Electric Power Research Institute Incorporated

John M Burke

Robert E Moser

James H Wilhelm

Sterling Gray

David R Owens

An improved magnesium-enhanced lime flue gas desulfurization system is provided which produces the high sulfur dioxide removal level of previous magnesium-enhanced lime flue gas desulfurization systems and additionally produce waste solids that have significantly better properties and are more easily dewatered than the solids produced by known systems. The magnesium-enhanced lime flue gas desulfurization system of the present invention includes a crystallizer-clarifier reaction tank (CCRT) which receives scrubber effluent and functions as a combined reaction tank and thickener. Clear liquor from the CCRT is sent to a scrubber to scrub the flue gas, and a portion of the CCRT--thickened solids are directed to a high pH premix slurry tank (PMST) where the crystallization environment can be controlled by reagent addition and pH. The PMST contents are circulated to the CCRT and are separated to produce a waste solids fraction that is easily dewatered. A fines removal system may also be employed to reduce the presence of fine solids and promote large crystal solids.

Clear liquor scrubbing magnesium-enhanced lime flue gas desulfurization

An improved wet magnesium-enhanced lime flue gas desulfurization system and process are provided. The magnesium-enhanced lime slurry process for removing sulfur dioxide from flue gas to produce gas that is substantially free from sulfur dioxide and calcium and sulfite-containing waste solids is modified to include the addition of process reagents to a separate premix slurry tank which has a controlled, high pH. The addition of slurry formed from the scrubber effluent to the premix slurry tank is controlled to maintain the pH above 10. The premix slurry tank mixture is circulated to a reaction tank for reaction with the scrubber effluent to produce large crystal, easily dewatered waste solids.

Modification of magnesium-enhanced lime flue gas desulfurization process

An improved magnesium-enhanced lime flue gas desulfurization system and process are provided which produce the high sulfur dioxide removal level of previous magnesium-enhanced lime flue gas desulfurization systems and additionally produce waste solids that have significantly better properties and are more easily dewatered than the solids produced by known systems. The magnesium-enhanced lime flue gas desulfurization system of the present invention includes a crystallizer-clarifier reaction tank (CCRT) which receives scrubber effluent and functions as a combined reaction tank and thickener. Clear liquor from the CCRT is sent to a scrubber to scrub the flue gas, and a portion of the CCRT-thickened solids are directed to a high pH premix slurry tank (PMST) where the crystallization environment can be controlled by reagent addition and pH. The PMST contents are circulated to the CCRT and are separated to produce a waste solids fraction that is easily dewatered. A fines removal system may also be employed to reduce the presence of fine solids and promote large crystal solids.

A wet, calcium-based, flue gas desulfurization process for reliably and cost effectively removing sulfur dioxide from the flue gas generated by the combustion of fossil flues containing sulfur includes the step of contacting the combustion flue gas preferably as a part of the scrubbing liquor, with an aqueous solution containing formate ions and a dissolved calcium concentration reduction agent. The latter reduces the dissolved calcium concentration present in the flue gas which, in turn reduces the coprecipitation and loss of formate within and from the system. Also, by contacting the flue gas with an aqueous solution comprising formate and thiosulfate ions, the formate coprecipitation within the system is reduced independent of the calcium concentration level within the system.

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Austin, TX, United States of America

John M Burke