Closed Circuit Water Treatment A brief overview
Closed Systems – Introduction
The following is designed to give a brief overview of water treatment for closed circuit systems. By its nature, the information is not fully comprehensive but we hope that it will give you an idea of the types of problems that may be encountered and common water treatment solutions to those problems. Further information is available from B&V Water Treatment’s technical specialists.
Closed Systems – The Basics
Closed systems face many of the same problems as open systems particularly corrosion and microbiological contamination.
Closed systems, however, are of fixed volume and low make-up, which makes it financially viable to dose water treatment products at a much higher level. This high level dosing combined with the generally lower dissolved oxygen level means that much better corrosion control should be expected in closed systems. Higher biocide levels and long contact times mean that good microbiological control in closed systems can also be achieved. Scaling is not generally a problem unless there is substantial make-up.
There are a number of different types of corrosion inhibitor which can be used in a closed system. Examples include azoles, phosphates, phosphonates, borates, silicates, molybdates, nitrates and nitrites. Care should be taken to choose a corrosion inhibitor suitable for the construction metal. Corrosion inhibitors work either by being adsorbed onto the metal surface forming a barrier between the metal and the system water or by reacting with metal ions produced during corrosion. This produces an insoluble material that forms a barrier between the metal and the system water or by promoting a state of passivity.
A biocide should be used for microbiological control thereby minimising the build up of biofilm. Non- oxidising biocides are recommended for use in closed systems; they kill micro-organisms typically by disrupting the organism’s metabolism or damaging the cell wall. Examples include isothiazolines, 2-2-Dibromo-3-nitrilopropionamide, 2-bromo-2-nitropropane-1,3-diol, glutaraldehyde, tetrakis(hydroxymethyl)phosphonium sulphate and triazines.
Old systems may contain pre-existing corrosion deposits. Flushing and cleaning products often containing chelating agents and/or phosphonates are available which mobilise the sludge and deposits within a system enabling it to be removed.
Antifreeze products allow closed circuit systems to be used safely at temperatures as low as -20oC. Other products sometimes used in closed circuit systems include antifoams, buffer solutions and on-line descaling products.
Testing should be conducted to ensure that any water treatment programme is working effectively. In general, the concentration of corrosion inhibitors should be measured and microbiological testing should be undertaken.
B & V Water Treatment Products
B & V Water Treatment have many products which have been optimised for different systems. We employ all of the technologies described above and many more. Our most popular closed circuit products are viewable here but please speak to us to see which product we recommend for your needs. We are also able to offer products in a solid form.