JPH08947A - Agent and process for treatment of exhaust gas - Google Patents

Abstract

PURPOSE:To provide an exhaust gas treatment agent, dry type or semi-dry type and inexpensive and of high activity, by using a calcium chloride alone, or in combination with a calcium compound as a substitution reactive substance for a substance to be treated in the exhaust gas. CONSTITUTION:A calcium chloride alone or in combination with a calcium compound such as calcium carbonate or calcium hydroxide is added as a substitution substance for a substance to be treated in exhaust gas. At that time, 99.9-1wt.% calcium chloride is contained, and the content weight ratio of calcium hydroxide to calcium sulfite is set to be 100:1 to 10:(1-30). Thus, calcium chloride is applied as an exhaust gas-treating agent, and also calcium carbonate is activate and converted to be highly functional to give an exhaust gas-treatment agent active even at low temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the application of calcium chloride, which has not heretofore been generally used, to a flue gas treatment agent and the flue gas treatment of calcium carbonate which has been conventionally effective only at high temperatures or in water. Regarding application to agents.

[0002]

2. Description of the Related Art Sulfur oxides, nitrogen oxides and the like contained in flue gas generated by the combustion of coal, heavy oil and the like not only harm buildings and structures, but also extremely affect animals, plants and the human body. It has been found that it has a great effect, and methods for removing the above substances in flue gas, that is, desulfurization and denitration methods have been studied, and various methods have been developed.

[0003] Desulfurization methods are roughly classified into dry, semi-dry and wet methods. The methods shown in Table 1 are known for the dry and semi-dry processes to which the present invention belongs.

[0004]

[Table 1] In the absorption method shown in Table 1, expensive NH ₃ is required for the regeneration of the reactants (recovery of sulfur or a sulfur compound) (active manganese oxide method), or a valuable reducing gas is required (alcalizing). (Alumina method), or the reaction temperature is high (alkaline alumina method, lime blowing method).

[0005] The adsorption method has the drawback that the activated carbon used is expensive and easily deteriorates. The catalytic oxidation method has the problems that the vanadium catalyst used is expensive, easily deteriorates and the reaction temperature is relatively high. There was a point.

On the other hand, the semi-dry desulfurization method mainly uses a method of using Ca (OH) ₂ as an absorbent.
Compared to the gypsum method, it is simple and low in cost, but has a low desulfurization performance, and there are problems such as an increase in running cost due to the use of expensive Ca (OH) ₂ .

In Japanese Patent Laid-Open No. 57139/1993, by adding calcium chloride to calcium carbonate, SO
₂ is disclosed. However, it is clearly described that the addition of calcium chloride in this known technique is characterized in that recalcification of calcium oxide or calcium hydroxide generated from calcium carbonate is suppressed, and calcium chloride and SO ₂ The reaction is not mentioned at all. Furthermore, this technique is effective only at a fairly high temperature.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve various problems of the conventional dry and semi-dry desulfurization methods,
An object of the present invention is to provide an inexpensive and high-performance flue gas treating agent.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a flue gas treating agent comprising calcium chloride as a reactant for replacing a substance to be treated in flue gas. When the substance to be treated is SO ₂ , the reaction is performed according to the following equation. CaCl ₂ + SO ₂ + H ₂ O → CaSO ₃ + 2HCl The HCl generated here is fixed by a calcium compound containing at least one compound selected from the group consisting of calcium carbonate, calcium hydroxide, calcium sulfite, and calcium sulfate.

This calcium compound may be present together with calcium chloride or may be present separately from calcium chloride. In case of coexistence, 9
It may be added in an amount of 9.9 to 1% by weight.

Ca used in the semi-dry or dry method
(OH) ₂ is considered to be reacting as in the following formula (1) or (2).

Ca (OH) ₂ + SO ₂ → CaSO ₃ + H ₂ O (1) Ca (OH) ₂ + SO ₂ + 1 / 2O ₂ → CaSO ₄ + H ₂ O (2) Calcium chloride reacts with SO _{2 in} flue gas as shown in the formulas (3) and (4) to fix SO ₂ as sulfite or sulfate.

CaCl ₂ + SO ₂ + H ₂ O → CaSO ₃ + 2HCl (3) CaCl ₂ + SO ₂ + H ₂ O + 1 / 2O ₂ → CaSO ₄ + 2HCl (4) Released by the equations (3) and (4) The hydrogen chloride reacts with calcium carbonate when the calcium compound is calcium carbonate, as shown in the formula (5), and becomes calcium chloride. (3), (4)
It is recycled to immobilize the SO ₂ in the equation.

CaCO ₃ + 2HCl → CaCl ₂ + CO ₂ + H ₂ O (5) As described above, the calcium chloride of the present invention is an active substance for the desulfurization reaction, and the calcium-based compound such as calcium carbonate is SO _2. It plays a role as a fixing substance of hydrogen chloride released in the absorption process.

On the other hand, with respect to calcium carbonate, the same reactions as in formulas (1) and (2) proceed as shown in formulas (6) and (7), and SO ₂ in flue gas is fixed as calcium sulfate or calcium sulfite. Can be removed and converted.

CaCO ₃ + SO ₂ → CaSO ₃ + CO ₂ (6) CaCO ₃ + SO ₂ → 1 / 2O ₂ → CaSO ₄ + CO ₂ (7) It is considered that the elementary reaction shown in the above formulas (3) and (5) is proceeding in the formula (6) due to the presence.

CaCl ₂ + SO ₂ + H ₂ O → CaSO ₃ + 2HCl (3) CaCO ₃ + 2HCl → CaCl ₂ + CO ₂ + H ₂ O (5) The HCl generated in the formula (3) is (5) In the formula, it reacts with unreacted calcium carbonate to produce calcium chloride. This calcium chloride is also used to fix SO ₂ in the reaction shown in equation (3).

Further, calcium chloride and calcium carbonate are effective for maintaining the desulfurization performance of calcium hydroxide.

The feature of the reaction according to the present invention is that a substance which is originally difficult to react can be converted to a substance which easily reacts and used effectively. Furthermore, the reaction temperature shown in equation (3) is unique in that there is a reaction in a relatively low temperature range of 100 ° C. or lower and a reaction that occurs in a relatively high temperature range of 100 ° C. or higher shown in formula (4). There is a nature.

Conventionally, calcium carbonate has been used as SO ₂ in flue gas.
Because of the low reactivity with, it was primarily 700 to 800 ° C. or more high temperature zone (furnace desulfurization) or reacted with SO ₂ in water (wet process) Then considered. Inventors have found that relatively low temperature removal of SO ₂ also in the gas phase by the addition of calcium carbonate to calcium chloride, the reaction was found to be accelerated by the addition of further calcium sulfite.

Calcium carbonate to which calcium chloride was added showed a remarkable improvement in activity as compared with the carbonate alone, but the initial activity was slightly low. In contrast, the third
It was found that by adding calcium sulfite as a raw material, the initial activity was improved and a high performance flue gas treatment agent was obtained. In addition, when calcium sulfite is not added, if the flue gas treatment agent is left in the air, its desulfurization and denitration activities gradually decrease, but the addition of calcium sulfite suppresses the decrease in activity. be able to.

The ratio of calcium chloride to calcium carbonate added is preferably 100: 1 to 10 by weight. If the addition amount is less than 1%, the effect of the addition is not sufficiently exhibited, and even if it exceeds 10%, the effect of the addition does not increase. The addition ratio of calcium sulfite is preferably 100: 1 to 30 by weight. If the addition amount is less than 1%, the effect of addition is not sufficiently exhibited, and even if it exceeds 30%, the effect of addition does not increase.

The calcium chloride used in the present invention includes calcium chloride alone and a substance containing calcium chloride, such as a snow melting agent, calcium chloride, calcium sulfate, calcium sulfite treated with hydrogen chloride generated during refuse incineration and smoke treatment. And the like.

The calcium-based compounds usable in the present invention include calcium carbonate, calcium hydroxide, calcium sulfite, calcium sulfate, and simple substances containing these compounds, for example, used flue gas treatment agents and natural products such as limestone. can give.

When calcium chloride and a calcium compound are used in combination, the calcium chloride layer and the calcium carbonate layer, for example, may be arranged in series or used in advance.

When calcium chloride and a calcium compound are used as a mixture, the mixing ratio of the calcium compound to calcium chloride varies depending on the concentration of the harm-reducing substance in the treated flue gas. 99% is preferable, and there is no problem even when two or more kinds of substances such as calcium compounds or magnesium are present.

The method for producing the flue gas treating agent of the present invention includes:
Any method such as a method of mixing the raw materials in the form of powder, a method of simultaneously pulverizing and mixing, a method of adding a calcium-based compound in the form of a solid, a slurry, or an aqueous solution to an aqueous calcium chloride solution can be adopted. When water is used for the addition operation, the water content after mixing is 1 per 100 parts by weight of dry matter.
0 to 500 parts by weight is suitable. After mixing, if necessary, drying, solidification, or molding by a known method to granulate.

The drying conditions are 50 to 500 ° C. and several seconds to 10 seconds.
Time is preferred.

The mixture obtained by the above method can be used as a flue gas treatment agent in the form of slurry, powder or granules.

When the slurry is used, it is sprayed into a flue through which flue gas to be treated passes or into a spray dryer, and collected and discharged by a known dust collector such as a bag filter.

When used in powder form, it can be carried out in accordance with a slurry or a method of supplying the powder to a fluidized bed or a spouted bed. When used in the form of powder, the powder can be formed by a known method such as a disk pelletizer and used in a moving bed, fixed bed, fluidized bed, or spouted bed. Exhaust gases that can be applied include coal, oil-fired boiler flue gas, and H
It is also possible to treat flue gas containing an acidic gas such as Cl, specifically, flue gas from a refuse incineration boiler or the like.

The processing temperature of the exhaust gas is from room temperature to 300 ° C., preferably from 60 to 200 ° C.

[0033]

【Example】

Example 1 A performance evaluation test was performed using only commercially available calcium chloride under the test conditions shown in Table 2, and total SO ₂ , N after passing gas for 3 hours was used.
Table 3 shows the amount of Ox absorption.

The measurement results of the specific surface area are also shown in the table. The specific surface area was measured by the BET method after degassing the sample at 300 ° C. for 1 hour.

[0035]

[Table 2] Example 2 A predetermined amount of commercially available calcium chloride was made into an aqueous solution at 95 ° C.,
Commercially available calcium carbonate was added thereto at a ratio shown in Table 2 to adjust the slurry concentration to 16.7%, stirred for 30 minutes, and then dried at 200 ° C. for 2 hours to obtain a flue gas treatment agent. The same performance evaluation test as in Example 1 was performed, and the results are shown in Table 3.

Example 3 Commercially available calcium chloride and calcium carbonate were mixed in powdered form at the ratio shown in Table 3 to obtain a flue gas treating agent. The same performance evaluation test as in Example 1 was performed, and the results are shown in Table 3.

Example 4 Commercially available calcium chloride and calcium carbonate, and a simulated used flue gas treatment agent (calcium chloride: calcium sulfite =
50:50) was mixed in a powder form at a ratio shown in Table 3 to obtain a flue gas treating agent. Perform the same performance evaluation test as in Example 1,
The results are shown in Table 3.

Example 5 Commercially available calcium chloride and calcium hydroxide were used in powder form.
The mixture was mixed in the ratio shown in to obtain a flue gas treatment agent. The same performance evaluation test as in Example 1 was performed, and the results are shown in Table 3.

Example 6 Commercially available calcium chloride, calcium carbonate, and a simulated used flue gas treatment agent (calcium chloride: calcium sulfate = 5)
0:50) in the form of powder as shown in Table 3 to obtain a flue gas treating agent. The same performance evaluation test as in Example 1 was performed, and the results are shown in Table 3.

Example 7 A commercially available calcium chloride was used as a spent flue gas treatment agent (CaCO₃ 
52.0%, CaSO _Four 40.5%, CaSO_Four 5.0
%) In the powder form in the proportion shown in Table 3
A smoke treating agent was obtained. The same performance evaluation test as in Example 1 was performed.
The results are shown in Table 3.

Example 8 Commercially available calcium chloride was added to limestone having a particle size of 375 μm or less,
And a simulated used flue gas treating agent (calcium chloride: calcium sulfite = 50: 50) was mixed in a powdered state at a ratio shown in Table 3 to obtain a flue gas treating agent. The same performance evaluation test as in Example 1 was performed, and the results are shown in Table 3.

Example 9 Commercial calcium chloride layer maintained at 130 ° C and 70 ° C
Commercially available calcium carbonate layers retained in No. 1 were arranged in series, and the same performance evaluation test as in Example 1 was performed. The results are shown in Table 4.

Example 10 130 with a commercially available calcium chloride layer maintained at 130 ° C
A commercial calcium carbonate layer kept at ℃ is arranged in series,
The same performance evaluation test as in Example 1 was performed, and the results are shown in Table 4.

Comparative Example 1 A performance evaluation test was performed on commercially available calcium carbonate, and the results are shown in Table 3.

Comparative Example 2 A performance evaluation test was performed on commercially available calcium sulfite.
The results are shown in Table 3.

Comparative Example 3 A performance evaluation test was conducted on commercially available calcium hydroxide,
The results are shown in Table 3.

Comparative Example 4 A performance evaluation test was conducted on commercially available calcium sulfate, and the results are shown in Table 3.

Comparative Example 5 A performance evaluation test was conducted on commercially available sodium chloride, and the results are shown in Table 3.

[0049]

[Table 3]

[0050]

[Table 4] Example 11 A test was performed on the difference in activity depending on the type of calcium chloride. Table 5 shows the results obtained by conducting the test under the conditions of Table 2 except that the amount of the absorbent was changed to 15 g.

[0051]

[Table 5] In the test of dihydrate at 130 ° C., it was found that the desulfurization activity was low in the initial stage of the reaction, and thereafter the performance gradually improved. It is considered that this is because the water of crystallization was released from the crystals due to the high reaction temperature and became an anhydrous salt. On the contrary, the reaction of the anhydrous salt at 70 ° C. had a high initial activity but was deactivated at a relatively early stage. This is thought to be due to the change from the anhydrous salt to the dihydrate.

Examples 12-1 to 12-6 A predetermined amount of commercially available calcium chloride was used as an aqueous solution at 95 ° C.
Commercially available calcium carbonate and calcium sulfite were added thereto at a ratio shown in Table 6 to give a slurry concentration of 16.7%.
After stirring for 30 minutes, the mixture was dried at 200 ° C. for 2 hours to obtain an exhaust gas treating agent. Using these agents, a performance evaluation test was conducted under the test conditions shown in Table 2 above (however, the reaction temperature was 70 ° C. only), and after 3 hours, the SO ₂ and NO _x absorption amounts were determined and Table 6
It was shown to.

The results of the measurement of the specific surface area are also shown in the table. The specific surface area was measured by the BET method after degassing the sample at 300 ° C. for 1 hour.

Examples 13-1 to 13-3 Commercially available calcium carbonate, calcium chloride and calcium sulfite were mixed in powdery proportions in the proportions shown in Table 3 to obtain smoke control agents. The same performance evaluation test as in Example 12 was performed, and the results are shown in Table 6.

Example 14 Commercially available limestone ground to 200 mesh or less and commercially available calcium chloride and calcium sulfite were mixed in powder form at the ratios shown in Table 6 to obtain a flue gas treating agent. The same performance evaluation test as in Example 12 was performed, and the results are shown in Table 6.

Example 15 Commercially available calcium chloride and calcium sulfite were added to the limestone slurry kept at 95 ° C. in the proportions shown in Table 6, stirred for 30 minutes, and then dried at 200 ° C. for 2 hours to treat smoke. I got an agent. The same performance evaluation test as in the previous example was performed, and the results are shown in Table 6.

Example 16 After leaving the flue gas treating agent obtained in Example 13-2 in the air for 15 days, a similar performance evaluation test was performed.
It was shown to.

Example 17 Predetermined amounts of commercially available calcium carbonate and calcium chloride were mixed as powders, 10% by weight of which was impregnated with a prescribed amount of sulfite water (concentration 6%), and then mixed with the whole. A flue gas treatment agent was obtained. The same performance evaluation test as in the previous example was performed, and the results are shown in Table 6.

Comparative Example 6 A performance evaluation test was conducted on the sample obtained in the same manner as in Example 12 except that calcium sulfite was not added, and the results are shown in Table 6.

Comparative Example 7 In Example 12-3, calcium sulfate was added instead of calcium sulfite, and a performance evaluation test was conducted on a sample obtained under the same conditions, and the results are shown in Table 6.

Comparative Example 8 In Example 12-3, limestone was added in place of calcium sulfite and a sample obtained under the same conditions was subjected to a performance evaluation test. The results are shown in Table 6.

Comparative Example 9 Powdery calcium carbonate and powdery calcium sulfite were mixed and a performance evaluation test was conducted. The results are shown in Table 6.

Comparative Example 10 A powdery calcium carbonate and a powdery calcium sulfate were mixed, and a performance evaluation test was carried out. The results are shown in Table 6.

Comparative Example 11 A performance test was conducted on a commercially available calcium carbonate alone, and the results are shown in Table 6.

Comparative Example 12 The sample obtained in Comparative Example 6 was allowed to stand in the air for 15 days, and then the same performance evaluation test was conducted. The results are shown in Table 6.

Comparative Example 13 In Example 12-4, a commercially available slaked lime was used in place of calcium carbonate, and a performance evaluation test was conducted on a sample obtained by the same operation. The results are shown in Table 6.

[0067]

[Table 6] Examples 18-1 to 18-4, Comparative Example 14 As shown in Comparative Example 3, calcium hydroxide has a high SO content.
_{2 It has a} removing ability, but its desulfurization rate decreases rapidly when the contact time with the gas to be treated becomes long. However, it has been found that the addition of calcium chloride or further calcium carbonate to calcium hydroxide results in a significant sustained performance.

The following table shows the desulfurization rate at a reaction temperature of 70 ° C. after passing gas for 15 hours under the test conditions shown in Table 2.

[0069]

[Table 7]

[0070]

EFFECTS OF THE INVENTION According to the present invention, calcium chloride, which has not been generally used in the past, can be applied to a flue gas treatment agent, and calcium carbonate which has been conventionally considered to be active only at high temperatures or in water. It has become possible to provide a flue gas treatment agent that is active at a much lower temperature by activating the above.

Claims (6)

[Claims] 1. A flue gas treating agent comprising calcium chloride as a substitution reaction substance for a substance to be treated in flue gas. 2. The method according to claim 1, wherein the calcium compound containing at least one compound selected from the group consisting of calcium carbonate, calcium hydroxide, calcium sulfite, and calcium sulfate is added with 99.9 to 1% by weight of calcium chloride. Item 10. A method for producing a flue gas treating agent according to item 1. 3. The weight ratio of calcium carbonate, calcium chloride and calcium sulfite is 100: 1 to 10: 1.
The flue gas treatment agent according to claim 2, which is -30. 4. The method for producing a flue gas treatment agent according to claim 2, wherein the calcium-based compound is added in the form of slurry or powder, and calcium chloride is added in the form of powder, particles or slurry. . 5. The method for producing a flue gas treating agent according to claim 4, wherein the added product is further dried, solidified and molded. 6. A flue gas treatment method, wherein flue gas containing a substance to be treated is first contacted with calcium chloride and then with a calcium compound.