Research on Treatment Technology of Oily Sludge in Oil and Gas Fields
The treatment of oily sludge in oil and gas fields is difficult, and most oil fields have not yet achieved harmless and resourceful treatment. Generally, they are stacked and dried after dehydration, which not only takes up a lot of land, but also causes pollution to air, water, soil, etc. Enterprises also need to pay a large amount of sewage charges. It is necessary to further study the treatment technology of oily sludge in oil and gas fields.
Treatment standard of oily sludge
The treatment standard of oily sludge in oil and gas fields usually depends on the purpose of the treated sludge. Generally speaking, the final disposal of this type of sludge at home and abroad is road construction and landfill, in order to avoid adversely affecting the soil of the landfill. All countries have put forward strict requirements on the heavy metal content and oil content of oily sludge after treatment. For example, the United States and France require oil content ≤ 2% (oil mass fraction) for oily sludge disposed of in landfills. Disposal of oily sludge requires its oil content ≤5% (mass fraction of oil).
China has also formulated relevant standards for the treatment of oily sludge, such as "Hazardous Waste Landfill Pollution Control Standards" (GB 18598-2001), etc., but there is no quantitative index for oil content after oily sludge treatment. The "Control Standards for Pollutants in Agricultural Sludge" (GB4284-84) specifies the mineral oil content in sludge, which is ≤0.3% (by mass fraction) . Regarding the heavy metal content in oily sludge, the "Control Standards for Pollutants in Agricultural Sludge" (GB4284-84) has also made provisions, such as ρ (Cu) 500 mg / kg, ρ (As) 75 mg / kg, etc. , Also regulated heavy metal emissions.
Treatment Technology of Oily Sludge in Oil and Gas Fields
1. Reduction treatment
The reduction treatment is a treatment measure that uses physical and chemical methods to separate the particulate matter in the sludge to achieve the reduction of pollutants. This method has the characteristics of low cost and easy operation.
1.1 Mechanical dehydration
Mechanical dewatering is to carry out various pretreatments such as conditioning and sorting of oily sludge, and then centrifuge at high speed to separate the three phases of oil, water and mud, and then use solidification technology and biotechnology to assist according to the treatment effect. Treatment to achieve harmless oily sludge. Generally speaking, the process is as follows.
(1) Adjust the particle structure of oily sludge with flocculant to enhance the dehydration of oily sludge.
(2) Use vacuum filtration dehydrator, high-speed centrifuge and other equipment for dehydration. Among them, flocculants are difficult to degrade, and poor treatment will lead to secondary pollution. Therefore, the selection of a wide range of applications, non-toxic and harmless high-efficiency, organic, and high-molecular flocculants are the key issues to consider. The polymer flocculant is a better choice.
Incineration is the main method used by sewage treatment plants to treat oily sludge. After dewatering the oily sludge, it is sent to the concentration tank and heated to 60 ℃, then flocculant is added, stirring and gravity settling are carried out, and then the water is separated into layers. After the above-mentioned treatment, the oily sludge can be dehydrated and dried again, made into a mud cake and burned in an incinerator, and finally the ash residue is treated. The effect of incineration treatment is very obvious, which can remove a variety of harmful substances, but some harmful gases will also be released during the incineration process, causing secondary pollution to the atmosphere. Finally, incineration requires higher equipment, which is also a condition that many oil and gas fields do not have.
2. Curing treatment
2.1 curing treatment
Solidification refers to the harmless treatment method of solidifying oily sludge, or contained in an inert solidification matrix. It is more suitable for the treatment of oily sludge containing CaCl2 and Na-Cl, and the treatment of sludge with lower oil content. At present, curing generally uses cement curing agent, which can meet the requirements of safe landfill treatment . The efficiency of curing treatment is high, and it can also be utilized after treatment. However, the properties of oily sludge in oil and gas fields are different, and the targeted development and use of curing agents is an important research direction.
2.2 Microbial treatment
Biological treatment refers to the technology of using microorganisms to degrade and mineralize oily sludge, and finally transform it into harmless inorganic substances. The use of microorganisms to treat oily sludge, the factors affecting the treatment effect include the following.
(1) The type and number of microorganisms.
(2) The growth environment of microorganisms, such as moisture content, temperature and oxygen concentration of nutrients.
(3) Biochemical characteristics of pollutants. Different microorganisms have different ability to degrade oily sludge. At the same time, a mixture of multiple microorganisms or strains can often achieve a more ideal degradation effect.
Secondly, the final product of microbial treatment is water, carbon dioxide and other harmless substances, which will not cause secondary pollution to the environment, nor will it cause pollutant transfer, and the cost is not high. It is an important research direction for the harmless treatment of oily sludge.
In an anoxic environment, the organic matter in the oily sludge can be decomposed into solid carbon, liquid fuel oil, etc., which are reusable resources. Related studies have found that the treatment of oily sludge through pyrolysis can more effectively recover oil and gas, and develop the utilization value of the residue again, which has better benefits.
Coking treatment is a technology that utilizes the coking reaction of residual oil and heavy oil to achieve high-temperature cracking or thermal contraction. Judging from the actual situation of the current oil and gas fields, the methods of coking oil-containing sludge mainly include the following two.
(1) Dehydrate the oily sludge first, then mix it with a suitable catalyst, and put it into the coking reactor to achieve the coking reaction. After condensation and cracking, non-condensable gas, conversation, and liquid oil are produced.
(2) Add an appropriate amount of carbonization additives and strength additives to the oily sludge, and then produce carbon-containing adsorbents and other products through the coking reaction.
2.3.3 Solvent extraction
Solvent extraction refers to the use of extractants to dissolve oily sludge. After stirring and centrifugation, the extractants are used to extract oil and organic matter, and then refining to produce fuel oil that can be used. Using recovery distillation technology, the extractant can also be recycled. However, it should be noted that the extractant usually needs to be applied together with other technologies to achieve a better recovery effect, such as combined use with a dispersant, combined with a mechanical agent, and low frequency sound waves.
Prospect of oil and gas sludge treatment technology trend in oil and gas fields
At present, the treatment of oily sludge abroad has been more advanced and developed, but the domestic has just started in this regard, many experiments are still in the laboratory research stage, and lack of typical demonstration projects. At the same time, most of the research focuses on the recovery of crude oil in oily sludge, but the research on oily sludge purification technology is also very limited. Although it is relatively simple to make oily sludge into mud cake or landfill, it will cause certain economic losses and environmental pollution. The use of various additives to treat oily sludge requires expensive costs, and some treatment methods can also cause secondary pollution problems. Although biological treatment has low operating costs and saves energy, waste disposal is also a problem.
With the continuous improvement of oily sludge treatment technology, the application of bio-chemical, physical-chemical and other joint technologies will become a major direction for oily sludge treatment in oil and gas fields. At the same time, the composition of oily sludge is more complex, and the Oily sludge also has its own characteristics. The actual situation of oil and gas fields in oil and gas fields is to classify and process oily sludge in stages, and finally realize the harmless treatment and resource utilization of oily sludge, which is also the main direction of future research.
Oily sludge is a serious source of pollution. The treatment of oily sludge is not only a requirement for environmental protection, but also a resource recycling requirement. At present, there are many technologies at home and abroad for the treatment of oily sludge, such as incineration, extraction, and microbial treatment, but the above various technical methods generally have certain limitations, and further strengthen the research of related technologies to achieve economic benefits. The double income of social benefits is a problem worthy of our consideration.