JP2005272238A - Method of producing slaked lime - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce slaked lime remarkably efficient to treat an SO<SB>2</SB>or the like-containing gas by using quicklime powder and a small quantity of a reaction retarder. <P>SOLUTION: The method of manufacturing slaked lime by slaking quicklime to produce slaked lime includes (a) a fine pore base construction step for preparing a "slaking liquid" containing 10-40 wt.% solid lime and 60-90 wt.% water by slaking quicklime for the "slaking liquid" with the excess quantity of a "slaking water" containing 2-50 pts.wt. reaction retarder per 100 pts.wt. quicklime for the "slaking liquid", (b) a pore growth step for producing wet slaked lime powder having 10-30 wt.% water using the "slaking liquid" obtained by (a) to slake quicklime for main slaking and (c) a drying step for obtaining dry slaked lime powder containing <1.0 wt.% water by heating at ≤500°C to dry or by adding a proper quantity of drying quicklime to react with water in the wet slaked lime to remove water. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing slaked lime particles, first digesting quick lime for "digestion liquid" with an excess amount of water containing a reaction retarder to obtain a mixture of lime and water named "digestion liquid" Next, the prepared “digestion liquid” is used for digestion of main digested quicklime to obtain wet slaked lime powder having a large pore volume, and finally the wet slaked lime powder is heated or added with quicklime for drying. The present invention relates to a method for producing slaked lime particles suitable for treatment of flue gas containing SO2 and the like by drying.

  Slaked lime has a wide variety of uses, including processes such as water treatment, removal of toxic gases from gas streams, and neutralization of acidic waste. The action and efficiency in these processes can be dramatically improved by utilizing slaked lime with properties that are adapted to the individual usage. For example, in the field of flue gas desulfurization and dehydrochlorination processes using dry slaked lime, slaked lime with a large pore volume usually cleans gas emissions, further improves operating efficiency, and uses lime It is generally believed that this can lead to significant cost savings.

  When quicklime is reacted with water, the quality and properties of the resulting slaked lime are: reactivity of quicklime to water, size distribution of quicklime, amount and quality of water used, water temperature, addition of lime and water It depends on the pattern. In addition, glycols, amines, alcohols, ketones, ethers, aldehydes, sugars, citric acid, etc., preferably ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol Use of reaction retardants such as tripropylene glycol, polypropylene glycol, monoethanolamine, diethanolamine, triethanolamine, methanol, ethanol, propanol, butanol, specially enhanced properties to fit the purpose It becomes an important means for producing slaked lime having slag.

  A conventional method for producing slaked lime is a reaction between water and quick lime that is 1.3 to 2 times the theoretical amount necessary to produce dry slaked lime powder. However, as already well known, since steam digestion occurs, most of the pores formed are within the range of macropores having a radius of 250 mm or more, and the reactivity of such conventional slaked lime to acid gas is The sludge that is very low and discharged from the gas cleaning / treatment process will contain a significant amount of unreacted lime.

  At present, slaked lime with a total pore volume of 0.200 cc / g or more having a clearly high reactivity to harmful gases is generally produced by a method using a reaction retarder. However, in the current method, the slaked lime dehydrated cake obtained by wet digestion or the slaked lime wet powder having a residual water content of 20-30% by weight is dried by heating, so that the drying cost is very high.

  The method disclosed in Japanese Patent Application Laid-Open No. 10-167775 uses slaked lime slurry and quick lime fine powder. However, this method adds a reaction retarder to the slurry only after the slurry is formed. Since the effect of pore formation of the reaction retarder is most exhibited only when it is used when the hydration reaction is occurring, the method of the present invention cannot be expected to have a sufficient effect. In addition, at the stage where the subsequent dry digestion process is performed, pore crushing is very likely to occur due to the intense reaction accompanying steam digestion. These reasons lead to a process of producing slaked lime with a pore structure that is not effective for reaction with harmful gases.

  As another method utilizing the advantages of wet digestion, U.S. Pat.No. 6,322,769 discloses a wet slaked lime with a moisture content of 21-23% by weight, and then dried to provide excellent processing characteristics such as SO2. It is described that a dry product having is obtained. However, this method requires a large amount of heat energy for drying.

JP 10-167775 A U.S. Patent No. 6322769

  The main object of the present invention is to provide a process for producing slaked lime that is extremely efficient for the treatment of gas containing SO2, etc. by using quick lime and a small amount of reaction retarder. The present invention also includes drying the wet slaked lime powder by heating or adding an appropriate amount of quick lime that does not impair the mesoporous structure in the wet slaked lime.

The method according to the present invention is a method for producing slaked lime showing high efficiency in the reaction with SO2 gas or the like,
(A) First, digestion of “digestion liquid” quicklime with 100 to 50 parts of “digestion liquid” quicklime with water containing 2-50 parts by weight of a reaction retarder, The pore foundation construction process to obtain a “digestion liquid” containing lime solids and 60-90% by weight moisture,
(B) A pore growth process to obtain wet slaked lime powder having a water content of 10-30% by weight, using the “digestion liquid” obtained from (a) to digest main digested quicklime;
(C) Drying to obtain dry slaked lime powder having a moisture content of less than 1.0% by weight by removing the wet slaked lime powder obtained from (b) by heating means or reacting with moisture by adding quick lime for drying Including a process.

  The inventors have found that slaked lime with a larger number of mesopores (pores with a radius of 10-250 mm), especially pores with a size in the range of radius 50-100 mm, has the same total pore volume. We found a tendency to be more effective in the reaction with SO2 contained in.

  Based on the above, the inventors considered that more slaked lime particles having pores mainly consisting of mesopores with a radius of 50-100 mm can be generated by using slurry and wet powder. In addition, the inventors devised so that a large number of mesopores having a radius of 50-100 mm formed as described above appear as they are in the dried slaked lime powder.

  Through various experiments, the inventors have found that the characteristics of pores formed, that is, pore volume, pore distribution, and the like, can be controlled by the type and amount of reaction retarder during wet digestion. The pore structure of slaked lime particles generated in the slurry has pores with a radius of 50-100 mm, which occupies about 20-30% by volume of the total pore volume, which is digested with pure water only. It was also found that the number of slaked lime particles in the obtained slaked lime slurry was very large compared to the pores having a radius of 50-100 mm. Furthermore, the inventors made the above-mentioned slaked lime slurry “digestion liquid”, digested main digested quicklime and obtained wet slaked lime containing 10-30% by weight of water, compared with “digestion liquid” The total pore volume was almost the same, but it was found that the pores in the radius range of 50-100 mm increased significantly, accounting for more than 50% by volume of the total pore volume. In particular, the “digestion liquid” has a foundation for constructing pores with a radius of 50-100 mm, and by using this for digestion of main digested quicklime, pores with a radius of 50-100 mm are developed. I thought it would be expanded.

  Wet slaked lime powder consisting of pores with a radius of 50-100 mm or more of 50% by volume or more of the total pore volume obtained as described above is heated at 500 ° C. or less, or an appropriate amount of dry lime is added. Slaked lime powder with excellent reactivity was obtained by carrying out drying.

  Accordingly, an object of the present invention is to provide a digestion process based on the area of wet digestion, and (a) 20-30% by volume of the total pore volume has a mesopore with a radius of 50-100 mm. The foundation of the pore structure was established, and then (b) the formation of new mesopores and at the same time the mesopore foundation was expanded and developed, so that the mesopores with a radius of 50-100 mm had more than half of the total pore volume. To make up. And it is to dry wet slaked lime by heating it or by adding an appropriate amount of quicklime for drying. The reaction between the dry lime for drying and the remaining moisture of the wet slaked lime powder proceeds slowly so that the mesopore structure of the wet slaked lime can be left intact.

  Throughout this specification, the term “digestion water” refers to an aqueous solution of a reaction retardant used to digest quick lime for “digestion liquid”, and the term “digestion liquid” refers to an excessive amount of “digestion water”. Represents a mixture containing 60-90 wt% moisture and 10-40 wt% lime solids obtained by digesting quick lime for "digestive liquid".

  In order to obtain suitable slaked lime having a pore distribution suitable for each intended gas absorption application, it is generally controlled by the type and amount of reaction retarder, but in the present invention, “digestion liquid” and wet By adjusting the water content of slaked lime, mesopores more optimal for gas absorption can be obtained.

  According to the method of the present invention, the first pore foundation construction step (a) is carried out by adding an excessive amount of “digestion” containing 2-50 parts by weight of a reaction retarder to 100 parts by weight of quicklime for “digestion liquid”. It can be achieved by reacting quick digestion liquid for “digestion liquid” with “water” to prepare “digestion liquid” which is a solid of 60-90 wt% water and 10-40 wt% lime. The “digestion liquid” preferably consists of 75-90% by weight moisture and 10-25% by weight lime solids.

  Further, in the pore growth process (b), using the “digestion liquid” obtained by the above process, the wet slaked lime powder contains residual moisture of 10-30 wt%, preferably 13-23 wt%. This can be achieved by digesting the main digested quicklime. From the viewpoint of energy saving, it is advantageous that the residual moisture of the wet slaked lime powder is 13 to 18% by weight.

  Finally, drying to obtain a dry slaked lime powder having a moisture content of less than 1% by weight from the wet slaked lime powder having a moisture content of 10-30% obtained by the above step (b) may be performed by hot air drying at a temperature of 500 ° C. or lower, or an appropriate amount. It can be carried out by adding quick lime for drying and reacting with moisture in the wet slaked lime to remove it. When performing hot air drying, etc., it is better to avoid hot air and atmosphere with high CO2 concentration. As is well known, slaked lime easily reacts with CO2 to form calcium carbonate. At this time, since the pore volume, specific surface area, and the like are reduced, the adsorption ability of acidic harmful gases such as SO2 is also lowered. Accordingly, contact with CO2 is avoided as much as possible during drying, and drying is preferably performed with hot air or an atmosphere having a CO2 concentration of 500 mg / Nm3 or less, which is the CO2 concentration in the air. Furthermore, regarding the temperature, the temperature at which slaked lime is dehydrated and converted to quick lime is 550 ° C., and it is necessary to carry out at 500 ° C. or less, which is slightly lower than this temperature. Considering thermal efficiency, it is desirable to dry at 350 to 450 ° C. On the other hand, drying using quicklime for drying can save the dryer and can reduce the drying energy, which is most preferable in terms of cost. Providing a pulverization / classification step after the drying step and adjusting to an appropriate particle size leads to an improvement in practical removal efficiency.

  The “digestion liquid” quicklime, the main digestive quicklime and the dry quicklime are preferably powders having a particle size of 5 mm or less, preferably powders having a particle size of 1 mm or less. In particular, quick lime for drying is very preferably a powder having a particle size of 1 mm or less so that uniform mixing with wet slaked lime can be easily performed. The reactivity of each quicklime is preferably quicklime-water activity t60 = 100 seconds or less, desirably 40 seconds or less. In order to obtain an “excess amount of water” for obtaining a “digestion liquid” consisting of 60-90% by weight of water and 10-40% by weight of lime in step (a), of course, digester, reaction conditions, etc. The amount of water is 250-1250 parts by weight with respect to 100 parts by weight of quicklime for “digestion liquid”.

(Example 1)
In the basic pore construction process of (a), JIS special quick lime (CaO 95% by weight or more, -0.1 mm powder, quick lime-water activity t60 = 20 s) manufactured by Yabashi Kogyo Co., Ltd. as quick lime for “digestion liquid” 200 g Was digested with 1860 g of water (35 ° C.) containing 60 g of polyethylene glycol for 5 minutes in a vessel equipped with a stirring blade. The resulting “digestion liquid” contained 87% by weight of water. Although the quick lime-water activity is t60, add 150g of quick lime in the specified range to 600mL of water at 20 ° C in the calorimeter, and measure the time required to reach 60 ° C. It was determined using a method conforming to the American Water Works Association (AWWA B202) and ASTM standard C110 lime physical property test.

  Then, in the pore growth process of (b), 1800 g of main digested quicklime was charged into the container and mixed with the “digestion liquid” for 10 minutes. The resulting wet slaked lime powder contained 19% water by weight.

  Finally, drying of the wet slaked lime (c) was carried out in a hermetic vacuum dryer at 120 ° C. to obtain a dry slaked lime powder having a moisture content of 0.3% by weight.

  The pore characteristics of slaked lime were measured using NOVA3000 gas sorption analyzer of Quantachrome corporation. The pore volume was determined by nitrogen absorption measurement within a radius of 5-1000 mm (calculated by the BJH method assuming that the pores are cylindrical). Therefore, throughout this specification, the total pore volume represents the volume of pores having a radius of 5-1,000 mm measured by nitrogen absorption based on the BJH method. With respect to Example 1, the slaked lime particles developed in the “digestion liquid” in the pore foundation construction stage have a total pore volume of 0.220 cc / g, and a pore with a radius of 50-100 mm has a pore size of 0.056 cc / g. (The range of radius 50-100 mm has been experimentally found by the inventors to be the optimum pore size in the SO2 gas reaction of slaked lime particles). Slaked lime particles produced in wet slaked lime during the pore growth process have a total pore volume of 0.227 cc / g, 0.124 cc / g occupying more than half of the total pore volume by pores with a radius of 50-100 mm Is occupied.

In addition, the reactivity of slaked lime with respect to SO2 was placed on the entire surface and uniformly as a adsorption surface in a reactor with a diameter of 34 mm, and 0.600 g of a sample crushed to 0.100 mm or less at 170 ° C. for 50 minutes. Measurements were made by passing the road gas mixture and analyzing the exhaust gas discharged from the reactor. The gas was roughly composed of 30% by volume of water, 1% by volume of SO2 and the balance of N2, and the total amount of gas charged in 50 minutes was a volume at which the Ca / S molar ratio was 2. The sample SO2 removal efficiency was calculated as the amount of SO2 retained in the sample relative to the total SO2 charged as follows.
SO2 removal efficiency% = (1-A / B) x100 Eq. (1)
here
A = SO2 in the gas discharged from the reactor
B = total SO2 charged to the reactor
The SO2 removal efficiency of the slaked lime according to Example 1 was 82%.

(Example 2)
Exactly the same procedure as in Example 1 except that drying was performed by adding 1000 g quick lime for drying to the wet slaked lime obtained from the pore growth process of (b). The obtained dry slaked lime had a total pore volume of 0.190 cc / g, and pores with a radius of 50-100 mm occupied 0.094 cc / g, accounting for nearly half of the total pore volume. The SO2 removal efficiency was 77%.

(Example 3)
400g, 1860g and 60g of "digestion liquid" quick lime, water and polyethylene glycol used for the pore basic construction process of (a), respectively, and 1850g of main digestion in the pore growth process of (b) Exactly the same procedure as in Example 1 except that lime was used. The “digestion liquid” obtained by (a) has a water content of 77% by weight, the slaked lime particles therein have a total pore volume of 0.214 cc / g, and a pore with a radius of 50-100 mm is 0.057 occupied cc / g. The wet slaked lime obtained from (b) has a water content of 13% by weight, the slaked lime particles therein have a total pore volume of 0.221 cc / g, and pores with a radius of 50-100 mm are 0.116 cc. / g, and thus more than half of the total pore volume was occupied. The SO2 removal efficiency was 80%.

Example 4
Exactly the same procedure as in Example 1 except that the drying of wet slaked lime according to (b) was carried out by adding 750 g of quicklime for drying. The obtained dry slaked lime had a total pore volume of 0.155 cc / g, and pores with a radius of 50-100 occupy 0.078 cc / g, and thus almost half of the total pore volume. The SO2 removal efficiency was 75%.

(Comparative Example 1)
1860 g of water containing 60 g of polyethylene glycol was digested with 2000 g of quicklime, and the resulting wet slaked lime powder with a moisture content of 19% by weight was dried in a vacuum dryer to obtain a dried slaked lime powder. The dried slaked lime had a total pore volume of 0.211 cc / g, and pores with a radius of 50-100 occupy 0.082 cc / g, less than 50% by volume of the total pore volume. The SO2 removal efficiency was 74%.

(Comparative Example 2)
2000 g of quicklime was digested with 1860 g of water containing 60 g of polyethylene glycol. The resulting wet slaked lime powder with a water content of 19% by weight was dried by adding 1000 g of quick lime. The wet slaked lime had a total pore volume of 0.215 cc / g, and pores with a radius of 50-100 mm occupied 0.081 cc / g. The dried slaked lime powder had a total pore volume of 0.163 cc / g, and pores with a radius of 50-100 occupy 0.068 cc / g, less than 50% by volume of the total pore volume. The SO2 removal efficiency was 68%.

(Comparative Example 3)
Using 400 g, 1860 g, and 60 g of quick lime, water, and polyethylene glycol, respectively, only the pore basic construction process of (a) was performed to obtain a “digestion liquid” having a moisture content of 77% by weight. Next, instead of performing a pore growth process, 2600 g of quicklime was added to the “digestion liquid” to obtain dry slaked lime. The slaked lime particles in the “digestion liquid” had a total pore volume of 0.224 cc / g, and pores with a radius of 50-100 mm occupied 0.067 cc / g. The dried slaked lime powder had a total pore volume of 0.132 cc / g, and pores with a radius of 50-100 occupy 0.038 cc / g, less than 50% by volume of the total pore volume. The SO2 removal efficiency was 59%.

(Comparative Example 4)
3000 g of quicklime was digested with 1860 g of water containing 60 g of polyethylene glycol. The resulting dry slaked lime powder had a total pore volume of 0.122 cc / g, and pores with a radius of 50-100 occupy 0.028 cc / g, less than 50% by volume of the total pore volume. The SO2 removal efficiency was 58%.

  From these examples, the slaked lime particles in the “digestion liquid” have an average total pore volume of 0.220 cc / g, and pores with a radius of 50-100 mm occupy about 25-30% by volume. It became clear that In addition, when digesting the main digested quicklime with this “digestive liquid”, the slaked lime particles obtained as wet slaked lime have a total pore volume of about 0.220 cc / g, and pores with a radius of 50-100 mm are total pores. Occupied more than 50% by volume. “Digestion liquid” has a foundation to build pores with a radius of 50-100 mm, and this is used for digestion of quick digestion lime to develop and expand pores with a radius of 50-100 mm. I think. Thus, the designation “pore foundation construction” process refers to the “digestion liquid” preparation process, and the “pore growth” process refers to the digestion process that produces wet slaked lime powder.

  From these examples, it has been clarified that the above-described process in the present invention can be used to drastically reduce drying costs and produce slaked lime with high reactivity to SO2 gas.

Table 1 shows the detailed experimental conditions and results of the examples and comparative examples.

  As mentioned above, although the Example of this invention was described, it cannot be overemphasized that this invention is not limited to the said Example, A deformation | transformation implementation is possible suitably in the range of the summary of this invention.

Claims (4)

In the method for producing slaked lime that produces slaked lime by digesting quick lime,
(A) About 100 parts by weight of quick lime for “digestion liquid” 10-40% by weight of lime by digesting quick lime for “digestion liquid” with an excessive amount of water containing 2-50 parts by weight of a reaction retarder And a stomatal foundation construction process for preparing a “digestion liquid” containing 60-90% by weight of water,
(B) a stomatal growth process for producing wet slaked lime powder having a water content of 10-30% by weight using the “digestion liquid” obtained from (a) in order to digest the main lime for digestion;
And (c) drying the wet slaked lime powder to obtain a dried slaked lime powder having a moisture content of less than 1.0% by weight. The method for producing slaked lime according to claim 1, wherein the drying process is performed by a heating means. The method for producing slaked lime according to claim 2, wherein the heating by the heating means is performed at a CO2 concentration of 500 mg / Nm3 or less in a dry atmosphere and at a temperature of 500 ° C or less. The method for producing slaked lime according to claim 1, wherein the drying process is performed by adding quick lime for drying and reacting and removing moisture.