Energy Vol. 18, No. 8, pp. 803-814, 1993 0360-5442/93 $6.00 + 0.00 Printed in Great Britain. All rights reserved Pergamon Press Ltd A FLASHING BINARY COMBINED CYCLE FOR GEOTHERMAL POWER GENERATION G. PALOSO JR. and B. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPO MOHANTY? Energy Technology Division, Asian Institute of Technology, G.P.O. Box 2754, Bangkok, Thailand zyxwvutsrqponm (Received 23 November 1992) Abstract-The performance of a flashing binary combined cycle for geothermal power generation is analysed. It is proposed to utilize hot residual brine from the separator in flashing-type plants to run a binary cycle, thereby producing incremental power. Parametric variations were carried out to determine the optimum performance of the combined cycle. Comparative evaluation with the simple flashing plant was made to assess its thermodynamic potential and economic viability. Results of the analyses indicate that the combined cycle can generate 13-28% more power than the conventional flashing plant. The economic assessment reveals that its unit generation cost is slightly less than that of a flashing-type system. The proposed cycle thus represents a more effective utilization of the resource, aside from helping to alleviate environmental degradation. INTRODUCTION Power production from geothermal energy is a maturing technology that is being widely implemented on a commercial scale in various parts of the world. Different techniques have been introduced to tap the abundant quantity and diverse types of geothermal resources. So far only the direct-flashing and the binary plants have proven to be economically competitive in comparison with other conversion systems utilizing conventional fuels. Most of the proven and developed geothermal resources are of the liquid-dominated type and are usually harnessed using flashing-type plants. These resources produce a two-phase steam/water mixture whose components are separated in a flash process. The generated steam is used to run a turbine while the residual hot brine is reinjected to the ground or, in a few cases, rejected in a thermal pond. Generally, the hot brine leaves the separator at a moderate temperature (140-180°C) and still possesses a considerable amount of energy. This otherwise rejected energy could be tapped to operate a binary cycle, which is technically suitable to the temperature level of the hot brine, thus providing incremental power and additional financial benefits. This paper aims to evaluate the technical and economic incentives of integrating a binary cycle into a flashing-type plant. It also looks into the possibilities of optimizing the power-production potential of the proposed flashing binary combined cycle with consideration of technical constraints in its operation. RESOURCE BASE AND CONVERSION TECHNOLOGIES Most of the known geothermal resources (about 95% of the world’s total estimate) are of the hot, dry rock type.’ These occur at moderate depths but are largely impermeable. Although the resource is abundant, the conversion process is prohibitively expensive. Other resources such as geopressured and magma bodies are also being developed. However, it will probably require 5-10 yr for their conversion technologies to become economically feasible.* __~~ __~_ t To whom all correspondence should be addressed. 803