At the recent Air-Tech exhibition at the NEC in Birmingham, Beko Technologies gave a presentation about the issues of having an air supply at, for example, 7 bar (g) venting down to atmosphere without doing any useful work or work that cannot be done more economically or safely by another medium… An example of this would be the use of blow guns to clean machinery down at the end of a production period i.e. could be three times per day. This practice was widespread and was wasteful in that the dirt/dust would resettle, the pressure was not often regulated and it is a potentially dangerous practice particularly if the operative has an open sore then compressed air can be potentially lethal. There is a simple answer, use a vacuum attachment to the airline or a ‘venturi’-assisted type which increases the flow at reduced pressure. The opportunities for saving were broken down into 3 key areas. The first was leaks and it is well-known that leaks from a compressed air system can be quite considerable. In fact, a system with 10 per cent leakage is regarded as a good one. Bearing in mind that 10 per cent of all power used in modern industrialised societies will be to compress air then we are wasting 1 per cent of all power even when we are good at housekeeping so it is clearly important that we make sure that the wastage is not significantly higher than this. Causes of leaks What causes leaks in a compressed air system? There are many opportunities for the compressed air network to develop leaks but the principle ones would be: • Corrosive condensate. The particulate material drawn into a compressor together with the small amount of oil carried over will become an acidic liquid when the compressed air cools and water vapour condenses out and mixes. • Poor installation. Pipe supports not adequately deigned causing stress on joints which become leaks. Cheap solutions such as hoses for temporary solutions which become permanent. • Impacts such as fork lift truck. • Poor maintenance. The maintenance engineer has to see the compressed air network as a part of his maintenance routine rather than a one-off occasional exercise to cull leaks. Also some machinery will be stopped at a point where a valve or orifice is open and will remain open until the machinery restarts. These may be small occurrences but the sum total of all these small leaks is normally in excess of 10 per cent and for example a 75kW compressor running on load for a year will cost more than £70,000. Therefore it is important to check leaks via an ultrasonic device, mark up the leaks in some kind of classification as to the severity of the problem then fix the worst ones. It is then important to realise that this is not ‘job done’. The leaks will in some cases come back because of poor installation or appear elsewhere as the corrosive condensate or an impact creates a new leakage. The second area is condensate draining and it is important to understand that the condensate has to be drained efficiently or can be re-entrained and cause moisture problems and as just indicated will create leaks in the distribution system. There are not too many old fashioned steam type traps used anymore because they were subject to blocking through debris falling onto the valve seat and also to hydraulic locking requiring the installation of a balance pipe. Solenoid drains became popular and are still widely used but are inefficient because of the number of variables involved such as compressed air flow, pressure, temperature and relative humidity. All of these combine to ensure that the condensate volumes are different from day to day, morning to evening, winter to summer, UK to China. Product of choice To be sure to get rid of the condensate then the blow down time will be set for the worst case, which will mean considerable wastage on every occasion that does not equate to this set time. The solution to this is the zero loss drain, which is becoming the product of choice because there are no losses of the expensive resource of compressed air. There is an investment cost but in nearly all cases the return on investment can be shown as being acceptable. There may be as many as 100 drain points in a large plant with outdoor piping so it is a simple but important area to consider for the maintenance routine. A customer in the Midlands recently asked Beko Technologiess to attend site because of a perceived drying problem. This problem existed and was being dealt with but as part of the routine checks the air receiver drain was checked. With no exaggeration 15 minutes was required to drain the large air storage vessel. If the condensate level had become much higher than serious amounts of the contaminated condensate would have been re-entrained into their system. The company are involved in an industry where it is vital to be ‘just in time’ and deliver direct to production lines. It is easy to imagine the large scale problems for this company and its customers if a large scale ingress of condensate had occurred. The installation of an efficient level sensing Bekomat solves a potentially disastrous situation at a small investment cost The other area where compressed air is wasted is in the drying process. There are many processes which require a dew point below the -3degC, which refrigeration dryers are capable of reaching. This could be for instrument air, for pneumatic conveying, food, beverage or medical grade compressed air to name a few processes. The lower dew point typically -40degC is achieved by use of a desiccant material which is unchanged by the process of attracting water vapour via molecular forces but will need to be regenerated in order to be used over multiple drying/regenerating cycles. One of the regeneration methods is heatless or cold regeneration which requires a part of the dried compressed air to be expanded to become super dry and then flowed through the wet desiccant bed. Nature does not like large gradients and the difference between the water content of the desiccant and the regeneration air will create the migration across to the compressed air which is then vented to atmosphere. In this method 15 per cent of the compressed air is used solely for drying which if we equate back to our 75kW compressor would mean a cost of £10,000 or more. The reason this genre of dryer was popular was because of low price and simplicity but it is clear that for systems above the 75kW level other methods should be applied. Controlling cost Zero Purge dryers are becoming the norm for larger installations. They use external heat to regenerate the desiccant and blown external air to cool meaning that the costs are kept to a sensible level for the drying process. An example given at Air-Tech was of a company in the automotive industry who had a part purge drying system so lost a smaller notionally 5 per cent of the compressed air but had heating costs and cooling costs. The offer of a zero purge system showed a payback of less than 2 years for the purchase, installation and commissioning of 4 large Beko FRA-V dryers. Ongoing annual savings of more than £250,000 where attractive but another important customer benefit was that they could abandon their plans to add another large compressor into their network. This would have been very costly because alongside the capital and running costs there would have to have been a large investment in creating a space suitable for a large compressor to add to their very large system. Users of oil free compressor should also the consider the use of ‘Heat of Compression’ types of dryer which take advantage of the higher temperatures generated in s dry compressor as opposed to an oil lubricated type, to use the heat for regeneration of a desiccant. The message is clear and simple. Compressed air is the 4th utility but it is expensive and should be used selectively. When looking at energy saving possibilities the factory engineer should be serious looking and thinking “Have I got these open ends to atmosphere?” If the answer is yes then an action plan to reduce or eliminate should be high on his agenda. www.beko-technologies.co.uk