Combustion system and combustion method

Abstract

To provide a combustion system and a combustion method capable of regulating a main steam temperature.SOLUTION: A combustion system 100 includes: a combustion furnace 2 for burning objects to be treated; a boiler 3 for guiding combustion gas that has passed through the combustion furnace 2; a superheater 4 provided in the boiler 3 and superheating main steam; a discharge path 5 for discharging the combustion gas that has passed through the boiler 3; and a return path 6 for returning the combustion gas in the discharge path 5 as recirculation gas. The return path 6 has: a first path 62 for sending part of the recirculation gas to the combustion furnace 2; and a second path 63 for sending the other part of the recirculation gas to an upstream side of the superheater 4 in the boiler 3.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a combustion system and method. [Background technology]

[0002] A combustion system such as a waste incinerator includes, for example, a combustion furnace for burning materials to be treated, and a boiler. The combustion system is required to burn the materials to be treated with high efficiency and stability while suppressing the generation of carbon monoxide, nitrogen oxides, etc. In the combustion system, the combustion state of the materials to be treated may fluctuate, resulting in low combustion efficiency.

[0003] The combustion furnace described in Patent Document 1 is equipped with a pipe that returns a portion of the combustion gas that has passed through the boiler to the combustion furnace as recirculated gas. In this combustion furnace, the combustion efficiency can be improved by returning the recirculated gas to the combustion furnace. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-191539 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-mentioned combustion system, the boiler may be equipped with a superheater to recover the heat of the combustion gas. In the superheater, the combustion gas heats the steam to produce superheated steam. The superheated steam is supplied to a waste heat utilization facility and used for power generation, etc. In a combustion system, it is sometimes required to adjust the temperature of the main steam obtained in the superheater, taking into consideration utilization in a waste heat utilization facility.

[0006] One aspect of the present invention aims to provide a combustion system and method that can regulate main steam temperature. [Means for solving the problem]

[0007] The combustion system according to a first aspect of the present invention includes a combustion furnace for burning a material to be treated, a boiler for introducing combustion gas that has passed through the combustion furnace, a superheater provided in the boiler for superheating main steam, an exhaust path for discharging the combustion gas that has passed through the boiler, and a return path for returning the combustion gas from the exhaust path as recirculated gas, the return path having a first path for sending a portion of the recirculated gas to the combustion furnace and a second path for sending another portion of the recirculated gas upstream of the superheater in the boiler.

[0008] A combustion system according to a second aspect of the present invention is the combustion system of the first aspect, wherein the return path further includes a base path for directing the recirculated gas from the exhaust path, and the first path and the second path branch off from the base path.

[0009] A combustion method according to a third aspect of the present invention includes burning a material to be treated in a combustion furnace, guiding the combustion gas that has passed through the combustion furnace to a boiler provided with a superheater, discharging the combustion gas that has passed through the boiler through an exhaust path, sending a portion of the recirculated gas, which is the combustion gas in the exhaust path, to the combustion furnace through a first path, and sending another portion of the recirculated gas to the boiler upstream of the superheater through a second path.

[0010] A combustion method according to a fourth aspect of the present invention includes burning a material to be treated in a combustion furnace, guiding the combustion gas that has passed through the combustion furnace to a boiler provided with a superheater, discharging the combustion gas that has passed through the boiler through an exhaust path, sending a portion of the recirculated gas, which is the combustion gas in the exhaust path, to the combustion furnace through a first path, and sending another portion of the recirculated gas to the boiler upstream of the superheater through a second path, and at this time controlling the flow rate of the recirculated gas based on the temperature of the main steam obtained in the superheater.

[0011] A combustion method according to a fifth aspect of the present invention is the combustion method according to the fourth aspect, wherein the flow rate of the recirculated gas is controlled by adjusting a blower that sends the recirculated gas. Effect of the Invention

[0012] According to the above aspects of the present invention, it is possible to provide a combustion system and a combustion method capable of adjusting the main steam temperature. [Brief description of the drawings]

[0013] [Figure 1] 1 is a configuration diagram showing a combustion system according to a first embodiment. [Diagram 2] FIG. 6 is a configuration diagram showing a combustion system according to a second embodiment. [Diagram 3] FIG. 4 is a configuration diagram showing a combustion system according to a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, a combustion system according to an embodiment of the present invention will be described with reference to the drawings.

[0015] [Combustion System] (First embodiment) FIG. 1 is a configuration diagram showing a combustion system 100 according to a first embodiment. As shown in FIG. 1, the combustion system 100 includes a supply section 1, a combustion furnace 2, a boiler 3, a superheater 4, an exhaust path 5, a return path 6, a temperature reducing device 51, a dust collector 52, a catalytic reaction tower 53, and a chimney 54.

[0016] The supply section 1 includes an input hopper 11, a chute 12, and a feeder 13. The input hopper 11 receives the material to be treated. The chute 12 guides the material to be treated. The feeder 13 supplies the material to be treated to the combustion furnace 2. The feeder 13 can adjust the amount of material to be treated that is supplied.

[0017] The combustion furnace 2 is, for example, a stoker furnace equipped with a conveying mechanism 21. The combustion furnace 2 combusts the material to be treated. The conveying mechanism 21 includes, for example, a drying zone 22 and a combustion zone 23. The drying zone 22 and the combustion zone 23 each have a plurality of stokers lined up in the conveying direction. The stokers convey the material to be treated by reciprocating with a driving source (not shown). A primary air supply unit that supplies air for primary combustion is provided below the drying zone 22 and the combustion zone 23.

[0018] The combustion furnace 2 includes a main body 24 and an extension 25. The main body 24 forms a primary combustion chamber 26 above the transport mechanism 21. The extension 25 is cylindrical and extends upward from the upper end of the main body 24. The space inside the extension 25 is a secondary combustion chamber 27.

[0019] The combustion furnace 2 includes a discharge section 28. The discharge section 28 discharges the remains of the material to be treated as incineration ash.

[0020] The boiler 3 guides the combustion gas that has passed through the combustion furnace 2. The boiler 3 has a plurality of flues. In this embodiment, the plurality of flues include a first flue 31, a second flue 32, and a third flue 33. The first flues 31, the second flues 32, and the third flues 33 are collectively referred to as "flues 31 to 33." The flues 31 to 33 are gas flow passages that run in the vertical direction. The flues 31 to 33 are arranged side by side, adjacent to each other, from left to right in FIG. 1.

[0021] Adjacent flue gas channels 31 to 33 have their upper ends (one end) and lower ends (the other end) alternately connected. In particular, the first flue gas channel 31 and the second flue gas channel 32 communicate with each other at their upper ends. The second flue gas channel 32 and the third flue gas channel 33 communicate with each other at their lower ends. The flue gas channels 31 to 33 have a serpentine shape due to their upper ends and lower ends being alternately connected.

[0022] The number of flue gases is not particularly limited. The number of flue gases can be one or more. The number of flue gases may be, for example, one, two, or any number of three or more. Adjacent flue gases among the multiple flue gases are alternately connected at one end and the other end.

[0023] The superheater 4 is provided at a midpoint in the longitudinal direction of the third flue 33. The superheater 4 includes a superheater tube 41 through which steam flows. The superheater tube 41 includes a plurality of straight sections 42 and a plurality of connecting sections 43. The straight sections 42 are arranged in parallel at intervals in the vertical direction. The connecting sections 43 connect one end and the other end of the straight sections 42 alternately. The superheater tube 41 has a serpentine shape as a result of one end and the other end of the straight sections 42 being alternately connected by the connecting sections 43. The superheater tube 41 is made of a metal such as stainless steel. The position of the superheater 4 in the third flue 33 may be any position in the longitudinal direction of the third flue 33.

[0024] One end of the superheater tube 41 is connected to a water supply source (not shown). The superheater tube 41 heats the steam supplied from the water supply source by heat exchange with the combustion gas, and obtains high-temperature superheated steam. The other end of the superheater tube 41 is connected to, for example, a waste heat utilization facility (not shown). The waste heat utilization facility 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 exhaust path 5 is connected to an upper end of the third flue 33. The exhaust path 5 exhausts the combustion gas that has passed through the boiler 3.

[0026] The desuperheater 51 cools the combustion gas as necessary to lower its temperature. The dust collector 52 collects and removes dust in the combustion gas using a bag filter or the like. The catalytic reaction tower 53 decomposes and removes, for example, nitrogen oxides in the combustion gas. Chimney 54 discharges the combustion gases into the atmosphere.

[0027] The return path 6 has a main path 61 , a first path 62 , a second path 63 , and a blower 64 . The base line 61 extracts the combustion gas as a recycle gas from the discharge line 5 (a position between the dust collector 52 and the catalytic reaction tower 53). The combustion gas extracted as a recycle gas contains oxygen (O2).

[0028] Valves for adjusting the flow rate may be provided in one or more of the base path 61, the first path 62, and the second path 63. In this embodiment, a first adjustment valve 8 is provided in the first path 62. A second adjustment valve 9 is provided in the second path 63. The first adjustment valve 8 adjusts the flow rate of the recirculated gas flowing through the first path 62. The second adjustment valve 9 adjusts the flow rate of the recirculated gas flowing through the second path 63.

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

[0030] A first pathway 62 and a second pathway 63 branch off from the main pathway 61 . The first passage 62 is connected to the extension 25 of the combustion furnace 2. The first passage 62 returns a portion of the recirculated gas to the secondary combustion chamber 27 of the combustion furnace 2.

[0031] The second passage 63 is connected to the third flue 33 of the boiler 3. More specifically, the second passage 63 is connected to the third flue 33 at a position upstream of the superheater 4. The second passage 63 returns a portion of the recirculated gas to the third flue 33 (at a position upstream of the superheater 4).

[0032] The connection position of the second passage 63 to the boiler 3 is not particularly limited as long as it is a position upstream of the superheater 4. The connection position of the second passage 63 may be the second flue 32. The connection position of the second passage 63 may be an upper part of the first flue 31.

[0033] [Combustion method] (First embodiment) Next, the combustion method of the first embodiment will be described by taking the case where the combustion system 100 is used as an example. The material to be treated is charged into a charging hopper 11. The material to be treated may be waste. The waste may be general waste such as municipal solid waste, or may be industrial waste. The material to be treated is guided through a chute 12 and fed to the combustion furnace 2 by a feeder 13.

[0034] The transport mechanism 21 transports the objects to be treated to the drying zone 22 and then to the combustion zone 23. The primary air supply unit supplies air (primary air) to the objects to be treated. During this transport process, the objects to be treated are combusted in the primary combustion chamber 26 by reaction with the primary air, generating combustion gas. The remaining remains of the objects to be treated are discharged from the discharge unit 28 as incineration ash.

[0035] The combustion gas generated by the combustion of the material to be treated is introduced into the boiler 3 through the secondary combustion chamber 27. The combustion gas is introduced into the first flue 31, rises inside the first flue 31, and is introduced from the upper end of the first flue 31 to the upper end of the second flue 32. The combustion gas falls inside the second flue 32, and is introduced from the lower end of the second flue 32 to the lower end of the third flue 33. The combustion gas rises inside the third flue 33, and is discharged from the upper end of the third flue 33 to the exhaust path 5.

[0036] In the combustion system 100, in order to prevent the generation of dioxins, it is necessary to ensure the conditions of a temperature of 850° C. or higher and a residence time of 2 seconds or more. In the combustion system 100, it is preferable that the space consisting of the secondary combustion chamber 27 and the first flue 31 satisfies these conditions.

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

[0038] The combustion gas discharged through the exhaust path 5 is introduced into a temperature reducing device 51. The temperature reducing device 51 adjusts the temperature of the combustion gas as necessary. The dust collector 52 collects and removes dust in the combustion gas. The catalytic reaction tower 53 decomposes and removes, for example, nitrogen oxides in the combustion gas. The chimney 54 releases the combustion gas into the atmosphere.

[0039] A portion of the combustion gas flowing through the exhaust line 5 is taken out as recirculated gas through a base line 61 of the return line 6. A portion of the recirculated gas is returned to the combustion furnace 2 (secondary combustion chamber 27) via the first path 62. If the combustion gas in the secondary combustion chamber 27 contains combustible components, some of the combustible components are combusted by reacting with oxygen in the recirculated gas.

[0040] Another portion of the recirculated gas (a portion of the recirculated gas other than the recirculated gas guided to the first path 62) is returned to the third flue 33 (a position upstream of the superheater 4) via the second path 63. The "position upstream of the superheater 4" is, for example, a position in the third flue 33 that is lower than the superheater 4.

[0041] The temperature of the combustion gas also increases or decreases depending on the heat content of the recirculated gas. For example, if the heat content of the recirculated gas is large, the temperature of the combustion gas flowing through the third flue 33 will also be high. Specifically, if the recirculated gas is hot and a large amount of it is returned, the temperature of the combustion gas will also be high.

[0042] [Effects of the Combustion System and Combustion Method of the Embodiment] The combustion system 100 includes a first path 62 for sending a portion of the recirculated gas to the combustion furnace 2 (secondary combustion chamber 27), and a second path 63 for sending another portion of the recirculated gas to the upstream side of the superheater 4 in the boiler 3. The combustion system 100 can adjust the flow rate and the amount of heat contained in the combustion gas in the third flue 33 (at a position upstream of the superheater 4) by adjusting the flow rate of the recirculated gas. Therefore, the temperature of the combustion gas can be set arbitrarily. Therefore, the temperature of the main steam obtained in the superheater 4 can be adjusted. As a result, for example, by increasing the temperature of the main steam, the power generation efficiency in the exhaust heat utilization facility (generator) can be increased.

[0043] The combustion system 100 includes a first passage 62 that sends a portion of the recirculated gas to the combustion furnace 2 (secondary combustion chamber 27). Therefore, in the secondary combustion chamber 27, the combustion gas can be combusted by reaction with the recirculated gas. Therefore, the combustion efficiency in the combustion system 100 can be improved.

[0044] FIG. 3 is a configuration diagram showing a combustion system 300 of a comparative example. As shown in FIG. 3, the combustion system 300 has the same configuration as the combustion system 100 (see FIG. 1) except that the second passage 63 is not provided. In the combustion system 300, when the amount of recirculated gas returned is increased, the combustion efficiency increases, and the temperature of the main steam obtained in the superheater 4 tends to increase. For example, the following calculation results can be given.

[0045] The amount of recirculated gas returned is 2023 [Nm 3 / h], the temperature of the main steam obtained in the superheater 4 is 447[℃]. The return amount of the recirculated gas is 2630[Nm 3 / h] (1.3 times the rated value), the main steam temperature will be 457[℃].

[0046] However, if the amount of recirculated gas returned is increased, the increase in gas flow rate may make it difficult to ensure the conditions required for the secondary combustion chamber 27 and boiler 3 to prevent the generation of dioxins (temperature of 850°C or higher, residence time of 2 seconds or more).

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

[0048] [Combustion System] (Second Embodiment) Fig. 2 is a configuration diagram showing a combustion system 200 according to a second embodiment. Components common to the combustion system 100 shown in Fig. 1 are given the same reference numerals and description thereof will be omitted.

[0049] The combustion system 200 differs from the combustion system 100 (see FIG. 1) in that the combustion system 200 includes a temperature sensor 7 and a control unit 10. The temperature sensor 7 detects the temperature of the main steam that has passed through the superheater 4 .

[0050] [Combustion method] (Second embodiment) In the combustion system 200, when returning a portion of the recirculated gas through the second path 63, the control unit 10 can operate the first regulating valve 8 and the second regulating valve 9 based on the temperature of the main steam detected by the temperature sensor 7. The first regulating valve 8 adjusts the flow rate of the recirculated gas flowing through the first path 62. The second regulating valve 9 adjusts the flow rate of the recirculated gas flowing through the second path 63. In this manner, the control unit 10 controls the flow rates of the recirculated gas through the first path 62 and the second path 63.

[0051] In the combustion system 200, the flow rate of the recirculated gas flowing through the second passage 63 is adjusted by the second adjusting valve 9 based on, for example, the temperature of the main steam. For example, the following operation example can be given. When the temperature of the main steam is 440[℃], the recirculation gas flow rate of the first path 62 and the second path 63 is 1613[Nm 3 When the temperature of the main steam is 450[℃], the flow rate of the recirculation gas flowing through the first path 62 and the second path 63 is set to 2179[Nm 3 When the temperature of the main steam is 460[℃], the flow rate of the recirculation gas flowing through the first path 62 and the second path 63 is 2792[Nm 3 / h]. In this manner, 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 through the first path 62 to the flow rate of the recirculated gas flowing through the second path 63 can be set arbitrarily between 1:0 and 0:1.

[0053] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0054] 1, the return path 6 includes 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 to this. The return path may include a first path that guides the recirculated gas directly from the exhaust path to the combustion furnace, and a second path that guides the recirculated gas directly from the exhaust path to the boiler.

[0055] In the combustion system 100 shown in FIG. 1, a stoker furnace is used as the combustion furnace, but a fluidized bed combustion furnace may also be used as the combustion furnace.

[0056] In addition, within the scope of the spirit of the present invention, it is possible to replace the components in the above-described embodiments with well-known components as appropriate, and the above-described embodiments and variations may be combined as appropriate. [Explanation of symbols]

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

Claims

1. A combustion furnace for burning the object to be treated; a boiler for introducing the combustion gas from the combustion furnace; a superheater provided in the boiler for superheating main steam; an exhaust path for exhausting the combustion gas that has passed through the boiler; A return path that returns the combustion gas from the exhaust path as a recirculated gas, The return path is: a first passage for sending a portion of the recycle gas to the combustion furnace; and a second passage for sending another portion of the recirculated gas upstream of the superheater in the boiler. Combustion system.

2. The return path further includes a base path for directing the recirculated gas from the exhaust path, the first pathway and the second pathway branch off from the base pathway; The combustion system of claim 1 .

3. The material to be treated is burned in a combustion furnace. The combustion gas passing through the combustion furnace is guided to a boiler equipped with a superheater, The combustion gas that has passed through the boiler is discharged through an exhaust path. A part of the recirculated gas, which is the combustion gas in the exhaust path, is sent to the combustion furnace through a first path, Sending another portion of the recirculated gas through a second path to a portion of the boiler upstream of the superheater. Combustion method.

4. The material to be treated is burned in a combustion furnace. The combustion gas passing through the combustion furnace is guided to a boiler equipped with a superheater, The combustion gas that has passed through the boiler is discharged through an exhaust path. A part of the recirculated gas, which is the combustion gas in the exhaust path, is sent to the combustion furnace through a first path, sending another part of the recirculated gas through a second path to a side upstream of the superheater in the boiler, and controlling a flow rate of the recirculated gas based on a temperature of the main steam obtained in the superheater. Combustion method.

5. 5. The method of claim 4, wherein the flow rate of the recirculated gas is controlled by adjusting a blower that blows the recirculated gas.

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