PACE Zenith Awards 2013: Oil & Gas category sponsored by AMS Instrumentation & Calibration
WINNER: Qenos – Altona Olefins
Project: Torque monitoring system for steam-turbine powered cracked-gas compressor
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 a more focused maintenance scope to be developed to return the system to its optimum operation and efficiency.
Australia’s sole manufacturer and supplier of polyethylene, Qenos, worked with Emerson Industrial Automation and supplier Rolling Bearings to deploy a torquemeter at its Alton Olefins site in order to diagnose the cause of a power loss in a steam-driven cracked-gas compressor train, and enable further tuning of the seal gas system on the compressor, to reduce turbine load.
The Qenos Altona Chemical Complex began production in the early 1960s and is the largest production centre for petrochemicals and plastics in Australia today. The Altona site covers 103 hectares and is located approximately 15 km west of the Melbourne central business district.
Within this complex, the Olefins plant produces ethylene for the company’s downstream plastic plants. It also supplies other manufacturers that use these basic raw materials. It has an ethylene capacity of more than 180,000 tonnes per year.
At the Altona Olefins plant, the operating cycle of the steam-driven, cracked-gas compressor train is 7 to 8 years. However, during this cycle the plant reached its production limitations because the compressor train encountered a power limit.
This power limit was not easy to diagnose. The cause had long been the subject of an engineering debate between the Machinery group, Process Engineering group and Operations department. Some thought it was due to compressor fouling, while others held turbine inefficiency to be the problem. Existing installed instrumentation did not provide the answers needed.
One proposal was to upgrade the turbine from 7.5 MW to 9 MW at a cost of $2 million. However, during one of the system's 8-year shutdowns, the company installed an Emerson Industrial Automation Powerlign torquemeter coupling.
Mike Elliott (R), NSW Sales Manager, AMS Instrumentation & Calibration congratulates winners Trevor Mayne (L) and Mark Ellul of Qenos.
The Kop-Flex Powerlign torquemeter from Emerson Industrial Automation utilises phase displacement technology for long-term reliability, eliminating need for re-calibration. Traditional torque monitoring based on heat balance, energy balance, and other methods utilises numerous parameters such as pressure, temperature, flow rate, gas composition, etc., which require precise instrumentation to properly measure with low uncertainty.
In contrast, phase displacement technology, like that used in the Powerlign torquemeter, can be used to accurately measure torque directly at the coupling to within one percent 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.
The installation of the torquemeter involved replacing the existing coupling spacer and flexible halves with a “drop-in” torquemeter and its integral flexible elements. Two rings with ferromagnetic pickup teeth are installed on a torsionally soft spacer, and intermeshed at a central location. Two monopole sensors 180 degrees apart are mounted on the coupling guard.
The torquemeter 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.
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 outputs torque, power, speed, and temperature, which can be easily integrated with any DCS system. On restarting the plant and having completed a number of compressor efficiency improvements, the torquemeter clearly showed the 7.5 MW turbine did not require an uprate and that the major power losses were coming from the compressor.
This saved the hassle and cost of a turbine upgrade. The torquemeter is now being used to monitor steam-turbine fouling issues and process-related compressor fouling for timely activation of online washing. Ultimately, data collected on the baseline loading of the drivetrain will help determine if the maximum continuous speed rating of the system can be increased. Data from the torquemeter may allow the system to reach potentials previously unimagined.
The torquemeter 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.
In awarding the win, PACE Zenith Awards judges said that the retrofitting of a torquemeter in a cracked gas compressor train at Qenos – Altona Olefins allowed monitoring of compressor efficiency and early corrective action and avoided major capital expenditure.
The 2013 PACE Zenith Oil & Gas Awards are sponsored by AMS Instrumentation & Calibration.
Read more: AMS Instrumentation and Calibration helps end-users optimise their processes and performance
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