October 2000

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HP Reliability: Digital control systems represent state-of-the-art

Control systems for steam turbines driving process compressors now provide many more functions beyond speed control. These systems can be custom programmed to provide whatever extent of..

Bloch, Heinz P., Hydrocarbon Processing Staff

Control systems for steam turbines driving process compressors now provide many more functions beyond speed control. These systems can be custom programmed to provide whatever extent of control is desired by the machinery end user. Integrating the turbine and compressor control functions provides many benefits, including a more responsive and capable control system, increased reliability through redundancy and a custom designed system capable of stabilizing the process during upset conditions.

In addition, an integrated system reduces the number of components required for maintenance, training and digital control systems' communication. This results in cost savings. Among the functions offered in an integrated turbine and compressor control system are:

  • Speed control
  • Extraction steam pressure / flow control
  • Inlet / backpressure control
  • Electronic overspeed trip
  • Startup sequencing (auto roll up)
  • Critical speed avoidance
  • Compressor antisurge protection / control
  • Compressor load / capacity control
  • Compressor inlet temperature control (quench)
  • Drum level control
  • Lube oil monitoring
  • Compressor seal monitoring
  • Alarm and trip functions
  • Compressor valve sequencing
  • Emergency shutdown logic (ESD).

Digital technology also provides a more complete picture of the turbine and compressor performance to engineers and operators through the use of PCs and graphic display programs. Serial and Ethernet communications transmit and receive data from external devices that can perform data logging and trending, event logging, sequence of event recording and pictorial representations of the operating data specific to the turbine / compressor train and process.

Even the compressor performance map can be displayed to the operator, along with the online performance data that pinpoint the operating point on the map. In this way, the operator literally has a picture of where the compressor is operating at all times.

Fault-tolerant, digital systems designed for high-speed control (Fig. 1) are the logical choice for true state-of-the-art plants. HP

Fig 1
 

Fig. 1. Fault-tolerant, digital control system for extraction steam turbine. (Courtesy of Woodward Governor Co., Loveland, Colorado.)

Click for enlarged view

Acknowledgment

Excerpted from Improving Machinery Reliability, 3rd Edition, 1998. This up-to-date, 680-page text was authored by HP's reliability and equipment editor, Heinz P. Bloch. You can order it from the Engineering Bookstore.

The author

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is a consulting engineer residing in Montgomery, Texas. He is the reliability/equipment editor for Hydrocarbon Processing and can be reached at hpbloch@juno.com. Note also that the above topic is the subject of a user presentation at the October 2000, International Process Plant Reliability Conference in Houston. Plan to attend and contact bjlowe@clarion.org for details.

The Author

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