JP2008012529A - Exhaust gas purification agent and method for uptaking trace of harmful element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas purification agent and a method for uptaking a trace of harmful element with such advantages that a large amount of initial investment can be dispensed with, large-scale additional facilities are not necessary, the concentration of the trace of harmful element can be reduced before the inflow of the trace of harmful element into water drainage treatment facilities. <P>SOLUTION: The exhaust gas purification agent, containing a trace of harmful element uptaking agent acts to uptake the trace of harmful element borne in an exhaust gas generated by coal burning, is used in finely powdered burning facilities 1 equipped with a finely powdered coal burning part 16 for burning a fuel. The trace of harmful element uptaking agent bears an alkali metal and/or its salts, or an alkaline earth metal and/or its salts. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purifying agent containing a harmful trace element scavenger that traps harmful trace elements in exhaust gas generated by combustion of fuel in a thermal power generation system, and to capture harmful trace elements using the exhaust gas purifying agent. Regarding the method.

  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, in which finely pulverized coal is blown into a combustion furnace and burned, is mainly used. 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 further contains a trace amount of harmful elements such as boron, fluorine, selenium, and arsenic (hereinafter, the harmful elements are referred to as “ "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.

  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 or gaseous form in the exhaust gas. Exists in a state.

  Most of the harmful trace element compounds present in solid form in the exhaust gas are treated together with coal ash in a dust collector. On the other hand, some harmful trace element compounds present in gaseous form in the exhaust gas may be dissolved in the desulfurization effluent discharged from the desulfurization apparatus. A part of the desulfurization effluent is circulated and used for the desulfurization treatment, but the other desulfurization effluent is sent to the wastewater treatment facility for treatment, and then discharged into the general river or sea area as treated water from the outlet.

  Here, in order to comply with laws and regulations such as the Water Pollution Control Law, the content of harmful trace elements in the discharged treated water must be less than the self-regulated value that is stricter than the regulated value set by each local government. There is. For this reason, it is desirable to use coal species with a low content of harmful trace elements as fuel. On the other hand, due to demands for reducing fuel costs, cheap coal types with a high content of harmful trace elements are used. Preferably it can be done.

Introducing a new wastewater treatment facility (wastewater treatment method) as a measure to use cheap coal as fuel with a high content of harmful trace elements so that the treated water does not exceed the specified regulation value Conceivable. 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, it is considered that in order to treat a large amount of wastewater containing boron, it is necessary to use a large amount of chemicals and boron adsorption resin. In this case, there is a problem of processing costs such as an increase in initial costs.

  As shown above, the treatment cost of harmful trace elements that have flowed into the wastewater treatment facility is high. Therefore, if it is possible to reduce the concentration of harmful trace elements before they enter the wastewater treatment facility, a large initial investment is not required, and a large additional facility is required. Instead, an inexpensive coal type with a high content of harmful trace elements can be used.

  The present invention has been made in view of the above-described problems, and does not require a large amount of initial investment, and does not require a large-scale additional facility. An object of the present invention is to provide an exhaust gas purifying agent capable of reducing the concentration of elements and a method for capturing harmful trace elements.

  (1) An exhaust gas purifying agent that is used in a thermal power generation system including a combustion boiler that burns fuel and includes a harmful trace element scavenger that traps harmful trace elements contained in exhaust gas generated by the combustion of the fuel. The harmful trace element scavenger is an exhaust gas purifying agent containing an alkali metal and / or a salt thereof, or an alkaline earth metal and / or a salt thereof.

  According to the invention of (1), the harmful trace element scavenger for capturing harmful trace elements contained in the exhaust gas is a chemical containing an alkali metal and / or a salt thereof, or an alkaline earth metal and / or a salt thereof. is there. Alkali metals and / or salts thereof, or alkaline earth metals and / or salts thereof are all readily available, do not require a large initial investment, and do not require large-scale additional equipment. That is, according to the invention of (1), a large amount of initial investment is not required, and the concentration of harmful trace elements is reduced before the harmful trace elements flow into the wastewater treatment facility without requiring large-scale additional equipment. It is possible to make it.

  “Harmful trace elements” are contained in coal such as boron, arsenic, bromine, chlorine, iodine, sulfur, nitrogen, phosphorus, tin, titanium, vanadium, tungsten, selenium, fluorine, nickel, magnesium, manganese, etc. , An element that can be harmful to humans.

  (2) The exhaust gas according to (1), wherein the alkali metal and / or salt thereof, or the alkaline earth metal and / or salt thereof includes at least one selected from the group consisting of limestone, slaked lime, and quicklime. Purifier.

  The exhaust gas purifying agent according to the invention of (2) uses a harmful trace element scavenger containing one or more selected from the group consisting of limestone, slaked stone, and quicklime. Limestone, slaked stone, and quicklime are all readily available, do not require significant initial investment, and do not require large-scale additional equipment, and are harmful before hazardous trace elements enter the wastewater treatment facility. It is possible to reduce the concentration of trace elements.

  (3) The exhaust gas purifying agent according to (1) or (2), wherein the harmful trace element is boron.

  Treatment of wastewater containing boron among other harmful trace elements is more difficult than treatment of wastewater containing other harmful trace elements. Or large additional equipment was required. According to the invention of (3), the concentration of harmful trace elements is reduced before the hazardous trace elements flow into the wastewater treatment facility without requiring a large initial investment and without requiring a large-scale additional facility. Is possible.

  (4) The exhaust gas purification according to any one of (1) to (3), so that the concentration of the alkali metal and / or the alkaline earth metal is 0.1% by mass or more and 20% by mass or less with respect to the fuel. A method for capturing harmful trace elements by adding an agent to the fuel.

  According to the invention of (4), it is possible to more effectively reduce the concentration of harmful trace elements before the harmful trace elements flow into the wastewater treatment facility. If the concentration of the alkali metal and / or the alkaline earth metal is less than 0.1% by mass with respect to the fuel, the effect of reducing the concentration of harmful trace elements becomes insufficient, such being undesirable. On the other hand, even if the amount exceeds 20% by mass, no significant improvement is observed in the effect of reducing the concentration of harmful trace elements, and a large amount of coal ash adheres to the inner wall of the furnace due to the melting point drop on the coal ash surface (slagging). ) Is not preferable. In the low temperature region up to the dust collector inlet, the amount of the exhaust gas purifier added to the fuel can be charged as long as the performance of the dust collector permits.

  (5) The thermal power generation system includes a dust collector provided to remove the dust contained in the exhaust gas, and the dust collector uses the dust collector to add the fuel to the combustion boiler. The method for capturing harmful trace elements according to (4), which is added before the step of removing dust.

According to the invention of (5), the addition timing of the exhaust gas purifying agent is from the step of adding fuel to the combustion boiler to the step of removing the dust by the dust collector. Even if an exhaust gas purifier is added in the downstream of the dust collector and harmful trace elements are trapped by the exhaust gas cleaner, the trace element in the gas is supplemented by the dust collector that cannot remove the exhaust gas cleaner. Cannot achieve the goal. If the exhaust gas purifying agent is limestone, the temperature for decomposing limestone is high. Therefore, the temperature for decomposing is the step before adding fuel to the combustion boiler, and the limestone is pyrolyzed (heat from CaCO ₃ to CaO). Decomposition) It is necessary to add an exhaust gas purification agent between the temperature ranges. An example of a temperature region where limestone is thermally decomposed includes, for example, the vicinity of a superheater. On the other hand, for example, slaked lime and quicklime can be used as an exhaust gas purifying agent without being decomposed, so that, for example, a coal supply unit, a pulverized coal generation unit, a pulverized coal combustion unit, a superheater vicinity, and a collection point after that Any of the low temperature range to a dust device may be sufficient.

  (6) The method for capturing harmful trace elements according to (4) or (5), wherein the thermal power generation system is a pulverized coal combustion type power generation system, and the exhaust gas purifying agent is added to the combustion boiler.

  The present invention can be applied to various types of thermal power generation among thermal power generation systems. As a suitable example of a thermal power generation system, a coal thermal power system (coal boiler), a heavy oil thermal power system (heavy oil boiler), a sludge thermal power system (sludge boiler), etc. can be considered. Moreover, among coal boilers, although it can be used for a pulverized coal combustion type (pulverized coal boiler), a pressurized fluidized bed combustion type (pressurized fluidized boiler), etc., a pulverized coal combustion type is preferable.

  According to the present invention, it is possible to reduce the concentration of harmful trace elements before they enter the wastewater treatment facility without requiring a large initial investment and without requiring large-scale additional equipment. is there.

<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 unit 16 and an exhaust gas / drainage treatment unit 18 for treating exhaust gas generated by the combustion of pulverized coal and further treating desulfurization wastewater 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.

<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 an air supply unit 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 air supply unit 142. Mix with fresh 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 combusts the pulverized coal generated by the pulverized coal generation unit 14, a heater 162 (heat exchange unit) that heats the furnace 161, and an air supply that supplies air to the furnace 161. Machine 163.

The furnace 161 is heated by the heater 162 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 air supply unit 163. By burning pulverized coal, coal ash 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 the exhaust gas and fly ash.

  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 exhaust 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 and a dust collector 181 (not shown). 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 is disposed in the vicinity of the burner zone 161a 'in the furnace 161. Moreover, the 1st superheater 161b (heat exchange unit) is arrange | positioned near the U-shaped top part in the furnace 161, and also the 2nd superheater 161c (heat exchange unit) is arrange | positioned from there. Yes. Further, from the vicinity of the end of the second superheater 161c, a primary economizer 161d (heat exchange unit) and a secondary economizer 161e (heat exchange unit) are provided in two stages. Here, the economizer (also referred to as ECO) is a heat transfer surface group provided for preheating boiler feedwater using heat retained by exhaust gas.

<A-4: Exhaust gas / wastewater treatment unit 18>
The exhaust gas / drainage treatment unit 18 removes fly ash in the exhaust gas discharged from the pulverized coal combustion unit 16, and desulfurization that removes sulfur oxides in the exhaust gas discharged from the dust collector 181. A device 182 and a waste water treatment facility 183 for treating the desulfurization waste water discharged from the desulfurization device 182 are provided.

  The dust collector 181 is a device that collects fly ash in exhaust gas with an electrode. The dust collector 181 is preferably provided in a plurality of stages. The fly ash collected by the dust collector 181 is conveyed to a coal ash recovery silo (not shown).

  The desulfurization apparatus 182 removes sulfur oxides in the exhaust gas. That is, the desulfurization device 182 sprays a mixed liquid (limestone slurry) of limestone and water on the exhaust gas, thereby absorbing the sulfur oxide contained in the exhaust gas into the mixed liquid to generate a gypsum slurry. The desulfurization device 182 generates gypsum by dehydrating the gypsum slurry. The desulfurization waste water discharged from the desulfurization device 182 is sent to the waste water treatment facility 183. Further, the desulfurized exhaust gas is discharged from a chimney (not shown).

  The wastewater treatment facility 183 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 183 is discharged from a discharge port to a general river or sea area.

<B: Harmful Trace Element Elution Control Method of the Present Invention>
The method for suppressing inflow of harmful trace elements into desulfurization waste water of the present invention includes alkali metal and / or salt thereof, or alkaline earth metal and / or salt thereof in coal as fuel in a coal-fired power generation system. By adding harmful trace element scavengers (including exhaust gas purifiers), the harmful trace elements discharged from the desulfurization device that removes sulfur oxides in the exhaust gas generated by the combustion of the coal can flow into the desulfurization effluent. This will be described using the pulverized coal combustion facility 1 described above. Preferably, it is performed in any of the coal supply unit 12, the pulverized coal generation unit 14, and the pulverized coal combustion unit 16.

  The coal thermal power generation system includes a coal supply step S10 for supplying coal, a pulverized coal generation step S20 for pulverizing the supplied coal to generate pulverized coal, and a pulverized coal combustion step S30 for burning the pulverized coal. And exhaust gas / drainage treatment step S40 for collecting fly ash in the exhaust gas, removing sulfur oxides in the exhaust gas, and treating wastewater including desulfurization wastewater, 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, and an exhaust gas / drainage treatment unit 18. The harmful trace element scavenger addition step S50, which is a feature of the present invention, is preferably performed in any one of the coal supply unit 12, the pulverized coal generation unit 14, and the pulverized coal combustion unit 16.

<Coal supply process S10>
First, in the coal supply step S <b> 10, 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 S20, 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 a harmful trace element scavenger is added.

<Pulverized coal combustion process S30>
Next, in the pulverized coal combustion step S <b> 30, 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. 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), 2 The next economizer 161e (heat exchange unit) is sequentially passed.

  As described above, the vicinity of this economizer is an area where the temperature is maintained at about 450 ° C. to about 500 ° C., and a heat transfer surface group provided for preheating boiler feedwater using the heat held by the exhaust gas. By passing through, 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, the exhaust gas is sent to a dust collector 181 and a desulfurizer 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 / wastewater treatment process 40>
Thereafter, the exhaust gas generated by the combustion of the pulverized coal is sent to a denitration device (not shown) and denitrated, and further, fly ash in the exhaust gas is collected by the dust collector 181. The exhaust gas collected by the dust collector 181 is sent to the desulfurizer 182 for desulfurization, and then released to the atmosphere by a chimney (not shown). The desulfurization waste water discharged from the desulfurization device 182 is sent to the waste water treatment facility 183 and processed together with other waste water.

<Harmful trace element scavenger addition step S50>
As shown in FIG. 1, the harmful trace element scavenger addition step S50, which is a feature of the present invention, which is a step of adding a harmful trace element scavenger, is preferably the above coal supply unit 12, pulverized coal generation unit 14, pulverized powder. This is performed for any of the charcoal combustion units 16 (S51, S52, S53 in FIG. 1 respectively).

  The place where the harmful trace element scavenger is added is not particularly limited as long as the coal is flowing. For example, a transfer path between the coal supply unit 12 and the pulverized coal generation unit 14 or pulverized coal generation. It may be performed in a transfer path between the unit 14 and the pulverized coal combustion unit 16.

  Specifically, for example, a method of supplying and mixing a harmful trace element scavenger on a belt conveyor when transporting from the coal feeder 122 to the coal pulverized coal machine 141, a harmful trace element scavenger for the coal pulverized coal machine 141 A method of directly charging into a coal hopper (not shown), a method of supplying an agent charging port in a pipe between the coal pulverized coal machine 141 and the furnace 161, a method of directly charging the furnace 161 with combustion air, a furnace 161, a method of adding to the vicinity of the heat exchange unit such as the heater 162, the superheaters 161b, 161c, the primary economizer 161d, the secondary economizer 161e, etc., which constitute a part of the 161, are limited to these. It is not something. 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 harmful trace element scavenger of the present invention is an agent containing an alkali metal and / or a salt thereof, or an alkaline earth metal and / or a salt thereof, but limestone (CaCO ₃ ), slaked stone (Ca (OH)) ₂ ) It is preferable that it is a chemical | medical agent containing 1 or more types selected from the group which consists of quicklime (CaO). Further, the harmful trace element scavenger is preferably granular or powdery, specifically, the average particle diameter is preferably 1 μm to 100 μm, more preferably 5 μm to 70 μm.

  It is preferable to add a harmful trace element scavenger so that the concentration of alkali metal and / or alkaline earth metal with respect to coal is 0.1% by mass or more and 20% by mass or less.

  By adding the above-mentioned harmful trace element scavenger, 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 into desulfurization wastewater include, but are not limited to, boron, arsenic, bromine, chlorine, iodine, sulfur, nitrogen, phosphorus, tin, titanium, vanadium, tungsten, selenium. , Fluorine, nickel, magnesium, manganese and the like. Among these, inflow of simple substances or compounds such as boron, fluorine and arsenic, which can be gaseous substances, into the desulfurization effluent can be further suppressed.

  The mechanism that can suppress the inflow of harmful trace elements contained in the exhaust gas into the desulfurization effluent in the present invention is as follows.

  When coal to which the harmful trace element scavenger is added burns in the furnace 161, the particle concentration in the exhaust gas generated by the combustion increases by the amount of the harmful trace element scavenger added. For this reason, there is a high possibility that gaseous harmful trace elements and their compounds are captured by coal ash, which is a combustion residue of coal, or a harmful trace element scavenger.

  In addition, gaseous harmful trace elements form compounds such as oxides composed of harmful trace elements by the oxidizing action of the harmful trace element scavenger. As a specific example, gaseous boron trapped by the harmful trace element trapping agent is oxidized by calcium oxide derived from the harmful trace element trapping agent, and is immobilized as hardly soluble or insoluble boron oxide. This boron oxide may be further captured by a harmful trace element scavenger.

  The harmful trace element compound captured by the harmful trace element scavenger is an alkali metal component or alkaline earth metal component in the harmful trace element capture agent in the exhaust gas cooling process or in the collected coal ash. It is believed that it reacts with to produce a poorly soluble or insoluble compound. Specifically, boron oxide, selenium oxide, arsenic trioxide, and hydrogen fluoride react to produce calcium borate, calcium selenite, calcium arsenate, calcium fluoride, etc., respectively. . Thus, the harmful trace element trapped by the harmful trace element trapping agent is immobilized on the harmful trace element trapping agent.

  Furthermore, another mechanism when a scavenger is introduced into the high temperature region of the boiler is a mechanism in which trace components in the gas are physically trapped and fixed in molten ash by promoting the lower melting point of coal ash. Can be mentioned. That is, under the conditions of 1300 ° C. to 1500 ° C. in the furnace 161, the addition of a harmful trace element scavenger which is a compound containing calcium softens (melts) the surface of the coal ash containing silica and alumina as main components, thereby causing viscosity. It is presumed that the coal ash particles having a slag come into contact with trace elements and are taken into the coal ash to lower the elution concentration. Thus, in the present invention, by adding a harmful trace element scavenger until the pulverized coal combustion step S30, the high temperature of the furnace in the pulverized coal combustion section is effectively utilized, and the elution of trace elements from the coal ash is achieved. It is to suppress.

  The gaseous harmful trace elements and their compounds captured or fixed in the clinker ash among the coal ash descend the furnace 161 together with the clinker ash and are discharged from the furnace 161, so that they may flow into the desulfurization effluent. Is low.

  In addition, gaseous harmful trace elements and their compounds that are physically captured by fly ash in coal ash, and gaseous harmful trace elements that are chemically captured and immobilized by harmful trace element capture agents and their compounds Since the compound collects fly ash or harmful trace element scavengers in the dust collector 181 of the exhaust gas / wastewater treatment unit 18, the possibility of the compound flowing into the desulfurization effluent is low.

  Thus, in the present invention, by adding a harmful trace element scavenger to coal, effectively utilizing the high temperature of the furnace in the pulverized coal combustion section, desulfurization of harmful trace elements, particularly gaseous harmful trace elements It is possible to suppress the inflow to the waste water.

  When the harmful trace element scavenger is added only to the vicinity of the inlet of the dust collector 181, the temperature in the vicinity of the economizer is relatively low, 850 ° C. to 900 ° C. Only compound formation occurs. For this reason, it is also effective to add harmful trace element scavengers only near the economizer.

  Hereinafter, the present invention will be described more specifically with reference to Examples, Comparative Examples, and Reference Examples.

<Example 1>
Using an apparatus as shown in FIG. 1 and FIG. 2, 100 parts by mass of at least one kind of coal from China, Australia and Indonesia and 1 part by mass of limestone were added and burned. Table 1 shows the boron concentration in the coal ash collected by the electric dust collector.

<Comparative Example 1>
The same operation as in the example was performed except that limestone was not added. Table 1 shows the boron concentration in the coal ash collected by the electric dust collector.

  As shown in Table 1, in the comparison of the calculated values, the boron concentration in the coal ash was higher when it was added than when limestone was not added. On the other hand, in the comparison with an actual machine, the boron concentration in coal ash is greater in the case where 1 part by mass of limestone is added to 100 parts by mass of coal and burned (Example 1) than in the case where limestone is not added. It turns out that becomes high. That is, in the example in which limestone was added to coal, limestone was decomposed by heat to generate calcium oxide, and boron was fixed to calcium oxide by contacting calcium oxide and boron. Think of things. On the other hand, in a comparative example, since limestone is not contained, boron is not fixed to calcium oxide. Therefore, the boron concentration in coal ash is higher in the example than in the comparative example.

<Reference Example 3>
Next, at least one type of coal from China, Australia, Indonesia, etc. was burned using an apparatus as shown in FIGS. Boron concentration (ppm) of desulfurization effluent at that time with the mass (%) of alkali and / or alkaline earth metal in coal corresponding to the mass (mg / kg) of boron in coal per unit time as the X axis Was taken on the Y axis, and a power approximation curve was created. This graph is shown in FIG. Moreover, the mass (%) of calcium oxide (CaO) in coal according to the mass (mg / kg) of boron in coal per unit time is taken as the X axis, and the boron concentration (ppm) of desulfurization waste water at that time A power approximation curve was created for the Y axis. This graph is shown in FIG. Also, the mass (mg / kg) of calcium oxide in ash according to the boron concentration (mg / kg) in coal per unit time is on the X axis, and the boron concentration (ppm) in the desulfurization waste water at that time is the Y axis. Therefore, a power approximation curve was created. This graph is shown in FIG.

  The boron concentration in the desulfurization effluent was measured by the methylene blue absorptiometric method of JISK0102. The ICP mass spectrometer was measured using a spectrophotometer U-3310 (manufactured by HITACHI). The sampling locations of the boron concentration in coal, the mass of coal and / or alkaline earth metals, the mass of calcium oxide in coal, and the mass of ash are based on the coal consumption system and coal ash of the coal-fired power plant. Is a payout system.

  According to the results of FIG. 3, when the boron concentration is high and the alkali element is low (X-axis 0 direction), that is, when the alkali metal and / or alkaline earth metal content is relatively low, The boron concentration is high. This indicates that if there are a large amount of alkali metal and / or alkaline earth metal in the combustion reaction or 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.

  Similarly, in FIGS. 4 and 5, when the boron concentration is high on the X axis and the calcium oxide is low (X axis 0 direction), that is, when the calcium oxide is relatively low, the boron concentration in the desulfurization effluent becomes high. Yes. This indicates that when the amount of calcium oxide is increased in the combustion reaction or in 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 as the content of alkali metal and / or alkaline earth metal in coal increases, harmful trace elements do not move to the desulfurizer 182 beyond the dust collector 181. In other words, by adding a harmful trace element scavenger containing an alkali metal and / or its salt or an alkaline earth metal and / or its salt to coal as fuel in the coal-fired power generation system, it can be discharged into desulfurization effluent. It is possible to suppress the inflow of harmful trace elements.

  The desulfurization effluent shown in FIGS. 3 to 5 is not discharged as it is into a general river or sea area, but is treated by a wastewater treatment facility, so that the regulation value can be fully observed.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to suppress inflow of a harmful trace element to the desulfurization waste_water | drain discharged | emitted from the desulfurization apparatus installed in the thermal power plant. That is, the present invention is a technique that enables a reduction in the cost of thermal power generation because an inexpensive coal species containing a harmful trace element at a high concentration can be used as a fuel.

  The following configuration may also be included in the present invention.

  (1) Combustion of coal by adding a harmful trace element scavenger containing alkali metal and / or salt thereof, or alkaline earth metal and / or salt thereof to coal as fuel in a coal-fired power generation system To suppress the inflow of harmful trace elements into the desulfurization effluent discharged from the desulfurization device that removes sulfur oxides in the exhaust gas generated by the process.

  According to the invention of (1), the means for suppressing the inflow of harmful trace elements into the desulfurization effluent is an alkali metal and / or salt thereof, or a harmful trace element scavenger containing alkaline earth metal and / or salt thereof. Therefore, the invention of (1) is an improvement of the existing equipment, that is, a large amount of initial investment is not required and a large-scale additional equipment is not required. It is possible to suppress the inflow to the water. As a result, according to the invention of (1), it is possible to use cheap crude charcoal containing a large amount of harmful trace elements as fuel, so that the fuel cost can be greatly reduced.

  “Harmful trace elements” are contained in coal such as boron, arsenic, bromine, chlorine, iodine, sulfur, nitrogen, phosphorus, tin, titanium, vanadium, tungsten, selenium, fluorine, nickel, magnesium, manganese, etc. , An element that can be harmful to humans.

  Moreover, the timing of addition of the harmful trace element scavenger is not particularly limited as long as it is added to the state of coal. For example, any of a coal supply part, a pulverized coal production | generation part, and a pulverized coal combustion part may be sufficient. This pulverized coal combustion section includes the vicinity of a heat exchange unit (so-called economizer) disposed downstream of the combustion boiler.

  (2) The harmful trace element scavenger is a harmful trace element scavenger containing at least one selected from the group consisting of limestone, slaked stone, and quicklime. How to control inflow.

  The harmful trace element scavenger according to the invention of (2) uses a harmful trace element scavenger containing one or more selected from the group consisting of limestone, slaked stone, and quicklime. Limestone, slaked stone, and quicklime are all readily available, do not require a large initial investment, and do not require large-scale additional equipment, and the above-mentioned harmful trace elements such as boron, fluorine, selenium, and arsenic In particular, it is possible to suppress the inflow of boron into the desulfurization effluent.

  (3) The method of suppressing the inflow of the harmful trace element into the desulfurization waste water according to either (1) or (2), wherein the harmful trace element is boron.

  Treatment of wastewater containing boron, among other harmful trace elements, is more difficult than treatment of wastewater containing other harmful trace elements. Necessary or required large-scale additional equipment. According to the invention of (3), it is possible to suppress the inflow of boron into the desulfurization waste water without requiring a large initial investment and without requiring a large-scale additional facility.

  (4) A harmful trace element scavenger containing alkali metal and / or salt thereof, or alkaline earth metal and / or salt thereof, which is added to coal as fuel in a coal-fired power generation system, A harmful trace element scavenger used to suppress the inflow of harmful trace elements into the desulfurization effluent discharged from the desulfurization device that removes sulfur oxides in exhaust gas generated by combustion.

  The invention of (4) captures the invention of (1) above as a harmful trace element scavenger, and the same effect as the invention of (1) can be obtained.

  (5) The harmful trace element scavenger according to (4), wherein the harmful trace element is boron.

  The invention of (5) captures the invention of (3) as a harmful trace element scavenger, and the same effect as the invention of (3) can be obtained.

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. An approximate power curve was created by taking the mass of alkali and / or alkaline earth metal in coal according to the mass of boron in coal per unit time as the X axis and the boron concentration of desulfurization effluent at that time as the Y axis. It is a graph. It is the graph which created the power approximation curve, taking the mass of calcium oxide in coal according to the mass of boron in coal per unit time as the X axis and the boron concentration of desulfurization waste water at that time as the Y axis. It is the graph which created the power approximation curve, taking the mass of calcium oxide in the ash according to the mass of boron in coal per unit time as the X axis and the boron concentration of 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 Air supply machine 16 Pulverized coal combustion part 161 Furnace 162 Heating machine 163 Air supply machine 18 Exhaust gas / drainage treatment part 181 Dust collector 182 Desulfurizer 183 Wastewater treatment facility S10 Coal supply process S20 Pulverized coal production process S30 Pulverized coal combustion process S40 Exhaust gas / wastewater treatment process S50 Hazardous trace element scavenger addition process

Claims (6)

An exhaust gas purifier containing a harmful trace element scavenger that is used in a thermal power generation system including a combustion boiler that burns fuel and traps harmful trace elements contained in exhaust gas generated by the combustion of the fuel,
The harmful trace element scavenger is an exhaust gas purifying agent containing an alkali metal and / or a salt thereof, or an alkaline earth metal and / or a salt thereof.   The exhaust gas purifier according to claim 1, wherein the alkali metal and / or salt thereof, or the alkaline earth metal and / or salt thereof includes one or more selected from the group consisting of limestone, slaked lime, and quicklime.   The exhaust gas purifying agent according to claim 1 or 2, wherein the harmful trace element is boron.   The exhaust gas purifying agent according to any one of claims 1 to 3, wherein the concentration of the alkali metal and / or the alkaline earth metal with respect to the fuel is 0.1 mass% or more and 20 mass% or less. A method for capturing harmful trace elements to be added.   The thermal power generation system includes a dust collector provided to remove dust contained in the exhaust gas, and the dust collector removes the dust from the step of adding the fuel to the combustion boiler with the exhaust gas purifying agent. The method for trapping harmful trace elements according to claim 4, which is added before the process.   The method for capturing harmful trace elements according to claim 4 or 5, wherein the thermal power generation system is a pulverized coal combustion type power generation system, and the exhaust gas purifying agent is added to the combustion boiler.

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