Design and Calculation Study on Circulating Fluidized Bed Boiler

Abstract: Circulating fluidized bed combustion (CFBC) is the new combustion technology developed in recent two decades. It has many advantages such as fuel flexibility, high combustion efficiency and low pollutant emissions. Now CFBC has been used in many industry equipments that include coal-fired boiler, MSW incinerator, roaster, coal gasifier and cement kiln.These years circulating fluidized bed combustion (CFBC) have acquired more and more recognized and developed quickly. Presently researchers are focusing on investigation into the scaling-up of CFB boiler and realization in integrated gasification combined cycle (IGCC) power generation. CFBC is one of the best commercial clean coal technologies up to now. Compared with traditional pc-fired boiler and stoker boiler, it has different characteristics of flow, heat transfer and combustion. So CFB boiler has different design and heat calculation method with traditional boiler. Deeply study in theory and experiment about CFB technology will help us further understand the intrinsic mechanism and design method, and it has much theoretical value and practice meaning.This thesis first summarized the design and heat calculating method on the basis of analysis of the fonner research and operating experience. And then, combined with author's research, the intrinsic flow, combustion, heat transfer and desulfurization process mechanisms in CFB boiler are introduced in detail. Making use of these theories and research result, author made careful analysis and discussion about the main factors influencing designing and cleared out some disadvantages in current design method.According to the special boiler components size requests for the intrinsic mechanism in CFB boiler, and considering features of structure design about exited CFB boiler, design method and demand for key parts are introduced and analyzed.Reference to the practical operating data in thermal CFBB and some laboratory result, the author put forward heat transfer coefficient calculating method in CFB boiler furnace, and give some analysis and improvement advice about heat transfercalculating of convective heating surface.Based on above-mentioned research results, the author gave a new heat calculation method for CFBB. Making use of the software C++ Builder, a new design and check program for heat calculating of CFBB is designed.The heat calculation is the necessary process when designing and reconstructing a CFB boiler, it can determine many parameters such as coal consumption, boiler thermal efficiency and the size of all kinds of heating surfaces. Because the calculating process is so complicated, more and more researchers begin to use computer to do it, which will greatly improve the accuracy and efficiency of calculation. Early boiler heat calculation computer program are all designed in DOS operating system, and nearly all use the computer language such as BASIC, FORTRAN or C, these language always exist some problem: 1) the interface is not friendly, and people can't understand quickly; 2) the program can't be used in a broad range and it must be corrected when use in another boiler; 3) it is not easy to maintenance.With the prevalence of Windows operating system and the broad application of visual programming technology, some technicians have used Visual Basic to design new thermal calculation programs, and get much improvement in interface. But it still can't solve the universal and maintainable problem. Now, this paper uses the software C++Builder developed by Borland Company to develop a new friendly interface and good maintainable universal program in heat calculation. Applying this program, the author has calculated two different capacity boilers, which is 35t/h and 75t/h CFB boiler. The calculating results are correct, which indicate that this program has some general utility…
Key words: Circulating fluidized bed boiler; CFB; design; heat calculation; separator; C++Builder; program design

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