Mechanism, Application And Model Research On Air-stage And Reburn Technology For Coal Combustion

With the industry development, the air pollution is becoming a austere challenge for people. In resent years, the emission of SO2 has been controlled gradually, and the nitrogen oxygen (NOx) emission becomes the main air pollution. In our country, coal is the primary energy, and the NOx emission during coal combustion is the main source of NOx. Its reduction is very significative.Aiming at exploring the best way to control the NOx emission during coal combustion, the NOx producing and reducing law during coal combustion is researched in this thesis. The experiment is carried out in a fixed-bed reactor firstly, then a drop tube reactor, and on the big boilers finally. An computing model is also made basing on the experiment result.In the fixed-bed reactor, the mechanism on NOx during the coal combusting and reburning is studied. The field quantity of NO, HCN and NH3 is measured and the conversion rate of the fuel-N to NO, HCN, NH3 and N2 is computed, which can represent the NOx reduction efficiency during coal combustion more exactly. At the experiment condition in this thesis, 1%-2% is the best concentration of oxygen at which the NOx emission is controlled best during the volatile combustion and NOx is reduced most by volatile during the volatile reburning. When the char combusting, the NOx emission and reduction is affected by many factors, in which the oxygen concentration effect is the most obvious. The higher the oxygen concentration, the more NOx emitted during char combustion.The air-staged combustion and reburning process is simulated in the drop tube reactor. In the initial stage of pulverized coal combustion, lots of NO is fielded at both air-rich atmosphere and fuel-rich atmosphere. The NO fielded will be reduced partially in the subsequent time. The reduction rate is higher at fuel-rich atmosphere than that at air-rich atmosphere. The optimal air coefficient in the first combustion zone is about 0.8 for air-staged combustion. Lower air coefficient will make the carbon content in fly ash increase quickly. Considering both the NOx controlling and the economic benefits, the optimal air coefficient in reburn zone is in the range of 0.8-0.85 for pulverized coal reburning. Both the air-staged combustion technology and the conventional pulverized coal reburning technology are utilized on large-scale plant boliers. The furnace temperature, the steam parameter, the NOx emission concentration and the boiler efficiency before and after the technical reformation is compared. The effect of the operation mode on the NOx control is also analyzed. The NOx reduction efficiency of the pulverized coal reburning technology exceeds 50% in the demonstration engineering.Finaly, a computing model is made up. It contains the pyrogenation and combustion model, the furnace temperature computing model and the NOx production and reduction model. The computing result of the model is consistent with the experiment. Using the engineering computing model, the nozzle position of the tertiary air, the reburn air and the burnout air is optimized. And the result can be used to direct the engineering design of the low NOx combustion technology.