Compressing costs

Compressors are so ubiquitous within process plants that they are often referred to as the ‘fourth utility’.

But with their voracious appetite for electricity, managing compressor costs is becoming an increasingly critical facet of plant management, say experts.

Just a single 3mm hole in a compressed air system creates a leak, which can cost a business an additional £1,000 a year in electricity costs

Carbon Trust’s Richard Rugg

UK businesses could save £110 million by using their compressed air systems more efficiently, according to a recent Carbon Trust study.

“There is a misconception that compressed air is a free or low cost resource, when in fact the opposite is true,” says Richard Rugg, director of Carbon Trust programmes.

“Just a single 3mm hole in a compressed air system creates a leak, which can cost a business an additional £1,000 a year in electricity costs.”

Mark Ranger, UK business line manager for Atlas Copco’s oil-free air division, says: “You cannot manufacture or process anything that we rely on in our working lives without the use of compressed air”.

Atlas Copco supplies a wide range of compressors, including ‘oil-free’ units that tend to dominate the high-end production sectors such as food, drink and beverages, as well as chemical, composites and pharmaceuticals.

An oil-free compressor is necessary in these environments to avoid compromising product quality by moisture, dirt or compressor oil carry-over, says Ranger.

One of Atlas Copco’s key objectives is to give its customers access to a ‘carbon neutral’ compressor installation, by utilising energy recovery, variable-speed drive technology and lower operational cost air quality solutions.

“We believe a combination of these could genuinely achieve a carbon-zero implementation,” he says.

However, uptime capability and reliability are still the most important aspects on a customer’s agenda, says Ranger.

There is still a commercial challenge in educating plant owners about the lifelong costs of a compressor, and the benefits of a solution that is energy efficient and environmentally friendly, verses the equipment cost on paper, he says.

“In the majority of cases, this rationale stops at the price on the quotation, without true consideration to the ‘Total Cost of Ownership’ over the life of the initial investment,” he says.

Energy recovery is an obvious cost-saving feature that can make a broad impact over the life of the compressor, says Ranger. “When you compress air, you create heat as a by-product which is then wasted,” he says.

“We can recapture that energy at the compression element while the air is hot, using heat exchangers.”

Energy recovery

Automotive textile manufacturer Autofil Worldwide recently achieved average cost savings of £37,000 a year and reduced annual CO2 emissions by 260,000 tonnes by adopting Atlas Copco’s energy recovery technology.

Autofil’s system comprises 12 compressors, including three GA 160+ units and a GA 250 compressor connected to a stand-alone ER-S5 energy recovery unit. As well as the considerable demand for compressed air on site, the dyeing process has a large requirement for hot water.

The by-product heat from the GA 250 compressor is used to pre-heat this water to around 50°C, rather than relying on additional gas power to heat it at point of use.

This is facilitated by the ER-S5 energy recovery unit, as hot oil from the compressor’s air end is diverted through a stainless steel plate heat exchanger. Heat from the oil is transferred to cool water on the opposite side of the exchanger, producing a continuous flow of hot water from the ER outlet.

To further this cause, Atlas Copco has recently launched an all-in-one Thermo Kit of energy recovery components that can provide supplementary hot water for no additional investment.

Using this system, the company says a typical Atlas Copco GA45+ compressor might achieve savings of £2,331 on a user’s annual gas bill.

“It should be possible to recover between 80 and 90% of the energy that the compressor ingests,” says Ranger, even taking into consideration external factors. Compressor supplier Boge has also been instrumental in helping some of its customers in the food industry to improve efficiency.

“Although customers want energy efficiency and environmentally friendly solutions, what we find above all is that they want a reliable air supply because they need compressed air within their processes,” says Ray Lawton, project sales manager at BOGE Compressors UK.

“When it comes to providing reliable equipment, it is partly a build quality issue, but it can also depend on how quickly you react to customers needing you onsite,” says Lawton.

“It is also important to design a system with some redundancy,” he says.

“If you are operating the system to its limit and something goes wrong, then you’ll have a major site problem.”

“One way to achieve this in sites with varying production needs,” says Lawton, “is to introduce variable speed drive, or intelligent control technology,” so equipment can still run efficiently in times of reduced demand.

“Efficiency of compressors can also be affected by operating factors such as pressure drops and leaks in the air distribution system. A compressor can run for quite a long time and you can keep replacing parts but the truth is that a 20-year-old compressor isn’t using the most innovative technology, isn’t going to be as energy efficient and the cost of parts will eventually become more expensive than replacing the unit,” says Lawton.

“You can keep patching it up but those failures will only become more frequent.”

Heat exchange

In the fresh food production process, compressed air has an important role in cleaning and sorting, while nitrogen is essential for preservation.

Germany-based Keltenhof Frischprodukte produces more than 80 different varieties of fresh produce daily and says it has saved more than €18,000 (£13,000) per year since it introduced the Boge’s Bluekat screw compressor, which supplies oil-free compressed air, and an N2 generator to produce nitrogen on demand.

It says the addition of the BOGE Duotherm external heat recovery system allowed it to recuperate up to 72% of the input energy used in compression in the form of heat, which is used elsewhere, such as heating administration rooms. Compressors are also very important in non-food applications such as at Halliburton’s Great Yarmouth sit, where a new rotary screw compressor was recently installed to improve the process of conveying drilling cement.

Halliburton says its existing diesel powered compressor had become unreliable, noisy and was prone to breakdown.

To replace it, Halliburton selected HPC’s 10kw HPC DSD202SFC rotary screw compressor, which injects dry compressed air into the drilling cement dry powder to ‘fluidise’ and smooth its flow during the conveying process from silo to tanker.

An appropriate power supply was a key issue at the remote site, however HPC was able to offer a guarantee for the performance data and electrical power of its unit.

Its frequency control features also offered additional protection against damaging current spikes.

“We really appreciate the performance of the HPC compressor and the levels of service and commitment of the HPC team,” says Paul Dickerson, operations manager at Halliburton’s Great Yarmouth site.

Determining the right type and size of compressor for a particular application is a very important consideration, says Steve Downes, northern Europe sales manager for Gardner Denver.

Downes says some customers specify the highest quality class specification for their application, whether it’s necessary to do so or not.

“I always recommend that process engineers seek advice on compressor selection to ensure they meet the required needs of the system profile, along with the required level of air quality,” he says.

“What matters most is what it will cost to run the compressor over its whole operational lifetime,” he says.

“Industry averages suggest that energy costs account for more than 80% of the total cost of ownership of a compressor, so installing a new energy-efficient model can soon reap rewards.” It’s also important to make sure that any downstream equipment, such as dryers and filters, are sized correctly for the application.

“Undersized equipment will cause excessive pressure drops, and will compromise the desired air quality as well as consuming excess energy,” he adds.

“When considering purchasing a new compressor or looking to upgrade an existing installation, we would always advise that the customer conducts an air audit,” he says.

This is a process where a data-logging unit is attached to each compressor in the network to show the exact pressure and flow demands of the complete system. By ensuring correct sized units are installed to optimise the system efficiency this can help to reduce energy consumption and increase reliability.

“Modern on board compressor controllers have also been developed to allow continuous data logging so if the system profile changes, compressors can also be switched to ensure the highest levels of efficiency are continually achieved,” he says.