Chemical Processing hosted a webinar in April that covered some common mistakes when making energy program decisions. Here, I summarize some of the key points.
Mark Krisa of Ingersoll Rand spoke on compressed air systems. Krisa leads a group of engineers who help clients reduce energy costs. Although he advocates going after "low-hanging fruit," he also warns about one of the latest fads in air compressing system: lowering air pressure of the entire system. It promises benefits including lower artificial demand and reduced compressor power. "There is a lot of misleading information out there associated with lowering pressure in a compressed air system," Krisa cautions. Artificial demand is the volume of compressed air consumed by the system associated with operating at a higher than necessary pressure. Demand is only reduced in areas that see the reduction in pressure, not across the entire system. Without quantifying the percentage of demand that is influenced, savings are over-estimated.
Savings from reduced compressor power are fairly easy to calculate for reciprocating and rotary compressors. You can save 1% or the power (kW) for every 2 psi change in pressure (within 10 psi of the compressor design). However, centrifugal and axial compressors don't provide such savings. In Krisa's example, a centrifugal compressor only provided a 1.8% savings for a 10 psi drop, which he calls "pretty good." He further warns that there may be no savings if the compressor is running near choke. "I have seen many times when a customer with 10,000 hp-worth of compressed air assumed significant savings and then when we look at the engineering details and the actual results, the savings are not there at all," he explains.
Kerry Phillips of Armstrong also advocates going after low-hanging steam fruit and during the webinar pointed to higher energy costs and reduced carbon footprint as reasons to have a good steam management system. Phillips cautions about not looking for the "root cause" of the problem. "Surveys typically should be performed by trained professionals who can identify root cause," he advises. Although steam system surveys are still the most common way of detecting leaks, new wireless monitoring systems have improved data collecting and response. "The devices are clamped on to your equipment in the field and send information wirelessly to the main gateway receiver," he explains. For some simple steam applications, these systems are too expensive but they can be money savers for more troubled, critical, or costly steam setups.
John Murphy from Infor, the third speaker, warned about using operational efficiency metrics that don't account for energy efficiency. Very rarely does an energy management program examine equipment that seems to be running properly, but these overlooked systems can provide low-hanging savings. As some equipment operates, it may be consuming more energy and that can cause performance issues due to degradation or energy waste. In his example, even though the equipment was at 100% operational efficiency, by replacing a $20 filter monthly instead of every four months, a chiller could recover more than $9,000 a year in energy losses. "Your enterprise asset management system needs to take into account real-time energy usage in order to take action," Murphy emphasizes.
As the final speaker, I addressed not incorporating process systems into heater assessments. While doing furnace assessments, it's important to ask, "is there something that can be improved in how you process that can reduce energy costs?" Over-fractionating is one example. In some cases, plants will go beyond specified targets without considering added energy requirements and how they affect heater efficiency. Look at that and ask, "can I use less energy and still meet my product demands?"
During the Q&A portion of the webinar, purchasing a leak detector was discussed. This leads to the common mishap of buying equipment to help energy management. Krisa suggested that purchasing a detector is good if there's dedicated personnel who will be trained to use it and who will constantly be working with it He also pointed out that detecting leaks was only the initial part of a good program. Once detected, understanding the costs of that leak and the costs to fix it are equally important. Krisa believes it's better to contract it if you aren't going to do it regularly.(You can hear the full webinar by going to www.ChemicalProcessing.com/articles/2010/091.html.)
Having an energy management program will definitely save money for your program, but it's also important to beware of some common mishaps that can make your program less efficient.
Gary Faagau is Chemical Processing's Energy Columnist. You can e-mail him at GFaagau@putman.net.