Compressed Air Best Practices - January 2009 - (Page 14)

| 01/09 Focus Industry ENERGY REBATES | COMPRESSED AIR AUDIT OF THE MONTH Nitrogen System Innovation at Boeing Boosters Add Storage Capacity How a Nitrogen Membrane Works Selectively permeable nitrogen membranes separate gases by the principle of selective permeation across the nitrogen membrane’s wall. For nitrogen polymeric membranes, the rate of permeation of each gas is determined by its solubility in the nitrogen membrane material and the rate of diffusion through the molecularfree volume in the nitrogen membrane wall. Gases that exhibit high solubility in the nitrogen membranes, and gases that are small in molecular size, permeate faster than larger, less soluble gases. Fast gases permeate through the nitrogen membrane wall more readily than “slow” gases, thus separating the original gas mixture into two streams. The purity of the desired streams can be adjusted by changing the operating conditions. The ability of nitrogen membranes to separate two gases is determined by their selectivity, the ratio of permeability of the two gases. The higher the selectivity, the more efficient the separation and less energy is needed to run the system. Boeing’s electricity bill includes both energy (kWh) and demand (kVa) components. The demand charge billed by the utility each month is calculated as the highest 15-minute peak recorded by the utility meter in the billing month. In Boeing’s case, the facility peak demand occurs at a low frequency — less than 4% of the time. Because of this and because the nitrogen system was designed with large storage, has numerous periods of inactivity and controllable compressors, the production can be turned off during peak plant electrical demand, thereby saving significant demand charges. Boeing’s control system uses a Manitoba Hydro supplied, specially programmed power meter that constantly monitors the total facility peak and automatically turns off one or two stages of compressor power, as required, to limit the demand contributed by the nitrogen system. This system has a bypass feature that allows full nitrogen production should storage be depleted and full production required. Boosting the nitrogen to pressures higher than it is used slightly increases the energy required for the smaller nitrogen flow produced by the membrane filters, but this is much less costly than producing the much larger amount of higher pressure air feeding the front end of the system. Storing the nitrogen at 330 psi in a 30,000-gallon storage receiver provides over 64,000 cubic feet of reserve capacity — enough nitrogen to fill the largest autoclave in 20 minutes. The plant nitrogen demand has very high peak flows during autoclave filling but low nitrogen demands during normal periods. This gives the system time to catch up after filling operations, slowly recharging the storage tank over a number of hours. During this filling operation the generator is kept at 100% output capacity, its most efficient point. When the storage is full, the control system completely turns off the generator, avoiding inefficient partial load operation. Off-Peak Savings With current production levels, the generator needs to run only 30% of the time. This gives the system the flexibility of selectively operating at only optimum times, allowing a further cost reduction opportunity through the elimination of the nitrogen generators’ peak demand from the total facility electrical demand. ANNUAL ENERGY (KWH) ANNUAL ENERGY COST DEMAND (KVA) ANNUAL DEMAND COST TOTAL SAVED % Old Design New Design with Demand New Design Off Peak 2,150,000 491,500 491,500 $55,685 $12,730 $12,730 225 195 0 $19,115 $16,590 $0 $74,800 $29,230 $12,730 — 61% 83% Table shows the savings for the new system and compares the charges with or without demand. 14 www.airbestpractices.com http://www.airbestpractices.com

Table of Contents Feed for the Digital Edition of Compressed Air Best Practices - January 2009

Compressed Air Best Practices - January 2009 Contents From the Editor Utility-Air News Compressed Air Audit of the Month: A Nitrogen Audit at Boeing Air Standards: New ASME & ISO Standards for Compressed Air System Assessments Energy Rebates Assist Industrial Sustainability Initiatives Seven Sustainability Projects for Industrial Energy Savings: Project #1: Lighting Optimization Minimum Supply Wire Size Recommendations for Compressor Packages Utilizing Variable Frequency Drives The Pneumatic Advantage: Pneumatics Bring Precision and Reliability to Furniture Industry Specialist Personal Productivity: Is Afternoon Fatigue Influencing Your Job Performance? The Explanation and Some Solutions. Resources for Energy Engineers: Training Calendar & Product Picks Wall Street Watch Advertiser Index Classifieds

Compressed Air Best Practices - January 2009

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