Saving energy and money through recycled compressed air

In the process industries, companies have already taken most of the measures available to optimize their processes in order to gain on productivity and reduce waste. However, there is some very tasty low-hanging fruit available to those who use compressed air, thanks to a newly developed air recovery system. For industries such as blow molding of PET containers, the fruit is easy pickin’ and highly rewarding. It has enabled some firms to gain some very lucrative rebates on electric power usage.

Until now, PET bottle molders, who use both high-pressure and low-pressure compressed air in their blow molding operations, were exhausting all residual compressed air from the high-pressure side out into the atmosphere. This was probably considered unavoidable and not especially wasteful – until electric energy prices started going through the roof, especially in regions such as New England and California.

“Many of these PET container producers have begun to view air as the fourth utility, along with gas, water and electricity,” says Chris Gordon, president of Blackhawk Equipment ( Arvada, Colo.). “So, you try to save money on compressed air in plants like these because they can theoretically net out some big energy savings. The question is, what technological development is going to enable you to do that?”

An air systems specialist and certified by the Department of Energy as an Air Master Plus certified consultant, Gordon takes care of the compressed air needs at many of the worldwide locations of container giant Ball Corporation. Some of these locations produce PET beverage bottles, and use a lot of compressed air and energy in the process.

Three years ago, Blackhawk Equipment was introduced to a new concept in recycling compressed air, the Air Recovery System (ARS). Developed by Technoplan Engineering SA of Geneva, Switzerland, the ARS essentially recovers compressed air that still has residual, albeit lower pressure, available. Gordon saw immediately that the ARS concept could be advantageous to the Ball Corporation PET bottle production operations, so he began to work with the licensed U.S. distributor of the system, Connell Industries ( Rahway, N.J.).

The ARS system is installed between a blow molder’s exhaust system and that plant’s low-pressure air system, capturing and storing almost 50 percent of the dry, oil-free air at a pressure of 12 bar (170 pounds per square inch). The ARS system returns reclaimed air to the plant’s low-pressure air system to be used as needed; that allows some compressors to rest, resulting in significant savings in energy and maintenance expenses.

“The PET molding process is a semi-wasteful one that requires ultra-high pressures,” in excess of 580 psig, Gordon says. “For the past several years, Ball Corporation has been very focused on energy savings. Compressors are the largest motors in any of its facilities, consuming millions of dollars worth of electric power every year. So, anything we can do to save energy is what we are focused on, especially if there is the potential for major energy savings like with the ARS concept.”

Gordon performed the pre- and post-M&V (measurement and verification), and the energy savings were very substantial (although confidential). A very large compressor was shut down, saving thousands of kilowatt-hours. Maintenance costs were also reduced as a consequence. The total savings generated by the ARS system enables a payback period that is typically eight to 12 months.

The potential for rebates on electric power consumption makes the payback even more attractive. In New England, for example, where the kilowatt-hour rates are three times that of much of the United States, the ARS system can qualify for about one-third of the total ARS purchase price.

“We have energy-efficiency programs designed to help customers with electric power usage to take some of the load off our system,” says Craig Trottier, an account executive with Public Service Company of New Hampshire, the state’s major electric power utility. “That helps defer the need for new investments in infrastructure. But, it also helps our customers manage their energy costs better so that they are more competitive.”

Trottier was recently involved in evaluating the rebate qualification of an ARS system installed at Southeastern Container’s Hudson , N.H. , facility, where large amounts of PET bottles are produced during every shift for Coca-Cola, it’s parent company.

“The results of the ARS installation were quite surprising, even better than projected,” Trottier says. “This is a unique system that we had never seen before, and is especially appropriate for PET bottle applications.”

“We have two ARS systems installed,” says John Fischer, the general manager for Southeastern Container’s Northeast Region. “One is on a two-liter bottle machine and one is on a 20-ounce machine. These are Sidel SB040s, which are big machines. The ARS systems are taking the residual high-pressure air and regenerating about 800 cubic feet per minute to the low-pressure side. That’s allowing our Centac compressors on the low-pressure side to rest. We actually valve-off the low-pressure feed to the machine and still continue making good quality bottles – and that’s the test.

“The results exceeded our expectations,” Fischer adds. “Public Service of New Hampshire, the utility, says we are saving at least 5 million kilowatt-hours per year, and could possibly double that depending on different production considerations. But in the first six months of this year, we’ve saved approximately $300,000. In fact, we’ve been able to speed up the machines with some engineering work and software programming, so we’re actually using less electricity and yet making about 6.5 to 7 percent more bottles than we did before. Our per-thousand-bottle costs have dropped dramatically. Based on all that and the utility’s rebate program, the payback period is less than a year – roughly about $400,000 invested less the rebate.”

Fischer adds that the biggest bang for the buck is on the two-liter machine.

“We’re considering adding ARS systems in plants that produce those, especially in regions were electric power is most expensive,” he says. “But in reality, the days of cheap electric power are evidently over, so we have to prepare for future rate increases even in areas where electricity is comparatively inexpensive today.”

Worldwide, there are approximately 350 ARS systems installed in PET blow molding plants today.

About the author:

Connell Industries is a control system integration company that can provide total control systems engineering, with expertise ranging from the design of Programmable Logic Control systems and operator interfaces as well as overall control management of facility compressed air systems. For more information, call 877-926-6635, e-mail Connell@Connell-Ind.com or visit www.connell-ind.com/recycling.html.