JPH08166110A - Combustion ash recycling method for fluidized bed boiler - Google Patents

Abstract

PURPOSE: To achieve a lowering of the amount of discharged combustion ash by a method wherein combustion ash collected following a cyclone is kneaded with water or water and a cement based hardening agent so solidify and pellets material produced by the solid matter is introduced into a combustor to raise a desulfurization rate while improving the utilization rate of calcium yet to be used in the combustion ash. CONSTITUTION: Combustion ash trapped mainly by a bag filter following a cyclone of a fluidized bed boiler comprising a combustor 1 having a fluidized bed, the cyclone, an external heat exchanger and a convection heat transfer section, combustion ash is used and gathered to an ash silo 21. Then, the ash is introduced into a kneader 22 to be kneaded with water and a cement C as required. The product is taken out of the kneader 22, transferred to a compression molding machine 23 and pressurized properly to mold. The pellets thus obtained are introduced into a high temperature section in the combustor 1 with a conveyor 33 to recycle. This can enhance combustion efficiency of the fluidized bed boiler and moreover improve desulfurization rate, utilizing calcium yet to be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention promotes the reaction of limestone that is supplied to a fluidized bed formed in a combustor and circulated in a circulation path to increase its utilization rate and to reduce the amount of combustion ash discharged. The present invention relates to a combustion ash recycling method for a fluidized bed boiler that can be reduced.

[0002]

2. Description of the Related Art As a boiler capable of efficiently burning solid fuel while satisfying exhaust gas emission standards,
Fluidized bed (dense bed) formed of relatively large particles
A circulation type fluidized bed boiler, in which a circulation layer of fine particles such as ash and limestone is arranged on the top, is disclosed in, for example, JP-A-52-5708.
It is known for the invention of No. 5, etc.

As shown in FIG. 6, this circulation type fluidized bed boiler has a combustor 1 which forms a fluidized bed in the lower part, a cyclone 2 which separates particles from combustion gas discharged from the combustor 1 and the cyclone 2. It is composed of an external heat exchanger 3 that uses the heat of the particles separated in step 1 and a convection heat transfer portion 4 that uses the heat of the exhaust gas. A dense bed 5 made of gravel or the like having a size of 10 to 20 mm is formed in the combustor 1. In addition to the gravel and the like, the dense bed 5 is made of a solid material recirculated after being put in for the purpose of capturing sulfur. Partly crushed limestone and coal which is a solid fuel are supplied, and limestone powder, coal ash, carbon and the like are mixed in a fluidized state.

Primary air is introduced into the dense bed 5 through the primary air system 6 at the bottom, the dense bed 5 is fluidized, and coal is burned by the fed primary air, which is generated by this combustion. Solids such as carbon, ash, limestone, and small particles of destroyed gravel reach the cyclone 2 through the connecting pipe 7 together with the high temperature gas. Particles such as carbon, ash, and limestone are separated in the cyclone 2, and the separated solid is supplied to the external heat exchanger 3 via the conduit 9.

Then, the solid recovered by the heat recovery by the heat exchanger 10 built in the external heat exchanger 3 and cooled is L
It recirculates through the valves 11 and 15 into the dense bed 5 below the combustor 1. On the other hand, the hot gas whose solids have been separated by the cyclone 2 is
To enter the convection heat transfer section 4, heat the water supplied into the heat transfer tube 13 to generate steam, and be cooled,
The dust collector and the bag filter 14 collect and discharge the dust.

As described above, the combustion ash, which is also called "bug ash" collected by the bag filter 14 or the like, cannot be discarded as it is, so it is mixed with water to be humidified and used for landfilling. . On the other hand, in the case of a large-scale coal-fired boiler for thermal power generation, a large amount of combustion ash is generated, and the effective use of this combustion ash is required, and it is used as a raw material for cement.

However, in a fluidized bed boiler of a general industrial factory, there is often no cement factory nearby, and a large amount of combustion ash is mainly used for landfill, which causes a problem of high freight cost. was there. Therefore,
In recent years, various methods of effectively utilizing such combustion ash have been studied mainly by electric power companies, etc., and roadbed materials related to earth construction, sand formed from coal ash as an aggregate substitute for cement and aggregate, Although it has been put to practical use, that method also has a problem in terms of profitability.

By the way, in a circulating fluidized bed boiler, limestone is introduced to absorb sulfur dioxide (SO ₂ ) produced from the sulfur content of coal. Therefore, the combustion ash contains not only coal ash but also about 30% ash derived from limestone. Of this, the amount of calcium that had been captured by sulfurous acid gas was about one-third, and the other two-third of the amount of limestone was that only the surface absorbed sulfurous acid gas and solidified, but the inside was limestone ( CaCO ₃ ) remains unreacted in the form of being converted into quick lime (CaO) by heating in the furnace.

Conventionally, the entire calcium content including these unused and unreacted components has been directly treated or used for landfill. Further, the combustion ash collected by a bag filter or the like has a size of 100 μm or less and is easily scattered as a fine powder. Therefore, even if this is recycled to the combustor section of the fluidized bed boiler, it is too fine and causes contamination of the heat transfer surface of the convection section. I wasn't killed.

On the other hand, quick lime has a characteristic that when water is added, it produces calcium hydroxide (Ca (OH) ₂ ) and rapidly expands due to heat. Therefore, if water is added to the combustion ash itself of the fluidized bed boiler, the quick lime hidden inside the reacted calcium component forming the surface layer expands rapidly, and as active calcium component on the ash surface. It is exposed and can absorb sulfur dioxide gas.

Therefore, the inventors of the present invention added water to the above combustion ash to generate calcium hydroxide, and at the same time, a granulated material of a size that does not contaminate the heat transfer surface of the convection section with the finely powdered combustion ash. Various experiments were carried out focusing on the fact that the whole amount of the combustion ash can be suitably recycled to the fluidized bed boiler if it is molded into, and the unused lime content can be effectively utilized for desulfurization and utilized as a resource.

As a result, when forming the above-mentioned granulated product, a strong granulated product can be prepared by adding an appropriate amount of water and hardly adding a cement-based solidified product. It was found that the use of the obtained granules has a higher desulfurization rate than the case where the combustion ash is recycled as it is, and further the desulfurization rate is higher than the case of using the ordinary limestone itself, and thus the present invention was reached.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems associated with the treatment of combustion ash collected by a bag filter or the like in the conventional circulation type fluidized bed boiler. The purpose is to recycle combustion ash to increase its desulfurization rate, improve the utilization rate of unused calcium in the combustion ash, and reduce the amount of combustion ash discharged. To provide the ash recycling law.

[0014]

A method for recycling combustion ash of a fluidized bed boiler of the present invention for achieving the above object is a combustor having a fluidized bed, a cyclone for receiving and treating combustion gas of the combustor, and separation by a cyclone. In a circulation type fluidized bed boiler composed of an external heat exchanger for receiving and heat exchanging powder particles and a convection heat transfer section for receiving combustion gas that has not been processed by the cyclone, it is collected after the cyclone. Combustion ash, a step of kneading with water or water and a cement-based solidifying agent to solidify, a step of crushing the solid matter to form a granulated material, and a step of introducing the granulated material into the combustor It is characterized by consisting of and.

The proportion of water added to the combustion ash is 10
Water is added 30 to 60% to 0 g. When the lime component in the combustion ash is 10% or less, a cement-based solidifying agent is added in an amount of 5 to 10%. Further, as a method for molding the granulated material, it is preferable to employ a pan-type granulator or a compression extrusion molding machine. Then, after the granulated material is molded by using such a granulator, the strength of the granulated material and the desulfurization reactivity are increased by curing the granulated material at ambient temperature for about 1 to 5 days. After curing the granulated material, it is preferable to use a method in which the particle size is reduced to 1 mm or less and the average particle size is about 500 μm by a crusher and the particles are fed into the furnace.

[0016]

[Operation] By the above combustion ash recycling method, it is possible to effectively use the combustion ash collected by a bag filter etc. as circulating particles in a fluidized bed boiler, and to utilize the unused calcium content in the combustion ash. As a result, the amount of combustion ash discharged from the boiler can be reduced.

[0017]

[Examples] An example of a recycling system applied to the combustion ash recycling method of the present invention will be described below with reference to the drawings. In this embodiment, like the conventional circulation type fluidized bed boiler of FIG. 6, a cyclone 2 of a fluidized bed boiler including a combustor 1 having a fluidized bed, a cyclone 2, an external heat exchanger 3 and a convection heat transfer section 4 is provided. The combustion ash mainly collected by the bag filter 14 is used, collected in the ash silo 21 shown in the flowchart of FIG. 1, and then introduced into the kneading machine 22, where it is kneaded with water W and cement C as necessary. To do.

At this time, in this embodiment, the kneading machine 2
2 to 30 weight of water in 100
Then add about 5 to 10 cement as a binder,
Mix well to make a paste. Depending on the properties of the combustion ash, there are a method of kneading with only water W and a method of kneading with water W and a cement-based solidifying agent. Which method is adopted depends on the properties of the combustion ash and the granulating material. It is better to decide what to use for the fluidized bed boiler.

After kneading as described above, the kneader is taken out of the kneader 22 and transferred to the compression molding machine 23, where it is appropriately pressurized and molded. This molding has a diameter of 40 to 60 mm, preferably 5
The cylindrical molded body has a length of 0 mm and a length of 50 to 200 mm, preferably 100 mm. Then, the molded body is taken out by the conveyor 30, the molded body layer 31 is piled up, and after curing for 1 to 5 days, it is introduced into the crusher 25 by the conveyor 32 and crushed therein to have a particle diameter of about 0.5 mm. Produce particles.

The granulated material thus obtained is fed to the conveyor 33.
In the same combustor 1 as the fluidized bed boiler of the conventional example shown in FIG. 6, it is recycled by being introduced into a high temperature part of, for example, 400 ° C. or higher. The broken line X in FIG. 2 shows the relationship between the combustion efficiency and the amount of ash recycled when the granulated product obtained as described above is recycled to the fluidized bed boiler.

The relationship between the desulfurization rate and the ash recycling amount is shown by the broken line X in FIG. Further, the relationship between the sand supply amount and the coal ash content is shown by the broken line X in FIG. The solid line Y in each of FIGS. 2, 3 and 4 shows a conventional example in which combustion ash is recycled as it is without granulation. As can be understood by comparing these curves, according to the present invention. The granulation material is
It is superior to the conventional example in all of a) combustion efficiency, b) desulfurization rate, and c) sand supply amount.

Next, FIG. 5 shows a comparative diagram of the desulfurization performance, with a solid line Y for limestone having a particle size of 1 to 1.6 mm and a broken line X for the granulated product according to the present invention. Shown respectively. Judging from this FIG. 5, even if limestone and the granulated material according to the present invention are compared, the granulated material of the present invention has a higher desulfurization rate. As mentioned above,
Since the granulated material according to the present invention is not in the form of fine powder such as combustion ash called bag ash, it has a low scattering property. Therefore, the residence time in the combustion section of the fluidized bed boiler is long, the unburned components in the ash can be completely combusted, and the boiler efficiency can be increased, and the utilization rate of unused calcium content is improved, and the desulfurization rate can be improved. Can be improved.

Further, when the combustion ash is recycled as it is, the heat transfer surface is contaminated in the convection section. According to the present invention, the reacted granulation material is discharged from the external heat exchanger 10 to the outside of the system. Therefore, since there are few fine particles flowing into the convection section, such a defect does not occur.

[0024]

As described above, according to the combustion ash recycling method of the present invention, a combustor having a fluidized bed, a cyclone that receives and processes combustion gas of the combustor, and a granular material separated by the cyclone are used to generate heat. In a circulating fluidized bed boiler composed of an external heat exchanger to be exchanged and a convection heat transfer section for receiving combustion gas not treated by a cyclone,
Combustion ash collected after the cyclone is kneaded with water or water and a cement-based solidifying agent to be solidified, a step of crushing the solid matter to form a granulated material, and the granulated material Is introduced into the combustor.

Therefore, since the combustion ash of the fluidized bed boiler can be self-treated in the factory, the combustion efficiency of the fluidized bed boiler can be increased and the desulfurization rate can be improved by utilizing the unused calcium content. And the utilization rate of unused calcium can be improved. Further, since the combustion ash is used as a raw material of the desulfurization material and is used as a constituent material of the fluidized bed, the replenishment amount of circulating particles in the fluidized bed boiler can be reduced,
The amount of combustion ash discharged from the boiler is reduced, and the heat transfer surface of the convection section is not polluted. In addition, since the combustion ash can be reduced, the cost required for processing the combustion ash can be reduced and the boiler can be operated efficiently.

[Brief description of drawings]

FIG. 1 is a flowchart according to an embodiment of a recycling system applied to the combustion ash recycling method of the present invention.

FIG. 2 is a diagram showing the combustion efficiency when the granulated product according to the present invention is recycled to a fluidized bed boiler and when the combustion ash is recycled as it is.

FIG. 3 is a diagram showing a desulfurization rate when a granulated product according to the present invention is recycled to a fluidized bed boiler and when combustion ash is recycled as it is.

FIG. 4 is a diagram of the sand supply amount when the granulated product according to the present invention is recycled to the fluidized bed boiler and when the combustion ash is recycled as it is.

FIG. 5 is a comparative diagram of desulfurization performance between a granulated product according to the present invention and limestone.

FIG. 6 is a schematic side view of a conventional circulation type fluidized bed boiler.

[Explanation of symbols]

1 Combustor 2 Cyclone 3 External heat exchanger 4 Convection heat transfer part C Cement W Water

Claims (1)

[Claims] 1. A combustor having a fluidized bed, a cyclone that receives and processes combustion gas of the combustor, an external heat exchanger that receives heat from powder particles separated by the cyclone, and combustion gas that has not been processed by the cyclone. In a circulation type fluidized bed boiler configured by a convection heat transfer section, a step of kneading and solidifying the combustion ash collected after the cyclone with water or water and a cement-based solidifying agent, and this solid matter A method for recycling combustion ash of a fluidized bed boiler, which comprises a step of pulverizing the granules to form a granulated material and a step of introducing the granulated material into the combustor.