Gasification system and method for high ash content feedstock

Abstract

A coal separation unit for a gasification system includes a vessel having a top portion and a bottom portion, a first inlet configured to receive a feed stream including at least coal and ash from a grinding unit, a second inlet configured to receive a wash fluid stream, a first outlet configured to convey a low-ash feed stream, and a second outlet configured to convey an ash-rich stream. In operation, the feed stream is washed with the wash fluid stream in the separation unit to separate at least a portion of the ash from the coal. The separated ash settles to the bottom portion of the vessel and is conveyed via the second outlet as the ash-rich stream. The separated coal floats to the top portion of the vessel and is conveyed via the first outlet to a gasification unit as the low-ash feed stream.

What is claimed is: 
     
         1 . A coal separation unit for a gasification system having a grinding unit and a gasification unit, said coal separation unit comprising:
 a vessel having a top portion and a bottom portion;   a first inlet configured to receive a feed stream comprising at least coal and ash from the grinding unit;   a second inlet configured to receive a wash fluid stream;   a first outlet configured to convey a low-ash feed stream; and   a second outlet configured to convey an ash-rich stream,   wherein in operation, the feed stream is washed with the wash fluid stream in said coal separation unit to separate at least a portion of the ash from the coal, the separated ash settling to said bottom portion of said vessel and conveyed via said second outlet as the ash-rich stream, and the separated coal floating to said top portion of said vessel and conveyed via said first outlet to the gasification unit as the low-ash feed stream.   
     
     
         2 . The coal separation unit of  claim 1 , further comprising a third inlet configured to receive an air stream to facilitate separation of the coal and the ash of the feed stream and/or flow of the coal to said vessel top portion. 
     
     
         3 . The coal separation unit of  claim 1 , wherein said coal separation unit is configured to receive a reagent stream to enhance hydrophobicity of the coal, and wherein the reagent stream is mixed with the high-ash feed stream before said first inlet. 
     
     
         4 . The coal separation unit of  claim 3 , wherein the reagent stream comprises at least one of diesel and a glycol based composition. 
     
     
         5 . The coal separation unit of  claim 2 , wherein said third inlet is located in said bottom portion of said vessel. 
     
     
         6 . The coal separation unit of  claim 1 , wherein said second inlet is located in said top portion of said vessel. 
     
     
         7 . The coal separation unit of  claim 1 , wherein said first outlet is located in said top portion of said vessel and said second outlet is located in said bottom portion of said vessel. 
     
     
         8 . A gasification system for high-ash content coal, said system comprising:
 a grinding unit configured to reduce the particle size of a high-ash feed stream comprising at least coal and ash;   a gasification unit configured to receive a low-ash feed stream and produce a syngas from the low-ash feed stream; and   a coal separation unit coupled between said grinding unit and said gasification unit, said coal separation unit comprising:
 a vessel having a top portion and a bottom portion; 
 a first inlet in flow communication with said grinding unit and configured to receive the high-ash feed stream having reduced particle size; 
 a second inlet configured to receive a washing fluid stream; 
 a first outlet coupled in flow communication with said gasification unit and configured to convey the low-ash feed stream thereto; and 
 a second outlet configured to convey an ash-rich stream, 
   wherein in operation, the high-ash feed stream is washed with the wash fluid stream in said coal separation unit to separate at least a portion of the ash from the coal, the separated ash settling to said bottom portion of said vessel and conveyed via said second outlet as the ash-rich stream, and the separated coal floating to said top portion of said vessel and conveyed to said gasification unit via said first outlet as the low-ash feed stream.   
     
     
         9 . The gasification system of  claim 8 , wherein said coal separation unit further comprises a third inlet configured to receive an air stream to facilitate separation of the coal and the ash of the feed stream and/or flow of the coal to said vessel top portion. 
     
     
         10 . The gasification system of  claim 8 , wherein said coal separation unit is configured to receive a reagent stream to enhance hydrophobicity of the coal, and wherein the reagent stream is mixed with the high-ash feed stream before said first inlet. 
     
     
         11 . The gasification system of  claim 10 , wherein the reagent stream comprises at least one of diesel and a glycol based composition. 
     
     
         12 . The gasification system of  claim 9 , wherein said coal separation unit is configured to receive the high-ash feed stream with an ash content greater than 20%, and to produce the low-ash feed stream with an ash content less than 20%. 
     
     
         13 . The gasification system of  claim 8 , wherein said second inlet is located in said top portion of said vessel. 
     
     
         14 . The gasification system of  claim 8 , wherein said first outlet is located in said top portion of said vessel and said second outlet is located in said bottom portion of said vessel. 
     
     
         15 . A method of reducing ash content of a high-ash feed stream in a gasification system, the method comprising:
 providing a coal separation unit, the coal separation unit including a vessel having a top portion, a bottom portion, a first and second inlet, and a first and second outlet;   providing the high-ash feed stream to the first inlet, the high-ash feed stream including at least coal and ash;   providing a wash fluid stream to the second inlet;   contacting the high-ash feed stream with the wash fluid stream in the vessel; and   separating at least a portion of the ash from the coal, wherein the separated ash settles to the bottom portion of the vessel and the coal floats to the top portion of the vessel.   
     
     
         16 . The method of  claim 15 , further comprising coupling a grinding unit to the coal separation unit and producing the high-ash feed stream in the grinding unit. 
     
     
         17 . The method of  claim 15 , further comprising drawing a low-ash feed stream from the first outlet and drawing an ash-rich stream from the second outlet. 
     
     
         18 . The method of  claim 17 , further comprising conveying the low-ash feed stream to a gasifier. 
     
     
         19 . The method of  claim 15 , further comprising providing a third inlet in the vessel and providing an air stream to the third inlet to facilitate separation of the ash from the coal of the high-ash feed stream and/or flow of the coal to the vessel top portion. 
     
     
         20 . The method of  claim 15 , further comprising providing a reagent stream to the high-ash feed stream before the first inlet, wherein the reagent stream enhances hydrophobicity of the coal of the high-ash feed stream.