Thermal Removal Of Mercury From Spent Powdered Activated Carbon (Pac) Sorbent In Coal-fired Electric Power Plants

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The US Environmental Protection Agency (EPA) issued the first ever federal rule to permanently cap and reduce mercury emissions from coal-fired power plants on March 15, 2005. The rule referred to as The Clean Air Mercury Rule (CAMR) when fully implemented, will reduce utility emissions of mercury from 48 tons a year to 15 tons by 2018, a reduction of nearly 70%. These mandatory declining caps coupled with significant penalties for noncompliance, will ensure that mercury reduction requirements are achieved and sustained. In anticipation of this rule, scientists and organizations in collaboration with EPA and US Department of Energy (DOE) are carrying out research to understand the science of mercury speciation, and its fate and transport within the atmosphere, in order to develop more efficient and cost-effective mercury control technologies and devices. This research develops and demonstrates a technology to liberate mercury adsorbed onto powdered activated carbon (PAC) sorbent by the TOXECON TM process, and recommends further evaluation of the regenerated PAC. The TOXECONTM process is the patent of Electric Power Research Institute (EPRI). It involves injecting activated carbon downstream of an existing primary particulate control device and upstream of a iiisecond particulate control device. The pilot scale (Air Scale) apparatus removed 65%, 83% and 92% of mercury without addition of catalysts when run at 900 o F, 1000 o F, and

1100 oF respectively at a constant rotary feed speed of 1200 rpm. The experimental results indicate that elemental mercury can be removed using the pilot scale (Air Slide) apparatus with reasonable efficiency. The bench scale experiment using thermogravimetric analyzer (TGA) removed 29%, 100%, 100%, and 100% at operation temperatures of 800 o

F, 900 o F, 1000 o F, and 1100 o F respectively without catalysts, and 100% mercury removal with catalysts at 700 o F and beyond. This bench scale result

demonstrates that mercury can be liberated with a higher efficiency in a controlled environment. It also demonstrates that a mixture of 1% copper (II) oxide (CuO) and 4% Iron (III) oxide (Fe2O3) catalyst, and 5% cuprous chloride can enhance mercury liberation at lower temperatures in the bench scale (TGA) experiments. The catalytic performance of 5% cuprous chloride (CuCl) was identical to that of the copper-iron mixture. Carbon loss as determined by loss on ignition (LOI) was minimal, but increased with temperature to a maximum of about 13% with and without catalysts. Scanning electron microscope (SEM) analysis on the PAC samples from the TOXECON TM process observed no change in particle aggregation.

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Thermal Removal Of Mercury From Spent Powdered Activated Carbon (Pac) Sorbent In Coal-fired Electric Power Plants

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