What is in this article?:
- Improving Compressed Air System Efficiency: Part 1
- Three concepts to remember
- Compressed air storage capacity
Carefully engineered responses to demand will result in more efficient systems and compressed air savings.
Compressed air storage capacity
Perhaps the most thought-provoking and overlooked issue in the system is storage capacity. For the most part, knowledge about this factor has come in pieces over the past 20 years or more. The supply industry looks at storage only from its own point of view. What I hear most often is that the seller of the compressor specifies the storage based on a "guesstimate" or said that his type of machine did not need a tank. Engineering decisions require more than such stabs in the dark.
Whether one compressor requires storage or not, all systems require storage. Storage serves many purposes in a system, such as:
• isolating events in the system, eliminating the need to keep energy online all of the time for the intermittent appearance of demand,
• protecting users from seeing the effect of other users,
• providing the ability to replace air usage over long periods of time and then use it at very high rates of flow. This can eliminate the need for a very large amount of energy, depending on the recovery time available between events served, and
• controlling the rate of change in the system based on scf per psid available. Without this being done properly, automation is a waste of time.
Changing our ways
In the mid '80s, I gave up the battle of point-of-use systems control. It was the exception rather than the rule when you could get operators in a plant to not fiddle with the regulators. An old timer explained it to me. He said that people played with regulators because they could . . . regulators have a handle.
Some things haven't changed at all. Compressed air is still the most expensive in-plant utilityr. It takes more than nine units of electricity (including auxiliary requirements) to generate one unit of air energy. Seldom if ever do I find a system that is achieving much more than a minimum acceptable result. Somehow, in the development of the industry's thinking, the concept of "more is better" got linked with compressed air. With the exception of storage, nothing could be farther from the truth.
We have learned to keep production complaints to a minimum with whatever resources are available to us . . . all too often more power. The demands on plant engineers, maintenance managers, and production engineering to control cost and improve quality will not allow us to "do what we did, and get what we got."
The merging of all of these topics is the magic of operating a best-in-class system. I invite your open-mindedness, as much of the information will be quite different and occasionally contradictory to what you may believe to be true. It is not the intent of this series of articles to "get the system to work" or "keep the equipment running." It is my intent to provide you with the concepts and information, as they apply to working systems, to improve the quality and quantity of production at a significantly lower compressed air cost. In Part 2 of this series, we will explore the best ways to design a new compressed air system.
What if we treated our electric systems the same way we treat compressed air?
1. We would have to remove all the nameplates from the motors and electrical devices. We normally have no idea what volume or pressure is required of air using devices other than by trial and error.
2. We would buy electrical-using equipment with no regard to voltage, amperage, or the effect that it might have on the system, assuming that the local utility would compensate for whatever the results were on the system.
3. We would remove all the circuit breakers, transformers, capacitors, and starters from the system and use only primary power, regardless of need. If a particular user required control, we would put rheostats on those applications and nothing on the balance of applications.
4. We would use one or two sizes of wire and connection components on all electrical applications, regardless of voltage or amperage, and expect maintenance and the local utility to correct the system to compensate for how the production works. The size and selection of those components would be determined by the stores department and purchased based on price, availability, and minimizing inventory. Example: Use ¼-in. hose and fittings on all applications regardless of flow or pressure. Once the connections are made, if the application doesn't work, you simply increase the pressure supplied to the equipment until it works the way we want it to. Wouldn't that be interesting to do with electricity?
5. Give every operator and supervisor the phone number of the local utility. If the equipment in production isn't working the way that they want it to — regardless of any changes in speeds, feeds, faults, or any other problem — they simply call the local utility, who will alter the way they are supplying electricity to the plant to correct that single problem. If they cannot correct the problem with more whatever, they will simply buy more whatever or build another power plant and try again to solve the problem that was reported over the telephone.
This example may seem ridiculous, but it would actually be a relatively close parallel to the way that most compressed air systems are operated. The sad part of this is that limited resources are available to learn more about compressed air.
R. Scot Foss is president of Plant Air Technology, Charlotte, N.C., which specializes in air system auditing and design. This series of articles is based on his book, Compressed Air System Solution Series. To order a copy, click here.