Coal gasification is one of the key clean coal projects in China. A partial coal gasification of CFBB co-generation cycle process is suggested by Tsinghua University, which takes the hot circulating ash as the heating source to pyrolyze the coal in a steam fiuidized gasifier to generate the coal gas and tar. The coal gas is the fuel of the gas turbine. The char is burnt in the furnace to generate steam. In this process, One of the key technology is to reduce the yield of tar and get more gas. In this paper, the experiment investigation of two main components in tar: benzene and toluene catalytic cracking over three kind of circulating ash particles from CFBB in a fixed bed reactor, is introduced. And the catalytic mechanics is also discussed. The experimental results show circulating ash promote the cracking reactions of tar, the cracking reactions active energy of the reactance decrease compared with that over quartz sand. The temperature needed for same conversion ratio is decreased 80 C to 160 C for different ashes. The cracking gas product is more for ash than for sand. The solid product is coke for both case, which deactivates the ash. While the activity of the ash can be regenerated by burning the coke on the surface of ash particles. The total yield of gas increases.

It was confirmed that the combustion action in dense bed is different between the bubbling bed and circulating fluidized bed by the measurement of the gas profile distribution and combustion fraction distribution along the furnace height. The bed quality results in the mass transfer resistance increasing, which effects the combustion reaction in dense bed. The combustion reaction in dense bed is in reduce condition. The combustion occurs all along the furnace even in the cyclone. A comprehensive model is proposed here to predict the axial gas concentration profile in the dense be, which is considered the mass transfer resistance between the solid and gas in dense bed. Calculations indicated that the resistance has a great effect on the combustion in the dense bed. Experimental data and results of the model are in good agreement.

Since the first pilot 75 t/h water cooled separator CFB boiler was in operation in 1996, a hot test program was been conducted by Tsinghua University and several boiler works, so as to promote the scaling of CFB boiler. The present paper introduces the test program and the primary results, such as the separator efficiency, material balance, solid bulk density, heat transfer along the height of the furnace, et al. Besides the traditional test technology, some new developed apparatus was used in the hot test. According to the experience obtained from the boiler, the improvement measure was taken for the second and third boiler, which were in commercial operation in 1998. The first operation experience of the second and third boiler proves the effect of the improvement. Considering the experience and the test program, the scaling up design of water cooled separator was done. The present paper also introduces the design consideration and feature of the 130 t/h and 220 t/h CFB boiler.

The material balance in CFB furnace has been proved important for the performance of the boiler. The bed inventory of CFB boiler is composed of fuel ash and sorbent additives. It is necessary for the engineer to know the ash size formation character of fuel before make a proper design of the boiler and the auxiliary system. Traditionally, the only way to know the ash formation information is by the fuel combustion test in pilot CFB furnace. Because of the high cost of the test and the insufficient information from the test, such test was rarely done. The present investigation is proposing a simple laboratory test procedure instead of the pilot CFB combustion. The validation of the method is introduced in present paper. Two kinds of coals include the coal from Gardanne 250MW CFB were tested by present method and the result is compared with the data from Gardanne boiler.

Studies on circulating fluidized bed (CFB) boilers have being conducted at the Tsinghua University (TH) for about two decades and much of works are done to link the fundamentals with practical application. A full set of design theory was developed and some key elements of this theory are presented in this paper. First, a classification of state of the solid-gas two-phase flow in CFB boiler is given. TH's studies validated that a CFB boiler can be generally described as the superposition of a fast bed in the upper part with a bubbling bed or turbulent bed in the bottom part. A concept model of material balance for the open system of CFB boiler was developed and later improved as a more comprehensive 1-D model taking ash formation, particle attrition and segregation in bed into account. Some results of the models are discussed. Then the concept of State Specification of a CFB boiler is defined and discussed. The State Specification is regarded as the first step to design a CFB and a base to classify different style of CFB boiler technologies for various CFB boiler manufacturers. The State Specification adopted by major CFB boiler makers is summarized and associated importance issues are addressed. The heat transfer model originally developed by Leckner and his coworkers is adopted and improved. It is further calibrated with experimental data obtained on the commercial CFB boiler measurements. The principle, improvements and application of the model are introduced. Some special tools developed for heat transfer field test are also given. Also, combustion behaviors of char and volatile content are studied, and the combustion difference between a CFB boiler and a bubbling bed is analyzed. The influence of volatile content and size distribution is discussed. The concept of vertical distribution of combustion and heat in CFB boiler furnace is introduced and discussed as well. In the last, the suggested design theory of CFB boiler is summarized.