Method and system for production of a clean hot gas based on solid fuels

摘要

Solid fuel can be converted into a clean hot flue gas with a low content of volatile organic compounds (VOC's), NOx and dust, and clean ash with a low carbon content by means of a stage-divided thermal reactor, where the conversion process of the solid fuel is in separate vertical stages (from below and up): ash burn-out, char oxidation and gasification, pyrolysis, drying, and a gas combustion stage where gas from the gasifier is combusted.

主权项

1. A method for converting a solid carbonaceous fuel into flue a gas and ash, said method comprising heating the fuel at separate coherent stages to temperatures causing the fuel to decompose into gaseous and solid components, the stages comprising:
a pyrolysis stage, in which the fuel is pyrolysed without addition of oxygen, a gasification and an oxidation stage, in which char is converted to gas, an ash burn-out stage to which oxygen is supplied, and a gas combustion stage to which oxygen is supplied, wherein the fuel at the pyrolysis stage is heated by the gases formed in the gasification stage, the oxidation stage and the gas combustion stage, wherein said solid carbonaceous fuel is converted into the flue gas and ash in a system comprising:I. a thermal reactor comprising i) an updraft gasification reactor for conversion of solid fuel into a burnable gas, wherein the updraft gasification reactor is configured as a moving-bed reactor having a drying stage, a pyrolysis stage, a char gasification and oxidation stage and an ash burn-out stage and ii) a gas combustion stage within the thermal reactor positioned directly above the updraft gasification reactor; andII. a plurality of nozzles configured to feed oxygen to the ash burn-out stage and to the gas combustion stage so that the gases produced in the updraft gasification reactor are converted into the flue gas, which has a NOx content below 300 mg/Nm3, CO content below 500 mg/Nm3, and oxygen content below 5% by weight,III. wherein heat is provided to the pyrolysis and drying stages in the updraft gasification reactor by radiation and convection from the gas combustion stage above the drying stage and by convection from the gasification and oxidation stage below the drying stage.