The dual effect evaporator is different from ordinary single effect falling film or multi effect falling film evaporators. MVR is a single evaporator that integrates multiple effect falling film evaporators, and adopts segmented evaporation according to the required product concentrationWhen the desired concentration cannot be achieved after passing through the effector, the product is pumped through the external pipeline of the effector to the upper part of the effector by the vacuum pump at the lower part of the effector after leaving the effector, and then repeatedly passes through the effector to achieve the desired concentration. /Low price disposal of idle second-hand double effect evaporators

The interior of the effect body consists of arranged thin tubes, with the product inside and steam outside. During the flow of the product from top to bottom, the area inside the tube increases, causing the product to flow in a film like form to increase the heating surface. A negative pressure is formed inside the effect body through a vacuum pump, reducing the boiling point of water in the product and achieving concentration. The evaporation temperature of the product is around 60 ℃.

The condensed water, some steam, and residual steam generated after the product is heated and evaporated by the effect body are separated together through a separator. The condensed water flows out from the lower part of the separator to preheat the product entering the effect body. The steam is pressurized by a fan booster (the higher the steam pressure, the higher the temperature), and then the pressurized steam is combined through a pipeline and passes through the effect body again.

When the equipment is started, a portion of the steam needs to be preheated. After normal operation, the required steam will be significantly reduced. During the process of pressurization of the secondary steam by the fan booster, electrical energy is converted into thermal energy of the steam. Therefore, the required steam during the operation of the equipment decreases, while the required electricity increases significantly.

The temperature of the product remains around 60 ℃ throughout the entire process of the effect flow, and the temperature difference between the heating steam and the product is also maintained at around 5-8 ℃. The smaller the temperature difference between the product and the heating medium, the more beneficial it is to protect product quality and effectively prevent tube sticking.

The commonly used partition heat transfer evaporators can be roughly divided into two categories based on the residence of the solution in the evaporator: circulation type and one-way type.

1、 Circulating evaporator

This type of evaporator allows the solution to circulate in the evaporator. Due to different causes of circulation, it can be divided into two categories: natural circulation and forced circulation.

1. Circulating tube evaporator, also known as standard evaporator. Its heating chamber is composed of vertical tube bundles, with a large diameter circulation tube in the middle, and the other smaller diameter heating tubes are called boiling tubes. Due to the larger size of the circulation tube, the heat transfer surface occupied by a unit volume of solution is smaller than that occupied by a unit volume of solution in the boiling tube. This means that the solution in the circulation tube and other heating tubes is heated differently, resulting in a lower density of the vapor-liquid mixture in the boiling tube compared to the solution in the circulation tube. In addition, the upward suction effect of rising steam will cause the solution in the evaporator to form a circulating flow that descends from the circulation tube and rises from the boiling tube. This kind of cycle is mainly caused by the density difference of the solution, so it is called natural cycle. This effect is beneficial for improving the heat transfer efficiency inside the evaporator.

In order to ensure good circulation of the solution, the cross-sectional area of the circulation tube is generally 40-100% of the total cross-sectional area of other heating tubes; The height of the heating tube is generally 1-2m; the diameter of the heating tube is between 25-75mm. This type of evaporator is widely used due to its compact structure, easy manufacturing, good heat transfer, and reliable operation. However, due to structural limitations, the cycling speed is not high. By continuously circulating the solution in the heating chamber, its concentration always approaches that of the complete solution, resulting in a high boiling point of the solution and a decrease in the effective temperature difference. This is a common drawback of circulating evaporators. In addition, the cleaning and maintenance of the equipment are not convenient enough, so this evaporator is difficult to fully meet the production requirements.

2. In order to overcome the disadvantages of easy crystallization, scaling, and difficult cleaning of the evaporating liquid in the circulating evaporator, a more reasonable improvement has been made to the structure of the standard evaporator, which is the suspended basket evaporator. Heating chamber 4 is like a basket, suspended at the lower part of the evaporator shell, and replaced with a circular channel between the outer wall of the heating chamber and the inner wall of the evaporator instead of a circulation tube. The solution rises along the heating tube and then flows downwards along the annular gap between the outer wall of the suspended basket heating chamber and the inner wall of the evaporator to form a cycle. Due to the annular gap area being approximately 100 to 150% of the total cross-sectional area of the heating tube, the solution circulation speed is higher than that of a standard evaporator, reaching up to 1.5m/s. In addition, the heating chamber of this evaporator can be removed from the top for maintenance or replacement, and the heat loss is also relatively small. Its main disadvantage is its complex structure and high metal consumption per unit heat transfer area.

3. The natural circulation evaporator mentioned above has a circulation speed that is not high enough, generally below 1.5m/s. To make the evaporator more suitable for evaporating solutions with high viscosity, easy crystallization or severe scaling, and to increase the solution circulation speed to extend the operating cycle and reduce the number of cleaning times. /Low price disposal of idle second-hand double effect evaporators

Its structural feature is the addition of a boiling chamber on top of the heating chamber. The solution in the heating chamber does not boil in the heating tube due to the static pressure added by the liquid column in the boiling chamber. It can only start boiling when it rises to the boiling chamber and the pressure decreases. Therefore, the boiling and vaporization of the solution move from the heating chamber to the boiling chamber without a heat transfer surface, thus avoiding the formation of crystals or dirt in the heating tube. In addition, the cross-sectional area of the circulation tube of this evaporator is about 2-3 times the total cross-sectional area of the heating tube, and the solution circulation speed can reach 2.5 to 3 m/s or more, so the overall heat transfer coefficient is also relatively high. The main disadvantage of this evaporator is the large temperature difference loss caused by the static pressure head effect of the liquid column (see 6.3.1 for details). In order to maintain a certain effective temperature difference, a high pressure is required for heating the steam. In addition, the equipment is large, consumes a lot of materials, and requires tall factories. In addition to the natural circulation evaporator mentioned above, a forced circulation evaporator is also used when evaporating materials with high viscosity, easy crystallization, and scaling.