Aggregate Crushing|Dry & Wet Fine Aggregates Crushing Process Operations
Aggregate Crushing Process Descriptions
Some mineral product industry sites include equipment and processes that involve aggregate crushing. Particulate emissions occur whenever aggregate and rock are mechanically shattered. The following calculation procedures to estimate aggregate crushing operation particulate emissions are based on Section 11.19.2 of AP-42 (1/95).
- Ea = Ua x EF x Ci x (1 - e)
- Eh = Uh x EF x Ci x (1 - e)
- Where:
- Ea = Annual emissions of each listed substance, (lbs/year)
- Eh = Maximum hourly emissions of each listed substance, (lbs/hour)
- Ua = Annual material throughput for each crusher, (tons/year)
- Uh = Maximum hourly throughput for each crusher, (tons/hour)
- EF = Particulate emission factor, (lbs/ton of material crushed)
- Ci = Concentration of each listed substance in each material processed, (lbs/lb)
- e = Control equipment efficiency, (%)
Aggregate Emissions Information
A series of meetings was held in 1995 and 1996 between AWR Consultants, the San Diego County Mineral Products Industry, and the District regarding particulate emission estimation techniques applicable to aggregate operations. A District policy was drafted on 4/9/96 regarding Mineral Industry calculation procedures. This policy included a standardized approach to evaluating emissions from mineral industry aggregates crushing operations.
In general, it was decided to classify all crushing operations as primary crushing, dry process aggregate crushing, wet process aggregates crushing, dry fines aggregate crushing processing, or wet fines aggregates crushing process. Standardized PM10 emission factors were assigned to each classification based on the expected annual average particle size distributions and moisture contents. Predetermined fugitive dust control efficiencies were also identified for specific types of devices and techniques.
These standardized emission factors are based on information published in Table 11.19.2- 2 of Section 11.19.2 of AP-42 (1/95). These emission factors are substantially different than those previously used by the District and are not affected by crusher type or crusher size. Emissions are dependent only on aggregate type and throughput. A summary of the crushing operation policy decisions is as follows:
Aggregate Classification Policy Decisions
| Aggregate Type | Description |
|---|---|
| Primary Aggregate | Feed streams with > 4 inch material (principally PE jaw crusher and gyratory crusher) |
| Process Aggregate | Feed streams containing 1/2 to 4 inch material (most standard and Short head cones with some gyradisc and impact crushers) |
| Fines Aggregate | Feed streams exclusively containing <1/2 inch aggregates or crushers whose product is 30% or more by weight smaller in size than #4 mesh |
Moisture Classification Policy Decisions
| Aggregate Type | Description |
|---|---|
| Dry Aggregate | Process aggregate with an average annual moisture content of < 1.5% by weight, and fines aggregate with an average annual moisture content of <3.0% by weight. |
| Wet Aggregate | Process aggregates with an average annual moisture content of 1.5% or more by weight, and fines material with an average annual moisture content of 3.0% or more by weight. |
Control Device Policy Decisions
| Control Equipment Type | Assumed Capture and Control Efficiencies |
|---|---|
| Water Spray Controls | Assume a fugitive dust control efficiency of 50% |
| Water Spray Controls With Surfactant | Assume a fugitive dust control efficiency of 75% |
| Covered Crusher w/Central Fabric Filter | Assume a fugitive dust capture efficiency of 95% and a ducted release rate of 0.008 grains/ft3 |
| Covered Crusher w/Insertable Fabric Filter | Assume a fugitive dust capture efficiency of 97.5% and a ducted release rate of 0.008 grains/ft3 |
Emission Factor Policy Decisions
| Aggregate Type | PM10 (lbs/ton processed) | TSP (lbs/ton processed) |
|---|---|---|
| Primary Crushing | 0.00070 | 0.00148 |
| Dry Process Aggregate Crushing | 0.00240 | 0.00507 |
| Wet Process Aggregate Crushing | 0.00059 | 0.00125 |
| Dry Fines Aggregate Crushing | 0.01500 | 0.03171 |
| Wet Fines Aggregate Crushing | 0.00210 | 0.00444 |
Trace metal concentrations in aggregate dust released from aggregate crushing operations can vary between sites. The following default trace metal concentrations should be used to estimate compound specific emissions where representative site specific information is unavailable.
