Gasification of carbonaceous materials using pulsed oxygen

Abstract

A process for the gasification of carbonaceous materials for the product of syngas. Pulsed oxygen is used to maintain the temperature of the gasification zones and to avoid hot spots in the gasification reactor.

1 . A method for controlling the temperature in a gasifier system designed for converting carbonaceous materials to a syngas:
 a) Introducing an effective amount of fluidizing gas (preferably steam) into a gasification reactor containing a fluidized bed of solids;   b) Introducing a fluidizing gas through a plurality of nozzles located within each stage of the gasifier system where thermal energy can be added to support the gasification reaction;   c) Operating said gasification stage or stages at a temperature of about 1200° F. to about 1800;   d) Operating other gasification stages where the partial or complete oxidation occurs at temperatures of 1200 to 1800 F.   e) pulsing oxygen, through said plurality of nozzles, into said gasification reactor in order to keep the temperature in the range from about 1200° F. to about 1800° F., and to keep the partial oxidation zone of said nozzles below the fusion temperature of the inorganic fraction of said carbonaceous material, wherein said nozzles are divided into one or more sets of nozzles wherein each set is pulsing an effective amount of oxygen at the same or at different times;   f) the flow rate at which O 2  is to be pulsed should be established such that the local temperature rise within the injection nozzle jet remains below 2000 F or less than the fusion temperature of the feed solids (whichever is lower)   g) The pulsing frequency of the O 2  injection should be less than the characteristic bubble detachment frequency for the nozzle system designed to maintain the appropriate fluidization.   
     
     
         2 . A process for converting a biomass feedstock to a synthetic gas in a two-stage gasification process unit, which process comprises:
 a) Introducing an effective amount of steam into a first gasification stage containing a fluidized bed of solids;   b) introducing a fluidizing gas through a first plurality of nozzles located at the bottom of said first gasification stage containing solids thereby resulting in and maintaining a fluidized bed of said solids;   c) Operating said first gasification stage at a temperature of about 1000° F. to about 1600° F.;   d) introducing a biomass feedstock in particulate form into a first gasification stage containing the fluidized bed of solids wherein the residence time of said biomass in said first gasification stage is from about 5 to 90 seconds, thereby resulting in a gaseous phase biomass product stream and a carbon-rich biomass particulate product;   e) pulsing oxygen, through said plurality of nozzles, into said first gasification stage in order to keep the temperature in the range from about 1000° F. but not greater than about 1600° F., and to keep the partial oxidation zone of said nozzles below the fusion temperature of the inorganic fraction of said biomass, wherein said nozzles are divided into one or more sets of nozzles wherein each set is pulsing an effective amount of oxygen at the same or at different times;   f) transporting at least a portion of said gaseous phase biomass product stream to a solid/gas separation unit wherein particles greater than a predetermined size are separated and returned to said first gasification zone and wherein the treated gaseous phase biomass product stream is transported to a second gasification stage;   g) Transporting solids and particulates from said first gasification stage to a second gasification stage;   h) introducing, through a second plurality of nozzles, an effective amount of a fluidizing gas into said second gasification stage thereby resulting in a second fluidized bed of biomass particulates and fluidizing solids;   i) operating said second gasification zone in the temperature range from about 1600 F to about 2000 F, but at a temperature at least 50° F. greater than the first gasification stage and at a residence time from about 1 to 3 times that of said first gasification stage;   j) pulsing an effective amount of oxygen through said second plurality of nozzles of said second gasification stage in order to maintain said second fluidized bed in the temperature range of about 1600° F. to about 2000° F., 1700 to 1800, and to keep the partial oxidation zone of said nozzles below the fusion temperature of the inorganic fraction of said biomass, wherein said nozzles are divided into one or more sets of nozzles wherein each set is pulsing an effective amount of oxygen at the same or at different times, thereby resulting in said biomass being converted to a gaseous phase and a solid phase;   j) returning at least a portion of said solids to said first gasification stage;   k) passing said syngas stream to a solids/gas separation zone wherein substantially all of said remaining solids are removed, thereby resulting in a substantially solids-free syngas stream;   l) passing said syngas product stream to downstream processing; and   m) removing any excess solids from the gasification process unit to maintain a predetermined balance of solids.