Multiple effect evaporator

In life, many women like to perm their hair, because perming gives people a brand new feeling and can enhance people's temperament. However, some perming methods require the use of a multi-effect evaporator during the perming process. This can promote the hair's absorption of chemical substances. They are all used to quickly deform the hair and achieve the shape the hairstylist wants. So what is a multi-effect evaporator?

Multi-effect evaporation is the name of a series evaporation device that uses the secondary steam from the previous effect as the heating steam for the next effect. In multiple-effect evaporation, the operating pressure of each effect, the corresponding heating steam temperature and the boiling point of the solution decrease successively.

principle

In evaporation production, the output of secondary steam is large and contains a large amount of latent heat, so it should be recovered and utilized. If the secondary steam is passed into the heating chamber of another evaporator, as long as the operating pressure and boiling point of the solution of the latter are lower than the operating pressure and boiling point of the original evaporator, the secondary steam introduced can still play a heating role. This operation mode is called multiple-effect evaporation.

Each evaporator in multiple-effect evaporation is called an effect. Any evaporator that is fed with heating steam is called the first effect, and the evaporator that uses the secondary steam from the first effect as the heating agent is called the second effect, and so on. The purpose of using a multiple-effect evaporator is to save the consumption of heating steam. Theoretically, 1 kg of heated steam can evaporate approximately 1 kg of water.

However, due to heat loss and the fact that the latent heat of vaporization of water in the separation chamber is greater than the latent heat of condensation in the heating chamber, more than 1 kg of heating steam is actually required to evaporate 1 kg of water. According to experience, the economy of steam (U=W/D) is 0.91 for single effect, 1.76 for double effect, 2.5 for triple effect, 3.33 for quadruple effect, 3.71 for quintuple effect, etc. It can be seen that with the increase of the effect number, the growth rate of W/D gradually decreases. For example, when changing from single-effect to double-effect, heating steam can be saved by about 50%; while when changing from quadruple-effect to quintuple-effect, heating steam can only be saved by 10%. However, as the number of effects increases, the temperature difference loss of heat transfer increases, which greatly reduces the production intensity of the evaporator and increases the equipment cost exponentially. When the efficiency increases to a certain level, the steam cost saved due to the increase in efficiency may not be worth the additional equipment cost.

In industry, a balance must be struck between operating costs and equipment costs to determine the most reasonable efficiency. The most commonly used are 2-3 effects, and the maximum is 6 effects.