Methodology and Thermo-Economic Optimization for Integration of Industrial Heat Pumps

Abstract

This thesis presents a systematic methodology, based on pinch analysis and process integration techniques, to integrate heat pumps into industrial processes. The main goals are to decrease the energy consumption and the corresponding operating costs, and therefore to increase the energy efficiency of an industrial process. The objective of this thesis is to identify heat pump opportunities, and to optimize simultaneously the energy conversion and utility system of a process. The process and utility integration is realized, using mixed integer linear programming (MILP). In order to find systematically the optimal operating conditions of heat pumps, an optimization framework combining linear and non-linear optimization methods is presented. Technologically feasible heat pumps are collected in a data base and proposed to the process. A multi-objective optimization, combined with process integration methods, gives the possibility to systematically identify optimal heat pump sizing and positioning solutions. Pinch analysis is a promising tool, however several limits have been discovered, and the basic methodology has been extended to obtain more realistic solutions. The first extension gives the possibility to integrate heat exchange restrictions due to industrial constraints (e.g. safety reasons, or long distances). A methodology, based on the decomposition into sub-systems, is developed to include heat exchange restrictions. The penalty of these heat exchange restrictions can be decreased by integrating intermediate heat recovery loops, which transfer heat indirectly between two sub-systems. A further developed extension, which enables to define subsystems at different levels, makes the approach very flexible and useful for many different application cases. The second extension is realized to integrate multi-period and multi-time slice problems. The main focus is the integration of storage units, to enable the heat recovery between different time slices. The interest in heat pumps can be increased when integrating storage units, because their working hours and profitability increase. The methodology and its extensions are tested and validated with several real industrial case studies. It is shown that there is a great potential for industrial heat pumps.