JP5420142B2 - Method for improving dust collection efficiency of dust collector - Google Patents

Description

  The present invention relates to a method for improving the dust collection efficiency of a dust collector that collects dust from combustion residues of coal in a thermal power generation system.

  There are various methods for burning coal in a coal-fired power generation system, which is an example of a thermal power generation system. Among them, so-called pulverized coal combustion is mainly used, in which particles obtained by pulverizing coal are blown into a furnace and burned. It has been adopted.

  By the way, the coal used as a raw material contains not only carbon but also sulfur compounds and nitrogen compounds, and also contains trace amounts of harmful elements such as boron, fluorine, selenium and arsenic (hereinafter referred to as “the harmful elements” "Harmful trace elements").

  When the sulfur compound contained in coal burns in a furnace with combustion of coal, sulfur oxide is generated. By removing this sulfur oxide with a desulfurization apparatus provided downstream of the coal-fired power generation system, the sulfur oxide is prevented from being released into the atmosphere. For example, in a desulfurization apparatus that uses lime slurry as a sulfur oxide absorber, sulfur oxide and lime slurry react to produce a gypsum slurry. In the desulfurization apparatus, gypsum is recovered by dehydrating the gypsum slurry. Part of this dewatered wastewater (hereinafter referred to as “desulfurization wastewater”) circulates and is used for desulfurization treatment, but other desulfurization wastewater is sent to wastewater treatment facilities for wastewater treatment and then treated. The water is discharged from the outlet to general rivers and sea areas. The content of harmful trace elements in the discharged treated water has a self-regulatory value that is stricter than that of each local government that is established for compliance with laws such as the Water Pollution Control Law.

  On the other hand, after combustion of coal, harmful trace element compounds contained in coal are contained in coal ash, which is a residue after combustion of coal, or in solid form (granular form) in exhaust gas. ) Or in a gaseous state.

  In the dust collector provided upstream of the desulfurizer, most of the harmful trace element compounds present in solid form in the exhaust gas are removed together with the coal ash. On the other hand, harmful trace element compounds present in gaseous form in the exhaust gas are dissolved in the desulfurization effluent in the desulfurization apparatus. Furthermore, when the coal ash particle size is smaller than the separation limit particle size of the dust collector, the compound of harmful trace elements that have been concentrated (condensed) on the surface of the coal ash because the coal ash has passed through the dust collector Elutes into the desulfurization effluent. Therefore, if a coal type with a high content of harmful trace elements is used and compounds of harmful trace elements are eluted (dissolved) more than expected in the desulfurization effluent, it cannot be treated with existing wastewater treatment facilities, and the regulations of each local government There is a risk that treated water containing harmful trace elements exceeding the value will be discharged into general rivers and sea areas.

  For this reason, it is desirable to use coal types with a low content of harmful trace elements as fuel in coal-fired power generation systems. It is preferable that various coal types can be used.

Introduce new wastewater treatment equipment (wastewater treatment method) as one measure to ensure that treated water complies with the regulated values and allows the use of inexpensive coal types with a high content of harmful trace elements. Can be considered. As a wastewater treatment method capable of treating harmful trace elements, for example, Patent Document 1 discloses a method of removing boron, which is a kind of harmful trace elements, as an insoluble precipitate by slaked lime or aluminum sulfate. A method of adsorbing and removing a boron compound with a boron adsorption resin is disclosed.
JP-A-10-225682 JP 2003-1112917 A

  However, in any of the above methods, in order to treat a large amount of wastewater containing boron, a large amount of chemicals and boron adsorption resin must be used. In this case, a problem of processing cost such as an increase in initial cost occurs.

  As shown above, the treatment cost of harmful trace elements that have flowed into the wastewater treatment facility is high. For this reason, if the concentration of harmful trace elements can be reduced before the harmful trace elements flow into the wastewater treatment facility and before flowing into the desulfurization equipment, the content of harmful trace elements is high and inexpensive. Various coal types can be used.

  As a measure therefor, a method of capturing harmful trace elements in exhaust gas by coal ash, etc., and removing the coal ash, etc., from which harmful trace elements have been captured before flowing into the desulfurization apparatus can be considered.

  The present invention has been made in view of the above-mentioned problems, and is required to collect dust in order to use an inexpensive coal species having a high content of harmful trace elements without requiring a large initial investment and large-scale additional equipment. It aims at providing the method of improving the dust collection efficiency of an apparatus.

  (1) In a coal-fired power generation system comprising a combustion boiler that burns coal, and a dust collector that is provided downstream of the combustion boiler and collects dust from the combustion residue of the coal, Soot dust is collected by the dust collector from the coal supply process for supplying the combustion residue of the fuel generated when the fuel is burned in another thermal power generation system different from the coal thermal power generation system to the combustion boiler. A method of capturing harmful trace elements in exhaust gas generated by combustion of the coal by adding it to the system up to the process.

  According to the invention of (1), in the coal-fired power generation system, only the combustion residue of the fuel generated when the fuel is burned in another thermal power generation system different from the coal-fired power generation system is added. It can be easily applied with the improvement. The timing of addition is not particularly limited as long as it is within the system from the step of transferring coal to the combustion boiler to the step of collecting soot dust by the dust collector, and a coal supply unit and a pulverized coal generation unit to be described later Any of the pulverized coal combustion part and the exhaust gas / drainage treatment part before the dust collector may be used. This pulverized coal combustion section includes the vicinity of a heat exchange unit (so-called economizer) disposed downstream of the combustion boiler.

  In addition, calcium oxide reacts with harmful trace element compounds contained in coal ash, such as selenium oxide, arsenic trioxide, and boron oxide, respectively, and calcium selenite, calcium arsenate, boric acid, respectively. A poorly soluble or insoluble compound such as calcium (hereinafter referred to as “slightly soluble insoluble compound”) is produced. That is, harmful trace elements are chemically trapped by calcium oxide to form a hardly soluble insoluble compound. For this reason, even if harmful trace elements flow into the desulfurization effluent, since the harmful trace elements are hardly soluble insoluble compounds, it is possible to suppress the elution of the toxic trace elements into the desulfurization effluent.

  According to the invention of (1), the combustion residue of the fuel in the other thermal power generation system is present in the system from the coal supply process for supplying coal to the combustion boiler to the process for collecting dust by the dust collector. Since it is transferred, the amount of calcium oxide contained in the fuel combustion residue increases. That is, an increase in the amount of calcium oxide in the combustion residue of the added fuel increases the chance of contact between the harmful trace element compound and the harmful trace element compound. For this reason, there is a high possibility that harmful trace elements are chemically trapped in calcium oxide and become insoluble insoluble compounds, and the elution of harmful trace elements into the desulfurization effluent is further suppressed.

  Further, as in the invention of (1), when the fuel combustion residue is transferred to the coal stage during or before combustion, the surface of the fuel combustion residue transferred by the heat in the furnace is melted. The surface of the fuel combustion residue comes into contact with harmful trace element compounds. The harmful trace element compound is taken into the fuel combustion residue by gradually solidifying (vitrifying) the surface of the fuel combustion residue. That is, harmful trace element compounds are physically trapped in the combustion residue of the fuel transferred into the system. The harmful trace element compounds that are physically captured are removed from the system together with the fuel combustion residue by a dust collector before flowing into the desulfurization effluent. It can be suppressed more.

  As described above, according to the invention of (1), the combustion residue of fuel captures harmful trace element compounds chemically and physically, thereby further suppressing the elution of harmful trace elements into the desulfurization effluent. Can do. Therefore, a new wastewater treatment facility is not required, and it is possible to use an inexpensive coal type having a high content of harmful trace elements without requiring a large initial investment and a large-scale additional facility.

  Further, according to the invention of (1), when a calcium compound for preventing the elution of harmful trace elements is used, specifically, limestone, slaked lime, quicklime, etc., the amount of use can be reduced. .

  “Harmful trace elements” refers to coal such as boron, arsenic, bromine, cyanide, chlorine, iodine, sulfur, nitrogen, phosphorus, silica, tin, titanium, vanadium, tungsten, selenium, fluorine, nickel, magnesium, manganese, etc. It is an element that can be harmful to humans.

  Moreover, the combustion residue of coal means clinker ash, cinder ash, fly ash, etc. so that it may mention later.

  (2) The method for capturing harmful trace elements in the exhaust gas according to (1), wherein the combustion residue of the fuel is added upstream from within the combustion boiler.

  (3) The method for capturing harmful trace elements in the exhaust gas according to (1), wherein a combustion residue of the fuel is added in the vicinity of a burner zone of the combustion boiler.

  (4) The method for capturing harmful trace elements in the exhaust gas according to (1), wherein the combustion residue of the fuel is added in the combustion boiler.

(5) The method for capturing harmful trace elements in the collected exhaust gas according to (1), wherein a combustion residue of the fuel is added in the vicinity of a heat exchange unit disposed downstream in the combustion boiler.
(6) The combustion residue of coal is transferred to the system between the outlet in the combustion boiler and the dust collector, and the trace amount element in the exhaust gas according to (1) is captured. Method.

  In the inventions of (2) to (6), the addition position of the combustion residue of coal is specifically defined. As a condition of the addition position of the coal combustion residue, the coal combustion residue needs to be an addition position that can physically or chemically capture harmful trace elements.

  The addition position of the fuel combustion residue specified in the inventions of (2) to (5) is a temperature range where the surface of the fuel combustion residue can be melted, specifically, a temperature of 1000 ° C. or higher. It is the position which has. For this reason, it is possible to physically capture harmful trace element compounds and the like by melting the surface of the combustion residue of the fuel.

  In addition, the fuel combustion residue addition positions specified in the inventions of (2) to (5) are both the combustion residue of the added fuel and the combustion residue of coal containing harmful trace element compounds in the exhaust gas. Is a position where contact is possible. For this reason, it is possible for the calcium oxide in the combustion residue of the added fuel to come into contact with the harmful trace element compound to chemically capture the harmful trace element compound.

  Therefore, according to the inventions of (2) to (6), the combustion residue of the added fuel captures the harmful trace element compounds chemically or physically, thereby leaching the harmful trace element into the desulfurization effluent. It can be suppressed more. As a result, a new wastewater treatment facility is not required, and it is possible to use an inexpensive coal type with a high content of harmful trace elements without requiring a large initial investment and a large-scale additional facility.

  In the invention of (2), “upstream from inside the combustion boiler” is, for example, a coal supply unit and a pulverized coal generation unit which will be described later. In the invention of (4), “inside the combustion boiler” includes addition to the piping when the combustion boiler is recirculating exhaust gas.

  In the invention of (5), the combustion residue of fuel is added in the vicinity of the heat exchange unit arranged downstream of the combustion boiler. This heat exchange unit is also called a superheater, a reheater, a economizer, an economizer (ECO), or the like, and is an area where the temperature is maintained from 850 ° C. to around 900 ° C.

  (7) The other thermal power generation system is a pulverized coal combustion system, and clinker ash is added as a combustion residue of the fuel to capture harmful trace elements in the exhaust gas according to any one of (1) to (6) Method.

  (8) The other thermal power generation system is a pulverized coal combustion system, and the combustion residue of the coal discharged from a economizer and the combustion residue of the coal discharged from an air preheater as the combustion residue of the fuel The method for capturing harmful trace elements in exhaust gas according to any one of (1) to (6), wherein cinder ash containing at least one selected from the group consisting of combustion residues of coal discharged from a denitration device is added.

  (9) The other thermal power generation system is a pulverized coal combustion system, and fly ash is added as a combustion residue of the fuel, improving the dust collection efficiency of the dust collector according to any one of (1) to (6) how to.

  (10) The other thermal power generation system is a heavy oil combustion system, and the dust collection efficiency of the dust collector according to any one of (1) to (6) is used in which the combustion residue of heavy oil is used as the combustion residue of the fuel. how to.

  (11) The dust collector according to any one of (1) to (6), wherein the other thermal power generation system is an organic waste combustion system, and the combustion residue of organic waste is used as the combustion residue of the fuel. To improve dust collection efficiency.

  The inventions of (7) to (11) specifically define the combustion residue of fuel. In this case, the addition of the clinker ash, the cinder ash, the fly ash, the combustion residue of heavy oil, and the combustion residue of organic waste can be easily applied by improving the existing equipment.

  According to the invention of (7), it is conceivable to add clinker ash which is a combustion residue of fuel into the furnace. Since clinker ash is an amorphous substance, it has a viscosity at a relatively low temperature (for example, about 1000 ° C.) with respect to a high temperature in the furnace (for example, about 1300 ° C. to 1500 ° C.). It becomes fluid. That is, the clinker ash is remelted at a relatively low temperature in the furnace.

  According to the invention of (8), it is conceivable to add cinder ash, which is a combustion residue of fuel, into the furnace. Since Cinder Ash is a partially amorphous material, it has a viscosity at a relatively low temperature (eg, about 1000 ° C.) with respect to a high furnace temperature (eg, about 1300 ° C. to 1500 ° C.), Fluidizes at high temperatures. That is, the cinder ash is remelted at a relatively low temperature in the furnace.

  In addition, according to the inventions of (9) to (11), it is conceivable to add fly ash, which is a combustion residue of fuel, a combustion residue of heavy oil, and a combustion residue of organic waste, into the furnace. The surfaces of fly ash, heavy oil combustion residue, and organic waste combustion residue added to the furnace are melted by heat in the furnace.

  With the above mechanism, the combustion residue of each added fuel can be melted. On the surface of the combustion residue of the softened fuel, harmful trace element compounds come into contact and condense. The harmful trace element compound is taken into the fuel combustion residue by gradually solidifying (vitrifying) the surface of the fuel combustion residue. That is, minute mineral particles and volatile components are physically captured (incorporated) into the combustion residue of coal.

  In addition, according to the inventions of (7) to (11), any added fuel combustion residue can chemically capture harmful trace element compounds.

  Therefore, according to the inventions of (7) to (11), the combustion residue of fuel captures harmful or trace element compounds chemically or physically, thereby further suppressing the elution of harmful trace elements into the desulfurization effluent. be able to. As a result, a new wastewater treatment facility is not required, and it is possible to use an inexpensive coal type with a high content of harmful trace elements without requiring a large initial investment and a large-scale additional facility.

  According to the present invention, since the amount of calcium oxide is increased by the amount of calcium oxide in the combustion residue of the added fuel, harmful trace elements can be chemically captured by calcium oxide and become a hardly soluble insoluble compound. It is highly possible to further suppress the elution of harmful trace elements into the desulfurization effluent. In addition, when the coal combustion residue is transferred to the coal stage during or before combustion, the surface of the coal combustion residue transferred by the heat in the furnace is melted and is in contact with the surface of the coal combustion residue. The trace element compound is taken into the coal combustion residue by gradually solidifying (vitrifying) the surface of the coal combustion residue. That is, the harmful trace element compound is physically captured by the combustion residue of coal transferred into the system, and the elution of the harmful trace element into the removed desulfurization effluent can be further suppressed.

  As described above, according to the present invention, the combustion residue of the fuel chemically and physically captures the harmful trace element compound, so that the elution of the harmful trace element into the desulfurization waste water can be further suppressed. Therefore, a new wastewater treatment facility is not required, and it is possible to use an inexpensive coal type having a high content of harmful trace elements without requiring a large initial investment and a large-scale additional facility.

<A: Configuration of pulverized coal combustion facility in coal-fired power generation system>
Hereinafter, an embodiment showing an example of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a pulverized coal combustion facility 1 in a coal-fired power generation system. Here, as shown in FIG. 1, the pulverized coal combustion facility 1 includes a coal supply unit 12 that supplies coal, a pulverized coal generation unit 14 that converts the supplied coal into pulverized coal, and a pulverized coal that burns pulverized coal. A combustion section (combustion boiler) 16 and an exhaust gas / drainage processing section 18 for processing exhaust gas generated by the combustion of pulverized coal and further processing desulfurization effluent discharged from a desulfurization apparatus described later are provided. FIG. 2 is an enlarged view of the vicinity of the furnace 161 in the pulverized coal combustion unit 16. FIG. 3 is an example of a schematic configuration diagram of another pulverized coal combustion facility that is an example of another coal-fired power generation system.

<A-1: Coal supply section>
The coal supply unit 12 includes a coal bunker 121 that stores coal, and a coal feeder 122 that supplies the coal stored in the coal bunker 121. The coal bunker 121 stores coal to be supplied to the coal feeder 122. The coal feeder 122 continuously supplies the coal supplied from the coal bunker 121 to the coal pulverized coal machine 141. Moreover, this coal feeder 122 is provided with the apparatus which adjusts the supply_amount | feed_rate of coal, and, thereby, the amount of coal supplied to the coal pulverizer 141 is adjusted. Further, a coal gate is provided at the boundary between the coal bunker 121 and the coal feeder 122, thereby preventing air from the coal feeder from flowing into the coal bunker.

<A-2: Pulverized coal generation unit>
The pulverized coal generation unit 14 includes a coal pulverized coal machine (mill) 141 that converts coal into pulverized coal capable of pulverized coal combustion, and a ventilator 142 that supplies air to the coal pulverized coal machine 141.

  The coal pulverized coal machine 141 pulverizes the coal supplied from the coal feeder 122 through the coal supply pipe to form fine pulverized coal, and is supplied from the pulverized coal and the ventilator 142. Mix with air. Thus, by mixing pulverized coal and air, the pulverized coal is preheated and dried to facilitate combustion. Air is blown onto the formed pulverized coal, thereby supplying the pulverized coal to the pulverized coal combustion unit 16.

  Examples of the type of the coal pulverized coal machine 141 include a roller mill, a tube mill, a ball mill, a beater mill, an impeller mill, and the like. However, the type of the coal pulverized coal machine 141 is not limited to these and may be any mill used in pulverized coal combustion.

<A-3: Pulverized coal combustion section>
The pulverized coal combustion unit 16 includes a furnace 161 that burns the pulverized coal generated by the pulverized coal generation unit 14, an air preheater 162 (heat exchange unit) that heats the furnace 161, and a ventilation that supplies air to the furnace 161. Machine 163.

  The furnace 161 is heated by a heater (not shown) and combusts the pulverized coal supplied from the coal pulverized coal machine 141 via the pulverized coal pipe together with the air supplied from the ventilator 163. The air preheater 162 (heat exchange unit, AH) performs heat exchange between the air (untreated gas) sent to the furnace 161 and the exhaust gas. The air preheater 162 has an ash treatment hopper 162f from which AH ash described later is discharged.

By burning pulverized coal, coal ash (coal combustion residue) such as clinker ash and fly ash is generated as a by-product. Clinker ash falls from the furnace 161 and is also referred to as bottom ash. Fly ash is the remaining dust. Further, together with coal ash, exhaust gases such as sulfur oxides (SOx) such as sulfur dioxide (SO ₂ ) and sulfur trioxide (SO ₃ ) and nitrogen oxides (NOx) are generated. Furthermore, among harmful trace elements such as boron, fluorine, selenium and arsenic contained in coal, boron, fluorine and selenium are gaseous compounds such as boron oxide, hydrogen fluoride and selenium oxide. It will be present in the exhaust gas. These harmful trace element compounds are sent to the exhaust gas / drainage treatment unit 18 together with exhaust gas, fly ash, and the like.

  The furnace 161 will be described in detail with reference to FIG. 2. In FIG. 2, the furnace 161 has a substantially inverted U shape as a whole, and after the combustion gas moves in an inverted U shape along the arrow in the figure. After passing through the secondary economizer 161e, it is again reversed into a U shape, and the outlet of the furnace 161 (the last arrow in FIG. 2) is connected to a denitration device 181 and a dust collector 182. In the pulverized coal combustion facility 1 according to the present embodiment, the height of the furnace 161 is 40 m to 60 m, and the total length of the exhaust gas passage ranges from 200 m to 800 m.

  Below the furnace 161, a burner 161a for burning pulverized coal in the vicinity of the burner zone 161a 'in the furnace 161 and an ash treatment hopper 161f for discharging clinker ash are disposed. The clinker ash discharged from the ash treatment hopper 161f is sent to a coal ash collection silo (not shown). Further, near the top of the U-shape in the furnace 161, a furnace upper dividing wall 161b, a final superheater 161b ′, and a first reheater 161f (all of which are heat exchange units) are arranged, and further placed horizontally from there. A primary superheater 161c (heat exchange unit) is subsequently arranged. Further, a second reheater 161f ′ is provided in parallel with the horizontal primary superheater 161c, and from the vicinity of the terminal end of the horizontal primary superheater 161c, a primary economizer 161d (heat exchange unit). A secondary economizer 161e (heat exchange unit) is provided in two stages. Here, the economizer (also called ECO) is a group of heat transfer surfaces provided to preheat boiler feedwater using the heat held by the combustion gas, and below it is collected by inertial collision. An ash treatment hopper 161g for discharging coal ash, so-called ECO ash, is provided. The ECO ash discharged from the ash treatment hopper 161g is sent to a coal ash recovery silo (not shown). In the present embodiment, in the furnace 161, the primary economizer 161d and the secondary economizer 161e are separately installed in two stages, but the present invention is not limited to such a form. That is, the furnace 161 may have only a single economizer.

<A-4: Exhaust gas / wastewater treatment unit 18>
The exhaust gas / wastewater treatment unit 18 includes a denitration device 181 that removes nitrogen oxides in the exhaust gas discharged from the pulverized coal combustion unit 16, and dust collection that removes fly ash in the exhaust gas discharged from the pulverized coal combustion unit 16. An apparatus 182, a desulfurization apparatus 183 that removes sulfur oxides in the exhaust gas, and a wastewater treatment facility 184 that processes desulfurization wastewater discharged from the desulfurization apparatus 182 are provided.

  The denitration device 181 removes nitrogen oxides in the exhaust gas. That is, ammonia gas is injected as a reducing agent into exhaust gas at a relatively high temperature (300 to 400 ° C.), and nitrogen oxides in the exhaust gas are decomposed into harmless nitrogen and water vapor by the action of a denitration catalyst, so-called dry ammonia contact. A reduction method is preferably used.

  The dust collector 182 is a device that collects fly ash in the exhaust gas with an electrode. The dust collector 182 is preferably provided in a plurality of stages. The fly ash collected by the dust collector 182 is conveyed to a coal ash collection silo (not shown).

  The desulfurizer 183 removes sulfur oxides in the exhaust gas. That is, the desulfurization device 183 sprays a mixed liquid (limestone slurry) of limestone and water onto the exhaust gas, thereby absorbing the sulfur oxide contained in the exhaust gas into the mixed liquid and generating a gypsum slurry. The desulfurization device 183 generates gypsum by dehydrating the gypsum slurry. The desulfurization waste water discharged from the desulfurization device 183 is sent to the waste water treatment facility 184. Further, the desulfurized exhaust gas is discharged from a chimney (not shown).

  The wastewater treatment facility 184 is a facility for treating wastewater containing desulfurization wastewater by a wastewater treatment device such as an aeration tank or a coagulation sedimentation tank (not shown). Waste water (treated water) treated by the waste water treatment facility 184 is discharged from a discharge port to a general river or sea area.

<B: Method for improving the dust collection efficiency of the dust collector of the present invention>
A method for capturing harmful trace elements in exhaust gas according to the present invention includes a combustion boiler that burns coal, and a dust collector that is provided downstream of the combustion boiler and collects dust from the combustion residue of the coal. In the coal-fired power generation system, from the step of transferring the coal to the combustion boiler, the combustion residue of the fuel generated when the fuel is burned in the other coal-fired power generation system is different from the coal-fired power generation system. This is a method of adding harmful trace elements in the exhaust gas generated by combustion of the coal by adding it into the system until the step of collecting dust by the dust collector. This will be described using the charcoal combustion facility 1. Preferably, it is performed in any of the coal supply step S10, the pulverized coal generation step S20, the pulverized coal combustion step S30, or the exhaust gas / drainage treatment step S40.

  This step includes coal supply step S10 for supplying coal, pulverized coal generation step S20 for pulverizing the supplied coal to generate pulverized coal, pulverized coal combustion step S30 for burning this pulverized coal, and this exhaust gas. An exhaust gas / drainage treatment step S40 that is processed and released to the atmosphere, and each of these steps includes a coal supply unit 12, a pulverized coal generation unit 14, a pulverized coal combustion unit 16, and a pulverized coal combustion unit 16, respectively. And in the exhaust gas / drainage treatment section 18. And combustion ash addition process S50 which is the characteristics of this invention is preferably performed in either of said coal supply process S10, pulverized coal production | generation process S20, and pulverized coal combustion process S30.

<Coal supply process S10>
First, in the coal supply process, the coal stored in the coal bunker 121 is supplied to the coal pulverized coal machine 141 by the coal feeder 122. The coal supplied to the coal pulverized coal machine 141 is specifically bituminous coal, subbituminous coal, lignite, or the like, but is not limited to these coals and may be coal capable of pulverized coal combustion. That's fine.

<Pulverized coal production process S20>
Next, in the pulverized coal production step, the coal supplied from the coal feeder 122 is pulverized by the coal pulverized coal machine 141, thereby producing pulverized coal. The generated pulverized coal is supplied to the furnace 161. At this time, the average particle size of the pulverized coal formed in the pulverized coal generation step may be a particle size range generally used in pulverized coal combustion, and generally 74 μm under 80 wt% or more. The degree of pulverization. This range can also be applied when combustion ash is added.

<Pulverized coal combustion process S30>
Next, in the pulverized coal combustion process, the pulverized coal generated by the coal pulverized coal machine 141 is burned by the furnace 161. As shown in FIG. 2, pulverized coal is burned in the burner zone 161a ′, and the temperature at this time ranges from 1300 ° C. to 1500 ° C. Among the coal ash generated by combustion, the clinker ash is a downward arrow. And is discharged from the ash treatment hopper 161f. The fly ash rises along the direction of the upward arrow, passes through the superheaters (heat exchange units) 161b and 161c together with the exhaust gas, and passes through the primary economizer 161d (heat exchange unit) and the secondary economizer 161e (heat exchange unit). ) In order.

  As described above, the vicinity of the economizer is an area where the temperature is maintained at about 850 ° C. to about 900 ° C., and the heat transfer surface provided for preheating boiler feedwater using the heat held by the combustion gas. By passing through the group, heat is exchanged, and the temperature decreases. The time required for the exhaust gas to reach the vicinity of the superheater from the burner zone 161a 'is approximately 5 to 15 seconds. Then, it is sent to a desulfurization device 181 and a dust collection device 182 at the subsequent stage. The coal ash produced in this pulverized coal combustion process is usually in the form of a powder having an average particle size in the range of 1 μm to 100 μm.

<Exhaust gas / drainage treatment process S40>
Thereafter, the exhaust gas generated by the combustion of the pulverized coal is sent to the denitration device 181 for denitration, and the fly ash in the exhaust gas is collected by the dust collector 182. The exhaust gas collected by the dust collector 182 is sent to the desulfurizer 183 for desulfurization, and then released to the atmosphere by a chimney (not shown). The desulfurization waste water discharged from the desulfurization device 183 is sent to the waste water treatment facility 184 and processed together with other waste water.

<Combustion ash addition step S50>
As shown in FIG. 1, the combustion ash addition process S50, which is a process for adding combustion ash, which is a feature of the present invention, is preferably the coal supply process S10, the pulverized coal generation process S20, the pulverized coal combustion process S30, and the exhaust gas. -It performs with respect to either one of waste water treatment process S40.

  In addition, the addition place of combustion ash will not be limited if it is in the system to a dust collector, For example, the transfer path between coal supply process S10 and pulverized coal production | generation process S20, pulverized coal production | generation process S20, and pulverization You may perform by the transfer path between charcoal combustion process S30, the transfer path between pulverized coal combustion process S30, and waste gas and waste water treatment process S40.

  Specifically, for example, a method of supplying and mixing combustion ash on a belt conveyor being transferred when transporting from the coal feeder 122 to the coal pulverized coal machine 141, a coal hopper of the coal pulverized coal machine 141 A method of directly supplying to a furnace (not shown), a method of supplying an agent charging port in a pipe between the coal pulverizer 141 and the furnace 161, and a furnace 161 (burner zone 161a ′) to be directly charged with combustion air. Method, furnace upper partition wall 161b, final superheater 161b ', first reheater 161f, horizontal primary superheater 161c, second reheater 161f', horizontal Examples include, but are not limited to, a method of adding to the vicinity of a heat exchange unit such as the primary superheater 161c, the primary economizer 161d, and the secondary economizer 161e. As described above, the method of the present invention does not require a new facility, and can be applied by a slight improvement of the existing facility. Therefore, the existing facility can be used effectively, which is advantageous in terms of cost.

  The combustion ash which is the combustion residue of the fuel of the present invention is a combustion residue of fuel produced when fuel is burned in another thermal power generation system different from the pulverized coal combustion facility 1 which is an example of the coal thermal power generation system. Specifically, the combustion ash means coal ash in the case of a coal boiler, and clinker ash, cinder ash, fly ash in the case of a pulverized coal combustion system (pulverized coal boiler).

  Here, clinker ash, cinder ash, and fly ash, which are combustion residues of coal in another pulverized coal combustion facility, will be described with reference to FIG. For convenience, the same reference numerals as those of the devices of the pulverized coal combustion facility 1 in the present embodiment are given.

  By burning pulverized coal in the furnace 161, coal ash (coal residue of coal) such as clinker ash and fly ash is generated as a by-product.

  The clinker ash falls from the furnace 161 to the furnace bottom and is cooled by water, and is also referred to as bottom ash. Clinker ash is porous and has drainage (water permeability) and breathability.

  The fly ash is the remaining soot and is collected (collected) by a dust collector 182 described later.

  In addition to the dust collector 182, the coal ash is also a small amount (total of about 1% to 2%) from the primary economizer 161d, the secondary economizer 161e, the air preheater 162, and the denitration device 181 described later. Is collected. The coal ash collected from the primary economizer 161d, secondary economizer 161e, air preheater (AH) 162, and denitration device 181 is called ECO ash, AH ash, and denitration device ash, respectively. This is called Cinder Ash. Since cinder ash contains a large amount of Fe and has a small amount of generation, unlike fly ash and clinker ash, it has not been used effectively. According to the present invention, it is possible to effectively use this cinder ash. In addition, the cinder ash should just contain at least 1 or more types chosen from the group of ECO ash, AH ash, and denitration apparatus ash.

  In the case of a heavy oil combustion system, combustion ash refers to heavy oil ash that is a combustion residue of heavy oil. In the case of organic waste combustion system, combustion ash refers to the combustion residue of organic waste. An example of organic waste is a thinned wood chip.

  The combustion ash is preferably granular or powdery, and specifically, the average particle diameter is preferably 1 μm to 100 μm, more preferably 5 μm to 70 μm.

  By adding the combustion ash described above, in the present invention, it is possible to suppress the inflow of harmful trace elements into the desulfurization effluent regardless of the type of harmful trace elements contained in the exhaust gas. Specific examples of harmful trace elements that can suppress inflow to desulfurization wastewater are not particularly limited, but boron, arsenic, bromine, cyanide, chlorine, iodine, sulfur, nitrogen, phosphorus, silica, tin, titanium, vanadium. , Tungsten, selenium, fluorine, nickel, magnesium, manganese and the like. Among these, inflow to desulfurization effluents such as boron, fluorine and arsenic, which can be a gaseous compound, can be further suppressed.

According to the present invention, it is possible to suppress the inflow of harmful trace elements into the desulfurization effluent of the desulfurization apparatus 183. The mechanism that can suppress the inflow of harmful trace elements into the desulfurization effluent of the desulfurization apparatus 183 in the present invention is as follows.

  By adding the combustion ash into the system up to the dust collector 182, the amount of calcium oxide contained in the combustion ash increases. Here, the calcium oxide reacts with harmful trace element compounds contained in the combustion ash, such as selenium oxide, arsenic trioxide, and boron oxide, respectively, and calcium selenite, calcium arsenate, boron, respectively. A poorly soluble or insoluble compound such as calcium acid (hereinafter referred to as “slightly soluble insoluble compound”) is produced. That is, harmful trace elements are chemically captured by calcium oxide to produce a hardly soluble insoluble compound.

  Therefore, by adding combustion ash into the system up to the dust collector 182, the amount of calcium oxide in the coal ashes in the system is increased, so that harmful trace elements are chemically captured by calcium oxide and hardly soluble. The possibility of becoming an insoluble compound is high, and the elution of harmful trace elements into the desulfurization effluent is further suppressed.

  Further, when the combustion ash is added to the stage of coal during or before combustion, the surface of the combustion ash added by the heat in the furnace is melted. A harmful trace element compound comes into contact with the surface of the added combustion ash. The harmful trace element compounds are taken into the combustion ash by gradually solidifying (vitrifying) the surface of the combustion ash. That is, harmful trace element compounds are physically captured by the combustion ash transferred into the system. Since the harmful trace element compounds that have been physically captured are removed from the system by the dust collector 182 and the like together with the combustion ash before flowing into the desulfurization effluent, the toxic trace elements are further eluted into the desulfurization effluent. Can be suppressed.

  As described above, by adding combustion ash into the system up to the dust collector 182, the combustion ash chemically and physically captures the compounds of harmful trace elements, so that harmful trace elements in the desulfurization effluent are removed. Elution can be further suppressed. Therefore, a new wastewater treatment facility is not required, and it is possible to use an inexpensive coal type having a high content of harmful trace elements without requiring a large initial investment and a large-scale additional facility.

  The present invention provides desulfurization drainage by adding coal ash, heavy oil ash, combustion ash of organic waste discharged from furnaces, air preheaters, denitration devices, dust collectors installed in other thermal power plants. It is possible to further suppress the elution of harmful trace elements. That is, the present invention is a technique that enables the use of an inexpensive coal type having a high content of harmful trace elements without requiring a large initial investment and large-scale additional equipment.

It is a schematic block diagram of the pulverized coal combustion facility in the coal thermal power generation system which shows one Embodiment of this invention. It is an enlarged view of the vicinity of the furnace in FIG. It is an example of the schematic block diagram of the pulverized coal combustion facility in another coal thermal power generation system (pulverized coal combustion system).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pulverized coal combustion facility 12 Coal supply part 121 Coal bunker 122 Coal feeder 14 Pulverized coal production part 141 Coal pulverized coal machine 142 Ventilator 16 Pulverized coal combustion part 161 Furnace 162 Air preheater 163 Air supply machine 18 Exhaust gas / drainage treatment part 181 Denitration equipment 182 Dust collector 183 Desulfurization equipment 184 Wastewater treatment equipment S10 Coal supply process S20 Pulverized coal production process S30 Pulverized coal combustion process S40 Exhaust gas / wastewater treatment process S50 Combustion ash addition process

Claims (3)

In a coal-fired power generation system comprising: a combustion boiler that burns coal; and a dust collector that is provided downstream of the combustion boiler and collects dust from the combustion residue of the coal.
In order to add a combustion residue of fuel generated when fuel is burned in another coal-fired power generation system different from the coal-fired power generation system, the combustion residue is generated in the other coal-fired power generation system. Cinder ash containing Cinder Ash is added at least in the vicinity of the burner zone of the combustion boiler, in the combustion boiler, or in the vicinity of the heat exchange unit disposed downstream of the combustion boiler, and is generated by combustion of the coal. To capture harmful trace elements in exhaust gas. The method for capturing harmful trace elements in exhaust gas according to claim 1, wherein the combustion residue is transferred into a system from an outlet in the combustion boiler to the dust collector. The cinder ash is composed of the combustion residue of coal discharged from the economizer, the combustion residue of coal discharged from the air preheater, and the combustion residue of coal discharged from the denitration device as the combustion residue of the fuel. The method for capturing harmful trace elements in exhaust gas according to claim 1 or 2, comprising at least one or more selected.

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