To produce polymer-grade ethylene and propylene, a butadiene rich C4 cut, an aromatic C6 – C8 rich-raw pyrolysis gasoline and high-purity hydrogen by using the T-PAR process for gas separation and product purification from raw cracked gas.
Effluents from cracking furnaces are cooled and processed for tar and heavy-gasoline removal. A multistage compressor, driven by a steam turbine, compresses the cooled gas. LP and HP condensates are stripped in two separate strippers where medium gasoline is produced and part of the C3+ cut is recovered respectively. A caustic scrubber removes acid gases. Compressed gas at 450 psig is dried and then chilled. A multistream heat exchanger chills the tail gas to – 265°F. Liquid condensates are separated at various temperatures, such as – 30°F, – 65°F, –100°F and –140°F, and are reheated against incoming cracked gas. The partially vaporized streams are sent to a deethanizer stripper operating at about 320 psig. The bottoms C3+ stream is sent to propylene and heavys recovery.
The overhead is reheated and enters an adiabatic acetylene hydrogenation reactor, which transforms the acetylene selectively to ethylene and ethane. As an alternate, a solvent-recovery process can be applied without reheating the gas.
Reactor effluent is chilled and light-ends are separated from the C2-hydrocarbons. The demethanizer overhead is processed for ethylene recovery while the bottoms is sent to ethylene/ethane separation. An open heat-pump splitter is applied, thus sending ethylene product to the gas pipeline from the discharge of the ethylene-refrigerant compressor. Dilute ethylene for chemical applications, such as styrene production, can be withdrawn downstream of the hydrogenation reactor. The ethylene content is typically 60 vol%. Catalyst suppliers have tested the hydrogenation step, and commercially available front-end catalysts are suitable for this application.