| Coal is important to the energy strategy in our country. While the SO2was effectively controlled, the pollution of NOx is becoming more and more serious. Then a lot of method and technique of controlling the emission of coal NOx was coming to the fore. Howere, the emission of NOx by the down fired boiler burning anthracite is much higher than the general. Due to the complexity of burning anthracite and the down fired boiler, the effective control method has not been found yet. Thus it is necessary to know the characters of burning anthracite and the emission of NOx, and to look for the burning technique which can effectively control the high emission of NOx by down fired boiler with anthracite.The article investigated the combustion characteristics of anthracite and the down fired boiler, and technology to control NOx emission of the down fired boiler, in according with research idea of "anthracite combustion and NOx generation mechanism-one-dimensional combustion test of anthracite-numerical simulation and cold state modeling test of down fired boiler-thermal modeling test of down fired boiler".Investigation on coal combustion effect is carried out with a thermogravimetry analysis test bed, and on basis of existing combustion indexes, a model for synthesized combustion effect based on attribute mathematics and connection mathematics was built. It’s found that pyrolysis of volatile is affected by coal quality mostly and the particle size has little influence on it; anthracite has high ignition temperature, common stable combustion and burn-off performance, and bad flammability; the anthracite was identified to be low-grade coal on combustion effect.Combustion characteristics and NOx formation mechanism of anthracite were investigated on a fixed bed test bed. The combustion velocity of anthracite is small, and NO generation reduces with higher temperature; the content of anthracite volatile is the key factor in coal quality, the content of N has no inevitable relationship with NO generation, and the influence of O on NO generation is similar with volatile. The transformation rule of anthracite fuel-N and NO reduction rule of anthracite char were investigated on a fixed bed system, and different research methods were compared. Under the test condition of this article, in1200℃,6%of O2concentration and66.5μm of particle size, the conversion rate of anthracite fuel-N is the lowest, but for char-N, the lowest point appears in1200℃,1%of O2concentration and44um of particle size; to make char in1000℃is the worst to control NO formation; char-NO takes up most of anthracite fuel-NO; conversion rate of volatile-N is bigger than fuel-N, which is bigger than char-N; the anthracite char made in800℃has the best NO reduction activity in condition of1200℃and66.5μm of particle size; the bigger value of CO/CO2could indicate worse NO reduction activity of the char; in the same condition, NO reduction activity of bituminite char is better than anthracite char, which is the key reason to that anthracite NO conversion rate is higher than bituminite NO conversion rate under the same condition. Based on the conclusion of the fixed bed experiment, a simplified conversion model of fuel-N and a simplified char-NO reduction model were built. The fuel-N conversion model can forecast the fuel-N conversion rule in different combustion conditions qualitatively, and it’s found that in different combustion conditions, different reactions play a leading role in fuel-N conversion; in the char-NO reduction model, the formula RNO=4.18×10-4exp(-17500/T)AcPNO is more appropriate to calculate the quantity of NO reduction.The combustion and NOx emission characteristics of anthracite in suspension burning were studied in a subsiding furnace. The best temperature for lowest NOx emission for anthracite is about1400℃, if air-staged combustion technology is adopted, a of the main combustion area should be0.8-0.9, and a of the burn-out area should be about1.1; burn-off rate of anthracite in a subsiding is low, and could be increased by more residence time in the furnace, therefore, a down fired boiler is the best furnace for anthracite combustion.On the basis of mechanism study and subsiding furnace combustion test, a fuel-N conversion model of anthracite in one-dimensional combustion was built, which simplified complex reactions in fuel-N conversion, and the calculated results were close to the actual measurement result. By the application of the model, it’s found that particle size had little influence to NO emission, and in air-staged technology, a of the main combustion area should be controlled in about0.8-0.9.A new technology-HAP low NOx combustion technology was proposed for combustion characteristics of the down fired boiler. The flow field of the boiler was calculated by FLUENT, and thermal calculation is adopted to watch the influence of HAP technology on furnace temperature and NOx emission, and at the same time, a cold state modeling test bed was set up in according with the results of calculation results, and some tests were carried on the test bed selectively. It’s found that HAP technology could optimize the flow field of the boiler, improve the slagging, and reduce NOx emission greatly; in the state of higher side wall nozzle of36°down declination angle and lower bottom ash hopper nozzle of90°up declination angle, jet flow depth of the primary air could be longer, the fullness of the down furnace would be higher, and the slagging danger would be decreased as possibly.On the largest3.5Me down fired boiler test bed in the country, a thermal modeling test was carried out after transformation, the influence of factors on combustion and NOX emission was investigated, and different air-staged technologies of down fired boiler were compared. The technology with independent OFA is better than the technology with exhaust air nozzle on side wall of the upper furnace; for the technology with independent OFA, the NOx emission would be decreased33.39%by adjustment of combustion. HAP low NOx combustion technology is suitable for a down fired boiler burning anthracite, and could reduce NOx emission with high combustion efficiency. |
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