Antipollution Vacuum Systems

Gases and vapors coming out from oil deodorization or fatty acid distillation plants, always contain small quantities of fatty material and the like, which pass over to the vacuum group main condenser, where vapor from the thermo-compressors or boosters is condensed. If a direct contact condenser is involved, the organic components are retained in the condensing water. A small quantity of them will always dissolve, the hotter, the larger, and the rest will remain finely suspended in the water, which, because of that, takes in a milky aspect.

The total amount of pollutants depends upon the gas scrubber installed at the exit of the plant. This gas scrubber reduces them considerably, but no matter how elaborated and sophisticated it might be, there will always be pollutants left, passing over to the vacuum group.


To solve these difficulties once and for all, the ideal procedure is to prevent the effluent gas and the tower cooling water from coming into contact.



It uses a surface condenser with condensation and washing system falling film using an alkaline solution in a closed circuit as shown in picture. The solution is spread evenly over the tubes to form an alkaline film continuously wash the inner walls while neutralized fatty acids. The soaps formed are dissolved, so that the circulating liquid is maintained clean. For the alkalinity does not decay and concentration of soap remains within desirable ranges, it is necessary to purge a portion of the flow and replace an equal amount of alkaline solution. The gases that reach the group snub little contaminated and may be expelled.



This system condenses vapor from the first booster with chilled water, flowing from a refrigerating machine. Thus, the main condenser works between 8 and 10 Torr, and only one thermocompressor is used. In this case, the second stage is short, since only non-condensable are to be aspirated. A refrigerating machine, which cools the alkaline solution, consumes most of the energy-load demanded by the group. The floating fats remaining and not eliminated by the deodorizator scrubber are easily removed from the chilled solution. The disadvantage of this system is the need to purge the circuit to eliminate the water condensed and replace caustic soda to maintain the pH at 10.
A variant possible would be to use a vacuum cooling system instead of a refrigerating machine, which does not reduce energy consumption, requires lower investment and maintenance, and does not require any continuous purge since the vapor condensation outflowing from the thermocompressor W is equal to the evaporation in the tower of the vacuum cooler.



During the last years, experiments have been made with “desublimation systems” or “dry vacuum systems”.
The basic principle used is to bring down vapor outflowing from the deodorizator at a temperature lower than 0°, so that it works with ice instead of condensate. Desublimation temperature is that which is in balance with vapor pressure outflowing from the deodorizator. The process is performed within a shell and tubes exchanger, in which vapor reaching the shell sides deposes as ice on the tubes. Chilled solution circulates within the tubes. There are two condensators, one in the desublimation mode receiving vapor from the deodorizator and the other in the defrosting mode, in which ice metls by using steam and the water, outflows togheter with the pollutants. The maneuver is conducted through two big automatic valves and two small valves located at the entrance of vapor of the condensers and at the download, and by other located in the chilled water solution, respectively, picture shows the operative scheme.



Utilising a classic system, with a modified cooling water circuit, is another way of obtaining anti-pollution results. Mixing condensers are still being used, here, but contaminated water recirculates and now integrates into a closed circuit. Contaminated and dirty water flows through a tank, where caustic soda has been added with the purpose of changing fat into soap. A set of two plate heat exchangers, one in service and other being cleaned, cool the recirculated contaminated water in tower refrigeration water.