Extraction is a well-known method used in chemical, food, pharmacy, and many other industries. It is used to extract active substances from raw or dried plant material. In these processes, various solvents can ‘wash out’ these compounds, based on which they got their name (ethanol extraction, CO2 extraction, etc.).
The solutions obtained in this process need additional refining to remove traces of solvents. It results in a more concentrated solution. That is necessary for food (skim milk, cream) and liquors because things like ethanol or glycerol can affect the taste. It is most often done by an evaporation process, which uses special devices known as evaporators.
There are different types of evaporators used for a variety of purposes. However, the most common is the use of a long-tube device that you have probably seen before. Its name is a falling film evaporator, and the way it works is quite simple, but that is not the only advantage of using it.
Low Operating Costs
Due to its relatively simple working principle, the falling film evaporator has lower running costs than other types of these devices. You can pour the solution into the head and is evenly distributed into its sections. This liquid forms a thin layer, known as film, on the tube walls. It does not overflood the tubes; it just passes through them.
When the device warms up, the film flows downwards and evaporates partially. The steam obtained in that process will serve for further heating of the device. It is a semi-closed setup, and the vapors in it circulate to some point. Finally, the end product (purified solution) and the steam both drop downwards.
Other reasons for the relatively low cost of this equipment are its simplicity and small dimensions. Separation of liquid and vapors takes place in the lower part of the device. The refined solution stays on the bottom of that vessel. The tube is on top of it and serves for feed entering.
Faster Work Rate
The inner tube surface (walls) acts as a heating media in falling-film evaporators. While the liquid slowly slips down the walls, it distributes evenly all over the tube sections. That maximizes the contact between the liquid and the surface through which the heating media passes.
A few factors contribute to this superior heat transfer, including the absence of a vapor barrier, the greater surface area, and better conduction of heat through the material. That provides a higher heat transfer rate from the media to the process fluid. A higher rate of this parameter means faster evaporation and a better overall extraction process.
In falling film devices, this process happens at the liquid-vapor interface. It means that the device can use a lower temperature, meaning less energy use and some other benefits. For example, as there is no nucleate boiling on the tube walls, the solution in the evaporator will not crystalize.
These long-tube devices are very energy efficient as they take advantage of gravity pulling the film down. It gets thinner and moves downward fast. While it passes, water or other mediums heat it. That provides high heat-transfer coefficients, as the moisture transfers heat soon after touching the tube wall. What this coefficient means, find out here.
When converting a liquid into steam, these vaporizing units need more energy than standard evaporators. Falling-film devices achieve high thermal performance in a short time, which makes them great for industrial use. That is the reason why many factories across most major industries update their old evaporators to falling film ones.
Due to the fast evaporation that happens when the liquid gets in touch with the surface, falling-film evaporators can be used with temperature-sensitive products. These are handy for utilization in processes where the temperature between the heating medium and the liquid is less than 15°F.
Falling film evaporators can function at low temperatures, unlike other types of these devices. These units employ advanced safety features to minimize damage in case of an accident. These include a contoured plate and a safety cover surrounding the entire heating surface. These safety features are designed to prevent burning and leakage.
These devices can adapt to heat-sensitive solutions poured into them. After being heated (which happens in a matter of seconds), it gets out, leaving purified solution behind. As this process is short, the device will not deteriorate.
Low Space Requirements
Another reason for the relatively low cost of this unit is its simplicity and small size. Compared to standard lab tools, these units do not need a large space to install. They have a compact design but are also suitable to connect with other pieces of extraction equipment.
Check the source below for safety guidelines on handling this equipment:
In modern industry, the goal is to rationalize costs but also production by environmental standards. The use of a falling film evaporator meets both requirements. Besides the benefits already mentioned, this device is a desirable part of plant material processing equipment.