Air Quality Control Systems and Components - Hitachi Power ...

Mercury ReductionAlways One Step AheadMercury reduction (Hg reduction) is becoming ever more important in air quality controlsystems. A precipitation rate of up to 80 % is needed for adherence to the ongoingdaily mean of 0,03 mg/Nm³. Various tests undertaken at power plants have confirmedthat HPE's existing system components keep to this standard.HPE, however, not only wants to keep up with things as they are but also to be one stepahead. That is why the engineers of Hitachi, Ltd., our parent company, are working on aprecipitation process in which the catalyst oxidizes the mercury (new catalyst). The mercurycan then be precipitated in the absorber.This process has a distinct advantage in that with low-chloride coals the new catalyst supportsoxidation of metallic mercury into ionic mercury. This oxidation rate rise is of significancesince it is precisely this oxidation process which is needed for mercury precipitation. It wasnoticed from examinations of the gaseous mercury loads in flue gases that a rising chloridecontent in the coal was accompanied by a comparative increase of the mercury gaseouschloride compound in the flue gas.The only operational findings available at the moments relate to the combustion of bituminouscoal with a low CI content. The expectation from using this catalyst is for the Hg oxidationto increase to over 80 % with the SO 2 -to-SO 3 conversion continuing to remain under 0.5%.Characteristics of new SCR CatalystSub-bituminous coalBituminous coal (eastern)100New catalystMercury oxidation (%)80604020Conventional catalystWithout catalyst020 40 60 80 100HCI concentration (ppm)10