METHOD FOR SIMULTANEOUSLY INJECTING A FUEL GAS AND AN OXYGEN-RICH GAS INTO A UNIT

Abstract

A burner comprises a primary nozzle for injecting an oxygen-rich gas. The primary nozzle is designed as a supersonic nozzle. A coaxial nozzle having an annular outlet opening is provided for injecting a fuel gas. The coaxial nozzle is designed as a subsonic nozzle and is coaxial to the primary nozzle. The primary nozzle has a convergent portion and a divergent portion, which adjoin each other at a radius of the narrowest cross-section. The annular outlet opening is located at an end face of the burner. The fuel gas, in the form of hydrogen or a mixture of hydrogen and a hydrocarbon-containing gas, is injected at a fixed inlet pressure and a fixed inlet volumetric flow rate, with respect to a planned thermal power of the burner. In contrast, the inlet pressure and the inlet volumetric flow rate of the oxygen-rich gas are varied according to the application.

Claims

1.-8. (canceled)

9. A method for simultaneously injecting a fuel gas and an oxygen-rich gas into a unit, comprising: providing a burner (1) which comprises a primary nozzle (2) for injecting the oxygen-rich gas, the primary nozzle being designed as a supersonic nozzle having a convergent portion (6) and a divergent portion (7) which adjoin each other at a radius of a narrowest cross-section (8), and a coaxial nozzle (3) having an annular outlet opening (4) for injecting the fuel gas located at an end face (5) of the burner (1), the coaxial nozzle being designed as a subsonic nozzle and being arranged coaxial to the primary nozzle (2); injecting the fuel gas, in the form of hydrogen or in the form of a fuel-gas mixture of hydrogen and a hydrocarbon-containing gas, at a fixed inlet pressure and a fixed inlet volumetric flow rate with respect to a planned thermal power of the burner (1); and varying an inlet pressure and an inlet volumetric flow rate of the oxygen-rich gas according to an application.

10. The method according to claim 9, wherein the hydrocarbon-containing gas is natural gas.

11. The method according to claim 9, wherein the inlet pressure of the oxygen-rich gas is varied with respect to the inlet pressure of the fuel gas by a factor in the range of 4 to 9.5.

12. The method according to claim 9, wherein the inlet volumetric flow rate of the oxygen-rich gas is varied with respect to the inlet volumetric flow rate of the fuel gas by a factor in the range of 1.20 to 1.80.

13. The method according to claim 9, wherein the oxygen-rich gas is injected with respect to a design state of the burner (1) at an inlet pressure in the range of 0.60 to 1.40.

14. The method according to claim 9, wherein the oxygen-rich gas is injected with respect to a design state of the burner (1) at an inlet volumetric flow rate in the range of 0.80 to 1.20.

15. The method according to claim 9, wherein the unit is selected from the group consisting of a basic oxygen furnace (BOF), an argon oxygen decarburization converter (AOD), a submerged arc furnace (SAF), an electric arc furnace (EAF), a shaft arc furnace (SHARC), a primary energy melter (PEM), a converter arcing (CONARC), a walking beam furnace, a walking hearth furnace, a pusher furnace, a single-chamber melting and casting furnace, a multi-chamber furnace, a universal rotary tilting furnace (URTF), a compact remelting plant (CTRP), a chip remelting furnace, a top blown rotary refiner (TBRR), a Peirce-Smith converter (PSC), an anode furnace, a drum furnace, a shaft furnace, a cupola furnace, a hearth furnace, a tilting furnace, a Kivcet furnace, a bath melting furnace, and a port furnace.

16. A method for adjusting a flame pattern of a burner (1) which comprises a primary nozzle (2) for injecting an oxygen-rich gas, the primary nozzle being designed as a supersonic nozzle having a convergent portion (6) and a divergent portion (7) which adjoin each other at a radius of a narrowest cross-section (8), and a coaxial nozzle (3) having an annular outlet opening (4) for injecting a fuel gas located at an end face (5) of the burner (1), the coaxial nozzle being designed as a subsonic nozzle and being arranged coaxial to the primary nozzle (2), the method comprising: injecting the fuel gas, in the form of hydrogen or in the form of a fuel-gas mixture of hydrogen and a hydrocarbon-containing gas, at a fixed inlet pressure and a fixed inlet volumetric flow rate with respect to a planned thermal power of the burner (1); and varying the inlet pressure and the inlet volumetric flow rate of the oxygen-rich gas according to an application.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIGS. 1a to 1c show a design variant of a burner in different operating phases.

[0035] FIGS. 2a to 2c show a schematic illustration of the different states of the burner.

[0036] FIGS. 3a and 3b show a comparison of a flame pattern in the designed and over-expanded state.

[0037] FIGS. 4a and 4b show a graphical illustration of the determined values of the respective flames from FIGS. 3a/3b in a diagram.

DETAILED DESCRIPTION

[0038] FIGS. 1a to 1c show a design variant of a burner 1 in different operating phases. The burner 1 is suitable for simultaneously injecting a fuel gas and an oxygen-rich gas, and comprises a primary nozzle 2 for injecting the oxygen-rich gas, which primary nozzle is designed as a supersonic nozzle and a coaxial nozzle 3 having an annular outlet opening 4, which coaxial nozzle is designed as a subsonic nozzle and is coaxial to the primary nozzle 2, which is located at an end face 5 of the burner 1. As shown by the illustration, the primary nozzle 2 has a convergent portion 6 and a divergent portion 7, which adjoin each other at a radius of the narrowest cross-section 8. The primary nozzle 2 has a port 9 at the rear region of the burner 1, through which the oxygen-rich gas, such as pure oxygen, can be guided to the burner 1 from a valve station (not shown). In the present design variant, the coaxial nozzle 3 has two ports 10, 11. Fuel gas can be supplied to the burner 1 through the rear port 10 and air can be supplied through the front port 11. In burner mode, the fuel gas can also be supplied to burner 1 via the port 11.

[0039] FIGS. 2a to 2c show a schematic illustration of the different states with the corresponding flame patterns of burner 1.

[0040] FIG. 2a shows the design state. The design state is present if, for a correctly designed Laval nozzle 2, the actual inlet pressure and inlet volumetric flow rate correspond to the so-called design pressure and design volumetric flow rate. The pressure at the outlet of the primary nozzle 2 then corresponds to the ambient pressure. In the design state, the oxygen-rich gas exits from the primary nozzle with maximum impulse flow, wherein the structure of the so-called supersonic free jet 12—in contrast to the classic subsonic free jet—is undisturbed and coherent. Consequently, its length L is also maximum. Therefore, the flame pattern is less pulsating.

[0041] Directly behind the outlet of the primary nozzle 2, a free jet core 13 is formed, in which the flow velocity, pressure and temperature are approximately constant. Such behavior is indicated in FIG. 2a by the homogeneous velocity profile 14, which is maximum in the design state. Downstream of the free jet core 13, the flow velocity, the pressure and the temperature decrease as a result of the increasing friction or dissipation effects, as the case may be, until the supersonic free jet 12 of the length L changes from the supersonic to the subsonic state at point 15. Consequently, the point 15 marks the position where the Mach number is equal to one (Ma=1). The premixed fuel gas free jet 16 exiting coaxially and parallel to the primary nozzle 2 from the coaxial nozzle 3 initially mixes only slightly with the significantly faster oxygen-rich jet, i.e. the fuel gas is only moderately entrained via the initially small vortex structures in a free jet shear layer 17. Such free jet shear layer 17 characterizes the interface between the primary and secondary jets 12, 16. The vortex size in the free jet shear layer 17 remains constant for a more or less long distance before the vortex size increases and more fuel gas is drawn in. The entire jet, i.e. the primary and secondary jets 12, 16, widens and slows down. The flame formed is long, efficient and the temperature maximum is well away from burner 1, which serves to protect burner 1 and its immediate surroundings in the meltdown unit. The burner mode according to FIG. 2a can be used primarily for superheating and keeping a melt warm over a long distance.

[0042] FIG. 2b shows an over-expanded state. This is characterized by a smaller inlet pressure compared to the design pressure. At the outlet of the primary nozzle 2, the oxygen-rich gas expands more than intended by the design state, such that so-called compression shocks are formed. As a result, more fuel gas is drawn into the oxygen-rich gas or the oxidizer free jet, as the case may be, and combustion occurs much earlier.

[0043] A compression shock is associated with an unsteady change in pressure, temperature, density, entropy, Mach number and flow velocity. While the pressure, temperature, density and entropy increase, the Mach number and flow velocity decrease. The free jet 12 constricts and the pressure in the center of the free jet 12 increases downstream to values above ambient pressure. The oblique compression waves 18 are reflected at the free jet edge 17 as expansion waves and the static pressure in the free jet 12 decreases. This process repeats periodically until the growing mixing zones at the free jet edge 17 dominate the flow field and the supersonic free jet 17 is transformed into a subsonic free jet.

[0044] The flow states significantly influence the mixing with the coaxially flowing secondary jet 16. Due to the downstream increasing interaction between the overlapping compression and expansion waves 18 and between the oxygen-rich gas and fuel gas, more fuel gas is drawn into the free jet 12, resulting in much earlier combustion. The flame becomes shorter than in the design state.

[0045] If, on the other hand, the inlet pressure is greater than the design pressure, the so-called under-expanded state is present (FIG. 2c). Expansion waves 18 attach to the outlet edge of the primary nozzle 2 and the free jet expands outside the primary nozzle 2. Moreover, in the under-expanded state, the coaxially outflowing fuel gas mixes intensively with the oxygen-rich gas in such a manner that the flame becomes even shorter and even wider than in the over-expanded state.

[0046] FIGS. 3 to 4 show results of a CFD simulation for the method in accordance with the invention. The following parameters were used for the simulation. [0047] Burner output: 5 MW [0048] Diameter of the narrowest cross-section of the primary nozzle: 15.4 mm [0049] Outlet diameter of the primary nozzle: 21.3 mm [0050] Gap height at the outlet of the coaxial nozzle: 6.1 mm

[0051] For the design state, the fuel gas, which consisted of a 50/50% by volume mixture of hydrogen and methane, was injected at an inlet volumetric flow rate of 773 Nm.sup.3/and at a pressure of 1.2 bar. The oxygen-rich gas (100% by volume oxygen) was injected at an inlet volumetric flow rate of 1159 Nm.sup.3/h and at a pressure of 8.3 bar. Such values correspond to a lambda value of 1.2.

[0052] For the over-expanded state, the oxygen-rich gas (100% by volume oxygen) was then injected at an inlet flow rate of 774 Nm.sup.3/h and at a pressure of 5.1 bar. Such values correspond to a lambda value of 1.0.

[0053] FIGS. 3a and 3b show the flow velocities of the two simulated flames (FIG. 3a) and the temperature field (FIG. 3b). As can be seen from the figures, a significantly shorter flame is formed in the over-expanding state, since the mixing and ignition of the fuel gas and oxygen occurs at an early stage. FIGS. 4a and 4b show the graphical illustration of the determined values of the respective flames from FIGS. 3a and 3b. OH concentration and flame temperature along the flame centerline are also shown. Depending on the definition of the flame length, a reduction in the range of 20 to 24% occurs by operating burner 1 in the over-expanding mode.

LIST OF REFERENCE SIGNS

[0054] 1 Burner [0055] 2 Primary nozzle/Laval nozzle [0056] 3 Coaxial nozzle [0057] 4 Outlet opening [0058] 5 End face [0059] 6 Convergent portion [0060] 7 Divergent portion [0061] 8 Radius of the narrowest cross-section [0062] 9 Port for oxygen-rich gas [0063] 10 Port for combustion gas [0064] 11 Port for air/fuel gas [0065] 12 Supersonic free jet/primary jet/free jet [0066] 13 Free jet core [0067] 14 Velocity profile [0068] 16 Point [0069] 16 Fuel gas free jet/secondary jet [0070] 17 Free jet shear layer/free jet edge [0071] 18 Compression waves [0072] L Length