Boiler, furnace, etc., and other means which are using coal and oil and other fossil fuels causing a great burden to the environment. Waste gas treatment is an extremely important issue, particularly the combustion exhaust gas of coal and oil , which are universally used due to the cheap price. There is higher nitride content in coal and oil, but relatively low sulfur content. Under such circumstances, nitrogen oxide emissions has become a serious problem worldwide.

 

The most effective measures to control nitrogen oxide currently is SCR denitration technology, the usually practice is adding ammonia to the boiler flue gas, and SCR denitration catalyst will turn NOx into non-toxic nitrogen and water under the temperature of 300 ℃ to 400 ℃. The main active ingredient is vanadium pentoxide, also there are some other metal oxides which play their own role.

 

In general, the coal containing 2%~20% iron compounds, they will stay in the coal particles during combustion of coal, which will resulting in SCR denitration catalyst poisoning, and decreasing the catalytic activity. The introduction of tungsten trioxide plays the role of increasing the SCR denitration catalyst activity. And it is worth mentioning that, the smaller particle size of the tungsten trioxide, the stronger activity the catalyst has, which requires the less amount of tungsten trioxide, the preferably particle is 5μm or bellow. when the average particle diameter is more than 5μm, the needed amount of tungsten trioxide will be a lot, and the excess powder may stick to the heating surface, thus cause the decreasing of heat capacity and causing economic loss or equipment failure.