TOC analysis in hydropower stations
author: Otis
2023-01-07
Brief introduction
The water in the hydropower station, especially the boiler feed water, is under strict analytical control. The organic impurities in the boiler feed water are easily oxidized under high pressure and high temperature, and may form corrosive organic acids and carbonic acid. Salt is usually added as an oxygen scavenger. TOC monitoring in the boiler feed water is the key to control this process. This is a problem of trace contamination in the TOC range below 1ppm. Wet chemical UV digestion is particularly suited for TOC determination in this concentration range and within this matrix, especially due to its large volume sample injection (up to 20 ml) and its high measurement sensitivity.
Experiment
Subricates similar to those generally found in plant water were synthesized and defined TOC content added.
The concentration and substance of the synthetic matrix are as follows:
(1) 7 g / l boric acid
(2) 1 mg/l of sodium
(3) and 7 mg/l of potassium
(4) 2 mg/l of lithium
(5) and 7 mg/l of ammonium
Then 300 µ g / l and 1000 µ g / l of µ g standard (potassium hydrogen phthalate) were added to this synthetic solution.
The thetic samples were adjusted to pH 2 using sulfuric acid of 2n.
The following method parameters are set on the instrument system.
| Measuring parameters | NPOC |
| Dissolution technology | Wet chemical UV digestion (185 nm and 254 nm) |
| Number of repeated measurements | 3 of 4 |
| Blow time | 300 Seconds |
| Injection volume | 5000μl |
| Additional reagent (oxidant) | NO |
The TIC control measurements ensure that the inorganic carbon and the dissolved carbon dioxide have been eliminated. An autosampler with a parallel purging and analysis function was used to feed the samples. This reduces the analysis time, and allows for a high sample throughput. The ratio of unpurified organic carbon (NPOC) is oxidized to CO2 in the UV reactor without the additional use of an oxidant and measured by an NDIR detector.
Calibration
The software of the analyzer allows combining a measurement method with multiple calibration ranges. The analyzer automatically selects the calibration curve for the calculation based on the surface integral. This will ensure that the optimal calibration range is always selected. This is particularly friendly and guarantees the highest accuracy and accuracy of measurements. A single point calibration method of 1000ppbTOC was prepared using potassium hydrogen phthalate.
Bear fruit
The table below shows the mean and relative standard deviation of the NPOC measurements.
| Sample | Average NPOC (μ g / l) | RSD NPOC(%) |
| The blank value of the prepared water (containing the matrix) was measured as 113.9 AU / ml immediately before the measurement, and then automatically deducted from the standard | ||
| 300 ppb KHP + matrix | 362.2 μg/l | 1.25% |
| Measure the curve | ||
| 1000 ppb KHP + matrix | 1060 μg/l | 0.89% |
| Measure the curve | ||
Summarize
The results show that sodium peroxide disulfide requires no complete oxidation of water. UV radiation and dissolved oxygen in the sample are sufficient to convert all organic compounds to CO2. The result is a very reliable TOC measurement in boiler feed water, other ultrapure water and even drinking water analysis.
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