A New Gas-Steam-Ammonia Combined Cycle to Reduce Cooling Water Consumption

Climatic changes and indiscriminate use of water resources have led to increasingly serious water shortages. This situation has been followed by more and more restrictive legislation aimed at limiting water consumption and thermal pollution. Rejecting enormous quantities of heat in large condensation type thermoelectric plants has become more and more of a problem. In some cases the solution has been found in the use of dry cooling towers that exploit the atmosphere's own cooling power. Given the very low density of the water vapour at the condenser, however, this solution calls for very big exchangers and leads to a rise in heat rejection temperature. To solve these and other problems, the idea of using alternative fluids in the cooling circuit, or even in the final phase of expansion, has been presented. Thus experimental systems have been built using ammonia both in dry cooling towers and in bottoming cycles. The main advantages of this system can be found in the reduction of cooling tower sizes and, at the same time, of the heat rejection temperature. Furthermore, the use of ammonia enhances the system's performance levels when operating in very low ambient temperatures. The application of these solutions for condenser cooling in combined gas-steam systems, where the presence of low temperature heat cascades is extremely interesting, since they permit an advantageous use of ammonia bottoming cycles.