Method of reducing hydrogen chloride in synthesis gas

Abstract

The invention is a method for reducing the hydrogen chloride content of a synthesis gas stream by (a) gasifying a carbonaceous feed material in an entrained flow gasifier to produce a gas/solids mixture of hydrogen, carbon monoxide, hydrogen chloride gas, and flyslag particles; (b) passing the gas/solids mixture solids removal zone where at least a portion of the flyslag particles are removed, to produce a gas stream; (c) mixing with the gas stream an alkali metal oxide, hydroxide, bicarbonate, or carbonate to produce a metals/gas mixture; (d) passing the metals/gas mixture to a ceramic candle filter; (e) reacting on the surface of the ceramic candle filter the alkali metal compounds with the hydrogen chloride to produce solid alkali metal chloride; and (f) recovering a gas stream from the ceramic candle filter substantially free of hydrogen chloride and solids.

What is claimed is: 
     
       1. A method for reducing the hydrogen chloride content of a synthesis gas stream comprising: (a) gasifying a carbonaceous feed material in an entrained flow gasifier under gasifying conditions thereby producing a gas/solids mixture comprising hydrogen, carbon monoxide, hydrogen chloride gas, and flyslag particles;   (b) passing said gas/solids mixture to a solids removal zone wherein at least a portion of said flyslag particles are removed, thereby producing a gas stream;   (c) admixing with said gas stream an alkali metal compound comprising at least one oxide, hydroxide, bicarbonate, or carbonate, of sodium or potassium, thereby producing a metals/gas mixture;   (d) passing said metals/gas mixture to a ceramic candle filter;   (e) reacting on the surface of said ceramic candle filter said alkali metal compounds, or thermal decomposition products thereof, with said hydrogen chloride thereby producing solid alkali metal chloride, wherein a cake of solids builds up on the surface of said ceramic candle filter thereby increasing the contact time between said hydrogen chloride and said alkali metal compounds or their thermal decomposition products;   (f) periodically removing at least a portion of said cake of solids; and   (g) recovering from said ceramic candle filter a gas stream substantially free of hydrogen chloride.   
     
     
       2. The method according to claim 1 wherein the carbonaceous feed material is coal. 
     
     
       3. The method according to claim 2 wherein the amount of alkali metal compounds admixed with the effluent of said solids removal zone is at least a stoichiometric amount of alkali metal compounds with respect to the hydrogen chloride content of the synthesis gas. 
     
     
       4. The method according to claim 3 wherein the amount of alkali metal compounds admixed with the effluent of said solids removal zone is not more than about 3 times the stoichiometric amount of alkali metal compounds with respect to the hydrogen chloride content of the synthesis gas. 
     
     
       5. The method according to claim 2 wherein said coal is a bituminous coal and wherein said admixing step (c) consists essentially of injecting said alkali metal compound into said effluent of said solids removal zone. 
     
     
       6. The method according to claim 3 wherein said coal is a sub-bituminous coal and wherein said alkali metal compound is sodium bicarbonate and wherein in admixing step (c) said sodium bicarbonate is dry at the point of admixture. 
     
     
       7. A method for reducing the hydrogen chloride content of a synthesis gas stream comprising: (a) gasifying a carbonaceous feed material in an entrained flow gasifier under gasifying conditions thereby producing a gas/solids mixture comprising hydrogen, carbon monoxide, hydrogen chloride gas, and flyslag particles;   (b) passing said gas/solids mixture to a first heat recovery zone wherein a portion of the sensible heat of the gas/solids mixture is recovered;   (c) passing said gas/solids mixture to a solids removal zone wherein substantially all of said flyslag particles are removed, thereby producing a gas stream;   (d) passing said gas stream to a second heat recovery zone wherein a portion of the sensible heat of the gas stream is recovered;   (e) admixing with the effluent of said second heat recovery zone a sodium compound comprising at least one oxide, hydroxide, bicarbonate, or carbonate of sodium, thereby producing a sodium/gas mixture;   (f) passing said sodium/gas mixture to a ceramic candle filter;   (g) reacting on the upstream surface of said ceramic candle filter said sodium compounds, or thermal decomposition products thereof, with said hydrogen chloride thereby producing solid sodium chloride, wherein a cake of sodium chloride builds up on the upstream surface of said ceramic candle filter thereby increasing the contract time between hydrogen chloride and said sodium compounds or thermal decomposition products thereof;   (h) periodically removing at least a portion of said cake of sodium chloride;   (i) recovering a gas stream effluent from said ceramic candle filter substantially free of hydrogen chloride; and   (j) passing said substantially-hydrogen-chloride-free gas stream to a third heat recovery zone wherein a portion of the sensible heat of the gas stream substantially free of hydrogen chloride is recovered.   
     
     
       8. The method according to claim 7 wherein the temperature in the gasifier is from about 1100° C. to about 2000° C. 
     
     
       9. The method according to claim 8 wherein the temperature in the gasifier is from about 1450° C. to about 1575° C. 
     
     
       10. The method according to claim 8 wherein the pressure in the gasifier is from about 200 psig to about 600 psig. 
     
     
       11. The method according to claim 9 wherein the pressure in the gasifier is from about 300 psig to about 450 psig. 
     
     
       12. The method according to claim 7 wherein the carbonaceous material is a bituminous or sub-bituminous coal, the alkali metal compound is sodium bicarbonate, and wherein prior to gasification the coal contains from about 0.01% by weight chlorine to about 0.35% by weight chlorine based on the coal as received and from about 95% by weight to about 99% by weight of the chlorine is removed in the ceramic candle filter in the form of sodium chloride. 
     
     
       13. The method according to claim 12 wherein prior to the reaction of the sodium carbonate or sodium oxide with the hydrogen chloride the gas stream contains from about 10 ppmv to about 1000 ppmv chlorine based on the gas volume and after the gas stream is recovered from said ceramic candle filter the gas contains from about 0.1 ppmv to about 5 ppmv of chlorine based on the gas stream. 
     
     
       14. The method of claim 7 wherein the carbonaceous feed is petroleum coke. 
     
     
       15. A method for reducing the hydrogen chloride content of a synthesis gas stream comprising: (a) gasifying a bituminous or sub-bituminous coal in an entrained flow gasifier at a temperature from about 1450° C. to about 1575° C. and wherein the pressure in the gasifier is from about 300 psig to about 450 psig, thereby producing a synthesis gas mixture comprising hydrogen, carbon monoxide, hydrogen chloride gas, and flyslag particles;   (b) passing said synthesis gas mixture to a first heat recovery zone wherein a portion of the sensible heat of the synthesis gas mixture is recovered;   (c) passing said synthesis gas mixture to a first solids removal zone wherein substantially all of said flyslag particles are removed and recovering the synthesis gas from said solids removal zone, thereby producing a gas stream;   (d) passing said gas stream to a second heat recovery zone wherein a portion of the sensible heat of the gas stream is recovered;   (e) injecting nahcolite into said gas stream for admixture therewith;   (f) substantially decomposing said nahcolite to sodium carbonate and sodium oxide, thereby producing a sodium/gas mixture comprising hydrogen, carbon monoxide, hydrogen chloride, sodium carbonate, and sodium oxide;   (g) passing said sodium/gas mixture to a ceramic candle filter;   (h) reacting on the upstream surface of said ceramic candle filter said sodium carbonates and sodium oxides with said hydrogen chloride thereby producing solid sodium chloride, wherein a cake of solid sodium chloride builds up on the upstream surface of said ceramic candle filter thereby increasing the contact time between hydrogen chloride and said sodium carbonates or sodium oxides;   (i) periodically removing at least a portion of said cake of sodium chloride;   (j) recovering from said ceramic candle filter a gas stream substantially free of hydrogen chloride; and   (k) passing said gas stream substantially free of hydrogen chloride to a third heat recovery zone wherein a portion of the sensible heat of the substantially-hydrogen-chloride-free gas stream is recovered.