JPH0233439B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating caustic soda wastewater containing phenols and COD substances discharged from oil refineries, petrochemical plants, etc. More specifically, the present invention supplies caustic soda waste containing harmful substances such as phenols discharged from oil refineries etc. to a crude oil desalter (hereinafter abbreviated as desalter) and processes it. The present invention also relates to a method for treating caustic soda waste liquid, the purpose of which is to purify the waste liquid by treating it with an activated sludge device. In petroleum refineries and petrochemical plants, a method of cleaning with caustic soda is generally employed to remove impurities such as hydrogen sulfide, mercaptans, and phenols contained in various exhaust gases and petroleum fractions. The caustic soda waste liquid used for this cleaning contains harmful substances such as sulfur compounds and phenols extracted from various exhaust gases and petroleum fractions. If the water is released into rivers, etc., it will cause enormous damage to fish, shellfish, and seaweed. Therefore, in order to purify the caustic soda waste liquid containing harmful substances, the caustic soda waste liquid has been treated in an activated sludge apparatus. As a result of extensive research into these problems, the inventors of the present invention have found that harmful substances such as phenols and COD substances in the neutralized caustic soda waste liquid can be removed by treating the waste liquid with a demineralizer. After confirming the facts, the present invention was completed. Therefore, the main object of the present invention is to effectively remove phenols and COD substances contained in caustic soda waste liquid discharged from petroleum refining and petrochemical equipment in a factory without installing special equipment. It is in. Another object of the present invention is to treat phenol, COD
To efficiently and stably treat caustic soda waste containing substances in an activated sludge apparatus without giving a poisonous shock. Furthermore, another object of the present invention is to remove phenols and COD substances from caustic soda waste liquid discharged from petroleum refining and petrochemical equipment with a simple operation. Still another object of the present invention is to prevent corrosion in the desalter by introducing caustic soda waste into the desalter. The present invention involves neutralizing caustic soda waste fluid containing phenols and COD substances discharged from oil refineries, petrochemical plants, etc. by adding mineral acids, supplying it to a desalter for treatment, and then treating it with phenols and COD substances. but
The present invention relates to a method for treating caustic soda waste, characterized in that demineralizer wastewater whose COD has been reduced to 100 ppm or less and 500 ppm or less is supplied to an activated sludge device for treatment. That is, the present invention provides (1) phenol and COD
(2) The neutralized caustic soda waste liquid is supplied as desalination water to a demineralizer to remove harmful substances such as phenols and COD substances from the waste liquid. and (3) supplying the caustic soda waste liquid whose content of harmful substances such as phenols and COD substances has been reduced below the permissible value to an activated sludge unit to purify the waste liquid. The present invention provides a method for treating waste liquid. The caustic soda waste liquid treated in the present invention is discharged from oil refineries, petrochemical factories, etc. Caustic soda waste used for cleaning petroleum fractions usually contains about 3 to 15% by weight of sodium sulfide, sodium bisulfide, soda carbonate, etc.
Approximately 0.5 to 5% by weight of mercaptans, approximately 0.5% to 5% by weight of phenols and cresols as sodium salts, respectively.
It contains 0.5 to 25% by weight. According to the conventional method, a certain amount of impurities such as phenols and mercaptans are decomposed by the activated sludge, so that the caustic soda waste liquid can be purified. However, when caustic soda containing a considerable amount of impurities such as phenol and mercaptan is supplied, microorganisms in the sludge are killed, and the activated sludge equipment is often unable to operate normally. Since the activated sludge device is installed at the end of the wastewater treatment system, malfunction of the activated sludge device will have a great negative impact on wastewater treatment work. Furthermore, the surplus sludge produced in large quantities in this activated sludge apparatus cannot be easily disposed of because it contains harmful substances. In view of these numerous problems, there is a strong desire for a method to effectively treat caustic soda waste liquid. The method of the present invention is effective in treating these caustic soda waste liquids, and contains 10,000 ppm or more of phenol,
Caustic soda waste liquid with a COD of 50,000 ppm or more can be targeted. Sulfuric acid is suitable as the mineral acid for neutralizing the caustic soda waste liquid. For example, it is economically preferable to use the sulfuric acid waste liquid discharged from an alkylation device. The amount of mineral acid added to neutralize the caustic soda waste liquid must be sufficient to reduce the pH of the waste liquid to 7 or less. In the salter, the acidic substances in the caustic soda waste decrease, so the PH value increases and the operating efficiency of the desalter may decrease. Generally, the desalination efficiency of crude oil increases as the pH decreases, but a pH below 3.5 is undesirable because it will cause corrosion of the desalter. In the present invention, process wastewater refers to all wastewater containing impurities and harmful substances generated from equipment such as oil refineries. Examples include oil-containing waste water from tank yards, cooling water used for heat exchange of crude oil and petroleum fractions, and steam condensate from boilers and distillation columns. Process wastewater often contains impurities such as COD, BOD, and oil, but these are efficiently removed in the desalter at the same time as the caustic soda wastewater, reducing the burden on the activated sludge equipment. The amount of process waste water to be mixed into the caustic soda waste liquid after neutralization may be appropriately determined depending on the amount of the caustic soda waste liquid to be treated and the alkali concentration. for example,
If the free alkali concentration is 5 to 15% by weight, the process wastewater is preferably mixed with a volume of 10 to 40 times the volume of the caustic soda waste. The diluted caustic soda waste is brought into contact with crude oil in a desalter. The caustic soda waste liquid is about 1 to 15% by weight, preferably about 3% by weight based on the crude oil.
It can be contacted at a proportion of ~10% by weight. The crude oil is not particularly limited, and any type of crude oil can be used. In other words, from light crude oil to heavy crude oil, from low sulfur crude oil to high sulfur crude oil,
It can be used regardless of its properties. The desalter used in the present invention is a device for chemically or electrically separating water, muddy substances, and the like containing salts such as sodium chloride and calcium chloride dispersed in the crude oil. Desalting methods include chemical desalting, in which chemicals are added to a stable emulsion of crude oil and water to facilitate the separation of crude oil and water, and chemical desalting, in which a high voltage is applied to the crude oil to be treated to destroy the emulsion. There are electrical desalination methods in which salt-containing water is separated by water, and desalination methods that use a combination of both methods, and the present invention can be applied to any of these desalination methods. In recent years, two demineralizers have been installed.
Although a two-stage desalination method has been adopted in which crude oil is desalted by connecting two demineralizers, in the present invention, a sufficient waste liquid treatment effect can be obtained by using only one of the demineralizers. The caustic soda waste is intensively mixed with the heated crude oil by a mixing valve at the desalter inlet. The emulsion of crude oil and waste liquid thus produced is ejected from the distributor of the desalter into a high-voltage electric field. This operation converts the emulsion-like caustic soda waste into phenol and
While most of the COD substances are taken away by the crude oil, the salt and mud in the crude oil are dissolved, and the high-voltage electric field between the electrodes turns them into huge water droplets that settle to the bottom of the desalter. The contact temperature between caustic soda waste and crude oil is approximately 200°C.
℃ or less, preferably in the range of 120°C to 150°C. In general, the higher the temperature of crude oil, the higher the desalting effect, and the better the purification rate of waste liquid, so higher temperatures are more suitable for carrying out the present invention. A desalter is usually 5 to 25 Kg/cm ² (especially about 10 to 15 Kg/cm ² ) in order to suppress the escape of low boiling point components and water vapor in crude oil.
It is operated at a pressure of In addition, the desalter maintains the pH within the range of 7.5 or less. It has been pointed out that, in general, crude oil desalters are susceptible to corrosion due to naphthenic acid originally contained in the crude oil and hydrogen chloride newly generated during the desalting process. Corrosion of the demineralizer due to such acidic components can be prevented by supplying caustic soda waste to the demineralizer according to the present invention. And for this reason, it is necessary to control the pH of the demineralizer to 4.0 or higher. However, when the pH becomes 7.5 or higher, the desalination effect decreases,
Since the removal rate of phenols etc. from the caustic soda waste liquid also decreases, it is necessary to adjust the amount of acid added in the neutralization step. The residence time of the caustic soda waste in the desalter is approximately 3 to 4 hours. An activated sludge device is a device for biochemically decomposing and removing impurities contained in caustic soda waste liquid and other process wastewater from a desalter. The equipment usually comprises an activated carbon absorption tower, pre-treatment equipment such as a pre-aeration tank, an aeration tank, a coagulation sedimentation tank, a treated wastewater tank, an excess sludge treatment equipment, and the like. However, in the present invention, most of the impurities such as hydrogen sulfide in the caustic soda waste liquid are removed by the demineralizer, so there is no need to install a pretreatment device such as an activated carbon absorption tower or a pre-aeration tank. Activated sludge, which is a floc-like colony of aerobic microorganisms such as bacteria, yeast, mold, and protozoa, is placed in the aeration tank, and is fluidized by the waste liquid flowing into the tank and the air blown into the tank. is circulating. Activated sludge is sensitive to impurities such as phenols and sulfur compounds, and if it comes into contact with waste liquid containing large amounts of these components, it will receive a toxic shock, making it impossible to operate the activated sludge equipment stably. It is necessary to strictly control the concentration. In particular, phenol is less than 100ppm,
It is preferable to reduce COD to 500 ppm or less. More preferably, phenol
The goal is to keep COD below 50ppm and below 300ppm. Activated sludge equipment has a pH of 6 to 8 and a temperature of 30 to 40℃.
It is preferable to drive at In addition, phenol in caustic soda waste liquid,
Compounds such as COD substances move to the crude oil side in the desalter and are transported to the distillation unit, but they react with hydrogen in subsequent processing equipment such as hydrotreating equipment and hydrodesulfurization equipment, and are removed or converted into hydrocarbons. etc., so there is no risk of ultimately deteriorating the quality of petroleum products. Next, an embodiment of the present invention will be explained with reference to FIG. The pH of the caustic soda waste liquid to be treated is first adjusted using sulfuric acid. The pH of sulfuric acid at the demineralizer inlet
A sufficient amount is added so that the ratio is 3.5 to 7. This neutralization process is performed by the neutralization drum 1.
The neutralization drum is maintained at approximately 30°C and is stirred. The neutralized caustic soda waste liquid is diluted in a deaerator 2 with process wastewater from which hydrogen sulfide and ammonia have been steam-stripped. The caustic soda waste liquid is mixed with crude oil heated in a heat exchanger and supplied to a desalter. The desalter has a pH of 4.0 to 7.5.
and operated at a temperature of 120-150℃. The caustic soda waste liquid supplied to the demineralizer is extracted from the channel 6 after a residence time of 3 to 4 hours. Next, the desalinated wastewater passes through a cooler 8 and an oil separator 9 and is supplied to an activated sludge device 10. The wastewater that has been treated with the activated sludge device and has reduced harmful substances is discharged from the guard basin 12 into the river. The crude oil treated with the desalter is extracted from the channel 7 and heated, then supplied to a distillation apparatus (not shown), treated in a conventional manner, and separated into various petroleum fractions. The present invention will now be described by way of examples. Example 1 Caustic soda waste liquid discharged from the gasoline washing process of an oil refinery was treated by the method of the present invention. First, a caustic soda waste solution containing 17,480 ppm of phenol and 83,020 ppm of COD substances (see Table 1) was neutralized by adding sulfuric acid. 1kl of this neutralized caustic soda waste liquid was mixed and diluted with 30kl of process wastewater generated within the same oil refinery. The pH of the waste liquid after dilution was 6.5. Next, this diluted waste liquid was mixed with 80kl of Middle Eastern crude oil that had been preheated in a heat exchanger.
The water was added at a rate of 31 kl as desalination water and supplied to the demineralizer. The desalter was operated at 130℃ and pH7.
The waste liquid was treated in a desalter for about 4 hours. As a result,
The caustic soda waste from the demineralizer contains phenols.
20ppm (removal rate 95%), COD140ppm (removal rate 88%)
It has become a characteristic of The number of crude oil desalters was 90%. The caustic soda waste from the desalter was mixed with 60kl of process wastewater, treated in an oil separator, and then supplied to an activated sludge unit for treatment. The activated sludge equipment is
It was operated at 30°C and pH 7 in the presence of aerobic bacteria. The waste liquid after activated sludge treatment contains phenol and COD.
Almost no harmful substances such as substances were detected.
The results are shown in Table 1. Note that the above process wastewater contained 4 ppm of phenol and 220 ppm of COD substances. Comparative Example 1 The same caustic soda waste liquid as in Example 1 (see Table 1) was used, and the treatment was carried out under the same conditions as in Example 1 except that the pH in the demineralizer was set to 5.5. That is, 17480 ppm of phenol and COD substances.
A smaller amount of sulfuric acid was added to the caustic soda waste solution containing 83020 ppm than in Example 1. 1kl of this caustic soda waste liquid was mixed and diluted with 30kl of process wastewater generated within the same oil refinery. Next, this diluted waste liquid was added as desalination water at a ratio of 30 kl to 80 kl of Middle Eastern crude oil preheated in a heat exchanger and supplied to the desalter. The desalter was operated at 130° C. and pH 8.6, and the waste liquid was treated in the desalter for about 4 hours. As a result, the caustic soda waste liquid from the desalter contained 180 ppm of phenol and
COD was 560ppm. The caustic soda waste from the desalter was mixed with 60kl of process wastewater, treated in an oil separator, and then supplied to an activated sludge unit for treatment. Activated sludge equipment is operated at 30℃ in the presence of aerobic bacteria.
I drove at PH7. The wastewater after activated sludge treatment had 130 ppm of phenol and 300 ppm of COD, and the removal rate of harmful components was lower than in Example 1. Example 2 17480ppm of phenol and COD substance
A larger amount of sulfuric acid than in Example 1 was added to the caustic soda waste solution containing 83020 ppm (see Table 1).
1kl of this caustic soda waste liquid was diluted by mixing 30kl of process wastewater generated within the same oil refinery.
Next, this diluted waste liquid was added as desalination water at a ratio of 31 kl to 800 kl of Middle Eastern crude oil preheated in a heat exchanger and supplied to the desalter. The desalter was operated at 130° C. and pH 4.1, and the waste liquid was treated in the desalter for about 4 hours. As a result, phenol in desalinated wastewater was 18 ppm.
COD decreased to 130ppm. Thereafter, activated sludge treatment was performed in the same manner as in Example 1, and the results shown in Table 1 were obtained. As explained above, the present invention is extremely effective in treating caustic soda waste liquid discharged from oil refineries and the like. That is, if the present invention is implemented, 1)
More than 95% of phenols and mercaptans contained in caustic soda waste can be removed, and 85% of COD substances are removed.
As mentioned above, it is possible to remove more than 50% of the oil content, 2) corrosion of the desalter can be prevented without reducing the crude oil removal rate in the desalter, and the activated sludge equipment can be operated stably, and 3) activation The work environment around the sludge equipment is improved, and the amount of harmful components contained in the surplus sludge can be reduced, making it easier to dispose of the surplus sludge externally. is extremely large. 【table】

[Brief explanation of drawings]

FIG. 1 is a process diagram showing the treatment of caustic soda waste liquid according to the present invention. 1...neutralization drum, 2...deaerator, 5...desalter, 9
...Oil separator, 10...Activated sludge device.

Claims (1)

[Claims] 1. After neutralizing caustic soda waste liquid discharged from oil refining or petrochemical equipment by adding mineral acid,
It is supplied as desalination water or as a part of it to a crude oil desalter and treated, and the phenol content is 100 ppm or less.
A method for treating caustic soda wastewater, which comprises supplying the demineralizer wastewater whose COD substances have been reduced to 500 ppm or less to an activated sludge device for treatment. 2. The treatment method according to claim 1, wherein the PH in the crude oil desalter is 7.5 or less. 3. The treatment method according to claim 1, wherein the caustic soda waste liquid is neutralized and then diluted with process wastewater.