Recovering Heat Helps Offset Energy Costs

This article is the second in a three-part series that examines ways to reduce compressed air energy costs. Part one, “How Much Does Your Air Compressor Really Cost?,” appeared on foodmanufacturing.com on October 13, 2009 and outlined 10 ways to reduce energy costs. Food manufacturing facilities require compressed air for a variety of uses and applications.

This article is the second in a three-part series that examines ways to reduce compressed air energy costs. Part one, “How Much Does Your Air Compressor Really Cost?,” appeared on foodmanufacturing.com on October 13, 2009 and outlined 10 ways to reduce energy costs.

Food manufacturing facilities require compressed air for a variety of uses and applications. While often viewed as a costly energy user, compressed air is a critical function of food manufacturing and processing. Continuous advancement in design and packaging help make today’s air compressors much more efficient than previous generations. Improved maintenance procedures and an increased attention to air usages also have helped lower operating costs while increasing productivity.

A properly maintained compressed air system is critically effective manufacturing tool.  Still, compressed air systems account for an average of approximately 10 percent of all industrial electricity consumption in the U.S. The cost of electricity to power compressors can be as high as 40 percent of a plant’s electricity bill.

For example, at .08/kWh the yearly energy bill for a 200 HP air compressor can reach $112,000.

Imagine if you could harness and recycle a portion of the energy used to power your air compressors. You could then save more than 80 percent on energy costs by using that recycled energy to heat water or direct warm air into a warehouse or loading dock.

It is little known, but that even within the most efficient compressed air systems, a small fraction of the energy input (10 to 15 percent) is actually delivered as compressed air energy. When an air compressor physically compresses air, most of the input electrical energy is converted into heat. For water-cooled compressors this heat is taken away from the compression elements, the oil cooler, intercooler and aftercooler, and is sent to a cooler or chiller to be cooled.  In air-cooled compressors the heat is discharged directly across air-to-air heat exchangers to the compressor room.

There are two typical ways to reuse this energy, depending on whether you have an air cooled or water cooled machine—through hot air or heated water.

With air-cooled compressors, the hot discharged cooling air is routed to a nearby warehouse or loading dock for supplemental heating during cool seasons, offsetting the energy otherwise required strictly and specifically to perform the same function.

With water-cooled compressors, a higher state of energy can be recovered. Built-in energy recovery systems on the compressor circulate cooling water through the compressor’s compression element water-jackets, air and water coolers to generate hot water at up to 90°C (194°F).

Especially in food manufacturing facilities, there is a ready need for hot water; whether for space heating, showers, clean-up or oil-heating.

The compressor now becomes the alternative energy source for scalding, cleaning, sterilization, heating and melting applications.

To help manufacturers realize greater savings and increase efficiency, Atlas Copco Compressors has developed the world’s first oil-free Carbon Zero compressor that now enables recovery of 90 percent of the electrical power needed input to the compressor  back as hot water. In specific design conditions, 100 percent of the electrical input power can be recovered.  in this case, the energy costs to operate the compressor becomes revenue neutral or ‘Carbon Zero’. Power that would have been used is readily offset or eliminated.

Energy costs have shown a steady increase in recent years, but that doesn’t mean that utility bills need to follow the same path. Taking advantage of cutting-edge engineering and technology can yield a number of positive returns.

This article is part two of a three-part series on reducing compressed air energy costs. The final article, slated for early December, will uncover the additional savings that can be realized with the use of variable speed drive technology.

For a free copy of Atlas Copco's 156-page Compressed Air Best Practices Guide, please send an e-mail to paul.humphreys@us.atlascopco.com. Put "Manual—Food Manufacturing" in the subject line and provide your delivery address in the body of the e-mail, and Atlas Copco will send you a complimentary copy.

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