An onshore field Central Processing Facility (CPF) separates crude oil from water and associated gas. Stabilised oil is exported by pipeline; water re-injected. Export gas is dew-pointed (refrigeration). De-ethanised condensate is exported via pipeline.
An add-on unit will process part of the C3+ condensate to meet a local LPG requirement of up to 100 metric ton per day.
Product LPG would be loaded onto trucks and the rejected C5+ recombined with the main export condensate.
LPG specifications are butane / propane volume ratio between 70/30 and 75/25. Ethane and pentanes plus contents are both below 2% vol.
Concept screening criteria of simplicity and low cost favoured a single column process over alternatives. Condensate composition varies with time; later life composition with lower butane-propane ratio and product compositions with higher butane- propane ratio requiring more separation energy than other cases.
An unexpected result - increasing feed rate reduces the required reboiler duty, up to a point, for each case. Beyond this optimum feed rate the duty and hence vapour traffic and column diameter increase.
To seek a better fundamental understanding of this phenomenon, it was investigated using Exergy analysis.
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