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.
This is another great example of industry becoming more efficient. As the article points out, industry uses a third of the energy used in the US. The opportunity to improve efficiency in these areas is great, and this opportunity comes mostly from better engineering. There is a lot of talk about green computing, but this is a much better area to concentrate on. The payback is greater.
IT should not be any surprise that using a VFD to reduce the power applied to any process that requires less than the maximum capability of a prime mover will reduce energy consumption and power waste.
Any process that does not need full power constantly should be examined as a candidate for a VFD, although in some situations it may not make economic sense. Variable energy input control can be extended to other areas as well. In pneumatic systems, as an example, all of the energynused pushing air through undersized piping to provide adequate flow is wasted. The fastest way to see if that is happening is to observe the cylinder pressure and see if it continues to rise after the cylinder stroke is completed. The same applies to hydraulic systems and cylinders. An added advantage is that larger piping can provide faster cycle time, usually without any increased energy consumption. OF course, in hydraulic systems a VFD can provide for inceased pump delivery only during the periods when high flow is required, which can result in a very large improvement in overall system efficiency, and as a free bonus it can reduce system cooling requirements quite a bit. In fact, in at least one application the use of a VFD for hydraulic pumps reduced power consumption by more than 50%, with no compromise in performance at all.
Good article. Certainly it's well-known that variable frequency drives will save on energy costs if properly applied. Vendors provide both assistance and calculator applications to help identify and cost justify these newer systems. But the potential savings also go beyond traditional pump and fan applications to other areas such as regen, power factor and common bus applications. Some companies seems determined to seek out savings while others are much less aggressive in investing the engineering it takes to reduce energy costs.
You're absolutely right, apresher. VFD's have a whole range of applications where they signficantly improve efficiency. I think the vendors need to be more proactive in selling these features and showing the cost savings.
Thanks for the comment, Jack. There definitely is a need for more education on energy saving possibilities with VFDs, although I think the suppliers are trying to be effective in this area. There are also different types of incentives to help accelerate and finance ROI.
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