Liquid Quench System on Centrifugal Compressor

[Laith Marwin]

Hello, one a refrigeration system with a centrifugal compressor one has two options for operating at reduced process loads (i.e. insufficient heat load to evaporate sufficient quantities of refrigerant).

1. To use a hot gas bypass to flow warm compressor discharge gas back to the chillers filled with refrigerant liquid and thus, "evaporate" additional mass to keep the compressor out of a surge condition.

2. To utilize a liquid quench system to inject cold liquid and utilize flash cooling of the liquid refrigerant with hot gas from the compressor discharge.

My question is simply what would be a good practice for designing the liquid quench system and refrigerant accumulator? Should there be sufficient inventory of refrigerant in the accumulator (i.e. sufficient cold liquid to inject) such that one can operate in full recycle at a low speed while keeping the flows within tolerance?

My second question is that to mechanically prove out the compressor prior to coming into full operation would one want to run the compressor in full recycle mode thus, to avoid building up heat one would need to have a constant supply of liquid refrigerant to inject to keep the temperatures in check and if so for how long?

[Magoo]

scary thought, high speed impellors and liquid droplets.
Have you considered speed control. For optimal impellor performance.
What refrigerant and what machine is envolved?.

[Laith Marwin]

scary thought, high speed impellors and liquid droplets.
Have you considered speed control. For optimal impellor performance.
What refrigerant and what machine is envolved?.

Hello, well I have a suction scrubber which will protect the machine from liquid droplets (so there is no concern there) and there is speed control (turbine engine) but like most centrifugals there is a limited operational envelope for them to operate. We are using propane for our refrigerant and based on using PH curves our optimal refrigeration cycle consists of two economizer stages.

The intent of the liquid quench system is to broaden the operational envelope (i.e. when we have lower heat duty loads). Your thoughts will be much appreciated.