The separation train of a cracker starts with the hot section where the cracked gas is quenched and cooled down, and heavy fractions are condensed and separated. Thereafter, the process steam is condensed and removed and the cracked gas is dried before it enters the compression section. The compression is typically done in four to five stages up to a pressure of approximately 36 bar.
The compressed cracked gas is separated into the C2 minus fraction, which is routed to the cold section for further separation, and the C3+ fraction. C2 minus and C3+ fractions are separated in sequences into the specified products. Thereby, unwanted impurities like acetylene and methylacetylene / propadiene are hydrogenated to ethylene and propylene. Pyrolysis gasoline requires also hydrogenation in order to match market specifications.
Some fractions (e.g. ethane, propane and butane / butenes) are recycled to the furnaces in order to improve overall yields.
The separation train of an olefin pant is a very complex process sequence that is optimised with respect to investment and energy consumption. The exact configuration is depending on feedstock and products in a particular project.
Linde Engineering is most successful among the few technology contractors for steamcrackers worldwide.