Investigation on thermal safety of high-temperature heating surfaces under 650-700°C USC condition

Abstract

The improvement of unit parameters has always been the main methods to improve the power generation efficiency. With the development of high temperature materials and large numbers of utilization 600-620 °C Ultra-Super Critical Units (USC), the further development of 650∼700 °C degree USC technology was becoming possible. Generally speaking, when the temperature and pressure of steam reaches around 700 °C and above 30MPa respectively, the power station efficiency can be further improved and closed to 50% when using double reheat technology. China has made great improvement on 600 °C degree USC power generation technology since 2005. Until now, the highest efficiency of 660MWe USC coal-fired power generation using double reheating technology is Guodian Suqian Power Plant, the efficiency of power generation is approximate 48.13%. There are almost 400 USC power plant unit boilers with the capacity of 600∼1000MWe in China, which lays a good foundation for developing the advanced 650∼700 °C A-USC power generation technology. In 2005, China began to implement the research program of 700 °C ultra supercritical power generation, which including the properties of nickel-based materials, the optimization of 700 °C USC thermal system and the key design and manufacturing technologies for 700 °C USC boiler and turbine etc. With the improvement of unit parameters, the allowable temperature margin of high-temperature materials becomes narrow, the wall temperature safety of high-temperature materials in boiler, especially for the operating conditions under variable loading conditions, is particularly becoming the most important key issue for A-USC boiler design and operating. In order to improve the prediction accuracy of material temperature of heat transfer in boiler under 650∼700 °C USC conditions, especially for the variable loading conditions, a method for predicting material wall temperature, which coupling with both heat transfer processes of flue gas and working fluid in tube has been established based on the relevant basic experimental data. In addition, the demonstration of 650 °C USC power generation technology, which are mainly based on austenitic steel has been put on the agenda in China recently. The demonstration of 650 °C USC power plant in China will greatly promote the development of 700 °C USC technology in the future.