The Effect of AVT (O) Method for HRSGs at Combined Cycle Power Plant
(Room Nile 3)
19 Sep 17
4:00 PM
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5:30 PM
Tracks:
Track C - Optimizing Plant Operation
Osaka Gas has provided city gas to over 7 million households in Kansai region, west side of Japan. Recently, Osaka Gas is engaged in electric power operations. Our total capacity is 3.0 GW and the biggest power plant is Senboku Natural Gas Power Plant located on Osaka bayside. This power plant is 1,109 MW CCGT plant. There are 4 units of single shaft combined cycle system. Two of HRSGs are manufactured by BHK, and others are by Nooter Eriksen. We started commercial operation from April 2009. During several years of operation, all volatile treatment (reducing), “AVT (R)”, using hydrazine and ammonia has been applied to feed water for HRSGs. Magnetite layer is formed on the surface of steel tubes under AVT (R). Although hydrazine is an effective scavenger of oxygen in feed water, it is a genotoxic carcinogen. And it is difficult for AVT (R) to prevent the flow accelerated corrosion, “FAC”, below pH=9.4. We have managed the thickness of the tubes from 2010, and signs of thinning were observed in economizer tubes. The indication of FAC was also observed. So we investigated some methods of water treatment and chose all volatile treatment (oxidizing), “AVT (O)”, in which no oxygen scavenger such as hydrazine. In the recent study, hematite layer using AVT (O) method showed higher anti-corrosion properties of steel materials. We adopted AVT (O) method from March 2015, and we cut out the economizer tubes for analysis after two months and a year. We preformed the visual inspection and analyzed inner surfaces of the tubes with the microscope and X-ray Raman spectrometry. We found both of magnetite and hematite layer on the surface of economizer tubes. The ratio of hematite in the upstream economizer is higher than that in the downstream. We compared the thinning rate of tubes between 2014 and 2016. As a result, the thinning rate in 2016 is half of that in 2014. Therefore, we could confirm that AVT (O) method showed higher anti-corrosion properties in economizer tubes.