Higher reliability handling dirty and wet vapors: There are VRU processes where the vapors can contain of heavy hydrocarbons and high content of water vapor; using liquid ring compressors, contaminants from the vapors can become trapped in the ring-liquid. These contaminants become concentrated as the liquid continues to recirculate, eventually causes damage and reduced life to the compressor. In this case, pre-separation and even filtration systems are required to ensure the liquid ring contamination is kept to acceptable levels and needs to be constantly renewed. Twin screw MPP don’t have these sore of issues, as it uses liquids, regardless its quality, chemical composition and/or viscosity to seal and compress the vapors.
Less water usage: In the case where water is used as liquid ring, as mentioned above, the water quality tends to degrade overtime and make-up water needs to be added to the system constantly. In MPP VRU’s, the liquids needed for sealing and compression is mostly condensed water out of the vapors plus any other liquid hydrocarbon available in the stream; therefore, the requirement for make-up water in much less.
Higher temperature capability: In thermal projects, the hot emulsion tanks must be kept heated, and the vapors have high amount of water in saturated condition. To avoid liquid ring compressor performance degradation, the vapors need to be cooled down to a specific temperature range before entering the compressor. Twin screw MPP can operate at much higher temperatures without impacting performance or reliability.
Higher flexibility and stable performance: The liquid ring compressors work with fixed speed, they start and stop acting on a pressure set point at the suction; however, the actual gas volume displaced by the compressor must be controlled by constant recirculation; in addition to this, liquid ring compressors are sensitive to liquid ring flow rate fluctuations, that will affect performance when is out of the range. Twin screw MPPs motors normally run on VFDs, modulating speed to meet the suction pressure setpoint and there is not limitation to the amount of liquid handled, as it can pump 100% liquid and up to 98% gas indefinitely.
Less equipment and systems auxiliaries: Based on the differences in operational principles, to support a flexible and reliable operation of a Twin Screw MPP in VRU service, it takes less equipment, instruments, and auxiliaries than for liquid ring compressors; this increases overall system reliability, footprint and costs.