System and method for preparation of solid biomass by torrefaction

• US 20100242351A1
• Filed: 03/25/2010
• Published: 09/30/2010
• Est. Priority Date: 03/27/2009
• Status: Active Grant

• Current Assignee: Terra Green Energy LLC
• Original Assignee: Terra Green Energy LLC
• Inventors: Causer, Thomas P.
• Granted Patent: US 8,276,289 B2
• Time in Patent Office: Days
• US Class Current: 44/505
• CPC Class Codes: C10B 49/02 with hot gases or vapours, e.g. hot gases obtained by partial combustion of the charge
• CPC Class Codes: C10B 53/02 of cellulose-containing material production of pyroligneous acid C10C5/00
• CPC Class Codes: C10B 57/14 Features of low-temperature carbonising processes
• CPC Class Codes: C10L 5/44 on vegetable substances
• CPC Class Codes: C10L 9/083 Torrefaction
• CPC Class Codes: F23G 5/027 pyrolising or gasifying stage pyrolisation of sludge C02F11/00; destructive distillation of carbonaceous materials C10B53/00
• CPC Class Codes: F23G 5/04 drying
• 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

Abstract

Methods and systems for preparing a torrefied biomass fuel are disclosed. Moisture is initially extracted from relatively wet biomass fuel to produce a relatively dry biomass fuel. Remaining moisture is then extracted from the relatively dry biomass fuel in a final drying stage, using steam at a temperature of about 900° F. The resulting dried biomass fuel is conveyed downward using gravity and undergoes torrefaction, which produces torrefied biomass fuel and torrefaction gases. A gaseous mixture of steam and torrefaction gases is vented to a heat exchanger, where the gaseous mixture is heated by a flue gas, and the heated gaseous mixture is used to support the extraction of the remaining moisture in the final drying stage and to support the torrefaction of the dried biomass fuel. Embodiments disclosed herein efficiently use available energy resources to the benefit of manufacturers, consumers, and the environment.

Claims

1. A method for preparing a torrefied biomass fuel, the method comprising:

extracting moisture from a relatively wet biomass fuel in a dryer to produce a relatively dry biomass fuel;

extracting all remaining moisture from the relatively dry biomass fuel using steam at a temperature of about 482°

C. (900°

F.) to produce a dried biomass fuel;

conveying the dried biomass fuel downward using gravity for subsequent processing;

torrefying the dried biomass fuel to produce the torrefied biomass fuel and torrefaction gases;

venting a gaseous mixture of the steam and the torrefaction gases to a heat exchanger;

heating the gaseous mixture via heat exchange with a flue gas; and

using the heated gaseous mixture to support the extraction of the remaining moisture from the relatively dry biomass and the torrefaction of the dried biomass fuel.

2. The method of claim 1, additionally including combusting a portion of the gaseous mixture to produce the flue gas.

3. The method of claim 2, additionally including providing the flue gas, cooled by transfer of heat to the gaseous mixture, to the dryer for moisture extraction.

4. The method of claim 2, further including combusting a portion of the relatively wet biomass fuel in a lower chamber of a combustion unit to support combustion of the gaseous mixture in an upper chamber of the combustion unit.

5. The method of claim 4, further including maintaining the combusted biomass in an upper chamber of the combustion unit for sufficient time to eliminate all organic compounds, particulates, and other hydrocarbons resulting from the combustion of the biomass.

6. The method of claim 4, further including combusting a gaseous supplemental fuel in the upper chamber to provide additional thermal energy for combustion of the gaseous mixture.

7. The method of claim 1, further including controlling flow of the heated gaseous mixture into an upper chamber of a torrefaction reactor and into a second chamber of a torrefaction reactor to maintain the upper chamber at about 482°

C. (900°

F.) and the lower chamber between about 250°

C.-300°

C. (482°

F.-572°

F.).

8. The method of claim 4, further including maintaining the lower chamber of the torrefaction reactor at a lower pressure than the upper chamber.

9. The method of claim 1, wherein extracting moisture from the relatively wet biomass fuel includes extracting about 80% of the moisture.

10. A torrefaction system comprising:

a dryer configured to dry a relatively wet biomass fuel and provide a relatively dry biomass fuel;

a torrefaction reactor comprising;

an upper chamber configured to remove all moisture from the relatively dry biomass fuel in an environment containing steam at a temperature of about 482°

C. (900°

F.), and

a lower chamber configured to torrefy dried biomass produced by the upper chamber at a temperature between about 250°

C.-300°

C. (482°

F.-572°

F.);

a combustion unit configured to combust a portion of a gaseous mixture of steam and torrefaction gases vented by the torrefaction reactor to produce a flue gas; and

a heat exchanger configured to exchange heat from the flue gas to the gaseous mixture to provide a heated gaseous mixture for provision to the torrefaction reactor.

11. The torrefaction system of claim 10, wherein the torrefaction reactor further includes a segregation barrier configured to maintain different thermal profiles in the upper chamber and the lower chamber.

12. The torrefaction system of claim 11, wherein the segregation barrier is further configured to enable co-current flow of gases from the upper chamber of the torrefaction reactor to the lower chamber.

14. The torrefaction system of claim 10, wherein the combustion unit comprises:

an upper chamber configured to combust the gaseous mixture and a supplemental fuel to produce the flue gas; and

a lower chamber configured to combust a portion of the relatively wet biomass fuel to support production of the flue gas in the upper chamber.

15. The torrefaction system of claim 14, wherein the temperature in the upper chamber is about 871°

C. (1600°

F.).

16. The torrefaction system of claim 10, wherein the dryer is a triple pass rotary drum dryer.

17. The torrefaction system of claim 16, wherein the dryer is configured to remove about 80% of the moisture from the relatively wet biomass fuel.

13. The torrefaction system of claim 13, wherein the torrefaction reactor further comprises entry ports coupled to a damper system, the damper system configured to supply and maintain a gas mixture temperature into the upper chamber to remain at about 482°

C. (900°

F.) and the temperature in the lower chamber to between about 250°

C.-300°

C. (482°

F.-572°

F.).