Inlet Guide Vanes (IGVs) and Inlet Butterfly Valves (IBVs) perform an important task—to regulate the airflow and pressure that enters a centrifugal compressor’s first stage of compression. Historically, IBVs had been the industry standard for centrifugal compressors. However, in the last twenty years, the IGV has come to the forefront as an option providing additional energy saving benefits.
The IBV directs the airflow into the first stage of compression in a straight line. The impeller then spins the air using power from the main driver, increasing air velocity and directing the flow into the diffuser portion of the compressor. When partially throttled, the IBV reduces the inlet pressure, wasting some of the available static pressure. The pressure ratio of the overall compressor now needs to be greater in order to meet the same discharge pressure.
Unlike the IBV, the IGV has multiple triangular-shaped vanes that allow the air to flow into the compressor in a swirl direction. The “pre-swirled” air reduces the amount of work needed from the main driver to spin the air entering the impeller. The directional flow increases as the vanes close, putting less stress on the impeller in comparison to an IBV, because of this inlet guide vanes are more efficient during turndown than inlet butterfly valves.
The main benefit of updating from an IBV to an IGV is the energy conservation gained from throttling the compressor. Compressors are designed to operate at the highest ambient temperature conditions—so when the temperature is lower, the ability to throttle extra air is paramount.
IGVs can save even more energy when the compressor is running at a throttled angle, which offers considerable brake horsepower (BHP) savings. The following chart demonstrates a compressor operating with a throttled IBV at 72% of the design flow, which has a power consumption of 72%. Under the same conditions, a compressor operating with a throttled IGV at 72% of the design flow, which now has a reduced power consumption of 63%. The result is up to 9% BHP savings when comparing the IBV and IGV.
Contact your local authorized FS-Elliott Channel Partner Representative to find out how an IGV upgrade may improve your operating costs.