| With the rapid development of China's economic, energy and environmental issues are given much more attention. Considering coal-fired utility boilers is one of the main sources of NOx emission in the environment, this paper hopes NOx emission from utility boilers could be controlled by low-cost way. Selective Non-Catalytic Reduction (SNCR) or hybrid reburning/SNCR technology could get middle and even higher denitrification efficiency, and could meet our country's NOx emission standards fully, but with lower investment and operation cost than Selective Catalytic Reduction (SCR) technology.Firstly, this paper studied basic Thermal DeNOx and NOXOUT process respectively through experiment and simulation. For NOXOUT process, a special experimental study of urea thermal decomposition was couducted. The results showed:urea could be completely decomposed at a pyrolysis temperature of 600℃within 2 s, the increment of temperature was basically favorable to the formation of NH3; Thermal DeNOx could achieve much higher denitration efficiency at a slightly lower optimum denitration temperature than NOXOUT under the same conditions. This paper studied the effects of some flammable gas constituent in the boiler on SNCR process through both experiment and CHEMKIN simulation also. The results implied:the increment of addition amount made the denitration efficiency curve, N2O conversion rate curve, N2 conversion rate curve, NH3 slip curve, and HNCO slip curve all shifted to lower temperature on the whole. In addition, this paper studied the impact of water vapor and sodium carbonate on denitrification process, and the results showed that:with the water vapor content increasing, the denitration efficiency curve significantly enlarged to higher temperature, the width of denitration temperature window increased, the optimum denitration temperature increased also, and the optimum denitration efficiency was improved. As long as a small amount of sodium carbonate was added, the denitration efficiency curve significantly enlarged to lower temperature, the optimum denitration efficiency improved significantly, and the hydrolysis rate of HNCO to NH3 was promoted also.Then, High temperature pyrolysis of pulverized coal ranked from bituminous to anthracite mainly was conducted using tubular furnace to investigate the dynamic yield performance of light volatiles which might have important effects on the reburning process and their production, composition, etc. On the basis of pyrolysis research, reburning experiment was carried out with five types of coal ranked from lignite to anthracite also. The experimental results showed:on mass terms, CH4, C2H4, CO and H2 accounted for the largest four kinds of reductive volatiles; as far as coal reburn denitration efficiency concerned, on the whole, lignite was the best, followed by bituminous coal, and anthracite was the worst.This paper studied anvanced reburing denitration performance using methane as the reburn fuel to simulate coal volatiles or natural gas. The results showed, advanced reburning could achieve much higher denitrification efficiency than conventional NOxOUT process, and the reducing agent had best inject into the the weak oxidizing atmosphere. When the reburning zone excess air ratio was a little larger, the addition of sodium carbonate could improve the denitration efficiency obviously in the entire experimental temperature range.Finally, particular experimental researchs on SNCR applied in a 410 t/h power plant boiler were carried out. The results showed that hybrid reburning/SNCR technology could make the NOx emissions lower than 200 mg/m3(standard condition,6%O2, dry gas) at all loads, and with ammonia slip less than 7.6 mg/m3 simutaneously. Experimental results also pointed out that the greater urea solution injection flux could lead to the much higher denitration efficiency, and there was an optimal atomization steam pressure which would result in the biggest denitration efficiency of SNCR under the other same experimental conditions. |
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