TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preparation: The process for preparing composite gas by biomass material with two-step method comprises biomass raw material comprising combustible of domestic garbage and farming and forestry waste such as branch, leaf, sawdust, straw of wheat, straw of corn, rice hull, rice seedlings, peanut seedlings, peanut shell and weed, etc., except the special condition, (such as too large volume to enter apparatus and water content is greater than or equal to 50%), original granularity and moisture is in a fixed (mobile) bed gasifier, high speed (30-280 m/seconds) sprayed oxygen (oxygen content is 70-100%) as he gasification medium for gasifying under 1000-1600 degrees C; material is dehydrated and decomposed to the gas and carbon by heating and gradually change the original shape, when the carbon gasification parses the dust component to prepare the combustible gas containing vapor, tar, hydrocarbons, CO2, CO, H2 and small amount of harmful component (such as HCl, H2S, organic chloride and organic sulfide); the gas enters an entrained-flow gasifier for gasification with pulverized coal, oxygen and vapor; in the entrained-flow gasifier, according to the gasification temperature, the coal supply is adjusted and the proportion of the oxygen and the coal is controlled to be 0.7-1.2 kg/kg coal, the proportion of the compensated vapor and the coal is controlled to be 0-0.2kg/kg coal; gasification temperature can reach to 1400-2000 degrees C with the generated heat energy by gasifying the pulverized coal (60-100%-200 meshes) and the oxygen (content is 80-100%) for reacting for 3-15 seconds; in co-gasifying process, the tar, hydrocarbons, H2O, CO2, organic chloride and organic sulfide are decomposed by the catalytic pyrolysis reaction to the tar by the carbon generated by parsing and volatilizing the pulverized coal so as to prepare the rough composite gas of which main component is CO and H2; there are two implementing methods for preparing the composite gas by the biomass and coal: one of biomass is gasified on the fixed bed up-draft gasifier, and enters to the other entrained-flow gasifier to prepare the composite gas with the pulverized coal and oxygen, liquid residual respectively; and the other method is: the upper part of a furnace is the biomass low-draft fixed gasifier, middle part is the pulverized coal + oxygen entrained-flow gasifier furnace, and the bottom is the outlet of the product from two furnace; the composite gas is prepared by co-gasifying the biomass with the rough fuel gas, vapor, carbon oxide, residual carbon and dust component entering the middle part of the entrained-flow gasifier with the ash coal and the oxygen, and the liquid residual and the rough composite gas are exhausted from the bottom outlet. A fully-dry three-step ash-removal, poison-elimination, and purification process for producing gas from domestic garbage comprises entering rough composite gas which is discharged out of the furnace in a movable bed granule-layer filter to be purified for the first step after it passes through a heat exchanger to be reduced as 100-500 degrees C in temperature, materials of heat exchanger can be steel as well as ceramics or glass, filtering material is alkali metal or articles of alkali metal which fit for the process; (a) purification of rough composite gas is performed under a natural pressure, a higher temperature (400-700 degrees C), air speed of 100-1000/hour, an apparent filtering speed of 0.002-1.0 m/seconds, and a down moving speed of 0.001-0.01 m/seconds of filtering material granule layer, where the ash removal, water removal, carbon dioxide removal and poison removal are performed at the same time; in movable bed granule layer filter, the ash, water, acid gases CO2, H2S and HCl in rough composite gas are removed greater than or equal to 99% at the same time, heavy metal vapor and compounds are removed greater than or equal to 80%; filtering materials is one-off, and it is no more regenerated; gas enters in a heat exchanger after being purified by movable bed granule layer filter and then it is cooled to less than or equal to 100 degrees C, and it further passes through a bag-type dust collector to be purified; and (b) purification to precise ash-removal which is controlled by a compact filter cloth, filter cloth is weaved by various fibers comprising plant, medical and compose fiber, and natural mineral fiber, and it has a thickness greater than or equal to 1 mm and interspaces not greater than 2 mu m; composite gas is discharged out of the bag-type dust collector enters fixed bed filter, under a lower temperature (from normal temperature to 120 degrees C) and a low filtering speed (0.01-0.8 m/seconds), various harmful components in gas are controlled by various special active carbon filled in by layer in the third step; special active carbon is private active carbon articles used for fine removals of H2S, CO2, and CS2, and also comprises carbon articles used for fine removals of HCl.