Why is inlet air filtration so important?

The inlet air pressure is also known as ambient air pressure, which varies depending on the sea level elevation of the facility. The ambient air pressure in the mountains might be 13, and near the coast it could be 14.5.

The ambient pressure is used to calculate the number of compression ratios that will be necessary to compress air to a certain pressure setpoint. A dirty inlet filter restricts the airflow, which lowers the pressure of the air before it enters the compressor.

A lower inlet pressure will increase the compression ratio, making the compressor work harder to compress the air to the pressure setpoint. This extra work generates more heat, which can lead to serious problems.

The impact is worse for a compressor producing a higher pressure than the standard 100 psi. Following are two examples from CompressorWise.com’s recent research.

Rotary example:

A 2-stage, oil-flooded rotary compressor, built for 145 psi, was installed in 2005. In March 2008, the compressor overheated, destroying the second stage airend. The root cause analysis found that a sensor failed to give a warning about a dirty air filter. The restriction reduced inlet pressure, which increased the compression ratios that generated the excessive heat that broke down the lubrication.

Here are the numbers:

The location had an ambient pressure of 14.2, which meant a total of 10.2 ratios were needed to deliver the 145 psi pressure (145 divided by 14.2). The dirty inlet air filter had reduced the inlet air pressure to 11, which meant a total of 13.2 ratios were needed to generate 145 psi (145 divided by 11).

The extra ratios generated excessive heat. This prevented the lubrication from effectively protecting the moving parts and caused the rotors to seize in the second stage airend.

Recip example:

A 2-stage reciprocating compressor operated since the 1970s, providing non-lubricated air at 150 psi. In July 2008, a high air temperature switch shut the compressor down.

The evaluation found nothing wrong with the water-cooling system or the mechanical components. The service technician solved the problem by replacing a dirty inlet air filter.

Here are the numbers:

The location had an ambient pressure of 14.5, which meant a total of 10.3 ratios were needed to deliver the 150 psi pressure (150 divided by 14.5). The dirty inlet air filter had reduced the inlet air pressure to 10.5, which meant a total of 14.3 ratios were needed to generate 150 psi (150 divided by 10.5).

The additional ratios produced enough heat for the temperature safety to shut down the compressor. This prevented major damage to the compressor, but caused production delays.

Summary

Modern compressors have sensors that monitor the inlet air filter, giving a signal when it is time to change the filter element. This works unless the warning signal is ignored or the sensor fails. This safety is useless if the compressor is old and does not have any filter monitoring sensors.

Regarding heat, users should also monitor the performance of the coolers by taking temperature readings of the inlet air, interstage air and discharge air. If a water-cooled unit is used, users also need to monitor inlet and discharge water temperatures.

The base line readings (when things are in good shape) will give users a standard to compare future readings. Watch for a change that signals the beginning of a problem.

Dirty or blocked coolers will also cause air temperatures to rise.

Any increase in temperatures should receive quick attention.

CompressorWise.com
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