also indicate the density of the coating, usually in units of pounds per gallon (lb/gal). The density of the coating can also be calculated, if it is not specified on the MSDS, by multiplying the specific gravity of the coating by 8.34 lb/gal, which is the density of water. (This is assuming that the coating is being applied at close to atmospheric conditions.)
Emission Calculations March 1999 Page 34 To quantify VOC emissions from surface coating operations, assume that all of the volatile matter in the coating is emitted to the atmosphere. The following example outlines the steps involved in quantifying VOC emissions from surface coating operations.
1. Identify the coating and amount used for a designated time period.
2. Locate the MSDS to identify the percent volatile by weight and the density of the coating.
3. Complete the calculations as indicated in Example #6. EXAMPLE #6: VOC Calculations
Coating A (assume the coating is solvent-based and applied as received) Volatile percent (by weight) = 40%
Density = 8.00 lb/gal
Usage Rate = 2500 gal/yr
= 1 gal/hr (average)
= 3 gal/hr (maximum, based on maximum production rate) Hours of operation = 2500 hr/yr
Permit limitations or other requirements = None that are federally enforceable Hours of continuous operation = 24 hrs/day x 7 days/week x 52 weeks/year
= 8760 hrs/yr Actual VOC Emissions:
Hourly average = 1 gal hr x 8.0 lb gal x 0.4 lb VOC lb coating = 3.2 lb VOC hr Annual = 2500 gal yr x 8.0 lb gal x 0.4 lb VOC lb coating x 1 ton 2000 lb = 4 ton VOC yr
Potential VOC Emissions: Hourly = 3 gal hr x 8.0 lb gal x 0.4 lbs VOC lb coating = 9.6 lbs VOC hr Annual = 9.6 lbs VOC hr x 8760 hr yr x 1 ton 2000 lb = 42 tons VOC yr
The coating may also include a hazardous air pollutant (HAP) as one of its constituents. The MSDS may indicate for example, the following:
Toluene = 10% (by weight)
n-Butyl Acetate = 10% (by weight)
Methyl Ethyl Ketone (MEK) = 10% (by weight) Xylene = 10% (by weight)
If so, you can estimate HAP emissions by assuming that the HAP is emitted into the atmosphere at the same percentage as it is found in the coating. For example using the previous example:
EXAMPLE #7: Hazardous Air Pollutants (HAP) emissions) Coating A
VOC Emission rate = 4.0 tons/year Toluene = 10% (by weight)
n-Butyl Acetate = 10% (by weight) MEK = 10% (by weight)
Xylene = 10% (by weight) Actual HAP Emissions (toluene):
Hourly = 1 gal hr x 8.0 lb gal x 0.1 lb Toluene lb coating = 0.8 lb Toluene hr Annual = 2500 gal yr x 8.0 lb gal x 0.1 lbs Toluene lb coating x 1ton 2000lb = 1.0 ton Toluene yr
Potential HAP Emissions (toluene):
Hourly = 3 gal hr x 8.0 lb gal x 0.1 lbs Toluene lb coating = 2.4 lbs Toluene hr Annual = 2.4 lbs Toluene hr x 8760 hr yr x 1ton 2000lb = 10.5 tons Toluene yr
Emission Calculations March 1999 Page 36 EXAMPLE #8: VOC Calculations
Estimating Emissions Using Mass Balance with a Single Component
In one process, Company C uses a solvent bath to clean its product, widgets. The solvent density is 7.7 pounds per gallon. (The density of the solvent is used to convert from gallons of solvent to pounds of solvent in the emission calculation). Xylene is the only substance in the solvent for which emissions must be quantified, and it constitutes 87% of the solvent by weight. At the beginning of the year, Company C had 7,500 pounds of this solvent in storage and purchased another 9 tons over the year. At the end of the year, the facility had 10,000 pounds in storage.
Assumptions: a. Xylene is a volatile organic compound and the total volume is usually emitted to the atmosphere. Thus, emissions equal amount of xylene used.
b. No control device is used to reduce the emissions of solvent.
Because emissions equal the amount of xylene used, emissions (ER) are determined using the following equation:
(20) ER = (SB + SI - SE) * F
Where:
ER = Annual emissions of xylene (lb/yr)
SB = Amount of solvent in storage at the beginning of the year (lb) SI = Amount of solvent purchased during the year (lb)
SE = Amount of solvent left in storage at the end of the year (lb) F = Fraction of xylene in the solvent, lb xylene/lb
ER = [7,500 lb + (9 tons x 2,000 lb/ton) - 10,000 lb]*0.87 lb xylene/lb solvent = 15,500 lbs x 0.87 lb xylene/lb solvent
Considerations When Calculating VOC Emissions
The VOC content of coating can be expressed in a number of different ways. Examples are: lbs of VOC/ gallon of coating or lbs of VOC/ gallon of coating minus water and exempt organic solvents. When calculating your annual emissions of VOC, make certain that the total gallons of coating used in a year is compatible with what is in the denominator of the VOC content of the coating.
EXAMPLE #9: VOC Calculations
Company D uses a coating that has a VOC content of 5.27 lb VOC /gal of coating minus water and exempt organic solvent. The company used 5,452 gallons of coating in the year. The percent by volume of water and exempt organic solvents in the coating is 5 % and 15 %, respectively. Calculate their annual emissions of VOCs.
Step 1 - Determine volume of water and exempt organic solvents
5,452 gallons coating * (5% + 15%) = 1,090 gallons of water and exempt organic solvents
Step 2 - Determine gallons of coating minus water and exempt organic solvents
5,452 - 1,090 = 4,362 gallons of coating minus water and exempt organic solvents
Step 3 - Calculate annual emissions of VOC
5.27 lb VOC/gallons of coating minus water and exempt solvent * 4,362 gallons of coating minus water and exempt solvents/year = 22,989 lbs VOC/year
Laboratory Hoods
There are no specific emission factors for calculating releases from laboratory hoods. The most common approach to estimating releases is the use of a combination of material balance and engineering calculations. In general, unless there is some information to the contrary, you can conservatively assume that 100 percent of the volatile materials collected by the hood are released to the atmosphere.
Emission Calculations 2002 Page 38 The key to making reasonable estimates of potential VOC emissions is to make sure that the product consumption rates used in the calculations represent the maximum or design capacity, rather than actual usage rates. For example, assume that your facility has been operating for only 5 days/week, 24 hours/day (or 6240 hours/year) over the past year, instead of the maximum possible 7 days/week, 24 hours/day (8760 hours/year). Production rates for the year at a laboratory hood thus reflect operations at about 70 percent of capacity, and should be scaled up to full production capacities to estimate potential releases.
EXAMPLE #10: Laboratory Hoods
Assume that in 1993 you consumed 3,800 lb of a volatile material at a laboratory hood and operated 6240 hours/year. Total potential VOC emissions could be calculated as:
Potential amount per year: 3800 lb year x 1 year 6240 actual hr x 8760 hours year = 5335 lb year max
Potential amount per hr: 5335 lbs year x 1 year 8760 hours = 0.6 lbs hour Combustion Sources
Fuel analysis can be used to predict emissions based on the application of mass balance. The presence of certain elements in fuels may be used to predict their presence in emission streams. These include toxic elements such as metals found in coal; as well as other elements such as sulfur, that may be converted to other compounds during the combustion process.
The basic equation used in fuel analysis emission calculations is: (21) ER = R * PC * (MWp/MWf)
Where:
ER = pollutant emission rate R = fuel flow rate (lb/hr)
PC = pollutant concentration in fuel ( %/100)
MWp = molecular weight of pollutant emitted (lb/lb-mole) MWf = molecular weight of pollutant in fuel (lb/lb-mole)
concentration of sulfur in the oil. This approach assumes complete conversion of sulfur to SO2. Therefore, for every pound of sulfur (MW = 32 g) burned, 2 lb of SO2(MW = 64 g) are emitted. The application of this emission estimation technique is shown in Example 11.
EXAMPLE #11: Calculations Using Fuel Analysis
Calculate the SO2emissions from the combustion of oil based on fuel analysis results and the fuel flow information.
fuel flow rate R = 46,000 lbs/hr percent sulfur (% S) in fuel = 1.17 ER = R * PC * (MWp/MWf)
= (46,000) * (1.17/100) * (64/32) = 1,076 lbs SO2/hr
Emission Factors and Emission Models What are Emission Factors?
An emission factor is a representative value that attempts to relate the quantity of a pollutant released to the atmosphere with an activity associated with the release of that pollutant. An emission factor is a ratio of the amount of a pollutant emitted per throughput of material (for example, pounds of NOx per gallon of residual oil burned). Emission factors are founded on the premise that there exists a linear relationship between the emissions of air contaminant and the activity level. A wide variety of sources can use emission factors to estimate their emissions.
The general equation for calculating uncontrolled emissions using an emission factor is: Eq (22) ERA = EFA* CF1* CF2* A1* A2* (100-EC/100)
Where:
ERA = emissions of pollutant A EFA = emission factor of pollutant A
CF = 1 or more conversion factors (if necessary) A = 1 or more activity values
