FEATURE COMPRESSED AIR
GO WITH THE FLOW I
Keith Barron, national sales manager at Atlas Copco Compressors, advises plant managers to give priority to pressure and flow when specifying compressed air systems in order to optimise performance and energy consumption
t is now widely accepted that compressed air accounts for on average
12 per cent of industrial electrical power consumption. In exceptional circumstances, it can even represent 30 per cent of a company’s energy consumption and therefore compressed air should arguably be seen as the UK’s ‘fourth utility’ along with electricity, water and gas. When specifying equipment for plant
air process applications every care should be taken to ensure the system’s performance and output is closely matched to the application need. However, in the past this was not always the case and as a result it was not an uncommon practice for suppliers to over-specify air compressors’ power and output ratings without challenge or regard to outcome. The legacy of this remains in many areas of industry, whereby the common benchmark for equipment performance comparison is restricted solely to the kW power rating of the installed motor drive. The compressed air equipment in an
installation determines the requisite working pressure of the system. This does not just depend on the air compressor, but also on the design of the system and all of its pipework, valves, dryers and filters. At the same time, the nominal air requirement for an application should be determined by calculating the air consumption for all the tools, machines and processes that will be connected. It should also include an estimate of their individual utilisation factors and also take into consideration leakage, wear, and future changes in the compressed air
Energy conscious manufacturers of
stationary oil-injected air compressors should seek to offer potential customers a number of pressure/flow variants in each kW category, and encourage installers to adopt the mantra: pressure + flow = energy = cost. Atlas Copco, for example, offers four options in each kW category across its entire range of rotary screw compressors. In the 11 kW range alone that can represent a 30 per cent differential in flow rate and over 32 per cent difference in unit costs. To illustrate this further, a 26 kW model is available as other offerings in this power sector are limited to a choice of 22 and 30 kW machines.
IT PAYS TO BE SURE One way to ensure a new compressed air system will be optimised, and provide the efficiency improvements that are promised, is by conducting an energy audit. This should be done both prior to replacement and at regular intervals after new equipment has been installed. Applying simple and non-intrusive air
requirement, which, experience shows, should be based on a probability factor that is close to 60 per cent. The laws of physics state that an
increase in pressure creates a decrease in flow. This correlation is important to bear in mind when suppliers seek to determine the required size of an air compressor based on its rated motor power. For example, a basic seven bar air compressor, driven by a 15 kW motor, will deliver compressed air at a maximum volume of approximately 45 l/s. However, the free air delivery from a 10 bar version will deliver only 37 l/s from the same power unit. Therefore, an increase in working pressure by one bar increases the power requirement by approximately six per cent.
Modern compressed air equipment can offer the benefits of reduced specific energy requirement.
Bottom left: An Atlas Copco Compressor installation example (McKinnon & Forbes)
audit data logging techniques to compressed air systems provides a true indication of an installation’s air use. Ultimately, it will flag up any wastage factors such as leakage and pressure drops. Most importantly, an audit establishes how well a compressed air system is actually performing and will highlight opportunities to increase production uptime, reduce maintenance and improve operating costs. As a result of these monitoring techniques, operating cost savings of as much as 40 per cent can be realised.
NEW DESIGNS, NEW OPPORTUNITIES Modern compressed air equipment, when correctly matched in terms of pressure and flow to process demands, can offer the benefits of reduced specific energy requirements (SER), improved productivity, and lower lifecycle costs. To take full advantage of the new oil-
lubricated rotary screw compressors that have been introduced in recent years, it pays to apply a few essential rules when deciding on a new compressor: Assess present and future needs by first checking out the existing system with a thorough air audit. Take account of all variables from air end output right through to point of use. Do not rely solely on stated motor power rating to match the compressor performance to the process air demand. Start with the pressure and flow requirement and then find the best fit in terms of drive motor power.
Atlas Copco Compressors
www.atlascopco.com T: 0845 601 0001
14 JULY/AUGUST 2017 | FACTORY EQUIPMENT / FACTORYEQUIPMENT
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