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Maximize steam unit performance with precise torque monitoring

05.01.2013  |  Mayne, T. ,  Qenos Olefins Australia, Melbourne, AustraliaEllul, M. ,  Qenos Olefins Australia, Melbourne, AustraliaPhillips, D. ,  Emerson Industrial Automation, Hanover, Maryland


All turbomachinery is subject to degradation that, over time, will affect the system’s efficiency and operational performance. Precise monitoring of turbomachinery performance with continuous torque-monitoring systems can be used to identify gradual efficiency loss, allowing for the development of a more focused maintenance scope to return the system to its optimum operation and efficiency.

Torque monitoring based on heat balance, energy balance and other methods utilizes numerous parameters such as pressure, temperature, flowrate, gas composition, etc., which require precise instrumentation to measure with low uncertainty.1 However, phase displacement technology can be used to accurately measure torque directly at the coupling to within 1% of full-scale torque, a combination of all electrical and mechanical sources of error. This accuracy provides the lowest amount of uncertainty when computing efficiency, compared to alternative methods.

A torque-monitoring system was recently installed on a cracked-gas compressor (CGC) train at Qenos Olefins in Australia to determine the causes of a power limitation. The torque-meter coupling utilizes phase displacement technology for long-term reliability, eliminating the need for recalibration.

Torque meter installation

The meter consists of two rings with pickup teeth installed on a torsionally soft spacer and intermeshed at a central location. Two monopole sensors 180° apart are mounted on the coupling guard. As the coupling rotates, the ferromagnetic teeth create an AC voltage waveform in the sensor coil, which is digitally processed using known calibration parameters. Due to the intermeshed pickup teeth, the system is referred to as a single-channel phase displacement system, producing two independent torque measurements (Fig. 1). The system will output torque, power, speed and temperature, which can be easily integrated with any DCS system (Fig. 2).

    Fig. 1.  The torque-meter coupling produces
  two independent torque signals.

  Fig. 2.  Typical output from the torque-meter coupling.

At the olefins plant, the operating cycle of the steam-driven, CGC train is 7–8 years. During this cycle, the plant reaches production limitations because this compressor train encounters a power limit. To determine the cause of the power limit as “turbine fouling” or “compressor fouling”—or a combination of both—was not confidently possible with the instrumentation installed.

One option was investigated to add more power by upgrading the turbine power rating from 7.5 MW to 9 MW. This required a capital investment of $2 million. The plant elected to defer this investment and, instead, a torque meter was installed during the major eight-year shutdown.

The installation involved replacing the existing coupling spacer and flexible halves with the “drop-in” torque meter’s integral flexible elements. The torque meter assembly was dynamically balanced to API standards, so it was not necessary for the user to return any coupling components for the retrofit. The coupling guard was modified so that the two variable-reluctance sensors could be installed, completing the mechanical installation (Figs. 3–5).

  Fig. 3.  Completed mechanical installation
  at Qenos Olefins.

  Fig. 4.  Torque-meter coupling retrofit
  at Qenos Olefins plant.

  Fig. 5.  Existing coupling arrangement (top)
  and retrofitted torque-meter coupling (bottom).


On restarting the plant and having completed a number of compressor efficiency improvements, the torque meter clearly showed that the 7.5-MW turbine did not require an uprate and that the major power losses were coming from the CGC. The torque meter also allowed online tuning of the seal gas system of the compressor to establish the lowest power draw from the recycles that the seal system introduces. An additional 200 KW of power was reduced from the turbine load, with the manual adjustments made on the seal gas system.

The torque meter is now being used to monitor turbine steam-fouling issues and process-related compressor fouling so that corrective online washing can be activated as soon as issues arise.

The historical data collected from the torque meter will also provide a baseline of mechanical loading through the drivetrain of the CGC over time. This data will be used to determine if increases in the maximum continuous operating speed rating of the compressor and the turbine can be accomplished at minimal costs. This would achieve increases in the operating envelope of the compressor.

Furthermore, the value of the torque meter justified the installation of a second system for the olefins plant’s second steam-cracking plant turbine/compressor train in October 2012. HP


1 Kurz, R., K. Brun and D. Legrand, “Field performance testing of gas turbine-driven centrifugal compressors,” Proceedings of the 28th Turbomachinery Symposium, Turbomachinery Laboratory, Texas A&M University, College Station, Texas, pp. 216–220, 1999.

The authors 
  Daniel Phillips is the field service engineering manager for Emerson Industrial Automation’s Kop-Flex brand of couplings in Baltimore, Maryland. He assists users with installation, commissioning and troubleshooting of power transmission products. Mr. Phillips has extensive experience with applying torque-monitoring solutions to increase the reliability and efficiency of equipment in the metals and oil and gas industries. He has a BS degree in mechanical engineering from the University of Maryland, Baltimore County, and he has 10 years of experience in the mechanical engineering field. 

  Mark Ellul has worked in Qenos Olefins Australia’s olefins refinery for 30 years as an instrument and electrical specialist. He has coordinated field maintenance activities and worked in the process and control applications group. Mr. Ellul has also been assigned to major rotating machinery instrument upgrade projects. 

  Trevor Mayne is the lead machinery engineer for Qenos Olefins Australia’s olefins refinery. He has worked with rotating equipment in the olefins refinery and in the plastics and synthetic rubber plants over the last 20 years. Mr. Mayne has held positions in reliability and in field maintenance, both at Qenos Olefins Australia’s Altona plant and in Saudi Arabia with ExxonMobil. 


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