For the evaporation of general solution, η can be taken as 0.98-0.7 (where X is the composition change of the solution, expressed in mass fraction). Where: Di — heating steam quantity of the ith effect, kg/H, when no additional steam is extracted, R I — vaporization heat of heating steam of the first effect, kJ/kg; R 'I — vaporization heat of secondary steam of the first effect, kJ/kg; C PO — Specific heat capacity of feed solution, kJ/ (kg · ); C PW — specific heat capacity of water, kJ/ (kg · ); T I, t i-1 — boiling point of the solution of the i-th effect and the (i-1) -th effect, ; ηi — heat utilization coefficient of the ith effect, dimension is one. For the consumption of heating steam (live steam), it can be obtained by listing the enthalpy balance formula of each effect and solving it with the formula (1-2). 4. Distribution of Heat Transfer Area and Effective Temperature Difference of Evaporator in Each Effect The heat transfer rate equation for any effect I 1-17 Where: Q I — heat transfer rate of the ith effect, W; K I — heat transfer coefficient of the ith effect, W; Si — heat transfer area of the ith effect, m2; T I — heat transfer temperature difference of the ith effect, . The purpose of effective temperature distribution is to calculate the heat transfer area Si of evaporation. Now take the triple effect as an example, namely 1-18 In the formula 1-19 1-20 In multi-effect evaporation, in order to facilitate manufacturing and installation, evaporators with equal heat transfer area of each effect are usually used. If the heat transfer areas obtained from Equation (1-18) are not equal, the areas shall be redistributed according to the principle of each effective area. Effective temperature difference. The method is as follows: Let t 'denote the effective temperature difference when the effective surfaces are equal, then Compared with the formula (1-18), Add the three formulas in formula (1-22) to get In the formula, ∑ t is the sum of the effective temperature difference of each effect, which is called the total effective temperature difference, . After the heat transfer area S is obtained from Equation (1-23), the effective temperature difference of each effect can be redistributed from Equation (1-22). Repeat the above steps until the obtained heat transfer area of each effect is equal, and the area is the required one. 3 Selection of evaporator As mentioned above, there are many types of evaporator structures. When selecting the type of evaporator or designing the evaporator, on the premise of meeting the requirements of production tasks and ensuring product quality, it is also necessary to take into account the simple structure, easy manufacture, convenient operation and maintenance, good heat transfer effect and so on. In addition, it is also necessary to have good adaptability to the process characteristics of the material to be evaporated,cbd centrifugal extractor, including the viscosity, heat sensitivity, corrosiveness of the material and whether it crystallizes or scales. The climbing film evaporator is suitable for evaporating low-boiling point alcohols or low-boiling point volatile organic compounds; The falling-film evaporator is suitable for the concentration of water-soluble substances and the evaporation of materials which are not easy to crystallize or scab; The horizontal falling film evaporator is suitable for the evaporation of volatile organic compounds with medium boiling points such as ethanol; The natural internal circulation evaporator is suitable for the concentration and evaporation of general materials; The forced external circulation evaporator is suitable for the evaporation and crystallization of high-concentration and easy-to-crystallize materials; The combination of falling film and forced external circulation evaporator is suitable for the concentration and crystallization of low-concentration and easy-to-crystallize materials; The combination of natural circulation and forced external circulation evaporator is suitable for the crystallization of the thickener of the medium and low concentration materials which are easy to crystallize; The combination of forced external circulation and multi-effect evaporation crystallization is suitable for secondary concentrated crystallization containing high-boiling inorganic or organic substances; Selection Criteria for Common Evaporation Equipment Return to Sohu to see more Responsible Editor:. toptiontech.com