Ultra-supercritical power generation, what is the "super power"?

Not long ago, Wang Zhigang, Minister of Science and Technology, mentioned ultra-supercritical power generation many times at the "China this decade" series theme press conference, he said that China has developed a million kilowatt-level ultra-supercritical efficient power generation technology for 15 consecutive years, and the current power supply coal consumption can reach a minimum of 264 grams per kilowatt-hour, which is much lower than the national average, and is also at the global advanced level. At present, ultra-supercritical efficient power generation technology and demonstration projects have been promoted throughout the country, accounting for 26% of the total installed capacity of coal power, and will be further promoted in the future.

On November 11, 2020, Datang Dongying Power Generation Co., Ltd. put into operation a million-kilowatt ultra-supercritical coal-fired generating unit.

"Ultra-supercritical power generation" has become a hot word, even in the stock market has become a hot concept. So what kind of scientific "superpower" does this awkward-sounding buzzword mean?

"Ultra-supercritical" focuses on "critical"

We all know that coal is used to generate electricity. But what is ultra-supercritical? This is the first to say what is "critical".

Based on physical knowledge, the general liquid pure substance will vaporize after heating or depressurization to a certain extent; The pure gaseous substance will condense when it is cooled or pressurized to a certain extent.

But any pure substance has a critical point, when the pressure is higher than the critical pressure, no matter how heated, the liquid will not vaporize; When the temperature is higher than the critical temperature, no condensation will occur, no matter how pressurized.

For example, under normal pressure, water heated to 100 ° C will continue to heat into steam; When the pressure of water is higher than 22.13 mpa (about 221 times atmospheric pressure), or the temperature is higher than 374.15 ° C, the evaporation and condensation process will no longer occur.

At critical pressure or critical temperature, the pure substance is in a "critical" state; Below the critical pressure or critical temperature, it is in a "subcritical" state; Above the critical pressure or temperature, it is a "supercritical" state.

Conventional thermal power generation units (including coal-fired power generation, biomass power generation, etc., excluding gas power generation) use coal and other fuels to burn in the boiler, heat water and boost pressure into high temperature and high pressure water vapor, promote the high-speed rotation of the turbine, and then drive the generator to generate electricity.

According to the law of thermodynamics, the efficiency of converting heat energy into electric energy in the thermal power generation process increases with the increase of the steam temperature at the boiler outlet, and the actual process needs to increase the steam pressure and unit capacity simultaneously to comprehensively improve the system efficiency.

After hundreds of years of development, Thermal generating units have generally experienced low temperature and low pressure (below 2.45 mpa, 400℃), medium temperature and medium pressure (3.9 mpa, 450℃), high temperature and high pressure (9.9 mpa, 540℃), ultra-high pressure (13.8 mpa, 540℃), sub-critical (16.7 mpa, 540℃), supercritical (22.4 mpa, 570℃), ultra-supercritical (25 to 31 mpa, 580 ° C to 620 ° C) and other parameter grades, is developing advanced ultra-supercritical (35 mpa, 700 ° C to 760 ° C) grade power generation technology.

Among them, the initial parameters of supercritical, ultra-supercritical, and advanced ultra-supercritical units under development are in supercritical state, and the initial parameters of other units are in subcritical state.

Strictly speaking, pure matter has only three states of "critical", "sub-critical" and "supercritical", and there is no "ultra-supercritical". The ultra-supercritical parameter is essentially a parameter higher than the previous supercritical parameter, which belongs to the scope of the industry agreement. The so-called "ultra-supercritical power generation technology" refers to the efficient power generation technology that uses the feed pump to boost the water to ultra-supercritical pressure, and then heats the water to ultra-supercritical temperature through the fuel combustion in the boiler, and generates electricity through the turbine generator set.

Ultra-supercritical power generation technology is the most advanced thermal power generation technology in the world, which can simultaneously achieve ultra-low emission of pollutants and reduce the coal consumption rate of power supply to less than 265 grams per KWH. Advanced ultra-supercritical power generation technology is being actively developed, and it is possible to further reduce the coal consumption rate of power supply to less than 225 grams per kilowatt-hour.

Ultra-supercritical power generation technology is an important way to achieve high quality development of energy and power under the basic national conditions of rich coal, poor oil and little gas in China.