阅读说明：本技术 流化床炉及其运转方法 (Fluidized bed furnace and method for operating the same ) 是由 小川祐司 五十岚实 前川勇 清水敬哲 武藤贞行 清泷元 福本康二 山田隆平 村冈利纪 于 2018-11-28 设计创作，主要内容包括：流化床炉具有：流化床部,其使燃料燃烧；自由空间部,其位于流化床部的上方；燃料投入口,其向自由空间部投入燃料；以及二次燃烧用气体提供部,其向自由空间部吹入通过在自由空间部中生成的燃烧废气调整了氧浓度的二次燃烧用气体,以抑制燃料在自由空间部中的异常燃烧。(The fluidized bed furnace has: a fluidized bed part that burns fuel; a free space part located above the fluidized bed part; a fuel inlet for introducing fuel into the free space; and a secondary combustion gas supply unit that blows a secondary combustion gas, the oxygen concentration of which is adjusted by the combustion exhaust gas generated in the free space portion, into the free space portion to suppress abnormal combustion of the fuel in the free space portion.)

1. A fluidized bed furnace having:

a fluidized bed part that burns fuel;

a free space portion located above the fluidized bed portion;

a fuel inlet for introducing the fuel into the free space portion; and

and a secondary combustion gas supply unit configured to blow a secondary combustion gas, the oxygen concentration of which is adjusted by the combustion exhaust gas generated in the free space portion, into the free space portion so as to suppress abnormal combustion of the fuel in the free space portion.

2. The fluidized bed furnace of claim 1,

the secondary combustion gas supply part includes an unburned gas supply port that blows the secondary combustion gas toward a position in the free space part that is downstream of the fuel inlet port with respect to the flow of the combustion gas and adjacent to the fuel inlet port.

3. The fluidized bed furnace of claim 1,

the secondary combustion gas supply unit includes a fuel chute blowing gas supply pipe that supplies the secondary combustion gas to a fuel supply path reaching the fuel inlet so that the secondary combustion gas is supplied from the fuel inlet in a state of being mixed with the fuel.

4. The fluidized bed furnace of claim 1,

the fluidized bed furnace further includes a tertiary combustion gas supply unit configured to blow a tertiary combustion gas, which has an oxygen concentration adjusted by the combustion exhaust gas and is higher than an oxygen concentration of the secondary combustion gas, into the free space portion at a position downstream of the secondary combustion gas supply unit in a flow of the combustion gas.

5. The fluidized bed furnace of claim 4,

the tertiary combustion gas supply portion includes a plurality of tertiary combustion gas supply ports that are dispersed in the flow direction of the combustion gas, and the plurality of tertiary combustion gas supply ports supply the tertiary combustion gas having a higher oxygen concentration on the downstream side of the flow of the combustion gas.

6. A fluidized bed furnace according to claim 4 or 5,

the tertiary combustion gas supply unit includes:

a temperature sensor that detects a temperature of a diffusion region of the tertiary combustion gas that is blown in; and

and a control device that adjusts the oxygen concentration of the tertiary combustion gas so that the detection value of the temperature sensor falls within a predetermined range by changing the mixing amount of the combustion exhaust gas with respect to air based on the detection value of the temperature sensor.

Technical Field

The present invention relates to a fluidized bed furnace and a method for operating the same.

Background

Conventionally, there has been known a fluidized bed furnace having a fluidized bed formed by fluidizing a fluidizing agent filled in a lower portion of a furnace by fluidizing gas blown out from a furnace bottom, and performing low air ratio combustion of fuel (combustion object) in the fluidized bed. Here, in the low air ratio combustion of the fuel, the air ratio of the flow gas is set to a low air ratio of less than 1, and the fuel is partially combusted, thereby drying and thermally decomposing the fuel to be gasified. Such a fluidized bed furnace is disclosed in patent documents 1 and 2.

The fluidized bed furnace of patent document 1 is composed of a fluidized bed portion and a free space portion located above the fluidized bed portion. In the fluidized bed furnace, a fluidizing gas having an air ratio of 0.3 to 0.6 is supplied to the bottom of the fluidized bed, combustion air for decomposing dioxins having an air ratio of 0.4 to 0.7 is supplied to the vicinity of the surface of the fluidized bed, and secondary air is supplied to the free space. Then, in the fluidized bed furnace, the fuel is partially combusted in the fluidized bed portion, and the generated gas and the char generated in the fluidized bed portion are combusted in the free space portion.

The fluidized bed furnace of patent document 2 includes a fluidized bed portion, a free space portion located above the fluidized bed portion, and a post-combustion region located above the free space portion. The air ratio of the primary air is 1 or less, the air ratio of the free space section is 1.0 to 1.5 in a high-oxidation atmosphere due to the blown secondary air, and the air ratio of the post-combustion zone is 1.5 or more due to the blown tertiary air. Then, in the fluidized bed furnace, the partial combustion of the fuel is performed in the fluidized bed portion, the generated gas generated in the fluidized bed portion is combusted in the free space portion, and the unburned gas component in the exhaust gas in the free space portion is combusted in the post-combustion zone.

Disclosure of Invention

Problems to be solved by the invention

As in patent documents 1 and 2, when the partial combustion of the fuel is performed in the fluidized bed portion, the proportion of the unburned portion (unburned char) of the fuel in the fluidized bed portion increases, and there is a possibility that the unburned char or its volatile matter causes a rapid combustion reaction in the free space portion or a subsequent combustion region.

When the surface layer portion of the fluidized bed portion is exposed to a high temperature due to a rapid combustion reaction, agglomeration occurs in the surface layer portion, and there is a possibility that the fluidized bed flow characteristics are deteriorated. Further, when the temperature in the furnace is locally high due to a rapid combustion reaction, furnace components such as the furnace wall are locally deteriorated. For these reasons, it is preferable to suppress a rapid combustion reaction in the free space portion or the subsequent combustion region.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a technique of: in a fluidized bed furnace having a fluidized bed portion for performing slow partial combustion of fuel and a free space portion provided above the fluidized bed portion, a rapid combustion reaction in the free space portion is suppressed.

Means for solving the problems

A fluidized bed furnace according to an embodiment of the present invention includes:

a fluidized bed part that burns fuel;

a free space portion located above the fluidized bed portion;

a fuel inlet for introducing the fuel into the free space portion; and

and a secondary combustion gas supply unit configured to blow a secondary combustion gas, the oxygen concentration of which is adjusted by the combustion exhaust gas generated in the free space portion, into the free space portion so as to suppress abnormal combustion of the fuel in the free space portion.

According to the fluidized bed furnace having the above configuration, the secondary combustion gas containing the combustion exhaust gas having an oxygen concentration lower than that of air is blown into the free space portion, thereby suppressing a local and rapid combustion reaction in the free space portion.

In the fluidized bed furnace, the secondary combustion gas supply portion may include an unburned gas supply port that blows the secondary combustion gas toward a position in the free space portion that is downstream of the fuel inlet port in a flow of the combustion gas and adjacent to the fuel inlet port.

Thus, by blowing the secondary combustion gas containing the combustion exhaust gas having an oxygen concentration lower than that of air directly downstream of the fuel inlet, the local and abrupt combustion reaction in the free space portion, particularly the fuel inlet and its periphery, is suppressed.

In the fluidized bed furnace, the secondary combustion gas supply unit may include a fuel chute blowing gas supply pipe that supplies the secondary combustion gas to a fuel supply path reaching the fuel inlet so that the secondary combustion gas is supplied from the fuel inlet in a state of being mixed with the fuel.

This suppresses a local and rapid combustion reaction of the fuel injected from the fuel injection port at and around the fuel injection port.

The fluidized bed furnace may further include a tertiary combustion gas supply unit configured to blow a tertiary combustion gas, which has an oxygen concentration adjusted by the combustion exhaust gas and is higher than an oxygen concentration of the secondary combustion gas, into the free space portion at a position downstream of the secondary combustion gas supply unit in a flow of the combustion gas.

In this way, by blowing the tertiary combustion gas containing the combustion exhaust gas having a lower oxygen concentration than air into the free space portion, the combustion of the combustible gas in the free space portion can be slowed.

In the fluidized bed furnace, the tertiary combustion gas supply portion may include a plurality of tertiary combustion gas supply ports dispersed in a flow direction of the combustion gas, and the plurality of tertiary combustion gas supply ports may supply the tertiary combustion gas having the higher oxygen concentration on a downstream side of the flow of the combustion gas.

Accordingly, the third combustion gas having a higher oxygen concentration can be supplied on the downstream side of the flow of the combustion gas, where the amount of unburned combustion gas is large, and thus the combustion of the combustible gas in the free space portion can be slowed, and a local and rapid combustion reaction can be suppressed.

In the fluidized bed furnace, the tertiary combustion gas supply portion may include: a temperature sensor that detects a temperature of a diffusion region of the tertiary combustion gas that is blown in; and a control device that adjusts the oxygen concentration of the tertiary combustion gas so that the detection value of the temperature sensor falls within a predetermined range by changing the mixing amount of the combustion exhaust gas with respect to air based on the detection value of the temperature sensor.

In this way, the oxygen concentration of the gas for tertiary combustion is adjusted so that the temperature of the free space portion is within the predetermined range, so that the combustion of the combustible gas in the free space portion can be slowed, and local and rapid combustion reactions in the free space portion can be suppressed.

Effects of the invention

According to the present invention, in the fluidized bed furnace having the fluidized bed portion in which the slow partial combustion of the fuel is performed and the free space portion provided above the fluidized bed portion, the rapid combustion reaction in the free space portion can be suppressed.

Drawings

Fig. 1 is a block diagram showing a schematic configuration of a combustion system including a fluidized bed furnace according to an embodiment of the present invention.

Fig. 2 is a view showing a schematic configuration of a fluidized bed furnace according to an embodiment of the present invention.

Fig. 3 is an enlarged view of the fluidized bed portion of the fluidized bed furnace.

Fig. 4 is an enlarged view of a fluidized bed portion of the fluidized bed furnace according to modification 1.

Detailed Description

[ Structure of Combustion System 100 ]

First, the configuration of the combustion system 100 including the fluidized bed furnace 1 according to the embodiment of the present invention will be described. The combustion system 100 shown in fig. 1 is a system that burns fuel (combustion target) such as coal, biomass, RDF, municipal waste, and industrial waste to recover waste heat thereof.

The combustion system 100 has a fluidized bed furnace 1 that burns fuel. A heat exchanging device 31, a cyclone type dust collector 32, a bag filter 33, and an induction blower 34 as an induction fan are provided in the combustion exhaust gas system 3 of the fluidized bed furnace 1. The combustion exhaust gas of the fluidized bed furnace 1 is recovered waste heat by the heat exchanger 31, dust is separated by the cyclone 32 and the bag filter 33, and a part of the dust is discharged to the outside of the system through a chimney not shown by the induction blower 34.

An exhaust gas recirculation system 4 is connected to the downstream side of the bag filter 33 of the combustion exhaust system 3. A gas recirculation blower 40 is provided in the exhaust gas recirculation system 4, and a part of the combustion exhaust gas system 3 is returned to the fluidized bed furnace 1 by the gas recirculation blower 40. The combustion exhaust gas returned to the fluidized bed furnace 1 by the exhaust gas recirculation system 4 is used as a fluidizing gas (primary combustion gas), a secondary combustion gas, and a tertiary combustion gas.

[ Structure of fluidized bed furnace 1 ]

Next, the structure of the fluidized bed furnace 1 according to an embodiment of the present invention will be described. The fluidized bed furnace 1 shown in fig. 2 has: a furnace main body 10 provided with a combustion chamber including a fluidized bed portion 11 in a furnace lower portion and a free space (free board) portion 12 above the fluidized bed portion 11; and an operation control device 15 that controls the operation of the fluidized bed furnace 1. A throttle portion 13 having a smaller cross-sectional area of the gas passage than the remaining portion of the combustion chamber is present in the lower portion of the free space portion 12. The combustion gas travels from bottom to top in the free space 12, and a heat transfer pipe constituting the heat exchanger 31 is provided in a flue connected to an upper portion of the free space 12.

Fig. 3 is an enlarged view of the fluidized bed portion 11. As shown in fig. 2 and 3, an internal circulating fluidized bed is formed in the fluidized bed portion 11 by a fluidized bed 51 filled with a fluidized medium such as silica sand, a fluidizing gas supplying means 52 for supplying fluidizing gas to the fluidized bed 51 from the bottom of the fluidized bed 51, and partition walls 41, 42 for partitioning the fluidized bed 51 into 3 cells 61, 62, 63 by the partition walls 41, 42.

The 1 st partition wall 41 partitions the lower portion of the furnace main body 10 including the fluidized bed portion 11 into a combustion zone 53 and a heat recovery zone 54. The 2 nd partition wall 42 is disposed close to the 1 st partition wall 41 in the heat recovery area 54 and in parallel with the 1 st partition wall 41. By these partition walls 41, 42, the fluidized bed portion 11 is partitioned into 3 units of "combustion unit 61" formed between the 1 st side wall 10a and the 1 st partition wall 41 of the furnace main body 10, "circulation unit 62" formed between the 1 st partition wall 41 and the 2 nd partition wall 42, and "endothermic unit 63" formed between the 2 nd partition wall 42 and the 2 nd side wall 10b of the furnace main body 10. The heat absorbing unit 63 is provided with a heat transfer pipe 64 such as a superheater tube or an evaporator tube. Heat recovery is performed by the heat medium passing through the heat transfer pipe 64.

A combustion chamber extending linearly in the vertical direction is formed above the combustion region 53. On the other hand, a ceiling wall 43 that closes an upper portion of the heat recovery region 54 is provided above the heat recovery region 54. The upper end of the 1 st partition wall 41 is close to the ceiling wall 43, and an upper communication port as an unburned gas supply port 68 is formed between the upper end of the 1 st partition wall 41 and the ceiling wall 43. The lower end of the 1 st partition wall 41 is higher than the lower end of the 2 nd partition wall 42, and thus a lower communication port 55 through which the flow medium flows is formed in the lower portion of the 1 st partition wall 41. Communication ports 56 and 57 through which the circulating unit 62 and the heat absorbing unit 63 communicate with each other and through which the flow medium flows are formed in the upper and lower portions of the 2 nd partition wall 42.

The fluidizing gas supply device 52 supplies fluidizing gas whose flow rate has been independently adjusted to each of the combustion unit 61, the circulation unit 62, and the heat absorption unit 63. One or more air-diffusing pipes 80 having a plurality of blow-out ports opening sideways are provided at the bottom of each of the combustion unit 61, the circulation unit 62, and the heat absorption unit 63. Each of the air diffusing pipes 80 is disposed below the lower ends of the 1 st partition wall 41 and the 2 nd partition wall 42. However, the flow gas supplying device 52 may have a bellows disposed at the bottom of each of the cells 61, 62, and 63, and a gas dispersing plate (not shown) provided to close the upper part of the bellows, instead of the gas dispersing pipe 80.

The air diffuser 80 is connected to each of the units 61, 62, 63 by a plug, and each plug is connected to a flow gas supply pipe 81, 82, 83 having a flow rate adjusting member 81a, 82a, 83a such as an air valve (or a valve) and a flow meter 81b, 82b, 83 b. The air is supplied by the pressure-feed blower 79 to a fluidizing gas supply pipe 81 connected to the air diffusion pipe 80 disposed at the bottom of the combustion unit 61 and a fluidizing gas supply pipe 82 connected to the air diffusion pipe 80 disposed at the bottom of the circulation unit 62. The exhaust gas recirculation system 4 is connected to the flow gas supply pipe 83 connected to the air diffusing pipe 80 disposed at the bottom of the heat absorbing unit 63.

The operation control device 15 operates the flow rate adjusting means 81a, 82a, 83a to adjust the flow rates of the fluidizing gas in the fluidizing gas supply pipes 81, 82, 83, based on the detection values of the flow meters 81b, 82b, 83b, and the like and temperature sensors (not shown) for detecting the temperatures of the combustion unit 61 and the heat absorbing unit 63 in the fluidized bed 51. Air is blown out from the bottom of the combustion unit 61 and the circulation unit 62 as a fluidizing gas, and combustion exhaust gas is blown out from the bottom of the heat absorbing unit 63 as a fluidizing gas.

Here, the flow rate of the gas for flow is adjusted so that the superficial velocity of the gas for flow of the combustion unit 61 is higher than the superficial velocity of the gas for flow of the heat absorption unit 63, and the superficial velocity of the gas for flow of the circulation unit 62 is higher than the superficial velocity of the gas for flow of the combustion unit 61 and the superficial velocity of the gas for flow of the heat absorption unit 63. Thereby, a flow of the flowing medium is generated as follows: the fluid medium in the combustion unit 61 moves to the circulation unit 62 through the lower communication port 55 of the 1 st partition wall 41, the fluid medium in the circulation unit 62 moves to the heat absorption unit 63 through the upper communication port 56 of the 2 nd partition wall 42, and the fluid medium in the heat absorption unit 63 circulates to the combustion unit 61 and the circulation unit 62 through the lower communication port 57 of the 2 nd partition wall 42. By such circulation of the fluid medium, the heat energy of the fluid medium at a high temperature in the combustion unit 61 is released to the outside in the heat absorbing unit 63, and the fluid medium having a lowered temperature is returned to the combustion unit 61, whereby the temperature rise of the fluid medium in the combustion unit 61 is suppressed.

The free space portion 12 has a fuel inlet 65 opened directly above the surface layer portion of the fluidized bed portion 11 during operation, i.e., on the 1 st side wall 10 a. The fuel inlet 65 is located upstream of the throttle 13 in the flow of the combustion gas. The fuel is supplied to the fuel inlet 65 by a fuel supply device not shown. The fuel introduced into the furnace through the fuel inlet 65 falls down to the upper part of the combustion unit 61 of the fluidized bed portion 11.

In the free space portion 12, an unburned gas supply port 68 is opened in the furnace wall on the downstream side of the fuel injection port 65 with respect to the flow of the combustion gas, that is, in the vicinity of the throttle portion 13. The mixed gas of the air and the combustion exhaust gas blown out into the fluidized bed 51 from the diffuser 80 arranged in the fluidized bed 51 of the heat recovery region 54 and passed through the fluidized bed 51 is blown out from the non-combustion gas supply port 68 as the secondary combustion gas.

In the free space portion 12, a plurality of tertiary combustion gas supply ports 69 are opened in the furnace wall on the downstream side of the unburned gas supply port 68 with respect to the flow of the combustion gas. The plurality of tertiary combustion gas supply ports 69 are provided at a plurality of positions in a dispersed manner, in other words, in the flow direction of the combustion gas. Flow rate adjusting members 88 and 89 such as air valves (or valves) are provided in supply paths for supplying air to the tertiary combustion gas supply ports 69 and supply paths for supplying combustion exhaust gas. A temperature sensor 70 is provided on a furnace wall included in a diffusion region of the tertiary air blown out from the tertiary combustion gas supply port 69.

[ method of operating fluidized bed furnace 1 ]

Here, a method of operating the fluidized bed furnace 1 configured as described above will be described. In the fluidized bed furnace 1, low air ratio combustion is performed in the fluidized bed portion 11. More specifically, the supply amounts of fluidizing air and secondary combustion gas to the combustion unit 61 and/or the air content thereof are adjusted so that the total air ratio of the fluidized bed portion 11 and the free space portion 12 becomes a value larger than 1, and the air ratio of the combustion unit 61 of the fluidized bed portion 11 (i.e., the primary air ratio) and the air ratio around the fuel inlet 65 (the secondary air ratio) are both low air ratios smaller than 1. Preferably the primary air ratio is lower than the secondary air ratio. For example, when the total air ratio of the fluidized bed unit 11 and the free space unit 12 is set to 1.2, the primary air ratio may be set to 0.4, and the secondary air ratio may be set to 0.8.

In the fluidized bed portion 11 of the reducing atmosphere having a low oxygen concentration, combustible thermally decomposed gas and thermally decomposed residue are generated due to slow drying and thermal decomposition of the fuel. The residues of the pyrolysis residue or the fuel are discharged to the outside of the furnace through the take-out port 72 for the fluidizing agent and the incombustibles provided at the bottom of the combustion unit 61 (i.e., at an intermediate position between the 1 st side wall 10a and the 1 st partition wall 41). The thermally decomposed gas generated in the fluidized bed portion 11 is combusted with the secondary combustion gas, the unburned portion of the combustion gas is completely combusted with the tertiary combustion gas, and the combustion exhaust gas is discharged to the combustion exhaust gas system 3.

In the combustion unit 61 of the fluidized bed furnace 1 configured as described above, since fuel is combusted at a low air ratio, the proportion of unburned components (unburned char) in the fuel in the combustion unit 61 is larger than that in the case where the air ratio is 1 or more. When the primary air ratio is set to 0.4 as in the above example, the proportion of unburned semicoke in the combustion unit 61 is particularly large as compared with the case where the conventional air ratio is about 0.8 to 0.9.

There is a possibility that unburned semicoke in the combustion unit 61 moves from the combustion unit 61 to the heat absorption unit 63 due to circulation of the fluid medium. However, it is not desirable to generate a combustion reaction in the heat absorbing unit 63.

Therefore, in the fluidized bed furnace 1, the combustion exhaust gas having a lower oxygen concentration than air is used as the gas for flowing the heat absorbing means 63, and the air ratio of the heat absorbing means 63 is made lower than that of the combustion means 61 and the circulation means 62, whereby the combustion reaction of the unburned semicoke in the heat absorbing means 63 is suppressed.

Further, when the proportion of fly ash containing unburned semicoke or volatile matter of unburned semicoke increases in the free space portion 12, a rapid combustion reaction may occur in the free space portion 12. When a rapid combustion reaction occurs in the free space 12 near the fluidized bed 51 of the fluidized bed 11, the surface layer of the fluidized bed 11 is exposed to a high temperature, and the agglomerates are generated in the surface layer, which may deteriorate the flow characteristics of the fluidized bed 11. Further, when a rapid combustion reaction occurs in the free space portion 12, explosive air expansion may occur to deteriorate the stability of the furnace operation or deteriorate the furnace main body 10.

Therefore, the fluidized bed furnace 1 includes the secondary combustion gas supply unit 86, and the secondary combustion gas supply unit 86 blows the secondary combustion gas whose oxygen concentration is adjusted by the combustion exhaust gas generated in the free space portion 12 into the free space portion 12, thereby suppressing the air ratio in the upstream portion of the free space portion 12 to less than 1. By this secondary combustion gas supplying portion 86, a secondary combustion gas containing combustion exhaust gas having an oxygen concentration lower than that of air is blown into the free space portion 12, and local and rapid combustion reaction and abnormal combustion in the free space portion 12 are suppressed.

In the free space portion 12, the vicinity of the fuel inlet 65 also has a large amount of unburned gas due to fine particles or volatile components thereof raised from the fuel introduced into the furnace from the fuel inlet 65. Therefore, the secondary combustion gas supply portion 86 includes the unburned gas supply port 68, and the unburned gas supply port 68 blows the secondary combustion gas toward the downstream side of the free space portion 12 with respect to the fuel inlet port 65 in the flow of the combustion gas and at a position adjacent to the fuel inlet port 65. The "position adjacent to the fuel inlet 65" refers to the periphery of the fuel inlet 65, and refers to a portion in which the amount of unburned components in the gas is particularly large due to the fine particles or volatile components thereof lifted from the fuel introduced from the fuel inlet 65. Thus, the secondary combustion gas containing the combustion exhaust gas having an oxygen concentration lower than that of air is blown into the fuel inlet 65 directly downstream thereof, and local and rapid combustion reaction in the free space portion 12, particularly the fuel inlet 65 and its surroundings, is suppressed.

In the present embodiment, the secondary combustion gas is blown into the throttle portion 13 directly downstream of the flow of the combustion gas from the non-combustion gas supply port 68 toward the fuel inlet port 65. The secondary combustion gas blown into the free space portion 12 from the non-combustion gas supply port 68 contains a large amount of combustion exhaust gas whose oxygen concentration is further reduced by the heat absorbing means 63, and therefore, it is expected that the combustion reaction at the fuel inlet 65 and its surroundings can be suppressed more effectively.

The fluidized bed furnace 1 further includes a tertiary combustion gas supply unit 87, and the tertiary combustion gas supply unit 87 blows a tertiary combustion gas whose oxygen concentration is adjusted by the combustion exhaust gas into the free space 12 at a position downstream of the unburned gas supply port 68 in the flow of the combustion gas. As described above, by blowing the tertiary combustion gas containing the combustion exhaust gas having an oxygen concentration lower than that of air into the free space portion 12 at a position on the downstream side of the unburned gas supply port 68 with respect to the flow of the combustion gas, the combustion of the combustible gas in the free space portion 12 becomes slow, and a local and rapid combustion reaction can be suppressed. The oxygen concentration of the gas for tertiary combustion is higher than the oxygen concentration of the gas for secondary combustion.

The tertiary combustion gas supply unit 87 includes a plurality of tertiary combustion gas supply ports 69 that are dispersed in the flow direction of the combustion gas, a temperature sensor 70 that detects the temperature of the diffusion region of the tertiary combustion gas that is blown in, and an operation control device 15 that adjusts the oxygen concentration of the tertiary combustion gas based on the detection value of the temperature sensor 70. The temperature of the diffusion region of the tertiary combustion gas blown out from each tertiary combustion gas supply port 69 is detected by the temperature sensor 70, and the operation control device 15 adjusts the oxygen concentration of the tertiary combustion gas blown out from each tertiary combustion gas supply port 69 so that the detected temperature falls within a predetermined range.

Specifically, the operation control device 15 changes the opening degree of the flow rate adjustment members 88 and 89 to change the mixing ratio of the air and the combustion exhaust gas, thereby adjusting the oxygen concentration of the gas for tertiary combustion. The operation control device 15 adjusts the opening degrees of the flow rate adjustment members 88 and 89 such that, when the temperature detected by the temperature sensor 70 at a certain location exceeds a predetermined range, the oxygen concentration of the tertiary combustion gas supplied to the location is decreased while maintaining the flow rate of the tertiary combustion gas at a predetermined flow rate, and that, when the detected temperature is below the predetermined range, the oxygen concentration of the tertiary combustion gas supplied to the location is increased.

The tertiary combustion gas having the higher oxygen concentration is supplied from the plurality of tertiary combustion gas supply ports 69 dispersed in the flow direction of the combustion gas toward the downstream side of the flow of the combustion gas. That is, the tertiary combustion gas having a higher oxygen concentration is supplied on the downstream side of the flow of the combustion gas, where the amount of unburned combustion gas is large. This slows down the combustion of the combustible gas in the free space 12, and can suppress a local and rapid combustion reaction.

Although the preferred embodiments of the present invention have been described above, the present invention also includes details of the specific structures and/or functions of the above-described embodiments which are modified within the scope not departing from the spirit of the present invention.

For example, in the fluidized bed furnace 1 of the above embodiment, the secondary combustion gas is blown into the free space portion 12 from the unburned gas supply port 68, but in addition to or instead of this, the secondary combustion gas may be supplied from the fuel inlet port 65 in a state of being mixed with the fuel. In this case, as shown in fig. 4, the secondary combustion gas supply portion 86 includes a fuel-chute blowing gas supply pipe 67, and the fuel-chute blowing gas supply pipe 67 supplies the secondary combustion gas to the fuel supply path 66 reaching the fuel inlet 65 so that the secondary combustion gas is supplied from the fuel inlet 65 in a state of being mixed with the fuel. Thus, the fuel is injected into the free space portion 12 together with the secondary combustion gas, and therefore, local and rapid combustion reaction at the fuel injection port 65 and the periphery thereof can be suppressed.

Description of the reference symbols

1: a fluidized bed furnace; 3: a combustion exhaust system; 4: an exhaust gas recirculation system; 10: a furnace main body; 10 a: 1 st side wall; 10 b: a 2 nd side wall; 11: a fluidized bed section; 12: a free space portion; 13: a throttle section; 15: an operation control device; 31: a heat exchange device; 32: a cyclone dust collector; 33: a bag filter; 34: an induction blower; 40: a gas recirculation blower; 41: a 1 st partition wall; 42: a 2 nd partition wall; 43: a top wall; 51: a fluidized layer; 52: a flowing gas supply device; 53: a combustion zone; 54: a heat recovery area; 55. 56, 57: a communication port; 61: a combustion unit; 62: a circulation unit; 63: a heat absorbing unit; 64: a heat conducting pipe; 65: a fuel inlet; 66: a fuel supply path; 67: a fuel chute blowing gas supply pipe; 68: an unburned gas supply port; 69: a tertiary combustion gas supply port; 70: a temperature sensor; 72: a take-out port; 79: pressing into a blower; 80: an air diffusing pipe; 81. 82, 83: a gas supply piping for flowing; 81a, 82a, 83 a: a flow rate adjusting member; 81b, 82b, 83 b: a flow meter; 86: a secondary combustion gas supply unit; 87: a tertiary combustion gas supply unit; 88. 89: a flow rate adjusting member; 100: a combustion system.