Efficient condenser operation is critical to minimizing the operating costs and improving the performance of a turbogenerator unit or power plant. Efficient condenser performance is recognized by an improvement in heat rate and generation capacity, less fuel is consumed and a significant reduction in CO2 emissions can be achieved. Condenser tube fouling, fouled external surfaces of Air-Cooled Condensers (ACC) and condenser air-inleakage have been found to have a significant impact on condenser performance and subsequently plant performance. State-of-the-Art technologies have been developed to effectively remove fouling and deposits from condenser tubes, finned external surfaces of ACC’s and to identify the location of air and water in-leakage into the condenser, providing a longer useful life cycle. In addition, application of these technologies results in improved condenser backpressure, a decrease in plant heat rate and a decrease in yearly fuel consumption. Overall, plant performance is improved and CO2 emissions are reduced. Technology and cases are presented.
The two most common condenser tube problems faced by chemists are internal tube fouling and tube failure. Fouling can have a major impact on power station generating efficiency and capacity, and tube leaks can seriously impact unit availability and reliability. Fundamental understanding of the root cause(s) of these issues, and their mitigation, is essential to resolving these problems and/or preventing their occurrence.
Identified as one of the single largest energy loss factors in power generation stations, condensers are a potential source of either savings or increased expenditure, especially as fuel prices increase. The performance of the condensers can be adversely affected by the build-up of sediment, scale, corrosion or biological growth inside the tubes. Conventional maintenance procedures to clean fouled tubes range from chemicals to off-line mechanical cleaners and brushes, to on-line systems and hydro-blasters. Sometimes, it takes an unconventional, innovative development in a cleaning system technology to combat ever-changing environmental challenges. Omaha Public Power District’s North Omaha Station had been drawing water from the Missouri River for many years with no discernable problems. Recently, they had experienced a steady rise in summertime backpressures, in the range of 3 to 3.5 in. HgAbs, resulting in poor condenser performance. Inspections revealed a build-up of calcium carbonate scale in the tubes. The station has five condenser units with a total of approximately 50,000 stainless steel condenser tubes, all displaying evidence of calcium carbonate build-up. A recently developed and patented mechanical system for the removal of calcium carbonate scale without any of the negative drawbacks of chemical alternatives was utilized at the station with excellent results, proven by subsequent observations. On completion of the process, back pressure dropped to around 2.0 in. HgAbs and overall performance improved markedly. While plant personnel strive to determine the cause of calcium carbonate buildup in the condenser, removing it from the station’s tubes is now a simple procedure and no longer a problem in search of a solution.
Maintaining clean condenser tubes is of vital importance for reliable, efficient power generation. Two major problems result from substances on the interior of tube surfaces: (1) Loss of heat transfer, and (2) Under-deposit corrosion. Internal tube fouling is nearly always detrimental to heat transfer, thus reducing the efficiency of steam condensing, resulting in a lower vacuum (higher pressure) and less efficient steam turbine operation. Under-deposit corrosion of tube material can result in through-wall leaks, permitting ingress of cooling water into high purity steam condensate. Because poor vacuum conditions in the condenser can reduce electric generating capacity, and contaminants in steam condensate can cause significant damage to boiler tubing and steam turbine materials, measures to prevent fouling or remove foulants must be applied. Early identification of fouling characteristics and a fundamental knowledge of cleaning system capabilities are essential in determining the most effective cleaning technology. Unique circumstances may require innovative solutions. The common causes of condenser tube fouling and the practical application and innovation of cleaning technology are discussed. State-of-the-Art methods for off-line mechanical tube cleaning are presented, and their effects on tube condition examined.
An essential element in the eddy current testing methodology is the use of multiple testing frequencies. A true volumetric inspection requires complete penetration of the tube wall from various perspectives. Since prime frequency is set to approximately thirty seven percent standard depth of penetration of the tube wall, additional frequencies are required to gain an accurate and detailed perspective of the defect. In fact, the need for additional frequencies is absolutely necessary to characterize particular defects such as under-deposit corrosion and microbiologically influenced corrosion. In such cases a minimum of three frequencies are required to perform optimum testing. The frequencies will vary from low, midrange to high depending on the material under test. A fourth frequency can also be used to identify tube supports and tubesheets. This paper demonstrates the effects and advantages of utilizing multiple frequencies in the testing process. The result of which is to provide the analyst with sufficient information to call the defects with greater accuracy and reliability. Utilizing a multi-frequency test instrument and standard probes commonly used for testing condenser tubes, tube samples with various defects will be examined utilizing one, two, three and four frequencies. Defect acquisition rates will also be varied and the results reported. The information is useful for determining the number of frequencies required for an effective eddy current test.
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