Compressed Air Best Practices-August 2008

Focus Industry COMPRESSED AIR AUDITS | 08/08 | Rotary Screws Designed for 15" HgV to 29.5" HgV The rotary screw vacuum pumps are designed for service in the vacuum range of 15" HgV to 29.5" HgV. When system vacuum level drops below 15" HgV, a modulating inlet valve built into the inlet of the vacuum pump begins to close. This valve is in place so that the pump side vacuum level does not drop below 15" HgV. If the vacuum level at the inlet to the rotary screw vacuum pump did drop below 15" HgV, high amp draw and motor overload would result. The 15" control valve keeps the mass flow low enough for reasonable motor performance. The 15" control valve is important in this system because as pressure differential modifications are made to the distribution system and production demand equipment, more air will be flowing into the system and system vacuum level will drop from the existing 16" HgV to some lower value, possibly as low as 12" HgV. When the system vacuum level drops to 15" HgV, inlet control valves on site vacuum pumps will begin to close and capacity delivered to the system will decrease. In this scenario, the 15" control valves will be counteracting the effects of decreasing the pressure differential by not allowing full delivered capacity. The result will be a cascading loss of vacuum. In other words, the existing vacuum pumps, by having builtin protection devices, will diminish system supply capacity when vacuum levels drop. Rotary Lobe Blowers There are two alternatives to the 15" control valve restriction. The first is to install more rotary screw vacuum pumps so that the additional air entering the system can be evacuated and system vacuum level will remain at 15" HgV or greater. It is estimated that this will require an additional 300 hp in rotary screw vacuum pump capacity to reach the new 16,000 acfm level required to keep the system vacuum level at 15" HgV. 300 hp will cost $98,000 per year for energy at $0.065 kW/h. Note that the primary goal is to increase vacuum holding force to use points in production machinery. The second and recommended alternative is to target 12" HgV vacuum levels. We will make modifications to production machinery and to distribution piping and then change vacuum supply technology from rotary screw to rotary lobe blower. Rotary lobe blowers typically operate in the 0–15" HgV vacuum range and are a more efficient technology than rotary screw in applications below 15" HgV. Given that table end vacuum levels are only 3" HgV and table inlet vacuums range from 5" HgV to 9" HgV, it would be much more efficient to supply high volume vacuum capacity at 12" HgV and have only 3" HgV to 4" HgV of total pressure differential and still supply vacuum to parts at 7" HgV to 8" HgV. This is 4" HgV to 5" HgV higher vacuum than what is currently available in production machinery and would eliminate part slippage and waste. E. Summary A furniture manufacturer was experiencing insufficient vacuum causing part slippage at the routing tables. This caused product rejects and production downtime. The proposed solution is to go from 15" HgV to 12" HgV vacuum and to increase flow from 11,000 to 16,000 acfm. Eliminating pressure losses in distribution systems and at the routing tables is a key concern. It is recommended to replace the rotary screw vacuum pumps with rotary lobe blowers, which operate more efficiently at 12" HgV. The resulting energy savings of the project are predicted to be $139,504 with a payback period of 3.3 years. For more information please contact Dan Bott, Dan Bott Consulting, tel: 251-609-1429, email: dan@dbott.com, www.danbottconsulting.com 15 http://www.mikroporamerica.com http://www.danbottconsulting.com http://www.mikroporamerica.com

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Compressed Air Best Practices- August 2008 Contents From the Editor Utility-Air News The August Audit of the Month: A Vacuum System Audit Energized for Savings at Seattle City Light and Tacoma Power Know Your System CASE: Compressed Air Supply Efficiency Ecos Air: Managing Incentive Programs Kaeser Compressors: Loyalty, Energy and Growth Building Relationships at Cummins-Wagner McIntire is Moving Forward The 2008 A.I.C.D. Conference & Exhibition Tuthill Vacuum and Blower Systems Resources for Energy Engineers: Training Calendar & Product Picks Wall Street Watch Advertiser Index Job Market

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