Contents Issue 6 (2000)

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Donald A. Palmer, Pascale Bénézeth, and David J. Wesolowski

Boric Acid Hydrolysis: A New Look at the Available Data

Boric acid is routinely used in primary circuits of PWR's as a chemical shim. Boric acid is also known to inhibit denting in steam generator tubes and has been recommended to combat stress corrosion cracking and intergranular attack. At normal loadings only hydrolysis of boric acid to give borate anions needs to be considered in modeling the aqueous chemistry in a power cycle. However, borates can concentrate in crevices where polyborate anions will eventually predominate. Therefore, these hydrolysis equilibria must also be quantified over ranges of temperature and ionic strength applicable to plant operating conditions. This paper addresses this need by reassessing the currently available thermodynamic data, although interactions with other species in solution are not considered here (e.g., the formation of lithium borate ion pairs and the formation of boric acid complexes with amines).

PowerPlant Chemistry 2000, 2(5)

Bo Yang

Advances in Localized Corrosion Control in Cooling Water Systems

Advances in localized corrosion control for carbon steel in cooling water systems by effective use of corrosion inhibitors, polymer dispersants, and biocides are described. Typical results obtained in laboratory studies and field applications of a new real-time localized corrosion monitor in optimization and control of various cooling water programs to minimize localized corrosion while still satisfying or exceeding other system performance requirements are presented.

PowerPlant Chemistry 2000, 2(6)

Geoff Spowart

Cooling Water Contamination - The People Issues

This paper looks at the people management issues surrounding the discovery of potentially lethal organisms on an industrial site. While the discussion relates to Legionella and Naegleria fowleri at Loy Yang Power, the concepts could equally be applied to other situations where a health and safety issue may have industrial relations consequences.

PowerPlant Chemistry 2000, 2(6)

Geoff J. Bignold

Chemistry in Combined Cycle Units - The National Power Experience

Between 1993 and 1998 National Power introduced four CCGT plants in the UK. The choice of operational chemistry regime has been made on a plant by plant basis. The HRSG manufacturer's views have provided the basis during commissioning and early operation. Adjustments to regimes have then been made as experience has accumulated.

The majority of HRSG manufacturers have recommended phosphate chemistries that should be easy to operate safely. However, these regimes have proved progressively more difficult to control because of phosphate hideout as newer, higher-pressure plants have been brought into service. Conversely, the use of all volatile treatment (AVT) successfully avoids the problem of hideout but introduces the risk of erosion-corrosion in low-pressure evaporators. Where AVT is used, consideration of methods of avoiding erosion-corrosion is always required. In practice, the chemistry options chosen to date have generally worked well, and provided security of operation, free of chemistry related failures.

PowerPlant Chemistry 2000, 2(6)

Siu-Kuen Hui and Chun-Pang Yuen

The Development of the Equilibrium Phosphate Treatment of the HRSG

For Black Point Combined Cycle Gas Turbine Power Station, the supplier recommended to adopt phosphate treatment for drum water chemistry. It was, however, not clear what kind of phosphate treatment and the control range to be recommended. Despite the fact that cycle chemistry was satisfactory at steady load operation, high-pressure circuits had suffered from pH depression during unit start-ups and no definite actions were recommended for rectifying the pH depression. After a extended discussion, Unit 1 was on caustic regime trial and other units remained on phosphate treatment with supplementary caustic dosing for rectifying the pH depression when required. Satisfactory results had been achieved in the caustic regime trial and pH depression occurring on other units was minimised and controlled with the assistance of supplementary caustic dosing. For the ease of operation, drum water chemical control is based on pH and cation conductivity/specific conductivity. Based on the chemical monitoring and metallurgical results to date and the experiences from Ontario Hydro and EPRI, phosphate treatment control practice has been recommended as the chemical control regime for all Black Point units.

PowerPlant Chemistry 2000, 2(6)

A.G.L. Zeijseink and R. Heijboer

Experience with Different Water/Steam Treatments in Combined Cycle Units in the Netherlands

The combined cycle units in the Netherlands differ considerably in size and design, from simple single-pressure units less than 100 MW to big 350 MW units with multi-pressure stage designs. The mode of operation varies from peak load units to base load operation. The availability and efficiency are usually high. In 1996, Eems power station was put into operation by EPON. This combined cycle plant of five units of 335 MW each is based on GE frame 9FA gas turbines rated at 230 MW and has an overall efficiency of 55%. Generally, the operational experience with combined cycle units is considered good. However, it is noted that several cases have been encountered where damages have occurred to combined cycle plants. Most of the damages could be attributed to design problems (problems with circulation or flue gas distribution), but other problems were clearly related to the chemistry control (or lack of).

The chemistry in combined cycle plants is not very different from the conventional plants. However, due to liberalisation of the electricity market, there is a lot of pressure on design of the plants. Condensate polishing is often considered too expensive, and a chemistry department is kept as small as possible, if any at all. Though often high rates of make up water are used in co-generation plants the same philosophies are applied to make up water treatment plants so that also their quality loss can be encountered. These developments are all obvious ingredients leading to damages in the later stage of operation, so that the price for the lower investment may be paid later. Organics have been of specific interest in the recent years, both in the make up and in the water steam cycle. It has been illustrated how organics may contribute to corrosion damage in the boiler, the suspected corrosion damage mechanisms in the LP turbine, and which organics may be causing the problems of high TOC levels in make up water plants.

PowerPlant Chemistry 2000, 2(6)

EPRI Sixth International Conference on Cycle Chemistry in Fossil Plants

The Sixth International Conference on Cycle Chemistry in Fossil Plants organized by EPRI (Electric Power Research Institute, Palo Alto, California, USA) took place in Columbus, Ohio, on June 27-29, 2000. This conference is the only international conference dealing exclusively with fossil plant cycle chemistry topics. Unfor-tunately, not every single interested person is able to attend this conference. For this reason, PowerPlant Chemistry presents the abstracts of all papers presented at the conference. The abstracts are taken over from the conference documents. In some cases, the abstracts were too short or were not included in the paper at all. PowerPlant Chemistry has extended the short, shortened the long, and written new abstracts for papers that were issued without any abstract. To recognize the original and edited or new abstracts, all abstracts that are not identical with the original abstract are marked with E (edited). Some authors have supplied the abstracts directly to PowerPlant Chemistry; such abstracts are marked with N (new). Both marks appear immediately after the paper title.

PowerPlant Chemistry 2000, 2(6)