JP5581827B2 - Waste gasification gas processing apparatus and processing method - Google Patents

Description

  The present invention relates to gasification gas when waste such as community waste (general waste) or industrial waste is pyrolyzed and partially oxidized to gasify it, and the resulting gas is used as fuel gas. The present invention relates to a purification apparatus and a purification method for waste gasification gas, and further to a treatment apparatus and a treatment method including treatment of washing water used for purification.

In recent years, the use of gas obtained by gasifying waste as fuel gas has been promoted. In addition to combustible gases such as hydrogen (H ₂ ), carbon monoxide (CO) and hydrocarbons, and gas components such as carbon dioxide (CO ₂ ), waste gasification gas includes hydrogen sulfide (H ₂ S), chloride When it is contained in a fuel gas such as hydrogen (HCl), problems occur, and gas components that must be removed, and evaporation of heavy metals such as iron, zinc, and lead are included.

For this reason, a technique for refining waste gasification gas as a fuel gas so as not to cause trouble has been studied (see Patent Document 1). In Patent Document 1, by spraying an acidic aqueous solution onto a waste gasification gas, quenching and washing, the synthesis of dioxins is prevented, and heavy metals such as iron chloride, zinc, and lead in the gasification gas are added. Dissolve or trap in an acidic aqueous solution (first cleaning step), and spray a neutral aqueous solution with a pH of 6.5 to 7.5 on the gasified gas after quenching and cleaning, to add hydrogen chloride (HCl) in the gasified gas. A method of absorbing and removing (second cleaning step) and further removing hydrogen sulfide (H ₂ S) with a desulfurizer is disclosed.

JP2003-3178

  However, the method described in Patent Document 1 is not a sufficient technique when the gasification gas contains a cyanide compound such as hydrogen cyanide and causes the following problems.

  When waste containing sulfur is gasified, hydrogen sulfide is generated. Therefore, the hydrogen sulfide is often removed by performing a desulfurization treatment in which the hydrogen sulfide is absorbed by a desulfurization solution containing an iron chelate complex. Further, when waste containing nitrogen is gasified, a small amount of cyanide compound such as hydrogen cyanide is generated and contained in the gasification gas. If nitrogen is contained in the waste, for example, in the form of heteronitrogen compounds such as amino bonds and urethane bonds, cyan compounds are likely to be generated.

  When waste containing sulfur and nitrogen is gasified, the ability of the desulfurization solution to absorb hydrogen sulfide is reduced by the amount of cyanide absorbed in the desulfurization solution in the desulfurization process, and the desulfurization rate is reduced accordingly. Problem arises.

  The present invention has been made in view of the circumstances as described above, and is a waste gasification gas purifier that does not cause a reduction in the desulfurization rate with respect to a waste gasification gas containing a cyanide compound and hydrogen sulfide. It is an object of the present invention to provide a treatment apparatus and a treatment method including a purification method, and further treatment of washing water used for purification.

<First invention>
A purification apparatus for waste gasification gas according to the first invention is a gas purification apparatus obtained by gasifying waste by thermal decomposition and partial oxidation, and cooling the gas by bringing acidic cleaning water into contact with the gas. Cooling and acidic water cleaning apparatus for cleaning, and alkaline water cleaning apparatus for cleaning the gas by bringing alkaline cleaning water having a pH of 7.5 or more and 8.2 or less into contact with the gas cooled and cleaned by the cooling / acidic water cleaning apparatus And a desulfurization device for removing hydrogen sulfide contained in the gas cleaned by the alkaline water cleaning device.

  If the pH of the alkaline washing water is lower than 7.5, the absorption of hydrogen cyanide from the gasification gas is reduced, so that all the hydrogen cyanide cannot be removed by the alkaline water washing apparatus, and the gas is used in the desulfurization process in the desulfurization apparatus. Hydrogen cyanide may remain in the forming gas. When the remaining hydrogen cyanide is absorbed in the desulfurization solution in the desulfurization step, for example, when desulfurization is performed by an iron chelate complex, iron and cyan of the iron chelate complex form a strong complex, Is reduced. Therefore, the amount of hydrogen sulfide absorbed is reduced accordingly, and the desulfurization rate is reduced. Or since thiocyan is produced | generated excessively, a desulfurization rate will fall.

  FIG. 1 is a graph showing the relationship between the pH of alkaline cleaning water and the desulfurization rate in the desulfurization treatment with an iron chelate complex. Here, the desulfurization rate is calculated by dividing the hydrogen sulfide concentration in the gas after the desulfurization treatment by the hydrogen sulfide concentration in the gas before the desulfurization treatment and multiplying by 100%. When the purified gas after desulfurization is used as the fuel gas, the desulfurization rate needs to be at least 90% or more, as shown in FIG. 1, when the pH of the alkaline washing water is 7.5 or more. The desulfurization rate is 90% or more.

  If the pH of the alkaline cleaning water is higher than 8.2, the alkaline cleaning water will absorb a large amount of hydrogen sulfide from the gasification gas in the alkaline water cleaning device. As a result, when hydrogen sulfide is oxidatively decomposed in the alkaline cleaning water used for cleaning the gasification gas, that is, in the cleaning water treatment of alkaline cleaning water containing hydrogen sulfide, the required amount of oxidant to be added for oxidative decomposition is reduced. It becomes excessive.

  FIG. 2 is a graph showing the relationship between the pH of alkaline cleaning water and the necessary ratio of oxidant. Here, the relative required ratio of the oxidant is a relative ratio in which the required amount of the oxidant when the pH of the alkaline cleaning water is 7 is 1. The oxidizer requirement ratio is not practical unless it is 3 or less. As shown in FIG. 2, the pH of the alkaline aqueous solution is 8.2 or less, and the oxidizer requirement ratio is 3 or less.

  In the present invention, by setting the pH of the alkaline cleaning water to 7.5 or more and 8.2 or less, a sufficiently high desulfurization rate is realized, and the cleaning water treatment of the alkaline cleaning water used for cleaning the gasification gas is performed. It is possible to prevent the amount of the oxidizing agent added in the process from becoming excessive.

It is preferable that the cooling / acidic water cleaning device removes at least iron chloride contained in the gas, and the alkaline water cleaning device removes at least hydrogen cyanide contained in the gas. If the iron chloride contained in the gas is not removed by the cooling / acidic water washing apparatus and is supplied to the alkaline water washing apparatus as it is, the iron chloride is removed together with hydrogen cyanide by the alkaline washing water. As a result, cyan ions and iron ions form hardly soluble cyano complex compounds such as iron cyano complex compounds (Fe ₄ [Fe (CN) ₆ ] ₃ ) in alkaline cleaning water used for gas cleaning. As a result, there are problems due to the presence of many solids in the alkaline aqueous solution. Therefore, by removing iron chloride from the gas with a cooling / acidic water washing device before the gas is supplied to the alkaline water washing device, the cyano compound is not formed in the alkaline washing water. The gas can be smoothly cleaned with the alkaline cleaning water.

<Second invention>
The waste gasification gas treatment apparatus according to the second invention is not limited to the above-described waste gasification gas purification apparatus, and further includes alkaline washing water used in the cooling and acidic water washing equipment and alkaline washing water used in the alkaline water washing equipment. A washing water treatment device for treating the washing water, the washing water treatment device mixing the acidic washing water and the alkaline washing water and reacting them, and oxidizing the mixed washing water extracted from the first reaction vessel And a second reaction vessel that can separate and remove cyanide by adding an agent.

<Third invention>
A waste gasification gas treatment apparatus according to a third aspect of the invention includes a washing water treatment apparatus for treating the alkaline washing water used in the alkaline water washing apparatus, in addition to the above-described waste gasification gas purification apparatus, and washing The water treatment apparatus includes an oxidative decomposition apparatus that oxidizes and decomposes cyanide by adding an oxidant to alkaline cleaning water.

<Fourth Invention>
A method for purifying waste gasification gas according to the fourth invention is a gas purification method in which waste is thermally decomposed and partially oxidized to gasify, and the gas is cooled by bringing acidic cleaning water into contact with the gas. Cooling and acidic water cleaning step for cleaning, and alkaline water cleaning step for cleaning the gas by bringing alkaline cleaning water having a pH of 7.5 or higher and 8.2 or lower into contact with the gas cooled and cleaned by the cooling and acidic water cleaning step And a desulfurization step for removing hydrogen sulfide contained in the gas cleaned by the alkaline water cleaning step.

  In the cooling / acidic water washing step, at least iron chloride contained in the gas is preferably removed, and in the alkaline water washing step, at least hydrogen cyanide contained in the gas is preferably removed.

<Fifth invention>
A waste gasification gas treatment method according to a fifth aspect of the present invention is a gas treatment method in which waste is pyrolyzed and partially oxidized to gasify, and the gas is cooled by bringing acidic cleaning water into contact with the gas. Cooling and acidic water cleaning step for cleaning, and alkaline water cleaning step for cleaning the gas by bringing alkaline cleaning water having a pH of 7.5 or higher and 8.2 or lower into contact with the gas cooled and cleaned by the cooling and acidic water cleaning step And a desulfurization process for removing hydrogen sulfide contained in the gas cleaned by the alkaline water cleaning process, a cleaning process for treating the acidic cleaning water used in the cooling / acidic water cleaning process and the alkaline cleaning water used in the alkaline water cleaning process A water treatment step, wherein the wash water treatment step comprises mixing the acid wash water and the alkaline wash water and reacting them, and after the first reaction step, an oxidant is added to the mixed wash water to produce cyan. It is characterized in that it comprises a second reaction step to be separated off.

<Sixth Invention>
A waste gasification gas treatment method according to a sixth aspect of the invention is a gas treatment method in which waste is thermally decomposed and partially oxidized and gasified, and the gas is cooled by bringing acidic cleaning water into contact with the gas. Cooling and acidic water cleaning step for cleaning, and alkaline water cleaning step for cleaning the gas by bringing alkaline cleaning water having a pH of 7.5 or higher and 8.2 or lower into contact with the gas cooled and cleaned by the cooling and acidic water cleaning step And a desulfurization step for removing hydrogen sulfide contained in the gas washed by the alkaline water washing step, and a washing water treatment step for treating the alkaline washing water used in the alkaline water washing step. It is characterized by comprising an oxidative decomposition step of oxidatively decomposing cyanide by adding an oxidizing agent to alkaline washing water.

  According to the present invention, a purified gas can be obtained without causing a reduction in the desulfurization rate with respect to a waste gasification gas containing a cyanide compound and hydrogen sulfide.

It is a graph which shows the relationship between the pH of alkaline aqueous solution, and the desulfurization rate in the desulfurization process by an iron chelate complex. It is a graph which shows the relationship between pH of alkaline aqueous solution, and oxidizing agent required ratio. It is a block diagram which shows the structure of the processing apparatus of the waste gasification gas which concerns on 1st embodiment of this invention. It is a block diagram which shows the structure of the processing apparatus of the waste gasification gas which concerns on 2nd embodiment of this invention.

<First embodiment>
Hereinafter, a first embodiment of a waste gasification gas treatment apparatus according to the present invention will be described with reference to the accompanying drawings.

FIG. 3 is a block diagram showing the configuration of the waste gasification gas treatment apparatus according to this embodiment. The waste gasification gas processing apparatus according to the present embodiment is provided at a subsequent stage of the gasification apparatus 10 that thermally decomposes and partially oxidizes waste supplied from the outside, and gasifies the waste. The gas purification device 20 that generates the purified gas by cleaning and desulfurizing the gasified gas (crude gas) generated in step 1 and the cleaning water used for the cleaning in the gas purification device 20 are processed to generate clean water. And a washing water treatment device 30. The crude gas includes hydrogen (H ₂ ), carbon monoxide (CO), hydrocarbon combustible gas, hydrogen cyanide (HCN), hydrogen sulfide (H ₂ S), hydrogen chloride (HCl), iron chloride, evaporated zinc, Lead, calcium (Ca) and the like are included.

  The gas purification device 20 is brought into contact with the gasification gas from the gasification device 10 by spraying an acidic aqueous solution as acidic cleaning water, etc., to cool and wash the gasification gas. A cooling / acidic water circulation device 22 for supplying acidic cleaning water to the cooling / acidic water cleaning device 21, and spraying an alkaline aqueous solution as alkaline cleaning water onto the gasification gas from the cooling / acidic water cleaning device 21. An alkaline water cleaning device 23 for cleaning the gasified gas, an alkaline water circulation device 24 for supplying alkaline cleaning water to the alkaline water cleaning device 23, and a desulfurization solution for the gas from the alkaline water cleaning device 23 A desulfurization device 25 for bringing the gas into contact with each other by spraying, etc., and a desulfurization liquid regeneration circulation device 26 for supplying a desulfurization liquid to the desulfurization device 25 It has.

  The cooling / acidic water cleaning device 21 is in contact with the gasified gas from the gasifier 10 by spraying acidic cleaning water, etc., and performs cooling / acidic water cleaning to cool and wash the gasified gas, Heavy metals such as iron chloride, zinc, and lead in the gasification gas are dissolved or captured in the acidic cleaning water and removed from the gasification gas. The acidic wash water has a pH of less than 7, more preferably less than 5. Thus, by setting the pH of the acidic wash water to less than 7 and more preferably less than 5, it becomes possible to effectively dissolve heavy metals such as zinc in the gas in the acid wash water. The lower limit of the pH of the acidic cleaning water is not particularly limited, but it is preferable to set the pH to 2 or more from the viewpoint of inhibiting corrosion of the cooling / acidic water cleaning apparatus 21. The cooling / acidic water cleaning device 21 may be configured as either an integral type or a separation type.

  The cooling / acidic water circulation device 22 supplies the acidic cleaning water to the cooling / acidic water cleaning device 21 and collects the acidic cleaning water used for gas cleaning in the cooling / acidic water cleaning device 21. The acidic cleaning water is circulated by supplying it to the cooling / acidic water cleaning device 21. The acidic cleaning water supplied to the cooling / acidic water cleaning device 21 is adjusted to have a pH of less than 7, preferably less than 5, by adding hydrochloric acid (HCl). Moreover, the components removed from the gasification gas are accumulated in the acidic cleaning water used for the gas cleaning in the cooling / acidic water cleaning apparatus 21. In the present embodiment, a part of the acidic cleaning water is extracted and sent to the cleaning water treatment device 30, and the cleaning water treatment is performed as described later.

  The alkaline water cleaning device 23 performs alkaline water cleaning to clean the gasified gas by bringing the gasified gas cleaned by the cooling / acidic water cleaning device 21 into contact with the gasified gas by spraying the alkaline cleaning water. Hydrogen cyanide (HCN) and hydrogen chloride (HCl) in the gasification gas are dissolved in alkaline washing water and removed from the gasification gas. The pH of the alkaline washing water is preferably 7.5 or more and 8.2 or less.

The alkaline water circulation device 24 supplies alkaline cleaning water to the alkaline water cleaning device 23, collects alkaline cleaning water used for gas cleaning in the alkaline water cleaning device 23, and again returns to the alkaline water cleaning device 23. The alkaline washing water is circulated by supplying to the tank. The alkaline washing water supplied to the alkaline water washing device 23 is adjusted to have a pH of 7.5 or more and 8.2 or less by adding sodium hydroxide (NaOH). Further, in the alkaline cleaning water used for the gas cleaning in the alkaline water cleaning device 23, hydrogen cyanide and hydrogen chloride removed from the gasification gas are accumulated. Hydrogen cyanide dissolved in alkaline washing water is contained as cyan ions (CN ⁻ ). In the present embodiment, as in the cooling / acidic water circulation device 22 described above, a part of the alkaline washing water is extracted and sent to the washing water treatment device 30, and the washing water treatment is performed as described later.

The desulfurization apparatus 25 makes the desulfurization liquid containing an iron chelating agent (iron chelate complex) contact the gasification gas cleaned by the alkaline water cleaning apparatus 23, and removes hydrogen sulfide (H ₂ S) from the gasification gas. The gasified gas from which hydrogen sulfide has been removed is sent out from the desulfurization apparatus 25 as a purified gas. Since a desulfurization method using an iron chelating agent as a desulfurization liquid is known, a description thereof is omitted here.

  The desulfurization liquid regeneration circulation device 26 is supplied with the iron chelating agent, supplies the desulfurization liquid containing the iron chelating agent to the desulfurization apparatus 25, and collects the desulfurization liquid used for the desulfurization in the desulfurization apparatus 25. To do. The desulfurization liquid regeneration circulation device 26 is supplied with air from the outside, reacts hydrogen sulfide contained in the recovered desulfurization liquid with air to generate sulfur, and discharges the sulfur to the outside. Then, the desulfurization liquid is circulated by supplying the desulfurization liquid from which sulfur has been removed to the desulfurization apparatus 25 again.

  In this embodiment, desulfurization is performed using an iron chelating agent. However, the desulfurization method is not limited to this, and for example, a desulfurization method using sodium naphthoquinonesulfonate, a desulfurization method using picric acid, or the like can be applied. . In the present embodiment, hydrogen cyanide is removed from the gasification gas by the alkaline water cleaning device 23 and the amount of iron chelate complex in the desulfurization liquid is not reduced. Therefore, desulfurization using an iron chelate complex is the most desulfurization. It is easy to show an effect. Examples of desulfurization using an iron chelate complex include a Sulferox method and a Lo-Cat method, but are not limited thereto.

  In this embodiment, since the lower limit of the pH of the alkaline cleaning water is set to 7.5 and hydrogen cyanide contained in the gasification gas is removed, hydrogen cyanide is not absorbed in the desulfurization liquid in the desulfurization step by the desulfurization apparatus 25. The iron chelate complex iron and cyan do not form a strong complex to reduce the amount of the iron chelate complex. Therefore, in the desulfurization step, the amount of hydrogen sulfide absorbed does not decrease and the desulfurization rate does not decrease. Moreover, since thiocyan is not produced excessively, the desulfurization rate does not decrease. In addition, since the upper limit of the pH of the alkaline cleaning water is set to 8.2, a large amount of hydrogen sulfide contained in the gasification gas is not absorbed by the alkaline cleaning water. The required amount of the oxidizing agent is not excessive in the washing water treatment with alkaline washing water.

  In the present embodiment, the pH of the alkaline cleaning water is 7.5 or more and 8.2 or less. However, when the pH of the alkaline cleaning water is 7.6 or more and pH 8.0 or less, the desulfurization treatment in the desulfurization apparatus 25 is performed. It is more preferable because the subsequent desulfurization rate can be further increased and the required amount of oxidant when treating the alkaline washing water after washing with the washing water treatment apparatus 30 can be further reduced.

  Next, the washing water treatment apparatus 30 for treating the acidic washing water and the alkaline washing water used for washing will be described. Components removed from the gasification gas are accumulated in the acidic cleaning water and the alkaline cleaning water used for cleaning the gasification gas in the gas purification device 20, and the cleaning water treatment device 30 includes the acidic cleaning water and The component is removed from the alkaline washing water to produce clean water.

  The washing water treatment device 30 includes a first solid-liquid separation device 31 that removes solids from the alkaline washing water partially extracted from the alkaline water circulation device 24, an alkaline washing water from which the solids have been removed, and a cooling / acidic water circulation device. And a first reaction tank 32 that mixes and reacts with acidic wash water partially extracted from the tank 22. The washing water treatment apparatus 30 receives the mixed washing water after the reaction from the first reaction tank 32, and precipitates a hardly soluble complex compound from cyan and iron contained in the mixed washing water to which an oxidizing agent is added. And a second solid-liquid separator 34 that separates and removes the deposited components, and further removes the components after depositing the predetermined components as will be described later. There are two sets of tanks and solid-liquid separators in series, ie, a third reaction tank 35 and a third solid-liquid separator 36, and a fourth reaction tank 37 and a fourth solid-liquid separator 38 in series. And a filtration device 39 for filtering the separated water from the fourth solid-liquid separation device 38, and an ion exchange device 40 for producing clean water by subjecting the filtered filtrate to ion exchange treatment.

  In the alkaline washing water circulated by the alkaline water circulation device 24, solid substances such as sulfides of low boiling point metals contained in the gasification gas are present together with cyan ions. The first solid-liquid separation device 31 receives a part of the alkaline washing water extracted from the alkaline water circulation device 24, and performs solid-liquid separation to remove the solid matter. The form of the first solid-liquid separation device 31 is not particularly limited, and a specific gravity sedimentation separation device, a centrifugal separation device, a filtration device, a microfiltration membrane device, a membrane separation device using an ultrafiltration membrane device, or the like is used. be able to. The same applies to the second solid-liquid separator 34, the third solid-liquid separator 36, and the fourth solid-liquid separator 38.

The alkaline washing water from which the solid matter has been removed by the first solid-liquid separation device 31 and the acidic washing water partially extracted from the cooling / acidic water circulation device 22 are supplied to the first reaction tank 32 and mixed. Hereinafter, the mixed alkaline washing water and acidic washing water may be simply referred to as “mixed washing water”. The gasification gas generated in the gasifier 10 contains iron, and the gasification in the gasifier 10 is performed in a reducing atmosphere. The iron content dissolved in water, in other words, the iron content contained in the acidic wash water supplied to the first reaction tank 32 is mainly divalent ferrous ions (Fe ²⁺ ). Cyan ions (CN ⁻ ) contained in the alkaline washing water from which the solid matter has been removed in the first reaction tank 32 react with ferrous ions (Fe ²⁺ ) contained in the acidic washing water as shown in (1) below. A ferrous cyano complex ion ([Fe (CN ⁻ ) ₆ ] ⁴⁻ ) is generated. In order to convert all cyan ions (CN ⁻ ) to iron cyano complex ions, ferrous ions (Fe ²⁺ ) that react with cyan ions (CN ⁻ ) must be sufficiently present. If the amount of iron ions (Fe ²⁺ ) is small, iron chloride (FeCl ₂ ) may be added. In order to cause the reaction (1) to occur smoothly in the first reaction tank 32, it is preferable that the pH of the mixed cleaning water of alkaline cleaning water and acidic cleaning water is 6.5 or less.

6CN ⁻ + Fe ²⁺ → [Fe (CN ⁻ ) ₆ ] ⁴⁻ (1)
The mixed washing water having undergone the reaction (1) in the first reaction tank 32 is supplied to the second reaction tank 33 and an oxidizing agent such as hydrogen peroxide (H ₂ O ₂ ) is added. In the second reaction tank 33, the divalent ferrous ions (Fe ²⁺ ) contained in the acidic wash water and contained in the mixed wash water are oxidized by the oxidizing agent to produce trivalent ferric ions (Fe ³⁺ ). To do. Further, the iron cyano complex ion and ferric ion (Fe ³⁺ ) contained in the mixed washing water react as shown in the following (2), and the iron cyano complex compound (Fe ₄ [Fe (CN ⁻ ) ₆ ] ₃ ) Is generated. This iron cyano complex compound is hexacyano iron (III) iron (II) (bitumen) and is a poorly soluble complex compound, which precipitates and precipitates. As the oxidizing agent, not only hydrogen peroxide but also oxidizing agents such as hypochlorous acid and ozone can be used.

3 [Fe ^(CN _{-) 6]} ^4- + ^{4Fe 3+} → Fe ₄ [Fe ^(CN _{-) 6] 3} (2)
Furthermore, in the second reaction tank 33, the pH is adjusted to 5.0 to 6.5 by adding sodium hydroxide (NaOH) to the mixed washing water in which the iron cyano complex compound is generated, and the remaining ferric iron is left. Ions (Fe ³⁺ ) are reacted with sodium hydroxide to precipitate iron hydroxide (Fe (OH) ₃ ). The mixed washing water in which the iron cyano complex compound and iron hydroxide are precipitated in the second reaction tank 33 is supplied to the second solid-liquid separator 34, and the iron cyano complex compound and iron hydroxide are separated and removed as a solid content.

  In the present embodiment, by removing the solid matter before supplying the alkaline washing water to the first reaction tank 32, the oxidizing agent is consumed in the oxidation of the solid substance in the second reaction tank 33. As a result, the ability to oxidize ferrous ions to ferric ions can be prevented from decreasing. As a result, it is possible to prevent the use amount of the oxidizing agent from becoming excessive.

  In the present embodiment, since the upper limit of the pH of the alkaline cleaning water used in the alkaline water cleaning device 23 is 8.2, the alkaline cleaning water absorbs a large amount of hydrogen sulfide from the gasification gas in the alkaline water cleaning device 23. There is nothing to do. Therefore, in the second reaction tank 33, the amount of oxidant added to oxidatively decompose hydrogen sulfide can be suppressed, and the amount of oxidant used can be prevented from becoming excessive.

The mixed washing water from which the solid material mainly composed of the iron cyano complex compound and iron hydroxide is separated by the second solid-liquid separator 34 is supplied to the third reaction tank 35. In the third reaction tank 35, sodium hydroxide is added to adjust the pH of the mixed washing water to 7.5 to 10, and zinc ions and lead ions in the mixed washing water are converted into hydroxides, that is, zinc hydroxide (Zn (OH ₂ ) and lead hydroxide (Pb (OH) ₂ ). Then, these hydroxides are separated and removed as a solid content by the third solid-liquid separator 36.

The mixed washing water from which the solid matter has been separated by the third solid-liquid separation device 36 is supplied to the fourth reaction tank 37. In the fourth reaction tank 37, sodium hydroxide is added to further increase the pH of the washing water, and Ca derived from the waste and contained in the mixed washing water is precipitated as calcium carbonate (CaCo ₃ ). Salts in the wash water are precipitated. Then, calcium carbonate or the like is separated and removed as a solid content by the fourth solid-liquid separator 38.

  The mixed washing water extracted from the fourth solid-liquid separation device 38 is subjected to filtration of the solid matter remaining by the filtration device 39, and then the ions to be removed by the ion exchange resin are further removed by the ion exchange device 40. Thereby, the washing water treatment is completed and clean water is generated.

  In this embodiment, cyan in the wash water is separated and removed by precipitating an iron cyano complex compound, so that the use of an oxidizing agent is used compared to the wash water treatment apparatus in another embodiment shown in FIG. 4 described later. The amount can be reduced.

<Second embodiment>
A second embodiment, which is another embodiment of the waste gasification gas processing apparatus according to the present invention, will be described with reference to FIG.

  FIG. 4 is a block diagram showing the configuration of the waste gasification gas processing apparatus according to the present embodiment. The configuration of the waste gasification gas processing apparatus of the first embodiment shown in FIG. The configuration of the apparatus is different, and the other configuration is the same. Specifically, the washing water treatment apparatus in the present embodiment is different from the first embodiment in that it does not have the first reaction tank and has an oxidative decomposition apparatus described later.

  The washing water treatment device 30 includes a first solid-liquid separation device 31 that removes solids from the alkaline washing water partially extracted from the alkaline water circulation device 24, and oxidizes cyan contained in the alkaline washing water from which the solids have been removed. And an oxidative decomposition apparatus 41 for decomposition. The washing water treatment device 30 receives the acidic washing water partially extracted from the cooling / acidic water circulation device 22 and the alkaline washing water from the oxidative decomposition device 41, and deposits predetermined components as described later. Three sets of reaction tanks and solid-liquid separators for removing components, that is, second reaction tank 33 and second solid-liquid separator 34, third reaction tank 35 and third solid-liquid separator 36, and fourth reaction tank 37 and a fourth solid-liquid separator 38 in series, a filtration device 39 for filtering the wash water from the fourth solid-liquid separator 38, and an ion exchange treatment of the filtered wash water And an ion exchange device 40 that generates clean water.

In the alkaline washing water circulated by the alkaline water circulation device 24, solid substances such as sulfides of low boiling point metals contained in the gasification gas are present together with cyan ions. The first solid-liquid separation device 31 receives a part of the alkaline washing water extracted from the alkaline water circulation device 24, and performs solid-liquid separation to remove the solid matter. The oxidative decomposition apparatus 41 oxidizes and decomposes cyanide by adding an oxidizing agent such as hydrogen peroxide (H ₂ O ₂ ) to the alkaline washing water from which the solid matter received from the first solid-liquid separation apparatus 31 has been removed. As the oxidizing agent used for the oxidative decomposition of the alkaline cleaning water, not only hydrogen peroxide but also oxidizing agents such as hypochlorous acid and ozone can be used.

  The form of the alkaline washing water solid-liquid separator 31 is not particularly limited, and a membrane separator using a specific gravity sedimentation separator, a centrifugal separator, a filtration device, a microfiltration membrane device, an ultrafiltration membrane device, etc. Can be used. The same applies to the second solid-liquid separator 34, the third solid-liquid separator 36, and the fourth solid-liquid separator 38.

  In this embodiment, since the upper limit of the pH of the alkaline cleaning water used in the alkaline water cleaning device 23 is 8.2, the alkaline cleaning water absorbs a large amount of hydrogen sulfide from the gasification gas in the alkaline water cleaning device 23. There is no. Accordingly, in the oxidative decomposition apparatus 41, the amount of the oxidant added to oxidatively decompose hydrogen sulfide can be suppressed, and the use amount of the oxidant can be prevented from becoming excessive.

In this embodiment, since iron chloride is removed from the gasification gas by the cooling / acidic water cleaning device 21 of the gas purification device, the alkaline cleaning water does not contain iron ions in the alkaline water cleaning device 23. Cyan ions in alkaline washing water do not form iron ions and hardly decomposable cyano complex compounds such as iron cyano complex compounds (Fe ₄ [Fe (CN) ₆ ] ₃ ). Therefore, cyan oxidative decomposition in the oxidative decomposition apparatus 41 can be performed smoothly.

  Further, in the present embodiment, by removing the solid matter before supplying the alkaline cleaning water to the oxidative decomposition apparatus 41, the oxidant is consumed in the oxidation of the solid substance in the oxidative decomposition apparatus 41. As a result, the oxidative decomposition ability of hydrogen cyanide can be prevented from being lowered. As a result, it is possible to prevent the use amount of the oxidizing agent from becoming excessive.

  The acidic washing water from the cooling / acidic water circulation device 22 and the alkaline washing water subjected to the oxidative decomposition treatment from the oxidative decomposition device 41 are supplied to the second reaction tank 33 and mixed. Hereinafter, the mixed acidic wash water and alkaline clean water are simply referred to as “mixed wash water”. The gasification gas generated in the gasifier 10 contains iron, and the gasification in the gasifier 10 is performed in a reducing atmosphere. The iron content contained in the acid wash water used, in other words, the acid wash water supplied to the first reaction tank 33 is mainly divalent ferrous ions. The ferrous ions are not easy to be removed by solid-liquid separation by depositing hydroxide by washing water treatment.

In the second reaction tank 33, an oxidizing agent such as hydrogen peroxide is added to the mixed cleaning water, and after ferrous ions are oxidized to trivalent ferric ions, sodium hydroxide (NaOH) is added, The pH of the mixed washing water is adjusted to 5.0 to 6.5, and ferric ions are precipitated as iron (III) hydroxide. In the first solid-liquid separator 34, the iron hydroxide (III) (Fe (OH) ₃ ) is separated and removed as a solid content. Even if a small amount of cyan ion remains in the alkaline washing water from the oxidative decomposition apparatus 41, the cyan ion is oxidized and decomposed by the oxidizing agent in the second reaction tank 33 and removed.

The mixed washing water from which the solid matter has been separated by the second solid-liquid separator 34 is supplied to the third reaction tank 35. In the third reaction tank 35, sodium hydroxide is added to the mixed washing water, the pH of the mixed washing water is adjusted to 7.5 to 10, and zinc ions and lead ions in the mixed washing water are used as hydroxides. Precipitate. Then, zinc hydroxide (Zn (OH) ₂ ) and lead hydroxide (Pb (OH) ₂ ) are separated and removed as solids by the third solid-liquid separator 36.

The mixed washing water from which the solid matter has been separated by the third solid-liquid separation device 36 is supplied to the fourth reaction tank 37. In the fourth reaction tank 37, sodium hydroxide is added to further increase the pH of the mixed washing water, and Ca derived from the waste and contained in the mixed washing water is precipitated as calcium carbonate (CaCo ₃ ). Salts in the mixed wash water are precipitated. Then, calcium carbonate or the like is separated and removed as a solid content by the fourth solid-liquid separator 38.

  The mixed washing water extracted from the fourth solid-liquid separation device 38 is subjected to filtration of the solid matter remaining by the filtration device 39, and then the ions to be removed by the ion exchange resin are further removed by the ion exchange device 40. Thereby, the washing water treatment is completed and clean water is generated.

  Waste gas containing urethane resin is gasified by supplying pure oxygen to the gasifier and gas reformed at 1200 ° C to produce gasified gas mainly composed of hydrogen, carbon monoxide and carbon dioxide The purification of cleaning gas and the treatment with washing water will be described as examples. This gasification gas contained hydrogen sulfide and hydrogen cyanide. The produced gas was cooled and washed with acidic washing water having a pH of 4 with a cooling / acidic washing apparatus to remove iron. Further, hydrogen cyanide was removed by washing with alkaline washing water adjusted to pH 7.8 with an alkaline water washing apparatus. Further, hydrogen sulfide was removed by a desulfurization apparatus using an iron chelate (including an iron EDTA complex) to obtain a clean gas. As a result, the desulfurization rate was 96%.

Comparative example

  In the comparative example, gas purification was performed in the same environment as the above-described example except that the alkaline washing water whose pH was adjusted to 7.2 with an alkaline water washing apparatus was used. As a result, the desulfurization rate was 56%.

  As can be seen by comparing the Examples and Comparative Examples, a high desulfurization rate can be obtained by setting the alkaline cleaning liquid within the pH range (7.5 or more and 8.2 or less) of the present invention with an alkaline water cleaning apparatus. It was confirmed.

21 Cooling / acidic water cleaning device 23 Alkaline water cleaning device 25 Desulfurization device 41 Oxidation decomposition device

Claims (4)

A waste gasification gas treatment device comprising a gas purification device gasified by thermal decomposition and partial oxidation of waste, and a washing water treatment device for treating the washing water used in the purification device ,
The purification apparatus includes a cooled acidic water cleaning apparatus that cools and cleans the gas by bringing acidic cleaning water into contact with the gas, and a gas that is cooled and cleaned by the cooling acidic water cleaning apparatus and has a pH of 7.5 or higher and 8.2. An alkaline water cleaning device for cleaning the gas by contacting with the following alkaline cleaning water, and a desulfurization device for removing hydrogen sulfide contained in the gas cleaned by the alkaline water cleaning device ,
The washing water treatment device is extracted from the first reaction tank, wherein the acidic reaction water used in the cooling acidic water washing device and the alkaline washing water used in the alkaline water washing device are mixed and reacted. processor of waste gasification gas added to cyan oxidant mixing washing water after the reaction, characterized in Rukoto and a second reaction tank to allow separated off was. A waste gasification gas treatment device comprising a gas purification device gasified by thermal decomposition and partial oxidation of waste, and a washing water treatment device for treating the washing water used in the purification device ,
The purification apparatus includes a cooled acidic water cleaning apparatus that cools and cleans the gas by bringing acidic cleaning water into contact with the gas, and a gas that is cooled and cleaned by the cooling acidic water cleaning apparatus and has a pH of 7.5 or higher and 8.2. An alkaline water cleaning device for cleaning the gas by contacting with the following alkaline cleaning water, and a desulfurization device for removing hydrogen sulfide contained in the gas cleaned by the alkaline water cleaning device ,
The washing water processing apparatus includes a processing unit waste gasification gas, characterized in Rukoto with oxidative decomposing oxidative cracker cyan adding an oxidizing agent to the alkaline washing water used in the alkaline water washing device. A method for treating a gas obtained by gasifying waste by thermal decomposition and partial oxidation,
A cooling acidic water washing step in which acidic washing water is brought into contact with the gas to cool and wash the gas;
An alkaline water cleaning step of cleaning the gas by contacting alkaline cleaning water having a pH of 7.5 or higher and 8.2 or lower with the gas cooled and cleaned by the cooling acidic water cleaning step;
A desulfurization step of removing hydrogen sulfide contained in the gas cleaned by the alkaline water cleaning step;
A washing water treatment step for treating the acidic washing water used in the cooling acidic water washing step and the alkaline washing water used in the alkaline water washing step,
In the washing water treatment step, the acidic washing water and the alkaline washing water are mixed and reacted, and after the first reaction step, an oxidizing agent can be added to the mixed washing water to separate and remove cyan. A waste gasification gas treatment method comprising: a second reaction step. A method for treating a gas obtained by gasifying waste by thermal decomposition and partial oxidation,
A cooling acidic water washing step in which acidic washing water is brought into contact with the gas to cool and wash the gas;
An alkaline water cleaning step of cleaning the gas by contacting alkaline cleaning water having a pH of 7.5 or higher and 8.2 or lower with the gas cooled and cleaned by the cooling acidic water cleaning step;
A desulfurization step of removing hydrogen sulfide contained in the gas cleaned by the alkaline water cleaning step;
A washing water treatment step for treating the alkaline washing water used in the alkaline water washing step,
The method for treating a waste gasification gas, wherein the washing water treatment step includes an oxidative decomposition step of oxidatively decomposing cyanide by adding an oxidant to alkaline washing water.

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