Incorporating fouling model in plate heat exchanger modelling and design

Abstract Efficient heat recuperation is of primary concern in resolving the problem of optimal energy usage. To achieve best results it requires the use of efficient compact heat exchangers among which Plate Heat Exchanger (PHE) is one of the most promising types. Its flexibility allows finding economically viable solutions in different processes of heat utilisation. But the fouling formation on surfaces of plates can lead to energy losses, additional power consumption and the costs of cleaning. This practical operational problem is a significant challenge in the progression towards sustainable development. The traditional two approaches to account for fouling in heat exchanger design are (1) to increase heat transfer surface by employing fixed fouling thermal resistance or (2) by introducing margin for heat transfer surface area. However the reliable data on fouling factors for different streams in PHEs are limited and both approaches can lead to significant errors in estimation of required heat transfer area in PHE, the increase of which can lead to lower flow velocities and higher fouling tendencies. The method of PHE based on the mathematical model accounting for local process parameters distribution along heat transfer surface is proposed. It is incorporating earlier developed fouling model (Arsenyeva et al., 2013). It requires the data of fouling monitoring for any heat exchanger working with considered streams to identify model parameters. Having these data the method can be used for design of new PHEs or for retrofitting the existing PHEs on considered enterprise for optimal performance. The applicability of the method is demonstrated with a case study for PHE working in food industry application. The PHE (290 plates) with heat transfer area 259.2 m2 was initially designed to heat glucose solution by another stream of glucose solution coming with 140 °C. The heavy fouling was observed, which required cleaning after one week of operation due to drop in heat transfer load and increase in pressure drop up to 1 bar. The redesigning of PHE with the proposed method has shown the possibility to decrease heat transfer area to 137.7m2 (155 plates) of the PHE by rearranging plates with different corrugation geometry and reducing their number on the same frame. The monitoring of PHE performance during one year of operation have shown that the same drop in heat transfer load and increase in pressure drop was observed only after a month of operation, the cleaning during that period was not required. It has reduced the capital cost of PHE, operating cost for cleaning and prolonged the service life time of rubber gaskets. The case study demonstrated the ability of the proposed method of PHE design to optimise the PHE performance with proper selection of PHE plates and complete use of available pressure drop to mitigate fouling formation.