Combustion system and combustion method

Abstract

A combustion system is provided with: a combustion furnace for combusting an object to be treated; a boiler that guides combustion gas passing through the combustion furnace; a superheater provided in the boiler and superheating the main steam; a discharge path for discharging combustion gas passing through the boiler; and a return path for returning the combustion gas in the discharge path as a recycle gas. The return path has: a first path for conveying a portion of the recycle gas to the combustion furnace; and a second path for conveying the other part of the recycle gas to the upstream side of the boiler relative to the superheater.

Description

TECHNICAL FIELD

[0001] The present application relates to a combustion system and a combustion method. This application claims priority based on Japanese Patent Application No. 2023-103228 filed in Japan on June 23, 2023, and the content thereof is incorporated herein by reference. BACKGROUND

[0002] A combustion system such as a waste incinerator has, for example, a combustion furnace that combusts a treated object, and a boiler. The combustion system is required to combust the treated object with high efficiency and stability while suppressing generation of carbon monoxide, nitrogen oxides, and the like. In the combustion system, sometimes the combustion state of the treated object fluctuates, resulting in a decrease in combustion efficiency.

[0003] The combustion furnace described in Patent Literature 1 has a pipe that returns a part of combustion gas that has passed through the boiler to the combustion furnace as recirculation gas. In this combustion furnace, by returning the recirculation gas to the combustion furnace, it is possible to improve the combustion efficiency. PRIOR ART DOCUMENTS PATENT LITERATURE

[0004] Patent Literature 1: Japanese Patent Application Publication No. 2016-191539 SUMMARY

[0005] In the above-described combustion system, sometimes a superheater that recovers heat of combustion gas is provided in the boiler. The superheater obtains superheated steam by heating steam with combustion gas. The superheated steam is supplied to a heat-recovery utilization device, and is used for power generation and the like. In the combustion system, sometimes it is required to adjust the temperature of main steam obtained by the superheater in consideration of utilization in the heat-recovery utilization device.

[0006] An object of one aspect of the present application is to provide a combustion system and a combustion method that can adjust the temperature of main steam.

[0007] The combustion system of Aspect 1 of the present application has: a combustion furnace that combusts a treated object; a boiler that guides combustion gas that has passed through the combustion furnace; a superheater that is provided in the boiler and superheats main steam; an exhaust path that exhausts the combustion gas that has passed through the boiler; and a return path that returns the combustion gas of the exhaust path as recirculation gas, the return path having: a first path that supplies a part of the recirculation gas to the combustion furnace; and a second path that supplies another part of the recirculation gas to an upstream side in the boiler compared with the superheater.

[0008] The combustion system of the present application of Mode 2 is, in the combustion system of Mode 1, the return path further has a main path that guides the recirculated gas from the exhaust path, the first path and the second path branch from the main path.

[0009] The combustion method of the present application of Mode 3 is, by combusting a treated object by a combustion furnace, guiding the combustion gas that passed through the combustion furnace to a boiler provided with a superheater, making the combustion gas that passed through the boiler pass through and be exhausted from an exhaust path, using a first path to transport a part of the recirculated gas of the combustion gas as the exhaust path to the combustion furnace, and using a second path to transport another part of the recirculated gas to an upstream side in the boiler compared with the superheater.

[0010] The combustion method of the present application of Mode 4 is, by combusting a treated object by a combustion furnace, guiding the combustion gas that passed through the combustion furnace to a boiler provided with a superheater, making the combustion gas that passed through the boiler pass through and be exhausted from an exhaust path, using a first path to transport a part of the recirculated gas of the combustion gas as the exhaust path to the combustion furnace, and using a second path to transport another part of the recirculated gas to an upstream side in the boiler compared with the superheater, at this time, controlling the flow rate of the recirculated gas based on the temperature of the main steam obtained by the superheater.

[0011] The combustion method of the present application of Mode 5 is, in the combustion method of Mode 4, the control of the flow rate of the recirculated gas is performed by adjusting a blower that transports the recirculated gas. Effects of the Invention

[0012] According to the above-described modes of the present application, it is possible to provide a combustion system and a combustion method that can adjust the temperature of the main steam. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a configuration diagram showing a combustion system of a first embodiment. Figure 2 is a configuration diagram showing a combustion system of a second embodiment. Figure 3 is a configuration diagram showing a combustion system of a comparative mode. DETAILED DESCRIPTION

[0014] Hereinafter, a combustion system of an embodiment of the present application will be described based on the drawings.

[0015] [Combustion System] (First Embodiment) Figure 1 is a configuration diagram showing a combustion system 100 of a first embodiment. As Figure 1As shown, the combustion system 100 has a supply section 1, a combustion furnace 2, a boiler 3, a superheater 4, an exhaust path 5, a return path 6, a cooling device 51, a dust collecting device 52, a catalyst reaction tower 53, and a chimney 54.

[0016] The supply section 1 has a feeding hopper 11, a chute 12, and a feeder 13. The feeding hopper 11 receives a treated material. The chute 12 guides the treated material. The feeder 13 supplies the treated material to the combustion furnace 2. The feeder 13 can adjust the supply amount of the treated material.

[0017] The combustion furnace 2 is, for example, a grate furnace having a conveyance mechanism 21. The combustion furnace 2 combusts the treated material. The conveyance mechanism 21 includes, for example, a drying belt 22 and a combustion belt 23. The drying belt 22 and the combustion belt 23 each have a plurality of grates arranged in a conveyance direction. The grates are moved reciprocally by a not-shown drive source, thereby conveying the treated material. Below the drying belt 22 and the combustion belt 23, a not-shown primary air supply section that supplies primary combustion air is provided.

[0018] The combustion furnace 2 has a main body section 24 and an extension section 25. The main body section 24 forms a primary combustion chamber 26 above the conveyance mechanism 21. The extension section 25 is provided as a cylinder shape that extends upward from an upper end of the main body section 24. A space inside the extension section 25 is a secondary combustion chamber 27.

[0019] The combustion furnace 2 has an exhaust section 28. The exhaust section 28 exhausts combustion residues of the treated material as incineration ash.

[0020] The boiler 3 guides combustion gas that passes from the combustion furnace 2. The boiler 3 has a plurality of flues. In the present embodiment, the plurality of flues includes a first flue 31, a second flue 32, and a third flue 33. The first flue 31, the second flue 32, and the third flue 33 are collectively referred to as "flues 31 to 33". The flues 31 to 33 are each a gas flow path along an up-down direction. The flues 31 to 33 are arranged adjacent to each other from left to right in the up-down direction. Figure 1

[0021] The upper end portions (one end portions) and the lower end portions (the other end portions) of the flues adjacent to each other in the flues 31 to 33 are alternately connected. In detail, the upper end portions of the first flue 31 and the second flue 32 are communicated with each other. The lower end portions of the second flue 32 and the third flue 33 are communicated with each other. The flues 31 to 33 are bent by alternately connecting the upper end portions and the lower end portions.

[0022] Further, the number of the flues is not particularly limited. The number of the flues can be one or more. The number of the flues can be, for example, one, two, or any number of more than three. The one end portions and the other end portions of the flues adjacent to each other in the plurality of flues are alternately connected.

[0023] ​The superheater 4 is provided at an intermediate position in the length direction of the third flue 33. The superheater 4 has superheater tubes 41 through which steam flows. The superheater tubes 41 have a plurality of straight portions 42 and a plurality of connecting portions 43. The plurality of straight portions 42 are arranged in the up-and-down direction at intervals. The connecting portions 43 alternately connect one end portions and the other end portions of the straight portions 42. The superheater tubes 41 are bent in shape by the one end portions and the other end portions of the plurality of straight portions 42 being alternately connected by the connecting portions 43. The superheater tubes 41 are made of metal such as stainless steel. Further, the position of the superheater 4 in the third flue 33 can be any position in the length direction of the third flue 33.

[0024] One end of the superheater tube 41 is connected to a steam supply source (not shown). The superheater tube 41 heats steam supplied from the steam supply source by heat exchange with combustion gas, and obtains superheated steam at a high temperature. The other end of the superheater tube 41 is connected to, for example, a heat-releasing utilization device (not shown). The heat-releasing utilization device is, for example, a power generation device. The power generation device includes a steam turbine and a generator driven by the steam turbine.

[0025] The discharge passage 5 is connected to the upper end portion of the third flue 33. The discharge passage 5 discharges combustion gas that has passed through the boiler 3.

[0026] The temperature of the combustion gas is reduced as needed by the temperature-reducing device 51. The dust-collecting device 52 collects dust in the combustion gas by a bag filter or the like, and removes it. The catalyst reaction tower 53, for example, decomposes and removes nitrogen oxides in the combustion gas. The chimney 54 releases the combustion gas to the atmosphere.

[0027] The return passage 6 has a main passage 61, a first passage 62, a second passage 63, and a blower 64. The main passage 61 takes out combustion gas from the discharge passage 5 (a position between the dust-collecting device 52 and the catalyst reaction tower 53) and uses it as recirculation gas. Oxygen (O2) is contained in the combustion gas taken out as recirculation gas.

[0028] Further, a valve for flow adjustment can be provided on one or two or more of the main passage 61, the first passage 62, and the second passage 63. In the present embodiment, a first adjustment valve 8 is provided in the first passage 62. A second adjustment valve 9 is provided in the second passage 63. The first adjustment valve 8 adjusts the flow rate of recirculation gas flowing in the first passage 62. The second adjustment valve 9 adjusts the flow rate of recirculation gas flowing in the second passage 63.

[0029] A blower 64 is provided in the main path 61. The blower 64 sends the recirculated gas in the main path 61. The blower 64 functions as a flow rate adjuster that arbitrarily adjusts the flow rate of the recirculated gas. The flow rate of the recirculated gas can be adjusted, for example, by the rotational speed of the blower 64.

[0030] The first path 62 and the second path 63 branch from the main path 61. The first path 62 is connected to the extension 25 of the combustion furnace 2. The first path 62 sends a part of the recirculated gas back to the secondary combustion chamber 27 of the combustion furnace 2.

[0031] The second path 63 is connected to the third flue 33 of the boiler 3. In detail, the second path 63 is connected to a position in the third flue 33 that is on the upstream side from the superheater 4. The second path 63 sends a part of the recirculated gas back to the third flue 33 (the position on the upstream side from the superheater 4).

[0032] The connection position of the second path 63 with respect to the boiler 3 is not particularly limited as long as it is a position on the upstream side from the superheater 4. The connection position of the second path 63 can also be the second flue 32. The connection position of the second path 63 can also be the upper portion of the first flue 31.

[0033] [Combustion method] (first embodiment) Next, a combustion method of the first embodiment will be described with an example in which the combustion system 100 is used. A treated object is fed to the feeding hopper 11. As the treated object, waste can be cited. The waste can be general waste such as municipal waste, or industrial waste. The treated object is guided to pass through the chute 12 and is fed to the combustion furnace 2 by the feeder 13.

[0034] The conveyance mechanism 21 conveys the treated object in the order of the drying belt 22 and the combustion belt 23. The primary air supply portion supplies air (primary air) to the treated object. In the course of this conveyance, the treated object is combusted by reaction with the primary air in the primary combustion chamber 26, and combustion gas is generated. The combustion residue of the treated object is discharged as incineration ash from the discharge portion 28.

[0035] The combustion gas generated by the combustion of the treated object is caused to pass through the secondary combustion chamber 27 and is introduced to the boiler 3. The combustion gas is introduced to the first flue 31 and rises in the first flue 31, and is introduced from the upper end portion of the first flue 31 to the upper end portion of the second flue 32. The combustion gas descends in the second flue 32, and is introduced from the lower end portion of the second flue 32 to the lower end portion of the third flue 33. The combustion gas rises in the third flue 33, and is discharged from the upper end portion of the third flue 33 to the discharge path 5.

[0036] In the combustion system 100, it is required to ensure a condition that the temperature is 850°C or higher and the residence time is 2 seconds or longer from the viewpoint of preventing generation of dioxins. In the combustion system 100, it is preferable that the space constituted by the secondary combustion chamber 27 and the first flue 31 satisfies this condition.

[0037] In the superheater 4, the low-temperature steam supplied from the supply source flows in the superheater tube 41. The low-temperature steam is heated by the combustion gas flowing in the third flue 33 during the flow in the superheater tube 41, and becomes high-temperature main steam. The main steam is used for power generation in, for example, a heat utilization device (for example, a generator).

[0038] The combustion gas discharged from the discharge path 5 is introduced into the temperature lowering device 51. In the temperature lowering device 51, the temperature of the combustion gas is adjusted as necessary. The dust collecting device 52 collects dust in the combustion gas and removes it. The catalyst reaction tower 53, for example, decomposes and removes nitrogen oxides in the combustion gas. The chimney 54 releases the combustion gas to the atmosphere.

[0039] A part of the combustion gas flowing in the discharge path 5 is taken out as the recirculation gas from the main path 61 of the return path 6. A part of the recirculation gas is returned to the combustion furnace 2 (the secondary combustion chamber 27) using the first path 62. In the case where combustible components are contained in the combustion gas in the secondary combustion chamber 27, a part of the combustible components is combusted by reaction with oxygen in the recirculation gas.

[0040] Another part of the recirculation gas (a part of the recirculation gas other than the recirculation gas guided to the first path 62) is returned to the third flue 33 (a position on the upstream side from the superheater 4) using the second path 63. The "position on the upstream side from the superheater 4" is, for example, a position lower than the superheater 4 in the third flue 33.

[0041] The temperature of the combustion gas also increases and decreases depending on the heat held by the recirculation gas. For example, if the heat held by the recirculation gas is large, the temperature of the combustion gas flowing in the third flue 33 also becomes high. Specifically, if the recirculation gas is high in temperature and the return amount is large, the temperature of the combustion gas also becomes high.

[0042] [Effects of the combustion system and the combustion method according to the embodiment] The combustion system 100 has the first path 62 that delivers a part of the recirculated gas to the combustion furnace 2 (the secondary combustion chamber 27) and the second path 63 that delivers another part of the recirculated gas to the upstream side in the boiler 3 compared with the superheater 4. The combustion system 100 can adjust the flow rate of the combustion gas in the third flue 33 (a position on the upstream side compared with the superheater 4) and the retained heat by adjusting the flow rate of the recirculated gas. Therefore, the temperature of the combustion gas can be arbitrarily set. Thus, the temperature of the main steam obtained by the superheater 4 can be adjusted. Thus, for example, by increasing the temperature of the main steam, the power generation efficiency in the exhaust heat utilization device (power generator) can be increased.

[0043] The combustion system 100 has the first path 62 that delivers a part of the recirculated gas to the combustion furnace 2 (the secondary combustion chamber 27). Therefore, in the secondary combustion chamber 27, the combustion gas can be combusted by the reaction with the recirculated gas. Therefore, the combustion efficiency in the combustion system 100 can be increased.

[0044] Figure 3 is a configuration view of a comparative combustion system 300. As Figure 3 indicated, the combustion system 300 has the same configuration as the combustion system 100 (refer to Figure 1 ) except that the combustion system 300 does not have the second path 63. In the combustion system 300, if the recirculated gas is increased in the amount of the return, the combustion efficiency becomes high, and thus there is a tendency that the temperature of the main steam obtained by the superheater 4 becomes high. For example, the following calculation result can be given.

[0045] When the amount of the return of the recirculated gas is set to 2023 [Nm 3 / h] as a rating, the temperature of the main steam obtained by the superheater 4 is 447 [°C]. If the amount of the return of the recirculated gas is set to 2630 [Nm 3 / h] (1.3 times the rating), the temperature of the main steam becomes 457 [°C].

[0046] However, if the amount of the return of the recirculated gas is increased, due to the increase in the flow rate of the gas, the securing of the conditions (the temperature of 850°C or higher and the residence time of 2 seconds or longer) required for the secondary combustion chamber 27 and the boiler 3 to prevent the generation of dioxin substances becomes difficult.

[0047] In contrast to this, Figure 1 In the combustion system 100 of the present embodiment indicated in the drawing, a part of the recirculated gas is returned to the third flue 33 through the second path 63, and thus the temperature of the main steam can be increased while satisfying the above conditions (the temperature of 850°C or higher and the residence time of 2 seconds or longer) in the secondary combustion chamber 27 and the first flue 31, for example.

[0048] [Combustion system] (2nd embodiment) Figure 2 is a configuration view of the combustion system 200 of the 2nd embodiment. For the common configuration of the combustion system 100 shown in Figure 1 , the same reference numerals are annotated and the explanation is omitted.

[0049] The combustion system 200 differs from the combustion system 100 (refer to Figure 1 ) in points having the temperature sensor 7 and the control section 10. The temperature sensor 7 detects the temperature of the main steam passing through the superheater 4.

[0050] [Combustion method] (2nd embodiment) In the combustion system 200, when a part of the recirculated gas is sent back using the 2nd path 63, the control section 10 can operate the 1st adjusting valve 8 and the 2nd adjusting valve 9 based on the temperature of the main steam detected by the temperature sensor 7. The 1st adjusting valve 8 adjusts the flow rate of the recirculated gas flowing in the 1st path 62. The 2nd adjusting valve 9 adjusts the flow rate of the recirculated gas flowing in the 2nd path 63. In this way, the control section 10 controls the flow rates of the recirculated gas of the 1st path 62 and the 2nd path 63.

[0051] In the combustion system 200, for example, based on the temperature of the main steam, the flow rate of the recirculated gas flowing in the 2nd path 63 is adjusted by the 2nd adjusting valve 9. For example, the following operation examples can be cited. When the temperature of the main steam is 440 [°C], the recirculated gas flow rates of the 1st path 62 and the 2nd path 63 are set to 1613 [Nm 3 / h]. When the temperature of the main steam is 450 [°C], the recirculated gas flow rates in the 1st path 62 and the 2nd path 63 are set to 2179 [Nm 3 / h]. When the temperature of the main steam is 460 [°C], the recirculated gas flow rates in the 1st path 62 and the 2nd path 63 are set to 2792 [Nm 3 / h]. In this way, the flow rate of the recirculated gas can be adjusted based on the temperature of the main steam.

[0052] The ratio of the flow rate of the recirculated gas flowing in the 1st path 62 to the flow rate of the recirculated gas flowing in the 2nd path 63 can be arbitrarily set between 1:0 and 0:1.

[0053] Furthermore, the technical scope of the present application is not limited to the above-described embodiments, and various changes can be made thereto without departing from the spirit of the present application.

[0054] Figure 1 In the combustion system 100 shown, the return path 6 has a main path 61 and a first path 62 and a second path 63 branched from the main path 61, but the configuration of the return path is not limited thereto. The return path can also have a first path that guides the recirculated gas directly to the combustion furnace from the exhaust path, and a second path that guides the recirculated gas directly to the boiler from the exhaust path.

[0055] Figure 1 In the combustion system 100 shown, a grate furnace is used as the combustion furnace, but a fluidized bed combustion furnace can also be used as the combustion furnace.

[0056] In addition, the configuration elements in the above embodiments can be appropriately replaced with known configuration elements, and the above embodiments and modified examples can be appropriately combined, without departing from the gist of the present application. Explanation of Reference Signs

[0057] 2... Combustion furnace 3... Boiler 4... Superheater 5... Exhaust path 6... Return path 31... First flue 32... Second flue 33... Third flue 61... Main path 62... First path 63... Second path 100, 200... Combustion system

Claims

1. A combustion system, wherein, Having: a combustion furnace that combusts a processed object; a boiler that guides combustion gas that has passed through the combustion furnace; a superheater that is provided to the boiler and superheats main steam; an exhaust path that exhausts the combustion gas that has passed through the boiler; and a return path that returns the combustion gas of the exhaust path as a recirculation gas, the return path has: a first path that supplies a part of the recirculation gas to the combustion furnace; and a second path that supplies another part of the recirculation gas to an upstream side of the boiler compared to the superheater.

2. The combustion system according to claim 1, wherein the return path further has a main path that guides the recirculation gas from the exhaust path, the first path and the second path branch from the main path.

3. A combustion method in which a processed object is combusted by a combustion furnace, combustion gas that has passed through the combustion furnace is guided to a boiler provided with a superheater, combustion gas that has passed through the boiler is passed through and exhausted from an exhaust path, a part of a recirculation gas that is the combustion gas of the exhaust path is supplied to the combustion furnace using a first path, and another part of the recirculation gas is supplied to an upstream side of the boiler compared to the superheater using a second path.

4. A combustion method in which a processed object is combusted by a combustion furnace, combustion gas that has passed through the combustion furnace is guided to a boiler provided with a superheater, combustion gas that has passed through the boiler is passed through and exhausted from an exhaust path, a part of a recirculation gas that is the combustion gas of the exhaust path is supplied to the combustion furnace using a first path, and another part of the recirculation gas is supplied to an upstream side of the boiler compared to the superheater using a second path, at which time the flow rate of the recirculation gas is controlled based on the temperature of main steam obtained by the superheater.

5. The combustion method according to claim 4, wherein the control of the flow rate of the recirculation gas is performed by adjusting a blower that supplies the recirculation gas.

Images