Isao Yuri

Structural Design and High-Pressure Test of a Ceramic Combustor for 1500°C Class Industrial Gas Turbine

The development of a high-temperature gas turbine is being carried out to improve the thermal efficiency on IGCC (Integrated coal Gasification Combined Cycle power plant), which is expected to be the thermal power plant of the future. A ceramic combustor for a 1,500 C, 20 MW class industrial gas turbine was developed and tested. This combustor has a hybrid ceramic/metal structure. To improve the durability of the combustor, the ceramic parts were made of silicon carbide (SiC), which has excellent oxidation resistance under high-temperature conditions as compared to silicon nitride (Si{sub 3}N{sub 4}), although the fracture toughness of SiC is lower than that of Si{sub 3}N{sub 4}. Structural improvements to allow the use of materials with low fracture toughness were made to the fastening structure of the ceramic parts. Also, the combustion design of the combustor was improved. Combustor tests using low-Btu gaseous fuel of a composition that simulated coal gas were carried out under high pressure. The test results demonstrated that the structural improvements were effective because the ceramic parts exhibited no damage even in the fuel cutoff tests from rated load conditions. It also indicated that the combustion efficiency was almost 100% even under part-load conditions.

Recession Rate Prediction for Ceramic Materials in Combustion Gas Flow

The influence of various basic factors of combustion gas flow conditions on the recession rate of silicon nitride, silicon carbide, and alumina has been experimentally clarified, and the recession rate equation is deduced using the dependence of influential factors on the recession rate and the mass transfer theory. The exposure tests are performed under various gas flow conditions (T = 1100–1500 °C, P = 0.3–0.7 MPa, V = 40–250 m/s, PH20 = 30–120 kPa, PO2 = 20–45 kPa). Recession rates mainly depend on water-vapor partial pressure, pressure, gas temperature, and Reynolds number in the gas flow conditions inside the specimen holder. The dependent on oxygen partial pressure is extremely low for silicon nitride and silicon carbide. The recession rates of silicon nitride, silicon carbide, and alumina in combustion gas flow are expressed in the form exp(−E/RT)·(PH20 )n · Re0–8 /P, and the predicted recession rates of silicon nitride shows good agreement with reported exposure test results under gas turbine conditions.Copyright

High Pressure Test Results of a Catalytically Assisted Ceramic Combustor for a Gas Turbine

A catalytically assisted ceramic combustor for a gas turbine was designed to achieve low NOx emission under 5 ppm at a combustor outlet temperature over 1300°C. This combustor is composed of a burner system and a ceramic liner behind the burner system. The burner system consists of 6 catalytic combustor segments and 6 premixing nozzles, which are arranged in parallel and alternately. The ceramic liner is made up of the layer of outer metal wall, ceramic fiber, and inner ceramic tiles. Fuel flow rates for the catalysts and the premixing nozzles are controlled independently. Catalytic combustion temperature is controlled under 1000°C, premixed gas is injected from the premixing nozzles to the catalytic combustion gas and lean premixed combustion over 1300°C is carried out in the ceramic liner. This system was designed to avoid catalytic deactivation at high temperature and thermal and mechanical shock fracture of the honeycomb monolith of the catalyst. A combustor for a 10 MW class, multican type gas turbine was tested under high pressure conditions using LNG fuel. Measurements of emission, temperature, etc. were made to evaluate combustor performance under various combustion temperatures and pressures. This paper presents the design features and the test results of this combustor.

Oxidation Behavior of Ceramics for Gas Turbines in Combustion Gas Flow at 1500°C

In order to evaluate the durability of silicon-carbides (SiC) and silicon-nitrides (Si3N4), we studied the oxidation behavior of SiC and Si3N4 in 1500°C combustion gas flow. We found that the exposure to the combustion gas flow resulted in the weight losses of those ceramics due to the partial disappearance of the oxidized surface layer.We investigated the effects of sintering aids and high speed gas flow as possible factors for the disappearance of the oxide layer. Two kinds of SiC, without sintering aids and sintered with B4C, were used as test specimens. After the exposure to combustion gas flow conditions of 1500°C, 150m/s, 0.18MPa, the weight loss rate and thickness of the oxide layer were quite the same for each specimen of SiC. The existence of sintering aids did not have any effect on the disappearance of the oxide layer. To investigate the effect of gas flow, we set each specimen in a tube made of SiC to protect it from the gas flow. The tube had two holes each acting both as inlet and exhaust vents. Consequently, the oxide layer formed thickly. But at the spots on the specimen facing the holes, the oxide layer was thin. Hollows occurred on the specimen of SiC at these spots. It seems that the existence of gas flow is a very important factor in the disappearance of the oxide layer.Alumina (Al2O3) and zirconia (ZrO2) as oxide ceramics were exposed to the combustion gas flow. The weight of these also decreased. There is a possibility that the weight loss of ceramics in combustion gas flow is caused by degradation of oxide layer on their surface from erosion and hot corrosion due to some oxide scales coming from the test equipment.Copyright

Strength Design and Reliability Evaluation of a Hybrid Ceramic Stator Vane for Industrial Gas Turbines

Employing ceramic materials for the critical components of industrial gas turbines is anticipated to improve the thermal efficiency of power plants. The authors developed a first-stage stator vane for a 1,300 C class, 20-MW industrial gas turbine. This stator vane has a hybrid ceramic/metal structure, to increase the strength reliability of brittle ceramic parts, and to reduce the amount of cooling air needed for metal parts as well. The strength design results of a ceramic main part are described. Strength reliability evaluation results are also provided based on a cascade test using combustion gas under actual gas turbine running conditions.

Exposure Test Results of Lu2Si2O7 in Combustion Gas Flow at High Temperature and High Speed

In order to understand recession behavior and the amount of recession of Lu2 Si2 O7 in the combustion gas flow, sintered Lu2 Si2 O7 specimens were manufactured by hot pressing and exposed under various combustion gas flow conditions (T = 1300–1500 °C, P = 0.3 MPa, V = 150 m/s, PH2O = 27–69 kPa, t = 10h). After the exposure tests, etch pits, which are assumed to form due to volatilization of SiO2 in the grain boundary phase, were observed at the surface of specimen. The amount of Lu2 SiO5 phase at the surface of specimen increased with the increase of gas temperature or water vapor partial pressure. A corresponding decrease in the amount of Lu2 Si2 O7 phase was observed. Furthermore, by using the average weight loss rate for exposure times of ten hours, the influence of gas temperature and water vapor partial pressure on weight loss rate was examined, and the amount of recession under gas turbine conditions was calculated.Copyright

Development of Silicon Nitride Components for Gas Turbine

Silicon nitride is one of the most practical candidates for ceramic gas turbines. The SN282 is silicon nitride material developed by Kyocera for gas turbines. Several new technologies have been developed to achieve materialization of ceramic gas turbines, such as material, fabrication process, evaluation / analysis technology. Recent technology is focused on recession of silicon-based ceramics under combustion gas. Environmental Barrier Coatings (EBCs) are developed to suppress these recession. We have found rare-earth element silicate and yttrium stabilized zirconium oxide (YSZ) have high corrosion resistance to the combustion gas. These materials were applied to the ceramic gas turbine components. The components with EBCs were evaluated in the actual engine tests. We have confirmed that the EBCs effectively work for the recession resistance.

Degradation of Silicon Carbide in Combustion Gas Flow at High-Temperature and Speed

Effects of various basic factors of combustion gas flow conditions on degradation behaviors of silicon carbide have been experimentally determined. The exposure tests were performed for widely varied experimental parameters of the gas temperatures (T = 900–1500°C), pressure (P = 0.3–0.8MPa), gas flow rate (V = 50–250m/s), water vapor partial pressure (PH2O = 32–82kPa) and oxygen partial pressure (PO2 = 24–44kPa). Degradation behaviors of silicon carbide were expressed as the weight loss of the substrate. The weight loss rate depends on the water vapor partial pressure remarkably. The effect of the oxygen partial pressure on the weight loss was smaller than that of the water vapor partial pressure, and the weight loss decreased with the increase of the oxygen partial pressure. Considering the effects of partial pressures of oxygen and water vapor, the gas temperature and the pressure didn’t have much effect on the weight loss. The weight loss depends on the gas flow rate, the increase rate of the weight loss for the gas flow rate becomes small with the gas flow rate. Consequently, the water vapor partial pressure, the oxygen partial pressure, the gas temperature, the pressure and the gas flow rate dependence of the weight loss rate is expressed as PH2O1.9 V0.6 P0.3 / PO20.6.Copyright

Development of Ceramic Stator Vane for 1500°C Class Gas Turbine

Employing ceramic materials for the critical components of industrial gas turbines is anticipated to improve the thermal efficiency of power plants. We have developed a first stage ceramic stator vane for a 1500°, 20MW class industrial gas turbine by improving our original one for a 1300°C class gas turbine. Our stator vane has a hybrid ceramic/metal structure composed of a ceramic shell, a metal core and a heat insulating layer. This composition increases the strength of the brittle ceramic parts and reduces the amount of cooling air. To improve the durability and reliability of the stator vane in 1500°C combustion gas, the ceramic shell uses silicon carbide instead of silicon nitride, and its configuration is improved. Furthermore, we use an internal cooling system to control the temperature of the metal core. Thermal loading cascade tests are conducted to prove the reliability and cooling performance of the stator vane.Copyright

Development and Evaluation of Ceramic Components for a Gas Turbine

An 8000 kW class Hybrid Gas Turbine (HGT) project, administered by the New Energy and Industrial Technology Development Organization (NEDO), was completed in March 2004. The targets of this project were improvement in thermal efficiency and output power by using ceramic components, and early commercialization of the gas turbine system. The ceramic components were used for stationary parts subjected to high temperature. It became clear that silicon nitride material showed significant recession under combustion gas. Kyocera and Central Research Institute of Electric Power Industry developed new EBCs to suppress this recession. These EBCs were evaluated by exposure test, heat cycle test and actual HGT engine test. One of the EBCs showed slight defects after the actual engine tests. However, all EBCs showed high corrosion resistance and good adhesion. It was confirmed that the all EBCs worked effectively.