Contents Issue 5 (1999)

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A. Bursik

State of the Art in Fossil Plant Cycle Chemistry on the Threshold of the Next Millenium

In the past five years, fossil power generation has undergone many significant changes. The most important changes which strongly influence power plant chemistry nowadays are privatization and power market deregulation in many countries, efforts to reduce carbon dioxide emissions and to increase units' efficiency, implementation of combined cycles/heat recovery steam generators in the power industry to an increased extend, and intensified pressure of competition among major power cycle component manufacturers as well as among suppliers of turnkey power plants on the world market.

Taking the report on the state of the art in fossil plant cycle chemistry presented in the course of the 12th International Conference on the Properties of Water and Steam 1994 as a starting point, the current state of the art in fossil plant cycle chemistry in the most important areas (feedwater and boiler water treatment, boiler tube failures, steam chemistry, turbine steam path damage, startup, cycling, shutdown, and lay-up, and chemistry in units with advanced parameters and in combined cycles) is discussed. Particular attention is drawn to current plant cycle chemistry needs and major fossil plant cycle chemistry problems. Thirty-five quotations of the most important publications from the last five years are presented.

PowerPlant Chemistry 1999, 1(5)

Andrew Howell:

Mitigation of Copper Deposition in High Pressure Turbines of Utility Drum Boilers

This issue contains only the German version. The English version of this contribution was printed in issue no. 4 (October).

Extensive deposition of copper on surfaces in the high-pressure section of the turbine at power-generating stations has become a significant industry problem. Original and secondary sources are discussed in detail as well as the respective release of copper. The modes of deposition and the transport pathways to the turbine are described. Particular attention is paid to mitigation or elimination of copper deposition and to removal of copper deposits from the turbine.

PowerPlant Chemistry 1999, 1(5)

Søren Kiil, Jan E. Johnsson, and Kim Dam-Johansen Name

Modelling of Limestone Dissolution in Wet FGD Systems: The Importance of an Accurate Particle Size Distribution

In wet flue gas desulphurisation plants, the most common reagent is limestone. Over the past 25 years, many attempts to model the transient dissolution of limestone particles in aqueous solutions have been performed, due to the importance for the development of reliable simulation tools. In this work, a critical examination of the models was conducted. The survey revealed that the models rely on the use of adjustable parameters in order to match experimental data. To investigate this, a simple particle model was set up. Model predictions were compared to experimental data for three different Danish limestone types with very different particle size distributions. All limestones were of a high purity. Model predictions were found to be qualitatively in good agreement with experimental data without any use of adjustable parameters. Deviations between measurements and simulations were attributed primarily to the limestone particle size distribution, which was used as model input. Those, measured using a laser diffraction-based Malvern analyser, were probably not representative of the limestone samples because agglomeration phenomena took place when the particles were suspended in a liquid solution. The analysis results were sensitive to the addition of a dispersing agent, the dispersion time, and the presence of ultrasound. It was found that the different particle size distribution influenced the simulated rate of dissolution significantly (i.e., from below to above the measured dissolution rate). The results of this work show that a representative particle size distribution is essential in order to model the rate of dissolution of limestone particles.

PowerPlant Chemistry 1999, 1(5)

Donald A. Palmer, Simon L. Marshall, J. Michael Simonson and Miroslaw S. Gruszkiewicz

The partitioning of acetic, formic, and phosphoric acids between liquid water and steam

The chemical carryover of impurities and treatment chemicals from the boiler to the steam phase, and ultimately to the low-pressure turbine and condenser, can be quantified based on laboratory experiments preformed over ranges of temperature, pH, and solution composition. The two major assumptions are that thermodynamic equilibrium is maintained and no deposition, adsorption or decomposition occurs. The most recent results on acetic, formic and phosphoric acids are presented with consideration of the effects of hydrolysis and dimerization reactions. Complications arising from thermal decomposition of the organic acids are discussed. The partitioning constants for these acids and other solutes measured in this program have been incorporated into a simple thermodynamic computer code that calculates the effect of chemical and mechanical carryover on the composition of the condensate formed to varying extents in the water/steam cycle.

PowerPlant Chemistry 1999, 1(5)

Chung-Hsien Liang, Yu-Ting, Ting-Chin Cheng, and Hsien-Cheng Wang

Root Cause of High Differential Pressure across Condensate Demineralizer during Plant Startup

According to our operation experience, no problems associated with plant startup after refueling outages have ever been raised since commercial operation at Taiwan Power Company Chinshan Nuclear Power Plant. However, the incident of high pressure drop of condensate polishers as well as high turbidity in raw condensate gas has occurred during the startup after EOC-15 of Chinshan Unit 2. The investigations using various analytical techniques including X-ray diffraction analysis, scanning electron microscopy, gamma scanning, and atomic emission spectroscopy with inductive-coupled plasma are described and the root cause of the incident is discussed.

Based on the investigation results and the course of the incident, maintaining the reactor water level and dumping the heavily radioactive reactor water into the hotwell after a reactor scram was identified as the incident root cause. In this way, large magnetite particles were released and transported into the condenser. Measures to prevent such incidents are proposed.

PowerPlant Chemistry 1999, 1(5)

Water Chemistry of Combined Cycle Power Plants - Standard Specifications

ABB Alstom Power

Three individual standard specifications for water chemistry in combined cycle power plants are presented:

• Standard specification for drum units,
• Standard specification for dual pressure LP drum and HP once-through boiler with reheat, and
• Standard specification for the purity of water and steam for gas turbine injection

All three are general specifications, valid for the plant type mentioned only. The criteria will be reviewed for a specific application and during commissioning.

PowerPlant Chemistry 1999, 1(5)