With an air-cooled compressor, the discharged hot air can be routed through ducts to a nearby warehouse space or loading dock. This supplements the facility’s heating costs in the winter.
Noted American philosopher and author Henry David Thoreau once quipped, “First, there is the power of the Wind, constantly exerted over the globe… Here is an almost incalculable power at our disposal, yet how trifling the use we make of it.”
Thankfully, technology and ingenuity have helped address Thoreau’s concerns for greater harmony between human ambition and our energy use.
Compressed air, often referred to as the fourth utility along with the Big Three - electricity, gas and water - is frequently utilized as a means to power applications throughout the manufacturing process. Technological advances, coupled with rising energy costs, have in recent years enabled - and, in many cases, required - manufacturers, much to Thoreau’s point, to make compressed air a more valuable and appreciated commodity.
While technology upgrades can certainly help improve efficiency, the compressed air process still requires intensive energy use. Within many compressed air systems, only about 15 percent of the energy input is ultimately delivered as compressed air energy. The remaining energy is converted to heat that is generated as a physical and natural byproduct when air is compressed. In order for a compressed air system to function properly, that heat must be removed before the air can be moved through a piping system. The more heat energy that can be recovered and reused throughout this process, the greater overall efficiency the system will exhibit. The temperature level of the recovered energy helps determine its end-use applications and, ultimately, its value.
Ways to Use Captured Heat
Utilizing heat recovery with a compressor can harness and recycle 90 percent (or more, in optimal conditions) of those energy costs as heat recovery from the compressed air process for alternative uses within the manufacturing process.
Two common ways to reuse this energy, which depend on the use of an air-cooled or water-cooled machine, are through hot air or heated water.
In an air-cooled compressor, the heat is immediately discharged directly across air-to-air heat exchangers to the compressor room. With an air-cooled compressor, the discharged hot air can be routed through ducts to a nearby warehouse space or loading dock. This supplements the facility’s heating costs in the winter by offsetting money and energy that would otherwise be used to heat this space - essentially eliminating a redundant function, at least in certain applicable situations. Air dampers, fans and thermostat controls can help regulate distribution of the heat recovery throughout the manufacturing facility and even into adjoining buildings.
With water-cooled compressors, which provide more efficient energy-recovery methods, this heat is pulled away from the compression elements as well as the oil cooler, the intercooler and aftercooler, and routed to a cooler or chiller. With water-cooled compressors, an even greater amount of energy can be recovered, yielding additional costs savings. Built-in energy recovery systems within the compressor circulate cooling water through the compression element water jackets, air and water coolers to generate hot water up to 194°F (90°C). This can be of particular use to food manufacturing and processing facilities, where there is a consistent need for readily available hot water for tasks such as equipment cleaning and sanitation, preheating water, cleanup and general heating. In these instances, the compressor becomes the alternative energy source for any scalding, cleaning, sterilization, heating and melting applications, providing year-round savings
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Return on investment for energy recovery systems through collected heat is usually as fast as one to three years. However, in order for recovery to remain reliable and regular, a stable heat energy demand is needed. To help manufacturers realize greater energy savings, some oil-free compressors can allow recovery of 90 percent of the electric power needed to operate the compressor as hot water. In optimal design conditions, heat recovery and use in other areas of the facility can provide a 100 percent return on the cost to operate the compressor - meaning managers can recoup all of the costs they would otherwise spend for these applications through compressor use, rendering the compressor revenue neutral or “carbon zero.” Any power that would have been used to otherwise heat water for these applications is offset or eliminated.
Energy costs have been on the rise throughout the last decade and show no signs of slowing down. But that does not mean that utility bills need to follow the same course. When electricity costs hold at $0.08/kWh, the annual cost to operate a 200 hp air compressor reaches $112,000. Utilizing heat recovery with a compressor can harness and recycle 90 percent (or more, in optimal conditions) of those energy costs.
Conserving energy is no longer a luxury that manufacturers can take to simply endear themselves with conservationists; saving energy is a crucial component to any manufacturer’s bottom line.