Process for preparing fuel gas through graded pyrolysis and gasification of powdered coal

A process for preparing fuel gas through graded pyrolysis and gasification of powdered coal, the process comprises the following steps:

• (1) contacting powdered coal having a particle size of not greater than 3 mm and ash residue in a riser reactor under hydrogenation conditions, performing a pyrolysis reaction and a gas-phase tar cracking reaction;
• (2) subjecting the product obtained from step (1) to a primary gas-solid separation to obtain a gasified gas containing fine particle semi-coke and a solid fraction containing coarse particle semi-coke;
• (3) subjecting the gasified gas containing fine particle semi-coke to a secondary gas-solid separation to obtain a solid fraction containing fine particle semi-coke and a gasified gas;
• (4) feeding at least a portion of the solid fraction containing coarse particle semi-coke obtained from the primary gas-solid separation into a stepped turbulent fluidized bed through a material-returning device of fluidized bed, and contacting with an oxidant and water vapor to carry out a gasification calcination reaction to obtain a first high-temperature gasified coal gas and a high-temperature ash residue, flowing the first high-temperature gasified coal gas and at least a portion of high-temperature ash residue upwards and feeding into the riser reactor to provide the hydrogen atmosphere and the ash residue in step (1);
• (5) feeding at least a portion of the solid fraction containing fine particle semi-coke obtained from the secondary gas-solid separation into an entrained-flow bed through a material-returning device of entrained-flow bed, and contacting with a gasifying agent to carry out a melting gasification reaction to obtain a second high-temperature gasified coal gas and a liquid residue, falling the liquid residue to the material-returning device of fluidized bed for cooling and solidification, and feeding the second high-temperature gasified coal gas to the riser reactor via a high-temperature gasified gas returning pipe to provide heat and hydrogenation atmosphere for the pyrolysis reaction and the gas-phase tar cracking reaction of step (1).