WO2010034124A1

WO2010034124A1 - System and method for burning fuel

Info

Publication number: WO2010034124A1
Application number: PCT/CA2009/001362
Authority: WO
Inventors: Darrell Bishop; Peter Dean; Kirby O'donnell
Original assignee: New Brunswick Power Generation Corporation
Priority date: 2008-09-29
Filing date: 2009-09-28
Publication date: 2010-04-01

Abstract

Burner systems for firing first and second fuels in a burner are described. The burner system has a solid fuel nozzle assembly provides a first fuel injected around a core flame produced by the second fuel in the burner. One or more adjustable dampers are provided to control airflow through one or more air zones in the burner to stage combustion air into the transport air for NO_x reduction during burning, and one or more adjustable swirl vanes are provided to control flame swirl and movement of the transport air and combustion air in the burner. Methods for firing first and second fuels in a burner are also described.

Description

SYSTEM AND METHOD FOR BURNING FUEL

This application claims the benefit of and priority from US Provisional Application 61/101,027, filed at the United States Patent and Trademark Office on September 29, 2009.

FIELD

[0001] The embodiments described herein, relate generally to fuel combustion burners, and more specifically to burners that combust multiple fuels simultaneously.

SUMMARY

[0002] Petroleum coke (petcoke) is a byproduct of the petrochemical industry where it is produced as a result of the oil refining process and is available at a relatively lower cost when compared to other fuels. Petcoke is a solid fuel and exhibits handling properties similar to coal. The use of petroleum coke is desirable for use in furnaces originally design for liquid fuel oil as its high heating value of approximately 32 MJ/kg is higher than many other conventionally used solid fuel sources. Additionally, petroleum coke has a relative low ash content compared to other solid fuels and is available in concentrations similar to heavy fuel oil. Petcoke is a low reactive fuel which typically has limited its application to furnace designs with longer combustion residence times.

Combustion residence time is a measure of the elapsed time required for the complete combustion of a fuel source. Highly reactive fuels have high concentrations of volatile matter which combust rapidly resulting in low combustion residence times. Liquid fuel oils are considered highly reactive fuels whereas solid fuels such as coal or petroleum coke are considered low reactive fuels due to relatively lower volatile matter content. Furnaces utilizing burners designed for use with highly reactive fuels have significantly shorter combustion residence time provisions than furnaces designed for solid fuel applications. As a result, conventional wisdom dictates that solid fuels cannot be utilized in furnace/burner applications originally designed for liquid fuel applications. The system and method described below tends to overcome this limitation and allows for solid fuels with low volatility concentrations, like petcoke, to be combusted in furnaces originally designed exclusively for highly reactive liquid fuels. Such furnaces would generally have a volumetric heat release greater than 30,000 Btu/hr-Ft and also a plan area release rate greater than two million Btu-hr-Ft².

[0003] In one embodiment, up to 80% of the total burner heat input is provided by petroleum coke which is ground such that a minimum of 90% of the total mass of the particles would pass through a 200 mesh screen. The increased surface area of the highly ground petcoke when combined with a highly reactive and centrally located heat source/secondary support fuel, improves the combustion reactivity of the petcoke and reduces the combustion time to within the limitations of a furnace originally designed exclusively for liquid fuel sources. [0004] In one embodiment, a burner system for firing first and second fuels in a burner is provided. The burner system comprises a solid fuel nozzle assembly having the first fuel passing there through and injecting the first fuel around a core flame produced by the second fuel; a fuel assembly having the second fuel passing there through, and forming the core flame zone; transport air passing through the windbox and conveying the first fuel to the burner one or more air zones to stage combustion air for NO_x reduction wherein airflow to the zones is controlled by dampers, and one or more swirl vanes, the one or more swirl vanes being adjustable to control the flame swirl within the burner during firing of the first and second fuels.

[0005] In an aspect of the invention, a burner system for firing first and second fuels in a burner is provided. The system comprises a solid fuel nozzle assembly having the first fuel passing therethrough and injecting the first fuel around a core flame produced by the second fuel in the burner; a fuel assembly having the second fuel passing therethrough, and forming the core flame for igniting the primary fuel; a windbox in communication with the solid fuel nozzle assembly, the windbox having transport air passing therethrough and conveying the first fuel to the burner; one or more adjustable dampers in the windbox to control airflow through one or more air zones in the burner to stage combustion air into the transport air for NO_x reduction during burning; and one or more adjustable swirl vanes in the windbox to control movement of the transport air and combustion air in the burner. The core flame ignites the first fuel in the burner and the one or more swirl vanes are adjustable to control movement of the primary fuel to the core flame for ignition and control flame swirl within the burner during firing of the first and second fuels. [0006] The fuel assembly may pass through the solid fuel nozzle assembly and windbox into the burner.

[0007] In another aspect of the invention, a method for firing first and second fuels in a burner is provided. The method comprises passing the second fuel through a fuel assembly into the burner and forming a core flame zone therefrom; passing transport air conveying the first fuel therein to the burner, the transport air passing through a solid fuel nozzle assembly and injecting the first fuel around the core flame zone produced by the second fuel; creating one or more air zones to stage combustion air into the transport air for NO_x reduction during burning, wherein airflow to the zones is controlled by dampers in the burner; and controlling one or more swirl vanes movement of the transport air and combustion air to provide ignition of the first fuel by the core flame zone provided by the second fuel, the one or more swirl vanes being adjustable to control flame swirl within the burner during firing of the first and second fuels.

[0008] The first fuel may be ground petroleum coke. The ground petroleum coke can be ground to at least 90% passing 200 mesh. The second fuel may be a highly volatile support fuel. The highly volatile fuel may be a heavy fuel oil. The highly volatile fuel may be a light fuel oil. The burner system may be designed exclusively for liquid fuel sources.

BRIEF DESCRIPTION OF THE DRAWING FIGURES [0009] For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, which show a preferred embodiment of the present invention and in which:

[0010] FIG. 1 is a block diagram of an embodiment of the components of a burner system;

[0011] FIG. 2 is a block diagram of an embodiment of the components of a grinding facility of the burner system of FIG. 1 ;

[0012] FIG. 3 is a block diagram of an embodiment of the components of a handling facility of the burner system of FIG. 1; [0013] FIG. 4 is a block diagram of a further description of the components of a handling facility of the burner system of FIG. 1;

[0014] FIG. 5 is a block diagram of an embodiment of a burner facility of the burner system of FIG. 1; [0015] FIG. 6 is a diagram illustrating the respective air zones of a petroleum coke burner in the burner facility of FIG. 6;

[0016] FIG. 7 is a diagram illustrating the components of a secondary air zone of the petroleum coke burner in the burner facility of FIG. 6;

[0017] FIG. 8 is a schematic diagram of an exemplary implementation of an embodiment of the burner system of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0018] The description which follows, and the embodiments described therein, are provided by illustration by way of an example, or examples, of particular embodiments of the principles of the present invention. These principles are provided for purposes of explanation, and not limitation of those principles, and of the invention.

[0019] The embodiments described herein, as will be more fully understood with the accompanying description, relate to the use of fuel sources in fuel fired burners. Reference is made to FIG. 1 , where a block diagram illustrating the general components of a burner system 10 is shown in one embodiment. The respective components of the burner system 10 are described in further detail below with respect to the respective figures. The burner system 10 may be used, for example, with any co-firing burner assemblies where a first, or primary, fuel source and a second, or secondary, fuel source are co-fired in one or more burners. The burner system 10 of the present invention comprises mechanisms and assemblies for preparation of the primary fuel source, and in one embodiment, the burner system 10 comprises a grinding facility 12, a handling facility 14, and a burner facility 16. The grinding facility in an exemplary embodiment, can be used to grind a primary fuel source that can be used by the burner facility 16. The primary fuel source described in the embodiments below is petroleum coke. [0020] The grinding facility 12 grinds the petroleum coke and the ground petroleum coke is then used by one of more burners capable of efficiently burning petroleum coke in the burner facility 16.

[0021] The handling facility 14 receives the ground petroleum coke and regulates the flow of the ground petroleum coke to the petroleum coke burners. The burner facility 16, and more specifically, the petroleum coke burners therein receive the ground petroleum coke and burn the ground petroleum coke along with a secondary, or support, fuel source. In the embodiment, the secondary fuel source may be chosen from any highly volatile fuel. Examples of highly volatile fuels that would aid the burning of the primary fuel source in the burner facility include, but are not limited to, a heavy fuel oil, light fuel oil. The burner facility 16 as described below can comprise one or more petroleum coke burners, and may also comprise burners that burn a primary fuel other than petroleum coke, and other secondary fuels.

[0022] Reference is now made to FIG. 2, where a block diagram illustrating the components of grinding facility 12 is shown in an exemplary embodiment. The components of grinding facility 12 can be used to process a primary fuel, such as the petroleum coke, such that a particulate size that allows for increased particulate surface area for burning within a burner designed for liquid fuels is provided. The grinding facility 12 has an input silo 30 that receives petroleum coke through an input channel 31. The petroleum coke is then provided to a pulverizer 32. The pulverizer 32 also receives as input, heat generated from a heating module 34. For purposes of illustration, the heating module 34 has been shown as a separate component, however, one of skill in the art will understand that the pulverizer 32 and heating module 34 may be part of the same unit in certain embodiments. The heating module 34 provides the heat necessary for the operation of the pulverizer 32. The heating module 34 receives three external inputs in one embodiment, including a fuel supply 36A, dry air 36B, and combustion air 36C. The air input is provided to remove the petroleum coke from the pulverizer, and the heating of the air allows for petroleum coke to be dried which prevents pulverizer clogging and increases its reactivity. The pulverizer 32, upon the grinding of the petroleum coke, provides the petroleum coke to an output collection silo 36 from where the flow of the petroleum coke to the respective handling and subsequent burning facilities 14, 16, respectively, is regulated. [0023] The pulverization of the petroleum coke is undertaken with reference use of vertical roller mill technology in one embodiment. The vertical roller mill technology is chosen to pulverize the petroleum coke in one embodiment because of the composition of the material that is being pulverized. Owing to the hardness of the petroleum coke and the desired particulate size (fineness), the vertical roller technology provides the appropriate desired results when used in the pulverization process.

[0024] The pulverization process employs a dynamic classifier that is used to separate the smallest petroleum coke particles from the air stream that is exiting the pulverizer, and provides the petroleum coke particles back to the roller mill for further grinding. The classifier receives air input which causes a cyclonic action that is used to separate the petroleum coke particles from the air. In an exemplary embodiment, the petroleum coke should be ground to above 200 mesh, where at least 90 % of the petroleum coke is ground to more than this mesh quality. Based on research conducted, however, it has been determined that burners which burn ground petroleum coke produce optimal results with regards to efficiency, where the petroleum coke is ground to 325 mesh above the 93% threshold. As the fineness of the ground primary fuel increases, the ignition time and combustion kinetics tend to improve, and thus in turn tends to permit increasing of the primary to secondary fuel ratios, such as the ratio of petroleum coke to a heavy fuel oil in an embodiment. [0025] Reference is now made to FIG. 3 and FIG. 4, where block diagrams illustrating the components of the handling facility 14 are shown in exemplary embodiments. The handling facility 14 as described above, receives the ground petroleum coke from the pulverizer 32 and regulates the flow of the ground petroleum coke to the respective burners that are illustrated in greater detail below. In exemplary operation, the ground petroleum coke exits the pulverizer 32 and is separated from its transport air stream via a baghouse, then transferred using a screw conveyor to silo 36. While in silo 36, the petroleum coke may be aerated, such as pneumatically, inside the silo 36 to keep it in suspension as required to maintain a stable feed flow to the feed silo 38. [0026] The collection silo 36 provides the ground petroleum coke to one or more feed silos 38, such as by pneumatic transport. Feed silos 38 can be used to regulate the flow of the ground petroleum coke to the burner assembly, or facility, 16, wherein the respective petroleum coke burners are resident. For purposes of illustration, the burner assembly 16 has been shown with two feed silos, but it will be understood by one of skill in the art that one or more feed silos may be used for the provision of petroleum coke. The feed silos 38 each comprise a rotary valve 40. The rotary valves 40 regulate the flow of petroleum coke to a gravimetric weight feeder 42, which in turn weigh the flow of petroleum coke injection into the burner assembly 16. The weight feeders 42 receive signals from and transmit signals to a control system 46 regarding the flow rate of the petroleum coke to the respective burners.

[0027] In exemplary operation, the petroleum coke exits from weigh feeder 42 and into a transport air flow, or air stream, for injection into the burner assembly 16. In the embodiment, the transfer from feeder 42 can by via two rotary valves in series (shown in FIG. 4) to transfer the petroleum coke into the transport air flow. The components of the handling facility described herein have been described for purposes of example, and various configurations of the components of the handling facility may be used to handle petroleum coke that will be used in a combustion process. Reference is now made to FIG. 4, where a block diagram illustrating the injection configuration of the components used to inject the ground petroleum coke into the liquid fuel burners is shown in an exemplary embodiment. The petroleum coke silo as discussed discharges the ground petroleum coke through rotary petroleum coke valves 40 to a gravimetric weigh scale 42. The gravimetric weighing device measures the mass of the petroleum coke and the speed at which a conveyor belt 43 is moving in order to measure the amount of petroleum coke that is being injected into the air stream. A secondary set of rotary valves 46 A, and 46B are used in an exemplary embodiment to control the flow of the petroleum coke to the air stream that will eventually provide the ground petroleum coke to the burners for combustion as described herein. The airstream that the ground petroleum coke is injected into is powered by an air fan 50, wherein the air is heated through an air heater 60 that is used to further dry the petroleum coke prior to its injection into the burners.

[0028] The injection process that is used to inject the petroleum coke into the burners tends to ensure that there is uniform distribution of the ground petroleum coke in the air stream. This thus tends to ensure that the petroleum coke enters into the dual fuel designed burners in a predictable and uniform manner, increasing the efficiency of the combustion process associated with the petroleum coke. Where the petroleum coke were not distributed uniformly in the air stream which would occur where the injection apparatus as described herein not used, the ground petroleum coke may not be uniformly distributed among the available burners thus reducing the efficiency of the burner assembly and output. The air stream that the ground petroleum coke is injected into uses sufficient turbulence to create an air stream for each burner that will be receiving the ground petroleum coke. For example, where there are four burners that will receive the ground petroleum coke, four air streams are created that receive a uniform distribution of the petroleum coke.

[0029] Reference is now made to FIG. 5, where the exemplary burner assembly 16 that comprises one or more petroleum coke burners is illustrated in greater detail. The burner assembly 16 in an exemplary embodiment may be comprised of one or more burners. The burners illustrated herein, are shown with the petroleum coke burners 50 that burn petroleum coke as their primary fuel source and additional burners that do not receive petroleum coke as a primary fuel source, such as the burning of a heavy oil as a secondary fuel source. The burners 50 as used herein are designed with the general characteristics associated with solid fuel burners, and the description of the system and methods herein allow for use of such burners to be utilized in a furnace originally designed exclusively for liquid fuel combustion to produce optimal results as described herein. The petroleum coke burners receive heat, provided by air heater 60. The precipitator 62 that is shown in the figure in an exemplary embodiment is used to remove the solid particles from the flue gas to reduce particulate emissions. Subsequent reinjection of the solid particles to the furnace improves carbon burnout. The flue gas scrubber 64 is used to remove sulfur dioxide and to remove any small aerosol particulates from the air stream, ensuring that the emissions associated with the burning of the petroleum coke are minimized. As illustrated with reference to FIG. 5, a burning facility 16 may comprise multiple types of burners. For purposes of this application, the petroleum coke burner, or burners 50 will be described in greater detail below.

[0030] Reference is now made to FIG. 6, where the exemplary petroleum coke burners 50 are illustrated in further detail. In exemplary operation, the injected secondary fuel source provides a central flame core in a burner 50. The injected petroleum coke envelopes the central flame core and is ignited by the heat from the flame. [0031] In FIG. 6, the air flow features of the petroleum coke burner are illustrated.

The air flow features of a petroleum coke burner 50 tends to allow for minimization of the NO_x that is a by product of the burning process. The petroleum coke burner 50 is shown in FIG. 6 with respect to its various air zones, or operation zones, including a flame core zone 70, a reduced reaction zone 72, middle air zone 74, an air rich outer zone 76, a fuel mixing zone 78 and a combustion zone 80. The secondary air zones 82 are used to control the mixing of air fuel in the primary burner area 84 and the operation of the secondary air zones 82 are illustrated in greater detail below.

[0032] The multiple air zones of the burner 50 allow for the creation and preservation of multiple streams of air that control the mixing of the fuels and air, which tend to improve the combustion reaction thus supporting higher petcoke to oil ratios. The flame core 70 that is produced by the centrally located oil burner is a high temperature core which causes earlier ignition of the ground petroleum coke. By igniting the petroleum coke quickly, the residence time associated with the burning of the petroleum coke is reduced and the flame stability is maximized as a result thus making it suitable for use in furnaces originally designed exclusively for combustion of liquid fuels which typically require low combustion residence times. The flame core zone 72 tends to allow for reduced levels of nitrogen to be released as a result of the injection of the respective primary and secondary fuels in a low stochiometric zone. The zones that are described herein allow for the combustion process to be undertaken in a staged and controlled manner. Conventional burner systems that do not rely on the zones as have been described herein do not allow for a controlled burn environment. The use of the zones tends to increase the turbulence and causes a recirculation of the hot gases which stabilizes the ignition point and flame front. [0033] Reference is now made to FIG. 7, where a cross sectional schematic illustrating a windbox/burner combination, is shown. The windbox/burner combination 82 in an exemplary embodiment encloses the burner, which comprises an innerzone damper 86, an outer zone damper 88, a fuel assembly 90, an inner zone 92, a middle zone 94, and an outer zone 96. The multiple zones of the burner allow for the thorough mixing and combustion of the primary and secondary fuel sources, in which the secondary fuel source provided through assembly 90 provides a stable heat source to ignite the primary fuel source carried in transport air passing through the windbox 82, and in which flame stability is maintained by the air zones and related air swirls into which transport air carrying the primary fuel is provided. The contact of the petroleum coke with the air swirl allows for the petroleum coke to be exposed to the entire flame and allows for early ignition of the fuel. The inner zone 92 has associated with it an inner zone damper 86, and the outer zone 96 has associated with an outer zone damper 88. The respective dampers 86, and 88, are to regulate air mass flow, and/or split, between the zones 82 and 84. The inner air zone 92 allows for the formation of a flame core in a fuel rich environment that has variable air flow and where the swirl of the flame may be adjusted. The middle air zone 94 is used to separate the inner air zone 92, which may also be referred to as a first combustion zone from the outer air zone, which may also for purposes of this description be referred to as a secondary combustion zone. The outer air zone 96 allows for variable air flow within the secondary combustion zone and staging of combustion air for NO_x reduction and also provides the mechanism by which the swirl of the flame may be adjusted. [0034] The use of swirl vanes in an exemplary embodiment that forces the air that is circulated within the assembly to rotate. Where the vanes have steeper angles there is a direct correlation between the angle and the rotational speed of the air. As rotating air is inherently unstable and therefore creates turbulence and recirculation, the angle of the swirl vanes is used in an exemplary embodiment to cause and control that effect. The generation of swirls, or swirl effects, can generate different burner characteristics, including providing control of the shape of the flame, flame detachment, NOx production and combustion efficiency.

[0035] The shape of the flame that is used in the petroleum coke burners 50 is controlled through the use of swirlers in the inner and outer air zones respectively, which are used as described above to create turbulence and increase combustion efficiency. In different embodiments, the swirlers, or swirl vanes, can be manually or automatically operated and controlled. The swirl vanes can be in a pre-set arrangement, or be continually adjustable to provide modulated control over the burning process.

[0036] Reference is now made to an exemplary process by which the respective primary and secondary fuel sources are provided to the burner 50. The ground petroleum coke and the secondary fuel are fired from the injector assembly to the respective petroleum coke burner 50 simultaneously. In an exemplary embodiment, the ground petroleum coke will be added in such a quantity so as to yield 80% of the total yield of heat generated by the burners, generated by the burning of petroleum coke, whereas 20% will be generated by the burning of a secondary fuel. The grinding of the petroleum coke to the particle size as described with reference to the pulverization method provides for increased reactivity due to the increased surface area of the fuel particle that is exposed to the flame source, which promotes early ignition. By surrounding an oil flame in an exemplary embodiment with the ground petroleum coke as described herein, the swirlers tend to induce mixing of the oil and petcoke flames. By ensuring that the oil flame and petroleum coke are mixed at the point of petcoke injection, the rapid ignition of the ground petroleum coke is ensured while retaining flame stability which eliminates potential flameouts which may be caused by flame detachment as a result of delayed petcoke ignition. Through the processes and systems described herein, the ground petroleum coke, which is generally considered a low reactive fuel, is being burnt in furnaces that are designed for liquid fuels. As furnaces that have been designed for liquid fuels have generally low combustion residence times, the preparation of the petroleum coke and injection of the petroleum coke into the burner assembly allows for use of the solid petroleum coke as a primary fuel source for furnace/burner combinations designed for liquid fuel. The details of an exemplary implementation of an embodiment of the above-described burner system is shown as a schematic diagram in FIG. 8. [0037] While the foregoing invention has been described in some detail for purposes of clarity and understanding, it will be appreciated by those skilled in the relevant arts, once they have been made familiar with this disclosure, that various changes in form and detail can be made without departing from the true scope of the invention in the appended claims. The invention is therefore not to be limited to the exact components or details of methodology or construction set forth above. Except to the extent necessary or inherent in the processes themselves, no particular order to steps or stages of methods or processes described in this disclosure, including the Figures, is intended or implied. In many cases the order of process steps may be varied without changing the purpose, effect, or import of the methods described.

Claims

1. A burner system for firing first and second fuels in a burner, comprising: a solid fuel nozzle assembly having the first fuel passing therethrough and injecting the first fuel around a core flame produced by the second fuel in the burner; a fuel assembly having the second fuel passing therethrough, and forming the core flame for igniting the primary fuel; a windbox in communication with the solid fuel nozzle assembly, the windbox having transport air passing therethrough and conveying the first fuel to the burner; one or more adjustable dampers in the windbox to control airflow through one or more air zones in the burner to stage combustion air into the transport air for NO_x reduction during burning; and one or more adjustable swirl vanes in the windbox to control movement of the transport air and combustion air in the burner, wherein the core flame ignites the first fuel in the burner and the one or more swirl vanes are adjustable to control movement of the primary fuel to the core flame for ignition and control flame swirl within the burner during firing of the first and second fuels.

2. The burner system of claim 1, wherein the first fuel is ground petroleum coke.

3. The burner system of claim 2, wherein the ground petroleum coke is ground to at least 90% passing 200 mesh.

4. The burner system of claim 3, wherein the second fuel is a highly volatile support fuel.

5. The burner system of claim 4, wherein the highly volatile fuel is a heavy fuel oil.

6. The burner system of claim 5, wherein the fuel assembly passes through the solid fuel nozzle assembly and windbox into the burner.

7. The burner system of claim 4, wherein the highly volatile fuel is a light fuel oil.

8. A burner system of claim 1, wherein the burner system is designed exclusively for liquid fuel sources.

9. A method for firing first and second fuels in a burner, the method comprising: passing the second fuel through a fuel assembly into the burner and forming a core flame zone therefrom; passing transport air conveying the first fuel therein to the burner, the transport air passing through a solid fuel nozzle assembly and injecting the first fuel around the core flame zone produced by the second fuel; creating one or more air zones to stage combustion air into the transport air for NO_x reduction during burning, wherein airflow to the zones is controlled by dampers in the burner; and controlling one or more swirl vanes movement of the transport air and combustion air to provide ignition of the first fuel by the core flame zone provided by the second fuel, the one or more swirl vanes being adjustable to control flame swirl within the burner during firing of the first and second fuels.

10. The method of claim 9, wherein the first fuel is ground petroleum coke.

11. The method of claim 10, wherein the ground petroleum coke is ground to at least 90% passing 200 mesh.

12. The method of claim 11 , wherein the second fuel is a highly volatile support fuel.

13. The method of claim 12, wherein the highly volatile fuel is a heavy fuel oil.

14. The method of claim 12, wherein the highly volatile fuel is a light fuel oil.

15. The method of claim 9, wherein the burner system is designed exclusively for liquid fuel sources.