Mercury control

The US Department of Energy has issued a license to private industry to commercially develop a promising low-cost, DOE-patented mercury control technology.

DOE’s National Energy Technology Laboratory issued the license on the technology - called the Thief Process - to Mobotec of Walnut Creek, CA, who plan to create prototype systems and conduct full-scale tests of the process.

As the exclusive licensee of the Thief patent, Mobotec will ultimately market and sell the technology.

Few technologies currently exist to consistently and cost-effectively remove mercury from power plant flue gas. Most of the technologies today use activated carbon in their processes, but the costs for its use are very high, ranging from $500 to $3,000 per ton.

NETL researchers developed and patented the Thief Process as a cost-effective alternative to the use of activated carbon. In the Thief Process, partially combusted coal is extracted from the boiler of a pulverised coal power plant and re-injected into the ductwork downstream of the air preheater.

By extracting the partially combusted coal, thermally activated sorbent is produced. Once it is introduced into the flue gas, the sorbent reacts with mercury and removes it from the flue gas stream. Since the cost of coal is relatively inexpensive, around $30 per ton, the resultant cost for the Thief sorbents is estimated to be between $90 and $250 per ton.

During earlier tests burning low-chlorine subbituminous coal, the Thief Process achieved mercury removal rates as high as 93 percent. Researchers were able to verify those results by applying the Thief Process at a working pilot plant. The Thief Process could be applicable to many power and industrial plants burning a range of coals and having various configurations of air control devices.

Although mercury naturally occurs throughout the environment, it primarily remains “locked up” in ores, though it can be released through human activities such as power plant combustion, municipal waste combustion, and medical waste incineration. Of these human activities, coal-fired plants annually emit about 48 tons of mercury, which is approximately 40 percent of total US mercury emissions and one percent of mercury emissions from all sources worldwide.