When we interview plant professionals about their experience with a product or service for a Plant Services Field Test, we usually hear about the good things it adds to their operations. In the case of Atlas Copco’s Z-Series oil-free screw compressors, the news was mainly about what they don’t get: contamination, high maintenance, breakdowns and excessive power bills.
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For example, Metal Improvement Company is a supplier to the Big 3 automakers and aerospace contractors. Its plant in Romulus, Mich., has two 800-hp ZR630 compressors running at 115 psi. "I have to rely on these things every day," says Perry Celsi, division manager at Metal Improvement. "They supply the compressed air that is the lifeblood of our shot peening business."
Clean, oil-free compressed air is a prerequisite for the continuity and quality of many manufacturing processes. Over the past decades, Atlas Copco has pioneered the development of oil-free rotary-tooth technology, resulting in a full range of highly reliable compressors delivering 100% oil-free and clean air. Developed especially for applications demanding the highest levels of purity, Atlas Copco’s ZR/ZT series compressors are certified Class 0 to eliminate risks of oil contamination.
In 2002, the ZR/ZT range evolved from a single-tooth to a double-tooth element configuration. They now use a symmetrical compression rotor that’s dynamically balanced by design and increases efficiency.
Maintenance personnel say Atlas Copco Z-Series oil-free rotary screw compressors are especially satisfying when backed by a service contract.
Recent units operate at sound levels as low as 63 dB(A) for integration into the workplace. Refrigeration or adsorption dryers can be included in the compressor package, which can further trim energy consumption, the total number of moving parts and system cost. Versions are available for high ambient (50°C) as well as standard conditions.
ZT units are air-cooled; ZR units are water-cooled. Both are available in fixed or variable-speed versions, and the model number represents the unit’s kilowatt input.
Brazos Electric Cooperative, Palo Pinto, Texas, has replaced all its compressors with Atlas Copco units, “Even on the boilers with low-pressure, high-volume instead of high-pressure, low-volume,” says Gary Bolin, maintenance supervisor at Brazos. “Now we have no compressed air problems.”
The facility’s Z-Series compressors include two ZR45s and one ZT75, supplying plant and instrument air for the past five years. Standardizing on Atlas Copco has simplified parts and service. “It makes it easier to troubleshoot problems because we have only one brand,” Bolin says.
Easy Foods Inc., Doral, Fla., makes tortillas for institutions. A ZT50 VSD is the main compressor, backed by a ZT37 in standby. “The main compressor has a standard operating pressure of 125 psi and we set it 115 psi for production,” says Felipe Cabeza, maintenance engineer at Easy Foods. This saves about 5% in energy costs. Easy Foods’ ZT37 has a standard operating pressure of 110 psi and is set 90 psi, which reduces its energy consumption by 10%. “With either compressor, we supply enough capacity for our pneumatic system,” Cabeza adds.
The compressors have been running for a year, “no problems in this period,” Cabeza says. “The key strength is that this oil-free screw compressor and excellent air filter system provide dry, clean air. Better than piston compressors.”
Easy Foods’ system is fully automatic with “an excellent programmable control,” says Cabeza. “It’s monitored with software that includes data capture in real time and a recorded history. We use it to evaluate the relationship between the pneumatic system and the plant electrical consumption and make an effective diagnosis of the compressor system behavior.”
Compressors are complex machines, and our plants’ experiences weren’t entirely trouble-free. That’s how they came to appreciate their service contracts.
“One dryer gearbox was replaced under warranty,” one manager told us. “It took a little longer than we expected, but Atlas Copco made sure we didn’t have any downtime. Their technicians are very knowledgeable and good to work with.
“Anyone who needs their air — who relies on it — should get the Atlas Copco warranty,” the manager adds. “It’s $35 per kW per year and worth it for the service we’ve needed. Running six days, three shifts, it’s a very good deal for us. The reliability and service is unmatched among the companies I’ve worked with in the past.”
Brazos has had a few problems, “mainly electrical,” Bolin says, with “contacts on a starting relay.” On units used outdoors, he’d like to see better waterproofing of the controllers. But he still sees reliability as the major ROI item. “I haven’t put a dollar amount on it,” he says, “but they’ve saved us on downtime, which costs big bucks in power plants.”
Easy Foods has a maintenance agreement. “This service has been excellent,” Cabeza says, adding, “I think that any automated industry or factory that needs clean and dry air for its pneumatic system can benefit from this advanced and energy-saving technology.”