Study On Optimization Regulate Of Flue Gas Temoerature For Improving SCR Reaction Efficiency

During the practical application of SCR (selective catalytic reduction) technology in domestic coal-fired power plant, the SCR reactor inlet flue gas temperature is always lower than optimum reaction temperature window or even the normal reaction temperature range of SCR catalyst under intermediate or low loads. As a result, the SCR reaction efficiency is obviously lowered, which would make serious effects on denitrification efficiency, NOx emission concentration and ammonia slip rate. And the increase of ammonia slip rate could cause air preheater fouling problem. Therefore, under the premise of normal overall operationg of the boiler, there is a need to improve the SCR reaction efficiency and maintain high activity of the SCR catalyst. Thus, the stable and efficient operation of SCR reactor would be assured and the air preheater fouling problem could also be successfully solved.A300MW unit in some key area was selected for the study. From the engineering point of view, the coordinated optimization control technology of flue gas temperature was seeked and developed for improving the SCR reaction efficiency.Four different control programs of flue gas temperature were firstly promoted in the paper and the high temperature flue gas bypass with maximum20%bypass flue gas ratio was selected as the final control program of flue gas temperature. And the SCR economizer was innovatively promoted to deal with the adverse effect of the rising exhaust gas temperature. Meamwhile, the area of SCR economizer (40%the original economizer area) was achieved by the boiler thermal calculation.The simulation study showed that with the regulation of the joint arrangement program between the high temperature flue gas bypass and SCR economizer, the SCR inlet flue gas temperature could be regulated to nearly340℃under the lowest flue gas temperature condition. While, under the highest flue gas temperature condition, the SCR inlet flue gas temperature would not be regulated, and the exhaust gas temperature could be decreased6.1℃. In this way, the highly efficient operation of catalyst at340℃or more of SCR inlet flue gas temperature and variation of exhaust gas temperature in much smaller and more optimal range were almost completely achieved under all operating conditions. If the annual average load was75%, the average exhaust gas temperature would approximately be dropped5.2℃and the standard coal consumption decreased was nearly1g/kWh.