With the further improvement of China's environmental protection standards, coal-fired power units that cannot meet the national environmental protection standards have successively carried out low-nitrogen or denitrification transformation. In low nitrogen burner and denitration system after modification, in the actual operation of NOx emissions can meet the 2011 edition "coal-fired power plant emissions standard" requirement, denitration system running normally.
1. Low-nitrogen combustion and denitrification technology
The low nitrogen combustion unit is mainly aimed at two main generating mechanisms of NOx, which reduce the oxygen concentration in the ignition area while reducing the combustion temperature. To inhibit the formation of furnace nitrogen oxides. By using the low NOx combustion technology in the furnace, the NOx emission concentration can be reduced by 30% ~ 60%. Currently, the commonly used low-nitrogen combustion technology is mainly through the transformation of low-nitrogen burner to realize the combustion characteristics of low-oxygen and graded blending in the furnace and reduce the emission reduction of NOx.
Due to the limitation of the low-nitrogen combustion technology in the furnace, the emission of NOx cannot meet the requirements of environmental protection. In order to further reduce the emission of NOx, it is necessary to denitrify the smoke after combustion. The current flue gas denitrification process can be divided into dry, semi-dry and wet processes. Including dry SCR denitration technology with its denitration device has simple structure, convenient operation and high reliability, high denitration efficiency, a lot of advantages, an investment is relatively low in our country has been widely commercial application.
The SCR denitrification reactor can be divided into high dust content and low dust content according to the installation position of relative dust collector. However, because the low dust content requires the installation of steam heater and gas heat exchanger (GGH), the system is complex and the investment is large, so the high dust content technology is generally chosen. The SCR device is mainly composed of the preparation system of denitrification reaction agent and the reactor body.
The NOx was reduced to nitrogen and water vapor by spraying the denitrification reagent NH3 into the reactor. Ammonia production generally has urea, liquid ammonia, ammonia water and other three methods. At present, urea and liquid ammonia are mainly used to make ammonia. The denitrification catalyst is usually supported by TiO2 and mixed with V2O5 and WO3. The activity of the catalyst temperature range from 300 ℃ to 420 ℃ range . There are two kinds of catalyst, honeycomb and plate.
2. NOx emission reduction unit type
At present, China's power plants, under the call of the corresponding national environmental protection, have carried out corresponding transformation of the thermal power plants with excessive NOx emission, which can be divided into four types according to the implementation type:
(1) the unit was originally designed as a low-nitrogen combustion mode and a flue gas denitrification device. Such units need not be modified;
(2) the original low-nitrogen combustion mode of the unit and the installation of denitrification device is reserved; In the design of this type of unit, considering the operation requirements of the denitrification device, only the denitrification device is added in the reconstruction.
(3) the original design of the unit was low-nitrogen combustion mode, and no denitrification installation position was reserved; In the design of this type of unit, the operation requirements of denitrification device were not taken into account. In the reconstruction, denitrification device was added and corresponding auxiliary machine was also reformed.
No low nitrogen combustion method and no denitrification device have been used before. In the modification of nitrogen oxide reduction, the modification range is large, the modification of low nitrogen burner and the addition of denitrification device. The above mentioned denitrification units have been modified with air preheater, dust collector and fan.