(192a) Tutorial: The Fundamentals of Dilution Steam Generator / Quench Water System Fouling

Dilution Steam Systems (DSS) separate and recover ethylene quench water from hydrocarbons, recover heat, and generate steam for pyrolysis furnaces. Dilution steam is essential to reduce hydrocarbon partial pressure, promote the formation of ethylene, reduce the formation of undesirable heavier compounds, and reduce coke formation in the furnace tubes. The DSS incorporates a number of individual functions including process water recovery, hydrocarbon stripping, and dilution steam generation. Each function is closely linked to changes in plant operation; i.e., cracking severity, feedstock, and imported or recycle streams into the plant. Typically, a DSS is comprised of the following units:

· Quench Water Tower (QWT)

· Quench Water Drum Separator (QWDS)

· Filtration, Fine Filtration, and Coalescer (DOX unit)

· Process Water Stripper (PWS)

· Dilution Steam Generator (DSG) and/or Feed Saturator

The dilution steam system reliability is extremely important when it comes to the ethylene plant’s energy balance.

The problems associated with the operation of the DSS are:

· Emulsion formation

· Fouling

· Corrosion

· Foaming

· Sodium carryover to furnaces

The paper will focus primarily on emulsions, fouling and corrosion and how to find the balance between the three through chemical, operations and mechanical means.