MXPA98002065A - Coherent jet of - Google Patents

Abstract

A system for producing a coherent jet of gas in which a flame current is established around a gas jet and directed towards the central axis of the jet of gas.

Description

GAS COHERENT JET BACKGROUND OF THE INVENTION Field of the Invention This invention is directed to coherent gas jets, methods for obtaining coherent gas jets, and apparatus that can be used to obtain coherent gas jets. Gas jets, ie gas that is expelled from a nozzle in a manner similar to high speed current, can exist in at least two ways. The two forms of the present interest are a conventional turbulent jet (or as used herein a "normal jet") and a coherent jet. In a normal jet, the gas expelled from a nozzle creates a jet of gas. The ambient gas enters a jet of gas causing the jet to expand. A normal jet is shown in Figure 1. The gas leaves a nozzle 1 and develops in a normal stream 2. The input regime of the ambient gas can be calculated from an equation given in the literature, "The Combustion of Pulverized Coal "by MA Field, D. W. Gilí, B. B. Morgan, and P. G. W. Hawksley, The British Coal Utilization Research Association, Chapter 2, Flow Patterns and Mixing, p. 46. This equation applies after a turbulent jet fully develops which occurs when x / d0 is about 6 A values less than 6, the input rate is lower.

In the previous formula, = Ratio of the mass of environmental gas that enters the original gas jet mass. Ha Po = Ratio of the density of the environmental gas to the density of the original gas jet. d = axial distance from the nozzle divided by the diameter of the nozzle. For fully developed turbulent flow, the input rate is very fast as indicated by the equation. For example, if the density of the ambient gas is equal to that of the original jet gas, then the mass of the gas entering by a jet length equivalent to three nozzle diameters could be approximately equal to the mass of the original jet gas. For jet lengths of 3, 6 and 9 nozzle diameters the mass of gas entering could be respectively 1, 2 and 3 times that of the initial jet gas. In contrast to a normal jet, there is very little ambient gas inlet in a coherent jet for a considerable distance from the face of the nozzle. The jet remains relatively coherent with very light expansion as shown in Figure 2. In Figure 2, the gas leaves a nozzle 1 and develops in a coherent jet 3. Typically, the jet can remain coherent for a jet length of about 50 nozzle diameters or more before it becomes a normal jet. In a torch oxicortante, the jet of oxygen is surrounded by a ring of reducing flames, either premixed, ie the fuel and oxidizing gases are mixed before leaving the nozzle or after mixing, ie the fuel and oxidants They mix after leaving the separate nozzles. Within this hot flame shell, the oxygen jet becomes coherent so that a straight uniform cut can be made as the oxygen jet hits the carbon steel. If the jet is not consistent, it could result in an uneven cut of poor quality. The equipment used to obtain a coherent oxygen jet in the prior art and to obtain the data used in the present application are shown in Figures 3A and 3B. As shown in Figures 3A and 3B, the main gas, in this case oxygen, passes through a converging-diverging nozzle 4 to obtain supersonic flow. An inner ring of the holes 5 for natural gas and an outer ring of the holes 6 for oxygen are also provided. In the test apparatus, the convergent-divergent nozzle 4. has a throat diameter of 1.0 8 cm. and an exit diameter of 1.47cm. The inner rings of the holes 5 were 16, each of 0.28 cm. in diameter and evenly spaced around a circle of 4.12 cm. The outer rings of the holes 6 were also 16, each one of 0.408 cm. in diameter and evenly spaced around a circle of 4.71 cm. diameter. Tests were carried out with this apparatus using a Pitot tube to determine the velocity of the jet along the axis of the jet. Methods for using a Pitot tube to measure gas velocity are well known in the art. Pitot tubes measure local or point velocities by measuring the difference between impact pressure and static pressure. Measurements were made with flames after combustion (1200 CFH of natural gas and 1200 CFH of oxygen) and also 2 without flames after combustion. The graphs of the gas velocity versus the axial distance of the nozzle are given in Figure 4. As can easily be seen from Figure 4, without the flames, there is a sharp drop in gas velocity along the jet shaft. With the flames, the jet velocity on the shaft remained essentially constant at a supersonic velocity (eg, Mach number 1 or more) for a jet length of 60.96 cm. (indicating that the jet was coherent) before starting to decline. The difference between the two curves in Figure 4 is very dramatic. The custom gas entry in the coherent portion of the jet was about 5% of that calculated using the equation for a normal jet.

If a normal argon jet is used to penetrate a bath of molten steel to induce agitation, to be effective it would have to be placed so close to the molten bath that the nozzle could corrode. If a normal jet of sufficient length is used to prevent corrosion of the nozzle, a large amount of ambient gas could enter before the jet hits the surface of the bath. Consequently, said normal jet could have a broad low speed profile and could be ineffective to penetrate the metal bath. Therefore, it is an object of this invention to provide a coherent jet of gas using a gas other than oxygen, to provide methods for obtaining coherent gas jets, provide improved coherent oxygen jets and provide apparatus that can produce jets of coherent gas. This invention contemplates the use of any gas, including reactive and inert gases. Consequently, we have developed coherent gas jets and methods and apparatus for forming them which were not available in the prior art. COMPENDIUM OF THE INVENTION Our invention includes coherent gas jets, where the jet gas can be reactive or non-reactive. Suitable gases include nitrogen, argon, carbon dioxide and fuel gases including natural gas or propane.

The present invention also includes a method for producing a coherent gas jet. This is achieved by surrounding the gas jet with flames which are deflected towards the central axis of the main gas jet. Using this method, a long coherent jet comprising any gas can be obtained. The present invention also includes the apparatus which can direct the flames toward the central axis of the gas jet and thereby obtain a long coherent jet. Said apparatus may include deflectors that narrow the flame cover surrounding the gas and direct the flames toward the axis of the gas jet. Said apparatus may be mounted on existing devices, such as those shown in Figures 3A and 3B, or they may be made completely again. Suitable devices include nozzle-type devices that can be placed over the flame / gas combination as the flames and gas initially exit and direct the flames inwardly. The invention also includes the apparatus that deflects the oxidizing gas in the fuel gas to cause the flames to be directed towards the main gas jet and the apparatus that probes the nozzles for the fuel and oxidant gases at an angle so that the flames leave the nozzles and be directed towards the lateral axis of the main gas jet to produce a coherent gas jet, without the use of additional deflection devices. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a representation of a conventional turbulent jet or a "normal" jet. Figure 2 is a representation of a coherent jet. Figures 3A and 3B are representations of equipment that can be used to obtain a coherent oxygen jet. Figure 3A is a cross-sectional view and Figure 3B is a top view. Figure 4 is a graph showing the speed along the axis for an oxygen jet with and without a flame cover. Figure 5 is a schematic of a flame deflector connected to the jet equipment illustrated in Figures 3A and 3B. Figure 6 is a graph showing the velocity along the jet axis for a nitrogen jet with and without the flame deflector. Figure 7 is a graph showing the velocity along the jet axis for an argon jet with and without a flame cover. Figure 8 is a graph comparing coherent oxygen jets (without a flame deflector) with coherent jets of nitrogen and argon (with flame deflectors). Figure 9 is a representation of another embodiment of a flame baffle which can be used in accordance with the present invention.

Figure 10 is a cross-sectional view of an embodiment of the invention that deflects the oxidizing gas to direct the flames towards the main gas jet. The numbers of the drawings are the same for the common elements. DETAILED DESCRIPTION OF THE INVENTION The present invention includes coherent gas jets.

Such coherent jets of gas maintain or closely maintain the velocity of the gas stream as it exits the nozzle with very slight expansion, since there is very little ambient gas inlet in a coherent jet for a considerable distance from the face of the gas. nozzle. A normal coherent jet can remain coherent for a jet length of approximately 50 nozzle diameters or more before transforming into a normal jet. The gases that can be used to form a coherent jet include inert or non-reactive gases and reactive gases. Examples of inert and non-reactive gas include nitrogen, argon and carbon dioxide. Gas mixtures can also be used to form the main gas jet. Examples of reactive gas that could provide useful coherent gas jets include oxygen and fuel gases, such as propane and natural gas as well as mixtures thereof. The coherent gas jets according to this invention are obtained by surrounding the gas which will form the jet, or main gas, with flames and directing the flames towards the central axis of the gas jet. The objects of the invention can be achieved with subsonic and supersonic gas velocities for the coherent jet. However, it is more effective if the gas velocity is supersonic, that is, Mach number 1 or greater. The device used to create a gas jet surrounded by flame can be of the same type of device previously treated in the present invention and shown in Figures 3A and 3B. In said apparatus, the gas that will form the jet is placed in the central part of a series of concentric rings. The jet gas is surrounded by two orifice rings, capable of separately supplying an oxidant and a fuel gas used to create the flames. The number, size and arrangement of holes for the oxidant and fuel gas is selected to allow the formation of a flame cover that can be deflected towards the center of the gas jet. As previously discussed in the device shown in Figures 3A and 3B, the inner ring of the holes are used for natural gas and the outer ring of holes are used for oxygen. It is also possible to operate with the inner ring of holes used for oxygen and the outer ring of holes used for natural gas. The fuel and oxidant gases can also be supplied via annular concentric rings. The gases used to create the flame cover surrounding the gas and jet can be any of those known to those skilled in the art. For example, oxidants containing a volume of 30 to 100% oxygen can be used. Oxidants with a volume of more than 90% oxygen are preferred. The fuel gas may be any of those known in the art, including hydrogen, propane, natural gas and other hydrocarbon fuel. The fuel and oxidant gases can be premixed or post-mixed. Post-mixed flames are preferred because they are safer. A coherent jet of gas is obtained using an apparatus that deflects the flames towards the central axis of the gas jet together with an apparatus such as that shown in Figures 3A and 3B. An example of such baffle is shown in Figure 5. This baffle can be placed on top of the structure shown in Figures 3A and 3B. It can be seen from the study of Figure 5 that the internal solid walls 7 of the deflector 8 converge towards the central axis of the main gas jet axis at an angle of approximately 25 degrees. This convergent wall structure causes the flame cover created by the non-existent leaving fuel and oxidizer to be directed towards the central axis of the jet gas as it exits the deflector at outlet 9., resulting in a coherent jet of gas. While the embodiment shown in Figure 5 shows a particular angle of deflection, the present invention is thus not limited. Any angle that causes the flames to be directed towards the gas jet and that provides a coherent jet of gas is within the scope of this invention. Deflection angles up to 90 degrees are therefore thought to be adequate. A flame is established around the main jet near the face of the nozzle deflecting the flame cover towards the main jet axis. The invention is demonstrated in the following examples. While the examples show specific flow regimes for the main gas, fuel and oxidant gases, it should be understood that the invention is not so limited and one of ordinary skill in the art can select the appropriate flow rates for these gases. EXAMPLE 1 The baffle exemplified in Figure 5 is connected to the gas jet and flame apparatus shown in Figures 3A and 3B. Flames were used after combustion, with 1200 CFH of natural gas coming out of the inner ring of the holes and 1200 CFH of oxygen coming out of the outer ring of the holes, to create a flame pattern. It was used in nitrogen as the main or jet gas at a flow rate of 21,000 CFH with a nozzle upstream pressure of 8.78 kg / cm2. The velocity of the gas along the axis of the jet was measured with a Pitot tube. Measurements were made with and without a flame defect. As can easily be seen in Figure 6, which is a graph of the speed along the axis of the measured nitrogen jet and without the flame effect, a noticeable improvement was obtained using the flame baffle. As shown in Figure 6, the nitrogen velocity remained above 456 meters per second (mps) by approximately 63.5 cm from the outlet of the nozzle with the flame deflector. Without the flame deflector, the nitrogen velocity, at a point 63.5 cm from the nozzle, was decreased by approximately 304 mps. Therefore the nitrogen jet was more consistent with the velocity being consistently higher along the jet axis when the flame deflector was used. EXAMPLE 2 Using argon as the main or jet gas, the flames after mixing (orifice size, geometry and flow rates) were the same as for the previously described tests with oxygen and nitrogen. The convergent-divergent nozzle, designed for argon, had a throat with a diameter of 1.11 cm. and a diameter of 1.38 cm. The flow rate of argon was 20,000 CFH with a pressure of 8.43 kg / cm2 upstream of the nozzle. The gas velocity measurements were made with a deflected flame and without the flame cover. The graphs of the velocity along the axis for the operation with and without the flames are given in Figure 7. With the flame and the deflector a long coherent jet was obtained. The difference between the operation with and without the flames was similar to the results with oxygen. A comparison of the jet velocity at a probe distance of 91.4 cm. The face of the nozzle was made with and without the flame deflector. The measured speed was 367.8 mps with the deflector and 258.4 mps without it. The flame deflector made a big difference. EXAMPLE 3 Figure 8 shows a direct comparison of the three gases (argon and nitrogen with the flame and oxygen deflector without the flame deflector). The speed was normalized, dividing the speed along the jet axes by the speed at the jet outlet. The graphs clearly show that using the flame baffle, coherent jets comparable to those bound with oxygen can be achieved with essentially any gas. The length of the coherent portion of the jet was increased in the progress of nitrogen to oxygen to argon. Probably it can be attributed to the increase in the density of the gas. It is expected that the length of the coherent jet could increase as the gas density increases. There are different ways of deflecting the fiama towards the jet axis to obtain coherent jets. Another preferred embodiment of a baffle is illustrated in Figure 9. In this embodiment, the space between the face of the nozzle for the main gas 4 and the baffle 10, is small resulting in an increased radial velocity of fuel gas, oxygen and combustion products towards the jet axis. Here the angle of deflection of the flames is approximately 90 degrees. In this embodiment, the flames are deflected towards the gas of the jet before leaving the exit of the deflector 11. Another approach to simulate the effect of a flame deflector could be to angle the orifices for the fuel gas and / or the oxygen towards the shaft of the jet. A preferred means for obtaining a coherent jet using a gas other than oxygen is described in Figure 10. Figure 10 shows a deflection device 12 which sits on a structure supplying gas 13. The main gas, shown as nitrogen in Figure 10 is supplied through the central nozzle 4, and the fuel and oxidant gases are supplied through the rings 14 and 15 respectively. As can be seen in Figure 10, the main gas and fuel gas flow up through the rings and nozzle 4 not impeded. The deflection device 12, however, directs the flow of oxidizing gas in a flow of fuel gas through the holes 17, fixed around the circumference, directed towards the main gas jet axis. Using the device shown in Figure 10, with nitrogen as the main gas and natural gas and oxygen to supply the flame cover, it was found that the oxygen stream for each orifice 17 penetrated the ring of natural gas, and a Flame around main jet in the face of the nozzle. Therefore, instead of using a solid baffle, oxygen gas was used at low speed to deflect the flame towards the main jet. It is thought that this method can be more effective than the other devices treated in the present when inert gases are used. A baffle can be used for all jet gases. For gases other than oxygen, the effect of the baffle can be very significant as illustrated here for tests with nitrogen or argon as the main gas. If oxygen is the main gas, the improvement using the baffle can be small. However, even with oxygen, the use of the baffle ensures that the conditions are favorable to obtain a long coherent jet. In the practice of the present invention it is not only important to deflect the flames towards the jet gas, it is also important to maintain the flow rates for the fuel and oxidant gas in order to create the flames surrounding the jet within certain guidelines. . The guidelines use the following symbols. Q - Ignition rate (LHV) for the fuel gas -MMBtu / hour (million Btu / hour) V - Volumetric flow rate for the oxidant - MCAH (thousands of cubic meters per hour) at 42.2 ° C and atmospheric pressure. P - Percent volume of the oxidant. D - Nozzle outlet diameter - centimeters. The percentage volume of oxygen in the oxidant (P) should be greater than 30% and preferably greater than 90%. The Q / D ratio should be greater than 0.6 and preferably approximately 2.0. the VP / D function must be greater than 70 and preferably approximately 200. Additionally, combustion instabilities, such as discontinuities in the flame or fuel and oxidant gases, should be avoided. The materials used to construct the nozzles and deflectors are well known in the art and include stainless steel, copper and in some refractory-type materials applications. The deflector nozzle can be cooled during operation, depending on the end use of the coherent jet. For example, if the jet is to be used in an oven, nozzle cooling may be appropriate. The methods known to those skilled in the art, including cooling by water and air could be adequate. As seen from the above description, we have succeeded in obtaining new coherent gas jets that are not limited to any particular type of gas. Neither the present invention is limited to any particular means for deflecting flares towards the central axis of a main gas to create a coherent jet.

Claims (10)

1. CLAIMS 1. A method for forming a coherent gas jet comprising: a) supplying a main gas through a nozzle, so that the main gas leaves the nozzle to form a main gas jet having a central axis; b) surround the main gas jet with a flame cover; and c) directing said flame cover towards the central axis of the main gas jet.
2. 2. The method according to claim 1, wherein the main gas exits the nozzle at a rate equal to or greater than about 1 Mach.
3. The method according to claim 1, wherein the flame shell is formed by an oxidizing gas and a fuel gas and wherein the oxidant contains oxygen at a percentage volume of 30% or more, the ratio of a regime of fire for the fuel gas, in Btu / hr per million, to the nozzle outlet diameter, in centimeters, is 0.6 or more of the volumetric flow regime for the oxidant, in thousands of cubic meters per hour, multiplied by the percentage oxygen of volume in the oxidant, divided by the outlet diameter, in centimeters, is greater than 70.
4. 4. The method of claim 1, wherein the main gas is selected from the group consisting of oxygen, argon. nitrogen and carbon dioxide.
5. 5. The method of claim 1, wherein the flame cover is directed towards the gas jet at an angle of about 25 to about 90 degrees.
6. 6. An apparatus for creating a coherent gas jet, comprising: a) a main gas nozzle capable of ejecting a main gas at high velocity to create a main gas jet having a central axis; b) means for creating a flame cover around said main gas jet; and c) means for directing said flame cover to said main gas jet.
7. The apparatus of claim 6, wherein the means for creating the flame cover comprises an inner circle of outlet orifices for a fuel gas and an outer circle of the outlet orifices for an oxidizing gas, wherein the circles exterior and interior are concentric with each other and the main gas nozzle.
8. The apparatus of claim 6, wherein the means for directing the flame cover comprises a baffle having angled walls towards the central axis of the main gas jet.
9. The apparatus of claim 6, wherein the means for directing the flame cover comprises means for directing an oxidizing gas to penetrate through a fuel gas used to create the flame cover, whereby the cover of flame is directed towards the main gas jet.
10. 10. A coherent jet of gas formed by the provision of a main gas through a nozzle so that the main gas leaves the nozzle to form a main gas jet having a central axis, surrounding the main gas jet with a Flame cover and directing said flame cover towards the central axis of the main gas jet. RESU MEN A system for producing a coherent gas jet where a flame cover is established around a gas jet and directed towards the central axis of the gas jet.