04 Fakultät Energie-, Verfahrens- und Biotechnik
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Item Open Access Entwicklung und Integration neuartiger Komponenten für Polymerelektrolytmembran- (PEM) Elektrolyseure(2018) Lettenmeier, Philipp; Friedrich, K. Andreas (Prof. Dr.)Item Open Access Combined electricity and water production based on solar energy(2015) Moser, Massimo; Thess, André (Prof. Dr.)Several studies carried out at DLR such as [AQUA-CSP 2007], [MED-CSD 2010] and [MENAWATER 2011] have shown that the current water supply of several countries of the Middle East and North Africa (MENA) relies to a large extent on fossil groundwater extractions. Such extractions are characterized by continuously increasing energetic and economic efforts, which causes depletion of precious water resources and negative impact on the environment. The gap between water resources and water demand is likely to be sharpened by global changes such as population and economic growth and climate change. However, a series of technical approaches exist in order to mitigate water scarcity. Amongst others, water supply can be increased by means of unconventional solutions such as seawater desalination. Thereby, large part of the greenhouse gases emissions related to this process can be avoided by the introduction of renewable energy technologies such as concentrating solar power (CSP), photovoltaic (PV) and wind power. The main objective of this dissertation is the development of a flexible model for the integrated techno-economic assessment of seawater desalination plants using renewable energy. A number of simulation models have already been implemented for the design and the simulation of renewable plants or desalination units. However, so far no established tool exists for the simulation of such integrated systems. The simulation tool INSEL has been selected for the analysis. This commercially available tool combines a modular structure with simple handling and low computational effort. The core of the present doctoral thesis consists in the extension of the currently available INSEL library with new models for a number of desalination technologies, i.e. multi-effect distillation (MED) and reverse osmosis (RO) as well as CSP components such as solar field, thermal energy storage and power block. One of the focuses of this work has been the techno-economic evaluation and comparison of MED and RO plants. In the last few years RO has gained a dominant position in the global desalination market. This success is due to low capital cost, significant improvements in membranes (salt rejection rate, life time) and reduction of specific energy consumption. The optimal recovery ratio of RO plants, i.e. the ratio between produced drinking water and feed water, results from a compromise between minimization of investment cost, energy consumption and risk of membrane fouling. Feed water pre-treatment represents a challenging issue for RO plants. MED is characterized by relatively high investment cost, which also depends to a large extent on metal price, higher water consumption than RO but less demanding feed water pre-treatment. Heat cost for MED is a function of power supply technology, fossil fuel price and heating steam pressure. The optimal number of stages in a MED plant results from a trade-off between minimization of thermal energy requirements and maximization of plant efficiency. The INSEL library has been further extended by a number of CSP components, which include parabolic trough, linear Fresnel and central receiver. The solar field models base on a steady-state thermal energy balance between incoming radiation, geometrical and optical losses, heat gains of the heat transfer fluid (HTF) and heat losses to the environment. The model takes into account layout and losses of the HTF system. In addition, transient effects are considered by means of a simplified approach. This is an important improvement which is not considered by the majority of the existing system analysis simulation tools. A two-tank molten salt storage has been selected as reference thermal energy storage, while the power block consists of a detailed thermodynamic model of a conventional Rankine cycle. The INSEL CSP models have been developed with information from the DLR groups of the Institute of Solar Research and of the Department of Thermal Process Technology. A potential application of the implemented INSEL models is shown in a final case study, which assesses the feasibility of combined power and water production plants. The analysis has been carried out for Marsa Alam, a remote touristic location in the South-East of Egypt. Under these assumptions RO provides slightly lower water production cost than MED; however, due to its robustness and simplicity of operation, MED could still be a competitive option wherever feed water pre-treatment is particularly challenging and RO plants would be prone to frequent fouling problems (e.g. Arabian Gulf). In addition, one of the main findings is that moving in due time towards an electricity supply system based on a mix of renewable and conventional technologies is not only convenient in the case of high fossil fuel price, but it also includes strategic advantages such as the reduction of the dependence on scarce resources and the stability of the supply cost.