JP2004174390A - Treatment method for treatment liquid of washing column of ethylene manufacturing plant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To recover an organic component contained in a recovered liquid, which is obtained by recovering the mist-like or liquid drop-like mixture produced from the region ranging from the middle part to upper part of the washing column of an ethylene manufacturing plant by the countercurrent contact of a decomposition gas of naphtha with a sodium hydroxide aqueous solution in the washing column, or contained in the separated liquid after a useful gas is separated from the recovered liquid before the organic component is discharged out of the system. <P>SOLUTION: In this treatment method for the treatment liquid from the washing column of the ethylene manufacturing plant, the separated liquid or recovered liquid itself is mixed with the alkali aqueous solution, of which the concentration is adjusted, supplied so as to be sent to a treatment process for the wastewater discharged from the lowermost stage part of the washing column of the ethylene manufacturing plant to reduce drain quantity, and the organic component contained in the wastewater and the separated liquid is efficiently extracted with an extraction solvent to be recovered by increasing the concentration of alkali in an extraction process. <P>COPYRIGHT: (C)2004,JPO

Description

【００３３】
（比較例１）
図３に示すエチレン製造工程で分解ガスａを流量２１０ｔ／ｈで洗浄塔１に供給する。５重量％水酸化ナトリウム溶液を２．５ｔ／ｈで供給する。一方水を１．７ｔ／ｈで供給する。排水ｅ’の流量は２．５ｔ／ｈで排水中の有機成分の１つであるベンゼン濃度は２４８重量ｐｐｍであった。この排水ｅ’は気液分離器１２’を経て排水ｈとなる。またｃより供給された洗浄水ｅは気液分離器１２を経由し分離液ｇとなる。分離液ｇの流量は１．７ｔ／ｈで、その中のベンゼン濃度は２０７ｐｐｍであった。この分離液ｇと排水ｈは混合された後、実施例１と同様に表１に示す抽出油Ｉを用い、抽出除去を行った。その後の抽出排水ｋ中のベンゼン濃度は８０重量ｐｐｍであった。従ってベンゼンを含有する抽出排水ｋを湿式酸化工程経由で４．２ｔ／ｈの流量で活性汚泥処理へ供給することができた。
【００３４】
（実施例２）
水酸化ナトリウム（関東化学（株）製試薬）を４重量％、硫化ナトリウム（関東化学（株）製試薬）を６重量％含む水溶液１２００ｍｌにベンゼン（和光純薬工業（株）製試薬）を２２重量％含む表２に示す有機液を１２０ｍｌ添加し室温で１Ｈｒ攪拌した。その後油水分離を行い、分離して得られた水溶液中のベンゼン濃度を測定すると１１２重量ｐｐｍであった。
【００３５】
【表２】

【００３６】
（比較例２）
実施例２で水酸化ナトリウム（関東化学（株）製試薬）を４重量％、硫化ナトリウム（関東化学（株）製試薬）を６重量％含む水溶液の代わりに水を用いた以外は、実施例２と同様にした。分離後の水溶液中のベンゼン濃度は１３５６重量ｐｐｍであった。
【００３７】
（比較例３）
実施例２で水酸化ナトリウム（関東化学（株）製試薬）を４重量％、硫化ナトリウム（関東化学（株）製試薬）を６重量％含む水溶液の代わりに水酸化ナトリウム（関東化学（株）製試薬）を１重量％、硫化ナトリウム（関東化学（株）製試薬）を１．５重量％含む水溶液を用いた以外は、実施例２と同様にした。分離後の水溶液中のベンゼン濃度は４１０重量ｐｐｍであった。
【００３８】
（結果）
油水分離する排水中のアルカリ濃度は高い方がベンゼンなどの有機液の溶解が少なく、抽出除去の効率がいいことが判る。従って抽出工程から排出される有機物濃度を低減するには、図１に示すような方法が従来の図３の方法に比べ抽出工程での排水中のアルカリ濃度を高く維持できるためベンゼンなど有機物の溶解濃度を低減できる。
【００３９】
【発明の効果】
この発明の方法により、有機成分を含有する回収液を洗浄塔に戻し、アルカリ水溶液として排水処理工程へ送ることで、エチレン製造プラントから系外に排出される有機成分の量をより抑えることができる。
【図面の簡単な説明】
【図１】エチレン製造プラントの、洗浄塔処理液の処理プロセスの例を示す模式図
【図２】エチレン製造プラントの、洗浄塔処理液の他の処理プロセスの例を示す模式図
【図３】従来のエチレン製造プラントにおける洗浄塔処理液の処理プロセスの例を示す模式図
【符号の説明】
１，１１ 洗浄塔
２，１２ 気液分離器
２’，１２’ 気液分離器
３，１３ 油水混合機
４，１４ 抽出槽
５，１５ タンク
６，１６ 湿式酸化槽
７，１７ 気液分離塔
Ａ，ａ ナフサ分解ガス
Ｂ，ｂ 水酸化ナトリウム水溶液
Ｃ，ｃ 水
Ｄ，ｄ 分解ガス中の有用なガス分
Ｅ，ｅ 回収された霧状物又は液滴状物を含む回収液
Ｅ’，ｅ’ 排水
Ｆ，ｆ 回収物を分離したガス
Ｇ，ｇ 回収物の分離液
Ｈ，ｈ 溶存ガスを除去した排水
Ｉ，ｉ 抽出用媒体
Ｊ，ｊ 抽出済媒体と抽出された有機成分を含む液
Ｋ，ｋ 抽出排水
Ｌ，ｌ 空気
Ｍ，ｍ 水蒸気
Ｎ，ｎ ｐＨ調整剤
Ｏ，ｏ 湿式酸化時に気化した成分を含む排ガス
Ｐ，ｐ 湿式酸化処理後の排液
Ｑ，ｑ 抽出排水[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for treating a treatment liquid generated in a washing tower of an ethylene production plant.
[Prior art]
[0002]
In the ethylene production process, generally, an operation of previously removing a sulfur component, which is a catalyst poison, from a naphtha decomposition gas is performed. First, naphtha is decomposed in a pyrolysis furnace, and then gas and liquid are separated in a fractionation tower. The obtained gas, that is, the cracked gas is sent to a washing tower to remove the sulfur content.
[0003]
As shown in FIG. 3, the process of removing the sulfur content fixed in the washing tower is performed by converting the decomposition gas a introduced from the lower part of the washing tower 11 into an aqueous sodium hydroxide solution b introduced into the middle part of the washing tower 11. To fix the sulfur content contained in the decomposition gas a, and then discharge it as waste water e ′ from the lowermost part of the washing tower 11, and then perform gas-liquid separation of the dissolved gas to obtain waste water h. This is a process in which this is converted to sodium sulfate by wet oxidation and discharged out of the system.
[0004]
However, the wastewater h contains not only the sulfur content but also organic components generated when naphtha is decomposed. If the wastewater h is subjected to wet oxidation as it is, the organic component is vaporized by the heat applied at that time, and a gas containing a large amount of the organic component is released to the atmosphere, which may cause environmental problems. Therefore, before the wet oxidation step, the drainage h is mixed with the extraction medium i by the oil-water mixer 13 and sent to the extraction tank 14, where the extracted medium and the extracted organic component j are separated from the extraction drainage k, h, reduce the concentration of organic components.
[0005]
The extraction wastewater k having a reduced organic component concentration is once stored in a tank 15 and then sent to a wet oxidation tank 16. At this time, sulfur is wet-oxidized to sodium sulfate by adding air 1 and steam m. At this time, the organic components remaining in the extraction wastewater q are gasified at the same time. These are sent to the gas-liquid separation tower 17, where the gas-liquid is separated while adding and neutralizing the pH adjuster n. The liquid component is treated as a drainage p and the gas component is released to the atmosphere as exhaust gas o. However, since the organic components are extracted in advance in the extraction tank 14, the amount of the organic components contained in the exhaust gas o and released to the atmosphere can be suppressed.
[0006]
On the other hand, from the middle to the upper part of the washing tower 11, a counter-current of the decomposition gas a and the aqueous sodium hydroxide solution b generated from the middle to the lower part generates a mist-like or droplet-like mixture. It is difficult to take out only the gas amount d. Then, by adding water c from the upper part of the washing tower and causing it to flow countercurrently, the above-mentioned mixture is recovered in the upper middle part of the washing tower 11, and only useful gas components d are taken out from the uppermost part of the washing tower 11. The collected liquid e in the form of a mist or droplets is further passed through a gas-liquid separator 12 to separate a separated liquid g. The gaseous component f is a flare treatment as an exhaust gas or a decomposition gas compression step as a fuel gas or a decomposition gas again. It is supplied to and collected. The separated liquid g is mixed with the waste water h as described in Non-Patent Document 1, and sent to the wet oxidation step via the extraction step.
[0007]
[Non-patent literature]
1998 Custom System in NALCO / EXXON ETHYLENE Symposium Tokyo, Japan (Operation of Customer Systems Free from Polymers (Red Oil))
[0008]
[Problems to be solved by the invention]
However, the recovered liquid e also contains an organic component contained in the decomposed gas. Even after the recovered liquid e is subjected to gas-liquid separation and the separation gas f is removed, the separated liquid g does not contain any organic components. May be included. After the separated liquid g is mixed with the waste water e ′ or the waste water h, the organic component is removed in the above-mentioned extraction step. However, if the amount of water c used is large, the alkali concentration in the extracted waste water k is diluted, and the waste water is removed. When the density decreases and the high specific gravity extraction oil is used, the specific gravity difference between the extracted medium j and the extraction wastewater k is reduced, and the oil / water separation is deteriorated. In addition, when the alkali concentration decreases, the concentration of the organic component dissolved in the wastewater increases, so that there is a problem that the extraction / separation performance is reduced. In order to maintain the oil-water separation performance, it is necessary to increase the specific gravity difference between the extracted medium j and the extraction wastewater k, and for that purpose, the alkali concentration of the wastewater h must be increased. Furthermore, when the organic component concentration in the extraction wastewater k reaches the equilibrium concentration, the flow rate of the extraction wastewater k determines the amount of discharge from the gas o or the wastewater p to the outside of the system. This is an important issue.
[0009]
Accordingly, the present invention is to recover the organic component as much as possible by suppressing the discharge flow rate discharged from the washing tower as much as possible when the organic component contained in the recovery liquid e is recovered before being discharged out of the system. With the goal.
[0010]
[Means for Solving the Problems]
The present invention cleans the decomposition gas by flowing the naphtha decomposed gas introduced into the lower part of the washing tower of the ethylene production plant countercurrently with the aqueous sodium hydroxide solution introduced into the middle part of the washing tower. Discharging the wastewater containing the organic component contained in the decomposition gas from the lowermost part of the washing tower and discharging the organic component through the extraction step of the organic component using an extraction medium, By causing the gas to flow countercurrently to the water introduced into the upper part of the washing tower, mist or droplets are collected from the washed decomposition gas, and the organic components contained in the collected liquid are collected. In the method for treating a treatment liquid for a washing tower of an ethylene production plant, which is recovered in the extraction medium,
The above object was achieved by directly mixing the recovered liquid or a part of the separated liquid obtained by gas-liquid separation of the recovered liquid with the aqueous sodium hydroxide solution and returning the mixed liquid to the washing tower.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0012]
The present invention is directed to an organic solvent contained in a collected liquid obtained by collecting a gas-liquid mixture generated in the upper part of the washing tower by using a treatment step of wastewater discharged from the washing tower with respect to the treated liquid generated in the washing tower of the ethylene manufacturing plant. In recovering the components before discharging to the outside of the system, the recovered liquid is returned to the cleaning tower to reduce the processing liquid, and thereby the discharge of the organic components to the outside of the system is reduced. Processing method.
[0013]
The washing tower treatment liquid refers to drainage after washing the sulfur content in the decomposition gas of naphtha with an aqueous solution of sodium hydroxide in the washing tower, and counterflow of the washed decomposition gas in the washing tower with water. And a recovery liquid that is recovered as a mixture of gas and liquid generated by the recovery.
[0014]
First, a first invention relating to a method for treating the above-mentioned treatment liquid in the ethylene production process will be described.
[0015]
The naphtha cracked gas A from which the liquid component has been removed by fractionation after coming out of the pyrolysis furnace is sent to the lower part of the washing tower 1 as shown in FIG. In the washing tower 1, an aqueous sodium hydroxide solution B is introduced from the middle stage, and countercurrently flows from the lower portion with the decomposed gas A from the lower portion, thereby reacting a sulfur component mainly composed of hydrogen sulfide in the decomposed gas A, Change to sodium sulfide or sodium hydrosulfide. These sodium sulfide and sodium hydrosulfide are discharged from the lowermost part of the washing tower 1 as waste water E '. The wastewater E 'further contains unreacted sodium hydroxide and organic components contained in the naphtha decomposition gas.
[0016]
Effluent E ′ discharged from the washing tower 1 passes through a gas-liquid separator 2 ′, and the dissolved gas contained therein is removed as F ′ after removing F ′, or directly discharged without passing through the gas-liquid separator 2 ′. As H (not shown, the drainage E ′ is indicated as H for convenience even when not passing through the gas-liquid separator 2 ′), mixed with the extraction medium I in the oil-water mixer 3 and sent to the extraction tank 4. Then, the extracted medium J, which is a mixture of the extraction medium and the extracted organic components, is separated from the extraction wastewater K so that the concentration of the organic components contained in the extraction wastewater K is lower than the original wastewater H. The extraction wastewater K is temporarily stored in the tank 5 and then sent to the wet oxidation tank 6.
[0017]
In the wet oxidation tank 6, air L and steam M are added to the extraction wastewater K sent from the tank 5, and sodium sulfide and sodium hydrosulfide in the extraction wastewater K are changed into sodium sulfate. At this time, at the same time, the organic components contained in the extraction wastewater K are gasified. However, since the concentration of the organic components is reduced in the extraction tank 4, the amount of gasification can be suppressed.
[0018]
After passing through the wet oxidation tank 6, it is sent to the gas-liquid separation column 7, and contains neutralized by adding the pH adjuster N, and contains gaseous exhaust gas O containing a trace amount of organic components and sodium sulfate. The liquid is separated into a drainage liquid P which is a liquid component. The exhaust gas O is released into the atmosphere. However, since the concentration of the organic components in the wastewater H is reduced in advance in the extraction tank 4, the amount of the organic components released into the atmosphere in the gas-liquid separation tower 7 can be suppressed. Further, the drainage liquid P is processed via activated sludge processing or the like.
[0019]
On the other hand, in the washing tower 1, the mixture of the processing liquid and the decomposition gas, which is formed into a mist or a droplet by the countercurrent of the lower part and rises, is added with water C from the upper part of the washing tower 1 to cause the countercurrent to flow. It is collected from the middle part of the washing tower 1.
[0020]
The recovered liquid E still contains an organic component similarly to the wastewater E ′. However, both the recovery liquid E and the waste water E ′ are originally processing liquids in the washing tower 1, and in addition to containing organic components, they are common in that they are aqueous solutions having different concentrations but containing sodium hydroxide. ing.
[0021]
Therefore, the recovered liquid E is not directly mixed with the wastewater H via the gas-liquid separator, but is directly mixed with the aqueous sodium hydroxide solution B which is an alkaline aqueous solution and returned to the washing tower 1. However, simple mixing only lowers the alkali concentration in the aqueous sodium hydroxide solution introduced into the column, and reacts the sulfur content of the decomposition gas A, which is mainly composed of hydrogen sulfide, to form sodium sulfide or sodium hydrosulfide. A problem occurs in that the conversion rate decreases. For this reason, the alkali concentration in the alkaline aqueous solution B is adjusted such that the alkaline concentration of the mixture of the recovery liquid E and the alkaline aqueous solution B becomes a predetermined concentration. Thereby, the flow rate of the alkaline aqueous solution supplied from B can be reduced, and the flow rate of the drainage liquid P finally discharged out of the system can also be reduced. Since this method does not pass through the gas-liquid separator 12 shown in FIG. 3 which has been conventionally used, the dissolved gas contained in the recovered liquid is discarded by flare treatment or recompressed in a fuel gas or cracked gas compression step. Since the decomposed gas is recovered as it is without recovery, the recovery efficiency is improved, and the energy consumption is also efficient.
[0022]
The recovered liquid E is mixed with the aqueous alkali solution B supplied to the washing tower 1 and the alkali concentration is adjusted to obtain the same high specific gravity wastewater E 'as in the past. Thereby, oil-water separation in the extraction tank 4 does not deteriorate. Further, the flow rate of the waste water H is smaller than the flow rate of the liquid mixture of the waste water h and the separated liquid g shown in FIG. For this reason, the amount of the organic component finally discharged from the exhaust gas O and the waste liquid P can be further reduced by the reduced flow rate, which is advantageous in terms of environmental protection. In addition, the amount of heat applied in the wet oxidation tank 6 can be reduced by the reduced flow rate, which is advantageous in terms of energy consumption.
[0023]
The extraction medium I is a hydrophobic organic liquid capable of extracting organic components such as benzene and toluene from an aqueous solution. When benzene is contained in the naphtha decomposition gas, the concentration of benzene contained in the extraction medium is desirably 5% by weight or less. Benzene is often considered to be particularly environmentally harmful among the organic components generated by the decomposition of naphtha, and it is desirable that the amount of benzene emitted into the atmosphere is even lower than that of other organic components. When the concentration of benzene contained in the extraction medium I is higher than 5% by weight, the amount of benzene remaining in the extraction wastewater K becomes a nonnegligible amount, and in some cases, the benzene concentration is higher than before the extraction work is performed. Things can happen. On the other hand, if the benzene concentration in the extraction medium I is set to 5% by weight or less, benzene can be more efficiently recovered in the extraction tank 4.
[0024]
Next, a second invention relating to a method for treating the above-mentioned treatment liquid in the ethylene production process will be described. Except for the treatment of the recovery liquid E, the separation gas (denoted as F in the second invention), and the separation liquid G, it is the same as the first invention shown in FIG.
[0025]
As shown in FIG. 2, in the cleaning tower 1, the mixture of the processing liquid and the decomposition gas which has been formed into a mist or a droplet by the countercurrent of the lower part and rises is added with water C from the upper part of the cleaning tower 1. It is collected from the upper middle part of the washing tower 1. The separation gas F is removed from a part or all of the recovered liquid E by the gas-liquid separator 2 to obtain a separated liquid G. The separated gas F is subjected to flare treatment as exhaust gas, or supplied to a decomposition gas compression step or the like as a fuel gas or again as a decomposition gas and collected.
[0026]
The separated liquid G separated by the gas-liquid separator 2 still contains an organic component like the recovered liquid E and the waste water H. However, the recovery liquid E, the separation liquid G, and the wastewater H are all treatment liquids in the washing tower 1 and are common in that they are aqueous solutions containing sodium hydroxide having a different concentration besides the organic components. .
[0027]
For this reason, the separation liquid G is mixed with the wastewater containing the organic component, and is mixed with the aqueous sodium hydroxide solution B introduced into the washing tower 1 and returned to the washing tower 1, and is allowed to flow countercurrently in the washing tower 1. And can be used again for cleaning. Further, if necessary, a part of the recovered liquid E can be directly mixed with the aqueous sodium hydroxide solution B without gas-liquid separation, and used for washing similarly. However, this causes a problem that the alkali concentration in the aqueous alkali solution is reduced, and the conversion of sodium sulfide or sodium hydrosulfide into sodium sulfide or sodium hydrosulfide is reduced by reacting the sulfur component mainly composed of hydrogen sulfide in the decomposition gas A. . For this reason, the concentration of the aqueous sodium hydroxide solution B is adjusted according to the flow rates of the separation liquid G and the recovery liquid E mixed with the aqueous sodium hydroxide solution B so that the alkali concentration after mixing does not excessively decrease. The countercurrent separated liquid G is discharged from the lowermost part of the washing tower 1 as drainage E '. Thereby, the flow rate of the alkaline aqueous solution supplied from B is reduced, and as a result, the flow rate of drainage P can also be reduced.
[0028]
When the separated liquid G is branched and one is sent to the washing tower 1 and the other is mixed with the wastewater H, the ratio of the amount to be branched, the flow rate of the collected liquid E to be returned directly to the washing tower 1 and the gas-liquid separator It is desirable that the ratio of the flow rate supplied to 2 is not fixed, but can be changed according to the operation status of the plant. For example, when Red Oil generated in the washing step accumulates in the washing tower, it is necessary to shorten the residence time of the wastewater in the system, and if the amount of the wastewater H sent to the extraction tank 4 can be adjusted, It is convenient for plant operation.
[0029]
In addition, the ethylene production plant is not limited to a plant that produces only ethylene, but also uses petroleum, coal, natural gas, etc., such as fuel gas such as methane and ethane, resin materials such as propylene, gasoline, and fuel oil. Is a generic term that includes plants that produce other organic chemical products.
[0030]
Also, in the washing tower, the uppermost part, upper part, middle upper part, middle part, lower part, the distinction of the lowermost part, and the range of upper part, middle part, lower part are basically the above order from the top, , They are not absolute, they are relative measures in their distinction and scope.
[0031]
(Example 1)
In the ethylene production process shown in FIG. 1, the decomposition gas A is supplied to the washing tower 1 at a flow rate of 210 t / h. A 15% by weight sodium hydroxide solution is fed at 0.8 t / h. On the other hand, water is supplied at 1.7 t / h. The flow rate of the wastewater E ′ was 2.5 t / h, and the concentration of benzene, one of the organic components in the wastewater, was 243 ppm by weight. Using the extracted oil I by-produced in the ethylene production process shown in Table 1, the benzene concentration in the extraction wastewater K after extraction and removal was 57 ppm by weight. Therefore, the extraction wastewater K containing benzene could be supplied to the activated sludge treatment at a flow rate of 2.5 t / h via the wet oxidation step.
[0032]
[Table 1]

[0033]
(Comparative Example 1)
In the ethylene production process shown in FIG. 3, the decomposition gas a is supplied to the washing tower 1 at a flow rate of 210 t / h. A 5% by weight sodium hydroxide solution is fed at 2.5 t / h. On the other hand, water is supplied at 1.7 t / h. The flow rate of the waste water e ′ was 2.5 t / h, and the concentration of benzene, one of the organic components in the waste water, was 248 ppm by weight. This drainage e 'becomes drainage h via the gas-liquid separator 12'. The washing water e supplied from c passes through the gas-liquid separator 12 to become a separated liquid g. The flow rate of the separated liquid g was 1.7 t / h, and the benzene concentration therein was 207 ppm. After the separated liquid g and the waste water h were mixed, extraction and removal were performed using the extracted oil I shown in Table 1 in the same manner as in Example 1. The benzene concentration in the subsequent extraction wastewater k was 80 ppm by weight. Therefore, the extraction wastewater k containing benzene could be supplied to the activated sludge treatment at a flow rate of 4.2 t / h via the wet oxidation step.
[0034]
(Example 2)
Benzene (reagent manufactured by Wako Pure Chemical Industries, Ltd.) was added to 1200 ml of an aqueous solution containing 4% by weight of sodium hydroxide (reagent manufactured by Kanto Chemical Co., Ltd.) and 6% by weight of sodium sulfide (reagent manufactured by Kanto Chemical Co., Ltd.). 120 ml of the organic liquid shown in Table 2 containing 1% by weight was added and stirred at room temperature for 1 hour. Thereafter, oil-water separation was performed, and the benzene concentration in the aqueous solution obtained by separation was 112 ppm by weight.
[0035]
[Table 2]

[0036]
(Comparative Example 2)
Example 2 Example 2 was repeated except that water was used instead of the aqueous solution containing 4% by weight of sodium hydroxide (a reagent manufactured by Kanto Chemical Co., Ltd.) and 6% by weight of sodium sulfide (a reagent manufactured by Kanto Chemical Co., Ltd.). Same as 2. The benzene concentration in the aqueous solution after separation was 1356 ppm by weight.
[0037]
(Comparative Example 3)
In Example 2, sodium hydroxide (Kanto Chemical Co., Ltd.) was used instead of the aqueous solution containing 4% by weight of sodium hydroxide (reagent made by Kanto Chemical Co., Ltd.) and 6% by weight of sodium sulfide (reagent made by Kanto Chemical Co., Ltd.). Example 2 was carried out in the same manner as in Example 2 except that an aqueous solution containing 1% by weight of sodium sulfide (a reagent manufactured by Kanto Chemical Co., Ltd.) was used. The benzene concentration in the aqueous solution after the separation was 410 ppm by weight.
[0038]
(result)
It can be seen that the higher the alkali concentration in the wastewater to be separated from oil and water, the less the organic liquid such as benzene is dissolved, and the higher the efficiency of extraction and removal. Therefore, in order to reduce the concentration of organic substances discharged from the extraction step, the method shown in FIG. 1 can maintain the alkali concentration in the wastewater in the extraction step higher than the conventional method of FIG. The concentration can be reduced.
[0039]
【The invention's effect】
According to the method of the present invention, the amount of the organic component discharged from the ethylene production plant to the outside of the system can be further suppressed by returning the recovery liquid containing the organic component to the washing tower and sending it to the wastewater treatment step as an aqueous alkaline solution. .
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of a process for treating a cleaning tower treatment liquid in an ethylene production plant. FIG. 2 is a schematic diagram showing another example of a treatment process for a cleaning tower treatment solution in an ethylene production plant. Schematic diagram showing an example of a treatment process of a treatment liquid for a washing tower in a conventional ethylene production plant [Description of symbols]
1,11 Washing tower 2,12 Gas-liquid separator 2 ', 12' Gas-liquid separator 3,13 Oil-water mixer 4,14 Extraction tank 5,15 Tank 6,16 Wet oxidation tank 7,17 Gas-liquid separation tower A , A Naphtha decomposed gas B, b Sodium hydroxide aqueous solution C, c Water D, d Useful gas content E, e in decomposed gas Recovered liquid E ', e' containing collected mist or droplets Wastewater F, f Gas G from which the recovered material is separated, g Separated liquid H from the recovered material, h Wastewater I from which dissolved gas is removed I, i Extraction medium J, j Liquid K containing the extracted medium and the extracted organic components, k Extraction wastewater L, 1 Air M, m Steam N, n pH adjuster O, o Exhaust gas P containing components vaporized during wet oxidation, p Wastewater Q after wet oxidation treatment Q, q Extraction wastewater

Claims (4)

The decomposed gas of naphtha introduced into the lower part of the washing tower of the ethylene production plant is counter-flowed with the aqueous sodium hydroxide solution introduced into the middle part of the washing tower, thereby washing the decomposed gas and removing the decomposed gas. The wastewater containing the organic components contained in the washing tower is discharged from the lowermost part of the washing tower, and is discharged out of the system through the extraction step of the organic components using the extraction medium, while the washed decomposition gas is washed in the washing tower. By flowing countercurrently with the water introduced into the upper part of the tower, mist or droplets are recovered from the washed decomposition gas, and the organic component contained in the recovered liquid is extracted by the extraction medium. In the method for treating a treatment liquid for a washing tower of an ethylene production plant,
The recovered liquid is mixed with the aqueous sodium hydroxide solution, returned to the washing tower, and allowed to flow countercurrently in the cleaning tower, and then discharged from the lowermost part of the washing tower, and the organic component contained in the recovered liquid is removed. A method for treating a treatment liquid in a washing tower of an ethylene production plant, wherein the treatment liquid is extracted by the extraction medium as an organic component contained in the wastewater. The decomposed gas of naphtha introduced into the lower part of the washing tower of the ethylene production plant is counter-flowed with the aqueous sodium hydroxide solution introduced into the middle part of the washing tower, thereby washing the decomposed gas and removing the decomposed gas. The wastewater containing the organic components contained in the washing tower is discharged from the lowermost part of the washing tower, and is discharged out of the system through the extraction step of the organic components using the extraction medium, while the washed decomposition gas is washed in the washing tower. By flowing countercurrently with the water introduced into the upper part of the tower, mist or droplets are recovered from the washed decomposition gas, and the organic component contained in the recovered liquid is extracted by the extraction medium. In the method for treating a treatment liquid for a washing tower of an ethylene production plant,
A separated liquid is taken out from the recovered liquid by a gas-liquid separator, and the separated liquid is mixed with a wastewater containing the organic component, mixed with the aqueous sodium hydroxide solution, and returned to the washing tower.
By causing the separated liquid returned to the washing tower to flow countercurrently in the washing tower, discharged as wastewater from the lowermost part of the washing tower, and sent to the extraction step together with the separated liquid mixed with the wastewater, A method for treating a treatment liquid in a washing tower of an ethylene production plant, wherein an organic component contained in the separation liquid is extracted by the extraction medium. The method according to claim 2, wherein a part of the recovered solution is directly mixed with the aqueous sodium hydroxide solution. 4. The treatment solution for a cleaning tower of an ethylene production plant according to claim 1, wherein the decomposition gas of naphtha contains benzene, and the concentration of benzene contained in the extraction medium is 5% by weight or less. Processing method.

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