MX2013011077A

MX2013011077A - Oxy-fuel furnace and method of heating material in an oxy-fuel furnace.

Info

Publication number: MX2013011077A
Application number: MX2013011077A
Authority: MX
Inventors: Aleksandar Georgi Slavejkov; Gregory J Buragino; Shailesh Pradeep Gangoli; Hiaoyi He
Original assignee: Air Prod & Chem
Priority date: 2011-04-05
Filing date: 2012-04-05
Publication date: 2013-10-17
Also published as: KR20130137036A; CA2853477C; EP2694877A1; CN103443541A; BR112013025347A2; WO2012138831A1; CA2853477A1; US20130095437A1

Abstract

An oxy-fuel furnace and method of heating material in an oxy-fuel furnace are disclosed. The method includes combusting oxygen and fuel with an oxy-fuel burner arrangement in the oxy-fuel furnace forming combustion gases, and maintaining a vortex including the combustion gases within a central region of an enclosure of the oxy-fuel furnace. The oxy-fuel burner arrangement includes a plurality of high momentum oxy-fuel burners arranged at an angle to generate the vortex, the angle being greater than 15 degrees but less than 75 degrees with respect to a furnace wall boundary of the enclosure, an angular velocity of greater than 0.07 radians per second, or a combination thereof. The furnace includes an oxy-fuel burner arrangement including at least two high momentum oxy-fuel burners having high shape factor nozzle geometries, and an enclosure. The vortex increases convective heating within the enclosure and uniformity of heating within the enclosure.

Description

OXI-COMBUSTIBLE OVEN AND METHOD FOR HEATING MATERIAL IN AN OXI-FUEL OVEN BACKGROUND OF THE INVENTION The present invention is directed to systems and methods for heating materials. More specifically, the present invention is directed to oxy-fuel furnaces and methods for heating material when using oxy-fuel furnaces.

The oxides of. Nitrogen (NOx) are among the primary air pollutants emitted by combustion processes. Because NOx promotes the formation of harmful atmospheric reaction products that cause esogony, air quality standards have been imposed by various government agencies to limit the amount of NOx that can be emitted into the atmosphere. As a result of increased environmental legislation in many countries and increased global awareness of air pollution, modern combustion technology has been improved to reduce NOx emissions from many types of combustion equipment.

The secondary metals industry is generally considered to be a major source of NOx contamination and is therefore subject to stringent regulations on NOx emissions. The reduction of NOx production in the combustion processes becomes more important in this industry as the demand for metals increases while the environmental regulations in the NOx. they become more and more rigorous. The complete oxy-fuel combustion theoretically can produce very low NOx emissions due to the lack of nitrogen in the oxidant.

The secondary metals industry has had innovation that reduces NOx emissions. Such a known system is described in U.S. Patent Application Publication No. 2007/0254251, which is incorporated herein by reference in its entirety. The known system achieves spacious combustion by dragging the furnace gases in a flame zone. Such a system reduces NOx emissions. However, additional reductions are desirable, especially if the additional combustion NOx reductions are balanced with the concerns of heat energy consumption, for example, by balancing the radiative and convective heat transfer components.

Traditional low-momentum oxy-fuel combustion is dominated by radiative heat transfer but lacks a convective heating component. The lack of the convective component is due to the low gas volumes and can increase the inconsistent or irregular heating potential, hot spots and the generation of NOx. In contrast, combustion of air-fuel lacks radiative heating efficiency due to the dilution of N2. However, air-fuel combustion can have a strong convective heat transfer component due to the higher flue gas volumes that can be useful in heating a product when combined with radiation. However, the radiation from an air-fuel flame is much lower than the radiation from an oxy-fuel flame.

An oxy-fuel furnace and method for heating material in an oxy-fuel furnace that does not suffer from one or more of the above disadvantages would be desirable in the art.

BRIEF DESCRIPTION OF THE INVENTION In an exemplary embodiment, a method for heating material in an oxy-fuel furnace includes burning oxygen and fuel with an oxy-fuel burner arrangement in the oxy-fuel furnace that forms combustion gases, and maintaining, a vortex that includes the combustion gases within a central region of an enclosure of the oxy-fuel furnace. The oxy-fuel burner arrangement includes a plurality of high-moment oxy-fuel burners arranged at an angle to generate the vortex, the angle that is greater than 15 degrees but less than 75 degrees with respect to a wall boundary of enclosure oven.

In another exemplary embodiment, a method for heating material in an oxy-fuel furnace includes burning oxygen and fuel with an oxy-fuel burner arrangement in the oxy-fuel furnace that forms combustion gases and maintaining a vortex that includes combustion gases within a central region of an enclosure of the oxy-fuel furnace. The vortex has an angular velocity greater than 0.07 radians per second.

In another exemplary embodiment, an oxy-fuel furnace includes an oxy-fuel burner arrangement that includes at least two high-moment oxy-fuel burners having high form factor nozzles and an enclosure. The oxy-fuel burner arrangement includes a plurality of high-moment oxy-fuel burners arranged at an angle to generate a vortex, the angle that is greater than 15 degrees but less than 75 degrees with respect to a wall boundary. enclosure oven. The vortex increases the convective heating within the enclosure and the heating uniformity within the enclosure.

Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF SEVERAL V OF THE DRAWINGS FIGS. 1 to 4 are schematic drawings of oxy-fuel furnaces according to embodiments of the description.

FIG. 5 is a three-dimensional schematic drawing of an oxy-fuel furnace according to one embodiment of the description.

FIG. 6 is a graphic comparison of an exemplary method for heating material in an oxy-fuel furnace according to the description and other methods for heating material.

FIG. 7 is a graphic illustration of the surface temperature as a function of time for an exemplary oxy-fuel furnace according to the description.

FIG. 8 is a comparative graphical illustration of surface temperatures of the walls of the furnace and the material due to the operation of an oxy-fuel furnace without formation of a vortex.

FIG. 9 is a graphic illustration of surface temperatures of furnace walls and material due to the operation of an oxy-fuel furnace that forms a vortex according to the description.

Whenever possible, the same reference numbers will be used by all the drawings to represent the same parts.

DETAILED DESCRIPTION OF THE INVENTION An exemplary oxy-fuel furnace and method for heating material in an oxy-fuel furnace are provided. The embodiments of the present disclosure increase the convective contribution of heat transfer in an oxy-fuel heating process, decrease the cycle time to achieve certain temperatures, increase efficiency or combinations thereof.

With reference to FIGS. 1 through 5, according to one embodiment, an oxy-fuel furnace 100 includes at least two high-moment oxy-fuel burners 102 and a generally 104 enclosure defining a combustion zone within the oxy-fuel furnace 100 The enclosure 104 is of any suitable geometry and is defined by a boundary of the furnace wall 108. For example, in one embodiment, the enclosure 104 is of a cuboid or generally cuboid geometry. In another embodiment, the enclosure 104 is of a cylindrical or generally cylindrical geometry. The enclosure includes a central region, for example, defined by the burner axis of each of the burners 102, the axis of the burner which is a line extending from the middle part of the burner. The oxy-fuel furnace 100 includes other suitable features as are necessary to maintain combustion, heating, other operational conditions or combinations thereof.

The enclosure 104 is configured to contain at least a portion of a vortex 106 of combustion gases, such as an oven-scale vortex. The vortex 106 is formed by deflecting the heating of the burners 102 which entrains the surrounding combustion gases in the flame zone within the enclosure 104, thereby resulting in a stirring (or gas equilibration) forming the vortex 106. , for example, when transporting the combustion gases. In one embodiment, vortex 106 is used with spacious combustion, combustion achieved by entraining furnace gases in a flame zone. In one embodiment, the burners 102 form two different gas recirculation streams from the furnace, for example, a horizontal component and a vertical component that contracts the vortex 106 due to the differential pressure within the enclosure 104.

The burners 102 are arranged and arranged to form the vortex 106. The oxy-fuel furnace 100 includes two of the burners 102 (see FIGS 1 and 2), three of the burners 102, four of the burners 102 (see FIG 3), or more than four of the burners 102. As shown in FIG. 1, in one embodiment, the burners 102 are positioned on opposite sides of the enclosure 104 at the boundary of the furnace wall 108, in a stepped orientation. As shown in FIG. 2, in one embodiment, two of the burners 102 are positioned in the boundary of the furnace wall 108 in an angular configuration. As shown in FIG. 3, in one embodiment, four of the burners 102 are positioned in the boundary of the furnace wall 108 in an angular configuration. Other modalities include combinations of these modalities.

The burners 102 are any of the suitable burners capable of being used under high moment conditions, such as, the burners disclosed in United States Patent Application Publication No. 2007/0254251, which is incorporated by reference in its whole and / or a high form factor burner. As used herein, the term "high moment" refers to the flow of gases through at least one burner passage channel 102 that is greater than about 0.69 kg-ft / s2 (5 lb-ft / s2). ). In some embodiments, the flow of gases through at least one passageway of the burner 102 is greater than about 1.38 kg-ft / s2 (10 lb-ft / s2), for example, as with the natural gas it has. a flow expense between approximately 1.38 kg-ft / s2 (10 lb-ft / s2) and 9.69 kg-ft / s2 (70 lb-ft / s2), allowing the heating at higher speeds, improving cycle times, reducing localized overheating (such as overheating of thermocouples) or combinations thereof. As used herein, the term "high form factor burner" refers to a burner having a nozzle perimeter or multiple perimeters that is / is larger than a perimeter of a circular nozzle. For example, a relative perimeter ratio (Prei) is a ratio of the nozzle perimeter (s) of a high form factor burner (such as a non-circular burner) as compared to the perimeter of a circular nozzle. For nozzles that have areas of 6.45 cm2 (1.0 inch2), a circular nozzle has a perimeter of 8.99 cm (3.54 inches). In this way, a high-form factor burner that has a nozzle with a 6.45 cm2 (1.0 inch2) has a perimeter that is greater than 8.99 cm (3.54 inches). In one embodiment, the high form factor burner has a relative perimeter ratio of 1.96.

With reference to FIGS. 4 and 5, in one embodiment, two or more of the burners 102 form the vortex 106 by being angled at an angle T, with respect to the boundary of the wall of the furnace 108. The angle T corresponds to the specific configuration of the oxygen furnace. -combustible 100 (for example, geometry, size or combinations thereof), materials that are heated (eg, metal or metallic materials, such as, ingots, sheets, casting materials, forged materials, aluminum, iron, steel, ferrous materials, non-ferrous materials or combinations thereof), other appropriate operating considerations (eg, flow expenses, oxy-fuel compositions, enclosing pressure, enclosing material, etc.) or a combination thereof. The heated material is positioned in any suitable portion within the enclosure 104, for example, at the bottom of the enclosure 104. In one embodiment, the oxy-fuel includes a composition of at least 50 mol% oxygen in the oxidant ( example, of an oxidative flow of 95% in mol of oxygen) and fuel (for example, natural gas, propane, synda, low Btu fuels, etc.).

In one embodiment, angle T is greater than 15 degrees, greater than 30 degrees, greater than 45 degrees, greater than 60 degrees, less than 75 degrees, less than 60 degrees, less than 45 degrees, less than 30 degrees or any interval , suitable sub-interval, combination or sub-combination thereof.

In one embodiment, the oxy-fuel furnace 100 increases the mixing and entrainment of gas from the furnace which reduces the peak flame temperature and generation of thermal NOx. The increased mixing is caused by the burners 102 creating a lower pressure region having a first pressure within the vortex 106 and a higher pressure region having a second pressure that is close to the boundary of the wall of the oven 108 of the confinement 104 The force (Fini) carried in the enclosure 104 of the furnace 100 by the flow of the combustion gases through the burner 102 can be represented as shown in Equation 1: Finí = Pinl · Qinl ß Uinl (Eq. 1) As used in Equation 1, pini refers to the combustion flux density entering the enclosure 104 (for example, as measured in lb / ft3, dependent on the flame temperature). Uini refers to the speed of inflows entering the enclosure 104 (for example, as measured in foot / s). Qini refers to the total input flow expense in the enclosure 104 (for example, as it is measured in foot / s).

In one embodiment, the entrainment of the furnace gases in the flame is increased by using nozzles in one or more of the burners 102 that have a high form factor. The actual flow achieved by the strong interaction of the nozzles with the furnace gases can be represented as shown in Equation 2: Finí = Pinl · (Qinl · Prel) · üini (EC.2) As used in Equation 2, Prei refers to the relative perimeter ratio and Qini · Prei refers to the total current inflow expense (for example, as measured in ft3 / s).

The vortex is generated by the balance of forces carried in the furnace and the viscous dissipation (FViSc) of these flows in the furnace, given by Equation 3: Fvisc = Pfurn · Vfurn · (UtVde) (EC.3) As used in Equation 3, PfUrn refers to the density of furnace gases within the enclosure 104 (for example, as measured in lb / ft3, dependent on the flame temperature). Vfurn refers to the volume of the enclosure 104 in the oxy-fuel furnace 100 (for example, as measured in pie3). ut refers to the tangential velocity of the Vortex in diameter within the enclosure 104 (for example, as measured in ft / s). de refers to a characteristic dimension of Vortex 106 (e.g., an equivalent diameter measured standing).

In one embodiment, the angular velocity (uj of vortex 106 is defined using Equation 4, which is based on the consolidation of equations 2 and 3: Uu = V (pfurn · ((Qinl · üinl · de) / Vfurn)) / nds (Eq. 4) As used in Equation 4, prat refers to an input flux density ratio (pini) to furnace gases (PfUrn) - The density ratio is between 0.8 for air-fuel combustion and 0.6 for air-fuel combustion. oxy-fuel combustion due to the difference in the temperature of the flame.

In one embodiment, the burners 102 increase a convective heat transfer component (in addition to a radiative heat transfer component) to increase the uniformity and / or efficiency of the heating. For example, in one embodiment, a vortex-induced component of the convective heat transfer component increases uniformity and efficiency when using the burners 102. The vortex-induced component is achieved by arranging and / or orienting the burners 102 such that the vortex 106 is formed and maintained within the enclosure 104. In one embodiment, the convective heat transfer reduces or eliminates the direct impact of a flame on the material that is heated.

In one embodiment, the vortex-induced component of the convective heat transfer component impacts between 15% and 75% of the area (plan view) of the enclosure 104. In additional embodiments, the convective heat transfer component impacts between 30% and 60%, between 30% and 45%, between 45% and 60%, approximately 15%, approximately 30%, approximately 45%, approximately 60%, approximately 75% or any suitable interval, sub-interval, combination or sub-combination thereof. In one embodiment, the vortex-induced component is increased by increasing the angular velocity (??) of vortex 106.

With reference to FIG. 6, the uniformity and efficiency of the heating with the burners 102 forming the vortex 106 is improved compared to the heating of a single side and opposite (but not stepped) burn. FIG. 6 shows profiles for heating steel ingots with the enclosure 104 which is in a pit furnace under different configurations. A vortex-induced heating profile 602 is d on using the burners 102 to form the vortex 106 as described herein. A heating profile of the single-side burner 604 is d on using one-sided heating, positioning the steel ingots at a distal end of a burner and moving the steel ingots toward an end near the burner. A heating profile of the opposite burner 606 is d on having two burners in opposite walls of a furnace. The jets collide and have a tendency to overheat the steel ingots in the center of the pit furnace. The heating profile of the opposite burner 606 also creates large heat flow gradients compared to the other configurations.

As shown in FIG. 6, the vortex-induced heating profile 602, which includes the vortex-induced component, is maintained within a temperature range of less than -3.88 ° C (25 ° F). In further embodiments, the vortex-induced heat profile 602 including the vortex-induced component is maintained within a temperature range of less than -12.22 ° C (10 ° F), less than -15 ° C (5 ° F) ), or is substantially constant. In contrast, the heating profile of the single side burner 604 and the heating profile of the opposite burner 606 exceeds the temperature range of -3.88 ° C (25 ° F).

With reference to FIG. 7, the surface temperature of the material heated under the vortex-induced heat profile 602 and the heating profile of the opposite heater 606 described above are shown over time. Each profile corresponds with a maximum surface face temperature profile 702 and an average face temperature profile 704. The maximum surface face temperature profile 702 is substantially consistent over time for the vortex-induced heat profile 602 and the heating profile of the opposite burner 606. The average face temperature profile 704 bifurcates through time allowing a decrease in cycle time to achieve a predetermined average face temperature under the vortex-induced heat profile 602 in comparison with the heating profile of the opposite burner 606. In one embodiment, the decrease in the cycle time is at least 10%, between 10% and 20%, approximately 15%, or any suitable interval, sub-interval, combination or sub-combination thereof.

FIGS. 8 and 9 comparatively illustrate the heating of the material within the enclosure 104 in accordance with the vortex-induced heat profile 602 (see FIG.9) in contrast to the heating profile of the opposite burner 606 (see FIG.8). Specifically, FIG. 8 illustrates the temperature of the walls within an enclosure heated by the heating profile of the opposite burner 606 and FIG. 9 illustrates the temperature of the furnace wall boundary 108 heated by the vortex-induced heat profile 602. FIG. 8 shows that the heating profile of the opposite burner 606 forms a hot spot 802. FIG. 9 shows that the vortex-induced heat profile 602 forms a more uniform temperature gradient, for example, that does not have regions of the furnace wall boundary 108 that exceeds the furnace wall boundary temperature 108 near the burner 102, to thereby allow the increased amounts of energy input in the furnace oxy-fuel 100 and / or reduce the cycle times to achieve a predetermined temperature.

In one embodiment, the enclosure 104 has dimensions of 7.32 m x 2.74 m x 4.26 m (24 feet x 9 feet x 14 feet). In a heating process achieved in enclosure 104, the heating process uses an average of approximately 10 MMBTU / hr of air-fuel heating expense and approximately 6 MMBTU / hr of oxy-fuel heating expense (assuming 45% and 75% heat 5 available in the enclosure 104, respectively) to form the vortex 106. The angular velocity (??) of the vortex 106 is calculated, for example, based on Equations 1 to 4 above and depends on the fuel used and the burner used. For example, combustion of air or fuel with a stepped burner configuration (see FIG.1) results in an angular velocity (??) of 0.099 rad / s and an angled burner configuration (see FIG.2) gives as a result an angular velocity (??) of 0.087 rad / s. The combustion of low moment oxy-fuel 15 with a stepped burner configuration (see Fig. 1) results in the angular velocity (??) of 0.035 rad / s and an angled burner configuration (see Fig. 2) results in an angular velocity (??) of 0.031 rad / s. The combustion of high-moment oxy-fuel with a stepped burner configuration (see Fig. 1) and circular nozzles results in an angular velocity (?) Of 0.079 rad / s and an angled burner configuration (see Fig. 1). FIG 2) results in an angular velocity (??) of 0.070 rad / s. The combustion of high-velocity oxy-fuel with a stepped burner configuration (see FIG.1) and non-circular nozzles results in an angular velocity (??) of 0.111 rad / s and an angled burner configuration (see FIG. FIG 2) results in an angular velocity (??) of 0.097 rad / s.

In view of such differences, in one embodiment of the description, the burners 102 of the furnace 100 are arranged and operated such that the vortex has an angular velocity that is greater than a corresponding angular velocity for an air-fuel combustion vortex that would be formed by the combustion of air-fuel, for example, which is at least 0.07 radians per second. In one embodiment, the vortex 106 formed by combustion of the oxy-fuel with the burners 102 having non-circular nozzles has an angular velocity, which is 10% greater than a vortex that would be formed by the combustion of air-fuel, 40% greater than the vortex 106 formed by the burners 102 having the circular nozzles, 200% larger than a vortex that would be formed by the combustion of the low-moment oxy-fuel or a combination thereof.

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes can be made and equivalents can be substituted by elements thereof without departing from the scope of the invention. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is proposed that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all modalities that fall within the scope of the appended claims.

Claims

1. A method for heating material in an oxy-fuel furnace, the method characterized in that it comprises: burn oxygen and fuel with an oxy-fuel burner arrangement in the oxy-fuel furnace that forms combustion gases; Y maintain a vortex that includes the combustion gases within a central region of an enclosure of the oxy-fuel furnace; wherein the oxy-fuel burner arrangement comprises a plurality of high-moment oxy-fuel burners arranged at an angle to generate the vortex, the angle which is greater than 15 degrees but less than 75 degrees with respect to a limit of the furnace wall of the enclosure.

2. The method according to claim 1, characterized in that at least one of the plurality of high-moment oxy-fuel burners includes a high-form factor nozzle.

3. The method according to claim 1, characterized in that the plurality of the high moment oxy-fuel burners includes step burners.

4. The method according to claim 1, characterized in that the plurality of high-moment oxy-fuel burners includes two burners.

5. The method according to claim 1, characterized in that the plurality of high moment oxy-fuel burners includes four burners.

6. The method in accordance with the claim 1, characterized in that the plurality of high-moment oxy-fuel burners includes more than four burners.

7. The method according to claim 1, characterized in that the vortex has an angular velocity that is greater than 0.07 radians per second.

8. The method according to claim 1, characterized in that the angle is between approximately 30 degrees and approximately 60 degrees.

9. The method according to claim 1, characterized in that the vortex induces convective heat in an area of the enclosure, the area that is between approximately 15%. and approximately 75% of the enclosure.

10. The method according to claim 1, characterized in that the vortex induces convective heat in an area of the enclosure, the area that is between approximately 30% and approximately 60% of the enclosure.

11. The method according to claim 1, characterized in that the enclosure has a first pressure within the vortex that is less than a second pressure that is close to the limit of the enclosure's furnace wall.

12. The method according to claim 1, characterized in that it also comprises heating metal inside the enclosure.

13. The method according to claim 1, characterized in that it also comprises heating aluminum inside the enclosure.

14. The method according to claim 1, characterized in that the vortex increases the convective heating within the enclosure.

15. The method according to claim 1, characterized in that the vortex increases the uniformity of heating within the enclosure.

16. A method for heating material in an oxy-fuel furnace, the method characterized in that it comprises: burn oxygen and fuel with an oxy-fuel burner arrangement in the oxy-fuel furnace that forms combustion gases; Y maintain a vortex that includes the combustion gases within a central region of an enclosure of the oxy-fuel furnace; where the vortex has an angular velocity greater than 0.07 radians per second.

17. The method according to claim 16, characterized in that at least one of the plurality of high moment oxy-fuel burners includes a non-circular nozzle geometry.

18. The method according to claim 16, characterized in that the plurality of high-moment oxy-fuel burners includes staggered burners.

19. The method according to claim 16, characterized in that the angle is greater than 15 degrees but less than 75 degrees with respect to a limit of the furnace wall of the enclosure.

20. An oxy-fuel furnace, characterized in that it comprises: an oxy-fuel burner arrangement that includes at least two high-moment oxy-fuel burners that have high form factor nozzles; and an enclosure; wherein the oxy-fuel burner arrangement comprises a plurality of high-moment oxy-fuel burners arranged at an angle to generate a vortex, the angle that is greater than 15 degrees but less than 75 degrees with respect to a limit of the furnace wall of the enclosure; where the vortex increases the convective heating within the enclosure and the heating uniformity within the enclosure.