The principle of short-path distillation

The duty of each distillation process consists in separating liquid mixtures into individual fractions or constituents. This process, however, becomes problematic if individual constituents decompose or polymerize at distillation temperature.

The rate of decomposition or polymerization in general increases linearly to the residence time and exponentially to the temperature. By generating vacuum in the distillation system, the evaporation temperature can be decreased according to the course of the steam pressure curve. In order to avoid pressure losses by vapour flow, the condenser is installed in the immediate proximity of the evaporator. This is why the unit is called short-path evaporator. This system permits medium high and high vacuum distillation (molecular distillation).

The special feature of Petrof Refining Technologies falling film evaporators operated in single pass is the particularly low product residence time. The substance mixture is only heated for a short period of time. By integrating the condenser in the evaporator, the vapour stream does not lose any pressure, and therefore the substance can be distilled at vacuum pressures in the range of 1 mbar down to below 0.001 mbar.

The Petrof Refining Technologies Falling Film Short Path Evaporator

The Petrof Refining Technologies falling film short-path evaporator mainly consists of 4 parts:

1) the product distribution system in the head of the unit

2) the calandria, in principle a vertical tubular heat exchanger

3) the condenser tubes

4) the lower part of the apparatus for separation of bottom product and distillate as well as a vacuum connection

As in the case of the conventional falling film evaporator, the feed-stock is evenly distributed onto the tube plate by the distribution system and flows on the internal walls of the vertical heating tubes as thin film. On the shell side, it is heated to temperatures above 350° C by hot water, heating steam or heat transfer oil. During heating, the low boiling product constituents are evaporated. A condenser tube is concentrically installed in each heating tube. The vapours are condensed as distillate and flow downwards on the external wall of the condenser tube. At the lower end of the tube bundle heat exchanger, the non-evaporated product constituents drip onto an inclined, heatable collecting plate and are discharged through a nozzle. The collecting plate contains an opening for each condenser tube. A distillate outlet and a vacuum connection are situated below the collecting plate.

The non-condensable product constituents are drawn off. Usually the evaporators are made of stainless steel 1.4301 according to the specified regulations and standards. Other materials such as C steel, higher-quality stainless steel, hastelloy or titanium can also be used.

The plant arrangement

In this field, Petrof Refining Technologies has already extensive expertise gained for a large part from applications in the Food, Beverage and Pharmaceutical industries. In these applications, temperature sensitive products are also concentrated in mostly multi-effect falling film evaporation plants. The product can be pumped repeatedly through the relevant evaporator in single pass. Prior to distillation in medium high vacuum, the feed-stock must be sufficiently degassed. Depending on the case of application there are different arrangement possibilities, which you can see from the example. Our engineers determine the optimum plant arrangement as well as the best suited peripheral units for your particular case of application for you.

Your advantages

The Petrof Refining Technologies falling film evaporator offers inter alia the following advantages to you:

1. simple design
   
2. no rotating parts, no mechanical wear and tear
   
3. low investment costs
   
4. suited for feed-stock quantities of up to 50 tons/hr

Cases of application

1. Omega- 3 bread recovery of Omega-3 fatty acids
   
2. solvents separation of residual solvents e.g. from oil
   
3. monoglyceride as emulsifying agent in the Food industry
   
4. cosmetics treatment of wool fatty acids etc.
   
5. vegetable and animal oils deacidification, recovery of carotenoids
   
6. vitamin E concentration e.g. as admixture in animal feed
   
7. waxes recovery of fractions with defined properties
   
8. polymers/oligomers monomer separation