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1、OPERATIONAL STATUS OF 135MWe CFB BOILERS IN CHINA Abstract: CFB boiler technology has been rapidly developed in China and China has the largestinstalled number and capacity of CFB boiler in the world. The number of 135MWe CFB boilers isover 150. The operational performance of 135MWe CFB boilers was
2、summarized in the article.And the reliability, economy, environmental protection index are also discussed in the article. Itnot only provides information of the development status of CFB industry, but also provides someexperience and guidance to improve the operation and to further develop CFB combu
3、stiontechnology.Keywords: 135MWe, CFB boilers, status, performance, summaryINTRODUCTIONOver the past two decades, because of its three outstanding advantages: broad fuel flexibility, excellent environmental performance, large range of load adjustment, CFB boiler technology has being under rapid deve
4、lopment and becomes an international acceptable commercial clean coal combustion technology (Lu et al.2006). CFB boiler has an irreplaceable position in Chinese boiler market. Up to now, the total number of CFB boiler operation is over 3,000, most of them are of small and medium capacity. The number
5、 of 410480t/h(100150MWe) CFB boilers is over 150 (Yue et al., 2006). CFB boilers are important for the improvement of the electric power supply structure. However, as the CFB boiler has only been adopted into coal combustion for less than 30 years and only is used power generation in recent years, m
6、any aspects are expected to be improved.The current status of the 135MWe is introduced in this paper. The aims of this paper are not only to provide information of the development status of CFB industry, but also to provide some experience and guidance to improve the operation and to further develop
7、 CFB combustion technology.RELIABILITY STATUSReliability is the fundamental of economy. Low reliability has been one of the main depute topics in CFB boiler development for years. The reliability of CFB boiler must be considered at first.In this article, two indices are used to measure the boilers r
8、eliability. One is unplanned outage times caused by various accidents and the other is continuous running time, namely the longest running time of the boiler.Unplanned outage timesFigure1 shows the variation of unplanned outage times for 135MWe CFB boilers in recent years. As the improving design an
9、d operations, the unplanned outage times decreases significantly. However, the times of unplanned outage for some boilers is still over 9.Continuous running timeAs CFB boilers were first appeared in China, they were frequently forced to shutdown by variousaccidents. Heating surface wear, slag discha
10、rger and crusher malfunction were the most common ones. Fortunately, with the improvement in design, manufacture operation and management, the continuous running time was prolonged gradually. As shown in Figure3, the continuous running time of 135MWe CFB boilers becomes longer and longer. To some CF
11、B power stations, the longest running time is more than 350 days, comparable to pulverized coal fired ones (Mao, 2006).ECONOMIC STATUSEonomic index includes carbon content in fly and bottom ash, loading rate, flue gas temperature, ignition and support oil, power consumption rate and supply coal cons
12、umption etc.Carbon content in fly and bottom ashFigure 4 shows that the carbon content in fly ash (LOI) for 135MWe boilers decreases in the year and the present average LOI is 7%.In the initial stage of CFB boiler commissioning and operation, the high LOI is often a severe problem, decreasing the ef
13、ficiency of CFB boiler. In some early CFB boilers, the LOI was as high as 40%. With better understanding CFB combustion theory and technology, LOI was decreased by optimizing the boiler design and operation (Xiao et al., 2005). Nowadays, LOI of some boilers is decreased by 2%, or even smaller (Hou e
14、t al., 2007). For most CFB units, the fuel is low rank coal or even coal stone, so LOI is relatively higher. However, for the same kind of coal, the combustion efficiency of CFB boiler is near to that of pulverized coal boiler.Average load rateFigure 5 shows the average load rate of CFB boilers in t
15、hese years. It can be seen that the load rate of 135MWe CFB boilers is only 64.4% in the year of 2007.That is because some 135MWe units used for mere power generation were regarded as smaller units which were allowed for limited operation time under the newly promulgated energy-saving policy. Howeve
16、r the load rate of some 135MWe CFB boilers used for self-supply power supply was more than 95%. Inevitably, the load rate variation affected the economic performance of units.Flue gas temperatureFlue gas temperature is an important factor for the boiler efficiency. Generally speaking, in CFB boilers, sulfur content in flue gas is relatively low and the low temperature corrosion is not serious, so the exhausted flue gas tempera
