محمدحسن ملک محمدی

A 320 MW steam power plant is studied and the energy and exergy analysis for the components as well as for the whole cycle of the plant is based on real data. Studies show that due to exergy dependence on ambient temperature, overall exergy efficiency increases by 5.93% with decreasing ambient temperature. Exergy degradation due to condenser temperature also leads to a 2.8% reduction in nominal load exergy degradation and 1.4% energy efficiency reduction in condenser temperature reduction. Also, the total exergy losses of the power plant cycle are about nominal output power, which however decreases by approximately 5% at nominal loads relative to the half load. The highest exergy losses were related to boilers and about 80% of total losses and the lowest exergy losses were for pumps and about 0.3%. Increasing the steam temperature of the boiler will also result in a 1.39% increase in energy efficiency and a 1.64% increase in the overall exergy efficiency of the plant. Therefore, the most cost efficient way of operating the power plant is at high and rated load conditions.

The water consumption of steam power plants is one of the big challenges in the world. One of the suggested methods for reducing water in these power plants is the utilization of forced dry cooling tower. However, these types of cooling towers are dependent on weather conditions and reduced power plant efficiency. One way to solve this problem is to downfall water on it during hot hours. In this article, the forced dry and cooling towers are studied analytically. Then, with the consideration of characteristics of a power plant, the size and characteristics of dry and wet cooling towers are computed according to design temperature. These results are compared with experimental data and wet cooling towers of a power plant, and their accuracy has been verified. Only at temperatures higher than the design temperature is water falling on the tubes and fins of cooling tower. Using data from the weather station of power plant location, the numbers of hours when the ambient temperature has been higher than the design temperature are calculated and water consumption is computed. Calculations show that for a power plant of 320 MW at design temperature of 30°C, ninety seven percent (97%) of the water consumption can be saved. The loss of power output due to the use of dry cooling tower electric fans and pumps is 3.93 percent of output power.

Using of dry cooling towers or hybridized dry-wet towers is one of the well-known solutions for this purpose. In this paper, dry Heller cooling tower was combined appropriately with existing wet cooling tower to reduce the water consumption. Simulation of dry Heller cooling tower of Shahid Montazery power plant and wet forced counter flow cooling tower of Isfahan power plant was performed. Two cases of parallel and series for combination of dry and wet cooling towers was considered. The results of simulation and analysis of executive methods show that parallel use of Heller tower with wet tower is not reasonable. But series case in various ambient temperatures in two situations of changing pump system and without changing it was recognized appropriate. It was shown that there was no need for changing the pump systems and condenser works in continuous desirable condition. Water saving is full for ambient temperature below 20oC, but in more ambient temperature water saving trend is decreasing.