The design of a single effect forced circulation evaporator is a complex and critical process that requires attention to the following aspects:
1、 Steam Overheating Problem
In the calculation of evaporators, designers usually use the temperature of secondary steam as the temperature of saturated steam under the pressure of the evaporator chamber. However, in some cases, this approach may not be appropriate. When the solution boils, the temperature of the vapor inside the bubble approaches the temperature of the solution, which causes the boiling point of the solution to rise and the vapor inside the bubble to overheat. The effect of superheated steam on heat transfer rate depends on whether the outer wall temperature of the pipeline is higher or lower than the steam condensation temperature. To solve the problem of secondary steam overheating, a condensate nozzle is generally installed at the elbow of the secondary steam pipeline at the top of the evaporation chamber to spray the condensate into a fine and uniform mist to reduce the steam temperature.
2、 Discharge of non condensable steam
When materials are concentrated, there may be insufficient sealing between the vacuum tank and the vacuum tube flange, resulting in a small amount of non condensable steam in the heating steam of the evaporator. These non condensable vapors can affect the efficiency and performance of the evaporator. Therefore, in the design, it is necessary to ensure that the discharge position of non condensable steam is correct to avoid gas release and leakage.
III. Material Characteristics and Preheating
Understanding and mastering the characteristics of materials is an important prerequisite for designing a single effect forced circulation evaporator. It is mainly necessary to grasp the scaling and coking situation of the material liquid during the evaporation process with the extension of production time, and whether it is accompanied by crystal precipitation. At the same time, mastering the boiling point increase values of the feed solution at different concentrations during the evaporation process is an important basis for designing and selecting steam compressors.
For materials with lower feed temperatures, preheating must be considered to bring the feed temperature to or near the boiling point before entering the evaporator for evaporation. Preheating can improve evaporation efficiency and reduce energy consumption.
4、 Selection of Steam Compressor
The steam compressor is one of the core components of a single effect forced circulation evaporator. When choosing a steam compressor, factors such as the evaporation rate of the material, the increase in boiling point, and the temperature range of the compressor need to be considered. For MVR evaporators equal to or less than 1000kg/h, Roots steam compressors are generally used. The temperature rise range of the compressor is generally between 10 and 16 ℃, with a maximum not exceeding 20 ℃. In addition, factors such as compressor adjustment margin and shaft power need to be considered to ensure the smooth progress of the evaporation process.
5、 Setting of Condenser
The condenser is another important component of a single effect forced circulation evaporator. When setting up a condenser, factors such as the amount of secondary steam entering the condenser and the heat exchange area of the condenser need to be considered. For MVR evaporators, the amount of secondary steam entering the condenser is generally calculated at 5% to 10% of the evaporation rate to meet production needs. The heat transfer area of the condenser needs to be calculated and determined based on specific design parameters and material characteristics.
6、 Equipment Material and Insulation
Due to the complex composition of wastewater and severe corrosion of equipment, suitable equipment materials need to be selected when designing a single effect forced circulation evaporator. The parts in contact with materials are generally made of stainless steel, such as 316L stainless steel. In addition, insulation treatment is required for the equipment to reduce heat loss and improve evaporation efficiency.
7、 Automation Control
In order to improve the automation level and operational convenience of single effect forced circulation evaporators, it is necessary to design a comprehensive automation control system. This system can achieve remote monitoring, automatic adjustment, and fault alarm functions of equipment, thereby improving the stability and reliability of the equipment.
The design of a single effect forced circulation evaporator needs to pay attention to issues such as steam overheating, discharge of non condensable steam, material characteristics and preheating, selection of steam compressors, condenser settings, equipment materials and insulation, and automation control. Only by comprehensively considering these factors can an efficient, stable, and reliable single effect forced circulation evaporator be designed.
