Compressed air dryer dew point monitoring prevents costly contamination and downtime
A compressed air dryer can appear to be operating normally while delivering air with an unacceptable dew point, increasing the risk of contamination, production downtime, equipment damage and unnecessary energy costs. Yet while most plants have compressed air dryers installed as standalone units or built into the compressor, fewer than five percent have a dew point performance monitoring system in place.
A standard refrigeration air dryer is fitted with a thermal probe that measures the physical temperature of the compressed air and not the actual moisture content in ppm or °C Td of the compressed air leaving the air dryer.Â
These probes are basic fitments to most air dryers. They normally measure the actual physical temperature in the compressed air/Freon heat exchanger – the coldest part of the dryer. It does not reflect the actual pressure dew point of the compressed air being introduced into the factory. The dew point (compressed air dryness) of the compressor system can fluctuate significantly for a number of reasons.
Causes of dew point variation can be the result of many factors. These are summarised as:
- Compressed air volume overloading, thus exceeding the dryer capacity and elevating dew points.
- Low inlet compressed air pressures; normally when < 7 bar G.
- A jammed condensate drain valve. Condensates are formed but are not drained.
- High inlet air temperatures and high compressor room temperatures, for example, above the dryer’s standard selection criteria.
- Poor setting of gas expansion and/or a hot gas bypass valve.
- A bypass valve left open.
- Poorly designed inlet/outlet air piping to the dryer.
- The air dryer’s refrigeration compressor is tripped on internal overload. Rarely is it ever reflected on a dryer’s fascia display.
- An Eskom mains failure, with no auto restart system on the air dryer.
These faults can dramatically affect an air dryer’s performance.
Most operators performing their shift walk-through will rarely spot the problem. And the majority will struggle to identify the cause of the fault. If one analyses the effect of any of the problems above, the results are a high-pressure dew point.
The solution is to fit an independent dew point monitor on the air line, after the air dryer, to highlight the high dew point problem. The S305 Suto Dew Point Monitor, from Artic Driers International, will sound a warning horn and flash large LED lights in the compressor room/area. The operator screen flashes its red backlight and the 4 … 20 mA output can be used to connect this dew point monitor to a PLC or a SCADA system. The S305 unit also has volt-free contacts.
It is advisable for every compressed air dryer to have an independent dew point monitor. The investment cost is very affordable, especially when compared to the cost of contamination to the compressed air system. There are also systems to monitor compressor oil vapour carry-over to the plant. The Suto S120 is for oil vapour and the S130 is a particle counter system. The S132 is an air quality system that includes all the outputs needed to monitor the system. The S305v is available in two measurement ranges: –60 to +20 °C Td and –20 to +50 °C Td.
Artic Driers International is a trusted supplier for compressed air treatment equipment. It now manufactures air dryers in South Africa, offering short lead times on local dryer builds. Other offerings include air leak detection, onsite mobile air quality measurement, pressure testing, air volume measurement, and also air dryer refurbishment, servicing, and hire. Special air dryer skid packages can be designed to the client’s specifications.
