Abstract: Aiming at the problems encountered in fluidized bed pyrolysis and gasification, the heating mode of pyrolysis furnace, coal particle size grading, primary cooling and dust removal of pyrolysis gas, and ash discharging mode were discussed to optimize the process. In the new process, the high temperature semicoke was chosen to offer heat for pyrolysis furnace. The low rank coal feed was grinded into submillimeter particle size in which the fine powder smaller than 0.1 mm was separated out and delivered to the matched entraind flow bed gasifier to conduct the melting slag gasify together with the fine powder from fluidized bed gasifier to raise the carbon conversion rate. The major powder with particle size between 0.1-1.0 mm was fed into the pyrolysis furnace. The outlet gas from furnace contacted with proper cut fraction of tar oil to remove the tiny particles and then cooled down to 350 ℃ and further cooled by indirect heat transfer method. By this way the amount of organic wastewater could be lowered close to zero to realize clean and high efficiency pyrolysis and gasification. Taking the fluidized bed pyrolysis gasification process of low rank coal with a scale of 4 600 t/d as an example, the dry coal coarse powder entered the pyrolysis furnace, and the drying unit generated about 480 kt/a water. No organic wastewater was produced in the pyrolysis unit, but about 1.09×10⁹ m³/a hydrogen and about 81 kt/a coal tar were obtained. The carbon conversion rate of the system was up to over 95%，the yields of tar oil, coal gas, and semicoke reached 8.97%, 110 m³/t, and 67.5%, respectively and the volume fraction of effective gas in outlet gas of semicoke gasifier was more than 80%.

Key words: low rank coal, pyrolysis and gasification, fluidized bed, entrained flow bed, clean utilization