Exhaust systems for industrial furnaces

Abstract

To provide an industrial furnace exhaust system capable of treating unburned fuel in an exhaust gas with a compact and low-cost constitution, and capable of detoxifying the exhaust gas.SOLUTION: An exhaust system includes: a self-sustained combustion generation portion 6 provided in an exhaust pipe 5 of an industrial furnace 1 for generating self-sustained combustion in unburned fuel in an exhaust gas E (in particular, unburned ammonia fuel in a case when a burner fuel is ammonia); an afterburner 7 provided at the upstream of the self-sustained combustion generation portion for enhancing the self-sustained combustion of the unburned fuel; a temperature sensor 11 and an unburned fuel detection sensor (ammonia detection sensor) 12 provided at the downstream of the self-sustained combustion generation portion for detecting the unburned fuel in the exhaust gas passing through the self-sustained combustion generation portion; and a controller 10 for controlling the afterburner on the basis of the results of detection obtained through the temperature sensor and the unburned fuel detection sensor.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an exhaust system for an industrial furnace that is capable of treating unburned fuel in the exhaust (particularly unburned ammonia fuel when the burner fuel is ammonia) with a compact and low-cost configuration and rendering the exhaust harmless. [Background technology]

[0002] Patent Documents 1 to 4 are known as technologies related to exhaust gas treatment from industrial furnaces. The "radiant tube burner equipment" of Patent Document 1 is a radiant tube burner equipment that supplies fuel gas and combustion air to a combustion burner section at one end of a radiant tube, burns the fuel gas in the radiant tube in the combustion burner section, and discharges the combustion exhaust gas after combustion from the other end of the radiant tube. In the radiant tube burner equipment, an exhaust gas treatment section containing a three-way catalyst is provided at a position downstream of the exhaust gas discharge direction of the radiant tube, and a post-combustion device that burns unburned component gas contained in the combustion exhaust gas discharged from the exhaust gas treatment section is provided at a position downstream of the exhaust gas treatment section in the exhaust gas discharge direction of the combustion exhaust gas.

[0003] The "industrial furnace" of Patent Document 2 is an industrial furnace in which fuel gas and combustion air are supplied to a combustion burner, the fuel gas is burned inside the furnace by the combustion burner, and the combustion exhaust gas after combustion is discharged from inside the furnace through an exhaust pipe. The exhaust pipe is provided with an exhaust gas treatment unit containing a three-way catalyst, and a post-combustion device is provided downstream of the exhaust gas treatment unit provided in the exhaust pipe in the exhaust direction of the combustion exhaust gas, for combusting unburned component gases contained in the combustion exhaust gas discharged from the exhaust gas treatment unit.

[0004] Patent Document 3, "Method and Apparatus for Reducing Nitrogen Oxides in Combustion Exhaust Gas," is a method in which ammonia is blown into a temperature range of 700 to 1300°C in a combustion device to decompose nitrogen oxides in the presence of oxygen. In this method, the exhaust gas after the decomposition process is passed through a catalyst layer having a catalyst surface arranged parallel to the flow direction of the exhaust gas in a range where the exhaust gas temperature after the decomposition process is 600 to 500°C, so that the remaining nitrogen oxides and ammonia in the exhaust gas are simultaneously decomposed and rendered harmless.

[0005] The "ammonia-containing exhaust gas abatement device" of Patent Document 4 includes a packed tube filled with a remover that removes harmful components except ammonia in the exhaust gas, an oxygen introduction section that adds an oxygen-containing gas to the exhaust gas discharged from the packed tube, and an ammonia decomposition tube filled with an oxidation catalyst that reacts the added oxygen with ammonia to decompose the ammonia into harmless nitrogen and water. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6525908 [Patent Document 2] Patent No. 6525909 [Patent Document 3] Japanese Unexamined Patent Publication No. 54-77277 [Patent Document 4] Japanese Patent Application Publication No. 11-42422 Summary of the Invention [Problem to be solved by the invention]

[0007] When burning fuel in a burner, if the air ratio is lower than "1," exhaust gas containing unburned fuel may be discharged into the atmosphere.

[0008] In the radiant tube burner of Patent Document 1 and the direct flame burner of Patent Document 2, a post-combustion device is provided downstream in the exhaust direction to combust unburned fuel.

[0009] Furthermore, when ammonia is used as the burner fuel, there is a risk that the ammonia will be discharged into the atmosphere as unburned fuel. Even a small amount of ammonia has a pungent odor and becomes an environmental problem when discharged into the atmosphere.

[0010] In Patent Documents 3 and 4, a detoxification device that decomposes ammonia using a catalyst is provided.

[0011] The post-combustion devices disclosed in Patent Documents 1 and 2 have to be operated continuously, which poses a problem of high fuel costs.

[0012] The detoxification devices disclosed in Patent Documents 3 and 4 are large-scale facilities, and therefore have the problem of requiring a large space for installation and incurring a large cost.

[0013] The present invention has been devised in consideration of the above-mentioned problems in the conventional art, and aims to provide an exhaust system for an industrial furnace that is compact and low-cost in configuration and is capable of treating unburned fuel in the exhaust and rendering the exhaust harmless. [Means for solving the problem]

[0014] The exhaust system for an industrial furnace according to the present invention is characterized in that it comprises a spontaneous combustion generation section provided in the exhaust flow path of the industrial furnace and causing spontaneous combustion in unburned fuel in the exhaust, a spontaneous combustion promotion means provided upstream of the spontaneous combustion generation section and promoting the spontaneous combustion of the unburned fuel, a detection means provided downstream of the spontaneous combustion generation section for detecting unburned fuel in the exhaust that has passed through the spontaneous combustion generation section, and a control means for controlling the spontaneous combustion promotion means based on the detection result of the detection means.

[0015] The spontaneous combustion generating section is a heat storage section that stores heat of the exhaust gas flowing through the combustion chamber.

[0016] The spontaneous combustion generating unit is characterized by being a catalyst.

[0017] The spontaneous combustion promotion means is characterized in that it is a heater that heats the exhaust gas.

[0018] The spontaneous combustion promotion means is characterized in that it is an air supply means for supplying air to the exhaust gas.

[0019] The spontaneous combustion promoting means is a burner for heating exhaust gas.

[0020] The detection means is characterized in that it is a temperature sensor.

[0021] The detection means is characterized in that it is an unburned fuel detection sensor.

[0022] The detection means is an oxygen detection sensor. Effect of the Invention

[0023] The exhaust system for an industrial furnace according to the present invention can process unburned fuel in the exhaust gas with a compact and low-cost configuration, and can render the exhaust gas harmless. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is an explanatory diagram illustrating a preferred embodiment of an exhaust system for an industrial furnace according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of an exhaust system for an industrial furnace according to the present invention will be described in detail with reference to the accompanying drawings.

[0026] The exhaust system for an industrial furnace according to this embodiment is provided in an industrial furnace 1 equipped with, for example, a radiant tube burner 2 or a direct-fired burner 3, as shown in FIG.

[0027] In the case of an industrial furnace 1 equipped with a radiant tube burner 2, a radiant tube 2a formed in a U-shape is disposed inside the industrial furnace 1.

[0028] Both ends of the radiant tube 2a extend through the furnace wall 1a to the outside of the industrial furnace 1, and combustion operation is carried out at one end of the radiant tube 2a using supplied fuel gas and combustion air. Exhaust E generated within the radiant tube 2a flows into an exhaust pipe 5 connected to the other end of the radiant tube 2a and is discharged to the outside through a chimney 4 to which the exhaust pipe 5 is connected.

[0029] In the case of an industrial furnace 1 equipped with a direct-fired burner 3, fuel gas and combustion air are supplied to the direct-fired burner 3 provided on the furnace wall 1a, and exhaust gas E generated within the industrial furnace 1 by the combustion operation of the direct-fired burner 3 flows through an exhaust pipe 5 connected to the furnace wall 1a and is discharged to the outside from a chimney 4 to which the exhaust pipe 5 is connected.

[0030] In the exhaust system for an industrial furnace according to the present embodiment, a case where ammonia (NH3) is used as the fuel gas will be described as an example. However, the same is true even when a fossil fuel containing carbon is used.

[0031] An exhaust pipe 5 constituting an exhaust passage of the industrial furnace 1 is provided with a spontaneous combustion generating unit 6 at an appropriate position along the exhaust pipe 5.

[0032] Spontaneous combustion refers to the spontaneous ignition of unburned fuel gas in the exhaust E, resulting in a combustion reaction (spontaneous combustion).

[0033] The spontaneous combustion generating portion 6 is a portion that satisfies the following conditions: the temperature is maintained at or above the ignition point (ignition point) of the fuel gas, and a sufficient amount of oxygen is maintained.

[0034] The spontaneous combustion generating section 6 is provided midway through the exhaust pipe 5 so as to separate the upstream side (the industrial furnace 1 side) and the downstream side (the chimney 4 side) of the spontaneous combustion generating section 6 while allowing the exhaust E to flow from the upstream side to the downstream side.

[0035] An example of the spontaneous combustion generating section 6 is constituted by a heat storage section that stores the exhaust heat of the exhaust gas E flowing through the exhaust pipe 5.

[0036] The heat storage section is configured, for example, by arranging two lattice members 6a spaced apart in the flow direction of the exhaust gas E within the exhaust pipe 5, and filling the space between these two lattice members 6a with a large number of ball-shaped heat storage materials 6b.

[0037] The exhaust gas E passes through gaps in the heat storage material 6b in the heat storage section which is the spontaneous combustion generating section 6, flows from the upstream side to the downstream side, and reaches the chimney 4.

[0038] When the exhaust gas E flows through the spontaneous combustion generating section 6, the heat storage material 6b burns the ammonia of the unburned fuel gas contained in the exhaust gas E through a spontaneous combustion reaction using the stored exhaust heat.

[0039] The exhaust pipe 5 is provided with a spontaneous combustion promotion means arranged upstream of the spontaneous combustion generating section 6 for promoting spontaneous combustion of unburned fuel.

[0040] An example of the spontaneous combustion promotion means is constituted by an afterburner 7 which heats the exhaust gas E by being combusted with supplied combustion air and fuel.

[0041] The afterburner 7 is operated by mixing combustion air and fuel, and start / stop and combustion control are performed by a controller 10 serving as control means, which will be described later.

[0042] A fuel supply pipe 8 and a combustion air supply pipe 9 are connected to the afterburner 7 .

[0043] The afterburner 7 increases the temperature of the exhaust gas E by being operated by combustion.

[0044] When the temperature of the exhaust gas E is increased, the temperature of the heat storage material 6b can be increased and the spontaneous combustion of ammonia can be promoted.

[0045] At this time, it is preferable that the afterburner 7 combusts at a stoichiometric air-fuel ratio (air ratio is 1.0).

[0046] On the other hand, by using the afterburner 7 for air-rich combustion with an excess of air, i.e., an excess of oxygen, oxygen can be supplied to the heat storage section (spontaneous combustion generating section 6), and the amount of oxygen in the spontaneous combustion generating section 6 that promotes spontaneous combustion can be increased.

[0047] The exhaust pipe 5 is provided with a temperature sensor 11 that detects the temperature inside the exhaust pipe 5 and an ammonia detection sensor 12 that detects ammonia, which is the unburned fuel, disposed downstream of the spontaneous combustion generation section 6, as detection means for detecting unburned fuel in the exhaust E that has passed through the spontaneous combustion generation section 6.

[0048] The temperature sensor 11 is disposed in the vicinity of the spontaneous combustion generating unit 6 and detects the temperature of the exhaust gas E that has passed through the spontaneous combustion generating unit 6 .

[0049] By detecting the temperature of the exhaust gas E in the vicinity of the spontaneous combustion generating section 6, the temperature of the spontaneous combustion generating section 6, which is approximately the same temperature as the exhaust gas E, is indirectly detected.

[0050] When the exhaust gas E passes through the heat storage material 6b, its heat is stored in the heat storage material 6b, and the temperature at the outlet of the spontaneous combustion generating section 6 becomes low.

[0051] Therefore, if the temperature of the exhaust gas E downstream of the spontaneous combustion generating section 6 is equal to or higher than the temperature at which spontaneous combustion occurs, the entire heat storage material 6b upstream of the outlet of the spontaneous combustion generating section 6 will be at or above the temperature at which spontaneous combustion occurs, and spontaneous combustion can be reliably achieved, so it is preferable to detect the temperature of the exhaust gas E downstream of the spontaneous combustion generating section 6.

[0052] The temperature sensor 11 and the ammonia detection sensor 12 are provided outside the exhaust pipe 5, and are connected to a controller 10 that controls the afterburner 7, which is a spontaneous combustion promotion means.

[0053] The controller 10 is connected to the fuel supply pipe 8 and the valves 8 a , 9 a of the combustion air supply pipe 9 of the afterburner 7 .

[0054] The controller 10 starts and stops the afterburner 7 and controls the combustion of the afterburner 7 by controlling the opening and closing of the valves 8 a , 9 a of the fuel supply pipe 8 and the combustion air supply pipe 9 .

[0055] Based on the detection results of the temperature sensor 11 and the ammonia detection sensor 12, the controller 10 starts up the afterburner 7 and performs combustion operation when the detected temperature is lower than the set temperature or when ammonia is detected.

[0056] At this time, the controller 10 controls the combustion in the afterburner 7 to have a stoichiometric air-fuel ratio or to be air-rich, as necessary.

[0057] On the other hand, when the detected temperature is higher than the set temperature and no ammonia is detected, the afterburner 7 is stopped.

[0058] Specifically, for example, when the temperature detected by the temperature sensor 11 is lower than a set temperature, the controller 10 opens and operates the valves 8a and 9a to supply fuel and combustion air to the afterburner 7 for combustion.

[0059] At this time, the set temperature is, for example, a temperature (ignition point) at which the ammonia contained in the exhaust gas E spontaneously combusts or a temperature higher than that.

[0060] In addition, for example, if the ammonia detection sensor 12 detects ammonia in the exhaust E that has passed through the spontaneous combustion generating section 6, the controller 10 opens and operates the valves 8a and 9a to supply fuel and combustion air to the afterburner 7 for combustion.

[0061] According to the exhaust system for an industrial furnace of this embodiment, inside the exhaust pipe 5, the exhaust E exposed to the combustion of the afterburner 7 upstream of the spontaneous combustion generating section 6 is heated and air is supplied thereto, thereby promoting spontaneous combustion and causing the unburned ammonia contained in the exhaust E to combust.

[0062] Furthermore, when the exhaust gas E passes through the spontaneous combustion generating section 6 together with the air, it is heated and combusted by the heat storage material 6b, and if ammonia remains in the exhaust gas E, the remaining ammonia can also be eliminated.

[0063] In this way, the exhaust gas E containing ammonia passes through the afterburner 7 and flows into the spontaneous combustion generating section 6. The ammonia in the exhaust gas E is heated by the afterburner 7 and supplied with air, and undergoes spontaneous combustion in the spontaneous combustion generating section 6, where it is decomposed into nitrogen and water. This makes it possible to render the exhaust gas E containing ammonia harmless within the exhaust pipe 5 and to prevent the ammonia from being discharged to the outside.

[0064] In addition, the afterburner 7 is ignited and combusted based on the detection results of the temperature sensor 11 and the ammonia detection sensor 12 provided downstream of the spontaneous combustion generating unit 6, so that it can be combusted only when necessary.

[0065] This allows fuel consumption to be reduced compared to when the fuel is burned continuously, leading to cost reduction.

[0066] In addition, since the afterburner 7, the spontaneous combustion generating unit 6, the temperature sensor 11 and the ammonia detection sensor 12, which constitute the spontaneous combustion promotion means, are provided in the exhaust pipe 5, the system can be made more compact than when a large-scale abatement device is provided.

[0067] In this way, the exhaust system for an industrial furnace according to this embodiment can process the unburned fuel in the exhaust gas E and render the exhaust gas E harmless with a compact and low-cost configuration.

[0068] In the above embodiment, an example was described in which the afterburner 7 was provided as a spontaneous combustion promotion means for heating and supplying air, but instead of the afterburner 7, a heater that simply heats the exhaust gas may be provided as a heating means.

[0069] Alternatively, instead of the afterburner 7, a combustion air supply pipe may be provided as a simple air supply means, which is connected to the exhaust pipe 5 and supplies air to the exhaust E in the exhaust pipe 5.

[0070] In the spontaneous combustion generating section 6, if the fuel is at or above the temperature at which it spontaneously combusts, the unburned fuel is simply mixed with air and combusted.

[0071] Furthermore, instead of the afterburner 7, both the heater and the combustion air supply pipe may be provided.

[0072] The operation of these heaters and combustion air supply pipes is also controlled by the controller 10.

[0073] It goes without saying that even these heaters and combustion air supply pipes can function as spontaneous combustion promotion means and provide the same effects as those of the above embodiment.

[0074] In the above embodiment, an example in which both the temperature sensor 11 and the ammonia detection sensor 12 are provided has been described, but the present invention is not limited to this, and a configuration in which either the temperature sensor 11 or the ammonia detection sensor 12 is provided may also be used.

[0075] In the above embodiment, an example has been described in which the heat storage material 6b is used as the spontaneous combustion generator 6, but the present invention is not limited to this, and a catalyst that has the effect of decomposing ammonia may be used instead of the heat storage material 6b.

[0076] In the case of a catalyst, the exhaust E, or the exhaust E heated by an afterburner 7 or a heater or to which air has been supplied under the control of the controller 10, flows into the catalyst, which is the spontaneous combustion generating unit 6, and the catalyst becomes activated by increasing its temperature, promoting the decomposition reaction of ammonia, which, together with the spontaneous combustion action, efficiently renders the exhaust E harmless.

[0077] In the above embodiment, an example has been described in which the ammonia detection sensor 12 is used as detection means for detecting unburned fuel contained in the exhaust gas E. However, the present invention is not limited to this, and instead of the ammonia detection sensor 12, an oxygen detection sensor 12a may be used.

[0078] When ammonia fuel is burned, ammonia reacts with oxygen to produce nitrogen and water (water vapor).

[0079] Therefore, when the temperature of the spontaneous combustion generating unit 6 is above the ignition point of ammonia and oxygen is detected in the exhaust E that has passed through the spontaneous combustion generating unit 6, it is determined that complete combustion of ammonia has been achieved and there is an excess of oxygen.

[0080] On the other hand, when the oxygen detection sensor 12a detects no oxygen or detects only a trace amount of oxygen, it is found that there is a high possibility that unburned ammonia remains in the exhaust gas E.

[0081] In this manner, even the oxygen detection sensor 12a can be used as a detection means for detecting unburned fuel contained in the exhaust gas E.

[0082] The controller 10 controls the afterburner 7 to perform combustion operation when the oxygen detection sensor 12a does not detect oxygen, and controls the afterburner 7 to stop combustion when the oxygen detection sensor 12a detects oxygen.

[0083] Furthermore, in the above embodiment, the industrial furnace 1 has been described as using an industrial furnace 1 that uses ammonia as fuel, but the present invention is not limited to this, and the industrial furnace 1 may be an industrial furnace that obtains combustion heat by using a fossil fuel (hydrocarbon fuel such as city gas or oil, the same applies below).

[0084] In the case of an industrial furnace 1 operated with fossil fuels, an oxygen detection sensor 12a is used as the detection means.

[0085] This makes it possible to prevent danger caused by unburned components contained in the exhaust E and to prevent waste of fuel.

[0086] In the combustion of fossil fuels, the fuel reacts with oxygen to produce a flame.

[0087] Therefore, when the temperature of the spontaneous combustion generating unit 6 is above the ignition point of the fossil fuel and oxygen is detected in the exhaust E that has passed through the spontaneous combustion generating unit 6, it is determined that complete combustion of the fossil fuel has been achieved and there is an excess of oxygen.

[0088] On the other hand, when the oxygen detection sensor 12a detects no oxygen or detects only a trace amount of oxygen, it is possible to know that there is a high possibility that fossil fuel remains in the exhaust E.

[0089] The controller 10 controls the afterburner 7 to perform combustion operation when the oxygen detection sensor 12a does not detect oxygen, and controls the afterburner 7 to stop combustion when the oxygen detection sensor 12a detects oxygen.

[0090] In this way, even if the exhaust system for an industrial furnace according to this embodiment is applied to an industrial furnace 1 that burns fossil fuel, it can achieve the same effects as the above embodiment.

[0091] The above-mentioned embodiment is for the purpose of facilitating understanding of the present invention, and is not intended to limit the present invention. The present invention can be modified or improved without departing from the spirit of the present invention, and it goes without saying that the present invention includes equivalents thereof. [Explanation of symbols]

[0092] 1 Industrial furnace 1a Furnace wall 2 Radiant tube burner 2a Radiant tube 3 Direct flame burner 4. Chimney 5. Exhaust pipe 6 Self-combustion generator 6a Lattice member 6b Heat storage material 7. Afterburner 8 Fuel supply pipe 8a Valve 9 Air supply pipe 9a Valve 10 Controller 11 Temperature Sensor 12 Ammonia detection sensor (unburned fuel detection sensor) 12a Oxygen detection sensor E Exhaust

Claims

1. a spontaneous combustion generating unit provided in an exhaust passage of the industrial furnace and causing spontaneous combustion of unburned fuel in the exhaust; a spontaneous combustion promotion means provided upstream of the spontaneous combustion generating portion and promoting spontaneous combustion of unburned fuel; a detection means provided downstream of the spontaneous combustion generating section for detecting unburned fuel in the exhaust gas that has passed through the spontaneous combustion generating section; a control means for controlling the spontaneous combustion promotion means based on a detection result of the detection means, The spontaneous combustion promotion means, a temperature sensor for detecting a temperature in the exhaust pipe, and the detection means are provided in the exhaust pipe, which is the exhaust flow path; the unburned fuel is an ammonia fuel, 13. An exhaust system for an industrial furnace, wherein the detection means is an oxygen detection sensor.

2. 2. The exhaust system of an industrial furnace according to claim 1, wherein the spontaneous combustion generating section is a heat storage section that stores heat of the exhaust gas flowing through the system.

3. 2. The exhaust system of claim 1, wherein the spontaneous combustion generator is a catalyst.

4. 4. The exhaust system for an industrial furnace according to claim 1, wherein the spontaneous combustion promoting means is a heater for heating the exhaust gas.

5. 4. The exhaust system for an industrial furnace according to claim 1, wherein the spontaneous combustion promoting means is an air supplying means for supplying air to the exhaust gas.

6. 4. The exhaust system for an industrial furnace according to claim 1, wherein the spontaneous combustion promoting means is a burner for heating the exhaust gas.

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