【Q&A Question 132】2017.05.12

At a certain temperature, when steam is introduced into the oil to be distilled, the sum of the vapor pressures of the oil and steam is lower than the total pressure in the equipment; under such conditions the oil will boil. The greater the amount of water vapor introduced, the higher the vapor pressure of water vapor, and accordingly the lower the vapor pressure required from the oil, resulting in a lower temperature needed for the oil to boil.

At a certain temperature, when steam is introduced into the oil being distilled, and the sum of the vapor pressures of oil and gas is lower than the total pressure in the equipment, the oil can boil. The greater the amount of steam introduced, the higher the vapor pressure of water formed, and accordingly the lower the vapor pressure required of the oil; this results in a lower temperature needed for the oil to boil

When water vapor is introduced into the wastewater, the wastewater begins to boil once the vapor pressure of the aqueous solution (equal to the sum of the vapor pressure of the volatile substances and that of water vapor) exceeds the external pressure; this accelerates the process by which volatile substances transition from the liquid phase to the gas phase. On the other hand, when water vapor passes through the water layer in the form of bubbles, a free interface is formed between the water and the bubble surfaces; at this point, liquid continuously evaporates and diffuses into the bubbles. When the bubbles rise to the surface of the liquid, they begin to burst, releasing the volatile substances contained within them. This method of distillation using water vapor is known as the stripping method. During the stripping process, a very large number of water vapor bubbles significantly increase the evaporation surface area, thereby enhancing the mass transfer process. Volatile dissolved substances in industrial wastewater, such as volatile phenols (phenol, cresol, formaldehyde, aniline, etc.), can be separated from the wastewater using stripping. The stripping process is generally carried out in a closed tower. After heating the wastewater, it is fed in from the top of the tower, while steam is fed in from the bottom. The stripping method was first used to recover volatile phenols from phenol-containing wastewater. The stripping tower is divided into upper and lower sections. The upper section serves as the stripping section, where steam is used to remove phenol from the wastewater through counter-current contact. The lower section is called the regeneration section, where alkali solution is used to absorb phenol from the steam, also via counter-current contact.

At a certain temperature, when the oil to be distilled passes through steam, if the sum of the vapor pressures of the oil and steam exceeds the total pressure in the equipment, the oil will boil. The greater the amount of water vapor introduced, the higher the vapor pressure of water vapor, and accordingly the lower the vapor pressure of the oil required; this results in a lower temperature needed for the oil to boil.

At a certain temperature, when the oil to be distilled passes through steam, if the sum of the vapor pressures of the oil and steam exceeds the total pressure in the equipment, the oil will boil. The greater the amount of water vapor introduced, the higher the vapor pressure of water vapor, and accordingly the lower the vapor pressure of the oil required; this results in a lower temperature needed for the oil to boil.

Lowering the partial pressure of oil and gas facilitates separation

The theoretical basis for stripping is Henry’s law: at a constant temperature, when phase equilibrium is reached between the gas and liquid phases, the partial pressure of the dissolved gas in the gas phase is proportional to its concentration in the liquid phase. Therefore, in actual production, air or water vapor can be used as the carrier gas to reduce the partial pressure of the solute in the gas phase, thereby causing the solute to precipitate from the solution, leaving a lean solution that can be recycled. This is what is known as gas lift

By reducing the partial pressure of other substances, under certain conditions the vapor pressure of a particular substance is proportional to its concentration in the liquid phase. An increase in the partial pressure of the stripping steam leads to a decrease in the partial pressure of that substance, thereby reducing its concentration in the liquid phase.

At a certain temperature, when the oil to be distilled passes through steam, if the sum of the vapor pressures of the oil and steam exceeds the total pressure in the equipment, the oil will boil. The greater the amount of water vapor introduced, the higher the vapor pressure of water vapor, and accordingly the lower the vapor pressure of the oil required; this results in a lower temperature needed for the oil to boil.

At a certain temperature, when the oil to be distilled passes through steam, if the sum of the vapor pressures of the oil and steam exceeds the total pressure in the equipment, the oil will boil. The greater the amount of water vapor introduced, the higher the vapor pressure of water vapor, and accordingly the lower the vapor pressure of the oil required; this results in a lower temperature needed for the oil to boil.