In the process of extraction, transportation, storage and processing of oil, oil sludge is inevitably formed. Such waste contains a large number of toxic compounds. Disposal of oil sludge is an urgent problem in the oil industry, as many enterprises store them on their territory for many years due to the lack of landfills for waste or the lack of processing plants. Meanwhile, these substances can be used as secondary material resources that bring economic benefits.
Oil sludge classification
Oil sludge is a complex mixture of heavy hydrocarbons containing a significant amount of oil products. The latter can be extracted in several ways and used for commercial purposes. The objects where oil sludge is stored are divided into 2 types: oil sludge lakes, barns and reservoirs. In the first case, the substances are poured directly on the ground, and the second - on a concreted area with clear boundaries.
Depending on the origin of oil sludge, they are divided into the following groups:
- appearing at the bottom of natural reservoirs after an emergency oil spill (bottom);
- formed in a mixture with drilling fluids during well construction;
- arising from oil refining;
- reservoir - consisting of liquid-viscous substances and gel-like substances formed on the walls;
- soil (when oil products get on the ground).
The chemical composition and content of solids in oil sludge varies greatly.
Disposal Methods
The most common oil sludge disposal methods are as follows:
- chemical;
- biological;
- thermal;
- physical;
- physical and chemical.
The rational choice of a method is determined by the content of petroleum products in the sludge.
Chemical method
Chemical processing and disposal of oil sludge is carried out by the method of encapsulation and neutralization in the reaction with alkaline earth metals (most often with quicklime). As a result of this process, a dry powdery substance is obtained in the form of small granules with a lime capsule. This product belongs to hazard class 4, that is, it is safe for the environment. It is used as a mineral additive in asphalt concrete and in the construction of earthen embankments.
A schematic diagram of the installation of oil sludge utilization by this technology is presented in the figure below.
Granules are characterized by high strength and tightness. For several months, the carbonization of their shells continues. The disadvantages of this technology include the fact that it is necessary to use special equipment, a large amount of high-quality quicklime. The impact of the final product on the environment is also not fully understood. The advantages of chemical neutralization are the relatively low cost and the ability to manufacture mobile plants.
Biological technology
Biological neutralization is the most environmentally friendly way, but its use is limited to the treatment of those types of oil sludge that are formed in tanks, as well as during spills on the ground or in natural water bodies. This is due to factors such as:
- high price of bioreagents;
- the need to allocate large tracts of land for landfills;
- the possibility of neutralization in the field only in the warm season;
- high risk of contamination of the earth with heavy metals and other harmful substances.
The essence of biological technology for the disposal of oil sludge is the use of microorganisms for biodegradation of oil.
There is also a processing method in a heated bioreactor. It is a chamber into which contaminated soil, water, fertilizers and beneficial microflora are fed. As a result of the creation of favorable conditions, microorganisms multiply rapidly and the substance stratifies - oil products accumulate in the upper part of the reactor, and water in the lower part. The remaining oil sludge is discharged to the drying sites. The duration of this process is 10-15 days, after which a new batch of secondary raw materials is fed into the chamber.
Thermal method
Thermal processing technology has several modifications:
- burning in stoves or in open furnaces;
- dehydration or drying, followed by return to production;
- thermal decomposition with a lack of air (pyrolysis);
- gasification (oxidation of oil sludge to produce gas used as fuel).
Incineration is the easiest way to recycle petroleum waste, but it requires the cleaning and neutralization of flue gases, which cause significant damage to the environment. Drying is accompanied by high energy costs.
One of the most promising areas is continuous pyrolysis. Thanks to such processing, synthetic oil and pyrolysis gas are obtained , which are used as fuel for the same process. Equipment for the disposal of oil sludge in this case is a plant, the main element of which is the pyrolysis chamber, in which thermal decomposition into fractions occurs at a temperature of about 500 ° C. The released gas enters the filters and condensers, where it is purified.
Using an additional cracking system from oil sludge you can get high-quality gasoline. The plant is capable of processing all types of sludge, but from an economic point of view it is more expedient to use solid waste oil products with a low degree of humidity.
Physical and physicochemical methods
Physical methods for the disposal of oil sludge include the following methods of separation into fractions:
- Simple upholding. This is the least costly and at the same time inefficient technology.
- Centrifugation Centrifugal equipment is also often used in the intermediate stage of the preparation of oil sludge for their processing in other ways.
- Introduction of surfactants (demulsifiers, wetting agents, solvents).
- Filtration.
- Extraction with organic solvents, waste from the production of ethylene and acetylene, liquefied gases or steam. This method is based on the mutual dissolution of polar compounds.
The disadvantages of all of the above technologies is the incompleteness of the separation of petroleum products.