Dryers 450: Environmental Impact of Drying Systems    

In today’s society the true environmental impact of our actions is becoming clearer everyday.  The process of drying does drive off harmful and unwanted gases or particulates.  It is important to know what those gases and particulates are and how to properly handle them to have a system that is as environmentally friendly as possible.  No matter what your business or industry is it is getting more difficult to build or expand plants as communities are more and more concerned about the environmental impact of your business on their community.  Doing the research and finding a Drying System that meets your environmental needs will be more critical than ever in the coming years.

There have been environmental problems in the ethanol industry as well as many other industries.  Many were drying system related due to the emission of non-condensable Volatile Organic Compounds (VOCs).  A Topeka alfalfa dehydrating plant was among the first in the nation to meet a strict air quality requirement without secondary clean up using EPA method five (the front half).  This was considered to be a clean air plant by the EPA.  The plant was not convinced that the emissions were truly clean, so they collected further data that indicated their drying systems were emitting from four to nine percent of the dry weight of material that they were processing as non-condensable VOCs, which was many times greater than the desired EPA limits at that time.  While the EPA tested for condensable VOCs emissions, their test did not measure non-condensable VOCs.  Although the plant met EPA method five standards, it was not truly clean.  This data was shown to the EPA in 1970, but at that time they had no way to accurately test for non-condensable VOCs.

In a similar situation, in 2002, Gopher State Ethanol in St. Paul, MN had a severe odor problem.  The plant apparently had passed all of the EPA method five tests.  However, because of the odor and complaints from local residents, the Minnesota Pollution Control Agency used the new EPA method 25a test which measured all VOCs. This revealed that the plant was emitting around 1,100-lbs/hr of VOCs.  This number was significantly greater than the 22-lbs/hr or less required by law when tested by the EPA test method five (the back half), which only captured the condensable VOCs. The EPA realized through testing of several other plants that all ethanol plants with dryers had a similar non- condensable VOCs emission problem. 

To solve this problem and protect the public, the EPA took drastic action and mandated that all ethanol plants must install thermal oxidation systems that reduced all VOCs by over 98% and the total VOCs emissions had to be less than 100-tons/year, or less than 22-lbs/hr, as verified by EPA test method 25a.  Because ethanol is an energy industry this was a more rigid requirement than similar industries had to meet.  The EPA set a standard making it next to impossible for any odors, harmful gases, or materials to leave the plant, cross the property line, and reach local residents insuring the public’s right to clean air and environment.  Emissions from ethanol plants are among the cleanest in any industry.