At the 2014 ASME Power Conference in Baltimore, David Moelling of Tetra Engineering presented the recent research paper titled: Role of Boiling Mode and Rate in Formation of Waterside Deposits in Heat Recovery Steam Generator Evaporator Tubes, written by David Moelling and James Malloy. The paper discusses results from research in the theory of boiling mode and deposit formation, employing advanced thermal simulation of evaporation in real boiler models, and compares results with actual experiences in recent years. See the abstract to the paper below:
Waterside Deposits in evaporator tubes have been an issue in steam generators as long as boilers have been used. Substantial experience in deposit formation and management has been gained in conventional goal and oil/gas boilers over time. The role of boiling modes in the steam generator tubes is very critical to areas of deposit formation. Incipient boiling, nucleate boiling and convective boiling modes all have different deposition behavior. When Gas Turbine Combined Cycle (GTCC) power plants of larger size (> 100 MW) began operation in the 1990’s, deposits in evaporator tubes were not considered a significant issue.
Operating boiler pressures were low (500-900 psig) as were flue gas temperatures, use of supplemental firing was limited.Other than known problems with feedwater contamination such as operation with leaking seawater-cooled condensers, deposits were not found to be forming. The rapid increase in size and operating pressures in HRSG’s raised the likelihood of waterside deposits developing. Both Vertical and Horizontal Gas Path HRSG designs are considered. Drawing on field observations, the morphology and location of HRSG deposits are reviewed, as are changes in deposit formation with the mode and rate of boiling.
The paper is available in the conference proceedings journal.
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Understanding variations in Flow-Accelerated Corrosion Wear Rates in HRSG Evaporator Tubes
Very large differences in tube wall thinning rates by flow-accelerated corrosion (FAC), or in some cases fluid erosion, are observed in the low-pressure (LP) evaporator tubes of certain HRSG designs. The tubes located near the duct wall and occasionally near the gaps between module bundles have more rapid thinning. Tubes in a given row nominally should have very similar process conditions, both on the gas-side and on the waterside. Different wall thinning rates mean that process conditions differ across the tube row.
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