ABB 2155 User Manual

Contents

Cation Exchange Column2155 1 Introduction2 IM/2155 Rev. G1 Introduction1.1 DescriptionThe measurement of contaminants by using ion exchangecolumns has been established in the power industry for manyyears.Alkaline chemicals such as Ammonia and Sodium Hydroxide areadded routinely to the feed and boiler water to control corrosionby increasing the pH. The effect of this is a significant increasethe conductivity of the water, thereby masking the conductivityof any contaminants.To counter this increased conductivity, a sample is passedthrough the ion exchange column where the alkali is removed.After the sample has passed through the ion exchange column,the conductivity of the contaminants can be measuredaccurately. For example, corrosive anion contaminants such aschloride, carbonate and sulphate can be found.Other similar systems include a conductivity measurementbefore the column in order to calculate the levels of pH andAmmonia.1.2 Ion-ExchangeIon exchange is the process where ions incorporated within asolid material (the ion exchange resin) are exchanged with ionsin a solution. This can be used to purify or remove unwantedchemicals from the solution.The resin has the appearance of smooth spherical beads usuallybetween 0.5 and 1 mm (0.02 and 0.04 in.) in diameter. However,at the molecular level each bead has a skeleton-like structurethat presents a large surface area to the solution. Feed water ispassed through the clear acrylic column containing the resinbeads.Before use, the resin is pre-treated with a Hydrochloric acidsolution to condition the resin into its hydrogen form. When putinto service the resin exchanges these hydrogen ions withcations (positive ions) from the solution forming acid equivalentsof the salts. For example:AmmoniaNH4 OH + RH <--> RNH 4 + H 2OSodium ChlorideRH + NaCl <--> RNa + HClThe above sodium reaction results in a three-fold increase inconductivity, therefore smaller levels of contaminants can bedetected.1.3 Ion Exchange Column ConstructionThe 2155 Cation Exchange Column is supplied as a singleacrylic column with quick-release couplings end fittings and aresin pack.Note. The connecting tubes and mounting clips are notsupplied.Fig. 1.1 Typical Cation Column ArrangementQuick-releaseCouplingEnd CapCation ColumnStainless SteelConductivityCellSampleOutletMounting ClipFlow Guage(optional)Isolation/FlowRegulationValveSample InletMounting ClipEnd CapQuick-releaseCoupling