JPH0663613B2 - Reburning method for unburned components in fluidized bed combustion boiler - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for reburning unburned components of a fluidized bed combustion boiler.

[Prior art and its problems] In a conventional fluidized bed combustion boiler, unburned ash re-combustion method in which an unburned content combustor is separately installed and unburned ash reburning method for increasing overall combustion efficiency. There is an unburnt ash recirculation system that returns the fluid to the fluidized bed.

In the former unburnt ash reburning method, as shown in FIG. 2, the fine particles that have flown out of the fluidized bed 2 in the fluidized bed combustion boiler 1 are partially burned by the freeboard 3 and then contact heat transfer is performed. After passing through the section 4, the exhaust gas and the exhaust gas pass through the duct 5 and enter the first multi-cyclone 6, where only those having a relatively large particle size are trapped and reburned in the unburned ash reburning furnace 7. The exhaust gas from the unburned ash reburning furnace 7 enters the second multi-cyclone 8, where as many particles as possible are captured, and the exhaust gas from the second multi-cyclone 8 is
After entering the air heater 9 together with the exhaust gas from the first multi-cyclone 6, the combustion air supplied to the fluidized bed combustion boiler 1 and the unburned ash combustion furnace 7 is heated to lower the temperature and then the dust collector. After entering 10 and being dust-removed, it is diffused into the atmosphere through the chimney 11.

However, this unburned ash combustion method requires the unburned ash combustion furnace 7, the facility cost of the plant is not high, the control system of the entire plant is complicated, and especially granulation is performed to suppress the NOx emission value. When doing so, the supply of unburned ash to the unburned ash reburning furnace 7 is extremely complicated.

Further, in the latter unburned matter recirculation system, as shown in FIG. 3, after part of the fine particles protruding from the fluidized bed 2 in the fluidized bed combustion boiler 1 are combusted in the freeboard 3,
First through the contact heat transfer section 4 and the exhaust gas through the duct 5
It enters the multi-cyclone 6, where only those having a relatively large particle size are captured, and this unburned ash is repeatedly burned until it is fed into the fluidized bed 2 through the circulation path 12 and is repeated. Further, the exhaust gas from the first multi-cyclone 6 enters the air heater 9, where the combustion air sent to the fluidized bed combustion boiler 1 is heated and the temperature thereof is lowered, and then the dust collector 10 is entered to remove dust. After that, it is released into the atmosphere from the chimney 11.

In this unburned matter recirculation method, unburned ash is absorbed by the contact heat transfer section 4 and is heated to a temperature of 300 to 360 ° C or less, and further, the temperature is lowered to about 150 ° C or less with an ash cooler for easy handling. Even if the unburnt ash is sent into the fluidized bed 2, it takes time to rise in temperature, and it scatters again from the fluidized bed 2 before it burns sufficiently. Since it cools down, a significant improvement in combustion efficiency cannot be expected. In addition, there is a problem in that the other fluid medium in the fluidized bed 2 is cooled, the combustion efficiency in the fluidized bed 2 is lowered, and the desulfurization and denitration reaction efficiency is not sufficiently increased.

[Technical Background of the Invention] In order to solve the problems of the prior art, the inventors of the present invention can remove the unburned component from the first multi-cyclone while maintaining the temperature state without lowering the temperature. It circulates in the freeboard and burns the unburned matter almost completely in this freeboard part, greatly improving the combustion efficiency in the fluidized bed combustion boiler, and promoting desulfurization and denitration reaction in the freeboard part, and desulfurizing agent. In order to reduce the required amount of NOx and to control the generation of NOx, the contact electric heating part up to the first multi-cyclone of the fluidized bed combustion boiler is almost eliminated, and the freeboard peripheral wall, exhaust gas duct, and this Most of the first multi-cyclone in the series has a heat insulating structure, and the particles containing unburned ash that have jumped out of the fluidized bed reach the first multi-cyclone from the freeboard through the exhaust gas duct. To a freeboard through a circulation path while keeping the high-temperature particles up to a high temperature, captured by the first multi-cyclone, and returning them to the freeboard through a circulation path repeatedly to reburn the unburned ash in the particles scattered from the fluidized bed. As a means for controlling the temperature in the freeboard to a temperature (800 to 1,000 ° C) suitable for desulfurization and denitration reactions, Japanese Patent Application No. 59-174262 has been proposed.
By this means, when the temperature in the freeboard exceeds 1,000 ° C, not only the desulfurization reaction is suppressed, but also some CaSO ₄ is thermally decomposed and returns to CaO + SO ₂ , and NO is not reduced by C. Therefore, there is a problem that SOx and NOx are frequently generated.

An object of the present invention is to provide a method capable of controlling the temperature condition of the freeboard to a temperature condition that does not interfere with the desulfurization reaction and the denitration reaction.

[Means for Solving the Problems] According to the configuration of the present invention for solving the problems of the prior art, the contact heat transfer section from the freeboard section to the first multi-cyclone of the fluidized bed combustion boiler is almost eliminated, and the freeboard peripheral wall is eliminated. The exhaust gas duct and most of the first multi-cyclone connected to the exhaust gas duct have a heat insulating structure so that particles including unburned ash scattered from the fluidized bed are passed from the freeboard to the first multi-cycle through the exhaust gas duct. Keeping the temperature high until it enters the cyclone, and returning the particles with a relatively large particle size captured by the first multi-cyclone to the lower part of the freeboard through a circulation path having an adiabatic structure at high temperature repeatedly. The concentration of CaO, which is a desulfurizing agent, and unburned carbon, which is a reducing agent, in the freeboard is increased to reburn the unburned components in the particles scattered from the fluidized bed, and Cooling some or all of the high temperature unburned ash returned from the cyclone to the freeboard through the circulation path, suppressing the combustion reaction in the freeboard, and further detecting the temperature in the freeboard, When the temperature reaches the desulfurization reaction and the temperature detection value that reaches the temperature that interferes with the denitration reaction, the cooling means is operated to cool part or all of the circulating high-temperature unburned ash to desulfurize the upper limit temperature of the freeboard. Control and maintain the temperature condition of 800 to 1,000 ℃, which does not disturb the denitration reaction, and keep the temperature at 800 to 1,000 ℃ or higher where unburned ash burns and can act as a reducing agent, and at the same time, CaO, which is a desulfurizing agent, reacts with SOx and CaSO _{It is 4} and is kept at a temperature in the range where it is not redissolved.

[Example] An example of the unburned portion re-combustion method in the fluidized bed combustion boiler of the present invention will be described. FIG. 1 schematically shows the structure of a fluidized bed combustion boiler plant for carrying out the present invention. First, the configuration of a fluidized bed combustion boiler plant for carrying out the method of the present invention will be described with reference to this figure.

Reference numeral 21 is a fluidized bed combustion boiler having a fluidized bed 22, a freeboard 23 and the like. A first multi-cyclone 25 is connected to an upper portion of the freeboard 23 via an exhaust gas duct 24, and a particle discharge port provided at a lower portion of the first multi-cyclone 25 and the freeboard 23 are provided with an inclined circulation path. Connect at 26. At least the peripheral wall of the freeboard 23 has a heat insulating structure that does not absorb heat, such as a furnace construction structure, and the contact heat transfer section to the first multi-cyclone 25 continuing to the lower end side of the freeboard 23 is almost eliminated. , Freeboard
The exhaust gas duct 24 having a heat insulating material 28 lined therein is directly connected to the upper end portion of 23. The heat insulating material 28 is lined on the inner surface of the first multi-cyclone 25 connected to the exhaust gas duct 24 so as not to absorb heat, and the circulation path 26 has the heat insulating structure as described above.

Further, a gas cooler 31 such as an evaporator or a economizer is provided as a contact heat transfer part in the middle of the exhaust gas duct 30 from the first multi-cyclone 25 to the second multi-cyclone 29. In the figure, 32 is an air heater, 33 is a dust collector, and 34 is a chimney.

In the plant shown in FIG. 1 for carrying out the present invention, a bypass passage 35 connected to the upstream side and the downstream side of the circulation passage 26 is provided in the circulation passage 26, and a cooler 36 is provided in the middle of the bypass passage 35. Is provided to cause heat exchange in the cooler 36, and the high temperature unburned ash is cooled while passing through the partial bypass flow path 35, and the cooled unburned ash is passed through the circulation path 26 and is the main stream of high temperature unburned ash. It is mixed in and returned to the freeboard 23, where it is burned again.

Further, in the plant shown in FIG. 2, a part of the circulation path 26 is surrounded by a cooler 37, and a part of the high temperature unburned ash passing through the circulation path 26 is cooled and returned to the freeboard 23, where it is recycled. It is designed to burn.

Also, although not particularly shown, each cooler of the above plant
It is desirable that 36 and 37 detect the internal temperature of the freeboard 23 and be controlled by this temperature detection signal. Further, as another means, although not particularly shown, a water jet nozzle is provided on the freeboard 23, and water is jetted into the freeboard 23 from the jet nozzle to supply unburned water to the freeboard 23. There is also a means of temporarily reducing the combustion of ash and controlling the combustion temperature.

Based on the above-mentioned boiler plant, a method for reburning unburned components of a fluidized bed combustion boiler according to the present invention will be described.

When the fluidized bed combustion boiler 21 is operated and the fluidized bed combustion is started, fine particles containing unburned ash are scattered from the fluidized bed 22 toward the freeboard 23. Since the peripheral wall of the freeboard 23 has the furnace construction structure 27, a part of the scattered fine particles is burned in the freeboard 23 without a temperature drop, and then passes through the exhaust gas duct 24 together with the exhaust gas to the first multi-cyclone 25. Incoming, where only particles of relatively large size are captured. At this time, the fluidized bed combustion boiler 21 has no or almost no contact heat transfer section connected to the freeboard 23, and the exhaust gas duct 24 and the first multi-cyclone 25 have heat insulating materials 28,2.
Since 8 is lined, the temperature of scattered particles in exhaust gas does not drop.

Then, the particles captured up to the first multi-cyclone 25 are returned from the first multi-cyclone 25 by gravity to the lower part of the freeboard 23 through the circulation path 26 while maintaining a high temperature of 800 to 1,000 ° C. Is burned again. After that, this process is repeated, and the unburned ash that has jumped out of the fluidized bed 22 is burned in the freeboard 23, and the unburned ash that has been sent to the first multi-cyclone 25 and captured is returned to the freeboard 23. It is returned and burned almost completely. In addition to the above-mentioned actions by the furnace construction 27 and the heat insulation structure 28, the freeboard 23 is kept at a high temperature to effectively perform the desulfurization and denitration reactions, and the SOx and NOx emission values in the exhaust gas are drastically reduced. Let

However, when the temperature inside the freeboard 23 is abnormal, more specifically, when the temperature rises above 1,000 ° C, the CaS that has undergone the desulfurization reaction has turned into
O ₄ was thermally decomposed and returned to the state of CaO + SO ₂ before desulfurization,
Further, the reaction of reducing NO with C is stopped, and SOx and NOx are increased.

Therefore, according to the present invention, the combustion temperature in the freeboard 23 is 1,00.
When it is detected that the temperature exceeds 0 ° C, or when the temperature rises to around 1,000 ° C, or when the SOx and NOx values exceed the reference values, the high temperature unreacted from the first multi-cyclone 25 into the circulation path 26 A part of the burned ash is guided to the bypass flow path 35, and the guided high temperature unburned ash is cooled by exchanging heat with the cooler 36 part,
This cooled unburned ash is mixed again with the mainstream high temperature unburned ash passing through the circulation path 26, and this is returned to the freeboard 23 and reburned. At this time, since the unburned ash is partly low in temperature, the combustion in the freeboard 23 is reduced, the temperature of the freeboard 23 is controlled in the range of 800 to 1,000 ° C., and the desulfurization and denitration reactions are effectively performed.

In addition, as another means, as shown in FIG.
Is passed through the cooler 37, heat of the high temperature unburned ash passing through the circulation path 26 is removed, and the high temperature unburned ash is cooled.
Is controlled in the range of ~ 1000 ° C., at the same time non-combusted ash is a temperature above 800 ° C. which may serve as a combustion reducing agent, retaining the temperature range is desulfurizing agent CaO does not react with CaSO ₄ becomes re decomposes SOx Be drunk

In addition, as another means, combustion is reduced by supplying water in the freeboard 23 in the form of spray, and the temperature is reduced to 800
Control to ~ 1,000 ℃.

Further, the exhaust gas containing the remaining fine particles captured by the first multi-cyclone 25 having a large particle size is discharged from the first multi-cyclone 25 and then is fed to a gas cooler (evaporator, economizer, etc.) 31. After cooling, it enters the second multi-cyclone 29, where it traps as many particles as possible. Then, the exhaust gas discharged from the second multi-cyclone 29 enters the air heater 32, where it is heat-exchanged with the combustion air to be fed to the wind box of the fluidized bed combustion boiler 21, and the exhaust gas having a lowered temperature is collected. After entering the container 33 and being dedusted, it is emitted from the chimney 24 into the atmosphere.

[Effects of the Invention] According to the configuration of the present invention as described above, the following effects can be obtained.

(A) By adding a system to the freeboard part, which collects unburned ash scattered from the fluidized bed at high temperature and circulates it to the freeboard, effective combustion of unburned ash is achieved and the freeboard is heated to a high temperature. Hold, the desulfurization and denitration reactions are promoted,
The NOx generation value can be significantly suppressed, and the desulfurizing agent can be saved. .

(B) Cooling some or all of the high temperature unburned ash when the amount of high temperature unburned ash that is circulated and reburned increases and is reburned in the freeboard and the temperature rises abnormally. Thus, the combustion of the freeboard can be reduced, the temperature can be controlled to a temperature suitable for the desulfurization and denitration reactions, and the desulfurization and denitration reactions can be greatly promoted.

[Brief description of drawings]

1 and 2 are schematic views of a fluidized bed combustion boiler plant for carrying out the method of the present invention, and FIGS. 3 and 4 are
It is a schematic diagram of the fluidized bed combustion boiler plant which implements the conventional unburned-contents recombustion method, respectively. 21 …… Fluidized bed combustion boiler, 22 …… Fluidized bed, 23 …… Freeboard, 24 …… Exhaust gas duct, 25 …… First multi-cyclone, 26 …… Circulation path, 27 …… Furnace construction structure, 28 …… Insulation, 35 ……
Bypass channel, 36, 37 ... Cooler.

Claims (1)

[Claims] 1. A contact heat transfer section from a freeboard section to a first multi-cyclone of a fluidized bed combustion boiler is almost eliminated.
The surrounding wall of the freeboard, the exhaust gas duct, and most of the first multi-cyclone connected to the freeboard are made into an insulating structure, and particles containing unburned ash scattered from the fluidized bed are passed from the freeboard through the exhaust gas duct. The temperature is kept high until it enters the first multi-cyclone, and the particles having a relatively large particle size captured by the first multi-cyclone are returned to the lower part of the freeboard through a circulation path having an adiabatic structure in a high temperature state. Repeatedly, increase the concentration of desulfurizing agent CaO and reducing agent unburned carbon in the freeboard,
Reburns the unburned matter in the particles scattered from the fluidized bed, and cools some or all of the high temperature unburned ash returned from the first multi-cyclone to the freeboard through the circulation path to free it. Suppresses the burning reaction on the board,
Detects the temperature inside the freeboard, and this temperature is the desulfurization reaction,
With the temperature detection value that reaches the temperature that prevents the denitration reaction, the cooling means is operated to cool part or all of the circulating high temperature unburned ash to the upper limit temperature of the freeboard, which does not interfere with the desulfurization and denitration reaction 800 The temperature is controlled to be maintained at ~ 1,000 ℃, and the temperature is set at 800 ~ 1,000 ℃ or higher at which unburned ash burns and can act as a reducing agent. At the same time, CaO, which is a desulfurizing agent, reacts with SOx and CaSO ₄
A method for recombusting unburned components in a fluidized bed combustion boiler, characterized in that the temperature is maintained within a range that does not cause re-decomposition.