Treatment technology of sulphide in oily wastewater

Abstract: S2-penetrability in oily wastewater is strong, which can easily perforate the pipe wall, destroy the pipeline system, and interfere with normal production. The treatment methods of sulfide in oilfield wastewater, such as chlorination, neutralization, aeration, oxidation and sedimentation, were introduced. Sulfur removal experiment was carried out on the sulfur containing sewage of Shuanghe Station by using oxidation and precipitation methods. In the experiment, self-made oxidizing agents Y-1, Y-2 and settling agents F-1 and F-2 were added. The experimental results show that the effect of Y-1 primer is better when the oxidation method is adopted, and the sulfur removal rate reaches more than 93%. In the case of precipitation, f-1 and F-2 primer are equally effective. When the dosage reached the maximum, the sulfur removal rate reached more than 99%.

Key words: oily wastewater, sulfide, treatment, oxidation, precipitation, reagents

0 lead it

In the present stage of oil and gas field exploitation technology in China, water injection is mostly adopted. In oilfield sewage, S, S2- and SO42- are the main existence modes of sulfur [1,2], and both S and SO42- can be reduced to S2- under the action of SRB sulfur salt. In water, S2- is highly penetrating and corrosive to steel because its outer electron cloud is prone to deformation, eventually perforating the pipe wall and interfering with normal production. The corrosion product is black colloidal FeS suspended matter insoluble in water, which leads to the increase of suspended matter. At the same time, FeS is a kind of emulsifier, which makes oil refining more difficult and clogs strata underground, reducing water flooding effect. In addition, it can clog the well and increase the frequency of well flushing and acidification. Therefore, more and more attention has been paid to the treatment of impurities such as sulfide in oily wastewater. The state and oil fields have strict standards for harmful sulfide in wastewater. This paper mainly introduces the treatment method of sulfide in oilfield sewage and the treatment example of sulfur-containing sewage in Shuanghe station of Nanyang Oilfield.

1 Processing Technology [3 ~ 6]

1.1 method of chlorine

When the high concentration of sulfide is contained in the wastewater, chlorination method can effectively remove the sulfide in oilfield wastewater. Process: the sulfurous waste water pump into the tank, and then to pool the cic with copperas and lime, copperas, lime, fully mixing wastewater, sulfur-containing wastewater pH adjustment to between 8 ~ 9, copperas sulfide interact with each other, and wastewater generated ferrous sulfide, gradually sinking to the bottom of the tank, reduce sulfur content in the waste water.

1.2 neutralization

When periods of low sulphur content in the oil field wastewater, multi-purpose neutralization method to remove the sulfur in the waste water, adopting the method of dealing with the low sulfur sewage is economic and efficient, handling process is: the alkaline sulfur-containing waste water pump into the first tank, at the same time, the flue gas through washing device in addition to deal with phenol and blowing into the tank of waste water in flue gas and sulfide, the wastewater pH 6.4 ~ 6.8, the 98% of the sulfur is removed, to purify waste water.

1.3 aeration method

Aeration method is to keep good contact between waste water and air, and to use air to oxidize sulfide to achieve the purpose of reducing sulfur. At present, there is a prerequisite for the treatment of sulphur-containing wastewater by aeration: the wastewater must contain a considerable amount of manganese salt in order to achieve a good purification effect. The treatment operation is as follows: first, add manganese salt (or sulfur salt) to the sulfur-containing wastewater, stir and mix thoroughly, then carry on natural or mechanical aeration, to achieve the purpose of removing sulfide.

1.4 oxidation

Low sulfur oxidation or high sulfur original to achieve the purpose of removing sulfide. When the concentration of hydrogen sulfide in the wastewater is not high, about 1 ~ 2 mg/L, ozone oxidation is the most economical, hydrogen peroxide, sodium hypochlorite, chlorine dioxide is also a good substitute, to remove 1 mg/L of hydrogen sulfide requires ozone 1 mg/L, sodium hypochlorite 8 mg/L, hydrogen peroxide (50% concentration) 20 mg/L.

1.5 precipitation

When sulfide is mainly divalent sulfur in sulfur-containing wastewater, good removal effect can be achieved by precipitation. Precipitation agents are mainly trivalent iron salt or copper salt (such as ferric chloride, copper chloride), when the pH value of the wastewater is too low (pH below 6.0) to add a certain amount of lime, sodium hydroxide, to regulate the pH value of the wastewater. Since Fe2S3 has a very low solubility in water, adding trace amounts of Fe3+ or Cu2+ to the water will quickly combine with Fe3+ and Cu2+ and form precipitation, so as to achieve the purpose of sulfur removal.

2 Application Examples

2.1 Status quo of sewage treatment in Shuanghe Sewage Station

Shuanghe oilfield is a low permeability oilfield, which requires high water injection quality. Processing method for conventional 2-phase "process, namely the emergence of the three-phase separator oily sewage after add water purifier and antiphase demulsifier, after two sedimentation tank to remove part of the oil and suspended solids (SS), and then through the secondary filter into the water injection system, allocation of water is installed between the fine filter, in order to ensure quality.

After adopting this treatment process, the water quality did not reach the standard, and the main indexes such as oil, S2- and SS were seriously exceeded, which seriously affected the development effect of water flooding. Table 1 shows the treatment effect of the original process.

2.2 The improved treatment method

The sulfur content in the sewage of Shuanghe Union station has been very high (40 ~ 50 mg/L), and the sewage is still high (30 ~ 40 mg/L) after treatment, which brings potential safety hazards to the production of oil field. By analyzing the water quality of Shuanghe station, it is found that the sulfur in sewage of Shuanghe Station is mostly divalent sulfur. To this end, the sulfur removal experiment was carried out on the sulfur-containing sewage of Shuanghe Station by using oxidation and precipitation methods. In the experiment, self-made oxidizing agents Y-1, Y-2 and precipitated agents F-1 and F-2 were added, and the results are shown in Table 2 and Table 3.

It can be seen from Table 2 and Table 3 that the oxidation method can remove the sulfur in the sewage of Shuanghe Station, and both the oxidizing agents Y-1 and Y-2 can meet the oilfield sewage treatment standard (S2-< 10 mg/L), and the treated water quality is improved compared with the original process water quality. However, compared with the two, the removal effect of Y-1 is better, with a removal effect (additive amount of 10 mg/L) up to 93.99%, and the water quality is also greatly improved after the removal of sulfur, while the removal effect of Y-2 is relatively poor, with only 89.45%.

In addition, the removal effect of f-1 and F-2 of the two agents is similar, and the effect can reach more than 90%. The treated water quality is also greatly improved compared with the original treatment process.

3 conclusion

◆ Through the above experiments, oxidation method and precipitation method can be used to treat the sulfur-containing sewage in Shuanghe Station. Y-1 has a good treatment effect when using oxidation method, while F-1 and F-2 have the same effect when using precipitation method. These two methods can also be used in the treatment of sulphide in sewage.

◆ As mentioned above, there are oxidation method, precipitation method, neutralization method and other methods in the treatment of sulfur-containing sewage. The appropriate sulfur removal method can be selected according to the water quality of sewage and the quality standards after treatment.

Author: Peng Bo, Li Penghua, Xie Shuixiang (Cheung Kong University)