High-pressure air recycling slashes blow molding costs

PET bottle molders that use both high-pressure and low-pressure compressed air in blow molding operations typically exhaust residual compressed air from the high-pressure side to the atmosphere.

But as the cost for power to run the compressors increases, “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.”

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 recovers compressed air that still has residual pressure. Gordon immediately saw that the ARS concept could be advantageous to PET bottle production operations, so he began to work with the licensed U.S. distributor of the system, Connell Industries (www.connell-ind.com/recycling.html).

“The PET molding process is a less than optimal one that requires ultra-high pressures, in excess of 580 psig,” Gordon says. The ARS system is installed between a blow molder’s exhaust system and the plant’s low-pressure air system, capturing, storing and returning almost 50% of the dry, oil-free air at a pressure of 12 bar (170 psi) to the plant’s low-pressure air system.

Gordon performed pre- and post-installation measurement and verification, and the energy savings were substantial. The total savings the ARS system generated enables a payback period of eight to 12 months.

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

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

Trottier recently evaluated the rebate qualification of an ARS system installed at Southeastern Container’s Hudson, N.H. facility, where 1.5 million PET bottles are produced per shift for Coca-Cola, its 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, general manager, northeast region, Southeastern Container, “one on a two-liter bottle machine and one on a 20 oz. These are Sidel SB040s, which are big machines. The ARS systems are taking the residual high-pressure air and regenerating about 800 CFM 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 says we’re 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% more bottles than we did before. Our per-thousand-bottle costs have dropped dramatically. Based on that and the utility’s rebate program, the payback period is less than a year with 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 other plants that produce those, especially in regions were electric power is most expensive. 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.”