Method of Drying Biomass

Abstract

A process for torrefaction of biomass is provided in which biomass are passed into a fluidized bed reactor and heated to a predetermined temperature in an oxidizing environment. The dried biomass is then fed to a cooler where the temperature of the product is reduced to approximately 100 degrees Fahrenheit.

1 . A single stage process for biomass torrefaction, comprising:
 charging biomass to a fluidized bed reactor, charging air to said fluidized bed reactor at a velocity of from about 4 to about 8 feet per second, subjecting said biomass to a temperature of from about 230 to about 350 degrees Centigrade, and removing the water from said biomass by torrefying said biomass, wherein:
 said biomass charged to said fluidized bed reactor has an average moisture content of from about 10 to about 50 percent, 
 said fluidized bed reactor is comprised of a fluidized bed with a fluidized bed density of from about 20 to about 50 pounds per cubic foot, whereby a dried, torrefied biomass is produced. 
   
     
     
         2 . The process of  claim 1 , wherein said biomass charged to said fluidized bed reactor has a minimum dimension of 3 mm to 10 mm. 
     
     
         3 . The process of  claim 1 , wherein said biomass charged to said fluidized bed reactor is wood, plant material or agricultural waste. 
     
     
         4 . The process of  claim 1 , wherein said biomass in said fluidized bed reactor is maintained at said temperature of from about 230-350 degrees Centigrade. 
     
     
         5 . The process of  claim 1 , wherein said fluidized bed is maintained at a fluidized bed density of from about 20 to about 50 pounds per cubic foot. 
     
     
         6 . The process of  claim 1 , wherein said biomass has a residence time in the reactor of 2 to 5 minutes. 
     
     
         7 . The process of  claim 1 , further comprising the step of heating said air prior to the time it is fed into said fluidized bed reactor using heat recovered from heated gas taken from said fluidized bed reactor. 
     
     
         8 . The process of  claim 1  wherein said cooler employs at least one of a mixing screw conveyor, hollow flight screw conveyor, a rotary drum and a rotary tube. 
     
     
         9 . The process of  claim 1 , further comprising:
 feeding said dried biomass into a cooler where it is cooled to a temperature near 100 degrees Centigrade and adding no more than 3% moisture to the dried biomass.   
     
     
         10 . The process of  claim 1 , wherein said cooler comprises at least one water spray and at least one temperature sensor to allow water to be applied to the biomass for at least one of progressively lowering the temperature of the biomass to less about 100 degrees Centigrade and adding up to 3 percent moisture to the biomass. 
     
     
         11 . The process of  claim 10  wherein the application of water is continuous. 
     
     
         12 . The process of  claim 10  wherein the application of water is intermittent. 
     
     
         13 . The process of  claim 1 , wherein said reactor comprises at least one water spray to aid in the control of reactor temperature. 
     
     
         14 . The process of  claim 13  wherein the application of water is continuous. 
     
     
         15 . The process of  claim 13  wherein the application of water is intermittent. 
     
     
         16 . A process for drying a material, comprising:
 directing the material to a fluidized bed reactor;   predrying the material with gasses exhausted from the fluidized bed reactor; and   subjecting said material within the fluid bed reactor to a temperature sufficient to torrefy the material and remove water therefrom.   
     
     
         17 . The process of  claim 16 , further comprising:
 adding fresh air to said fluidized bed reactor to adjust the oxygen content of the gasses within the fluidized bed reactor.   
     
     
         18 . The process of  claim 16  wherein said material is at least one of biomass and coal. 
     
     
         19 . The process of  claim 16  wherein said fluidized bed reactor has an aspect ratio is no greater than about 2. 
     
     
         20 . The process of  claim 16  further comprising directing heated air to the fluidized bed reactor with a startup heater.