The evaporator for demanding applications

For the thermal separation of a mixture a thin film is produced at the heated wall of a cylindrical or conical evaporator. A distribution ring on the rotor distributes the liquid evenly across the periphery. Then, the blades fitted at the rotor spread the liquid as a thin film of min. 0.5 mm over the heat transfer surface.

The model concept for the flow in the thin film evaporator assumes that prior to each rotor blade a bow wave is formed. In the gap between the rotor blade and the heating surface, fluid is supplied from the bow wave of a highly turbulent area with intense heat and mass transport. This results in a good heat transfer performance even with viscous products. In addition, the formation of deposits is avoided and the intensive mixing also protects temperature-sensitive products from overheating. 

Another important task of the rotor is to stabilize the liquid film on the heating surface at high evaporation rates. On the one hand evaporation in the area of nucleate boiling is possible without ruptures of the film. On the other hand the liquid film is pressed against the heating surface by the centrifugal force. This avoids the adverse evaporation mode, in which a vapour layer with insulating effect is formed under the liquid film. Therefore, due to the functional principle extremely high specific evaporation rates are achievable in thin film evaporators.

Thin film evaporators are designed in vertical and horizontal orientation with cylindrical and conical heating jackets. In vertical evaporators, the product which has to be processed is fed at the upper end of the apparatus. Depending on the application the volatile components evaporate and are taken out at the upper or the lower end of the evaporator. Entrained droplets or foam are removed from the vapor before the vapor is fed to further process steps.

Typical thin film evaporator designs are the cylindrical body design DVN („LUWA“) and DVB („SAMBAY“) with vertical orientation as well as the conical body design  vertical and the conical DKH („SAKO“® KH) with horizontal orientation. BPSPS installs rigid blade rotors in the DVN and in the conical thin film evaporators which are suitable for products with viscosities up to 70,000 mPas. Because of the closed design this kind of rotors are particularly easy to clean. Through the adjustment of the rigid blade rotor in axial direction it is possible to adjust the gap width and thus the film thickness in the conical evaporators. This can be the decisive advantage for an application with degassing of products up to minimum residues of low-boiling components.

In the thin film evaporators type DVB, rotors are equipped with hinged wiper blades that can be optimally adapted to the task. The centrifugal force presses the wiper blades to the heating surface, so that high evaporation ratios can be achieved at low flow rates. The hinged wiper blade types of evaporators are particularly suitable for products with fouling tendency.

For other applications such as the separation of monomers from pre-polymers and polymers, vertical thin film evaporators type DVF with spring wiper elements and DVS with Smith-Rotor are available. The specially designed wiper elements out of PTFE or graphite are partially spring loaded and support the liquid in the film.

Applications:

• Distillation, Separation, Concentration, Stripping, Deodorization, Degassing, Reaction
• Heat sensitive, viscous, fouling and foaming products
• Continuous processing

  Oils, fats and food Separation of free fatty acids from edible oils and fish oils Pesticide removal from edible oils and fish oils Fractionation of tall oil Concentration of monoglyceride Concentration of EPA and DHA in fish oil esters Concentration of tocopherols Concentration of carotene Drying of lecithin Pesticide removal from lanolin Colour improvement of lanolin Concentration of sorbitol	impurities Distillation of fatty acid amide Concentration and purification of dimeric fatty acids Removal of volatile components from silicones and silicone
  Chemical, agro chemical and pharmaceutical products Concentration of polyphenyl compounds Separation of aromatic amines from secondary components Purification of amines Concentration and colour improvement of amino alcohols Separation of long-chain acid chlorides from high boiling	resins Concentration and purification of esters Concentration of insecticides, fungicides and herbicides Concentration and purification of glycerol Fractionation and removal of low boiling components from
  Petrochemical products Separation of microcrystalline wax from vacuum residues of crude oil Fractionation of synthetic and petrochemical waxes	natural waxes Colour improvement of waxes Deodorisation, removal of pesticides Concentration and purification of lactic acid Colour improvement of lanolin Distillation of acrylic acid and acrylic ester Distillation of pharmaceutical intermediates Distillation of pharmaceutically active substances
  Polymers Purification and concentration of monomers Purification and concentration of polymers Purification of plasticisers Minimisation of solvents and monomers in polymers	Fragrances and flavors Elimination of terpenes and concentration of essential oils Separation of solvents of odorous substances Concentration of lemon flavors Concentration of pepper and chilli extracts
  Recycled materials  Refining of used oils Purification of used lubricants, brake fluids, glycerol and trans- former oils Recycling of dimethyl sulfoxide (DMSO) mother liquors Recycling of sulfolane Recycling and reprocessing of mother liquors of pharmaceutical processes Recycling of organic intermediates Recycling of mono-chlorinated acids from mother liquors