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Sliding pressure turbine integrated with seawater desalination facility (multi-effect distillation - med)

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This paper presents the technological features of the MED desalination plant integrated with a sliding-pressure ultra-supercritical steam turbine plants of the Tianjin project, in which the MED desalination units operate with a wide range of steam pressures.

In general, clean and cost-effective power generation is of paramount importance to cope with the the increasing energy demand throughout the world. Investment and fuel costs are the main contributors to the cost of electricity Due to environmental awareness in recent years, the amount associated with CO2 emissions have attracted more and more attention. The efficiency of the power plant, as one key value, affects both the fuel costs and the amount of CO2 emitted to the environment. As coal is more abundant in many parts of the world, coal prices are less volatile and more stable than those of natural gas. However, larger CO2 emissions increase the need for more efficient coal-based power generation. Ultra-supercritical (USC) steam power plants meet the requirements for high efficiencies to reduce both fuel costs and emissions, as well as for a reliable supply of electric energy at low cost. Furthermore, recent developments in steam turbine technology and materials able to sustain high-temperatures allow for significant efficiency gains.

70% of China's total energy consumption comes from coal, and the country still has huge reserves. Burning the coal has severely damaged the environment. In northern China cities such as Beijing and Shenyang have some of the world's highest readings for total suspended particulates and SO2, with coal burning being a major source of this. In southern China, large areas have increasing acid rain problems. Because of its reserves, China continues to rely on coal and is using advanced technologies to reduce pollutants.

In the Tianjin Beijing power plant, 2 x 1000 MW ultra-supercritical coal-fired power units have been integrated with 4x MED-TVC25,000 m3/day desalination plant that provides fresh water. The 2x1000 MW ultra-supercritical steam turbine uses grid frequency regulation and overloads control through an overload valve, is manufactured by Shanghai Turbine Company using Siemens technology. Through optimization, the grid load is regarded as the criterion between constant pressure and sliding pressure operation.

Constant pressure implies stable pressure of the steam generator and main steam line over the units load range. Meanwhile, the basic nature of a simple, rotating turbine is to require less pressure as the load and flow rate are reduced, and if the main steam pressure is limited to only that required for each load, this mode is referred to as pure sliding pressure and increases the unit operation efficiency.

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