The Sodium Chlorate Process

Aker Solutions is the world leader in sodium chlorate technology for both on-site and merchant facilities. Our sodium chlorate technology is based on our research efforts as well as the experience gained from the design, construction, start up and operation of plants worldwide.

The Aker Solutions sodium chlorate electrolytic system consists of electrolyzers, a reactor, a cooler and the inter-connecting piping. When direct current is applied, the hydrogen gas produced displaces liquor and reduces the specific gravity of the electrolyzer and the outlet piping contents. The resultant specific gravity differential between the liquor in the electrolyzer and that in the reactor creates a high rate of circulation.

This natural circulation system for chlorate production, which was developed by Aker Solutions, provides the desired flow rate through the cells which is necessary for efficient operation. The heat produced in the electrolyzers is removed by an external cooler, which maintains the electrolytic system at its optimum operating temperature. The reactor is designed to provide the retention time required for conversion of intermediate reaction products to sodium chlorate.

The sodium chlorate production rate is controlled by varying the direct current to the electrolyzers and the desired chlorate/chloride concentration in the product is achieved by adjusting the brine feed to the system and by regulating the quantity of water evaporated from the process by the chlorate crystallizer. The chlorate solution product is displaced from the reactor and flows by gravity to the downstream storage and processing areas.

The Overall Sodium Chlorate Production Process

Electrolytic Process

The electrolysis of an aqueous solution of sodium chloride to produce sodium chlorate is the result of complex electrochemical and chemical reactions that are dependent upon temperature, pH, composition and concentration of the electrolyte, anode and cathode potentials and over-voltages, and the design of the electrolyzers and the electrolytic system.  The principal chemical reaction is as follows:

Aker Solutions' electrolytic system consists of electrolyzers, a reactor, a cooler and the inter-connecting piping.  When direct current is applied, the hydrogen gas produced displaces liquor and reduces the specific gravity of the liquor in the electrolyzer and outlet piping. The resultant specific gravity differential between the liquor in the electrolyzer and that in the reactor creates a high rate of circulation from the bottom of the reactor, through the cooler, into the bottom of each cell in the electrolyzer, between the anodes and cathodes in the cells where electrolysis occurs, up the riser pipes to the degasifier (where the hydrogen separates) and back to the top of the reactor.  This natural circulation system for chlorate production, which was developed by Aker Solutions, provides the desired flow rate through the cells which is necessary for efficient operation.  The heat produced in the electrolyzers is removed by the external cooler, which maintains the electrolytic system at its optimum operating temperature. This heat may be recovered and used where an appropriate requirement exists.  The reactor and retention tank are designed to provide the optimum retention time required for conversion of intermediate reaction products to sodium chlorate.

The sodium chlorate production rate is controlled by varying the direct current to the electrolyzers and the desired chlorate/chloride concentration in the product is achieved by adjusting the brine feed to the system.  The chlorate solution product is displaced from the reactor and flows by gravity to the downstream storage and processing areas. 

Electrolyzers

Sodium chlorate is produced by the electrolysis of sodium chloride in Aker Solutions' unique, patented, commercially proven metal electrode electrolyzers.  The Aker Solutions M-M-P Electrolyzer (multi-monopolar) is designed and constructed to safely, efficiently and reliably produce sodium chlorate.

An Aker Solutions sodium chlorate plant can be tailor-made to meet each client’s individual needs by prudent choice of the following:

• Number of electrolyzers
• Number of cells per electrolyzer
• Size of cell and its anode area (m2)
• Operating current density (kA/m2)

For any plant capacity, the above factors can be varied to obtain the optimum combination of capital cost, operating cost and operating flexibility.

The cells in an electrolyzer are arranged in parallel for liquor flow and in series for current flow.  The feed enters the bottom of each cell and flows upward between the electrodes where electrolysis occurs.  The chlorate liquor and the co-product hydrogen exit at the top of each cell and flow up a riser pipe to a liquor/gas separation header.  The direct current enters each electrolyzer through a busbar connection to the anode end carrier plate.  The current flow is through the anodes, across the electrolyte gap and through the cathodes to the inter-cell carrier plate which separates adjacent cells.  The current passes through all the cells in the electrolyzer is a similar fashion, finally leaving the cathode end carrier plate to the busbar and the next electrolyzer.  This current arrangement is known as multi-monopolar.

Features

• Custom designed cells to match existing transformers / rectifier capacity
• Plants to produce crystal or liquor products
• Optimization of cell parameters such as electrode area, electrode sizes, thickness, etc.
• Select steel cathodes to prevent hydrogen blistering in service
• Industry’s leading tech service and warranty programs

Crystallization

If dry crystalline sodium chlorate is required as a final product, the electrolysis product liquor is first treated to remove the residual corrosive sodium hypochlorite, and is then fed to a crystallization system. The crystallization system consists of a crystallizer and its vacuum equipment, a centrifuge, and a chlorate crystal dryer.

The crystallizer operates under vacuum conditions. In the vessel, water is flashed from hot incoming hypo-free chlorate liquor and crystal formation and growth takes place. Growing crystals are circulated from the lower portion to the boiling surface where super-saturation is most intense. Since sufficient seed crystal is maintained at the surface, the super-saturation is relieved via crystal growth and crystal deposition on equipment surfaces is minimized. Surrounding the circulating slurry are annular settling zones from which streams of mother liquor bearing only fine crystals are removed and recirculated through an external heater. Heat added to these streams destroys the chlorate crystal fines and provides the make-up heat required to achieve the design evaporation load. Destruction of fine crystals ensures a uniform crystal size and achieving the design evaporation load ensures that the crystal production capacity is met.

A portion of the circulating crystal chlorate slurry is pumped from the bottom of the crystallizer to a continuous centrifuge where the crystals are separated from the chlorate solution, washed and gravity fed to the chlorate drying system.

Aker Solutions uses modern fluidization technology to remove moisture from the wet chlorate crystals. The drying system consists of a dryer, as well as equipment to feed the wet crystal, supply hot air for fluidization, and to scrub any dust from the exhaust air. The advantages of this type of sodium chlorate dryer include minimum capital cost, simplicity of operation and minimum maintenance and down time.

Aker Solutions' considerable experience with plants to produce crystal sodium chlorate enables it to design and select efficient and reliable equipment.