In early 2011 water was found leaking from the lagging of the high-pressure (HP) feedwater line during operation start-up at a combined cycle gas turbine (CCGT) plant in Ireland. After investigation, the leak was found to be from a small pinhole at the outside of a 90° bend (elbow) immediately downstream of a flow restriction orifice on the equalisation pipe. A microscopic examination of the cut-out elbow showed evidence of heavy erosion taking place. This was confirmed by the presence of heavy twinning, which is indicative of mechanical deformation. It is possible that the impact from the water removed the protective oxide leaving the base material exposed to attack. The operating temperature of the feedwater line is below the usual temperature range expected for flow-accelerated corrosion (FAC). Additionally the characteristic features expected for FAC were not evident in the samples examined microscopically. FAC damage occurs only under specific conditions of flow, water chemistry, geometry, and material type [1]. The type of attack seen on the sample received appears to initially start with erosion of the protective oxide and then is followed by a corrosive attack, which leads to cracking and further weakening of the material. While the term "flow-accelerated corrosion" is preferred as it reflects the chemical nature of the attack, "erosion corrosion" would be more appropriate in this instance, as it appears to be primarily a mechanical means of damage accumulation, which then results in a corrosive attack.

During the last few years Enel has installed zero liquid discharge (ZLD) systems to treat and recover flue gas desulfurization (FGD) wastewater from five coal-fired power plants. Each of these systems relies on the operation of a softening-evaporation-crystallization plant, committed to evaporating wastewater to a pure reusable distillate. The power plants burn a wide variety of coal with corresponding large fluctuations in the FGD wastewater blowdown quantity and quality. So chemistry control of the upstream evaporation becomes a relevant issue to allow the systems to operate properly. Recent efforts have been aimed at also including wastewater coming from other treatment plants into the ZLD systems. One of the critical issues that emerged after the initial operational experience is related to gypsum and calcite saturation in circulating water. In the major installed systems water desaturation has been achieved through operational arrangements and additional capital expenses, so now the ZLD systems are working properly, allowing full wastewater recovery with no liquid discharge from the power plant. The same results are to be achieved for all the remaining systems in the very near future. This paper discusses design considerations and operational issues related to ZLD systems that were faced after a few years of operational experience.

Water treatment performance and determination of purity have depended on sodium measurement for nearly four decades, over which period the ion-selective electrode method has continuously been refined. Described here are further improvements to sodium measurement technology including a combination electrode system that measures pH as well as sodium to assure proper reagent delivery. The presented analyzer provides enhanced ability to reliably monitor water quality while minimizing operator time requirements.

This is the first of a three-part publication series on the findings from investigations performed at the Shand Power Station of SaskPower to determine a hitherto unfamiliar source(s) of chloride contamination to the water/steam circuit. For this plant, which is usually on automatic grid control, unit ramping is common and there is some reason to associate this with the initiation of the chloride ingress. The present paper presents a systematic approach to examining the various familiar sources currently known to plant operators, chemists and the like as potential culprits and provides the bases for eliminating these as responsible agents in this case. Based on routine plant operating data and purposeful intermittent grab sample analyses as well as numerical analysis of chloride cycling in the boiler, these well-known potential causative factors, which include condenser tube water leaks, make-up chloride, halo-organics from the water treatment plant, and contaminated ammonia feed sources, could not be found to individually or cumulatively account for the magnitude of chloride contamination observed in this plant. The extent of the chloride cycling required too frequent blowdowns from the boiler, and a cost analysis of the implications from such frequent blowdowns is also presented as one of the incentives that drove the search for the root cause of such a level of contamination. There were some indications that surplus condensate from the hotwell to the boiler make-up storage tanks was a significant chloride origin, but this could not account for the level of contamination, and the source seems to be distinctly different from the traditionally known condenser tube water leaks. Furthermore, there were some indications that ammonia injection was associated with the chloride crises, although there was ample evidence to eliminate this as the source. These associations formed the basis for further investigations, the findings of which will be reported as Part II and Part III of this series.

Organic compounds in the water-steam cycle are an emerging issue at recovery boiler plants. Decomposition products of organic compounds, mainly organic acids with low molecular weight and carbon dioxide, are often related to corrosion. Removal of organics from recovery boiler make-up water with activated carbon (AC) was investigated both in pilot and full scale experiments. AC was used in a novel way to remove organic compounds from demineralized water. AC is conventionally used before demineralization, but when implemented later in the process the lifetime of AC can be extended. Total organic carbon (TOC), conductivity, silica concentration and composition of organic compounds were monitored during the experiments. Results show that AC filtration is a suitable technology for TOC removal from demineralized water. A TOC reduction of 38–70 % was achieved. Mixed-bed ion exchange after the AC filters proved to be necessary to remove conductivity, which was increased in the AC bed.

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