Gasification of black liquor

Claim 1

A process for treating a concentrated aqueous black liquor carbonaceous material and alkali metal sulfur compounds to form a combustible gas and a sulfide-rich melt comprising: (a) providing a gasifier vessel maintained at a pressure of from about 1 to 50 atmospheres and containing a relatively shallow molten salt pool at its bottom within a sump equipped with an overflow discharge, said vessel having (I) a black liquor drying zone at its upper parts, (ii) a black liquor solids gasification zone located below the drying zone, and (iii) a molten salt sulfur reduction zone comprising said molten salt pool; (b) introducing into the top of said drying zone the concentrated aqueous black liquor containing carbonaceous material and alkali metal sulfur compounds; (c) evaporating water from said concentrated aqueous black liquor in said drying zone by direct contact of said aqueous black liquor with the hot gas rising from the gasification zone to produce dried black liquor solids, which fall into said gasification zone, and a cooled combustible gas container water vapor said combustible gas being at a temperature below the melting point of entrained droplets of the molten salt causing solification of said droplets; (d) introducing a first portion of an oxygen-containing gas into the gas space in the gasification zone located below the drying zone immediately above the molten salt pool to partially oxidize and gasify a fraction of the carbonaceous material in said dried black liquor solids falling through said zone to form a hot combustible gas; (e) introducing a second portion of said oxygen-containing gas beneath the surface of said molten salt pool in an amount sufficient to cause gasification of essentially all carbonaceous material entering the pool from the gasification zone but not sufficent to create oxidizing conditions in the pool, the formed gas rising from said pool, the total amount of said first and second portion of oxygen-containing gas constituting between 25 and 55% of the amount of oxygen-containing gas required for complete combustion of the black liquor feed and representing the total amount of oxygen-containing gas fed to said gasifier vessel; (f) withdrawing said cooled combustible gas having a higher heating value of at least about 90 Btu/scf (dry basis) from an upper portion of said drying zone; and (g) withdrawing from said overflow discharge in the molten salt reduction zone a melt in which the sulfur content is predominantly in the form of alkali metal sulfide.