Evaporator Assembly Call

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I. Scraper-type thin-film evaporator: The scraper-type thin-film evaporator is a highly efficient device for evaporation or distillation, which uses a rapidly rotating scraper to spread the liquid into a uniform thin film. It can also be used for operations such as deodorization, defoaming, as well as heating and cooling. It is widely applied in industries such as pharmaceuticals (both traditional Chinese and Western), food processing, light industry, petroleum, chemicals, and environmental protection. Scraper types include centrifugal scrapers, articulated scrapers, fixed scrapers, etc. It is characterized by low vacuum pressure drop, low operating temperature, short heating time, high evaporation intensity, and great operational flexibility. Working principle: It mainly consists of a heating jacket and a scraper. Heating steam is passed through the jacket, while the scraper is mounted on a rotatable shaft; it maintains a very small gap with the inner wall of the heating jacket, usually ranging from 0.5 to 1.5 mm. After preheating, the feed liquid is introduced tangentially from the upper part of the evaporator; under the action of gravity and rotating scrapers, it spreads along the inner wall to form a downward-moving film. As it descends, it is continuously evaporated and concentrated. The liquid product is discharged from the bottom, while the secondary steam escapes from the top. II. Falling-film evaporator: The falling-film evaporator is a highly efficient, single-pass, non-circulating membrane evaporation device. Its membrane evaporation principle confers upon it advantages such as high heat transfer efficiency, low temperature difference losses, short heating time for the material, reduced risk of product deterioration, ease of operation in multi-effect configurations, low energy consumption, and compact equipment size. It is particularly suitable for heat-sensitive materials and those with low concentrations that are difficult to crystallize. Working principle: Falling film evaporation involves feeding the liquid feed into the upper tube bank of the heating chamber of the falling film evaporator; through a liquid distribution and film-forming device, it is evenly distributed across the various heat exchange tubes. Under the influence of gravity, vacuum, and air flow, it flows in a uniform film form from top to bottom. During the flow process, the liquid is heated and vaporized by the heating medium in the shell side; the resulting steam together with the liquid phase enters the separation chamber of the evaporator. There, the steam and liquid are thoroughly separated, with the steam going into the condenser to be condensed (in a single-effect operation) or entering the next stage of the evaporator as a heating medium, thereby enabling multi-effect operation. The liquid phase, on the other hand, is discharged from the separation chamber. III. Film-evaporator type evaporators: These types of evaporators require careful design and operation; the secondary steam inside the heating tubes must have a high velocity, as well as a high heat transfer coefficient, so that the feed liquid can reach the desired level of concentration after passing through the heating tubes just once. Generally, at normal pressure, it is appropriate to maintain the velocity at the outlet at the upper end of the tube at 20–50 m/s; during reduced-pressure operations, this velocity can reach 100–160 m/s. The rising-film evaporator is suitable for processing solutions with a high evaporation rate, thermal sensitivity, low viscosity, and a tendency to foam; however, it is not suitable for solutions with high viscosity, those prone to crystal precipitation, or those likely to cause scaling. Compared to falling film evaporators, its installed power is relatively low. Working principle: The heater consists of heat exchange tubes and a housing, while the heating chamber of the rising film evaporator is made up of vertical long tube bundles. Typically, the diameter of the heating tube is 25–50 mm, with a length-to-diameter ratio of 100–150. After the feed liquid is preheated to the boiling point or near it, it is introduced from the bottom of the heating chamber. Driven by the high-speed rising secondary steam, it flows along the inner wall of the heat exchange tubes while evaporating; the desired concentration is achieved at the top of the heating chamber. The resulting liquid is discharged from the bottom of the separation chamber, and the secondary steam generated is freed of bubbles, water droplets, and impurities through the separation plate assembly installed at the upper part, thereby becoming the heat source for the next stage. IV. MVR Evaporator The MVR evaporator is a technology that reuses the energy of the secondary steam it generates, thereby reducing the need for external energy sources. The MVR evaporator is a mechanical thermal compression evaporator, representing a new type of efficient evaporation device. Its working principle involves the generation of secondary steam in the evaporator; this steam is then compressed by a mechanical thermal compressor, resulting in an increase in temperature and pressure as well as an increase in enthalpy. The resulting hot fluid is used again as a heating source for the evaporation chamber, thereby keeping the liquid material in a boiling state. Apart from starting the operation by driving the engine, no steam is required throughout the evaporation process; fresh steam is used only to compensate for heat losses and to replenish the heat energy of the feed and product, thereby significantly reducing the evaporator’s consumption of external fresh steam and minimizing pollution. The steam that would otherwise have been wasted is now fully utilized, the latent heat of vaporization is recovered, and thermal efficiency is improved. Furthermore, by replacing steam input with electrical power input, the MVR reduces operating costs. MVR evaporators can achieve low-temperature evaporation. Performance features: low energy consumption, low operating costs ； Small footprint ； Fewer utility facilities are required, the total project investment is low, operation is stable, and the degree of automation is high ； No native steam required ； Since a single effect is commonly used, the product retention time is short; the process is simple and highly practical, with excellent performance under partial load operation. V. Natural circulation evaporators: In natural external circulation evaporators, the solution circulates due to the difference in density between the liquid and the vapor. To prevent scaling and crystallization, the heating tube should be operated with it fully submerged. This type of evaporator is suitable for the concentration of solutions with mild scaling and low corrosivity. Its advantages are a simple structure, ease of manufacturing, and low power consumption. The disadvantages are that the solution circulation speed is slow, making it unsuitable for materials with high viscosity or a large amount of crystals; it is not possible to clean the system on-site, the materials are exposed to heat for too long, and it is not appropriate for heat-sensitive materials. Working principle: External heating natural circulation evaporator: The liquid is heated inside the tubes of the heating chamber; as its temperature rises, its density decreases. This creates a density difference with the cold solution in the circulation pipes, prompting the liquid to circulate upward inside the heating tubes and downward inside the circulation pipes. The heated solution enters the evaporation chamber in the form of sensible heat to flash and cool down. It then moves downward into the circulation tube, where it is heated and evaporated in a cyclic manner. The circulation speed of the solution within the equipment is not high, generally less than 1 meter per second. VI. Forced-circulation evaporator: A forced-circulation evaporator relies on an external force, namely a circulation pump, to circulate the liquid and increase the flow rate of the solution. Its heating chamber is available in both horizontal and vertical configurations, and the liquid circulation speed is regulated by a pump. Depending on the positions of the inlet and outlet for the liquid circulating in the separation chamber, it can be further divided into positive-circulation forced evaporators and reverse-circulation forced evaporators. The circulation speed of the liquid inside the heating tube is usually in the range of 1.2 to 3.0 meters per second (a lower value is chosen when there are many particles in the suspension, the material of the tube used has low hardness, and the viscosity of the liquid is high). The heating tube can be of vertical single-pass or vertical double-pass type, or horizontal single-pass or horizontal double-pass type; the latter two types have a lower overall height, but the tubes are difficult to clean and their walls tend to wear out more easily. Advantages of this type of evaporator: high heat transfer coefficient, resistance to salinization and scaling, good adaptability, and easy cleaning ； Disadvantages: long solution residence time, slightly higher cost and maintenance expenses, high power consumption. Working principle: The circulation of the solution within the device relies primarily on forced flow generated by an external power source. The circulation speed can generally reach 1.2–3.0 meters per second. It has high heat transfer efficiency and production capacity. The raw material liquid is pumped in from below by a circulation pump and flows upward along the tubes in the heating chamber. After entering the evaporation chamber, the mixture of steam and liquid droplets separates; the steam is discharged from the top, while the fluid falls under pressure and is drawn in by a circulation pump through the conical bottom, then enters the heating tubes to continue the cycle. VII. Multi-effect evaporators: Multi-effect evaporation is an evaporation process in which several evaporators are operated in series, allowing the thermal energy of steam to be utilized multiple times and thereby improving the efficiency of heat utilization; it is widely used in the treatment of aqueous solutions. In the process of triple-effect evaporation, the first evaporator (referred to as the first effect) uses raw steam as the heating steam, while the remaining two evaporators (referred to as the second and third effects) use the secondary steam from the preceding effect as their heating steam, thereby significantly reducing the amount of raw steam required. The temperature of the secondary steam in each effect is always lower than that of the heating steam; therefore, in multi-effect evaporation, the operating pressure and the boiling temperature of the solution decrease sequentially in the direction of steam flow. Based on the flow direction of the secondary steam and the solution, the multi-effect evaporation process can be divided into: ① Co-current process. The solution and secondary steam pass through each stage in the same direction sequentially. Since the pressure before the effect is higher than that after, the material fluid can flow due to the pressure difference. However, the concentration of the final-stage solution is high and the temperature is low, resulting in high solution viscosity and thus a low heat transfer coefficient. ②Counterflow process. The solution flows in the opposite direction to the secondary steam. A pump is required to transfer the solution to the previous stage with higher pressure. The effects of concentration and temperature on viscosity in each stage roughly cancel each other out, and the heat transfer conditions in all stages are essentially the same. ③Counterflow process. Secondary steam passes through each effect in sequence, but the feed liquid enters and exits each effect separately; this process is suitable for feed liquids in which crystals precipitate.