Method for the torrefaction of lignocellulosic material

Abstract

A method for torrefaction of lignocellulosic biomass comprising: continuously feeding the biomass to an upper inlet to the torrefaction reactor vessel such that the biomass material is deposited on an upper tray assembly of tray assemblies stacked vertically within the reactor; as the biomass moves over each tray assembly, heating and drying the biomass material with a non-oxidizing gas under a pressure of at least 3 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 the tray of the next lower tray assembly; discharging torrefied biomass from a lower outlet of the torrefaction reactor, and circulating gas extracted from the reactor vessel back to the reactor.

What is claimed is: 
     
         1 . A method for torrefaction of lignocellulosic biomass using a torrefaction reactor vessel having stacked tray assemblies, the method comprising:
 feeding the biomass to an upper inlet to the torrefaction reactor vessel such that the biomass material is deposited on an upper tray assembly of a plurality of tray assemblies stacked vertically within the reactor;   as the biomass moves across each tray of the tray assembly, heating and drying the biomass material with a gas injected into the vessel, wherein the gas is substantially non-oxidizing of the biomass and is under a pressure of at least 3 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 the tray of the next lower tray assembly;   discharging torrefied biomass from a lower outlet of the torrefaction reactor, and   circulating gas extracted from the reactor vessel back to the reactor.   
     
     
         2 . The method of  claim 1  wherein the gas includes a substantial portion of a least one of superheated steam or nitrogen. 
     
     
         3 . The method of  claim 1  further comprising pressurizing the biomass before the feeding of the biomass into the vessel with a pressure transfer device. 
     
     
         4 . The method of  claim 1  wherein the trays of each of the tray assemblies have 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 gas entering at least one of the tray assemblies enters through a pipe at substantially a similar elevation as an extraction pipe which extracts gases from an immediately above tray assembly. 
     
     
         6 . The method of  claim 1  wherein each tray assembly includes a rotating scraper device above the tray. 
     
     
         7 . The method of  claim 1  wherein gas injected into the vessel at the tray assemblies for torrefaction is hotter than gas injected at the tray assemblies for drying. 
     
     
         8 . The method of  claim 1  wherein a cooling zone for the biomass is below an elevation of the vessel having the tray assemblies and adjacent the lower outlet. 
     
     
         9 . The method of  claim 1  wherein the circulated gas is processed to remove at least a portion of gaseous byproducts of the torrefaction reaction. 
     
     
         10 . The method of  claim 1  wherein the gas is substantially nitrogen. 
     
     
         11 . The method of  claim 1  wherein gases byproduct from the torrefaction reaction in the vessel are circulated back to the vessel. 
     
     
         12 . The method of  claim 1  wherein a total number of tray assemblies in the vessel is in a range of 4 to 20, and a lower most tray of the tray assemblies discharges the biomass to a pile of biomass in the vessel. 
     
     
         13 . The method of  claim 1  wherein the torrefaction of the biomass begins in the tray assemblies and is completed in a pile of the biomass below the tray assemblies. 
     
     
         14 . The method of  claim 13  further comprising cooling the biomass in a lower portion of the pile of the biomass adjacent the lower outlet. 
     
     
         15 . The method of  claim 1  wherein the gas flow through the biomass on each tray assembly is in a range of 2 to 4 per kg of biomass on the tray. 
     
     
         16 . The method of  claim 1  wherein a height of the biomass on each tray is between 150 and 1000 millimeters or greater than 1000 millimeters. 
     
     
         17 . The method of  claim 1  wherein the extracted gas extracted by suction of a blower or compressor, and the extracted gas is reheated and injected into one or more of the tray assemblies of the reactor. 
     
     
         18 . The method of  claim 1  further comprising moving gases extracted from one or more of the tray assemblies through a cyclone or filter to remove particles from the gasses and feed the gases to a blower or compressor. 
     
     
         19 . The method of  claim 1  further comprising moving gases extracted from one or more of the tray assemblies through a condenser, removing condensable by-products from the extracted gases, and a blower or compressor. 
     
     
         20 . The method of  claim 1  wherein the gases extracted from at least one of the tray assemblies is at least partially directed to a treatment process or combustion process separate from the vessel. 
     
     
         21 . The method of  claim 1  wherein gases extracted from one or more of the tray assemblies, which have a high concentration of torrefaction reaction byproduct compounds, is at least partially directed to a treatment process or combustion process separate from the vessel. 
     
     
         22 . The method of  claims 1  wherein gases extracted from one or more of the tray assemblies are at least partially directed to a treatment process or combustion process separate from the vessel. 
     
     
         23 . The method of  claim 1  further comprising cooling the torrefied biomass material by injecting a cooling gas into the vessel, wherein the cooling gas is cooler by 10 to 30 degrees Celsius that the gas injected into the torrefaction tray assemblies. 
     
     
         24 . The method of  claim 1  further comprising cooling the torrefied biomass material by injecting a cooling gas which suppresses the torrefaction reaction in the biomass.