Rockwell Automation won the tender to upgrade compressor systems at Harmony Gold Mining Co’s No. 7 and 8 shafts in Evander, South Africa in mid-2010. The upgrade was the result of the mine’s optimisation strategy in Evander and its drive to do so in the most energy-efficient way possible. According to Riccardo Fachin, Rockwell’s Systems & Solutions Business Project Manager, saving energy with compressors is not an often used solution in industry, and this was a unique project to showcase its possibilities.
“We held discussions with Harmony’s Electrical personnel on what extra equipment should be installed with the view of measuring and reporting energy usage and eventually, savings,” explains Fachin.
The No.1 compressor is a 1987 Demag VK 32C with a discharge pressure of 6.7 bar and an inlet of 35,000 m3/h, and the synchronous motor 2,900 KW 6,6KV needed an upgrade on the electrical MV switchgear, as well as the control system.
“The mechanical upgrade essentially consisted of new electrically controlled inlet and outlet vane valves for surge control. The electrical upgrade consisted of new 6.6kV switchgear, but we reused the oil cooled reactor starter.”
Automatic solid state DC excitation was accomplished on the existing synchronous motor with the use of a DC control and power monitoring system from Rockwell Automation. “This system has proven its reliability where the power factor is being held at unity under all load conditions.
“The real test was to envisage the control and instrument system and prove not only energy saving, but provide a true model of the much needed surge control of which there was no information on the existing system.”
Rockwell Automation engineers implemented a new Allen-Bradley ControlLogix PAC (programmable automation controller), complete with GEM standard ICS-Triplex for compressor control software into a new motor control centre (MCC), ready for connection to instruments. The ICS Triplex compressor control software, exclusive to Rockwell Automation, allowed engineers to easily calculate and load the most appropriate surge control for the conditions that the compressor No.1 worked at, together with two other compressors. The control of the inlet vane through the surge control constituted a considerable energy saving.
To collect all relevant information indicating aspects such as pressures, temperatures, power factor, power usage, airflow, trips and alarms, the SCADA system (FactoryTalk View) was installed.
During the first month of operation, the energy saving from compressor No.1 was already significant. Harmony was particularly impressed with the new installed control software, Rockwell reports.
The first compressor was completed towards the end of 2010, and Rockwell Automation is currently working on the second compressor.
“Plans are afoot to upgrade other compressors working on the same manifold, thereby the ICS-Triplex software with an Allen-Bradley ControlLogix will allow for proper load sharing or shifting between compressors and we envisage an even more substantial saving,” concludes Fachin.