Process streams in ethylene units contains acid gases, like carbon dioxide and hydrogen sulfide, as a result of cracking and coking/decoking reactions in the furnaces. The acid gases are typically removed in the caustic tower, which is integrated into the charge gas compressor. Other components, like aldehydes and ketones, are present as contaminants in the cracked gases and can polymerize under basic conditions to form aldol condensation polymer. The polymer can deposit on the internals of the caustic column and in the downstream spent caustic process like tankage, caustic stripper and/or wet air oxidizer. The fouling can have a huge impact on the overall plant performance.
The fouling has a significant effect on the efficiency and reliability of the caustic column operation and is heavily affected by operational process parameters. A global benchmarking study identified the most important parameters such as temperature profiles, caustic strengths, and aldehyde content. The process conditions were then simulated in the laboratory to better quantify their impact on polymer formation.
A new analytical method was also developed for quantifying the red oil polymer during the laboratory work and the results favorably compared with the traditional manpower-intensive analytical method (polymer extraction with solvent). The new method has now been deployed to the field, where it reduces the analysis time from several hours to minutes and has shown to be very accurate.
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