This is the modern soap plant able to produce soap and glycerin starting from vegetable oils and animal fats. During the last decades continuous saponification plant is replacing the kettle saponification plant, due to the reasons described in the previous chapter. This type of saponification plant is used to produce soap with medium/big capacities, variable from 3 to 15 Tons of full boiled soap per hour.
The oil blend, the lye (Caustic Soda + Brine + Water) are dosed in correct proportions through Filters into the suction side of Recycle Pump installed under the Saponification Reactor, by a Dosing Group that consists of a set of frequency variable volumetric Pumps and related Flow-meters. The oil blend and the lye are heath by means of heat exchangers.
The recycle pump pushes great amount of soap across the Saponification Reactor that consists of a Static Vessel with internal special geometry working under pressure works with a temperature of about 130 - 140°C. Conditions inside are such that the raw materials react promptly. Reaction is also induced by the fact that the relatively small quantity of raw materials is injected into the stream of already formed soap.
The reactor is connected to the Cooler, where the soap/lye mixture is cooled down to graining temperature, thus being prepared for static separation. This occurs inside the Static Separator. The soap, being the lighter phase floats on the top of the lye. These “Spent Lye” (NAOH is present only in traces) contain high percentage of glycerin and are usually sent to the Glycerin Plant.
The soap from Static Separator overflows into Constant Level Tank inside the Static Separator, from where it is pumped into the Washing.
The Washing Column is of Rotary Disc Contactor type, where a Washing Solution, obtained combining caustic soda, brine and water, heated in a Heat Exchanger, is distributed inside stream of soap by rotary action of a pack of flat disks mounted on a vertical rotor shaft.
The washing solution, during its downward passage across the Washing Column gets enriched in glycerine and gathers at the bottom of the Washing Column. What comes out from the Washing Column is called Half Spent Lye because it is still rich in NaOH; these lye are dosed by another Pump directly to the Saponification Reactor where free caustic is saponified. .
The soap from Washing Column overflows into a Constant level Tank, from where it is pumped into the Centrifugal Separator/s.
Soap leaving the Centrifuge Separator/s usually has an excess of NaOH that has to be neutralized therefore the soap is conveyed into the Neutralizing Section composed of Neutralizer Mixer and Recycle Pump that establishes a vigorous flow of soap across the Neutralizing Mixer which is in fact a Crutcher equipped with enclosed screw, thus providing for additional mixing.
Quantity of neutralizing agent (Coconut Oil, PKO or DFA) is dosed by the Dosing Pump.
The produced soap is called Full Boiled Soap and usually has a TFM of about 62%. When the soap is ready, it is pumped to the vacuum drying plant.