Using wireless technology to monitor energy consumption, Part 1
We may be getting a temporary break from high energy costs, but few people are under the illusion it will last long. In fact, the experience of the last couple years shows that companies will get little advanced warning about dramatically rising energy costs. The prudent step is to continue to invest in practices and techn ologies that reduce energy consumption.
It’s difficult, however, to reduce energy consumption if you can’t measure it. Yet the cost of traditional wired sensing systems can erase much or all of the financial gains of greater energy efficiency. The solution in many cases is wireless monitoring.
A principal of Lean manufacturing is that waste is costly, and in the case of energy usage, the cost of waste is pretty clear. Yet often, companies have little understanding of how energy is used beyond the overall plant level. It’s simply too expensive to do any more than the absolute minimum required monitoring for safety and product quality. For example, all plants will know how much total natural gas they consume, but it’s more challenging to get good information at the furnace load level. More and better sensors would enable the plant to optimize the use of multiple furnaces based on production load, understand which processes are less efficient, and in general improve the predictability of gas usage.
Steam usage represents another area of opportunity for improved sensing. Industrial plants use steam in large quantities in various operations, and often do so inefficiently. Studies of this problem reveal that steam loss originates primarily from steam traps used to remove condensate from the steam lines between the boiler and the various points of use. A calculation of the magnitude of the problem shows probable loss of between US$100,000 and $150,000 worth of energy each year for a typical industrial plant. Sensors could help pin-point problem areas and provide overall improved visibility into how and where energy is used.
Instrument air compressors represent yet another potential area for efficiency improvements. These compressors are vital to a plant’s safe operation, but companies typically run multiple compressors to the same header with a pressure valve on each compressor venting to the atmosphere to prevent overpressure. Flow meters could highlight opportunities to safely turn off one of the compressors or reduce its speed to save electricity.
All of these benefits are possible if the cost per sensing point is low enough to allow for an adequate return on the investment.
Wiring the plant
In some situations, such as in our steam example, manual leak detection is an option, but it is both costly and not always vigilant enough for compliance or safety requirements. So in most cases, the traditional approach has been to wire a monitoring system. And it’s not cheap. At a minimum, most hazardous areas will cost US$40 per foot to wire for monitoring. As a result, the cost of wiring can quickly exceed US$30,000 for a 750-foot run per monitored point. And a typical refinery or chemical complex can have 10,000 monitoring points.
Moreover, difficult environmental conditions mean additional problems depending on the industry.ll is subject to intense heat, mechanical impact from steel scrap that falls outside the furnace and the occasional open flame. Conduits from wired instruments are inevitably a weak point in the system. Predictably, the measurements fail, and cable and conduit needs to be replaced.
Cement manufacturing faces special challenges as well. A key stage in cement manufacturing is the heating of a fine “rawmix” of limestone and clay or shale to sintering temperature in a rotary kiln. Wiring a rotating tube for sensing is tricky, even without scorching temperatures. One traditional option is contact-type sensing, in which a copper ring is placed around the kiln and the reading of thermocouple mounted inside the kiln is transmitted through brushes getting the electrical signal from the rotating ring. Dust, dirt and grease tend to reduce reliability, and failure of the measurement system is common due to friction between the measuring point and the kilns’ rotating surface. Inadequate measurement results in overheating the kiln, and thereby increased energy use. In addition to inconsistent product quality, the total bill runs to US$60,000-$90,000 per kiln.
Infrared pyrometers are only a half-step improvement. These devices measure the surface shell temperature of the kiln, which require special protection against the extreme temperatures and tend to be less accurate leading to increased energy costs and/or inconsistent product quality.
In the end, plant managers are left to determine how little sensing they can get away with, rather than how much energy or process efficiency could be achieved with a comprehensive sensory network.
This article was provided to Control Engineering by Jeff Becker, director of global wireless, and Brendan Sheehan, vertical industries marketing manager, for Honeywell Process Solutions .
Part two to this article, which will debut in next month’s Sustainable Engineering newsletter, will focus on the processes involved in unwiring a plant and a case study example of exploring the ROI of wireless to make the decision on whether to go wireless or not.