Device And Method Of Combusting Solid Fuel With Oxygen

Abstract

The present invention is a method of combustion of a solid fuel stream with oxygen. The present invention includes introducing a first stream, comprising a first portion of substantially pure oxygen, into a first conduit. The present invention includes introducing a second stream, comprising a solid fuel stream and a conveying media, into a second conduit, wherein the second conduit is concentric with, and surrounding, the first conduit. The present invention includes introducing a third stream, comprising a second portion of substantially pure oxygen, into a third conduit, wherein the third conduit is concentric with, and surrounding, the first conduit and the second conduit. The present invention includes igniting the first stream, the second stream, and the third stream as they exit the first conduit, the second conduit and the third conduit, in such a way as to create a flame. The present invention includes introducing a fourth stream, comprising a first portion of ballast gas, into a fourth conduit, wherein the fourth conduit is concentric with, and surrounding, the first conduit, the second conduit, and the third conduit. The present invention includes introducing a fifth stream, comprising a second portion of ballast gas, into a fifth conduit, wherein the fifth conduit is concentric with, and surrounding, the first conduit, the second conduit, the third conduit and the fourth conduit.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/050,515, filed May 5, 2008, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to a method combusting solid fuel with oxygen.

BACKGROUND

With the increasingly stringent environmental restrictions, particularly in terms of the production of CO₂ and NO_x, the combustion of a fuel using oxygen or a high-oxygen-content gas is becoming increasingly attractive for the combustion of fossil fuels. However, the conventional combustion devices using air as oxidizer do not always have the geometry, nor the requisite materials, for operating with oxygen or a high-oxygen-content gas. This is because the absence of the nitrogen ballast in high-oxygen or all-oxygen combustion significantly modifies the heat transfer modes, the species concentrations, and the pressure conditions in the combustion chamber.

In order to operate with all-oxygen combustion in these installations, one proposed solution is to reinject flue gas produced by the said combustion or another combustion to partly make up for the absence of nitrogen. This procedure serves to avoid a high production of NO_x due both to the absence of nitrogen, and also to a lower flame temperature than in all-oxygen combustion. However, the reinjected flue gas often nullifies the benefits of oxycombustion, such as, in particular, lower downstream flue gas treatment, efficiency increase due to high temperature combustion process etc.

Coal is a major source of fuel in the world. Different devices and methods are available today to combust coal. Coal is usually combusted with air or with a mixture of oxygen and flue gases (‘synthetic air’). Prior art exists today where oxygen is mixed with flue gas and introduced into the combustor. Separate injection of fuel, oxygen, and flue gas have been proposed for gaseous and liquid fuels, where the mixing of fuel and oxidants are relatively easy. Also, there is no conveying media required to transport gaseous or liquid fuels, whereas such a conveying media is required for a solid fuel combustion.

Synthetic air requires mixing of oxygen with flue gases and there is less flexibility with respect to the oxygen to flue gas ratio (typically about 18% to about 40%) due to safety and technical issues. Synthetic air also dilutes the combustion which makes it difficult to burn low quality coal.

Therefore, there exists a need in the industry for a solution that will allow the above problems to be circumvented.

SUMMARY

The present invention is a method of combustion of a solid fuel stream with oxygen. The present invention includes introducing a first stream, comprising a first portion of substantially pure oxygen, into a first conduit. The present invention includes introducing a second stream, comprising a solid fuel stream and a conveying media, into a second conduit, wherein said second conduit is concentric with, and surrounding, said first conduit. The present invention includes introducing a third stream, comprising a second portion of substantially pure oxygen, into a third conduit, wherein said third conduit is concentric with, and surrounding, said first conduit and said second conduit. The present invention includes igniting said first stream, said second stream, and said third stream as they exit said first conduit, said second conduit and said third conduit, in such a way as to create a flame. The present invention includes introducing a fourth stream, comprising a first portion of ballast gas, into a fourth conduit, wherein said fourth conduit is concentric with, and surrounding, said first conduit, said second conduit, and said third conduit. The present invention includes introducing a fifth stream, comprising a second portion of ballast gas, into a fifth conduit, wherein said fifth conduit is concentric with, and surrounding, said first conduit, said second conduit, said third conduit and said fourth conduit. The present invention includes surrounding said with said fourth stream and said fifth stream, as they exit said fourth conduit and said fifth conduit.

BRIEF DESCRIPTION OF DRAWINGS

The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, and in which:

FIG. 1 is a schematic representation of one embodiment of the present invention.

FIG. 2 is a schematic representation of another embodiment of the present invention, indicating the fourth stream being divergent and the fifth stream being convergent.

FIG. 3 is a schematic representation of another embodiment of the present invention, indicating the swirling devices in the fourth and fifth streams, as well as the dampers.

FIG. 4 is a schematic representation of another embodiment of the present invention, indicating the control system and swirling devices in the 2^nd stream.

DESCRIPTION OF PREFERRED EMBODIMENTS

The proposed method detaches the oxygen and flue gas introduction and improves the flexibility of having a broad range to the oxygen to flue gas ratio. The proposed method takes advantage of oxycombustion to generate high temperatures, thereby accelerating the devolatilization of coal and thus the combustion of the coal. This dilution happens only after the combustion with pure oxygen to maintain the required furnace wall temperature.

The present invention proposes an innovative device and method to combust solid fuel such as coal with pure oxygen. Fuel, oxygen, and flue gases are introduced separately into the boiler via the proposed device/burner. This device enables independent flow control of flue gas and oxygen compared to the state of the art, where oxygen and flue gas are mixed then introduced. The proposed method enhances the devolatilization of fuel with the use of pure oxygen and thus improves the combustion process. This promotes the utilization of low quality coals which are difficult to burn with air or synthetic air with existing technologies.

Turning to FIG. 1, injector 100 is presented. Coal is introduced through coal pipe 102 (second stream) of the burner, with a conveying media, preferably recycled flue gas (either alone or combined with oxygen). The coal may be injected with or without inducing a swirl, depending on the quality of the coal, flame length required etc. A first portion of the substantially pure oxygen is introduced through lance 101 (first stream), to improve the flame stability. A second portion of substantially pure oxygen is introduced into oxygen orifice 103 (third stream). Oxygen orifice 103 (third stream) surrounds coal pipe 102 (second stream) and is introduced to facilitate the complete combustion of coal in an oxygen environment. First recycled flue gas stream 104 (fourth stream) and second recycled flue gas stream 105 (fifth stream) are introduced on the outer perimeter of oxygen orifice 103 (third stream), thereby maintaining the furnace temperature to an acceptable level. The oxyflame is diluted to the required extent with recycled flue gases (104, 105) (fourth stream and fifth stream) around the pure oxygen injection (103).

Turning to FIG. 2, injector 200 is presented. Coal is introduced through coal pipe 202 (second stream) of the burner, with a conveying media, preferably recycled flue gas (either alone or combined with oxygen). The coal may be injected with or without inducing a swirl, depending on the quality of the coal. A first portion of the substantially pure oxygen is introduced through lance 201 (first stream), to improve the flame stability. A second portion of substantially pure oxygen is introduced into oxygen orifice 203 (third stream). Oxygen orifice 203 (third stream) surrounds coal pipe 202 (second stream) and is introduced to facilitate the complete combustion of coal in an oxygen environment. First recycled flue gas stream 204 (fourth stream) and second recycled flue gas stream 205 (fifth stream) are introduced on the outer perimeter of oxygen orifice 203 (third stream), thereby maintaining the furnace temperature to an acceptable level. The oxyflame is diluted to the required extent with recycled flue gases (204, 205) (fourth stream and fifth stream) around the pure oxygen injection (203). In this embodiment, in order to improve the mixing of the dilutant/flue gases (204, 205) with the flame (201, 202, 203) the flue gases (204, 205) can be injected in a non-axial fashion as shown in FIG. 2. The majority of the flue gases are preferably injected at an angle that is divergent from the axial centreline CL of injector 200, with a minor flow being injected at an angle that is convergent with the axial centreline CL.

Turning to FIG. 3, injector 300 is presented. Coal is introduced through coal pipe 302 (second stream) of the burner, with a conveying media, preferably recycled flue gas (either alone or combined with oxygen). The coal may be injected with or without inducing a swirl, depending on the quality of the coal, flame length required etc. In order to further improve the combustibility of very low quality solid fuel, a secondary fuel such as oil or gas may be injected along with the solid fuel into coal pipe 302 (second stream). It is also possible to valorize low quality secondary fuel when the solid fuel does not need the assistance of the secondary fuel (i.e. good quality solid fuel). A first portion of the substantially pure oxygen is introduced through lance 301 (first stream), to improve the flame stability. A second portion of substantially pure oxygen is introduced into oxygen orifice 303 (third stream). Oxygen orifice 303 (third stream) surrounds coal pipe 302 (second stream) and is introduced to facilitate the complete combustion of coal in an oxygen environment. First recycled flue gas stream 304 (fourth stream) and second recycled flue gas stream 305 (fifth stream) are introduced on the outer perimeter of oxygen orifice 303 (third stream) thereby maintaining the furnace temperature to an acceptable level. First recycled flue gas stream 304 (fourth stream) may be introduced with a clockwise swirl A or a counter-clockwise swirl B. Second recycled flue gas stream 305 (fifth stream) may be introduced with a clockwise swirl C or a counter-clockwise swirl D.

The oxyflame is diluted to the required extent with recycled flue gases (304, 305) around the pure oxygen injection (303). In this embodiment, in order to improve the mixing of the dilutant/flue gases (304, 305) with the flame (301, 302, 303) the flue gases (304, 305) can be injected in a non-axial fashion as shown in FIG. 3?. The majority of the flue gases are preferably injected at an angle that is divergent from the axial centreline CL of injector 300, with a minor flow being injected at an angle that is convergent with the axial centreline CL.

In order to further improve the mixing of the flue gases (304, 305) with the flame (301, 302, 303), swirl can be introduced into the flue gases (304, 305). As shown in FIG. 3, opposite swirls are preferably induced in the two zones of flue gas injection by element 306. The flow between the two flue gas injection zones can be changed with damper 307 positioned between these zones.

Turning to FIG. 4, injector 400 is presented. Coal is introduced through coal pipe 402 (second stream) of the burner, with a conveying media, preferably recycled flue gas (either alone or combined with oxygen). The coal may be injected with or without inducing a swirl, depending on the quality of the coal, flame length required etc. A first portion of the substantially pure oxygen is introduced through lance 401 (first stream), to improve the flame stability. A second portion of substantially pure oxygen is introduced into oxygen orifice 403 (third stream). Oxygen orifice 403 (third stream) surrounds coal pipe 402 (second stream) and is introduced to facilitate the complete combustion of coal in an oxygen environment. First recycled flue gas stream 404 (fourth stream) and second recycled flue gas stream 405 (fifth stream) are introduced on the outer perimeter of oxygen orifice 403 (third stream), thereby maintaining the furnace temperature to an acceptable level. The oxyflame is diluted to the required extent with recycled flue gases (404, 405) around the pure oxygen injection (403). In this embodiment, in order to improve the mixing of the dilutant/flue gases (404, 305) with the flame (401, 402, 403) the flue gases (404, 405) can be injected in a non-axial fashion as shown in FIG. 4. The majority of the flue gases are preferably injected at an angle that is divergent from the axial centreline CL of Injector 400, with a minor flow being injected at an angle that is convergent with the axial centreline CL.

In order to further improve the mixing of the flue gases (404, 405) with the flame (401, 402, 403), swirl can be introduced into the flue gases (404, 405). As shown in FIG. 4, opposite swirls are preferably induced in the two zones of flue gas injection by element 406. The flow between the two flue gas injection zones can be changed with damper 407 positioned between these zones.

A control system 408 may automatically adjust the combustion disturbances that may be caused with changing quality of coal or other purturbences. The staging of oxygen between lance 401 and surrounding the coal pipe 402 can be changed along with the distribution of recycled flue gases in the two surrounding zones (404, 405). The combustion characteristics can be measured by monitoring the flue gases (409) and the information then being fed to the control system.

In another embodiment, in order to improve the efficiency of the combustion process, the oxygen can be preheated to a higher temperature before introduction into the burner. The heat source may be the flue gas exiting the boiler, or any other locally available heat source, or heat source that is part of the present process. It is also envisioned that the oxygen streams (101,201,301,401, 103,203,303,403) can be injected in many different ways such as, but not limited to, axial, radial, convergent, divergent, with and with out swirl or the combination of some of these.

Illustrative embodiments have been described above. While the method in the present application is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings, and have been herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the method in the present application to the particular forms disclosed, but on the contrary, the method in the present application is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the method in the present application, as defined by the appended claims.

It will, of course, be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but, would nevertheless, be a routine undertaking for those of ordinary skill in the art, having the benefit of this disclosure.

Claims

1. A method of combustion of a solid fuel stream, comprising:

a) introducing a first stream, comprising a first portion of substantially pure oxygen, into a first conduit,

b) introducing a second stream, comprising a solid fuel stream and a conveying media, into a second conduit, wherein said second conduit is concentric with, and surrounding, said first conduit,

c) introducing a third stream, comprising a second portion of substantially pure oxygen, into a third conduit, wherein said third conduit is concentric with, and surrounding, said first conduit and said second conduit,

d) igniting said first stream, said second stream, and said third stream as they exit said first conduit, said second conduit and said third conduit, in such a way as to create a flame,

e) introducing a fourth stream, comprising a first portion of ballast gas, into a fourth conduit, wherein said fourth conduit is concentric with, and surrounding, said first conduit, said second conduit, and said third conduit, and

f) introducing a fifth stream, comprising a second portion of ballast gas, into a fifth conduit, wherein said fifth conduit is concentric with, and surrounding, said first conduit, said second conduit, said third conduit and said fourth conduit.

2. The method of claim 1, wherein said conveying media is recycled flue gas, substantially pure oxygen, or a combination.

3. The method of claim 1, wherein said solid fuel is coal.

4. The method of claim 1, wherein said first portion of ballast gas is recycled flue gas.

5. The method of claim 1, wherein said second portion of ballast gas is recycled flue gas.

6. The method of claim 1, wherein said first conduit has a longitudinal axis, wherein said fourth conduit directs said first portion of ballast gas flow in a direction essentially divergent from said longitudinal axis.

7. The method of claim 1, wherein said first conduit has a longitudinal axis, wherein said fifth conduit directs said second portion of ballast gas flow in a direction essentially convergent from said longitudinal axis.

8. The method of claim 1, wherein said fourth conduit creates a clockwise swirl in said first portion of ballast gas flow.

9. The method of claim 1, wherein said fourth conduit creates a counter-clockwise swirl in said first portion of ballast gas flow.

10. The method of claim 1, wherein said fifth conduit creates a clockwise swirl in said second portion of ballast gas flow.

11. The method of claim 1, wherein said fifth conduit creates a counter-clockwise swirl in said second portion of ballast gas flow.

12. The method of claim 1, further comprising at least one damper situated on the perimeter of said fourth conduit, wherein said at least one damper allows the ratio of said first portion of ballast gas flow and said second portion of ballast gas flow to be varied.

13. The method of claim 12, wherein at least three dampers are spaced equidistant around the perimeter of said fourth conduit.

14. The method of claim 12, further comprising sensing devices situated in said first conduit, said second conduit, said third conduit, on said at least one damper, and in the recycled flue gas stream.

15. The method of claim 12, wherein said sensing devices are connected to an automatic control system.

16. The method of claim 1, wherein said substantially pure oxygen is preheated prior to introduction into said first conduit.

17. The method of claim 1, wherein said substantially pure oxygen is preheated prior to introduction into said third conduit.

18. The method of claim 1, wherein said second stream, further comprises a secondary fuel stream.

19. The method of claim 18, wherein said secondary fuel stream is selected from the group consisting of fuel oil or fuel gas.

20. The method of claim 18, wherein said secondary fuel stream comprises process off-gas.

21. The method of claim 1, wherein said first stream and said first conduit are eliminated, and said second stream and said second conduit are the centremost.