Reciprocating Compressor Performance Predictions: Control Methodologies from the PLC to the PC
Control of compressors is typically done with clearance pockets, speed adjustments, end deactivation, timed suction valve closings, suction throttling and bypass. Some of these methods are more likely than others to contribute to excessive pulsations. Additionally, concerns with curve crossing, net rod loads, non-reversing rod loads, high interstage temperatures and pressures, low volumetric efficiencies, blank-off, and stage throttling can quickly arise. As such, more demanding methods for control must be employed. Today's advanced PLCs can handle the requirements for today's newer, more robust and exacting control methodologies. This paper will cover theoretical predictions for BHP and flow for single and multistage compressors, implementation of those methods into PLCs with minimal coding, and methodologies for using real-time measured BHPs and flows to fine-tune the theoretical predictions. Various software packages will be employed to assist in the learning of these processes, as well as spreadsheets to indicate the simplicity of the algorithms going into the PLCs, including flow balancing and gas compressibility algorithms, valve loss and parasitic loss horsepowers, and flow slippage. Finally, results of some recent implementations into PLCs will be presented.