Pretreatment process for oily watewater of cold rolling mill

Abstract

The invention relates to a process for pre-treating wastewater containing oil of a cold rolling mill, which solves the problems of poor demulsification effect, high investment, high energy consumption, low recovery rate of waste oil, mass waste residue generation and substandard treated effluent existing in the prior process for pre-treating wastewater containing oil of the cold rolling mill. Recycling of waste oil can be realized through acidification demulsification, oil reclaiming treatment, re-demulsification treatment, flocculation treatment and air floatation separation by steam introduction and the acidification demulsification, so that reclamation rate of the waste oil is improved, energy consumption and investment are reduced, the amount of the waste residue is small, and each index of the pretreated wastewater can be reduced to meet the requirement of secondary treatment so as to greatly reduce the load of the secondary treatment.

Description

technical field [0001] The invention relates to a wastewater treatment process in the metallurgical industry, in particular to a pretreatment process for oily wastewater in a cold rolling mill. Background technique [0002] The oily wastewater from cold rolling mainly comes from the rolling mill unit, roll room, strip degreasing unit, skin pass unit, and oil depot drainage of each unit. It is one of the most difficult wastewater to treat in the steel industry. According to the shape and separation characteristics of oil, oily wastewater can be divided into floating oil, dispersed oil, emulsified oil, dissolved oil and oil two solids. Among them, the emulsified oil is milky in the sewage, and the particle size of the oil droplet is generally 0.1-25 μm. The surface of the oil droplet is wrapped with a negatively charged hydration film. It remains stable for a long time and is difficult to separate by mechanical means. The main characteristics of oily wastewater from rolling ...

AI Technical Summary

Problems solved by technology

The biggest disadvantage of using this method to treat oily wastewater is that the quality of the effluent after treatment is unstable and often does not meet the standard, and the application effect in major domestic iron and steel enterprises is not satisfactory.

The main reason is that the emulsion oily wastewater with high degree of saponification and long molecular chain will block the surface of the ultrafiltration membrane, so that the ultrafiltration cannot continue, so the soluble COD cannot be removed.

At the same time, the method occupies a large area and requires high investment.

(2) The chemical pretreatment process represented by demulsification usually adopts one-time chemical demulsification plus air flotation treatment, and the treatment effect for high-concentration cold rolling oily wastewater is not ideal, mainly because (1) the concentration of this type of oily wastewater If the temperature is too high, the ideal treatment effect cannot be achieved by only relying on the commonly used demulsifier (such as polyaluminum, etc.) for one demulsification; (2) The temperature of oily wastewater is low, generally lower than 60 ° C, which will affect the demulsification of oil. precipitation

After this pretreatment process, the oil content of oily wastewater can be reduced to 30mg / L at most, COD Cr The maximum reduction is 2000mg / L, thereby increasing the secondary treatment load, seriously affecting the secondary treatment effect, and directly causing the wastewater discharge to fail to meet the standard

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