The fluidization technology for gas-solid systems was overviewed. The stress was put on behavior of gas bubbles, properties of emulsion phase, description of powder groups, axial mixing of solids, and modeling of fluidized-bed contactors. The fluidization of ultrafine particles was also mentioned.

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To discuss the feasibility of the high velocity fluidized-bed (CFB) technology, brief reviews on the history of the development of CFB and on its fluidization behaviors are presented. It is also discussed the reasons why the circulating fluidized-bed boilers (CFBC) are appeared before the footlight recently. CFB is pronounced technology for the new boiler systems and also it has sufficient possibility to be applied on the new solid-gas contact systems. To support these technology, much more fundamental research works on the solid-gas multiphase system including CFB are required.

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After introducing the system of coal fueled bubbling type dense fluidized bed, the relationship between coal combustion process and the characteristic phenomena occurring in the fluidized bed was described and NOx formation mechanisms during these processes were discussed. NOx reduction reactions occurring on the surfaces of fluidizing materials and burning char with the chemical compounds such as amines, cyanides formed from fuel-N and of CO, H₂ were described.
Finally, the combustion methods for the NOx in-furnace reduction were discussed.

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The first commercial Multi-Solid Fluidized Bed (MSFB) Boiler in Japan was constructed by Mitsui Engineering and Shipbuilding Co., Ltd. and has been operated as a captive power plant for Kuraray Co., Ltd., a chemical textiles manufacturer.
This paper describes the concept and features of MSFB, the operation data and the technical points which were established to have stable and reliable operating conditions in dense bed and solid circulating system, introducing a few examples of various and complicated behaviours in multiphase flow of MSFB system.

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Atmospheric fluidized bed combustion (AFBC) boiler is one of the important break-through in the area of coal combustion technology, Recently a number of demonstration plants of AFBC boiler have been constcted by utility companies in the world.
The coal feed system of AFBC boilers plays an important role for successful operation of AFBC boilers. Employing the unerbed feed system, we have developed a feed system for AFBC boilers and carried out experimental study using a pilot plant. The developed feed system achieved stable transportation of dense coal-air mixture and uniform distribution with the multi-outlet distributor.

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Fluidized bed combustion (FBC) boilers are capable of burning high moisture, low calorie and other low quality coals. And FBC also makes it possible to employ the in-furnace desulfurization that simplifies the conventional desulfurizing systems with saving of construction costs. Because of its merits, the development of the FBC technologies has has been actively carried out in many countries.
This paper describes the current status and the development of FBC technologies.

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