It’s no secret that commodity prices in the cement and aggregates markets are sensitive to ever-fluctuating economic conditions. While cement and aggregate producers may have little control of external market variations, many are taking steps to lower operating costs to get a leg up on the competition.
Transportation, personnel, and other overhead costs are often targets for cuts. But one company has identified another “low-hanging fruit” to reduce operating costs and improve plant reliability at the same time.
Siemens' G150 variable frequency drive.
In 2008, TXI Operations LP (TXI), a leading supplier of cement, aggregate, and consumer product building materials, began a companywide initiative to enhance efficiency and reduce overall operating costs. TXI is the largest low-cost cement producer in Texas and has a significant presence in California. The company is also a leading low-cost aggregate supplier to Texas, Louisiana, and Oklahoma.
As part of the initiative, TXI took a hard look at its Mill Creek, Okla., crushed stone operation. Opened in 2002, the facility supplies crushed stone to the Dallas/Fort Worth and Beaumont markets primarily by rail. The Mill Creek operation boasts a very large stone reserve -- with 5 million tons per year-plus of capacity expected to provide a 100-year lifecycle.
VFDs replace mechanical flow system
Increasing energy prices and energy supply concerns have placed pressure on TXI and other companies to reduce energy consumption. On a national scale, the industrial sector consumes one-third of the energy in the US, making it a prime target for energy consumption reduction. And, since industrial electric motors represent the single largest consumer of energy in the industrial sector today (65 percent), TXI identified them for reductions.
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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