A Comprehensive Introduction of the World First Elevated and Conventional Turbine-Generators Layout Design Double-Reheat Coal-Fired Power Unit

Abstract Although theoretically double-reheat units are more efficient than single-reheat ones, the practical application results worldwide show that the efficiency improvement of the conventional double-reheat unit is not obvious, and the cost performance is not outstanding. One of the main reasons is the larger pressure loss, heat dissipation loss and related investment cost caused by the excessively long pipeline, especially the second reheat system. The patented elevated and conventional turbine-generators layout introduced in this paper solves this problem well in principle. By placing the HP and IP1 turbine cylinders on a high platform very close to the boiler outlet headers, the technology can shorten the associated expensive critical pipes by more than 85 percent, which means not only reducing investment, but also eliminating corresponding pressure and heat loss, resulting in higher unit efficiency. At the same time, other patented innovations, such as the Generalized Regeneration technologies, can be combined with double reheats system to further reduce energy losses such as losses in the condenser and improve unit efficiency. The R&D and integration of these technologies have been applied in the Pingshan Phase 2 1350MW elevated and conventional turbine-generators layout double-reheat unit, a national demonstration project in China. During the design process, the project also encountered challenges such as the stress problem caused by the extremely short but high temperature steam pipe between the elevated turbine and the boiler header, and the overspeed problem of the elevated turbine-generator. Fortunately all of them were well solved through innovative technical means. In addition to the world first elevated and conventional layout design, the project also applies a number of pioneering energy-saving technologies such as primary air Generalized Regeneration technology. After the project was put into commercial operation, the test results of the third-party test in 2022 shows that the UNE (unit net efficiency) was as high as 49.4% (LHV) under rated conditions, and still as high as 46.8% at 50% load. In addition, the unit achieved safe and environmentally friendly operation in reasonable efficiency under 20% load during commissioning, making it the largest capacity unit to achieve this goal. The unit’s state of the art high efficiency and flexibility make it a new benchmark for worldwide coal-fired units.