A client in India installed three units of C-45.4 reciprocating compressors, in which two were running and one was standby.
A few weeks after installation, there was a failure on a driver fan of two running machines, which was repaired by replacing the original fan with the new designed one.
Those two machines have worked well since then without any failures recorded. Couple of years later, the client replaced the capacity control system of the third machine by a so called HydroCOM system, the same driver fan failure re-occurred.
Referring to the previous experiences, the client replaced the fan with the new design as they did before. However, the driver fan kept on failing.
After several costly replacements, Howden Thomassen Compressors, as an OEM of those compressors, was contacted to conduct a feasibility study, aiming to review and solve the fan problem, at the same time to give advice on what can be done to combine those three units with the usage of HydroCOM system, while maintaining the existing equipment as much as possible.
The study consisted of different performance checks and unique calculations provided by HTC regarding the impact of HydroCOM system in the operation of those three units.
The study result showed that the natural frequency of HydroCOM system coincided with the natural frequency of the external fan, of the main driver, which was the main reason causing the fan to break.
The solution, therefore, was simply pointed out, which was changing the natural frequency of either the main driver, or the whole drivetrain.
After consideration and further calculations on torsional analysis, changing the frequency of the drivetrain was proven the most feasible comparing to other options.
A heavier flywheel was applied to replace the existing barring wheel in the compressors, which helped to move the natural frequency of the fan out of the coincidence with the natural frequency of the external fan.
By doing that, the natural frequency of those components would not amplify and the fan was prevented from cracking.