The evaporator is a high-efficiency evaporation crystallizer, which is called a thin-film evaporator together with a rising film evaporator and a scraped film evaporator. It is used in chemical plants, light industry and food processing industry to achieve the effect of liquid extraction. The structure of the falling film evaporator is actually not complicated. It can be interpreted as a set of film cloth equipment added to the column type tube heat exchanger, but it has another significant difference from the general heat exchanger. Its shell side is not fixed. The moving is the heating liquid, and the fixed tube is the volatilized raw material. The raw material in the tube side of the falling film evaporator also enters the heat exchanger from the top of the tube, and relies on its own force to move along the wall of the tube. Before entering the heat exchanger, it needs to pass through the film cloth device, so it enters the heat exchange It will be viscous when it is put into the container, and the water is volatilized during the process of raw materials from top to bottom to achieve the effect of raw material extraction. If the shell side is heated by steam condensation or heat transfer oil, if steam is used, it will go up. Bottom out, if high temperature heat transfer oil is used, it must be from bottom to top. It is not difficult to see that the flow direction of the medium inside and outside the pipe is not necessarily all reverse flow.
Analysis of the advantages of the evaporator:
(1) The residence time of raw materials in the heat exchanger is short, and it will not affect the physical properties of heat-sensitive materials;
(2) The raw materials in the heat exchanger are viscous and the air flow rate is fast, and the volatilization heat transfer coefficient is large;
(3) The pressure drop is basically 0, and the raw material of the tube side is in a natural environment of natural pressure, and it drips down along the inner cavity of the tube purely by its own force, which can be environmentally friendly and energy-saving;
(4) Because the raw material of the tube side drops down along the inner cavity of the tube by its own force, and is not promoted by the pressure difference, a low temperature difference can be selected;
(5) The amount of raw materials in the indoor space of the tube is very small;
(6) The heating of the material in the tube side is reflected by convection boiling, so the surface condition of the heat exchanger basically does not affect the boiling of the material.
Analysis of evaporator defects:
(1) The volatilization effect of machinery and equipment has a lot to do with the distributor, and the production, design and installation specifications of the distributor are very high;
(2) The requirements for installation equipment are strict, and the specific performance is that the vertical angle is specified. Assuming that the length of the heat exchanger is 9m, the vertical angle of the equipment is required to be ≤ 6.4mm;
(3) It is necessary to ensure that the inner cavity of the heat exchanger of the equipment is completely moist but the thickness of the cloth film should not be too large. It is necessary to carry out special design calculations on the amount of raw materials and the length of the heat exchanger to meet these requirements;
(4 Due to the very high production design requirements, the cost of machinery and equipment products is very high;
(5) It is not suitable for raw materials that are easy to foul or contain liquid suspended solids.