The biggest energy consumer in many factories is the compressor station. A 200 kW air compressor when serviced by a main line compressor company and with a power cost of R1,10 kWhr, will cost R1,3 million a year when operated continuously.
Auditing is a real need and the cost savings that can be achieved are huge. What do the various components of a comprehensive air audit tell you?
Air flow testing
Often older compressors deliver air flows well below the rated catalogue figures, yet still have high power rates. A good air flow audit will present a multi-axis graph over a number of days, showing air flow, pressure, velocity and power in one document.
While velocity may not be the final pointer for poor pipeline design and layout, it often identifies a problem found in many facilities. Many compressor manufacturing companies supply compressor packages with small discharge ports. This practice can lead to high air line velocities. Undersized air piping strangles the air mains. It creates back pressures that are enough to push compressors into an off-load position, while within the factory, production lines are suffering from a lack of pressure. This scenario misleads compressor operators into starting up yet another compressor to make up for the lack of pressure in the plant. This just adds to the problem of too much air being forced down too small a pipe, wasting more energy.
High line velocities can carry over waste condensate into the air line from the quiet zones within a dryer, thus re-polluting the air line. High velocities also carry air line contamination straight to the point of use. A good auditor will survey the plant room and not only monitor the compressors and pipe line pressures within it, but also downline in the plant to check the air distribution piping’s ability to transmit compressed air efficiently without pressure losses.
Along with the velocity, pressure is an indicator of what’s really going on. On occasions we have found that the compressor’s discharge pressures have been increased in the plant room to overcome a poorly designed or overloaded distribution system, causing even more demand for power.
Dew point and air dryness
A blocked condensate drain, an open bypass valve, or worse still a fractured heat exchanger are causes of water pollution in a factory. A dew point probe identifies a water contamination problem faster than any machine minder. Many dryers are on line showing a dew point of 3°C but are passing thousands of litres of water a week into the plant due to a simple fault such as a stuck auto drain.
Air dryers are not fitted with dew point probes as these are quite expensive. The dryer’s fascia merely monitors the air temperature in the main heat exchanger or the suction gas line to the freon compressor. A fault can be present and the dryer will still indicate a 3 or 4 degree dew point. A dew point meter will identify the problem in minutes and can sound an alarm. Dew point probes can also be connected to a factory’s scada system. A good air audit will show the flow, pressure, relative humidity and dew point in one concise graph.
Leak detection is also an area where speed, quality of ultrasonic detection equipment and methodology are critical. Equipment should have the ability to estimate leak losses via sampled sound bites. The leak sites have to be tagged, photographed and documented in a clear and concise manner. If at all possible, the leak loss total value should be verified by a separate leak rate check with the plant in shutdown mode. The total leak loss should be expressed in a volume and in kW and a cost for the kilowatts used.
Auditing is a science
Auditing has now become a science, it’s no longer just a look at a compressor system. Many companies can capture data, but few have insight into the status of their compressed air system and the potential for optimisation and power saving. Auditing is the first step in achieving an optimised compressed air system.
Artic Driers has the ability to carry out full audits, as well as the experience and knowledge to analyse and interpret the data to provide a meaningful report to the client.
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