Process For Converting Carbonaceous Material Into Low Tar Synthetic Gas

Abstract

A continuous multi-stage vertically sequenced gasification process for conversion of solid carbonaceous fuel material into clean (low tar) syngas. The process involves forming a pyrolysis residue bed having a uniform depth and width to pass raw syngas there through for an endothermic reaction, while controlling the reduction zone pressure drop, resident time and syngas flow space velocity during the endothermic reaction to form substantially tar free syngas, to reduce carbon content in the pyrolysis residue, and to reduce the temperature of raw syngas as compared to the temperature of the partial oxidation zone.

The embodiments of the invention for which an exclusive property or privilege is claimed are defined as follows: 
     
         1 . A continuous multi-stage vertically sequenced gasification process for conversion of solid carbonaceous fuel material into clean (low tar) syngas in a gasifier comprising:
 i) a pyrolysis zone,   ii) a partial oxidation zone located vertically downstream of the pyrolysis zone,   iii) a reduction zone located vertically downstream of the partial oxidation zone and comprising an downwardly angled perforated floor and a deflector located in the center of the floor;   said process comprising the steps of:   a) feeding the carbonaceous fuel material through the upper portion of the pyrolysis zone vertically downward towards the lower portion of the pyrolysis zone, while pyrolyzing said fuel into pyrolysis vapours comprising tar, and pyrolysis residue comprising char containing ash and carbon;   b) optionally adding a first oxidant to the lower portion of said pyrolysis zone to achieve a temperature greater than 200° C.;   c) directing said pyrolysis vapours to said partial oxidation (POX) zone, and directing said pyrolysis residue downwardly to the reduction zone via a separation member positioned between said pyrolysis zone and said partial oxidation zone, the separation member comprising a plurality of slanted vents;   d) adding a second oxidant in the partial oxidation zone to achieve a temperature greater than 900° C. to reform said pyrolysis vapours into raw syngas containing significantly reduced levels of tar;   e) forming a bed of pyrolysis residue having a uniform depth from the pyrolysis residue formed in step c) on the floor of the reduction zone;   f) passing said raw syngas from step d) downward through said pyrolysis residue (char) bed formed in step e), and carrying out an endothermic reaction using CO 2  and H 2 O in the said raw syngas and carbon of the char in the pyrolysis residue bed, while controlling the reduction zone pressure drop, resident time and syngas flow space velocity during the endothermic reaction to form substantially tar free syngas, to reduce carbon content in the pyrolysis residue, and to reduce the temperature of raw syngas as compared to the temperature of the partial oxidation zone.   g) passing said substantially tar free syngas from step f), in upward counter-current flow, to heat the pyrolysis zone and subsequently cool the substantially tar free syngas;   h) collecting said cooled tar free syngas; and   i) collecting clean ash and/or slag from the bottom of gasifier.   
     
     
         2 . The process of  claim 1 , wherein the process is performed entirely in one chamber 
     
     
         3 . The process of  claim 1 , wherein said process is performed in separate chambers or a combination of chambers in a vertical configuration. 
     
     
         4 . The process of  claim 1 , wherein said process is carried out under pressure, preferably greater than full vacuum and less than 600 psig, more preferably between atmospheric pressure and 100 psi. 
     
     
         5 . The process of  claim 1 , wherein the syngas composition has a H 2 :CO ratio from about 0.5 to about 1.5, preferably about 0.8 to about 1.0. 
     
     
         6 . The process of  claim 1 , wherein the carbonaceous fuel material comprises biomass fuel selected from wood chips, railway tie chips, waste wood, forestry waste, sewage sludge, pet coke, coal, Municipal Solid Waste (MSW), Refuse-derived Fuel (RDF), or any combination. 
     
     
         7 . The process of  claim 6 , wherein the biomass fuel is formed by a chipping, shredding, extrusion, mechanical processing, compacting, pelletizing, granulating, or crushing process. 
     
     
         8 . The process of  claim 6 , where the biofuel has been sprayed with, coated with or impregnated with liquid or solid carbonaceous materials. 
     
     
         9 . The process of  claim 1 , wherein the POX stage temperature is greater than 1250° C., or greater than the ash fusion temperature to create liquid slag. 
     
     
         10 . The process of  claim 1 , further comprising processing and cooling said tar free syngas to be used for electric power generation and chemical production, such as methanol, DME gasoline, and Fischer Tropsch liquids, such as syndiesel, synthetic jet fuel and synthetic wax. 
     
     
         11 . The process of  claim 1 , wherein the first and the second oxidant comprises air, enriched air, oxygen with purity greater than 85 wt %, oxygen with purity greater than 95 wt %, or a combination thereof. 
     
     
         12 . The process of  claim 11 , wherein the first and the second oxidants are same. 
     
     
         13 . The process of  claim 11 , wherein the first and the second oxidants are different. 
     
     
         14 . The process of  claim 11 , wherein the first oxidant and/or the second oxidant further comprises H 2 O and/or CO 2 . 
     
     
         15 . The process of  claim 14 , wherein the first oxidant comprises air, enriched air, oxygen with purity greater than 85 wt %, oxygen with purity greater than 95 wt %, or a combination thereof, and the second oxidant comprises at least one of air, enriched air, oxygen with purity greater than 85 wt %, oxygen with purity greater than 95 wt %, premixed with H 2 O and/or CO 2 . 
     
     
         16 . The process of  claim 1 , wherein the lower portion of the pyrolysis zone has a perimeter greater than that of the upper portion. 
     
     
         17 . The process of  claim 1 , further comprising agitating and/or rotating said pyrolysis residue bed. 
     
     
         18 . An apparatus for a continuous multi-stage vertically sequenced gasification process for conversion of solid carbonaceous fuel material into clean (low tar) syngas, the apparatus comprising:
 i) a pyrolysis zone having,   ii) a partial oxidation zone located vertically downstream of the pyrolysis zone for conversion of pyrolysis vapours into syngas and;   iii) a reduction zone located vertically downstream of the partial oxidation zone;   iv) a separation member positioned between said pyrolysis zone and said partial oxidation zone, said separation member comprising a plurality of vertically inclined vents to allow pyrolysis vapours into the partial oxidation zone, wherein said separation member is configured to direct the pyrolysis residue into the reduction zone;   v) an outlet for ash, positioned downstream of the reduction zone; and   vi) an outlet for the syngas positioned after the reduction zone;
 wherein said reduction zone is provided with an downwardly angled perforated floor and a deflector located in the center of the floor, wherein the floor and deflector are configured to form a bed of pyrolysis residue having a uniform depth. 
   
     
     
         19 . The apparatus of  claim 18 , wherein said pyrolysis zone, said partial oxidation zone and said reduction zone are comprised with one container/chamber. 
     
     
         20 . The apparatus of  claim 18 , further comprising an outer shell having a shell inlet in communication with the syngas outlet, and a shell outlet, wherein said outer shell encircles/surrounds said pyrolysis zone, said partial oxidation zone and said reduction zone to form a channel for flow of the syngas toward the shell outlet. 
     
     
         21 . The apparatus of  claim 18 , wherein said shell outlet is provided on an upper portion of the shell to allow the syngas to move upward in the channel to provide indirect thermal contact between the syngas and the pyrolysis zone. 
     
     
         22 . The apparatus of  claim 18 , wherein said pyrolysis zone, said partial oxidation zone and said reduction zone are comprised within separate containers/chambers. 
     
     
         23 . The apparatus of  claim 18 , wherein the perimeter of the lower portion of the pyrolysis zone is greater than the perimeter of the upper portion. 
     
     
         24 . The apparatus of  claim 18 , wherein said floor of the reduction zone is configures to be agitated.