An efficient and economical process for continuously gasifying particulate carbonaceous material under selective conditions to produce, in an environmentally-acceptable manner, a gaseous product rich in carbon monoxide and hydrogen using pressurized gasifier means having a lower, dense-phase, fluidized bed of the material and contiguous to the upper phase boundary of the bed, an upper dilute-phase, particulate-entrained, gas zone which comprises
- introducing, in the gasifier, particulate carbonaceous material at a pressure slightly in excess of the pressure in the gasifier, at a temperature from about ambient to 1,000.degree. F., and with amounts of the material at a rate sufficient to maintain the upper phase boundary of the fluidized bed at a given level of about 4 to 20 feet above the lower phase boundary of the fluidized bed wherein the ratio of the height of the diute phase, gas zone to the height of the fluidized bed is from about 3:1 to 10:1;
- introducing oxygen-containing gas with up to about 50 percent (vol.) of steam at average bulk temperatures up to about 1000.degree. F., at a pressure slightly in excess of that in the gasifier, at spatially-separate points, substantially uniformly distributed circumferentially, at different levels in the gasifier and in amounts sufficient to substantially uniformly contact and gasify the constituents of the fluidized bed under controlled selective reaction conditions;
- introducing at least about 50 percent (wt.) of the steam being introduced into the fluidized bed, at the lower phase boundary of the fluidized bed, at spatially-separate points, substantially uniformly distributed circumferentially, at a temperature up to about 1200.degree. F., at a pressure slightly in excess of that in the gasifier, and at a rate sufficient to fluidize the lower portion of the bed;
- gasifying the material in the fluidized bed to provide a maximum temperature in the gasifier in the range of about 1500.degree. to 2400.degree. F. and at a bulk temperature in the dense phase below the softening temperature of any ash contained in the material to produce a gaseous reaction product including carbon monoxide, hydrogen, carbon dioxide, methane and diluents, which product evolves into the dilute phase, and in conjunction with such production partially spent char solids are produced;
- introducing additional increments of oxygen-containing gas with up to about 10 percent (vol.) of steam at or just above the phase boundary between the fluidized bed and dilute phase at spatially-separate points, substantially uniformly distributed circumferentially, in amounts sufficient to react with carbon values leaving the fluidized bed, thus increasing the temperature in the dilute-phase, and to enhance the carbon-conversion efficiency of the process to provide a raw product gas containing at least about 50 percent of the oxidized carbon in the form of carbon monoxide;
- passing the gaseous reaction product through the dilute phase at a superficial velocity well above the point of incipient fluidization and up to about 20 feet per second, and for a residence time in the dilute-phase of about 2 to 5 seconds to undergo further gasification and produce a raw product gas, maintaining the dilute-phase at a maximum temperature possible commensurate with the properties of any contained ash;
- removing the raw product gas from said upper dilute-phase zone;
- removing up to about 60 percent (wt.) of partially spent char from the bottom of the bed and containing the char with steam being introduced into the bed at the lower phase boundary to recover sensible heat from the char and preheat the steam;
- providing a cooled product gas from said raw product gas, said cooled product gas having less than about 4 grains of solid per standard cubic foot of gas at approximate gasifier pressures and at temperatures better suited for further processing, wherein substantial amounts of partially spent char are removed from the raw product gas for discharge from the process or for recycle or for reprocessing under different conditions, and wherein the cooling of the raw product gas to temperatures of about 200.degree. F. to 500.degree. F. is conducted in a heat recovery zone to recover heat values;
- employing recovered heat values from said heat recovery zone to produce steam, a portion of which is utilized in the process;
- conducting the cooled product gas, cooled in a heat recovery zone at the heat recovery zone pressures, which are less than the pressures in the gasifier, through a high efficiency, high pressure-drop type, scrubber to remove fine partially spent char particles and provide a gas product containing less than about 0.1 grains of solids per standard cubic foot of gas, a carbon monoxide content of at least about 10 percent (vol.), a hydrogen content of at least about 10 percent (vol.), and a BTU content of at least about 90 BTU per standard cubic foot;
- and
- maintaining the pressure in the gasifier at super-atmospheric pressures including pressures above about 1.5 atmospheres absolute by means of back-pressure control applied to the gas system at a point downstream of the gasifier.