1、PDF外文：http:/ A 英文 资料（ 原文 ） Research on Carbon Content in Fly Ash from Circulating Fluidized Bedboilers Xianbin Xiao,Hairui Yang,Hai Zhang,Junfu Lu, andGuangxi Yue Department of Thermal Engineering, Tsinghua University, Beijing 100084, China Received December 12, 2004 Revised Manuscript R
2、eceived March 9, 2005 Abstract The carbon content in the fly ash from most Chinese circulating fluidized bed (CFB) boilers is much higher than expected, which directly influences the combustion efficiency. In the present paper, carbon burnout was investigated in both field tests and laboratory exper
3、iments. The effect of coal property, operation condition, gas-solid mixing, char deactivation, residence time, and cyclone performance are analyzed seriatim based on a large amount of experimental results. A coal index is proposed to describe the coal rank, having a strong effect on the char burnout
4、. Bad gas-solid mixing in the furnace is another important reason of the higher carbon content in the fly ash. Some chars in the fly ash are deactivated during combustion of large coal particles and have very low carbon reactivity. Several suggestions are made about design, operation, and modificati
5、on to reduce the carbon content in the fly ash. Introduction With the advantages of fuel flexibility and low pollutant emission, circulating fluidized bed (CFB) combustion technology has been developed rapidly in power generation. The capacity of CFB power plants has been growing steadily ever
6、 since the commercialization of the technology in the late 1970s. Currently, the maximum capacity of a single CFB utility boiler is on the order of 300 MWe and more large capacity units of 600 and 800 MWe supercritical pressure CFB boilers are developing. The development of CFB boilers in China star
7、ted in the 1980s, and the maximum capacity for a single unit has been increasing year after year, as shown in Figure 1. There are over 1000 CFB boilers in operation up to 2004, including over 20 units above 135 MWe. In addition, 80 units of 135 MWe and 10 units of 300 MWe CFB boilers are in construc
8、tion or on order. Figure 1 Maximum capacity for a single unit. However, it is a fact that the combustion efficiency of CFB boilers is lower than that of pulverized coal fired (PC) boilers, though high combustion efficiency was reported in the CFB market abroad.1 Brown coals, with high activit
9、y, are commonly burned abroad, which is the main reason for low carbon content in the fly ash. In China, on the contrary, most CFB boilers burn hard coals such as anthracite, bituminous, and coal wastes； the carbon content in the fly ash is much higher than expected,2 especially for the large-capaci
10、ty CFB boilers manufactured with imported technology. At the same time, the high carbon content in the fly ash limits the potential utilization as cement materials.3 It has become the bottleneck reducing the competitive power of the CFB boiler. Coal combustion processes in CFB boiler are very
11、complex, undergoing the following interrelated sequences:4 heating and drying, devolatilization and volatile combustion, swelling and fragmentation, and burning of char. The unburned carbon content in the fly ash is believed to be the final results for characterizing the combustion efficiency. To op
12、timize the process and make predictions of the combustor performance in a broad range of operating conditions, it is necessary to understand the combustion efficiency, especially the unburned carbon in the fly ash. The carbon burnout in Chinese CFB boilers was investigated in both field tests
13、and laboratory experiments to identify the major factors affecting the carbon content in the fly ash. Experimental Section The experimental investigations include a great deal of field tests and laboratory experiments, such as sampling of coal and fly ash, control and measurements of the operation parameters, measurements of oxygen concentration and solid suspension density, size distribution measurement of fly ash, measurement of carbon content in the fly ash, coal analysis, and char reactivity measurement, etc.
