CHALLENGE - A general design procedure have been developed for the application of the Immersed Particle Heat Exchanger to a novel, small scale, externally fired combined cycle capable of generating electrical and
thermal power from carbon-neutral biomass. The Immersed Particle Heat Exchanger serves as the high
temperature heat exchanger needed to couple the Brayton cycle with an external combustor of biomass.
SOLUTION - In order to accomplish the task of designing the part of both column needed to achieve the desired heat exchange efficiency, an optimization process design is performed in modeFRONTIER coupling MOGA-II genetic algorithm with a CFD analysis of the heat exchange between the particles and the gas within both columns. The parameters chosen for MOGA II are number of heat exchangers, height and diameter of the top column, height and diameter of the bottom column, particle diameter. The objectives are the minimization of the overall heat exchange surface and the minimization of the difference between the predicted temperature of the air exiting the bottom column and the desired fixed inlet temperature of the gas turbine. The minimization of the overall heat exchange surface was chosen as objective because it is important to design the heat exchanger as compact as possible: the bulkier the heat exchanger, the more expensive the overall cost. The second objective was chosen because the Immersed Particle Heat Exchanger must provide a desired heat exchange efficiency and hence a desired inlet temperature for the turbine.
BENEFITS - The optimization process allowed the determination of the Pareto Front where the minimization of temperature difference (between the predicted temperature of the air exiting the bottom column and the desired fixed inlet temperature of the gas turbine) was preferred. According to this strategy, the individual 2302
was selected because it has the lowest surface. With regard to the result of the optimization procedure, it was found that the Immersed Particle Heat Exchanger must be split into two modules having small size, showing the feasibility of the project in terms of dimensions.