Compressed Air Best Practices - March 2008 - (Page 30)

| 03/08 Compressed Air Industry FOOD PROCESSING | B E S T P R A C T I C E S — M U LT I - M O D U L E PROCESS AIR DRYERS system, air circuit and condensate removal system, and a shared chilled glycol system. Given the unique attributes and associated benefits of this multi-module design, it is worth examining each of the six critical factors in detail for this approach. Initial Cost: While not the least expensive of the four approaches, the multi-module dryer provides the redundancy of small individual dryers with the compactness and economy of scale of the single large dryer. The design features a circulating chilled glycol loop with the dedicated refrigeration system of each module contributing to the cooling of the glycol, which is ultimately stored in a central glycol storage tank. Without the need for a second, full-capacity dryer, the multi-module approach affords the security of inherent redundancy without the initial cost of a full size standby dryer. Cost of Operation: With the MultiPlex™ design, cycling operation enables the dryer to match energy consumption to the compressed air load through thermal energy storage and by turning on and off individual refrigeration systems. When the glycol/water temperature is higher than the operating set point by 1 ˚F, a refrigeration module is turned on. If the glycol/water temperature is 2 ˚F off the set point, two systems are turned on (as available). When the operating temperature is lower than set point by 1 ˚F a system is turned off, and so on. Energy matching saves operating cost by reducing electrical power consumed. Additional savings of this design can be realized from increased compressor operating efficiency and power delivered at lower ambient air temperatures (both daily and seasonal) with the capability of ramping down smoothly to zero air load. Through each module’s dedicated digital performance controller, refrigeration on/off set points can be easily adjusted to equalize refrigeration compressor operating hours. To illustrate the savings afforded by the cycling design of the MultiPlex™ dryer, consider our 8,000 scfm, 100 psig system operating at an average reduced load of 6,550 scfm at 100 psig. This average figure takes into account a peak demand of 8,000 scfm but also reduced loads associated with varying usage of processes and second and third shift workloads. When compared to a non-cycling dryer, which will run continuously regardless of load, the MultiPlex™ cycling design will save the user, based on $0.10/kWh and 8,736 hours of operation, $25,000 or more annually, taking into account the effects of daily and seasonal changes of the ambient temperature, which in turn reduce the compressed air inlet temperature and refrigeration condensing temperature. Pressure drop is also a significant factor in the operating cost of large volume air systems. Every psi of added pressure drop adds 0.5% to the cost of operating the compressor. MultiPlex™ multi-module dryers are designed to minimize their contribution of pressure drop on the compressed air system. For this example, the 8,000 HSFM model’s 3.0 psi pressure drop, when compared to the 5 psi pressure drop of typical dryers, results in significant energy savings. Based on $0.10/ kWh, a system running 8,000 scfm at 8,736 hours per year will save over $15,930 annually. In addition, because of a unique heat exchanger design, inlet filtration is not required for most system conditions thereby further reducing the dryer’s contribution to system pressure drop and operating cost of the air compressor. Footprint: Even with the recommended minimum of three feet of space around the dryer required for maintenance, the multimodule dryer configuration occupies less floor space than the other three approaches to air dryer installation. For air-cooled installations, condensers are mounted on the top of the dryers, eliminating the additional compressor room space to accommodate remote or outboard air condensers. Continuity of Operation: Perhaps the most valuable feature of the multi-module design is the ability to continue to operate the dryer during an upset condition. Should a problem occur with one of the dryer’s modules, provisions exist on the dryer to allow it to continue to operate at slightly reduced performance. Take, for example, our 8,000 scfm, 100 psig application. These conditions would typically size to a four-module, 8,000 scfm dryer. Should a problem arise in one of the dryer’s modules, the module can be de-energized and the balance of the dryer permitted to continue operation. In this upset condition, the two remaining refrigeration systems, both focused on cooling the glycol common to all modules, will continue to use their full capacity to reduce the temperature of the glycol. With the unique piping arrangement of the glycol system, the remaining glycol circulation pumps (one per module) will continue to pump chilled glycol to all three modules. Although the pressure dew point will decay from 38 ˚F to 42 ˚F, the compressed air system remains on-line until the repair is completed. With this unique feature, continuity of operation of the compressed air system is preserved under upset conditions without the need for a full-size back of dryer. As such, significant savings on initial capital cost, installation cost and compressor room space are realized. Maintainability: Unique to the MultiPlex™ design is the ability to execute preventative maintenance tasks and dryer repairs while the dryer remains operational. While preventative maintenance tasks are minimal, each module is equipped with the means to electrically isolate the module from the balance of the dryer. This allows for 30 www.airbestpractices.com http://www.airbestpractices.com

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Compressed Air Best Practices - March 2008 Contents From the Editor Utility-Air News The Compressed Air Audit of the Month: Saving Energy with Blowers in Canada Do You Provide World-Class Service? Managing Rotary Screw Air Compressors at Midwest Bakery The Difference Between Acfm and Scfm for Proper Vacuum Sizing Best Practices — Multi-Module Process Air Dryers The Vacuum Formation Process in Building Compressed Air Filter Elements Solberg Manufacturing Real World Best Practices: Measuring Pressure Dewpoint in a Compressed Air System Resources for Energy Engineers: Training Calendar & Product Picks Wall Street Watch Advertiser Index Job Market

Compressed Air Best Practices - March 2008

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