Qinggang Lv

Particle characteristics of anthracite powder preheated quickly in circulating fluidized bed

Experimental studies were carried out on a bench-scale rig of pulverized anthracite combustion preheated by circulating fluidized bed (CFB). The preheated anthracites were sampled at the outlet of CFB and the effect of preheating temperature on particle characteristics was investigated. The particle size distribution of preheated anthracite powder was tested by a Malvern Mastersizer 2000 laser analyzer. The specific surface area, pore volume and pore diameter were analyzed by nitrogen absorption method. Scanning electron microscope (SEM) was used for a better observation on particle surface. It is found that when the preheat temperature is 900°C, the 50% cut size (d50) of the anthracite before and after being preheated decrease from 82 μm to 23 μm. For the preheated fuel, the pores in micro-size with the diameter smaller than 2 nm and meso-size with the diameter ranging from 2 nm to 10 nm are major contributors for the overall specific surface area and pore volume. Furthermore, variations of specific surface area and pore volume versus preheating temperature can be divided into two regions: below 900°C and above 900°C. In the first region, the specific surface area and pore volume increase as the preheating temperature increases, while in the second region they decrease with the increase in the preheating temperature. Based on the SEM analysis, after being preheated, a lot of cracks and pores appear on the particle surface, and the pore structure is well developed.

Effect of Pulverized Coal Concentration on Emission Characteristics of NOx

In order to analyze the forming and suppressing mechanism of NO x under the different pulverized coal concentration, the emission characteristics of NO x , along the axial direction of furnace and in the primary igniting zone, was investigated by the one-dimensional drop-tube furnace, and the relations between the pulverized coal concentration and the different reductive gases (CO/CH4/H2) produced during the combustion as well as the conversion ratio of fuel nitrogen to NO were discussed, then the effects of the pulverized coal concentration on the contaminative gases were analyzed. The results show that the emission of NO x both along the axial direction of furnace and the dynamic process in the primary igniting zone is of three obvious stages and NO x is mainly produced in the igniting zone. Under the different pulverized coal concentration, the conversion ratio of volatile nitrogen to NO is higher than that of coal char nitrogen to NO, the emission of NO x is dependent on the conversion of both volatile nitrogen and char nitrogen to NO under the low pulverized coal concentration, while the formation of NO x is mainly governed by the conversion of volatile nitrogen to NO under the high pulverized coal concentration, and NO is the dominant component and most sensitive to pulverized coal concentration among the different nitrogen oxides formed during the combustion of pulverized coal. Moreover, three nitrogen oxides (NO/N2O/NO2) are reduced to some extent with the increase of pulverized coal concentration, but the total amount of NO and N2O is invariable under the different temperature of furnace. The higher the pulverized coal concentration is, the more obvious the homogeneous reductive reactions of CO are, and the high concentration of pulverized coal is very favorable to promote the formation of the reductive gases, which contributes to the conversion of NO x to N2. Under the combustion of high pulverized coal concentration, the emission of NO x reduces greatly, and the second pollution is not induced, which is a very clean combustion technology and suitable to popularize in the engineering.