JP2003160823A - Method for recovering all aluminum components from waste halide absorbent, method for regenerating halide absorbent, and method for continuously removing halide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a waste halide absorbent to be recycled, reduce a discarded amount of the absorbent, and save a raw material for the absorbent. <P>SOLUTION: This recovering method comprises dissolving the waste halide absorbent in water, which has absorbed a halide in a high-temperature reducing gas, separating all aluminum contents contained in the waste absorbent, by a wet process of adjusting the hydrogen ion concentration (pH) of the solution into 3 to 9, and recovering them. The method for preparing the halide absorbent again, which contains an alkali aluminate, is characterized by adding alkali metals to the recovered aluminum contents. Furthermore, the continuous halide removal is realized by carrying out regeneration of the halide absorbent, along with halide removal from gasified gas. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering all aluminum components from a used halide absorbent and a method for regenerating the halide absorbent. More specifically, the present invention relates to a method for recovering all aluminum components that enables recycling of a used halide absorbent, and a method for regenerating a halide absorbent using the recovered aluminum components.

[0002]

2. Description of the Related Art In recent years, various methods have been proposed in which a gas obtained by directly gasifying coal or heavy oil is used for power generation. For example, a coal gasification complex that burns a gas obtained by gasifying coal (hereinafter, simply referred to as gasification gas) to drive a gas turbine, and also uses a heat generated in a gasification process or a combustion process to drive a steam turbine. Power generation is a typical example. Further, a power generation method for directly converting gasified gas into electric power with high efficiency by a molten carbonate fuel cell or the like has been actively studied.

By the way, the gasified gas usually contains tens to hundreds of ppm of halides, that is, hydrogen chloride, hydrogen fluoride and the like, and from the viewpoint of pollution prevention,
From the viewpoint of preventing performance deterioration of equipment and the like that uses gasification gas, it is required to remove halide from the gasification gas. In particular, when the gasified gas is used as the fuel of the fuel cell, it is essential to remove the halide contained in the gasified gas to 1 ppm or less in order to maintain the power generation performance of the cell.

In this case, in consideration of energy efficiency, it is desirable to use a dry method system for removing halides. The dry method is a method of solidifying a halogen component by a chemical reaction with an alkaline solid substance to remove it from a gas by utilizing that the halide is an acidic substance. Compared with the wet method that uses a water scrubber, the dry method processes gas at high temperature, so there is no decrease in energy efficiency due to raising and lowering the gas temperature, and gas / gas heat exchangers, wastewater treatment facilities, etc. There is a feature that the equipment is unnecessary and the system becomes simple.

Since the halide removal system by the dry method largely depends on the reaction characteristics of the substance that reacts with the halide, it depends on the composition, temperature and pressure of the target gasification gas and the removal concentration level of the halide. It is essential to develop an absorbent that contains different absorbent substances. Therefore, as a halide absorbent suitable for use in such a dry method, conventionally, an alkali aluminate is used as a halide absorbent, and an absorbent containing sodium aluminate is contained in the high temperature coal gasification gas. It has been proposed to remove hydrogen to 1 ppm or less (Japanese Patent Laid-Open No. 2000-
15091).

[0006]

In the halide removal by the dry method, the absorbing substance contained in the absorbent reacts with the halide in the gas. Since the absorbing material after the reaction does not have a halide removing performance, the used absorbent is sequentially generated in the dry method halide removing system. Therefore, in the absorbent containing an alkali aluminate, a spent absorbent containing an alkali halide and aluminum oxide is generated as the halide is absorbed and removed. For example,
When the absorbent containing sodium aluminate (NaAlO ₂ ) removes hydrogen chloride, 2NaAlO ₂ + 2HCl → 2NaCl + Al ₂ O ₃ + H ₂ O ... Reaction formula (1): Reaction of halide removal reaction proceeds, Sodium chloride (NaCl) and aluminum oxide (Al ₂ O ₃ ) are produced. Since these products are very stable, it is difficult to regenerate the absorbent and utilize it again for halide removal by the conventional method of circulating a regeneration gas containing oxygen like a dry desulfurization agent, It is considered necessary to dispose of used absorbent as it is. Therefore, the disposal of the used halide removing agent may become a problem in the future.

Therefore, it is an object of the present invention to provide a method for recovering an aluminum component which is an absorbent constituent material from a used halide absorbent. Another object of the present invention is to provide a method for resynthesizing a halide absorbent by using the recovered constituent substance / aluminum component as a raw material. That is, it is an object of the present invention to enable the reuse of a used halide absorbent, reduce the amount of absorbent waste, and save the absorbent raw material.

[0008]

In order to achieve the above object, a method for recovering all aluminum components from a used halide absorbent according to the present invention is a method for absorbing a used halide absorbing a halide in a high temperature reducing gas. All the aluminum components contained in the used absorbent are separated and recovered by a wet treatment in which the agent is dissolved in water and the hydrogen ion concentration (pH) of the solution is adjusted from 3 to 9.

When a solution obtained by a wet treatment in which a used halide absorbent is dissolved in water is filtered to recover a solid component, aluminum oxide is recovered but a water-soluble alkali halide is not contained. This is due to the difference in solubility between the alkali halide and aluminum oxide in water, and this method cannot separate and recover all aluminum components from the used absorbent.

The used absorbent contains unreacted alkali aluminate, and the aluminum component corresponding to the amount is ionized and dissolved in water. for that reason,
The above-mentioned wet treatment cannot sufficiently recover the aluminum component contained in the used absorbent. In the present invention, not only the used halide absorbent is wet-processed (dissolved in water), but also the wet-processed solution is adjusted to have a hydrogen ion concentration of 3 to 9 by adding an acidic reagent, for example. The ionized and dissolved aluminum component is converted into a solid form by a chemical reaction and can be recovered by filtration. By this operation, it becomes possible to improve the recovery rate of the aluminum component from the used absorbent.

Further, in the present invention, an alkali metal is added to the aluminum component recovered from the used halide absorbent to prepare a halide absorbent containing alkali aluminate again. By this operation, the aluminum component contained in the halide absorbent can be repeatedly used, and the amount of the aluminum component required when synthesizing the halide absorbent can be reduced.

Further, in the continuous halide removal method of the present invention, the regeneration treatment of the halide absorbent according to claim 2 is carried out in parallel with the removal of the halide from the gasification gas to remove the aluminum component. It is designed to realize continuous halide removal by recycling. In this case, while removing the halides contained in the exhaust gas from the power generation plant that uses high-temperature reducing gas, such as coal gasification gas as fuel, recover all the aluminum components from the used halide absorbent. Then, by using this to prepare a halide absorbent, continuous operation becomes possible. That is, although the halide absorbent filled in the reactor is gradually consumed by the progress of the halide removal reaction, the used halide absorbent is sequentially taken out from the reactor and the aluminum component is recovered by the wet treatment and the halide absorbent is removed. By re-synthesizing and re-charging into the reactor, a system for continuously removing halide is realized.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The structure of the present invention will be described below in detail based on the embodiments shown in the drawings.

Reuse of the halide absorbent according to the present invention is carried out by wet treatment with water. The absorbent after removing the halide contains alkali halide and aluminum oxide, which are reaction products, and
Part of the alkali aluminate that did not react with the halide remains. When the used absorbent is subjected to a wet treatment, water-soluble alkali halide and alkali aluminate among these substances are ionized and dissolved, whereas aluminum oxide is insoluble and precipitates as a solid. For example, with the sodium aluminate absorbent used to remove hydrogen chloride, the following reactions proceed during the wet treatment process. _{2NaCl + Al 2 O 3 → 2Na} + + 2Cl - + Al 2 O 3 ↓ ... Reaction Formula (2): dissolution reaction of the reaction product ^{_{NaAlO 2 → Na + + AlO 2}} - ... Scheme (3): unreacted absorption Dissolution reaction of the agent Substances ionized after the wet treatment, that is, sodium ions, chlorine ions, and aluminate ions are dissolved in water, but aluminum oxide is not dissolved but is precipitated. Therefore, it is possible to separate and collect aluminum oxide from the used absorbent by filtering the solution subjected to the dissolution treatment.

Further, in the present invention, the hydrogen ion concentration (pH) of the aluminum component which does not precipitate due to the dissolution of unreacted alkali aluminate is adjusted to the range of 3 to 9 by adding an acidic reagent or a solution thereof. And collect. Alkali aluminate as described above aluminate ions by wet processing ^- changes to, (AlO ₂₎
It is dissolved in water. Since alkali aluminate is a basic substance, its solution shows alkalinity, but when an acidic reagent is added thereto, aluminum hydroxide is produced and precipitated by the following reaction. _{^{AlO 2 - + H 2 O +}} H + → Al (OH) 3 ↓ ... Reaction Formula (4): the aluminum component was dissolved as aluminate ions by precipitation reaction The reaction of the dissolved aluminum component in the form of aluminum hydroxide In order to change it, it is necessary to adjust the hydrogen ion concentration (pH) of the solution after adding the acidic reagent within the range of 3 to 9.
This is because if the hydrogen ion concentration (pH) is higher than 9, it will remain in the solution as aluminate ions, and if it is lower than 3, the aluminum hydroxide once formed will become aluminum ions and dissolve again. In order to efficiently change the aluminum component into the form of aluminum hydroxide, the hydrogen ion concentration (pH), which is the condition under which aluminum hydroxide is stably present, is preferably 4 to 8, and most preferably the condition of weak acidic to neutral The hydrogen ion concentration (pH) is in the range of 5 to 7. Any acidic reagent can be applied as long as it generates hydrogen ions (H ⁺ ) in the solution, but hydrochloric acid, sulfuric acid, nitric acid and acetic acid are preferable. Since the precipitated aluminum hydroxide can be recovered by filtration, it is possible to improve the recovery rate of the aluminum component by adding an acidic reagent during the wet treatment of the used absorbent.

In the present invention, the aluminum component recovered by the above method is applied as a raw material for newly preparing a halide absorbent. That is, the aluminum component recovered from the used absorbent is mixed with an aqueous solution of an alkali metal salt, and the solution is dried and calcined to synthesize a halide absorbent that reuses the aluminum component.

For example, a halide absorbent re-synthesized from an aluminum component recovered from a used absorbent and sodium carbonate (Na ₂ CO ₃ ) contains sodium aluminate produced by the following reaction. Al ₂ O ₃ + Na ₂ CO ₃ → 2NaAlO ₂ + CO ₂ ... Reaction formula (5): Re-synthesis reaction of halide absorbent Sodium aluminate is a reaction component of halide absorbent and aluminum component was reused. Also for the halide absorbent, it is possible to remove hydrogen chloride in the gasification gas to a low concentration by the halide removal reaction of the reaction formula (1). Therefore, the aluminum component contained in the halide absorbent can be repeatedly used by the method for recovering the aluminum component and the method for resynthesizing the halide absorbent of the present invention, and the amount of aluminum used in synthesizing the halide absorbent can be increased. Can be reduced.

The halide absorbent regenerated by the regeneration treatment of the present invention reacts with the halide in the gas at a temperature of about 200 ° C. or higher and can be removed to a low concentration for a long time. It can be used for removing a halide in a fuel gas in a power plant or the like by circulating a target gas in a reactor filled with the absorbent. The reactor at that time may be of a type in which the solid absorbent and the gas halide sufficiently react. Specifically, fixed beds, fluidized beds, moving beds, etc. can be applied, but in order to efficiently extract the used absorbent and supply the re-synthesized absorbent, it is necessary to replace the absorbent even during operation. It is a system that is more suitable for moving beds.

Regarding the reuse of the used halide absorbent, it is desirable to carry out it in parallel in the same plant as the halide removal. That is, it is desirable to carry out the regeneration treatment of the halide absorbent in parallel with the removal of the halide from the gasification gas. The used absorbent, which is sequentially withdrawn from the reactor during halide removal, is wet-processed in situ to re-synthesize the halide absorbent and supply it again to the reactor to remove the aluminum component in the absorbent. A continuous halide removal system using recycling is realized. In the halide removal system including the absorbent reuse process, the only raw material consumed is the alkali metal salt, and for example, the halide absorbent containing sodium aluminate as the reaction component is only sodium carbonate. Considering that sodium carbonate alone cannot be used to efficiently remove halides to low concentrations, the combination of reusable aluminum components produces high absorbent performance, allowing halides to be efficiently and continuously reduced to low concentrations. Can be removed.

Here, the spent halide absorbent is removed from the reactor and the regenerated halide absorbent (including the necessary amount of fresh halide absorbent, if necessary supplemented) is fed to the reactor. Recycle the halide absorbent that was regenerated while taking out the used halide absorbent from the bottom of the reactor, or take out the entire amount of the used absorbent for each reactor and recycle it. You may make it throw in. In the case of a fixed bed type reactor, it is preferable to take out and recharge all the used halide absorbent for each reactor, and in the case of a fluidized bed or moving bed type reactor, it is used from below the reactor. A method is preferred in which the regenerated halide absorbent is charged from above while taking out the halide absorbent.

The above-mentioned embodiment is an example of the preferred embodiment of the present invention, but the present invention is not limited to this, and various modifications can be made without departing from the gist of the present invention. For example, in the present embodiment, the step of dissolving the used halide absorbent in water and the step of adjusting the hydrogen ion concentration are:
Although the steps are sequentially performed as separate steps, in some cases, it is possible to directly dissolve the used halide absorbent with a hydrochloric acid solution adjusted to a required concentration and omit the step of dissolving in water. That is, the recovery of all aluminum components is 1
It is also possible to complete it in a few dissolution steps. But,
The amount of acid (hydrochloric acid) added at that time depends on the amount of unreacted absorption component (sodium aluminate), so to complete in one dissolution step, it is included in the used halide absorbent. It is necessary to accurately estimate the amount of unreacted components. Therefore, as an actual work, it is easier and more realistic to adjust the pH after dissolution.

[0022]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

(Recovery of Aluminum Component) The aluminum component was recovered from the used halide absorbent containing sodium aluminate by the following method. 1.0 g of halide absorbent was loaded into a fixed bed flow reactor,
React with hydrogen chloride until it breaks through completely, about 9.1 mmol
Absorbed chlorine. The absorbent after the reaction was taken out from the fixed bed reactor, pulverized and then dissolved in 100 ml of distilled water.
The solution became cloudy and some solid components were precipitated, and the hydrogen ion concentration (pH) was 11, indicating alkaline. The solid matter in the solution was separated by suction filtration, washed with a small amount of distilled water, and then dried at 60 ° C for 12 hours to recover 0.48 g of an aluminum component contained in the absorbent in the form of alumina. By this method, about 80% of the aluminum component contained in the halide absorbent before the reaction was recovered.

(Improvement of aluminum component recovery rate) The aluminum component recovery rate from the used halide absorbent was improved by the following method. Halide absorber
1.0 g was loaded into a fixed bed flow reactor and reacted with hydrogen chloride until complete breakthrough, absorbing about 9.1 mmol chlorine. The absorbent after the reaction was taken out from the fixed bed flow reactor, pulverized and then dissolved in 100 ml of distilled water. The solution became cloudy and some solid components were precipitated, and the hydrogen ion concentration (pH) was 11, indicating alkaline. To this solution, 1.5 ml of 2 mol / l hydrochloric acid was added to adjust the hydrogen ion concentration to 5 to 6 so that it was slightly acidic. The solid matter in the solution was separated by suction filtration, washed with a small amount of distilled water, and then dried in air at 60 ° C for 12 hours to recover 0.54 g of an aluminum component contained in the absorbent in the form of alumina. . By this method, the recovery rate of the aluminum component was improved, and about 90% of the aluminum component contained in the halide absorbent before the reaction was recovered.

(Preparation of Resynthesized Halide Absorber) Using the aluminum component recovered from the used halide absorbent, the halide absorbent was again prepared by the following method. A fixed bed flow reactor was charged with 6.2 g of a halide absorber and reacted with hydrogen chloride until complete breakthrough, absorbing about 57 mmol of chlorine. After the reaction, remove the absorbent from the fixed bed reactor and grind it to 200 ml.
Dissolved in distilled water. To this solution, 6 ml of 2 mol / l hydrochloric acid was added, and the hydrogen ion concentration (pH) was adjusted to 5 to 6 to be weakly acidic.
The solid in solution was separated by suction filtration and added to 19 ml of 2 mol / l sodium carbonate solution. The mixture was evaporated to dryness in air at 80 ° C. and then calcined at 700 ° C. for 4.5 hours to obtain 6.7 g of a halide absorbent in which an aluminum component was reused.
X-ray structural analysis of this reused halide absorbent confirmed that sodium aluminate was the main component.

(Evaluation of Halide Removal Performance of Resynthesized Halide Absorber) The halide removal performance of the reused halide absorbent containing sodium aluminate obtained by the above method was evaluated. Reused halide absorber 1.
0 g was loaded in a fixed bed flow reactor, and a simulated coal gasification gas containing 200 ppm of hydrogen chloride was circulated. Hydrogen chloride reacts with the recycled halide absorbent and is removed from the gasification gas. In this evaluation test, hydrogen chloride in the gasification gas was about
Removed to less than 1 ppm over 1020 minutes. That is, it was found that the recycled halide absorbent of the present invention removes hydrogen chloride contained in a high temperature gasified gas to an extremely low concentration.

[0027]

As is apparent from the above description, according to the present invention, all aluminum components can be recovered from the used halide absorbent. Moreover, according to the present invention, it becomes possible to prepare a halide absorbent again using the recovered aluminum component as a raw material. Therefore,
Since it is not necessary to dispose of the used halide absorbent as it is, and it is possible to repeatedly use the aluminum component as a constituent component, it is possible to reduce the amount of waste of the used absorbent and to prepare the raw material for preparing the halide absorbent. Savings are made.

Further, the halide absorbent regenerated according to the present invention contains sodium aluminate as a main component like the new absorbent (see FIG. 1) and is used in a high temperature reducing gas such as coal gasification gas. It has the ability to absorb and remove the halides of (1) to extremely low concentrations (see FIG. 2). Therefore, according to the present invention, the use of the halide absorbent regenerated by reusing the aluminum component recovered from the used halide absorbent can reduce the halide to a sufficiently low concentration by using only the sodium component. . That is, the amount of the halide absorbent used can be reduced. It should be noted from FIG. 1 that sodium aluminate (NaAlO ₂ ) contained in the new absorbent is sodium chloride (NaCl) after use.
It is clear that the conversion to the above and the reuse method of the present invention again gives an absorbent containing sodium aluminate (NaAlO ₂ ). Further, FIG. 2 shows that the recycled halide absorbent absorbs and removes hydrogen chloride in the simulated coal gas to 1 ppm or less.

Furthermore, the wet treatment of the used halide absorbent and the recycling treatment of the reused halide absorbent are carried out in parallel with the removal of the halide from the gasification gas, thereby recycling the aluminum component. A continuous halide removal system is realized. In this case, while removing the halide contained in the high-temperature reducing gas, recover all aluminum components from the used halide absorbent and use this to synthesize the halide absorbent and then re-input. By doing so, continuous operation becomes possible.

[Brief description of drawings]

FIG. 1 is a chart showing the X-ray diffraction analysis results of a new, used and re-synthesized halide absorbent.

FIG. 2 is a graph showing the results of a halide removal performance evaluation test of the reused halide absorbent of the present invention, showing the change over time in the hydrogen chloride concentration in the reactor outlet gas.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yuzo Shirai             2-6-1 Nagasaka, Yokosuka City, Kanagawa Foundation Law             Human Power Central Research Center Yokosuka Research Center F-term (reference) 4D004 AA47 BA05 CA35 CA41 CC03                       DA03 DA10                 4K001 AA02 BA24 CA49 DB23

Claims (3)

[Claims] 1. A used halide absorbent that has absorbed a halide in a high-temperature reducing gas is dissolved in water and used by wet treatment to adjust the hydrogen ion concentration (pH) of the solution from 3 to 9. A method for recovering all aluminum components from a used halide absorbent, which comprises separating and recovering all aluminum components contained in the absorbent. 2. The method according to claim 1, wherein an alkali metal is added to the aluminum component recovered from the used halide absorbent to prepare a halide absorbent containing alkali aluminate again. A method for regenerating a halide absorbent. 3. A continuous halogen characterized in that the aluminum component is recycled by carrying out the regeneration treatment of the halide absorbent according to claim 2 in parallel with the removal of the halide from the gasification gas. Removal method.