JP3282955B2 - Hot air circulation system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot air circulating system for forming a strong circulating flow by taking out gas in a furnace once out of the furnace and then increasing the speed of the gas back into the furnace.

[0002]

2. Description of the Related Art Conventionally, a combustion gas is forcibly circulated in order to flatten a furnace temperature or the like. For example, as shown in FIG. 6, a circulating flow 103 is formed in the furnace 104 by a hot air circulating fan 101 and a duct 102 which takes out gas in the furnace out of the furnace 105 and returns the gas to the furnace 104 again. .

[0003]

However, since the strong circulating energy is determined by the flow rate and pressure of the airflow,
According to the conventional system for forcibly circulating hot air, there is a limit to the strong circulation that can be obtained. That is, since the pressure is proportional to the square of the flow velocity, in order to increase the flow velocity, the pressure must be increased in proportion to the square of the flow velocity. However, when the pressure increases by the square, the power of the circulation fan increases extremely, so that the discharge pressure cannot be increased and the circulation amount is limited.

[0004] In addition, if an attempt is made to use high-temperature hot air, cooling of heat-resistant blades and fan shafts is required, and the number of failures increases. Therefore, there is no fan that can withstand high-temperature hot air. It was difficult to circulate high-temperature hot air. For this reason, in the conventional hot air circulation system,
The maximum gas temperature that can be circulated outside the furnace is around 650 ° C,
It is usually only applicable to low temperature furnaces, e.g.

Therefore, according to the conventional hot air circulation system, the effect of circulating the gas in the furnace is insufficient, and there has been a problem that the furnace cannot be made compact and high performance.

[0006] An object of the present invention is to provide a hot air circulation system capable of generating a strong circulation flow at a high temperature. It is another object of the present invention to provide a hot air circulation system that can secure a high temperature and a large amount of circulation with low power.

[0007]

In order to achieve the above object, a hot air circulation system according to the present invention takes out a burner for a heat source which forms a flame in a furnace and burns it, and takes out combustion gas in the furnace to the outside of the furnace and re-exposes it. And a circulation path outside the furnace for refluxing from another place into the furnace. The circulation path outside the furnace is provided with a heat storage body at a take-out port and a return port part close to the furnace and has a circulation fan, and the suction port side and the discharge port side of the circulation fan are either one of the heat storage bodies. A flow path switching device that selectively connects to each other and relatively switches a flow direction of an airflow with respect to the heat storage body to alternately take out combustion gas from the furnace through the heat storage body and supply it to the furnace; and A flow switching device having a heat removal means for performing heat removal or dilution for changing the gas property of the air flow in the extra-circulatory circulation path between both heat storage bodies, and alternately burning and synchronizing the heat source burners. Thus, a high-temperature strong circulation flow that periodically reverses the flow direction of the gas flow is formed in the furnace.

[0008] Therefore, a part of the gas in the furnace is introduced into the circulation path outside the furnace by the negative pressure generated by the circulation fan, and after being pressurized by the circulation fan, injected again into the furnace at a high speed and strongly circulated in the furnace. Form a flow. At this time, the in-furnace gas passes through the regenerator on the suction side of the out-of-furnace circulation system, and the sensible heat is discarded to the regenerator to be cooled. Then, it is introduced into the circulation fan in a low temperature state, and after being pressurized, passes through the heat storage body on the opposite side, is heated again by direct heat exchange there, and is then injected into the furnace.

[0009] A high-velocity flow of in-furnace gas that causes strong circulation in the furnace usually lowers the flame temperature and causes misfire. However, in the case of the first aspect of the present invention, since the temperature of the gas in the furnace is higher than the ignition temperature of the fuel even if the flow velocity increases,
Since the temperature at the ignition point does not drop so much, it has excellent ignitability, flame stability, and the flame does not blow out. In addition, the high-speed jet of the gas in the furnace causes a strong circulation of the combustion gas in the furnace, so that the temperature in the furnace is flattened (averaged) and a local high-temperature region is not generated. That is, if the fluid can be supplied at a high speed, the amount of gas circulated in the furnace can be significantly increased in a wide area of the heating space by the momentum. As a result, the gas temperature difference in the furnace is reduced, and the temperature field can be made ultra-flat, so that a local high-temperature region is not generated.
For this reason, the furnace average temperature can be raised to near the limit temperature, and the amount of heat transfer can be increased.

On the other hand, in the extra-furnace circulation system, the gas properties of the circulating airflow are changed by heat removal or dilution by the heat removal means, thereby preventing the equilibrium temperature from rising. Here, the equilibrium temperature and the return port temperature due to the heat removal of the circulating airflow are represented by the following Equation 1.

[0011]

(Equation 1)

The airflow equilibrium temperature tc of the circulating fan suction port is governed by the temperature difference Δt of the circulating airflow and the temperature efficiency of the heat storage body.
In the case of 00 ° C., the relationship is as shown in FIG. The equilibrium temperature and the return port temperature due to the dilution of the circulating airflow are represented by the following equation (2).

[0013]

(Equation 2)

The airflow equilibrium temperature tc at the circulating fan suction port is governed by the amount of diluted air ΔG to the circulating airflow and the temperature efficiency of the heat storage body.
When the temperature is 000 ° C. and the atmospheric temperature to is 20 ° C., the relationship is as shown in FIG. Thus, an increase in the equilibrium temperature is prevented from being caused by a change in the gas properties due to an appropriate amount of heat removal or dilution in the extra-furnace circulation system.

Here, the heat removal means is not particularly limited to the installation location as long as it is between the heat storage bodies at both ends provided at the take-out port and the return port near the furnace of the extra-furnace circulation system. It is preferable to be arranged between the road switching device and the suction side of the circulation fan. In addition, the heat removal means is, for example, a means for injecting a small amount of diluting gas such as air or exhaust gas into the circulating gas, a heat exchanger, a material preheating section of a heating facility, or a heat retaining means for a flow path between both heat storage bodies. It is constituted by making it thin.

Further, in the hot air circulation system of the present invention, the heat source burner includes a heat storage body, and supplies combustion air or exhausts gas in the furnace through the heat storage body.
It is preferred to use a regenerative burner system that alternately burns the set of burners.

In this case, when the combustion gas is exhausted, the sensible heat is recovered by the heat storage body, and is then used again for preheating the combustion air with extremely high thermal efficiency and returned to the furnace.
The temperature of the combustion air can be set at a high temperature close to the temperature of the combustion exhaust gas flowing out to the regenerator, and high thermal efficiency can be maintained. Further, since the combustion position in the furnace is switched in a short time and the injection direction of high-temperature hot air, that is, the direction of the flow of the circulating flow, is switched accordingly, a non-standing flame in which the flame position changes frequently becomes a non-standing flame and the temperature distribution in the furnace. Can be made more uniform, and uneven heating can be reduced.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail based on the preferred embodiment shown in the drawings.

FIG. 1 shows an embodiment of a heating facility to which the hot air circulation system of the present invention is applied. This hot air circulation system includes a furnace 1, a burner 3 for a heat source which forms a flame in the furnace 2 and burns the furnace, and a furnace which takes out combustion gas from the furnace 2 and returns it to the furnace 2 from another place again. It is mainly composed of an external circulation system 4. The heat source burner 3 is constituted by a pair of burners 3A and 3B that burn alternately. It is preferable that these burners 3A and 3B are arranged at a position suitable as a heat source and at a position as far away as possible so that the temperature distribution in the furnace is not deviated. The circulation path 4 outside the furnace is
A high-temperature strong circulation flow that periodically reverses the flow direction of the air flow according to the switching of the heat source burner 3 is provided in the furnace 2. The in-furnace gas inlets and outlets 9A and 9B of the out-of-furnace circulation system 4 are arranged side by side with the burner throat of the heat source burner 3, and are provided so that a high-temperature strong circulation flow induces the flame and the combustion gas 17 along the object to be heated. Have been. In the present embodiment, the circulating gas inlets and outlets 9A, 9B of the extra-furnace circulation system 4 are provided closer to the object to be heated. However, the present invention is not particularly limited thereto. In some cases, the burners 3A, 3B are closer to the object to be heated. May be provided.

On the other hand, as the heat source burner 3, in the case of this embodiment, a heat storage type burner system is employed. The heat storage type burner system includes heat storage bodies 11A and 11A, respectively.
B and a pair of burners 3A and 3B
Selectively connected to the air supply system 13 or the exhaust system 14 via the air supply system, and used for heating the object to be heated W from the stopped one while burning one of the pair of burners 3A and 3B. Combustion gas is exhausted. Each burner 3
A and 3B are installed, for example, on both side walls of the furnace 1 so as to face each other and operate alternately. Each burner 3
A and 3B do not necessarily need to be separately arranged on both side walls of the furnace 1 so as to face each other. For example, they may be arranged side by side on one wall of the furnace 1. Incidentally, reference numeral 16 in the drawing denotes a fuel nozzle.

The heat accumulators 11A and 11B are housed in a burner body or a casing separate from the burner body.
A, 3B. This heat storage body 11A, 11
B exchanges heat with the passing exhaust gas to recover waste heat and preheats the combustion air with the recovered heat. The heat storage bodies 11A and 11B of each burner 3A and 3B
15 is connected to the port of the four-way valve 12. An air supply system 13 and an exhaust system 14 are connected to the other ports of the four-way valve 12, respectively. Therefore, by switching this four-way valve 12, each burner 3A, 3B
One of the heat storage bodies 11A and 11B is selectively connected to the air supply system 13 and the other is selectively connected to the exhaust system 14.

On the other hand, the out-of-furnace circulation system path 4 includes heat storage elements 5A and 5B at portions close to the furnace 1 and has a circulation fan 6, and connects the suction port side and the discharge port side of the circulation fan 6 to the heat storage elements. 5A and 5B are selectively connected to each other to relatively change the direction of the flow of the airflow with respect to the heat accumulators 5A and 5B, thereby removing the combustion gas from the furnace 2 through the heat accumulators 5A and 5B and the furnace. A flow switching device 7 for alternately supplying air to the inside 2 and a heat removal means 8 for performing heat removal or dilution for changing the gas property of the airflow. A high-temperature strong circulation flow 10 whose direction is reversed is formed in the furnace 2.

Here, as the heat storage bodies, the heat storage bodies 11A and 11B used in the burner for the heat source and the heat storage bodies 5A and 5B disposed in the extra-furnace circulation system 4 are relatively low in pressure loss. It is preferable to use a cylinder having a large number of honeycomb-shaped cell holes formed of a material having a large heat capacity and high durability, for example, a ceramic. For example, a high temperature fluid of about 1000 ° C. like combustion exhaust gas and 20 ° C. like combustion air
For heat exchange with the low-temperature fluid before and after, it is preferable to use a honeycomb-shaped one manufactured by extrusion molding using a ceramic such as cordierite or mullite as a material. The honeycomb-shaped regenerator is made of a material other than cordierite and mullite, such as a material other than alumina and ceramics, such as a metal such as heat-resistant steel, or a composite of ceramic and metal, such as a metal melted in pores of a ceramic having a porous skeleton. Al ₂ O ₃ -Al composite, SiC-
It may be manufactured using an Al ₂ O ₃ —Al composite or the like.
Although the honeycomb shape originally means a hexagonal cell (hole), the present specification includes not only an original hexagon but also an infinite number of square or triangular cells. Alternatively, a honeycomb-shaped heat storage body may be obtained by bundling tubes or the like without forming them integrally. In addition, the shape of the heat storage body is not particularly limited to the honeycomb shape, and a flat or corrugated heat storage material is radially arranged in a cylindrical casing, or a fluid passes in a pipe-shaped heat storage material in the axial direction. As described above, the casing may be filled in a cylindrical casing. Alternatively, a cylindrical casing that is formed by partitioning into two chambers in the circumferential direction and allows fluid to pass in the axial direction is prepared, and a spherical, short pipe, short rod, strip, nugget-shaped It may be configured by filling a mass of a heat storage material such as a net.

A dilution air inlet 8 a as a heat removal means 8 is provided between the suction side of the circulation fan 6 and the flow path switching device 7.
Is provided. Normal-temperature air is injected from the dilution air injection port 8a so that heat extraction corresponding to the temperature efficiency of the heat storage elements 5A and 5B can be performed. The amount of heat removed by the injection of the normal-temperature air is represented by Expression 3.

[0025]

(Equation 3)

The airflow equilibrium temperature tc at the circulating fan suction port is governed by the amount of diluted air ΔG to the circulating airflow and the temperature efficiency of the heat storage material.
When the temperature is 00 ° C. and the atmospheric temperature is 20 ° C., the relationship is as shown in FIG. Therefore, in order to prevent an increase in the equilibrium temperature, the gas property is changed by an appropriate amount of dilution in the extra-furnace circulation system. Usually, when the temperature efficiency of the heat storage bodies 5A and 5B is about 80 to 90%, the dilution rate is 0.1 to 0.1%.
It is set in the range of 0.25. Using a regenerator with a temperature efficiency of ηto = 0.9 at a dilution rate ΔG / G = 0 at a circulating air flow outlet temperature th of 1000 ° C.,
Equilibrium temperature tc and temperature efficiency η when diluted at G = 0.1
t, the circulating airflow temperature tl at the return port is calculated as <tc = 38
0 ° C., ηt = 0.855 and tl = 910 ° C.

According to the thermal circulating system configured as described above, a high-temperature strong circulating flow is formed in the furnace as described below, so that the furnace temperature can be made flat and high.

One set of burners 3 constituting the heat source burner 3
A and 3B are alternately fired to form a non-standing flame in the furnace 2.

For example, when operating the burner 3A, the four-way valve 12 is switched so that the burner 3A is connected to the combustion air supply system 13, and one fuel control valve is opened and the other fuel control valve is opened. close. As a result, the supplied combustion air is preheated to a high temperature close to the exhaust gas temperature, for example, about 800 to 1000 ° C. while passing through the heat storage body 11A, and then flows into each burner throat, and is injected from each fuel nozzle. Combustion is mixed with. On the other hand, the combustion gas is discharged from the burner 3B connected to the exhaust system. At this time, the heat of the combustion gas (exhaust gas) used for heating the object to be heated W is recovered by the heat storage body 11B.

When a predetermined time (for example, 20 seconds to 60 seconds) has elapsed since the burner 3A started operating,
As the four-way valve 12 switches, one of the fuel control valves closes and the other opens in conjunction with this. Thereby, burner 3
While the combustion air and fuel are supplied to the B side to start combustion, the burner 3A enters a non-operation standby state. At this time, the combustion air supplied to the burner 3B side is preheated by the heat storage body 11B heated by the waste heat of the exhaust gas, and becomes extremely high temperature (for example, about 800 to 1000 ° C.).

Normal-temperature combustion air or 300 to 400
In the case of general combustion using combustion air preheated to about ° C, it is difficult to burn with insufficient or excessive air. However, if the combustion air becomes such a high temperature, the temperature of the mixed gas itself becomes close to or higher than the ignition temperature of the fuel, even if the air is insufficient or excess, the reaction speed increases and the flammability limit greatly increases. Contributes significantly to the stabilization of combustion and burns relatively well.

Thereafter, the burners 3A and 3B alternately operate at predetermined time intervals, and repeat alternate combustion using very high temperature combustion air.

Here, maximizing the amount of heat transfer by high-efficiency heat transfer is a method of reducing the amount of heat energy supplied to the heat device by improving the heat transfer efficiency. For that purpose, the average heat flux must be increased, so that an increase in the heat transfer coefficient and an increase in the temperature of the temperature field are fundamental. Therefore, if the temperature level of the entire furnace can be increased to the maximum allowable value under the condition that the amount of heat energy supplied to the heating device is constant, the amount of heat transfer increases. Then, in order to return the increased heat transfer amount to the same amount as before, the amount of heat energy supplied to the heating device may be reduced. This is energy saving by "maximizing the amount of heat transfer by high-efficiency heat transfer".

However, in the conventional ordinary combustion technique, when an attempt is made to increase the temperature level in the furnace, a region where the allowable maximum value is always locally generated. That is, in order to stably burn the turbulent diffusion flame in normal combustion, it is essential to form a flame holding region. Therefore, in the normal combustion, a high-temperature region is generated centering on the flame holding region, so that a temperature distribution having a large bias is inevitably formed in the heat device. As a result, this is a constraint, and it has been considered that a method of improving the average heat flux, that is, a method of forming an appropriate high-temperature field is poorly feasible.

When the amount of gas circulated in the furnace is relatively small, the amount of radiant heat transfer from the flame region to the object to be heated increases drastically as the furnace temperature rises, and the heat capacity of the gas flowing in the furnace becomes small. The heat transfer from the high-temperature gas part of the furnace volume plays a large part in the amount of heat given to the object to be heated. The gas in the other area where the temperature has fallen outside the flame area is retained in the furnace only because the temperature is still too high to be discharged outside the furnace as it is, and for the purpose of slight heat transfer to the object to be heated and heat retention It's being used. For this reason, a general furnace has a larger volume than necessary, despite the fact that most of the volume of the furnace contributes to heat transfer. If the furnace is made compact, the gas temperature at the furnace outlet will increase, and if the amount of heat recovery is not sufficiently increased, the amount of exhaust heat will increase and the thermal efficiency of the furnace will decrease.

On the other hand, the hot air circulation system of the present invention
It recovers the sensible heat of the gas inside the furnace and
Because it is a method of returning the combustion exhaust gas to the inlet and ejecting it at high speed, the flow rate of the gas flowing in the furnace is the sum of the amount of air and fuel input plus the amount of circulating gas, and the amount of circulating gas increases The gas flow in the furnace becomes intense, which promotes mixing and increases the amount of convective heat transfer, resulting in a smooth temperature distribution.

Further, when the gas circulation rate is increased by the high-speed injection of the circulating airflow, the maximum temperature of the flame is greatly reduced due to an increase in the heat capacity of the combustion gas. That is, when the amount of circulating gas increases, the local temperature rise due to combustion decreases in inverse proportion to the amount of flowing gas in the furnace, and the axial distribution of the temperature in the furnace flattens. In addition, the maximum temperature in the furnace decreases in inverse proportion to the increase in the gas circulation rate, but the average temperature in the furnace hardly decreases, and the maximum temperature in the furnace approaches the average temperature in the furnace, and the temperature distribution in the furnace averages. It will become.

As described above, in the heating method of the present invention, the average gas flow rate in the furnace is determined by the air (+ fuel) flowing into the furnace.
The amount of gas circulation can be increased while maintaining the high temperature, and the temperature rise due to combustion can be relatively reduced to 300 to 500 ° C.

In this embodiment, the case where the present invention is applied to a heat storage type burner system in which a pair of burners 3A and 3B having a heat storage body are alternately burned has been described. However, the present invention is not particularly limited thereto. Even in the case of oxy-burner combustion, it can be adopted as a heat source in which the flame temperature and the combustion gas temperature become high as in the regenerative burner system.

Further, the heat removing means 8 is not limited to a specific one, and for example, means for directly extracting heat from the circulating air flow may be employed. FIG. 2 shows an example of another embodiment. This hot air circulation system uses a heat exchanger 8 b as the heat removal means 8. In this case, the properties shown in Equation 4 and FIG. 4 are established by changing the properties of the circulating gas by heat exchange.

[0041]

(Equation 4)

FIG. 3 shows an example of another embodiment. This hot air circulation system utilizes a preheating section 8c of a heating facility 1 'as a heat removal means 8. in this case,
Heating equipment 1 ′ between the flow path switching device 7 and the circulation fan 6
The preheating section 8c is connected to remove the heat by preheating the object to be heated W. The heating unit 2 'of the heating equipment 1' is connected to the heat source burner 3 and the extra-furnace circulation system 4 to form a high-temperature strong circulation flow 10.

Further, although not shown, the heat removal means 8 can also be constituted by reducing the heat retention of the flow path between the heat storage bodies 5A and 5B. In this case, although the heat use efficiency is reduced, there is an advantage that the heat insulating material is reduced in terms of equipment.

[0044]

As is apparent from the above description, according to the hot air circulation system of the present invention, the gas in the furnace passes through the heat accumulator on the suction side of the circulation path outside the furnace and the sensible heat is discarded to the heat accumulator to reduce the temperature. After that, it is introduced into the circulating fan in a low-temperature state, and after being pressurized, passes through the heat storage body on the opposite side, is heated again by direct heat exchange there, and is then injected into the furnace. It can be used to form a high temperature strong circulating air flow in the furnace. That is, since the temperature of the gas in the furnace circulating in the hot air circulation system outside the furnace is low, the size of the circulation fan can be increased (capacity can be increased), and the discharge flow rate can be increased to generate strong circulation.

This high flow velocity of the gas in the furnace usually causes a flame temperature drop and causes a misfire.
Even if the flow velocity rises, the temperature is higher than the ignition temperature of the fuel, so that the temperature at the ignition point does not drop so much, so that the ignitability is excellent, the flame is stable, and the flame does not blow out. In addition, the high-speed jet of the gas in the furnace causes a strong circulation of the combustion gas in the furnace, so that the temperature in the furnace is flattened (averaged) and a local high-temperature region is not generated. That is, if the fluid can be supplied at a high speed, the amount of gas circulated in the furnace can be significantly increased in a wide area of the heating space by the momentum. As a result, the gas temperature difference in the furnace is reduced, and the temperature field can be made ultra-flat, so that a local high-temperature region is not generated. For this reason, the furnace average temperature can be raised to near the limit temperature, and the amount of heat transfer can be increased. In addition, since the maximum temperature in the furnace is reduced, it is possible to reduce NOx.

Therefore, the hot air circulation system of the present invention reduces the thermal stress on the furnace structure because the temperature difference in the furnace is reduced by making the temperature in the furnace uniform, and the conventional heat resistant technology is used by reducing the maximum temperature. It is possible to sufficiently cope with the problem and to reduce damage due to local high temperature. In addition, since the average temperature in the furnace can be increased, the entire furnace can be used for heating, which increases the amount of convective heat transfer to the same object to be heated.

Further, in the hot air circulation system of the present invention, since the equalization of the furnace temperature makes the volume ratio of the furnace space effective for heat transfer to the object to be heated larger than before, the combustion load ratio is reduced. It is possible to reduce the furnace volume or to improve the productivity, so that the furnace can be made more compact.

In the case of the invention of claim 7, in the heat source burner, even if the combustion gas is exhausted at a high temperature, the sensible heat is recovered when the exhaust gas is exhausted through the heat accumulator, and again with extremely high thermal efficiency. Since it is used to preheat combustion air and returned to the furnace, high thermal efficiency can be maintained. In addition, since the combustion position in the furnace can be switched in a short period of time, the flame becomes a non-stationary flame with frequently changing flame positions, the furnace temperature distribution can be made more uniform, heating unevenness is reduced, and equipment is compact and simple. Can be.

[Brief description of the drawings]

FIG. 1 is a principle view showing an embodiment of a hot air circulation system of the present invention.

FIG. 2 is a principle view showing another embodiment of the hot air circulation system of the present invention.

FIGS. 3A and 3B are principle diagrams showing still another embodiment of the hot air circulation system of the present invention, in which FIG. 3A is a cross-sectional view along a workpiece feeding direction, and FIG.

FIG. 4 is a graph showing the relationship between the airflow equilibrium temperature of the circulation fan suction port and the difference in the degree of heat removal of the circulation airflow in relation to the temperature efficiency of the heat storage body.

FIG. 5 is a graph showing the relationship between the airflow equilibrium temperature of the circulation fan suction port and the dilution air rate in relation to the temperature efficiency of the heat storage body.

FIG. 6 is a principle diagram showing an example of a conventional hot air circulation system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Furnace 2 Furnace 3 Heater burner 4 Out-of-furnace circulation system path 5A, 5B Heat storage material 6 Circulation fan 7 Flow path switching device 8 Heat removal means

Continuation of the front page (72) Inventor Yoshiki Fujii 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd. (56) References JP-A-9-53886 (JP, A) JP-A-8-128620 ( JP, A) JP-A-8-104918 (JP, A) JP-A-6-281350 (JP, A) Fully open Showa 57-104103 (JP, U) Fully open Showa 52-153131 (JP, U) Really open 52-161533 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F23C 9/00 F23L 15/02 F23C 11/00 F27D 7/04 F27B 9/36 C21D 1/76

Claims (7)

(57) [Claims] 1. A heat source burner for forming a flame in a furnace and burning it, and an extra-furnace circulation system for taking out combustion gas in the furnace out of the furnace and returning the gas to the furnace from another place again. And, the extra-furnace circulation system includes a heat storage body at a take-out port and a return port portion close to the furnace and has a circulation fan, and the suction port side and the discharge port side of the circulation fan are one of the ones. A flow that selectively connects to the heat storage body and relatively switches the direction of the flow of the air stream with respect to the heat storage body to alternately take out combustion gas from the furnace through the heat storage body and supply the combustion gas to the furnace. A path switching device and heat removal means for performing heat removal or dilution for changing the gas property of the airflow in the extra-furnace circulation path between the two heat storage elements, and alternately burn and synchronize the heat source burners with the heat source. The said flow A hot air circulation system, wherein a high-temperature strong circulation flow that periodically reverses the flow direction of the airflow by a path switching device is formed in the furnace. 2. The hot air circulation system according to claim 1, wherein said heat removal means is disposed between said flow path switching device and a suction side of a circulation fan. 3. The hot air circulation system according to claim 1, wherein said heat removal means injects a small amount of a dilution gas. 4. The hot air circulation system according to claim 1, wherein said heat removal means is a heat exchanger. 5. The hot air circulation system according to claim 1, wherein the heat removal means is a material preheating section, and the material preheating section removes heat of the circulating gas. 6. The hot air circulation system according to claim 1, wherein said heat removal means is constituted by reducing heat retention of a flow path between both heat storage bodies. 7. A regenerative burner system in which the heat source burner includes a regenerator and supplies a combustion air or exhausts gas in the furnace via the regenerator to burn a set of burners alternately. The hot air circulation system according to any one of claims 1 to 6, wherein