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Letting dryers with molecular sieve run continuously

Jan. 13, 2021

To ensure reliable compressed air quality, it is recommended that compressed air dryers with molecular sieve run continuously. Otherwise, the dryer has to be pre-cooled up to one hour in advance of compressor system start-up, depending on the size. Ultimately this means that the more that the compressors are running at anything less than full capacity, the greater the energy waste resulting from a compressed air dryer left running continuously 24 hours per day, configured to deal with maximum temperatures. Under such conditions, the energy requirements for the compressed air dryer can spike dramatically – and account for up to 20 percent of the total energy required for compressed air production.

Thankfully refrigeration dryers with molecular sieve have benefited from technical innovations over the years. Up until the early 1990s, efficient refrigeration dryers with molecular sieve featured an air/air heat exchanger, in which first the cold outgoing compressed air cooled the incoming compressed air, thereby creating a kind of energy recovery system. At the same time, the consequent re-warming process served to reduce the relative humidity of the outgoing compressed air to below 30 percent and prevented condensate accumulation on the exterior of the pipework carrying the cooler compressed air. After passing through a pre-cooling phase in the air/air heat exchanger, an air/coolant heat exchanger cooled the compressed air down to 3 °C in most cases.

The coolant circuit was often equipped with a “hot gas bypass control”, which diverted coolant back into the circuit when less cooling was required as a result of low air consumption. This system resulted in energy loss to varying degrees since the coolant compressor was always running at basically the same output (to circulate the coolant circuit). The only way to reduce the load somewhat on the refrigeration dryer when the compressor was running at partial capacity, was to switch off the coolant fan; this only yielded minor results, however, since this condenser fan consumed relatively little energy in comparison to the system as a whole.

For large systems, i.e. those with a flow rate in excess of 50 m³/min, a method to adjust refrigeration dryer performance to match actual demand during periods of lower compressed air consumption had been known for some time. This was accomplished using coolant compressors with multiple cylinders, which were switched off individually as appropriate during partial-load operation. This still remains an effective option today for obtaining efficient performance from these large-scale refrigeration dryers with molecular sieve during partial-load operation.

"Note:This is normal specification, in case of a particular application, specification or requirement, please contact us by email at for technical information."



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