Views: 888 Author: Yosun Publish Time: 2025-01-20 Origin: Site
Oil refineries refers to a factory that processes crude oil extracted from underground through distillation, catalysis, cracking, pyrolysis, hydrorefining and other technological processes to produce products such as diesel, gasoline, kerosene, lubricating oil, petroleum coke, asphalt and ethylene.
The classification of oil refineries can generally be divided into three types.
1. Fuel-oriented refineries. They produce clean fuels, and some of these refineries also produce lubricating oils.
2. Integrated oil and chemical refineries. They not only produce oil products (mainly fuels and lubricating oils), but also produce chemical raw materials (olefins, aromatics, etc.).
3. Chemical-oriented refineries. They mainly produce chemical raw materials (olefins, aromatics).
Dissolved air flotation (DAF) is a highly efficient solid-liquid separation technology that plays a key role in the refinery wastewater treatment process, mainly in the following aspects:
Removal of suspended solids
Principle: Air is dissolved in water to form dissolved air water, which produces tiny bubbles when it is released under reduced pressure. These bubbles attach to the suspended solid particles, making their density less than water, thus floating to the surface of the water to form scum to be scraped off.
Role: Refinery wastewater contains suspended impurities such as catalyst particles, rust, sediment, etc. If not removed in time, it will cause wear and tear of the subsequent equipment, clogging, affecting the treatment effect. Dissolved air flotation can effectively remove these suspended solids, reduce their content, and provide relatively clean water for subsequent treatment units.
Separation of oil
Principle: For dispersed oil and emulsified oil with small particle size, the bubbles generated by dissolved air flotation can be adsorbed on the surface of the oil droplets, and bring the oil droplets to the surface of the water as the bubbles rise.
Role: The oil refining process will produce a large amount of oily wastewater, dissolved air flotation can separate most of the oil substances, reduce the oil content of the wastewater, reduce the load of the subsequent deep treatment process to remove the oil, to prevent the toxicity of the oil substances on the microorganisms inhibitory effect, and to ensure the normal operation of the biological treatment unit.
Dissolved air flotation flotation and sedimentation tank sedimentation are two important solid-liquid separation technology in sewage treatment, they are in the principle, equipment structure, scope of application and other aspects of the differences, the following for you to introduce in detail:
Principle
Dissolved air flotation: Under a certain pressure, a large amount of air is dissolved in water to form dissolved air water, and then released through decompression, so that the dissolved gas in the form of tiny bubbles precipitated. These tiny bubbles adhere to the suspended particles in the sewage (e.g. algae, fibers, oil droplets, etc.), forming an air buoyant body with a specific gravity less than that of water, which floats to the surface of the water under the action of buoyancy, thus realizing solid-liquid separation.
Precipitation tank sedimentation: based on gravity, the use of suspended particles and water density difference, so that the suspended particles in the water sink under the action of gravity, and gradually separated from the water. Heavier particles (e.g., sediment, metal hydroxides, etc.) will sink to the bottom of the pool more quickly in the settling pool, thus achieving the purpose of water purification.
Equipment structure
Dissolved air flotation equipment: usually consists of dissolved air system, release system, air flotation tank, scraping system and other parts. Dissolved gas system includes dissolved gas tank, water pump, etc., used to produce dissolved gas water; release system through the releaser to release the bubbles in the dissolved gas water; air flotation pool is to realize the separation of air flotation; scraping system will float in the water surface of the scum scraping out.
Sedimentation tank: generally consists of inlet area, sedimentation area, outlet area, sludge area and buffer area. The water inlet area makes the sewage enter the sedimentation area evenly; the sedimentation area is the main area for particle precipitation; the outlet area collects the treated water and discharges it; the sludge area stores the precipitated sludge; the buffer area prevents the precipitated sludge from being stirred up by the water flow.
Treatment effect
Dissolved air flotation: It has high efficiency in removing suspended particles with density close to water and small particle size as well as hydrophobic pollutants, such as emulsified oil and some colloidal substances. Solid-liquid separation can be realized quickly, usually in a shorter residence time (generally 15 - 30 minutes) to achieve better separation results, the effluent water quality is relatively clear.
Sedimentation tank sedimentation: Removal of solid particles of large density and large size of the suspended solids effect is significant, such as sediment, large particles of organic matter and so on. However, for some fine particles and colloidal substances, it may be difficult to completely remove them by precipitation alone, and it is necessary to add chemicals such as coagulants to improve the precipitation effect. Sedimentation time is relatively long, usually takes 1 - 3 hours.
Scope of application
Dissolved air flotation flotation: It is suitable for the treatment of oily wastewater, papermaking wastewater, printing and dyeing wastewater, etc. The pollutants in these wastewater are characterized by hydrophobicity or density close to water. In drinking water treatment, it can also be used to remove algae and low-temperature low-turbidity water.
Sedimentation tank sedimentation: widely used in a variety of industrial wastewater and domestic sewage pretreatment and primary treatment, such as the primary sedimentation tank of municipal wastewater treatment plant, can remove a large number of suspended solids and some organic matter. It is also suitable for treating wastewater with high sand content or as a pre-treatment unit for subsequent deep treatment process.
Advantages and disadvantages
Dissolved air flotation flotation
Advantages: fast separation speed, small footprint; strong adaptability to changes in water quality and water quantity; can effectively remove some pollutants that are difficult to remove by sedimentation method.
Disadvantages: the equipment is relatively complex, requires a specialized dissolved gas system and release system, the investment cost is higher; the operation process needs to consume a certain amount of electricity and gas, the operation cost is relatively high.
Sedimentation tank sedimentation
Advantages: simple equipment structure, convenient operation, stable operation; lower investment cost, suitable for large-scale sewage treatment.
Disadvantages: limited removal effect on fine particles and colloidal substances; larger floor space, longer settling time, relatively low treatment efficiency.
