JP5177965B2 - A method for capturing harmful trace elements in exhaust gas. - Google Patents

Description

  The present invention relates to a method for capturing harmful trace elements in exhaust gas generated by coal combustion 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. Therefore, if a coal type with a high content of harmful trace elements is used, and the harmful trace element compounds are dissolved (eluted) more than expected in the desulfurization effluent, the existing wastewater treatment facilities will not be able to handle them, 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-described problems, and an object of the present invention is to provide a method for capturing harmful trace elements in exhaust gas without requiring a large initial investment and large-scale additional equipment.

  (1) 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. The coal combustion residue is transferred into the system from the coal supply process to the boiler to the process where the dust is collected by the dust collector, and harmful trace elements in the exhaust gas generated by the combustion of the coal are captured. how to.

  According to the invention of (1), since the coal combustion residue is only transferred into the system from the coal supply process for supplying coal to the combustion boiler to the process for collecting dust by the dust collector, It can be easily applied by improving the equipment.

  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), since the combustion residue of coal is transferred into the system between the step of transferring coal to the combustion boiler and the step of collecting dust by the dust collector, the combustion of coal The amount of calcium oxide contained in the residue increases. That is, an increase in the amount of calcium oxide in the combustion residue of the transferred coal 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 coal combustion residue is transferred to the stage of coal during or before combustion, the surface of the coal combustion residue transferred by the heat in the furnace is melted. The surface of the coal combustion residue comes into contact with harmful trace element compounds. The harmful trace element compound is taken into the coal combustion residue by gradually solidifying (vitrifying) the surface of the coal combustion residue. That is, harmful trace element compounds are physically trapped in the combustion residue of coal transferred into the system. The harmful trace element compounds that have been physically captured are removed from the system together with the coal 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 coal captures harmful and trace element compounds chemically and physically to further suppress the release 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 coal is transferred upstream from within the combustion boiler.

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

  (4) The method for improving the dust collection efficiency of the dust collector according to (1), wherein the combustion residue of the coal is added in the combustion boiler.

  (5) The method for capturing harmful trace elements in the exhaust gas according to (1), wherein the combustion residue of the coal is transferred to the vicinity of a heat exchange unit disposed downstream in the combustion boiler.

  (6) The method for capturing harmful trace elements in the exhaust gas according to (1), wherein the coal combustion residue is transferred into a system from an outlet in the combustion boiler to the dust collector.

  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 transfer positions of the coal combustion residues defined in the inventions of (2) to (5) are all in a temperature range where the surface of the coal combustion residues can be melted, specifically, a temperature of 850 ° C. or higher. It is the position which has. For this reason, when the surface of the combustion residue of coal is melted, it is possible to physically capture harmful trace element compounds and the like.

  In addition, the transfer positions of the coal combustion residues defined in the inventions of (2) to (6) are all the coal combustion residues transferred and the coal combustion residues containing compounds of harmful trace elements 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 transferred coal 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), toxic trace elements are eluted into the desulfurization effluent by transporting the coal combustion residue of the captured coal chemically or physically to capture the harmful trace element compounds. 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, when the combustion boiler is recirculating exhaust gas, transfer to the piping.

  Moreover, in invention of (5), the combustion residue of coal is transferred to heat exchange unit vicinity arrange | positioned downstream of a 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 method for capturing harmful trace elements in exhaust gas according to any one of (1) to (6), wherein the coal-fired power generation system is a pulverized coal combustion system and transports clinker ash as a combustion residue of the coal. .

  (8) The coal-fired power generation system is a pulverized coal combustion system, and the combustion residue of the coal discharged from a economizer, the combustion residue of the coal discharged from an air preheater as the combustion residue of the coal, 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 transferred.

  (9) The coal-fired power generation system is a pulverized coal combustion system, and transports fly ash as the combustion residue of the coal. (1) to (6) The method for capturing harmful trace elements in exhaust gas according to any one of (6) .

  The inventions of (7) to (9) specifically define coal combustion residues. In this case, the transfer of clinker ash, cinder ash and fly ash can be easily applied by improving existing equipment.

  According to the inventions of (7) to (9), when coal combustion residue is added to coal, low melting point of coal ash is caused by calcium oxide contained in coal ash.

  Moreover, according to invention of (7), clinker ash which is a combustion residue of coal is put in the system between the coal supply process which supplies coal to a combustion boiler, and the process from which dust is collected by a dust collector. Transport. 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.

  Further, according to the invention of (8), since the cinder ash which is a combustion residue of coal is partly an amorphous substance, it is relatively low with respect to the furnace temperature (for example, about 1300 ° C. to 1500 ° C.) which is a high temperature. It has a viscosity at a low temperature (for example, about 1000 ° C.), and further fluidizes at a high temperature. That is, the cinder ash is remelted at a relatively low temperature in the furnace.

  Moreover, according to invention of (9), adding fly ash which is a combustion residue of coal to a furnace is considered. The surface of the fly ash transferred into the furnace is melted by the heat in the furnace.

  With the above mechanism, it is possible to melt the combustion residue of each transferred coal. On the surface of the softened coal combustion residue, harmful trace element compounds come into contact and condense. The harmful trace element compound is taken into the coal combustion residue by gradually solidifying (vitrifying) the surface of the coal 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 (9), any transferred coal combustion residue can chemically capture harmful trace element compounds.

  Therefore, according to the invention of (7) to (9), the combustion residue of coal captures harmful 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 added coal combustion residue, harmful trace elements can be chemically captured by calcium oxide and become insoluble insoluble compounds. 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 coal chemically and physically captures the harmful trace element compound, so that the elution of the harmful trace element into the desulfurization effluent 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. Combustion section (combustion boiler) 16, exhaust gas generated by combustion of pulverized coal, exhaust gas / drainage processing section 18 for processing desulfurization effluent discharged from a desulfurization apparatus described later, and combustion residue of coal And a coal ash mixing unit 20 for mixing a certain coal ash. 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 the pulverized coal combustion facility 1.

<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.

  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, a small amount of coal (total of about 1% to 2%) from the primary economizer 161d, the secondary economizer 161e, the air preheater 162, and the denitration apparatus 181 described later is also used. Ashes are collected. The coal ash collected from the primary economizer 161d, secondary economizer 161e, air preheater 162 (AH), 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.

Further, together with the above 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 the exhaust gas and fly ash.

  The furnace 161 will be described in detail with reference to FIGS. 2 and 3. In FIG. 2, the furnace 161 has a substantially inverted U shape as a whole, and the combustion gas is inverted U-shaped along the upward arrow in the figure. After passing through the secondary economizer 161e, it is inverted again into a small U shape, and the outlet of the furnace 161 (the last arrow in FIG. 2) is connected to the denitration device 181 and the dust collector 182. Yes. 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 161 f is sent to the coal ash mixing unit 20. 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 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 161 g is sent to the coal ash mixing unit 20 as cinder ash. 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 183 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. Part of the desulfurization effluent discharged from the desulfurization device 183 is circulated, and the rest is sent to the wastewater 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.

<A-5: Coal ash mixing part>
The coal ash mixing unit 20 includes a mixing tank 201. The mixing tank 201 includes clinker ash discharged from the ash treatment hopper 161f of the furnace 161 of the pulverized coal combustion unit 16, and ash treatment of the furnace 161 (the primary economizer 161d and the secondary economizer 161e) of the pulverized coal combustion unit 16. ECO ash discharged from the hopper 161g, AH ash discharged from the ash treatment hopper 162f of the air preheater 162 of the pulverized coal combustion unit 16, and discharge from the ash treatment hopper 181f of the denitration device 181 of the exhaust gas / drainage treatment unit 18 This is a tank that mixes the cinder ash in which the denitration device ash is collected and the fly ash discharged from the ash treatment hopper 182f of the dust collector 182 of the exhaust gas / drainage treatment unit 18.

  In the present embodiment, the coal ash may include at least one selected from the group consisting of clinker ash, cinder ash, and fly ash.

<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, the combustion residue of the coal is transferred into the system from the step of transferring the coal to the combustion boiler to the step of collecting dust by the dust collector, and the combustion of the coal This is a method of capturing harmful trace elements in the generated exhaust gas, and this will be described using the pulverized coal combustion facility 1 described above. Preferably, it is performed in any one of a coal supply step S10, a pulverized coal generation step S20, a pulverized coal combustion step S30, and an exhaust gas / drainage treatment step S40 described later.

  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, An exhaust gas / drainage treatment step S40 that removes nitrogen oxides, fly ash, and sulfur oxides and treats wastewater including desulfurization wastewater, and a coal ash mixing step S45, each of which is described above. The pulverized coal combustion facility 1 includes a coal supply unit 12, a pulverized coal generation unit 14, a pulverized coal combustion unit 16, an exhaust gas / wastewater treatment unit 18, and a coal ash mixing unit 20. And coal 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, pulverized coal combustion process S30, and waste gas and waste water treatment process S40.

<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 generation step, the coal supplied from the coal feeder 122 is pulverized by the coal pulverized coal machine 141, thereby generating 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 the transferred coal 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 the subsequent dust collector 182 and desulfurizer 181. 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.

<Coal ash mixing step S45>
In the coal ash mixing step S45, clinker ash, cinder ash, and fly ash are mixed in the mixing tank 201, and in the next step, the coal ash addition step S50, the coal supply unit 12, the pulverized coal generation unit 14, the pulverized coal. It is transferred to either the combustion unit 16 or the exhaust gas / drainage treatment unit 18.

<Coal ash transfer process S50>
As shown in FIG. 1, the coal ash transfer step S50, which is a step of transferring coal ash, which is a feature of the present invention, is preferably the above-described coal supply step S10, pulverized coal generation step S20, pulverized coal combustion step S30, exhaust gas. -It is performed with respect to any of the wastewater treatment step S40.

  Note that the coal ash transfer location is not limited as long as it is within the system up to the dust collector. For example, the transfer path between the coal supply step S10 and the pulverized coal generation step S20, or the pulverized coal generation step S20 and the pulverized powder. 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.

  Coal ash, which is a combustion residue of coal of the present invention, is clinker ash discharged from the ash treatment hopper 161f of the furnace 161 of the pulverized coal combustion unit 16, and the furnace 161 of the pulverized coal combustion unit 16 (the primary economizer 161d and the secondary unit). ECO ash discharged from the ash treatment hopper 161g of the carbonizer 161e), AH ash discharged from the ash treatment hopper 162f of the air preheater 162 of the pulverized coal combustion unit 16, and a denitration device 181 of the exhaust gas / drainage treatment unit 18 Coal ash containing at least one or more of Cinder Ash collected from denitrification ash discharged from the ash treatment hopper 181f of the ash, and fly ash discharged from the ash treatment hopper 182f of the dust collector 182 of the exhaust gas / drainage treatment unit 18 It is preferable that The coal ash is preferably granular or powdery, and specifically, the average particle size is preferably 1 μm to 100 μm, more preferably 5 μm to 70 μm.

  By transferring the above coal ash, in the present invention, it is possible to suppress the inflow of harmful trace elements into the desulfurization effluent regardless of the kind 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 transferring the coal ash into the system up to the dust collector 182, the amount of calcium oxide contained in the coal ash increases. Here, calcium oxide reacts with harmful trace element compounds contained in coal ash, for example, 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 transferring the coal 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.

  Moreover, when coal ash is transferred to the stage of coal during combustion or before combustion, the surface of the coal ash transferred by the heat in the furnace is melted. A harmful trace element compound comes into contact with the surface of the transferred coal ash. The harmful trace element compounds are taken into the coal ash by gradually solidifying (vitrifying) the surface of the coal ash. That is, harmful trace element compounds are physically captured by the coal 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 coal ash before flowing into the desulfurization effluent, the toxic trace elements are more easily eluted into the desulfurization effluent. Can be suppressed.

  As described above, by transferring the coal ash into the system up to the dust collector 182, the coal ash captures the chemical and physical compounds of the harmful trace elements, so that the 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.

  Hereinafter, the present invention will be described more specifically with reference examples.

<Reference example>
By using an apparatus as shown in FIG. 1 and FIG. 2, at least one kind of coal from China, Australia, Indonesia, etc. was burned. The power approximation curve was created by taking the ash content (%) in the coal per unit time on the X axis and the boron concentration (ppm) in the desulfurization effluent at that time on the Y axis. This graph is shown in FIG.

  In addition, the density | concentration of the boron in desulfurization waste_water | drain was implemented by the methylene blue absorptiometry of JISK0102. The ICP mass spectrometer was measured using a spectrophotometer U-3310 (manufactured by HITACHI). The sampling locations for the mass of ash are the coal consumption system of coal-fired power plants and the coal ash discharge system.

  According to the result of FIG. 4, when there is little ash content (X-axis 0 direction), the boron concentration in desulfurization waste_water | drain is high. This indicates that if the ash content is large in the combustion reaction or the flue, harmful trace elements do not move beyond the dust collector 181 to the desulfurizer 182. That is, it shows that harmful trace elements are recovered by the dust collector 181.

  As a result of the above, it can be seen that, in the pulverized coal combustion facility, as the ash content in the coal increases, harmful trace elements do not move to the desulfurization device 182 beyond the dust collector 181. It is considered that this is because ash in coal, that is, coal ash, captures harmful trace elements chemically and physically, thereby further suppressing the elution of harmful trace elements into the desulfurization effluent.

  As a result of the above, when coal combustion residue is transferred into the system from the step of transferring coal to the combustion boiler to the step of collecting soot dust by the dust collector, coal ash is a compound of harmful trace elements. By chemically and physically trapping, the elution of harmful trace elements into the desulfurization effluent 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.

  In addition, since the desulfurization waste water shown in FIG. 4 is not discharged into general rivers and sea areas as it is, but is treated by waste water treatment equipment, it is possible to fully comply with the regulation value.

  By adding coal ash discharged from a furnace, an air preheater, a denitration device, and a desulfurization device installed in a thermal power plant, the present invention can further suppress the elution of harmful trace elements into the desulfurization effluent. . 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 a coal thermal power generation system. It is the graph which created the power approximation curve, taking the ash content (%) in coal per unit time as the X axis and the boron concentration (ppm) in the desulfurization waste water at that time as the Y axis.

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 / wastewater treatment part 181 Denitration equipment 182 Dust collector 183 Desulfurization equipment 184 Wastewater treatment equipment 201 Mixing tank S10 Coal supply process S20 Pulverized coal production process S30 Pulverized coal combustion process S40 Exhaust gas / drainage treatment process S45 Coal ash mixing process S50 Coal ash addition process

Claims (1)

In a coal-fired power generation system comprising a combustion boiler that burns coal, and a dust collector that is disposed downstream of the combustion boiler and collects dust from the combustion residue of the coal , the outlet from the combustion boiler A method of transferring the combustion residue of coal into a system up to a dust collector and capturing harmful trace elements in exhaust gas generated by combustion of the coal,
The coal-fired power generation system is a pulverized coal combustion system, the combustion residue of the coal discharged from a coal-saving device, the combustion residue of the coal discharged from an air preheater, and a denitration device A method for capturing harmful trace elements in an exhaust gas, wherein a cinder ash containing at least one selected from the group consisting of combustion residues of the discharged coal is transferred.

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