Method of drying biomass

• US 8,956,426 B2
• Filed: 04/12/2011
• Issued: 02/17/2015
• Est. Priority Date: 04/20/2010
• Status: Active Grant

• Current Assignee: Biomass Secure Power Inc.
• Original Assignee: River Basin Energy, Inc. (Biomass Secure Power Inc.)
• Inventors: Sethi, Vijay, Camper, Clinton B.
• Primary Examiner(s): McAvoy, Ellen
• Assistant Examiner(s): Po, Ming Cheung
• Application Number:
  US13/084,697
• Publication Number:
  US 20120023813A1
• Time in Patent Office: 1,407 Days
• Field of Search: 446/05
• US Class Current: 44/605
• CPC Class Codes: C10B 49/10 according to the "fluidised bed" technique
• CPC Class Codes: C10B 53/02 of cellulose-containing material production of pyroligneous acid C10C5/00
• CPC Class Codes: C10L 5/447 Carbonized vegetable substances, e.g. charcoal, or produced by hydrothermal carbonization of biomass
• CPC Class Codes: C10L 9/083 Torrefaction
• CPC Class Codes: Y02E 50/10 Biofuels, e.g. bio-diesel
• CPC Class Codes: Y02E 50/30 Fuel from waste, e.g. synthetic alcohol or diesel
• CPC Class Codes: Y02P 20/145 the feedstock being materials of biological origin

Abstract

A process for torrefaction of biomass is provided in which biomass are passed into a fluidized bed or a non-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.

Claims

1. A process for biomass torrefaction, comprising:

adding biomass to a reactor;

adding a first gas to said reactor, wherein the first gas comprises an oxygen concentration from about 10 vol % to about 21 vol %;

controlling an oxygen concentration of a second gas exiting said reactor, wherein said oxygen concentration of the second gas is less than about 8 vol %;

initiating heating of said biomass by increasing a temperature of said reactor;

heating said biomass to a biomass temperature between about 250°

C. to about 325°

C. by partial combustion of said biomass with oxygen in the first gas in said reactor; and

maintaining the biomass temperature within said reactor for a predetermined time by spraying water into said reactor, whereby

a portion of moisture is removed from said biomass,

volatile organic compounds associated with said biomass are removed,

and said biomass is torrefied to produce a torrefied biomass with a moisture content from about 0 wt % to about 2 wt %.

2. The process of claim 1, wherein said biomass is not primarily heated by external sources after said initiating step.

3. The process of claim 1, wherein said biomass has an average moisture content of from about 10% to about 50% and said reactor is not fluidized.

4. The process of claim 1, wherein a pressure within said reactor is near ambient.

5. The process of claim 1, further comprising chipping said biomass to a maximum size of about 1.5 in.×

1.5 in.×

0.4 in. before said biomass is heated.

6. The process of claim 1, further comprising pelletizing the torrefied biomass to a maximum size of about 1.5 in.×

1.5 in.×

0.4 in.

7. The process of claim 1, wherein said initiating step entails raising the temperature of said reactor by a startup procedure comprising:

providing a starting heater;

slowly increasing heat within said reactor with said starting heater;

feeding said biomass to said reactor when the temperature of said reactor is between about 275°

C. to 315°

C.;

releasing heat by combustion of said biomass; and

adding small amounts of said torrefied biomass to said reactor to maintain a steady rise in temperature.

8. The process of claim 1, wherein said biomass added to said reactor has a minimum dimension of between 3 mm to 10 mm.

9. The process of claim 1, wherein said biomass comprises at least one of wood, plant material, and agricultural waste.

10. The process of claim 1, wherein said predetermined time is between about 5 to 30 minutes.

11. The process of claim 1, further comprising heating the first gas added to said reactor before feeding the first gas to said reactor using heat from the second gas exiting said reactor.

12. The process of claim 1, further comprising cooling the torrefied biomass with a cooler that includes at least one of a mixing screw conveyor, hollow flight screw conveyor, a rotary drum, and a rotary tube.

13. The process of claim 1, wherein substantially all sulfur is removed from said biomass.

14. The process of claim 1, wherein at least about 70% of chlorine found in said biomass is removed.

15. The process of claim 1, wherein the temperature of said reactor is controlled by a feed rate of said biomass and said spraying of water directly into said reactor.

16. The process of claim 1, wherein the temperature of said reactor is controlled by the oxygen concentration of the first gas added to said reactor.

17. The process of claim 1, wherein said reactor is a fluidized bed reactor.

18. The process of claim 1, wherein said biomass has an average moisture content of from about 10% to about 50% and said reactor is comprised of a fluidized bed with a fluidized bed density of from about 5 to about 30 pounds per cubic foot.

19. The process of claim 17, wherein the first gas is added to said fluidized bed reactor at a velocity from about 4 to about 8 feet per second.

20. The process of claim 19, wherein the first gas added to said fluidized bed reactor is sufficient to produce the torrefied biomass, such that the torrefied biomass has less than about 10 wt % moisture and possesses at least about 80% of the energy content of said biomass added to said fluidized reactor.

21. The process of claim 1, further comprising:

feeding the torrified biomass into a cooler where the torrified biomass is cooled to a temperature near 100°

C. by adding no more than about 3 wt. % moisture to the dried biomass.

22. The process of claim 21, wherein said cooler comprises at least one water spray and at least one temperature sensor to allow water to be selectively applied to the torrified biomass.

23. The process of claim 22 wherein the at least one water spray is intermittent.

24. The process of claim 17, wherein said fluidized bed reactor has an aspect ratio is no greater than about 2.

25. The process of claim 1, wherein said biomass and coal are added to said reactor.

26. The process of claim 1, wherein said biomass is selected from the group consisting of wood, forestry waste, energy crops, municipal waste, plant materials, agricultural waste, and combinations thereof.

27. The process of claim 17, wherein said fluidized bed is maintained at a fluidized bed density of from about 20 to about 50 pounds per cubic foot.

28. The process of claim 1, wherein said biomass has a residence time in said reactor of 2 to 5 minutes.

29. The process of claim 17, wherein said fluidized bed reactor has an aspect ratio is no greater than about 2.

30. The process of claim 1, further comprising modifying a feed rate of said biomass to selectively control the temperature of said reactor.

31. The process of claim 21, wherein said cooler comprises:

at least one water spray to allow water to be applied to the torrified biomass for at least one of progressively lowering the temperature of said torrified biomass to less than about 100°

C. and adding up to 3 wt. % moisture to said torrefied biomass; and

at least one temperature sensor.

32. A single stage process for biomass torrefaction, comprising:

charging biomass to a fluidized bed reactor, said biomass selected from the group consisting of wood, forestry waste, energy crops, municipal waste, plant material, straw, agricultural waste, and combinations thereof;

charging a fluidizing gas to said fluidized bed reactor at a velocity of from about 4 to about 8 feet per second;

combusting an amount of said biomass in said fluidized bed reactor;

spraying liquid water into said fluidized bed reactor to assist with control of a temperature of said fluidized bed reactor from about 230°

C. to about 350°

C.;

maintaining an oxygen content of less than about 15 vol. % in an exiting gas leaving said fluidized bed reactor;

removing moisture from said biomass, wherein said biomass charged to said fluidized bed reactor has an average moisture content of from about 10% to about 50%, and

wherein 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 torrefied biomass is produced.

33. The process of claim 32, wherein said biomass charged to said fluidized bed reactor has a minimum dimension of 3 mm to 10 mm.

34. The process of claim 32, wherein said biomass charged to said fluidized bed reactor is wood, plant material, straw, or agricultural waste.

35. The process of claim 32, wherein said fluidized bed is maintained at a fluidized bed density of from about 20 to about 50 pounds per cubic foot.

36. The process of claim 32, wherein said biomass has a residence time in said fluidized bed reactor of 2 to 5 minutes.

37. The process of claim 32, further comprising heating said fluidizing gas to form a heated fluidizing gas before feeding said heated fluidizing gas into said fluidized bed reactor using heat recovered from said heated fluidizing gas taken from said fluidized bed reactor.

38. The process of claim 32, further comprising a cooler that employs at least one of a mixing screw conveyor, hollow flight screw conveyor, a rotary drum and a rotary tube.

39. The process of claim 32, wherein the liquid water is sprayed into said fluidized bed reactor continuously.

40. The process of claim 32, wherein the liquid water is sprayed into said fluidized bed reactor intermittently.

41. The process of claim 32, wherein an amount of heat released by the combustion of said biomass is balanced by an amount of heat required to accomplish drying of said biomass and torrefaction of said biomass added to said fluidized bed reactor.

42. The process of claim 32, further comprising modifying a feed rate of said biomass to selectively control the temperature of said fluidized bed reactor.

43. The process of claim 32, further comprising:

feeding said torrefied biomass into a cooler and cooling said torrefied biomass to a temperature near 100°

C. and adding no more than 3 wt. % moisture to the torrefied biomass.

44. The process of claim 43, wherein said cooler comprises:

at least one water spray to allow water to be applied to the torrified biomass for at least one of progressively lowering the temperature of said torrified biomass to less than about 100°

C. and adding up to 3 wt. % moisture to said torrefied biomass; and

at least one temperature sensor.

45. The process of claim 44 wherein the water is applied continuously.

46. The process of claim 44 wherein the water is applied intermittently.

47. The process of claim 32, wherein said biomass and coal are directed to the fluidized bed reactor.