Design and optimization of air bottoming cycles for waste heat recovery in off-shore platforms

• Theory of power maximization used to design an air bottoming cycle.
• Theory of power maximization extended by a multi-objective optimization method.
• Three objective functions considered: net power output, recuperator volume and net present value.
• Comparison between the theory of power maximization and the multi-objective optimization method.
• Case study: a methodology applied to recover exhaust heat on off-shore platforms.

This paper aims at comparing two methodologies to design an air bottoming cycle recovering the waste heat from the power generation system on the Draugen off-shore oil and gas platform. Firstly, the design is determined using the theory of the power maximization. Subsequently, the multi-objective optimization approach is employed to maximize the economic revenue, the compactness and the power production of the air bottoming cycle. The system compactness is assessed by introducing a detailed model of the shell and tube recuperator and including geometric quantities in the set of optimization variables. Findings indicate that using the power production, the volume of the recuperator and the net present value as objective functions the optimal pressure ratio (2.52) and the exhaust gas temperature (178.8 °C) differ from the values (2.80 and 145.5 °C) calculated using the theory of the power maximization. The highest net present value (2.8 M$) is found for a volume of the recuperator of 128 m3. Thus, it can be concluded that the multi-objective optimization approach enables extending the theory of power maximization bridging the gap between a mere optimization of the thermodynamic cycle and the practical feasibility of a power generation system.