An investigation of mercury distribution and speciation during coal combustion

A multi-field electrostatic precipitator (ESP) and a two-stage condensing heat exchanger (CHX(R)) have been added to the pilot scale Vertical Combustion Research Facility (VCRF) in CETC-O to further research into integrated emissions control for coal fired power plants. A series of combustion trials were conducted on the VCRF with three different coals (bituminous, sub-bituminous and lignite) to study mercury distribution and speciation at various VCRF locations. Results showed that, with the bituminous coal, as the flue gas cools down from 700 to 200degreesC, 80% of total mercury in the gas phase existed in oxidized form and 20% in elemental form. For sub-bituminous and lignite coals, elemental mercury was the dominant form throughout the system. Analysis of deposited ash samples showed that oxidized mercury can be absorbed on carbon-rich ash deposits, although overall only a very small percentage of total mercury was absorbed on the ash. The potential of the CHX(R) at removing mercury from the flue gas was also explored. Results indicated that, using wet scrubbing, the CHX(R) was able to remove 98% of oxidized mercury. Though elemental mercury went through the system unabated, it is suggested that, with appropriate agent to oxidize elemental mercury in the CHX(R), it is conceivable to use CHX(R) to remove both oxidized and elemental mercury. Finally, mercury balance was performed and good mercury balance was obtained across the VCRF, validating our sampling procedures and analysis methods. Crown Copyright (C) 2004 Published by Elsevier Ltd, All rights reserved.,