Propane-Propylene Splitter (PPS)

The Propylene Splitter unit, Unit 18, produces dry propane and propylene products (petrochemical feedstock) from a mixed propane / propylene feed stream. The feed is the Propane / Propylene mix production from the #1 and #2 Fluid Catalytic Cracking units, with makeup being supplied from storage. The unit has a design capacity of 1,300 BPSD. The Propylene Splitter consists of a molecular sieve drier and fractionator columns, containing 150 sieve-type trays. The large number of separation trays is necessitated due to the very close boiling point temperatures of the propane and propylene. In this unit the use of a single very large tower is avoided by utilizing two separate towers each with 75 distillation trays – effectively a stripping section and a rectifying section.

The feed stream is dried in the molecular sieve drier section, preheated against propane product and then charged into the top of the stripper column. Propane is withdrawn as product from the bottoms of the stripper column. The stripper is reboiled by 150 psig/steam. The overheads from the stripper column feeds directly into the rectifying column. The bottoms from the rectifying column also feeds directly back to the top of the stripper column. The rectifying column has a total condensation overheads system and the propylene is drawn as a sidedraw product from close to the top of the rectifying section column. Propylene is sold as a petrochemical feedstock for the production of plastics.