DL/T 1358-2014Analytical methods of steam and water in power plants - Determination of total organic carbon (English PDF)

5.3 TOC stock solution (1000 mg/L). Accurately WEIGH 2.3770 g of superior

grade pure sucrose (C12H22O11) which has been dried at 100°C for 2 h. USE reagent water to dissolve it, quantitatively TRANSFER it into a 1000 mL volumetric flask, USE reagent water to dilute it to the mark. This solution shall be stored in the refrigerator, which is valid for three months.

5.4 TOC standard solution (10 mg/L). Accurately PIPETTE 1.00 mL of TOC

stock solution into a 100 mL volumetric flask, USE reagent water to dilute it to the mark, the solution shall be prepared before use.

5.5 Ammonia buffer solution 1 (ammonia content approximately 1200 mg/L).

PIPETTE 10 mL of superior grade pure ammonia into a 200 mL volumetric flask,

USE reagent water to dilute it to the mark. This solution shall be stored in the refrigerator, which is valid for three months.

Appendix A (Informative)

Decomposition products and potential hazards of organics in water

A.1 Heat system organic material origin and potential hazards

When organic compounds do not contain halogens, sulfur, and other heteroatoms, the decomposition products in the thermal system include formic acid, acetic acid and other low-molecular organic acids, and carbon dioxide;

when organic compounds containes chlorine, sulfur and other heteroatoms, its decomposition products in the thermal system include chloride, sulfate and other anions in addition to the above anions. Studies have shown that excessive levels of organic compounds in water steam will lead to corrosion of the turbine's low-pressure cylinder blades. Since the corrosion of low- molecular-weight organic acids is far less than chloride, sulfate, and other strong-acid anions, the organic substances corrosion against equipment is closely related to the heteroatom contents such as sulfur and chlorine in organic materials. For example, if the seriously polluted cooling water leaks into the condensate, the quality of the added medicine in the system is unqualified, the feed water source is polluted seriously, the desalination system is not efficient in removing organic matter, and the leachables of the resin are large, it may introduce organic substances containing halogen, sulfur and other heteroatoms into the steam system. The case of many power plants shows that when the total organic carbon (TOC) content in the water has not exceeded the standard, the TOCi content has exceeded the standard seriously. At this time, the steam hydrogen conductivity has exceeded the standard and the low-pressure cylinder blade of the turbine has severe corrosion. Therefore, to prevent the corrosion of the turbine low-pressure cylinder blades, it shall monitor and control the TOCi content in the water steam.

A.2 Differences between TOC and TOCi measurement indicators

A.2.1 Meaning of TOC measurement indicator

Total carbon content in organic matter. The measuring principle is to calculate the total carbon content in organic matter by measuring the change of carbon dioxide content before and after the complete oxidation of organic matter, and convert it to carbon content. The measurement can be performed using the membrane conductance method or the non-dispersive infrared detector. No matter how the organic composition changes, the TOC content in the water steam only expresses the total carbon content in the organic matter, and the content of heteroatoms is not reflected.

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