JPH0942614A - Recycle method of combustion ash in fluidized bed boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the consumption of limestone and the discharging amount of ash by a method wherein reactivated ash is obtained by the hydrating reaction of combustion ash, collected by a dust collector, through humidification as well as mixing and, thereafter, the combustion ash is dried to resupply it into a combustor. SOLUTION: Combustion ash A, collected principally by a dust collector 114, is supplied from an ash silo 21 into a mixer 22 through a combustion ash supplying port 27, then, water W, supplied from a line L3, is mixed into the ash A to humidify it. According to this method, the hydrating reaction of ash, which is caused by unreacted limestone existing in the combustion ash A, is effected and calcium hydroxide is produced whereby sudden heat generation and expansion are effected and activated calcium constituent is exposed on the surface thereof thereby producing reactivated ash. A temperature in the mixer 22 is increased to about 150 deg.C by the heat generating and expanding operations while the reactivated ash (a) is dried and powdered by the temperature increasing operation. The reactivated ash (a), dried and powdered in such a manner, is resupplied into a combustor 1 through a line L1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion ash recycling method for a circulation type fluidized bed boiler which has low NOx and is suitable as a relatively large-sized steam generator.

[0002]

2. Description of the Related Art As a boiler capable of efficiently burning solid fuel while satisfying exhaust gas emission standards, fine particles such as ash and limestone are formed on a fluidized bed (dense bed) formed of relatively large particles. A vertical type flow boiler in which a circulation layer is arranged is known, for example, from the invention of JP-A-52-57085.

As shown in FIG. 4, this circulation type fluidized bed boiler has a combustor 1 for forming a fluidized bed in the lower portion, a cyclone 2 for separating particles (solids) from combustion gas discharged from the combustor 1, and the like. It is composed of an external heat exchanger 3 that uses the heat of the solid separated by the cyclone 2 and a convection heat transfer unit 4 that uses the heat of the exhaust gas.

In the combustor 1, there are 10 to 2
A dense bed 5 made of about 0 mm of gravel is formed, and in addition to gravel, crushed limestone that becomes a part of the recycled solid material after being put in for the purpose of capturing sulfur, Coal, which is a fixed fuel, is 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 and cooled by the heat exchanger 10 built in the external heat exchanger 3 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,
It is adapted to be collected and discharged by a dust collector 14 such as a dust collector or a bag filter.

As described above, the combustion ash, which is also referred to as "bug ash" collected by the dust collector 14 or the like, usually has a very small particle size of 20 to 30 μm, and therefore easily scatters and remains as it is. Since it cannot be discarded, it is used as landfill after mixing with water to make it humid. On the other hand, in the case of large-scale coal-fired boilers for thermal power generation, a large amount of combustion ash is generated, and the effective use of this combustion ash is required, and most of them are 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 treatment 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.

On the other hand, in the circulation type fluidized bed boiler,
Limestone is added to absorb sulfur dioxide (SO ₂ ) generated from the sulfur content of coal. Therefore, the combustion ash contains not only coal ash but also about 30% ash derived from limestone. Of the sulfurous acid gas, the amount of reacted calcium is about one-third, and the other two-third remains unreacted. Therefore, a method has been implemented in which the combustion ash collected by the dust collector is re-supplied into the combustor to obtain high desulfurization performance with a small amount of limestone supplied.

[0010]

However, it is not possible to sufficiently improve the performance by the method of simply resupplying the combustion ash collected by the dust collector into the combustor as described above. That is, the ash derived from the unreacted limestone described above reacts with sulfurous acid gas (SO ₂ ) and its surface is CaSO ₄
It is covered with, is inactivated, and the inside is quick lime (Ca
Since it is converted into O), even if the ash whose surface is inactive is re-supplied into the combustor as it is, sufficient performance cannot be improved.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and includes a combustor having a fluidized bed, and a solid combusted by receiving combustion gas of the combustor. A cyclone to be separated, an external heat exchanger for receiving the solid and exchanging heat, a convection heat transfer section for introducing the combustion gas in which the solid is separated by the cyclone, and a collector arranged behind the convection heat transfer section. In a circulation type fluidized bed boiler further comprising a dust device, the first step of humidifying and mixing and stirring the combustion ash collected by the dust collecting device to cause a hydration reaction to reactivate ash, and It is intended to provide a combustion ash recycling method for a fluidized bed boiler, which comprises a second step of drying the activated ash and a third step of re-supplying the dried reactivated ash to the combustor.

When the collected combustion ash is humidified and mixed and stirred, preferably 10 to 40 g per 100 g of combustion ash.
Water is added. According to the method for recycling the combustion ash of the fluidized bed boiler, water is added to the combustion ash collected by the dust collector, that is, water permeates to the inside through the reacted calcium components forming the surface when humidified, Hydration reaction with the quicklime inside produces calcium hydroxide (Ca (OH) ₂ ), which rapidly expands exothermically and is exposed as active calcium on the surface to become reactivated ash.

In this case, since water is added and mixed and stirred at the same time, a small amount of water such as 10 to 40 is added to 100 g of combustion ash.
A homogeneous hydration reaction is carried out with g of water. This reactivated ash is dried in the next step. Actually, it is heated and dried at, for example, about 150 ° C. by its own heat generation or, if necessary, by indirect heating by heat from another heating source. Then, the reactivated ash thus dried is resupplied into the combustor.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a recycling system required for 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 described with reference to FIG. 6, a fluidized bed including a combustor 1 having a fluidized bed, a cyclone 2, an external heat exchanger 3 and a convection heat transfer section 4. The combustion ash A mainly collected by the dust collector 14 after the cyclone 2 of the boiler is used.

Then, after the combustion ash A is collected in the ash silo 21 shown in the flow chart of FIG. 1, it is introduced into the mixing stirrer 22, where it is humidified and mixed to be reactivated ash, and then dried in the same apparatus. Are re-supplied to the combustor ₁ from the line L ₁ . More specifically, a hollow shaft 24 having a stirring blade 23 is provided in the mixing stirrer 22.
4 is rotated by a motor 25 and the hollow shaft 2
4, the heating steam S is supplied from a line L ₂ having a control valve 26.

A line L ₃ for supplying water W is arranged on the combustion ash supply port 27 side of the mixing and stirring machine 22. On the other hand, a temperature detector 29 is provided on the line L ₁ for supplying reactivated ash connected to the combustion ash outlet 28, and the control valve 26 is controlled by the signal V of the temperature detector 29. Has become. Also, 30 is the line L ₃
The line L ₄ is a vapor extraction line communicating with the hollow shaft 24, and the line L ₅ is a vapor extraction line communicating with the mixing agitator 22 and having a suction device 32.

In the above structure, the combustion ash is ash silo 21.
Is supplied to the mixing agitator 22 through the combustion ash supply port 27, and is mixed with the water W supplied from the line L ₃ to be humidified. The water W is preferably supplied from several locations (two locations in the illustrated example) in the axial direction of the mixing stirrer 22. And this water supply rate is preferably 1
It is adjusted by the adjusting valve 30 to be 10 to 40 g with respect to 00 g.

That is, when a large amount of water W is added, it becomes a slurry state, and solidified matter in this slurry sticks to the line L ₁ to cause a trouble, and thermal loss in the combustor 1 becomes large. Therefore, it is preferable to recycle the ash as a dried powder, but the amount of heat for this drying is required. Therefore, it is preferable to supply the amount of water as described above. The combustion ash A thus supplied into the mixing and stirring machine 22 is humidified and also stirred by the motor 25 to be uniformly humidified.

The ash derived from unreacted limestone present in the combustion ash undergoes a hydration reaction to produce calcium hydroxide, which rapidly expands due to heat generation and is exposed on the surface as an active calcium component and regenerated. It becomes activated ash. Quick lime (Ca) due to unreacted ash derived from limestone present in this combustion ash
The conversion rate from O) to calcium hydroxide (Ca (OH) ₂ ) by hydration is about 70% in 20 minutes as shown in FIG.
However, since about 80% of the reaction is completed in 40 minutes, a time of about 20 to 40 minutes is set for humidification and mixing and stirring in the mixing and stirring machine 22.

Due to this exothermic expansion effect, the temperature inside the mixing and stirring machine 22 rises to about 150 ° C., and the reactivating ash a is dried into powder by this temperature increasing effect. At this time, the temperature inside the mixing and stirring machine 22 is detected by the temperature detector 29. When the temperature is lower than a predetermined temperature, the control valve 26 is controlled to supply the heating steam S from the line L ₂ into the hollow shaft 24 to indirectly heat the same. Thus, the inside of the mixing stirrer 22 is maintained at a predetermined temperature.

The dried and powdered reactivated ash a is re-supplied to the combustor 1 through the line L _1. The reactivated ash a has calcium hydroxide exposed on its surface. Therefore, the sulfur dioxide gas generated from the sulfur content of coal is easily absorbed, and as a result, the desulfurization performance is improved. FIG. 3 shows the amount of recycled combustion ash on the horizontal axis and the desulfurization rate on the vertical axis, showing the conventional simple combustion ash recycling and the combustion ash recycling according to the present invention.

[0022]

As is apparent from the above description, according to the combustion ash recycling method of the fluidized bed boiler according to the present invention, the unreacted portion of the ash derived from limestone present in the combustion ash is subjected to the hydration reaction. While converting to calcium hydroxide,
Since the reactivated ash exposed on the surface was re-supplied into the combustor, not only the desulfurization performance could be improved, but also it was supplied to the re-supply system after it was dried, so that it might stick to the pipe. There is an effect that it will not be lost.

[Brief description of drawings]

FIG. 1 is a flowchart according to an embodiment of a recycling system required for a combustion ash resile method for a fluidized bed boiler according to the present invention.

FIG. 2 is a relationship diagram of a mixing and stirring time and a conversion rate in a hydrogenation reaction.

FIG. 3 is a relationship diagram of a combustion ash recycle amount and a desulfurization rate.

FIG. 4 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 5 Dens bed 6 Primary air system 7 Communication pipe 9, 12 Communication pipe 10 Heat exchanger 11, 15 L valve 13 Heat transfer pipe 14 Dust collector 21 Ash silo 22 Mixing Stirrer 23 Stirring blade 24 Hollow shaft 25 Motor 26 Control valve 27 Combustion ash supply port 28 Combustion ash outlet 29 Temperature detector 30 Adjustment valve 31 Air blower

Claims (2)

[Claims] 1. A combustor having a fluidized bed, a cyclone that receives combustion gas from the combustor to separate solids, an external heat exchanger that exchanges heat by receiving the solids, and a combustion in which solids are separated by the cyclone. In a circulation type fluidized bed boiler consisting of a convection heat transfer part for introducing gas and a dust collector arranged behind the convection heat transfer part, the combustion ash collected by the dust collector is humidified and mixed. A first step of stirring and hydrating to make reactivated ash;
A combustion ash recycling method for a fluidized bed boiler, comprising a second step of drying the reactivated ash and a third step of resupplying the dried reactivated ash to the combustor. 2. The method for recycling combustion ash of a fluidized bed boiler according to claim 1, wherein 10 to 40 g of water is added to 100 g of combustion ash to humidify, mix and stir to carry out a hydration reaction.