JP6744401B2 - Pulverized coal supply device and method for suppressing elution of harmful trace elements - Google Patents

Description

The present invention relates to a pulverized coal supply device and a harmful trace element elution suppressing method. In particular, a pulverized coal supply device used in a coal-fired power generation facility that uses pulverized coal as a fuel for a boiler and a method for suppressing toxic trace element elution, wherein an elution inhibitor that suppresses elution of harmful trace elements from coal combustion residue is pulverized. The present invention relates to the structure of a pulverized coal supply device and a method for suppressing harmful trace element elution, which can be reliably added to coal at a constant rate.

For example, a coal-fired power plant uses pulverized coal as a fuel for a boiler. In this coal-fired power plant, coal stored in a coal storage yard is discharged, and coal is conveyed to a pulverized coal supply device by a coal conveying mechanism such as a conveyor. This pulverized coal supply device includes a coal pulverizer (mill) that pulverizes lump coal until it becomes fine and produces pulverized coal.

The pulverized coal produced by the coal pulverizer is sent to the boiler and burned in the boiler. This combustion heats the water to generate steam. Note that oil may be supplied to the boiler during ignition inside the boiler.

The steam generated in the boiler is supplied to the steam turbine, the steam turbine drives a generator, and the generator can supply electric power. The steam that has passed through the steam turbine is condensed in a condenser and is condensed in the boiler together with makeup water.

The pulverized coal supply device described above includes a coal bunker that stores coal, a coal feeder, and a coal pulverizer. In the coal bunker, coal transported by the coal transport mechanism from the coal storage yard is temporarily stored. Then, coal is supplied from the coal bunker to the coal feeder through the first coal feeding pipe.

The coal feeder is provided with a conveyor inside, and the coal supplied from the coal feeding pipe is horizontally transferred by the conveyor. Then, the coal is discharged from the transfer conveyor to the coal dropping port formed at the end of the transfer conveyor. Further, the coal is fed into the coal pulverizer through the second coal feeding pipe formed so as to be connected to the coal dropping port. In the above-mentioned pulverized coal supply device, a coal gate valve for opening and closing the first coal feeding pipe is arranged directly above the coal feeding machine. This call gate valve can be opened and closed manually.

By the way, when the coal gate valve is manually driven in the closing direction to close the first coal feeding pipe, coal remains in a state of being accumulated between the coal feeding pipe after the coal gate valve and the conveyor. As a result, the first coal feeding pipe may be clogged with coal. Then, there is disclosed a pulverized coal supply device capable of stably supplying coal to the coal pulverizer even when the coal pulverizer is restarted after being stopped for a long time (see, for example, Patent Document 1). ..

On the other hand, in coal-fired power generation using pulverized coal as a fuel for a boiler, coal ash, which is a residue after combustion, contains trace amounts of harmful trace elements such as boron, fluorine, selenium, arsenic, and hexavalent chromium. Therefore, a technique for reducing the elution concentration of harmful trace elements contained in coal ash to be equal to or lower than the legally regulated value is being studied.

For example, when an elution inhibitor for coal addition consisting of calcium carbonate (CaCO ₃ ) is added to coal, many harmful trace elements are transferred to ash coal ash by the action of calcium oxide (CaO), and the action of alkali is also added. Discloses a method for suppressing the elution of harmful trace elements, which contributes to the suppression of elution of harmful trace elements (see, for example, Patent Document 2).

JP 2012-26724A JP 2008-275181 A

The harmful trace element elution suppressing method according to Patent Document 2 can be easily applied by improving existing equipment because the elution inhibitor is not added in the coal ash after burning but in the stage of coal before burning or before burning. , And. Further, the harmful trace element elution suppressing method according to Patent Document 2 is not particularly limited as long as the timing of addition is addition in the state of coal, and may be any of a coal feeder, a coal pulverizer, and a boiler. I am trying.

However, the method for suppressing the elution of harmful trace elements according to Patent Document 2 discloses the timing of the addition of the elution inhibitor for harmful trace elements, but does not specify the location of the elution inhibitor for harmful trace elements.

For example, when granular calcium carbonate (CaCO3) is mixed on a conveyor that conveys coal to a coal bunker, calcium carbonate having a particle size much smaller than that of agglomerated coal first falls to the bottom of the coal bunker, and the This results in variations in the mixing ratio of calcium carbonate. Further, since the mixing ratio of coal and calcium carbonate does not fall within a certain numerical range, there was a concern that harmful trace elements could not be successfully suppressed. There is a concern that it may be difficult to add the elution inhibitor for harmful trace elements to the coal in an appropriate ratio in the subsequent step of the coal bunker.

A pulverized coal supply device used in a coal-fired power generation facility that uses pulverized coal as a fuel for a boiler, and a harmful trace element elution suppressing method, wherein the mixing ratio of the coal and harmful trace element elution inhibitor may fall within a certain ratio. There is a demand for a pulverized coal supply device and a method for suppressing the elution of harmful trace elements. The above is the subject of the present invention.

The present invention has been made in view of such a problem, and is a pulverized coal supply device and a harmful trace element elution suppressing method used in a coal-fired power generation facility that uses pulverized coal as a fuel for a boiler, and coal and harmful An object of the present invention is to provide a pulverized coal supply device and a harmful trace element elution suppressing method capable of keeping the mixing ratio of the trace element elution inhibitor within a fixed ratio.

The present inventors comprise a pulverized coal supply device, which is a conveyor for conveying coal, and a coal pulverizer which is arranged below the end on the downstream side of the conveyor and pulverizes coal to produce pulverized coal. , A conveyor, or from above the coal pulverizer, an elution inhibitor that suppresses the elution of harmful trace elements is dropped into the coal pulverizer to keep the mixing ratio of coal and harmful trace element elution inhibitors constant. Therefore, based on this, the inventors have invented the following new pulverized coal supply device and harmful trace element elution suppressing method.

(1) A pulverized coal supply device according to the present invention is a coal bunker that stores coal, and a coal feeder having therein a conveyor that conveys coal supplied from the coal bunker from one end to the other end, And a pulverized coal supply device provided with a coal pulverizer that pulverizes the coal charged from the other end of the coal feeder to produce pulverized coal, wherein the coal feeder discharges coal. A box-shaped frame in which the coal dropping port is opened at the lower part of the other end, and an elution inhibitor that suppresses the elution of harmful trace elements from the combustion residues of coal can be dropped toward the coal dropping port of the frame. An elution preventing agent adding device , wherein the elution preventing agent adding device is a hopper that stores the elution preventing agent, and a screw that sends out the elution preventing agent supplied from the hopper toward a coal dropping port of the frame. A feeder, wherein the coal dropping port is disposed directly below the dropping port of the dissolution preventing agent dropped from the dissolution preventing agent adding device through the screw feeder, and the frame and the coal pulverizer are provided. And a first motor for driving the conveyor, the coal pulverizer includes coal and an elution inhibitor for the first coal feed. An upper portion that can be dropped from a pipe, the elution preventing agent adding device includes a second motor that drives the screw feeder and adjusts a rotation speed corresponding to a rotation speed of the first motor; The coal bunker has a second coal feeding pipe connected to one end of the coal feeding machine, a call gate valve that opens and closes a pipe line of the second coal feeding pipe, and a third driving gate valve. Including a motor, after rotating the output shaft of the third motor to close the pipeline of the second coal feeding pipe, when the predetermined first time has elapsed, stop the coal feeding machine, Further, it is controlled so that the coal pulverizer is stopped when the second time has elapsed .

(2) The elution inhibitor preferably contains at least one selected from the group consisting of limestone, slaked lime , and quick lime .

(3) It is preferable that the dissolution preventing agent is formed of a granular body or a powder body.

(4) The harmful trace element elution suppressing method according to the present invention is a harmful trace element elution suppressing method in a coal-fired power generation facility including a pulverized coal supply device having a coal bunker storing coal, wherein the pulverized coal supply device is A conveyor for conveying coal, a coal pulverizer arranged below the end on the downstream side of the conveyor, for pulverizing coal to generate pulverized coal, and one of coal supplied from the coal bunker. And a coal feeder having the conveyor inside for transporting from the end to the other end, wherein the coal feeder accommodates the conveyor, and the coal dropping port from which coal is discharged is the conveyor. A box-shaped frame that opens at the bottom of the other end of the, and an elution inhibitor that suppresses the elution of harmful trace elements from the combustion residues of coal toward the coal dropping port of the frame. A device, wherein the dissolution preventing agent adding device is a hopper that stores the dissolution preventing agent, and a screw feeder that discharges the dissolution preventing agent supplied from the hopper toward the coal dropping port of the frame. Comprising, the coal dropping port is arranged directly below the dropping port of the dissolution preventing agent dropped from the dissolution preventing agent adding device through the screw feeder, and connects the frame and the coal pulverizer. 1 consists of an inlet opening of a coal feeding pipe, the coal fine crusher has an opening at an upper portion so that coal and an elution inhibitor can be dropped from the first coal feeding machine, and a pipe line of the coal feeding pipe of the coal bunker is closed. After that, when a predetermined first time elapses, the coal feeding machine that conveys coal is stopped, and when the second time elapses, the coal pulverizer is stopped .

The pulverized coal supply device according to the present invention is formed at the end of the conveyor, and the elution inhibitor addition device is arranged above the coal dropping port where coal is discharged, and elution of harmful trace elements in the elution inhibitor addition device is performed. By storing the inhibitor and supplying the elution inhibitor for harmful trace elements from the elution inhibitor addition device toward the coal dropping port, the mixing ratio of the elution inhibitor for coal and harmful trace elements can be made constant.

The harmful trace element elution suppressing method according to the present invention is a harmful trace element elution suppressing method in a coal-fired power generation facility including a pulverized coal supply device, wherein the pulverized coal supply device is a conveyor that conveys coal, and a downstream of the conveyor. Equipped with a coal pulverizer that is disposed below the end on the side and that pulverizes coal to generate pulverized coal, and prevents elution of harmful trace elements from above the conveyor or the coal pulverizer. By dropping the agent to the coal pulverizer, the mixing ratio of the coal and the elution inhibitor for harmful trace elements can be made constant.

It is a schematic diagram showing the composition by an example of the coal-fired power generation equipment using the pulverized coal supply device by one embodiment of the present invention. It is a front view showing composition of a pulverized coal supply device by one embodiment of the present invention.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
(Composition of coal-fired power plant)
First, a configuration of an example of a coal-fired power generation facility using a pulverized coal supply device according to an embodiment of the present invention will be described.

FIG. 1 is a schematic diagram showing a configuration of an example of a coal-fired power generation facility using a pulverized coal supply device according to an embodiment of the present invention. FIG. 2 is a front view showing the configuration of the pulverized coal supply device according to the embodiment of the present invention.

Referring to FIG. 1, a coal-fired power generation facility 100 according to an example of the present invention includes a pulverized coal supply device 10 and a boiler 20. The coal-fired power generation facility 100 also includes a steam turbine 30 and a condenser 40.

Referring to FIG. 1 or 2, the pulverized coal supply device 10 includes a coal bunker 11 and a coal feeder 12. Further, the pulverized coal supply device 10 includes an elution inhibitor addition device 13 and a coal pulverizer 14.

Referring to FIG. 1 or 2, lump coal C is transported to a coal bunker 11 from a coal storage yard (not shown) by a conveyor 15 having a dustproof cover. Then, in the coal bunker 11, lumpy coal C is temporarily stored. The coal C stored in the coal bunker 11 is supplied to the coal feeder 12.

Referring to FIG. 2, the coal feeder 12 includes a transfer conveyor 12c inside. The conveyor 12c can convey the coal C supplied from the coal bunker 11 from one end to the other end. The coal pulverizer 14 can pulverize the coal C fed from the other end of the coal feeder 12 to produce pulverized coal.

Referring to FIG. 1, the boiler 20 has a combustion chamber 2r in which the pulverized coal produced by the coal pulverizer 14 is used as a fuel. In the example shown in FIG. 1, oil is sent to the combustion chamber 2r via an oil feed pipe (not shown). Then, in the combustion chamber 2r, it is possible to burn petroleum and pulverized coal. Combustion air is sent to the combustion chamber 2r by a fan. Thus, the two-stage combustion is performed in the combustion chamber 2r of the boiler 20. By this combustion, the water supplied from the water supply pump 41 is heated to become superheated steam, and this superheated steam is sent from the boiler 20 to the steam turbine 30.

Referring to FIG. 1, the steam turbine 30 includes a turbine (impeller) inside. By sending superheated steam to the turbine from its axial direction, the turbine can be rotated. The rotating shaft of the turbine is connected to the rotor of the generator 31. When superheated steam is sent to the steam turbine 30, the rotor of the generator 31 rotates to supply electric power.

Referring to FIG. 1, the superheated steam that has consumed kinetic energy in the steam turbine 30 is returned to water by being cooled and condensed in the condenser 40. In other words, it will be condensed. This condensed water is circulated to the boiler 20 by the water supply pump 41 together with the makeup water.

As described above, referring to FIG. 1 or FIG. 2, the coal-fired power generation facility 100 heats water in the boiler 20 using pulverized coal as fuel to generate superheated steam, and sends the superheated steam to the steam turbine 30. Power can be supplied by the generator 31.

[Composition of pulverized coal supply device]
Next, the configuration of the pulverized coal supply device 10 according to the embodiment of the present invention will be described.

(Coal bunker composition)
First, the configuration of the coal bunker 11 according to the embodiment will be described. Referring to FIG. 2, the coal bunker 11 is composed of an inverted conical main body 11b having an open top surface and a coal feeding pipe 11p extending from the bottom of the main body 11b. The coal feeding pipe 11p is connected to one end of the coal feeding machine 12. The massive coal C stored in the main body 11b can be dropped inside the coal feeder 12 via the coal feeding pipe 11p.

Referring to FIG. 2, a coal gate valve 11c is arranged along the coal feeding pipe 11p. The call gate valve 11c is internally provided with a valve body capable of opening and closing the pipeline of the coal feeding pipe 11p. The call gate valve 11c connects the third motor 11m.

Referring to FIG. 2, the call gate valve 11c internally includes a conversion mechanism (not shown) that converts the rotational movement of the third motor 11m into the forward/backward movement of the valve body. By rotating the output shaft of the third motor 11m in one direction, the pipeline of the coal feeding pipe 11p can be opened. By rotating the output shaft of the third motor 11m in the other direction, the pipeline of the coal feeding pipe 11p can be closed.

With reference to FIG. 2, the pulverized coal supply device 10 stops the coal feeder 12 when a predetermined first time elapses after closing the pipeline of the coal feed pipe 11p, and then further Since the coal pulverizer 14 is controlled to stop when the time of 2 has elapsed, the coal C in the coal feeding passage after the coal gate valve 11c is supplied to the coal feeder 12 and the coal gate valve 11c The coal C does not stay in the subsequent coal feeding passages. Therefore, even if the coal pulverizer 14 is stopped for a long period of time, it is possible to prevent coal clogging in the coal feeding passage.

(Structure of the coal feeder)
Next, the configuration of the coal feeder 12 according to the embodiment will be described. Referring to FIG. 2, the coal feeder 12 includes a box-shaped frame 12f and a conveyor 12c. The frame 12f opens a coal dropping port 12s from which the coal C is discharged, at a lower part of the other end.

Referring to FIG. 2, as a substance, the coal dropping port 12s is an inlet opening of a coal feeding pipe 14p that connects the frame 12f and the coal pulverizer 14. Pulverized coal can be generated by charging the coal C discharged to the coal dropping port 12s into the coal pulverizer 14 and crushing the lump coal C by the coal pulverizer 14.

Referring to FIG. 2, the conveyor 12c is composed of a pair of rollers 121 and 122 and an endless belt 12v. The pair of rollers 121 and 122 are arranged apart from each other. The pair of rollers 121 and 122 is wound around the endless belt 12v. In the example shown in FIG. 2, the roller 121 is the driving wheel and the roller 122 is the driven wheel.

Referring to FIG. 2, the drive-side roller 121 is connected to the first motor 12m. When the first motor 12m is rotated in one direction, the upper side of the endless belt 12v can travel from one end to the other end, and the coal C supplied from the coal bunker 11 is conveyed toward the coal dropping port 12s. it can. Moreover, the 1st motor 12m can adjust the input amount of the coal C input into the coal pulverizer 14 per unit time by controlling the rotation speed.

(Configuration of dissolution inhibitor addition device)
Next, the configuration of the dissolution preventing agent adding device 13 according to the embodiment will be described. Referring to FIG. 2, the dissolution preventive agent adding device 13 includes an inverted conical hopper 13h having an open upper surface and a screw feeder 13f. The hopper 13h stores the elution preventive agent Ea. The elution inhibitor Ea can suppress the elution of harmful trace elements from the combustion residue of coal.

Referring to FIG. 2, a gate valve 13v is provided between the hopper 13h and the screw feeder 13f. The gate valve 13v can open and close the conduit extending from the hopper 13h to the screw feeder 13f. By operating the handle, the conduit extending from the hopper 13h to the screw feeder 13f can be opened and closed.

Referring to FIG. 2, the screw feeder 13f can send the elution preventing agent Ea supplied from the hopper 13h toward the coal dropping port 12s of the frame 12f. The screw feeder 13f is connected to the second motor 13m.

Referring to FIG. 2, when the second motor 13m is rotated, the spiral screw 13s can be rotated to send out the elution preventive agent Ea in the axial direction. Further, the second motor 13m changes its rotation speed. By controlling, it is possible to adjust the amount of the dissolution preventing agent Ea to be charged into the coal pulverizer 14 per unit time via the coal dropping port 12s.

With reference to FIG. 2, the rotation of the second motor 13m in response to the rotation speed of the first motor 12m, that is, in response to the amount of coal C fed into the coal pulverizer 14 per unit time. By adjusting the speed, the amount of the elution inhibitor Ea added can be adjusted at an appropriate ratio.

[Operation of pulverized coal supply device]
Next, the operation and effect of the pulverized coal supply device 10 according to the embodiment will be described.

Referring to FIG. 1 or FIG. 2, the pulverized coal supply device 10 is formed at the end of the conveyor 12c, and above the coal dropping port 12s from which coal is discharged, a hopper 13h with a screw feeder 13f is arranged. The elution inhibitor Ea for harmful trace elements is stored in the hopper 13h, the screw feeder 13f is driven, and the elution inhibitor Ea for harmful trace elements is supplied from the hopper 13h to the coal dropping port 12s, so that the harmful trace elements are prevented. The mixing ratio of the trace element elution inhibitor Ea can be made constant.

Referring to FIG. 2, the coal feeder 12 includes a first motor 12m that drives the conveyor 12c. Further, the dissolution preventing agent adding device 13 includes a second motor 13m that drives the screw feeder 13f. By adjusting the rotation speed of the second motor 13m in accordance with the rotation speed of the first motor 12m, that is, in accordance with the amount of coal C charged into the coal pulverizer 14 per unit time, The addition amount of the dissolution inhibitor Ea can be adjusted at an appropriate ratio.

With reference to FIG. 2, the elution inhibitor Ea contains at least one selected from the group consisting of limestone, slaked lime , and quick lime . The dissolution inhibitor Ea is preferably composed of a granular material or a powder material. It is preferable that the average particle diameter of the elution inhibitor Ea does not exceed 200 μm. It becomes possible to mix the pulverized coal and the elution inhibitor Ea and send them to the boiler 20.

With reference to FIG. 1 or FIG. 2, it is preferable that the coal pulverizer 14 be provided with a classifying device utilizing centrifugal force, that is, a so-called dry cyclone inside. After pulverizing the pulverized coal and the elution preventing agent Ea pulverized by the coal pulverizer 14, the pulverized coal and the elution preventing agent Ea can be sent to the boiler 20.

With reference to FIG. 2, the means for supplying the dissolution preventive agent Ea to the coal feeder 12 is not limited to the screw feeder 13f. As long as it is a transportation means suitable for powder transportation, the kind of the feeder or the conveyor serving as the supply means is not limited.

With reference to FIG. 2, the elution preventive agent Ea may be dropped on the conveyor 12c, and the elution preventive agent Ea that suppresses elution of harmful trace elements from above the coal finer grinder 14 is added to the coal finer. By dropping it in No. 14, the amount of the elution inhibitor Ea added to coal can be adjusted at an appropriate ratio.

The pulverized coal supply device according to the present invention is provided with separate means for injecting the coal and the elution inhibitor into the coal feeder, thereby adding the elution inhibitor in accordance with the rotation speed of the first motor that drives the conveyor. You can adjust the amount.

The harmful trace element elution suppressing method according to the present invention can separately supply the coal and the elution inhibitor on the upstream side of the coal pulverizer without mixing the coal and the elution inhibitor on the conveyor that conveys the coal to the coal bunker. Therefore, the amount of the elution inhibitor added to the coal can be adjusted.

The pulverized coal supply device according to the present invention can be expected to have the following effects.
(1) Mixing with pulverized coal, sending an elution inhibitor with a proper composition to the boiler and burning it at a high temperature, it is possible to promote the incorporation of harmful trace elements into the coal ash.
(2) Since an elution inhibitor having a proper composition mixed with pulverized coal is sent to the boiler and burned at a high temperature, harmful trace elements flowing from the exhaust gas into the desulfurization device can be suppressed.

10 Pulverized coal supply device 11 Coal bunker 12 Coal feeder 12c Conveyor 12f Frame 12s Coal drop port 13 Elution inhibitor addition device 14 Coal pulverizer C Coal Ea Elution inhibitor

Claims (4)

A coal bunker that stores coal, a coal feeder having a conveyor for transporting the coal supplied from the coal bunker from one end to the other end, and from the other end of the coal feeder. A pulverized coal supply device equipped with a coal pulverizer that pulverizes the input coal to produce pulverized coal,
The coal feeder is
A box-shaped frame in which the coal dropping port from which coal is discharged is opened at the bottom of the other end,
To the coal dropping port of the frame, an elution preventing agent adding device that can drop an elution preventing agent that suppresses elution of harmful trace elements from coal combustion residues is provided,
The dissolution preventing agent adding device,
A hopper that stores the dissolution inhibitor,
A screw feeder that feeds the elution inhibitor supplied from the hopper toward the coal dropping port of the frame,
The coal dropping port is arranged immediately below the dropping port of the elution preventing agent dropped from the elution preventing agent adding device via the screw feeder, and connects the frame with the coal pulverizer. It consists of the inlet opening of the coal pipe,
The coal feeder includes a first motor that drives the conveyor.
The coal pulverizer has an upper opening that allows the coal and the dissolution inhibitor to be dropped from the first coal feeding pipe,
The dissolution preventing agent adding device includes a second motor that drives the screw feeder and adjusts a rotation speed of the first motor in accordance with a rotation speed of the first motor,
The coal bunker is
A second coal feeding pipe connected to one end of the coal feeding machine;
A call gate valve that opens and closes the pipeline of the second coal feeding pipe;
A third motor for driving the call gate valve,
After the output shaft of the third motor is rotated to close the pipeline of the second coal feeding pipe, the coal feeding machine is stopped when a predetermined first time has elapsed, and the second time is further elapsed. A pulverized coal supply device, which is controlled so as to stop the coal pulverizer after a lapse of time. The pulverized coal supply device according to claim 1, wherein the elution inhibitor contains at least one selected from the group consisting of limestone, slaked lime , and quick lime . The pulverized coal supply device according to claim 2, wherein the elution inhibitor is a granular material or a powder material. A method for suppressing elution of harmful trace elements in a coal-fired power generation facility including a pulverized coal supply device having a coal bunker that stores coal,
The pulverized coal supply device,
A conveyor for conveying coal,
A coal pulverizer that is disposed below the downstream end of the conveyor and that pulverizes coal to produce pulverized coal.
A coal feeder having the transfer conveyor for transferring the coal supplied from the coal bunker from one end to the other end ,
The coal feeder is
A box-shaped frame that accommodates the transport conveyor and opens a coal dropping port from which coal is discharged at the lower end of the other end of the transport conveyor,
To the coal dropping port of the frame, an elution preventing agent adding device that can drop an elution preventing agent that suppresses elution of harmful trace elements from coal combustion residues is provided,
The dissolution preventing agent adding device,
A hopper that stores the dissolution inhibitor,
A screw feeder that feeds the elution inhibitor supplied from the hopper toward the coal dropping port of the frame ,
The coal dropping port is arranged immediately below the dropping port of the elution preventing agent dropped from the elution preventing agent adding device via the screw feeder, and connects the frame and the coal pulverizer to the first feed. It consists of the inlet opening of the coal pipe,
The coal pulverizer has an upper opening that allows the coal and the dissolution inhibitor to be dropped from the first coal feeding pipe,
After closing the pipeline of the coal feeding pipe of the coal bunker, the coal feeding machine that conveys coal is stopped when a predetermined first time has elapsed, and the coal pulverizer is further activated when the second time has elapsed. The method of controlling the elution of harmful trace elements is controlled so as to stop.

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