How Problems with Higher Stages of Compression can affect your Overall Production Throughput

By January 10, 2019 Tech Tip No Comments

It is obvious that an inefficiency of your first stage of compression can greatly hinder your production, but have you ever wondered how problems with your later stages of compression can negatively affect your overall throughput?

To answer this question, let’s look a little more closely at the math behind the flow rate calculation that Detechtion uses in the Enalysis compressor diagnostic report.

Flow Rate = Piston Displacement x Volumetric Efficiency

where Piston Displacement represents the geometry of your cylinder and engine speed and Volumetric Efficiency represents the thermodynamic conditions of your compression such as temperature and pressures as well as clearance and gas composition.

VE2As you experience a problem in the later stages of compression, the problematic cylinder begins to require a higher suction pressure in order to maintain the flow rate of its previous stage counterparts.

This increase in suction pressure translates to a similar increase in the discharge pressure of the previous stage, effectively increasing the compression ratio of that previous stage.

If we look at the Volumetric Efficiency calculation, we can see that an increase in Compression Ratio inversely affects volumetric efficiency.  The higher the compression ratio, the lower the volumetric efficiency:

Volumetric Efficiency = 1.00 - L - (CL/100) [Zs/Zd (Compression Ratio)1/k - 1]

And as volumetric efficiency is reduced, as will the flow rate of that cylinder as well:

Flow Rate = Piston Displacement x Volumetric Efficiency

Volumetric Efficiency

This negative effect is most evident in the immediately previous stage but does have a cascading effect as we move to earlier stages.  In other words, the previous stage takes the brunt of the effect, but this phenomenon does have a ripple effect until we get to the first stage of compression.  The same can be said about a growing interstage restriction.  A plugged up cooler or filter device will effectively raise the discharge pressure of previous stage, once again raising the compression ratio of that stage unnecessarily and hindering the volumetric efficiency accordingly.

If you have any questions about your compression, please feel free to reach out to your engineer at Detechtion Technologies.