CLEANING SYSTEM FOR AN OUTPUT OF A GASIFIER
BACKGROUND OF THE INVENTION

[0001] The subject matter disclosed herein relates to gasification systems and, more particularly, to a cleaning system for an output of a gasifier.

[0002] In general, biomass such as wood and other plant biomass can be processed by two methods: biochemical methods such as fermentation; and thermochemical methods such as gasification. Biochemical methods use micro¬organisms to break down the biomass into simpler compounds such as ethanol. However these reactions are quite slow, and it can take at least several weeks to process a given batch. Due to factors like this, the biochemical processes, presently, are not in a state of direct industrial applicability.

[0003] Thermochemical methods involve processes such as biomass gasification. A typical, small scale (e.g., lOOkW - 5MW) fixed bed reactor (e.g., fixed bed gasifier) is capable of generating energy from various solid feedstock, such as the aforementioned biomass materials. The fixed bed reactor may convert the solid feedstock into a combustible gas (i.e., syngas, producer gas) by reaction with oxidant (air, enriched air, or oxygen), steam, or a combination thereof. This combustible gas may be used in a variety of applications such as for chemical production or in a combustion engine for use in the generation of electricity.

[0004] The syngas is then transformed into various fuel compounds, using a variety of techniques such as Fischer Tropsch Techniques. These techniques are somewhat analogous to coal gasification, and the subsequent conversion to liquid fuels. During gasification, volatile matter is released at relatively lower temperatures. A large part of this volatile matter is responsible for the tar formation during gasification of biomass. Tar levels in the product gas also depend on the gasifier configuration. In an updraft fixed bed gasifier that operates between about 300° C. and about 1000° C, the product gas contains up to 35000ppm tar. In a downdraft configuration, the tar level in product gas is comparatively low, but still contains about 100 to about 200 ppm tar. Depending on the gasifier configuration, tars tend to deposit on the walls of gasification equipment, or get transported downstream with the product gas. The tar deposits create the need for frequent maintenance, and may also reduce the operating life of the gasification equipment. The carryover of tar can deposit on and block filters, pipes, valves and turbochargers, leading to a decrease in performance. In some instances, elaborate cleaning systems are required to address these problems, thereby adding cost and complexity to the overall system.

BRIEF DESCRIPTION OF THE INVENTION

[0005] According to one aspect of the invention, a cleaning system for an output of a gasifier includes an outlet line located downstream of a grate of the gasifier and configured to route a gas product away from an outlet of the gasifier. Also included is a fluid source fluidly coupled to the outlet line with a fluid introduction line configured to route a fluid from the fluid source to the outlet line.

[0006] According to another aspect of the invention, a gasification system includes a fixed bed gasifier configured to gasify a feedstock, the fixed bed gasifier having a grate, an ash output unit, and an outlet configured to output a gas. Also included is an outlet line located downstream of the ash output unit and configured to route the gas away from the outlet. Further included is a fluid source fluidly coupled to the outlet line with a fluid introduction line configured to route a fluid from the fluid source to the outlet line to reduce tar from the gas.

[0007] These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWING

[0008] The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

[0009] FIG. 1 is a schematic illustration of a gasification system having a cleaning system for an output of a gasifier;

[0010] FIG. 2 is a schematic side view of a portion of the cleaning system introducing a fluid to an outlet line of the gasifier; and

[0011] FIG. 3 is a schematic top view of a portion of the cleaning system introducing the fluid to the outlet line of the gasifier.

[0012] The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.

DETAILED DESCRIPTION OF THE INVENTION

[0013] Referring to FIG. 1, a gasification system 10 is schematically illustrated. The gasification system 10 includes a fixed bed gasifier 12 (also referred to as a fixed bed reactor or simply a reactor) that operates to convert solid feedstock, such as biomass, into combustible gas (e.g., syngas). In general, biomass is biological material derived from living or recently living organisms, such as wood chips, rice hulls, corn stalks or other agricultural waste. Additional types of biomass include various waste products, such as municipal solid waste, industrial waste, and other types of waste.

[0014] The fixed bed gasifier 12 may vary in design. For example, the illustrated embodiment is a schematic illustration of a co-current fixed bed gasifier. The fixed bed gasifier 12 includes an enclosure 14, a feedstock inlet 16, an oxidant inlet 18, an outlet 36, an ash outlet 22, and a fixed bed 24. The enclosure 14 may have a hollow annular shape (e.g., cylindrical wall) with an upper dome 26. The feedstock inlet 16 is configured to receive a feedstock 28 at or near the upper dome 26 of the enclosure 14. The oxidant inlet 18 is configured to receive at least one oxidant 30, such as air, enriched air, or oxygen, for example. In the illustrated embodiment, the oxidant inlet 18 is located proximate the upper dome 26 of the enclosure 14, but it is to be appreciated that the oxidant inlet may be located on a side of the enclosure 14 above the fixed bed 24. An additional inlet may be included to facilitate the introduction of an agent, such as steam, into the fixed bed gasifier 12. Although the preceding description refers to the terms "enclosure" and "upper dome," it is to be appreciated that the fixed bed gasifier 12 is open to the atmosphere and a negative pressure is maintained in the system using a blower in a downstream section, such as after a tar removal section 40 (i.e., gas cleaning section), for example, which is described below.

[0015] The fixed bed 24 is configured to support the feedstock 28 while allowing flow of the at least one oxidant 30 and/or agent downward through the feedstock 28. The fixed bed 24 may include a grate 32 with openings (not shown). The gasification of the feedstock 28 occurs during passage through multiple zones 33 of the reaction chamber, which operate at different temperatures and/or pressures. Upon initiation of gasification, steam and/or the at least one oxidant 30 flow through the feedstock 28 resting on the fixed bed 24. Ash is generated from the gasification reaction and falls through the openings of the grate 32 down an ash output unit 34. The outlet 36 is configured to output a gas product 38. After gasification of the feedstock 28, the gas product 38 flows through the openings of grate 32 and exits via the outlet 36 to an outlet line 39.

[0016] Although the fixed bed gasifier 12 is illustrated and described above as a co-current fixed bed gasifier, it is to be appreciated that a counter-current fixed bed reactor may be employed for the gasification process. Regardless of the type of fixed bed gasifier employed in the gasification system 10, the outlet 36 is configured to route the gas product 38 to an outlet line 39 for further processing and conditioning of the gas product 38. The additional processing may include cleaning the gas product 38 in a tar removal system 40 prior to sending the gas product 38 to an engine 42. The gas product 38 exiting the fixed bed gasifier 12 contains heavy molecular weight tar content that needs to be separated prior to sending the gas to the engine 42. The removal of tar particles within the tar removal system 40 is carried out by spraying a large quantity of chilled water or solvent.

[0017] To reduce or eliminate the chilled water or solvent requirements of the tar removal system 40, a cleaning system 44 is integrated into the gasification system 10. The cleaning system 44 facilitates tar cracking proximate the outlet 36 and/or outlet line 39 of the gasification system 10. The outlet 36 is located downstream of the grate 32 and ash output unit 34, with the outlet line 39 configured to route the gas product 38 away from the outlet 36. The cleaning system 44 includes a fluid source 45 that is a volume of stored fluid or may simply be an inlet region configured to ingest a fluid. The fluid source 45 is fluidly coupled to the outlet 36 and/or outlet line 39 via a fluid introduction line 46. The fluid introduction line 46 is a pipe or other conduit configured to route the fluid into the outlet 36 and/or outlet line 39. The fluid is at least one of atmospheric air, enriched air, and steam.

[0018] A controller 48 is included and is in operative communication with the outlet line 39 and/or the outlet 36. The controller 48 is configured to monitor a temperature of the gas product 38 flowing within the outlet line 39. Upon introducing the fluid into the outlet 36, a combustion process occurs with the fluid and the gas product 38, thereby increasing the temperature of the gas product 38. Although the specific temperature ranges will vary depending upon the particular application and conditions, in one embodiment the gas product 38 exits the fixed bed gasifier 12 via the outlet 36 at about 550°C to about 600°C. The combustion process with the fluid introduced via the fluid introduction line 46 of the cleaning system 44 increases the temperature of the gas product 38 to about 800°C to about 900°C, which facilitates cracking of the tar molecules present in the gas product 38.

[0019] To ensure that a sufficient temperature is obtained to facilitate tar cracking, the fluid may be heated with a heating system in the fluid introduction line 46 prior to introduction of the fluid to the outlet 36. As noted above, the controller 48 monitors the temperature within the outlet 36 and/or outlet line 39. Based on the temperature reading therein, the controller 48 selectively regulates the flow rate of the fluid by controlling a valve 50 located within the fluid introduction line 46.

[0020] Referring to FIGS. 2 and 3, it is shown that a plurality of fluid introduction lines 52 may be included to route the fluid from the fluid source 45 to the outlet 36 and/or outlet line 39. The plurality of fluid introduction lines 52 lead to various introduction locations. For example, as illustrated the plurality of fluid introduction lines 52 may be spaced axially (FIG. 2) in relation to a predominant direction of flow of the gas product 38, as well as circumferentially (FIG. 3). Injection of the fluid at multiple locations along the outlet 36 and/or outlet line 39 enhances the effective mixing of the heated fluid and gas product 38.

[0021] Advantageously, the tar content of the gas product 38 is significantly reduced, which reduces the chilled water or solvent consumption at the tar removal system 40. The overall complexity and size of the tar removal system 40 is decreased as a result, thereby lowering cost of the system.

[0022] While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

We claim:

1. A cleaning system for an output of a gasifier comprising:
an outlet line located downstream of a grate of the gasifier and configured to route a gas product away from an outlet of the gasifier; and
a fluid source fluidly coupled to the outlet line with a fluid introduction line configured to route a fluid from the fluid source to the outlet line.

2. The cleaning system as claimed in claim 1, wherein the outlet line is located downstream of an ash output unit of the gasifier.

3. The cleaning system as claimed in claim 1, wherein a valve is located within the fluid introduction line configured to regulate a flow rate of the fluid within the fluid introduction line.

4. The cleaning system as claimed in claim 3, wherein a controller is in operative communication with the outlet line and the valve, wherein the controller is configured to monitor a temperature of the gas product within the outlet line and to control the valve in response to the temperature of the gas product.

5. The cleaning system as claimed in claim 1, wherein a plurality of fluid introduction lines are configured to route the fluid from the fluid source to the outlet line.

6. The cleaning system as claimed in claim 1, wherein the fluid comprises a combination of air and steam.

7. The cleaning system as claimed in claim 1, wherein the fluid comprises enriched air.

8. The cleaning system as claimed in claim 1, wherein the fluid comprises atmospheric air.

9. The cleaning system as claimed in claim 1, wherein the fluid introduction line comprises a heating system configured to heat the fluid prior to routing the fluid to the outlet line, wherein the heating system comprises a heat recovery assembly configured to recover heat from a surface of the gasifier and from the gas product, wherein the fluid is heated and routed directly into the outlet line.

10. The cleaning system as claimed in claim 1, wherein the cleaning system is operatively integrated with a fixed bed gasifier.

11. A gasification system comprising:
a fixed bed gasifier configured to gasify a feedstock, the fixed bed gasifier having a grate, an ash output unit, and an outlet configured to output a gas;
an outlet line located downstream of the ash output unit and configured to route the gas away from the outlet; and
a fluid source fluidly coupled to the outlet line with a fluid introduction line configured to route a fluid from the fluid source to the outlet line to reduce tar from the gas.

12. The gasification system as claimed in claim 11, wherein a valve located within the fluid introduction line is configured to regulate a flow rate of the fluid within the fluid introduction line.

13. The gasification system as claimed in claim 12, wherein a controller in operative communication with the outlet line and the valve, wherein the controller is configured to monitor a temperature of the gas within the outlet line and to control the valve in response to the temperature of the gas.

14. The gasification system as claimed in claim 11, wherein a plurality of fluid introduction lines are configured to route the fluid from the fluid source to the outlet line.

15. The gasification system as claimed in claim 11, wherein the fluid comprises a combination of air and steam.

16. The gasification system as claimed in claim 11, wherein the fluid comprises enriched air.

17. The gasification system as claimed in claim 11, wherein the fluid comprises atmospheric air.

18. The gasification system as claimed in claim 11, wherein the fluid introduction line comprises a heating system configured to heat the fluid prior to routing the fluid to the outlet line.

19. The gasification system as claimed in claim 11, wherein the fixed bed gasifier comprises a co-current fixed bed reactor.

20. The gasification system as claimed in claim 11, wherein the fixed bed gasifier comprises a counter-current fixed bed reactor.