Dynamic Modelling of a Heat Exchanger Network for a Dairy Plant

In co-and trigeneration plants with internal combustion engines, waste heat from their cooling system can be fed to a heat exchanger network for office heating, hot water production, or used in industrial processes. At the same time, care must be exerted not to cool the return fluid below a threshold, in order to avoid piston seizure. In this work, the heat exchanger network is that of a gas-engine trigeneration system for a large dairy plant in Rome. Since its daily and weekly production schedule is subject to several changes, temperature control must be both precise and efficient. A thermal-hydraulic, dynamic (i.e. time-dependent) model of the heat exchanger network was developed in Matlab/Simulink, to obtain the instantaneous pressure, mass flowrate and temperature of the fluids along the network. The approach is mixed, a lumped-parameter description of the hydraulic and thermal networ, and finite volumes for the heat exchangers. The model has been verified and validated with experimental, steady-state data from the dairy plant and the results found satisfactory.