Modern ethanol plants have been designed to incorporate a variety of emission control equipment to make the plants safe, efficient, and to control potential pollutants. It is important for project developers, and regulatory officials, to be familiar with the regulated pollutants. Plant emissions may vary slightly depending on process, design, plant type and feedstock. The typical ethanol production process includes feedstock delivery to the plant, feedstock handling and milling. During this process, tiny particles (particulate matter less than 10 microns in diameter, PM10) are released into the air. PM10 is also emitted during the drying process.
During fermentation, distillation and drying, volatile organic compounds (VOCs) are released. Some VOCs are known as hazardous air pollutants (HAPs). These include some or all of the following: acetaldehyde, acrolein, ethanol, formaldehyde, 2-furaldehyde, methanol, acetic acid and lactic acid. Potential emissions of these compounds must be measured and appropriate controls included in plant design regardless of the biofuel technology being considered.
Carbon monoxide, nitrogen oxides, and sulfur oxides are also generated from combustion in the boilers at the plant. Carbon monoxide may also be generated in the drying process if such a process is included in the plant design. Modern emissions control equipment is included in most plant designs. However, potential emissions must be calculated and appropriate control strategies included in permit applications.
Other emissions may result from activities not associated with the production process. These may include: hydrogen sulfide and VOCs released from the wastewater treatment process; PM10 from the cooling towers; fugitive PM10 and VOC emissions from haul road traffic and equipment leaks, respectively; PM10, NOx, SOx, CO and VOCs from emergency equipment; and potential VOC evaporative loss emissions from the wet distillers grains solids storage piles if dryers are not in use at the plant.