In the process of constant pressure heating of water, under each pressure, water will go through an unsaturated water (O) point, a saturated water (A) point, a wet saturated steam (X) point, a dry saturated steam (B) point until a superheated steam (E) point. With the increase of pressure, point A tends to move to the right, point B tends to move to the left, and the vaporization stage gradually shortens with the increase of pressure. When point A and point B coincide, this is the critical point of water, and there is no difference between saturated water and saturated steam.
Therefore, the critical point of water is P=22. 129MPa and T=374. 12℃.
Steam parameters of subcritical thermal power unit: P= 16~ 19MPa, T= 538℃/ 538℃ or T= 540℃/ 540℃.
When the parameters of steam exceed the critical state point of water, they are collectively called supercritical units, and (supercritical) is represented by (SC). The steam pressure of a general supercritical unit is 24~26MPa, and its typical parameters are: P=24. 1 MPa, 538℃/538℃; The parameters of 600MW supercritical unit under construction in China are: P=25.4MPa, 538℃/566℃; Or P=25.4MPa, 566℃/ 566℃.
In fact, the ultra-supercritical unit is to further improve the steam pressure and temperature on the basis of the parameters of the supercritical unit. Internationally, a unit with main steam pressure of 24. 1~3 1MPa and main steam/reheat steam temperature of 580℃~600 ℃/ 580℃ ~ 6 10℃ is usually defined as an efficient supercritical unit, commonly known as ultra-supercritical unit. The main steam of USC under construction in China is P= 25~26.5MPa, T= 600℃/600℃.
Supercritical is a special state of matter. When the ambient temperature and pressure reach the critical point of matter, the phase interface between gas and liquid disappears and becomes a homogeneous system. When the temperature and pressure rise further, that is, when the temperature and pressure exceed the critical point, the substance is in a supercritical state and becomes a supercritical fluid. Supercritical water is an important supercritical fluid. In supercritical state, water has good fluidity similar to gas, and its density is much higher than that of gas. Supercritical water is a good reaction medium with unique physical and chemical properties, such as high diffusion coefficient, high mass transfer rate, low viscosity, good miscibility, low dielectric constant and complete miscibility with organic and gas components. Low solubility in inorganic substances, favorable for solid separation, high reaction activity and strong decomposition ability; Supercritical water itself can participate in free radical and ion reactions and so on.
Subcritical boiler: the outlet pressure of main steam is 15.7~ 19.6MPa.
Supercritical boiler: main steam outlet pressure ≥22MPa.
Ultra-supercritical boiler: commercial name, without clear physical definition, only indicating a technical parameter or technical development stage, indicating higher pressure and temperature, with different definitions of starting point.
1. Japan: greater than 24.2 MPa, or reaching 593℃
2. Denmark: more than 27.5 MPa
3. Siemens: Distinguish from the grade of materials.
4. China Electric Power Encyclopedia: higher than 27MPa.
Question 2: What is supercritical? Supercritical is a state.
Since Andrews first discovered the critical phenomenon in 1869, various researches have been carried out one after another, including Hannay and Hogarth measuring the solubility of solids in supercritical fluids in 1879, Michels et al. accurately measuring the state of CO2 near the critical point in 1937 and so on. On the phase diagram of pure matter, the gas-liquid equilibrium line of general fluid has an endpoint-critical point, where the corresponding temperature and pressure are critical temperature (Tc) and critical pressure (Pc). When the temperature and pressure of the fluid are higher than Tc and Pc, the fluid is in supercritical state (SC state for short). Many physical and chemical properties of supercritical fluid are between gas and liquid, which have the advantages of both, such as solubility and heat transfer coefficient close to liquid, viscosity coefficient and diffusion coefficient close to gas. At the same time, it also has characteristics obviously different from gas and liquid:
(1) Any density between gas and liquid can be obtained;
(2) Near the critical point, a small change in pressure can lead to a huge change in density.
In supercritical state, fluid has dual characteristics of gas and liquid, which not only has high diffusion coefficient and low viscosity equivalent to gas, but also has density similar to liquid and good solubility to substances. Its density is very sensitive to the change of temperature and pressure, and it is directly proportional to solubility in a certain pressure range, so the solubility of substances can be changed by controlling temperature and pressure. Supercritical fluid has been used in the extraction, synthesis, analysis and processing of drugs.
For the power industry, the definitions of so-called supercritical units and ultra-supercritical units are not strict. A boiler whose main steam pressure is greater than the critical pressure (22.064MPa) but less than 26MPa and whose temperature is less than 57 1 degree is called a supercritical boiler, and its supporting steam turbine is called a supercritical steam turbine. The main steam pressure of the boiler is between 26 ~ 3 1 MPa, the boiler with a temperature of about 600 degrees is called ultra-supercritical boiler, and the supporting steam turbine is called ultra-supercritical steam turbine.
Question 3: What are subcritical, supercritical and ultra-supercritical? The critical pressure of water is 22. 1 15MPa, and the critical temperature is 374. 15℃. If it exceeds this state, there will be a state of mixing steam and water, and water will become steam without latent heat of gasification, and the efficiency will be greatly improved.
Subcritical, supercritical and ultra-supercritical are all artificially defined:
Subcritical:14-22.115mpa.
Supercritical: 22. 1 15-25MPa.
Ultra-supercritical: the European definition is greater than 25MPa, and the Japanese definition is greater than 600℃. Domestic definition is more than 25MPa, 600℃
Question 4: What exactly do supercritical and ultra-supercritical power plants mean? Supercritical and ultra-supercritical generator sets have been widely used in developed countries. The reliability data of foreign units show that ultra-supercritical units can achieve high reliability like supercritical generating units. From the perspective of environmental protection measures, foreign ultra-supercritical units are equipped with flue gas desulfurization, denitrification and high-efficiency dust removal devices at the tail of boilers, which can realize low pollutant emission and meet strict emission standards. For example, the emission index of ultra-supercritical units in Japan can reach 70 mg/m3 of SO2 (standard state, the same below), 30 mg/m3 of NO and 5 mg/m3 of dust, indicating that ultra-supercritical coal-fired units can realize clean power generation like units burning natural gas and oil. At the same time, the ultra-supercritical unit improves the efficiency and correspondingly saves the water consumption for power generation.
Ultra-supercritical unit is a mature and advanced technology, which is comparable to subcritical unit in reliability, availability, thermal operability and unit life, and has more commercial operation experience. Ultra-supercritical coal-fired power generation technology is of great significance to realize the adjustment of thermal power structure in China and should be developed vigorously.
Through technology introduction and digestion and absorption during the Seventh Five-Year Plan and the Eighth Five-Year Plan, China has already possessed the design and manufacturing technology of subcritical 300MW and 600MW units. In 1990s, China introduced a batch of supercritical units and some design and manufacturing technologies, and basically mastered the design, installation, commissioning and operation and maintenance technologies of supercritical units. During the Tenth Five-Year Plan period, the research and development of ultra-supercritical coal-fired power generation technology and the construction of ultra-supercritical 1000MW units in Huaneng Yuhuan Power Plant have made the overall level of China's power industry develop by leaps and bounds.
Question 5: What exactly are supercritical and ultra-supercritical in power plants? They refer to the parameters of the thermal system of the generator set. The critical parameter points of water are 22. 12Mpa and 374. 12 degrees. Below this parameter belongs to subcritical, above this parameter belongs to supercritical. After the critical state, the specific gravity of water and steam is the same, so natural circulation cannot be used for boiler heating, and forced circulation must be used.
For the thermal equipment boilers and steam turbines of generator sets, the rated steam parameters exceed 22. 12Mpa, that is, supercritical. However, the steam pressure of general supercritical units is above 24Mpa, and the temperature is not high, which is still maintained at 545 degrees and 550 degrees. However, the steam pressure of ultra-supercritical unit is slightly higher than 25Mpa, and the temperature has greatly jumped to 600 degrees. This is the specific meaning of supercritical and ultra-supercritical
Question 6: What are subcritical, supercritical and ultra-supercritical water? During heating, water will evaporate, and the saturation pressure must correspond to the saturation temperature.
In the process of constant pressure heating of water, under each pressure, water will go through an unsaturated water (O) point, a saturated water (A) point, a wet saturated steam (X) point, a dry saturated steam (B) point until a superheated steam (E) point. With the increase of pressure, point A tends to move to the right, point B tends to move to the left, and the vaporization stage gradually shortens with the increase of pressure. When point A and point B coincide, this is the critical point of water, and there is no difference between saturated water and saturated steam.
Therefore, the critical point of water is P=22. 129MPa and T=374. 12℃.
Steam parameters of subcritical thermal power unit: P= 16~ 19MPa, T= 538℃/ 538℃ or T= 540℃/ 540℃.
When the parameters of steam exceed the critical state point of water, they are collectively called supercritical units, and (supercritical) is represented by (SC). The steam pressure of a general supercritical unit is 24~26MPa, and its typical parameters are: P=24. 1 MPa, 538℃/538℃; The parameters of 600MW supercritical unit under construction in China are: P=25.4MPa, 538℃/566℃; Or P=25.4MPa, 566℃/ 566℃.
In fact, the ultra-supercritical unit is to further improve the steam pressure and temperature on the basis of the parameters of the supercritical unit. Internationally, a unit with main steam pressure of 24. 1~3 1MPa and main steam/reheat steam temperature of 580℃~600 ℃/ 580℃ ~ 6 10℃ is usually defined as an efficient supercritical unit, commonly known as ultra-supercritical unit. The main steam of USC under construction in China is P= 25~26.5MPa, T= 600℃/600℃.
Supercritical is a special state of matter. When the ambient temperature and pressure reach the critical point of matter, the phase interface between gas and liquid disappears and becomes a homogeneous system. When the temperature and pressure rise further, that is, when the temperature and pressure exceed the critical point, the substance is in a supercritical state and becomes a supercritical fluid. Supercritical water is an important supercritical fluid. In supercritical state, water has good fluidity similar to gas, and its density is much higher than that of gas. Supercritical water is a good reaction medium with unique physical and chemical properties, such as high diffusion coefficient, high mass transfer rate, low viscosity, good miscibility, low dielectric constant and complete miscibility with organic and gas components. Low solubility in inorganic substances, favorable for solid separation, high reaction activity and strong decomposition ability; Supercritical water itself can participate in free radical and ion reactions and so on.
Subcritical boiler: the outlet pressure of main steam is 15.7~ 19.6MPa.
Supercritical boiler: main steam outlet pressure ≥22MPa.
Ultra-supercritical boiler: commercial name, without clear physical definition, only indicating a technical parameter or technical development stage, indicating higher pressure and temperature, with different definitions of starting point.
1. Japan: greater than 24.2 MPa, or reaching 593℃
2. Denmark: more than 27.5 MPa
3. Siemens: Distinguish from the grade of materials.
4. China Electric Power Encyclopedia: higher than 27MPa.
Why?