Cumberland Products

The need for Disinfection

Many industries today use large quantities of water for process cooling and applications needing disinfected water. Power generation plants, chemical plants, refineries, LNG facilities, paper mills, steel works etc. In addition in many areas of the World desalination of seawater and brackish water by flash evaporation, distillation or membrane process is commonplace. In most case the presence of biofouling such as molluscs, algae or slime, cause numerous problems for downstream plant and equipment. Fouling can adversely affect system hydrodynamics, restricting flow, increasing pumping pressures and accelerating corrosion potential. Such problems will shorten the life of pumps, screens, heat exchangers, condensers and other plant items as well as increase the operation and maintenance costs. The treatment of biofouling problems is generally acceptably controlled by the addition of a disinfection process into the system. Commonly gas chlorination or commercially available bulk hypochlorite has been the historic choice. Increasingly a more efficient and environmentally sustainable technology is being chosen.... Electrochlorination also known as hypochlorination. Electrochlorination is the 'onsite' instantaneous production of sodium hypochlorite solution at a safe, dilute concentration suitable for direct injection into process. The elimination of transportation and storage of chlorine gas or other disinfection chemicals means electrochlorination is now a more viable, cleaner, safer technology for today's industries. PANCLOR™ and ELCHLOR™ systems have demonstrable benefits in terms of safe, reliable, economic and maintenance free operation at hundreds of installations throughout the World.

Electrolytic Hypochlorite Generation

The electrolysis of seawater or artificial brine in an electrochemical cell produces sodium hypochlorite by a combination of electrochemical and chemical reactions. As seawater passes through the cell, the addition of direct current will produce certain chemical reactions, at the anode, the oxidation of chloride ions to produce chlorine takes place; 2Cl -> Cl2 + 2e− At the cathode the reduction of water to produce hydrogen takes place together with the corresponding formation of OH− ions; 2H20 + 2e− -> H2 + 2OH− The electrolysis takes place in an undivided cell with slightly alkaline pH so that as soon as chlorine is liberated at the anode it immediately reacts with water to produce hypochlorite; Cl2 + H20 -> HOCl + H+ + Cl− The overall process therefore can be summarised as the reaction of salt with water according to; NaCl + H20 -> NaOCl + H2 Chemical and electrochemical side reactions also occur simultaneously such as the decomposition of hypochlorite to chloride, the oxidation of hypochlorite to chlorate and the evolution of oxygen. In addition certain cations present in all seawater will form hydroxides and carbonates and whilst most of the suspended solids are transported out of the cell naturally by the seawater flow, some will inevitably deposit at the cathode surface. These deposits can be easily removed using weak acid solution. In standard seawater applications using PANCLOR™ and ELCHLOR™ systems, the available chlorine concentration in the produced hypochlorite is typically in the range 1000 – 2000 ppm. Hypochlorite is a powerful biocide and although it eventually decomposes back to chloride ions and oxygen it has the advantage over other biocides in that it is relatively stable.