Integrated Thermal-Fluids System Modeling of an Ocean Thermal Energy Conversion Power Plant for Analysis and Optimization

Abstract

This report focuses on the development of an integrated model of a closed-cycle Ocean Thermal Energy Conversion (OTEC) power plant for the purpose of analyzing the relative effects of key design parameters on the performance of the plant’s main sub-systems. The model was then used to analyze the effects of cascaded stages within the power cycle, as an example of using the model for analysis and optimization. The analysis led to the conclusion that 2–5 stages are most beneficial. A simplified thermodynamic model of the power cycle was developed to estimate the power produced, as well as the water mass flow rates required for the necessary heating and cooling rates. A simplified pipe flow model was then integrated into the power plant model to calculate the pumping power required to run the power cycle. The pumping power demand was subtracted off the thermodynamic model to provide the net power out of the cycle. Since the thermodynamic efficiency of the OTEC power cycle is inherently low, the water flow rates are substantial, and so are the power requirements of their pumps. Therefore, it is important to optimize the design parameters of an OTEC plant to minimize water mass flow rate relative to the power output of the plant. The thermodynamic performance analysis consists of first establishing a base-line reference power plant and a reference set of input variables. Plant design variables, such as the number of power cycle stages, are then varied up and down about the reference point; the outputs are then compared to the reference output.