Grain elevators and feed mills emission calculations

This method may be used to develop an editable spreadsheet containing detailed emissions calculations for operations in a grain elevator or feed mill, including grain receiving, grain loadout, grain cleaners, internal handling, bin vents, grain dryers, grain milling, pellet cooling, and feed loadout. 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 equipmentInclude 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.
  • Capacity – For a country grain elevator, the “capacity” can be calculated by taking the highest grain throughput out of the previous 5 years of operation, and multiplying that by a factor of 1.2; that calculated capacity can then be used for each individual operation at the facility. For a terminal grain elevator or a feed mill, the capacity of each emission unit is the maximum physical capacity of the equipment.
  • 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, Fifth Edition Compilation of Air Pollutant Emission Factors, Volume 1: Stationary Point and Area Sources (most commonly used for grain elevators and feed mills), 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 viewable in each spreadsheet cell for which there is a calculation (for example, Steps 3, 4, 6, 7, 8 and 9 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 grain operation 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. (If you have any fuel-burning equipment at the Facility, for example a boiler, furnace, dryer, or engine, you must also include emission calculations for the fuel combustion emissions following the instructions provided at External Combustion Units or Internal Combustion Engines)

Step 1. Pollutant – For each pollutant listed below, calculate the emissions.

  • 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

Step 2. Emission factor – For each pollutant, include the emission factor for the operation. Remember to use uncontrolled emission factors, and include the applicable units. Show any calculations used to determine maximum continuous rates. Include the source of the emission factors used.

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 Capacity (unit/hr)

Exception for “grain handling”:  AP-42, Fifth Edition Compilation of Air Pollutant Emission Factors, Volume 1: Stationary Point and Area Sources, Section 9.9.1.3 describes how to use the emission factor for “grain handling.” For grain handling, since grain is typically handled multiple times in the process, you must account for each time the grain is handled. Multiply the emission factor by the amount of grain that can be received, plus the amount of grain that can be loaded out, plus the amount of grain that can be dried, plus the amount of grain that can be cleaned:

  • Grain Handling emission rate (lb/hr) = Emission factor (lb/unit) x (Receiving capacity (unit/hr) + loadout capacity (unit/hr) + Drying capacity (unit/hr) + Capacity of externally vented internal vibrating cleaners (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 applying 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 applying 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 step if applying for 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 propose to comply with more a stringent limit, you should state this clearly and show the resulting allowed emissions in this calculation.

Step 9. Fugitive Emissions

You need to include fugitive emissions in your potential to emit calculations only if the facility is subject to federal NSPS Subpart DD – Standards of Performance for Grain Elevators, or any other NSPS that was effective as of 8/7/1980.  If your facility is not subject to Subpart DD or any other NSPS that was effective on 8/7/1980, you can skip this step.

Possible sources of fugitive sources at a grain elevator or feed mill are paved and unpaved roads, wind erosion from outside storage piles, and handling of grain (adding and removing) at outside storage piles.  Methods for calculating potential emissions from fugitive sources can be found in AP-42, Fifth Edition, Volume 1: Chapter 13: Miscellaneous Sources.

Step 10. Actual controlled emissions - If this is an existing facility 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, and you must include fugitive emissions in your calculation.] If this is a new facility or no records exist, use a reasonable estimate of how many hours the unit will be operated, how much grain will be processed, etc. Report actual emissions in tons/year.

  • Actual controlled emissions (ton/yr) = Emission Factor (lb/unit) x Actual Annual Grain Throughput (units/year) x ([100 - Control Efficiency] ÷ 100)  x [1 ton/2000lb]