Oily sludge is one of the dangerous substances in the process of petroleum development, refining, processing, transportation and production. It has a large output in the petroleum industry, and if it is not handled properly, it will pollute the surrounding environment. Harmless and resource treatment of oily sludge is an urgent problem to be solved, and it is also the requirement of sustainable development.

Classification of oily sludge

1. Oily sludge produced during crude oil exploitation. In the drilling operation, when the oil layer is detected,
 the operation of drilling and well testing may cause oil spill or blowout and produce oily sludge due to the action of ground pressure.
 In the process of crude oil production, crude oil detection, plugging, tubing fracture, workover operations, etc., may produce landing oil mud.
This oily sludge has the characteristics of large oil content, fine particles, large viscosity and difficult water removal.

2. Oily sludge produced in the gathering and transportation process of oil fields.
Oil field gathering and transportation is the process of collecting and treating the crude oil produced by each oil well in the oil field and transporting it to the oil depot or the export station respectively.
The gathering station is a place where oil, water and gas are separated from the extracted crude oil, and the sewage station treats the separated water and refills the oil well.
The gathering station and the sewage station are called the combined station. In order to maintain the formation pressure, most of the crude oil is injected with water first and then surfactant. After the formation pressure exists, the crude oil is transported to the surface through the oil well. With the deep exploitation of the oil field, the water content in the produced oil is increasing. Therefore, the oily sludge produced in the oil-water separation process of the joint station usually has a high oil content and water content, and a low solid content, which not only has asphaltene, aging crude oil, bacteria, but also has corrosion inhibitors, scale inhibitors, flocculants and other agents added in the sewage treatment process. There are two sources of oily sludge in the joint station: one is the bottom sludge of crude oil storage tank, settling tank and sewage tank; The second is the oily sludge formed by the overflow of sewage storage tank.

3. Oily sludge produced by the refinery sewage treatment process. Oil-bearing sludge in oil refinery, commonly known as "three mud", has a large output, and usually has the characteristics of complex composition, difficult degradation, difficult settlement, difficult concentration and difficult treatment.

Characteristics and hazards of oily sludge

Oily sludge density is generally larger than water, oil content is high, generally 10%-50%, water content is 50%-90%, viscosity is large,
dehydration is difficult, is a black viscous semi-fluid. The composition of oily sludge is complex, not only with a large number of aging crude oil, asphaltene,
wax, colloids, bacteria, solid suspended matter, salts, corrosive products, acid gas, etc., but also in the production process added corrosion inhibitors,
coagulants, fungicides, scale inhibitors and other water treatment agents, is one of the main pollution sources in the oil industry.

Oily sludge is rich in organic matter, salt, nitrogen, phosphorus, sulfur and other nutrients. If it is directly discharged into the surface water body or under the action of precipitation, the organic matter and ammonia nitrogen will consume a large amount of oxygen in the water body, resulting in eutrophication of the water body and seriously affecting the balance of the aquatic ecosystem. In addition, oily sludge also contains heavy metals such as copper, zinc, chromium, cadmium, mercury, lead and pathogenic bacteria, parasites (eggs), polychlorinated biphenyls, dioxins, radionuclides and other toxic and harmful substances that are difficult to degrade, which will not only pollute the environment, but also affect human health, leading to many fatal diseases, and even carcinogenic, teratogen, mutagenic effects. Therefore, in 1998, the State Environmental Protection Bureau classified oily sludge as waste mineral oil and mineral oil waste (HW08 item) hazardous solid waste, and required harmless disposal before discharge.

Xi 'an KOSUN oily sludge treatment process

The processing process is: The material to be treated is fed by the belt conveyor into the spiral sand washing machine,
the sand treated by the spiral sand washing machine enters the fine particle sand removal machine, the fine particle sand is crushed and cleaned,
part of the oil is separated into the oil storage tank by the scraper, the sediment is transported to the vibrating screen by the centrifugal pump for dehydration,
 and the particles larger than 0.5mm are separated. >74 micron <0.5mm particles and sediment are processed by centrifugal pump into cyclone,
<74 micron particles are separated and dehydrated by centrifuge, and <2 micron materials are processed by air flotation machine.
The sand after air flotation treatment is discharged and dried, and the water after air flotation treatment is reused by spiral sand washing machine.
The oil sewage of the spiral sand washing machine enters the oil sand separation tank for treatment. After treatment,
the oil enters the oil storage tank for recovery through the scraper. The fine sediment after precipitation is transported to the vibrating screen by the centrifugal pump.