Experiment And Numerical Simulation Of SNCR In Large-scale Grate-firing Furnace

Based on the situation of nitrogen oxides emission in China and comparison and analysis of all kinds of De NOx technologies. The selective non-catalytic reduction(SNCR) technique can be used on industrial grate-firing furnace for low nitrogen transformation scheme was proposed. Combustion calculation and denitrification study of SNCR process was performed by the way of combining numerical simulation with engineering experiment in a 35 t/h grate-firing furnace in this paper.Firstly, on the basic of the calculated flow field, temperature field and gas concentration distribution, the load of boiler and residence time to coal impacted on the calculation of combustion was investigated, the changes of the quality and temperature of the coal–bed was analyzed, burning rate of this boiler was also counted. The results show that, CO and O2 concentration was reduced with the increase of boiler load, but CO2 concentration and flue gas temperature of outlet was increased. Gas temperature of boiler outlet was increased, O2 concentration was reduced and burning rate was lower with residence time to coal was shorter, when the residence time was 50 min, 60 min, 70 min, the corresponding rate of burnout was 90.5%, 92.9%, 93.6% respectively. The temperature of the coal particles gradually reduced with the bed height declining. The diameter of coal particle should not be too large to avoid incomplete combustion. Burning rate of this calculation is high with the value of 93.3%. The volatile quickly burned out at the distance of 2.5m of the coal inlet while burning rate of coke is 92.8% at the end of grate.Then, explored SNCR process on this furnace, the results show that, when arranged spray guns with the number of eight, dentration rate was better with the value of 46.2%. larger NSR with a higher dentration rate, the best particle size was300 ~ 400 μm, the maximum denitration efficiency is 54.7%, smaller atomization angle result to a better dentration rate, when the jet velocity from 15 m/s increased to60 m/s, dentration rate increased by 7.4%. Downward arrangement of the spray guns lead to higher dentration rate. Arrangement method 1 and spray guns of staggeredarrangement lead to a better ruslt, dentration rate is 54.9%.Finaly, experimental study of denitrification with SNCR was conducted. The types of reductant, flow rate of the reducing agent, arrangement of spray guns was investigated, the results show that, application of SNCR technology can achieve 13%to 32% denitration rate, denitration rate of urea is higher than ammonia about 4% to10%, larger flow rate and spray guns was arranged on elevation of 5500 mm lead to a better dentration rate. The calculation results can well consistent with experimental results.