Operations
CHLOR-ALKALI
Overview
Coogee Chlor-alkali is Australia’s second largest manufacturer of chlor-alkali products with two separate, but similar sized, chlor-alkali plants operating in the Perth region of Western Australia. The plants were established to service the local titanium dioxide pigment industry as dedicated suppliers of chlorine and caustic soda feedstock.
The plants use Lurgi membrane cell technology to produce chlorine and caustic soda by the electrolysis of pure brine.
The first plant, located at Kemerton, near Bunbury, commenced production in 1988 and supplies the Cristal pigment plant. The second plant, located at Kwinana, commenced production in 1991, and supplies the Tiwest Joint Venture pigment plant.
Co-produced products include hydrochloric acid and sodium hypochlorite, and these two products, together with caustic soda surplus to the two pigment plant’s requirements, are sold into the chemical, mineral processing, mining, water treatment, galvanizing and swimming pool markets.
Our Products
Chlorine gas, caustic soda, and hydrogen gas are produced simultaneously in the chlor-alkali process.
Chlorine
Chlorine is produced on demand and, after purification, is supplied directly by pipeline into the adjoining pigment plant as a pure, dry, compressed gas.
Caustic Soda
Caustic soda is produced as a 32% solution. Some of this is supplied directly to the adjoining pigment plants. Most of the caustic soda is concentrated to 50% strength and distributed to a wide range of customers throughout Western Australia by road tanker, or by pipeline via Coogee’s Kwinana tank terminal.
Hydrogen
A small amount of the co-produced hydrogen is reacted with chlorine gas to produce high purity hydrochloric acid. The rest is burned as a fuel to generate steam for internal use.
Hydrochloric Acid
Pure 32% hydrochloric acid is used internally in the chlor-alkali process, and some is sold, in bulk, by road tanker to industrial customers.
Coogee Chlor-alkali also markets by-product hydrochloric acid produced by the Tiwest pigment plant.
Sodium Hypochlorite
Concentrated sodium hypochlorite solution (bleach) is manufactured as a secondary product by reacting chlorine gas with caustic soda. Sodium hypochlorite is sold as a bleaching agent for water treatment and for swimming pool chlorination.
The Chlor-alkali Process
Chlorine is produced by the electrolysis of purified sodium chloride brine solution in ion exchange membrane electrolysis cells. Product chlorine is purified, then sent via a small intermediate buffer storage system into a fixed export pipeline into the pigment plant process. Chlorine is produced on demand, with production rate determined by customer requirements.
Sodium hydroxide and hydrogen are also produced as co-products of the electrolysis process.
The process uses an electrolytic cell, or electrolyser, to produce chlorine, caustic soda solution and hydrogen simultaneously by passing an electric current through purified salt solution.
Ion exchange membrane electrolysis was first commercialised around 1980 and is the cleanest and most energy efficient process for manufacture of chlorine and caustic soda. Many different designs of membrane electrolyser have been developed by specialist technology suppliers. The Coogee Chlor-Alkali plants use German designed, Lurgi electrolysers.
The electrolysers are fed with purified, near-saturated brine, and 30% caustic soda solution.
An electric current is passed to decompose the salt and produce chlorine gas at the electrolyser anodes, and caustic soda and hydrogen at the cathodes. The two halves of the process are separated by an ion-exchange membrane that prevents re-mixing of the products and permits a 95% efficiency of power usage.
Weak brine leaves the electrolysers, and is stripped free of dissolved chlorine.
A portion of the depleted brine is purged to waste to prevent sodium sulphate impurities that enter with the raw salt from accumulating in the recirculating brine loop and damaging the membranes.
The balance of the dechlorinated weak brine is recycled through the brine preparation plant where it is re-saturated with salt and purified in a three stage process by chemical precipitation, filtration, and ion exchange.
Chlorine gas from the cells contains about 2% oxygen and is saturated with water vapour.
The wet impure chlorine gas is cooled, dried, compressed, and liquefied by chilling to below -34°C. The oxygen impurity in the chlorine is eliminated at the liquefaction step, and is passed to atmosphere via the chlorine absorption and scrubbing system.
Liquid chlorine is drained by gravity into one of three 25 tonne capacity storage tanks filled in rotation. The plant operating licences limit the maximum inventory of liquid chlorine permitted on site to 50 tonnes. When a storage tank is selected for export the liquid chlorine is forced by nitrogen pressure through a steam-heated vaporiser into the export gas pipeline.
Caustic soda solution leaves the electrolysers at about 32% strength. Part of this is bled off and concentrated for sale in a steam heated evaporator, and the rest is diluted with water and recycled to the electrolysis cells.