Precise torque monitoring

All turbo machinery is subject to degradation that, over time, will affect the system’s efficiency and operational performance. Precise monitoring of turbo machinery performance with continuous torque-monitoring systems can be used to identify gradual efficiency loss, allowing a more focused maintenance scope to be developed to return the system to its optimum operation and efficiency. Torque monitoring based on heat balance, energy balance, and other methods utilize numerous parameters such as pressure, temperature, flow rate, gas composition, etc., which require precise instrumentation to properly measure with low uncertainty. [Kurz, R., Brun, K., and Legrand, D., 1999, “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.] 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 system of this type was recently installed on a cracked-gas compressor train at Qenos Olefins in Australia to determine the causes of a power limitation. The Kop-Flex Powerlign system utilizes phase displacement technology for long-term reliability, eliminating need for re-calibration. Two rings with pickup teeth are installed on a torsionally soft spacer, and are intermeshed at a central location. Two monopole sensors 180 degrees 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. Because of the intermeshed pickup teeth, the system is referred to as a single channel phase displacement system, producing two independent torque measurements. The Powerlign system will output torque, power, speed, and temperature, which can be easily integrated with any DCS system. At the Olefins plant the operating cycle of the steam-driven, cracked-gas compressor 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. The cause had long been the subject of an engineering debate between the Machinery group, Process Engineering group and Operations department. One option to add more power by upgrading the turbine power rating from 7.5 MW to 9 MW was investigated. This required a capital investment of $2 million. The plant elected to defer this investment and instead installed a torque meter at the major 8-year shutdown. The installation involved replacing the existing coupling spacer and flexible halves with a “drop-in” torque meter and integraAir Max 20K T8 Shoes