JP5434149B2 - Highly reactive and low adhesion slaked lime and method for producing the same - Google Patents

Description

The present invention is slaked lime mainly used for absorbing and removing acidic gas from exhaust gas at a garbage incineration plant, and is particularly reactive, and adheres to equipment such as piping and bag filter filter cloth for transporting slaked lime. It relates also to the manufacturing method with respect to the thing with low property.

For the purpose of adsorbing and removing acidic gases such as hydrogen chloride and sulfur oxides in the exhaust gas from the garbage incineration plant, a highly reactive slaked lime is blown into the flue. As this slaked lime, JIS special name is widely used. In order to reduce the amount of slaked lime used and to reduce the amount of fly ash generated, the specific surface area is increased and the pore volume is increased. What has improved the reactivity with gas is desired.

In response to this request, so-called “high-reactivity slaked lime” has been provided, but for highly reactive slaked lime, the fluidity is poor, it tends to adhere to transport piping, the differential pressure rise in the bag filter is significant, etc. The problem often occurs. Therefore, various attempts as described below have been made with the intention of eliminating the trouble caused by such characteristics of highly reactive slaked lime.

One of them is mixing slaked lime with a substance that reduces adhesion, and “low adhesion slaked lime and a method for modifying it” (Patent Document 1) is 98: 2 to 70 by weight of quick lime. : Mixing at a ratio of 30 and adding a specific amount of at least one additive selected from glycols, glycol ethers or ethanolamines.

Another technique (Patent Document 2) proposed with the title of the same invention is that, in addition to quick lime, pulp is added to slaked lime, and the mixture obtained by addition is irradiated with electromagnetic microwaves. It is proposed to heat-treat.

Furthermore, the proposal (patent document 3) which also becomes the name of the same invention is still more adhesive by irradiating one of the above slaked lime compositions with microwaves and heating for 1 to 30 minutes. Teaching that improvements can be made.

As an improvement measure different from these, "Adhesion-improving slaked lime" (Patent Document 4) discloses that 1 to 5% by weight of pearlite powder is added to slaked lime. The pearlite powder preferably has an average particle size of 50 μm or less. The technology is said to be able to cope with the problem that the addition of organic substances limits the use of slaked lime.

The countermeasure which paid attention to the quick lime used as a raw material has proposed what digested quick lime whose activity is 20-150 mL, Preferably 40-100 mL as "adhesion suppression type | mold slaked lime" (patent document 5). The activity is such that 50 g of quick lime having a particle size of 10 to 3 mm is put into 2 liters of water to which phenolphthalein is added as an indicator, and 4N hydrochloric acid is added dropwise with stirring, so that the solution is slightly red. It is expressed as the hydrochloric acid consumption (mL) after 5 minutes.
JP-A-8-73216 JP-A-8-73217 JP-A-8-109016 JP 2003-252621 A JP 2006-273600 A

However, the countermeasures described above are not necessarily highly effective, and there are drawbacks that some of them are not realistic in terms of cost. In addition, the problems associated with the use of highly reactive slaked lime are, of course, closely related to the facilities and operating conditions of individual garbage incineration plants. It was experienced that there was a big hindrance at the factory.

The object of the present invention is to reduce the adhesion to equipment such as piping and bag filter filter cloth for transporting slaked lime while maintaining high reactivity with acid gas, and causes troubles in any garbage incineration plant An object of the present invention is to provide slaked lime that is highly reactive and has low adhesion, which can be used for exhaust gas treatment without any problems. Providing a method for producing such slaked lime is also included in the object of the present invention. Here, “transport” of slaked lime includes both dry air feeding and wet slurry liquid feeding.

The slaked lime having high reactivity and low adhesion according to the present invention is a slaked lime with relatively low carbonation reactivity, characterized in that the time to reach pH 11 is 10 minutes or more and 20 minutes or less in the carbonation reaction test. is there. The carbonation reaction test is a test method established by the applicant for investigating the reactivity between slaked lime as a product and carbon dioxide gas, and slaked lime is dispersed in water to form a 5% by weight slurry. Is stirred at a high speed of 6,000 rpm, carbon dioxide gas is blown into it at a speed of 640 mL / min, and the time (min) until the pH drops to 11 is measured. The shorter this time, the higher the reactivity of the slaked lime with carbon dioxide, and the lower the time, the lower the reactivity. On the other hand, slaked lime with too low carbonation reactivity has low reactivity with acidic gases other than carbon dioxide gas, so a limit of 20 minutes or less is provided from the viewpoint of maintaining high reactivity.

The method of the present invention for producing highly reactive and low adhesive slaked lime has a 30 second value as a raw material in a hydration activity test according to a measurement method defined by ASTM C110 (hereinafter abbreviated as “ASTM method”). Quick lime having a temperature of 60 ° C. or less and ΔT ₂ = 180 seconds value−30 seconds value of 15 ° C. or more is used, and this is supplied to a continuous digester and consists of alcohols and ethanolamines in water. It is a manufacturing method characterized by adding one or two or more additives selected from a group at a ratio of 0.1 to 5 parts by weight with respect to 100 parts by weight of slaked lime as digestive water.

If slaked lime with high reactivity and low adhesion of the present invention is used, piping that transports slaked lime at the time of use while maintaining the high reactivity that appears as the ability to remove acidic gas contained in the exhaust gas of the garbage incineration plant, The degree of adhesion to equipment such as bag filter cloth is low, and it is possible to surely obtain the advantage that troubles such as piping blockage and operation stoppage due to excessive increase of the bag filter differential pressure are less likely to occur.

According to the method for producing slaked lime having high reactivity and low adhesion according to the present invention, it is possible to reliably produce slaked lime having a property that the time to reach pH 11 in the carbonation reaction test is 10 minutes or more and 20 minutes or less. it can. The slaked lime of the present invention has been confirmed in the operation of an actual incineration plant to exhibit low adhesion, both when it is put on compressed air and when it is sent as a slurry.

In the following, the process leading to the completion of the present invention will be described, the reasons for limitation will be explained, and preferred embodiments will be shown. First, when obtaining and analyzing slaked lime fixed to a pipe from a garbage incineration site that caused a pipe clogging trouble, it was found that the content of CO ₂ was remarkably increased compared to before use. Therefore inventors speculated to be related to the reactivity of the adhesion and CO ₂ of slaked lime was investigated and highly reactive calcium hydroxide, the association of reactivity with CO _2. The procedure is as follows.
1) Disperse 20 g of slaked lime in 380 g of water to make a 5% water slurry.
2) While stirring the water slurry at a high temperature (6,000 rpm) at a temperature of 20 ° C., CO ₂ gas is blown into the water slurry at a speed of 640 mL / min.
3) Record the change with time of pH (12.0 to 12.9 at the time of slurry formation) and record the time (minutes) until the pH drops to 11. The shorter the time, the higher the reactivity with CO ₂ . (This test method is nothing but the carbonation reaction test described above.)

The results are as shown in FIG. 1, and one kind of slaked lime that is likely to cause clogging of the piping has a high “carbonation reactivity”, that is, the pH reduction time in the carbonation reaction test is 8 minutes or less, while clogging occurs. There was a clear difference between the two types of slaked lime that were difficult to produce, 11 minutes or longer. In the end, the above assumption was true, and slaked lime with a pH reduction time of 10 minutes or more in the carbonation reaction test should be used in order to treat exhaust gas without causing blockage of the piping. I understood it.

Furthermore, the inventors conducted the following experiment in order to confirm the relationship between the carbonation reactivity and fixation of slaked lime. Highly reactive after carbonated slaked lime 100g by the exposed to CO ₂ gas or humidified CO ₂ gas (to use the humidified gas is to promote carbonation), taking it from 15g The mold was put into a 40 mm diameter mold and pressed under a pressure of 24.5 × 10 ⁶ Pa, and the resulting molded body was measured for breaking strength by a three-point load using a Kiyama hardness tester. Some samples were dried after being dried in a low-temperature drier, and then compared for breaking strength before and after drying. This low temperature drying is a simulation of drying by contact with flue gas. Table 1 below shows the compressive strength and the values of CO ₂ content and water content in each case.

Table 1

The compressive strength of the compacted slaked lime sample is a measure of the progress of fixation due to carbonation, and is understood to indicate a mechanism that makes it difficult for slaked lime attached to piping and equipment to fall off. Also from this aspect, it can be seen that the carbonation reactivity is important for the adhesion of slaked lime and the adhesion of slaked lime.

On the other hand, slaked lime suitable for this application, which has a high acid gas removal rate when used for waste gas treatment at a garbage incineration plant, and is highly reactive and requires only a small amount of use, has a wide specific surface area, Moreover, it is known that the pore volume is large. And it is also known that such slaked lime can be obtained when raw lime is used as a raw material in terms of the degree of calcining of limestone. Then, the above-mentioned knowledge that starting with quick lime with low hydration activity should be obtained in order to obtain slaked lime with low carbonation reactivity, and these common senses need to be balanced. The conclusion is reached that the activity needs to be selected appropriately.

Thus, the inventors have sought raw lime that gives slaked lime that has high reactivity but low carbonation reactivity. Hydration known as “t ₆₀ value” because the activity expressed by hydration reactivity of quick lime, which is the raw material for digestion, may affect the carbonation reactivity of slaked lime obtained by digestion. Eleven kinds of quicklime with various activities ranging from 24 seconds to 62 seconds were digested, and the carbonation reactivity of the obtained slaked lime was examined. As is well known, the t ₆₀ value indicates that the water temperature reaches 60 ° C. while stirring 150 g of quick lime having a particle size of −210 μm into 600 mL of water at 20 ± 0.5 ° C. and stirring at a speed of 300 rpm. The shorter the time, the quicker the hydration activity, and the shorter the time, the lower the time.

The results of the experiment, t ₆₀ value is low, that is, as slaked lime hydration activity is obtained by digesting a high quicklime, relations of a high carbonation reaction could be confirmed. Described above, quicklime value of carbonation reaction test gives slaked lime is at least 10 minutes, more than 50 seconds in the t ₆₀ value, hydration activity was found to be one rather low.

By the way, the t ₆₀ value is an index indicating the initial state of the hydration reaction, and the state after the middle period cannot be understood by itself. However, the inventors have predicted that the reactivity after the middle period will also be important for the hydration of raw quicklime in order to obtain slaked lime that maintains high reactivity while suppressing carbonation reactivity. The raw quicklime was defined by the ASTM method which can know the sum characteristics not only in the initial period but also in the middle period and thereafter. As a result, “the quick lime whose 30 second value is 60 ° C. or lower and ΔT ₂ = 180 second value−30 second value is 15 ° C. or higher in the hydration activity test by the ASTM method described above was obtained. Is the limitation. Speaking of this, it is “quick lime whose initial reaction is a little slow, but the subsequent reaction is large” regarding hydration.

As is well known to those skilled in the art, the hydration activity test by the ASTM method is a method in which quick lime is put into water placed in a Dewar bottle and a temperature rise curve is recorded. The water temperature after a second represents the rate of the initial reaction. Quick lime whose temperature exceeds 60 ° C. does not give good slaked lime because its initial reactivity is so high. On the other hand, ΔT ₂ = 180 seconds value−30 seconds value indicates the elongation of the subsequent reaction, and quick lime whose value is too small has too high initial hydration reactivity or hydration after the middle period. Reactivity is low and in any case does not give the preferred slaked lime. The quick lime whose difference does not reach 15 ° C. even if the value for 30 seconds is 60 ° C. or less, the firing degree is too high, the hydration reaction is slow, and digestion cannot often be performed properly. Reactivity with acid gas is unsatisfactory.

In digestion, the ratio of digested water to quicklime is preferably in the range of H ₂ O / CaO = 0.8 to 1.2 (weight ratio). This amount of digested water corresponds to about 2.5 to 3.7 times the theoretical amount of water required for digestion. In order to obtain highly reactive slaked lime, it is necessary to use a relatively large amount of digested water so that the mixture of quicklime and water is as high as possible. If the water ratio does not reach 0.8, the amount of digestion water is insufficient. On the other hand, if the amount of digestion water exceeds a certain limit, the agitation load of the digester increases, which is inappropriate for industrial continuous production. In addition, there is a problem that energy consumption for drying excess water after digestion becomes excessive. The above-mentioned digestion water amount ratio of 0.8 to 1.2 was selected in consideration of the performance expected from the product slaked lime and the production cost.

One or more additives selected from the group consisting of alcohols and ethanolamines, the product slaked lime has a large specific surface area and a large pore volume, so that the acid gas in the exhaust gas to be treated It is effective in obtaining a high removal rate. As the alcohols, various kinds of alcohols from monohydric alcohols such as methanol and ethanol to polyhydric alcohols such as diethylene glycol and dipropylene glycol can be used. As the ethanolamine, monoethanolamine, diethanolamine, and triethanolamine can be used, and triethanolamine is preferable.

Digestion is preferably carried out under conditions where the temperature at the outlet of the digester is 70 ° C or lower. This temperature is, of course, the temperature at the outlet of the aging machine when an aging machine is attached to the digester. Conditions at an outlet temperature of 70 ° C. or less ensure that digestion is sufficiently performed. Sufficient digestion maintains the acid gas removal performance of product slaked lime high, and as a result, the use of slaked lime used in exhaust gas treatment Contributes to the improvement of basic unit. The time required for digestion, that is, the residence time inside the digester, is determined by the volume of the digester (including the aging machine if included). If sufficient residence time is secured, the hydration reaction will be completed, so the digest temperature will be lower on the outlet side, but if you try to increase production, the residence time will naturally be shortened, so The outlet side temperature increases. It has been experienced that slaked lime leaving the digester at high temperatures is incompletely digested and highly cohesive and therefore poorly dispersible when used. Such agglomeration apparently reduces the surface area that reacts with the acid gas, which may lead to an increase in slaked lime unit. The utility of performing digestion so that the temperature of the slaked lime at the outlet of the digester is 70 ° C. or less was confirmed from the results of the use of highly reactive slaked lime with an actual machine.

In the slaked lime of the present invention, the abundance of particles having a diameter of 45 μm or more is preferably 10% by weight or less from the viewpoint of particle size distribution. Since particles of relatively large diameter tend to settle and accumulate in horizontal piping, for example in a flue, keeping the proportion low can provide the benefit of preventing clogging caused by deposition.

Using quick lime having hydration reaction characteristics as shown in Table 2 as a raw material, digestion water containing 1% by weight of diethylene glycol with respect to CaO is added so that the weight ratio of water becomes 1.0. And digested. The situation of carbonation reaction of the obtained slaked lime was examined, and the result shown in FIG. 2 was obtained. The measured carbonation rate is shown in Table 2 together. The two types of slaked lime in the examples satisfy the condition that the 30 second value of the ASTM test of quick lime used as a raw material is 60 ° C. or less and ΔT ₂ is 15 ° C. or more, and the carbonation rate is Meet the condition of 10 minutes or more

Table 2

The obtained slaked lime was used for the purpose of treating the exhaust gas from the garbage incineration plant to remove acid gas, and the number of cleaning intervals required for the equipment was examined. The results are also shown in Table 2. By using the slaked lime of the present invention, it has been proved that adhesion of slaked lime to equipment and piping is remarkably reduced and the maintenance burden is reduced.

It is the data of the experiment conducted in the formation process of this invention, Comprising: The graph which shows the result of the carbonation reaction test of slaked lime with high adhesiveness to piping, when used for exhaust gas treatment, and low slaked lime. The graph similar to FIG. 1 which shows the result of a carbonation reaction test about the slaked lime manufactured and used in the Example of this invention.

Claims (5)

Carbonation reaction test by digesting quick lime whose 30 second value is 60 ° C. or less and ΔT ₂ = 180 second value −30 second value is 15 ° C. or more in the hydration activity test defined in ASTM C110 (Slaked lime is dispersed in water to form a 5% by weight slurry, and while stirring the slurry at a high speed of 6,000 rpm, carbon dioxide gas is blown into it at a speed of 640 mL / min until the pH drops to 11. A highly reactive and low adherence slaked lime characterized in that the time to reach pH 11 is 10 minutes or more and 20 minutes or less in the unit “minute”). The slaked lime according to claim 1, wherein the abundance of particles having a diameter of 45 µm or more is 10% by weight or less. As a raw material, quick lime having a 30 second value of 60 ° C. or lower and a ΔT ₂ = 180 second value−30 second value of 15 ° C. or higher in a hydration activity test defined in ASTM C110 is used. The water which supplied to the digester and added 1 or 2 or more types of additives selected from the group consisting of alcohols and ethanolamines at a ratio of 0.1 to 5 parts by weight with respect to 100 parts by weight of slaked lime. A method for producing slaked lime that is highly reactive and has low adhesion, which is added as digestive water. The percentage of digested water for _quicklime, H 2 O / CaO = _0.8~1.2 slaked lime manufacturing method of claim 3 implemented as (weight ratio). The method for producing slaked lime according to claim 3, wherein the digestion is performed under a condition that the temperature at the outlet of the digester is 70 ° C or lower.

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