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Newsletter Contents:
From the CAC President Jim McAuley, Honeywell, Inc. As President I want to welcome you to the inaugural issue of the CAC "Pressure Point" newsletter. Our objective is to provide American industry with the technical information and practical tools to effectively reduce energy costs and improved air system reliability. If this material is of value to you we encourage you to distribute this CAC newsletter as widely as possible to your own colleagues and contacts. As always, the non-profit CAC continues to offer high quality technical training and other technical products. Those of you who have attended our "Fundamentals" or "Advanced" trainings know first hand the value of CAC technical materials. As detailed in this newsletter, the benefits of these products have been clearly established by an independent evaluation funded by the US Department of Energy. In addition to our long term services I also wanted to introduce you to two new exciting developments at the CAC. The first is more effective promotion of CAC training and technical products; the second is the prospects for an Internet-based format for the "Fundamentals" training. It is clear that the CAC has developed excellent technical products and training that make a real impact on industrial operating costs. However, we have only scratched the surface in terms of reaching the large industrial audience which could benefit from the CAC technical "message". The wide distribution of Pressure Point (with your help), new CAC brochures and other promotional materials represents the beginning of an ambitious new promotional effort recently approved by the Advisory Board. As a first step, take a look at our new brochures, services and information at the CAC website, www.compressedairchallenge.org. If you have questions or ideas on how to promote CAC products or need copies of our new marketing materials feel free to contact our new Marketing Coordinator, Hale Powell, at CAChallenge@comcast.net or (978) 337- 4284. Internet-Based Technical Training - Although The Compressed Air Challenge has held more than 200 technical trainings around the country, traveling to remote workshop locations represents a real barrier for many potential attendees, particularly in certain areas of the country. To address this issue, the CAC is currently exploring the development of fully interactive Internet based training for our one-day Fundamentals workshops. At the October Board meeting we reviewed an excellent proposal from an experienced developer of "distance learning" technical and vocational curricula. The development of this new CAC training format would eliminate the need for travel off-site and would bring the Fundamentals training directly into the worksite or attendee's home on a much more flexible schedule. Prior to authorizing development, the CAC Board would like your input and ideas on this Internet- based approach. To obtain that input we have posted a five minute "Elearning Survey" at www.compressedairchallenge.org. Preliminary feedback has been very positive about the feasibility and interest in this new project. I am personally very enthusiastic about increasing the exposure of our excellent CAC products and the expansion of our training to an Internet format. I hope you share some of the excitement about getting our message out more effectively. Please feel free to contact me with any questions Jim McCauley
USDOE Study Confirms CAC Training Benefits Aimee McKane, Lawrence Berkeley National Laboratory In May 2004 the US Department of Energy completed a thorough assessment of the actual impact of the CAC "Fundamentals" and "Advanced" technical training programs. Extensive interviews of 200 industrial end-users and compressed air professionals confirmed clear energy efficiency, reliability and commercial benefits of both the "Fundamentals" and "Advanced" CAC workshops. Remind me: Exactly what is CAC training? The Fundamentals session is a one-day technical workshop which serves as an thorough introduction to efficient compressed air system operation and management. It is oriented to the needs and technical background of plant personnel and compressed air system vendors. The two day Advanced workshop is designed to provide facility engineers, maintenance supervisors, equipment distributors and other key personnel with the most up-to-date, in-depth technical information on how to troubleshoot and implement improvements to industrial compressed air systems. Key findings of the USDOE Evaluation include the following: > The CAC training is highly cost-effective for businesses and attendees. At current national industrial electricity rates, the average value of savings achieved by program participants who implemented measures was $7,428. With a typical "Fundamentals" tuition of $299, this results in a simple payback of less than a month. > Attendees of the CAC training workshops find them both useful and of high quality. High percentages of both end-users and compressed air professionals reported a strong positive impression of the training sessions. According to the study, the CAC training has been very effective in providing high quality technical information to plant managers and technical staff as well as by targeted constituencies on the supply side of the market, which consists of compressed air system equipment distributors and consulting engineers. Moreover, the training sessions were positively rated by the substantial number of government officials, engineering faculty, and utility energy efficiency program operators who attended the CAC trainings. > End-users who implemented compressed air system efficiency measures achieved high levels of energy savings. The USDOE study estimated that attendees who implemented compressed air system efficiency measures after completing the training saved, on average, 149 megawatt hours (MWh) per year, or roughly 7.5% of pre-project system energy. As a point of reference, compressed air system efficiency experts find that, for the typical compressed air system, 30% of system energy usage can be saved through cost-effective measures. > Workshop attendees who implemented recommended compressed air system efficiency measures experienced improvements in reliability and other non-energy benefits. A full 76% of end-users who implemented system efficiency measures reported experiencing benefits such as: reduced downtime, reduced moisture and contamination in the system air, more consistent system pressure, and restored delivery of adequate pressure to all system components. Other benefits reported included improved consistency of pressure in the system, and restoration of usable pressure to all areas of the plant. > The majority of CAC attendees use materials directly from the CAC trainings in making efficiency improvements to their compressed air systems. In fact, 76% percent of the sample end-user representatives reported that they had made significant capital and/or operating improvements to their compressed air system since attending the CAC training. Two-thirds of end-users who made such improvements reported that they had used materials and knowledge gained from the training to guide the improvements they made. The most common capital improvements made were the replacement of current compressors with more efficient models (18%), reconfiguring system piping (10%), and adding air storage capacity (8%). In addition, about half of end-user attendees said they had implemented changes to their compressed air system maintenance procedures following CAC training. > CAC Training materials are highly useful to compressed air professionals. A large majority of vendor participants have used CAC training workshop materials or information when they evaluate customer compressed air systems. A similarly high percentage of vendors have used the CAC workshop materials in diagnosing their customers' compressed air system operating problems. Interested in Further Information? Clearly, the CAC workshops have been highly successful and effective. For the entire USDOE report or more general information about CAC training, visit the CAC website at www.compressedairchallenge.org. For detailed information on scheduling or hosting a CAC workshop please contact Pat Vazquez, the CAC Training Coordinator at info@compressedairchallenge.org or (301) 751-0115. Back to top
New Developments at the CAC Hale Powell, HPowell Energy Associates, Editor, CAC Pressure Point 2004 has been a year of positive change at the CAC. In recent months a number of new projects and personalities have injected new energy. We now have new officers, an aggressive marketing plan, and enhanced web site and the prospects of expanding the "Fundamentals" training to an on-line format. In addition, the CAC will soon have a new Executive Director. New Leadership of the CAC. The CAC Board of Directors is comprised of representatives from the 14 sponsor organizations. See www.compressedairchallenge.org for sponsor details. At the October 2004 Board meeting the following individuals were selected to be officers.
In January 2005 the CAC Executive Director, Bruce Medaris, will be retiring after more than 4 years of active commitment. At present, the CAC is beginning a executive search for his replacement. We welcome suggestions of qualified candidates. Please feel free to contact the above CAC officers if you have general questions or comments about the CAC. New "Fundamentals" Instructors. In anticipation of increased CAC workshop activity we have added six new "Fundamentals" Instructors following a rigorous and comprehensive selection process. They are:
Congratulations are in order! New CAC Marketing Campaign - As discussed in the President's letter, the CAC has embarked upon an ambitious six month effort to market all of our products and services. We have produced a whole new series of brochures for both training and hosting training, and have established a hosting page on the CAC website. We will be attempting to exploit contacts with professional and trade associations, and have created a marketing plan to expand training and hosting into areas previously underserved by the CAC. If you would like to assist us in this endeavor, contact Hale Powell at cachallenge@comcast.net. To Help: Please forward this newsletter to friends and colleagues in the compressed air industry! New CAC Hosting Page - In September 2004 a major enhancement was added to the CAC website, www.compressedairchallenge.org. The new "hosting page" is intended to provide clear guidance and current information for those interested in hosting CAC training workshops. Included are the following resources:
Ordering the Best Practices Manual Order The CAC Compressed Air Best Practices Manual The recently released Best Practices for Compressed Air Systems is now available. "Best Practices" is the best and most complete technical reference resource for compressed air system improvement. Written by internationally recognized compressed air experts, it reflects technical consensus among manufacturers, end users, and systems experts on strategies to reduce compressed air operating costs and improve overall system reliability. Go to www.compressedairchallenge.org or call (800) 262-0115 for details and ordering. Back to top
CAC at Conferences and Trade Shows Ed Ball, Power Supply Industries Starting in September 2004 the CAC has begun an effort to increase its visibility at a variety of conferences and trade shows. We encourage you to help us elevate the CAC profile and promote our technical message at these events. From September 26-29 the CAC participated in the Chicago Railroad Show in association with the display of dominick hunter inc. of Charlotte, NC, and Power Supply Industries of Fenton, Missouri. During the course of the show PSI and dominick hunter introduced booth visitors to the CAC and the Best Practices Manual as a means of improving "Stationary Rail Air Systems". The new CAC brochures and other materials were distributed. During the Railroad Show the CAC received almost 100 inquiries about our products. During January the CAC will be finalizing a professionally designed "tabletop display" that will highlight our products during future events. We encourage our sponsors and supporters to utilize this display in coordination with their own exhibits at upcoming conferences. This is a unique opportunity to associate your organization with the CAC in a public setting. Please contact Hale Powell (CAChallenge@comcast.net) with questions about obtaining the CAC display or with suggestions of conferences that would be suitable for a CAC presence. Back to top
Lead Technical Article: The Effect of the Quality of Ambient Air and Cooling Water on Compressed Air System Supply Side Performance David M. McCulloch, C.Eng., Mac Consulting Services, and William Scales, P.E., Scales Air Compressor Corporation The quality of the air going through air compressors and other system components to end-uses can adversely affect not only their energy efficiency but also their reliability and maintenance requirements. This article will provide detail on strategies to effectively address issues such as inlet air and cooling water contamination, temperature and other factors that impact air compressor performance and efficiency. Inlet Air - particulate A factor often overlooked is the quality of the ambient air going to the intake of the compressor. To protect the compressor from harmful particulate, an inlet filter normally is supplied, or recommended, by the compressor manufacturer. It should be noted that the filtration rating chosen for this filter is to protect the compressor from potential damage, but may not be adequate to protect other downstream system components and end-use applications. To protect these, additional filtration usually is required. The lubricant filter often has a finer filter rating than the air inlet filter. It will filter out material not stopped by the air inlet filter and usually requires more frequent changes. In lubricant injected rotary compressors, the air/lubricant separator has a coalescing filter element that has a much finer filtration rating than the standard air inlet filter and the lubricant filter. Particulate matter smaller than the rating of the compressor inlet filter and lubricant filter can accumulate in the separator element, reducing the interval between required changes. In addition, as the particulate accumulates, the pressure drop across the separator element increases, requiring a higher discharge pressure from the air end. This requires 1% more power for every 2 psi increase in its discharge pressure. "Heavy duty" inlet filters are recommended for dusty atmospheres, common in textile, cement and paper plants. These usually are 2 stage arrangements and require frequent monitoring and element change out, depending on the harshness of the environment. The initial pressure drop across a new air inlet filter should not exceed 6" water gauge and the pressure drop should be monitored and trends established, so that timely servicing can be implemented. When the compressor inlet filter is not properly maintained, the pressure drop across the inlet filter increases and has the same effect as inlet throttling, reducing the mass flow through the compressor and increasing the overall compression ratio. At a pressure drop of 20 " water gauge, the mass flow of air through the compressor is reduced by approximately 5%. In positive displacement compressors, a decrease in inlet pressure reduces the mass flow but this is off-set by an increase in the compression ratio, with very little change in energy consumed. In a centrifugal compressor, not only is the mass flow reduced but the reduction in the air inlet pressure also reduces the pressure head making capability, further reducing the output at the same discharge pressure. Altitude has a similar impact on mass flow to inlet valve modulation. For every 1,000 ft above sea level, the mass flow decreases by approximately 3.5% and the compression ratio increases by approximately 3.3%. The reduction in the density of the ambient air to the fans of air cooled heat exchangers also decreases their effectiveness and resultant cooling. Electric motor drivers also have similar limitations and require special designs over 3,300 ft. above sea level. Inlet Air - location Often it is recommended that ambient air going to the compressor inlet be taken from outside the building. As in most designs, compromises may be necessary. The coolest location normally is a north-facing wall, having the least direct sunrays. Means of preventing rainwater entry must be included. A filter mounted at, or above, roof level may receive excessive heating in summer conditions and in severe winter conditions, required servicing may be neglected. Accumulated snow and ice also can restrict inlet air flow creating a dangerous condition for the compressor. To avoid excessive pressure drop in the inlet air piping, it is recommended that the pipe diameter should be increased by one pipe size for every 10 ft. of length from the compressor. It also is recommended that the piping be of a material that will not rust. In cases where a duct system has been provided for compressor inlet air, the system should be designed with a minimum of bends so the overall pressure drop across the duct system is 0.25" water gauge or less. Limiting this pressure drop will prevent reduction in pressure at the inlet to the compressor and reduction in its performance. Compressor packages with built-in filter panels also need frequent servicing to prevent a reduction in the capability of cooling fan(s) within the package. Inlet Air - other contaminants In industrial plants there may be fumes from other processes, or even diesel engine exhausts, which can be ingested into the compressor, sometimes with adverse effects on the compressor, lubricants, etc. At one automotive plant, a sample of condensate from an intercooler of a centrifugal compressor, showed a pH value of 3.5, extremely acidic. The problem came from the location of the air intake and the fumes present in that area. It is important to position inlet openings to eliminate, or minimize, the ingestion of these contaminants. In some cases, special scrubbers may be needed to accomplish this. Inlet Air - temperature Ambient air drawn from outside the building may be cooler, particularly in winter conditions, providing an increase in mass flow of air through the compressor. However, compressor capacity controls and/or sequencer should be set to shut down unneeded compressor capacity, or efficiently reduce compressor output to match demand and reduce energy consumption. When air is drawn from within the compressor room, the maximum temperature is an important consideration. It has been common for compressors to be located in a boiler room where temperatures can be very high. Most standard compressor packages (and their electric motor drivers) are designed for a maximum ambient temperature of 40 °C (104 °F). It should be remembered that the air end and its motor driver usually are inside a package enclosure, where the temperature can be higher than outside the enclosure. In addition, where the compressor is air cooled, the final discharge air temperature will be about 15 to 20 F degrees higher than the ambient cooling air being blown across the aftercooler. This may result in the air inlet temperature to a compressed air dryer being above 100 °F, at which dryers normally are rated, affecting the attainable pressure dew point. Increased air inlet temperature to the compressor reduces the mass flow of the air going through the compressor. For every 20 degrees F increase in ambient temperature, the mass flow decreases by approximately 3.7%. Conversely, a 20 degrees F reduction in ambient temperature, the mass flow increases by approximately 3.7%, except in the case of lubricant injected rotary compressors, where the reduction in ambient temperature is off-set by the pre-heating effect of lubricant injection, so that the increase in mass flow realized is only about 2%. When air is drawn from inside the compressor room, it is essential that adequate ventilation be arranged, to prevent a build-up of heat within the room. An obvious indication of a ventilation problem exists when there is difficulty in opening the door to the compressor room. This results from a negative pressure within the room. A negative pressure means a reduced inlet pressure and reduced mass flow. In the case of lubricant injected rotary compressors, higher compressor discharge temperatures can adversely affect the life of the compressor lubricant. Lubricant life may be halved for each 20 °F over the recommended maximum operating temperature. In addition, the higher the temperature of the air/lubricant mixture leaving an air end, the more difficult it is to get good separation, some of the lubricant being in a more gaseous state. In the case of centrifugal compressors, the pressure head making capability also is affected by the decrease in the density of the air entering the first stage impeller. On the other hand, a decrease in air inlet temperature increases both the mass flow and the pressure head making capability. This is illustrated in the following graph:
Figure 1. Effect of inlet temperature on centrifugal compressor performance. Centrifugal air compressor performance normally is stated at an ambient temperature of 95 °F. Specifying a larger motor can allow the increased mass flow in winter conditions to be handled efficiently and may allow another compressor to be shut down. Inlet Air - humidity For the same relative humidity, the amount of moisture contained in ambient air essentially doubles for every 20 F degrees increase in temperature. This means that when the air has been compressed, cooled and dried, there is less volume (referred to ambient pressure and temperature) than what entered the compressor. For example, at sea level and an ambient temperature of 90°F and 50% relative humidity, an increase of almost 2 ½ % of inlet air, compared with dry air, will be needed to account for the condensate which will be removed in cooler(s) and dryer(s) before the air is delivered to the system. An increase in relative humidity also results in an increase in the amount of condensate to be handled by aftercoolers. The heat load to condense the moisture can exceed the heat load to cool the air over the same temperature range and will impact cooler selection and performance. Aftercoolers should be selected, taking into account the anticipated maximum ambient temperature and relative humidity. An appropriate fouling factor also should be included to allow for some fouling prior to required cleaning. In the case of air cooled coolers, external surfaces can become severely fouled in some industrial plants and must be cleaned regularly. Condensate discharging into local sewer systems also must be treated to meet Federal, State and Local ordinances. Moisture in the air can result in condensate, not only after the aftercooler but also in the compressor, if the pressure dew point is reached. In a lubricant injected rotary compressor, the injected lubricant also takes away the heat of compression. If the resulting discharge temperature of the air/lubricant mixture is not above the pressure dew point, condensed moisture will result and contaminate the lubricant, sometimes causing a serious reaction. Some systems sense and control the lubricant injection temperature by having a portion of the lubricant bypass the lubricant cooler. This means that the discharge temperature can vary with varying ambient temperatures. Other systems sense and control the discharge temperature, allowing the injection temperature to vary. A common recommendation is a filter before a compressed air dryer, to avoid particulates and liquid condensate slugs from entering the dryer. In the case of a regenerative desiccant type dryer, a coalescing filter before the dryer also minimizes contamination of the desiccant bed by lubricant carry-over. A particulate filter also is recommended after a desiccant dryer to prevent desiccant "fines" from being carried downstream to end-use applications. Each filter should be fitted with a differential pressure gauge to indicate pressure drop across the filter and determine when an element change is needed. Be aware of the quality of air entering your compressed air system and its potential consequences. Cooling Air Quality Many industrial plants, including, but not limited to, cement, foundry, paper and textile, can create the potential for environments which can cause significant fouling of the extended surfaces of air-to-air heat exchangers. This results in loss of effective cooling in aftercoolers and lubricant coolers. The approach temperature (the difference between the temperature of the cooling air supply to the cooler and the temperature of the compressed air or lubricant leaving the cooler) is increased and the temperature of the air or lubricant leaving the cooler(s) also is increased. Increased air temperatures can result in the temperature of air entering a dryer to be above design and with a substantial increase in the moisture content of the air. This can result in an increase in the pressure dew point of the air leaving the dryer and may not meet the requirements of downstream processes or end uses. In extreme cases, the dryer may shut down on high refrigerant head pressure resulting in moisture- laden air in the distribution system. Where the environmental condition cannot be improved by re-locating the coolers, regularly scheduled maintenance must be carried out. When coolers are mounted outdoors, the location and orientation should prevent the cooling fan from fighting the prevailing wind. Protection against potential freezing of condensate and restrictions from snow and ice (winter operation) also must be provided. Air compressors often are located in boiler rooms, or rooms with inadequate ventilation, resulting in a cooling air supply temperature above design. Most standard air compressor packages and coolers (and their electric motor drivers) are designed for an ambient temperature of 40 °C, or 104 °F. Assuming the correct approach temperature, any ambient temperature above 104 °F will result in an increase in the temperature of the compressed air or lubricant leaving the cooler(s). Cooling Water Quality Various cooling water sources are found in industrial plants. Where city water is used, the quality of the water generally is good but in some areas treatment for hardness may be needed to avoid fouling of cooling surfaces. Water analysis should be conducted to determine any treatment needs. Water should be checked for pH level and concentrations of suspended solids, especially calcium, iron and other metals. Another major consideration is the cost, not only of the water supply but also of the sewer costs for disposal. Well water also must be analyzed to determine need for treatment. In one plant, it was found that the 75 ft. deep well was in the middle of a layer of gypsum, producing a real quality problem. As is the case for air cooled coolers, fouling of tube surfaces will result in a deterioration of cooler approach temperature. One major advantage of city or well water is that the temperature of the supply does not vary too widely from season to season. A closed loop cooling system generally means that the cooling water is being cooled by a water-to-air heat exchanger. The ambient air quality and temperature will determine the cooling water temperature available. However, this temperature often is higher than desirable. A trim cooler heat exchanger, using city water, often is necessary in warmer environments. Cooling towers will provide cooling water temperatures which vary from day-to-night and season-to-season, within 7 or 8 degrees of the wet bulb temperature and, therefore, below the dry bulb temperature. This compares very favorably with closed loop dry coolers, which produce cooling water temperatures above the dry bulb temperatures. They require a quantity of make-up water to allow for evaporation and regular maintenance. Water treatment is essential. The ingress of foreign material into cooling towers is a recurring problem and location should take into account any upstream potential hazardous conditions. For all coolers, inlet and outlet temperatures should be recorded regularly and any trends established to allow for preventive maintenance and proper remedial action. Conclusions The old adage, "If it ain't broke, don't fix it", can be a costly approach to compressed air systems. The cost of making recommended improvements can be much less than the cost of not implementing them. The energy costs associated with a compressed air system often are unknown or hidden among other operating costs. This article highlights a few of the things that need to be considered in the installation and efficient operation of a compressed air system. The Compressed Air Challenge® conducts training in Fundamentals and Advanced Management of Compressed Air Systems, in an effort to reduce energy costs and to make industrial plants in the U.S.A. more efficient and reliable. Readers are encouraged to check out the CAC web site at: www.compressedairchallenge.com |
