Soap stock is fed in to acid
oil reaction vessel, in which it is heated at 90- 95 degree Celsius
temperature with steam. After this temperature is obtained, sulfuric acid is
slowly added in to the soap stock. According to the TFA (total fatty acid)
in the soap stock, its quantum to be added is determined, normal range is 12
to 15%. In order to complete the reaction, the mixture of sulfuric acid and
soap stock is kept in the vessel for about 15 minutes. The mixture is then
heated and kept at boiling temperature for 2 to 3 hours. The oil is heated
until the acid oil splits. The mixture is then kept in the vessel for at
least six hours in order to settle down completely.
After the solution gets settle down completely, 3 layers are formed in which the upper layer is of acid oil, middle layer is acidic sludge and the bottom layer is of acidic water. Firstly, bottom layer that is of acidic water gets discharged through the outlet valve in to the acid oil/water trap tank. Then, it is further pumped to acidic water storage tank. After this, second layer of acidic sludge is pumped into a sludge storage tank through a screw pump. At the last, the final layer, i.e. acid oil, is pumped into acid oil storage tank.
The acidic water from acidic water storage tank is not required into the effluent treatment plant, hence, treated in equalization tank with wash water generated from the refinery. Through this treatment, the pH level of the acidic water gets reduced and with it the traces of oil from wash water is also trapped. After the treatment, the final mixture of wash water and acidic water is discharged through a trap, to catch oil traces, into the effluent treatment plant.
Finally, the acidic fumes generated from the reaction vessel are passed through water circulation and scrubbed by fumes scrubber to prevent corrosion in plant.