System and method for dual fluidized bed gasification

Abstract

A method for deep desulfurization of synthesis gas comprising introducing carbonaceous material and optionally steam into a gasifier comprising a heat transfer media, extracting a first heat transfer stream comprising heat transfer media and optionally unconverted carbonaceous material from the gasifier, and introducing at least a portion of the first heat transfer stream into a combustor, introducing oxidant and optionally a fuel into the combustor, extracting a second heat transfer stream comprising heat transfer media from the combustor, and introducing at least a portion of the second heat transfer stream into the gasifier, introducing a compound capable of reacting with sulfur to produce sulfate, sulfide or both, extracting a purge stream comprising ash, sulfate, halide, or a combination thereof from the second heat transfer stream, extracting a flue gas from the combustor, and extracting a gasifier product synthesis gas stream comprising less than 1000 ppm sulfur from the gasifier.

What is claimed is: 
     
         1 . A method for deep desulfurization of synthesis gas, the method comprising:
 producing a flue gas and a gasifier product synthesis gas in a dual fluidized bed loop by:
 introducing a carbonaceous material and optionally steam into a fluid bed gasifier comprising a heat transfer media; 
 extracting a first heat transfer stream comprising heat transfer media and optionally unconverted carbonaceous material from the fluid bed gasifier, and introducing at least a portion of the first heat transfer stream into a fluid bed combustor, wherein the first heat transfer stream has a first temperature; 
 introducing oxidant and optionally a fuel into the fluid bed combustor, whereby unconverted carbonaceous material in the first heat transfer stream, fuel, or both is combusted and the temperature of the heat transfer media is raised; 
 extracting a second heat transfer stream comprising heat transfer media and having a second temperature from the fluid bed combustor, and introducing at least a portion of the second heat transfer stream into the fluid bed gasifier, wherein the second temperature is greater than the first temperature; 
 introducing a compound capable of reacting with sulfur to produce sulfate, sulfide or both into the dual fluidized bed loop; 
 extracting a purge stream comprising ash, sulfate, halide, or a combination thereof from the second heat transfer stream; 
 extracting the flue gas from the fluid bed combustor; and 
 extracting the gasifier product synthesis gas stream comprising less than 1000 ppm sulfur from the fluid bed gasifier of the dual fluidized bed loop. 
   
     
     
         2 . The method of  claim 1  wherein said compound capable of reacting with sulfur is selected from the group consisting of lime, limestone, sodium carbonate, sodium bicarbonate, magnesium oxide, and combinations thereof. 
     
     
         3 . The method of  claim 1  wherein the gasifier product synthesis gas comprises more than about 1 ppm sulfur. 
     
     
         4 . The method of  claim 1  further comprising introducing Fischer-Tropsch tailgas produced in a downstream Fischer-Tropsch synthesis into the fluid bed gasifier, into the fluid bed combustor, or both. 
     
     
         5 . The method of  claim 1  further comprising introducing slurry wax produced in a downstream Fischer-Tropsch synthesis into the fluid bed gasifier, into the fluid bed combustor, or both. 
     
     
         6 . The method of  claim 5  wherein the slurry wax comprises iron-based Fischer-Tropsch catalyst. 
     
     
         7 . The method of  claim 1  wherein the oxidant consists essentially of air. 
     
     
         8 . The method of  claim 1  wherein the heat transfer media comprises alumina, silica, olivine, or a combination thereof. 
     
     
         9 . The method of  claim 1  wherein the fluid bed gasifier is fluidized by a gas selected from the group consisting of steam, synthesis gas, Fischer-Tropsch tailgas, and combinations thereof. 
     
     
         10 . The method of  claim 1  wherein the fuel introduced into the fluid bed combustor comprises Fischer-Tropsch tailgas. 
     
     
         11 . The method of  claim 1  wherein the carbonaceous material comprises one or more component selected from the group consisting of RDF, municipal sludge, biomass, coal, and petroleum coke. 
     
     
         12 . The method of  claim 1  further comprising introducing sulfur-containing hydrocarbons into the fluid bed gasifier along with the carbonaceous material, or separately therefrom. 
     
     
         13 . The method of  claim 1  wherein the carbonaceous material is introduced into the fluid bed gasifier as a slurry. 
     
     
         14 . The method of  claim 1  wherein the oxidant comprises air in excess of the stoichiometrically required amount for combustion. 
     
     
         15 . The method of  claim 1  comprising introducing gas turbine exhaust into the fluid bed combustor. 
     
     
         16 . The method of  claim 1  wherein the heat transfer material comprises a nickel alumina catalyst, whereby chlorine is captured and removed via the purge stream. 
     
     
         17 . The method of  claim 1  further comprising introducing the gasifier product gas and a contaminant removal agent into a gas/solids separation unit configured to separate a cleaned synthesis gas stream from a contaminant stream. 
     
     
         18 . The method of  claim 17  further comprising introducing the contaminant stream into the fluid bed combustor. 
     
     
         19 . The method of  claim 18  wherein the contaminant stream is introduced into the fluid bed combustor via the first heat transfer stream. 
     
     
         20 . The method of  claim 18  wherein the contaminant removal agent is a sulfur-removal compound. 
     
     
         21 . The method of  claim 1  wherein the first heat transfer stream comprises a lower loop seal.