As the ethanol market continues to expand and attract new investors, there is increasing concern about the environmental and human health impact these plants will have on local communities. Exponential growth in fuel ethanol production in order to provide the nation with clean, renewable energy has captured the interest of state and federal regulators. As a result, volatile organic compounds (VOCs)—many of which are considered hazardous air pollutants (HAPs) by the U.S. EPA—and other pollutants are increasingly regulated. For example, there are new "leak detection and repair" (LDAP) and NOx monitoring requirements for "new source performance standards" (NSPS). 
 
 In order to understand HAPs—described in this article as "ethanol-related HAPs" (ERHs)—each step in the production process must be evaluated. This should give producers some valuable insight into attaining compliance within the confines of an appropriate operating permit. Conducting these evaluations via specific calibration gases can provide a foundation from which air pollutants are properly measured. 
 
 It may be most effective to picture the inside of an ethanol plant when thinking about ERHs. The first area of concern for ERHs is the cooker area. Here, it is essential to determine what off-gases will need to be monitored and how often stack emissions testing will be required if equipment is replaced. The specific ERHs produced by the cookers may include acetaldehyde, acrolein, ethanol and methanol. These pollutants can be released from vents, fittings or leaks in the pipes and tanks.
 
 Continuing this virtual tour through the plant, another potential area for ERHs is the fermentation tank area. The concerns here are similar to those mentioned in the cooker area. In addition to ERHs generated during the cook stage, it may be necessary to quantify the levels of formaldehyde and carbon dioxide emitted in the fermentation area. Some regulations require formaldehyde emissions to be less than 81 parts per billion (ppb). At this stage, you can also evaluate whether or not you can pass EPA Method 18 or 25a for the prescribed ERH.
 
 Next in the production process is the carbon dioxide scrubber, where any alcohols, acetaldehydes and other VOCs are removed from carbon dioxide. First, you will want to determine whether the scrubber is working properly. You should consider analyzing the collected carbon dioxide to determine the purity level, particularly if the carbon dioxide will be sold to other industries such as beverage manufacturing. It is important that you ensure the analyzer is properly calibrated using a high-quality calibration gas. This will assure that the carbon dioxide is not contaminated with other pollutants.
 
 After the fermentation tank area, the next areas to examine are the distillation column/molecular sieve and ethanol storage areas of the plant. During the distillation process, multiple VOCs—acetaldehyde, acrolein, ethanol and methanol—are generated. In the ethanol storage areas, there are several major considerations. First, how well is the storage area contained? Second, are there organic compound leaks? Leak checking is particularly important when coupled with ambient VOC monitoring in the vicinity of the storage area. Therefore, it is important to be aware of potentially hazardous conditions in that area of the plant. This quick check and proper documentation can save years of potential liability from future air pollution claims. EPA Method 18 is the best way to identify the specific ERHs detected.

 
 After reviewing the storage area, the evaluation moves on to the rotary drum dryer and the evaporation system areas of the facility. These are additional areas where VOCs and primary pollutants may be generated. Again, various EPA methods such as Method 6c, 25a, 10, and 18 may be applicable to monitor and quantify air pollutants.
 
 This virtual plant walk-through is almost finished, but first we must look at the boiler, one of the biggest sources of ERHs and criteria pollutants. Emissions vary depending on the type of fuel the plant uses. Therefore, it's important to first look at this and ask a few questions. First, is the plant subject to the 2007 Boiler Maximum Achievable Control Technology? Second, is the facility subject to the Code of Federal Regulations (CFR) 40 part 60 pollution reporting requirements? Once these questions have been addressed, plant management personnel can begin looking at emissions and determine what reports and detailed documentation will be required. The first order of business is determining the primary pollutants emitted at this stage, which include sulfer dioxide, NOx, carbon monoxide, and carbon dioxide. Next, evaluate whether or not the combustion is efficient to minimize these emissions. Finally, determine whether your air pollution permit requires an annual Relative Accuracy Test Audit for part 60, or 7e for NOx. Depending on the plant size and amount of ethanol produced, any number of these factors may come into play.
 
 The last stop is the thermal oxidizer, which controls emissions from many of the process steps illustrated above, including the dryer, fermentation tanks, distillation units and other areas. Since all pollutants from previous stages are vented through the thermal oxidizer, it is a significant source of ERHs and the most common and effective piece of pollution control. Likewise, this can be a focal point in controlling ERHs and carbon monoxide (using EPA Methods 10 and 18). It is also important to note that thermal oxidizers and waste-heat boilers used at ethanol plants are subject to New Source Performance Standards subpart Db and may require a continuous emission monitor (CEM) for NOx.
 
 As you can see, there are many ethanol production processes that have the potential to emit hazardous air pollutants. Over the past few years, tremendous activity in ethanol production has led to the introduction of increasingly effective emissions-reduction technologies. Testing and monitoring using pollutant-specific calibration gases are essential to quantify plant emissions and remain compliant with your air permit. As you perform these tests, make sure that you properly document the use of calibration gases for the proper tests. To ensure unhindered growth in the industry, ask a specialty gas company for calibration gases specific to your facility. 
 
 Ed Wisler is the business development manager for Scott Specialty Gases. Hillary Teller is a business develop associate for Scott Specialty Gases. For more information and a copy of available hazardous air pollutant calibration gases, contact Scott Specialty Gases at <a href=mailto:"ethanol@scottgas.com">ethanol@scottgas.com</a> or call (215) 766-8861.

Measuring Ethanol-Related Hazardous Air Pollutants Via Specific Calibration Gases

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Upcoming Events

2024 International Fuel Ethanol Workshop & Expo

Biodiesel Summit: Sustainable Aviation Fuel & Renewable Diesel

Carbon Capture & Storage Summit

North American SAF Conference & Expo

2025 International Biomass Conference & Expo

Measuring Ethanol-Related Hazardous Air Pollutants Via Specific Calibration Gases