Performance analysis of a modular air cooled condenser for a concentrated solar power plant

The use of air cooled condensers in power generation facilities is increasing in arid regions around the world. There is a specific requirement for more efficient air cooling technologies to be developed for Concentrated Solar Power (CSP) plants. This paper aims at determining the effects of various condenser design features on CSP plant output. In particular this paper considers a modular condenser and focuses on designing a suitable compact heat sink to be coupled with a variable speed fan array. Tube banks with radial fins have been used for decades to heat and cool gases and numerous correlations exist to predict the performance of such a heat exchanger. The initial design of this air-cooled condenser is essentially a tube bundle consisting of 6 rows of helically finned round tubes in an equilateral staggered arrangement. A laboratory-scale steady state test facility was designed to investigate the accuracy of the relevant correlations for the given design. Due to an undesired phenomenon which exists in multi-row condensers known as backflow, an investigation was performed to analyze the performance of the tube bank with fewer tube rows. The thermal and hydraulic performance for a tube bundle with a different number of tube rows was measured and found to be within 10-18% of the existing correlations. New correlations for heat transfer and pressure drop for the given design are presented for greater accuracy in the calculation of the condenser performance. These correlations, based on the measured data were combined with performance characteristics from a steam turbine to model the thermodynamic plant performance incorporating the various condenser designs. The investigation shows that for each condenser size, design and ambient temperature, an optimum fan speed exists which maximizes plant output. Further analysis shows that for a 1000 module condenser, a 4 row condenser results in the highest plant output, with a loss in efficiency due to condenser operation of 1.85%. A 2 row condenser also performs relatively well with 600 or more modules. This analysis shows that a condenser consisting of a series of such modules, can tightly control and optimize the net plant output power by simply varying fan speed.