With closed loop adsorption dryer systems, operating in accordance with the total output flow principle previously described, the following special features must always be taken into consideration: Only drying media which is 100% waterproof can be utilised in an adsorber with a loading factor of 12 - 14%. Ducting the compressed air through the entire system. Two adsorbers, many valves, coolers, separators and costly piping arrangements result in a pressure drop far exceeding the corresponding values with other dryer systems. The condensate4, fed into the compressed air system from oil free compression, develops strongly acidic characteristics down to a ph-value of 4. Assuming an operating pressure of 7 bar absolute at the inlet to the dryer, the following pressure losses are to be expected in practice: Closed loop adsorption dryers up to 0. 6 bar
Other adsorption dryers up to 0.15 bar When comparing the systems, the user of an installation, making his final analysis, attaches importance to which operating pressure is available in the end to the compressed air network after treatment and for productive purposes. Practical experience suggests that the following comparison of pressure losses realistically describes the situation: With closed loop systems pa = 7 - 0.60 = 6.40 bar abs.
With other systems pa = 7 - 0.15 = 6.85 bar abs. Expressed differently: If the supply pressure available to the compressed air network immediately after treatment is reduced from p = 6.85 bar abs. to p = 6.4 bar abs, the appropriate laws (Formula 4.6.2.4) establish a loss of performance from 6.852 to 6.42, i.e. by 14.5%. This loss has to be compensated for by additional compressor performance. When regenerating by part-current, work energy is lost through reducing the main air flow. Looked at dispassionately, energy costs are, therefore, more or less the same for all processes. On the one hand, the heat for desorption is already available, on the other hand, when compressor heat is used for regeneration in adsorption dryers of closed loop design, this advantage has to be paid for by higher pressure losses as compared with other systems. With oil free compression, internal losses of the compressor stage are higher than with oil injected compression. The sum total from compressor and dryer performance of the differing systems is, therefore, just about the same. If different results are reported, these are based on marketing considerations without taking into account the fact that compressor plus adsorption dryer form one unit. 4oil/water emulsions ph-value = 7
