The present invention relates to a burner used in combustion installations and combustion furnaces, such as heat-treatment furnaces and melting furnaces (said combustion installations and combustion furnaces being referred to hereinafter collectively as "Combustion Device(s)"), and more specifically to a multi-tube combustion burner comprising a fuel supply flow path in an inner tube and a combustion supporting gas supply flow path in an outer tube.

Various types of burners are installed in furnaces and used to suit the process requirements. For specific purposes such as, for example, the treatment of glass in a glass melting furnace, it is necessary to adapt the flame properties of the burner so as to change the condition of heating applied to the object to be heated depending on such factors as the heat-treatment specifications (including composition and amount of the object to be heated) and treatment stage. Conventionally, such methods have been adopted which involve changing the position of the burner to change the position of the flame, or changing the amount or flow rate of the fuel or oxidant to change the length of the flame.

As a method, for example, of changing the flame length while keeping the supply of the fuel or oxidant at a constant rate, the so called "nozzle mix" type gas burner can be used with which the combustion air and fuel gas are led separately to the burner tip and are then mixed for the first time at the tip of the burner and combusted simultaneously, as shown in Figure 3 (A) and (B), (see for example Japanese published unexamined patent application 1973-30995). More specifically, a gas burner that has been proposed has a structure in which a branched flow path 1 13 for combustion air is formed by passing a small-diameter cylindrical body 112 through the axial core section of combustion air flow path 1 02 formed by a separate larger cylindrical body 101 . Multiple combustion gas pipes 103 are arranged in a tubular manner inside aforementioned outer combustion air flow path 102. A combustion gas and combustion air mixing combustion chamber 104 is formed at the tips of the combustion gas pipes 103, air supply opening 105 from which air is blown in from the tangential direction of the combustion air flow path 102 is located at its upstream section of the airflow direction. A movable damper that changes the opening area of the opening 105 is installed. A separate air flow path 114 that changes the amount of airflow due to changes in the opening area of opening 105 with damper 106 connected with opening 105 is installed at the upstream section of the airflow of the combustion air branched flow path 1 13. Connecting hole 1 15 that connects the branched flow path 1 13 to the separate airflow path 1 14 is located at cylindrical body 1 12. While this burner allows arbitrarily adjusting such factors as the form of the combustion flame and flame intensity with simple operation, it also maintains the amount of air at a constant rate regardless of the adjustment, and hence allows sound and excellent initial combustion. Here, 107 and 109 are ports, 108 and 1 10 are air-supply pipes, and 1 1 1 is a flange outfitted to the gas burner.

A specifically useful burner is described in EP-A-0763692. Said burner comprises an outer oxidant tube, an intermediate fuel tube and an inner oxidant tube. The characteristics of the flame produced by the burner are controlled by varying the relative flow rates of the inner and outer oxidant flows.

With the gas burners described above or other conventional gas burners, however, the following various problems are known to occur:

(i) I n a type that changes the mounting position of the gas burner installed in a high-temperature furnace to change the location of the flame, the gas burner can be thermally deformed and becomes inoperable due to the high-temperature atmosphere inside the furnace;

(ii) Overheating of the burner by the high-temperature atmosphere inside the furnace can be suppressed by increasing the flow rate of the oxidant to remove the heat. However, when the flow rate of the oxidant is increased, the air-gas ratio changes;

(iii) To suppress overheating, the diameter of the burner nozzle can also be reduced. However, this results in a faster flow rate of the combustion supporting gas and the desired flame form may not be achieved;

(iv) In burners such as shown i n F igure 3, the required distributive mechanism that changes the ratio of the supply flow rate may cause complications in the layout of the device and increase the size of the burner.

The object of the present invention is to provide a burner that is capable of generating a stable and uniform flame under a stable condition, and enables changing the position of the flame with a simple structure and method.

In view of the above-described problems, the present inventors conducted intensive research and discovered that the aim can be reached by means of the com bustion burner described below.

The present invention relates to a burner comprising a fuel gas flow path and a combustion supporting gas flow path for producing a high-temperature flame due to the reaction of the fuel gas and combustion supporting gas. The fuel gas flow path is formed by an inner tube and the combustion supporting gas flow path is formed by an outer tube into which the inner tube is inserted so that the outer tube surrounds the inner tube. The tip of said inner tube on the flame generating side (i.e. the fuel injection nozzle) is positioned to protrude from the tip of the combustion supporting gas flow path on the flame generating side (i.e. the combustion supporting gas injection nozzle of the outer tube). The said inner tube is also movable within the combustion supporting gas flow path, so as to change the distance or length by which the tip of the inner tube protrudes from the tip of the combustion supporting gas flow path.

As described previously, combustion burners used in Combustion Devices are required to produce stable flame condition, preferably with a simple configuration and simple operation.

The present invention has made it possible to produce heating that can be adapted to the requirements of the heating process while maintaining stable combustion by changing the position of the fuel gas supply nozzle at the tip of the burner thereby changing the flame condition, and more specifically the flame length, without the need for changing the supply condition (compositions and flow rates) of the fuel gas and combustion supporting gas. Here, it has become possible to conveniently and easily change the position of the fuel gas supply nozzle and at the same time to maintain a stable high-temperature flame by configuring the inner tube to be movable within the double-tube (inner tube or outer tube) burner structure, and by configuring the tip of the inner tube to protrude from the tip of the combustion supporting gas flow path on the flame generating side.

In the present invention in particular, it was found that the change in flame length resulting from the protruding configuration of the tip of the inner tube and its movement can be as much as a multitude to over ten times the distance the over which the inner tube tip is moved. In other words, the present invention makes it possible to bring the tip of the flame close to the object to be heated while maintaining a sufficient distance between the burner and said object.

The invention thus provides a combustion burner that produces stable and uniform flame, and allows changes in the position of the flame with a simple configuration and simple method.

The term "fuel gas" as used herein refers to fuel that is supplied to the combustion burner in a gaseous state, and as described later, it is not limited to such gaseous fuel under ambient temperatures and pressures, such as city utility gas, but includes atomized fuels that are supplied by atomizing liquid fuels and gas propelled particulate fuels.

The term "combustion supporting gas" as used herein refers to a gas containing an oxidant for the combustion of the fuel gas. The combustion supporting gas may be air, oxygen-enriched air or oxygen (i.e. a gas containing at least 90% vol O2) . Oxygen enriched air and oxygen are preferred combustion supporting gases.

The present invention relates in particular to the burner in which the fuel gas flow path is formed by a cylindrical inner tube, and the combustion supporting gas flow path is formed by an outer tube concentric with said inner tube. Preferably, said inner tube and said outer tube are connected by a metal fixing bracket that can be fixed by tightening.

Hereafter, specific embodiments of the present invention will be described on the basis of the drawings.

Figure 1 is a schematic illustration of the basic configuration example of a burner of the invention.

Figure 2 is an illustration of the results obtained with the burner of Figure 1 .

Figure 3 is a schematic illustration of a configuration example of a known burner designed to permit changing of the flame properties.

Figure 1 (A) is a schematic illustration of a basic configuration example of the inventive burner (referred hereinafter as "This Burner"). This Burner is generally mounted on or in a wall F of a Combustion Device by flange f, and used for heat treatment such as annealing, melting, refining, etc. by directing a flame towards the object to be heated (not shown in Figure). The object to be heated may be introduced into the Combustion Device (e.g. glass or metal to be melted) or may be or part of the Combustion Device (e.g. a furnace wall). Multiple units of This Burner are generally installed on or in wall F of the Combustion Device. This Burner comprises a fuel gas flow path 1 and a combustion supporting gas flow path 2. A high-temperature flame 3 is produced by the combustion reaction of the fuel gas and the combustion supporting gas. Flame 3 is formed by fuel gas jet flow 1 a and combustion supporting gas jet flow 2a, said flame having length L desired at this moment in time. The object to be heated is located in the direction of the tip of flame 3, and the desired heating condition is obtained in particular by the high-temperature flame tip.

A double tube structure is formed by inserting fuel gas flow path 1 into combustion supporting gas flow path 2. Fuel gas flow path 1 is formed by inner tube 4, and combustion supporting gas flow path 2 is formed between the outer surface of inner tube 4 and the inner surface of outer tube 5. The burner is also configured so that tip 4a of inner tube 4 protrudes from tip 5a of outer tube 5 on the flame generating side by a distance Y. With this configuration, a stable jet flow 1 a is formed since the fuel gas jet flow 1 a from the nozzle-shaped opening of tip 4a is restricted by the opening section, and the desired flame length L is formed due to the combustion supporting gas jet flow 2a. More specifically, jet flow 2a from the opening at tip 5a of outer tube 5 is diffused when it exits from combustion supporting gas flow path 2, and its flow rate in the flow direction (X-X) lowers. With This Burner with the double-tube structure, when the flow rate of the combustion supporting gas injected from the outer tube 5 lowers without changing the flow rate of the fuel gas injected from the center (i.e. from inner tube 4), the form of flame 3 becomes long in the flow direction. Moreover, since jet flow 2a is, at the same time, formed in a manner supporting jet flow 1 a from its periphery, flame 3 can be further lengthened in a stable manner, and at the same time, it is possible to adjust flame length L by adjusting the flow rate of jet flow 2a within the range of a specified oxygen-fuel ratio.

It is desirable that the inner diameter of outer tube 5 is small to suppress overheating by the high-temperature atmosphere inside the furnace. Although it is difficult to change the inner diameter of inner tube 4 since it is necessary to ensure the fuel gas supply flow rate to form the heating condition set in advance, the flow rate of the combustion supporting gas flowing in supporting gas flow path 2 can be increased by reducing the inner diameter of outer tube. As described above, in general, if the flow rate of the combustion supporting gas is increased, flame 3 shortens, but if tip 4a of inner tube 4 protrudes beyond tip 5a of outer tube 5 as in This Burner, a stable and long flame 3 can be obtained since the flow rate of jet flow 2a of the combustion supporting gas at the nozzle-shaped opening of tip 4a where jet flow 1 a of the fuel gas occurs has been dampened and slowed.

In This Burner, inner tube 4 is structured so that it can move within combustion supporting gas flow path 2 (i.e. within outer tube 5). This makes it possible to produce a heating condition that corresponds to the required condition of the object to be heated. More specifically, by changing tip 4a to protrude by distance Y from tip 5a as shown in Figure 1 (A), it is possible to bring flame 3 extremely close to the object to be heated. That is, flame 3 with the desired length L is formed due to jet flow 1 a that is restricted by the nozzle-shaped opening and jet flow 2a at a tip 4a as shown in Figure 1 (A). It is possible to further lengthen flame 3 formed by jet flow 1 a since jet flow 2a supplied from tip 5a can form a flow that contains more components of the flow for a longer distance along the outer circumference of inner tube 4, by changing the condition so that tip 4a protrudes by a greater distance Y' from tip 5a as shown in Figure 1 (B). As described in more specific terms below, it was found that flame length L can be changed by several times the distance by which tip 4a had been moved. This allows to change the position of the tip of the flame to be extremely close to the object to be heated by a distance combining the distance of the movement of the tip of the inner tube and the additional increase in the length of the flame. Moreover, since the diffusion of jet flow 2a at this time becomes greater than before the tip was moved, diffusion and mixing of the fuel and oxygen are also activated to produce a broader high-temperature-range flame.

The fuel gas is introduced from fuel gas introduction section 1 b and injected as jet flow 1 a from tip 4a of inner tube 4 via fuel gas flow path 1 (inside inner tube 4). Meanwhile, the combustion supporting gas is introduced from combustion supporting gas introduction section 2b and injected as jet flow 2a from tip 5a of outer tube 5 via combustion supporting gas flow path 2 (inside outer tube 5). The injected fuel gas is ignited in a state mixed with the combustion supporting gas (suitable ignition means are known in the art and commercially available), and due to the combustion reaction of the fuel gas and combustion supporting gas, high-temperature flame 3 is produced. Flame 3 is stabilized by the fuel gas supplied from jet flow 1 a and the combustion supporting gas supplied from jet flow 2a. Jet flow 1 a injected from tip 4a of inner tube 4 supplies fuel to the center of flame 3 and forms flame 3 while mixing with the combustion supporting gas at its surface. Jet flow 2a is transported along the outer surface of inner tube 4, merges with jet flow 1 a at tip 4a, and is supplied to flame 3 as a source of oxygen. Even when inner tube 4 is moved with respect to outer tube 5, a similar state along the direction of each jet flow from the position of tip 4a is maintained to form a stable combustion condition of flame 3.

As for the fuel gas, such hydrocarbon system gases as city gas (aka town gas) or natural gas that are mainly composed of such gases as methane, ethane and propane, or such industrial-use fuel gases mainly composed of carbon monoxide and hydrogen, such as gasification gas, pyrolysis gas and synthesis gas may be used. Moreover, with This Burner, it is also possible to atomize and use such liquid fuels as kerosene, light oil and a mixture of light and heavy oil. As for the combustion supporting gas, while air is used in many cases, it is also possible to use high-purity oxygen and oxygen-enriched gases. The types and supply flow rates of the fuel gas and combustion supporting gas used in This Burner are set according to such factors as the scale of the Combustion Device, volume and shape of the object to be heated, composition and structure of the object to be heated, temperature to which the object is to be heated, the structure of the burner, etc.

Due to its uncomplicated construction, the dimensions of the burner can be limited and the burner can be used in Combustion Devices with severe space restrictions, for example, the burner can be installed through a small opening in a wall of a combustion furnace.

The burner can also be used intermittently, for example as a top-up burner when extra and localized heat is required in a Combustion Device or for preheating or annealing a Combustion Device after an interruption in operation. By changing the flame length in accordance with the invention, heat can be supplied locally where required and overheating of the object to be heated and/or of the Combustion Device can be avoided. This is important as overheating can affect the quality of the object to be heated and cause damage to the Combustion Device.

This Burner having the configuration as described above is used to perform heat treatment in the Combustion Device in accordance with the following heat treatment processes (operation of the Combustion Device is omitted). For each process, a case in which the operation of the burner as illustrated in figure 1 is controlled by the control section (not shown in Figures) is explained as an example.

Example

(1 ) Mounting of This Burner and setting the fuel gas and supporting gas

Mount This Burner to furnace wall F of the Combustion Device using flange f. Set the fuel gas so that it can be introduced from fuel gas introduction section 1 b, set the combustion supporting gas so that it can be introduced from combustion supporting gas introduction section 2b, and close the on-off valves (not shown in Figures) on the supply side of the fuel gas and combustion supporting gas. (2) Setting the position of the inner tube tip

Set the position of tip 4a of inner tube 4 so that it is at an optimal position (i.e. the distance Y over which it protrudes from the tip 5a of outer tube 5) determined in advance. When inner tube 4 is moved to the desired position, fix it by tightening the metal fixing bracket.

(3) Supplying and igniting the fuel gas and supporting gas

By starting the supply of the fuel gas and combustion supporting gas and igniting them to initiate their combustion reaction, high-temperature flame 3 is produced. More specifically, activate the on-off valves to supply the gases from the fuel gas flow path and combustion supporting gas flow path at preset pressures and flow rates, and activate the ignition means (not shown in Figures) after a certain set period of time (several seconds) to ignite. At this time, it is desirable to monitor the condition of flame 3 to make sure it is in a desired condition. Monitoring flame 3 can be performed visually if there is a window in the furnace wall of the Combustion Device, or automatically if there is an imaging means for monitoring.

(4) Adjusting the position of the inner tube tip (fine adjustment of fuel gas and supporting gas flow rates)

In the event monitored flame 3 is not in a desired condition, and in particular when monitored flame 3 does not have the desired length U, adjust the position of inner tube tip 4a with respect to outer tube tip 5a (i.e. distance Y') . First adjust the position of inner tube 4a while maintaining the preset oxygen-fuel ratio. In the event, the condition of flame 3 is still insufficient after the above adjustment, then finely adjust the combustion supporting gas flow rate. At this time, it is effective to make the adjustment in combination with the position of inner tube tip 4a. In the event, the condition of flame 3 is still insufficient after such adjustments, then finely adjust the fuel gas flow rate. At this time, it is effective to make the adjustment in combination with the position of inner tube tip 4a and the combustion supporting gas flow rate.

(5) Heat treating the object to be heated

Heat treatment is applied by directing flame 3 towards the object to be heated (not shown in Figures) introduced to into the Combustion Device or part of the Combustion Device (not shown in Figures). It is desirable to monitor the heat treatment condition together with the condition of flame 3 to make sure it is in a desired condition.

The flame initiation of This Burner was tested and verified as follows by supplying the fuel gas and combustion supporting gas to an actual working model. (a) Test conditions

Using This Burner shown in Figure 1 , the flame initiation was verified by using natural gas as the fuel gas (flow rate of 6m ³ /h) and 1 00% oxygen as the combustion supporting gas, and by changing the position of the inner tube tip 4a (distance Y, Y' from the outer tube tip 5a is used as the index) under the conditions shown in Table 1 below.

Table 1 (b) Test results

The test results are shown in Table 2 below. It was verified that it is possible to form a stable flame by making the position of the inner tube tip (fuel gas outlet) to protrude from the outer tube tip (combustion supporting gas outlet) in the gas flow direction X-X, and at the same time, it is possible to extend the length L of the flame by increasing the distance of protrusion of the position of the inner tube tip. In other words, it is possible to make the position of the tip of the flame closer to the object to be heated by a distance combining the distance the position of the inner tube tip was moved and the increased portion of the flame length.

As described above, the usefulness of this burner has been verified.

Table 2 Explanation of codes

1 Fuel gas flow path

1 a Fuel gas jet flow

1 b Fuel gas introduction section

2 Combustion supporting gas flow path

2a Combustion supporting gas jet flow

2b Combustion supporting gas introduction section

3 Flame

3a Flame tip

4 Inner tube

4a Inner tube tip-mixing

5 Outer tube

5a Outer tube tip

F Furnace wall

f Flange

L Flame length