Flashing is the saturation of a high-pressure, saturated liquid into a relatively low-pressure vessel, which causes the saturated liquid to become a portion of the saturated vapor and saturated liquid at the vessel pressure due to a sudden drop in pressure.
Phenomenon
The boiling point of a substance increases as the pressure increases, and the lower the pressure, the lower the boiling point. In this way, the high-pressure high-temperature fluid can be depressurized to lower its boiling point and enter the flash tank. At this time, the fluid temperature is higher than the boiling point at the pressure. The fluid is rapidly boiled in a flash tank and subjected to two phase separation. The equipment that vaporizes the fluid is not a flash tank, but a pressure relief valve. The role of the flash tank is to provide a space for rapid gasification and vapor-liquid separation of the fluid.
Causes
When water is heated under atmospheric pressure, 100 ° C is the maximum temperature allowed for liquid water at that pressure. Reheating also does not increase the temperature of the water, but only converts the water into steam. The heat absorbed by water before it rises to the boiling point is called "sensible heat", or it is called sensible heat of saturated water. The heat required to convert saturated water to steam at the same atmospheric pressure is called "latent heat." However, if the water is heated under a certain pressure, the boiling point of the water is higher than 100 ° C, so more sensible heat is required. The higher the pressure, the higher the boiling point of water and the higher the heat content. The pressure is reduced and part of the sensible heat is released. This part of the excess heat is absorbed in the form of latent heat, causing some of the water to be "flashed" into steam.
Flash drying
The hot air enters the dryer from the cyclone at the bottom of the dryer in the tangential direction, and generates a high-speed swirling ascending airflow; the material to be dried is transported by the feeder into the drying chamber, and the high-speed swirling airflow and the bottom agitator work together. The agglomerated material is continuously broken, dispersed, boiled and dried. The dry qualified material is taken out from the upper outlet of the dryer by the airflow, and the dried product is obtained after being collected; the material with too large or high humidity is blocked by the grading raft in the upper part of the drying chamber, and further continues in the drying chamber. Dry until it is carried out by the air stream.
Flashing is mainly used in the recovery of boiler drainage and geothermal power generation in thermal power plants.
