JPH0635885B2 - Heat storage type radiant tube burner - Google Patents

Description

TECHNICAL FIELD The present invention relates to a radiant tube burner. More specifically, the present invention is equipped with a pair of burners having built-in heat storage bodies at both ends of a radiant tube, and the heat storage type radiant in which the heat of the combustion gas discharged by alternately burning the burners is recovered by the heat storage bodies. Regarding tube burners.

(Prior Art) In recent years, a preheating technology for combustion air has been developed in order to recover a considerable amount of heat from waste gas and improve thermal efficiency. For example, a burner having a heat storage body is provided at both ends of a radiant tube, and these are burned alternately so that the combustion gas is discharged through the heat storage body on the burner side that has not been burned, and the combustion gas stored in the heat storage body A radiant tube burner that uses heat to preheat combustion air has been proposed (US Pat. No. 4,460,501). As shown in FIG. 6, this burner is provided with a cone-shaped heat storage body 102 in a burner shell 104 surrounding a fuel nozzle 103 protruding into a radiant tube 101 outside the furnace,
The combustion air is supplied or the combustion gas is discharged through the heat storage body 102. Reference numeral 105 is a furnace wall, 106 is a blower, 107 is a four-way rotary valve, and 108 is an ejector.

(Problems to be solved by the invention) However, in the heat storage type radiant tube burner described above, since the combustion air is heated to about 1000 ° C. by the preheat using the stored heat, the flame temperature becomes extremely high, There is a drawback that a large amount of NOx is generated. Emissions regulated by the Japan Air Pollution Control Act (12
There is a drawback that NOx of 700 ppm or more, which is much higher than 0 ppm), is generated.

An object of the present invention is to provide a low NOx heat storage type radiant tube burner.

(Means for Solving Problems) In order to achieve such an object, the heat storage type radiant tube burner of the present invention has a heat storage body having a honeycomb structure for injecting combustion air in an axial direction and for penetrating a burner gun. Has a hole in the center of the burner gun and a hole larger in diameter than the hole for penetrating the burner gun is provided downstream of the burner gun's injection port to form a recess surrounding the primary fire. Combustion air is injected in two stages downstream of the injection.

Further, the heat storage type radiant tube burner of the present invention has, in the burner gun, a pilot burner tube longer than an internal ignition electrode in the burner gun, and a pilot fuel having a pilot amount less than a theoretical amount and above a lower limit of flammability limit. A pilot burner for supplying air is provided, and primary air below the flammable limit is supplied to the burner gun together with the main fuel.

(Operation) Therefore, the combustion air is supplied through the heat storage body in two stages at the recess surrounded by the heat storage body around the injection port of the burner gun and further downstream thereof, and in the first stage surrounded by the heat storage body, the air is supplied. Combustion is performed in an insufficient state, and insufficient air is supplied in the second stage radiant tube to achieve complete combustion. Further, the combustion gas is discharged through the heat storage body of the non-burning burner on the opposite side of the radiant tube.

(Example) Hereinafter, the structure of the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 is a schematic explanatory view showing an embodiment of the whole system of the heat storage type radiant tube burner of the present invention.

This radiant tube burner is equipped with burners 3 and 3 for inserting the heat storage body 2 at both ends of the radiant tube 1, and these burners 3 and 3 are connected to a combustion air supply system 9
And the combustion gas exhaust system 10 are selectively connectable, the burners 3 are alternately burned, and the combustion exhaust gas is discharged through the heat storage body 2 of the burner which is not burned and the heat storage body 2 of the combustion side burner 2 It is configured to supply combustion air through the.

The burner 3 includes a burner gun 4 for injecting gas combustion supplied from a fuel supply system 7, and a burner tube 5 for surrounding the burner gun 4 and injecting combustion air around the burner gun 4.
And the heat storage body 2 filled between the burner gun 4 and the pilot burner 6 and the burner tube 5 arranged in the burner gun 4. Reference numeral 24 is an electromagnetic valve.

Each burner pipe 5 is provided so as to be selectively connectable to a combustion air supply system 9 and a combustion gas exhaust system 10 via a four-way switching valve 8. Then, the combustion air supplied from the forced air blower 11 of the combustion air supply system 9 is supplied to one of the burners 3 for combustion, and the combustion gas is exhausted through the heat storage body 2 of the other burner 3 to the exhaust blower 12. It is provided to attract and exhaust air. The flow of combustion air and combustion gas is switched by using a timer (not shown) at regular intervals or by measuring the temperature of the combustion gas passing through the heat storage body 2 with a thermo sensor (not shown) and reaching a predetermined temperature. At this time, the switching valve 8 is driven so that the flow can be switched in synchronization with the fuel injection. The burner tube 5 has a flange 2
3 is detachably connected to the radiant tube 1.

The heat storage body 2 is for storing the sensible heat of the combustion gas discharged from the tube 1, and is generally used as a heat storage body and does not react with the combustion gas or adversely affect the combustion air. It can be used even if it is made of material. Generally, the heat storage body 2 is required to have a large heat transfer area and a small pressure loss and to have excellent heat resistance, thermal shock resistance, and corrosion resistance. Further, the heat storage body 2 of the present invention has a honeycomb structure in which combustion air is circulated in the axial direction. Therefore, for example, so-called honeycomb ceramic in which a large number of honeycomb-shaped cell holes 13 are formed along the flow direction of the combustion gas by using a breathable ceramic foamed in the shape of a sponge is adopted. In the present specification, the heat storage body is
Not only the material or the material itself being porous, but also the material capable of structurally ensuring air permeability even if the material itself does not have air permeability.

The heat storage body 2 is filled in the burner tube 5 and the radiant tube 1. This heat storage body 2 has a hole 14 for passing the burner gun 4 in the center and a hole 15 having a larger diameter downstream thereof.
Is formed so as to inject the combustion air in two stages around the injection port of the burner gun 4 and further downstream thereof. For example, as shown in FIG. 2, it may be divided into two stages by a clear step portion, and as shown in FIG. 3, a cannonball-shaped hole in which the hole gradually expands as it goes downstream from the ejection port of the burner gun 4. 15 may be formed. Further, as shown in FIGS. 4 (A) and 4 (B), the longitudinal cross-sectional shape of the heat storage body 2 on the inlet side is made the same as that on the outlet side to make the flow rate of each cell hole 13 the same, or As shown in FIG. 5, the flow rate of the cell holes 13 is kept different and
It is preferable that the hole diameter is increased toward the outer diameter side to make the pressure loss uniform.

A pilot burner 6 is inserted in the burner gun 4. The pilot burner 6 includes a mixing section 16 for mixing pilot fuel and pilot air and the pilot burner pipe 1.
7 and an ignition electrode 18 penetrating therethrough. The ignition electrode 18 is usually made of Kanthal wire, stainless steel, or the like. The electrode 18 is surrounded by an insulator 19 such as a silicon tube or quartz glass, and is further installed at the center of the pilot burner tube 17 via an insulator 20 such as a star insulator. The use of an electrode that is too long tends to cause current leakage in the middle of the process and makes the flying of the sparks unstable at the tip, thus causing poor ignition.
On the other hand, the short pilot burner 6 does not ignite because the flame does not fly to the exit of the burner gun 4. Therefore, the electrode 18 is not made too long, and the pipe 2 is added to the tip of the pilot burner pipe 17.
It is designed to connect 1 to reach the exit of the burner gun 4 with the pilot flame. If the connecting pipe 21 is too long, the flame will be cooled too much to cause misfire, and if it is too short, no flame will be formed up to the tip of the burner gun. Therefore, the total length l of the pilot burner pipe including the additional pipe 21 is 1/2 to the total length L of the burner gun.
It is preferably in the range of 2/3, most preferably 2/3
It should be as long as possible within the following range. The pilot gas burner 6 is not limited to the above. For example, a combustion cylinder to be inserted into the radiant tube may be provided, and the burner gun 4 and the pilot burner 6 may be installed in parallel in the combustion cylinder. in this case,
The heat storage body 2 is filled between the combustion tube and the radiant tube 1, and / or between the combustion tube and the burner tube 5.

An expansion part such as a surging tank 22 is provided at the entrance of the burner gun 4, for example, in the main combustion supply system 7 connected to the burner gun 4. In this case, the pilot fuel Fp and the main fuel are fed by one control system (for example, one solenoid valve).
When supplying Fm and Fm at the same time, pilot fuel Fp
The main fuel Fm can be injected later than that. The delay of the main combustion Fm may be a short time in millisecont unit.

The radiant tube 1 may be of a known shape such as a straight shape (straight tube shape), a U shape, a T shape, a W shape, an O shape, an L shape, or a new shape.

The radiant tube burner configured as described above operates as follows. First, the pilot burner 6 is supplied with an appropriate amount of pilot fuel (gas fuel) and pilot air below the theoretical air amount and above the lower limit of the flammability limit, for example, pilot air of about λp = 0.5, and ignited. At the same time as the gas fuel is supplied to the burner gun 4, primary air outside the flammability limit, for example, extremely small primary air of λ = 0.05 is added to this fuel. The main fuel once expands in the surging tank 22 and is supplied slightly later than the pilot fuel.

Therefore, the air-fuel mixture in the flammable limit range is supplied to the pilot burner 6, but the pilot burner 6 is ignited once at the tip of the pilot burner 6. However, this flame is cooled while flowing in the additional pipe and becomes a low temperature red flame 25 having no ignition ability, and unburned pilot fuel and air flow in a laminar flow around it. Then, at the outlet of the additional pipe 21, the unburned pilot fuel Fp is ignited by the small amount of primary air A ₁ flowing in the burner gun 4. This flame reaches the tip of the burner gun 4. After that, the main combustion Fm that arrives late causes the air in the burner gun 4 to become overwhelmingly insufficient, so the above-mentioned flame will be misfired, but the misfire point starts from the tip of the additional pipe 21 and reaches the tip of the burner gun 4. Although there is a moment at the tip of the burner gun 4, there is a moment when the pilot flame, the main combustion Fm, and the secondary air A ₂ flowing around the burner gun 4 coexist, at which time the main combustion Fm is ignited. Therefore, in this burner, the pilot frame in the burner gun 4 is extinguished after the main combustion ignition, and only the low temperature red frame 25 having no ignition capability is left.

The combustion air supplied by the forced air blower 11 passes through the heat storage body 2 and the large diameter hole 1 around the ejection port of the burner gun 4.
It is supplied in two stages into the concave portion 5 and the radiant tube 1 further downstream thereof, and is burned in two stages. On the other hand,
The combustion gas is discharged through the heat storage body 2 of the burner 3 which is not combusted by the operation of the exhaust fan 12. The heat of the exhausted combustion gas is recovered while passing through the heat storage body 2. After a certain period of time, the burner 3 on the opposite side, which had been stopped, is burned, and the burner 3 burned until then is stopped,
Combustion gas is discharged through the cooled regenerator 2 on the opposite side.
On the other hand, the combustion air is supplied after being preheated to a high temperature of, for example, 700 to 1,000 ° C. by collecting the heat of the combustion exhaust gas discarded in the heat storage body 2. The combustion and discharge are alternately repeated to gradually raise the temperatures of the radiant tube 1 and the heat storage body 2.
When the tube 1 and the heat storage body 2 reach the set temperature, the steady combustion starts. The combustion air and the combustion gas are switched at appropriate intervals, for example, at 20 seconds to 5 minutes, or when the discharged combustion gas reaches a control temperature of, for example, about 200 ° C.

(Effect of the invention) As is clear from the above description, the heat storage radiant tube burner of the present invention has a heat storage body having a honeycomb structure for injecting combustion air in the axial direction, and has a hole for penetrating the burner gun. A hole portion having a larger diameter than the hole is provided in the center and downstream of the burner gun, and combustion air is injected along the burner gun, and two stages of combustion air are provided around the injection port of the burner gun and further downstream thereof. Since it is divided into two parts and injected, the first stage surrounded by the heat storage body burns in an air-deficient state, and the radiant tube in the second stage supplies insufficient air to completely burn the NOx as a whole. It is possible to realize a two-stage combustion in which the amount generated is extremely low. Moreover, since the burner gun and the pilot burner are surrounded by the heat storage body and are not directly exposed to the high-temperature combustion gas, there is no risk of burning.

In addition, since the pilot burner is installed in the burner gun, it is possible to install the pilot burner inside the burner tube and radiant tube that are narrow and filled with heat storage material, and the pilot burner can be installed very easily and in a small space. Without taking it, the ignition becomes reliable.

Further, since the heat storage body protects the radiant tube in the bang portion from the flame and prevents uneven heating due to the pilot burner, it is possible to prevent rupture of the radiant tube in the bang portion and its vicinity.

Furthermore, when a surging tank is provided in the main fuel supply system,
At the same time, even if the pilot fuel and the main fuel are supplied, a slight delay occurs on the main fuel side and the ignition is reliably performed.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a heat storage type radiant tube burner system of the present invention, FIG. 2 is a schematic view for enlarging and explaining a heat storage body portion in detail, and FIG. 3 is another embodiment of the heat storage body. A central longitudinal sectional view showing an example, FIGS. 4 (A) and 4 (B) are central longitudinal sectional views showing still another embodiment of the heat storage body, and FIG. 5 is a transverse sectional view showing another embodiment of the heat storage body, FIG. 6 is a sectional view showing an example of a conventional heat storage type radiant tube burner. 1 ... Radiant tube, 2 ... Heat storage body, 3 ... Burner, 4 ... Burner gun, 5 ... Burner tube, 6 ... Pilot burner, 7 ... Fuel supply system, 8 ... Four-way valve, 9 ... Air supply system, 10 ... Exhaust system, 13 ... Cell hole, 14 ... Hole for penetrating burner gun, 15 ... Hole with diameter larger than 14 hole, 17 ... Pilot burner tube, 18 ... Ignition Electrodes, 21 …… Additional tubes, 22 …… Surging tank.

Claims (3)

[Claims] 1. A heat storage system in which a burner having a built-in heat storage body is alternately burned and its combustion gas is discharged through the heat storage body of a non-combustion side burner, while combustion air is supplied through the heat storage body in the combustion side burner. In the radiant tube burner, the heat storage body has a honeycomb structure for injecting combustion air in the axial direction, and has a hole for penetrating the burner gun at the center and the hole for penetrating the burner gun downstream of the injection port of the burner gun. A heat storage characterized by forming a recess having a larger diameter to surround a primary fire and injecting combustion air in two stages into a recess around the injection port of the burner gun and further downstream thereof. Radiant tube burner. 2. A burner gun is provided with a pilot burner tube longer than an internal ignition electrode, and a pilot burner is provided to supply pilot air to a pilot fuel at a theoretical amount or less and at a lower limit of flammability or more, and the burner gun. The heat storage type radiant tube burner according to claim 1, wherein primary air below the flammable limit is supplied together with the main fuel. 3. The heat storage type radiant tube burner according to claim 2, wherein a surging tank is provided in the middle of a system for supplying the main fuel to the burner gun.