Utilising a high pressure, cross flow, stainless steel fintube heat exchanger for direct steam generation from recovered waste heat

Around the world the implementation of heat recovery systems is playing an increasingly important role in the engineering inqustry. The recovered energy is utilised in the plants and saves companies millions in expenses per year. Not only is this seen on the grand scale of industry, but also in everyday life, where for instance turbochargers are used to boost the performance of automobiles by utilising the wasted energy expelled along with exhaust gasses. The aim of this project is to investigate a small scale waste heat recovery system, and to determine the optimum method by which to convert the recovered energy into electrical energy, which can be used as a secondary energy source. The research contained in this thesis, centres on the main components and theory needed for the construction of a small scale waste heat recovery system. Also included, is a theoretical analysis concerning the design and construction of the system, utilising researched theory and a simulation program of the recovery system. The simulation is control volume-based and generates property data on the fluid and exhaust gas throughout the heat exchanger. The final design included a finite element stress analysis of certain parts of the system to ensure safe testing at high pressures and temperatures. The final design resulted in a high pressure, cross flow, stainless steel fintube heat exchanger that, by using a continuous combustion unit as energy source and water as the working fluid, reached efficiencies of up to 74% in direct steam generation testing. The tube-side of the heat exchanger was designed to withstand pressures of up to 2MPa (20bar), which is imperative for the implementation of the next phase, where a turbocharger will be connected to the heat exchanger. The completion of this part of the project has paved the way for further development and implementation of the heat recovery system. 111 Stellenbosch University http://scholar.sun.ac.za