How do compressor guide vanes work?

The inlet guide vanes are the passages designed at the entry of a compressor inlet. The dotted lines in the above illustration indicate these inlet guide vanes. In essence, these guide vanes function as blades that are integrated into the casing. But what advantages do these passages provide?

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When gas enters the compressor, it does so with high velocity and turbulence. The guide vanes effectively streamline the gas flow through distinct passages. If gas were to enter a large open area without guidance, it would remain turbulent. However, with the presence of inlet guide vanes that restrict the cross-sectional area for the gas to enter, the turbulence diminishes, allowing for the conversion of this kinetic energy into gas pressure. This process ultimately enhances the compressor's efficiency.

Another critical role of these guide vanes is to regulate the gas flow into the compressor. By adjusting the position of the inlet guide vanes, we can either reduce the gas flow into the compressor (by closing the vanes) or increase it (by opening the vanes).

Inlet Guide Vanes (IGVs) and Inlet Butterfly Valves (IBVs) are crucial components that regulate the airflow and pressure entering the first stage of a centrifugal compressor. Traditionally, IBVs have been the norm for centrifugal compressors.However, over the past two decades, IGVs have emerged as a preferred option due to their significant energy-saving benefits.

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Inlet Butterfly Valve Function

The IBV directs airflow into the compressor's first stage of compression in a straight line. The impeller spins the air, powered by the main driver, increasing its velocity and directing it into the compressor's diffuser section. When partially throttled, the IBV reduces inlet pressure, which can waste some available static pressure. Consequently, for the same discharge pressure, the overall compressor must now maintain a greater pressure ratio.

Inlet Guide Vane Function

In contrast to the IBV, the IGV comprises multiple triangular-shaped vanes, which allow air to enter the compressor in a swirling motion. This 'pre-swirled' air minimizes the workload on the main driver by facilitating air entry into the impeller. The directional flow increases as the vanes close, exerting less strain on the impeller compared to an IBV. Hence, inlet guide vanes are more efficient during lower operating conditions than inlet butterfly valves.

Manufacturing Benefits of Upgrading to an IGV

One of the primary advantages of transitioning from an IBV to an IGV is the energy conservation achieved by throttling the compressor. Compressors are engineered to function optimally under high ambient temperature conditions, making the ability to throttle excess air critical when temperatures drop.

IGVs can further enhance energy savings when the compressor operates at a throttled angle, resulting in significant brake horsepower (BHP) reductions. The following chart demonstrates a compressor running with a throttled IBV at 72% of the design flow, consuming 72% power. In contrast, the same compressor operating with a throttled IGV at the same flow rate consumes only 63% power, leading to roughly 9% BHP savings in comparison.

Is an IGV Right for Your Centrifugal Compressor?

Reach out to your local authorized FS-Elliott Channel Partner Representative to discover how an IGV upgrade may contribute to lowering your operating costs.

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