Treatment of cold rolling wastewater in steel plant
Wedge wire screen filter element is widely used in cold rolling wastewater treatment of steel plants.
The quality and quantity of cold rolling wastewater are closely related to product variety and process conditions.
Cold rolling wastewater, oily wastewater, and emulsion wastewater are some of the high concentration and refractory wastewater which are difficult to treat.
In order to eliminate the deformation heat in the rolling process, a large number of emulsion wastewater and oil-bearing wastewater from rolling parts such as roller and roller bearing are produced by using emulsion 17 liquid or palm oil for cooling and lubrication.
This kind of wastewater has the characteristics of large discharge, a large range of water quality change, good chemical stability, and difficult treatment. Direct emission is not only a waste but also serious pollution to the environment. Therefore, the emulsion wastewater must be treated strictly and effectively and discharged after reaching the standard.
Generally, the oil content of oily wastewater ranges from tens of milligrams per liter to tens of thousands of milligrams per liter. According to the existing form of oil, the oil in oily wastewater can be divided into the following types:
- Floating oil with a particle size of 100 μ The oil layer or oil film can be produced when it floats on the water surface;
- Dispersed oil is suspended on the water surface in the form of small drops, which are unstable and may become oil slick after a period of time. The particle size is usually kept at 10 ~ 100 μ m;
- Emulsified oil, if there is an active agent in the wastewater or the mixture after high-speed rotation, the oil droplets can become emulsions and stably dispersed in the water, the particle size is usually small, no more than 10 μ m. Between 0.1 and 2.0 μ It is difficult to achieve separation only by standing;
- Dissolved oil, i.e. oil dissolved by some chemical method, is dispersed and has a small particle size, usually within 0.1 μ Within 5 m. Because the solubility of oil in water is very small, only 5 ~ 51mg / L, so the proportion of this part is usually not more than 0.5%.
The emulsion is often used as lubricant and coolant in cold rolling, while lubricating oil is used in cold rolling of carbon steel, stainless steel, or very thin strip steel. Generally, after 2-3 months of use, it needs to be discharged and renewed to produce oily emulsion wastewater. When the cooling strip is annealed and palm oil is used, it needs to be degreased with an alkaline solution before annealing to produce alkaline oily wastewater.
The composition of the wastewater is complex, the concentration of oil is high, and it can not meet the discharge standard. The ceramic microfiltration membrane was used to treat oily wastewater. The effects of operating conditions, such as operating pressure difference, temperature, membrane surface flow rate, and feed liquid mass fraction, on membrane flux, were investigated.
However, if high-precision filter materials are used to treat wastewater directly, it will cause blockage and waste expensive filter materials, so it is necessary to pretreat wastewater.
Wedge wire screen filter is the best choice, it is not easy to block, large filtration area, low pressure.