Method and system for the torrefaction of lignocellulosic material

Abstract

A method for torrefaction of biomass using a torrefaction reactor vessel having stacked trays including: feeding the biomass to an upper inlet of the vessel; cascading the biomass down through the trays by passing the biomass through an opening in each of the trays to deposit the biomass on a lower tray; heating the biomass material with an oxygen deprived gas; extracting moisture from below each of the upper trays; as the biomass undergoes torrefaction in the lower trays retaining the gas with the biomass until the biomass falls from the stacked trays to a pile of biomass in the reactor vessel; exhausting gases containing organic compounds through a gas outlet at an elevation between the stacked trays and the pile of biomass, and discharging torrefied biomass from the torrefaction reactor vessel.

What is claimed is: 
     
         1 . A torrefaction reactor vessel configured for subjecting biomass to a torrefaction process, the reactor comprising:
 inlet nozzles injecting an oxygen deprived gas into the vessel, wherein the gas temperature of the oxygen deprived gas injected through the nozzles at upper elevations in the vessel is lower than the gas temperature of the oxygen deprived gas injected through the inlet nozzles at lower elevations;   a rotatable shaft extending vertically down into the vessel;   a stack of scrapers and trays extending into the vessel from the top plate, wherein each scraper is fixed to and rotates with the shaft and is immediately above an associated stationary tray, each tray is perforated to allow passage of gas and block passage of biomass and has an opening through which biomass falls;   the stack includes a gas extraction chamber at an elevation below one of the trays and above one of the scrapers, wherein the gas extraction chamber receives the gas passing through the one of the trays and includes a gas extraction port to exhaust gas passing through the tray;   the stack includes a plurality of lower scrapers and trays which are below the gas extraction chamber and have no gas extraction chamber between the lower scrapers and trays;   a torrefaction chamber in the vessel and below the stack, wherein the torrefaction chamber holds a pile of biomass discharged from the stack;   a torrefaction gas exhaust outlet on the vessel and at an elevation below the stack and above an upper surface of the pile of biomass, and   a biomass outlet at a lower region of the vessel.   
     
     
         2 . The reactor vessel of  claim 1  wherein the shaft includes an insulated upper coupling configured to connect to a motor drive system external to the vessel. 
     
     
         3 . The reactor vessel of  claim 1  wherein each of the scrapers and trays are strapped together, and the strapped tray assemblies and scraper devices are coaxial with the shaft of the vessel. 
     
     
         4 . The reactor vessel of  claim 1  wherein each of the trays are coaxial and coextensive with each other, each of the scrapers are coaxial and coextensive with each other, and the trays and scrapers are coaxial. 
     
     
         5 . The reactor vessel of  claim 1  further comprising an isolation plate below the gas extraction chamber, wherein the isolation plate is coaxial and coextensive with the trays and includes a walled chute extending through the gas extraction chamber and to the scraper immediately below the isolation plate. 
     
     
         6 . The reactor vessel of  claim 5  wherein immediately below the isolation plate and above the immediately below scraper is a gas distribution chamber having an inlet nozzle in a wall of the vessel to receive an oxygen deprived drying gas. 
     
     
         7 . The reactor vessel of  claim 1  wherein the torrefaction gas exhaust outlet is a single outlet through which substantially torrefaction gas exhausts from the vessel except for the gas which flows with biomass through the biomass outlet. 
     
     
         8 . The torrefaction vessel of  claim 1  further comprising an oxygen deprived gas inlet nozzle on an outer wall of the vessel and at an elevation below the upper surface of the pile of biomass. 
     
     
         9 . A method for torrefaction of biomass using a torrefaction reactor vessel having stacked trays including:
 feeding the biomass to an upper inlet of the vessel such that the biomass material is deposited on an upper tray of a vertical stack of trays in the reactor;   cascading the biomass down through the trays by passing the biomass through an opening in each of the trays to deposit the biomass on a lower tray;   as the biomass moves around each of the stacked trays, heating the biomass material with an oxygen deprived gas injected into the vessel;   as the biomass is dried in upper trays of the stacked trays, extracting moisture containing gas having passed through the biomass on the upper trays wherein the extraction is immediately below each of the upper trays;   as the biomass undergoes torrefaction in the lower trays of the stacked trays, retaining the gas with the biomass until the biomass falls from the stacked trays to a pile of biomass in the reactor vessel;   exhausting gases containing organic compounds volatized by the torrefaction of the biomass through a gas outlet on the vessel at an elevation between the stacked trays and the pile of biomass, and   discharging torrefied biomass from a lower outlet of the torrefaction reactor vessel.   
     
     
         10 . The method of  claim 9  further comprising circulating extracted gas from the vessel, removing the volatized organic compounds from the extracted gas to clean the gas, and feeding the cleaned gas to one or more of the stacked trays. 
     
     
         11 . The method of  claim 10  wherein the cleaning of the gas includes cooling the gas to condense the organic compounds and separating the condensate from the gas. 
     
     
         12 . The method of  claim 10  wherein the feeding of the biomass and the discharge of the torrefied biomass are continuous. 
     
     
         13 . The method of  claim 8  wherein the oxygen deprived gas includes nitrogen gas. 
     
     
         14 . The method of  claim 8  further comprising moving the biomass around each tray by a scraper device associated with each tray. 
     
     
         15 . The method of  claim 8  wherein the oxygen deprived gas is injected under a pressure of at least 3 bar gauge and the interior of the vessel is under the pressure of at least 3 bar gauge. 
     
     
         16 . A method for torrefaction of lignocellulosic biomass using a torrefaction reactor having stacked tray assemblies comprising:
 continuously feeding the biomass to the torrefaction reactor such that the biomass material is deposited on a first tray assembly of a plurality of tray assemblies stacked vertically within the reactor;   as the biomass cascades down through drying trays in the tray assemblies, heating the biomass material with an oxygen deprived gas injected at a temperature below a threshold torrefaction temperature, wherein the oxygen deprived gas.   extracting from the vessel gases flowing through each of the drying trays before the gas flows to the biomass on a next lower tray;   as the biomass cascades down through torrefaction trays in the tray assemblies, wherein the torrefaction trays are below the drying trays, heating the biomass material with an oxygen deprived gas injected at a temperature above the threshold torrefaction temperature to promote a torrefaction reaction in the biomass on the torrefaction trays;   containing the oxygen deprived gas passing through the torrefaction trays in the vessel as the oxygen deprived gas and biomass pass through a plurality of torrefaction trays, and exhausting the oxygen deprived gas having passed through the torrefaction tray from the vessel, and   discharging torrefied biomass from a lower outlet of the torrefaction reactor.   
     
     
         17 . The method of  claim 16  wherein the threshold torrefaction temperature is in a range of 230° C. to 280° C. 
     
     
         18 . The method of  claim 16  further comprising cleaning the exhausted gas by removing volatized organic compounds and feeding the cleaned gas to the vessel. 
     
     
         19 . The method of  claim 18  wherein the cleaning of the gas includes cooling the gas to condense the organic compounds and separating the condensate from the gas. 
     
     
         20 . The method of  claim 16  wherein the oxygen deprived gas includes a substantial portion of nitrogen gas. 
     
     
         21 . The method of  claim 16  further comprising moving the biomass around each tray by a scraper device associated with each tray. 
     
     
         22 . The method of  claim 16  wherein the biomass is retained in the reactor vessel for a period of 15 to 60 minutes. 
     
     
         23 . The method of  claim 16  wherein the oxygen deprived gas is injected under a pressure of at least 3 bar gauge and the interior of the vessel is under the pressure of at least 3 bar gauge.