Why is your system pressure so high? There could be a number of reasons, starting with end user requirements, pressure differentials, compressor control characteristics, etc. Often the operators of the system don’t know the answer to the question. Many times the pressure is set at a certain level because that is the rating of the compressor. It is important to know what your actual pressure requirements are, and realize that supplying excess pressure causes your compressors to consume more power than necessary, with typically no additional production improvements (Figure 3). If you find there is no good reason for high pressure, then lower it.
7. Improve air treatment efficiency
An air compressor produces hot, wet, oily air that must be conditioned so as not to contaminate downstream machinery or processes. The compressed air is dried using air dryers and is typically filtered in some fashion to remove contaminants. Compressed air treatment equipment can be a significant source of energy loss through purge loss (for desiccant dryers), electrical power consumption (refrigerated dryers), pressure loss (causing the compressor to consume more power), or through excessive drainage while removing the captured liquids from the system (Figure 4).
The selection of more efficient air dryers that use less power through efficient design, low- or no-purge flow, and/or lower designed pressure differential is a good energy efficiency measure. Airless condensate drains will reduce the compressed air waste that might be occurring if cracked open manual drains or timer style drains are normally used to expel liquids from the system. Every psi reduction in pressure differential or reduced cfm of wasted compressed air translates to less energy being consumed at the air compressors.
8. Upgrade plant piping
Undersized compressed air piping can cause a restriction to flow in compressed air systems, which forces compressor discharge pressures higher to compensate. Often the compressor room header system and distribution piping was sized many years ago. Over a period of time the plant may have grown and compressed air demands increased to the point where the original piping is too small. As part of the system optimization process, the compressed air piping pressure differential should be measured to determine if there is a problem. Piping modifications such as looping the system may improve things, or pipe size increases may be required. A good system should have no more than 10% pressure differential across the complete system from the compressor room to the end use piping drop. An excellent system will have no more than 2% drop.
9. Reduce component pressure loss
A significant and important item to check is how much pressure differential exists between the piping drop and the actual end use of the compressed air. It is common to see the biggest pressure differential occurring in the “Dirty Thirty,” i.e. the last 30 feet of pipe. In that last section of piping, there may be undersized filters, regulators, lubricators, connectors, and hoses, all elements that can contribute to significant pressure differential. This differential can also be inside the production machinery itself.
When major pressure differentials occur in this section of the system, the discharge pressures at the air compressor end of the system must rise to compensate, increasing the power costs. Care and attention to sizing these components for low pressure differential at peak flows can often cost only a few hundred dollars, but yield thousands of dollars in annual savings at the air compressors.
10. Implement leakage detection and repair
On average about 25-30% of all the compressed air produced by the air compressors never makes it to the end user. If there is no leakage detection and repair program in the plant, this number can be much higher, and in extreme cases can up to 80% of the average air demand can be leakage. The repair of compressed air leaks is one of the easiest ways to gain energy savings in a compressed air system – all you need in most cases is a keen sense of hearing, some time, and a few wrenches. And if better tools are used, like implementing ultrasonic leak detection into a regular maintenance program, improved results can be achieved (Figure 5). A good target to aim for would be a leak level of 10% of the average compressed air flow.