Plate heat exchanger design for the utilisation of waste heat from exhaust gases of drying process

Highlights: • The mathematical model of steam condensation in the presence of noncondensing gas is developed. • The modelling accounts for the change of local process parameters along the PHE channels. • PHE for waste heat utilisation from exhaust gases after tobacco drying is designed. • The application of PHE resulted in heat energy saving up to 640 kW. • The proposed model can be used in various applications at the industry. The vapour condensation is typical for processes of waste heat recovery from exhaust gases. It complicates the selection of condensers and requires reliable correlations for estimation of heat transfer coefficients and pressure drop in the unit. In the presented paper, a novel model was elaborated to be applied for commercially produced plate heat exchangers (PHEs) assembled from plates with different geometries of corrugations, which accounts the change of process parameters at the main corrugated field, in PHE collectors and channels distribution zones. The process of waste heat recovery from exhaust gases after tobacco drying is discussed in the case study. The pilot unit assembled with PHE of TS-6MFG type manufactured by Alfa Laval was installed at a tobacco factory. The examined condensing media was an incoming air-steam mixture with 10% of air content and temperature equal to 140 °C. The comparison of modelling results and data of industrial operation has shown good accuracy of prediction. It allowed recommending obtained correlations and developed mathematical model for the design of plate heat exchangers in applications with heat utilisation from exhaust gases after drying processes in the industry, with a considerable saving of heat energy. In the considered example, it is up to 640 kW or 2090 kJ/kg of exhaust gases.