Pretreatment of fiberous biomass

Abstract

A conventional agricultural “cuber” machine was modified to transform fibrous, low density cellulosic biomass into a mechanically stable form suitable for use as a feed stock to a bulk flow torrefier process without requiring the addition of a “binder” or other such adjuvant. Certain disclosed embodiments of the product concern a compact “cube” or “thin puck” of raw cellulosic biomass having a density of from 4 to 15 times the bulk density of the shredded raw biomass or from 20 to 32 lb/cu ft. The moisture content is below 10%, typically 3-8%. The strength of the product as measured by dropping the product onto a hard surface from a height of 3 ft. will not produce more than 10% breakage. The products of the present invention can be produced having any desirable dimensions, such as substantially square-, rectangular- or parallelogram-shaped product having at least one dimension of from about 5 to about 30 millimeters, which corresponds to the dimension of the die 2 in FIG. 2. The length of each extrudate is determined by the angle of the deflector plate 1 in FIG. 2.

We claim: 
     
         1 . A method, comprising:
 providing biomass; and   processing the biomass to produce a mechanically stable puck suitable for use as a torrefaction feed stock without requiring a binder.   
     
     
         2 . The method according to  claim 1 , comprising processing the biomass using a cuber comprising a rotating press wheel that forces low density, fibrous feed stock into a straight or tapered die that forms the puck, wherein the puck has a relatively uniform size and a density substantially higher than the feed stock. 
     
     
         3 . The method according to  claim 2  wherein the biomass has an initial density of 1-2 lb/ft 3 . 
     
     
         4 . The method according to  claim 3  wherein the puck comprises raw cellulosic biomass having a density of from 4 to 15 times the bulk density of the shredded raw biomass. 
     
     
         5 . The method according to  claim 4  wherein the puck has a density of from 20 to 32 lb/ft 3 . 
     
     
         6 . The method according to  claim 2  wherein the cuber comprises:
 a controller to provide a controlled extrusion length for thin pucks produced by the process; and 
 a temperature controller to control the temperature of the dies to a a temperature of from about 70° C. to about 150° C. 
 
     
     
         7 . The method according to  claim 1  wherein the moisture content of the puck is less than 25%. 
     
     
         8 . The method according to  claim 7  wherein the moisture content of the puck is from about 3% to about 10%. 
     
     
         9 . The method according to  claim 4  wherein the density of the puck is from 20 to 32 lb/ft 3  and the moisture content is from 3% to 8%. 
     
     
         10 . The method according to  claim 1  wherein the puck has a substantially square, rectangular or parallelogram shape having dimensions corresponding to the dimensions of the die. 
     
     
         11 . The method according to  claim 1 , further comprising:
 using the puck as a feed stock for a torrefaction reactor; and   torrefying the mechanically stable form.   
     
     
         12 . The method according to  claim 11 , comprising:
 converting the puck to a feed stock having a smaller size than the puck;   optionally drying the feed stock using a continuous direct air heated dryer to provide a dried feed stock having a controlled residual moisture content of 25 wt % or less based on total weight of the biomass;   feeding the dried feed stock to a torrefier to produce a torrefied product;   cooling the torrefied product; and   discharging cooled torrefied product from the torrefier.   
     
     
         13 . The method according to  claim 12 , further comprising:
 milling the cooled torrefied product to a smaller size suitable for densification; and   densifying milled, torrefied product to produce a torrefied, high density fuel.   
     
     
         14 . A method, comprising:
 providing a product made according to  claim 1 ; and   using the product as a torrefaction feed stock.   
     
     
         15 . A method, comprising:
 providing a product made according to  claim 11 ; and   using the product as a fuel.   
     
     
         16 . A product, produced according to the method of  claim 1 . 
     
     
         17 . A torrefied product, produced according to the method of  claim 11 .