TOC Monitoring in Boiler Feed and Cooling Water of Fossil-Fuel-Fired and Nuclear Power Plants Application Note · multi N/C UV HS

Introduction

Water within power plants, and particularly boiler feed water, is subject to strict analytical control. Organic impurities in the boiler feed water can easily oxidize under high pressure and high temperatures and may lead to the formation of corrosive organic acids and carbonic acid. State-of-the-art feed water production therefore uses reverse osmosis or ultrafiltration membranes and ion exchangers to reduce and control the corrosion potential of the final feed water. Rule of thumb: the higher the operating pressure of the boiler system, the lower the recommended contaminant levels set, e.g., TOC < 0.5 mg/L at pressures above 31 bar, or TOC < 0.2 mg/L above 62 bar .

The condensate return has to be checked for TOC levels as well to monitor for contamination, for example contamination caused by leakages in the steam pipes or heat exchangers. In addition salts are often added as oxygen scavengers, as are neutralizing amines or boric acid to regulate pressurized-water reactors in nuclear power plants.

Wet chemical UV digestion is particularly suited for TOC determination within the ppb concentration range accompanied by specific additive sample matrix. multi N/C® UV HS was used for the sample measurements. Various types of autosamplers, such as AS 10, AS 21, and AS vario, which offer different sample rack capacities, provide a high degree of automation.

multi N/C® UV HS offers the possibility of injecting very large volumes up to 20 mL and hence highest measurement sensitivity. The integrated high-power UV reactor utilizing two hard UV wavelengths (185 nm and 254 nm) simultaneously ensures powerful sample oxidation even for salt matrices. There is no need for TOC blank loaded oxidation reagents allowing unspoiled/unadulterated direct TOC readings in the trace range.