Shinichi Higuchi

Test Results From the Advanced Humid Air Turbine System Pilot Plant: Part 2—Humidification, Water Recovery and Water Quality

The AHAT (advanced humid air turbine) system has been studied to improve thermal efficiency of gas turbine power generation. This is an original gas turbine power generation system which substitutes the WAC (water atomization cooling) system for the intercooler system of the HAT cycle. A pilot plant was built to verify feasibility of the AHAT system, which is composed of a gas turbine, a humidification tower, a recuperator and a water recovery system. Firstly, characteristics of the humidification tower were examined. The experimental results of the humidification rate agreed with the calculation results within a deviation of 1%. Humidification increased the heat recovery, and the electrical efficiency exceeded 40%. Secondly, characteristics of the spray-type water recovery system were examined. 95% of water consumed by the humidification tower was recovered, and a significant reduction of the make-up water for the HAT cycle was confirmed. Thirdly, concentrations of impurities within the circulating water of the AHAT system were measured when the recovered water was recycled without any purification process.Copyright

Test Results From the Advanced Humid Air Turbine System Pilot Plant: Part 1—Overall Performance

The AHAT (advanced humid air turbine) system is based on a recuperated cycle using high-humidity air. This system improves thermal efficiency by using the high-humidity air as working gas. After many studies and elemental tests, a 4MW-class pilot plant was planned and built in order to verify feasibility of the AHAT system from the viewpoints of heat cycle characteristic and engineering. This plant consists of a gas turbine, a recuperator, a humidification tower, a water recovery system, an economizer, and other components. The gas turbine consists of a two-stage centrifugal compressor (pressure ratio of 8), a reverse-flow type single-can combustor, and a two-stage axial-flow turbine. In overall performance tests, the plant thermal efficiency exceeded 40%LHV.Copyright

Development of Flaw Sizing Technique by Radiographic Testing - Application of the "GUCHI" Technique

Many successful flaw sizing applications have been reported on various ultrasonic testing (UT) for the cracks detected in in-service stage. But due to the configuration of the component which is difficult for scanning with search units, other appropriate sizing technique is required. Since nowadays there are some digital imaging processes on radiographic testing (RT) and real-time calculations with personal computer available, RT were considered to be the most relevant ones. Practical experiments have been performed to verify the capability of an improved RT technique named “GUCHI” (Geometric Unravel for Crack Height Image) for sizing. Feature of this technique is that base line marker such as small diameter copper wire shall be placed on the crack, and twice of exposures shall be performed for the crack. The sources are positioned in parallel to a film or an imaging device. The size of crack will be estimated by several theoretical calculations with geometrical arrangement of taking radiograph and dimensional data measured on each radiograph. Digitizing System is useful for flaw sizing. This paper presents the fundamentals of the GUCHI technique and data obtained from experiments on the test specimens with fatigue crack, surface planar flaws embedded in weld and artificial EDM slits. Introduction When the flaw is detected during the in-service inspection of components, sizing should be performed to evaluate the flaw. Regarding flaw sizing techniques, several papers relating to ultrasonic testing (UT) are available[1][2][3]; however, it seems that radiographic testing (RT) has seldom been applied to flaw sizing. An improved RT technique for sizing called “GUCHI” (Geometric Unravel for Crack Height Image) has been developed by Hitachi, and demonstrated at AN committee of JWES, to size of cracks in the test pieces. In addition, experiment on RT flaw sizing technique was carried out at Hitachi using test specimen with fatigue crack, EDM slits and the results compared with data obtained by UT-TOFD, Phased Array and Crack Tip technique.[4][5][6] Fundamentals of GUCHI Technique The fundamentals of this technique based on the geometrical calculation by two radiographic images, which are taken by different angles. Baseline marker such as a small diameter copper wire being placed on the crack, and two X-Ray orγ-Ray exposures being taken. The sources are 1) Application of NDT Techniques for Industrial Field. 2) Japan Welding Engineering Society Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 1316-1323 doi:10.4028/www.scientific.net/KEM.270-273.1316

Design Study of a Humidification Tower for the Advanced Humid Air Turbine System

The AHAT (advanced humid air turbine) system, which can be equipped with a heavy-duty, single-shaft gas turbine, aims at high efficiency equal to that of the HAT system. Instead of an intercooler, a WAC (water atomization cooling) system is used to reduce compressor work. The characteristics of a humidification tower (a saturator), which is used as a humidifier for the AHAT system, were studied. The required packing height and the exit water temperature from the humidification tower were analyzed for five virtual gas turbine systems with different capacities (1MW, 3.2MW, 10MW, 32MW and 100MW) and pressure ratios (π = 8, 12, 16, 20 and 24). Thermal efficiency of the system was compared with that of a simple cycle and a recuperative cycle with and without the WAC system. When the packing height of the humidification tower was changed, the required size varied for the three heat exchangers around the humidification tower (a recuperator, an economizer and an air cooler). The packing height with which the sum total of the size of the packing and these heat exchangers became a minimum was 1m for the lowest pressure ratio case, and 6m for the highest pressure ratio case.Copyright

Conjugate Heat Transfer Analysis in an Actual Gas Turbine Rotor Blade in Comparison With Pyrometer Data

Conjugate Heat Transfer (CHT) was analyzed in a first stage rotor blade in an actual gas turbine. The main objectives of this research were to simulate and validate improvements to the accuracy of predicting temperature on the surfaces of rotor blades in a gas turbine and compare these with experimental results.This simulation was carried out under similar conditions to those during gas turbine operation. Computational grids were generated based on CAD data obtained from the rotor blades with fully resolved rib turbulators and pin fins for both fluid and solid domains during CHT analysis. A tetrahedral mesh with prism layers was used and the y+ of the first mesh adjacent to the wall was kept at less than 1.0 over the whole surface. Thermal barrier coating was modeled by adding thermal resistance at the fluid-solid interfaces. Inlet boundary conditions for the external- and internal-gas-flow regions were defined based on one-dimensional analysis and measured results. Steady Reynolds-averaged Navier-Stokes simulation was carried out using the Shear Stress Transport (SST) turbulence model. The simulated results were compared with measured data obtained from a pyrometer and thermocouple.The temperature distributions predicted from CHT analysis agreed with those obtained from an experiment near the leading edge of the rotor blades. However, the temperature distribution at the center of the pressure side had a difference of 50 K with that obtained from the experimental data. The heat transfer coefficients on the surfaces of the blades were almost equal to those on the pressure side. Thus, we considered that the internal cooling flows contributed more to temperature distributions on the surfaces of the blades rather than the external gas flows. The main stream in the internal cooling flow passages leaned toward one side of the walls and the temperatures on this side became lower than those obtained from the experimental results. Therefore, we suspect CHT analysis underestimated the mixing effect generated by the rib turbulators. It is important to solve the complex flow phenomena in internal cooling passages to better predict the accuracy of temperature distributions on the surfaces of blades.Copyright

Experimental and Analytical Study on the Operation Characteristics of the AHAT System

Operational flexibility, such as faster start-up time or faster load change rate, and higher thermal efficiency, have become more and more important for recent thermal power systems. The AHAT (advanced humid air turbine) system has been studied to improve operational flexibility and thermal efficiency of the gas turbine power generation system. AHAT is an original system which substitutes the WAC (water atomization cooling) system for the intercooler system of the HAT cycle. A 3MW pilot plant, which is composed of a gas turbine, a humidification tower, a recuperator and a water recovery system, was built in 2006 to verify feasibility of the AHAT system. In this paper, ambient temperature effects, part-load characteristics and start-up characteristics of the AHAT system were studied both experimentally and analytically. Also, change in heat transfer characteristics of the recuperator of the 3MW pilot plant was evaluated from November 2006 to February 2010. Ambient temperature effects and part-load characteristics of the 3MW pilot plant were compared with heat and material balance calculation results. Then, these characteristics of the AHAT and the CC (combined cycle) systems were compared assuming they were composed of mid-sized industrial gas turbines. The measured cold start-up time of the 3MW AHAT pilot plant was about 60min, which was dominated by the heat capacities of the plant equipment. The gas turbine was operated a total of 34 times during this period (November 2006 to February 2010), but no interannual changes were observed in pressure drops, temperature effectiveness, and the overall heat transfer coefficient of the recuperator.Copyright