Emulsion breaker programmes to provide fast oil/water separation.
Ethylene is mainly produced by stream cracking. This process includes thermal cracking, cooling, compression and separation. Hot cracked gases are immediately quenched in oil quench and water quench columns. The purpose of the cooling is to prevent polymerisation and formation of unwanted byproducts. The water quench column operates at low-pressure drop. The residual heat of the pyrolysis gas is recovered through absorption in hot quench water. In the oil/water separator, the hydrocarbons are removed from the quench water. The quench water from the oil/water separator is split with some being recirculated back to the water quench column.
Often the separated quench water still contains higher amounts of soluble and insoluble oils. Emulsification of hydrocarbons and water in the quench water can cause difficulties. Poor oil-water separation can result in sporadic loss of quench water. Negative impacts are level problems, fouling and corrosion of downstream equipment. Particularly affected are quench exchangers, the DSG system and process water stripper. Some plants install specially designed DOX units (Dispersed Oil Extractor). It is a skid-mounted system for oil-water separation. The emulsified oil and suspended solids are extracted from quench water. DOX units are designed to remove hydrocarbon concentrations down to 20 ppm or less. Emulsification problems may require a change out of DOX filter media.
A capable demulsifier programme can be applied to improve the separation of hydrocarbons and water. An overdose of the demulsifier should be avoided. The emulsion breaker additives have surfactant properties. They may have the tendency to act as an emulsifier at very high concentrations. A perfect demulsification can readily be recognised by visual inspection. Emulsified quench water´s appearance will vary from slightly hazy to milky/hazy.
In most cases, a demulsification of oil-in-water emulsions is required. Kurita provides high-performing demulsifier programmes. The hydrocarbons generally carry a negative charge at their surface. Hydrocarbons are steadily dispersed into small droplets because of their repellent forces. A cationic charged demulsifier programme neutralizes the negatively charged oil droplets. The repellent forces are weakened and oil droplets are brought together. The demulsifier resolves the emulsion of water and oil. Our emulsion breaker additives accelerate the demulsification process. The oil-water separation involves three steps:
1. Agglomeration is the association of small dispersed phase droplets (clusters).
2. Creaming is the concentration of the dispersed phase.
3. Coalescence is the drainage of oil droplets, collected at the surface.
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