What is subcritical, supercritical, ultra-supercritical?

Deciphering the mysteries of the state of matter:subcritical,supercritical and ultra-supercritical

In the fields of physics and chemistry,the state of matter is a fundamental and complex subject.With changes in temperature and pressure,substances can be converted between solid,liquid and gas.However,under certain conditions of temperature and pressure,matter can also exhibit more special states,namely subcritical,supercritical and ultra-supercritical.This article will explore these three states in depth and explain their applications in industry and science.

Subcritical:the transitional stage of a state of matter

Subcritical is a state condition in which a substance exists at a temperature above its boiling point but below its critical temperature,while at the same time present in a fluid form with a pressure below its critical pressure.To better understand subcritical states,we need to first understand what critical temperature and critical pressure are.

The critical temperature is the temperature at which a substance cannot be liquefied under a particular pressure,no matter how much pressure is applied.In other words,when the temperature exceeds the critical temperature,the substance can no longer be liquefied,regardless of the pressure.In contrast,the critical pressure is the minimum pressure required to liquefy a substance at a critical temperature.

In the case of a gas,when the temperature does not exceed a certain value,the gas can be liquefied by pressurizing it.However,above this temperature,no matter how much pressure is applied,the gas cannot be liquefied,and this temperature is the critical temperature of the gas.At the critical temperature,the pressure necessary to liquefy the gas is the critical pressure.

In the subcritical state,the substance still maintains certain fluid properties,but does not fully meet the definition of liquid or gas.This state has many applications in industry,especially in fields such as specialty vegetable oil extraction.For example,in the extraction process of grape seed oil,subcritical state is often used for efficient extraction.

Supercritical:A revolutionary shift in the state of matter

The supercritical state is a special state of matter.When the ambient temperature and pressure reach the critical point of matter,the phase interface of the two phases of gas and liquid disappears and becomes a homogeneous system.Further increasing the temperature and pressure,the substance will enter a supercritical state and become a supercritical fluid.

Supercritical fluids have many unique properties,such as high solubility,high diffusivity and high reactivity.These properties make supercritical fluid have a wide application prospect in chemical reaction,material synthesis,extraction and separation.

Supercritical carbon dioxide,for example,has significant advantages as an extractant in the food and pharmaceutical industries.Since the dissolution capacity of supercritical carbon dioxide is closely related to temperature and pressure,its dissolution capacity can be controlled by adjusting temperature and pressure,so as to achieve efficient extraction.In addition,supercritical carbon dioxide also has the advantages of non-toxic,non-flammable and no residue,making it an ideal extractant.

In the field of coal power production,supercritical state is also of great significance.When the pressure and temperature of the working medium(usually water)in the boiler exceed the critical point,the water will enter a supercritical state.Supercritical water has extraordinary solubility,compressibility and mass transfer properties,which make it more efficient in the process of power generation.Therefore,supercritical coal power generation technology has become one of the mainstream technologies in the field of coal power.

Ultra-supercritical:The ultimate pursuit of energy efficiency

The ultra-supercritical state is a further upgrade of the supercritical state,which refers to the state of the medium under higher temperature and pressure conditions.In the field of coal power production,ultra-supercritical state refers to the state of water.The higher the steam pressure,temperature and other parameters,the higher the energy efficiency.Therefore,ultra-supercritical coal power generation technology has become the ultimate pursuit of energy efficiency improvement in the current coal power field

At 22.115 mpa pressure and 374.15°C,the density of water vapor increases to that of liquid water,a condition known as the critical parameter of water.When the pressure and temperature of steam exceed this critical parameter,it enters a supercritical state.When the steam temperature in the furnace is not lower than 593°C or the steam pressure is not lower than 31 mpa,it is called ultra-supercritical state.

Ultra-supercritical coal-fired power generation technology uses high-temperature and high-pressure steam to drive the turbine unit to do work,so as to efficiently convert the chemical energy in the fuel to electric energy.Because steam in the ultra-supercritical state has a higher temperature and pressure,it is able to transfer heat and do work more efficiently,thereby increasing the efficiency of power generation.In addition,ultra-supercritical coal power generation technology also has the advantages of environmental protection,energy saving,low carbon and so on,in line with the current global energy transformation and green development trend.

Practical application:the leap from theory to practice

Subcritical,supercritical and ultra-supercritical states not only have great significance in theory,but also play a great role in practical application.Here are a few typical application areas:

Chemical industry:supercritical fluid extraction technology has become an important separation technology in the chemical industry.Using the high solubility and high diffusivity of supercritical fluids,an efficient and environmentally friendly extraction process can be achieved.In addition,supercritical fluids can also be used in the synthesis of new materials,preparation of drugs and other fields.

Coal power field:supercritical and ultra-supercritical coal power generation technology is one of the mainstream technologies in the current coal power field.By increasing the temperature and pressure of steam,power generation efficiency can be significantly improved and energy consumption and emissions reduced.This is of great significance for relieving energy pressure and reducing environmental pollution.

Food industry:supercritical carbon dioxide extraction technology is widely used in the food industry.It can be used to extract natural ingredients in food,such as flavors,colors and so on.Because supercritical carbon dioxide has the advantages of non-toxic,non-flammable and no residue,it can ensure the safety and quality of food.

Environmental protection:supercritical water oxidation technology is an efficient wastewater treatment technology.In the supercritical state,the organic matter in the water can be rapidly oxidized and decomposed,so as to achieve the purification treatment of wastewater.In addition,supercritical water can also be used to treat solid waste and exhaust gas.

Future outlook:Challenges and opportunities

With the progress of science and technology and the promotion of energy transformation,the application prospects of sub-critical,supercritical and ultra-supercritical states will be broader.However,the research and application of these states also face many challenges.For example,the properties of substances in supercritical and ultra-supercritical states are complex and changeable,and more in-depth research and understanding are needed.At the same time,these states also have higher requirements for equipment and processes,requiring continuous technological innovation and optimization.

Nevertheless,we still have reason to believe that with the continuous progress of science and technology and people's continued attention to energy,environmental protection and other fields,the application of sub-critical,supercritical and ultra-supercritical states will achieve more significant results.They will play a more important role in promoting energy transition and green development.

Conclusion

Subcritical,supercritical and ultra-supercritical are the special states of matter under different temperature and pressure conditions.They not only have great significance in theory,but also have wide application prospects in chemical industry,coal power,food,environmental protection and other fields.By deeply studying the nature and application of these states,we can make better use of their unique advantages to promote scientific and technological progress and social development.At the same time,we also need to continue to face challenges,continue to innovate and optimize technology to achieve more efficient,environmentally friendly and sustainable energy use.