What is in this article?:
- Opportunities abound for Saving Energy
- Artificial demand
Looking to slash your electric bill? The more pneumatics your plant uses, the more opportunities exist to save money.
More often than not, certain processes require a minimum pressure. These “requirements” should always be traced to their origin. Are they actual OEM specifications or simply the perception of an operator? Higher-than-necessary pressure can also be caused by excessive system pressure fluctuation, which is either a piping, regulator, or sometimes compressor control problem.
“My grinders need 98 psi to run properly. Therefore, the air system should run at 98 psig or higher.” When you hear these words, what is the operator really telling you? Probably, when the system header pressure falls below 98 psig, the grinders don’t work well. Production personnel probably don’t know the actual pressure at the tool or how much air the tool uses.
We found this scenario during a recent air system energy audit. The plant could’ve run at 80 psig, but it ran at 98 because the grinding area supposedly required it. Furthermore, grinding accounted for only 20% of the demand, so 80% of the plant was supplied with air at a much higher pressure than needed. We could calculate how much the higher pressure was costing, but rather than belabor the point, let it suffice that the energy used to maintain the higher pressure throughout the plant amounts to thousands of dollars a year.
Testing revealed that the actual inlet pressure to the tool was 63 psig at load, but the header pressure stayed at 98 psig. In other words, a 35-psi pressure loss occurred through the plumbing between the header pipe and each grinder. Further investigation revealed that the grinders needed only 75 psig.
In this case, operators found the recommended ½-in.- hose to be too heavy, so ⅜-in. hose was used instead. The smaller hose restricted air flow, which created a substantial pressure drop. Furthermore, the ⅜-in. hose used ⅜-in. disconnects, which contributed even more to the high pressure drop.
We changed the standard ⅜-in. quick disconnects (which accounted for a combined pressure loss of 23 psig per station) to industrial quick disconnects at $2.50 extra per set — a whopping $5.00 per station. Doing so reduced the combined pressure loss to only 5 psi per station.
The ⅜-in. hose was replaced with a 1-in. pipe running to the base of the station at a cost of $30 per station. A regulator was selected to deliver full flow to the grinders at 75 psig with 80 psig feed pressure. we were then able to reduce the header pressure to a controlled 85 psig. Results after 18 months:
• Tool repair costs went down for the grinders.
• Production was increased throughout the plant by 30% — even after installing more grinders and other new equipment.
• The cost of materials to implement the changes amounted to $1362.00 for all nine grinders.
Even with the increased production and additional equipment, the average total air demand fell from 1600 to 1400 cfm. The key to this success was measuring the end use workstation inlet pressure when equipment was idle and when working while simultaneously measuring the header pressure. If the header pressure stays steady, and the process inlet pressure falls, then the restriction is in the feed line from the header to the process.
Running at high pressure to serve a small demand — A compressed air audit should always check whether or not the highpressure air is actually required. If so, can the end use be modified to lower the pressure requirement? For example, installing a larger bore air cylinder may reduce the pressure requirement. If this cannot be done, local high-pressure could be supplied by a small, dedicated high-pressure compressor or a pressure booster rather than running the whole system at high pressure. Measure the air flow and pressure requirements and the cycle time. Knowing this data allows calculating the most effective and efficient solution.
Other causes — A final but overlooked item in the air piping system that causes pressure loss is equipment left installed but no longer in use. Such components as flow meters, filters, and separators often are left in an air system even though they no longer are used. Because they are not used or maintained, they often fill with sludge, rust, and scale, causing ever increasing blockages and pressure drop as the air flows past. This requires a corresponding increase in header pressure to maintain the required process pressure.
Regulators wide open
Often a regulator at the point of use is opened to header pressure because a droop was not allowed for. But sometimes, even when the regulator was selected correctly, the delay in signal time has the regulator opening at the end of the action, leaving only the feed line storage volume to handle the process. If, during that delay, adequate volume does not exist to hold the required pressure at the end use, the pressure drops, production slows, and the operator opens the regulator up to full line pressure. This negates the effectiveness of the regulator and immediately creates an artificial demand.
A fix for this problem is to size a small storage vessel between the regulator and the process to hold pressure until the regulator opens. To size this, measure the flow volume, time required, and allowable pressure drop.
Training, training, training
Working toward energy savings requires many individuals to contribute to the effort. However, to be effective they must understand the cost of compressed air and the interdependency of the components of an air system.
Companies that have trained their people on the importance of saving energy have earned the greatest payback. This type of training pays off quickly because energy savings go directly to the bottom line and make a big impact on profitability.
Even though compressed air costs seven to eight times that of electricity, it remains ignored or misunderstood, which results in millions of dollars of wasted energy every day. Control and management of this utility poses significant opportunities at both the supply and demand side to save money. In order for any program to optimize these opportunities, those responsible for short and long term implementation must focus on all the interrelated parts of the system and understand its working parts. This is often best accomplished by a professionally implemented compressed air system evaluation or general audit to develop an accurate profile the system.
More savings await
Even more energy- saving techniques for plant air systems are contained in the author’s book, Energy Savings in Compressed Air. The hard-bound textbook contains five chapters on compressors, plus individual chapters on capacity controls, determining air requirements, distribution systems, dryers, condensate removal, flow measurement, and more.