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.

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.

The effect of boundary layer reactions on the conversion of char-N to NO, N2O and HCN was studied by a coupled experimental/theoretical approach. In the experimental part, the evolution of HCN at conditions of a batch fluidized bed reactor was studied. The results show that the char-N conversion to HCN is very low under normal oxidizing conditions. This explains why it was not detected by early studies of this system. The results also suggest that the release of HCN is related to gases released when the char is oxidized rather than to late devolatilization reactions. The product distribution is modeled using heterogeneous reactions on the char surface coupled to homogeneous reactions in the gas phase. Three cases were analyzed. In Case A, only the heterogeneous production of N2O and NO was considered. Case B considered HCN and NO heterogeneous production. Finally, Case C combined cases A and B by allowing the heterogeneous production of NO, N2O and HCN. Cases A and B predict most of the qualitative trends for the char-N conversion to N2O reported in the literature. However, Case A fails to predict the experimentally observed release of HCN when oxidation around the particle is suppressed. Among the three cases, Case C is the one that closely predicts experimental observables. Finally, the predictions obtained by the model are used to define further experiments, particularly on the evolution of gas concentration in the boundary layer with char burnout, that can be useful in order to obtain more insight in the mechanism of nitrogen oxide formation during char oxidation.

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.

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.