Load-shifting opportunities for typical South African cement plant
By RT Lidbetter and L Liebenberg, North-West University; Consultants to TEMM International and HVAC
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Electricity+Control, May 2013 (pages 46 – 52)
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A South African cement plant allowed a load-shifting strategy to be investigated on one of its raw mills. The simulation indicated that there was considerable opportunity to reduce electrical costs by shifting the loads of the specific raw mill to off-peak periods.
From the pilot study, however, it was evident that performing a load-shifting strategy according to idealised theoretical results would be difficult. The mill’s operating hours are easily influenced by unpredictable breakdowns. This, with changes in production, often requires the mills to run whenever possible to meet demand. Therefore electrical cost savings become a lower priority for plant managers.
Despite this, the electrical cost of load-shifting can be realised if incident hours do not interfere with production, such as shown with the RM3 pilot study. The ease of shutdown and start-up of the mill motor allows the mill to be turned off without excessive inconvenience to operators – and saves money. For cement mills, however, the influence of the mill temperature over the cement setting quality may deter cement plants from initiating a load-shifting scheme.
It is therefore suggested that a flexible load-shifting scheme be developed with more focus on load-shifting hours. This silo simulation took into account the changing incident hours of the mills and auxiliary equipment, but did not allow for an adaptable load-shifting scheme.
- In a typical South African cement plant, the major portion of electrical demand is taken by machine-driven processes.
- Shifting load can be achieved in such a plant, and would result in reduced peak-time energy purchases.
- Simulation studies on a real plant, considering various scenarios, indicated that substantial savings’ potential exists.