Last updated: 06.12.2018

Contents Issue 06 (2017)

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Use of Control Charts in Monitoring Water-Steam Cycle Chemistry
Adrian Dennehy

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Control of chemical parameters within a power plant's water-steam cycle is necessary in order to identify deviations from normal operation. Historically, values for normal operation were set by the original equipment manufacturer (OEM), which closely followed international guidelines. The VGB PowerTech (VGB) Standard "Feed Water, Boiler Water and Steam Quality for Power Plants / Industrial Plants" recommends that values for normal operation (N-range) should be set for each plant specifically and that statistical process control (SPC) charts for variables (commonly known as control charts) can be used to monitor system performance.

This study used online and grab sampling data from an operating power plant and applied statistical tools using a statistical software package called Minitab to implement the VGB Standard's recommendations (N-range and control charts) for the chemical control of three key chemistry parameters.

It found that for two key parameters, high-pressure (HP) main steam conductivity after cation exchange (CACE) and feedwater CACE, the existing values for normal operation set by the OEM were easily met by the plant studied to such an extent that it is possible for chemical contamination to enter the system in small amounts and not trigger any warnings or alarm. In this respect, optimisation of the normal limit values is possible following the VGB approach. The process capability analysis suggested that in order to achieve a process capability index, Cp, greater than 1, 125 % of the VGB N-range should be used.

For the other key parameter, the existing value for normal operation as set by the OEM was fit for purpose (Cp > 1) and no optimisation of the value as per VGB should be undertaken as this would result in a Cp < 1.

PowerPlant Chemistry 2017, 19(6), 291–300
Optimization of Chemistry in Himeji No. 2 Leads to Significant Reduction of Total Iron
Haruka Kido, Sho Shinotsuka, Akihiro Hamasaki, Satoshi Umeda, and Jun Hishida

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The revised Japanese Industrial Standard "Water Conditioning for Boiler Feed Water and Boiler Water" (JIS B 8223) was issued in 2015. The upper limit value of feedwater pH in the absence of copper-based materials was increased as a countermeasure against flow-accelerated corrosion (FAC). In addition, hydrazine is being used less often as an oxygen scavenger since it is considered to be a carcinogen and because of concerns regarding an increase in FAC.

To avoid single-phase FAC problems and the possible impact of hydrazine on health, Himeji No. 2 Power Station in Japan adopted a treatment with a high pH in the feedwater under low oxidizing conditions, which means the concentration of dissolved oxygen is under 5 µg · L–1 without dosing an oxygen scavenger such as hydrazine. This treatment is being successfully applied at Himeji No. 2 combined cycle power plant based on the revised JIS B 8223 issued in 2015.

PowerPlant Chemistry 2017, 19(6), 245–311
Report on the Power Cycle Chemistry Working Group Meeting in Kyoto, Japan
Michael Rziha and Tapio Werder

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This report summarizes the work of the Power Cycle Chemistry (PCC) working group (WG) during the 2017 Annual Meeting of the International Association for the Properties of Water and Steam (IAPWS) in Kyoto, Japan. Nearly 30 members of the PCC WG and additional guests attended the meetings, joint workshops, and task group sessions of the PCC WG during the week. Highlights of the week as well as an overview of all the activities within the working group are given in this report.

PowerPlant Chemistry 2017, 19(6), 313–317
Report on the PowerPlant Chemistry Forum in Bangkok, Thailand
Tapio Werder

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This contribution is a report on the fourth PowerPlant Chemistry Forum, held in Bangkok, Thailand, on October 11–12, 2017. The forum consisted of six sessions covering different aspects of water/steam cycle chemistry: life-cycle chemistry optimization, film forming amines, condensate polishing, zero liquid discharge, case studies, and monitoring and analytics were the topics covered during the two days. Each session consisted of two to three presentations given by an expert in the field, followed by open floor discussions at the end of each day. A short summary of each presentation is given in this report.

PowerPlant Chemistry 2017, 19(6), 323–331
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