Formation of fouling layers on a heat exchanger element exposed to warm, humid and solid loaded air streams

In consideration of the very high energy consumption of drying processes it is astonishing and disadvantageous that the majority of industrial dryers are offered and operated without energy recovery. The avoidance of fouling is here the key issue concerning an efficient heat recovery from dryer exhaust gases. By the present state of knowledge, fouling mechanisms under the specific conditions of dryer exhaust gases-intensified and additionally complicated by the interrelated process of condensation of vapors-are neither clarified nor predictable. The objective of the present investigations is a phenomenological description and quantification of the dynamics of fouling layer formation, with identification of ranges of influential process conditions responsible for the onset of formation of fouling layer, its growth and destruction. To analyze the formation of fouling layers on cold heat exchanger surfaces, a specialized experimental facility, which contains a so-called dryer exhaust gas simulator and a cooled probe tube in a measuring section has been designed and built. In the present, selected results from the first group of experiments carried out with this facility are presented and discussed. Solids in the gas stream have been CaCO3 with d(p) = 40 mum, parameters affecting vapor condensation have been varied. (C) 2002 Elsevier Science Inc. All rights reserved.