Modification of Heat Exchanger Network Design by Considering Physical Properties Variation

S. H. A. Nejad, F. Shahraki, M. R. S. Birjandi, A. Kovac Kralj and F. Fazlollahi

Abstract
The temperature dependency of streams’ physical properties can have a significant effect on heat exchanger networks (HENs) design. An average value can be utilized during each temperature interval in order to determine the physical properties of the streams. Another method is the use of the physical properties’ values, which vary with regard to temperature along each stream. In this paper, the energy targeting for an ammonia plant has already been done before using both methods, with and without stream segmentation. Pinch temperature, ΔTmin, and the values of the hot and cold utilities in both cases are different and so the HEN has to be changed. The results demonstrates that when splitting streams into two or more segments within the existing ammonia plant, the pinch point increases by about 3 °C, and hot and cold utilities consumption increases by approximately 23 % and 11 %, respectively. The area of the heat exchanger network also is increased by about 50 %. Finally, an aggregation diagram is introduced for the evaluation of specific heat capacity distribution along the whole streams of the network.

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Keywords
Heat exchanger networks, heat integration, pinch technology, physical properties variation, aggregation diagram