Compressed Air Best Practices - April 2008 - (Page 10)

| 04/08 Focus Industry PLASTICS BLOW-MOLDING | CO2 O kW Creating Stable Operating Pressures Blow-pres Blow-pressure fluctuates in virtually all PET blow-molding facilities from 3 bar to as much as 6 bar. This forces the operating pressures to maximum levels in order to prevent low-pressure events from impacting the production processes. These fluctuations are caused by: 1. 2. 3. Poor air system controls P Inadequate storage In Installed pressure differential at the blow-molding machines In C onth of the M Air Audit d ompresse Minimizing ng low-Moldi B Pressure tuations Fluc Smith By Dean Previous technical evaluations confirm that this is the case at many other facilities (within this industry). Controlling header pressure and blow-pressures more accurately and at more indu appropriate levels can reduce compressed air energy costs by more than 20%. appr A re reduction in molding pressure results in a proportional reduction in high-pressure air consum consumed (assuming that most of the regulators are wide open) and with an automated supply system with appropriate storage, the energy will also be reduced proportionally. If the compressor set-points are adjusted based on the reduced header pressures, then there w be an additional reduction in energy. With three-stage high-pressure reciprocating will compressor reducing discharge pressure (within the normal operating pressure range) reduces compressors, the energy r required at the compressors by a ratio of 5 to 1, meaning a 5% reduction in discharge pressure pr provides a 1% reduction in energy on the compressor. April Audit of the Month Where: Western U.S. Industry: PET Plastic Blow-Molding Issue: Pressure Fluctuations Affecting Blow-Molding Pressures Audit Type: Supply and Demand Side Compressed Air Energy Costs: Existing: $1,399,000* Proposed: $1,248,000 Savings: $151,000 Audit Financial Summary: Savings: $151,000 Capital Cost: $266,000 ROI: < 22 month simple payback Audit Summary: 1. Stabilize low-pressure system pressure by adjusting control set-points on the VSD low pressure compressor 2. Reduce blow-air demand by stabilizing and reducing internal pressure at the blow-molding machines 3. Prevent loss of molding pressures and minimize unloaded compressor energy costs by automating the air compressors and using air storage *Per Year Energy Costs Calculated at $0.0722/kWh. Optimizing the Air Supply System The high-pressure compressors are started and stopped manually at this plant to prevent unnecessary starts on the motors. The lack of storage in the system results in rapid changes in pressure whenever a Sidel blow-molder starts or stops. It becomes necessary to keep a compressor running in the unloaded state so that it is prepared for the next Sidel to start. In addition, there are control problems with several of the compressors causing them to respond erratically to changes in system demand and pressure. The first step to managing these compressors without a significant investment is to install a signal header in each compressor area: a. The signal header should be ¾" to 1" stainless pipe which connects to the header downstream of all dryers and filters so that it reflects header pressure. Each compressor is then connected to the signal header and its’ controls can be adjusted to coincide with the settings of the other compressors Choosing one compressor to auto-start in case of a compressor failure or a unexpected increase in air demand can prevent the low pressure level alarms which occasionally occur b. 10 www.airbestpractices.com http://www.airbestpractices.com

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Compressed Air Best Practices - April 2008 Contents From the Editor Utility-Air News The Compressed Air Audit of the Month: Minimizing Blow-Molding Pressure Fluctuations AF Compressors: Focused on 40 Bar, Oil-Free Air for the PET Industry Real World Best Practices: PET Plants Using Boosters for High-Pressure Air Guaranteeing Audit ROI for Blow-Molders Managing Vacuum Pressure Differential Are You Taking Full Advantage of Pneumatic Valve Technology? Are You Strategic? Resources for Energy Engineers: Training Calendar & Product Picks Wall Street Watch Advertiser Index Job Market

Compressed Air Best Practices - April 2008

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