Method for the production of pellets or briquettes

Abstract

A method is provided for the production of pellets or briquettes from lignin containing material in the form of processable particles wherein the method includes the steps of: passing the material having a relative moisture content of more than about 20%, by weight, to a drying step and drying it to a relative moisture content of about 0-30% by weight; passing the material to a heat treatment step and heating the material to about 180-235° C. by injecting steam into a reactor; maintaining the material in the reactor at the temperature reached for a sufficient time to soften the material and release lignin; reducing the pressure in the reactor in at least one step; and pelletizing or briquetting the treated material. The invention also concerns pellets or briquettes produced by the method.

What is claimed: 
     
         1 . A method for the production of pellets or briquettes from a lignin containing material, comprising the steps of:
 passing the lignin containing material having a moisture content less than about 30% by weight into a reactor;   heating the lignin containing material to 180-235° C. by injecting steam into the reactor causing a pressure in the reactor;   maintaining the material in the reactor within the range for at least 30 seconds to 60 minutes to release lignin;   reducing the pressure in the reactor and removing the lignin containing material from the reactor; and   forming substantially all of the cellulose, hemicelluloses and lignin of the removed material into pellets or briquettes wherein the moisture content of the pellets or briquettes is less than the moisture content of the lignin containing material before being passed into the reactor.   
     
     
         2 . The method of  claim 1 , wherein the lignin containing material is lignocellulosic material, wood comprising material, wood, bamboo, bagasse, straw, or grass. 
     
     
         3 . The method of  claim 1 , wherein the lignin containing material is in the form of dust, saw dust, chips, splinters, coarse particles, chippings, shavings, or cuttings. 
     
     
         4 . The method of  claim 3 , wherein the coarse particles are cellulose chips. 
     
     
         5 . The method of  claim 4 , wherein the chips have a length of about 25 mm. 
     
     
         6 . The method of  claim 1 , wherein the lignin containing material is divided before passing into the reactor. 
     
     
         7 . The method of  claim 6 , wherein the length of the lignin containing material is less than about 3 mm. 
     
     
         8 . The method of  claim 1 , wherein the moisture content of the lignin containing material is reduced in the range of about 1-5% units of relative moisture of the lignin containing material. 
     
     
         9 . The method of  claim 1 , wherein the steam injected into the reactor is superheated at about 350° C. and about 20 bar. 
     
     
         10 . The method of  claim 1 , wherein the pellets or briquettes have a relative moisture content less than about 5% by weight. 
     
     
         11 . The method of  claim 1 , wherein the pellets or briquettes have an energy content of greater than about 5.0 MWh/tonne. 
     
     
         12 . The method of  claim 1 , wherein the material is dried to a relative moisture content of 5-15% by weight before it passes to the reactor. 
     
     
         13 . The method of  claim 1 , further comprising the step of:
 maintaining the removed material at substantially the same moisture level said removed material is at when removed from the reactor without any significant further wetting or drying of the material.   
     
     
         14 . The method of  claim 1 , further comprising the step of:
 drying the lignin containing material prior to heating the lignin containing material.   
     
     
         15 . The method of  claim 1 , further comprising the step of:
 passing the material, it has a moisture content of more than 20% by weight, to a drying step and drying it to a relative moisture content of 0-20% by weight prior to passing the lignin containing material to a heat treatment process.   
     
     
         16 . The method of  claim 1 , further comprising the step of:
 mixing the treated material with a lignin containing material.   
     
     
         17 . The method of  claim 15 , wherein the admixed lignin containing material has a moisture content of less than 18% by weight. 
     
     
         18 . The method of  claim 15 , wherein the admixed lignin containing material has a typical particle size of less than 2 mm. 
     
     
         19 . The method of  claim 1 , further comprising the step of:
 passing the pellets or briquettes to a cooler through which air is passed for a controlled cooling of the pellets or briquettes whereby the volume of fines is reduced.   
     
     
         20 . A lignin containing pellet or briquette utilized as a fuel source produced by the process, comprising the steps of:
 passing the lignin containing material having a moisture content less than about 30% by weight into a reactor;   heating the lignin containing material to 180-235° C. by injecting superheated steam into the reactor;   maintaining the material in the reactor within the range for at least 30 seconds to 60 minutes to release lignin;   reducing the pressure in the reactor and removing the lignin containing material from the reactor; and   forming substantially all of the cellulose, hemicelluloses and lignin of the removed material into pellets or briquettes wherein the moisture content of the pellets or briquettes is less than the moisture content of the lignin containing material before being passed into the reactor.