Pollution control equipment can generally fall between two categories: Volatile Organic Compounds (VOC) and Hazardous Air Pollutant (HAP) Control, or Odor Control. But what is the difference between these two classifications?
VOC: The Environmental Protection Agency classifies Volatile Organic Compounds (VOCs) to mean “any compound of carbon, excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium carbonate, which participates in atmospheric photochemical reactions.”
Odor: The EPA refers to this category as “nuisance odors.” A nuisance odor is any strong smell coming from a facility, that could potentially disrupt the community. These odors are generally the result of cooking or processing of organic compounds.
Although the chemical makeup of some odors are regulated by the EPA, these nuisance odors are not generally regulated at a federal level; however, many state and local agencies have established nuisance odor guidelines and limitations. Failure to plan for appropriate odor control often leads to complaints, unplanned shutdowns, as well as sometimes pricey equipment upgrades and retrofits.
Before the 1970s, there were no regulations in place for odor control in the United States. However, a study commissioned by the National Air Pollution Control Administration of the US Public Health Service concluded there was likely a need for some level of regulation; no actions were taken. A second study, completed the following year by the EPA, examined the social and economic impact of odors in communities. Although it determined that there were obvious impacts on the community as a whole, it did not feel the results were conclusive enough to implement any action plan. A third study in 1972 confirmed that odor control guidelines must be implemented, but determined that the solutions presented by the panel involved in the study were “too cumbersome for routine application.” Following the final study, state and local regulatory bodies began to take notice and implement a number of different plans to reduce odor and hold facilities accountable.
Applications prone to nuisance odors:
- Wastewater Treatment
- Rendering and fat processing
- Solid Waste Management
- Pulp & Paper
- Animal Agriculture
Nuisance odors must be controlled for a number of reasons. The first being that any strong, misplaced odor, generally prompts a response from the surrounding communities. In addition to being annoying and disruptive to everyday life, these odors can bring down property values, and effect industries such as tourism.
Odors are caused by the release of process emissions, where organic materials are cooked, melted, or refined. Compounds such as sulfur, methane, mercaptans, ammonia, amines, and organic fatty acids are generally considered the most offensive (noticeable) odor causing emissions and encompass a large portion of regulated compounds. Although odor alone is not federally regulated, some of the compounds that cause odors are. This is where the divide between odor control and VOC control blurs.
Some of the effects of the more serious, and highly regulated odor causing compounds include skin, eye, and membrane irritation or damage, nausea and gastrointestinal issues, respiratory distress, asthma, neurological issues and loss of consciousness, pulmonary edema, fatigue, and even cancer. Compounds associated with these effects generally fall under VOC restrictions, not odor control, unless they are in very small and inconsequential concentrations.
Because every area has different regulatory limits, questions regarding odor control should be addressed through the local regulatory agencies where a facility plans on operating. It should be noted that an application emitting an odor deemed “not unpleasant” will likely still be required to install some method of odor control.
How do we treat odors?
From a pollution control equipment standpoint, odors are essentially VOCs and handled as such. Which solution is the best depends on the volume and VOC concentration of the exhaust streams and the required rate of destruction.
There are a few pollution control solutions that excel in odor control. However, Regenerative Thermal Oxidizers (RTOs) have become a “fan favorite” due to their destruction rate efficiency (DRE) capabilities and available heat recovery options which offset operational costs. Developed for large volumes, and low VOC or odor concentration air pollution applications, this solution is often considered the best available technology for odor control.
RTO technology delivers low operating costs for these high air flow, low volatile organic compound and/or fume streams. Rather than allowing the clean hot air to exhaust to atmosphere, the RTO unit captures up to 95% of the heat prior to exhausting it to atmosphere. This recovered heat can be used to power the equipment or provide other off-setting energy options to the facility.
The RTO works in a 2-step process.
Step 1: The RTO unit is brought up to combustion temperature using supplemental fuel such as natural gas, propane, diesel or biofuel. During this start up period, the RTO unit initially purges itself with fresh air and continues to process fresh air until it reaches combustion temperature equilibrium. The RTO unit is now ready to switch over to process air and begin the thermal oxidation of VOCs and / or odors with destruction efficiency up to 99%.
Step 2: The RTO switches from start-up mode running on clean air to operating on VOC or odorous process air from the source. To maximize heat recovery, the RTO will automatically cycle or alternate the inlet and outlet via a series of pneumatic, hydraulic, or electric dampers.
Because the RTO is so efficient at reclaiming effluent heat, the units often times are capable of sustaining combustion temperatures without any supplemental fuel utilizing the VOC as the only source of fuel.
Three canister solutions are often chosen for odor control applications because they great at handling highly vaporous streams, like those found in rendering and animal products. Three-can RTO systems are the best solution for vapor-tolerant and aqueous applications. The high DRE, in excess of 99%, ensures the odor and organic material is nearly completely destroyed. Through this process, the RTO converts the pollutants in the stream into carbon dioxide and water vapor, all while recovering thermal energy that could be used to reduce the cost of operating the equipment. The process in which this is accomplished is very similar to that of a two-canister RTO. The exhaust stream, laden with VOCs or odors, enters the heat exchange bed using a high-pressure fan system. Here, the stream passes directly through the media, heating it in preparation for the combustion chamber. The combustion chamber then heats the stream further, using burners, to the optimal temperature for combustion to complete the oxidization process. After that, the clean stream is sent to the heat recovery chamber, where it passes through the media bed which cools the air and heats the media. The final step, which makes the 3-can regenerative thermal oxidizer more efficient, occurs in the final chamber, which traps any remaining VOCs or odors in the “clean” stream by purging the stream with clean air. This final step is not available in a 2-can RTO, which is why a 3-can RTO can achieve a slightly higher DRE.
Gulf Coast Environmental Systems has extensive experience partnering with a multitude of industries in need of odor control solutions. Our team of experts has over 2-centuries of combined experience in odor control and continues to work daily at finding the best available technology for each application. If you have questions regarding odor control, please contact us at firstname.lastname@example.org or 832.476.9024
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