LESSONS FROM THE FIELD - EJECTOR SYSTEMS
Hydrocarbon Engineering has previously reported on ejector system fundamentals, operating characteristics, and guides for troubleshooting. Moving on from that stage, the current article provides real world ejector system performance limitations uncovered during routine performance surveys. Corrective action undertaken to improve performance is documented and discussed in detail. Principles from the initial article are used as the tools to define the cause of a particular limitation and the eventual solution. It should be noted that the corrective actions described were unique to the particular problems discussed. It will not always be possible to apply the same procedure to a comparable performance problem. A review of general corrective techniques is discussed where applicable. Ejector system manufacturers should be consulted as a first course of action, and guide fixes are often possible.
Survey 1 - nylon intermediate production facility
Nitrogen gas bleed for pressure control A North American petrochemical company manufacturing nylon intermediates was operating a vacuum flasher supported by a precondenser and two stage ejector system. Overhead load from the vacuum flasher consisted of 160 000 pph (72 600 kg/hr) of mixed nitriles at a pressure of approximately 35 torr.
The precondenser produced adequate vacuum, but the two stage ejector system that extracted non-condensibles from the precondenser was performing in an unstable manner. Suction pressure of the first stage ejector was cycling between the design 35 torr and up to as high
as 75 - 80 torr.
Vacuum flasher pressure was unaffected by the ejector instability, however, plant personnel had concerns that poor ejector performance may at some point have a negative impact on vacuum flasher operating pressure....
