Method and system for the torrefaction of lignocellulosic material

Abstract

Systems and methods for producing torrefied lignocellulosic material in a commercially suitable process.

What is claimed is: 
     
         1 . A method for the torrefaction of lignocellulosic material comprising the steps of:
 drying lignocellulosic material to remove at least a portion of moisture contained within the lignocellulosic material;   reacting the dried lignocellulosic material at a pressure between 1 and 50 bar and at a temperature between 100 and 1000° C. in a torrefaction reactor to generate torrefied biomass and torrefaction gas;   recycling at least a portion of the torrefaction gas back to the torrefaction reactor;   cooling the torrefied biomass in a cooler operating in a substantially oxygen-free environment;   recycling inert gas to the cooler and recycling inert gas to the torrefaction reactor;   supplying make-up inert gas to the cooler;   wherein the method uses the inert gas as at least a partial medium for transferring heat among the torrefaction reactor and the cooler.   
     
     
         2 . The method of  claim 1 , wherein the cooler is a fluidbed cooler, and wherein the method further comprises a step of separating the torrefied biomass and inert gas in a cyclone. 
     
     
         3 . The method of  claim 1 , wherein the inert gas comprises nitrogen. 
     
     
         4 . The method of  claim 1 , wherein the step of drying removes moisture present in the lignocellulosic material such that an absolute moisture content of the lignocellulosic material is less than 15% of the total weight of the lignocellulosic material. 
     
     
         5 . The method of  claim 1  further comprising the step of combusting at least oxygen and a portion of the torrefaction gas produced in the torrefaction reactor to produce a hot flue gas. 
     
     
         6 . The method of  claim 1  further comprising the step of providing the hot flue gas to the dryer at a temperature of up to 1,000° C. 
     
     
         7 . The method of  claim 1  further comprising the step of compacting in a pelletizer the torrefied biomass solids obtained from the cooler. 
     
     
         8 . The method of  claim 1  further comprising the steps of separating air into at least a first stream comprising oxygen and a second stream comprising nitrogen and using the nitrogen as the inert gas. 
     
     
         9 . The method of  claim 1 , wherein reacting the dried lignocellulosic material occurs at a pressure between 5 and 20 bar. 
     
     
         10 . The method of  claim 1 , wherein reacting the dried lignocellulosic material occurs at a temperature of about 220-300° C.