Across the U.S. Southern region, industrial-scale wood pellet manufacturing facilities are converting trees into wood pellets and shipping them to Europe and the Pacific Rim to be burned to produce electricity. The industry has grown almost 10-fold since the early 2000’s, converting millions of tons of trees into wood pellet fuel for power plants.
The demand for economical and sustainable fuel sources like wood pellets continues to grow. As in many other industries, air emission control is required to prevent VOCs (Volatile Organic Compounds) and HAPs (Hazardous Air Pollutants) that are emitted in the pellet manufacturing process from entering the atmosphere unabated. Compliance requirements typically come into play for facilities that are producing more than 200-250,000 metric tons per year (mpty) of pellets. Initially, air emission compliance focuses on the plant’s dryer exhaust, which requires a particulate control device prior to the Regenerative Thermal Oxidizer (RTO) if fly ash is generated from the dryer heat source.
Softwoods like pine generate a much higher level of VOCs than hardwoods. However, hardwood pellets release more HAPs and therefore can result in non-compliance with the EPA’s Maximum Achievable Control Technology (MACT) standards that limit the emission of ten tons per year for an individual hazardous air pollutant and 25 tons per year for all HAPs combined.
“Until recently, many permitting authorities simply assumed the hammermills, pellet presses, and pellet coolers did not emit any VOCs at all. That assumption began to fall apart in 2012, when a large facility, Georgia Biomass in Waycross, Georgia, decided to test all the facility’s units for VOC emissions. The results showed that not only did these units emit VOCs after all, they emitted a lot of them. Georgia Biomass found that their hammermills, pellet presses, and pellet coolers emitted more than 1,000 tons per year of VOCs, whereas the facility and the state previously believed the entire facility emitted less than 250 tons per year. This meant the facility had been operating in violation of its permit limits and the Clean Air Act’s major source requirements for several years, leading Georgia to levy heavy fines and issue a consent order requiring the facility to reduce its facility-wide VOC emissions to below 250 tons per year”. https://www.eenews.net/assets/2018/04/26/document_daily_02.pdf
NESTEC has developed a proprietary air emission control system for the wood pellet industry with Particulate Matter (PM), VOC, and HAP control that covers all sources or just individual sources, as needed. Numerous systems have been installed by NESTEC that meet or exceed all current compliance standards. Furthermore, these units are engineered to operate with little or no additional fuel requirements.
A complete NESTEC system features several unique features to provide the best and most economical solution for air emission compliance, including:
- Dryer TPM control with one or more addons:
- WESP (Wet Electrostatic Precipitator)
- ESP (Dry Electrostatic Precipitator)
- Regenerative Catalytic Oxidizers (RCOs) which typically operate at or near self-sustaining operation (no fuel) (See NESTEC’s Jan 2019 newsletter)
- Forced Draft Fans (FD)
- Substantial annual operational savings over an Induced Draft Fan (ID)
- Continuous, stable fan RPM operation
- Reduced cycling of the VFD and motor, and associated maintenance
- Much faster response to process changes
- An energy feedback loop that enables a 70% flow turn down when mills and coolers are shut off. At all times the system maintains duct velocities to help prevent condensable and particulate drop out in the ducts, as well as allow for a mist fire suppression system instead of a water spray deluge, which can cause a flooded duct condition.
- On line bake out with:
- Bakeout schedules based on the RTO need and not the availability of a process shutdown, which reduces the potential for condensable organic build up — a common cause of runaway fires
- Reduced energy consumption
- Depending on plant arrangement, combined source control can be accomplished with a reduced capital cost
The performance of the NESTEC typical wood Pellet installation is shown below:
If you have an application that requires air emission compliance and would benefit from conservation technologies that will substantially reduce your energy bill, contact NESTEC today for a free process analysis.
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