Modeling and Control

A compressor going into stall is like jumping off a cliff with a bungee cord. If the bungee cord has no losses to dampen the oscillation, we have something akin to surge. A 0.5% drop in efficiency can occur for each surge cycle. Several surge cycles can occur due to delays and lags in high …

Part 1 of the centrifugal compressor efficiency series addressed the measurements and parameters that are used to calculate compressor efficiency. In Part 2 of this series we examine how these measurements are used to calculate the enthalpy of the gas stream at the compressor suction and discharged for the refrigerant R134a. This calculation utilized bilinear …

We conclude with a summary on how you can avoid bursts of oscillations, get to setpoint faster, choose the right execution time and filter, coordinate the speed of loops, optimize operations without while protecting equipment, provide a consistent flow response for model predictive control, eliminate limit cycles, and improve analyzer and wireless control loops (all …

As addressed in Part 1 of the centrifugal compressor efficiency series, the enthalpy of the gas stream at the compressor suction and discharge must be known to determine the compressor efficiency. Also, the isentropic enthalpy must be determined based on the gas stream entropy at the compressor suction and the compressor discharge pressure. These properties …

To support the check list in part 8 to get the most out of your PID, we offer some of the considerations in the use of PID features. The number of PID options and parameters can seem overwhelming at first. Hopefully the knowledge gained here will foster an appreciation of the flexibility and capability leading to a …

Centrifugal compressors play an important role within the process industry. In some cases compressor capacity may determine the throughput of a plant. If a compressor is used for refrigeration then any variation in compressor operation may directly impact the temperature control in key unit operations such as flash vessels and exothermic reactors. Also, the compressor …

The missing piece for success is the center piece of the loop, the PID controller. There is an incredible offering of PID features and options. To help utilize the full potential of the PID, here is a check list as a guide. While the full aspects of the PID capability are book worthy, the following …

In June, 2100 the International Electrotechnical Commission (IEC)  distributed a new project proposal 65E/199/NP, Devices and integration in enterprise systems; Field Device Integration (FDI) – Part 1 to 7. Voting on this proposal was completed in October, 2011 and the new project was approved. Within IEC the SC65E WG7 committee will address converting the draft FDI …