JP2015131750A - Highly reactive hydrated lime and production method of the same, and exhaust gas treatment agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide highly reactive hydrated lime having a low COD value, and a large BET specific surface area and pore volume.SOLUTION: Hydrated lime is provided which is obtained by hydrating caustic lime with hydration water. The hydrated lime is produced by adding in hydration one or more kinds of sodium compound selected from water glass, sodium hydroxide, sodium carbonate, sodium fluoride, and sodium silicofluoride. The hydrated lime has a COD value of 30 mg or less measured according to JIS K0102,17, a BET specific surface area of 25 m/g or more, and/or a pore volume of 0.15 cm/g or more. The water glass is especially suitable as the sodium compound. The water glass of 0.5-1.5 wt.% is preferably added to the caustic lime.

Description

  The present invention relates to highly reactive slaked lime that is highly reactive and suitable as a treatment agent for exhaust gas such as acid gas, and a method for producing the same.

  Slaked lime obtained by digesting quick lime is widely used as an exhaust gas treatment agent that removes acidic gas by putting it in an exhaust gas flue in a garbage incinerator or the like.

  Since slaked lime has higher reactivity with acidic gas as the BET specific surface area and pore volume are larger, slaked lime with larger BET specific surface area and pore volume is used as an exhaust gas treatment agent. Various methods have been proposed for manufacturing the. Specifically, when digesting quicklime with digestion water, a method using oxycarboxylic acid, ethanolamines, ethylene glycol or the like as an additive, or combining an organic compound having a hydroxyl group with an inorganic compound containing silicon dioxide Methods have been proposed (for example, Patent Documents 1 and 2). In addition, there is a method using only an inorganic compound such as silicon dioxide as an additive during digestion (for example, Patent Document 3). However, when only an inorganic material is used, the method is obtained as compared with the method using the organic compound. The BET specific surface area of slaked lime is small.

  By the way, the slaked lime after being put into the exhaust gas flue and reacting with the acid gas is often landfilled. Since slaked lime after landfill is exposed to rainwater and the like, it is required that the elution water does not contain environmental pollutants. In particular, low COD (chemical oxygen demand) is required.

JP 2012-66976 A JP 2013-166676 A JP 2011-116573 A

  In the technique described in Patent Document 1 described above, COD in the elution water can be reduced by about half compared to the case where only an organic compound is used as an additive during digestion, but even in that case, the COD is several tens of ppm ( mg / L) and cannot be said to be sufficiently low. On the other hand, as described in Patent Document 3, when only an inorganic compound is used, the COD value is lowered, but if the amount of the inorganic compound used as an additive is not increased to some extent, slaked lime having a large BET specific surface area is obtained. It ’s difficult. In addition, when the amount of the inorganic compound as an additive is increased, the obtained slaked lime has a higher content of inorganic compound, resulting in a decrease in the content of slaked lime, thereby improving the reactivity with acidic gas. I can't.

  This invention is made | formed in order to solve the said subject, and makes it a subject to provide the highly reactive slaked lime with a low COD value, a BET specific surface area, and a large pore volume.

  In order to solve the above-mentioned problems, the present inventors have used BET specific surface area and pore volume when using a sodium compound containing water glass or the like as an additive used when digesting quick lime to produce slaked lime. The present inventors have found that large slaked lime can be obtained and have reached the present invention.

That is, the highly reactive slaked lime of the present invention is slaked lime obtained by digesting quick lime with digested water, and at the time of digestion, one or more selected from water glass, sodium hydroxide, sodium carbonate, sodium fluoride, sodium silicofluoride In which the COD value measured by JIS K010217 is 30 mg / L or less, the BET specific surface area is 25 m ² / g or more and / or the pore volume of 1000 Å or less is 0.15 cm ³ / G or more slaked lime. In the highly reactive slaked lime of the present invention, the pore volume of pores of 100 to 400 mm is 0.1 cm ³ / g or more.

  Moreover, the exhaust gas treating agent of the present invention contains the highly reactive slaked lime.

In the method for producing slaked lime of the present invention, in the step of reacting by adding digested water to powdered or particulate quicklime, and in the step of reacting, the digested water or the reaction system contains a substantial amount of organic as an additive. A step of adding one or more sodium compounds selected from water glass, sodium hydroxide, sodium carbonate, sodium fluoride, and sodium silicofluoride without containing a compound, and drying the slaked lime after the reaction are included.
“Contains no substantial amount of organic compounds” clearly does not mean that organic substances that are inevitably contained or organic substances that are inevitable to be mixed or added so as not to affect the COD value are excluded. It is a thing.

  In the method for producing slaked lime of the present invention, the drying step is preferably performed while sending hot air of 100 ° C. or higher.

The slaked lime of the present invention has a low COD, a high BET specific surface area, a large pore volume and high reactivity, and is suitable as an acidic gas treating agent containing HCl and SO _x . In particular, when the pore volume of pores of 100 to 400 mm is 0.1 cm ³ / g or more, a high SO _x trapping effect can be obtained.

The figure which shows the outline | summary of the slaked lime manufacturing method of this invention. (A) is a figure which shows the scanning electron microscope (SEM) photograph of the highly reactive slaked lime of this invention (Example 1), (b) is a figure which shows the SEM photograph of JIS special name slaked lime. The graph which shows the difference in the BET specific surface area of slaked lime when the water glass addition rate is changed. The graph which shows the difference in the pore volume of slaked lime when the water glass addition rate is changed. The figure which shows the test apparatus for evaluating an exhaust gas processing agent.

Hereinafter, the embodiment of the highly reactive slaked lime of the present invention and the manufacturing method thereof will be described.
The highly reactive slaked lime of the present invention is produced by digesting quick lime, but by using a specific additive during digestion, the BET specific surface area and pore volume can be obtained while having a very low COD value. Is characterized by a large. First, the manufacturing method of the highly reactive slaked lime of this invention is demonstrated.

  As the raw lime used as a raw material, calcinated limestone or shellfish can be used, and the purity is preferably 95% or more. Moreover, it is preferable that the COD value of quicklime is 10 mg / L or less. In general, the COD value of quicklime obtained by firing limestone or shellfish is about 1 mg / L, but is higher when an organic grinding aid is used. Even in this case, if the COD value is 10 mg / L or less, slaked lime with a low COD value can be obtained. As for the shape of quicklime, it is desirable to use a powdery thing. The particle diameter of the powder is not particularly limited, but is preferably 600 μm or less.

  Water (digested water) is added to such quicklime to perform a digestion reaction. Digested water is used at around 100 parts by weight, for example, about 90 to 110 parts by weight with respect to 100 parts by weight of quicklime. The temperature of digestion water is preferably 60 ° C. or less, and more preferably from room temperature (25 ° C.) to 60 ° C. The COD value of industrial water generally used as digestion water is about several mg / L to 8 mg / L.

Additives added when quick digestion is added to quick lime to react are water glass (Na ₂ O · nSiO ₂ (n = 2 to 4)), sodium hydroxide, sodium carbonate, sodium fluoride, sodium silicofluoride. It is one or more sodium compounds selected and does not contain organic compounds. By using these additives, the BET specific surface area and pore volume of the slaked lime generated can be greatly increased compared with the case where no additive is used, and the BET specific surface area is almost the same as when using an organic substance. can do. Among these inorganic compounds, water glass, sodium hydroxide, and sodium carbonate are particularly preferable, and water glass is most preferable. By using water glass or sodium carbonate as an additive, the slaked lime produced has a BET specific surface area of 30 m ² / g or more and a pore volume (0 to 1000 Å pores) of 0.2 cm ³ / g or more. Can do. Moreover, by using water glass or sodium hydroxide as an additive, the pore volume of pores of 100 to 400 mm can be increased to 0.1 cm ³ / g or more.

  The addition amount of the inorganic compound is preferably 0.5% to 1.5% by weight, more preferably 0.6 to 1.0% by weight with respect to quick lime as a raw material. The inorganic compound mixed in digestion water may be added to the reaction system, or may be added to the reaction system separately from digestion water.

  In the reaction, quick lime is charged into a reactor (tank) 10 with a stirrer as shown in FIG. 1, and then digested water and additives are charged from a water supply pipe 11 and a chemical supply pipe 12 installed at the top of the apparatus, respectively. The reaction is carried out with stirring. Or you may throw in from the water supply pipe | tube 11 what dissolved the additive so that it might become a predetermined density | concentration in digestion water. The reaction time is usually about 30 to 60 minutes although it varies depending on the amount of quicklime and digested water to be added. After completion of the reaction, the obtained slaked lime is transferred to the drying device 20 and dried while sending hot air at 100 to 110 ° C. The hot air drying time is 15 minutes or longer, preferably 20 minutes or longer. By drying with hot air, the generated slaked lime particles can be prevented from aggregating, and particles having a large specific surface area can be obtained. Further, by drying with hot air, moisture contained in the pores can be sufficiently removed, and particles having a large pore volume can be obtained. The slaked lime powder after drying can be classified according to the use and the like to obtain a desired average particle size slaked lime.

  According to the method for producing slaked lime of the present invention, by using only an inorganic compound as an additive without using a substantial amount of an organic compound, the COD value of the produced slaked lime is comparable to that of JIS special slaked lime. By using an inorganic compound of the type described above, slaked lime having a large BET specific surface area and a large pore volume can be obtained.

The highly reactive slaked lime of the present invention has a BET specific surface area of 25 m ² / g or more, or a pore volume (volume of 0 to 1000 細孔 pores) of 0.15 cm ³ / g or more, and has a COD value (JIS K0102 17 Is the same, and the same applies hereinafter) is 30 mg / L or less. The COD value is preferably 20 mg / L or less, more preferably 10 mg / L or less. The highly reactive slaked lime of the present invention can be manufactured under conditions that limit the mixing of organic substances, and can be preferably manufactured by the manufacturing method described above. When the highly reactive slaked lime of the present invention is used as an exhaust gas treating agent, the BET specific surface area is preferably 30 m ² / g or more, and the pore volume is 0.20 cm ³ / g or more. The BET specific surface area and the pore volume are values measured by a nitrogen gas adsorption method (BJH method). Moreover, the highly reactive slaked lime of the present invention preferably has a pore volume of 100 to 400 Å pores of 0.1 cm ³ / g or more, more preferably 0.15 cm ³ / g or more. The pore volume of 100 to 400 mm pores can be increased by adjusting the type and amount of additive (inorganic compound) in the production method described above.

Since the highly reactive slaked lime of the present invention has a large BET specific surface area, it has high reactivity with acidic gases such as HCl, NO _x , and SO _x and is suitable as an acidic gas treating agent. The large pore volume, especially since the pore volume of pores of 100~400Å large, high capture rate of SO _x, it is preferable to higher exhaust gas treatment of SO _x ratio.

  The COD value of the highly reactive slaked lime of the present invention is 30 mg / L or less, and it varies depending on the organic matter inevitably mixed up to the production process or COD measurement, so it varies within the range of 30 mg / L or less. When no organic compound is used as an additive, the amount can be 3 mg / L or less. This value is comparable to the JIS special slaked lime COD (about 1 to 3 mg / L). This value is, for example, 1/40 to 1/50 of the COD value (= 120 mg / L) of slaked lime (using diethylene glycol and sodium silicate as additives) described in the examples of Patent Document 2, which is sufficiently low It turns out that it is a value. The COD value is a value measured in accordance with JIS K010217 factory drainage test method (measures the amount of oxygen consumed when a sample is oxidized with potassium permanganate at 100 ° C. for 30 minutes).

  The particle diameter (median diameter) of the highly reactive slaked lime obtained by the above-described production method is 5 to 15 μm, but when the highly reactive slaked lime of the present invention is used as an acid gas treating agent, the median diameter is preferably 7 to 10 μm.

The exhaust gas treating agent of the present invention contains the highly reactive slaked lime described above. Particularly highly reactive calcium hydroxide, BET specific surface area of ^{30 m} 2 / g or more, a pore volume (1000 Å or less) 0.22 cm ³ / g or more, a pore volume (100～400A) is 0.1 cm ³ / g or more It is preferable to use highly reactive slaked lime. Such highly reactive slaked lime may be used alone as an exhaust gas treatment agent, or other exhaust gas treatment agents and additives may be mixed and used. Examples of other exhaust gas treatment agents include activated carbon and activated clay.

The exhaust gas treating agent of the present invention, like the known exhaust gas treating agent, blows a powdery material into, for example, a flue of a garbage incineration facility and reacts with an acid gas flowing through the flue. The input amount of the exhaust gas treating agent is appropriately determined in consideration of the acid gas concentration in the exhausted gas. For example, the concentration of acidic gas in exhaust gas discharged from an incinerator of a garbage disposal facility for household waste is about 30 to 100 ppm for SO ₂ and about 200 to 1000 ppm for HCl, and reacts with these acidic gases. About 1 to 2.5 times the stoichiometric amount is added according to the flow rate of the exhaust gas. The exhaust gas treating agent after the reaction is recovered as fly ash by a dust collector connected to the flue.

The exhaust gas treating agent of the present invention has a large BET specific surface area and pore volume, and can react with an acidic gas such as HCl and SO _x to achieve a high removal rate. Especially capture rate of the SO _x is higher the larger the pore volume of 100～400A. Therefore, since a high exhaust gas treatment can be performed with a relatively small amount, the amount of fly ash that is the final treated product can be reduced. Moreover, since the COD value is low, even when fly ash is reclaimed, the COD in the elution water is low, and the possibility of polluting the environment is low.

  Examples of the present invention will be described below. In the following examples, “%” and “parts” are based on weight unless otherwise specified.

<Example 1>
500 g of quick lime (powder quicklime manufactured by Okutama Kogyo Co., Ltd.) was added to the reaction apparatus as shown in FIG. 1, 500 g of digested water containing water glass was added from the top of the reaction apparatus, and the reaction was allowed to proceed while stirring. The amount of water glass added was 4 g (0.8%) per 1 kg of quicklime. After reacting for about 30 minutes, in a drying apparatus, it was dried with hot air (temperature: 110 ° C.) for 20 minutes to obtain slaked lime having a water content of 1% or less and a particle size (median diameter) of 10 μm.

  An electron microscope (SEM) photograph of this slaked lime is shown in FIG. As a reference example, an SEM photograph of JIS special slaked lime is shown in FIG. As can be seen from FIG. 2, the slaked lime of Example 1 was finer than the reference slaked lime, and fine irregularities were observed on the particle surface. Further, the BET specific surface area, pore volume (1000 Å or less), and pore volume (100 to 400 Å) of the obtained slaked lime were measured by a nitrogen gas adsorption method (BJH method). Further, the COD value was measured by the factory drainage test method of JIS K0102 17. The results are shown in Table 1.

<Examples 2 to 5>
Slaked lime was produced in the same manner as in Example 1 except that sodium hydroxide, sodium carbonate, sodium fluoride, and sodium silicofluoride were used instead of water glass as an additive to be added when digesting quicklime.

The BET specific surface area, pore volume value, median diameter, and COD value measured for Examples 2 to 5 are shown in Table 1 together with the values of Example 1.

As can be seen from the results shown in Table 1, slaked lime having a BET specific surface area of 25 m ² / g or more and a pore volume (0 to 1000 kg) of 0.18 cm ³ / g or more can be obtained by using a sodium compound as an additive. In particular, when water glass and sodium carbonate were used, slaked lime having a BET specific surface area of 30 m ² / g or more and a pore volume (0 to 1000 cm) of 0.2 cm ³ / g or more was obtained. Moreover, when water glass and sodium hydroxide were used, slaked lime having a pore volume (100 to 400 kg) of 0.14 cm ³ / g or more was obtained. Overall, the best results were obtained when water glass was used. Moreover, about COD, it is equal to or less than COD (1.1-2.2 mg / L) of JIS special name slaked lime, and COD (170, 350, 570 mg / L) of three types of commercially available highly reactive slaked lime. L) was significantly lower than L).

<Examples 6 to 9, Comparative Example 1>
Slaked lime was produced in the same manner as in Example 1 except that the amount of water glass added to quicklime was changed to 0.4%, 0.6%, 1.0%, and 1.5%. Further, as Comparative Example 1, slaked lime was produced in the same manner as in Example 1 except that no additive was added. The water content and particle size of the slaked lime of Examples 6 to 9 were almost the same as those of Example 1.

Table 2 shows the BET specific surface area and the pore volume values measured for Examples 6 to 9 and Comparative Example 1. The results of BET specific surface area and pore volume of Examples 1 and 6 to 9 are shown in FIG. 3 and FIG.

As is apparent from the results shown in Table 2 and FIG. 3, when the amount of water glass added was changed from 0.4% to 0.6%, the BET specific surface area increased sharply and became 0.6% or more. The BET specific surface area showed a high value of 33 m ² / g or more. As a result, it was confirmed that the addition of water glass as an additive has a critical effect at about 0.5%.

As shown in Table 2 and FIG. 4, the pore volume (less than 1000 liters) showed a large value of 0.20 cm ³ / g or more, but when the added amount of water glass exceeded 1%, the pore volume The tendency for the volume to decrease was observed, and it was confirmed that a large value of 0.22 cm ³ / g or more could be obtained by setting it to 1% or less. In particular, with respect to the pore volume of 100 to 400 mm, there was a tendency that the amount of water glass added was relatively small, and a large value of 0.14 cm ³ / g or more was obtained at less than 1%. The COD values of Examples 6 to 9 and Comparative Example 1 were almost the same as those of Example 1.

<Examples 10 to 13>
The amount of water glass added to quicklime is the same as in Example 1 (0.8%), and the ratio (weight ratio) of digested water to quicklime is changed to 0.9, 0.95, 1.05, and 1.1. Otherwise, slaked lime was produced in the same manner as in Example 1. The water content and particle size of the obtained slaked lime were almost the same as in Example 1.

Table 3 shows the BET specific surface area and pore volume values measured for Examples 10-13. The values of Example 1 are also shown in Table 3 for reference.

  As can be seen from the results shown in Table 3, it was found that slaked lime having a large BET specific surface area and a large pore volume can be obtained if the ratio (water ratio) of digested water to quick lime is around 1: 1. The pores are thought to be formed by the loss of moisture during drying, and it is necessary that appropriate water is present before drying, but if the water ratio is too large, aggregation tends to occur, It is considered that the specific surface area and pore volume are reduced. In the method for producing slaked lime according to the present invention, a highly reactive slaked lime having a large pore volume can be obtained by using a predetermined sodium compound and setting an appropriate water ratio so that the reaction proceeds without causing aggregation. .

<Example 14>
The ratio of the raw material to be used was the same as that in Example 1, and the slaked lime was produced in the same manner as in Example 1 except that the amount was about 3000 times that of Example 1 and the rest was the same. Table 4 shows the BET specific surface area, pore volume, median diameter, and COD value measured for samples (Examples 14-1 to 14-3) having the same production conditions but different lots.

  As can be seen from the results in Table 4, there are variations due to lots, but when manufactured on a factory scale, the BET specific surface area was improved. Moreover, although the COD value increased with the increase in scale as compared with Example 1 and the like, all were 10 mg / L or less, which was sufficiently lower than the conventional highly reactive slaked lime.

<Examples of exhaust gas treatment agent>
In order to evaluate the effect when using the slaked lime prepared in the example as an exhaust gas treating agent, a test apparatus 50 as shown in FIG. 5 was prepared. The test apparatus 50 includes a gas mixing unit 51, and a reaction unit 52 connected to the gas mixing unit 51 and a heating conduit 55. The gas mixing unit 51 includes an acid gas-containing gas supply source (not shown) and moisture. A heating conduit 55 connected to the contained gas supply source is connected, and a mixed gas imitating exhaust gas is sent to the reaction section 52. The reaction section 52 is provided therein with an acid gas treatment agent fixing layer 53 in which an acid gas treatment agent is fixed in a heat-resistant mesh member, and the mixed gas introduced into the reaction section 52 is an acid gas treatment agent fixing layer. When passing through 53, it reacts with the acid gas treating agent, and the reacted gas is discharged from the reaction section 52. The reaction unit 52 is provided with a heating device 56 so that the acidic gas treating agent fixing layer 53 can be heated to a predetermined temperature.

Using such a test apparatus 50, the mixed gas was processed as follows.
First, 373 mg of the slaked lime of Example 14-1 was used as the acid gas treating agent, and the temperature of the stationary phase 53 was set to 325 ° C. The conduit from the gas supply source and the conduit from the gas mixing section 51 to the reaction section 52 were heated to about 300 ° C. In this state, an acidic gas containing gas and a gas moisture containing gas are supplied to the gas mixing unit 51 to obtain a mixed gas of 1500 ppm acidic gas component (SO ₂ ) and 8% moisture, and supplied to the reaction unit 52 at a flow rate of 700 mL / min. The mixed gas was allowed to flow for about 120 minutes. The acid gas component (SO ₂ ) in the gas after reaction discharged from the reaction section 52 was measured with an analyzer (infrared gas concentration analyzer) 54. The acid gas removal rate was determined by the following calculation. The results are shown in Table 5.
[Acid gas removal rate] =
{([Acid gas component contained in mixed gas]-[Acid gas component in reaction gas]) ÷
[Acid gas component contained in mixed gas]} × 100

表５に示す結果からわかるように、従来の高反応性消石灰と同程度の酸性ガス除去率が得られた。 As a reference example, instead of the slaked lime of Example 14-1, highly reactive slaked lime “Tamacalc-Sponge Acal (TK-SP)” (BET specific surface area 45 m ² / g, pore volume (1000 kg or less) 0.20 cm ³ / G, COD 150 mg / L, manufactured by Okutama Kogyo Co., Ltd.), and the acid gas removal rate was determined in the same manner as in the above Example. The results are shown in Table 5.

As can be seen from the results shown in Table 5, an acid gas removal rate comparable to that of conventional highly reactive slaked lime was obtained.

  ADVANTAGE OF THE INVENTION According to this invention, the highly reactive slaked lime which is suitable for exhaust gas treatment etc. and does not pollute the environment even when discarded as fly ash is provided.

DESCRIPTION OF SYMBOLS 10 ... Reaction apparatus, 11 ... Digestion water supply pipe | tube, 12 ... Additive supply pipe | tube, 20 ... Drying apparatus, 50 ... Test apparatus.

Claims (11)

Slaked lime obtained by digesting quick lime with digested water, and is produced by adding one or more sodium compounds selected from water glass, sodium hydroxide, sodium carbonate, sodium fluoride, sodium silicofluoride during digestion. The slaked lime whose COD value measured by JISK0102 17 is 30 mg / L or less and whose BET specific surface area is 25 m ² / g or more. Slaked lime obtained by digesting quick lime with digested water, manufactured by adding one or more sodium compounds selected from water glass, sodium hydroxide, sodium carbonate, sodium fluoride, sodium silicofluoride during digestion, Slaked lime having a COD value measured by JIS K0102 17 of 30 mg / L or less and a pore volume of 1000 kg or less of 0.15 cm ³ / g or more. The slaked lime according to claim 1, wherein the pore volume of 1000 kg or less is 0.15 cm ³ / g or more. A slaked lime according to any one of claims 1 to 3 is the pore volume of pores of 100~400Å is 0.1 cm ³ / g or more slaked lime.   The slaked lime according to any one of claims 1 to 3, wherein the COD value measured according to JIS K010217 is 3.0 mg / L or less.   The slaked lime according to any one of claims 1 to 3, wherein the sodium compound is water glass.   An exhaust gas treating agent comprising the slaked lime according to any one of claims 1 to 6. A step of adding digested water to powdered quicklime and reacting,
In the reacting step, the digestion water or reaction system does not contain a substantial amount of an organic compound as an additive, and is one or more selected from water glass, sodium hydroxide, sodium carbonate, sodium fluoride, sodium silicofluoride Adding a sodium compound of
And drying the slaked lime after the reaction. A method for producing slaked lime according to claim 8,
The drying step includes a step of drying while sending hot air of 100 ° C. or higher. A method for producing slaked lime according to claim 8 or 9,
The method for producing slaked lime is characterized in that the step of adding the sodium compound is a step of adding to the digested water.   It is a manufacturing method of the slaked lime of Claim 8, Comprising: The addition amount of the said sodium compound is 0.5 to 1.5 weight% of the quicklime which is a raw material, The manufacturing method of the slaked lime characterized by the above-mentioned.

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