WO2008008296A2

WO2008008296A2 - Feed system

Info

Publication number: WO2008008296A2
Application number: PCT/US2007/015635
Authority: WO
Inventors: Bertil Stromberg; Lawrence Joseph Nemeth; Thomas Pschorn
Original assignee: Andritz Inc
Current assignee: Andritz Inc
Priority date: 2006-07-11
Filing date: 2007-07-09
Publication date: 2008-01-17
Anticipated expiration: 2009-01-11
Also published as: WO2008008296A3; WO2008008295A3; WO2008008295A2; WO2008008296A8

Abstract

A gasifier feed system includes a buffer assembly that receives material, such as comminuted cellulosic material to be fed to a gasifier and includes structure that pre-processes the material for delivery to the gasifier. A source of pressurized inert gas is coupled with the buffer assembly. A rotary valve is positioned relative to the buffer assembly to receive the material from the buffer assembly. The rotary valve conveys the material to the gasifier and includes a gas lock that prevents gas from escaping the gasifier.

Description

TITLE OF THE INVENTION

FEED SYSTEM

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent

Application Serial No. 60/819,646, filed July 11 , 2006 and U.S. Provisional Patent Application Serial No. 60/908,495, filed March 28, 2007, the entire contents of which are herein incorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] (NOT APPLICABLE)

BACKGROUND OF THE INVENTION

[0003] The invention relates generally to feed systems and, more particularly, to a feed system for feeding comminuted cellulosic material to a pressurized gasifier.

[0004] The byproducts of an industrial plant process, such as those of a paper mill, can be used to produce fuel and/or electrical power using a gasifier. Feed material introduced into the gasifier is combusted at high temperatures. The contents of the gasifier are explosive and/or corrosive in nature and must be contained within the gasifier during normal operations and during startup and shut down of the gasifier. It is important that contents from the gasifier are prevented from entering upstream components that feed material to the gasifier. [0005] Existing feed systems require batch feeding arrangements using multiple hatches to contain the gasifier contents or large alternating valve arrangements combined with pressurized feed-hoppers or the like. Such arrangements are expensive to manufacture and inefficient to operate.

BRIEF SUMMARY OF THE INVENTION

[0006] It would thus be desirable to provide a feed system and method that more efficiently processes cellulosic material and/or other waste products for delivery to a gasifier. The feed system described herein includes structure that feeds the material while preventing the contents of the gasifier from coming in contact with upstream components and from escaping to the atmosphere.

[0007J In an exemplary embodiment, a gasifier feed system includes a buffer assembly that receives material, such as comminuted cellulosic material to be fed to a gasifier and includes structure that pre-processes the material for delivery to the gasifier. A source of pressurized inert gas is coupled with the buffer assembly. A rotary valve is positioned relative to the buffer assembly to receive the material from the buffer assembly. The rotary valve. conveys the material to the gasifier and includes a gas lock that prevents gas from escaping the gasifier.

[0008] In another exemplary embodiment, the gasifier feed system includes a buffer bin positioned to receive material to be fed to a gasifier, a plug screw feeder disposed in communication with the buffer bin and receiving the material from the buffer bin to form a plug of the material, and a screw transfer conveyor disposed in communication with the plug screw feeder and receiving the material plug from the plug screw feeder to provide a buffer volume of the material. A source of inert gas is coupled with the screw transfer conveyor, preferably adjacent an entry for the material plug, which source introduces pressurized inert gas into the screw transfer conveyor. A rotary valve, which may be a wet feeder or a dry feeder, is positioned relative to the screw transfer conveyor to receive the material from the screw transfer conveyor. The rotary valve conveys the material to the gasifier and includes a gas lock that prevents gas from escaping the gasifier. [0009] A back stop may he disposed at a downstream end of the plug screw feeder for closing off the plug screw feeder from downstream equipment. Additionally, a source of steam may be coupled with the buffer bin for adding steam to the material. The system may also include drying units disposed upstream of the buffer bin and/or between the screw transfer conveyor and the rotary valve.

[0010] In yet another exemplary embodiment of the invention, a method of feeding a comminuted cellulosic material to a gasifier includes the steps of (a) receiving the cellulosic material in a buffer bin; (b) feeding the cellulosic material to a plug screw feeder disposed in communication with the buffer bin and forming a plug of the cellulosic material; (c) conveying the material plug to a screw transfer conveyor and providing a buffer volume of the cellulosic material; (d) introducing inert gas into the screw transfer conveyor; (e) transferring the cellulosic material to a rotary valve from the screw transfer conveyor; and (f) conveying with the rotary valve the cellulosic material to the gasifier while preventing gas from escaping the gasifier.

BRIEF DESCRIPTION OF THE DRAWINGS

[001 IJ These and other aspects and advantages of the present invention will be described in detail with reference to the accompanying drawings, in which:

[0012] FIGURE 1 is an exemplary schematic illustration of a gasifier feed system; and

[0013] FIGURE 2 is an exemplary schematic illustration of a gasifier feed system, including one or more dryers. DETAILED DESCRIPTION OF THE INVENTION

[0014] FIG. 1 is an exemplary schematic illustration of a feed system for feeding comminuted cellulosic material to a pressurized gasifier. Wood chips or other comminuted cellulosic fibrous material are conveyed from a storage silo or pile 1 to a buffer bin 2. The buffer bin 2 may be a chip bin such as the DIAMONDBACK ^® chip bin sold by Andritz Inc. of Glens Falls, New York or other similar chip bin. The chip bin 2 may include a source of steam such that steam may be added to the cellulosic material. The steam source is optional. [0015] From the buffer bin 2, the cellulosic material is fed to a plug screw feeder 3. Any type of known plug screw feeder may be utilized. Once in the screw feeder 3, a plug of the cellulosic material is formed and is moved toward a discharge end 4 of the screw feeder 3. A back stop or blowback valve (blowback damper) 5 is disposed adjacent the discharge end of the plug screw feeder 3. The back stop 5 serves to close off the plug screw feeder 3 from downstream equipment if the flow of material or density of the plug inside the plug screw feeder 3 is lost. That is, the back stop 5 comprises a preloaded valve or cone that closes the feeder in the event of a pressure drop in the feeder. The back stop 5 serves to prevent the escape of any gas from the gasifier into the atmosphere or other equipment upstream of the gasifier. [0016] The plug screw feeder 3 may be designed with holes or slots in the screw-housing/basket or the following spool piece to squeeze-out water/moisture (to increase the dry-content of the feed material), extractives and/or other volatile components, thus simplifying the gas cleaning process after the gasifier.

[0017] The plug of cellulosic material formed in the plug screw feeder 3 is discharged into a screw transfer conveyor 6. At the feed end 7 of the screw transfer conveyor 6 where the material plug enters the screw transfer conveyor 6, a continuous flow of inert gas (such as nitrogen, argon, carbon dioxide, and/or any other non-dangerous gas) is introduced from an inert gas source 8 to the screw transfer conveyor 6. This continuous flow of inert gas 8 is provided at a higher pressure than the pressure in the gasifier, thereby providing a continuous purging of the screw transfer conveyor 6 to keep any dangerous gases from escaping from the gasifier into the atmosphere or to the conveyor 6 or to the plug screw feeder 3. Rather, due to the higher pressure gas supply, in the event of any exposure of the gasifier entrance, the harmless inert gas flows into the gasifier, and the gasifier contents are prevented from escaping. In the screw transfer conveyor 6, the material plug is broken up for further processing.

[0018] The screw transfer conveyor 6 provides a buffer volume of cellulosic material upstream of a rotary valve 9. The rotary valve 9 provides for conveyance of the cellulosic material into the gasifier 10 as well as providing a gas-lock to prevent the escape of gases from the gasifier 10 and mixing with the cellulosic material while it is a plug. Any known rotary valve suitable for this purpose may be used. The rotary valve can be a wet or dry feeder such as a "Bauer Rotary Valve" or a low pressure feeder available from Andritz Inc.

[0019] The inert gas 8 could be used to purge the rotor of the rotary valve 9. The gasses would be purged into the gasifier 10. In light of the high pressure inert gas (i.e., a pressure higher than a pressure in the gasifier), the rotary feeder serves to keep mixing of the gasifier contents and conveyor to a minimum, should the screw transfer conveyor lose its pressure holding capability.

[0020] The cellulosic material is conveyed from the rotary valve 9 and enters the gasifier 10.

[0021] FIG. 2 shows an alternative feed system including one or more dryers 12. As shown, a dryer 12 may be disposed upstream of the buffer bin 2 and/or between the screw transfer conveyor 6 and the rotary valve 9. The dryer(s) 12 may be vertical or horizontal dryers and serve to extract moisture from the feed material prior to delivery to the gasifier 10 and/or to de-volatize the feed material into the gasifier.

[0022] Moreover, with continued reference to FIG. 2, in the gasifier feed arrangement, there is a volatile extraction and moisture conditioning due to the high compression generated in the plug screw feeder 3. The feed material can be wood chips, wood waste, saw dust and shavings, annual fiber residual and other cellulosic feed material. With the drying units 12, the feed material may be dried before being fed to the plug screw feeder 3. The plug screw feeder 3 or similar device (cylindrical with increasing root diameter screw or conical screw and housing) provides a pressure seal by forming a solid plug of feed material (plug or pipe shape at discharge of unit).

[0023 J The unit may include a perforated screen or bar cage in the compression housing to squeeze and extract, for example, wood extractives such as pitch, turpentine, tannin and other extractives as well as volatile compounds that can be collected for a controlled removal (concentrated effluent stream) and/or can be collected for recovery. This arrangement serves to increase the uniformity of the feed material (i.e., bulk density, size, moisture etc.), and increases dryness to make the moisture content more uniform and condition the feed material.

[0024] The plug screw feeder 3 can be driven by a constant or variable speed drive. The discharge from the feeder 3 goes into a spool piece, pipe or similar device such as the transfer conveyor 6, which may also include a blowback damper. Water or chemicals may be injected at discharge/spool piece or the following connection pipe. [0025] The gasifier 10 may also be termed a boiler.

[0026] The process can be efficiently utilized to produce syngas.

[0027] In this process, the NCG (Non-Condensable-Gases), vent, etc. can be collected/sent to a closed collection system, an anaerobic system, etc. [0028] With this system, comminuted cellulosic material can be fed to a pressurized gasifier while preventing any gases from the gasifϊer from escaping the gasifier into the atmosphere or other equipment upstream of the gasifier. [0029] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it •is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A gasifier feed system comprising: a buffer bin positioned to receive material to be fed to a gasifier; a plug screw feeder disposed in communication with the buffer bin, the plug screw feeder receiving the material from the buffer bin and forming a plug of the material; a screw transfer conveyor disposed in communication with the plug screw feeder, the screw transfer conveyor receiving the material plug from the plug screw feeder and providing a buffer volume of the material; a source of inert gas coupled with the screw transfer conveyor that introduces pressurized inert gas into the screw transfer conveyor; and a rotary valve positioned relative to the screw transfer conveyor to receive the material from the screw transfer conveyor, the rotary valve conveying the material to the gasifier and including a gas lock that prevents gas from escaping the gasifier.

2. A gasifier feed system according to claim 1, further comprising a back stop disposed at a downstream end of the plug screw feeder, the back stop closing off the plug screw feeder from downstream equipment.

3. A gasifier feed system according to claim 1, wherein the inert gas source is coupled with the screw transfer conveyor adjacent an entry for the material plug.

4. A gasifier feed system according to claim 1 , wherein the material is comminuted cellulosic material.

5. A gasifier feed system according to claim 1, further comprising a source of steam coupled with the buffer bin, the steam source adding steam to the material.

6. A gasifϊer feed system according to claim 1 , wherein the source of inert gas supplies gas including at least one nitrogen, argon, carbon dioxide, and any other non-dangerous gas.

7. A gasifier feed system according to claim 1, wherein the rotary valve comprises one of a wet feeder and a dry feeder.

8. A gasifier feed system according to claim 1 , further comprising a drying unit disposed upstream of the buffer bin for drying the material.

9. A gasifier feed system according to claim 1 , further comprising a drying unit interposed between the screw transfer conveyor and the rotary valve for drying the material.

10. A gasifier feed system according to claim 9, further comprising a drying unit disposed upstream of the buffer bin for drying the material.

11. A gasifier feed system according to claim 1 , wherein a pressure in the screw transfer conveyor via the source of inert gas is higher than a pressure in the gasifier.

12. A gasifϊer feed system comprising: a buffer assembly that receives material to be fed to a gasifier, the buffer assembly including structure that pre-processes the material for delivery to the gasifier; a source of pressurized inert gas coupled with the buffer assembly; and a rotary valve positioned relative to the buffer assembly to receive the material from the buffer assembly, the rotary valve conveying the material to the gasifier and including a gas lock that prevents gas from escaping the gasifier.

13. A gasifϊer feed system according to claim 12, wherein the buffer assembly comprises a buffer bin positioned to receive the material, a plug screw feeder receiving the material from the buffer bin and forming a plug of the material, and a screw transfer conveyor providing a buffer volume of the material to the rotary valve.

14. A gasifϊer feed system according to claim 13, wherein the source of inert gas is coupled with the screw transfer conveyor and introduces the inert gas into the screw transfer conveyor.

15. A gasifier feed system according to claim 12, wherein a pressure in the buffer assembly via the source of inert gas is higher than a pressure in the gasifier.

16. A method of feeding a comminuted cellulosic material to a gasifier, the method comprising:

(a) receiving the cellulosic material in a buffer bin;

(b) feeding the cellulosic material to a plug screw feeder disposed in communication with the buffer bin and forming a plug of the cellulosic material;

(c) conveying the material plug to a screw transfer conveyor and providing a buffer volume of the cellulosic material;

(d) introducing inert gas into the screw transfer conveyor;

(e) transferring the cellulosic material to a rotary valve from the screw transfer conveyor; and

(f) conveying with the rotary valve the cellulosic material to the gasifier while preventing gas from escaping the gasifϊer.

17. A method according to claim 16, further comprising, before step (c), squeezing extratives through the plug screw feeder.

18. A method according to claim 16, wherein step (d) is practiced by pressurizing the screw transfer conveyor to a pressure that is higher than a pressure in the gasifier.