Multiblend Formulations

Many smaller vertical and horizontal fire tube boilers, as well as some coil and electrode boilers, are treated with multiblend or multicomponent, one-drum products. 

These features may indeed provide cost-effectiveness and other tangible benefits however, unless the boiler plant operates constantly and FW quality remains consistent, these benefits are unlikely to be fully realized. Where operating conditions vary, the use of multiblend programs exposes the potential for constant readjustment, poor waterside treatment (scales, deposits, oxygen pitting, etc.), and water-level control problems. 

Similarly, where a facility uses both well water and city water as sources of MU, this generally produces FW with periodically widely differing contaminant concentrations. The resultant changes in demand for DCA concentration and adjustments to alkalinity also prove difficult to match when one-drum programs are used. 

For the smallest low-pressure heating boilers, simple one-drum programs that are designed for greater than 99% condensate return are used. Where condensate is only 70 to 80%, boiler waterside surfaces get dirty quickly, under-deposit and oxygen pitting corrosion may develop, and tubes may fail. 

Traditional Multiblend, One-Drum Programs, Based on Sulfite Materials Formulation 

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The problem of color due to tannin can be annoying, although not insurmountable. For small, simple boiler plants, the presence of color is, in fact, a benefit, as the depth of color is more or less related to the inhibitor concentration and the BW conductivity and TDS levels. Where multiblended formulations are employed, if the color is within range, then other parameters are also likely to be acceptable. Also, electrical conductivity is unaffected by color, and tannins do not appreciably add to the measurable TDS of the BW. 

An example of a fairly complex, combined phosphate-carbonate cycle, liquid, multiblend formulation dating from the 1970s is provided below. 

It is also true that the use of multiblend formulations helps to raise operator confidence levels, and, provided the technical support function justifies this confidence by a proactive and responsive approach, there is further added value in the blend. 

Chelant-based cleaners are also used, however, for many situations, and it is now becoming more common to use a slow and steady on-line cleaning protocol by the use of polymer/phosphonate-based, multiblend formulations. These programs employ relatively high doses of active product and can be expensive to use in large volume systems, but are unlikely to cause blockages, corrosion, or other damage to the system itself or any sensitive components. 

Tannin-based multiblends cannot incorporate amines directly into their formulations (unlike sulfite-based multiblends). The neutralizing amine component must be added separately when using tannin multiblends. 

Today, with the advent of specific iron control terpolymers, new formulations are becoming available that use these and other multiblend polymers as the basis of on-line iron removal programs. Such formulations may employ 2 to 3 specific polymers, plus phosphonate, citric acid, PEG, surfactant, etc. 

The whole issue of the inhibitor minimum active requirements is complicated by the fact that water treatment service companies do not use single ingredient formulations. All formulations utilize multiblends, with each component having differing individual and collective synergistic properties. 

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