What is the Working Principle of Evaporators

1. What is the Working Principle of Evaporators? Evaporation is the process by which an element or compound changes from its liquid to a gaseous state below the boiling point. In most cases, it is critical that the product undergoes minimal thermal degradation. This necessitates minimizing temperature and time exposure. Along with other requirements imposed by the physical properties of the processed product, this has resulted in the development of a diverse range of evaporator types. By all means, evaporation plants are widely used in the field of thermal concentration technology for the concentration of liquids in the form of solutions, suspensions, and emulsions. Established in 1989, we at ALAQUA have more than 25 years of experience. We are leading manufacturers, offering a supply of evaporators, distillation plants, crystallizers, solvent recovery systems, and other process equipment.

2. Types of Evaporators: 1. Falling Film Evaporators In falling film evaporators, liquid and vapors flow downward in parallel flow. The concentrated liquid is preheated to boiling temperature. Through a distribution device in the evaporator’s head, an even thin film enters the heating tubes, flows downward at boiling temperature, and is partially evaporated. The co-current vapor flow augments the gravitationally- induced downward movement. evaporators can operate with very small temperature differences between the heating media and the boiling liquid. They have very short product contact times, typically only a few seconds per pass. These properties make the falling film evaporator ideal for heat-sensitive products, and it is now the most commonly used type of evaporator. Falling film However, falling film evaporators must be carefully designed for each operating condition. Adequate wetting of the heating surface by liquid is critical for the plant’s trouble-free operation. Dry patches and incrustations will form if the heating surfaces are not sufficiently wetted; at worst, the heating tubes will become completely clogged. In critical cases, extending or dividing evaporator effects while maintaining the benefits of single-pass operation can increase the wetting rate. To achieve full and even product wetting of the tubes, the liquid distribution system must be properly designed. 2. Rising Film Evaporators These work on the basis of the “thermo-siphon” principle. As the feed enters the bottom of the heating tubes, steam begins to form. Because of the ascending force of the steam produced during boiling, liquid and vapors flow upwards in parallel flow. Simultaneously, vapor production increases and the product is pressed as a thin film on the walls of the tubes. As a result, the liquid rises upwards. This co-current upward movement has the advantageous effect of increasing turbulence in the liquid. This is beneficial when evaporating highly viscous products or products

3. that tend to foul the heating surfaces. Typically, the temperature difference between the heating and boiling sides of this type of evaporator must be quite large. Otherwise, the vapor flow’s energy is insufficient to convey the liquid and produce the rising film. Typically, the length of the boiling tubes will not exceed 23 feet. This type of evaporator is frequently used in conjunction with product recirculation, in which some of the formed concentrates are reintroduced back into the feed inlet. This is to produce sufficient liquid loading inside the boiling tubes. 3. Forced Circulation Evaporator Forced circulation evaporators are used to avoid boiling the product on the heating surfaces due to the product’s fouling characteristics. The circulating liquid is heated as it flows through the heat exchanger and then partially evaporated as the pressure in the separator is reduced, allowing the liquid to cool to the boiling temperature corresponding to this pressure. Because the liquid is typically only heated a few degrees for each pass through the heat exchanger, the recirculation flow rate must be high. As there is no evaporation and thus no concentration increase on the heat transfer surface, this type of evaporator is also used in crystallizing applications. When the liquid is flash-evaporated in the separator vessel, it evaporates. This is where crystals form in crystallizer applications, and special separator designs are used to separate crystals from the recirculated crystal slurry. Depending on the specific requirements, the heat exchanger can be arranged horizontally or vertically. 4. Plate Evaporators Plate evaporators are small in size. Short interconnecting pipework connects the separators to the plate packages. As a result, space requirements are minimal, and heights are typically limited to 20 to 25 feet (6-8 meters). As a result, plate evaporators can be installed in the majority of buildings. Framed plates can be used as a heating surface instead of tube and shell heat exchangers. These plate assemblies are similar to plate heat exchangers but have larger vapor flow passages. A product plate and a

4. steam plate are connected alternately in these units. The product passage is designed to ensure even liquid distribution on the plate surfaces and a low- pressure drop in the vapor phase. Because the plate package is easily opened, surfaces can be inspected, individual plates can be changed as needed, and the evaporation rate can be adjusted by adding or removing individual plates. The units can be designed to meet USDA Dairy sanitation standards. Read More: What is the Working Principle of Evaporators?