Secondary combustion furnace, method of using secondary combustion furnace, secondary combustion method

Abstract

To provide a secondary combustion furnace, a use method for the secondary combustion furnace and a secondary combustion method capable of burning a combustible gas discharged from a primary combustion furnace in a stable atmosphere while suppressing a generation amount of carbon dioxide.SOLUTION: A secondary combustion furnace 10 for burning a combustible gas discharged from a primary combustion furnace 30 includes: a furnace body 11 having a furnace chamber 111; an introduction passage 12 for introducing the combustible gas to the furnace chamber 111; a burner 13; a fuel supply system 14 and a first air supply system 15 connected to the burner 13; a first air supply fan 151 connected to the first air supply system 15; and a control device 17 having a heating mode of allowing fuel supply to the burner 13 and controlling output of the burner 13 by adjusting air output of the first air supply fan 151 and a first cooling mode of regulating the fuel supply to the burner 13 and controlling a furnace temperature by adjusting air output by using the first air supply fan 151.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a secondary combustion furnace for burning combustible gas discharged from a primary combustion furnace, a method for using the secondary combustion furnace, and a secondary combustion method.

Background Art

[0002] For example, furnaces for heat-treating objects to be treated, such as heat treatment furnaces, annealing furnaces, rotary furnaces, atmosphere furnaces, firing furnaces, drying furnaces, combustion furnaces, etc., often have unburned fuel gas and NO in the exhaust gas from the furnace. x 、SO x etc., which are gases that impose a burden on the environment. Therefore, some furnaces are provided with a secondary combustion furnace that heat-treats the exhaust gas of the primary combustion furnace to thermally decompose environmental load gases in the exhaust gas, in addition to the primary combustion furnace for heat-treating the object to be treated. The secondary combustion furnaces disclosed in Patent Documents 1 to 4 burn fuel with a burner provided in the furnace and burn and treat the gas to be treated with the combustion heat. In other words, they directly burn the gas to be treated with the thermal power of the burner. Since these secondary combustion furnaces directly burn the gas to be treated with the thermal power of the burner, a large amount of fuel is required to obtain the thermal power of the burner, and furthermore, a large amount of carbon dioxide generated by burning fuel with the burner is discharged. Recently, due to the increasing awareness of environmental considerations such as carbon neutrality, the amount of carbon dioxide emissions, which is a greenhouse gas, has been regarded as a problem, and such carbon dioxide is also included in environmental load gases. Therefore, there is a demand for a secondary combustion furnace that can suppress the emission of carbon dioxide, which is an environmental load gas. The secondary combustion furnace disclosed in Patent Document 5 adjusts the air supply amount of a burner provided in the furnace, swirls the gas to be treated in the furnace, and ensures a long residence time of the gas in the furnace, thereby completely burning the gas to be treated and treating it. This secondary combustion furnace can also stop the fuel blown into the burner and only perform air supply when the temperature of the primary combustion furnace rises, and can suppress carbon dioxide emissions by the amount of fuel blown into the burner that is stopped.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0004] The exhaust gas discharged from the primary combustion furnace contains unburned fuel gas, evaporation gas formed by evaporation of oil such as lubricant attached to the object to be treated, and atmospheric gas such as oxidizing gas and reducing gas supplied to the primary combustion furnace. These gases consist of hydrogen, carbon monoxide, methane, propane, butane, etc., and are combustible gases. When the exhaust gas is burned in the secondary combustion furnace, the combustible gas contained in the exhaust gas raises the furnace temperature by generating combustion heat. It is difficult to control the combustion of this combustible gas, and depending on the introduced amount of the combustible gas, the furnace temperature may rise excessively, making the furnace atmosphere in the secondary combustion furnace unstable. As a result, it affects the progress of chemical reactions related to the combustion treatment of exhaust gas, and problems such as the generation of environmental load gases occur instead. Therefore, the secondary combustion furnace is required not only to suppress the emission of carbon dioxide, which is an environmental load gas, but also to stably maintain the furnace atmosphere during the treatment.

[0005] The present invention aims to solve the problems of such prior art, and provides a secondary combustion furnace capable of burning the combustible gas discharged from a primary combustion furnace in a stable atmosphere while suppressing the generation amount of carbon dioxide, a method for using the secondary combustion furnace, and a secondary combustion method.

Means for Solving the Problems

[0006] In order to solve the above problems, the invention according to claim 1 is a secondary combustion furnace for burning the combustible gas discharged from a primary combustion furnace, comprising: a furnace body provided with a furnace chamber inside; an introduction passage connected to the furnace body for introducing the combustible gas into the furnace chamber; a burner attached to the furnace body; a fuel supply system connected to the burner and a valve connected to the fuel supply system; a first air supply system connected to the furnace body via the burner and a first air supply fan connected to the first air supply system; a control device that permits the fuel supply from the fuel supply system to the burner by the valve, adjusts the air output by the first air supply fan, and controls the output of the burner in a heating mode, and regulates the fuel supply from the fuel supply system to the burner by the valve, adjusts the air output by the first air supply fan, and controls the temperature of the furnace chamber in a first cooling mode. The invention according to claim 2 is the invention according to claim 1, further comprising a second air supply system connected to the furnace body and a second air supply fan connected to the air supply system, wherein the control device has a second cooling mode of maintaining the air output by the first air supply fan at a maximum value and adjusting the air output by the second air supply fan to control the temperature of the furnace chamber. The invention according to claim 3 is the invention according to claim 2, wherein the second air supply fan has a larger air volume than the first air supply fan. The invention according to claim 4 is characterized in that, in the invention according to any one of claims 1 to 3, it further comprises an exhaust duct connected to the furnace body and a damper attached to the exhaust duct. The invention according to claim 5 is a method of using a secondary combustion furnace that uses the secondary combustion furnace according to any one of claims 1 to 4 to burn combustible gas discharged from a primary combustion furnace, for a burner attached to the furnace body, allowing fuel supply from a fuel supply system connected to the burner by a valve connected to the fuel supply system, supplying air from a first air supply system connected to the burner by a first air supply fan connected to the first air supply system, burning a fuel-air mixture in the burner, and performing a temperature-raising operation of raising the temperature of a furnace chamber inside the furnace body to a temperature at which the combustible gas self-ignites, after the temperature-raising operation, a fuel stop operation of regulating the fuel supply to the burner by the valve, after the fuel stop operation, introducing the combustible gas into the heated furnace chamber and performing a combustion operation of burning the combustible gas by self-ignition, and in the combustion operation, based on the temperature rise of the furnace chamber due to the combustion of the combustible gas, performing a first cooling operation of supplying air from the first air supply fan to the furnace chamber through the first air supply system to cool the furnace chamber. The invention according to claim 6 is a method of using a secondary combustion furnace that uses the secondary combustion furnace according to any one of claims 2 to 4 to burn combustible gas discharged from a primary combustion furnace, for a burner attached to the furnace body, allowing fuel supply from a fuel supply system connected to the burner by a valve connected to the fuel supply system, supplying air from a first air supply system connected to the burner by a first air supply fan connected to the first air supply system, burning a fuel-air mixture in the burner to raise the temperature of a furnace chamber inside the furnace body to a temperature at which the combustible gas self-ignites, after the temperature-raising operation, a fuel stop operation of regulating the fuel supply to the burner by the valve, After the fuel stop operation, introducing the combustible gas into the heated furnace chamber and burning the combustible gas by self-ignition, a combustion operation; In the combustion operation, based on the temperature rise of the furnace chamber due to the combustion of the combustible gas, performing air supply to the furnace chamber from the first air supply system via the first air supply fan, and a first cooling operation for cooling the furnace chamber; In the first cooling operation, when the air output by the first air supply fan is 100%, performing air supply to the furnace chamber from the second air supply fan via the second air supply system, and a second cooling operation for cooling the furnace chamber, which is the gist. The invention according to claim 7 is the invention according to claim 5 or 6, wherein in the temperature raising operation, the air excess ratio (λ) of the exhaust gas discharged into the furnace chamber by burning the air-fuel mixture with the burner is 1.1 or more and 1.43 or less (1.1 ≦ λ ≦ 1.43), which is the gist. The invention according to claim 8 is a secondary combustion method using a secondary combustion furnace including a furnace body provided with a furnace chamber inside, an introduction path connected to the furnace body for introducing the combustible gas into the furnace chamber, a burner attached to the furnace body, a fuel supply system connected to the burner, a first air supply system connected to the furnace body via the burner, and a second air supply system connected to the furnace body, for burning the combustible gas discharged from a primary combustion furnace, For the burner, supplying fuel from the fuel supply system and supplying air from the first air supply system, burning the air-fuel mixture with the burner, raising the temperature of the furnace chamber to the temperature at which the combustible gas self-ignites, and then a temperature raising step of stopping the supply of the fuel to the burner; After the temperature raising step, introducing the combustible gas from the introduction path into the heated furnace chamber and burning the combustible gas by self-ignition in the furnace chamber, a combustion step; In the combustion step, when the temperature of the furnace chamber rises due to the combustion of the combustible gas, performing either a first cooling operation of supplying air to the furnace chamber via the first air supply system or a second cooling operation of supplying air to the furnace chamber via the second air supply system in parallel with the first cooling operation, and a cooling step of cooling the furnace chamber by executing any of these operations, which is the gist. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a secondary combustion furnace, a method for using the secondary combustion furnace, and a secondary combustion method that can burn the combustible gas discharged from the primary combustion furnace in a stable atmosphere while suppressing the amount of carbon dioxide generated. [Brief Description of the Drawings]

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

[0009] The matters shown here are exemplary and for exemplarily explaining the embodiments of the present invention, and are described for the purpose of providing an explanation that can most effectively and without difficulty understand the principle and conceptual features of the present invention. In this regard, it is not intended to show the structural details of the present invention to an extent greater than necessary for a fundamental understanding of the present invention, and it is to clarify to those skilled in the art how some forms of the present invention are actually embodied by the description in combination with the drawings.

[0010] [1] Secondary combustion furnace The secondary combustion furnace of the present invention is a secondary combustion furnace that burns the combustible gas discharged from the primary combustion furnace, a furnace body provided with a furnace chamber inside, an introduction path connected to the furnace body for introducing the combustible gas into the furnace chamber, a burner attached to the furnace body, a fuel supply system connected to the burner and a valve connected to the fuel supply system, A first air supply system connected to the furnace body via the burner and a first air supply fan connected to the first air supply system, a control device that allows the valve to supply fuel from the fuel supply system to the burner, adjusts the air output by the first air supply fan, and controls the output of the burner in a heating mode, and regulates the fuel supply from the fuel supply system to the burner by the valve, adjusts the air output by the first air supply fan, and has a first cooling mode for controlling the temperature of the furnace chamber, The secondary combustion furnace further includes a second air supply system connected to the furnace body and a second air supply fan connected to the air supply system, The control device can have a second cooling mode in which the air output by the first air supply fan is maintained at a maximum value and the air output by the second air supply fan is adjusted to control the temperature of the furnace chamber.

[0011] Specifically, as shown in FIG. 1, the secondary combustion furnace 10 is for burning combustible gas discharged from the primary combustion furnace 30, and includes a furnace body 11 provided with a furnace chamber 111 inside, an introduction path 12 connected to the furnace body 11, and a burner 13 attached to the furnace body 11. A fuel supply system 14 is connected to the burner 13. A flow rate adjustment valve 141 and an electromagnetic valve 142 are connected to the fuel supply system 14 as valves.

[0012] A first air supply system 15 is connected to the furnace body 11 via the burner 13. A first air supply fan 151 and a first flow rate control valve 152 are connected to the first air supply system 15 as valves. In addition, a second air supply system 16 can be connected to the furnace body 11. A second air supply fan 161 and a second flow rate control valve 162 are connected to the second air supply system 16 as valves. The secondary combustion furnace 10 includes a control device 17. The control device 17 is electrically connected to the above-described flow rate adjustment valve 141, first flow rate control valve 152, and second flow rate control valve 162.

[0013] (1) Furnace body The furnace body 11 is for burning the exhaust gas discharged from the primary combustion furnace 30, and burns the combustible gas contained in the exhaust gas. The furnace body 11 is not particularly limited in terms of its configuration, material used, shape, size, furnace internal volume, etc., as long as it is applicable to the treatment related to secondary combustion.

[0014] Specifically, as shown in FIG. 1, the furnace body 11 is formed in a hollow box shape, and a furnace chamber 111 is provided inside. The furnace body 11 is connected to an introduction path 12 for introducing the exhaust gas discharged from the primary combustion furnace 30 into the furnace chamber 111. The introduction path 12 is formed in a tubular shape, and its interior communicates with the furnace chamber 111. The furnace body 11 can be provided with a holder 112 for attaching a burner 13. The holder 112 is formed in a hollow shape, and its interior communicates with the furnace chamber 111.

[0015] The introduction path 12 can be connected to the exhaust section 31 of the primary combustion furnace 30 through a gas introduction system 121. The exhaust section 31 of the primary combustion furnace 30 is for exhausting the exhaust gas generated when the object to be processed W is heat-treated in the primary combustion furnace 30 to the outside of the primary combustion furnace 30. The exhaust gas discharged from this exhaust section 31 can be sent to the introduction path 12 through the gas introduction system 121 and introduced from the introduction path 12 into the furnace chamber 111.

[0016] A furnace pressure control valve 122 can be connected to the gas introduction system 121. The furnace pressure control valve 122 has the purpose of controlling the furnace pressure of the primary combustion furnace 30 by adjusting the amount of exhaust gas sent to the introduction path 12 through the gas introduction system 121. That is, when the exhaust gas is discharged excessively from the primary combustion furnace 30 and the inside of the furnace becomes negative pressure, problems such as air flowing into the furnace and the furnace atmosphere not being maintainable, or abnormal combustion occurring inside the furnace may occur. The furnace pressure control valve 122 can adjust the amount of exhaust gas sent from the primary combustion furnace 30 to the introduction path 12 via the gas introduction system 121, and control the furnace pressure of the primary combustion furnace 30, thereby suppressing the furnace interior of the primary combustion furnace 30 from becoming negative pressure.

[0017] An exhaust duct 113 for exhausting the gas in the furnace chamber 111 can be connected to the furnace body 11. The exhaust duct 113 is formed in a tubular shape, and its interior communicates with the furnace chamber 111. A damper 114 for opening and closing the exhaust duct 113 can be attached inside the exhaust duct 113. The damper 114 has the purpose of adjusting the amount of exhaust of the gas (exhaust gas) in the furnace chamber 111 to the outside of the furnace via the exhaust duct 113, and adjusting the furnace pressure so that the furnace pressure of the furnace chamber 111 does not become negative pressure. Specifically, the damper 114 slightly opens the exhaust duct 113 during normal times, and largely opens the exhaust duct 113 when the furnace pressure is excessive. That is, the damper 114 adjusts the furnace pressure of the furnace chamber 111, and has a function of releasing the pressure in the furnace chamber 111 to the outside of the furnace so that the furnace pressure does not become negative pressure, like a so-called relief valve. The damper 114 is not particularly limited with respect to the operation method such as manual type or electric type as long as it can adjust the furnace pressure of the furnace chamber 111, and is also not particularly limited with respect to types such as an air volume control damper (VD), a motor damper (MD), and an air-operated damper (AD) operated according to air pressure.

[0018] (2) Burner The burner 13 is attached to the holder 112 provided on the furnace body 11 so as to be inserted from the outside of the furnace body 11. The burner 13 is for raising the temperature of the furnace chamber 111 and for supplying air to the furnace chamber 111. That is, the burner 13 can raise the temperature of the furnace chamber 111 by burning a mixture of fuel and air (air) and ejecting the high-temperature combustion gas generated by the combustion into the furnace chamber 111. Further, the burner 13 can be used like a nozzle by supplying only air without supplying fuel, and by ejecting the supplied air into the furnace chamber 111, air can be supplied to the furnace chamber 111. The burner 13 is not particularly limited in terms of its type, configuration, etc., as long as it can eject gases such as combustion gas and air into the furnace chamber 111. Usually, a combustion burner can be used as the burner 13.

[0019] (3) Fuel supply system The fuel supply system 14 is for supplying fuel to the burner 13 and is connected to the burner 13. The fuel is not particularly limited in terms of the state of substances such as liquid and gas, type, etc., as long as it can make the temperature of the furnace chamber 111 (hereinafter also referred to as "furnace temperature") suitable for the treatment related to secondary combustion. Specific examples of the fuel include liquid fuels such as kerosene and heavy oil, and gaseous fuels (fuel gases) such as city gas, LP gas, and methane gas. Among these, fuel gases such as city gas, LP gas, and methane gas are preferred from the viewpoints of being easy to handle and having suitable heat quantity during combustion.

[0020] In the fuel supply system 14, with the side connected to the burner 13 (furnace body 11) being the downstream side and the opposite side being the upstream side, a flow rate regulating valve 141 and a solenoid valve 142 are connected in order from the upstream side. The flow rate regulating valve 141 has the purpose of controlling the mixing ratio of fuel and air in the air-fuel mixture burned by the burner 13 by adjusting the flow rate (m 3 / min) of the fuel in the fuel supply system 14.

[0021] The mixing ratio controlled by the flow rate regulating valve 141 is set to a value corresponding to the fuel used and is not particularly limited. For example, when this mixing ratio is indicated by the air excess ratio (λ) of the combustion gas due to the combustion of the air-fuel mixture, the air excess ratio (λ) is preferably 1.1 or more and 1.43 or less (1.1 ≤ λ ≤ 1.43). Here, the air excess ratio (λ) represents the multiple of the theoretical amount of air supplied relative to the fuel. That is, for fuel and air supplied at a predetermined flow rate (m 3 / min), the minimum air flow rate L0 (m 3 / min) required to theoretically burn the fuel of that flow rate (m 3 / min) is used as the reference. When the actual air flow rate supplied is L (m 3 / min), λ is calculated from the formula λ = L / L0.

[0022] Specifically, the flow rate adjustment valve 141 adjusts the fuel flow rate based on the air output by the first air supply fan 151, in other words, the air flow rate in the first air supply system 15 controlled by the first flow control valve 152, so that the air excess ratio (λ) is between 1.1 and 1.43. If the air excess ratio (λ) is too low, that is, the air-fuel mixture is too rich, unburned gas (hereinafter also referred to as "unburned gas") is likely to be generated. Even if the combustible gas is burned in the furnace chamber 111, it may not be possible to completely burn the unburned gas, and problems such as the unburned gas being discharged outside the furnace may occur. If the air excess ratio (λ) is too high, that is, the air-fuel mixture is too lean, the heat loss during the combustion of the combustible gas in the furnace chamber 111 increases, making it difficult to maintain the furnace temperature in the furnace chamber 111.

[0023] In addition, the flow rate adjustment valve 141 has the purpose of adjusting the output (heating power) of the burner 13 when the temperature of the furnace chamber 111 is rising by increasing or decreasing the fuel flow rate in the fuel supply system 14. That is, the flow rate adjustment valve 141 can adjust the intensity of the heating power of the burner 13 by increasing or decreasing the fuel flow rate in the fuel supply system 14 while maintaining the air excess ratio (λ) set by the control device 17. The solenoid valve 142 is for allowing or restricting the fuel supply from the fuel supply system 14 to the burner 13. That is, the solenoid valve 142 has the purpose of opening the fuel supply system 14 when the temperature of the furnace chamber 111 is rising by the burner 13 and closing the fuel supply system 14 when air is supplied to the furnace chamber 111 through the burner 13.

[0024] Regarding the types of valves used for the flow control valve 141 and the solenoid valve 142, etc., those suitable for respective purposes can be selected and are not particularly limited. For example, for the flow control valve 141 and the solenoid valve 142, from the viewpoints of responsiveness and control, preferably, a pneumatic valve or a solenoid valve can be used.

[0025] (4) Air supply system The first air supply system 15 has the purpose of supplying air for combustion to the burner 13 and the purpose of supplying air to the furnace chamber 111 via the burner 13. The first air supply system 15 is connected to the burner 13 and is connected to the furnace body 11 via this burner 13.

[0026] That is, the first air supply system 15 has the purpose of supplying air for fuel combustion to the burner 13 to which fuel is supplied. In addition, the first air supply system 15 has the purpose of cooling the furnace chamber 111 by supplying air to the furnace chamber 111 via the burner 13. In the first air supply system 15, with the side connected to the burner 13 (furnace body 11) being the downstream side and the opposite side being the upstream side, in order from the upstream side, a first air supply fan 151 and a first flow control valve 152 as a valve are connected.

[0027] The first air supply fan 151 is for taking in air (air) from outside the furnace body 11 and sending out the taken-in air (air) to the furnace chamber 111 via the first air supply system 15. The type of fan used for the first air supply fan 151, etc. is not particularly limited as long as it can send air (air) to the furnace chamber 111. Examples of the type of fan, etc. include an axial flow fan, a double-inverse fan, a centrifugal fan, a sirocco fan, etc. Among these, the axial flow fan and the double-inverse fan are preferable because they can send a large amount of air (air) to the furnace chamber 111. The first air supply fan 151 takes in air from outside the furnace body 11. Therefore, the air sent from the first air supply fan 151 to the furnace chamber 111 has a temperature lower than the furnace temperature and can cool the furnace chamber 111.

[0028] The first flow control valve 152 has the purpose of adjusting the air output when the first air supply fan 151 sends air to the furnace chamber 111 through the first air supply system 15 by controlling the air flow rate in the first air supply system 15. That is, the first flow control valve 152 is controlled by the control device 17 to increase or decrease the air flow rate (m 3 / min) in the first air supply system 15. When the air flow rate (m 3 / min) in the first air supply system 15 is increased, the amount of air sent from the first air supply fan 151 to the furnace chamber 111 increases, so the air output by the first air supply fan 151 rises. Also, when the air flow rate (m 3 / min) in the first air supply system 15 is decreased, the amount of air sent from the first air supply fan 151 to the furnace chamber 111 decreases, so the air output by the first air supply fan 151 drops.

[0029] The first flow control valve 152 preferably has a linear characteristic as the inherent flow characteristic of the control valve. In this case, the air output corresponds to the valve opening degree. Regarding the adjustment range of the air output of the first air supply fan 151 by the first flow control valve 152, the lower limit value is 0% when the first flow control valve 152 is in the fully closed state, and the upper limit value is 100% when the first flow control valve 152 is in the fully open state. Also, the air output can be increased or decreased linearly within the range of 0% to 100%.

[0030] Moreover, the first flow control valve 152 also has the purpose of adjusting the firing power of the burner 13 when the temperature of the furnace chamber 111 is rising. That is, the first flow control valve 152 has the purpose of adjusting the intensity of the flame of the burner 13 by increasing or decreasing the air output by the first air supply fan 151 (the flow rate of air in the first air supply system 15). As described above, the adjustment of the mixing ratio of fuel and air (air excess ratio (λ)) in the air-fuel mixture is performed by the flow control valve 141 connected to the fuel supply system 14. That is, based on the air flow rate controlled by the first flow control valve 152, the control device 17 adjusts the fuel flow rate in the fuel supply system 14 by the flow control valve 141 so that the air excess ratio (λ) is 1.1 or more and 1.43 or less.

[0031] Regarding the type of valve used for the first flow control valve 152 and the like, those corresponding to each purpose can be selected and are not particularly limited. For example, for the first flow control valve 152, from the viewpoints of responsiveness and control, preferably, a pneumatic valve or an electromagnetic valve can be used.

[0032] The second air supply system 16 is connected to a holder 112 provided on the furnace body 11. In addition to supplying air from the first air supply system 15 for cooling the furnace chamber 111, the second air supply system 16 has the purpose of further supplying air to the furnace chamber 111 to cool the furnace chamber 111. That is, when the cooling of the furnace chamber 111 is insufficient only by the air supply from the first air supply system 15, the second air supply system 16 is for preferably cooling the furnace chamber 111 by supplying air to the furnace chamber 111 through the holder 112 of the furnace body 11. In the second air supply system 16, with the side connected to the holder 112 (furnace body 11) as the downstream side and the opposite side as the upstream side, in order from the upstream side, a second air supply fan 161 and a second flow control valve 162 as a valve are connected.

[0033] The second air supply fan 161 is for taking in air (air) from outside the furnace body 11 and sending out the taken-in air (air) to the furnace chamber 111 through the second air supply system 16. The type of the fan used for the second air supply fan 161 is not particularly limited as long as it can send air into the furnace chamber 111. Examples of the type of the fan include an axial flow fan, a double reversing fan, a centrifugal fan, a sirocco fan, etc. Among these, an axial flow fan and a double reversing fan are preferable because they have a high air volume for sending air into the furnace chamber 111. The second air supply fan 161 takes in air from outside the furnace body 11. Therefore, the air sent from the second air supply fan 161 into the furnace chamber 111 has a temperature lower than the furnace temperature and can cool the furnace chamber 111.

[0034] For the second air supply fan 161, one with a larger air volume can be used compared to the first air supply fan 151. That is, the second air supply fan 161 preferably uses one with a larger air volume than the first air supply fan 151 so that it can sufficiently compensate for the excess or deficiency of the air supply by the first air supply fan 151 for the purpose of compensating for the excess or deficiency of the air supply by the first air supply fan 151 during the cooling of the furnace chamber 111.

[0035] The air volume of the first air supply fan 151 and the air volume of the second air supply fan 161 can be set according to the amount of combustible gas burned in the furnace chamber 111 and are not particularly limited. When the air volume of the first air supply fan 151 is Af1 (m 3 / min) and the air volume of the second air supply fan 161 is Af2 (m 3 / min), Af2 is preferably 3 times or more and 35 times or less of Af1 (3 ≤ (Af2 / Af1) ≤ 35), more preferably 4 times or more and 20 times or less (4 ≤ (Af2 / Af1) ≤ 20), and even more preferably 6 times or more and 10 times or less (6 ≤ (Af2 / Af1) ≤ 10).

[0036] The second flow control valve 162 has the purpose of adjusting the air output when the second air supply fan 161 sends air into the furnace chamber 111 through the second air supply system 16 by controlling the flow rate of the air in the second air supply system 16. That is, the second flow control valve 162 is for the flow rate of the air (m3 It is controlled by the control device 17 so as to increase or decrease (m / min). The flow rate (m 3 / min) of the air in the second air supply system 16 increases, the amount of air sent from the second air supply fan 161 to the furnace chamber 111 increases, and thus the air output by the second air supply fan 161 rises. Also, when the flow rate (m 3 / min) of the air in the second air supply system 16 decreases, the amount of air sent from the second air supply fan 161 to the furnace chamber 111 decreases, and thus the air output by the second air supply fan 161 drops.

[0037] The adjustment of the air output by the second air supply fan 161 is appropriately performed according to the air output of the first air supply fan 151 and the furnace temperature of the furnace chamber 111 in order to preferably cool the furnace chamber 111 and suppress excessive cooling. That is, regarding the cooling of the furnace chamber 111, the air supply from the second air supply system 16 has the purpose of compensating for the excess or deficiency of the air supply from the first air supply system 15. For this reason, it is preferable to adjust the air output of the second air supply fan 161 when the air output of the first air supply fan 151 is in a 100% state.

[0038] The second flow control valve 162 preferably has a linear characteristic as the inherent flow characteristic of the control valve. In this case, the air output corresponds to the valve opening degree. Regarding the adjustment range of the air output of the second air supply fan 161 by the second flow control valve 162, the lower limit value is 0% when the second flow control valve 162 is in a fully closed state, and the upper limit value is 100% when the second flow control valve 162 is in a fully open state. Also, the air output can be linearly increased or decreased within the range of 0% to 100%. Regarding the type of valve and the like used for the second flow control valve 162, those corresponding to the purpose can be selected and are not particularly limited. For example, for the second flow control valve 162, from the viewpoints of responsiveness and control, preferably a pneumatic valve or an electromagnetic valve can be used.

[0039] (5) Control device The control device 17 is provided for the purpose of controlling the atmosphere in the furnace chamber 111 during the secondary combustion process. The control device 17 is electrically connected to a flow rate adjustment valve 141, a first flow rate control valve 152, a second flow rate control valve 162, etc. In addition, a thermocouple 171 for measuring the furnace temperature of the furnace chamber 111 is attached to the furnace body 11, and this thermocouple 171 is electrically connected to the control device 17.

[0040] The control device 17 is constituted by a so-called electronic computer, and a program related to the control of the atmosphere in the furnace chamber 111 is stored therein. Further, the lower limit value (A °C) and the upper limit value (B °C) are registered as the set temperature related to the furnace temperature (T R ) of the furnace chamber 111. In addition, the control device 17 has a function of monitoring the furnace temperature by detecting the furnace temperature measured by the thermocouple 171.

[0041] The control device 17 has a heating mode for controlling the mixing ratio (air excess ratio (λ)) of fuel and air and adjusting the output (heating power) of the burner 13 in accordance with the stored program, etc., and a first cooling mode and a second cooling mode for controlling the temperature of the furnace chamber 111. Each mode is mainly selected and executed according to the registered set temperature and the change of the furnace temperature, etc. The flow rate adjustment valve 141, the first flow rate control valve 152, the second flow rate control valve 162, etc. are controlled according to each mode.

[0042] Specifically, the heating mode is selected and executed when the temperature of the furnace chamber 111 is rising by the burner 13, that is, when the furnace temperature of the furnace chamber 111 is lower than the lower limit value of the set temperature. The control device 17 sets the heating mode until the furnace temperature (T R ) becomes equal to or higher than the lower limit value (A °C) of the set temperature (T R ≧ A). The control device 17 in the heating mode allows the fuel supply from the fuel supply system 14 to the burner 13 by operating the electromagnetic valve 142 or the like.

[0043] In addition, the control device 17 in the heating mode controls the mixing ratio of fuel to air (air excess ratio (λ)). This control is performed by adjusting the fuel flow rate in the fuel supply system 14 by the flow rate adjustment valve 141 based on the air flow rate (air output of the first air supply fan 151) in the first air supply system 15 controlled by the first flow rate control valve 152.

[0044] Furthermore, the control device 17 in the heating mode adjusts the output (heating power) of the burner 13. This adjustment is performed by increasing or decreasing the air flow rate (air output of the first air supply fan 151) in the first air supply system 15 by the first flow rate control valve 152, and increasing or decreasing the fuel flow rate in the fuel supply system 14 by the flow rate adjustment valve 141 so that the mixing ratio (air excess ratio (λ)) corresponding to the increase or decrease is obtained.

[0045] The first cooling mode is selected and executed when the furnace temperature rises during combustion of the combustible gas in the furnace chamber 111, specifically, when the furnace temperature (T R ) of the furnace chamber 111 exceeds the upper limit value (B °C) of the set temperature (T R > B). The control device 17 sets the furnace temperature (T R ) to the first cooling mode until it becomes equal to or lower than the upper limit value (B °C) of the set temperature (T R ≤ B). The control device 17 in the first cooling mode stops the fuel supply from the fuel supply system 14 to the burner 13 by operating the electromagnetic valve 142 or the like. In addition, the control device 17 in the first cooling mode cools the furnace chamber 111 and controls the furnace temperature by supplying air from the first air supply system 15 to the furnace chamber 111 via the burner 13. This control is performed by increasing or decreasing the air flow rate (air output of the first air supply fan 151) in the first air supply system 15 by the first flow rate control valve 152.

[0046] The second cooling mode is selected and executed when the furnace temperature rises even when the air output by the first air supply fan 151 is set to the maximum value (100%) during the cooling of the furnace chamber 111 in the first cooling mode. The control device 17 is such that when the furnace temperature (T R ) becomes equal to or lower than the upper limit value (B °C) of the set temperature (T R ≦ B), the second cooling mode is set. The control device 17 in the second cooling mode, similar to the first cooling mode, stops the fuel supply from the fuel supply system 14 to the burner 13 by operating the solenoid valve 142 or the like. Also, the control device 17 in the second cooling mode cools the furnace chamber 111 by supplying air from the first air supply system 15 and the second air supply system 16 to the furnace chamber 111 to control the furnace temperature. This control is performed by maintaining the air output by the first air supply fan 151 at the maximum value (100%) and increasing or decreasing the air flow rate (the air output of the second air supply fan 161) in the second air supply system 16 by the second flow control valve 162.

[0047] (6) Primary combustion furnace and object to be processed The primary combustion furnace 30 is a furnace for heat-treating the object to be processed W, and generates combustible gas that is burned in the secondary combustion furnace 10 during the heat treatment of the object to be processed W. This primary combustion furnace 30 includes a heat source 32 such as a burner or a heater for heat-treating the object to be processed W in the furnace, and an exhaust section 31 for exhausting exhaust gas containing combustible gas from the furnace. The primary combustion furnace 30 is not particularly limited as long as it is a furnace for heat-treating the object to be processed W and the exhaust gas exhausted during the heat treatment contains combustible gas. Specific examples of the primary combustion furnace 30 include a heat treatment furnace, an annealing furnace, a rotary furnace, an atmosphere furnace, a firing furnace, a drying furnace, a combustion furnace, and the like.

[0048] The object to be processed W is not particularly limited as long as it is heat-treated using the above-described furnace. Examples of the object to be processed W include products and parts made of materials such as metal, glass, and ceramics, combustibles such as plastic waste and combustible waste. Among the workpieces W described above, metal products and metal parts, particularly metal products and metal parts such as wire materials, pipe materials, and column materials, often have oil such as lubricants adhering to their surfaces. This oil contains organic compounds and evaporates during the heat treatment in the primary combustion furnace 30 to generate combustible gas. Therefore, metal products and metal parts with oil adhering to their surfaces are preferable as workpieces W.

[0049] Here, as long as the oil such as lubricant contains organic compounds, the type, composition, use, form, etc. are not particularly limited. For example, it includes powdery solid lubricants adhered to the surface of the workpiece for use, and liquid lubricants used by immersing the workpiece or coating the surface of the workpiece. The organic compounds are not particularly limited in terms of type, composition, etc. Examples of such organic compounds include compounds having functional groups such as carboxyl groups, hydroxyl groups, and enol groups.

[0050] Examples of the above-mentioned oil include lubricants containing stearic acid-based compounds or ester-based compounds as organic compounds. The stearic acid-based compound is a compound composed of stearic acid having a carboxylic acid skeleton (-COOH) in the molecule. The ester-based compound is a compound having an ester bond (R-COO-R’) in the molecule. Specific examples of the above-mentioned organic compounds include metal soaps composed of fatty acids such as stearic acid, lauric acid, ricinoleic acid, and octylic acid, and metals such as lithium, magnesium, calcium, barium, and zinc, more specifically calcium stearate and sodium stearate. The lubricant containing the above-mentioned organic compounds generates combustible gases such as carbon monoxide (CO) and hydrogen (H2) when the organic compounds thermally decompose or transform in a high-temperature environment where the furnace temperature during heat treatment exceeds 350°C and is 1000°C or lower.

[0051] (7) Combustible Gas and Its Combustion The combustible gas is contained in the exhaust gas discharged from the primary combustion furnace 30 that heat-treats the object to be treated W and introduced into the secondary combustion furnace 10. The type of the combustible gas and the like are not particularly limited. Examples of the combustible gas include, for example, the evaporation gas of the oil adhered to the object to be treated W as described above, the unburned gas by the fuel gas used in the primary combustion furnace 30, the oxidizing gas used in the primary combustion furnace 30, the reducing gas, the decarburizing gas, the carburizing gas and other atmosphere gases, and the gas generated from the object to be treated W during the heat treatment in the primary combustion furnace 30. Specific examples of the combustible gas include hydrogen (H2) gas, carbon monoxide (CO) gas, methane (CH4) gas, propane (C3H8) gas, butane (C4H 10 ) gas and the like. When the combustible gas reaches a high temperature in an atmosphere where oxygen is sufficiently present, it has self-ignition properties, that is, it can spontaneously ignite and burn without the need for a fire source such as fuel combustion.

[0052] The secondary combustion furnace 10 described above utilizes the combustible gas contained in the exhaust gas introduced from the primary combustion furnace 30, and burns the combustible gas by self-ignition in the furnace chamber 111 at a high temperature, thereby obtaining the heat quantity required for the combustion treatment. That is, the secondary combustion furnace 10 executes the combustion treatment by utilizing the combustion of the combustible gas discharged from the primary combustion furnace 30 by self-ignition, and substantially stops the supply of fuel to the burner 13 during the combustion of the combustible gas (exhaust gas). Therefore, the secondary combustion furnace 10 can reduce the amount of fuel used for combustion, and as a result, can suppress the generation of carbon dioxide due to the combustion of the fuel.

[0053] Even when the furnace temperature of the furnace chamber 111 rises due to the combustion of the combustible gas by self-ignition, the secondary combustion furnace 10 can control the furnace temperature by cooling the furnace chamber 111 by the air supply from the first air supply system 15 or the second air supply system 16. That is, the secondary combustion furnace 10 obtains the heat quantity required for combustion by the combustion due to the self-ignition of the combustible gas. However, even when the furnace temperature rises significantly due to the combustion of the combustible gas, the furnace chamber 111 can be cooled by the air supply from the first air supply system 15 and the second air supply system 16. Therefore, the secondary combustion furnace 10 can obtain the heat quantity required for combustion by the combustion due to the self-ignition of the combustible gas, and can control the furnace temperature by cooling the furnace chamber 111, and can perform the combustion treatment while maintaining the furnace chamber 111 in a stable atmosphere.

[0054] In addition, the air supply by the first air supply system 15 and the second air supply system 16 has the purpose of maintaining the oxygen concentration in the furnace chamber 111 suitably by supplying oxygen required for the combustion of the combustible gas to the furnace chamber 111 in addition to the purpose of cooling the furnace chamber 111. That is, the air (air) supplied from the first air supply system 15 and the second air supply system 16 to the furnace chamber 111 is the one taken in by the first air supply fan 151 and the second air supply fan 161 outside the furnace body 11, that is, "outside air". Therefore, the air supply by the first air supply system 15 and the second air supply system 16 can supply oxygen to the furnace chamber 111 and stabilize the oxygen concentration in the furnace chamber 111, and can prevent the explosive combustion of the combustible gas due to a rapid change in the oxygen concentration.

[0055] Regarding the set temperature of the furnace temperature (T R ) in the above-described control device 17, the lower limit value (A ° C) is preferably set to be equal to or higher than the temperature at which the combustible gas self-ignites. Specifically, preferably 600 ° C or higher (T R ≧600), more preferably 650 ° C or higher (T R ≧650), and even more preferably 700 ° C or higher (T R ≧700). Also, the upper limit value (B ° C) of the set temperature of the furnace temperature (T R ) is preferably 900 ° C or lower (T R ≦900), more preferably 850 ° C or lower (T R ≦850), and even more preferably 800 ° C or lower (T R ≦800) from the viewpoint of making the furnace chamber 111 in a stable atmosphere.

[0056] [2] Method for using the secondary combustion furnace The method for using the secondary combustion furnace of the present invention is a method for using the secondary combustion furnace that burns the combustible gas discharged from the primary combustion furnace by using the above secondary combustion furnace, For the burner attached to the furnace body, the fuel supply from the fuel supply system connected to the burner is allowed by the valve connected to the fuel supply system, and the air supply from the first air supply system connected to the burner is performed by the first air supply fan connected to the first air supply system. The air-fuel mixture is burned in the burner to raise the temperature of the furnace chamber inside the furnace body to the temperature at which the combustible gas self-ignites, and After the temperature-raising operation, a fuel stop operation for regulating the fuel supply to the burner by the valve, After the fuel stop operation, the combustible gas is introduced into the heated furnace chamber, and a combustion operation for burning the combustible gas by self-ignition, In the combustion operation, based on the temperature rise of the furnace chamber due to the combustion of the combustible gas, air supply is performed from the first air supply fan to the furnace chamber through the first air supply system, and a first cooling operation for cooling the furnace chamber is provided. Furthermore, in addition to the above operations, in the first cooling operation, when the air output by the first air supply fan is 100%, air supply is performed from the second air supply fan to the furnace chamber through the second air supply system, and a second cooling operation for cooling the furnace chamber can also be provided.

[0057] (1) Temperature-raising operation The temperature-raising operation is performed to raise the temperature of the furnace chamber 111 of the furnace body 11 of the secondary combustion furnace 10 to the temperature at which the combustible gas discharged from the primary combustion furnace 30 and introduced into the furnace chamber 111 self-ignites. Specifically, in the temperature-raising operation, the heating mode is executed in the control device 17, the solenoid valve 142 connected to the fuel supply system 14 is opened, and the fuel supply from the fuel supply system 14 to the burner 13 is allowed. Further, the first air supply fan 151 connected to the first air supply system 15 is operated, the first flow control valve 152 is opened, and air supply from the first air supply system 15 to the burner 13 is performed. In the temperature-raising operation, the burner 13 supplied with fuel and air heats up the furnace chamber 111 by burning the fuel-air mixture.

[0058] In the temperature-raising operation, the burner 13 heats up the furnace chamber 111 by burning the fuel-air mixture and discharging the combustion gas into the furnace chamber 111. Regarding the fuel and air supplied to and mixed in the burner 13, the mixing ratio thereof is adjusted by the control device 17 controlling the flow rate adjustment valve 141 of the fuel supply system 14. That is, based on the air flow rate (air output) controlled by the first flow rate control valve 152 of the first air supply system 15, the control device 17 controls the flow rate adjustment valve 141 to adjust the fuel flow rate in the fuel supply system 14 and adjust the mixing ratio of fuel and air.

[0059] The mixing ratio of fuel and air can be represented by the air excess ratio (λ) of the combustion gas due to the combustion of the mixture. The air excess ratio (λ) is calculated from the formula λ = L / L0, where L0 is the minimum air supply amount theoretically required for fuel combustion and L is the actually supplied air supply amount. Specifically, the air excess ratio (λ) is preferably 1.1 or more and 1.43 or less (1.1 ≤ λ ≤ 1.43), more preferably 1.2 or more and 1.4 or less (1.2 ≤ λ ≤ 1.4), and even more preferably 1.25 or more and 1.35 or less (1.25 ≤ λ ≤ 1.35).

[0060] In the temperature-raising operation, the firing power (output) of the burner 13 is adjusted by the flow rate adjustment valve 141 of the fuel supply system 14 and the first flow rate control valve 152 of the first air supply system 15. That is, the fuel and air supplied to the burner 13 are adjusted in the mixing ratio (air excess ratio (λ)) by the flow rate adjustment valve 141, and the flow rate to the burner 13 is increased or decreased by the flow rate adjustment valve 141 and the first flow rate control valve 152. Then, as the flow rates of fuel and air increase, the firing power (output) of the burner 13 becomes stronger, and as the flow rates of fuel and air decrease, the firing power (output) of the burner 13 becomes weaker. The adjustment of the combustion power (output) of the burner 13 may be automatically performed by the control device 17 controlling the flow rate adjustment valve 141 and the first flow rate control valve 152 according to the rate of increase of the furnace temperature or the like, or may be manually performed by an operator operating the flow rate adjustment valve 141 and the first flow rate control valve 152.

[0061] (2) Fuel stop operation The fuel stop operation is executed to stop the combustion of the air-fuel mixture in the burner 13 after the temperature increase operation. Specifically, in the fuel stop operation, after it is confirmed that the furnace temperature of the furnace chamber 111 has reached a temperature equal to or higher than the self-ignition temperature of the combustible gas by the temperature increase operation, the solenoid valve 142 connected to the fuel supply system 14 is closed. In the fuel stop operation, by closing the solenoid valve 142, the fuel supply from the fuel supply system 14 to the burner 13 is regulated by the solenoid valve 142, and the combustion of the air-fuel mixture in the burner 13 stops.

[0062] (3) Combustion operation The combustion operation is executed to burn the combustible gas contained in the exhaust gas discharged from the primary combustion furnace 30 in the furnace chamber 111 of the furnace body 11 of the secondary combustion furnace 10. Specifically, in the primary combustion furnace 30, the furnace pressure is controlled based on a set value. In the combustion operation, in order to prevent the furnace pressure of the primary combustion furnace 30 from becoming negative, the furnace pressure control valve 122 is opened according to the set value of the furnace pressure, and the exhaust gas sent from the exhaust section 31 of the primary combustion furnace 30 to the gas introduction system 121 is sent to the introduction path 12 of the furnace body 11 through the gas introduction system 121 and introduced into the furnace chamber 111. The exhaust gas introduced into the furnace chamber 111 contains combustible gas, and the furnace temperature of the furnace chamber 111 after the fuel stop operation is equal to or higher than the self-ignition temperature of the combustible gas. Therefore, the combustible gas introduced into the furnace chamber 111 burns by self-ignition, and the exhaust gas is burned by the heat obtained from the combustion of the combustible gas.

[0063] Note that the gas after combustion treatment in the furnace chamber 111 can be exhausted outside the furnace body 11 through the exhaust duct 113. That is, a damper 114 is attached to the exhaust duct 113. This damper 114 adjusts the exhaust volume through the exhaust duct 113, and operates to release the furnace pressure in the furnace chamber 111 to the outside of the furnace by adjusting the exhaust volume. For example, during the combustion operation, the damper 114 releases the exhaust duct 113 with the exhaust volume reduced to release the furnace pressure so that the furnace chamber 111 does not become negative pressure. On the other hand, when the furnace pressure control valve 122 is opened and the exhaust gas to be newly processed is introduced into the furnace chamber 111, the damper 114 greatly opens the exhaust duct 113 to increase the exhaust volume in order to release the furnace pressure so that the furnace pressure in the furnace chamber 111 does not become excessive. At that time, the gas in the furnace chamber 111 after the combustion treatment is pushed out of the furnace through the opened exhaust duct 113 by the exhaust gas newly introduced into the furnace chamber 111 and exhausted.

[0064] (4) First cooling operation The first cooling operation is executed to cool the furnace chamber 111 when an increase in the temperature of the furnace chamber 111 due to the combustion of the combustible gas is confirmed during the combustion operation. Specifically, in the first cooling operation, when the control device 17 detects that the furnace temperature (T R ) exceeds the upper limit value (B °C) of the set temperature (T R < B), the first air supply fan 151 is operated to supply air from the first air supply system 15 to the furnace chamber 111 through the burner 13. Also, in the first cooling operation, the control device 17 constantly detects the furnace temperature, and according to the detection result, appropriately controls the opening degree of the first flow control valve 152 to increase or decrease the air output of the first air supply fan 151 in the range of 0% to 100%.

[0065] That is, in the first cooling operation, the air output of the first air supply fan 151 is linearly adjusted by the control device 17 according to the degree of increase in the furnace temperature, so that it becomes higher if the increase in the furnace temperature is rapid, or lower if the increase in the furnace temperature is gentle. As a result of the first cooling operation supplying air from the first air supply system 15 to the furnace chamber 111 through the burner 13 by the first air supply fan 151 with the air output linearly adjusted, the furnace temperature (T R) becomes equal to or lower than the upper limit value (B °C) of the set temperature (T R ≦B), when it is detected, the control device 17 adjusts the air output by the first air supply fan 151 to 0%, and ends.

[0066] In the first cooling operation, since the temperature increase by the burner 13 is not required, the solenoid valve 142 connected to the fuel supply system 14 is closed, and the fuel supply from the fuel supply system 14 to the burner 13 remains regulated. Also, in the first cooling operation, the air output by the first air supply fan 151 can be adjusted by controlling the air flow rate in the first air supply system 15 with the first flow control valve 152.

[0067] (5) Second cooling operation The second cooling operation is executed to cool the furnace chamber 111 when, in the combustion operation, it is confirmed that the temperature of the furnace chamber 111 has risen due to the combustion of the combustible gas after the first cooling operation has been executed. Specifically, in the second cooling operation, in the first cooling operation, the air output by the first air supply fan 151 is set to the maximum value (100%), and still, the furnace temperature (T R ) exceeds the upper limit value (B °C) of the set temperature (T R <B), when detected by the control device 17, the second air supply fan 161 is operated to supply air from the second air supply system 16 to the furnace chamber 111. Also, in the second cooling operation, the air output by the first air supply fan 151 is maintained at 100%, and the air supply from the first air supply system 15 to the furnace chamber 111 via the burner 13 continues. Furthermore, in the second cooling operation, the control device 17 constantly detects the furnace temperature, and according to the detection result, appropriately controls the opening degree of the second flow control valve 162 to increase or decrease the air output by the second air supply fan 161 in the range of 0% to 100%.

[0068] That is, the second cooling operation is an operation performed to cool the furnace chamber 111 when the cooling of the furnace chamber 111 is insufficient in the first cooling operation. In the second cooling operation, the air output by the second air supply fan 161 is linearly adjusted by the control device 17 according to the degree of increase in the furnace temperature. Specifically, if the increase in the furnace temperature is very rapid, the air output will increase; if the increase in the furnace temperature is slightly rapid, the air output will decrease. In the second cooling operation, the air supply to the furnace chamber 111 is carried out by the first air supply fan 151 with the air output maintained at 100% and the second air supply fan 161 with the air output linearly adjusted. As a result, the furnace temperature (T R ) becomes equal to or lower than the upper limit value (B °C) of the set temperature (T R ≤ B). When this is detected, the control device 17 adjusts the air outputs of the first air supply fan 151 and the second air supply fan 161 to 0%, thereby ending the operation. Also, in the second cooling operation, the air output by the second air supply fan 161 can be adjusted by controlling the air flow rate in the second air supply system 16 with the second flow control valve 162.

[0069] [3] Secondary combustion method The secondary combustion method of the present invention uses a secondary combustion furnace comprising a furnace body with a furnace chamber provided inside, an introduction path connected to the furnace body for introducing the combustible gas into the furnace chamber, a burner attached to the furnace body, a fuel supply system connected to the burner, a first air supply system connected to the furnace body via the burner, and a second air supply system connected to the furnace body. It is a secondary combustion method for burning the combustible gas discharged from the primary combustion furnace, and a temperature-raising step in which fuel is supplied to the burner from the fuel supply system and air is supplied from the first air supply system to burn the fuel-air mixture in the burner, raising the temperature of the furnace chamber to the temperature at which the combustible gas auto-ignites, and then stopping the supply of the fuel to the burner; a combustion step in which, after the temperature-raising step, the combustible gas is introduced into the heated furnace chamber from the introduction path and burned by auto-ignition in the furnace chamber; In the combustion process, when the temperature of the furnace chamber rises due to the combustion of the combustible gas, a first cooling operation of supplying air to the furnace chamber through the first air supply system, or a second cooling operation of supplying air to the furnace chamber through the second air supply system in parallel with the first cooling operation, is performed to cool the furnace chamber, and a cooling process is provided. It is characterized by this.

[0070] That is, the secondary combustion method is a method of burning the combustible gas discharged from the primary combustion furnace 30 using the above secondary combustion furnace 10. The above secondary combustion furnace 10 includes a furnace body 11 provided with a furnace chamber 111 inside, an introduction path 12 connected to the furnace body 11 to introduce combustible gas into the furnace chamber 111, a burner 13 attached to the furnace body 11, a fuel supply system 14 connected to the burner 13, a first air supply system 15 connected to the furnace body 11 through the burner 13, and a second air supply system 16 connected to the furnace body 11.

[0071] Figure 2 is a flowchart showing a specific example of the secondary combustion method. In the secondary combustion method, first, as a temperature rising process, the temperature of the furnace chamber 111 is raised (step S11). In the temperature rising process, when the furnace temperature (T R ) detected by the control device 17 is not equal to or higher than the lower limit value (A °C) of the set temperature (T R ≧ A °C) (step S12; No), the temperature rising of the furnace chamber 111 continues. On the other hand, when the furnace temperature (T R ) is equal to or higher than the lower limit value (A °C) of the set temperature (T R ≧ A °C) (step S12; Yes), the combustion process is performed.

[0072] In the secondary combustion method, after the temperature rising process, as a combustion process, the combustion of the combustible gas in the furnace chamber 111 is performed (step S13). In the combustion process, the furnace temperature (T R ) is measured, and when a temperature rise is confirmed, specifically, when the furnace temperature (T R ) exceeds the upper limit value (B °C) of the set temperature (T RWhen it is (>B °C) (step S14; Yes), a cooling process is performed (step S15). On the other hand, the furnace temperature (T R ) is measured. When no temperature increase is confirmed (step S14; No), the combustion process is continued without performing the cooling process, and the operation is terminated.

[0073] (1) Heating process The heating process is a process of raising the furnace temperature (T R ) of the furnace chamber 111 to be equal to or higher than the lower limit value (A °C) of the set temperature. This heating process is performed by executing the heating operation and the fuel stop operation in the above-described method of using the secondary combustion furnace 10.

[0074] FIG. 3 is a flowchart showing a specific example of the heating process. In the heating process, first, as the heating operation, the fuel supply from the fuel supply system 14 to the burner 13 is started (step S21A), and the air supply from the first air supply system 15 is started (step S21B). Next, as the heating operation, the burner 13 is ignited (step S22), and the mixture of fuel and air is burned to start heating.

[0075] Next, as the heating operation, the flow rate adjustment valve 141 and the first flow rate control valve 152 are used to adjust the flow rates of fuel and air respectively (step S23), and the output (heating power) of the burner 13 is adjusted. When adjusting the output (heating power) of this burner 13, the air excess ratio (λ) is appropriately adjusted as the fuel-air mixing ratio by the flow rate adjustment valve 141 controlled by the control device 17.

[0076] The heating operation measures the furnace temperature (T R ), and when the furnace temperature (T R ) is not equal to or higher than the lower limit value (A °C) of the set temperature (T R ≧ A °C) (step S24; No), it is continuously executed. On the other hand, the furnace temperature (T R ) is measured, and the furnace temperature (T R ) is equal to or higher than the lower limit value (A °C) of the set temperature (T RWhen it is (≥A°C) (step S24; Yes), the fuel supply from the fuel supply system 14 to the burner 13 is stopped by the fuel stop operation (step S25). And by stopping the fuel supply from the fuel supply system 14 to the burner 13, the temperature increase operation ends and the temperature increase process ends. In the temperature increase process, the lower limit value (A°C) of the set temperature of the furnace temperature (T R ) is the temperature at which the combustible gas auto-ignites. Specifically, as the temperature at which the combustible gas auto-ignites, the lower limit value (A°C) is preferably 600°C or higher (T R ≥600°C), more preferably 650°C or higher (T R ≥650°C), still more preferably 700°C or higher (T R ≥700°C).

[0077] (2) Combustion process The combustion process is a process of burning the combustible gas discharged from the primary combustion furnace 30 in the furnace chamber 111. This combustion process is carried out by performing the combustion operation among the above-described methods of using the secondary combustion furnace 10. Specifically, the combustion process is carried out by introducing the combustible gas discharged from the primary combustion furnace 30 from the introduction path 12 into the furnace chamber 111. In the combustion process, the furnace chamber 111 has its furnace temperature (T R ) increased to a temperature at which the combustible gas auto-ignites with the lower limit value (A°C) and is higher than the lower limit value (A°C) (T R ≥A°C) by the temperature increase operation in the temperature increase process. Therefore, the combustible gas introduced into the furnace chamber 111 burns by auto-ignition, and the combustion treatment is carried out by the heat generated by the combustion.

[0078] (3) Cooling process The cooling process is a process of cooling the furnace chamber 111 when the temperature of the furnace chamber 111 rises due to the combustion of the combustible gas in the combustion process. This cooling process is carried out by performing the first cooling operation or the second cooling operation among the above-described methods of using the secondary combustion furnace 10. Specifically, the cooling process is when the furnace temperature (T R ) exceeds the upper limit value (B°C) of the set temperature (T R>B °C) case (Figure 2, step S14; Yes), it is performed (Figure 2, step S15).

[0079] Figure 4 is a flowchart showing a specific example of the cooling process. In the cooling process, first, the first cooling operation is started (step S31). In the first cooling operation, the control device 17 controls the first flow control valve 152 to increase (step S32) the air output by the first air supply fan 151. After that, the furnace temperature (T R ) is below the upper limit value (B °C) of the set temperature (T R ≦ B °C), in this case (step S33; Yes), the first cooling operation is terminated (step S34). In the cooling process, the upper limit value (B °C) of the set temperature of the furnace temperature (T R ) is preferably 900 °C or less (T R ≦ 900 °C), more preferably 850 °C or less (T R ≦ 850 °C), still more preferably 800 °C or less (T R ≦ 800 °C).

[0080] On the other hand, when the furnace temperature (T R ) is not below the upper limit value (B °C) of the set temperature (T R ≦ B °C) (step S33; No), and when the air output by the first air supply fan 151 has not reached 100% (step S35; No), the increase in the air output by the first air supply fan 151 is continued. And when the air output by the first air supply fan 151 has reached 100% (step S35; Yes), the second cooling operation is started (step S36). When starting the second cooling operation, the first cooling operation is continued while maintaining the air output of the first air supply fan 151 at 100%.

[0081] In the second cooling operation, the control device 17 controls the second flow control valve 162 to increase (step S37) the air output by the second air supply fan 161. After that, the furnace temperature (T R) is not less than the upper limit value (B °C) of the set temperature (T R ≦ B °C), the increase in the air output by the second air supply fan 161 is continuously performed (step S38; No). On the other hand, when the furnace temperature (T R ) is less than or equal to the upper limit value (B °C) of the set temperature (T R ≦ B °C) (step S38; Yes), the second cooling operation is terminated (step S39). After the second cooling operation is completed, the first cooling operation is completed (step S34), and the cooling process is completed.

Industrial Applicability

[0082] The present invention relates to a secondary combustion furnace that burns combustible gas discharged from a primary combustion furnace, and can burn in a stable atmosphere while suppressing the amount of carbon dioxide generated, and is particularly useful for environmental considerations such as carbon neutrality.

Explanation of Symbols

[0083] 10; Secondary combustion furnace 11; Furnace body, 111; Furnace chamber, 112; Holder, 113; Exhaust duct, 114; Damper 12; Introduction path, 121; Gas introduction system, 122; Furnace pressure control valve 13; Burner 14; Fuel supply system, 141; Flow rate adjustment valve, 142; Solenoid valve 15; First air supply system, 151; First air supply fan, 152; First flow rate control valve 16; Second air supply system, 161; Second air supply fan, 162; Second flow rate control valve 17; Control device, 171; Thermocouple 30; Primary combustion furnace, 31; Exhaust part, 32; Heat source W; Object to be processed

Claims

1. A secondary combustion furnace for burning combustible gas discharged from a primary combustion furnace, comprising: a furnace body provided with a furnace chamber inside; an introduction passage connected to the furnace body for introducing the combustible gas into the furnace chamber; a burner attached to the furnace body; a fuel supply system connected to the burner and a valve connected to the fuel supply system; a first air supply system connected to the furnace body via the burner and a first air supply fan connected to the first air supply system; a control device that permits fuel supply from the fuel supply system to the burner with the valve, adjusts the air output by the first air supply fan, and controls the output of the burner in a heating mode, and regulates fuel supply from the fuel supply system to the burner with the valve, adjusts the air output by the first air supply fan, and controls the temperature of the furnace chamber by supplying air from the first air supply system to the furnace chamber via the burner in a first cooling mode; the control device: executes the heating mode in a temperature raising operation of raising the temperature of the furnace chamber to a temperature at which the combustible gas auto-ignites; A secondary combustion furnace characterized in that when a temperature rise of the furnace chamber due to combustion of the combustible gas is confirmed during a combustion operation of burning the combustible gas in the furnace chamber, the first cooling mode is executed in a first cooling operation of cooling the furnace chamber.

2. further comprising a second air supply system connected to the furnace body and a second air supply fan connected to the air supply system; the control device has a second cooling mode of maintaining the air output by the first air supply fan at a maximum value and adjusting the air output by the second air supply fan to control the temperature of the furnace chamber; The secondary combustion furnace according to claim 1, wherein the control device executes the second cooling mode in a second cooling operation of cooling the furnace chamber when the first cooling operation is executed during the combustion operation and a temperature rise of the furnace chamber due to combustion of the combustible gas is confirmed.

3. The secondary combustion furnace according to claim 2, wherein the second air supply fan has a larger air volume than the first air supply fan.

4. The secondary combustion furnace according to any one of claims 1 to 3, further comprising an exhaust duct connected to the furnace body and a damper attached to the exhaust duct.

5. A method of using a secondary combustion furnace for burning combustible gas discharged from a primary combustion furnace, using the secondary combustion furnace according to any one of claims 1 to 4, For a burner attached to a furnace body, allow the fuel supply from the fuel supply system connected to the burner by a valve connected to the fuel supply system, supply air from the first air supply system connected to the burner by a first air supply fan connected to the first air supply system, burn the fuel-air mixture in the burner, and perform a temperature-raising operation to raise the temperature of the furnace chamber inside the furnace body to the temperature at which the combustible gas self-ignites, and After the temperature-raising operation, perform a fuel stop operation to regulate the fuel supply to the burner by the valve, After the fuel stop operation, introduce the combustible gas into the heated furnace chamber and perform a combustion operation to burn the combustible gas by self-ignition, In the combustion operation, based on the temperature rise of the furnace chamber due to the combustion of the combustible gas, perform a first cooling operation to supply air to the furnace chamber from the first air supply fan through the first air supply system to cool the furnace chamber. A method of using a secondary combustion furnace is characterized by comprising the above.

6. A method of using a secondary combustion furnace that uses the secondary combustion furnace according to any one of claims 2 to 4 to burn the combustible gas discharged from the primary combustion furnace, For a burner attached to a furnace body, allow the fuel supply from the fuel supply system connected to the burner by a valve connected to the fuel supply system, supply air from the first air supply system connected to the burner by a first air supply fan connected to the first air supply system, burn the fuel-air mixture in the burner to raise the temperature of the furnace chamber inside the furnace body to the temperature at which the combustible gas self-ignites, and perform a temperature-raising operation, and After the temperature-raising operation, perform a fuel stop operation to regulate the fuel supply to the burner by the valve, After the fuel stop operation, introduce the combustible gas into the heated furnace chamber and perform a combustion operation to burn the combustible gas by self-ignition, In the combustion operation, based on the temperature rise of the furnace chamber due to the combustion of the combustible gas, perform a first cooling operation to supply air to the furnace chamber from the first air supply fan through the first air supply system to cool the furnace chamber, and In the first cooling operation, when the air output by the first air supply fan is 100%, perform a second cooling operation to supply air to the furnace chamber from the second air supply fan through the second air supply system to cool the furnace chamber. A method of using a secondary combustion furnace is characterized by comprising the above.

7. In the temperature-raising operation, the air excess ratio (λ) of the combustion gas discharged into the furnace chamber by burning the air-fuel mixture with the burner is 1.1 or more and 1.43 or less (1.1 ≤ λ ≤ 1.43). The method for using a secondary combustion furnace according to claim 5 or 6.

8. A secondary combustion method using a secondary combustion furnace comprising a furnace body provided with a furnace chamber inside, an introduction path connected to the furnace body for introducing the combustible gas into the furnace chamber, a burner attached to the furnace body, a fuel supply system connected to the burner, a first air supply system connected to the furnace body via the burner, and a second air supply system connected to the furnace body, for burning the combustible gas discharged from the primary combustion furnace, a temperature-raising step of supplying fuel from the fuel supply system to the burner, supplying air from the first air supply system, burning the air-fuel mixture with the burner, raising the temperature of the furnace chamber to the temperature at which the combustible gas auto-ignites, and then stopping the supply of the fuel to the burner; a combustion step of introducing the combustible gas from the introduction path into the furnace chamber whose temperature has been raised after the temperature-raising step, and burning the combustible gas by auto-ignition in the furnace chamber; a cooling step of performing either a first cooling operation of supplying air to the furnace chamber through the first air supply system and the burner when the temperature of the furnace chamber rises due to the combustion of the combustible gas during the combustion step, or a second cooling operation of supplying air to the furnace chamber through the second air supply system in parallel with the first cooling operation, to cool the furnace chamber. This is a characteristic of the secondary combustion method.

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