JP2003003178A - Cleaning method of gas generated by gasification of waste - Google Patents

Abstract

(57) [Summary] PROBLEM TO BE SOLVED: To clean a gas generated by gasification of waste and to treat a cleaning liquid, in a method of cleaning gas generated by gasification of waste. Provided is a method for cleaning gas generated by gasification of waste, which can increase the content of valuable substances in solids when recovering valuable substances such as zinc into solids by solid-liquid separation of a cleaning liquid. SOLUTION: In the method for cleaning gas generated by gasification of waste by cleaning gas generated by gasification of waste and treating a cleaning liquid, the gas is cooled and washed with an acidic aqueous solution, and then pH = 6.5. To 7.5, an alkaline agent is added to a mixed aqueous solution of the aqueous solution used in the washing and the acidic aqueous solution used in the cooling and washing, and the resulting mixed aqueous solution is subjected to solid-liquid separation. Cleaning method for gas generated in

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to waste treatment for gasifying waste such as community waste (general waste) or industrial waste and recovering the obtained gas as fuel gas. Further, the present invention particularly relates to a method for cleaning a gas produced by gasification of waste, in which the above gas is cleaned and a cleaning liquid is treated, such as zinc (hereinafter also referred to as Zn) in a gas derived from the waste. The present invention relates to a method for cleaning a gas produced by gasification of waste, which can increase the content rate of valuable substances in the solid content when the valuable substances are collected in the solid content by solid-liquid separation of the cleaning liquid.

[0002]

2. Description of the Related Art In recent years, practical use of recovery of fuel gas, slag, and metal by gasification of waste has been rapidly promoted from the viewpoint of preventing the generation of harmful substances such as dioxins and effectively utilizing the waste. There is. The above waste treatment method is
This is a waste treatment method in which waste is gasified, the obtained gas is rapidly cooled and washed, and it is recovered as fuel gas, and the residue is recovered as slag and metal.

On the other hand, in the gasification of waste, the gases generated by the gasification of waste (hereinafter, also referred to as waste gasification gas or simply gasification gas) include H ₂ , CO, and CO.
_In addition to gas components such as ₂ , depending on the type of waste, N
It includes gas components such as H ₃ , H ₂ S and HCl, and evaporated components of iron, aluminum and heavy metals such as zinc and lead.

Therefore, a technique for recovering the waste gasification gas as a fuel gas and the heavy metal in the gasification gas as a valuable substance has been studied. As the above-mentioned technology, by spraying an acidic aqueous solution onto the gas generated by the gasification of waste, quenching and washing, the synthesis of dioxins is prevented, and iron chloride, evaporated zinc, evaporated in the gasified gas. A method is disclosed in which impurities such as lead are transferred to the acidic aqueous solution side, and the gasified gas after rapid cooling and washing is further sprayed with an alkaline aqueous solution to absorb and remove HCl in the gas (Japanese Patent Laid-Open No. 10- 165743 gazette).

According to the above method, the gas is sprayed with an acidic aqueous solution, quenched and washed, and then neutralized by spraying an alkaline aqueous solution having a pH> 8. In the next step, H ₂ S and other residual impurities are removed. Remove. By the rapid cooling / washing with the above acidic aqueous solution, NH ₃ , FeCl ₃ , FeCl ₂ and heavy metals such as Zn and Pb in the gas and fine carbon particles produced by the rapid cooling / washing are dissolved or captured in the acidic aqueous solution.

Further, by spraying an alkaline aqueous solution having a pH> 8, quenching with an acidic aqueous solution such as HCl in the gas
Various components in the gas that could not be absorbed or captured by cleaning are absorbed and removed. Further, according to the above method, a part of each of the above acidic aqueous solution and alkaline aqueous solution is extracted, and iron, lead, zinc and the like are recovered in the solid content by a two-step hydroxide precipitation reaction and solid-liquid separation.

The gas (refined gas) purified by the above-mentioned method is used as a fuel gas, moves to the acidic aqueous solution side and the alkaline aqueous solution side, and iron, aluminum, etc. recovered by solid-liquid separation react at high temperature. After returning to the furnace, lead, zinc, etc. are used as valuable substances. However, the method described above is effective in terms of purification of gasified gas, removal of impurities from cleaning water, and reuse of cleaning water, but in order to concentrate and effectively use heavy metals such as Zn and Pb, Some issues remain, and it is not a sufficient technology from the viewpoint of recovery of valuable substances.

That is, in the case of the above-described method, especially when the valuable substance such as Zn contained in the gasification gas is recovered in the solid content by solid-liquid separation of the cleaning liquid, the Zn content in the solid content is small. In order to effectively use the recovered material as a raw material for smelting non-ferrous metals, it is essential to increase the content of valuable substances in the recovered material.

[0009]

DISCLOSURE OF THE INVENTION The present invention provides a method for cleaning gas produced by gasification of waste and treating a cleaning liquid with a method for cleaning gas produced by gasification of waste, in which heat generated from waste is removed. When valuable substances such as zinc (: Zn) in the decomposition gas are recovered into solids by solid-liquid separation of the cleaning liquid, it is generated by gasification of waste that can increase the content ratio of valuables in the solids. It is an object of the present invention to provide a method for cleaning a gas that does.

[0010]

According to the present invention, there is provided a method for cleaning a gas produced by gasification of waste and treating a cleaning liquid with a gas produced by gasification of waste, wherein the gas is an acidic aqueous solution. After cooling and washing with water, washing with an aqueous solution of pH = 6.5 to 7.5, more preferably pH = 6.5 to 7.25, an alkaline agent is added to the mixed aqueous solution of the aqueous solution used for the washing and the acidic aqueous solution used for the cooling / washing. A method for cleaning gas produced by gasification of waste, characterized in that the mixed aqueous solution obtained by addition is subjected to solid-liquid separation.

In the present invention described above, it is preferable to recover iron hydroxide and / or aluminum hydroxide by the solid-liquid separation. Further, in the above-mentioned present invention, it is preferable to recover the valuable substance by the solid-liquid separation. The valuable substance is preferably zinc hydroxide or lead hydroxide.

Further, in the above-mentioned present invention, the pH of the acidic aqueous solution is preferably less than 5, more preferably 3 or less, and particularly preferably 2-3.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below. FIG. 2 is a flow sheet showing an example of the waste treatment facility according to the present invention. The waste treatment facility in Figure 2
It consists of I. high temperature reaction tower, II. Gas purification equipment, and III. Wash water treatment equipment.

First, I. high temperature reaction tower, II. Gas purification equipment, and III. Wash water treatment equipment according to the present invention will be described below. [I. High-temperature reaction tower:] In a high-temperature reaction tower (hereinafter, also referred to as a reaction tower), oxygen is blown into the lower part of the reaction tower while waste is introduced.

The inside of the high temperature reaction column (: reaction column) is maintained at 1000 ° C. or higher by partial oxidation of waste by oxygen.
The waste introduced into the reaction tower is gasified by partial oxidation or thermal decomposition, and the produced gas (: gasified gas) is discharged from the top of the reaction tower and sent to the gas purification facility.

The gas treated in the gas refining facility (hereinafter also referred to as a refined gas) is used as a fuel gas or the like. In addition, incombustibles such as glass, pottery, and metals in the waste are melted at the bottom of the reaction tower to produce molten slag and molten metal. Molten slag and molten metal are separated by specific gravity separation, the cooled and solidified slag is used as roadbed material, cement raw material, and the cooled and solidified metal is used as non-ferrous smelting raw material, iron manufacturing raw material, etc. To use.

The form of the waste to be put into the high-temperature reaction tower is not particularly limited, but from the viewpoint of the treatment efficiency of the high-temperature reaction tower, the waste that has been previously subjected to carbonization / carbonization treatment as waste. It is also possible to add carbonization and carbonization. [II. Gas purification facility:] Waste gasification gas (: gasification gas) discharged from the top of the reaction tower is sent to the gas purification facility.

The gasification gas sent to the gas purification facility is
First, in a gas quenching / cleaning device (hereinafter, also referred to as a first cleaning device), cooling / cleaning is performed with an acidic aqueous solution. In this process, the high temperature gas is rapidly cooled, synthesis of dioxins is prevented, and ammonia, iron chloride, evaporated zinc, evaporated lead and fine carbon particles in the gas are dissolved or captured in the acidic aqueous solution.

The rapidly cooled and washed gas is further washed in a gas washing device (hereinafter, also referred to as a second washing device) and is not absorbed by the acidic aqueous solution of the first washing device.
Absorbs and removes gas, etc. The gas cleaned again in the gas cleaning device (: second cleaning device) is subjected to treatment such as desulfurization in the gas purification device.

The purified gas released from the gas purification device is
It is effectively used as a fuel gas. [III. Washing water treatment facility:] In the gas quenching / washing device (: first washing device) in the above-mentioned gas purification facility, cooling / washing water (acidic aqueous solution) is circulated / reused, and
The cleaning water is also circulated and reused in the gas cleaning device (: second cleaning device).

In this case, impurity components accumulate in the cooling / washing water of the first washing device and the washing water of the second washing device. Therefore, gas quenching / cleaning device (: first cleaning device)
Cooling and cleaning water and gas cleaning device (: second cleaning device)
A part of each of the washing water in 1 above is appropriately extracted and sent to the washing water treatment facility for treatment.

That is, the cooling / cleaning water of the first cleaning device and the cleaning water of the second cleaning device are fed to the first neutralization tank, and the mixed aqueous solution of the cooling / cleaning water and the cleaning water An alkaline agent such as NaOH is added to treated water) to raise the pH of the mixed aqueous solution (: treated water). As a result, iron ions and aluminum ions in the water to be treated are precipitated as iron hydroxide and aluminum hydroxide.

The water to be treated which has been treated in the first neutralization tank is sent to the first solid-liquid separation device for solid-liquid separation, and iron hydroxide and aluminum hydroxide are separated and collected as solid contents. These are recycled to the high temperature reactor and recovered as metal and slag for reuse. The water to be treated from which iron hydroxide and aluminum hydroxide have been separated by solid-liquid separation is sent to the second neutralization tank,
Add an alkaline agent such as NaOH to further increase the pH of the water to be treated.

As a result, zinc ions and lead ions in the water to be treated are precipitated as zinc hydroxide and lead hydroxide, respectively.
The water to be treated treated in the second neutralization tank is sent to the second solid-liquid separation device for solid-liquid separation, and zinc hydroxide, which is a valuable substance,
Separation and recovery of lead hydroxide as solid content. The water to be treated from which zinc hydroxide and lead hydroxide have been separated by solid-liquid separation is sent to the purification device in the next step. Further, the clean water obtained by removing salts can be used as cooling / washing water for the above-mentioned gas purification facility of the waste treatment facility according to the present invention, makeup water for washing water, and the like.

The waste treatment facility according to the present invention has been described above. The present inventors have conducted an experiment using the waste treatment facility shown in FIG. Good results were obtained in terms of removing impurities from water, but there was a problem in recovering valuable metals such as zinc in the gasification gas. That is, the present inventors treat general waste using the waste treatment equipment of FIG. 2 described above, and in the wash water treatment equipment, the representative waste contained in industrial waste such as general waste and construction waste. A recovery experiment of zinc, which is a heavy metal, was conducted.

In the zinc recovery experiment, iron hydroxide, aluminum hydroxide and carbon particles were separated by the first solid-liquid separator shown in FIG. A hydroxide of a heavy metal such as lead was deposited, and solid-liquid separation was performed by the second solid-liquid separator to recover a hydroxide of a heavy metal such as zinc and lead. Table 1 shows the experimental conditions and the experimental results.

As shown in Table 1, the solid content (residue after solid-liquid separation), which is the recovered material obtained by the second solid-liquid separation apparatus after the second neutralization tank, contains zinc and is recovered. In order to effectively use the product, it is considered effective to use the recovered product as a raw material in zinc smelting and the like. However, the zinc content in the recovered material (solid content) was as low as 18.4% by mass, and the recovered material contained calcium carbonate.

As a result, in order to effectively utilize the solid content (residue after solid-liquid separation), which is the recovered material obtained by the second solid-liquid separation device, as the zinc raw material, the Zn content in the recovered material should be increased. Became mandatory.

[0029]

[Table 1]

Based on the above experimental results, the present inventors can reduce the precipitation amount of calcium carbonate at the time of precipitation of hydroxides of heavy metals such as Zn and Pb, and increase the content of heavy metals in the recovered product. The possible cleaning method of waste gasification gas was examined. In the process of cooling and cleaning the gasified gas with the acidic aqueous solution in the gas quenching / cleaning device (: first cleaning device) shown in Fig. 2, calcium is captured in the acidic aqueous solution (circulating water) along with heavy metals such as zinc and lead. , Accumulated.

On the other hand, the gas quenching / cleaning device (: the first cleaning device) is provided on the downstream side, and absorbs HCl in the gasification gas.
In a gas cleaning device (: second cleaning device) for the purpose of neutralizing acidic components, an alkaline aqueous solution (circulating water) having a pH> 8 is conventionally used as cleaning water. In this case, especially in alkaline aqueous solutions with pH> 8, CO in the gasification gas
₂ is bicarbonate ion ^- dissolved as (HCO _3).

Further, in this case, since CO ₂ is present in the gasified gas at a high concentration, it is considered that the amount of CO ₂ dissolved in the alkaline aqueous solution depends substantially on the pH. That is, the higher the pH of the alkaline aqueous solution, the greater the amount of CO ₂ dissolved in the alkaline aqueous solution. In the waste treatment facility shown in FIG. 2 described above, the inventors of the present invention used a solution for extracting an alkaline aqueous solution (circulation water) from a gas cleaning device (: second cleaning device) that absorbed and dissolved a large amount of CO ₂ described above. The second neutralization tank and the second solid-liquid separation tank of the cleaning water treatment equipment are used to mix the mixed aqueous solution of the acidic quenching / cleaning device (: the first cleaning device) provided upstream with the extraction liquid of the acidic aqueous solution (circulation water). It was thought that separation would be difficult when treated with an alkaline agent such as NaOH because the pH range in which zinc is deposited as hydroxide and the pH range in which calcium is deposited as calcium carbonate almost overlap.

Therefore, cleaning water (circulating water) in the gas cleaning device (: second cleaning device) of the gas purification facility shown in FIG.
The experiment was conducted by changing the pH of the solution from the alkaline range to the neutral range. Table 2 shows the experimental conditions, and FIG. 1 shows the experimental results.

[0034]

[Table 2]

As shown in FIG. 1, a gas scrubber (:
By changing the pH of the washing water in the second washing device) to the neutral range of pH = 6.5 to 7.5 instead of the conventional alkaline range of pH> 8, the precipitation amount of calcium carbonate in the second neutralization tank is reduced. However, it has been found that it is possible to remarkably increase the zinc content of the solid content (residue after solid-liquid separation) which is the recovered product obtained by the second solid-liquid separation device.

That is, by changing the pH of the cleaning water in the gas cleaning device (: second cleaning device) to the neutral range of pH = 6.5 to 7.5 instead of the conventional alkaline range of pH> 8, the solid content is It has become possible to increase the zinc content about twice as much as before. Furthermore, as shown in FIG. 1, the pH of the cleaning water in the gas cleaning device (: second cleaning device) is 6.5.
It was found that the zinc content in the solid content can be increased to 40% by mass or more by setting the neutral region of up to 7.25.

In this experiment, the gas cleaning device (:
By setting the pH of the washing water in the second washing device) to a neutral region, the substance to be trapped by the alkaline aqueous solution cannot be trapped, or the acidic substance in the gas after the gas washing device causes the downstream pipe and the gas purifying device to We also examined and investigated the possibility of corrosion progressing, but the downstream gas purification process,
It did not affect the gas purifier.

As described above, in the present invention, in the method for cleaning the gas generated by the gasification of the waste, the gas generated by the gasification of the waste is treated, and the cleaning liquid is treated.
After cooling and washing the gas with an acidic aqueous solution, pH = 6.5 to 7.
5, more preferably washed with an aqueous solution having a pH of 6.5 to 7.25, an alkaline agent is added to a mixed aqueous solution of the aqueous solution used for the washing and the acidic aqueous solution used for the cooling and washing, and the obtained mixed aqueous solution is solidified. Separate the liquid.

The present invention is preferably used as a method for recovering heavy metals such as zinc derived from wastes in waste gasification gas. More preferable conditions in the present invention are as follows. (1) pH of cooling / washing water (acidic aqueous solution) in the gas quenching / washing apparatus (first washing apparatus): the first in the present invention
It is preferable that the pH of the acidic aqueous solution in the cleaning apparatus is made less than 5 by adding an acid such as hydrochloric acid. It is more preferably 3 or less, and particularly preferably 2-3.

This is because by setting the above pH to less than 5, it becomes possible to effectively dissolve and absorb heavy metals such as Zn in the gas into the acidic aqueous solution. Although the lower limit of the pH is not particularly limited, it is preferable to set the pH to 2 or more from the viewpoint of inhibiting corrosion of the first cleaning device. (2) p of cleaning water in the gas cleaning device (second cleaning device)
H: As described above, in the present invention, the pH of the washing water in the second washing device is limited to 6.5 to 7.5.

When the pH of the wash water is more than 7.5, the zinc content of the solids, which is the recovered product obtained by the second solid-liquid separator, decreases, and when the pH of the wash water is less than 6.5, the HC
The effect of removing acidic components such as l decreases. It is more preferable to adjust the pH of the washing water in the second washing device to 6.5 to 7.25.

(3) pH of treated water in the first neutralization tank: In the present invention, the pH of treated water in the first neutralization tank is
It is preferable to adjust to 5 to 6.5 by adding an alkaline agent such as NaOH. This is because iron ions and aluminum ions in the water to be treated can be selectively precipitated as hydroxides by adjusting the pH to 5 to 6.5.

(4) pH of water to be treated in the second neutralization tank: In the present invention, the pH of water to be treated in the second neutralization tank is
It is preferable to adjust to 7.5 to 10 by adding an alkaline agent such as NaOH. This is because zinc ions and lead ions in the water to be treated can be selectively precipitated as hydroxides by adjusting the pH to 7.5 to 10.

(5) Alkaline agent: The alkaline agent in the present invention is not particularly limited, but NaOH is used as the alkaline agent from the viewpoint of reducing the content of salts due to the alkaline agent in the recovered product. It is preferable. (6) Solid-liquid separation method: The solid-liquid separation method of the present invention in the first solid-liquid separation apparatus, the second solid-liquid separation apparatus, etc. is not particularly limited, and the specific gravity sedimentation separation method, centrifugal separation method, filtration method. A membrane separation method using a microfiltration membrane, an ultrafiltration membrane, a reverse osmosis membrane, or the like can be used.

Although the present invention has been described above, according to the present invention, when the gas produced by gasification of waste is cooled and washed with an acidic aqueous solution and then acidic components such as HCl are washed, By adjusting the pH of the wash water used to 6.5 to 7.5, and more preferably 6.5 to 7.25, zinc in the recovered product (residue after solid-liquid separation) from the wash water and the mixed aqueous solution of cooling and wash water is adjusted. It has become possible to remarkably increase the content of such as.

As a result, zinc, which is a valuable substance in the gasified gas, can be effectively used as a raw material in zinc smelting and the like.

[0047]

EXAMPLES The present invention will be described more specifically below based on examples. In this example, general waste was treated using the waste treatment facility shown in FIG. 2 and a zinc recovery experiment was conducted in the wash water treatment facility. That is, general waste is injected into the lower part of the high temperature reaction tower (: reaction tower) where oxygen is blown and maintained at 1100 ° C or higher, the combustibles in the waste are gasified, and the incombustibles in the waste are combusted. Melted.

The gas produced in the reaction tower was sent to a gas purification facility and recovered as a purified gas. Further, the molten slag at the bottom of the reaction tower, molten metal is separated by specific gravity separation,
After cooling and solidification, it was recovered as slag and metal. In the gas purification facility, the gas fed from the reaction tower was treated by the following method to recover the purified gas.

That is, the gas fed from the reaction tower is
First, a gas quenching / cleaning device (: first cleaning device) was used to quench cooling / cleaning by spraying an acidic aqueous solution (circulating water) adjusted to pH = 2.5 supplied from a cooling / cleaning water circulation device. The rapidly cooled and cleaned gas was further cleaned by spraying cleaning water adjusted to pH = 7.0 by adding NaOH in the gas cleaning device (: second cleaning device).

The gas after the above cleaning was fed to a gas purifier, and purified by desulfurization using a desulfurization liquid containing an Fe chelate complex to obtain a purified gas. On the other hand, the cooling / washing water and the washing water, which were partially extracted from the cooling / washing water circulating device of the first washing device and the washing water circulating device of the second washing device, were fed to the washing water treatment facility.

In the washing water treatment facility, first, NaOH is added to the cooling / washing water and the washing water mixed aqueous solution in the first neutralization tank to adjust the pH of the mixed aqueous solution to 5.5,
Iron hydroxide, aluminum hydroxide, etc. were deposited and the solid content was separated by the first solid-liquid separator. Next, the mixed aqueous solution (: water to be treated) from which the solid content was separated by the first solid-liquid separator was fed to the second neutralization tank, and the pH was adjusted to 9 by addition of NaOH, and zinc hydroxide and hydroxide were added. Lead and the like were deposited, and the solid content was separated by the second solid-liquid separation device, and zinc hydroxide, lead hydroxide and the like as valuable substances were recovered as the solid content.

Next, the water to be treated from which the solid content was separated by the second solid-liquid separation device was fed to the purification device of the next step. In the treatment of the general waste described above, the zinc content of the solid content (collected material, residue after solid-liquid separation) separated by the second solid-liquid separation device was 45% by mass. That is, according to the present invention, in the gas cleaning device (: second cleaning device) disposed on the downstream side of the gas quenching / cleaning device (: first cleaning device), the cleaning water in the alkaline region having pH> 8 is used. In the solid content (residue after solid-liquid separation), which is the recovered material, against the zinc content of solid content after solid-liquid separation in the conventional method for cleaning the gas generated by gasification of waste, which is 18% by mass. It has become possible to significantly increase the zinc content of.

[0053]

According to the present invention, in the method for cleaning the gas produced by the gasification of waste and treating the cleaning liquid with the gas produced by the gasification of the waste, the pyrolysis gas derived from the waste is used. When recovering valuable substances such as zinc in the liquid by solid-liquid separation of the cleaning liquid, it has become possible to remarkably increase the content of valuable substances in the solid content of the recovered product.

As a result, according to the present invention, it has become possible to effectively utilize valuable substances such as zinc in waste as a raw material in zinc smelting.

[Brief description of drawings]

FIG. 1 pH of wash water of waste gasification gas, Zn content of solid content obtained by solid-liquid separation in the wash water treatment step, Ca
It is a graph which shows the relationship with content.

FIG. 2 is a flow sheet showing an example of a waste treatment facility according to the present invention.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C02F 1/62 C02F 1/64 Z 1/64 C10J 3/00 F C10J 3/00 B09B 3/00 ZAB F Terms (reference) 4D004 AA01 AA46 BA02 BA03 BA05 CA12 CA27 CA29 4D020 AA04 AA10 BA12 BA23 BB03 CB25 CD10 DA03 DB08 4D038 AA08 AB59 AB60 AB69 AB74 BB13 4H060 AA01 BB23 CC01 CC04 DD28 FF11 GG08

Claims (4)

[Claims] 1. A method for cleaning a gas produced by gasification of waste and treating a cleaning liquid for treating a gas produced by gasification of waste, wherein the gas is cooled and washed with an acidic aqueous solution, and pH = Characterized in that it is washed with an aqueous solution of 6.5 to 7.5, an alkaline agent is added to a mixed aqueous solution of the aqueous solution used in the washing and the acidic aqueous solution used in the cooling and washing, and the obtained mixed aqueous solution is subjected to solid-liquid separation. For cleaning the gas produced by the gasification of waste. 2. Iron hydroxide and / or iron hydroxide by the solid-liquid separation
Alternatively, the method for cleaning the gas produced by the gasification of waste according to claim 1, wherein aluminum hydroxide is recovered. 3. The method for cleaning gas produced by gasification of waste according to claim 1, wherein the valuable substance is recovered by the solid-liquid separation. 4. The method for cleaning gas produced by gasification of waste according to claim 1, wherein the acidic aqueous solution has a pH of less than 5.