Method and system for the torrefaction of lignocellulosic material

Abstract

A method for torrefaction of lignocellulosic biomass using a torrefaction reactor vessel having stacked trays, the method including: continuously feeding the biomass to an upper inlet of the torrefaction reactor vessel such that the biomass material is deposited on an upper tray of a plurality of trays stacked vertically within the reactor; as the biomass moves across an upper surface of each of the trays, heating and drying the biomass material with a gas injected into the vessel, wherein the gas is substantially non-oxidizing of the biomass, is under a pressure of at least 20 bar gauge and at a temperature of at least 200° C.; 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; discharging torrefied biomass from a lower outlet of the torrefaction reactor vessel, and circulating gas extracted from a lower elevation of the reactor vessel to an upper region of the reactor vessel.

What is claimed is: 
     
         1 . A method for torrefaction of lignocellulosic biomass using a torrefaction reactor vessel having stacked trays, the method comprising:
 continuously feeding the biomass to an upper inlet of the torrefaction reactor vessel such that the biomass material is deposited on an upper tray of a plurality of trays stacked vertically within the reactor;   as the biomass moves across an upper surface of each of the trays, heating and drying the biomass material with a gas injected into the vessel, wherein the gas is substantially non-oxidizing of the biomass, is under a pressure of at least 20 bar gauge and at a temperature of at least 200° C., and   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;   discharging torrefied biomass from a lower outlet of the torrefaction reactor vessel, and   circulating gas extracted from a lower elevation of the reactor vessel to an upper region of the reactor vessel.   
     
     
         2 . The method of  claim 1  wherein the gas is at least one of superheated steam, carbon dioxide and nitrogen. 
     
     
         3 . The method of  claim 1  further comprising a pressurizing the biomass before the feeding of the biomass into the vessel with a pressure transfer device. 
     
     
         4 . The method of  claim 1  wherein at least the upper trays are a mesh, screen or have perforations and the heating and drying of the biomass includes passing the gas through the biomass and the trays. 
     
     
         5 . The method of  claim 4  wherein the trays below the upper trays are solid such that the gas does not pass through the tray. 
     
     
         6 . The method of  claim 1  wherein the lower elevation of the vessel where the gas is extracted is adjacent a lower tray of the trays. 
     
     
         7 . The method of  claim 1  wherein gas is injected into the vessel at two elevations wherein the gas is hotter when injected at a lower elevation of the two elevations than the gas injected at an upper elevation of the two elevations. 
     
     
         8 . The method of  claim 1  wherein below an elevation of the vessel from which the gas is extracted, the biomass continues to cascade down through at least one of the trays. 
     
     
         9 . The method of  claim 1  further comprising injecting the gas in the biomass to purge oxygen from the biomass. 
     
     
         10 . The method of  claim 9  wherein the injection occurs before the biomass enters the vessel or as the biomass enters the vessel. 
     
     
         11 . A torrefaction pressurized reactor vessel assembly comprising:
 a stack of trays housed within the vessel;   a source of a pressurized, reduced oxygen gas coupled to the vessel to allow the gas to flow into at least an upper region of the vessel, wherein the gas is at a pressure of at least 20 bar gauge and at a temperature of at least 200° C.;   an upper inlet to the vessel through which biomass enters the pressurized reactor vessel, wherein a chute aligned with the upper inlet directs the biomass from the inlet to an upper tray of the stack of trays;   a scraper device associated with an upper surface on each of the trays, wherein at least one of the scraper device and tray rotates within the vessel;   a lower outlet in the vessel through which torrefied biomass is discharged from the torrefaction reactor vessel, and   a gas circulation system through which gas extracted from a lower elevation in the vessel flow to an upper elevation of the reactor vessel.   
     
     
         12 . The torrefaction pressurized reactor vessel assembly of  claim 11  wherein the wherein the source of a pressurized, reduced oxygen gas is a source of at least one of superheated steam, carbon dioxide and nitrogen. 
     
     
         13 . The torrefaction pressurized reactor vessel assembly of  claim 11  further a pressure transfer device which pressurizes and feeds the biomass to the reactor vessel. 
     
     
         14 . The torrefaction pressurized reactor vessel assembly of  claim 11  wherein at least one of the upper trays of the stack of trays is a mesh, screen or has perforations. 
     
     
         15 . The torrefaction pressurized reactor vessel assembly of  claim 14  wherein trays below the upper trays are solid such that the gas does not pass through the tray. 
     
     
         16 . The torrefaction pressurized reactor vessel assembly of  claim 11  wherein a lower elevation of the vessel at where the gas is extracted for circulation is adjacent a lower tray. 
     
     
         17 . The torrefaction pressurized reactor vessel assembly of  claim 11  wherein the gas circulation system further comprises a heat exchanger. 
     
     
         18 . The torrefaction pressurized reactor vessel assembly of  claim 11  further comprising a vertical rotating shaft extending through a center axis of the reactor vessel and at least one of the scraper device and trays are fixed to the shaft. 
     
     
         19 . The torrefaction pressurized reactor vessel assembly of  claim 11  wherein the reactor vessel includes a lower region devoid of trays and receiving the biomass material. 
     
     
         20 . The torrefaction pressurized reactor vessel assembly of  claim 11  further comprising biomass supply bin a conduit conveying the pressurized, reduced oxygen gas to the biomass supply bin.