JP4671976B2 - Hazardous trace element elution inhibitor addition amount calculation method and harmful trace element elution suppression method using the same - Google Patents

Description

  The present invention relates to a harmful trace element elution inhibitor for calculating the amount of harmful trace element elution inhibitor used to suppress the elution of harmful trace elements from combustion residues of coal as a fuel in a coal-fired power generation system. The present invention relates to an addition amount calculation method and a harmful trace element elution suppression method using the same.

  There are various methods for burning coal in a coal-fired power generation system. Among them, a so-called pulverized coal combustion method in which finely pulverized coal is blown into a furnace and burned is mainly employed. A part of the coal ash, which is a residue after combustion, is used as civil engineering and building materials such as concrete and soil improvement materials from the viewpoint of effective use of resources, but the surplus is disposed of in landfills.

  By the way, coal used as fuel contains a trace amount of harmful elements such as boron, fluorine, selenium, arsenic and hexavalent chromium in addition to carbon. For this reason, in consideration of the environment, the allowable concentration of harmful trace elements from coal ash is regulated by law. However, there are over 100 coal types exported to Japan per year, and not all of them satisfy the above-mentioned regulatory values. For this reason, the technique for reducing the elution density | concentration of the harmful trace element contained in coal ash to below a regulation value is examined.

  For example, a method of adding a trace element elution inhibitor such as a chelating agent to coal ash, or a method of solidifying coal ash with cement or the like is performed (see Patent Documents 1 to 3).

Furthermore, in Patent Document 4, coal is burned in a combustion furnace (A), the exhaust gas is treated with an electric dust collector, and the resulting dust collection ash is used as a main fuel in the combustion furnace (B), Disclosed is a method for treating combustion ash by which the incinerated ash that has been burned again with the addition of a calcium source has a boron content of 1.0 mg / l or less by a dissolution test method based on Notification No. 18 of the 2003 Environment Agency. According to this treatment method, since coal ash is burned again in a combustion furnace to which a calcium source can be added, elution of boron contained in the incinerated ash can be suppressed. It is said that it can be used soon.
JP 2003-164886 A JP 2003-200132 A JP 2002-194328 A JP 2005-134098 A

  However, the conventional techniques described in Patent Document 1 to Patent Document 3 reduce the elution concentration of harmful trace elements by adding an additive to coal ash that is a combustion residue. In this case, silos, water tanks, mixing equipment, etc. are required on a large scale as equipment for adding and mixing additives to coal ash, resulting in high processing costs and new equipment space. is there.

  Further, in the conventional techniques described in Patent Document 1 to Patent Document 3, although prevention of elution of heavy metals has been studied, studies on prevention of elution of light elements such as boron and fluorine have been insufficient.

  About the processing method of patent document 4, the dust collection ash obtained with the combustion furnace is burned again with limestone etc., and possibility of the processing cost of dust collection ash becoming high is high. Furthermore, the means for adding limestone has not been clarified and may require additional equipment. Moreover, in the processing method of patent document 4, the combustion temperature at the time of a coal ash process is as low as 700 to 900 degreeC, and cannot implement it suitably in a high temperature furnace. In addition, this treatment method cannot be suitably implemented even in a pulverized coal combustion furnace or the like. Moreover, the element used as the object of elution prevention is restricted to boron, and cannot be used as a general elution prevention method for trace metals.

  Incidentally, when coal containing a large amount of calcium is burned in a combustion furnace, it has been known that the melting point of coal ash is lowered, causing problems such as slagging and fouling. For this reason, when the coal and coal ash and the calcium source are made to coexist and burn as in Patent Document 4, it is necessary to pay attention so that the melting point of the generated coal ash does not decrease too much. In the invention described in Patent Document 4, such consideration is not made when adding a calcium source, and there is a risk of damaging the combustion furnace.

  The present invention has been made in view of the above-described problems, and does not require a large initial investment, and does not require large-scale additional equipment. Elution of harmful trace elements from coal combustion residues in a coal-fired power generation system Is a harmful trace element elution control method that reduces the risk of damaging the combustion furnace, and is used in determining the amount of harmful trace element elution inhibitor added in this method. It is an object to provide a method for calculating the addition amount of a trace element elution inhibitor.

(1) In coal-fired power system comprising a combustion furnace for burning coal, harmful trace elements eluted inhibitor amount for calculating the amount of harmful trace elements elution suppressing agent to be added due to adverse trace elements elution preventing the coal In the calculation method, the harmful trace element elution inhibitor includes at least one selected from the group consisting of limestone, quicklime, and slaked lime, and the harmful trace element elution inhibitor addition amount calculation method includes the coal the harmful trace elements elution inhibitor when burned in the combustion furnace by adding a predetermined amount, measuring the content of calcium oxide remaining in the coal ash, calcium element content of calcium oxide amount measuring step of converting the to And, the calcium oxide content measured in the calcium oxide content measurement step is converted into the calcium element content, and the calcium element conversion of the harmful trace element elution inhibitor Subtracting the content of calcium oxide converted to the amount of calcium element from the amount added in step, and calculating the amount of calcium element contributing to the melting of the coal ash in the combustion furnace, Determine the upper limit of the amount of harmful trace element elution inhibitor to be added, as long as the amount of calcium that contributes to melting of the coal ash calculated in the coal ash melting contribution calcium amount calculation step does not melt the coal ash in the combustion furnace. A harmful trace element elution inhibitor addition amount determination step, comprising: a harmful trace element elution inhibitor addition amount determination step.

  When a harmful trace element elution inhibitor containing at least one selected from the group consisting of limestone, quicklime, and slaked lime is added to coal and burned in a combustion furnace, the limestone and slaked lime are pyrolyzed to produce calcium oxide. . A part of these calcium oxide and calcium oxide contained in quicklime reacts with silica, alumina, etc. in coal ash to form a low melting point compound. On the other hand, the calcium component that does not form the low-melting-point compound is transferred as it is to the coal ash as calcium oxide.

  Here, when a harmful trace element elution inhibitor is added to coal, the melting point of coal ash decreases depending on the formation of low melting point compounds, and the calcium oxide remaining in the coal ash is coal ash. Does not contribute to the lowering of the melting point.

  According to the invention described in (1), the content of calcium oxide contained in coal ash when a predetermined amount of harmful trace element elution inhibitor is added to coal and burned in the calcium oxide amount measuring step. In the process of calculating the calcium content that contributes to coal ash fusion, subtract this amount of calcium oxide from the added amount of the toxic trace element elution inhibitor, and suppress the toxic trace element elution in the process of determining the added amount of toxic trace element elution inhibitor In order to determine the upper limit value of the additive amount of the agent, it is possible to extract only elements that contribute to the decrease in the melting point of coal ash and determine the upper limit value of the additive amount of the harmful trace element elution inhibitor. Therefore, it is possible to calculate the exact value of harmful trace element elution inhibitor that can be added to coal, and to prevent harmful trace element elution to the maximum extent without adversely affecting the combustion furnace. Can be easily determined.

  (2) In the harmful trace element elution inhibitor addition amount determination step, an upper limit value of the additive amount of the harmful trace element elution inhibitor is determined for each coal type of the coal to be burned in the combustion furnace. (1) 4. The method for calculating the amount of harmful trace element elution inhibitor added according to 1.

  In general, the content of calcium contained in coal differs depending on the coal type of coal, and this calcium content also contributes to the lowering of the melting point of coal ash. According to the invention described in (2), since the upper limit value of the addition amount of the harmful trace element elution inhibitor is determined for each coal type, more accurate addition amount can be calculated.

  (3) The combustion furnace is a pulverized coal combustion furnace, and in the harmful trace element elution inhibitor addition amount determination step, the addition amount of the harmful trace element elution inhibitor so that the melting point of the coal ash is 1200 ° C. or higher. The method for calculating the additive amount of the harmful trace element elution inhibitor according to (1) or (2), wherein an upper limit value is determined.

  Generally, in the pulverized coal combustion furnace, the temperature of the pulverized coal combustion section ranges from 1300 ° C to 1500 ° C. According to the invention described in (3), since the upper limit value of the amount of harmful trace element elution inhibitor is determined so that the melting point of coal ash is 1200 ° C. or higher, coal ash is slugged even in a pulverized coal combustion furnace. To the extent that fouling occurs, it does not melt excessively and does not damage the combustion furnace.

  (4) The harmful trace element elution inhibitor addition amount calculation method further dissolves 10 parts by mass of coal ash in 100 parts by mass of water based on the content of calcium oxide measured in the calcium oxide amount measurement step. Including a pH calculation step for calculating the pH at the time of addition, and the addition of the harmful trace element elution inhibitor in the range in which the pH calculated in the pH calculation step is 12 or more in the harmful trace element elution inhibitor addition amount determination step The method for calculating the addition amount of a harmful trace element elution inhibitor according to any one of (1) to (3), wherein a lower limit value of the amount is further determined.

  According to the invention described in (4), the lower limit value of the addition amount of the harmful trace element elution inhibitor is determined within a range in which the pH is 12 or more when 10 parts by mass of coal ash is dissolved in 100 parts by mass of water. can do. Since many harmful trace elements have the property that elution is suppressed under high pH conditions, according to the invention described in (4), the addition amount of the harmful trace element elution inhibitor is reduced by the amount of harmful trace elements. It can be determined within a range in which elution can be effectively suppressed.

  (5) Combustion furnace combustion within the range of the addition amount calculated by the method for calculating the addition amount of the harmful trace element elution inhibitor according to any one of (1) to (4). A harmful trace element elution suppression method of adding quick lime and / or slaked lime to a downstream part of a combustion part of a combustion furnace and / or coal ash.

  According to the invention described in (5), the harmful trace element elution inhibitor is added in the addition amount calculated by the method for calculating the harmful trace element elution inhibitor addition amount described in any of (1) to (4). Therefore, the elution of harmful trace elements from the generated coal ash can be minimized while minimizing the adverse effects on the combustion furnace.

  In addition, in the invention described in (5), by adding a harmful trace element elution inhibitor to coal and adding quick lime and / or slaked lime to the coal ash, sufficient elution of the harmful trace element from the coal ash is sufficient. Since it can suppress, the cost required for prevention of the elution of harmful trace elements from coal ash can be minimized, and further, new capital investment can be minimized.

  (6) The harmful trace element elution suppression method according to claim 5, wherein quick lime and / or slaked lime is added in a range of 0.3 to 50 parts by mass with respect to 100 parts by mass of the coal ash.

  According to invention of (6), since the addition amount of quick lime and / or slaked lime added to coal ash is 0.3 parts by mass or more with respect to 100 parts by mass of coal ash, quick lime and / or slaked lime is added. The effect of adding can be obtained effectively. Moreover, since the addition amount of quicklime and / or slaked lime is 50 mass parts or less, it is economical, without adding these additives exceeding the amount required for the elution prevention effect.

  According to the hazardous trace element elution control method of the present invention, the cost required for suppressing the elution of harmful trace elements from coal ash can be minimized, and further, the capital investment of new equipment can be minimized. Can do. In addition, when performing this harmful trace element elution suppression method, the harmful trace element elution inhibitor addition amount calculation method of the present invention is used, so that harmful effects from coal ash are minimized while minimizing adverse effects on the combustion furnace. Trace element elution can be minimized.

  Furthermore, since the method for calculating the addition amount of harmful trace element elution inhibitor according to the present invention is calculated by subtracting the amount of calcium oxide that does not contribute to the decrease in the melting point of coal ash, it suppresses the dissolution of harmful trace elements that can be added to coal. The added amount of the agent can be accurately calculated.

  Hereinafter, an embodiment showing an example of the present invention will be described with reference to the drawings. In the present embodiment, a pulverized coal combustion furnace that is an example of a coal-fired power generation system will be described as an example.

<A: Configuration of pulverized coal combustion facility in coal-fired power generation system>
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. 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. FIG. 2 is an enlarged view of the vicinity of the combustion 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 141 (mil) that converts coal into pulverized coal that can be combusted with pulverized coal, 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 supplies air to the combustion furnace 161 that combusts the pulverized coal generated by the pulverized coal generation unit 14, a heater 162 (heat exchange unit) that heats the combustion furnace 161, and the combustion furnace 161. And an air supply machine 163 for carrying out the operation.

  The combustion furnace 161 is heated by the heater 162 (heat exchange unit), 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 is generated and discharged to the coal ash treatment unit 18 together with the exhaust gas.

  The combustion furnace 161 will be described in detail with reference to FIG. 2. In FIG. 2, the combustion furnace 161 has a generally inverted U shape as a whole, and the combustion gas moves in an inverted U shape along the arrow in the figure. After that, it is inverted again into a small U shape, and the outlet of the combustion furnace 161 (the last arrow 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 this embodiment, the height of the combustion 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 combustion furnace 161, a burner 161a for burning pulverized coal is disposed in the vicinity of the burner zone 161a 'in the combustion furnace 161. Also, near the top of the U-shape in the combustion 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 from there A standing 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 combustion furnace 161, the primary economizer 161d and the secondary economizer 161e are installed separately in two stages, but the present invention is not limited to such a form. That is, the combustion furnace 161 may have only a single economizer.

<A-4: Coal ash treatment unit>
The coal ash treatment unit 18 includes a denitration device 181 that removes nitrogen oxides in the exhaust gas discharged from the pulverized coal combustion unit 16, a dust collector 182 that removes soot in the exhaust gas, and coal ash collected by the dust collector 182. A coal ash recovery silo 183 for primary storage.

  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 ° C. to 400 ° C.), and nitrogen oxides in the exhaust gas are decomposed into harmless nitrogen and water vapor by the action of a denitration catalyst. A catalytic 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 is a facility that primarily stores the coal ash collected by the dust collector 182.

<B: Method for calculating addition amount of harmful trace element elution inhibitor of the present invention>
As shown in FIG. 3, harmful trace elements eluted inhibitor additive amount calculating method of the present invention is a coal-fired power generation system, the amount of harmful trace elements elution suppressing agent to be added to coal for trace elements elution preventing A method for calculating a harmful trace element elution inhibitor addition amount to be calculated, wherein the harmful trace element elution inhibitor includes at least one selected from the group consisting of limestone, quicklime, and slaked lime, and The inhibitor addition amount calculation method is a calcium oxide amount measurement step S110 that measures the content of calcium oxide remaining in coal ash when a predetermined amount of harmful trace element elution inhibitor is added to coal and burned in a combustion furnace. And the content of calcium oxide measured in the calcium oxide amount measurement step S110 is converted into calcium element conversion, and in terms of calcium element of harmful trace element elution inhibitor A coal ash melting contribution calcium amount calculating step S120 for subtracting the calcium oxide content converted to the calcium element amount from the added amount to calculate the amount of calcium element contributing to coal ash melting in the combustion furnace 161, and coal ash melting Hazardous trace element elution that determines the upper limit of the amount of harmful trace element elution inhibitor within the range in which the calcium amount that contributes to the melting of coal ash calculated in the contributing calcium amount calculation step S120 does not melt the coal ash in the combustion furnace 161 Inhibitor addition amount determination step S130.

  Furthermore, in the harmful trace element elution inhibitor addition amount calculation method of the present invention, if necessary, 10 parts by mass of coal ash is added to 100 parts of water based on the content of calcium oxide measured in the calcium oxide amount measurement step S110. In a range where the pH calculated in the pH calculation step S120 ′ is 12 or more in the harmful trace element elution inhibitor addition amount determination step S130, including the pH calculation step S120 ′ for calculating the pH when dissolved in parts by mass. A lower limit value of the addition amount of the harmful trace element elution inhibitor may be determined.

<Calcium oxide amount measurement step S110>
The calcium oxide amount measuring step S110 measures the content of calcium oxide remaining in coal ash when a predetermined amount of harmful trace element elution inhibitor is added to coal and burned in the combustion furnace 161.

(Addition of harmful trace element elution inhibitor to coal (S111))
The method of adding a harmful trace element elution inhibitor to coal is not particularly limited as long as it can be carried out in the harmful trace element elution suppression method described later. That is, if the harmful trace element elution inhibitor is, for example, the pulverized coal combustion facility 1, the transfer path between the coal supply unit 12 and the pulverized coal generation unit 14, the pulverized coal generation unit 14 and the pulverized coal combustion unit 16, It may be carried out by a transfer path between the two. Moreover, you may add a harmful | toxic trace element elution inhibitor with the heated air directly to the combustion furnace 161, and may add it by mixing the powdered coal and the harmful | toxic trace element elution inhibitor. Such an addition method is performed by the same method as or a method similar to the addition method that is actually employed in the harmful trace element elution suppression method, in order to increase the accuracy of the method for calculating the addition amount of the harmful trace element elution inhibitor. It is preferable.

(Combustion in coal combustion furnace (S112))
It does not specifically limit as a method of burning coal which added the harmful trace element elution inhibitor. That is, a harmful trace element elution inhibitor may be mixed with coal and actually burned in the pulverized coal combustion facility 1 or may be burned in a test furnace such as a horizontal steel furnace boiler or a drop tube furnace. Good. Here, when the coal to which the harmful trace element elution inhibitor is added is burned, the combustion temperature is preferably approximately the same as the combustion temperature in the combustion furnace in which the harmful trace element elution suppression method is actually carried out. For example, when the harmful trace element elution suppression method is implemented in the pulverized coal combustion facility 1, the combustion temperature is preferably 1300 ° C. or higher and 1500 ° C. or lower. As a combustion furnace for burning coal to which a harmful trace element elution inhibitor is added, it is preferable to use a test furnace from the viewpoints of cost required for testing, ensuring safety, ease of implementation, and the like. More preferably, the combustion temperature is 800 ° C. or higher and 1600 ° C. or lower.

(Collecting coal ash (S113))
After burning coal to which harmful trace element elution inhibitor is added, coal ash produced by combustion is collected. When coal is burned in a test furnace to measure the content of calcium oxide, all generated coal ash is collected as much as possible regardless of coal ash generation conditions, and all coal ash is averaged. It is preferable to take a sample. In addition, when coal is burned in the pulverized coal combustion facility 1 or the like, clinker ash falling immediately below the burner zone 161a ′, cinder ash falling near the economizer, fly ash collected by the dust collector 182 The sample is preferably collected and mixed at a ratio corresponding to the amount of the product produced and averaged.

(Measurement of calcium oxide content in coal ash (S114))
Measurement of the amount of calcium oxide is based on the Cement Association Standard Test Method (JCAS) "Quantification Method A for Free Calcium Oxide" (ethylene glycol method), "Quantification Method for Free Calcium Oxide B Method" (glycerin-alcohol method), etc. It can carry out by the well-known method. The amount of calcium oxide is preferably calculated by setting a plurality of addition amounts of the harmful trace element elution inhibitor and obtaining a regression curve by a known method from the relationship between the addition amount and the measurement amount. In particular, when coal is burned in the pulverized coal combustion facility 1 or the like, a large amount of harmful trace element elution inhibitor cannot be added to the coal. It is effective to measure the calcium content, obtain a regression line, and estimate the calcium oxide content when a large amount of harmful trace elements are added.

  It is preferable to perform the above operation for different types of coal. That is, depending on the type of coal, the content of calcium contained in the coal is different, so the behavior of the calcium component when a harmful trace element elution inhibitor is added is also expected to be different. For this reason, the content of calcium oxide in coal ash is measured for coal of coal types that are subject to actual implementation of harmful trace element elution suppression methods, or coal of similar types, and harmful trace elements for each. It is preferable to determine the optimum amount of the dissolution inhibitor. In addition, coal is classified into multiple groups based on the calcium content, the content of alumina, silica, and other compounds, as well as information on the production area, etc., and only for the coal types that represent each group. The amount of calcium oxide in the coal ash may be measured.

<Coal ash melting contribution calcium amount calculation process S120>
Coal ash melting contribution calcium amount calculation step S120 converts the calcium oxide content measured in calcium oxide amount measurement step S110 into calcium element amount, and calculates the amount of harmful elemental element elution inhibitor added from calcium element equivalent calcium element. The amount of calcium element that contributes to melting of coal ash in the combustion furnace 161 is calculated by subtracting the content of calcium oxide converted into the amount. As described above, the harmful trace element elution inhibitor includes at least one selected from the group consisting of limestone, quicklime, and slaked lime, but in the coal ash melting contribution calcium amount calculating step S120, the harmful trace element elution inhibitor. What is necessary is just to subtract the content of calcium oxide measured in the said calcium oxide amount measurement process S110 from the content of these calcium elements contained in this, and converted into the amount of calcium elements.

(Conversion to the amount of calcium element)
In converting the amount of calcium oxide into the amount of calcium element, the measured amount of calcium oxide may be divided by the molecular weight of calcium oxide and integrated by the atomic weight of calcium. That is, if the amount of calcium oxide is X, the calculation may be performed using the formula X ÷ 56.08 × 40.08.

［式（１）中、ｐＫｂは水酸化カルシウムの塩基解離定数を表し、［Ｃａ^２＋］、及び［Ｃａ（ＯＨ）_２］はそれぞれ、水溶液中におけるカルシウムイオン、及び水酸化カルシウムの濃度である。］ <PH calculation step S120 '>
In the pH calculation step S120 ′, based on the calcium oxide amount measured in the calcium oxide amount measurement step S110, the pH when 10 parts by mass of coal ash is dissolved in 100 parts by mass of water is calculated. As for a specific pH calculation method, a simulation may be used, or a regression line may be obtained and calculated based on a plurality of test results. In the aqueous solution, almost all calcium oxide is converted to calcium hydroxide. For this reason, when using the simulation, the pH is calculated on the assumption that all of the calcium oxide has been converted to calcium hydroxide. The contribution of calcium hydroxide to pH is calculated by the following equation (1).

[In formula (1), pKb represents the base dissociation constant of calcium hydroxide, and [Ca ²⁺ ] and [Ca (OH) ₂ ] are the concentrations of calcium ions and calcium hydroxide in the aqueous solution, respectively. ]

  In the actual calculation of pH, other components included in the coal ash also affect the pH fluctuation, and therefore it is preferable to calculate the pH taking these components into consideration. Specifically, sodium oxide, potassium oxide, magnesium oxide, iron oxide, and the like tend to increase the pH, and silicon oxide, aluminum oxide, sulfur oxide, and the like tend to decrease the pH. In calculating the contribution of these compounds to pH, a method similar to that for calcium oxide can be used.

<Harmful trace element elution inhibitor addition amount determination step S130>
The harmful trace element elution inhibitor addition amount determining step S130 is a harmful trace element within a range in which the amount of calcium contributing to coal ash melting calculated in the coal ash melting contributing calcium amount calculating step S120 does not cause the coal ash to melt in the combustion furnace 161. The upper limit value of the amount of the dissolution inhibitor added is determined. In determining the addition amount of the harmful trace element elution inhibitor, in addition to the calcium amount contributing to the melting of the coal ash calculated in the coal ash melting contributing calcium amount calculating step S120, the content of various components in the coal ash is determined. The melting point of coal ash at a given amount of calcium may be predicted, and the amount of harmful trace element elution inhibitor added may be determined within a range where the melting point of coal ash does not fall below a predetermined value.

  In addition, in the harmful trace element elution inhibitor addition amount determination step S130, when the lower limit value of the harmful trace element elution inhibitor addition amount is determined so that the pH calculated in the pH calculation step S120 ′ is 12 or more. Good.

[Determination of Upper Limit of Addition Amount of Harmful Trace Element Elution Inhibitor S131]
(Calculation method of melting point of coal ash)
The calculation method of the melting point of coal ash is not particularly limited, and a known simulation or the like can be used. That is, the melting point of coal ash is greatly influenced by the components of the coal ash, and when there is a large amount of iron (III) oxide, calcium oxide, magnesium oxide, sodium oxide, potassium oxide, etc. in the coal ash, the coal ash The melting point of the coal ash tends to be relatively low. When a large amount of silicon oxide, aluminum oxide, titanium oxide, or the like is present in the coal ash, the melting point of the coal ash tends to be relatively high. In the simulation of the melting point of coal ash, the melting point of coal ash is calculated from the content of these components contained in the coal ash and the calcium amount contributing to the melting of the coal ash calculated in the coal ash melting contributing calcium amount calculating step S120. Can be estimated.

  Conventionally known component composition data of coal ash can be used for the value of the content of the compound used when calculating the melting point of coal ash. Moreover, about coal of each coal type, it can acquire also by measuring content of each component with methods, such as a quantitative method, an atomic absorption method, ICP method, and a fluorescent X ray analysis method.

  In the simulation, the melting point of coal ash generated as a result of combustion is preferably set to be 1200 ° C. or higher, and more preferably set to be 1300 ° C. or higher. Since the melting point of coal ash is 1200 ° C. or higher, it is possible to prevent slagging and fouling from occurring due to excessive melting of coal ash in the combustion furnace 161 when a harmful trace element elution inhibitor is added to coal. Can do. Furthermore, when the melting point of coal ash is 1300 ° C. or higher, the effect of preventing the occurrence of such slugging and fouling can be obtained more strongly.

[Determination of lower limit of addition amount of harmful trace element elution inhibitor S132]
The addition amount of the harmful trace element elution inhibitor is set to a lower limit value so that the pH calculated in the pH calculation step S120 ′ is 12 or more. The pH is preferably 12.5 or more, and more preferably 13.0 or more.

<C: Method for suppressing the elution of harmful trace elements of the present invention>
The harmful trace element elution suppression method of the present invention will be described using the pulverized coal combustion facility 1. The harmful trace element elution suppression method is added to the combustion part of the combustion furnace 161 or the upstream part thereof. By adding a harmful trace element elution inhibitor within the range of the amount calculated by the calculation method, and adding quick lime and / or slaked lime to the downstream part of the combustion part of the combustion furnace 161 and / or coal ash, A harmful trace element elution suppression method for suppressing the elution of harmful trace elements from the combustion residue of coal, wherein the harmful trace element elution inhibitor is one or more selected from limestone, slaked stone, and quicklime as a main component. A harmful trace element elution inhibitor is used.

  The harmful trace element elution suppression method according to the present embodiment includes a coal supply step S210 for supplying coal, a pulverized coal generation step S220 for pulverizing the supplied coal to generate pulverized coal, and burning this pulverized coal. It includes a pulverized coal combustion step S230 for generating coal ash and a coal ash treatment step S240 for collecting and storing the coal ash, each of which includes a coal supply section of the pulverized coal combustion facility 1 described above. 12, the pulverized coal generation unit 14, the pulverized coal combustion unit 16, and the coal ash treatment unit 18. And harmful trace element elution inhibitor addition process S250 which adds a harmful trace element elution inhibitor to the combustion part of the combustion furnace 161, or its upstream part, Preferably said coal supply part 12, pulverized coal production | generation part 14, and The coal ash additive addition step S260, which is performed in any of the pulverized coal combustion unit 16 and adds quick lime and / or slaked lime to the downstream portion of the combustion furnace 161 and / or the coal ash, is performed in the coal ash processing unit 18 or the like. .

<Coal supply process S210>
First, in the coal supply step S <b> 210, 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 can be pulverized coal combustion. Good.

<Pulverized coal production process S220>
Next, in pulverized coal production | generation process S220, the coal supplied from the coal feeder 122 is grind | pulverized by the coal pulverized coal machine 141, and, thereby, pulverized coal is produced | generated. The generated pulverized coal is supplied to the combustion 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 elution inhibitor is added.

<Pulverized coal combustion process S230>
Next, in the pulverized coal combustion process S <b> 230, the pulverized coal generated by the coal pulverized coal machine 141 is burned by the combustion furnace 161. As shown in FIG. 2, the pulverized coal is burned in the burner zone 161a ′, and the temperature at this time ranges from 1300 ° C. to 1500 ° C., and the coal ash generated by the combustion rises in the direction of the arrow. And the exhaust gas through the furnace upper dividing wall 161b, the final superheater 161b ', the first reheater 161f, the second reheater 161f', and the horizontal primary superheater 161c (all of which are heat exchange units). The primary economizer 161d (heat exchange unit) and the secondary economizer 161e (heat exchange unit) are sequentially passed. The vicinity of this heat exchange unit is an area where the temperature is maintained at about 450 ° C. to about 900 ° C., and passes through a heat transfer surface group provided for preheating boiler feedwater using the heat held by the combustion gas. As a result, heat exchange occurs and the temperature decreases. The time required for the exhaust gas to reach from the burner zone 161a ′ to the vicinity of the economizer is approximately 5 to 10 seconds. Then, it is sent to a denitration device 181 and a dust collector 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.

<Coal ash treatment process S240>
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 dust collector 182 is preferably provided in a plurality of stages.

<Harmful trace element elution inhibitor addition step S250>
As shown in FIG. 1, the harmful trace element elution inhibitor addition step S250, which is a step of adding a harmful trace element elution inhibitor, is preferably the above-described coal supply unit 12, pulverized coal generation unit 14, and pulverized coal combustion unit. (S251, S252, and S253 in FIG. 1 respectively).

  In addition, the addition place of a harmful | toxic trace element elution inhibitor will not be specifically limited if it is the state of coal, For example, the transfer path between the coal supply part 12 and the pulverized coal production | generation part 14, and the pulverized coal production | generation part 14 It may be performed by a transfer path between the pulverized coal combustion unit 16 and the like.

  Specifically, for example, a method of supplying and mixing a harmful trace element elution inhibitor on a belt conveyor that is being transferred when transporting from the coal feeder 122 to the coal pulverizer 141, a harmful trace element elution inhibitor, A method of directly feeding into a coal hopper (not shown) of the coal pulverized coal machine 141, a method of supplying an agent inlet in a pipe between the coal pulverized coal machine 141 and the combustion furnace 161, and combustion air to the combustion furnace 161 However, it is not limited to these methods. 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 elution inhibitor of the present invention contains one or more selected from the group consisting of calcium compounds such as limestone (CaCO ₃ ), slaked stone (Ca (OH) ₂ ) and quicklime (CaO). Further, the harmful trace element elution inhibitor is preferably granular or powdery. Specifically, the average particle size is preferably 10 μm to 100 μm, more preferably 10 μm to 80 μm, and more preferably 10 μm to 60 μm. More preferably. When the average particle size is less than 10 μm, the average particle size is too fine and it is not practical as a harmful trace element elution inhibitor. When the average particle size exceeds 100 μm, the effect of adjusting the average particle size can hardly be obtained. Moreover, when making an average particle diameter into 80 micrometers or less, the particle size of a harmful | toxic trace element elution inhibitor can be adjusted using the coal pulverizer 141, and it is efficient. Furthermore, when the average particle size is 60 μm or less, the limestone powder used in the desulfurization apparatus can be used as it is, so it is economical and by adjusting the particle size of the harmful trace element elution inhibitor. A sufficient effect can be obtained.

  The amount of harmful trace element elution inhibitor added to coal can be the amount determined by the above-mentioned method of calculating the amount of harmful trace element elution inhibitor added, but in general, with respect to 100 parts by mass of coal. The harmful trace element elution inhibitor is preferably 0.1 parts by mass or more and less than 10 parts by mass. When the amount is less than 0.1 parts by mass, the effect of adding the harmful trace element elution inhibitor cannot be substantially obtained. On the other hand, the harmful trace element elution inhibitor lowers the melting point of coal ash, so that it is preferably less than 10 parts by mass and 6.0 parts by mass or less from the viewpoint of preventing slugging and fouling. More preferably, it is 1.0 mass part or less.

<Coal ash additive addition process S260>
The coal ash additive addition step S260 is performed by adding quick lime and / or slaked lime to the downstream portion of the combustion portion of the combustion furnace 161 and / or the coal ash. That is, quick lime and / or slaked lime are part of the combustion furnace 161, the furnace upper dividing wall 161b, the final superheater 161b ′, the first reheater 161f, the second reheater 161f ′, and horizontally placed. It may be added in the vicinity of the heat exchange unit such as the primary superheater 161c, or may be added to the coal ash recovery silo 183 that is a part of the coal ash treatment unit 18 (for example, S261 in FIG. 1). . Quick lime and slaked lime are preferably granular or powdery, and specifically, the average particle diameter is preferably 10 μm to 100 μm, more preferably 10 μm to 70 μm.

  The addition amount of quicklime and slaked lime is preferably added so that the total amount of quicklime and slaked lime is in the range of 0.3 to 50 parts by mass with respect to 100 parts by mass of coal ash. Since the total amount of quicklime and slaked lime is 0.3 parts by mass or more with respect to 100 parts by mass of coal ash, the effect of adding these components can be sufficiently obtained, and the total amount of quicklime and slaked lime is 50 masses. Therefore, it is economical that these components are not added beyond the amount required for the elution prevention effect. The upper limit is more preferably 30 parts by mass, and particularly preferably 10 parts by mass. By adding quick lime and slaked lime in the above amounts, the amount of free lime in coal ash can be kept within a desired range. The amount of free lime to be present in the coal ash is preferably 0.5% by mass or more, more preferably 3.0% by mass or more in terms of calcium oxide, and 10.0% by mass or more. Is particularly preferred.

  By adding quick lime and slaked lime to coal ash, calcium oxide derived from them reacts with selenium oxide, arsenic trioxide, boron oxide, etc. present in coal ash, respectively, and calcium selenite and arsenate, respectively. Since insoluble or insoluble compounds such as calcium and calcium borate are generated, elution of trace elements in coal ash can be suppressed.

  Furthermore, calcium oxide exhibits basicity when dissolved in water. Elements such as selenium, boron, and arsenic have a property that the higher the pH of coal ash, the more difficult it is to elute from coal ash. For this reason, by adding the coal ash additive of this invention, pH when coal ash melt | dissolves in water is kept high, and it can suppress effectively that these elements elute from coal ash. Here, the addition amount of the coal ash additive is preferably added so that the pH of the aqueous solution generated by adding 10 parts by mass of coal ash is 12.0 or more with respect to 100 parts by mass of water. It is more preferable to add so that it may become 12.5 or more, and it is still more preferable to add so that it may become 13.0 or more.

  Calcium oxide is present in large quantities in coal ash, thus acting as a pH lowering preventive agent that prevents the pH of the aqueous solution from decreasing, and suppressing the elution of harmful trace elements even when placed in acidic soil. There is an effect to. Furthermore, calcium oxide added to coal ash has an effect of suppressing the elution of harmful trace elements regardless of the pH when coal ash is dissolved. Such an effect can be obtained more efficiently as the amount of calcium oxide in the coal ash increases, and even in a state where the effect of the increase in pH in the aqueous solution due to the presence of calcium oxide has reached its peak, By making many calcium oxides exist, a better elution suppression effect can be obtained. For this reason, it is preferable that the content of calcium oxide in the coal ash is large.

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. FIG. 2 is an enlarged view of the vicinity of a combustion furnace in FIG. 1. It is a flowchart which shows the outline of the harmful trace element elution inhibitor addition amount calculation method of this invention.

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 | generation part 141 Coal pulverized coal machine 142 Air supply machine 16 Pulverized coal combustion part 16b 1st heat exchange part 16d 2nd heat exchange part 161 Combustion furnace 161a Burner 161a 'Burner zone 161b First superheater 161c Second superheater 161d Primary economizer 161e Secondary economizer 162 Heater
163 Air supply machine 18 Coal ash treatment unit 181 Denitration equipment 182 Dust collector 183 Coal ash recovery silo S210 Coal supply process S220 Pulverized coal generation process S230 Pulverized coal combustion process S240 Coal ash treatment process S250 Hazardous trace element elution inhibitor addition process S260 Coal ash Additive process

Claims (6)

In coal-fired power system comprising a combustion furnace for burning coal, hazardous trace elements eluted inhibitor additive amount calculating method for calculating the amount of harmful trace elements elution suppressing agent to be added due to adverse trace elements elution preventing the coal There,
The harmful trace element elution inhibitor contains at least one selected from the group consisting of limestone, quicklime, and slaked lime,
The harmful trace element elution inhibitor addition amount calculation method is:
When the harmful trace elements eluted inhibitor is combusted in the combustion furnace by adding a predetermined amount of the coal, calcium oxide amount measuring step of measuring the content of calcium oxide remaining in the coal ash,
The calcium oxide content measured in the calcium oxide content measurement step is converted into the calcium element content, and the calcium oxide content converted into the calcium element content from the added amount of the harmful trace element elution inhibitor in terms of calcium element. Subtracting and calculating the amount of calcium element that contributes to the melting of the coal ash in the combustion furnace,
In the range where the amount of calcium contributing to melting of the coal ash calculated in the coal ash melting contribution calcium amount calculating step does not melt the coal ash in the combustion furnace, A method for calculating an addition amount of a harmful trace element elution inhibitor to be determined.   The said poisoning trace element elution inhibitor addition amount determination process WHEREIN: The upper limit of the addition amount of the said hazardous trace element elution inhibitor is determined for every coal type of the said coal burned with the said combustion furnace. Method for calculating the amount of harmful trace element elution inhibitor added.   The combustion furnace is a pulverized coal combustion furnace, and in the harmful trace element elution inhibitor addition amount determination step, an upper limit value of the harmful trace element elution inhibitor addition amount so that the melting point of the coal ash is 1200 ° C. or higher. The harmful trace element elution inhibitor addition amount calculation method according to claim 1 or 2, wherein: The harmful trace element elution inhibitor addition amount calculation method is based on the calcium oxide content measured in the calcium oxide amount measurement step, and the pH when 10 parts by mass of coal ash is dissolved in 100 parts by mass of water. Including a pH calculation step of calculating
2. The lower limit of the addition amount of the harmful trace element elution inhibitor is further determined in the harmful trace element elution inhibitor addition amount determination step in a range where the pH calculated in the pH calculation step is 12 or more. To 4. The method for calculating the additive amount of harmful trace element elution inhibitor according to any one of items 1 to 3. The said harmful trace element elution inhibitor is the combustion part of a combustion furnace within the range of the addition amount computed by the said harmful trace element elution inhibitor addition amount calculation method in any one of Claim 1 to 4 or its upstream Added to the part,
A harmful trace element elution suppression method of adding quick lime and / or slaked lime to a downstream portion of a combustion portion of a combustion furnace and / or coal ash.   The harmful trace element elution suppression method of Claim 5 which adds quick lime and / or slaked lime in the range of 0.3 to 50 mass parts with respect to 100 mass parts of the coal ash.

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