JP2019070508A - Method for operating coal combustion facility - Google Patents

Abstract

To provide a method for operating a coal combustion facility excellent in quality of gypsum collected by a wet desulfurizer.SOLUTION: A method for operating a coal combustion facility is directed to operate a coal combustion facility comprising: a furnace configured to combust fuel coal; an electric precipitator configured to remove particles from exhaust gas discharged from the furnace; and a wet desulfurizer configured to remove a sulfur oxide from the exhaust gas from which the particles are removed by the electric precipitator, with use of the limestone-gypsum method. For coal used as the fuel coal, a content of ash having a grain diameter of 1.0 μm in ash obtained with heating and ashing is equal to or more than 0.20 mass% with respect to the fuel coal.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method of operating a coal combustion facility.

  For example, combustion equipment using coal as fuel, such as thermal power generation equipment having a coal boiler, generally uses an electric precipitator for removing fly ash which is fine particles (dust) in exhaust gas, and a desulfurization device for removing sulfur oxides in exhaust gas And

As a desulfurization apparatus, the sulfur oxide (SO ₂ ) in the exhaust gas is reacted with lime (CaCO ₃ ) by bringing the exhaust gas into contact with a slurry (absorbent liquid) in which limestone is dispersed in water, and the sulfur content is gypsum (CaSO ₃ ). wet desulfurization system is widely used by ₄ · 2H 2 _O) limestone gypsum method to recover as. When using such a wet desulfurization device, operating costs can be reduced by selling the gypsum recovered in the desulfurization device.

  However, since particulates can not be completely removed in the electrostatic precipitator, some of the particulates that have passed through the electrostatic precipitator mix in the gypsum recovered by the wet desulfurization apparatus. When the mixing amount of such fine particles is increased, the quality of gypsum is reduced, and thus the value of gypsum is reduced.

  For example, in JP-A-11-179147, a slurry containing a large amount of dust, for example, by a simple settler (gravity sedimentation separator), a magnetic dust separator, a centrifuge, etc. A flue gas treatment method is proposed to obtain a slurry with high gypsum purity by separating

Japanese Patent Application Laid-Open No. 11-179147

  The method described in the above publication is costly in separating a dust-rich slurry, and is also costly in treating a slurry containing a large amount of separated dust.

  In view of the above problems, the present invention has an object to provide a method of operating a coal combustion facility which is excellent in the quality of gypsum recovered by a wet desulfurization apparatus.

  The present inventors particularly focused on unburned carbon particles that color the gypsum and greatly reduce the quality of the coal ash collected by the electrostatic precipitator of the coal combustion facility and the gypsum collected by the wet desulfurization apparatus. I observed it in detail. The shape of the unburned carbon particles was in the form of a hollow particle having a particle size distribution having a peak at about 70 μm to 90 μm, and the outer shell thereof was porous with fine pores.

  The present inventors have found that the unburned carbon particles contain fine particulate ash in the outer shell, and the unburned carbon particles in the coal ash collected by the electrostatic precipitator are in the outer shell. I got the impression that it contained more ash. For this reason, the present inventors multilaterally examine the influence of the ash content on the removal rate in the electrostatic precipitator, and the larger the ash content of the unburned carbon particles, the higher the removal rate in the electrostatic precipitator, and the wet desulfurization device It was confirmed that the quality of the recovered gypsum was high.

  As a result of further researches, the inventor found that there is a correlation between the ash content in the unburned carbon particles and the particle size distribution of the ash obtained by heat-ashing fuel coal. Completed the invention.

  The operating method of coal combustion equipment according to the present invention made to solve the above problems comprises: a furnace for burning fuel coal, an electrostatic precipitator for removing particulates from exhaust gas discharged from the furnace, and particulates with this electrostatic precipitator And a wet desulfurizing apparatus for removing sulfur oxides from the exhaust gas from the waste gas by the limestone gypsum method, wherein the particle size of 1.0 μm in the ash content obtained by heat-ashing as the fuel coal. It is characterized by using coal whose ash content below is 0.20 mass% or more of the above-mentioned fuel coal.

  The operation method of the coal combustion facility is by using, as fuel coal, coal having an ash content with a particle diameter of 1.0 μm or less in the ash obtained by heat ashing and having a content of 0.20 mass% or more of the fuel coal As a result of being able to improve the removal rate of unburned carbon in the electrostatic precipitator, the unburned carbon content in the gypsum recovered by the wet desulfurization apparatus is small, and gypsum excellent in quality can be obtained.

  In the method of operating the coal combustion facility, coal mixed with coal to satisfy the ash content may be used as the fuel coal. According to this method, the fuel can be easily obtained, so that the increase in fuel cost can be suppressed.

  In the method of operating the coal combustion facility, it is preferable to use bituminous coal as the fuel coal. According to this method, high-quality gypsum can be obtained as a by-product while suppressing the unit cost of heat.

  In addition, "heat ashing" is performed according to the procedure of the heat ashing in "the ash content determination method" of JIS-M8812 (2006). Also, "particle size" means the particle size measured by laser diffraction scattering method. In addition, “ash content” is a value on an air-dry basis. Moreover, "bituminous coal" is a carbon type prescribed | regulated to JIS-M1002 (1978).

  As mentioned above, the operation method of the coal combustion equipment concerning the present invention is excellent in the quality of the plaster collected with a wet desulfurization device.

It is a schematic diagram which shows the structure of the coal combustion installation which can be used for this invention. It is a graph which shows the particle size distribution of the ash content after heat-ashing of several fuel coal. It is a graph which shows the relationship between the ash content with a particle size of 1.0 micrometer or less in the ash obtained by heat-ashing fuel coal, and the unburned carbon content in the gypsum collect | recovered.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

[Coal combustion equipment]
FIG. 1 shows a schematic configuration of a coal combustion facility used in the present invention. The coal combustion facility includes a furnace 1 for burning fuel coal, an electric precipitator 2 for removing particulates from the exhaust gas discharged from the furnace 1, and sulfur oxide by the limestone gypsum method from the exhaust gas from which particulates are removed by the electrostatic precipitator. And a wet desulfurization device 3 for removing the In addition, the coal combustion facility further includes a chimney 4 that finally releases the exhaust gas to the atmosphere.

<Fuel furnace>
The furnace 1 is not particularly limited as long as it burns fuel coal, for example, a boiler, a heating furnace, etc., but a scale capable of recovering a reusable amount of gypsum, specifically 10,000 kW or more, preferably 100,000 It is economically reasonable that the furnace has a calorific value of kW or more.

  Examples of the combustion method of the furnace 1 include a fixed bed combustion method, a fluidized bed (bubble fluidized bed or circulating fluidized bed) combustion method, a spouted bed (pulverized coal) combustion method and the like.

<Electric dust collector>
The electrostatic precipitator 2 is a device that charges fine particles (fly ash) in the exhaust gas by corona discharge from the discharge electrode, attracts the charged fine particles to the electrode (collection electrode), separates from the exhaust gas and collects it.

  The discharge method of the electrostatic precipitator 2 may be direct current discharge or pulse discharge. In addition, the electrostatic precipitator may be a dry electrostatic precipitator that cleans off particulates adhering to the dust collection electrode by vibration, or may be a wet electrostatic precipitator that flushes fine particles adhering to the dust collection pole with water.

<Wet desulfurization system>
The wet desulfurization apparatus 3 causes a slurry (absorbent liquid) in which limestone is dispersed in water to be brought into contact with exhaust gas, thereby causing lime to react with sulfur oxides to absorb sulfur oxides and recover gypsum as a by-product It is an apparatus.

  As the wet desulfurization apparatus 3, a spray-type apparatus for spraying the absorbing liquid to the exhaust gas, a grid-type apparatus for promoting gas-liquid contact by arranging a grid-like filler in the flow path of the exhaust gas, and bubbling the exhaust gas into the absorbing liquid It is possible to use an apparatus for

[how to drive]
One embodiment of a method of operating a coal combustion facility according to the present invention comprises, as fuel coal burning in the furnace 1, coal having a relatively large ash content with a particle size of 1.0 μm or less in the ash obtained by heat ashing. Use.

  As the reason for increasing the ash content with a particle size of 1.0 μm or less in the ash content obtained by heat ashing, the small diameter ash content is included in the unburned carbon particles in the exhaust gas produced when the fuel coal is burned in the furnace 1 This is because the chargeability of the unburned carbon particles in the electrostatic precipitator 2 is improved and the unburned carbon particles are easily removed.

  The lower limit of the ash content with a particle size of 1.0 μm or less in the ash obtained by heat-ashing fuel coal is 0.20 mass%, preferably 0.25 mass%, and 0.30 mass% preferable. On the other hand, as an upper limit of ash content with a particle diameter of 1.0 micrometer or less in the ash content obtained by heat-ashing fuel coal, 1.5 mass% is preferable, 1.0 mass% is more preferable, and 0.8 mass % Is more preferred. Contained in unburned carbon in exhaust gas generated by combustion of fuel coal in furnace 1 when ash content with particle diameter of 1.0 μm or less in ash obtained by heat-ashing fuel coal does not reach the above lower limit As the amount of ash decreases and the removal rate of unburned carbon in the electrostatic precipitator becomes insufficient, the gypsum recovered by the wet desulfurization device 3 may be colored. Conversely, when the ash content of the particle size of 1.0 μm or less in the ash content obtained by heat-ashing fuel coal exceeds the above upper limit, the amount of coal ash in the exhaust gas becomes large, so that the coal passing through the electrostatic precipitator The total amount of ash increases, and the quality of gypsum recovered by the wet desulfurization apparatus 3 may be degraded.

  The lower limit of the total content of ash in fuel coal is preferably 2%, more preferably 3%. On the other hand, as an upper limit of ash content of fuel coal, 20% is preferred and 18% is more preferred. When the ash content of fuel coal is less than the above lower limit, the content of ash having a particle diameter of 1.0 μm or less in the ash obtained by heat-ashing is insufficient and the gypsum recovered by the wet desulfurization apparatus 3 May be colored. Conversely, when the ash content of the fuel coal exceeds the above upper limit, the total amount of coal ash passing through the electrostatic precipitator may increase and the quality of gypsum recovered by the wet desulfurization apparatus 3 may be degraded.

  Anthracite coal, bituminous coal, sub-bituminous coal etc. can be used as said fuel coal. Among them, bituminous coal is particularly preferably used as the above-mentioned fuel coal because it can suppress the unit cost of heat than anthracite coal and has a higher amount of heat than subbituminous coal.

  Moreover, you may use coal coal mixed so that the said ash content may be satisfy | filled as fuel coal. By using mixed coal as fuel coal, it becomes easy to obtain fuel, so it is possible to suppress an increase in fuel cost.

<Advantage>
As described above, in the method of operating the coal combustion facility, coal having a relatively large ash content with a particle size of 1.0 μm or less in the ash obtained by heat-ashing is used as the fuel coal burned in the furnace 1 As a result, the removal rate of unburned carbon particles in the electrostatic precipitator 2 can be improved, and the amount of unburned carbon contained in gypsum recovered in the wet desulfurization apparatus 3 can be reduced, so high quality gypsum can be obtained. . For this reason, the recovered gypsum can be sold at a relatively high price, and the operating cost of the coal combustion facility can be reduced as a whole.

Other Embodiments
The above embodiment does not limit the configuration of the present invention. Therefore, the above-mentioned embodiment can omit, substitute or add the components of each part of the above-mentioned embodiment based on the description of the present specification and technical common sense, and all of them are interpreted as belonging to the scope of the present invention It should.

  The coal combustion equipment used for the operation method of the coal combustion equipment is an economizer that heats water with the heat of exhaust gas, an air heater that heats combustion air with the heat of exhaust gas, and heat recovery from exhaust gas upstream of a wet desulfurization device Additional devices such as a gas-gas heater heat recovery unit (GGH), a selective catalytic reduction denitrification unit (SCR), and the like may be provided to reheat the exhaust gas having passed through the wet desulfurization unit.

  Hereinafter, the present invention will be described in detail based on examples, but the present invention is not to be construed as being limited based on the description of the examples.

  At a power plant where a coal-fired boiler is installed as a furnace and a selective catalyst reduction denitrification unit, an electric precipitator and a wet desulfurization unit are installed in this order as a coal combustion facility, the particle size distribution of ash obtained by heating ashing Several different fuel coal No. 1 to 5 were burned to check whether the gypsum recovered by the wet desulfurization apparatus was colored. In addition, fuel coal No. 1, 5 are bituminous coal produced in Indonesia; 2 to 4 are Australian bituminous coals.

  Fuel coal No. The total ash content is measured according to JIS-M8812 (1978) “ash determination method”, and the particle size distribution of the incinerated sample is measured by the laser diffraction scattering method, and each The cumulative content was calculated based on the mass of the fuel coal with an ash content less than the particle size. The results are shown in Table 1 below. In Table 1, the above-mentioned fuel coal No. 1 to 5 are also shown together with the presence or absence of coloring in the gypsum recovered by the wet desulfurization device by burning in the coal combustion facility.

  As shown in Table 1, fuel coal No. While No. 1 to 3 did not have significant coloring to gypsum, No. 1 fuel coal No. In 4 and 5, coloring to gypsum (blackening with unburned carbon particles) was observed.

  As shown in FIG. The particle size distribution of the ash content obtained by heat-ashing 1-5 is shown. In FIG. 2, those without significant coloration to gypsum are shown using white markers, and those having coloration to gypsum are shown using filled markers.

  As shown in the figure, the fuel coal No. 1 in which the deterioration in the quality of gypsum due to the blackening was not confirmed. In the fuel coal No. 1 to 3, fuel ash having a relatively large content of ash having a small particle size in the ash obtained by heat ashing was used, and the quality of gypsum was deteriorated due to blackening. As for 4,5, the content of the small particle size ash content in the ash content obtained by heat ashing was relatively small. On the other hand, no significant correlation was found between the content of ash having a large particle size in the ash obtained by heat ashing and the blackening of gypsum.

  The effect of the ash in the fuel coal on the prevention of blackening of gypsum is greater as the particle size of the ash obtained by heat-ashing the fuel coal is smaller, and the ash exceeding a certain particle size after heating-ashing prevents the blackening of gypsum It is thought that it does not contribute to More specifically, the presence or absence of coloring of gypsum obtained by the wet desulfurization apparatus in the operation of the coal combustion facility is determined by the mass of the ash coal having a particle size of 1.0 μm or less in the ash obtained by heating the fuel coal. It is considered appropriate to judge by the reference content rate.

  Specifically, a wet desulfurization apparatus is used by using coal having an ash content with a particle diameter of 1.0 μm or less in the ash obtained by heat ashing as 0.20% by mass or more of the fuel coal as the fuel coal. It is believed that the coloration of the resulting gypsum can be prevented.

  Furthermore, in order to confirm the relationship between the ash content in the ash content obtained by heat ashing and the particle size of 1.0 μm or less in the ash content and the color of gypsum recovered by the wet desulfurization apparatus, by mixing plural types of coal Then, a fuel coal having a particle size of 1.0 μm or less and different in ash content in the ash content obtained by heat ashing was prepared. The fuel coal thus obtained by mixed coal was burned using the same coal combustion facility, and the content of unburned carbon in gypsum recovered by the wet desulfurization apparatus was measured in accordance with JIS-M 8819 (1997) .

  Fig. 3 shows the relationship between the measured value of the ash content with a particle size of 1.0 μm or less in the ash obtained by heat-ashing and the measured value of the unburned carbon content in gypsum recovered by the wet desulfurization device Shows a graph plotting.

  As shown in the figure, although there is some variation, coal having an ash content with a particle size of 1.0 μm or less in the ash obtained by heat ashing is 0.20 mass% or more of the above fuel coal as fuel coal By using it, it has been confirmed that the unburned carbon concentration in gypsum obtained by the wet desulfurization apparatus, that is, the coloration of gypsum can be sufficiently suppressed.

  The operation method of the coal combustion facility according to the present invention can be suitably used particularly as an operation method of a coal-fired power plant.

1 furnace 2 electric precipitator 3 wet desulfurization device 4 chimney

Claims (3)

A furnace for burning fuel coal, an electrostatic precipitator for removing particulates from exhaust gas discharged from the furnace, and a wet desulfurization apparatus for removing sulfur oxides from the exhaust gas from which particulates are removed by the electrostatic precipitator by limestone gypsum method A method of operating a coal combustion facility,
Operation of a coal combustion facility characterized by using, as the fuel coal, coal having an ash content with a particle diameter of 1.0 μm or less in the ash obtained by heat-ashing and having an ash content of 0.20 mass% or more of the fuel coal Method.   The method for operating a coal combustion facility according to claim 1, wherein coal mixed with coal to satisfy the ash content is used as the fuel coal.   The method according to claim 1 or 2, wherein bituminous coal is used as the fuel coal.

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