Contents Issue 3 (2001)

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Hans D. Pflug, Eric V. Maughan, Georg Müller, and Gottfried Betz

Central Control Unit for On-Line Power Plant Chemistry, Part 2

In Part 1, the acquisition and processing of analytical data was described. In this part, the application of the new Central Control Units (CCU) in programmed control of cycle chemistry and other chemistry-related areas is demonstrated. Major topics are unattended cycle conditioning (e.g., analytical criteria for feedback control, dosage control, adjusting of dosage to changing operational conditions), calibration of pH motoring equipment, operation of sampling and monitoring systems, and operational control of auxiliary chemical plans (e.g., raw water treatment, cooling systems, wet flue gas desulfurization).

The CCU has been developed out of many years' experience with power plant operation. It was designed to meet practical users' needs and to reduce the risk of pilot errors. It can be operated independently of larger existing control systems.

PowerPlant Chemistry 2001, 3 (3)

Heinz-Peter Borchardt, Carsten Holst, and Th. Peters

Special Features of the Chemical Cleaning of HRSGs with Horizontal Evaporator Tubing

Planning and implementation of a chemical cleaning of heat recovery steam generators (HRSGs) has to consider specific design peculiarities of these boilers, particularly the arrangement of the boiler tubing (vertical or horizontal). Examples of actual cleanings of HRSGs with horizonal tubing are presented. The cleans were performed with inhibited 1% hydrofluoric acid.

Particular attention is paid to the design and limitations of the autocirculation technique.

PowerPlant Chemistry 2001, 3 (3)

Margareta Bugajski, Bruno Wilhelmi, and Markus Horn

Refractory Non-Basic Mixes and Systems for Applications in Waste Incineration Units

Refractory used in mainly water-cooled combustion areas of incinerators should protect the waterwalls against corrosion and abrasion. Moreover, the control of heat transfer in incinerators can be adjusted through the correct refractory selection. Another multi-functional action of refractories is the prevention of slag corrosion and gas penetration. The results of laboratory investigations into the newly developed abrasion, slag and infiltration-resistant mixes are reported and some of the potential applications of the new refractory systems (SiC bricks, SiC plates + free-flowing Al2O3-SiC castables) are demonstrated. The new mixes should preferably be used for waterwalls protection and heat transfer control and for the complex geometry of the combustion area including disposal/combustion in fluidized-bed processes or in other new high-temperature technologies.

PowerPlant Chemistry 2001, 3 (3)

Tamara I. Petrova, Andrei Yu. Petrov, Julia V. Zhgenti and Barry Dooley

Behavior of Acetate and Formate in Liquid Film in Steam Turbines

During steam expansion in turbines, organic species (acetate and formate) concentrate in the early condensate; therefore, they will be present in relatively large amounts in the liquid film on the surfaces of turbine blades and disks.

This, in combination with an acidic environment, may be one of the reasons for the corrosion of metal in steam turbines. Therefore, makeup treatment should include procedures aimed at maximum removal of the organic impurities capable of forming acetic and formic acids during thermal decomposition from water used for steam generation.

PowerPlant Chemistry 2001, 3 (3)

Albert Bursik and Ulrich W. Staudt

Carbon Is Not Equal to Carbon

The current discussion on TOC is based more on progress in a technical development of surveillance instrumentation than on the actual demand. To evaluate the real impact of organics on the major cycle components, investigations with respect to selective corrosion effects on turbine materials are required. Here, in particular the effect of low-molecular acids and carbon dioxide on stress corrosion cracking and corrosion fatigue is not yet completely understood.

Any tightening of TOC target values does not seem to be required. Appropriate materials used within the cycle and correct design of the cycle components together with a proper cycle treatment (conditioning) ensure failure-free operation even in presence of the low levels of organics (including organic cycle additives) and/or carbon dioxide in steam.

PowerPlant Chemistry 2001, 3 (3)

Barry Dooley and Warren P. McNaughton

Appropriate Controls for Phosphate Boiler Water Treatments to Avoid Acid Phosphate Corrosion

The identification of the acid phosphate corrosion (APC) mechanism in the early 90s following years of hideout and hideout return with congruent phosphate treatment lead to the development and adoption of equilibrium phosphate and phosphate treatment. These treatments have eliminated APC and the need for acid phosphate additions, and rely solely on trisodium phosphate with possible small additions of NaOH, up to 1 mg kg-1. Procedures have been consolidated over the last 10 years for conversion to these treatments.

However, recent experiences confirm that unless particular care is given to the contaminant cycles, there is a possibility that hydrogen damage can emanate in boilers operating with either of these treatments, particularly in those operating with EPT.

PowerPlant Chemistry 2001, 3 (3)