25 March 2012
Fresh thinking on air use
Compressors are taken for granted in many factories – until something goes wrong. So it's worth taking some time to step back and reconsider your system. Laura Cork asks the experts for their top tips
Compressors are found in factories large and small, in every sector, in every corner of the UK. Without them, production would grind to a halt. Yet until the relatively recent surge in energy prices, most manufacturers paid little attention to these workhorses unless they failed. The energy-efficiency argument changed all that.
Installing new equipment can pay dividends (see box p53). But there are also ways to optimise an existing system by checking whether it meets current requirements and ensuring appropriate measures are in place to maximise efficiency. The following is by no means comprehensive, but is a useful checklist to ensure you squeeze every drop of value from your compressor investment.
- Leak detection
Leaks cost money – the experts reckon anywhere between 25-30% of the energy used in compressed air systems is wasted.
Worse still, many systems have multiple leaks, says Andy Jones of compressor manufacturer Mattei: "The Carbon Trust suggests that air escaping through a single
3 mm hole could cost a business around £700 per year in energy costs, but a typical system will have more than just one leak – we often find systems with anywhere between 150 and 300. For a company using 50m3 of compressed air per minute, this could equate to savings of around £63,000 if the leaks were repaired."
Since air is non-hazardous, leaks in pipework can go undetected for a long time, often being considered too costly to rectify, warns CompAir's Richard Hilton. In his view, 25% of system energy is typically wasted in this way.
Jeremy Salisbury of MRO business Brammer recommends ultrasound for leak detection: "Every leak in a compressed air system produces a sound pitch which is often impossible to hear with the human ear over the background of a noisy factory. However, the output can be detected and read by ultrasound equipment, with each leak tagged and numbered."
Jones says annual leak detection surveys are ideal, but essential before new equipment is specified. Without a survey, he says, new kit is a "false economy".
- Correct specification
All too often, compressors are incorrectly specified, agree the experts. Mattei's Jones cites a case in point: "We recently found a company running a 75kW compressor which could actually fulfil its compressed air requirements with a 45kW machine, with estimated savings being in the region of £12,000 a year."
New equipment will almost certainly result in energy savings – but savings won't be maximised if the kit is just upgraded on a like-for-like basis, says Jones.
Make sure you use the right technology, urges CompAir's Hilton: "For example, if your application demands the highest quality air, you should specify an oil-free compressor to eliminate the risk of contamination."
Correct specification should also extend to location. Some compressors can be sited close to production lines, but not all. Check out the noise implications on nearby workers.
- Fixed or variable?
It's not the case that variable speed drives are right for everyone, says Jones. "Sometimes we find a company is running a variable speed compressor when a fixed speed machine would be better. In recent years, variable speed compressors have been seen as a key way to reduce energy consumption... but they aren't right for every application."
VSDs will only save energy, he counters, if there are real peaks and troughs in air demand – and then only if these variations fall within the efficient working band of the compressor. "This sounds obvious but it's surprising how many [VSDs] are installed in workplaces with constant demands or where air demand lies outside the compressor's most efficient working range," Jones adds.
In the right environment, however, variable speed compressors can benefit performance and the bottom line. Sean Fairest of Atlas Copco explains: "In 70% of installations, load cycle lies between 40-80%, so there is a big potential for energy saving if VSD compressors are used instead. VSD compressors use an integrated frequency inverter that varies the speed of the compressor motor to match its output to air demand: this can provide energy savings averaging 35%."
- Maintenance and compliance
Whether it's pipework, the compressor or ancillary kit such as drains and filters, it's vital to ensure everything is maintained correctly. "In extreme cases, a poorly maintained compressor might even catch fire or explode," warns Jones.
It's because of this that written schemes of examinations are a legal requirement under the Pressure Systems Safety Regulations 2000. The document should cover the parts of the system that need to be examined, the nature of the examination, the preparatory work needed and the maximum interval between examinations. "There seem to be many organisations that aren't aware of this – but there is a potential fine of up to £20,000 for not having this document, so managers should familiarise themselves with this regulation and have a written scheme of examination drawn up," Jones urges.
Good upkeep saves money, too. "Regular servicing will reduce the energy running costs of a compressor significantly, so the potential gains are enormous," Fairest advises. "A clogged filter or inefficient dryer will create a pressure drop and reduce energy efficiency. On average, for every one bar pressure drop, an extra 7% of electrical power will be required to meet production needs."
Brammer's Salisbury agrees: "Some systems have a manual drain which can overfill, causing the oil and water mixture to be agitated if it is not emptied in time." A way around this, he says, is to fit an automatic drain operated by condensate levels, or a drain with a timer which can be set to empty periodically.
- Heat recovery
All the experts agree that heat recovery can be a valuable sideline to compressor use – and the heat can be used for water or space heating. "Most of the electrical power used by a screw compressor is transformed into heat, but up to 94% of compressor generated heat can be recovered rather than wasted," Fairest points out. A well-planned investment in energy recovery can provide a payback within one to three years, he states.
Heat from a water-cooled, oil-injected compressor can be recovered as hot water, Fairest adds. "Connecting it to a heating boiler's return circuit helps reduce heating costs of washroom supply, radiators and process operations. In the case of air-cooled compressors, the hot air can be ducted for direct space heating."
All well and good, though Jones reminds companies that location is an important consideration: "If the hot water is used some considerable distance away across the other side of the factory to where the compressor is sited, it probably isn't going to be efficient."
- Total cost of ownership
In common with many machines or items of equipment around the factory, the upfront purchase (or lease) costs are the tip of the iceberg. It's the ongoing cost of operation that forms the majority of the lifetime cost.
Atlas Copco's Sean Fairest says electricity accounts for around 80% of the typical lifecycle cost of a compressor, and the others agree – it's hardly surprising, then, given the exhorbitant rises in electricity prices, that compressor system energy efficiency is so high on the agenda.
Quality, cost, delivery
Insulation board maker Celotex reckons it can save £6,000 per year for the next three years, thanks to a new compressor from Atlas Copco.
Celotex relies on dry compressed air for insulation board assembly at its Hadleigh, Suffolk facility. By replacing two fixed-speed, oil-free compressors and refrigerant dryers with a single air-cooled, variable speed machine incorporating a heat regenerative IMD dryer, the company has improved air quality and cut energy use.
The integrated dryer eliminates moisture and doesn't require any external energy to dry the air.
The kit was supplied as a 'full feature' solution – where the compressor is pre-wired and pre-piped for fast installation.
"I was very impressed with the speed and quality of Atlas Copco's installation operation," says Celotex's process improvement manager, Jason Walker. "It allowed us to make a seamless switchover from the old plant to the new without any interruption to production."
As for energy savings, he says, "it looks like we can expect to gain at least £6,000 per annum over the next three years".
Atlas Copco Compressors
Compair Demag Ltd
Mattei Compressors Ltd
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