In 2014, the Turkey Point Nuclear Power Plant experienced a hole and a steam leak through the shell of the Unit 4, #3B Low Pressure (LP) Feedwater Heater (FWH) near the drains outlet nozzle. Although the location of the hole in the shell was below the centerline of the heater in the Drain Cooler (DC) Zone, a video probe inspection through the drains outlet nozzle revealed that the cause of the leak was actually a hole through the DC top plate, which then allowed the steam to penetrate into the DC zone and erode the shell. The shell was able to be repaired in 2014, however there was not enough time to try to fix the hole in the top plate at that time. During a planned refueling outage in 2017, an access window was cut into the shell and the DC boundary repaired using a custom fit plate to cover the hole and prevent further leakage of steam into the DC zone. The unusual configuration of the DC sealing plates in that area made the repair challenging, but overall the repair was successful and the FWH was able to be returned to service. Additionally, during the maintenance outage, two leaking tubes were discovered on the periphery of the bundle near one of the Steam Inlet Nozzles. In order to determine the source of the tube failure, a video probe inspection of the shell side of the heater was conducted. It was determined that Foreign Material (FM) was the cause of the failures. By removing the steam inlet piping elbow, the Foreign Material was able to be retrieved and removed from the heater.

The design and certification of a high performance recuperator for micro gas turbines is presented. The component has been developed and built for a 100kWel micro gas turbine. The recuperator heated up compressed air at 3.5 bar with exhaust gas near atmospheric pressure and recuperates 300 kWth at an effectiveness of 90%. This concept can readily be adapted for other micro gas turbines due to its modular design. The certification has been realized under Pressure Equipment Directive 97/23/EC, equivalent to ASME Boiler and Pressure Vessel Code, covering closed pressurized devices. However, minor leakage in the recuperator is allowed, thus requiring an inventive design and validation approach for meeting the certification requirements. This leak is caused by weld porosity: the heat exchanging core plates are laser welded, having over 1200 meters of sealing weld length in a single recuperator. The maximum allowable leak amounts to 3 10 −6 mm 2 per meter weld length. The maximum leak was 0.2% of the massflow on the pressurized side at the nominal operating point, and therefore did not adversely affect the effectiveness of the recuperator. The finite element calculations and the resulting design loops on components and weld connections are presented. Validation of the entire component is done under the Experimental Design Method. A hydrostatic pressure test at 8.4 bar and ambient temperature is executed in the presence of a certified notified body to demonstrate that the welds are sufficiently robust. This pressure is higher than the operating pressure to simulate the effect of temperature on the steel properties. A laser scanner is used to map the deformation of the unit under pressure and subsequently referenced to its original state. The maximum deviation measured is equal to 0.26 mm for the pressurized part, which is acceptable considering the size of the unit is 1000mm × 600mm × 1000mm. The strain levels went back to the values before putting the unit under pressure, indicating there are no residual deformations. The test is further accompanied with leakage rate measurements before and after the hydrostatic pressure test. If the difference between these leakages rates is within limits, the recuperator will pass the test. The measured total leakage area is 0.4 mm2, well below the maximum allowable value, and equivalent to 0.01% of the massflow at the nominal operating point. This means the recuperator passed the test successfully. Furthermore, a burst test was executed to determine the safety factor and to identify the weakest element of the design. The burst pressure is observed at 18.3 bar, resulting in a safety margin of 218% and 523% in reference to the PED and operational design pressures, respectively. The component responsible for failure has been further optimized for the next generation of recuperators. Field data confirm that the lifetime of the high performance recuperator meets the requirements of 40.000 h operating time. Additionally, the traceability of the serial produced components is handled by the audited quality management system. It covers the used materials, including lot traceability, the measured process characteristics and welder certifications. The approach can also be used for ASME certification.

In this work, we present the design and fabrication a high-pressure pool boiling facility to conduct pool boiling experiments on horizontal heated surfaces under elevated pressures, up to 20 bar. Previous research has shown that micro- and/or nano-structured surfaces and coated surfaces will increase heat transfer coefficients up to one order of magnitude at atmospheric pressure. However, most boiling applications are subjected to high pressure, especially in the power industry. Pressure inside a boiling water reactor in a nuclear power plant will reach as high as 75 atm (75.99 bar). In order to determine how heat transfer is enhanced at increased pressures, with deionized water and refrigerants, on modified surfaces, a special experimental setup needs to be designed and fabricated. Difficulties in making such an experimental setup come from stabilizing the system pressure, sealing the test setup and visualizing the boiling conditions in the vessel. Both advantages and disadvantages of this design will be discussed and possible methods for improvements will be proposed. Preliminary test results on a plane copper surface are also included. Future research will be focusing on boiling of water and refrigerants on micro-structured copper surfaces, graphene coated, and Teflon© coated surfaces under high pressure.

The secondary air flow system of a gas turbine performs the cooling and sealing applications in those parts of the turbine which would otherwise be exposed to the high temperatures resulting in their life reduction or even failures. Accurate analysis of the secondary system is therefore necessary to ensure the safe design of the engine and accurate life predictions. The secondary system is analyzed through the flow network analysis which comprises of chambers or cavities connected through flow passages or restrictions (e.g. seals). The narrow flow channels form a majority of these passages especially in the turbine blades cooling system. This paper provides a detailed formulation of a one-dimensional model for steady, compressible flow inside a channel which is based on the solution of two equations for a coupled system of mass, momentum and energy equations. The model is applicable over a wide range of subsonic to supersonic flow conditions. It has been validated for the choked flow situation and also has the capability to capture normal shocks. Hence, this model provides a fast, accurate and robust channel simulation technique that is compatible with a complex network analysis.

In the Spring of 2012 a 1950’s vintage natural gas unit located on a lake in Texas encountered multiple condenser tube failures of its Admiralty Brass tubes. Due to time and cost restraints, the option of retubing was not chosen to prepare the unit for the summer run. Instead, the full-length of approximately 5,500 tubes were epoxy coated. This included 1,150 tubes which had been plugged as leakers, but were unplugged and coated using a special leak sealing method of applying the epoxy lining. The coating process was completed in 10 days and all but 55 tubes were sealed by the coating process. These tubes were plugged and the unit was put into service. The unit has been running successfully since the project was completed with no heat rate penalty. The circumstances leading up to this situation are discussed along with the details of the coating process.

Plant management had a mission: to make the Midwestern 646-megawatt power plant a leader in the clean and safe handling of PRB coal. To accomplish that goal, the organization embarked on an ambitious five-year plan to upgrade the plant’s coal handling system. The plant improved its conveyor transfer points, and installed new dust management systems, controlling dust and spillage, and improving plant safety and efficiency. This presentation will discuss the initial surveys that led to the development of the 5-year plan, and the resulting project priorities, the problem areas, application points identified, and the various technologies applied. Included in the goals for the upgraded systems installed were the elimination of spillage through the improvement of transfer points on coal-handling conveyors using improved belt support and sealing systems. In addition, new air cleaners were installed at seven loading zones, and a foam dust-suppression system added at one location to provide dust management throughout the plant’s coal handling system. These new dust control systems allowed the plant to eliminate its older central dust collection system that had greater risks of explosions. A continued series of monthly inspection and service visits by conveyor maintenance technicians helps continue the coal handling system’s high levels of performance. This five-year plan helped the power plant take “great leap forward” in controlling dust and spillage from handling PRB coal.

This paper describes a modification to a standard reheat HRSG (Heat Recovery Steam Generator) enabling it startup faster. It also allows the plant to operate the gas turbine in simple cycle and to operate the HRSG as a stand-alone auxiliary boiler. An external fan, pre-heater and burner are connected to the diffuser of the HRSG. When the gas turbine is out of service, the fan and burner are actuated, providing enough flue gas to allow the HRSG to operate as a small auxiliary boiler. Steam produced during this operation pressurizes the drum, heats the steam lines provides sealing steam for the steam turbine, and allows a vacuum to be maintained in the condenser. The system is designed to produce enough steam to synchronize a steam turbine. When the HRSG, condenser, circulating water system or steam turbine is removed from service, the HRSG is drained and the fan turned on without the burner, mixing tempering air to the exhaust of the gas turbine operating in a simple cycle mode. The tempering air lowers the flue gas temperature enough to allow the operation of the SCR system while preventing damage to the carbon steel tubes of the HRSG.

The efficient handling of coal on belt conveyors is essential to coal-fired power plants. The conveying of coal is prone to problems including the escape of spillage and airborne dust. These problems lead to excessive, expensive, and sometimes hazardous maintenance requirements. The failure to provide this essential maintenance leads to more fugitive material and more problems in material handling. The key to efficient conveyors are the implementation of advanced systems to improve performance and prevent fugitive material including dust, combined with the training of plant personnel in the operation and maintenance of these sophisticated systems. This presentation looks at “new generation” conveyor architecture that combines better control of fugitive material with improved serviceability and increased employee safety. These systems feature engineered chutes that channel the material stream to reduce the entrainment of air into the material flow, and so minimize the release of dust. And this next generation system feature a modern architecture with improved belt support and sealing systems that reduce maintenance requirements and allow maintenance work to be performed from safely outside enclosures and away from moving parts. An important consideration in these advanced systems is the training of plant personnel on the operations and maintenance of these systems. This presentation will also consider this essential training, and propose several methods to achieve these training requirements.

Flow accelerated corrosion (FAC) is a combined form of erosion, corrosion and Cavitation. This is prominent in steam condensate lines which results in fast reduction of thickness in piping, piping components and valves. It is estimated that this problem is faced by majority of plants. There has been an increased emphasis on correcting these problems due to fatal accidents that occurred in 1986, 1995, 1996 and 2004 at various locations around the world. [3] After commissioning of the plant, Steam condensate system erosion/corrosion problem started appearing within one year of operation. To ensure uninterrupted plant running on line sealing was done and monitoring was done by proper thickness checking. These on line sealing points were replaced during available opportunity. In some cases plant shutdown was taken to replace leaking piping components & these incidents resulted into revenue loss to company. Aggressive inspection programs were taken up for thickness measurement on condensate lines and as a proactive measure, elbows were encapsulated with higher size elbows, reducers by on line welding/furmaniting with special clamps. Similarly gate and globe valves in condensate service also started failing as a result of erosion of body seat rings. Globe valves installed on bypass lines of control valves were found passing. Once these valves were operated for maintenance of control valves they could not be closed. In some cases valve body developed leak due to high velocity erosion. Various studies conducted for replacing these components by higher schedule fittings & pipes but it did not improve the situation except for slight increase in life of these components. Velocities were calculated at various locations and higher velocity, condensate impingement/cavitation was found as root cause of problems. This problem was solved by various methods like using higher metallurgy P11, P22 material, line size increase with increase in control valve sizing, lay out changes etc. This helped in improving reliability of condensate system and reducing risk associated with failure of piping. This paper presents a variety of cases where single-phase and two-phase steam flows, caused erosion-corrosion damage mainly at turn points of elbows and valves. It was observed that the presence, even of a small amount of the vapor phase can significantly increase the velocity of the condensate. This paper describes the mechanism of failures by study of the failed components, operating conditions & piping lay out. In this study velocity of steam /condensate at reducing section was found to be very high. Other various contributing factors like control valve / piping sizing, metallurgical requirements, effectiveness of steam traps, flow velocity and valve design (globe & gate) were also studied. The main causes of the failures are discussed and recommendations are provided to rectify the root cause of the problems & avoid similar problems in the future.

Xcel Energy’s Riverside Repowering Project was a voluntary emissions reduction project with the goals of improving air quality in Minnesota while, at the same time, increasing the amount of electricity produced. The Riverside Plant was converted from being a coal-fired facility to a combined-cycle facility firing natural gas. The fuel switch resulted in significant plant emission benefits, with emissions of sulfur dioxide decreasing by 99%, nitrogen oxides (NO x ) decreasing by 96%, and mercury being eliminated entirely. Plant output increased from a nominal generating capacity of 386 MW to a summer day net output of 472 MW. The three existing coal-boilers were retired. Two F-technology combustion turbine generators (CTGs) and two heat recovery steam generators (HRSGs) were installed. Each CTG fires natural gas with dry low-NO x combustors. Each HRSG includes a selective catalytic reduction (SCR) section supplied with aqueous ammonia. Steam generated from the HRSGs is fed to an existing steam turbine. The low-pressure steam from the HRSG is admitted into the steam turbine through a new connection. The steam turbine extraction lines for feedwater heating are capped. To accommodate the resulting increased flow through the turbine, two rows of blades were replaced. A new full-flow steam turbine bypass system operates during plant startup and shutdown. An auxiliary boiler was added to provide warming and sealing steam to the steam turbine. A new distributed control system (DCS) operates the facility, with workstations located in the plant’s existing control room. The existing once-through circulating water system on the Mississippi River was modified with the addition of wedgewire screens to comply with the Clean Water Act Section 316(b). The CTGs and HRSGs are fully enclosed in a new building that is integrated with the structure for the steam turbine. Due to the proximity of residential housing, sound attenuation is critical. Space for the new building was created by demolishing formerly retired units. Reclaiming this area resulted in a unique layout. The HRSGs are constructed over wood piles installed in 1914–22. The HRSG foundation consists of an elevated slab supported on concrete walls distributing load to the original pile caps. Between the HRSGs and the CTGs are retired concrete coal hoppers that divide the site. The CTGs sit approximately 20 feet higher than the base of the HRSGs. The combined cycle achieved commercial operation on May 1, 2009.

The DOE Office of Nuclear Energy and Sandia National Labs are investigating supercritical CO 2 Brayton cycles as a potentially more efficient and compact power conversion system for advanced nuclear reactors, and other heat sources including solar, geothermal, and fossil or bio fuel systems. The focus of this work is on the supercritical CO 2 Brayton cycle which has the potential for both high efficiency, in temperature range (400–750 C), and for reduced capital costs due to very compact turbomachinery. The cycle achieves high efficiency due to the non-ideal behavior of supercritical CO 2 , and it achieves extremely high power density because the fluid in the turbomachinery is very dense, 10%–60% the density of water. Sandia and its contractor Barber Nichols Inc. have fabricated and are operating a supercritical CO 2 (S-CO 2 ) compression test-loop to investigate the key technology issues associated with this cycle. The compression loop is part of a multi-year phased development program to develop a megawatt (MW) heater-class closed S-CO 2 Brayton cycle to demonstrate the applicability of this cycle to heat sources above 400 C. Other portions of the program include modifications to the compression loop to operate it as a simple heated Brayton loop by adding a small turbine and a heater, but with no recuperator. The early testing of this simple Brayton cycle is under way. A more ambitious effort is currently constructing a recompression cycle Brayton loop (1) which is some times called a split-flow Brayton cycle. This cycle is used to increase the efficiency of the system by providing large amounts of recuperation using printed circuit heat exchangers. The re-compression (or split-flow) Brayton cycle is designed to operate at 1000 F (538 C) and produce up to 250 kWe with a 1.47 ″ OD radial compressor and a 2.68 ″ OD radial turbine. The current compression loop uses a main compressor that is identical to the main compressors in all the Brayton cycles that are being developed at Sandia. The key issues for the supercritical Brayton cycle include the fundamental issues of compressor fluid performance and system control near the critical point. Near the critical point very non ideal fluid behavior is observed which means that standard tools for analyzing compressor performance cannot be used. Thus one of the goals of the program is to develop data that can be used to validate the tools and models that are used to design the turbomachinery. Other supporting technology issues that are essential to achieving efficiency and cost objectives include bearing type, thrust load and thrust load balancing, bearing cooling, sealing technologies, and rotor windage losses. The current tests are providing the first measurements and information on these important supercritical CO 2 power conversion system questions. Some of this data is presented in this report. In the testing to date, the turbomachinery has reached maximum speeds of 65,000 rpm, peak flow rates of over 9 lb/s and pressure ratios of just over 1.65. Compressor inlet fluid densities have been varied from 14% to 70% the density of water. Although the data from these tests are only the first results to be analyzed, they indicate that the basic design and performance predictions are sound. The loops have operated the turbo-compressor on the liquid and vapor side of the saturation curve, very near the critical point, above the critical point and even on the saturation dome. We have also operated the compressor near the choked flow regime and even in surge. At the current operating speeds and pressures, the observed performance map data agrees extremely well with the model predictions. These results have positive implications for the ultimate success of the S-CO2 cycle. In general the main compressor shows no adverse behavior while operating over a wide range of normal operating conditions. It operates reliably and with performance values that are very near the predicted results. Future efforts will focus on operating the Brayton cycle loop at sufficiently high temperatures that electrical power can be produced near the end of 2009. The compression-loop hardware is now the test bed for confirming the remaining parameters to support the next stage of development — which is the 1 MW heater-class split-flow or re-compressor Brayton cycle.

Applicable industrial standards for centrifugal pumps endorse several different sealing options as “best practice.” However, the overall acceptance of best practice techniques seems slow and is linked to the fact that sealing devices account for only a small fraction of the energy consumed by pumps. Yet, regardless of perception, significant energy conservation has been achieved by thoughtful sealing practices, as this paper will show. It will highlight case studies that provide guidance on issues of increasing technical and societal concerns relating to fluid emissions. Special attention will be directed to barrier fluid circulation devices used in dual mechanical seal arrangements as described by API-682 (Ref.1), a Standard widely used in the oil refining and petrochemical industries. The applicability of these ciculation devices to the Power Industry will be explained. Comparisons of three of the most widely used conventional integral flow induction/pumping ring devices will be made and the results of extensive testing presented. The paper and presentation also quantifies the value of advanced sealing technologies for pumps and highlights configurational differences between the newer and the more traditional (older) devices. Without exception, international utilities and power producers know that both energy and maintenance expenditures are affected by availability and reliability considerations relating to power generators and their turbine drivers. But feed water pumps and cooling water issues play their part as well. Consequently, a measure of attention has been given to “other big ticket items”, such as cooling tower losses and the like. However, there is compelling evidence that additional, less prominent or less obvious opportunities exist and that these can no longer be overlooked. Pump sealing falls into that category, although sealing devices and seal cooling account for only a small fraction of the energy consumed by pumps. In can be readily shown that significant energy savings have been achieved by thoughtful sealing practices. The general narrative and the implications conveyed by our case studies give visibility to the issues and provide guidance to the user.

In the past, several 300 MW steam turbine rotors were affected by vibrations, which appeared at bearing #1 during load conditions. At certain loads, vibrations of the #1 bearing increased considerably. Near full load the amplitude of vibration sometimes reduced to acceptable levels. Practically, the phenomena were partially cured by trim balancing of the HP rotor, readjusting the valve opening characteristics and by correction of the clearances in the sealing system. The results are briefly summarized. On the other hand, the simulation of the various parameters using rotordynamic codes was conducted to explain the phenomena analytically. In this part, the rotordynamic rotor model was constructed and the following simulations were carried out: rotor bearing instability, effect of the destabilizing steam forces on the rotor at the first row, effect of the seal rotordynamic forces and the valve opening sequence on the rotor stability. All results were analyzed to present general conclusions.

San Onofre Nuclear Generating Station, SONGS, Unit 3 experienced substantial turbine damage in early 2001 after the turbine bearings lubrication oil supply failed. During a loss of off-site power incident, power was lost to the two AC powered turbine lubrication oil pumps due to a breaker failure in the switchgear and the DC powered emergency bearing lubricating oil pump failed to start due to a breaker trip. The SONGS turbine generators have no shaft driven bearing lubricating oil pumps and consequently the turbine generator coasted down from full speed to a full stop without lubricating oil. This resulted in significant bearing, journal and steam path damage that required a four-month duration repair outage during a time period where electricity was in short supply in the State of California. The generator hydrogen sealing system remained operable during this event, however it was discovered during the event follow up investigation that this system had vulnerabilities to failure similar to the bearing lubrication system. In order to prevent a reoccurrence of this extremely costly event, SONGS has taken actions to modify both of these critical turbine generator systems by adding additional, continuously operating pumps with new, independent power source and independently routed cables. The main challenge was to integrate the additional equipment into the existing lubrication and seal oil systems. The SONGS approach and findings are discussed as well as a summary of the work performed. This technical paper will be of interest to utilities with a need to improve turbine generator reliability issues.

The HEAT™ (High Efficiency Advanced Technology) steam turbine utilizes high reaction technology [1], which is significantly influenced by the effectiveness of sealing between the stages. The thermal-mechanical analysis based clearance design and the combination of labyrinth sealing with abradable coatings offer an effective solution to minimize bucket and nozzle tip leakage through transient and steady state operation of the turbine. The aim of this paper is to describe the clearance design process and the development of abradable-labyrinth seal configurations. The paper describes extensive testing and detailed analysis conducted to evaluate seal properties and behaviors. Properties investigated included corrosion, erosion and in particular, rub characteristics. Rub behavior is investigated in a high temperature, high speed test apparatus designed to simulate clearance changes during transient periods of start-up, shutdown and hot re-start which often result in interference between the sealing components. This paper will discuss the method to predict differential rotor to stator movements and the resulting abradable incursion during the various operating transients. The seal tooth to coating contact is then simulated with component testing for multiple incursion modes (i.e. radial, axial and a combination of the two) and rates. The discussion will also include the application of the clearance design and sealing technology to a reaction type steam turbine.

The integral diagnostics factor used for the evaluation of turbine island condition is the turbine heat rate corrected to constant steam parameters and condenser pressure which is called “corrected turbine heat rate”. In case of excessive deviation of corrected heat rate from its normal value, it is necessary to implement a diagnostic subsystem for determining the source of the deviation. The following subsystems of the turbine island have to be taken into consideration: turbine steam path, turbine end seals, control valves, etc. For each subsystem it is necessary to select the calculated or measured parameter(s), which will be used as diagnostic factors for turbine condition evaluation purposes. For the turbine steam path subsystemthe internal efficiency of the high pressure turbine (HP) and intermediate turbine (IP) can be used. Selection of the internal efficiency as diagnostics factor is based on its high sensitivity to variations in steam path conditions (erosion, steam path fouling and so on), as well as to steam path diaphragm and radial sealing conditions. However, the basic internal efficiency calculation results of HP and IP turbines at different loads, using measured parameters, show very high sensitivity of the calculation results to random measurement errors, random components of the regulation process and variations in spatial and time distribution of the temperature and pressure fields. This high sensitivity causes the uncertainty of the calculation results to approach ± 1.5 % and means that the results can not be used for diagnostic purposes. To achieve acceptable results for uncertainty (± 0.3 %) special methods of mathematical analysis need to be applied, including robust estimation, precise multivariate approximation, filtration and others. Furthermore, the HP turbine internal efficiency depends on control valve position and thus can not be directly used as a diagnostic factor in an on-line turbine diagnostic system. To solve this problem, special methods were developed for correcting the real efficiency value to the valve wide open position. The developed method was verified by a set of specially designed tests and results have shown that this technique can be applied for on-line calculations. The described system for on-line turbine internal efficiency monitoring was developed in cooperation between IEC and Berman Engineering Ltd. The system was implemented on a 550 MW unit and has been in operation for two years. The results of operation show that the system yields the required expanded uncertainty in the range of ± 0.3 %. The system is characterized by high reliability and a friendly interface.