Application Note | January 30, 2009

TOC Measurement Of High-Purity Boiler Feed Water In Power Plants

Source: Hach Company

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Application Note: TOC Measurement Of High-Purity Boiler Feed Water In Power Plants

By Hach Company

High-pressure boilers require high purity feedwater to limit the effect of corrosion and deposits that damage steam circuits.

Typical corrosives are acid salts such as chlorides or sulfates, which form corrosive compounds. Chlorides are usually present in raw water, residual trace chlorine, and in the halo-organic form present in deionized water. The most common sulfate ion producer is the decomposition of sulfonic acid–based cationic resins.

The objective is to prevent sulfate ions generated in the demineralization plant or the condensate polishing plant from contaminating the high-purity circuit. Sulfate ion concentration is difficult to measure in a plant environment, especially in low µg/L levels. The only effective technology is ion chromatography, which does not respond quickly enough.

However, if sulfates are a result of the decomposition of the resins, and the decomposition also causes a release of organic molecules, then TOC can be used as a tracer. This method will infer the presence of sulfates and detect the formation of corrosive carbon dioxide gas (caused by the destruction of organic molecules in the boiler).

An additional benefit of this approach is the ability to monitor the presence of contaminating lubricants. This alerts plant personnel of turbine or pump rotating seal leakage before the situation becomes critical.

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Application Note: TOC Measurement Of High-Purity Boiler Feed Water In Power Plants