Dynamic study of local integration of high temperature heat pumps (HTHPs) in a food processing line

Sammanfattning

This thesis conducts a dynamic integration of high temperature heat pumps (HTHPs) in a food processing line, based on the thermodynamic efficiency and coefficient of performance. The main goals are to decrease the energy consumption in the industry and further the operational costs, and thereby increase the energy efficiency in the unit processing line. The objective of this thesis is to assess the potential of HTHPs for food industrial energy recovery by evaluating the thermodynamic principles governing heat pumps. The modeling integration is performed, using the objective oriented language Modelica and implemented in Dymola. In order to simulate a model inside an industrial alpha configuration double acting Stirling cycle based high temperature heat pump. The case study of simulation and integration were based on dairy processing line, specifically in raw milk. The two units processing lines were pasteurization and sterilization (UHT) based on the provided data by Tetra Pak. The range of temperatures were different for each case, from 40 °C to 90 °C for pasteurization and 65 °C to 160 °C for sterilization (UHT). The lower temperature was the cold inlet source and the higher temperature was the hot sink for both cases. The results shown that the heat pump had variations of power consumption and heating flow as the crankshaft radius and frequency piston were varied in the simulations. Higher piston frequencies and greater crankshaft radius lead to increased power consumption, especially under higher heating flow conditions, for both cooling and heating operations. The coefficient or performance (COP) was measured using two equations, calculating the COPcarnot based on the difference of temperatures and COPh based on the power consumption and heating flow. For each case of study both COP were estimated and the results showed that for pasteurization the COPcarnot presents higher values than for UHT due to the high temperature difference for the sterilization case. The COPh remains the same for both cases since the rate between the power consumption and useful heating flow increase or decrease at the same time for full capacity operation of the heat pump