Oil removal process for oily wastewater

Description of oil removal process for oily wastewater

1、 Introduction of oil removal equipment for oily wastewater in China

1. Equipment for handling floating oil:

The floating oil absorber in the sewage regulating tank, the "tank in tank technology" in the sewage regulating tank, the horizontal cyclone oil remover, the vertical polymerization separation oil remover, etc.

2. Equipment for handling emulsified oil:

The main equipment consists of cavitation air flotation and dissolved air flotation.

All oil removal equipment are now produced by special companies with mature technology. The oil-water cyclone separation technology is a kind of high-efficiency energy-saving separation technology developed in the 1980s. The key part of the hydrocyclone is hydrocyclone, which can separate the oil-water mixture with the particle size of more than 15 microns. Compared with other oil removal equipment, hydrocyclone has the advantages of compact structure, small volume, light weight, high oil removal efficiency, no moving parts, long service life and closed process.

2、 Oil removal pretreatment process of oily wastewater

The above-mentioned oil-water separation unit equipment is widely used in the oil-bearing wastewater treatment of major oil refining and petrochemical enterprises without system specification, and the treatment capacity and effect of each unit equipment are limited, such as the oil content of wastewater after tank in tank technology treatment is ≤ 150mg / L, while the oil content of sewage treated by horizontal cyclone oil remover and vertical polymerization separation oil remover is ≤ 50mg / L, and the influent water is not more than 50mg / L It is required that the oil content of the air flotation equipment for treating emulsified oil should not be greater than or equal to 500mg / L, while the oil content in the inlet water of the air flotation equipment for treating emulsified oil should be ≤ 50mg / L, and the oil content in the effluent should be ≤ 20mg / L, etc.

Through the understanding, summary and analysis of the monomer of each treatment unit, as well as the accumulated actual situation of field treatment, the system standardizes the post forming cost pretreatment process, so that each unit equipment can give full play to its own advantages, develop advantages and avoid disadvantages, and complete the oil-water separation function by combination, so as to meet the oil content requirements of the later advanced treatment.

The common pretreatment processes of oily wastewater are as follows:

"Tank in tank technology in sewage regulation tank + horizontal oil-water separator + dissolved air flotation machine".

3、 Process description

(1) Sump: the oily sewage is transported to the original sump through the blowdown pipeline in the plant area, and is lifted to two three-phase separation regulating tanks by the lift pump in the pool.

(2) Sewage regulating tank: oily sewage oil-water separation and regulating tank (referred to as tank in tank technology) mainly plays the role of three-phase (water, oil, slag) separation, storage and regulation of oily sewage. The tank is equipped with an oil-water separation and floating oil collection and oil discharge combination device, which forms a "tank in tank technology" with sewage regulating tank. It not only has the function of water regulation, but also can realize the separation of water, oil and slag. The sludge separated from the tank is discharged into the sludge tank, and the floating oil is discharged into the sewage tank after being collected, and the effluent is discharged into the horizontal oil-water separator by the lifting pump.

(3) Horizontal oil-water separator: horizontal oil-water separator is a high-efficiency oily wastewater treatment device which integrates fluid dynamics, rotating liquid centrifugal separation technology and coarse-grained technology in the same device. The device can effectively remove the small oil particles which can not be removed from the sewage regulating tank (including the tank in the tank). Without transmission device, it can operate continuously and reliably for a long time. The effluent from horizontal oil-water separator flows into dissolved air flotation machine.

(4) Dissolved air flotation machine: the oily water contains a small amount of emulsified oil and dissolved oil, which are difficult to remove by simple physical means. It is necessary to add chemicals to the mixing tank at the front end of the air flotation machine. Through the mechanical stirring in the mixing tank, the chemicals can fully contact with the oil in the sewage, and demulsification and flocculation reactions will occur to produce flocs and precipitate from the water. The oily sewage after dosing reaction enters the dissolved air flotation machine. In the contact area of the air flotation machine, a large number of micro bubbles produced by the releaser contact with the micro suspended solids in the sewage; in the separation area, due to the buoyancy generated by the micro bubbles, the suspended solids float up and separate from the water, and the sewage is purified. The drainage of air flotation machine can meet the requirements of biochemical system for petroleum index (petroleum ≤ 20mg / L).

The treated sewage is directly transported to the biochemical system of the sewage treatment plant in the plant for biochemical treatment.