Performance Calculation Of Combined Water And Power Generation System

Water is the source of life, but the freshwater resources that humans can use are very limited. Today, the shortage of water resources has become a bottleneck that restricts economic development and social progress. Developing seawater desalination technology, getting freshwater from the ocean, is the most effective way to solve the contradiction between supply and demand of water. The combined water and power generation system can use the steam and electricity of the power plant to provide heat source and allocate electricity and water production reasonably, in order to achieve energy efficient utilization and reduce desalination costs.A combined water and power generation system was formed based on the supercritical 350MW condensing steam turbine and low-temperature multi-effect distillation device. The performance of steam turbine with steam extraction and the cogeneration system were calculated and the economy on coal consumption was discussed. The off-design condition calculations included the calculation of varied steam quantity and fixed steam quantity entered the turbine.The varied steam quantity off-design condition calculation results showed that extracting steam from the fifth extraction port of the turbine to desalinate seawater, the coal consumption increased as the steam extraction using in desalination increased with the same power load, and the increment was 50 kg per ton steam extraction. With different steam extraction using in desalination, the coal consumption differences between separate systems and cogeneration system (i.e. absolute coal consumption saving) were all greater than zero. It showed that it's more economical with cogeneration system than separate systems. The ratio of the coal consumption difference and the coal consumption of separate systems (i.e. relative coal consumption saving) increased as the power load decreased. With the same power load, the relative coal consumption saving increased as the steam extraction increased, i.e., it's more economical with cogeneration system than separate systems on coal consumption.Extracting steam from different extraction ports of the turbine to desalinate seawater, with the same steam extraction, the absolute coal consumption savings with each power load all increased as the extraction parameters decreased. With the same extraction port, the absolute coal consumption saving increased as the power load increased. With the same power load, the lower extraction parameters were, the less coal consumption of unit steam extraction cost. With the same extraction port, the coal consumption of unit steam extraction increased as the power load decreased.Taking a 4 effect TVC-LT-MED device for example, this thesis has calculated the gained output ratio of desalination using a parallel feed MED seawater desalination device simulation software. The calculation results showed that with the same power load, as the extraction parameters decreased the coal consumption of unit water production decreased, although the gained output ratio was decreasing. It showed that using the lower parameter steam could improve the economical performance of the combined water and power generation system. With the same extraction port, the higher power load was, the greater gained output ratio and the less coal consumption of unit water production were.Taking 1079300 kg/h as the steam quantity entered the turbine in the fixed steam quantity variable condition calculation. The calculation results showed that, with the same extraction port, as the steam extraction increased the power load decreased linearly, the coal consumption of steam extraction using in desalination increased, the coal consumption of unit steam extraction increased and the coal consumption of unit water production increased. With the same steam extraction, as the extraction parameters decreased, the power load increased, the coal consumption of steam extraction using in desalination decreased, the coal consumption of unit steam extraction decreased and the coal consumption of unit water production decreased.