In order to prevent excessive NOx pollution after burning coal in the boiler, SCR denitration technology is a post combustion denitration technology, and it is also a currently mature flue gas denitration technology. The coal is subject to denitration treatment. Nitric acid treatment can be divided into pre combustion denitration, combustion process denitration, and post combustion denitration. It has a very good effect on NOx control of kiln flue gas. It covers a small area and is easy to operate. It is the main means for China's coal-fired power plants to control NOx pollution. Now let's learn about the SCR denitration technology of waste gas treatment.
Characteristics of SCR denitration:
The technology is mature and reliable, the denitration efficiency exceeds 90%, and the ammonia spray that reduces the corrosion and blockage of the air preheater is uniform, with low resistance, low ammonia consumption and low operation cost; Ammonia emission is less than 2.5ppm, reducing secondary pollution; The reaction speed is fast, so/so conversion rate is less than 1%, one-time investment is saved, and it can be applied to low-temperature flue gas denitration; The denitration equipment does not affect the normal production operation of the production line, with optimized design and reasonable layout, low energy consumption for long-term operation and good environmental protection benefits.
Factors affecting SCR denitration performance:
Catalyst type, reaction temperature, flue gas velocity, structure and surface area, and the mixing effect of flue gas and ammonia. In addition, the increase of NOx production leads to the change of catalyst material and the decrease of catalyst activity. The larger the surface area of the catalyst in the reactor, if the catalyst continues to operate at low temperature, it will cause damage to the catalyst. When the reaction temperature is too high, NH3 is easy to oxidize. The higher the removal efficiency of no, the less ammonia escape.
NH3 input not only ensures the removal efficiency of NOx in SCR system, but also ensures the low escape rate of ammonia. Provide a mixing flue with sufficient length for ammonia and smoke, and adopt a reasonable nozzle grid. Only if the gas flow in the reactor is evenly distributed and the flow direction is adjusted properly, can the NOx conversion rate, ammonia escape rate and catalyst life be guaranteed. A series of problems caused by uneven mixing of ammonia and smoke can be avoided.
Application fields of SCR denitration:
It is widely used in coal-fired power plants to control NOx pollution. In addition to the power industry, there are a large number of industrial kilns, cement glass kilns, metallurgical steel sintering furnaces, chemical plants and pickling equipment in non power industries where the total emission of nitrogen oxides exceeds the standard.
Selective catalytic reduction (SCR) flue gas denitration system uses ammonia (NH3) as the reduction medium, and SCR reactor is usually arranged between the outlet of boiler economizer and the inlet of air preheater. It is mainly composed of ammonia supply and injection system, catalytic reactor, flue gas pipeline and control system. It is evenly mixed with flue gas and then enters the reactor. Under the action of catalyst in the reactor, the hot flue gas leaving the economizer sprays spray (NH3) to the upstream flue leaving the SCR reactor before entering the SCR reactor, and selectively reacts with NOx (mainly no and a small amount of NO2) in the flue gas to convert NOx into harmless nitrogen N2 and water vapor) H2O) to complete the denitration process. The pure flue gas after denitration flows out of the bottom of the reactor and enters the downstream air preheater through the outlet flue.