Method for manufacture of plant biomass solid fuel

Abstract

A solid fuel is formed in a cuber to form body pieces formed of materials extruded through a die with a density greater than 35 lbs/cu ft; an energy content greater than 6500 BTU/lb; transverse dimensions less than 1.5 inches; and a length less than 4 inches; from plant biomass material which contains components when extended of greater than 1.0 inch. Primarily the materials are paper or other cellulose product and crop residue such as wheat straw. The cellulose and lignin from these materials act without additional binders as binders and encasing materials. The moisture content is maintained at a target value by mixing selected quantities of the materials without drying. The cubing machine has a feeding system where the space between the inner rotor and outer casing is smaller than 4 inches and the height of the outer flight is less than 1 inch.

1 . A method for manufacturing solid fuel material for combustion comprising,
 providing a first shredded plant biomass material;   providing a second shredded plant biomass material;   mixing the first and second materials to form a mixed feed material;   compressing the mixed feed material into a series of dies so that the compressed feed material is extruded through the dies at a pressure sufficient to generate steam from moisture in the mixed feed material;   providing in the mixed feed a binding material activated by the steam such that the extruded material binds together to form a solid extruded stream;   separating the solid extruded stream into separate body pieces;   cooling the separate body pieces;   the mixed feed material prior to extrusion having a target moisture content in the range 10 to 25% and a maximum moisture content of 25%;   arranging the first shredded plant biomass material to have a moisture content less than the target moisture content;   the second shredded plant biomass material having a moisture content higher than the target moisture content;   and drying the second shredded plant biomass material from the higher moisture content such that the mixed feed material has a moisture content in the range 10 to 25%, substantially without drying by application of heat, by admixing the first plant biomass material with the second plant biomass material.   
   
   
       2 . The method according to  claim 1  wherein, when the amount of moisture in the second plant biomass material increases, the moisture content of the mixed feed material is maintained in the range by increasing the amount of the first plant biomass material in the mixed feed material. 
   
   
       3 . The method according to  claim 1  wherein, when the amount of moisture in the second plant biomass material decreases, the moisture content of the mixed feed material is maintained in the range by decreasing the amount of the first plant biomass material in the mixed feed material. 
   
   
       4 . The method according to  claim 1  wherein the target moisture content is of the order of 17%. 
   
   
       5 . The method according to  claim 1  wherein the first plant biomass material provides the binder and wherein the mixing of the first and second plant biomass material is arranged to maintain a quantity of the first plant biomass material above a predetermined minimum quantity despite increase of the moisture content above the target value. 
   
   
       6 . The method according to  claim 1  wherein the first plant biomass material comprises refined cellulose. 
   
   
       7 . The method according to  claim 6  wherein the material forming the refined cellulose is formed from steam exploded wheat and/or barley straw. 
   
   
       8 . The method according to  claim 6  wherein the material forming the refined cellulose is paper. 
   
   
       9 . The method according to  claim 1  wherein the first plant biomass material has a moisture content in the range 6 to 8%. 
   
   
       10 . The method according to  claim 1  wherein the cooling is effected by passing air through the body pieces for a cooling time sufficient that the body pieces are cooled to a temperature such that the binder is set. 
   
   
       11 . The method according to  claim 10  wherein the air is ambient unheated air. 
   
   
       12 . The method according to  claim 1  wherein the process is carried out substantially without application of external heat. 
   
   
       13 . The method according to  claim 10  including increasing the cooling time in the event that the moisture content of the mixed feed material exceeds the target value such that the moisture content of the body pieces exceeds a predetermined maximum allowable value. 
   
   
       14 . The method according to  claim 10  wherein the cooling time is maintained such that the moisture content of the body pieces after cooling is in the range 6 to 8%. 
   
   
       15 . The method according to  claim 1  wherein the compression is greater than 6000 psi so as to generate body pieces having a density greater than 35 lbs/cu ft. 
   
   
       16 . The method according to  claim 1  wherein the dies are arranged such that the extruded stream has dimensions in the transverse direction which are all less than 1.5 inches. 
   
   
       17 . The method according to  claim 1  wherein the first and second materials are shredded so as to contain at least some components which have a dimension when extended of greater than 1.0 inch. 
   
   
       18 . The method according to  claim 1  wherein the plant biomass material comprises a quantity of cellulose sufficient under heat and pressure to effect binding of the materials within the body pieces. 
   
   
       19 . The method according to  claim 1  wherein the plant biomass material comprises a quantity of lignin sufficient to generate an exterior casing around the peripheral surface of polymerized lignin. 
   
   
       20 . The method according to  claim 1  wherein the solid streams from the dies are separated such that substantially all of the body pieces have a length less than 2 inches. 
   
   
       21 . The method according to  claim 1  wherein the first and second materials consist essentially of plant biomass material selected when mixed to provide a quantity of cellulose sufficient to effect binding under heat and pressure of the materials within the body pieces and to include a quantity of lignin sufficient to generate an exterior casing formed from polymerized lignin. 
   
   
       22 . The method according to  claim 21  wherein the feed materials contain at least 10% by weight of cellulose. 
   
   
       23 . The method according to  claim 21  wherein the feed materials contain 0.5 to 5% by weight of lignin. 
   
   
       24 . The method according to  claim 1  wherein the feed materials contain comminuted components where the proportion of components having a dimension when extended of less 0.5 inches is less than 40%. 
   
   
       25 . The method according to  claim 1  wherein the compressed materials consist essentially of wheat and/or barley straw and a material forming a refined cellulose. 
   
   
       26 . The method according to  claim 1  wherein the pressure on the material in the die is greater than 6000 psi. 
   
   
       27 . A method for manufacturing solid fuel material for combustion comprising:
 providing a first shredded plant biomass material;   providing a second shredded plant biomass material;   mixing the first and second materials to form a mixed feed material;   the mixed feed material having a target moisture content in the range 10 to 25% and a maximum moisture content of 25%;   compressing the mixed feed material into a series of dies so that the compressed feed material is extruded through the dies at a pressure sufficient to generate steam from moisture in the mixed feed material;   providing in the mixed feed a binding material activated by the steam such that the extruded material binds together to form a solid extruded stream;   separating the solid extruded stream into separate body pieces;   cooling the separate body pieces by passing air through the pieces for a cooling time sufficient that the body pieces are cooled to a temperature such that the binder is set;   and increasing the cooling time in the event that the moisture content of the mixed feed material exceeds the target value so as to maintain the moisture content of the body pieces below a predetermined maximum allowable value.   
   
   
       28 . The method according to  claim 27  wherein the air is ambient unheated air. 
   
   
       29 . The method according to  claim 27  wherein the process is carried out substantially without application of external heat.