Removal of excess water and thereby concentrating useful solids available in any liquid product is a necessity in many process industries such as Dairy, Fruit Juices, Starch, Malt, Sugar, Chemicals, Paper and Pulp and other similar industries.


In falling film evaporators the product to be concentrated is introduced into the top part of the evaporator. A distribution plate distributes the product evenly on the surface of heated tubes, creating a down flowing thin film. As the product flows downwards at boiling temperature, evaporation takes place thus removing liquid and concentrating the product.

The solution boils at low temperatures because of the vacuum inside the evaporator. Due to the low boiling temperatures, ranging from as low as 40 deg. C to 70 deg. C, and short product contact times, these properties make falling film evaporation technology suitable for handling of heat-sensitive products. The falling film evaporators are the most used ones in the food industry.



Two of more effects can be combined in order to create a multi stage evaporator, or multiple-effect evaporator. The vapors from the preceding stage are used as the heating media of the next stage, thus improving the overall efficiency. Each stage operates at a lower pressure and temperature than the preceding stage, in order to maintain the temperature difference. The energy of the vapor can be added by thermal vapor recompression or mechanical vapor recompression.
Because multi-stage falling film evaporators extract water from the products at extremely low energy consumption, this and the above mentioned properties make this technology suitable in commercial applications. Ralli Oy (Ltd.) specializes in the design, fabrication, supply and commissioning of multi-stage falling film evaporators. A team of experts make thorough studies in close association with the clients, resulting in an optimum design in terms of capacity and layout.



TVR system is mostly adopted either for high boiling point elevation products or in countries with high electricity costs. TVR is used to give better efficiency by means of steam ejector. In steam ejector motive steam speed is increased around 1000m/s thus making vacuum and picking up vapor from separator. The vapor extracted from one stage is used, if necessary after recompression, as the heating medium for the next state at a lower temperature and pressure to improve evaporator efficiency. Number of stages is limited by overall temperature difference of system or investments costs against running costs. Temperatures are mainly determined by the heat sensitivity and viscosity of the product.



MVR is superior both in running economy and gentle handling of the product. Minimum energy consumption with maximum concentration is the base for MVR evaporator technology. In MVR evaporators very low single boiling temperature and low temperature difference can be achieved and therefore the heat load to product is absolutely minimum. MVR compressor or high pressure fan run by motor, compresses vapor sucked from separator to higher pressure, thus increasing vapor temperature and enthalpy. This vapor is fed outside of tubes and is used as heating medium for evaporation in the next stage.


We at RALLI OY (Ltd.) are experts of several kinds of evaporation technologies, including multi-staged falling film evaporators, using thermal vapor recompression (TVR) or mechanical vapor recompression (MVR). We have more than 30 years of expertise in designing, commissioning and refurbishing evaporation systems. If you have a need for a new or used evaporator or want to increase the capacity of your existing evaporation solution, contact us. Our team of experts will find the best suitable solution for you.