Manage the Risk of Turbine Rotor Failure

Turbine rotors failure has resulted in a broad spectrum of events ranging from catastrophic burst to prolonged forced outages that ultimately have significant economic costs for affected utilities. Avoiding turbine rotor failure and its associated cost requires a detailed understanding of the operational reliability of power generation equipment. Nearly all large body turbine and generator rotors manufactured in the United States typically have a central bore hole that provides suitable access from which to conduct various material inspections. The term “boresonics” has become synonymous with the procedure for performing ultrasonic examination of turbine rotor material as conducted from the surface of a central bore cavity. Boresonics is now a fairly common and accepted practice throughout the utility industry. In general, boresonics involves passing ultrasonic transducers through the rotor bore to search a given volume of material for flaws at different locations and orientations within a rotor forging. Each individual ultrasonic transducer has specific inherent performance characteristics based on known wave physics that governs the art of ultrasonic testing. The results of boresonic inspections offer utility engineers a basis for making intelligent decisions on the condition of turbine and generator rotors. This paper describes how boresonic inspections are typically performed in the industry. Furthermore, the paper will give a description of the equipment and required skills of the system operators and will present examples of findings based on KEMA’s experience in this field.

Analysis of Combustion Flame of Syngas-Air Mixtures

In the proposed paper for this conference, three typical mixtures of H2, CO, CH4, CO2 and N2 have been considered as representative of the producer gas (syngas) resulting from biomass gasification. Syngas is being recognized worldwide as a viable energy source, particularly for stationary power generation. However, there are gaps in the fundamental understanding of syngas combustion characteristics, particularly at elevated pressures that are relevant to practical combustors. In this work, constant volume spherical expanding flames of three typical syngas compositions have been employed to measure the laminar burning velocity for pressures ranges between 1.0 and 20 bar. Over the ranges studied, the burning velocities are fitted by the functional formula of Metghalchi and Keck. Conclusion can be drawn that the burning velocity decreases with the increase of pressure. In opposite, the increase of temperature induces the increase of burning velocity. The higher burning velocity value is obtained for the downdraft syngas. This result is endorsed to the higher heat value, lower dilution and higher volume percentage of hydrogen in the downdraft syngas.

Pressure Testing Feedwater Heaters and Power Plant Auxiliary Heat Exchangers

This paper discusses factory and field pressure testing of tubular heat transfer equipment such as closed feedwater heaters, steam surface condensers and power plant auxiliary heat exchangers built to Section VIII Division 1 of the ASME Boiler and Pressure Vessel Code (the ASME Code) and repaired or altered in accordance with the National Board Inspection Code (NBIC). It discusses the ASME Code’s and the NBIC’s requirements for hydrostatically testing unfired pressure vessels which includes tubular heat transfer equipment. It points out that using pressure gage indications of pressure loss to determine if there is a leak from the tube side to the shell side when the back face of the tubesheet is not visible does not reveal very small leaks or weeping. For the purposes of this paper, we define weeping, VRRLeak, as a leak of 20 drops per hour or approximately 1 cm3 [0.061 in3]. During typical half-hour hydrostatic test pressure holding periods, such weeping would amount to 10 drops of water on the tubesheet face or 0.5 cm3 [0.0305 in3]. Weeping through tube-to-tubesheet joints of high-pressure feedwater heaters can lead to wire drawing (wormholing), which can materially reduce the heater life. Leaks from the channel to the shell side of steam surface condensers and auxiliary condensers can introduce brackish water into the condensate. Depending upon the fluid flowing in the tubes, contaminants can enter the shell side of other auxiliary equipment when the channel pressure is higher than that of the shell. The paper concludes that Users must advise Designers and Manufacturers of the hazards of small leaks through the tube-to-tubesheet joints. It recommends that these three entities must agree on suitable leak tests.

Technical and Economic Analysis of Cogeneration Systems for Refinery Power Plant Applications

This paper shows the main results from a technical and economical study for the implementation of new cogeneration systems in Mexican refineries. At least three cogeneration alternatives to match a 50% additional energy requirement (thermal and electric) for a refinery are analyzed. A balance simulator tool developed specially for the electric and steam refinery systems is used in order to obtain the technical parameters for the alternatives, which allows obtaining system performance indicators such as fuel consumption, cooling water requirement, electric and combined efficiency. Standard techniques as net present value, internal rate of return, and payback period are used for the economic analysis. According to the results, the best alternative was a gas turbine-heat recovery steam generator arrangement fueled by natural gas, including the respective adjustments of the refinery electrical and steam systems.

Numerical Simulation and Experimental Study of a Two-Floor Structure Pumping System

The two-floor flow passages pumping system with the simple structure is well practical in the Basin of Yangzi River downstream. However, this kind of pumping system has some disadvantages, such as low efficiency, easy to appear submerse vortex in discharge flow passages which causes the unit vibration and does harm to the operating of pump unit. In order to solve these problems, the design scheme with a new curve of diffusing outlet structure and inlet cone put forward, which are used in the renovation of the two-floor flow passages pumping station. With the numerical simulation of the two-floor flow passages pumping system, the flow fields are analyzed, and the external performance curves are obtained. To verify the calculation, a model tests were done using the standard model of pump. The test results are compared with the performance curves of numerical simulation. Good agreement of two results is found in the high efficiency area, which can show the calculation is believable. The new design improves the efficiency of pumping system significantly and eliminates the submerse vortex, also can guarantees the economy and security of operating.

Successful Replacement of a Condemned HP/IP Turbine by Weld Process

During the summer of 2008, a power plant performed a routine maintenance outage and discovered two cracks in the bore of their HP/IP rotor. The customer worked with the OEM to investigate the cracks in the rotor. The OEM recommended the following: perform a bottle-bore procedure, perform mechanical integrity calculations, and manufacture a new rotor in parallel. The duration of this repair would take over 24 months to complete. Alstom was contacted by the customer to supply repair recommendations. After an inspection of the unit and the boresonic data, Alstom proposed manufacturing a new replacement with a shorter lead-time. The process would involve join welding two stock forgings and adding some additional weld build up. The customer selected Alstom’s proposal, which could provide a replacement rotor in six months. The work scope included: join welding two rotor forgings together, shaft weld build up, extensive machining, and in parallel the manufacturing and installation 17 rows of turbine blades. This paper will discuss and document the case of the condemned HP/IP rotor.

Evaluating the Impact of the Uncertainty of Evaporative Cooler Effectiveness on the Net Power for a PTC 46 Test

This paper discusses how relative humidity impacts the effectiveness of an evaporative cooler, the uncertainty of the calculated effectiveness and the corresponding impact of the limits of this uncertainty on the power output. This is particularly related to a combined cycle facility where performance guarantees are based upon the evaporative cooler being in service. Different options for testing with and without the evaporative cooler in service are discussed as well as the need for an uncertainty when using a K factor.

Applying the X-Ratio Correction to Calculated Air Heater Efficiency: An Alternate Method

ASME PTC 4.3 on testing Air Heaters provides guidance for the calculation of gas-side efficiency as a measure of air heater performance. This code also provides for calculation of air heater X-ratio (XR), which is the ratio of the heat capacity (mass flow times specific heat capacity) of the air flowing through the heater to that of the flue gas. The code acknowledges the impact of XR on air heater efficiency, and dictates that the gas temperature leaving the air heater (and hence, air heater efficiency) be corrected for deviation from design XR by the use of “appropriate design correction curves” [1]. Unfortunately, such curves are rare, and therefore this important correction is usually ignored in routine air heater test calculations by power plant testing personnel, resulting in an incorrect calculation of air heater efficiency. This is particularly true for balanced draft boilers burning coal that are aged and have a significant amount of air leakage into the boiler setting. On these boilers, the ratio of combustion flue gas mass flow to combustion air mass flow is changed significantly from the original design, and therefore applying an XR correction factor is essential to calculating and reporting accurate air heater efficiency. This paper presents a method to calculate and correct for a deviation from design X-ratio based on standard heat exchanger analysis techniques, namely the ε-NTU method, which utilizes the concept of heat exchanger effectiveness (ε). A solution that results in applying the ratio of the design to actual XR’s as the correction factor is developed. The paper also provides empirical data from testing on a coal-fired boiler to validate the alternate correction method.

Preliminary Research of a Zero CO2 Emission Power Generation System

CO2 is a main greenhouse gas fazing the Earth. So countries around the world are actively studying the methods of capturing CO2 to reduce emission. In this paper, firstly a brief review was carried out on the research development and technical problems of three typical near-zero CO2 emission power generation systems. Focus was made on the construction of one possible commercially applied zero emission system, which has new principle but relatively conservative sections. Preliminary analysis and calculation of energy and mass flow have been finished to evaluate its performance. The results showed that apart from zero CO2 emission, a relatively tempting efficiency could be sustained. Theoretically, higher than 90% purity of CO2 and 63% generation efficiency of the whole system can be achieved.

Mitigation of Fires in Coal-Handling Facilities: Continuous Monitoring of Carbon Monoxide

While many power companies across the country rely on coal-burning facilities, fires and explosions in coal-handling facilities are of increasing concern. While facility housekeeping by means of controlling dust and preventing spills is very important, a good risk management plan must also include continuous monitoring of toxic and combustible gases. The use of carbon monoxide gas detectors has proved for years to be a very effective early fire detection system. This paper describes a risk-management system that can greatly mitigate the possibility of fire by means of alarming at low levels of CO concentration. The authors present a pro-active approach, focusing not on detecting smoke, which indicates fire, but rather on detecting CO, which indicates the potential for fire. Covered are the benefits of CO monitoring over thermal monitoring and IR scanning, the importance of monitoring for any continual trend upward from background levels, and discussion of how proper alarm setpoints are determined, using case studies.