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Session: Parallel Session: Systems Design, Optimization and Applications II
Session starts: Friday 23 September, 09:00
Presentation starts: 10:40
Room: Senaatszaal

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Trond Andresen (sintef energy research)
Yves Ladam (sintef energy research)
Petter Nekså (sintef energy research)

Abstract:
Aluminium production generates vast amount of heat. In Norway, smelting plants are installed in remote places were there is no market for the surplus heat as such. Conversion to electricity is an attractive alternative. However, power production from medium to low temperature heat sources is today impeded by high investment cost and poor efficiency. Cycle optimization is critical. One interesting heat source in an aluminium smelter is the pot gas. This is a sensible heat source, in which temperature decrease as heat is recovered. In order to recover more heat, the area of the Heat Recovery Heat Exchanger (HRHE) has to be increased. As the conversion efficiency from heat to power decreases with the heat source temperature, increase of power production will come to the expense of a large increase of HRHE area and therefore will lead to a non linear increase of plant cost. An in-house power cycle simulator based on physical heat exchanger geometry has been implemented. It allows for simultaneous optimization of power cycle parameters (heat uptake pressure and working fluid mass flow) and HRHE geometry, such that for a given maximum area of the HRHE, a maximum net power output is found. External constraints such as maximum cooling of the heat source can be taken into account in the optimization procedure. The case of a typical aluminium smelter was investigated. Typical power production potential and heat exchanger size and optimal layout were obtained. The performance of subcritical R134a cycles and supercritical carbon dioxide cycles are compared.