Tomoharu Fujii

Development of a low NOx catalytic combustor for a gas turbine

Abstract Catalytic combustion is an advanced combustion technology and is effective as a NO x control for a 1300°C class gas turbine for power generation, but the catalyst reliability at high temperatures is still insufficient. To overcome this difficulty, catalytic combustors combined with premixed combustion were designed. In this concept, it is possible to obtain combustion gas at a temperature of 1300°C while keeping the catalyst bed temperature below 1000°C. Catalyst segments are arranged alternately with premixing nozzles for the mixing of catalytic combustion gas and fresh premixture. An air bypass valve was fitted to this combustor for extending the range of stable combustion. As a result of the atmospheric combustion tests, NO x emission was lower than 5 ppm, combustion efficiency was almost 100%, and high combustion efficiency was obtained in the range of 900–1300°C of the combustor exit gas temperature. A full-pressure combustion test is planned to prove the combustor performance.

Estimation of Thermophysical Properties and Microstructure of Aged Thermal Barrier Coatings

A thermal barrier coating (TBC) is used for protecting hot gas path parts, and is useful for allowing the turbine inlet gas temperature to be increased. In order to quantitatively evaluate the performance of TBCs, the thermal conductivity of TBCs on the combustor of a gas turbine were measured. The results indicate that the thermal conductivity of age-deteriorated TBCs were higher than that of the as-sprayed TBC. This finding suggested that the thermal barrier performance of the TBC had deteriorated. When the thermal barrier performance of a TBC deteriorates, the temperature of the metal substrate rises, shortening the service life of hot gas path components. Accordingly, using experimental TBCs, laboratory-scale studies were performed to identify the causes of the deterioration of thermal barrier performance in TBCs. Six types of TBCs, prepared from six grades of plasma spray powder of yttria stabilized zirconia (YSZ), were tested. Average powder size, powder configuration, and percentage of yttria were the parameters of plasma spray powder taken to measure the thermophysical properties and carry out microstructural analyses on the as-sprayed TBCs and heat-treated TBCs.The results of the thermophysical property measurements indicate that the thermal barrier performance of heat-treated TBCs were two to three times greater than that of the as-sprayed TBCs. The results of the microstructural analyses revealed that the deterioration in performance was caused by changes occurring in the crystalline structure and the reduction of the non-contact area as in TBCs. The changes in thermal conductivity of TBCs were expressed as coefficients of porosity, crystalline structure, and heating time and temperature.Copyright

Numerical Analysis of Temperature Distribution of a Film-Cooled and TBC Coated Blade

In order to contribute to assessment of structural integrity of a gas turbine cooled-blade, numerical estimation of temperature distributions of the blade was conducted. Steady-state simulations by means of one-way coupling of a CFD calculation with thermal conduction analysis were developed and executed to estimate the temperature distributions with using a realistic blade model. Thermal protection schemes applied to the target blade analyzed are external surface film cooling, internal convective cooling and thermal barrier coating (TBC). Non-conformal multi-block meshes were adopted in the analyses for the purpose of reducing turnarounds required in the simulations of real blades, so as to cope with a compound domain including film-cooling holes of various directions. The CFD was applied to flow fields inside and outside of the blade in order to estimate thermal loads imposed on the blade. The temperature distribution of the blade was calculated with the thermal conduction analysis under the conditions based on the CFD calculation. The calculated temperature profiles are in reasonable agreement with local temperature which was estimated on the basis of micro-structural observations of an ex-service blade. The present calculations can also predict influence of lower internal cooling performance on the temperature distribution of the blade.Copyright

Development of Risk-Based Maintenance Software for Gas Turbines

Risk-based maintenance software has been developed to perform risk-based maintenance and inspection planning on gas turbine hot gas path components. The software allows the user to easily prepare a risk matrix, plotting every active damage mechanism for each hot gas path component. Based on the result of the risk assessments the components can be ranked, allowing inspection plans to be focused and prioritized and aiding the user to identify the most appropriate and effective risk mitigating activity within the software. Risk assessments are performed on a component-by-component basis, with the software’s scope including all combustor and turbine hot gas path components. The software also contains comprehensive help documents to aid the user in identifying and assessing peculiar damage mechanisms and prescribing the most effective inspection methods for gas turbines.Copyright

Development of Actual TBC Exposure Temperature Prediction Method

Gas turbines are being operated at ever-higher temperatures in order to increase their efficiency. As a result, thermal barrier technology to protect the gas turbine hot gas path parts from high-temperature combustion gas is becoming increasingly important, making it necessary to evaluate the thermal barrier performance of the thermal barrier coating (TBC) coated on these gas turbine hot gas path parts. Thermal barrier performance of the TBC deteriorates with the number of operating hours of the gas turbine. The degradation of TBC thermal barrier performance raises substrate temperature, and this rise in substrate temperature reduces the remaining life of the substrate. We proposed an effective nondestructive inspection (NDI) method to evaluate the thermal barrier performance of the TBC by infrared transient heating of the TBC surface. The temperature behavior closely correlated with the thermal barrier performance of the TBC. The results of numerical analysis and laboratory tests showed that the proposed NDI method was effective for evaluating the thermal barrier performance of TBC. So we developed NDI apparatus to inspect the thermal barrier performance of actual combustion liner TBC. In this NDI apparatus, the surface of the TBC was heated using a CO2 laser, and the temperature of the heated surface measured using an infrared camera. The CO2 laser and infrared camera were fixed, while the measured combustion liner was traversed continuously. The NDI apparatus developed enabled us to inspect the whole inner surface of an actual gas turbine combustion liner. We also showed the correlation with thermal conductivity of a virgin TBC, thermal conductivity of an inspected TBC, operating hours and TBC exposure temperature in our TBC thermophysical property study. The combination of this method and the NDI apparatus developed proved an effective way of clarifying the operating temperature of the hot gas path parts of the gas turbine. In this paper, we show a method for predicting actual gas turbine TBC exposure temperature, important when evaluating the remaining life of gas turbine substrate by the NDI apparatus developed and method of predicting TBC exposure temperature.Copyright

Development of a Crack Growth Prediction System for First Stage Nozzle of Gas Turbine

A system was developed for predicting the length of cracks generated in the first-stage nozzles of 1100 °C class gas turbines. The system consists of three programs, namely, crack input, crack display, and crack predicting programs, and a database containing data on 210,000 cracks generated in first-stage nozzles gathered from existing maintenance records maintained at three major power plants in Japan. The crack database also contains numerous crack data collected during inspections, operating hours and number of starts of gas turbine up to the time of inspection. The distinctive features of the system are 1) the crack data can be input as an image over the drawing of first-stage nozzles with a mouse, 2) by accumulating crack data, the sections in which most cracks occur in the first-stage nozzles can be clarified, 3) the correlation of crack length to operating time and number of starts can be analyzed simply, and 4) the length of cracks growing in any direction of any section of first-stage nozzles can be predicted.Crack data collected from three power plants were analyzed. It was found that the cracks that were comparatively long and grew in proportion to an increase in operating time and number of starts were only 11 crack patterns as compared to the entire first-stage nozzles. The length of these 11 crack patterns was predicted for new first-stage nozzles and compared with the measured values obtained from inspection. As a result, it was verified that the crack length could be predicted.Copyright

High Pressure Test Results of a Catalytic Combustor for Gas Turbine

Recently, use of gas turbine systems such as combined cycle and cogeneration systems has gradually increased in the world. But even when a clean fuel such as LNG (liquefied natural gas) is used, thermal NOx is generated in the high temperature gas turbine combustion process. The NOx emission from gas turbines is controlled through selective catalytic reduction processes (SCR) in the Japanese electric industry.If catalytic combustion could be applied to the combustor of the gas turbine, it is expected to lower NOx emission more economically. Under such high temperature and high pressure conditions as in the gas turbine, however, the durability of the catalyst is still insufficient. So it prevents the realization of a high temperature catalytic combustor.To overcome this difficulty, a catalytic combustor combined with premixed combustion for a 1300°C class gas turbine was developed. In this method, catalyst temperature is kept below 1000°C and a lean premixed gas is injected into the catalytic combustion gas. As a result, the load on the catalyst is reduced and it is possible to prevent the catalyst deactivation.After a preliminary atmospheric test, the design of the combustor was modified and a high pressure combustion test was conducted. As a result, it was confirmed that NOx emission was below 10ppm (at 16% O2) at a combustor outlet gas temperature of 1300°C and that the combustion efficiency was almost 100%.This paper presents the design features and test results of the combustor.Copyright

Development of Nondestructive Testing Method for Examining Thermal Resistance of Thermal Barrier Coatings on Gas Turbine Blades

In order to improve the efficiency of electric power generation with gas turbines, the turbine inlet gas temperature needs to be increased. Hence, it is necessary to apply thermal barrier coatings (TBCs) to various hot gas path components. Although TBCs protect the substrate of hot gas path components from high-temperature gas, their thermal resistance degrades over time because of erosion and sintering of the topcoat. When the thermal resistance of TBCs degrades, the surface temperature of the substrate becomes higher, and this temperature increase affects the durability of the hot gas path components. Therefore, to understand the performance of serviced TBCs, the thermal resistance of TBCs needs to be examined by the nondestructive testing (NDT) method. This method has already been reported for TBCs applied to a combustion liner. However, recently, TBCs have been applied to gas turbine blades that have complex three-dimensional shapes, and therefore, an NDT method for examining the thermal resistance of TBCs on blades was developed. This method is based on active thermography using carbon dioxide laser heating and surface temperature measurement of the topcoat by using an infrared camera. The thermal resistance of TBCs is calculated from the topcoat surface temperature when the laser beam heats the surface. In this study, the developed method was applied to a cylindrical TBC sample that simulated curvature on the suction side of a blade, and the results showed the appropriate laser heating condition for this method. Under the appropriate condition, this method could also examine the thermal resistance of TBCs present at 70% of the height of the blade. With these results, this method could determine the thermal resistance within an error range of 4%, as compared to destructive testing.Copyright

Development of Non-Destructive Heat Resistance Evaluation System for TBC on Gas Turbine Blade

The use of thermal barrier coatings (TBCs) is the key technique for realizing high-efficiency gas turbine combined cycles. Hence, TBCs are applied to various hot gas path components such as combustors, blades, and vanes. The application of a TBC causes a significant decrease in the temperature of the base metal surface. Consequently, the lifetime of the component is increased. However, it is reported that under high-temperature operating conditions, the heat resistance of the TBC decreases gradually because of sintering and erosion of the TBC layer. Accurate evaluation of changes in the TBC heat resistance is very important for evaluating the residual lifetime of a given component. We have previously developed a nondestructive technique for measuring the heat resistance of TBCs applied on the inner surface of a combustion liner. In this technique, the TBC surface is heated by a laser beam, and the temperature change of this heated point is measured by an IR camera. The heat resistance is calculated from the measured temperature. On the basis of this concept, we have made improvements to this technique so that it can be used to measure the heat resistance of a TBC layer on a blade surface. However, several difficulties are encountered whenusing this technique for the abovementioned purpose. For example, the blade has a three-dimensional (3D) surface and complex internal cooling paths, as opposed to the combustion liner, which has a simple cylindrical shape. Hence, it is difficult to keep the same heating condition at any surface. To overcome these difficulties, we propose a new concept and develop a system for measuring the heat resistance of the TBC layer on a blade. This system is mainly composed of a carbon dioxide laser, a robot arm, and an IR camera. In this paper, we present an overview of the developed system. Copyright

Development of Gas Turbine Hot Gas Path Parts Maintenance Planning Support System

Since the hot gas path parts such as combustors, blades, and vanes are subject to extremely severe working conditions, the parts must be inspected and repaired at relatively short intervals. Therefore, it is essential to reduce the maintenance costs for economic reasons. Furthermore, since the hot gas path parts have cooling structures with advanced design and coated with various types of coatings, the prices of parts are usually very high. Therefore, using the parts efficiently and extending the service life of the parts are needed to significantly reduce the maintenance costs. In such a situation, a platform free system of “Gas Turbine Hot Gas Path Parts Maintenance Planning Support System” has been developed. This system can be used to decrease parts disposal loss by optimizing parts rotation plans. In this paper, main functions of this system and the results of some case studies by this system are described.Copyright