18 August 2011
Almost two decades ago, Hobbs installed five vacuum pumps and five compressors to supply its printing machines. Following a recent decision to upgrade the installation the company took the opportunity to find ways of enhancing its energy efficiency as well as boosting overall capacity.In response to these requirements, the Elmo Rietschle engineers at Gardner Denver Alton Ltd developed a solution based on the latest dry rotary claw pumps and compressors. Not only are these machines inherently more energy efficient than their carbon-vane predecessors, but they also respond well to speed control.Their output can, therefore, be continuously varied to match actual demand from the printing machines. This is much more energy efficient than using fixed speed pumps and compressors that need to run at full speed even when demand is low, with the result, in the case of compressors, that valuable compressed air is often simply vented to atmosphere via a relief valve.To complement the new pumps and compressors, the Elmo Rietschle engineers selected NXS-series AC variable speed drives from Vacon. A particular benefit of these drives in the Hobbs application is their integral Multimaster option which allows the drives used for the three new vacuum pumps to be linked so that when demand is low, only one pump runs, with the second and third pumps starting automatically as required when demand increases. The Multimaster facility also rotates the lead pump duty, so that wear on the pumps is equalised. A similar arrangement is used for the compressors, although in this case only two new machines are involved.The operating speed of both the pumps and compressors is controlled via PID loops, again a standard feature of the NXS drives, the inputs to the loops being provided by pressure sensors. To further enhance the energy efficiency of the installation, use is also made of the sleep function provided by the drives. This allows the pumps and compressors to be stopped completely when demand is zero, but to respond instantly when it starts to increase.“We have the extra capacity we needed and equally important, we are making big energy savings. It’s hard to quantify these exactly as the demand on the plant is so variable, but we are confident that because it is so much more energy efficient, the new plant will easily pay for itself in five years at the most, and probably much sooner” concludes Russell Hack, operations manager at Hobbs the Printers.
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