BOC improves effluent quality for Kimberly Clark
Kimberly Clark needed to replace their conventional mineral acid dosing water treatment system at their Andrex toilet tissue plant in Northfleet Mill, Kent.
The company was looking for an environmentally prudent solution to improve the quality of its borehole derived water - which was saline and highly corrosive - and to treat its alkaline site effluent.
Paul Bradford, Kimberly Clark's Process Engineer at the Northfleet Mill site, explained that the company chose BOC's Solvocarb carbon dioxide (CO2) dosing system partly because it is considered the most environmentally friendly option. CO2 dosing drastically improves water quality by reducing pH.
Environmental requirements are becoming ever stricter and so wastewater can only be discharged within a narrow pH range, typically near neutral (pH 7.0). BOC's Solvocarb systems use CO2 to neutralise alkaline waters.
BOC's Customer Engineering Services team installed it's Solvocarb systems to control the pH of water used in Kimberly Clark. The company used its Solvocarb B and Solvocarb R variations to treat the water.
Solvocarb B process neutralises alkaline waters in lagoons or tanks. The CO2 dissolves in water through perforated aeration hoses. The CO2 is injected uniformly into the water, thus ensuring optimum utilisation. When the CO2 is switched on, the pores in the hose open and small bubbles of gas are released. The Solvocarb R system injects CO2 by means of special reactors.
Rem Van Woerkom of BOC explains why Solvocarb was the right solution for Kimberly Clark.
"CO2 controls pH effectively and injecting CO2 into water using the Solvocarb system means that there is no need for an additional energy source"
Typically, CO2 is stored within vacuum insulated vessels and liquid CO2 is supplied in road tankers.
CO2 is added after the site's borehole water passes through the site's reverse osmosis plant, which removes chlorides and carbonates from the borehole derived water (this allows the site to recirculate water). CO2 is added prior to the addition of calcium hydroxide, which re-mineralises the water. The remineralised water is then combined with the effluent treatment plant's final effluent after sand filtration and the water is re-used.
The CO2 dosing system runs automatically at Kimberly Clark's site and since its installation and full commissioning in the summer of 2014, it is achieving excellent results. Water flow is around 150 m3 h-1 and the system uses around 0.65 tonnes per day of CO2.
Some 70 per cent of the water used at the mill is recycled although the borehole derived water is of highly variable quality. 'When CO2 is added to the water it controls the pH, hardness and alkalinity, making the water quality more consistent', stated Paul Bradford.
Because BOC's Solvocarb systems use CO2 to neutralise alkaline waters, the process is environmentally friendly. When dissolved in water, CO2 forms carbonic acid which reduces the pH of the water. CO2 and carbonic acid has numerous advantages over conventional mineral acids:
•CO2 is an excellent, economical and ecological alternative to mineral acids
•CO2 is not harmful to water when compared to mineral acids
•CO2 is safe, simple to use, store and transport
•CO2 does not form additional salts when dissolved in water such as chlorides and sulphates so there is no increase in salt loading
•CO2 can treat alkaline water and wastewater in many industrial applications including: food and drink, petrochemical, pharmaceutical, dairy, bakery, butchery, electroplating, cement, dye and dyestuff, textiles and pulp and paper.