JPH0830566B2 - Circulating fluidized bed boiler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention supplies coal, which is a solid fuel, onto a fluidized bed formed of relatively large particles such as gravel, and further uses sand as a heat transfer body. In a circulating fluidized bed boiler that circulates fine particles such as to improve thermal efficiency, a part of the circulating bed material of the heat exchange part of the external heat exchanger is refluxed into the hot well, and the temperature in the hot well is controlled. The present invention relates to a circulating fluidized bed boiler in which the abnormal occurrence of harmful gas is prevented by adjusting the amount within a predetermined range.

[Prior art]

As a boiler that can efficiently burn solid fuel while satisfying the exhaust gas emission standards, sand, ash, limestone, etc. are formed on a fluidized bed formed of relatively large particles such as gravel, that is, a dense bed. A circulating fluidized bed boiler having a fine particle recirculation layer has been proposed.

This circulating fluidized bed boiler is a SO that is generated from coal by mixing particulate limestone into coal that burns in a dense bed.
_{2 It} absorbs most of the gas and other harmful gases, forms CaSO ₄ (calcium sulfate), and circulates in the boiler as a part of the circulating bed material, making most of the exhaust gas harmless. It is an excellent boiler that can do it.

The circulation bed material is divided into two chambers of a hot well and a heat exchange section in an external heat exchanger during circulation.
The circulating bed material that recirculates via the hot well is
This is for keeping the inside of the combustor at a predetermined concentration. The circulating bed material that recirculates via the heat exchange section controls the combustion temperature in the combustor.

By the way, the circulation bed material supplied to the hot well is promoted to flow by the fluidized air supplied below the hot well, but at the same time, the unburned portion of the coal contained in the circulation bed material is burned and heated. To be done.

The circulating bed material supplied to this hot well corresponds to the temperature at the top of the combustor and is about 870 ° C.

However, while the circulating bed material is being fluidized by the fluidizing air, the unburned portion of the coal burns and the temperature rises.

When the temperature exceeds about 800 ° C., the CaSO ₄ is decomposed in the reducing atmosphere and reduced to SO ₂ gas again to generate a harmful gas, which is discharged to the atmosphere as it is.

Therefore, prior to explaining the present invention, an outline of a circulating fluidized bed boiler will be described below with reference to FIG.

This boiler includes a combustor 1 which is a combustor, an external heat exchanger 2 provided adjacent to the combustor 1, and an external heat exchanger 2 which is provided on the top of the combustor 1 and a connecting duct 3. And the fluid supply port is connected to the cyclone 4 and the like.

The inside of the external heat exchanger 2 is divided into two parts by a partition wall 5, a hot well 6 is formed on one side, and a heat exchange part 7 is formed on the other side, and fluidized air is supplied to the lower part of the external heat exchanger 2. A tube 21 is provided. Further, a heat transfer section 22 is provided in the heat exchange section 7, and the water W supplied to the heat transfer section 22.
Is heated to generate steam S.

The combustor 1 is composed of a lower dense bed area A and a large diameter freeboard area B above the dense bed area A.

In the dense bed area A, a dense bed 9 is formed in which the dense bed material 8 made of gravel or the like is accommodated. Further, crushed limestone, which is a part of the circulating bed material, is supplied from the supply pipe 11 to the dense bed 9 for the purpose of capturing coal 10 as a solid fuel and sulfur content.

Further, a fluidizing air system constituted by a supply pipe 13 and the like is provided at the lowermost portion of the dense bed area A, and the fluidizing air a for fluidizing the dense bed 9 is provided in the combustor 1.
Supplied within.

This fluidized air a is sent over the entire area of the depth bed 9 by a dispersion plate or the like, and serves to fluidize the dense bed material 8 as a whole.

On the other hand, the freeboard area B formed in the enlarged portion in the upper part of the combustor 1 is a circulation layer in which carbon and ash generated by combustion or pulverized limestone in the dense bed area A and the lower portion of the freeboard area B are circulated. Forming 16. The circulation layer 16 has a secondary air system.
Secondary air c is supplied from 17 for more complete combustion.

As described above, although the solid fuel such as coal 10 is burned in the combustor 1, the circulating bed made of carbon or ash generated in the dense bed area A and the freeboard area B, or pulverized limestone, etc. The gas g containing the material r is supplied into the cyclone 4 via the connection duct 3, and is separated into the gas g and the circulating bed material r here, and the gas g is supplied to a convection boiler (not shown) to generate an energy source for steam generation. Used as.

The circulating bed material r made of limestone, ash, carbon, etc. falls by its own weight into the hot well 6 of the external heat exchanger 2 from the take-out pipe 20 extending to the lower portion of the cyclone 4,
Supplied. Air is supplied from the flowing air supply pipe 21 into the external heat exchanger 2, so that the circulating bed material r is fluidized.

Circulating bed material r supplied into the hot well 6
Overflows from the upper end of the partition wall 5 and the heat transfer tube 22
Flows into the heat exchange section 7 in which the heat is absorbed, and heat is recovered there to generate steam S. In the heat exchange section 7, the ash d contained in the circulation bed material r floats above the fluidized circulation bed material r, and the exhaust pipe 23 provided above the heat exchange section 7 It is discharged to the outside via.

The lower part of the hot well 6 and the lower part of the combustor 1 are connected by a hot recycle pipe 24, and the lower part of the heat exchange part 7 and the lower part of the combustor 1 are connected by a cold recycle pipe 25. Then, the circulating bed material r having a temperature higher than that of the hot well 6 flows back into the fluidized bed region A via the hot recycle pipe 24 and is heat-exchanged in the heat exchange section 7,
The circulating bed material r whose temperature has dropped is a cold recycle pipe
Reflux into the dense bed area A via 25. The high-temperature circulating bed material r that recirculates in the hot recycle pipe 24 is for keeping the dense bed area A and the freeboard area B at a predetermined concentration. The low-temperature circulating bed material r that recirculates in the cold recycle pipe 25 controls the combustion temperature.

It should be noted that one end of the gas vent pipe 27 is connected to the top of the external heat exchanger 2, and the other end is connected to the large diameter portion forming the freeboard area B of the combustor 1, and the gas inside the external heat exchanger 2 is connected. Is returned to the freeboard area B of the combustor 1.

As a known technique for a circulating fluidized bed boiler, Japanese Patent Laid-Open No. Sho 61
-186705 and JP-A-61-205710 have been proposed. The former is a combustor, cyclone, external heat exchanger,
Regarding the boiler in which the external heat exchanger and the combustor are connected by the hot recycle pipe and the cold recycle pipe, the temperature of the hot well side of the external heat exchanger is properly adjusted and the external heat exchanger is Controlling the temperature of the circulating bed material that is recirculated to the combustor to control the temperature of the lower part of the combustor, that is, the dense bed region to control the temperature of the entire combustor to control the overall combustion state of the circulating fluidized bed boiler. is not.

The latter relates to a device provided with a cooler in a circulation path connecting the cyclone and the freeboard area above the combustor, or a device provided with a cooler in a bypass passage provided in parallel with this circulation path. However, in this device, the temperature of the freeboard area above the combustor is controlled by the freeboard material flowing back from the external heat exchanger, and the temperature of the hot well side of the external heat exchanger is adjusted to Accordingly, the temperature of the entire combustor including the dense bed formed under the combustor is not controlled all at once.

[Problems to be Solved by the Present Invention]

By the way, in such a boiler, as described above, a part of the circulating bed material discharged from the top of the combustor is supplied to the hot well, and the rest is supplied to the heat exchange part. Is hot, so
The unburned content of coal contained in the circulating bed material is burned by the fluidized air, and the temperature is further raised.

The temperature of this circulating bed material is about 800 in a reducing atmosphere.
At temperatures above ℃, Ca that forms part of the circulating bed material
There was a problem that SO ₄ was thermally decomposed into SO ₂ gas again.

When the temperature in the hot well exceeds about 800 ° C., a large amount of SO ₂ gas is generated as shown in FIG. It was very difficult to make SO ₂ gas generated in such a large amount react with limestone in the combustor to absorb it and render it harmless.

[Object of the Invention]

The present invention solves the problems of the conventional circulating fluidized bed boiler, in which the temperature inside the hot well is controlled to prevent the abnormal occurrence of SO ₂ gas, and the reflux is further performed from an external heat exchanger. An object of the present invention is to control the combustion temperature of a fluidized bed boiler rapidly and entirely by adjusting the temperature in the combustor from the dense bed region using a circulating bed material.

[Structure of Invention]

DISCLOSURE OF THE INVENTION The present invention for achieving the above-mentioned object is a dense bed A
A combustor 1 having a lower part, a cyclone 4 communicating with an upper part of the combustor 1 and a lower part communicating with an external heat exchanger 2, and a lower part of the external heat exchanger 2 communicating with a lower part of the combustor 1. In the circulating fluidized bed boiler, the external heat exchanger 2 includes a heat exchange section 7 and a hot well 6
Is formed by partitioning with a partition wall 5, and a supply pipe 32 that connects the lower part of the heat exchange part 7 and the upper part on the hot well 6 side is provided, and the lower part of the heat exchange part 7 is connected via this supply pipe 32. Is a circulation type fluidized bed boiler in which a part of the circulating bed material is divided into the upper part of the hot well 6 to control the temperature in the hot well 6.

In the external heat exchanger, the hot well and the heat exchanging portion are adjacent to each other and are partitioned by a partition wall. The temperature in the hot well is almost the same as the temperature at the top of the tower, but the temperature in the heat exchange section is considerably lower than the temperature in the hot well because heat is absorbed by the heat transfer tubes.

According to the present invention, a supply pipe penetrating the partition wall is provided, and a part of the circulating bed material having a low temperature in the heat exchange section is supplied through the supply pipe into the hot well having a higher temperature. It is a thing.

For example, when the temperature in the hot well is 800 ° C to 1000 ° C and the temperature in the heat exchange part is 300 ° C to 600 ° C, a part of the low temperature circulation bed material in the heat exchange part is fed into the hotwell via the supply pipe. Temperature of 800 to 900 in the hot well
It can be controlled to be below ℃.

The suction port of the supply pipe is preferably provided in a portion where the circulating bed material in the heat exchange section is cooled by the heat transfer pipe (cooling pipe) and has the lowest temperature, and is usually provided below the partition wall.

Further, the discharge port of the supply pipe is so arranged that the low-temperature circulating bed material can be uniformly mixed with the high-temperature circulating bed material in the hot well, and preferably, it can be dispersed and supplied to the upper layer portion of the circulating bed material in the hot well. To do.

Further, an air pump, an air carrier, a screw conveyor, or the like is attached to the supply pipe as a means for transferring the circulating bed material.

The supply pipe may be introduced to the outside of the external heat exchanger via the cold recycle pipe, and may be introduced into the hot well from the supply pipe branched from the cold recycle pipe.

As described above, a part of the circulation bed material whose temperature on the heat exchange section 7 side of the external heat exchanger 2 is lowered is supplied to the hot well 6 side to adjust the temperature of the circulation bed material at this portion to adjust the temperature of this hot well. The abnormal temperature on the 6 side is suppressed. By adjusting the temperature of the circulating bed material that flows back from the external heat exchanger 2 to the dense bed area of the combustor 1, a series of temperatures from the dense bed area to the freeboard area is controlled to control the overall combustion state of the combustor. Can be well controlled.

〔Example〕

Next, a first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 shows an enlarged sectional view of the external heat exchanger 2 shown in FIG.

Inside the external heat exchanger 2, there is provided a temperature adjusting device 30 including a through pipe 31, a supply pipe 32, an air pump 35, and a fixing member 36 for fixing the supply pipe 32.

The through pipe 31 is fixed by penetrating it below the partition wall 5 that divides the hot well 6 and the heat exchange part 7, and has an inlet 33 opened to the heat exchange part 7 side. An air pump 35 is provided in the.

Further, from the air pump 35, the supply pipe 32 is connected to the partition wall 5.
The upper end of the partition wall 5 is located above the partition wall 5.

At the tip of the supply pipe 32, a discharge port 34 is provided toward the center of the hot well 6, and by driving an air pump 35, the low temperature circulation bed material R2 in the heat exchange section 7 is discharged from the discharge port.
Discharge from 34 into the hot well 6.

In this external heat exchanger 2, the high temperature circulation bed material R1 in the hot well 6 is burned by the unburned coal of coal by the fluidized air h supplied from the fluidized air supply pipe 21, and the take-out pipe 20
The temperature rises further than the temperature at which it was supplied, and approaches the reducing atmosphere.

In the reducing atmosphere, CaSO ₄ decomposes to generate SO ₂ . As shown by the experimental data in the line graph of FIG. ₂ , it is known that the SO ₂ concentration increases at an accelerating rate when the temperature rises above 900 ° C.

Therefore, in order to prevent the abnormal occurrence of SO ₂ , it is necessary to control the temperature of the high temperature circulating bed material R1 in the hot well 6 to 800 to 900 ° C or lower.

In the present embodiment, the low temperature circulating bed material R2 of about 300 ° C. to 600 ° C. in the heat exchange section 7 is supplied into the hot well 6 via the temperature control device 30, so that the hot well 6
The temperature inside can be controlled below about 800-900 ° C.

The supply amount of the circulation bed material R2 can be freely adjusted by operating the air pump 35 by remote manual operation or remote automatic operation (not shown).

Next, a second embodiment of the present invention will be described with reference to FIG.

In this embodiment, the temperature control device 40 is provided on the partition wall 5 for partitioning the hot well 6 and the heat exchanging portion 7, which is an air transfer type.

The temperature control device 40 includes a through pipe 41, a supply pipe 44, an air header 47, a fluidizing air pipe 48, and a riser air pipe 49.

One end of the through pipe 41 is attached to the partition wall 5 and has a suction port 42 on the heat exchange section 7 side, and the other end is connected below a supply pipe 44 extending upward along the partition wall 5. It 43 is a reinforcing bracket.

The upper end of the supply pipe 44 has a discharge port 45 toward the center of the hot well 6, and is fixed to the partition wall 5 by a fixing member 46.

An air header 47 is installed in the hot well 6, and a fluidized air pipe 48 branched from the air header 47 is introduced into the through pipe 41. Further said air header 47
From, a riser air pipe 49 branches and penetrates into the supply pipe 44.

In the second embodiment configured as described above, the fluidizing air u is supplied by the fluidizing air pipe 48 to the low temperature circulating bed material R2 in the through pipe 41 and in the vicinity thereof to be fluidized.

On the other hand, the riser air tube 49 allows the riser air v
However, since it is supplied from below the supply pipe 44, the fluidized low temperature circulation bed material R2 is conveyed upward by the riser air v that rises in the supply pipe 44 in the form of bubbles.
It is discharged from the discharge port 45 into the hot well 6.

As described above, in the second embodiment, the low temperature circulating bed material R2 is supplied into the hot well 6 as in the first embodiment by constantly supplying a predetermined compressed air to the air header 47 during the operation of the boiler. Therefore, the temperature in the hot well 6 can be controlled to about 800 to 900 ° C. or less.

Further, instead of the riser air v, a screw conveyor may be provided in the supply pipe 44 and the screw may be driven to transfer the low temperature circulating bed material R2.

〔The invention's effect〕

As described above, the circulating fluidized bed boiler according to the present invention includes the combustor 1 having the dense bed A in the lower part, the cyclone 4 communicating with the upper part of the combustor 1 and the lower part communicating with the external heat exchanger 2, and In the circulating fluidized bed boiler in which the lower part of the external heat exchanger 2 and the lower part of the combustor 1 are communicated with each other, the external heat exchanger 2 is formed by partitioning the heat exchange part 7 and the hot well 6 with a partition wall 5. A supply pipe 32 that connects the lower part of the heat exchange part 7 and the upper part on the hot well 6 side is provided, and a part of the circulating bed material under the heat exchange part 7 is connected to the hot well via the supply pipe 32. The temperature is adjusted in the hot well 6 by branching to the upper portion of the inside of the hot well 6, and the following effects can be obtained.

A) By supplying the circulating bed material cooled from the heat exchange part 7 side to the upper part of the hot well 6, the temperature of the circulating bed material in the hot well 6 is adjusted to a temperature at which CaSO ₄ is not thermally decomposed. Therefore, it is possible to prevent the abnormal occurrence of SO _{2 in} the hot well 6 by a simple means.

B) Moreover, as the temperature adjusting means of the circulating bed material in the hot well 6, the circulating bed material cooled by the heat transfer in the heat exchange part 7 is supplied to the upper part in the hot well 6. A highly efficient and economical device can be realized without making a major design change to the boiler body or the external heat exchanger.

C) In the present invention, the temperature-controlled circulation bed material flows back to the dense bed area A below the combustor 1 through the hot recycle pipe 24, and the dense bed area A and the freeboard area B are combined and burned. -The temperature inside the combustor 1 that affects the removal of pollutants can be controlled.

D) Further, a part of the circulating bed material in the heat exchange part 7 of the external heat exchanger 2 is transferred to the upper part of the hot well 6 to adjust the temperature of the hot well 6, so that the apparatus is extremely simple. Instead, it is possible to simply carry out without the need to separately provide a cooling means such as a cooler.

[Brief description of drawings]

FIG. 1 is a sectional view of an external heat exchanger showing a first embodiment of a circulating fluidized bed boiler according to the present invention, and FIG. 2 is a temperature condition and SO ₂
FIG. 3 is a line graph showing the relationship with the concentration, FIG. 3 is a sectional view showing a second embodiment of the temperature adjusting device for the external heat exchanger, and FIG. 4 is a general explanatory view of the conventional circulating fluidized bed boiler. 2 ... External heat exchanger, 4 ... Cyclone, 5 ... Partition wall, 6 ... Hot well, 7 ... Heat exchange part, 20 ... Extraction pipe, 21 ... Fluidized air supply pipe, 22 ... Transmission Heat tube, 30,40 ……
Temperature control device, 31,41 …… Through pipe, 32,44 …… Supply pipe, 3
3,42 ... Suction port, 34,45 ... Discharge port, 35 ... Air pump, 36,46 ... Fixing member, 47 ... Driving air header, 4
8 …… Fluidizing air pipe, 49 …… Riser air pipe, R1 ……
High temperature circulating bed material, R2 ... Low temperature circulating bed material.

Continuation of the front page (72) Inventor Tamotsu Takebayashi 5-14-1 Wada, Tamano City, Okayama Prefecture (72) Inventor Tatsuo Mitsui 3-19-7 Tsukiko, Tamano City, Okayama Prefecture (56) Reference JP-A-61-186705 ( JP, A) JP 61-205710 (JP, A)

Claims (1)

[Claims] 1. A combustor 1 having a dense bed A in a lower part, a cyclone 4 communicating with an upper part of the combustor 1 and a lower part communicating with an external heat exchanger 2, a lower part of the external heat exchanger 2 and the In the circulating fluidized bed boiler communicating with the lower part of the combustor 1, the external heat exchanger 2 is formed by partitioning the heat exchange part 7 and the hot well 6 with a partition wall 5, and the lower part of the heat exchange part 7 A supply pipe 32 that connects the upper part on the hot well 6 side is provided, and a part of the circulating bed material at the lower part of the heat exchange section 7 is diverted to the upper part inside the hot well 6 via this supply pipe 32. A circulating fluidized bed boiler in which the temperature inside the hot well 6 is adjusted.