Experimental Study And Kinetic Analysis On NO_x Reduction With Pulverized Coal Reburning

Emission of NOX from coal combustion has increasingly become a worldwide concern. It is of great necessity to develop clean coal technology and control the NOX emission from coal fired utility boiler. Ruburning with coal has been proved a effective low NOX emission combustion technology。In this Ph.D Thesis, the reaction mechanisms of reburning have been investigated, and the homogeneous and heterogeneous reduction of NOX have been analyzed in details. A series of reburning experiments have been carried out on an entrained-flow reactor, in which two kinds of coals with different particle sizes have been used. The NOX reduction characteristics under different reburn fuel ratios, oxygen densities in reburn zone, coal particle sizes and reaction temperatures have been analyzed. During the experiments, chars are collected under different reburning condition. The element compositions of the collected ashes have been measured. The element release rates under different reburn condition have been discussed.In order to determinate the combustion and burn out characteristics of the reburn fuel, the combustion experiments of the collected ash samples have been carried out in a thermal gravimetric analyzer. The ignition temperatures and the maximum weight loss rates have been registered. According to the experiment results and Arrhenius law, HF indicating the comprehensive combustion characteristic has been put forward. The HF of different chars indicates that decreasing coal particle size and increasing oxygen density lead to increased burn out characteristic of chars. A mathematic model concerns with pyrolysis, combustions of volatile and char, reactions between volatiles and char with NOX is developed. The experimental reburn processes have been simulated. According to the simulations, the contributions to NOX reduction by HCN, C2H4 and char are compared, the reaction ways of HCN, C2H4 and char-N are analyzed in details.At last, the Non-Fourier heat diffusion in coal particles are investigated by calculations. Two Non-Fourier heat diffusion models of CV model and DPL model are applied, the calculation results of different model are compared. The influence of the Non-Fourier heat diffusion effect on the temperature history is discussed.