Measurement of organic halogens in boiler feedwater

Materials of steam water cycles can suffer from corrosion induced by halide anions in feedwater. Organic halogen compounds in feedwater can be degraded and release halide anions under high temperature and pressure. Therefore it is necessary to be able to measure the organic halogen concentration. Existing measurements including Adsorbable Organic Halogens and Gas Chromatography are either not convenient, affordable, accurate or reproducible enough at these very low concentrations, meaning a new method should be developed. In this research the option of destroying the organic compounds to release the halide anions and measure them with ion chromatography was studied. The question is, which is the best way to destroy the organic compounds and release the halides anions. Six organic halogen model compounds were tested: aliphatic and aromatic fluorine, chlorine and bromine containing compounds. Two main methods were studied: UV/vacuumUV (VUV) photolysis and wet chemical oxidation with K2S2O8. There are three phases in the research: 1. Study different UV lamps and oxidants on the target compounds and find the optimal combinations. 2. Try different dosages of K2S2O8 and find an optimum. 3. Test halide release of target compounds in power plant conditions. In the experiments, three kinds of lamps were applied: VUV, low pressure (LP) lamp and medium pressure (MP) lamp. H2O2 and TiO2 were used as a catalyst. Last but not least, wet chemical oxidation was tested, with varying dosages of K2S2O8. The experiments were executed with both single compounds and mixed compounds. The results show that the organic fluorine is the hardest to degrade while organic bromine is the easiest. Aromatic compounds are easier to degrade than aliphatic compounds. This happens not only in AOP process, but also in power plant conditions. The recovery of bromide and chloride in most methods could reach 95% while aliphatic fluorine could only reach at most 70%. It can be concluded that MP/H2O2 is the most effective method for degradation of organic halogen compounds since it requires less time for the reaction to be completed, but wet chemical oxidation also showed high recoveries for all halide anions. The advantage of wet chemical oxidation is simple equipment and universality. The method with the lowest degradation rate and recovery is UV/TiO2. Table of