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Energy Drive has successfully collaborated with a client in the metals sector to achieve a 47,33% reduction in energy consumption on basic oxygen furnace (BOF) induced draft (ID) fans in Gauteng, South Africa. There are three BOFs in operation at our client’s site used for steel making. Two BOFs are usually in production at all times, while the third undergoes maintenance. The capacity for each BOF per day is 24 heats, and heats are shared evenly between the BOFs in production. Each heat takes 24 minutes. During these heats, the oxygen lance is submerged, referred to as the ‘blowing’ cycle. During the ‘blowing’ cycle of 24 minutes, gases from each BOF are extracted through a two stage venturi scrubber by a centrifugal induced draft (ID) fan.

The ID fan is driven by a 1550kW, 11kV slip-ring induction motor, consuming 31,01 GWh per year. Our optimised, fully automated variable speed drive system now uses 16,33 GWh per year. This new system directly controls the speed of the BOF ID fans, ensuring operating pressure and flow is available when the process requires it, with power demand being reduced as the process allows.

Before Energy Drive, the second stage of the wet venturi scrubber involved a Pease-Anthony (P-A) damper which is used to regulate the gas flow through the system. Idle damper positions had been established to minimise flow rates and power usage during charging and tapping cycles, when gas extraction wasn’t required. Following initial assessments, our team understood that a high gas flow rate is required during the ‘blowing’ cycle to ensure effective function of the venturi scrubber and therefore, the dampers should not be operated below partially open during this period.

The new Energy Drive system was installed as an add-on to the existing BOF plant off-gas system. Using variable speed drives (VSDs) to achieve process control and energy saving optimisation, the Energy Drive system now controls the speed of the ID fans. Energy savings are achieved by reducing the fans’ speeds during the times the P-A dampers are in the idle position, when gas extraction isn’t required. During the blowing, splashing, and fluxing cycles (dampers partially open) the fans revert to the speed required for optimal operation.

Following an initial assessment of the facility, Energy Drive presented a proposal detailing the technical solution and zero-capex commercial solution to be approved by the client. Once the proposal was accepted, Energy Drive initiated the project phase, creating a functional design specification and technical design specification for approval by the client and Energy Drive technical teams.

Our highly collaborative team then came up with innovative solutions to produce the best possible results for our client’s needs. While there was space available to house the VSD system in the motor control centre (MCC) it was very limited, making fitting 3 MV drives and related switchgear difficult. Our team chose to use LSiS 11kV drives instead, which have a much smaller footprint due to having power cells on both sides of the drive. The entrance to the MCC also wasn’t high enough for a 10 ton forklift to drive through, so, our team designed and fabricated a form of ‘roller skates’ that the drives were placed on and pushed into the control centre. Finally, we expected the client’s MCC’s forced ventilation system to handle the additional heat load added by the three new VSDs, however due to sub optimal cooling we were required to fit an industrial cooling system to handle the increased heat load generated by the drives after commissioning, due to higher than expected operating temperatures.

The Energy Drive system consists of three 2000kVA, 11kV VSDs; three 4-way RMU arrangements to allow any VSD to power any motor; a control system; and three industrial cooling systems and redundant capacity being online. New XPLE cables connect from the switchgear to the RMUs to the VSDs and finally out to the motors. This equipment was installed and is now housed in the client’s existing motor control centre. Energy Drive are proud to have worked with a group of valued collaborators on this project, namely:

ICS Electrical Projects – Full Installation

LS Electric Co., Ltd. – VSD Commissioning