A station uprate provides an economical opportunity to improve the generation capacity of a power plant if all the major system components are able to handle the effects of increased generation. The magnitude of uprate from increased steam generation will be limited by the maximum capacity of the weakest link in the cycle, which for many plants is the condenser. The condensers on many units are already pushed to their limit. This is especially true if a cooling tower is employed, where the condenser inlet cooling water temperatures are high on high wet-bulb temperature days. This condition forces many units to throttle down load to prevent excursions above the backpressure limits on their turbines. For condensers limited by the present duty, however, the options have been historically limited to rebundling the whole condenser with a larger surface area design and perhaps changing the tube material to a material with a higher heat transfer coefficient. Recently, a very low cost option has been demonstrated that should be considered by any plant looking to increase condenser duty or prevent station power reductions. Advances in the proper management of steam, condensate and noncondensable flows have permitted an upgrade for almost all vintage condensers, unlocking inactive surface area without a bundle replacement or complete redesign. This paper reports the results of a condenser retrofit effort, with emphasis on an upgrade applied to a load limited condenser concurrent with a major reduction in its operating backpressure. The performance of the condenser is presented before and after the upgrade showing significant backpressure reduction and heat transfer improvement accompanied by exceptional condensate chemistry results. It will be shown that 30% of the effective condenser surface area (or similarly, an additional 30% average heat transfer coefficient) was unlocked by activating the previously idle surface area.

Low cost, reliable and accurate real time measurement of individual tube condenser cooling water flow rate, cooling water outlet temperature and tube side fouling for the purpose of condenser performance monitoring and troubleshooting is presented. The importance and the effects of these parameters on condenser performance are well understood and periodically estimated using indirect measurements such as dye dilution testing to represent average tube circulating water velocities, distributed temperature sensors in waterboxes and differential pressure measurements between inlet and outlet waterboxes. These measurements, while useful, are not always effective to identify performance inhibiting issues quickly and accurately. This paper presents a cooperative study on the effects of circulating water flow and fouling and protective tube coatings for the purpose of condenser performance and monitoring improvement. The objective of the study was to evaluate new Circulating Water Flow and Fouling (CWFF) instrumentation [1], [2], [3] to evaluate impact of tube coating [4] on heat transfer and biofouling, and to examine the effect of other variables on on-going Microbiologically Influenced Corrosion (MIC) attack on the SS condenser tubes. However, in addition to providing useful information on the coated tubes, the study unveiled a number of other condenser performance related issues. Real-time in-situ circulating water flow and fouling data over an entire 1-year period will be presented that: • Correlates real-time flow measurements to fouling as it occurs; • Assists in the evaluation of different circulating water pump capacities and configurations; • Identifies flow stratification within the water box and identifies whether or not waterboxes are filled; • Evaluates the heat transfer coefficient differences between the coated and uncoated tubes; • Identifies other performance related findings.

Performance parameters and flow characteristics on the shell side of surface condensers are becoming better understood. Contributing to this knowledge base is the recent ability to measure the physical properties as well as the quantity of gases being removed from the condenser by air removal equipment. Reviewed here are the commonality of these data from many operating condensers obtained over the past six years and other known condenser measurements, theory and laboratory experiments. These are combined to formulate global theoretical description of condenser dynamics describing the mechanism responsible for aeration and de-aeration, excess back pressure buildup due to air ingress or generation of other noncondensable gases, and the dissolubility of corrosive gases in condensate. The theoretical description supports a dynamic model useful for deciding condenser configuration design and design improvements. Features of design found in many operating condensers that promote aeration and resulting corrosion are presented. The benefits of the model and engineering design modifications to plant life cycle management, improved condenser performance, outage reduction and reliability improvements, lost load recovery and fuel savings are discussed.

Recent considerations of steam and air mixture dynamics in operating condensers has led to a more thorough understanding of how condenser performance is affected by air in-leakage. Results of this model-based theoretical description, which are in agreement with measurement data from operating condensers, are reviewed and used to propose beneficial design features for new and re-tubed condenser assemblies. It is anticipated from this work, that condensers can be designed which significantly reduce the amount of dissolved oxygen in condensate from locations of free air ingress above the hotwell level. This reduction also applies to other undesirable noncondensables that enter condensate driven by the same mechanism contributing to dissolved oxygen. When air in-leakage becomes sufficiently high, it contributes to excess back pressure on the turbine. In this region of high air in-leakage, the amount of dissolved oxygen can become very high. The design therefore, minimizes or eliminates the corrosive effects of air inleakage, both high and low, which is particularly important during periods of high demand when load must be maintained.

A comprehensive theoretical development, confirmed by inplant measurements, will be summarized showing the dependence of condenser air in-leakage and exhauster capacity on build up of excess back pressure caused by the establishment of a zone of stagnation near the condenser’s air removal section. It has been generally believed that there will not be a zone of stagnation and an associated excess back pressure, above the design pressure, provided the exhauster capacity for air removal remains higher than the air in-leakage regardless of the leakage size. This paper will show, however, that excess back pressure can occur at high air in-leakage, even though exhauster capacity is adequate. A gradual increase in the concentration of non-condensables as steam scavenges these gases toward the air removal section is presented. This results in a reduction of individual tube heat transfer coefficient in the high air concentration region which is accompanied by an increase in condenser pressure. It will be shown that this may be the condition of heat transfer reduction that many authors have used throughout the 20 th century to describe the effect of air on all tubes in the condenser. An associated condition will also be discussed related to subcooling of the gas and vapor space between tubes within the region of reduced heat transfer. With high air in-leakage and high exhauster capacity, it will be shown that near the air removal section the large amount of air flow will scavenge steam through the subcooled region, directed toward the vent line, causing generation of a condensate mist that becomes suspended in the moving air. The reported theoretical explanation is derived using a condenser model developed earlier by the author. The results are confirmed from measurement data taken on an operating plant using a RheoVac ® condenser performance and diagnostic instrument, the description of which may be found in the open literature.

How well a condenser is performing is shown to be difficult to determine. The result obtained by using defined measurements in this determination is sometimes biased by shell side conditions that are often not well understood, leading to gross error in calculated condenser performance parameters. This paper describes some of these conditions, identified through recent research findings, and introduces methods to minimize the extent of the error. The discussion addresses how these condenser operating conditions have impact on calculated condenser performance parameters and how they may be properly understood by making use of relatively new measurements or through the application of comprehensive knowledge of the water vapor and noncondensable gas mixture dynamics. Such conditions as measured air in-leakage, and knowledge of no or very low tube fouling based on recent cleaning, are important for the purpose of quantifying the impact of design deficiencies on calculated condenser performance parameters. With proper condenser monitoring, telltale indicators of these deficiencies are clearly observed and will be presented. An investigation program that identifies the amount of performance loss, and the recoverable portion through condenser modifications, is discussed.