The caustic soda produced from electrolyzer system, and is required to be concentrated to 50% concentrated caustic soda or 99% caustic soda flakes accordingly. 

        A double-effect falling film evaporator and a flash evaporator are adopted for concentrating 50% caustic soda up to 99%, and then a flaker is used for transforming 99% caustic soda liquor into 99% caustic soda flakes.  

System Configuration

        A double-effect falling film evaporator: the 50% caustic soda is concentrated up to 61% in the first effect evaporator, and then the 61% caustic soda is concentrated up to 98.3% furtherly in the second effect evaporator;

        Flash evaporator: after concentration in the double-effect falling film evaporator, the 50% caustic soda has concentrated up to 98.3%, and it would be continued to be concentrated up to 99% in a flash evaporator;

        Flaker: the 99% caustic soda liquor from the flash evaporator is processed into 99% caustic soda flakes by the flaker. 

        Molten salt system: The molten salt system is adopted for providing heat to the final concentrator. The molten salt @ 395°C is heated up to 425°C in the molten salt furnace, and the molten salt @425°C is send into the final concentrator providing heat for concentration of caustic soda. After heat exchange, the molten salt returns to the molten salt tank.

        DCS control system is used for remote automation control;

        Regulation valves is used at position which are  of higher operation frequency;

        The key parameters including temperature, flow rate, pressure, current are displayed on the DCS station, and could be used as signal source of regulation valves.

Product Specification 

Process Description 

       Doule falling film evaporator is adopted to increase caustic soda liquor from 50% to 98.3%, and a flash evaporator is adopted to increase the caustic soda liquor from 98.3% to 99%, and a rotary cooling flake is used to transform 99% caustic soda liquor into caustic soda flakes.  

        >>> Double-effect falling film evaporator 

50% caustic soda liquid is pumped from the bottom of the Effect II falling film evaporator in to the Effect I falling film evaporator by the Effect II alkali pump. In the Effect I falling film evaporator, the concentration is increased up to 60%. The secondary steam produced flows into the heater of the Effect II evaporator and acts as heat source. The 50% caustic soda liquid is preheated by the condensate of the live steam.

The 60% caustic soda liquid is discharged from the bottom of the Effect I falling film evaporator by the Effect I alkali pump and is delivered to the final concentrator. In order to keep the final concentrator from corrosion, 10% sucrose solution is fed into the 60% caustic soda liquid. The sucrose solution is prepared in a preparion tank, and is added into the process pipeline through a metering pump, the adding volume is 10L/h.

The 60% caustic soda solution is concentrated up to 98.5% in the final concentrator. The caustic soda solution is heated by molten salts, and the secondary steam produced is used for heating the Effect II falling film evaporator.

The concentratd caustic soda liquid flows through a liquid sealing tank under the action of gravity, and flows into the flaker. After being transformed into low-temperature flakes, the flakes fall into the material hopper and then into the air tight packing scale.

The packing scale is equipped with pumping facitlity, which is able to pump the dust from the feeder of the packing scale. After packing, the bags are sealed manually.

>>>Molten salt heating unit  

Molten salt system: molten salts at 380℃ from a molten salt storage tank are heated up to 410℃ in the molten salt furnace and are delivered into the falling film tubes. After heat exchanging, the molten salts return to the molten salt storage tank again. The molten salt furnace adopts natural gas as heating source, which is stable in operation and environmental friendly.

Process Flow Chart