Discussion and application of oil water separation technology

1、 Preface

Water is an indispensable material resource in human life and production activities. With the development of petroleum and petrochemical industry, industrial wastewater has become one of the main causes of environmental pollution. With the gradual improvement of environmental protection laws and regulations, sewage treatment technology is facing severe challenges. In order to realize the harmony between energy, environment and social responsibility, and support and implement the sustainable development strategy, the application and development of sewage treatment technology in China is becoming more and more important. Understanding and analyzing the present situation of oily wastewater treatment technology is of great significance to the treatment and purification of oily wastewater in China. Because of its low operating pressure and simple structure, the rotary oil separator is a promising oil-bearing wastewater treatment equipment.

2、 Present situation of oily wastewater treatment technology

1. Gravity settlement

The main process flow is: natural sedimentation → coagulation sedimentation → filtration → effluent (three-stage process). The mechanism of gravity sedimentation is to separate oil from water by using the density difference of oil and water and the immiscibility of oil and water. It includes natural oil removal method, floating separation method, inclined plate oil removal method and mechanical separation method. It has the advantages of stable effect, low operation cost and convenient management, but the equipment occupies a large area. Reasonable hydraulic design and residence time of sewage are two important factors affecting oil removal efficiency. The longer the retention time, the better the treatment effect.

2. Cyclone separation technology

The main process flow is: oily wastewater → cyclone separator → filtration → effluent. Hydrocyclone technology is a promising oil-water separation technology. The mechanism is to separate the oil droplets with smaller density from water by means of centrifugal force. The hydrocyclone is composed of four parts: cylinder vortex section, concentric necking section, fine cone section and parallel tail section. The hydrocyclone has the advantages of light weight, small volume, large water treatment capacity, fast processing speed, insensitivity to movement, wide operating pressure range and less than 40 mg / L hydrocarbon content in treated water. Compared with the mechanical separator, namely sedimentation centrifuge, filter centrifuge and separation centrifuge, their separation factors are similar, but the cyclone has no moving parts, so it is superior to mechanical separator in price, performance and operation. Compared with the horizontal flow type, flat plate type and inclined plate type, the cyclone separator has higher efficiency and smaller particle size. For oil-water mixture with oil drop size less than 50um, it should be used instead of oil separator. Compared with the two-stage flotation technology, the two technologies have the same particle size, but the hydrocyclone has the advantages of high oil removal efficiency, small one-time investment, small floor area and low maintenance cost.

3. Air flotation technology

The main process flow is as follows: oily sewage → air flotation device → filtration → effluent. Air floatation is to pass air into oily sewage or try to produce gas in water, so that emulsified oil with particle size of 0.25-25 μ m and dispersed oil or suspended particles in water adhere to bubbles, float up to the water surface with bubbles and recover them, so as to achieve the purpose of removing oil and suspended solids from oily water. At present, air flotation technology is widely used in oily wastewater treatment.

4. Membrane separation technology

With the rapid development of membrane science, using membrane to treat oily wastewater has been gradually accepted and applied in industry. Membrane separation technology is known as the water treatment technology in the 21st century, which has been studied and used abroad. A large number of literatures and experiments show that it is feasible to use polypropylene hollow fiber membrane and ultrafiltration membrane in oil-water separation. At present, the treatment of oily wastewater by membrane separation technology is just in the experimental stage in China.

3、 Application of hydrocyclone separation technology in treatment of industrial oily wastewater

1. Water quality analysis

The oily sewage mainly comes from light hydrocarbon fractionation company. The oil in the sewage includes floating oil, dispersed oil, emulsified oil, attached oil and dissolved oil, among which floating oil and dispersed oil are the main ones. It also contains acetic acid, methanol and other pollutants, with a certain pungent odor.

2. Cyclone oil-water separator

Rs-300 hydrocyclone oil-water separator is selected for the device.

3. Basic principle of rs-300 hydrocyclone oil water separator

Hydrocyclone is an oil-water separator based on Hydrocyclone technology.

The swirl pipe is composed of inlet, swirl chamber, contraction chamber, tail cone, tail pipe, underflow port and overflow port. The demulsifier is added before the industrial sewage enters the oil-water separator to ensure that the oil content in the effluent is less than 300mg / L, which provides ideal treatment effect for the oil removal of the subsequent air flotation process. After mixing and reacting with demulsifier, the industrial sewage enters the separator from the inlet of the swirl chamber after lifting, forming a spiral flow. Through the contraction cavity and the tail cone, the fluid speed is increased and a stable centrifugal force field is formed inside the separator. According to Stokes's law, the oil and water are discharged from the bottom of the separator in the form of heavy oil and water.

4. Process flow

After the oily sewage enters into the cyclone oil-water separator, it forms spiral flow in the separator, and shrinks through the contraction chamber and tail cone to increase the fluid speed and form in the separator In a stable centrifugal force field, the light phase oil in the oil-water mixture coalesces to the center of the separator to form an oil core, which is discharged from the oil discharge port and enters the waste oil storage tank V101 through the residual pressure. The oil removal rate reaches 95%, and the heavy phase water is thrown to the inner wall of the cyclone under the strong centrifugal force, and is discharged from the water outlet in a spiral state, and enters the combined air flotation machine through the residual pressure The removal effect of chemical waste oil can reach the water inlet condition of biochemical treatment unit.

4、 Conclusion

1. The oil removal rate of the oil-water separator reaches 95%, which effectively separates the oil and water in the oily wastewater, but the outlet concentration can not meet the requirements of biochemical treatment

2. As a low-cost separation technology, swirl separation technology is becoming a hot spot of new oil-water separation technology. Therefore, swirling oily wastewater treatment equipment has broad market potential and application prospect

3. The hydrocyclone oil-water separator can be directly applied to the pretreatment of industrial oily wastewater due to its small volume and small external interference; because of its low operating pressure and simple structure, it will become an irreplaceable oil-bearing sewage treatment equipment.