A compressed air generator is not the most glamorous part of a factory, but it is one of the most important – and expensive. To demonstrate, let’s start with a quick maths test. Pencils at the ready.
If you have a 50 kilowatt (kW) compressor, running for 4,000 hours per year, how many kilowatt hours (kWh) of energy will it make in that year? And, if electricity is priced at 10p per kWh, how much will it cost to run your compressor?
The answer, of course, is 200,000kWh of energy, costing £20,000 per year. That’s a lot of money, just to run an air compressor. However, Ken Revell, business line manager at Atlas Copco Compressors, is adamant that a few simple savings and a bit of careful planning can help save you both energy and money when it comes to your compressed air.
Back to basics
The first step, says Revell, is to go back to basics. “Take it back to when you were designing your factory and working out the processes,” he explains. “The bit that people barely think about is the air intake. Your air compressor is going to be more efficient at cooler temperatures; it’s going to be affected by dust in the atmosphere, by moist environments and chemicals in the air.”
All this means that you have to be mindful of a number of things when looking to fit a new compressor. As Revell continues: “You have to think about where you are taking air from; if you put the intake next to a car park or loading bay, you will be sucking all that pollution into your compressor and down the lines. If we can get that bit right, already we have lengthened the lifespan of the compressor and reduced the need to purify the air.”
And it doesn’t stop there. Revell describes how every decision you make when specifying a compressor can have a knock-on effect further down the line. “For example, how much filtration do you need? Every filter comes with a cost, both in terms of maintenance and pressure drop. Every bit of pressure drop that you build into the system will affect your process and, ultimately, cost you money. Likewise, how moist do you need your compressed air? You have to consider what your operations involve. If you are working with powders, you’ll need dry air – which is more costly. If you’re working with general pneumatics, for example, you will still need it dry, but not to the same level.”
Plan carefully, is Revell’s advice, or risk serious failings further down the line. Take air receivers, which act as a storage buffer between the compressor and the consumption system. There is a simple formula that calculates the size of air receiver in relation to the compressor; but, says Revell, this may be leading many astray. “It’s a very general formula, and doesn’t apply to everyone. You have to think hard about whether you need such a big receiver. If you are running a variable speed design, all you are doing is taking the pulses out and making sure you can manage your air at a constant level. If, however, you are using great big wallops of air coming out in an instant, you will need a big receiver. Maybe you need a big receiver but a smaller compressor? It all boils down to the same idea, though: get the design right.”
Small changes go a long way
Think also about the design of your piping network. “Many factories use pipes made of rough steel,” says Revell. “The fittings are screwed in, and the pipe joints will be a bit rough. This creates a lot of eddy currents. All those turbulences will cause a pressure drop, which will cost you efficiency and money. The more elbows and Ts you have when designing the system, the more eddies you create. We are looking to design systems that have low-resistance in the pipework, made of smooth-bore aluminium, to help combat this. A turbulence-free, lamina flow will deliver the same pressure at the end as at the start.”
Compressing air is not an efficient process. To produce 1kW of compressed air uses 8kW of energy. About 70% of the cost of a compressor is powering it, according to Revell. However, with careful management, 90% of the energy you put into the compressor can be recovered and used elsewhere. “If we can use the energy produced by the compressor, in the form of heat, to warm your warehouse, or power a machine, you will see massive efficiency gains for your business,” explains Revell.
It’s the little things that add up to make a big difference. For instance, if the temperature of the air coming into the compressor increases by just 5oC, you will reduce efficiency by 2%. “If you go and simply open up your vents to stop that temperature increase happening, you’ve saved a significant amount of money straight away,” says Revell. Likewise, a drop in air intake pressure of just 25 millibars (mb) will also result in a 2% efficiency loss.
Importance of maintenance
All of these savings can be made by simply having a good maintenance system. “The average compressed air system, after five years, will have leaks in about 20% of its joints,” warns Revell. “In the movements of pipework and so on, leaks appear around joints. This means a lot of energy – and money – is being thrown into the atmosphere.” Regular maintenance, plus good housekeeping (turning unused machines off) will help combat these leaks.
Choosing the correct oil, even if it comes at a premium, to seal, cool and lubricate your compressor is also vital, says Revell. “The oil in a compressor is doing a lot of work. It is being compressed, bubbled with air, taken out, sent through the cooler, cooled again, having the air stripped out and then being compressed again – every 20 seconds or so. If you think you are going to save 50p per litre of oil by buying a product that has not been designed to, for instance, remove foaming and cleaning agents, you will suffer immensely. Using the incorrect oil will also eat into the lifecycle of the compressor.”
That’s an awful lot to think about, and keeping on top of it can be daunting to many. However, technology is helping manufacturers get to grips with managing their compressed air supply. “The Internet of Things, and the amount of connectivity we can put on compressors now, means we can predict and advise what you need to change,” says Revell. “For example, you may have too big a machine, or a variable speed one where you don’t need it. We can remotely monitor what you’re doing and how you’re doing it. The IoT is proving to be a game-changer in compressed air management. It allows you, the user, to take control, and not just on an ad hoc basis.”
Without the correct planning and management, compressed air costs can spiral out of control. However, with some careful thought, and clever use of technology, your costs and energy usage can be brought back in line.
Compressor savings tips
- Choose carefully – What type of compressor do you need? Don’t ‘over-specify’ your compressor, if a simpler (and cheaper) one will work just fine.
- Keep control – Being able to effectively control your air is crucial to saving money: look at your receivers, drains and oil/water separators.
- Be energy-smart – About 90% of the electricity you put into the compressor can be reused elsewhere – convert the energy into heating your warehouse, for example.
- Maintenance is key – Keep on top of your maintenance, and don’t skimp on costs – for instance, buying cheaper oil isn’t going to help at all in the long-run.
- Utilise technology – Use monitors to understand how your compressor is running, and predict if and when it is set to go wrong.
This article is based on Ken Revell’s conference session, Smarter Strategies for Optimised Compressed Air Management, at the Manufacturing Management Show on 24 November.