At first glance, the government's ESOS (Energy Saving Opportunities Scheme) may not seem relevant to most in production and maintenance engineering. After all, it only applies to £40 million-plus businesses, so the mandatory energy audits (due by 5 December this year) are, for the vast majority, somebody else's problem. Also, the fact is that plant and factory machinery has to run – and do so as efficiently as possible – so surely the key driver must remain the relentless focus on flexible, yet lean operations?
Well, yes. But there's no getting away from the increasing importance of energy costs and related carbon emissions, not only to the government and the EC, but also to firms' directors, whatever the turnover. So, for manufacturers of all sizes, ESOS should act as a trigger. We need to revisit our factories, process plants and warehouses – invariably, by far the greatest energy consumers – conducting 'eyes wide open' energy surveys, with a view to embarking on some serious cost- and carbon-saving projects.
Easy to say, but where should you start? Well, unsurprisingly, it's all about priorities and, naturally, those depend hugely on the nature of your production. Obvious candidates for review may well include: power-hungry electric motors (the classic being installing drives, particularly where pumps and fans are concerned, to match demand more closely to supply); lighting; boiler plant; heat treatment, chilling and refrigeration systems; and HVAC plant. Clearly, however, you need to focus on seeking out realistic candidates with the greatest potential for power turn-down.
Bear in mind, some projects may involve adapting existing equipment, while others may mean installing alternative, more energy-efficient technologies. If it's the latter, look for obsolete and/or less reliable equipment if you want management buy-in. Sometimes, you may also need to challenge accepted wisdom, even beyond the known main energy-consuming utilities. For example, on waste water treatment plant, it increasingly makes sense to consider installing smaller scale AD (anaerobic digestion) systems and CHP (combined heat and power) plants to recoup latent energy, rather than paying clean-up fees.
So, with the field now open for consideration, let's examine some wholly realistic prospects beyond what might be considered the norm. Take compressed air, which is generally accepted as accounting for at least 10% and in many cases 30% of a plant's electrical demand. Everyone in the industry will tell you that compressors should be specified to match the demand requirement as closely as possible and certainly not according only to purchase price alone (small compared to lifetime costs) or rated power (look at rated air delivery and compare). However, according to Andy Jones, managing director of Mattei, too many factories are using variable speed compressors when fixed speed machines would be more appropriate – and vice versa. And, it's all too common to find standard industrial compressors (designed to produce 8–13bar) on low-pressure duties.
Free air?
"We often find compressors rated at 10bar and above working in a system that only requires 6–7bar, which is a very inefficient way to operate a compressed air system," asserts Jones. "In some applications, there may be no requirement to compress air at all. The process might only involve moving something, so a blower might be a better, more efficient, solution." And it's a similar story with using compressed air to clean off machinery or workbenches.
Why the common misapplication? Because so many still see air as free. Hence also the tendency to leave them running, even when the machines they serve have been switched off – despite the Carbon Trust estimating that idling compressors run at around 40% of full load. If you're not already shutting them down when they're not required, now is the time to implement some simple controls.
And remember it's not just about the compressor: ensuring that your pipework is of the correct gauge and material (ideally, smooth stainless steel or aluminium) to meet factory demand, and that it has been installed with as few bends as possible (to minimise pressure drop) is just as important. Additionally, a programme of leak detection and repair could pay rapid dividends. Carl Sharpe, Boge's compressor energy efficiency specialist, suggests that it's not uncommon to see 40–50% leakage rates where air pipework has not been maintained properly.
And he adds: "If those leaks are at, say, 10bar, rather than the 6bar they need, that's a lot of money just hissing away."
Meanwhile, if your factory is using compressed air for cleaning, drying or cooling, consider changing to nozzles, air amps, air curtains or high thrust jets, such as those from Meech, rather than what amount to open pipes. All are designed to entrain ambient air (at a ratio up to 25:1) and hence boost the air supply. Meech business unit director Iain Cameron reckons some plants could reduce their pressure by more than 50%, pointing out that a 1bar reduction in operating pressure reduces energy consumption by 7%.
What about steam systems? It's been said before, but the fact remains that on average a staggering 22% of steam generated is wasted. We shouldn't be that shocked. As AVT Reliability's Hans de Kegel says, something as small as a 3mm orifice under 7bar (100 psi) means losses of 25 tonnes of steam per annum. And it doesn't stop there: drops in system pressure tend to force higher boiler firing rates, meaning higher energy costs, more carbon emissions and lower operating efficiency.
Additionally, over time the corrosive power of steam can cause equipment failure, resulting in expensive repairs or replacements and potentially serious injury. Hence the HSE's (Health and Safety Executive) Pressure Systems Safety Regulations (PSSR 2000), with the focus on materials, safety devices and the requirement for suitable maintenance programmes – although there is no standard practice.
From an energy audit perspective, it's worth remembering that steam leaks can occur in many places, including from valve stems, pressure regulators and flanges. That said, the greatest and most expensive source is generally failed steam traps, originally installed in the pipe network to control and eliminate condensate so that steam reaches its points of use as dry as possible.
So best advice is, whether your plant uses thermostatic, mechanical or thermodynamic traps, invest in an initial survey and a repair/replace programme – and then make this part of routine inspection and maintenance on your CMMS. The only caveat: be aware that, while contractors may use any or all of visual observation, and thermal and ultrasound measurement techniques, skill is required and it is possible to miss leaking traps or misdiagnose them.
Clearly, there are many other energy-saving opportunities in factories and plants worth serious consideration. But finally, if your primary concern is a warehouse or logistics centre with a large conveyor estate, you might want to consider replacing conventional 400V motor-driven technology for decentralised 24V systems, such as Interroll's RollerDrives. This system involves a decentralised structure of drives installed on conveyor zones. Each is switched on and off individually under automatic control, such that only those required to transport goods are consuming energy.
Hermes Fulfilment in Germany took that plunge several years ago, and Michael Schekatz, head of the technical services department, reports energy savings of 25%, while noise levels have fallen and maintenance costs reduced. He also points to the implementation of braking energy recovery in the firm's high bay warehouse at Haldensleben, as well as energy-efficient lighting, and a CHP plant as major contributors to energy reduction at the site.
