JP6248695B2 - Method for producing calcium fluoride and method for removing hydrogen fluoride from exhaust gas - Google Patents

Description

  The present invention relates to a method for producing calcium fluoride from hydrogen fluoride contained in exhaust gas, and more specifically, a method for producing calcium fluoride by neutralizing exhaust gas containing hydrogen fluoride, and exhaust gas The present invention relates to a method for removing hydrogen fluoride by neutralization treatment.

  Fluorocarbons collected and incinerated to deal with general household waste, various industrial wastes, and the ozone depletion problem contain components that contain fluorine atoms. In the exhaust gas to be contained, hydrogen fluoride (HF) is contained. In addition, hydrogen chloride (HCl) and sulfur oxides (SOx) are generated from the components containing chlorine atoms and sulfur atoms in the waste, so that hydrogen chloride (HCl) and sulfur oxides ( SOx) is often contained. In addition, exhaust gas containing hydrogen fluoride, hydrogen chloride and other acidic components is also generated in the exhaust gas treatment process of the semiconductor manufacturing process and the aluminum refining process.

  In this specification, the gas before removing hydrogen fluoride with the exhaust gas generated when the waste or the like is burned in an incinerator or the like is referred to as “exhaust gas”. In addition, the chemical formula of the compound may be written in parentheses after the compound name. Furthermore, a chemical formula may be used in place of the compound name.

  Conventionally, exhaust gas containing acidic gas such as hydrogen fluoride, hydrogen chloride, sulfur oxide is neutralized with alkaline chemicals such as hydroxide of alkaline earth metal, and then discharged into the atmosphere. The product resulting from the neutralization reaction is often disposed of by landfilling or the like (see, for example, Patent Document 1). However, effective use of the product of the neutralization reaction is required from the viewpoint of effective use of resources.

On the other hand, hydrogen fluoride is industrially produced by reacting fluorite (calcium fluoride ore) and concentrated sulfuric acid as shown in the following formula (1).
_{CaF 2 + H 2 SO 4 →} 2HF + CaSO 4 ............ (1)
By this reaction, hydrogen fluoride is extracted as a gas. Since the extracted hydrogen fluoride gas contains impurities such as sulfur oxide and dust, it is washed with sulfuric acid, and then condensed, rectified, and stripped. It refine | purifies by performing operation of these etc. (for example, refer patent document 2).

However, in such a method for producing hydrogen fluoride from fluorite, the raw material fluorite may be depleted as a natural resource. In addition, a part of SiO ₂ contained as an impurity in natural fluorite reacts with the generated hydrogen fluoride, passes through silicon tetrafluoride (SiF ₄ ), and hydrosilicofluoric acid (H ₂ SiF ₆ ). Therefore, there is a problem that the hydrogen fluoride generated by the reaction (1) is consumed wastefully. Therefore, there is a demand for a raw material that can efficiently produce hydrogen fluoride without using natural fluorite.

Regarding calcium fluoride (CaF ₂ ), which is a raw material for producing hydrogen fluoride, in a system that burns PFC (perfluoro compound), hydroxides of alkaline earth metals such as slaked lime (calcium hydroxide) and calcium carbonate In addition, a method for recovering high-purity calcium fluoride by using a column carrying a drug such as carbonate has been proposed (see, for example, Patent Document 3).

  However, in the method described in Patent Document 3, not only a large amount of exhaust gas cannot be treated, but if the exhaust gas contains hydrogen chloride or sulfur oxide in addition to hydrogen fluoride, There was a problem that pure calcium fluoride could not be obtained.

  Furthermore, there is a method in which exhaust gas containing hydrogen fluoride is brought into contact with a liquid containing calcium to recover the fluorine content in a wet manner. However, in this method, acid gases other than hydrogen fluoride can be used to protect environmental standards. It is necessary to perform processing with a similar device. Therefore, there has been a problem that the purity of the obtained calcium fluoride is reduced due to the mixture of products derived from acidic gases other than hydrogen fluoride.

JP 2000-153130 A JP-A-4-228401 JP 2004-331432 A

  The present invention has been made in response to the above problems, and an object of the present invention is to provide a method for efficiently producing high-purity calcium fluoride from exhaust gas containing hydrogen fluoride.

In the method for producing calcium fluoride of the present invention, the exhaust gas containing hydrogen fluoride and at least one of hydrogen chloride and sulfur oxide is neutralized to produce calcium fluoride as a raw material for producing hydrogen fluoride. The neutralization treatment is performed in a two-stage process, and in the first-stage neutralization treatment process, the exhaust gas and slaked lime powder are brought into contact at a temperature of 180 ° C. or higher and 400 ° C. or lower to obtain calcium fluoride. Is generated.

  In the calcium fluoride production method of the present invention, in the second stage neutralization treatment step, the exhaust gas neutralized in the first stage neutralization treatment step is preferably brought into contact with sodium bicarbonate. In addition, it is preferable that at least a part of the product generated in the second-stage neutralization treatment step is dissolved in water and subjected to wastewater treatment.

  The concentration of hydrogen fluoride in the exhaust gas is preferably 10 to 1,000 ppm. Moreover, it is preferable that the amount of slaked lime brought into contact with the exhaust gas is 0.2 to 5 in an equivalent ratio to the amount of hydrogen fluoride contained in the exhaust gas in the first stage neutralization treatment step. Further, in the first-stage neutralization treatment step, the amount of slaked lime that is brought into contact with the exhaust gas is 0.02 or more in terms of an equivalent ratio to the total amount of hydrogen fluoride, hydrogen chloride, and sulfur oxide contained in the exhaust gas. Is preferably less than .7.

  Furthermore, in the manufacturing method of the calcium fluoride of this invention, it can have the process of removing the solid substance in the said waste gas before the said neutralization process process of the 1st step | paragraph. Moreover, the product produced | generated at the neutralization process process of the said 1st stage can have the process of mixing and stirring with water or dilute hydrochloric acid whose pH value is 7 or less, and carrying out solid-liquid separation.

  The method for removing hydrogen fluoride in exhaust gas of the present invention is characterized in that hydrogen fluoride in the exhaust gas is removed using the method for producing calcium fluoride of the present invention.

  According to the production method of the present invention, high-purity calcium fluoride suitable for producing hydrogen fluoride is efficiently obtained from exhaust gas containing hydrogen fluoride and further containing at least one of hydrogen chloride and sulfur oxide. be able to. Moreover, hydrogen fluoride in the exhaust gas can be efficiently removed.

In one Embodiment of this invention, it is a flowchart which shows the flow of the substance at the time of manufacturing calcium fluoride from waste gas.

  Embodiments of the present invention will be described below.

  In the method for producing calcium fluoride of the present invention, the neutralization treatment of the exhaust gas containing hydrogen fluoride and hydrogen chloride and / or sulfur oxide comprises two steps of neutralization treatment steps of the first stage and the second stage. Have. In the first stage neutralization treatment step, the exhaust gas and slaked lime powder are brought into contact at a temperature of 180 ° C. or higher and 400 ° C. or lower to neutralize the exhaust gas containing hydrogen fluoride to generate calcium fluoride. To do. Further, in the second-stage neutralization treatment step, the exhaust gas and sodium hydrogen carbonate are brought into contact with each other to remove the acid gas remaining in the exhaust gas.

  Hereinafter, the exhaust gas to be neutralized, the first and second neutralization treatment steps, and the reaction product obtained in the first neutralization treatment step (hereinafter referred to as the first neutralization product). The collected product (hereinafter referred to as the first-stage collected product), the reaction product (hereinafter referred to as the second-stage neutralized product) and the collected product (hereinafter referred to as the second-stage neutralized product). The second stage collected material will be described.

<Exhaust gas>
The exhaust gas to be neutralized in the present invention is exhaust gas generated by incineration of general waste, industrial waste, or recovered chlorofluorocarbon gas, and contains hydrogen fluoride (HF). In addition to hydrogen fluoride, it contains at least one of hydrogen chloride (HCl) and sulfur oxide (SOx). The concentration (content ratio) of hydrogen fluoride in the exhaust gas is not particularly limited. The concentration of hydrogen fluoride is in the range of 10 to 1,000 ppm, which is a concentration contained in exhaust gas generated when incineration of general waste and industrial waste or incineration of CFCs with those wastes. It is preferable. If the concentration of hydrogen fluoride is within the above range, a sufficient amount of high-purity calcium fluoride can be obtained by the production method of the present invention.

  Further, the concentration of hydrogen chloride and sulfur oxide in the exhaust gas is not particularly limited. Hydrogen chloride and sulfur oxide are concentrations contained in exhaust gas generated when incinerating general waste or industrial waste or incinerating such waste. Usually, hydrogen chloride is in the range of 100 to 10,000 ppm, and sulfur oxide is preferably in the range of 100 to 10,000 ppm.

<Pretreatment>
In the exhaust gas, fine solid particles called fly ash derived from combustion products are mixed. Before the first stage neutralization treatment step, it is preferable to install an electric dust collector or bag filter for removing fly ash to remove fly ash. Since fly ash often contains Si, if the exhaust gas containing fly ash is treated in the first-stage neutralization process described later, fly ash containing Si is likely to be mixed in the reaction product. Production efficiency when producing hydrogen fluoride from calcium fluoride is reduced. By removing the fly ash by performing the pretreatment, the purity of calcium fluoride can be increased and the efficiency of hydrogen fluoride production can be increased.

<First stage neutralization process>
In the first neutralization process, exhaust gas and slaked lime powder are brought into contact at a temperature of 180 ° C. or higher and 400 ° C. or lower, and hydrogen fluoride and slaked lime in the exhaust gas are reacted in a dry manner to produce calcium fluoride. To do.

  The contact between the exhaust gas and the slaked lime powder is a temperature of 180 ° C. or more and 400 ° C. or less introduced into the flue from the exhaust gas generation source to the first stage dust collector, or into the reaction vessel or reaction chamber of the exhaust gas and slaked lime powder. It is preferable to carry out by a method such as blowing slaked lime powder into the exhaust gas. The reaction vessel or reaction chamber is a bug with a filter (filter cloth) in a moving bed type or fluidized bed type dust collector or a dust collector so that the contact time between exhaust gas and slaked lime powder can be controlled. A filter is preferred. It is also preferable to use a catalyst filter carrying a dioxin decomposition catalyst. Moreover, it is preferable to use a ceramic filter made of a ceramic material in processing in a high temperature region where a general-purpose material cannot be used.

From the viewpoint of reaction efficiency and ease of handling, the particle diameter of the slaked lime powder is preferably 1 to 100 μm, more preferably 5 to 50 μm, and even more preferably 8 to 20 μm in terms of volume average particle diameter. Specifically, as slaked lime, use of slaked lime with a special name of JIS standard is preferable. From the viewpoint of reaction efficiency, it is more preferable to use highly reactive slaked lime having a larger pore volume and BET specific surface area than the special slaked lime. 10-80 m < ² > / g is preferable and, as for the BET specific surface area of the slaked lime to be used, 40-60 m < ² > / g is more preferable. Slaked lime having a BET specific surface area of 10 m ² / g or less is not preferable because the reaction efficiency is lowered. It is technically difficult to obtain slaked lime having a BET specific surface area of 80 m ² / g or more.

The pore volume of the slaked lime powder is suitably 0.15 cm ³ / g or more, more preferably 0.2 cm ³ / g or more, with a pore volume having a pore diameter of more than 0 to 1000 mm.

  Here, since the reactivity of hydrogen fluoride, hydrogen chloride, sulfur oxide and slaked lime decreases in the order of HF> HCl> SOx, the first stage in which exhaust gas containing these gases and slaked lime powder are brought into contact with each other. In the neutralization treatment step, hydrogen fluoride in the exhaust gas preferentially reacts with slaked lime to produce calcium fluoride.

The amount of slaked lime to be brought into contact with the exhaust gas is preferably 0.2 to 5, more preferably 0.4 to 4, more preferably 0.5 to 3 with respect to the amount of hydrogen fluoride contained in the exhaust gas. A range is particularly preferred. In addition, the equivalent ratio of slaked lime with respect to hydrogen fluoride shows the ratio of the amount of slaked lime with respect to the theoretical mole number (= 0.5 mol) of slaked lime required for reaction with 1 mol of hydrogen fluoride. When the equivalent ratio of slaked lime to hydrogen fluoride is less than 0.2, the amount of hydrogen fluoride neutralized by slaked lime is too small, so the amount of hydrogen fluoride remaining in the exhaust gas after the first neutralization treatment step Increases, which is not preferable. When the equivalent ratio of slaked lime to hydrogen fluoride exceeds 5, since neutralization reaction between slaked lime and hydrogen chloride or slaked lime and sulfur oxide increases, together with calcium fluoride in the first stage neutralization treatment step, A large amount of calcium chloride (CaCl ₂ ) and calcium sulfate (CaSO ₄ ) is produced, and high-purity calcium fluoride cannot be obtained.

  The amount of slaked lime with respect to the total amount of hydrogen fluoride, hydrogen chloride and sulfur oxide contained in the exhaust gas (hereinafter referred to as the total amount of acid gas) is preferably 0.02 or more and less than 0.7 in terms of equivalent ratio. 0.05 or more and less than 0.5 is more preferable. In addition, the equivalent ratio of slaked lime with respect to the total amount of acidic gas becomes the total of the equivalent ratio of slaked lime with respect to each component of acidic gas. And the equivalent ratio of slaked lime to hydrogen chloride indicates the ratio of the amount of slaked lime to the theoretical number of moles of slaked lime (= 0.5 mol) required for reaction with 1 mol of hydrogen chloride, and the equivalent ratio of slaked lime to sulfur oxide Indicates the ratio of the amount of slaked lime to the theoretical number of moles of slaked lime required for reaction with 1 mol of sulfur oxide (= 1 mol). For example, the theoretical number of moles of slaked lime required for neutralizing the acidic component of a gas containing 1 mol, 2 mol, and 3 mol of hydrogen fluoride, hydrogen chloride, and sulfur oxide, respectively is 1 × 0.5 + 2 × 0.5 + 3 X1 = 4.5 mol, and the preferable amount of slaked lime input in this case is calculated to be 0.09 to 3.15 mol.

  When the equivalent ratio of slaked lime to the total amount of acid gas is less than 0.02, it is difficult to neutralize and remove a sufficient amount of hydrogen fluoride in the exhaust gas after the first stage neutralization treatment step. The amount of remaining hydrogen fluoride increases, which is not preferable. When the equivalent ratio of slaked lime with respect to the total amount of acid gas is 0.7 or more, the neutralization reaction between slaked lime and hydrogen chloride or slaked lime and sulfur oxide increases, and fluorination occurs in the first-stage neutralization treatment step. A lot of calcium chloride and calcium sulfate are produced together with calcium, and high-purity calcium fluoride cannot be obtained. The equivalent ratio of slaked lime to the total amount of acid gas is more preferably 0.05 to 0.5.

  Thus, when a relatively small amount of slaked lime is added to the total amount of hydrogen fluoride, hydrogen chloride, and sulfur oxide contained in the exhaust gas, the slaked lime reacts preferentially with hydrogen fluoride, Pure calcium fluoride is obtained. When the amount of slaked lime is sufficient to react with hydrogen fluoride in the exhaust gas, most of the hydrogen fluoride in the exhaust gas reacts with slaked lime and is removed.

  In addition, the reactivity between hydrogen fluoride and slaked lime is larger than the reactivity between hydrogen chloride or sulfur oxide and slaked lime, and the tendency of slaked lime to preferentially react with hydrogen fluoride is the gas temperature. Therefore, the temperature of exhaust gas when contacting with slaked lime is 180 ° C. or higher. The temperature of the exhaust gas is more preferably 190 ° C. or higher, and further preferably 200 ° C. or higher. If the temperature of the exhaust gas is 180 ° C. or higher, slaked lime reacts more preferentially with hydrogen fluoride, and the tendency to react with hydrogen chloride or sulfur oxide is reduced, so that high-purity calcium fluoride is obtained. In addition, the temperature of exhaust gas shall be 400 degrees C or less. More preferably, it is 250 degrees C or less. When the temperature of the exhaust gas is 400 ° C. or lower, it is possible to efficiently perform neutralization treatment of hydrogen chloride and sulfur oxide in the exhaust gas after removing the hydrogen fluoride content. If it is 250 degrees C or less, it will become unnecessary to use a special material for a filter. Thus, the exhaust gas temperature is preferably 180 to 400 ° C, more preferably 190 to 250 ° C, and further preferably 200 to 250 ° C.

  In the first stage neutralization treatment step, a product such as calcium fluoride (first stage neutralized product) generated by the reaction between exhaust gas and slaked lime is collected and recovered together with unreacted slaked lime. These are preferably captured by a bag filter or the like.

<First stage neutralized product and first stage collected product>
In the first-stage neutralization treatment step, the first-stage collected product captured and recovered by a bag filter or the like includes, in addition to calcium fluoride, calcium chloride, which is a reaction product of hydrogen chloride and slaked lime, Calcium sulfate, which is a reaction product of sulfur oxide and slaked lime, and unreacted slaked lime are included. Furthermore, calcium carbonate (CaCO ₃ ), which is a reaction product of slaked lime and carbon dioxide, may be included. Calcium fluoride, calcium chloride, and calcium sulfate are referred to as a first stage neutralized product.

Among the first-stage collected materials, calcium fluoride as the target product does not dissolve in water, but calcium chloride dissolves in water. In addition, when calcium chloride is mixed in calcium fluoride, hydrogen chloride is by-produced in the hydrogen fluoride production process in which it is reacted with concentrated sulfuric acid. As a result, the utilization efficiency of concentrated sulfuric acid is reduced and the purity of the obtained hydrogen fluoride is reduced.
Calcium sulfate hardly dissolves in water and dilute hydrochloric acid, but does not react with concentrated sulfuric acid. Therefore, in the production of hydrogen fluoride by reaction with concentrated sulfuric acid, the effect is that the concentration of calcium fluoride, which is a raw material, is diluted to lower the concentration. Effect.

  In addition, unreacted slaked lime and calcium carbonate in the first-stage collected product react with concentrated sulfuric acid to generate calcium sulfate. Therefore, when manufacturing hydrogen fluoride by reaction with concentrated sulfuric acid, the utilization efficiency of concentrated sulfuric acid is reduced. Moreover, although these all have low solubility in water, they react with dilute hydrochloric acid to produce water-soluble calcium chloride.

  Thus, among the first-stage collected material, calcium chloride, unreacted slaked lime and calcium carbonate all reduce the utilization efficiency of concentrated sulfuric acid in the process of producing hydrogen fluoride from calcium fluoride. , Reducing the purity of the resulting hydrogen fluoride. Therefore, the first-stage collected product can use hydrogen fluoride as a raw material for production as it is, but as shown below, after performing a concentration operation to increase the concentration of calcium fluoride, It is preferable to use it.

  That is, water-soluble calcium chloride is removed by washing the first-stage collected material with water. When the first-stage collection is washed with dilute hydrochloric acid, calcium chloride dissolves in dilute hydrochloric acid, and unreacted slaked lime and calcium carbonate react with dilute hydrochloric acid to form calcium chloride, which is dissolved and removed in the same manner. Calcium fluoride and calcium sulfate remain as solids. The remaining solid content is settled and concentrated, separated into solid and liquid, further washed with water and then dehydrated to obtain a solid content in which calcium fluoride and calcium sulfate are mixed.

  For precipitation concentration, a known method such as a gravity type such as thickener or a centrifugal type such as screw decanter can be used. For the solid-liquid separation, a known method such as a centrifugal sedimentation separation method such as a screw decanter, a filtration method such as a filter press, a belt filter, or a leaf filter can be used.

  In this way, the first-stage collected material is mixed and stirred with water having a pH of 7 or less or dilute hydrochloric acid, and the insoluble matter obtained by solid-liquid separation is used, so that the first-stage collected material is more than used as it is. A raw material for producing hydrogen fluoride containing calcium fluoride at a high concentration can be obtained. In particular, it is preferable to wash the first stage collected product with dilute hydrochloric acid. Furthermore, the first-stage collected material is mixed and stirred with water having a pH of 7 or less or diluted hydrochloric acid, and the pH value is adjusted to 5 or less, and aerated with a gas such as air or nitrogen for 30 minutes or more to dissolve calcium carbonate-derived material. It is preferable to remove the carbon dioxide gas. When aeration is not performed, washing with water having a pH value of 5 or more generates calcium carbonate from carbonic acid and calcium ions present in the liquid, and the purity of calcium fluoride decreases. The gas to be blown when aeration is performed is more preferably nitrogen containing no carbon dioxide than air containing a small amount of carbon dioxide. When the first stage pre-collected product is washed with dilute hydrochloric acid, the remaining solid content other than calcium fluoride is only calcium sulfate. As described above, calcium sulfate does not lower the purity of hydrogen fluoride and the utilization rate of concentrated sulfuric acid in hydrogen fluoride production.

  From the above, in order to obtain a hydrogen fluoride raw material containing calcium fluoride at a higher concentration, the exhaust gas and slaked lime powder are treated at a high temperature (specifically, the slaked lime and sulfur oxide are difficult to react). It is understood that the contact is preferably performed at a temperature of 180 ° C. or higher.

  Thus, in the first stage neutralization treatment step, hydrogen fluoride in the exhaust gas mainly reacts with slaked lime to produce a first stage neutralized product mainly composed of calcium fluoride. Then, the exhaust gas from which hydrogen fluoride has been removed is introduced into the second-stage neutralization treatment step. In the present specification, the exhaust gas after the first-stage neutralization treatment step is simply referred to as the second-stage exhaust gas.

<Second stage neutralization process>
In the second stage neutralization treatment step, the remaining acidic gas in the second stage exhaust gas is neutralized and removed. The remaining acidic gas in the second-stage exhaust gas includes an acid gas other than hydrogen fluoride as a main component, but also includes hydrogen fluoride that has not been removed in the first stage. The acidic gas other than hydrogen fluoride in the second stage exhaust gas is at least one gas when the exhaust gas contains at least one of hydrogen chloride and sulfur oxide, and both hydrogen chloride and sulfur oxide. In case of containing both gases. That is, the remaining hydrogen fluoride and hydrogen chloride and / or sulfur oxide in the second stage exhaust gas are neutralized in the second stage neutralization process.

  As a method of the second stage neutralization treatment, a dry method in which a powder of a neutralizing agent such as slaked lime or sodium hydrogen carbonate is blown into and contacted with the second stage exhaust gas, or an alkaline solution such as an aqueous sodium hydroxide solution is used. A known method such as a wet method in which exhaust gas is passed through an aqueous solution can be used.

  Among these, a dry method in which sodium hydrogen carbonate powder is blown into the second-stage exhaust gas is preferable from the viewpoints of reactivity with the high-temperature acidic gas, controllability of operation, and reduction of reaction products. Moreover, in the neutralization process by blowing in sodium hydrogen carbonate powder, only a water-soluble compound is generated, and therefore, the disposal of the reaction product is easy. Hereinafter, the neutralization process of the 2nd step | stage by blowing of sodium hydrogencarbonate powder is demonstrated.

  In the second-stage neutralization treatment step, as in the first-stage neutralization treatment step, a sodium hydrogen carbonate moving bed type or fluidized bed type dust collector or bag filter as a neutralizing agent is used. The use of a bug filter is preferred. From the viewpoint of reaction efficiency, the sodium bicarbonate has a volume average particle size of preferably 100 μm or less, preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 15 μm or less. The sodium hydrogencarbonate powder may be either a method of blowing a previously pulverized powder or a method of pulverizing and blowing just before blowing.

  The contact temperature between the second-stage exhaust gas and sodium hydrogen carbonate powder, that is, the temperature of the exhaust gas when sodium hydrogen carbonate powder is blown is not particularly limited, but is preferably 150 to 400 ° C from the viewpoint of reactivity, 180 to 250 degreeC is more preferable and the range of 190-250 degreeC is especially preferable. When the temperature is lower than 150 ° C., the burden for cooling the first-stage gas increases, which is not preferable. When the temperature is 400 ° C. or higher, the reaction efficiency between sodium hydrogen carbonate and acid gas is lowered, and unless a large amount of sodium hydrogen carbonate is added, neutralization to the target acid gas concentration cannot be achieved, increasing the cost burden.

  The amount of sodium hydrogen carbonate to be added is preferably an amount that provides a concentration that satisfies the standard of the gas to be discharged. For example, the amount of sodium hydrogen carbonate relative to the total amount of hydrogen fluoride, hydrogen chloride, and sulfur oxide at the outlet of the first stage bag filter is 0.6 to 2, more preferably 0.7 to 1.5, Furthermore, the target neutralization is attained by setting it as 0.8 to less than 1.4.

  In the second stage neutralization treatment step, hydrogen chloride and sulfur oxide, which are acidic gases remaining in the second stage exhaust gas, are removed. Further, hydrogen fluoride that cannot be removed in the first stage and remains in the exhaust gas in the second stage is also removed in the same manner as hydrogen chloride and sulfur oxide by the neutralization process in the second stage. And, since the concentrations of hydrogen fluoride, hydrogen chloride and sulfur oxide in the exhaust gas after the second stage neutralization treatment process can all be below the emission standard, a nitrogen oxide removing device is necessary. After passing through a treatment device such as a chimney, it can be safely discharged into the atmosphere from an exhaust mechanism such as a chimney.

<Second stage neutralized product and second stage collected product>
In the second stage neutralization process using sodium hydrogen carbonate powder, sodium chloride, a reaction product of hydrogen chloride and sodium hydrogen carbonate, sulfur oxide and hydrogen carbonate are used as the second stage neutralization product. Sodium sulfate which is a reaction product with sodium is obtained. Further, the second-stage collected product captured by the bag filter or the like includes sodium carbonate, which is a thermal decomposition product of unreacted sodium hydrogen carbonate, in addition to these second-stage neutralized products.

  All of these second-stage collected products are water-soluble and substantially do not contain a fluorine compound (sodium fluoride) that generates fluorine ions. Therefore, the second-stage collected material can be discarded by dissolving it in water as it is, or after adjusting the pH, and then discharging it into sewage or rivers. That is, when the exhaust gas introduced into the second stage neutralization treatment process contains hydrogen fluoride, sodium fluoride is produced as a second stage neutralization product, and a part of the sodium fluoride dissolves to form fluorine ions. However, it is difficult to treat water in order to comply with the wastewater standards. However, since hydrogen fluoride is substantially sufficiently removed in the first stage neutralization process, the second stage neutralized product The second-stage collected product containing can be discarded without generating solid waste only by adjusting the pH of the aqueous solution after being dissolved in water.

Note that “substantially sufficiently removed” means that the substance does not exceed the emission standard when the substance is drained or discharged into the atmosphere from an exhaust mechanism such as a chimney, or the substance is drained. It means that the processing cost for reducing below the emission standard when processing or discharging into the atmosphere does not become a problem.
And, “substantially sufficiently removed” for the hydrogen fluoride means that the fluorine in the wastewater treatment of the reaction product containing sodium fluoride, which is a reaction product of sodium hydrogen carbonate and hydrogen fluoride. It means that it does not exceed the discharge standard of the ion concentration, or that the processing cost for reducing the fluorine ion concentration when the reaction product is discharged to the discharge standard or less is not problematic.

  Next, an example of the manufacturing method of the present invention will be described with reference to FIG. FIG. 1 is a flow diagram showing the flow of substances when producing calcium fluoride from exhaust gas in one embodiment of the present invention.

  In one embodiment of the present invention, as shown in FIG. 1, an exhaust gas 1a containing HF and containing at least one of HCl and SOx, generated from the exhaust gas generation source 1 by combustion of waste, is After fly ash is removed by a dust bag filter or the like, the fly ash is introduced into the first-stage dust collecting device 2 and neutralized at the first stage.

  The exhaust gas 1a is adjusted to have a temperature of 180 ° C. or higher and 400 ° C. or lower in the vicinity of the inlet of the first stage dust collector 2, and the exhaust gas 1a thus adjusted has an equivalent ratio to HF in the exhaust gas 1a. An amount of slaked lime powder of 0.2 to 5 or an equivalent ratio with respect to the total amount of HF, HCl and SOx of 0.02 to 0.7 is blown. In addition, in order to adjust the temperature of the waste gas 1a to the temperature of 180 degreeC or more and 400 degrees C or less, a well-known technique can be used. For example, it is preferable to adopt a method of cooling the exhaust gas 1a of several hundred degrees or more emitted from the exhaust gas generation source 1 with a cooler or the like.

By blowing slaked lime powder, HF in the exhaust gas 1a reacts with slaked lime deposited on the filter of the first-stage dust collector ₂ to generate CaF ₂ . As a result, HF is removed from the exhaust gas 1a. As described above, since slaked lime reacts preferentially with HF over HCl and SOx, HCl and SOx in the exhaust gas do not react with slaked lime, or even if reacted, CaCl ₂ and the reaction product CaSO _4, so easily converted to CaF ₂ reacts with HF to coexist, first stage precipitator 2, mainly CaF ₂ is generated.

Thus, the collected matter (first-stage collected matter) deposited on the filter of the first-stage dust collector 2 is high-purity CaF ₂ , and this is directly used as hydrogen fluoride by reaction with concentrated sulfuric acid. Can be used as a raw material for manufacturing. Moreover, it is also possible to use it as a raw material for hydrogen fluoride raw material production after the above-described concentration operation.

The second-stage exhaust gas 2a from which most of the HF has been removed by the first-stage dust collector 2 is then introduced into the second-stage dust collector 3, and the second-stage neutralization process is performed. In the second-stage dust collector 3, NaHCO ₃ is blown into the exhaust gas 2a near the entrance. As a result, HCl and SOx in the exhaust gas 2a react with NaHCO ₃ deposited on the filter of the second-stage dust collector 3 to generate NaCl and Na ₂ SO ₄ , respectively, and are removed from the exhaust gas 2a. . Since most of the HF in the exhaust gas 1a is removed by the neutralization treatment in the first stage dust collector 2, HCl and SOx in the exhaust gas 2a are mainly removed in the second stage dust collector 3. . The exhaust gas 3a after the removal of HCl and SOx is finally discharged from the chimney 4 in a state where the exhaust gas standard is satisfied.

The collected matter (second-stage collected matter) deposited on the filter of the second-stage dust collector 3 is NaCl, Na ₂ SO ₄ , which is a reaction product of the exhaust gas 2a and NaHCO _3, and unreacted NaHCO _{3. 3} and Na ₂ CO ₃ , both of which are dissolved in water. In addition, the collected material has a very small content ratio of the fluorine-based compound. Therefore, the second-stage collected matter can be dissolved in water, the aqueous solution is stored in the waste water treatment tank 5, and after adjusting the pH, etc., it can be discharged as it is into sewage and rivers, and the fluorine ion concentration is discharged. There is no need to perform wastewater treatment to reduce it below the standard.

  Thus, with the production method of the present invention, calcium fluoride useful as a raw material for industrially producing hydrogen fluoride can be obtained with high purity. And, by using the production method of the present invention, hydrogen fluoride in the exhaust gas can be efficiently removed, and the concentration of the fluorine component in the exhaust gas and the waste water can be reduced below the emission standard. Is also useful.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to a following example.

Example An exhaust gas containing HF, HCl, and SOx and having an HF concentration of 201 ppm, an HCl concentration of 1843 ppm, and an SOx concentration of 804 ppm was continuously neutralized in accordance with the flowchart of FIG.
The flow rate per unit time of the exhaust gas is 12,000 Nm ³ / hr, and after removing fly ash etc. contained in the exhaust gas with a dust bag filter, the gas temperature is 240 ° C. in the front part of the first stage dust collector. In this state, highly reactive slaked lime having a BET specific surface area of 47 m ² / g was blown. The input amount of highly reactive slaked lime per unit time was 10 kg / hr, and the reaction product with slaked lime was collected by the first stage dust collector. This is an amount equivalent to 2.5 with respect to HF and equivalent to 0.14 with respect to slaked lime necessary for neutralization of all of HF, HCl, and SOx.

The amount of reaction product generated in the first stage was about 12.9 kg / hr. The concentration of the acidic gas component at the outlet of the first-stage dust collector was 4 ppm, 1,597 ppm, and 796 ppm for HF, HCl, and SOx, respectively. The amount of NaHCO ₃ input corresponding to equivalent reaction with these acidic gases is 139 kg / hr.

Next, in the second stage dust collector, NaHCO ₃ (manufactured by Asahi Glass Co., Ltd., product name: Acrecia, volume-based average particle diameter 8.5 μm) was blown at an input amount of 141 kg / hr, and the reaction product was 2 Collected with a stage dust collector. This corresponds to 1.014 times the required number of equivalents. At this time, the temperature at the inlet of the second stage dust collector was 220 ° C. The amount of the second stage reaction product generated was 108 kg / hr. Furthermore, the concentrations of HF, HCl, and SOx at the outlet of the second stage dust collector were 1 ppm, 32 ppm, and 40 ppm, respectively.

Using the fluorine content, chlorine content, and sulfuric acid content analyzed by applying the following method to the composition of the first-stage collected matter collected by the first-stage dust collector, CaF ₂ , CaCl ₂ , Converted to CaSO ₄ , the composition in the first stage collected material was calculated. Components other than the above were CaCO ₃ and unreacted slaked lime residue.
Fluorine content: JIS K 0102-34.1
Chlorine content: JIS K 0102-35.3
Sulfuric acid content: JIS K 0102-41.2

Thus, in the first stage the collected _{matter, CaF 2, CaCl 2, CaSO} 4 and unreacted slaked lime (Ca _{(OH) 2)} and CaCO ₃ each content is 32.0 wt%, 56.6 wt %, 4.5% by mass, and 6.9% by mass.

The first-stage collected product was dispersed in water, and the pH value was adjusted to 4 using dilute hydrochloric acid, and aerated with air to drive out dissolved carbon dioxide. Further, the solid content was settled and separated, water was added to adjust the pH value to 6.4, dehydration was performed with a filter press, and the obtained solid content was dried with a dryer. When the composition of the solid content thus obtained was analyzed in the same manner as the first-stage collected product, it was found that CaF ₂ was 87% by mass and CaSO ₄ was 13% by mass. Hereinafter, this solid content is referred to as recovered calcium fluoride.

  Subsequently, when concentrated sulfuric acid was added to the recovered calcium fluoride to generate hydrogen fluoride, high-purity hydrogen fluoride was obtained.

  Moreover, when the 2nd stage collection thing collected with the 2nd stage dust collector was dissolved in 40 times as much water, 98 mass% or more of the 2nd stage collection substance melt | dissolved in water. And when the fluorine ion concentration of this aqueous solution was measured by the fluorine ion electrode method, it was 6.4 ppm and was below the drainage standard.

  ADVANTAGE OF THE INVENTION According to this invention, the high purity calcium fluoride suitable for manufacture of hydrogen fluoride can be efficiently obtained from the waste gas generated when incinerating a waste. Moreover, hydrogen fluoride in the exhaust gas can be efficiently removed.

  DESCRIPTION OF SYMBOLS 1 ... Exhaust gas generation source, 1a ... Exhaust gas, 2 ... First stage dust collector, 2a ... Second stage exhaust gas, 3 ... Second stage dust collector, 4 ... Chimney.

Claims (9)

An exhaust gas containing hydrogen fluoride and at least one of hydrogen chloride and sulfur oxide is neutralized to produce calcium fluoride as a raw material for producing hydrogen fluoride.
While performing the neutralization process in a two-stage process,
In the first-stage neutralization treatment step, the exhaust gas and slaked lime powder are brought into contact at a temperature of 180 ° C. or higher and 400 ° C. or lower to produce calcium fluoride.   The method for producing calcium fluoride according to claim 1, wherein in the second stage neutralization treatment step, the exhaust gas neutralized in the first stage neutralization treatment step is brought into contact with sodium hydrogen carbonate.   The manufacturing method of the calcium fluoride of Claim 2 which melt | dissolves in water at least one part of the product produced | generated at the neutralization process process of the said 2nd step | stage, and performs wastewater treatment.   The manufacturing method of the calcium fluoride of any one of Claims 1-3 whose density | concentration of the hydrogen fluoride in the said waste gas is 10-1,000 ppm.   The amount of slaked lime brought into contact with the exhaust gas in the first-stage neutralization treatment step is 0.2 to 5 in an equivalent ratio with respect to the amount of hydrogen fluoride contained in the exhaust gas. A method for producing calcium fluoride according to claim 1.   In the first stage neutralization treatment step, the amount of slaked lime brought into contact with the exhaust gas is 0.02 or more and 0.7 in terms of an equivalent ratio to the total amount of hydrogen fluoride, hydrogen chloride, and sulfur oxide contained in the exhaust gas. The manufacturing method of the calcium fluoride of any one of Claims 1-5 which is less than.   The manufacturing method of the calcium fluoride of any one of Claims 1-6 which has the process of removing the solid substance in the said waste gas before the said neutralization process process of the 1st step | paragraph.   The product produced | generated at the said neutralization process process of the said 1st stage has the process of mixing and stirring with water or dilute hydrochloric acid whose pH value is 7 or less, and carrying out solid-liquid separation of any one of Claims 1-7. A method for producing calcium fluoride.   A method for removing hydrogen fluoride in exhaust gas, wherein hydrogen fluoride in the exhaust gas is removed using the method for producing calcium fluoride according to any one of claims 1 to 8.

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