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

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.

Towards practical solutions for energy efficiency of large-scale industrial sites

Nasibeh Pouransari

This thesis investigates a set of advanced topics inspired from the heat integration and the pinch technology, all tied around the challenge of identifying energy savings in large-scale chemical industrial plants. In search for a general-purpose methodology for energy efficiency, it has been observed that some well established methods exist already, but either they are case specific or relatively short handed when it comes to dealing with the large size plants. A general multi-step methodology is proposed in this thesis and then continuously improved, with a particular focus on the industrial realism and the usability for large-scale problems. The general methodology has been first put in practice to identify energy savings options in real case applications with the purpose of identifying the challenges to be tackled. Different aspects of large scale systems integration are being tackled: we start by studying issues experienced during the data gathering stage and come up with a multilevel data extraction approach. It is based on the different representation of the process unit heat transfer interfaces that satisfy the same heat requirement and let us tune the required level of detail with respect to how detailed the energy requirement definition needs to be for the site scale integration. The combination of those heat requirement levels is then applied to the Total Site Integration (TSI), alleviating the difficulties of the data extraction for large-scale problems. The heat recovery targets of the total site are then explored to identify further energy savings by the introduction of advanced technologies such as the heat pump and the Mechanical Vapor Recompression (MVR). Following the heat recovery improvement target, the study investigates the integration of one of the major heat consumers in the chemical processes : the distillation columns. The thermodynamic optimization of distillation columns has been examined together with the TSI and the integration of advanced separation concepts like Dividing-Wall Columns has been investigated considering a holistic site scale approach. The retrofit of the Heat Exchanger Network (HEN) of large-scale plants has been studied next. The definition of the same heat requirement presenting different heat transfer units has been used to introduce the existing network into the optimization model. The purpose is to evaluate and to minimize the required modifications to the existing system. We have proposed a multi-objective optimization with the evolutionary algorithm and a Mixed Integer Linear Programming (MILP) model. The optimal Pareto-frontier has been generated with respect to the minimum operating cost, the investment cost, the number of required modifications and the thermal exergy destruction. This approach offers two main advantages: (i) it is helpful to predict the region of good solutions without going through numerous iterations between targeting levels, usually required in the classical heat integration methodology for the evaluation of the retrofit of existing facilities and (ii) it helps considerably reduce the size of the posterior HEN re-design problem by minimizing the number of streams to be considered. The concluding chapters consider ways to reduce the size and the computational complexities of the HEN design for industrial size problems, with a main focus on the Heat Load Distribution (HLD) subproblem.

EPFL2015

Investment Planning Methodology for Complex Urban Energy Systems Applied to a Hospital Site

Francesca Belfiore, Bastien Maxence Bornand, Luc Girardin, François Maréchal, Jean-Loup Sylvain Robineau

Industrial process integration based on mixed integer linear programming has been used for decades to design and improve industrial processes. The technique has later been extended to solve multi-period and multi-scale problems for the design of urban energy systems. Assistance is indeed required for the elaboration of coordinated investment scheduling strategies to promote renewable and efficient urban energy infrastructure shaping the future energy context for the next decades. Major energy consumers, such as hospital complexes, airports, or educational campuses can act as a driving force for the development of renewable energy cities by attracting profitable large-scale energy networks and infrastructure. The proposed methodology generates optimal alternatives for the replacement, in a long-term perspective, of the various energy supply units and systems considering the evolution of the energy demand and the availability of the energy resources. Energy integration techniques are coupled to a parametric multi-objective optimization routine to select and size the energy equipment with both financial profitability and CO2 emission reduction as objectives. The originality of the developed method lies in the integration of a multi-period mixed integer linear programming formulation to generate long-term investment planning scenarios. The method has been demonstrated on a complex of eight hospitals totaling 466,000 m2 and an operating budget of 1.85 billion USD per year. The energy integration of new centralized and decentralized equipment has been evaluated on a monthly basis over four periods until the year 2035. The results show that among the four scenarios identified, the most optimistic alternative allows to decrease the final energy consumption of about 36%, cut the CO2 emissions by a half, multiply the renewable energy share by a factor 3.5 while reducing the annual total cost by 24%. This scenario considers mainly the integration of a very low temperature district heating with decentralized heat pumps to satisfy the heat requirements below 75°C, as well as heat recovery systems and the refurbishment of about 33% of the building stock.

2020

Process integration and opportunity for heat pumps in industrial processes

Helen Carla Becker, François Maréchal

Process integration methods allow one optimizing industrial processes. The main goals are decreasing energy demand and operating costs as well as reduction of pollutants emissions. High fuel costs promote installation of heat pumps. In a heat pump process waste energy is valorized by electrical power to produce higher quality energy. That is used to satisfy a part of the process demand so that less fuel is required and CO2 emission will decrease. This paper presents a methodology, based on pinch analysis, which demonstrates the opportunity of integrating heat pumps in industrial processes. The method considers the whole process including utilities and the energy conversion system. A combined analysis which considers thermal and material streams in the process is realized to optimize the heat recovery and the integration of energy conversion units. By analogy all material streams are listed and the potential of water recuperation is obtained. The combination of appropriate refrigeration and heat pump cycles leads to an important energy saving potential. The respective ﬂow rates are deﬁned by optimization. The application case of a dairy is used to calculate the energy and operating cost savings potential.