External combustion units emission calculations

This method may be used to develop an editable spreadsheet containing detailed emissions calculations for external combustion units, including boilers, furnaces, ovens and dryers. Each step in your calculation(s) needs to be clear and easy to follow.

Include the following information with your calculations

  • AQ Facility ID No. – Include your Air Quality (AQ) facility Identification Number (ID No.). This is the first eight digits of the permit number for all permits issued under the operating permit program. If your facility has never been issued a permit under this program, do not include at this time.
  • AQ File No. – Include your AQ File Number, if known. This number can be found in the “cc” section of correspondence from the MPCA. If you do not know this, or can’t find it, do not include it at this time.
  • Facility name – Include your facility name.
  • Emission unit ID(s) – Include the identification number of each emission unit. Obtain this number from your Form GI-05B, or the appropriate form related to the permit you are applying for, or your existing permit. If you are applying for a registration permit Option D, just provide a description of the emission unit.
  • Stack/Vent designation number(s) – Include the designation number of the stack(s) or vent(s) through which the unit will exhaust into the atmosphere. Obtain these numbers from Form GI-04, or the appropriate form related to the permit you are applying for, or your existing permit. If you are applying for a registration permit Option D, just provide a description of the control equipment.
  • Control equipment Include a description of the type of control equipment. Use either the identifying number from Form GI-05A, or the appropriate form related to the permit you are applying for, or your existing permit. If none, indicate no control equipment. If you are applying for a registration permit Option D, just provide a description of the control equipment.
  • Maximum rated capacity – Include the manufacturer's maximum rated capacity for each fuel that may be used in the unit. If the unit has been de-rated, attach supporting documentation explaining the de-rating.
  • Fuel Parameters: For each type of fuel used, include the following information.
    • Fuel type – Include each fuel type used by the unit (e.g., natural gas, No. 2 fuel oil).
    • Weight % Sulfur ­­– Indicate the sulfur content of the fuel in weight percent, if applicable.
    • Weight % Ash – Indicate the ash content of the fuel in weight percent, if applicable.
    • Heating value – Include the heating value of the fuel. Indicate the applicable units (i.e., BTU/ton, BTU/gal or BTU/cf).
    • Fuel consumption rate – Include the manufacturer's maximum fuel consumption rate, or calculate it using the following equation. Indicate the applicable units (ton/hr, gal/hr or cf/hr).
      • Fuel consumption rate = (Maximum rated capacity) ÷ (Heating value of the fuel)
  • Source of emission factors – Indicate the source of your emission factors. Possible sources include those listed on the Emissions Calculations page and those described in Minn. R. 7005.0100, subp. 10. If the emission factor is from AP-42, cite the exact section or table used. If emission factor is from some other source, attach a photocopy of the information used, or provide an exact internet address, so the information can be verified.
  • Formula/Equation – The formula and/or equation needs to be available in each spreadsheet cell for which there is a calculation (for example, Steps 3, 4, 6, 7, 8, 10, 11 and 12 below.)
  • Operating limitations – Describe in detail any permit limits you plan to take to restrict your potential-to-emit (fuel type and/or usage, hours of operation, bottlenecks, etc. - see Proposing Synthetic Minor Permit Limits). Attach additional spreadsheets or other information, if needed. Describe the limiting factors, cite any rules that apply (e.g., Standards of Performance for Stationary Sources (NSPS, 40 CFR part pt. 60), Best Available Control Technology [BACT]). The associated limit must be used to calculate your potential-to-emit after permit limits in Step 8. If you used vendor certification or stack test data to limit your potential-to-emit, the factor you used will become your permit limit. Include all proposed limits on Form CD-01, and anywhere else as instructed in the application forms.

Emissions Calculations

Follow these steps for calculating emissions for each external combustion unit at the Facility. Each step should generally correlate to a column in your spreadsheet. Additional columns can and should be included in the spreadsheet to indicate additional calculation steps or information specific to your process.

Step 1. Pollutant — For each pollutant listed below, calculate the unit’s emissions when combusting the primary fuel.

  • PM = particulate matter
  • PM10 = particulate matter smaller than 10 microns in aerodynamic diameter
  • PM2.5 = particulate matter smaller than 2.5 microns in aerodynamic diameter
  • SO2 = sulfur dioxide
  • NOX = nitrogen oxides
  • VOC = volatile organic compounds
  • CO = carbon monoxide
  • HAPs = hazardous air pollutants – each individual hazardous air pollutant. See EPA's Web site for more information.
  • Total HAPs = All individual HAPs added together
  • Greenhouse Gas (individual greenhouse gases, and as CO2e) See: Greenhouse Gas Emissions: Instructions for Emission Calculations Spreadsheets.

Step 2. Emission factor — For each pollutant, include the emission factor for your primary fuel. Remember to use uncontrolled emission factors, and include the applicable units. Show any calculations used to determine maximum continuous rates, and include the source of the emission factors used. Attach a separate sheet, if necessary.

Step 3. Emission rate — Calculate the Emission Rate in lb/hr. Calculate the emission rate by using this method:

  • Emission rate (lb/hr) = Emission factor (lb/unit) x Fuel consumption rate (unit/hr)

Step 4. Maximum uncontrolled emissions — The Maximum Uncontrolled Emissions in tons/yr is required in the middle column for item 3e on Form GI-07. Use this method for calculations:

  • Maximum uncontrolled emission (ton/year) = Emission rate (lb/hr) x 8760 (hour/year) x (1 ton/2000 lb)

Step 5. Pollution control efficiency — The pollution control efficiency is the product of the capture efficiency and the destruction/collection efficiency indicated on Form GI-05A or the appropriate form related to the permit you are applying for, or your existing permit. If you are using this form for Registration Permit Option D, the control efficiency is indicated on Form RP-D2. Enter this number here and remember to include on Form CD-05 a plan to demonstrate and maintain the destruction/collection efficiency (unless you are using this form for Registration Permit Option D - in that case, Form CD-05 does not apply and you are simply required to operate the control equipment as described in Minn. R. 7011.0075-0080). The control efficiency should be expressed for each pollutant. If there is no control for a particular pollutant, indicate “zero” as the control efficiency.

Step 6. Maximum controlled emissions rate [lb/hr] — This is the maximum controlled emissions rate in lb/hr required in the first column of item 3e on Form GI-07. Use this method for the calculation:

  • Maximum controlled emissions rate (lb/hr) = Emission rate (lb/hr) x ([100 - Control Efficiency] ÷ 100)

Step 7. Maximum controlled emissions — Calculate the Maximum Controlled Emission in tons/year. Use this method for the calculation:

  • Maximum controlled emissions (ton/year) = Maximum Uncontrolled Emissions (ton/yr) x ([100 - Control Efficiency] ÷ 100)

Step 8. Limited controlled emissions — [Skip this item if you are working on calculations for a Registration Permit Option D.] The limited controlled emissions are calculated by taking into account all limitations on operation of the source that you are proposing to comply with in this application. These limitations include limits on hours of operation, on the amount of fuel combusted, etc. You start the calculation of Limited Controlled Emissions by repeating the calculation of Emission Rate (Step 3) but taking into account the limits you propose.

If an emission unit is subject to an emission limitation specified in 40 CFR pt. 60, 40 CFR pt. 61, 40 CFR pt. 63 or Minn. R. ch. 7011, you must show this requirement in the calculation of Limited Controlled Emissions and take this into account in calculating the Limited Controlled Emissions. If you choose to propose to comply with more a stringent limit, you should state this clearly and show the resulting allowed emissions in this calculation.

Step 9. Actual annual fuel use — Use the average quantity of fuel used per year for the past two years, unless you are applying for Registration Permit Option D. If you are applying for Registration Permit Option D, use the quantity of fuel used during the most recent 12 months (for example, if you are doing these calculations in July, use the quantity of fuel used starting July 1 of last year through June 30 of this year).

Step 10. Actual controlled emissions — If this is an existing unit and historical records exist, calculate actual emissions using the average of the previous two calendar years of usage data, or average the previous two emission inventory reports if an inventory was submitted. [Note: If you are calculating actual emissions for Registration Permit Option D, you may base this calculation on the previous 12 months of operation.] If this is a new unit or no records exist, use a reasonable estimate of how many hours the unit will be operated, how much fuel will be used, etc. Report actual emissions in tons/year.

  • Actual controlled emissions (ton/yr) = Emission Factor (lb/unit) x Actual Annual Fuel Use (units) x ([100 - Control Efficiency] ÷ 100)
  • Additional fuels – If the unit is able to combust a backup fuel or any other additional fuels, repeat Steps 1 through 10 for each fuel. Then, create a potential to emit (PTE) summary for the unit using Steps 11 and 12.

Step 11. PTE Before operating limits — Compare the Maximum Uncontrolled Emissions columns for all types of fuel used. For each pollutant, indicate the highest potential-to-emit (before limits) for the external combustion unit.

Step 12. PTE After operating limits — Compare the Limited Controlled Emissions columns for all types of fuel used. For each pollutant, indicate the highest potential-to-emit (after limits) for the unit.