Isobutylene Liquid Transfer/Vapor Recovery Compressor Package

S&S Technical was approached to manufacture a compressor package that would be used to transfer Isobutylene from railcars to storage. Because Isobutylene is a liquefied gas and transported in pressurized railcars, a compressor is typically used for the application. The compressor system is designed to draw Isobutylene vapors from the storage vessel, compress the vapors and push them to the vapor space in the railcar. This creates a pressure differential between the railcar and storage vessel causing the liquid to flow from the railcars to the storage vessel.

Isobutylene Liquid Transfer:Vapor Recovery Compressor Package

For this application, a Corken FT691 compressor was selected. The FT691 is a single-stage, triple-packing, oil-free, reciprocating compressor. This unit was outfitted with a packing purge kit which provides zero-emission operation by passing nitrogen through the distance pieces, aiding in packing actuation and removing and gas that has potentially leaked past the packing.

The packaged system includes an automated 4-Way valve that allows the operator to select the liquid transfer operation or vapor recovery operation – used to recover the transfer vapors from storage during the liquid transfer phase. This ensures the customer is receiving all of the product in each railcar which is not possible when using a pump on a pressurized railcar due to the top emptying design. Also included is an ASME suction scrubber with pressure relief valve, drain valve and two liquid level switches – one for alarm and the other for shut-down. The compressor is protected using United Electric J120 pressure switches and a B121 temperature switch.

Our design team included a fully automated PLC control panel that monitors the compressor suction and discharge pressures, oil pressure, discharge temperature as well as the liquid level in the suction scrubber and provides the user the ability to remotely start and stop the compressor and receive remote alarm/shut-down indication.

For more information on this compressor system please feel free to contact Jim Zuccarell at

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