Chelant Program Chemistries

Chelant programs are solubilizing programs and are commonly prescribed for both FT and WT boilers either as replacements for, or used in combination with, phosphate precipitation programs. 

Chelants are relatively high molecular weight compounds and react stoichiometrically with cations. In higher hardness waters the consumption of chelant-based programs may be both excessive and expensive consequently, they are not normally employed with high hardness FW sources. 

Chelants tend to be used in the following types of situations  

In low-hardness FW hardness boilers, where very clean waterside surfaces are needed to maximize heat transfer. Here the formulation may be essentially a straight chelant with minimal additional ingredients, or it may be a balanced chelant-polymer program. 

As a continuous support to an existing program that is straggling to maintain overall effectiveness. Here a straight chelant formulation may be used. 

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Because of their high degree of hydrolytic stability and the extended abilities and effectiveness of these novel chemistries, wherever phosphate-cycle or chelant programs are employed, the circumstances generally permit all-polymer/all-organic programs to be used as technically and economically viable alternatives. 

Where chelant or chelant/polymer programs are used, typically, instructions are given to maintain a specific chelant reserve. In practice, this is not always achievable because of test method limitations and internal water chemistry constraints. 

Every water treatment service company has several dual-function or multifunction programs in their BW product range based on chelant, phosphate, or polymer. Which of these particular chemistries takes the lead position depends on the type of waterside problems likely to be encountered (in some ways this is related to the particular market sector) and the positioning of the company within the overall BW treatment marketplace. 

Alkalinity boosters, which are vitally necessary to enable carbonate, phosphate, balanced polymer (polymer plus phosphate or chelant), and some other program types to function, are perhaps best described as conjunctional treatments, whereas oxygen scavengers, antifoams, and condensate line corrosion inhibitors are adjuncts. Programs such as phosphate-tannin mixtures are sometimes described as adjunct treatments. The chemistries and applications of various types of conjunctional treatments and adjuncts are described in this chapter. 

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