Combined Exergy and Pinch Analysis for Optimal Energy Conversion Technologies Integration

Exergy concept combined with pinch based approach are used for studying the optimal integration of energy conversion systems. The analysis first considers the representation of the hot and cold composite curves of the process and defines the energy and the exergy requirements. The basic assumption of the DTmin required for the pinch analysis is represented as an exergy loss that increases the exergy requirement of the process. The exergy composite curves put the focus on the opportunities for heat pumping in the process. The optimal integration of the utility system is then realised by extracting the energy conversion system configuration from a superstructure using a Mixed Integer Linear Programming formulation in which the heat cascade definition and the combined heat and power production balances are introduced as constraints and where the exergy losses minimisation is used as an objective function. The balanced exergy composite curves are used to visualise the exergy losses in the heat exchanges and the analysis of the results is made using a definition of the exergy efficiency that accounts for the pinch point location, the process exergy and the exported energy services.

Energy and Exergy Analysis of a Cruise Ship

Karin Andersson, Francesco Baldi, Tuong-Van Nguyen

In recent years, the International Maritime Organization agreed on aiming to reduce shipping’s greenhouse gas emissions by 50% with respect to 2009 levels. Meanwhile, cruise ship tourism is growing at a fast pace, making the challenge of achieving this goal even harder. The complexity of the energy system of these ships makes them of particular interest from an energy systems perspective. To illustrate this, we analyzed the energy and exergy flow rates of a cruise ship sailing in the Baltic Sea based on measurements from one year of the ship’s operations. The energy analysis allows identifying propulsion as the main energy user (46% of the total) followed by heat (27%) and electric power (27%) generation; the exergy analysis allowed instead identifying the main inefficiencies of the system: while exergy is primarily destroyed in all processes involving combustion (76% of the total), the other main causes of exergy destruction are the turbochargers, the heat recovery steam generators, the steam heaters, the preheater in the accommodation heating systems, the sea water coolers, and the electric generators; the main exergy losses take place in the exhaust gas of the engines not equipped with heat recovery devices. The application of clustering of the ship’s operations based on the concept of typical operational days suggests that the use of five typical days provides a good approximation of the yearly ship’s operations and can hence be used for the design and optimization of the energy systems of the ship.

2018

Energy efficiency and conversion in complex integrated industrial sites

Zoé Périn-Levasseur

This thesis presents a methodology to analyse the integration of heat recovery energy conversion technologies and biorefinery concepts in existing pulp and paper facilities. By using innovative process integration techniques and thermo-economic optimisation tools, efficient energy saving opportunities can be obtained and guidelines can be applied to implement energy efficiency enhancing measures. The objective is to provide engineers a decision support tool for the design of heat exchangers networks. The system approach used in this work is based on the development of a framework that implements existing simulation tools and process integration methods. The first contribution of this work resides in the establishment of a reconciled model of a complex pulping facility where utility and process measurements are studied simultaneously. Derived operating nominal conditions are validated through a complete sensitivity analysis. The resulting base case model is considered to be representative of the original process and constitutes the basis of the process energy integration definition problem. The core of the methodology consists in the application of two successive approaches: the top-down and the bottom-up approach. The top-down approach allows to identify which sub-systems of the facility consume more energy and could eventually lead to large energy savings. Conversion technologies used to produce utilities and their distribution to the process are also identified. The bottom-up approach benefits from the results of the top-down approach in order to evaluate the energy saving potentials. Systematic definition of the process heat transfer requirement defined as hot and cold streams is obtained according to different heat-temperature profiles. The exergy concept is employed to explain how using different heat-temperature profiles of the same energy requirement is changing the perspective of the energy use in the facility and therefore make possible the identification of energy saving opportunities with different levels of process modifications. An innovative way of considering the steam producers using as a main feed process materials in the definition of the process integration problem is also presented. The development of scenarios using systematically all energy requirement definitions is done and allows the elaboration of a decision support tool that point out the critical process modifications necessary to achieve interesting energy savings. A detailed example of the complete methodology developed in this thesis is illustrated using the multi-effect evaporator. The optimal integration of combined heat and power production and heat pumps is also presented. Finally, the interest of using this methodology is demonstrated in the case of a biorefinery integration by the development of a trade-off between the conversion of lignocellulosic materials into bio-materials and energy.

EPFL2009

Method for the systematic integration of multi-energy networks and low carbon resources in cities

Luc Girardin, François Maréchal, Paul Michael Stadler, Raluca-Ancuta Suciu

The design and operation of building energy systems (BES) has become a subject of great interest, given the latest energy policies adapted around the world, namely increasing the energy efficiency and the share of renewable energy sources (RES) while reducing greenhouse gas emissions related to the provision of domestic energy services. Within the latter context, this work addresses the issue of optimal sizing and operation of BES while integrating an advanced CO2 based district energy network. Indeed, unlike common water based networks which use sensible heat, the former exploits the phase change enthalpy to realize the heat transfer when interacting with the different end users as well as with the environment [1]–[4]. The related optimization problem is formulated using a mixed integer linear programming (MILP) technique, a suitable method to represent both the continuous and discrete behaviour of BES [5]. The objective function is represented by the sum of the operating and annualized investment costs (i.e. the total annual project expenses) while the integrated system is subject to mass and energy balances, heat cascade and other additional constraints. In order to decrease the computational complexity of the aforementioned problem a PAM algorithm is implemented, thus generating several typical operating periods regarding the region of interest [6]. Different case studies are performed in view of fully assessing the potential of advanced CO2 based district energy network; the different technologies include water-water heat pumps, photovoltaic arrays, water based buffer tanks and electric storage units. In addition, in regard to the implemented model formulation [7], [8], heat might be stored directly in the dwelling, thus providing a further storage capacity. The presented study hence tackles multiple research questions among which, the optimal network distribution operating conditions (i.e. supply and return temperatures) when considering optimal on the end-user side. Indeed, in regard to the different temperature thresholds related to the different domestic heating requirements, trade-off solutions must be defined to assess the best system efficiency, i.e. considering the COPs of both the network and the dwelling operators. Another aspect considered is the building construction period, which has a strong impact on both the thermal energy demand and the required temperatures of supply. Therefore, two types of buildings are considered, namely existing and new, during the different case studies, based on their respective shares in the built environment. Finally, in order to address the impact of the novel district energy network on the use of electricity storage units, different RES penetration levels are analysed. References [1] C. Weber, “CO2 BASED DISTRICT ENERGY SYSTEM,” 2008. [2] S. Henchoz, C. Weber, F. Maréchal, and D. Favrat, “Performance and profitability perspectives of a CO2 based district energy network in Geneva’s City Centre,” Energy, vol. 85, pp. 221–235, Jun. 2015. [3] Raluca Suciu, Paul Stadler, Araz Ashouri, and François Maréchal, “Towards energy-autonomous cities using CO2 networks and Power to Gas storage, ECOS Proceedings 2016.” ECOS Proceedings 2016, 2016. [4] R. Suciua, L. Girardin, and F. Marechal, “Energy integration of CO2 networks and Power to Gas for emerging energy autonomous cities in Europe,” Submitt. 30th Int. Conf. Effic. Cost Optim. Simul. Environ. Impact Energy Syst., 2017. [5] A. Bemporad and M. Morari, “Control of systems integrating logic, dynamics, and constraints,” Automatica, vol. 35, no. 3, pp. 407–427, Mar. 1999. [6] J. M. F. Rager, “Urban Energy System Design from the Heat Perspective using mathematical Programming including thermal Storage,” EPFL thesis nr. 6731. [7] A. Ashouri, “Simultaneous Design and Control of Energy Systems,” Diss., Eidgenössische Technische Hochschule ETH Zürich, Nr. 21908, 2014, 2014. [8] L. Girardin, F. Marechal, M. Dubuis, N. Calame-Darbellay, and D. Favrat, “EnerGis: A geographical information based system for the evaluation of integrated energy conversion systems in urban areas,” Energy, vol. 35, no. 2, pp. 830–840, 2010.

Energy efficiency and conversion in complex integrated industrial sites

Zoé Périn-Levasseur

EPFL2009

Method for the systematic integration of multi-energy networks and low carbon resources in cities

Luc Girardin, François Maréchal, Paul Michael Stadler, Raluca-Ancuta Suciu