Auto parts: case study

Purpose

To provide the auto parts sector with guidance on how to report to the National Pollutant Release Inventory (NPRI).

Scenario

A facility, Example Industries, operates an auto parts painting facility that employs 15 full-time staff. Auto parts are prefabricated and transported to the facility for finishing. The facility may be subject to NPRI reporting requirements. Therefore, the facility is required to estimate emissions from its operation to determine if it met the thresholds and reporting criteria. There is no monitoring performed at this facility and no stack test has been performed. There is a filter for the painting operation. The first step is to identify the criteria for NPRI reporting.

Step 1 - Employee Criteria

The total number of hours worked by employees at the facility exceeded the 20 000-hour employee threshold.

Step 2 - Identify the Emission Sources at the Facility

After reviewing the Guide for Reporting to the National Pollutant Release Inventory a survey of the facility's emission sources was performed. Based on the survey, the following sources were identified:

Source 1: A boiler of 25 Megawatts (85 million BTU/hour) capacity firing natural gas and Number 6 fuel oil (residual oil), vented by a stack measuring 12 meters in height (uncontrolled emissions).

Source 2: An open-top vapor degreaser for cleaning metal parts (no stack, uncontrolled emissions).

Source 3: Painting operation for the final product, vented by a stack measuring 52 meters in height (emissions controlled by a filter).

Step 3 - Calculate Emissions for Each Identified Source

Emission source 1 - Boiler of capacity 25 Megawatts (85 million BTU/hour) firing natural gas and Number 6 fuel oil (residual oil).

Step 3a - Identify the Method(s) of Estimating Emissions

Since the facility does not have any monitoring equipment installed or stack testing performed, an appropriate method to use is emission factors (EFs). Determine if there are any manufacturer-supplied boiler specific emission factors for both fuels. If none are available, an appropriate emission factor is the one published by the U.S. EPA, in the AP-42 document (see note below) or the latest version of WebFIRE (see note below). calculate emissions for each type of fuel (natural gas and fuel oil) used in the boiler:

  • AP-42: compilation of Air Pollutant Emission Factors, AP-42, Fifth Edition, Volume I: Stationary Point and Area Sources;
  • WebFIRE is a database and accessing software containing U.S. EPA's recommended emission estimation factors for criteria and hazardous air contaminants.

Step 3b - Calculate Boiler Emissions for Each Type of Fuel (Natural Gas and Fuel Oil) Used in the Boiler

Natural Gas:

Annual consumption: 4 x 106 cubic meters (4 million cubic meters)

The following tables provide emission factors (from section 1.4 of AP-42 or the WebFIRE database) for natural gas combustion:

Table 1: Emission Factors for the Release of Part 1 Substances from the Combustion of Natural Gas
NPRI Substance Emission Factor (kg/106 cubic meters of natural gas)
Formaldehyde 1.2

Note: Many Part 1 and 2 substances are released in the combustion of natural gas. For the sake of brevity and clarity only formaldehyde is shown as an example in this case study.

Table 2: Emission Factors for CAC Release from the Combustion of Natural Gas
NPRI Substance Emission Factor
(kg/106 cubic meters of natural gas)
Total particulate matter (TPM) 30.4
Particulate matter <= 10 microns (PM10) 30.4
Particulate matter <= 2.5 microns (PM2.5) 30.4
Volatile organic compound (VOC) 88
Oxides of nitrogen (NOx) 1 600
Sulphur dioxide (SO2) 9.6
Carbon monoxide (CO) 1 344


Table 3: Emission Factors for Part 5 Releases from the Combustion of Natural Gas
NPRI Substance Emission Factor
(kg/106 cubic meters of natural gas)
Benzene 0.0336
N-butane 33.6
Formaldehyde 1.2
n-Hexane 28.8
N-pentane 41.6
Propane 25.6
Toluene 0.0544

1 Megawatt = 3.41 million BTU/hr
Emission Factor (EF) for SCC: 10100602 Boiler < 100 million BTU/hr
Particulate matter emissions from natural gas combustion are <1.0 micron in diameter. Therefore, the same emission factor (EF) is used for all three particulate fractions (TPM contains both PM10 and PM2.5 fractions).
EF is converted from lb/million cubic feet to kg/million cubic meters using a conversion factor of 16. Check this Web site for more details.
EFs also conform to the latest available WebFIRE database.

The general equation that is used for estimating uncontrolled emissions from natural gas combustion in boilers is:

Emission = Fuel consumption (million cubic meters) x EF (kg/million cubic meters)

Example Calculation:

VOC emissions = (4 x 106 cubic meters) x (88 kg/ 106 cubic meters)

= 352 kg
= 0.352 tonnes

Use the same method to calculate other emissions using emission factors.

The following table shows uncontrolled emissions from the boiler as a result of natural gas combustion:

Table 4: Uncontrolled Annual Part 1 Emissions from the Combustion of Natural Gas
NPRI Substance Annual Uncontrolled Emissions (tonnes)
Formaldehyde 0.005


Table 5: Uncontrolled Annual CAC Emissions from the Combustion of Natural Gas
NPRI Substance Annual Uncontrolled Emissions (tonnes)
TPM 0.122
PM10 0.122
PM2.5 0.122
VOC 0.352
NOx 6.400
SO2 0.038
CO 5.376
Table 6: Uncontrolled Annual Part 5 Emissions from the Combustion of Natural Gas
NPRI Substance Annual Uncontrolled Emissions (tonnes
Benzene 0.000
N-butane 0.134
Formaldehyde 0.005
n-Hexane 0.115
N-pentane 0.166
Propane 0.102
Toluene 0.000

Number 6 Fuel Oil:

Annual consumption: 300 000 liters
Sulphur content: 1%

Since there are no boiler-specific emission factors provided by the manufacturer, the appropriate emission factors to use are those published by the U.S. EPA, in the AP-42 document Section 1.3, Table 1.3 for boilers using Number 6 fuel oil (less than 100 million BTU/hour) and the WebFIRE database.

The following table shows uncontrolled emission factors for the boiler burning Number 6 fuel oil:

Table 7: Emission Factors for the Release of Part 1 Substances from the Combustion of Number 6 Fuel Oil
NPRI Substance Emission Factor
(kg/1 000 liters of fuel oil)
Formaldehyde 0.0051

Note: Many Part 1 and 2 substances are released in the combustion of residual oil (No. 6 fuel oil). For the sake of brevity and clarity only formaldehyde is shown as an example in this case study.

Table 8: Emission Factors for the Release of CAC from the Combustion of Number 6 Fuel Oil
NPRI Substance Emission Factor
(kg/1 000 liters of fuel oil)
TPM (9.19 x S + 3.22) x 0.12
PM10 (7.17 x (1.12 x S + 0.37)) x 0.12
PM2.5 (4.67 x (1.12 x S + 0.37)) x 0.12
VOC 0.0336
NOx 6.6
SO2 18.84 x S
CO 0.6


Table 9: Emission Factors for the Release of Part 5 Substances from the Combustion of Number 6 Fuel Oil
NPRI Substance Emission Factor
(kg/1 000 liters of fuel oil)
Benzene 0.000132
Formaldehyde 0.0051
Toluene 0.001056
Isomers of Xylene 0.0009

Notes:

1 Megawatt = 3.41 million BTU/hr
EFs from Section 1.3 of AP-42
EFs converted from lb/1 000 gallons to kg/1 000 liters using a conversion factor of 0.12

S= Sulphur content in the fuel oil, expressed as a percentage
VOC emission factor from Table 1.3-3 (Non Methane Total Organic Compound)

The general equation for estimating uncontrolled emissions from fuel oil combustion in boilers is:

Emissions = Fuel consumption in liters x Emission factor (kg/1 000 liters)

Example Calculations:

Sulphur dioxide emission factor = 18.84 x (S) kg/1 000 liters of fuel oil, where S is the weight percent of sulphur in the oil
SO2 emission factor = 18.84 (1) kg/1 000 liters of fuel oil = 18.84 kg/1 000 liters of fuel oil
SO2 emissions = Fuel oil consumption in liters x EF (kg/1 000 liters)
SO2 emissions = 300 000 liters of fuel oil consumed x 18.84  kg/1 000 liters of fuel oil
= 5 652 kg/year x 0.001 tonnes/kg
= 5.652 tonnes per year

TPM emission factor = (9.19 x S + 3.22) x 0.12
TPM emission factor = (9.19 x 1 + 3.22) x 0.12
TPM emission factor = 1.49 kg/1,000 liters
TPM emission = 1.49 kg/1000 liters x 300,000 liters = 447 kg = 0.447 tonnes

The following table provides details of the uncontrolled emissions from the boiler as a result of fuel oil combustion:

Table 10: Uncontrolled Annual Part 1 Emissions from the Combustion of Number 6 Fuel Oil
NPRI Substance Annual Uncontrolled Emissions (tonnes)
Formaldehyde 0.002


Table 11: Uncontrolled Annual CAC Emissions from the Combustion of Number 6 Fuel Oil
NPRI Substance Annual Uncontrolled Emissions (tonnes)
TPM 0.447
PM10 0.385
PM2.5 0.250
VOC 0.010
NOx 1.980
SO2 5.652
CO 0.180


Table 12: Uncontrolled Annual Part 5 Substance Emissions from the Combustion of Number 6 Fuel Oil
NPRI Substance Annual
Uncontrolled Emissions
from Residual Oil Combustion (tonnes)
Benzene 0.000
Formaldehyde 0.002
Toluene 0.000
Xylene 0.000

Step 4 - Add Emissions from Natural gas and Fuel Oil Combustion

Table 13: Total Part 1 Substance Emission from the Boiler
NPRI Substance Annual
Uncontrolled
Emissions from Combustion
(tonnes)
Formaldehyde 0.007
Table 14: Total Part 4 Substance Emissions from the Boiler
NPRI Substance Annual
Uncontrolled
Emissions from Combustion
(tonnes)
TPM 0.568
PM10 0.507
PM2.5 0.372
VOC 0.362
NOx 8.380
SO2 5.690
CO 5.556


Table 15: Total Part 5 Substance Emissions from the Boiler
Part 5 Substance Annual
Uncontrolled
Emissions from Combustion
(tonnes)
Benzene 0.000
N-butane 0.134
Formaldehyde 0.007
n-Hexane 0.115
N-pentane 0.166
Propane 0.102
Toluene 0.000
Xylene 0.000

Step 5 - Calculate Emission from Source 2

Operating Parameters:

At the beginning of each month 200 liters of solvent with a density of 0.95 kg/liter is added to the open-top degreaser. During the month, an additional 50 liters is added to replenish losses. At the end of the month 200 liters of waste solvent is sent for off-site recycling. About 1 kg of solid waste is collected for disposal. The solvent is 100% VOC (100% Trichloroethylene from the MSDS), the waste solvent is 98% VOC and the solid waste is 5% VOC.
Note: Volatile organic compounds (VOC) are located in the Part 1, Part 4, and Part 5 groups of substances.

Step 5a - Identify the Appropriate Estimation Method

Knowing the VOC content of all solvents, the appropriate estimation method is mass balance.

Step 5b - Calculate Solvent Used per Month

Solvent in = (New solvent + Replenishment solvent) x density
= (200 liters/month + 50 liters/month) x 0.95 kg/liter
= 237.5 kg solvent /month
=0.238 tonnes solvent

Step 5c - Calculate Waste Solvent Generated per Month

Solvent out = (liters of solvent sent for recycling x solvent density x waste solvent VOC content) + (solid waste x solid waste VOC content)
= (200 liters solvent/month x 0.95 kg/liter of solvent x 0.98) + (1 kg of waste/month x 0.05)
= 186.25 kg solvent/month
= 0.186 tonnes solvent per month

Step 5d - Calculate VOC Emitted

VOC emission = Solvent in - Solvent out
= 237.5 kg/month - 186.25 kg/month
= 51.25 kg/month
Annual VOC emission = 51.25 kg/month x 12 months/year
= 615 kg/year
= 0.615 tonnes

Step 5e - Part 5 Substances

Annual VOC emission from degreaser = 0.615 tonnes
An analysis of the solvent Material Safety Data Sheet (MSDS) indicates that the solvent is 100% volatile and comprised solely of Trichloroethylene. The annual VOC emission from the degreaser is 0.615 tonnes of Trichloroethylene.

Step 6 - Calculate Emissions from Source 3

Operating Parameters:
Example Industries uses "COAT-ABC" as a surface-coating compound. Last year it used approximately 20 000 liters of the compound.

  • Spray booth type: dry filter spray booth
  • Spray gun transfer efficiency: 70%
  • Dry filter collection efficiency: 99%

Step 6a - Identify the Appropriate Method

Since there are no emission factors available for this type of operation, the appropriate estimation method is the mass balance.

The mass balance equation is:

ME = MI - MO - MA - MR

Where:
ME= Mass of coating compound emitted, kg
MI= Mass of coating compound in the input stream, kg
MO= Mass of coating compound in the output stream in the finished product, kg
MA= Mass of coating compound accumulated in the system, kg
MR = Mass of coating compound captured for recovery or disposal,  kg

Step 6b - Identify the VOC Content in the Coating Material

To apply the mass balance approach, the VOC content in the coating compound must be determined. In many instances, the Material Safety Data Sheet (MSDS) for that compound will indicate percent weight content of the predominant VOC (if not, the supplier may be contacted to obtain this information). The annual consumption of the compound could be obtained from the facility's operation log or sales slips.

Sample MSDS for "COAT-ABC"

MATERIAL SAFETY DATA SHEET

SECTION 1 - CHEMICAL PRODUCT AND COMPANY IDENTIFICATION

PRODUCT NAME: COAT-ABC
SUPPLIER: ABC CORP

SECTION 2 - COMPOSITION / INFORMATION ON DANGEROUS INGREDIENTS
Chemical Name CAS # Percent by Weight
Methyl ethyl ketone 78-93-3 20%
Xylene 1330-20-7 25%
Ethylbenzene 100-41-4 20%
Toluene 108-88-3 15%

SECTION 3 - PHYSICAL AND CHEMICAL PROPERTIES

Specific Gravity: 1.35
Percent volatile: 80% by weight

Note: In some cases, the percent of volatiles value reported in the MSDS contains water and other non-VOC components. The quantities of these components, if they can be identified, should be excluded from the percent volatiles during VOC emission calculations.

For this coating operation there is no loss of coating compound to the coating equipment and no loss to the system's liquid/solid waste streams. All of the volatiles are assumed to have been released into the atmosphere.

Step 6c - Calculate VOC Emissions

It is assumed that all VOCs in "COAT-ABC" were released into the atmosphere [MA = MR = MO = 0 and ME = MI]. The facility used more than 25 000 kg/year of COAT-ABC, but the threshold criteria for VOC must still be assessed based on the specific gravity and percent volatiles.

ME = Q x D x c

Where:
ME = Total uncontrolled VOC emission, kg
Q = Total annual consumption of coating material, liters = 20 000 liters
D = Density of coating material, kg/liter = 1.35 x 1 kg/liter = 1.35  kg/liter (from MSDS)
c = VOC content by weight in coating material,% = 80% (from MSDS)

ME = 20 000 liters of coating x 1.35 kg/liter x (80/100 VOC content)
= 21.6 kg
= 21.600 tonnes

Step 6d - Calculate Uncontrolled Particulate Matter Emissions

Coating density of solid content = Density of coating - Density of volatile content
= 1.35 kg/liter - (1.35 x 80/100) kg/liter
= 0.27 kg solids/liter

Uncontrolled PM emissions = Density of solid content x annual usage x (1 - transfer efficiency)
= 0.27 kg/liter x 20 000 liters/year x (1 - 0.7)
= 1620 kg/year x 0.001 tonnes/kg
= 1.62 tonnes

Step 6e - Estimate Controlled Particulate Matter Emissions

Controlled PM emissions = Uncontrolled PM x (1 - control efficiency)
= 1.62 tonnes x (1 - 99/100)
= 0.0162 tonnes

As the PM emissions are from a spray operation and pass through a filter, the PM that is emitted is assumed to be PM2.5 and as a result the TPM and PM10 would also be 0.0162 tonnes.

Step 6f - Part 5 Substances

Total VOC emission from painting operation = 21.6 tonnes

An analysis of the paint Material Safety Data Sheet (MSDS) indicate that there are three VOC species that are listed in part 5. Using the annual VOC (Part 4 Substance) emission from the painting operation, calculate the emission of VOC species.

Example Calculation

VOC species - Methyl Ethyl Ketone (MEK)
Weight Percent = 20
MEK Emission = Total annual consumption of coating material, liters x percent weight MEK x density of coating material, kg/liter
MEK emission = 20 000 liters x 20/100 x 1.35 kg/liter = 5 400 kg=5.400  tonnes

Using the same method, calculate emission for each substance in the coating material:

Table 16: Emissions of each Substance in the Coating Material
Part 5 Substance CAS No. Percent Weight Paint Booth Emissions (tonnes)
Methyl ethyl ketone 78-93-3 20 5.400
Xylene 1330-20-7 25 6.750
Toluene 108-88-3 15 4.050

Step 7 - Add Emissions from All Sources

The next step is to add emissions from each source and calculate the total emissions from the facility in order to determine if the NPRI thresholds were met.

Part 1 Substances

A facility is required to report Part 1 substances if the facility manufactured, processed, or otherwise used the Part 1 substances at a quantity and concentration meeting or exceeding each substance's specific threshold. The total weight of by-products at any concentration must also be included in the calculation of the prescribed threshold for each Part 1 substance.

Table 17: Annual Emissions from Part 1 Substances
NPRI Part 1 Substance Annual Boiler Emissions (tonnes) Annual Degreaser Emissions (tonnes) Annual Coating Emissions (tonnes) Total Facility Emissions (tonnes) Total Emissions from Point Sources (tonnes) Total Emissions from Fugitive Sources (tonnes)
Formaldehyde 0.007 0.000 0.000 0.007 0.007 0.000

This facility will not be required to report for formaldehyde because it did not manufacture, process, or otherwise use 10 tonnes or more of it.

Part 4 Substances

A facility is required to report any Part 4 substances that it released to the air at a quantity that meet or exceeds that substance's specific threshold.

Table 18: Annual Emissions from Part 4 Substances
NPRI Part 4 Substance Annual Boiler Emissions (tonnes) Annual Degreaser Emissions (tonnes) Annual Coating Emissions (tonnes) Total Facility Emissions (tonnes) Total Emissions from Point Sources (tonnes) Total Emissions from Fugitive Sources (tonnes)
VOC 0.362 0.615 21.600 22.577 21.962 0.615
TPM 0.568 0 0.0162 0.584 0.584 0
PM10 0.507 0 0.0162 0.523 0.523 0
PM2.5 0.372 0 0.0162 0.389 0.389 0
NOx 8.380 0 0 8.380 8.380 0
SO2 5.690 0 0 5.690 5.690 0
CO 5.556 0 0 5.556 5.556 0


Table 19: Comparison of Annual Emissions to the NPRI Reporting Thresholds
NPRI Part 4 Substance Total Facility Emissions (tonnes) NPRI Threshold (tonnes) NPRI Threshold Exceeded? Rationale
VOC 22.577 10 Yes Facility emission is > than NPRI threshold
TPM 0.584 20 No Facility emission is < than NPRI threshold
PM10 0.523 0.5 Yes Facility emission is > than NPRI threshold
PM2.5 0.389 0.3 Yes Facility emission is > than NPRI threshold
NOx 8.380 20 No Facility emission is < than NPRI threshold
SO2 5.690 20 No Facility emission is < than NPRI threshold
CO 5.556 20 No Facility emission is < than NPRI threshold

Note: > Indicates greater than
< Indicates less than

Conclusion:

Since the VOC and PM2.5 emissions for the year from the facility exceed their respective thresholds Example Industries must submit an NPRI report for these two pollutants (VOC and PM2.5).

Part 5 Substances

Facilities with sources of VOC may be required to report additional information on VOC species. If a facility meets the 10-tonne total VOC threshold, it must report for all VOC species that are released to air in a quantity greater than or equal to 1 tonne.

Table 20: Comparison of Part 5 Annual Emissions to the NPRI Reporting Thresholds
Part 5 Substance CAS No. Boiler Emissions (tonnes) Degreaser Emissions (tonnes) Painting Emissions (tonnes) Total Emissions (tonnes) Exceeds Reporting Threshold of 1 tonne?
Benzene 71-43-2 0.000 0 0 0.000 N
N-butane 106-97-8 0.134 0 0 0.134 N
Formaldehyde 50-00-0 0.007 0 0 0.007 N
N-pentane 109-66-0 0.166 0 0 0.166 N
Propane 74-98-6 0.102 0 0 0.102 N
Toluene 108-88-3 0.000 0 4.050 4.050 Y
N-hexane 110-54-3 0.115 0   0.115 N
Methyl ethyl ketone 78-93-3 0 0 5.400 5.400 Y
Xylene 1330-20-7 0.000 0 6.750 6.750 Y

Since the release threshold for VOC species is 1 tonne, the facility must report methyl ethyl ketone, xylene, and toluene individually as well as a value for other VOCs not listed in part 5.

Step 8 - Reporting Information for Stacks with a Height > 50 Meters Above Grade

If the facility has a stack with a height greater than or equal to 50 meters above grade, additional reporting may be required. The stack emission and physical parameter details must be provided by the facility if the emission quantity from the stack exceeds the stack threshold as shown in the table below.

The painting operation has a stack that is 52 meters in height above grade. VOC emissions from the painting operation are 21.6 tonnes that exceeds the tall stack threshold of 5 tonnes. Therefore, the facility must report VOC emissions for that stack.

Note: The "stack >= 50 meters" criteria are applicable only when the facility exceeds the NPRI threshold for any CAC substance. The following table provides the CAC thresholds that would apply at this facility for a stack >= 50 meters for which the facility must consider when reporting:

Table 21: Emissions from Stacks with a Height Above 50 Meters
NPRI Substance For a Stack >= 50 meters - Stack threshold (tonnes) Paint Booth Emissions (tonnes)
PM10 0.25 0.0162
PM2.5 0.15 0.0162
VOC 5.00 21.600

Step 9 - Calculate the Monthly Breakdown of Annual Releases to Air by Percentage

Detailed emission estimates show that the facility is required to report to the NPRI. Additional reporting such as monthly breakdown of emissions by percentage for each pollutant, must be reported.

Example

Usage of natural gas, fuel oil, coating and degreaser solvent for each month is obtained from records kept at the facility. Emission can be calculated for each month and then added to get the annual total. Using the annual total, calculate the monthly emission percentage using the following equation:

January emission percentage = (January emission / Annual emissions) x 100

For example, add the VOC emission from each source for the month of January. If the January emission of VOC from the three emission sources is 1.100 tonnes, the January percentage VOC emission is:

1.100 tonnes / 22.577 tonnes x 100 = 4.87%

Step 10 - Reasons for Change in Quantities Released from Previous Year

In section B14.0 of the reporting software you are required to select all applicable reasons for changes in substance releases from the previous reporting year (check the applicable boxes from B14.1a through B14.1i).

Step 11 - Anticipated Releases to Air

Users are required to estimate anticipated releases for each substance released to the air from the facility for the next three years. Reporting anticipated releases for the two years following that is optional. Enter the information for each substance in field B15.1 of the reporting form.

Step 12 - Pollution Prevention (P2) Activities

If the facility has employed P2 activities, it should be noted in section B30.0 of the reporting form (check the applicable boxes from B30.1a through B30.1g).

References

US EPA AP-42: compilation of Air Pollution Emission Factors, AP-42, Fifth Edition, Volume 1: Stationary Point Area Sources, 2004

US EPA WEBFire Factor Information REtrieval (FIRE), December 2005

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