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Linsheng - Influence Of Intake Conditions On Centrifugal Air Compressor

Update:18-11-2019
Summary:

Linsheng   - The     Air Compressor Suppliers     here […]

Linsheng   - The     Air Compressor Suppliers     here outlines how various air intake conditions affect the performance of the centrifugal air compressor.

 

Environmental parameters affect centrifugal performance
CABP: Can you clarify how the intake conditions affect the performance of a centrifugal compressor system?

CAGI: Centrifugal technology is based on dynamic compression. In a dynamic compressor, air is drawn in between the blades of a rapidly rotating impeller and accelerated to high speed. The air is then discharged through a diffuser where kinetic energy is converted to static pressure. Most dynamic compressors are turbo compressors with axial or radial flow patterns and are designed for greater volumetric flow rates.

The performance of dynamic compressors is highly dependent on environmental conditions. We will explain the effects of different environmental parameters and their impact on performance below. When considering the investment in a centrifugal compressor, the annual limit and average conditions must be considered when determining the size of the equipment for optimum performance.

The environmental parameters that affect performance are:

Inlet temperature
Inlet pressure
Relative humidity
Cooling water temperature

CABP: How does providing an understanding of how these parameters affect performance?

CAGI: To understand the impact of these parameters, we first need to look at the performance curve of the dynamic compressor and observe how changes in environmental parameters affect performance.

 

Inlet temperature
The inlet temperature of the air affects the density of the air at the compressor inlet and affects the kinetic energy transferred from the blades to the air. The increased density at lower intake temperatures will result in higher free air delivery (acfm) and higher power consumption of the compressor.

Another effect of changes in air or gas density is the available adjustment ratio of the compressor. Within this flow range, it can be effectively adjusted by using a throttle or intake guide vanes. The lower the temperature, the larger the adjustment range.

 

Changes in inlet temperature can cause large changes in performance. If the size of the drive provides the extra power required, the centrifugal centrifuge can deliver more air in cold weather than in warm weather.

Lower inlet temperature:

Increase surge pressure.
Increase the maximum capacity (weight flow) at a given discharge pressure.
Increase power consumption (horsepower).

 

Higher inlet temperature:

Reduce surge pressure.
Reduce the maximum capacity (weight flow) at a given discharge pressure.
Reduce power consumption (horsepower).

The parameters mentioned have a similar effect on compressor performance.

 

Inlet pressure
A decrease in inlet pressure will reduce the density of air at the compressor inlet. As the temperature increases, this will result in a reduction in free air delivery and power. Variations in inlet filter fouling or pressure can cause inlet pressure changes. The same is true for the available regulators - a lower intake pressure will result in a smaller available regulator.

Lower inlet pressure:

Reduce discharge pressure along the entire curve.
Reduce the maximum capacity (weight flow).
Reduce power consumption or horsepower (due to reduced weight flow).

 Relative humidity (RH)
An increase in relative humidity (RH) reduces flow and power, while a decrease in RH increases flow and power. Adding water vapor to the air will humidify the air and reduce the air density. This is because the molar mass of water is less than the molar mass of air.

Higher relative humidity:

Reduce the discharge pressure during surge.
Reduce the maximum flow (weight flow).
Reduce the flow of surges.
Reduce power consumption (horsepower).
At high humidity, higher condensate loss results in reduced flow to the plant air system.

 

Cooling water temperature
The cooling water temperature will affect the intake air temperature of the second stage and any other stage (if present). Colder water increases flow and power, while hotter water reduces flow and power.

CABP: So, how do you recommend taking this into account when choosing a centrifugal compressor size?

CAGI: To determine the size of a centrifugal compressor, you should consider the flow pattern of the user's job site and consider the on-site intake conditions (min/average/height) for optimum performance.

Another important consideration is the size of the motor. If the motor/driver is selected based on performance at lower inlet temperatures, it will ensure that the motor has sufficient power to ensure increased flow even at lower inlet temperatures. Customers can take advantage of the increased flow provided by their compressors.

The cooling water temperature will affect the performance of the compressor stage after the first stage. The performance impact is similar to the intake air temperature. Of course, this is true because the temperature change of the cooling water will directly affect the temperature of the air entering the second, third and subsequent stages, and there is an intercooler between the second, third and subsequent stages.

Lower cooling temperature:

Increase the discharge pressure.
Increase the maximum capacity (weight flow).
Increase power consumption (horsepower).

Higher cooling water temperature:

Reduce discharge pressure.
Reduce the maximum capacity (weight flow).
Reduce power consumption (horsepower).

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