Strip Cool Pumps Energy Reduction
Energy Drive has collaborated with a client in the metals sector to achieve an 80% energy reduction on strip cool pumps in Gauteng. There are a total of eight pumps at the mill, with four pumps in operation at any given time. Each pump is driven by a 522 kW motor, with the original system run by motors connected in a direct-online configuration, consuming 13.9 GWh per year. The optimised VSD system now uses 2.7 GWh per year, with the strip cool pumps still supplying the required amount of cool water to the laminar sprays situated at the run-out table used for strip cooling.
Before Energy Drive, the four pumps ran continuously at full speed, pumping water into the six run out table (ROT) tanks. Once their levels were full, the tanks would overflow, wasting energy. Despite being inter-connected, these tanks also had different overflow levels. After the Energy Drive system was installed, the water flow rate was adjusted by controlling the speed of the four pumps. A reduction in speed can be efficiently accomplished by using a variable speed drive, a technology proven to assist with achieving process control and, in this instance, energy saving.
The new Energy Drive system uses the same signals initially used to monitor the level of the ROT tanks to control the VSD output. By using the ROT tank with the highest overflow level for the VSD control, it is ensured that all ROT tanks are full before slowing the pumps down. The tank level is now maintained within a suitable range when the laminar spray’s valves are open, and the pumps’ capacities are at an energy efficient optimum speed of 30% when overflowing. Energy wastage from overflow is at a minimum, while still allowing a minimum flow for the pumps, to prevent cavitation.
After an initial investigation of the facility, Energy Drive presented the client with a proposal detailing the technical solution and zero-capex commercial solution to be approved by the mine. Once the proposal was approved, Energy Drive initiated the project phase, creating both a functional design specification (FDS) and technical design specification (TDS).
The first challenge was one of financial viability. The system consists of four MV pumps, and small MV drives are expensive which could have made the project commercially unviable. Energy Drive overcame this by using one large MV drive to power all four pumps.
An e-Cabin fitted with air conditioning, fire suppression and a control system was constructed outside the pump house to safely store the MV drive. Individual circuit breakers with protection relays were installed between the drive and the motors for further security. Energy Drive are proud to have worked with a group of valued collaborators on this project, namely:
Parkhome – eCabin Construction
Consolek – Switchgear
ICS Electrical Projects – Full Installation