What Is Flash Evaporation?

Flash evaporation is a phenomenon in which high-pressure saturated liquids enter a relatively low-pressure container, and due to the sudden reduction in pressure, these saturated liquids become saturated steam and saturated liquid under the pressure of the container.

Flash

The boiling point of a substance increases with increasing pressure, and the lower the pressure, the lower the boiling point. In this way, the high-pressure and high-temperature fluid can be depressurized to reduce its boiling point and enter the flash tank. At this time, the temperature of the fluid is higher than the boiling point at this pressure. The fluid rapidly boils and evaporates in a flash tank and undergoes two-phase separation. The device to vaporize the fluid is not a flash tank, but a pressure reducing valve. The role of the flash tank is to provide space for rapid gasification of the fluid and vapor-liquid separation.

When water is heated at atmospheric pressure, 100 ° C is the highest temperature allowed for liquid water at that pressure. Reheating does not increase the temperature of the water, but only converts it into steam. The heat absorbed by water before it reaches the boiling point is called "sensible heat," or saturated water sensible heat. The heat required to convert saturated water into steam at the same atmospheric pressure is called "latent heat." However, if water is heated under a certain pressure, the boiling point of water will be 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 decreases and part of the sensible heat is released. This part of the excess heat will be absorbed in the form of latent heat, causing some water to be "flashed" into steam.

Flash evaporation occurs in the piping system, and it is easy to cause cavitation damage to the valve. An anti-cavitation high-pressure valve can be selected, which is characterized by multiple throttling to share the pressure difference, and can also use cavitation-resistant erosion materials.

Flash steam can also be used as energy, which is used in the recovery and drainage of boiler drainage in thermal power plants.

Hot air enters the dryer from the cyclone at the bottom of the dryer along the tangent direction and generates a high-speed swirling updraft; the material to be dried is transported by the feeder into the drying chamber, and under the combined action of the high-speed swirling airflow and the bottom mixer , Lump-like materials are constantly broken, dispersed, boiled and dried. Qualified dry materials are taken out of the upper outlet of the dryer by the air flow, and the dried products are obtained after capture; materials with too large particles or high humidity are blocked by the class weir plate set in the upper part of the drying room, and continue to be further Dry until carried away by airflow.

Flash evaporation is mainly used in the recovery of boiler drainage and geothermal power generation in thermal power plants.