石炭の加圧流動層燃焼技術

Abstract

This article describes the present status of pressurized fluidized bed combustion (PFBC) technologies for coal. PFBC technology is commonly recognized as a future generation coal combustion technology and R&D has been done among advanced countries. PFBC technology offers a high efficiency and low emission combustion technology of coal by using a combined cycle power generation system. Wide variety of coal, lignite to anthracite, can be burned by PFBC technology, and coal energy can be converted to electricity with higher thermal efficiency. PFBC technology has recently entered the commercial stage. In Japan, three units have been under commercial operation. In other countries, some commercial units are under construction or operation. Their operability and performance are good enough to be a commercial plant. Especially, NOx, SOx and particulate emissions are acceptably low.Thermal efficiency of PFBC technology, however, is not high enough among the advanced coal based power generation technologies, such as integrated coal gasification combined cycle power generation (IGCC), integrated coal gasification fuel cell power generation (IGFC). Net thermal efficiency of PFBC is near 40%, because inlet temperature of gas turbine is limited. On the contrary, IGCC or IGFC gives high net thermal efficiency higher than 45%. In order to increase thermal efficiency, a new type of PFBC (advanced PFBC, A-PFBC) is now being developed. A-PFBC can improve inlet temperature of gas turbine and gives higher thermal efficiency as same as that of IGCC.Current PFBC technology seems to be not suitable for large scale commercial power generation, because of its higher construction and operational cost. It is very difficult to scale-up PFBC unit to very large scale as same as conventional pulverized coal combustion system. Other usage of PFBC may be more possible, because PFBC has high potential in the flexibility of fuel. Medium scale PFBC less than 50MWe is another choice. It can burn wide variety of fuels including wastes, and produces electricity and heat.In order to improve PFBC technology, fundamental research works are needed. Fundamental research on combustion behaviors of wide variety of fuels, combustion rate, agglomeration are presented.