Most membrane treatment systems require some chemical injection package in to source water. Type of required pretreatment and chemical injection package system depends on feed water quality, membrane type, and design criteria for the membrane unit. Almost the chemical injection process before reverse osmosis units consists of the following treatment steps:
1. REDOX CONTROL
Free chlorine is dangerous for RO membranes, so chlorine dosage rate must be closely controlled. The various types of polyamide R.O. membrane cannot tolerate chlorine or other strong oxidants and de-chlorination process, such as activated carbon filtration or sodium bisulfate dosing must be used. Residual chlorine is controlled by the O.R.P. controller at R.O. inlet.
1. SCALING CONTROL
Anti-scalant (scale inhibitor) is used to control scaling. The dosing is done by anti-scalant dosing pumps controlled manually via dosing control paddlewheel by 10-100% of dosing pump capacity.
Scale inhibitors are very effective at preventing the fouling of RO membrane elements due to the formation of scale. They slow the precipitation process by inhibiting salt crystal growth.
Cooling Tower chemical injection package:
Water is used in cooling systems as a heat transfer medium and frequently also as the final point to reject heat into the atmosphere by evaporating inside cooling towers. Depending on the quality of available fresh water supply, waterside problems develop in cooling water systems from:
• Scaling
• Corrosion
• Dirt and dust accumulation
• Biological growth
So the following solutions are proposed to prevent the above problems:
Chlorine Dosing
Powerful chemical oxidants, which kill virtually all micro-organisms, including bacteria, algae, fungi and yeasts. Common oxidizer is chlorine slow release compounds. Chlorine is one of the most widely used, cost effective biocides and is available in liquid, gaseous or solid form. Its effectiveness is increased when used with non-oxidizing biocides and biological dispersants. Chlorine is the most widely adopted biocide for large circulating water systems. It provides a Residual biocide in the treated water and can be readily checked. It is cheap and readily Available as a pure gas, as well as in the form of various liquid and solid compounds. Its Effectiveness increases when it is used with dosing another non-oxidizing biocides and biological dispersants.
Corrosion Inhibitor Dosing
Corrosion is defined as the destruction or loss of metal through chemical or electrochemical reaction with its surrounding environment. Mild steel is a commonly used metal in the cooling water system that is most susceptible to corrosion. Other metals in general, such as copper, stainless steel, aluminum alloys also do corrode but the process is slow. Also oxidizing chemicals may sometimes be corrosive. So corrosion inhibitors shall be added to cooling tower circulation water to ensure compatibility.
PH Adjustment
Control of scale with pH adjustment by acid addition is a simple and cost effective way to reduce the scaling potential. It functions via chemical conversion of the scale forming materials to more soluble forms. For example: Calcium carbonate is converted to calcium sulfate (using sulfuric acid), a material several times more soluble.
Anti-scalant Dosing
Scale is a hard deposit of predominantly inorganic material on heating transfer surfaces caused by the precipitation of mineral particles in water. As water evaporates in a cooling tower or an evaporative condenser, pure vapor is lost and the dissolved solids concentrate in the remaining water. If this concentration cycle is allowed to continue, the solubility of various solids will eventually be exceeded. The solids will then settle in pipelines or on heat exchange surfaces, where it frequently solidifies into a relatively soft, amorphous scale.
So Anti-scalants shall be added and selected to ensure compatibility.
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