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INDUTHERM®
Inductive heating up to 500 °C
Thin Film Evaporator HYVAP DZH
Thin film evaporator with hygienic design
- Thin film evaporator Hyvap DZH
General Description of Thin Film Distillation
- Fig. 1: a) inner shell b) rotor blade c) gap between rotor and inner shell I) film zone II) bow wave III) gap zone
Basics
Thin Film Evaporation refers here to the thermal separation of products in a mechanically generated, thin and highly turbulent liquid film.
After entering the Thin Film Evaporator, the product comes into contact with the rotor: it is uniformly spread on the periphery by the distribution ring, then picked up by the first rotor blades and immediately formed in to a film (0.5 - 3.5 mm) on the heat transfer surface. In front of each rotor blade, the fluid creates a bow wave (Fig. 1).
The fluid in the gap between the heat transfer surface and the rotor blade tip is highly turbulent and this leads to intensive heat and mass transfer rates.
This turbulence produces high heat transfer coefficients even with highly viscous products.
Due to the intensive mixing action within the bow wave, temperature sensitive products are prevented from over heating and fouling on the heat transfer surface can be reduced or eliminated.
- Fig. 2: Cylindrical design Type "Luwa" and "Sambay"
Working Principle of vertical Thin Film Evaporators
The product to be treated is continuously fed into the vertical Thin Film Evaporator above the heating jacket (Fig. 2) and is spread on to the periphery by the distribution ring.
The product is then picked up by the rotor blades and immediately formed in to a thin turbulent film on the heat transfer surface.
The volatile components of the feed stock are therefore very quickly evaporated and flow counter-currently with reference to the feed, up towards the top of the evaporator to the rotating separator. Here, entrained droplets or foam are knocked out of the vapour steam and return to the evaporation zone. The evaporated components (low boilers) then flow out of the evaporator in to the condensation stage, column or to another downstream process step. For special applications co-current vapour/product flow can be used in which case a separation vessel is fitted at the bottom of the evaporator below the rotor in place of the normal rotor mounted separator and the upper vapour outlet nozzle.
The non volatile components of the feed stock (high boilers) flow in a spiral path down the heat transfer surface to the bottom of the evaporator, arrive to the bottom part of the heat transfer zone in a single pass within a matter of seconds and leave the evaporator.
The working principle of vertical, conical Thin Film Evaporators (Fig. 3) is similar to the one of the horizontal, conical Thin Film Evaporators.
- Fig. 3: Vertical conical design type "Sako KV"
Working Principle of horizontal Thin Film Evaporators
The product is fed continuously to the horizontal Thin Film Evaporator (Fig. 4) at the larger diameter end, picked up by the rotor blades and spread immediately in a thin turbulent film on the heat transfer surface.
The evaporator's conical form results in a centrifugal force being imparted on the product by the rotor which effectively has two components: one perpendicular to the heat transfer surface and the other in the direction of the body's larger diameter end (Remark: the same effect occurs in the vertical conical Thin Film Evaporator also). The product hold up created by these forces and that of the incoming product ensures that the heat transfer surface is fully wetted independent of the evaporation ratio and/or the feed rate. Localised product over heating and thermal degradation are thereby reduced or avoided altogether.
- Fig. 4: Horizontal conical design type "Sako KH"
The product vapour (low boilers) flows co-currently through the horizontal Thin Film Evaporator and in to the rotating separator. Here, entrained droplets and foam are knocked out and pass in to the liquid phase outlet (high boilers). The dry vapour then passes in to the condensation stage, column or to another downstream stage.
