Two-stage gasification of coal with forced reactant mixing and steam treatment of recycled char

Abstract

Abstract A PROCESS FOR THE TWO-STAGE GASIFICATION OF COAL TO PRODUCE METHANE-RICH FUEL GAS. IN THE FIRST STAGE, RECYCLED PROCESSED CHAR PASSES UPWARDLY WHILE REACTING WITH STEAM AND OXYGEN TO YIELD A FIRST STAGE SYNTHESIS GAS CONTAINING HYDROGEN AND OXIDES OF CARBON. IN THE SECOND STAGE, THE SYNTHESIS GAS PASSES UPWARDLY WITH COAL AND STEAM WHICH REACT TO YIELD PARTIALLY GASIFIED CHAR ENTRAINED IN A SECOND STAGE PRODUCT GAS CONTAINING METHANE, HYDROGEN AND OXIDES OF CARBON. THE PRODUCT GAS FROM THE SECOND STAGE IS SEPARATED FROM THE CHAR AND IS PURIFIED BY CONVERSION AND REMOVAL OF CARBON OXIDES, HYDROGEN SULFIDE AND OTHER IMPURITIES, AND THE PURIFIED SECOND STAGE PRODUCT GAS IS METHANATED TO PRODUCE THE DESIRED FUEL GAS. CHAR SEPARATED FROM THE SECOND STAGE PRODUCT GAS IS PASSED THROUGH A FLUIDIZED BED AND SCRUBBED WITH STEAM TO REMOVE PRODUCT GAS AND OTHER VOLATILE MATERIALS WHICH ARE CARRIED BY THE SCRUBBING STEAM TO THE SECOND STAGE PRODUCT GAS CARRIED TO PURIFICATION. THE SCRUBBED RECYCLE CHAR IS CARRIED BY STEAM AT HIGH PRESSURE AND RETURNED TO THE FIRST STAGE. AGGLOMERATION OF COAL IN THE SECOND STAGE IS PREVENTED BY THE RAPID HEATING OF THE COAL TO A TEMPERATURE ABOVE ITS RANGE OF PLASTICITY BY MIXING IT WITH THE HOT PRODUCTS FROM THE FIRST STAGE. IN THE FIRST STAGE THE RATIO OF CHAR AND STEAM TO OXYGEN IS SELECTED TO OBTAIN A REACTION TEMPERATURE ABOVE THE ASH MELTING POINT. THE PRESSURE IN EACH STAGE EXCEEDS 500 P.S.I.G. THE SECOND STAGE TEMPERATURE EXCEEDS 1500*F. AND THE FIRST STAGE TEMPERATURE EXCEEDS 2200*F. GAS VELOCITIES IN BOTH STAGES ARE MAINTAINED BETWEEN 2 AND 12 FEET PER SECOND WHILE THE RESIDENCE TIME OF SOLIDS IN THE FIRST STAGE IS FROM ONEHALF TO FIVE SECONDS AND, IN THE SECOND STAGE, FROM FIVE TO FIFTEEN SECONDS. A MIXING STAGE BETWEEN THE FIRST AND SECOND STAGES PROVIDES A RESTRICTED AREA FOR THE INJECTION OF COAL AND STEAM INTO THE UPWARDLY FLOWING SYNTHESIS GAS TO SEPARATE SOLIDS AND GASES ENTERING THE SECOND STAGE FROM THE FIRST STAGE AND TO ASSURE RAPID MIXING AND REACTION OF THE REACTANTS OF BOTH STAGES. SLAG IS REMOVED FROM THE LOWER END OF THE FIRST STAGE FOR QUENCHING AND DISPOSAL THROUGH A SLAG REMOVAL PORT OF SMALL CROSS SECTIONAL AREA COMPARED TO THE CROSS SECTIONAL AREA OF THE FIRST STAGE. THIS ASSURES RESIDENCE AND REACTION TIME OF THE CHAR IN THE FIRST STAGE SUFFICIENT FOR ITS GASIFICATION WITH STEAM AND OXYGEN AT TEMPERATURES ABOVE THE ASH MELTING POINT. THE RELATIVELY SMALL AREA OF THE SLAG REMOVAL PORT PERMITS CONTROLLED REMOVAL OF MOLTEN SLAG WHILE RESTRICTING THE GRAVITATION OF CHAR TO THE SLAG QUENCHING STAGE. D R A W I N G

Inventors

• 👤 E Donath

Bibliographic Details