PRINCIPLE
The falling film principle requires an even distribution of the feed liquid. To achieve this distribution one or more distribution trays are located in the top head of the evaporator over the complete tube sheet.
Our proven distribution devices make sure that the inner surface of each individual tube is properly wetted. The liquid film moves down the tubes by gravity force. Heat applied through the tube wall effects boiling-off the light fraction from the film.
CONSTRUCTION
The construction of the falling film evaporator is different than the rising film, its tube length varies from 10 to 12 meter. In this evaporator the heating unit consists of steam jacketed tubes. The feed inlet is from the top of the steam compartment. The other provision such as steam inlet, vent and condensate outlet remains same as in rising film evaporator. The outlet for the product is provided at the bottom and is connected to a vapour separator. Juice recirculation provided from the bottom portion of the evaporator.
WORKING
Steam is supplied into the steam compartment. Feed enters the top of the tube. The temperature of the boiling liquid is same as that of the vapour head. The feed flows down the walls of the tubes. The liquid gets heated rapidly. The liquid boils and becomes vapour in form of smaller bubbles. These tends to fuse to form layers of bubbles, which travels downwards the tube. Juice get concentrated during this downwards journey. Vapour and liquids are separated in the vapour separator. Juice recirculation connection provided at the bottom portion of the evaporator and pumps are provided for the juice recirculation. Thick juice transferred to next body either by gravity or by pumping.
ADVANTAGES
- Falling film evaporator is suitable for high viscous liquids because the flow of vapour film assisted by gravity.
- The liquid is not over heated during passage and heat transfer coefficients are high even at low boiling temperature.
- Boiling point elevation due to head is completely eliminated in falling film evaporator as juice comes down inside the tube.
Falling Film Evaporator is a device to concentrate juice, especially with heat sensitive materials.
In Falling Film evaporators, juice usually enters from the top. It is evenly distributed into the heating tubes. Thin film enters the heating tube and it flows downwards at boiling temperature. In the process, it is partially evaporated.
Steam enters in the jacket through slots in calandria. Juice and vapor both flows downward in a parallel flow. This gravity-induced downward movement is increasingly augmented by the co-current vapor flow. Separation of concentrated juice from vapor takes place in juice tank and separator.
Falling Film evaporator can be operated with very low temperature difference between the heating media and the boiling liquid. It has very short retention time, typically just a few seconds. These characteristics make the falling film evaporator particularly suitable for heat-sensitive products, and are today the most frequently used type of evaporator.
THERMAL FEATURES:
Thin film of juice and absence of a hydrostatic head in
the FFE tubes lead to better heat transfer
Minimal scale formation
Better Evaporation Rate
Complete wetting of Tubes
Minimum ∆T i.e. 6 - 7°C
DESIGN FEATURES:
Wetting Rate 16 - 18 l/cm/h
Evaporation Rate 28 - 30 kg/m²/h
Proper Juice Distribution in each tube
Vapor Separator inside the FFE, it requires less space
Recirculation Inlet from the Top of the tower
Tube Rinsing arrangement
Fully Automated control system
JUICE DISTRIBUTOR SYSTEM:
Notch is specially designed where juice falls as a droplet on tube sheet of ligament; therefore it works proper juice distribution in each tube