Gary Allen, TXI crushed stone general operations manager, says the pumps controlling the water flow to wash the aggregate at the Mill Creek plant had been operating at fixed speeds since it was opened. Output flow was controlled manually via valves on the outlet lines, while the motor continued to run at full speed and amperage.
When considering the total cost of ownership for an industrial electric motor system, 95 percent to 99 percent of the cost is expended on motor energy requirements. As with TXI, many industrial motor systems have inefficient mechanical control methods. This means the motor operates at 100 percent speed, while the load does not necessarily require 100 percent output -- needlessly wasting energy.
By optimizing the speed of motors to correspond to the load requirements, energy savings can be immediately achieved. The most effective and efficient method of controlling motor speed is with energy-efficient variable frequency drives.
“Crushed stone plants are historically high movers of water,” Allen says. “With the original arrangement, we had to turn the whole system on to run even small amounts of water, with no way to decrease the cost of pumping. It left a big carbon footprint, consumed a lot of energy, and put a strain on the mechanical system.”
The cost-saving strategy to replace the “historic monster,” Allen says, was to rip out the electromechanical, fixed-speed flow control system and standardize on SINAMICS G150 variable frequency drives (VFDs) from Siemens Industry Inc.
The drive is enclosed, air-cooled, and designed for applications that do not require regeneration back into the power supply system. This compact, quiet drive includes an AC/AC power module with IGBT power semiconductors and an innovative cooling concept that provides low-loss operation for extremely high energy efficiency. All units include a controller (CU320) with a PROFIBUS port, an advanced operator panel (AOP30), and a terminal module (TM31) for digital and analog inputs and outputs.