Staged biomass pyrolysis process and apparatus

Abstract

A biomass pyrolysis process in which biomass feedstock particles (having a d5o mean particle size of at least 1 mm) are thermally treated substantially in the absence of oxygen to pyrolyse the biomass feedstock particles. The thermal treatment of the biomass feedstock particles includes a heat treatment drying step at a temperature in the range 100° C. to 250° C. Then, at a pre-pyrolysis heating location in a heat treatment system, the biomass feedstock particles are heated to a temperature in the range 280° C. to 350° C., held within the same temperature range for a time of at least 5 seconds and then moved from the pre-pyrolysis heating location to a pyrolysis heating location by a conveyor system for heating to a temperature above 350° C. for pyrolysis.

1 . A biomass pyrolysis process in which biomass feedstock particles are thermally treated substantially in the absence of oxygen to pyrolyse the biomass feedstock particles, wherein the thermal treatment of the biomass feedstock particles includes a step in which at least 50% of the mass of the biomass feedstock particles is heated to a temperature in the range 280° C. to 350° C., held within the same temperature range for a time of at least 5 seconds and then heated to a temperature above 350° C. for pyrolysis, the biomass feedstock particles having a d 50  mean particle size of at least 1 mm, wherein d 50  denotes a number length mean particle size such that 50% of particles have volume smaller than a sphere of diameter d 50  and 50% of particles have volume larger than a sphere of diameter d 50 . 
     
     
         2 . A biomass pyrolysis process according to  claim 1  wherein the biomass feedstock particles are subjected to a heat treatment drying step at a temperature in the range 100° C. to 250° C., before being heated to the temperature in the range 280° C. to 350° C. 
     
     
         3 . A biomass pyrolysis process according to  claim 1  wherein when the biomass feedstock particles are subjected to pyrolysis at a temperature in the range 350° C. to 550° C. 
     
     
         4 . A biomass pyrolysis process according to  claim 1  wherein in the step in which at least 50% of the mass of the biomass feedstock particles is heated to a temperature in the range 280° C. to 350° C. and held within the same temperature range for a time t 280-350 , the following relationship is satisfied:
   t 280-350 ≧Cd 50  
 
 
       in which d 50  is the number length mean particle size in metres and C is a constant and is at least  5000  seconds per metre. 
     
     
         5 . A biomass pyrolysis process according to  claim 1  wherein the biomass feedstock particles are heated to the temperature in the range 280° C. to 350° C. at a pre-pyrolysis heating location in a heat treatment system and subsequently the biomass feedstock particles are heated to the temperature above 350° C. for pyrolysis at a pyrolysis heating location in the heat treatment system. 
     
     
         6 . A biomass pyrolysis process according to  claim 5  wherein the biomass feedstock particles are moved between the pre-pyrolysis heating location and the pyrolysis heating location by a conveyor system. 
     
     
         7 . A biomass pyrolysis process according to  claim 5  wherein the biomass feedstock particles are moved between the pre-pyrolysis heating location and the pyrolysis heating location substantially without reduction in temperature. 
     
     
         8 . A biomass pyrolysis process according to  claim 5  wherein the conveyor system is a screw or auger. 
     
     
         9 . A biomass pyrolysis process according to  claim 5  wherein the pre-pyrolysis heating location and the pyrolysis heating location are parts of a heat treatment kiln, at different temperatures. 
     
     
         10 . A biomass pyrolysis process according to  claim 5  wherein the conveyor system conveys the biomass feedstock particles at a substantially uniform rate, the residence time of the biomass feedstock particles in the pre-pyrolysis heating location and the pyrolysis heating location being determined by the spatial extent of the pre-pyrolysis heating location and the spatial extent of the pyrolysis heating location, and on the rate of conveyance of the biomass feedstock particles. 
     
     
         11 . A biomass pyrolysis process according to  claim 1  wherein in the step in which at least 50% of the mass of the biomass feedstock particles is held within the same temperature range for a time of at least 5 seconds, the temperature range is 280° C. to 320° C. 
     
     
         12 . A biomass pyrolysis apparatus for thermal treatment of biomass feedstock particles substantially in the absence of oxygen to pyrolyse the biomass feedstock particles, the apparatus providing a pre-pyrolysis heating location for heating the biomass feedstock particles to a temperature in the range 280° C. to 350° C. and for holding the temperature of the biomass feedstock particles in the range 280° C. to 350° C. for at least 5 seconds, the apparatus further providing a pyrolysis heating location for subsequently heating the biomass feedstock particles to a temperature above 350° C. for pyrolysis. 
     
     
         13 . A biomass pyrolysis apparatus according to  claim 12  wherein the pre-pyrolysis heating location and the pyrolysis heating location are parts of a heat treatment kiln, at different temperatures. 
     
     
         14 . A biomass pyrolysis apparatus according to  claim 13  further providing a conveyor system for moving the biomass feedstock particles between the pre-pyrolysis heating location and the pyrolysis heating location. 
     
     
         15 . A biomass pyrolysis apparatus according to  claim 14  wherein the conveyor system is a screw or auger. 
     
     
         16 . A biomass pyrolysis apparatus according to  claim 14  wherein the biomass feedstock particles are moved between the pre-pyrolysis heating location and the pyrolysis heating location substantially without reduction in temperature. 
     
     
         17 . A biomass pyrolysis apparatus according to  claim 14  wherein the conveyor system conveys the biomass feedstock particles at a substantially uniform rate, the residence time of the biomass feedstock particles in the pre-pyrolysis heating location and the pyrolysis heating location being determined by the spatial extent of the pre-pyrolysis heating location and the spatial extent of the pyrolysis heating location, and on the rate of conveyance of the biomass feedstock particles. 
     
     
         18 . A biomass pyrolysis apparatus according to  claim 12  further providing a heat carrier recycling system for at least partial recycling of heat carrier material from the pre-pyrolysis heating stage and/or from the pyrolysis heating stage to one or more of the pre-pyrolysis heating stage and the pyrolysis heating stage.