Rock Crushing Plant Applications Advice

Rock crushing plant

This guidance is intended to help applicants prepare applications and certifications with a reduced amount of effort, yielding clearer and more accurate applications. We hope to steer new applicants around some common mistakes, allowing them to prepare applications which are complete on their first try.

The process involves preparation of facility descriptions, emissions estimates, and completion of some administrative forms. Two passes through the process may be required, calculating emissions and adjusting emissions if any level of significance is exceeded.

The pollutants of concern are particulate matter. If the facility has stationary engines (such as generators), you will also need to address nitrogen oxides (NOx), carbon monoxide (CO), and volatile organic compounds (VOC), particulate matter (PM), and sulfur dioxide (SO2). These are referred to a “criteria pollutants.” In addition, there may be emissions of hazardous air pollutants (HAPs), primarily formaldehyde.

In general, a rock crushing plant will have a primary crusher, primary screen, secondary crusher(s) and secondary screen(s), and associated conveyors and stockpiles. It may also involve portable generators powered by diesel engines. Emissions of each criteria pollutant must be less than 100 TPY for the facility to be a minor source.

Administrative Forms for Rock Crushing Plant

The first thing to do is acquire a copy of the forms….

• Log onto the DEQ web page: www.deq.state.ok.us
• Go to the “Air Quality” page
• Select “Forms”
• Select either “ Rock crushers , Sand Gravel Application” or “Non-metallic Mineral Processing Minor Facility Air Quality General Permit Application.”

If you download the MS Word copies of these documents, they may be filled in on computer and stored for later needs.

Rock Crushing Plant Applications Advice

On the “General Facility Information” Form 100-884, please do not mark both construction and operating permits as this makes your application self-contradictory. Construction permits and operating permits are applied for separately. Minor source applications are all listed as “Tier I.” The “SIC Code” means “Standard Industrial Classification Code,” 1422 for limestone, 1423 for granite, 1429 for other crushed stone, 1442 for sand and gravel, and 1221 for coal.

The “Landowner Notification Affidavit” must be completed and signed for all applications, but it is commonly overlooked, resulting in delays in processing applications and issuing permits.

Rock Crushing Plant Basic Information

Please be certain that your application technical information contains the following items:

• List plant equipment: each crusher, screen, conveyor, stacker, engine, organic liquids storage tank, Include make, model, serial number, and date of manufacture (the date the plant was first constructed or moved into the US).
• if any baghouse, wet scrubber, cyclone, etc., is used, stack height, diameter or dimensions, flow rate, and temperature.
• Emissions control device effiency, including pressure differential range.
• For stationary engines: fuel type(s) and sulfur content, HP rating.
• Maximum anticipated production (tons per hour and tons per year).
• Capacity (gallons), maximum annual throughput, and date of manufacture of all hydrocarbon (fuel) storage tanks associated with the plant.

Rock Crushing Plant Applications Advice

Preparing Emissions Estimates Emissions factors for most are obtained from EPA’s TTN web site:

• Log onto EPA’s “Technology Transfer Network,” www.epa.gov/ttn
• Select “CHIEF” (Clearinghouse for Inventories and Emissions Factors)
• Select “Emission Factors”
• Select “AP-42”
• Select Chapter 11 and download Section 11.19.2 for “Crushed Stone Processing.”
• For engines, select Chapter 3 and download Section 3.3 for diesel engines smaller than 600 HP and Section 3.4 for diesel engines larger than 600 HP.
• For batch drop operations (unloading by front-end loaders), download Section 13.2.4. A 70% control efficiency may be applied for damp material.
• For storage piles, download Section 8.19.1. A 70% control efficiency may be applied for damp material.

If the any unit venting into a baghouse was constructed after August 31, 1983, PM emissions estimates from equipment using a baghouse are best prepared based on stack flows and the federal limit (40 CFR Part 60, Subpart OOO) of 0.022 grains per dry standard cubic foot. Here, “grains” refers to the unit of weight; 7,000 grains equals one pound. At the temperatures and moisture contents normally seen, ACFM is nearly equal to SCFM. For a hypothetical plant with a baghouse and stack flow of 4,000 SCFM, the emission rate would be 4,000 SCFM * 0.022 gr/DSCF * 60 min/hr / 7,000 gr/lb = 0.75 lb/hr. If this plant operates up to 1,200 hours per year, annual emissions are 0.75 lb/hr * 1,200 hours/year / 2,000 lb/ton = 0.45 TPY from the stack in question. Please be sure to include the stack height and dimensions.

Rock Crushing Plant Process Rates

Provided that 100 TPY of any criteria pollutant is not exceeded, it is recommended that conservatively-high estimates of operating hours and process rates are made. The capacity of the primary crusher is generally known, and therefore the process weight of the primary crusher, primary conveyor, and primary screen. After this point, it is frequently not easy to tell what process rates will be.

The material processed at the primary crusher and screen will be oversized and undersized. Oversized material is returned to the primary crusher, but the total of new material and returned material cannot exceed the capacity of the primary crusher.

Rock Crushing Plant Applications Advice

A common source of confusion is in estimating material flows following the primary screen. You may pick reasonable percentages, such as 20% of material from the primary screen being returned to the primary crusher and 80% proceeding to the second crusher, or you may use worst-case flows. Worst-case flows will result in showing the discharges from a unit to be higher than the input. Although that is impossible, it is used only for estimating maximum emissions from each unit.

AP-42 is periodically updated, so limits based on these factors may become out-of-date. It may be to your advantage to include a safety factor on calculations provided that the resultant emissions do not exceed any level of significance such as a regulatory limit or a major source threshold.