JP2000337614A - Radiant tube combustion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure a much larger space by making compact a venturi mixer for recirculating exhaust gas for reducing NOx and a pipe for recirculating the exhaust gas, and prevent a sucking force for the recirculating exhaust gas from becoming sufficient when temperature is high. SOLUTION: A radiant tube combustion device has such an arrangement that fuel gas is alternately supplied to regenerative burners 2a, 2b which are, respectively, mounted to both ends of a radiant tube 1, and that charge and discharge of gas to and from both of the burners 2a, 2b are switched by a four-way valve 3. By providing a communicating pipe 4 for communicating a discharging side of the four-way valve 3 with a charging side thereof and sending high-pressure air to a venturi mixer 5 which is provided in the communicating pipe 4, a portion of the exhaust gas is recirculated to the charging side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a NOx reduction in a radiant tube combustion device using a regenerative burner.

[0002]

2. Description of the Related Art This type of radiant tube combustion apparatus is for performing indirect heating in a heat treatment furnace or the like.
Normally, two regenerative burners are used in pairs, and each burner is alternately burned at intervals of several tens of seconds, and the exhaust heat is recovered by the built-in heat storage body, and the heat is used to preheat the combustion air. Although heat recovery can be performed with high efficiency by the heat storage body, there is a problem that NOx is easily discharged because the temperature of combustion air is high. In addition, the burner for radiant tube heating has a smaller combustion space than the burner for direct flame heating, so it is difficult to reduce NOx by devising a flame shape.Therefore, a method of forcibly recirculating exhaust gas outside the furnace Are often adopted.

[0003]

As means for recirculating exhaust gas of this kind, there are the following four methods. A method in which exhaust gas before entering the heat storage body is sucked by a combustion airflow (FIG. 1). A method of sucking the exhaust gas after leaving the regenerator with the air pressure for combustion (FIG. 2). A method of sucking the exhaust gas after exiting the regenerator with the combustion gas pressure (FIG. 3). A method of sucking flue exhaust gas with a blower for combustion air (Fig. 4). Of these, the application of the Venturi effect is to suck the exhaust of the burner or the exhaust of the flue on the non-combustion side, but the exhaust gas is recirculated on the higher temperature side than the regenerator A as shown in FIG. The exhaust gas to be suctioned has a high temperature, so that the exhaust gas recirculation pipe 17 needs to have a heat insulating structure. Therefore, it is difficult to secure a work space by taking a place for heat insulating coating on the front of the furnace. In addition, as a countermeasure against this, if the exhaust gas recirculation pipe 17 is housed in a furnace or a furnace wall, there is a problem that the structure becomes complicated and the cost increases.

In another method, as shown in FIG. 2, a venturi mixer 19 for sucking exhaust gas by supply air pressure at a lower temperature side than the heat storage body A is provided.
When the temperature rises, the pressure in the radiant tube 1 increases and the suction force of the venturi mixer 19 decreases, so that the air supply blower 15 needs to be considerably enlarged to cover this. Further, as shown in FIG. 3, the exhaust gas is sucked by the fuel gas pressure, and using the medium-pressure city gas as it is to increase the gas pressure has many problems in terms of safety management. Therefore, it is usually necessary to provide a booster to increase the pressure of the low-pressure city gas. However, the normal booster has a problem that the suction force of the venturi mixer 20 at the time of high temperature is insufficient. As described above, when the venturi mixer is used at a lower temperature than the heat storage body A, there is a problem that the suction capacity is insufficient due to an increase in the internal pressure of the radiant tube 1 or the size of the blower 15 is increased.

In another method, as shown in FIG. 4, a part of exhaust gas is sucked from a flue 18 using a blower 15 for combustion air. Usually, the four-way valve 3 is connected to the four-way valve 3 from the opposite direction. Therefore, there is a problem in that the arrangement of the ducts or the installation location of the blower is restricted in order to connect them, and it is also difficult to secure a work space. Therefore, the present invention solves the various problems described above, and takes up as little installation space as possible on the front surface of the radiant tube, which is usually complicated by a large number of pipes and valves. It is an object of the present invention to provide a simple venturi-type exhaust gas recirculation means.

[0006]

According to the present invention, as shown in FIG. 5, fuel gas is alternately supplied to regenerative burners 2a and 2b mounted on both ends of a radiant tube 1, respectively, and both burners 2a and 2b are supplied. In the radiant tube combustion device in which the supply and exhaust to the four-way valve 3 are switched by a four-way valve 3, a communication pipe 4 for connecting the exhaust side and the air supply side of the four-way valve 3 is provided, and a venturi mixer 5 interposed in the communication pipe 4 A part of the exhaust gas is recirculated to the air supply side by feeding high-pressure air to the ventilator 5 and the venturi mixer 5 and the communication pipe 4 for exhaust gas recirculation are reduced in size by using high-pressure air. In addition, by securing a slightly larger work space and increasing the suction pressure of the venturi mixer 5, recirculation, which is often insufficient in this type of radiant tube burner, And it has a feature that can ensure air amount.

[0007]

FIG. 1 shows an embodiment of the present invention, in which regenerative burners 2a and 2b are mounted on both ends of a radiant tube 1, respectively, and fuel valves 7a and 2b are provided.
The fuel gas is alternately supplied to both burners 2a and 2b through 7b, and at the same time, the supply and exhaust are switched by the four-way valve 3, so that the two burners 2a and 2b alternately burn every tens of seconds. . As shown in FIGS. 6 (a) and 6 (b), the four-way valve 3 is formed of a drum-shaped cylinder, and an air supply inlet 8 and an exhaust outlet 9 are provided at two opposing positions on the peripheral surface of the cylinder. And two burners 2a, 2b
Are provided with air supply / exhaust ports 6a and 6b. A blade 1 driven by an air cylinder 11 in this cylinder
0 rotates, and the supply and exhaust of both burners 2a and 2b are alternately switched. In the present invention, as shown in the figure, on one end surface of the cylindrical body, an exhaust inlet 12 is provided near the air supply inlet 8, and an exhaust suction port 13 is provided near the exhaust outlet 9.
And a connecting pipe 4 for connecting the exhaust inlet 12 and the exhaust suction port 13 outside the cylindrical body, and a venturi mixer 5 is interposed in the connecting pipe 4 to connect the compressor 14 to the venturi mixer 5. By supplying high-pressure air, a part of the exhaust gas is recirculated from the exhaust passage to the air supply passage.

In FIG. 5, arrows indicate the flow of air supply and exhaust when the right burner 2a is switched to air supply. At this time, the fuel valve 7a is opened to supply fuel gas to the burner 2a. The combustion air is supplied from the four-way valve 3 through the regenerator A, and the air preheated by the heat stored in the regenerator A burns the right burner 2a, while the left burner 2b passes through the regenerator A inside the tube 1. The high-temperature exhaust gas is sucked, and the exhaust gas whose temperature has decreased through the heat storage body is sucked into the exhaust blower 16 through the four-way valve 3. At this time, a part of the exhaust gas is sucked from the exhaust suction port 13 in FIG.
It is sent from the exhaust inlet 12 through the communication pipe 4 to the supply side section of the four-way valve 3, where it is mixed with fresh air sent from the supply air blower 15 to reduce the oxygen concentration of the combustion air. To lower the flame temperature,
Oxification is realized.

[0009]

According to the present invention, as described above, by increasing the suction pressure of the venturi mixer 5 using high-pressure air for exhaust suction, the venturi mixer 5 and the exhaust gas recirculation pipe 6 are reduced in size. This has the advantage that a large work space can be ensured, and that the amount of recirculated exhaust gas that can easily be deficient with this type of radiant tube burner can be ensured.
Since the compressor 14 that has supplied high-pressure air to the driving air cylinder 11 of the blade plate 10 can be used as it is, there is an advantage that it can be configured relatively inexpensively.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a conventional example.

FIG. 2 is a system diagram showing another conventional example.

FIG. 3 is a system diagram showing a conventional example.

FIG. 4 is a system diagram showing still another conventional example.

FIG. 5 is a system diagram showing one embodiment of the present invention.

FIG. 6 is a front sectional view and a side sectional view of the four-way valve used in the above.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Radiant tube 2a, 2b Regenerative burner 3 Four-way valve 4 Communication pipe 5 Venturi mixer 6a, 6b Supply / exhaust port 7a, 7b Fuel valve 8 Supply air inlet 9 Exhaust outlet 10 Blade plate 11 Air cylinder 12 Exhaust intake 13 Exhaust suction port 14 Compressor 15 Air supply blower 16 Exhaust blower 17 Exhaust recirculation pipe 18 Flue 19 Venturi mixer 20 Venturi mixer A Heat storage element

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference) 3K017 BA06 BB05 BE04 BE05 BE11 3K023 QA03 QB02 QB09 QB13 QB18 QB19 QC07 3K065 TA01 TC03 TD05 TE04 TE07 TH09 TL02 TL03 TL04 TM02 TP03 3K091 AA15 BB07 BB22 EA06

Claims (2)

[Claims] 1. A radiant tube combustion apparatus in which fuel gas is alternately supplied to regenerative burners mounted on both ends of a radiant tube, and supply and exhaust to both burners are switched by a four-way valve. A communication pipe connecting the exhaust side and the air supply side is provided, and high-pressure air is supplied to a venturi mixer interposed in the communication pipe, whereby a part of the exhaust gas is recirculated to the air supply side. Radiant tube burning device. 2. A radiant tube combustion apparatus in which fuel gas is alternately supplied to regenerative burners mounted on both ends of a radiant tube and supply and exhaust to both burners are switched by a four-way valve. It is composed of a drum-shaped cylindrical body, and the peripheral surface of the cylindrical body
An air supply port and an air exhaust port are provided at two locations, and air supply and exhaust ports connected to both burners are provided at two intermediate points between them, and the air supply and exhaust of both burners are alternately switched by rotating a blade plate in the cylinder. In addition, on one end surface of the cylindrical body, an exhaust intake port is provided near the air supply port and an exhaust suction port is provided near the exhaust port, and the exhaust suction port and the exhaust air intake port are provided outside the cylinder. A radiant tube combustion device characterized in that a communication pipe for communicating the inlet is provided, and high-pressure air is supplied to a venturi mixer interposed in the communication pipe, whereby a part of the exhaust gas is recirculated to the air supply side. .