Fugitive emissions, in their simplest form, are the uncontrolled release of gases to the atmosphere. Each one of us may contribute fugitive emissions when we fill our automobile gas tanks. The displacement of air inside the gas tank causes gasoline vapor emissions (hydrocarbons) to exit out the fill spout (un-controlled) to the atmosphere. Some states require the use of "Vapor Recovery" nozzles which capture the vapor emissions, returning them to the underground gasoline tanks. The vapors then become liquid again, reducing the "loss" of gasoline, as well as removing hydrocarbons from the air, which means less air pollution.
There are two aspects to controlling emissions of Volatile Organic Compounds (VOCs): collection of VOC emissions (commonly called “capture”) and removal of the collected VOC emissions from the airstream using a control device (commonly called “control”). Together, capture and control determine how much VOC is released to the atmosphere. The combination of capture and control is commonly referred to as “overall control” or control efficiency.
The three types of capture strategies we will be discussing in this series are:
In this blog, we will look at Close Capture Hooding.
You might have a close capture hood in your home. In residential and commercial kitchens, a close capture hood is used to provide ventilation of steam and odors emitted while cooking.
In general, proper hood design is based on the following factors:
- Height – Y
- Distance – X
- Capture velocity – v1
Potential hazardous and pollution applications require special solutions. Always check local regulations.
To gain good capture, the hood must be positioned as close to the source as possible without impeding access to the source.
Overall control is defined as the percent capture (or removal [R]) multiplied by the percent control (or destruction [D] if a thermal oxidizer is used), and divided by one hundred. Thus, in the illustration above, if the VOC capture efficiency is determined to be 70% and the control efficiency of the thermal oxidizer is determined to be 95%, the overall control efficiency (or DRE) is (70 x 95)/100 = 66.5%.
Because a well-built thermal oxidizer typically destroys more than 98% of all VOCs, fugitive emissions are often the single biggest contributor to overall VOC emission rates. Fugitive VOC emissions can be either eliminated by effective design of either Close Capture Hooding or a Permanent Total Enclosure (PTE). In either case, rigorous USEPA test methods are used to demonstrate VOC capture efficiency.
Close capture hooding is a means to collect emissions from a variety of point sources. Hooding as a standalone method is least desirable, but in some cases, it may be the only appropriate method.
Watch for our upcoming blogs, where we will discuss Permanent Total Enclosures (PTE) and Temporary Total Enclosures (TTE). We are happy to answer any questions you may have in the meantime; please contact us.
At Catalytic Products International, we work to make sure that our customers have the best solutions to their air pollution remediation needs and that they have the knowledge to continue to meet these needs as they grow and change. For more examples of how our expertise helps our clients find success, please read our Customer Testimonials.