Engineering Steel Belgium is an electric steelmaker at Seraing, in the eastern part of that country, that produces carbon and light-alloy steel blooms and bottom-poured ingots for forging and other hot-forming operations. Recently, a change in power supply for its melt shop has led to savings of nearly $65,000 per year in energy costs for the company.
ESB took the advice of an electric motor distributor—Leclercq Energy, representing WEG Industries— to adopt three WEG W22 132-kW, IE2 high-efficiency motors for the cooling pumps on one of its electric arc furnaces. The new motors are controlled by WEG CFW-09 variable-speed drives, and the new arrangement was coordinated and commissioned by Processautomation, including control panel with drives, soft starters, PLC, and Profibus-DP process supervision.
Steelmaking is very energy intensive so even small improvements in process efficiency can lead to significant energy savings and operating cost reductions. ESB aimed to reduce the energy consumption of its 85-MVP EAF, in particular the closed-circuit cooling system involving three large pumps driven by 132-kW motors, to keep the vessel from overheating even as it melts thousands of tons of steel.
ESB decided to replace the existing standard motors with three of WEG’s W22 high-efficiency motors, which reportedly exceed the energy-performance requirements of the IEC60034-30 energy efficiency standard to reduce energy loss by 10-40% versus standard motors.
Although the new motors reduced energy consumption of the three pumps, greater savings were possible by updating the motor control system to optimize the speed of the motors according to the EAF’s cooling requirements.
ESB appointed contract engineering group Processautomation, to perform a complete analysis of the furnace cooling process to maximize the energy-saving potential of the application.
Processautomation began by conducting a threepart audit of pump system’s operating hours: normal weekday operation of two pumps (the third is a standby) totaling 94 hours a week; weekend operation, which occurred on six weekends per year to counteract the threat of frost; and operation during the Christmas shutdown, for a total of 16 days, also due to the threat of frost. During all these periods the pumps were running at full speed, even during the frost-prone periods.
Based on these operat ing hours, Processautomation estimaged that the total annual cost for operating the pumps on the cooling system at about $168,000, based on local electric uti l ity rates. It further calculated that more energy could be saved by adopting variable speed drives to the pump motors, in conjunction with a PLC-based process automation system.
The WEG CFW-09 132-kW inverter drives chosen as motor controllers are matched to the W22 motors, producing the optimum operating characteristics for high-efficiency operation. The CFW09 is capable of self-tuning automatically to match the drive to the motor and load, relieving the user of the task of entering a motor map.
Following installation, normal weekday operation between 3:00-8:00 p.m. requires the operation of one pump running 70% of maximum speed due to the variable control provided by the WEG CFW-09 drive. From 8:00 p.m. to 11:00 a.m., two pumps are in operation, running at 89.2% of maximum speed, also due to variable- speed drive control. On weekends and during the Christmas shutdown, when frost could be a problem, two pumps are still required, operating at 89.2% of maximum speed.
However, with the flexible control provided by the WEG variable-speed drives, the pumps are only required to run for five minutes every half hour, which saves a considerable amount of electric energy.
This contribution, plus the large savings during normal weekday operation, means that the total annual energy cost for operating the pump cooling system is reduced to an estimated $103,500, based on local electrical utility rates. The annual savings—estimated here at $65,000, or 38.5%—are a bottom-line improvement for ESB that ensures a quick return on investment.