JPH0658166B2 - 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, which not only increases the installation cost of the plant but also complicates the control system of the entire plant, and particularly granulates 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 method, as shown in FIG. 3, the fine particles protruding from the fluidized bed 2 in combustion in the fluidized combustion boiler 1 are partially burned in the freeboard 3 and then contact-transferred. After passing through the heat section 4, the exhaust gas and the exhaust gas enter the first multi-cyclone 6 through the duct 5, where only those having a relatively large particle size are captured, and the unburned ash is sent into the fluidized bed 2 through the circulation path 12. The re-combustion 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. Since the unburnt ash is sent to the fluidized bed 2, it takes a long time for the temperature to rise, and the unburned ash is re-scattered from the fluidized bed 2 before it is sufficiently burned. Since it cools down to a large extent, a drastic 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 heat transfer section 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 connected to the above has an adiabatic structure, and particles containing unburned ash protruding from the fluidized bed reach the first multi-cyclone from the freeboard through the exhaust gas duct. Retain the unburned ash in the particles scattered from the fluidized bed by repeatedly holding the particles at a high temperature until the first multi-cyclone and returning the relatively large particles captured in the first multi-cyclone to the freeboard through a circulation path in a high temperature state. 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. In order to keep the temperature conditions suitable for the reaction, it may not be possible to effectively control the combustion by circulating unburned ash.

The object of the present invention is to pulverize a part of the supplied coal, to introduce the pulverized coal together with the supplied coal, and to cause the pulverized coal to immediately undergo a combustion reaction so that the temperature condition of the freeboard is always desulfurized,
An object of the present invention is to provide a method for reburning unburned components that can be applied to 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. It is kept at a high temperature until it enters the cyclone, and the particles with 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. By increasing the concentration of CaO, which is the desulfurizing agent, and unburned carbon, which is the reducing agent, in the freeboard, the unburned components in the particles scattered from the fluidized bed are recombusted and Pulverized coal obtained by crushing a part of the fed coal above the bed and having a particle size distribution adjusted beforehand by mixing pulverized coal that immediately burns in the freeboard is fed into the fluidized bed. The pulverized coal that has jumped out to the freeboard without reaching the temperature is burned with the circulating unburned ash, etc., and the temperature inside the freeboard is detected, and the amount of coal that pulverizes the supplied coal is controlled by the temperature detection signal. By doing so, the temperature of the freeboard section can be always 800-1,000 for desulfurization and denitration reaction.
° C. Controls maintained at a temperature of, at the same time non-combusted ash is a combustion by reducing agent and to be worked 800 ° C. or higher, the temperature range is desulfurizing agent CaO does not react with CaSO ₄ becomes re decomposes SOx To keep.

[Example] An example of the stomach of the method for reburning unburned components 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. And, at least, the peripheral wall of the freeboard 23 is made a heat insulating structure that does not absorb heat such as the furnace construction structure 27, and most of the contact heat transfer parts to the first multi-cyclone 25 downstream of the freeboard 23 are provided. The exhaust gas duct 24 lined with a heat insulating material 28 is directly connected to the upper end of the freeboard 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.

Then, the boiler plant for carrying out the present invention has a main system 35 of the supplied coal (for example, a maximum diameter of 32 mm) for the fluidized bed 22 connected to the lower part of the freeboard 23, and a bypass system 36 of the supplied coal.
A rotary valve 38 whose rotation speed is adjusted by a temperature detection signal of a temperature sensor 37 provided on the freeboard 23 is provided on the upstream side of the bypass system 36, and on the downstream side of the rotary valve 38. A crusher mechanism 39 is provided, and a part of the supplied coal is crushed by the crusher mechanism 39. Then, the downstream side of the bypass system 36 is connected to the main system 35, and the pulverized pulverized coal that can jump out into the freeboard 23 and immediately undergo a combustion reaction without reaching the inside of the fluidized bed 22 is the fluidized bed 22. It is designed such that it can be thrown into the freeboard 23 together with the supply coal having a maximum diameter of 32 mm which is supplied inside and burned here.

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, the particles containing unburned ash are freeboarded from the fluidized bed 23.
Scatter in the direction. 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 a heat insulating material 2.
Since 8 and 28 are lined, the temperature of scattered particles in exhaust gas does not drop.

Then, the particles captured by the first multi-cyclone 25 are kept at a high temperature of 800 to 1,000 ° C.
It is returned from 25 to the lower part of the freeboard 23 by gravity through the circulation path 26, and is burned again in the freeboard 23. 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 sent to the multi-cyclone 25 and captured is returned to the freeboard 23 again and is almost completely burned. Then, in addition to the actions of the furnace construction structure 27 and the heat insulation structure 28 described above, the freeboard 23 is kept at a high temperature to effectively perform desulfurization and denitration reactions, and the SOx and NOx emission values in the exhaust gas are greatly increased. Lower.

On the other hand, the pulverized coal mixed in the feed coal fed from the main system 35 is supplied to the freeboard 23 as it is without being intervened in the fluidized bed 22 and burned, and the pulverized coal is free. The board 23 immediately undergoes a combustion reaction to keep the temperature in the free board 23 at a high temperature of 800 to 1,000 ° C. This can be due to reduced load or freeboard
When a fuel with a low combustion ratio in 23 is used, the temperature of the freeboard 23 drops, and 800 to 800 required for desulfurization and denitration reactions
When the temperature condition of 1,000 ℃ cannot be obtained, keep the temperature of the freeboard 23 at 800 to 1,000 ℃ and keep it at 800 ℃ or higher where unburned ash can burn and work as a reducing agent. A certain CaO reacts with SOx to become CaSO ₄ and keeps the temperature within the range where it does not decompose again.

There are the following means for supplying pulverized coal to the freeboard 23.

(a) A part of the supplied coal is guided to a bypass system 36 connected to the main system 35 of the supplied coal, which is crushed by a crusher mechanism 39 provided in the bypass system 36, and the pulverized pulverized coal is again used as the above-mentioned main Supply and mix to the lower side of system 35 to change the particle size distribution of coal and mix the supplied coal as a freeboard as shown in the figure.
Below 23, that is, above the fluidized bed 22, coal with a large particle size is fed into the fluidized bed 22 and pulverized coal is fed into the freeboard 23 in a floating state without reaching the fluidized bed 22.

(b) The number of rotations of the rotary valve 38 provided in the bypass system 36 is adjusted by the temperature detection signal of the freeboard 23, the amount of the supplied coal to be crushed is changed to crush it, and the obtained pulverized coal is Input as in (a).

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. It can be retained, the desulfurization and denitration reactions can be promoted, the desulfurization agent can be saved, and the NOx emission value can be significantly suppressed.

(b) The fine coal, which is intentionally mixed in the supplied coal to be fed, is supplied to the freeboard and immediately undergoes a combustion reaction in the part, so that the temperature of the freeboard can be secured at 800 to 1,000 ° C., Not only desulfurization, but also denitration reaction is effectively performed.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a fluidized bed combustion boiler plant for carrying out the method of the present invention, and FIGS. 2 and 3 are schematic diagrams of a fluidized bed combustion boiler plant for carrying out a conventional unburned matter recombustion method, respectively. Is. 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 …… Main system, 36 …… Bypass system, 37 …… Temperature sensor, 38 …… Rotary valve, 39 …… Crusher mechanism.

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 to increase the concentration of desulfurizing agent CaO and reducing agent unburned carbon in the freeboard to reburn the unburned components in the particles scattered from the fluidized bed and above the fluidized bed. Was obtained by crushing a part of the feed coal, and the pulverized coal that immediately burns in the freeboard was mixed to feed the feed coal with a particle size distribution adjusted in advance to the fluidized bed. Burn the pulverized coal that has jumped to the freeboard without reaching the moving bed together with the circulating unburned ash, etc., and further detect the temperature in the freeboard, and finely pulverize the supplied coal by the temperature detection signal. By controlling, the temperature of the freeboard part is controlled and maintained at a temperature condition of 800 to 1,000 ° C where desulfurization and denitration reactions can be performed at all times.
At a temperature of 800 ° C or higher where unburned ash burns and can act as a reducing agent, 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.