JP6079940B2 - Arsenic elution suppression method - Google Patents

Description

  The present invention relates to an arsenic elution suppression method for suppressing elution of arsenic from combustion residue (coal ash) of coal used as fuel in a thermal power plant that generates power by burning coal.

  Conventionally, when coal is burned in a combustion furnace such as a power plant, by adding a calcium-containing substance such as limestone as an additive, trace substances such as arsenic contained in coal are eluted from coal ash, which is a combustion residue. There has been proposed a method for suppressing the elution of trace substances that is difficult to perform (see, for example, Patent Document 1).

JP 2008-170110 A

  However, when an additive is added to coal and burned, the amount of additive is small compared to the amount of coal, so it may be difficult to burn in a state where coal and additive are uniformly mixed. And the arsenic elution suppression effect from the combustion residue may not be stable.

  Therefore, an object of the present invention is to provide an arsenic elution suppression method capable of suppressing arsenic elution from coal combustion residue more stably.

The present invention mixes a plurality of types of coal including a first coal having an arsenic concentration of 2.0 ppm or more by mass and one or more other types of coal other than the first coal. An arsenic elution suppression method that suppresses arsenic elution from the combustion residue of coal by burning, and the mass of the total alkaline earth metal amount in terms of oxide with respect to the total arsenic amount in the total coal after mixing The present invention relates to an arsenic elution suppression method in which mixing is performed so that the ratio P ₀ is 2000 or more.

Further, in the first coal, for arsenic amount, it is preferred weight ratio P ₁ of the alkaline earth metal of the oxide-equivalent is less than 2000.

Further, the in other coal, relative to the total arsenic content, it is preferred weight ratio P ₂ of the total alkali earth metal of the oxide-equivalent is 2000 or more.

Further, it is preferable that the mass ratio _{P 2} and [Delta] P ₌ P 2 -P ₁ is the difference _{P 1} is 1000 or more.

  Moreover, it is preferable that the said 1st coal is 10% or more and 90% or less.

  The arsenic elution suppression method preferably further includes an arsenic elution inhibitor.

  According to the arsenic elution suppression method of the present invention, arsenic elution from coal combustion residues can be suppressed more stably.

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

<A: Configuration of pulverized coal combustion facility in coal-fired power plant>
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 plant to which the present invention is applied. 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. The combustion part 16 and the coal ash process part 18 which processes the coal ash produced | generated by combustion of pulverized coal are provided.

<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 bunker 121 includes, for example, a plurality of coal storage tanks that are partitioned from each other, and each of the plurality of coal storage tanks can store and manage different types of coal. The coal feeder 122 continuously supplies the coal supplied from the coal bunker 121 to the coal pulverized coal machine 123. 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 123 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.

<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 that heats the furnace 161, and an air supply unit 163 that supplies air to the furnace 161. Prepare.

  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. In the furnace 161, coal ash is produced by burning pulverized coal. The coal ash generated in the furnace 161 is divided into fly ash that moves to the coal ash treatment unit 18 side as floating particles together with exhaust gas, and clinker ash that drops and accumulates at the bottom of the furnace 161 due to aggregation of a plurality of particles. Broadly divided.

  The furnace 161 will be described in detail with reference to FIG. 2. In FIG. 2, the furnace 161 has a substantially inverted U shape as a whole, and after the combustion gas moves in an inverted U shape along the arrow in the figure. Then, it is reversed again into a U-shape, and the outlet of the furnace 161 (the last of the arrows in FIG. 2) is connected to the denitration device 181 and the dust collector 182 in FIG. In the pulverized coal combustion facility 1 according to the present embodiment, the height of the furnace 161 is 30 m to 70 m, and the total length of the exhaust gas flow path ranges from 300 m to 1000 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. Further, near the top of the U-shape in the furnace 161, a furnace upper dividing wall 161b, a final superheater 161b ′, and a first reheater 161f (all of which are heat exchange units) are arranged, and further placed horizontally from there. A primary superheater 161c (heat exchange unit) is subsequently arranged. Further, a second reheater 161f ′ is provided in parallel with the horizontal primary superheater 161c, and from the vicinity of the terminal end of the horizontal primary superheater 161c, a primary economizer 161d (heat exchange unit). A secondary economizer 161e (heat exchange unit) is provided in two stages. Here, the economizer (also referred to as ECO) is a heat transfer surface group provided for preheating boiler feedwater using heat held by combustion gas. 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: Coal ash treatment unit>
The coal ash treatment unit 18 collects the denitration device 181 that removes nitrogen oxides in the exhaust gas discharged from the pulverized coal combustion unit 16, the dust collector 182 that removes soot (coal ash) in the exhaust gas, and the dust collector 182. And a coal ash recovery silo 183 for primarily storing the coal ash thus obtained.

  The denitration device 181 removes nitrogen oxides in the exhaust gas. In other words, ammonia gas is injected as a reducing agent into exhaust gas at a relatively high temperature (300 to 400 degrees), and nitrogen oxides in the exhaust gas are decomposed into harmless nitrogen and water vapor by the action of a denitration catalyst. A reduction method is preferably used.

  The dust collector 182 is a device that collects coal ash in the exhaust gas with an electrode. The coal ash collected by the dust collector 182 is conveyed to the coal ash collection silo 183. Further, the exhaust gas from which the coal ash has been removed is discharged from the chimney after passing through a desulfurization apparatus (not shown).

  The coal ash collection silo 183 primarily stores the coal ash collected by the dust collector 182.

<B: Arsenic elution suppression method of the present invention>

Coal used as fuel contains silicon, aluminum, calcium, magnesium, and the like as ash in addition to carbon as a main component. Coal contains trace amounts of harmful elements such as selenium, fluorine, boron, and arsenic.
Here, the various components contained in the coal vary greatly depending on the coal type. For this reason, depending on the type of coal used as fuel, the concentration of harmful elements eluted from coal ash, which is a combustion residue, increases, which may affect the environment.

  On the other hand, by adding calcium-containing substances such as limestone as an additive, a method for suppressing the elution of trace substances that makes it difficult to elute trace substances such as arsenic contained in coal from coal ash, which is a combustion residue, is proposed. Has been. However, when an additive is added to coal and burned, the amount of additive is small compared to the amount of coal, so it may be difficult to burn in a state where coal and additive are uniformly mixed. It may occur, and the elution suppression effect of harmful elements from the combustion residue may not be stable.

  The inventors pay attention to the fact that the content of various components varies greatly depending on the coal type of coal, and the mass ratio of the total alkaline earth metal amount in terms of oxide to the total amount of arsenic contained in the coal to be burned is predetermined. Found that the leaching of arsenic from coal ash is suppressed when it is within the range, and even when coal with a high arsenic concentration is used, this coal is mixed with other coal that satisfies the specific composition Thus, the present invention has reached the present invention that can stably suppress elution of arsenic from the combustion residue.

More specifically, the arsenic elution suppression method of the present invention includes a first coal having an arsenic concentration of 2.0 ppm or more by mass ratio, and one or more other coals other than the first coal. Is a method for suppressing arsenic elution by suppressing arsenic elution from coal combustion residue (coal ash) by mixing and burning a plurality of types of coal, including all arsenic in all coal after mixing The mass ratio P ₀ of the total alkaline earth metal amount in terms of oxide to the amount (P ₀ = total alkaline earth metal amount in terms of oxide / total arsenic amount) is 2,000 or more. Hereinafter, the present invention will be described using the pulverized coal combustion facility 1 described above.

The arsenic elution suppression method of the present invention includes coal supply step S10 for supplying coal, pulverized coal generation step S20 for pulverizing the supplied coal to generate pulverized coal, and burning the pulverized coal to generate coal ash. The pulverized coal combustion step S30 and the coal ash treatment step S40 that collects and stores the coal ash, each of which includes the coal supply unit 12 and the pulverized coal of the pulverized coal combustion facility 1 described above, respectively. It is performed in the generation unit 14, the pulverized coal combustion unit 16, and the coal ash processing unit 18.
And mixing of the multiple types of coal which is the characteristics of this invention is preferably performed in said coal supply process S10.

<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.
In the present invention, the coal pulverizer 141 has a mass ratio P ₀ (P ₀ = total alkali in oxide equivalent) of the total alkaline earth metal amount in terms of oxide to the total amount of arsenic in the total coal after mixing. A plurality of types of coal are mixed and supplied so that (earth metal amount / total arsenic amount) is 2000 or more.

  Coal mixing in the coal supply step S10 is performed by, for example, storing a plurality of types of coal including a first coal having an arsenic concentration of 2.0 ppm or more in a mass ratio in a plurality of coal storage tanks in the coal bunker 121. When paying out one coal from the coal storage tank, the coal stored in the other coal storage tank is dispensed at the same timing so as to have a predetermined ratio with respect to the first coal. The coals are joined together on a belt conveyor or the like and supplied to the coal pulverizer 141. Thereby, a plurality of types of coal are supplied to the coal pulverized coal machine 141 at a substantially equal ratio.

As the first coal, arsenic concentration is as high as 2.0 ppm or more in mass ratio, and conventionally, it is possible to use a coal type that has been difficult to use as fuel in a thermal power plant. Among them, in the present invention, as the first coal, the mass ratio P _{1 of the} amount of alkaline earth metal in terms of oxide to the amount of arsenic (P ₁ = amount of alkaline earth metal in terms of oxide / arsenic amount) is set. Coal with a relatively low alkaline earth metal content, less than 2000, can also be used.

As other coals, when mixed with the first coal, the mass ratio P ₀ of the total alkaline earth metal amount in terms of oxide to the total amount of arsenic in the coal after mixing P ₀ (P ₀ = total alkali in terms of oxide) From the viewpoint of keeping the amount of earth metal / total amount of arsenic in a suitable range, the mass ratio P ₂ of the total alkaline earth metal amount in terms of oxide to the total amount of arsenic (P ₂ = total alkaline earth metal in terms of oxide) It is preferable to use coal whose amount / total arsenic amount is 2000 or more.

  Moreover, it is preferable that the ratio of the 1st coal contained in coal after mixing is 10% or more and 90% or less by mass ratio from a viewpoint of making it easy to mix multiple types of coal uniformly.

The difference between the mass ratio _{P 2} and _{P 1} described above (ΔP ₌ P 2 -P ₁₎ is preferably 1000 or more. By selecting another coal in such a combination that ΔP is 100 or more with respect to the first coal, in the case where the first coal is used as fuel, arsenic elution from coal ash is effectively prevented. Can be suppressed.

<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.

<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. The coal ash (fly 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.

<Coal ash treatment process S40>
Thereafter, the coal ash generated by burning pulverized coal is discharged to the denitration device 181 together with the exhaust gas, and sent to the coal ash recovery silo 183 through the dust collector 182.

The coal ash recovered in the coal ash recovery silo 183 through the above steps has a reduced arsenic elution amount. This is because the alkaline earth metal element contained in the coal softens the surface of the coal ash due to the high temperature in the furnace 161, and the viscous coal ash particles come into contact with arsenic and take arsenic into the coal ash. It is estimated that
Moreover, in this embodiment, focusing on the alkaline earth metal content and arsenic content which differ for every charcoal type, the elution of arsenic can be stably suppressed by mixing multiple types of coal. This is considered due to the fact that the alkaline earth metal can be distributed more uniformly than when limestone or the like is added as an additive. This effect can be further improved by setting the ratio of the first coal contained in the coal after mixing to 10% or more and 90% or less by mass ratio.
In addition, the mass ratio P ₀ of the total alkaline earth metal amount in terms of oxide to the total arsenic amount in all coal after mixing is adjusted (P ₀ = total alkaline earth metal amount in terms of oxide / total arsenic amount). Therefore, a small amount of an arsenic elution inhibitor made of limestone or the like may be added.

Hereinafter, the present invention will be described more specifically with reference to examples.
[Ingredient composition for each coal type]
For 36 types of coal 1 to coal 36 shown in Tables 1 to 4 below, the amount of alkaline earth metal (calcium oxide and magnesium oxide) in ash, the ash content, and the amount of arsenic in coal were measured. Further, to determine the mass ratio P ₀ of the total alkali earth metal of the oxide in terms to the total arsenic content. As shown in Tables 1 to 4, it can be seen that the content of various components varies greatly depending on the coal type.

  The arsenic concentration in the coal was obtained by performing elemental analysis by ICP mass spectrometry after the pretreatment. The amount of alkaline earth metal in the coal was determined as the total amount of calcium oxide and magnesium oxide by determining the ash content in the coal and then analyzing the ash composition by fluorescent X-ray analysis.

[Arsenic elution test from coal ash]
<Examples 1-11, Comparative Examples 1-9>
As shown in Tables 5, 7, 9, and 11, the first coal and other coals were selected. And in the above-mentioned coal supply part 12, two types of coal were mixed with the blend ratio shown in Tables 6, 8, 10, and 12, and burned in the pulverized coal combustion part 16. Thereafter, the elution concentration of arsenic was measured for the coal ash recovered by the coal ash recovery silo 183. The results are shown in Tables 6, 8, 10, and 12.

  In addition, the measurement result of the elution concentration shown below is obtained by performing an elution operation according to Environment Agency Notification No. 46, preparing a test solution, and measuring the concentration of arsenic in this test solution. The arsenic concentration was measured by ICP mass spectrometry.

As shown in Tables 5 to 12, in Examples 1 to 11 in which the mass ratio P ₀ of the total alkaline earth metal amount in terms of oxide to the total amount of arsenic in the total coal after mixing is 2000 or more, P ₀ It can be seen that the arsenic elution concentration is suppressed to less than 0.020 mg / l, as compared with Comparative Examples 1 to 9 having a value of less than 2000. In particular, in Examples 1 to 4 where P ₀ is 6000 or more, it can be seen that the elution concentration of arsenic is greatly suppressed to less than 0.010 mg / l.

[Arsenic dissolution test 2 from coal ash]
Coal ash with properties similar to fly ash by pulverized coal combustion in a coal-fired power plant was generated using a small combustion test device, and further investigation was conducted on the elution of arsenic from the generated coal ash.

<Example 13, Comparative Example 9>
For two types of coal 37 and coal 38 shown in Table 13 below, the amount of alkaline earth metal (calcium oxide and magnesium oxide) in ash, the ash content, and arsenic in coal were measured. Moreover, mass ratio P of the total alkaline-earth metal amount of oxide conversion with respect to the total amount of arsenic was calculated | required.

[Generation of coal ash]
As shown in Table 14, the coal 37 is the first coal, the coal 38 is the other coal, and two types of coal are mixed at the blend ratio shown in Table 14 and burned in a small combustion test apparatus. Coal ash was recovered.

A vertical tubular furnace provided with a combustion tube made of zirconia having an inner diameter of 50 mmΦ × 1200 mmL was used as a small combustion test apparatus.
The coal used in the test was first put in a drying apparatus adjusted to a specified temperature (107 ° C. ± 2 ° C.) in the form of pulverized coal, and continued to be dried until the loss on drying was less than 0.1% per hour. . Thereafter, the dried pulverized coal was mixed at a predetermined ratio. Next, pulverized coal mixed in a stainless steel fuel hopper disposed at the upper part of the combustion pipe was filled, and supplied to the upper part of the combustion pipe heated to 1450 ° C. by an electric screw feeder at 2 g / min for combustion. The supply of pulverized coal to the combustion tube was performed together with the supply of nitrogen gas to the combustion tube, thereby preventing backfire inside the combustion tube. Combustion air (atmosphere) was supplied at 200 cc / min from two locations, the upper and lower portions of the combustion tube.
The coal ash produced by burning inside the combustion tube was collected by suction from the lower side surface of the combustion tube. And the elution density | concentration of boron was measured about the collect | recovered coal ash. The results are shown in Table 14.
In addition, a result is shown by the relative value when the elution density | concentration of Example 12 is set to 100.

From the results of Table 13 and Table 14, even in the coal ash that is simply generated using a small combustion test apparatus, the mass of the total alkaline earth metal amount in terms of oxide relative to the total amount of arsenic in the total coal after mixing. In Example 12 in which the ratio P ₀ was large, it was confirmed that the elution concentration of arsenic was suppressed as compared with Comparative Example 10 in which P ₀ was less than 2000.

DESCRIPTION OF SYMBOLS 1 Pulverized coal combustion facility 12 Coal supply part 121 Coal bunker 122 Coal feeder 14 Pulverized coal production | generation 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 Coal ash treatment part 181 Denitration device 182 Dust collector 183 Coal ash recovery silo

Claims (6)

By mixing and burning a plurality of types of coal including a first coal having an arsenic concentration of 2.0 ppm or more by mass ratio and one or more other coals other than the first coal An arsenic elution suppression method for suppressing arsenic elution from coal combustion residues,
In all coal in after mixing, to the total arsenic content, arsenic elution suppressing method of mixing as the weight ratio P ₀ of the total alkali earth metal of the oxide in terms becomes 2000 or more. Wherein in the first coal, arsenic elution suppressing method according to claim 1 for the arsenic content, the weight ratio P ₁ of the alkaline earth metal of the oxide-equivalent is less than 2000. Wherein the other coal, relative to the total arsenic content, arsenic elution suppressing method according to claim 1 or 2 weight ratio P ₂ of the total alkali earth metal of the oxide-equivalent is 2000 or more. The arsenic elution suppression method according to claim 3, wherein ΔP = P ₂ −P ₁ which is a difference between the mass ratios P ₂ and P ₁ is 1000 or more.   The arsenic elution suppression method according to any one of claims 1 to 4, comprising 10% or more and 90% or less of the first coal. The arsenic elution suppression method according to any one of claims 1 to 5, further comprising an arsenic elution inhibitor.

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