Other treatment methods of oily sewage
Gravity separation method is a typical primary treatment method, which uses the density difference between oil and water and the incompatibility between oil and water to separate oil droplets, suspended solids and water in a static or flowing state. Oil droplets dispersed in water slowly float and stratify under buoyancy, and the floating speed of oil droplets depends on the size of oil droplets, the density difference between oil and water, the flow state and the viscosity of fluid. The relationship between them can be described by Stokes and Newton's laws.
cross-flow oil remover
The cross-flow oil removal equipment for oily sewage is developed on the basis of the inclined plate oil remover, which consists of two parts: the coalescence area and the separation area of oily sewage. Oily sewage first passes through a cross-plate coalescer, so that small dispersed oil droplets are coalesced into large oil droplets, and small solid substances are flocculated into large particles, and then the coalesced oil droplets and solid substances are separated from water through a transverse flow separation plate area with unique channels. Gas (natural gas) can be separated at the same time as oil-water and solid matter separation.
Corrugated plate coalescence oil-water separator
The principle of oil removal by corrugated plate is mainly to use the density difference between oil and water to make oil beads float on the peak of the plate and separate and remove them. The key point is to make a corrugated plate with variable spacing and variable water flow streamline with the help of Hazen shallow pool sedimentation principle. The cross section of water is changed, and the water flows alternately in the state of diffusion and contraction, resulting in pulsating (sinusoidal) water flow, which increases the collision probability between oil beads.
Aggregation type oil-water separator
The Austrian Ferrer Company took the lead in developing the CPS integrated corrugated plate gravity accelerated aggregation type oil-water separator in the world. The corrugated board is a patented product of Ferret Company. It is based on polypropylene and contains many additives, which makes it oleophilic but non-stick and anti-aging. Corrugated plates are stacked one by one, and the spacing is generally 6 mm (when the content of suspended solids in water is high, the design of spacing of 12 mm can be adopted).
High-efficiency elevation free water separator
The horizontal and vertical free water separators are combined, and the elevation angle design is adopted, which overcomes the shortcomings of small coverage area of oil-water interface in vertical container, short distance between oil-water interface and water outlet in horizontal container and insufficient separation time. The incoming liquid inlet is located at the upstream end of the tubular container, and the oil beads in the water can coalesce and climb up to the top oil outlet, while the water sinks to the bottom water outlet for discharge. The equipment has an elevation angle of less than 12, a length of 18.3 m and a diameter of 1 372 mm and 914 mm. Only when the oil content is below 3 mg/L and contains other harmful substances that need biodegradation will it be considered for use, generally not just for degreasing. Oil-bearing wastewater from petroleum refinery can be treated by biological method after physical degreasing.
chemical method
chemical method is mainly used to treat some colloids and soluble substances in wastewater that cannot be removed by physical or biological methods alone, especially emulsified oil in oily wastewater. Include coagulation and precipitation, chemical transformation and neutralization.
physical and chemical methods
physicochemical treatment methods of oilfield sewage usually include air flotation and adsorption.
air flotation is to inject air into water in the form of tiny bubbles, so that the tiny bubbles adhere to oil particles suspended in water, and float up because its density is less than that of water, forming a scum layer to be separated from water. Flotation agents are often added to improve the flotation effect. Flotation agents have demulsification and foaming effects on the one hand, and adsorption bridging effect on the other hand, which can make colloidal particles aggregate and float with bubbles. Generally, the treatment process of oily wastewater is to carry out initial oil-water separation (such as oil separation) before the second oil-water separation (floating or coagulation). This process can not only prevent the treatment device from being blocked by oil products, but also give full play to the oil removal performance of each device. In the process, if the oil is removed once before lifting by pump, the degree of emulsification can be reduced.
for wastewater with small specific gravity difference between oil and water, or when the treated water is reused, a filtering device should be used. For oily wastewater with large particle size and high freezing point, there should be heating and heat preservation equipment in the treatment device, and the influence of temperature should be considered in the material selection of the treatment device.