Manabu Yagi

Development of an Advanced Microturbine System Using Humid Air Turbine Cycle

A prototype machine for a next generation microturbine system applying a simple humid air turbine system (design target of electrical output: 150 kW, electrical efficiency: 35% LHV) was developed for its laboratory evaluation. A low NOx combustor which applied a lean-lean zone combustion concept and water lubricated bearings were developed for the prototype machine. Operation using two water lines for the humid air turbine (HAT) was proposed as an effective way to obtain rated electric output to ambient temperature of 40 deg C. Tests for the main components were done successfully. Motoring tests, full speed test with no load, 50% load and 70% load tests as preliminary tests for rated load tests were also carried out successfully. Low NOx emission of 7.6 ppm and high efficiency of 95.6% for the power conversion system were achieved in the partial load tests. At the first rated load test without HAT and Water atomizing inlet air cooling (WAC) that followed those partial load tests, 150.3 kW electric output with electrical efficiency of 32% was obtained.© 2004 ASME

Performance Improvement of a Centrifugal Compressor Stage by Increasing Degree of Reaction and Optimizing Blade Loading of a 3D Impeller

Performance improvement of 3D impellers in a high specific speed range was investigated using computational fluid dynamics analyses and experimental tests. In order to reduce the loss production within the stator passages, the backsweep angle of the impellers was increased. At the same time, the inlet-to-exit relative velocity diffusion ratio was also increased by increasing the impeller exit width to prevent the reduction in the pressure ratio. Moreover, the blade loading distribution at the impeller shroud side was optimized to suppress the surge margin reduction caused by the increased relative velocity diffusion ratio. Five types of unshrouded impellers were designed, manufactured, and tested to evaluate the effects of blade loading, backsweep angle, and relative velocity diffusion ratio on the compressor performance. The design suction flow coefficient was 0.125 and the machine Mach number was 0.87. Test results showed that the compressor stage efficiency was increased by 5% compared with the base design without reducing the pressure coefficient and surge margin. It was concluded that an increased relative velocity diffusion ratio coupled with large backsweep angle was a very effective way to improve the compressor stage efficiency. An appropriate blade loading distribution was also important in order to achieve a wide operating range as well as high efficiency.

Development of a 150kw Microturbine System Which Applies the Humid Air Turbine Cycle

A prototype machine for a next generation microturbine system incorporating a simplified humid air turbine cycle has been developed for laboratory evaluation. Design targets of electrical output were 150 kW and of electrical efficiency, 35% LHV. The main feature of this microturbine system was utilization of water for improved electrical output, as lubricant for bearings and as coolant for the cooling system of the generator and the power conversion system Design specifications without WAC (Water Atomizing inlet air Cooling) and HAT (Humid Air Turbine) were rated output of 129 kW and efficiency of 32.5% LHV. Performance tests without WAC and HAT were done successfully. Electrical output of 135 kW with an efficiency of more than 33% was obtained in the rated load test. Operation tests for WAC and HAT were carried out under the partial load condition as preliminary tests. Water flow rates of WAC were about 0.43 weight % of inlet air flow rate of the compressor and of HAT, about 2.0 weight %. Effects of WAC and HAT were promptly reflected on electrical output power. Electrical outputs were increased 6 kW by WAC and 11kW by HAT, and efficiencies were increased 1.0 pt % by WAC and 2.0 pt % by HAT. Results of WAC and HAT performance tests showed significant effects on the electrical efficiency with an increase of 3.0 point % and electrical output with an increase of 20% by supplying just 2.4 weight % water as the inlet air flow rate of the compressor.Copyright

Improving Flow Distribution in a Suction Channel for a Highly Efficient Centrifugal Compressor

Design parameters for suction channels of process centrifugal compressors were investigated, and an optimization method to enhance stage efficiency by using the new design parameters was proposed. From results of computational fluid dynamics, the passage sectional area ratios , and were found to be the dominant parameters for the pressure loss and circumferential flow distortion, where , and are passage sectional areas for the casing upstream side, casing entrance and impeller eye, respectively. The Base suction channel was optimized using the new design parameters, and the Base and Optimized types were tested. Test results showed that the Optimized suction channel achieved 3.8% higher stage efficiency than the Base suction channel while maintaining the same operating range.

Optimizing a Suction Channel to Improve Performance of a Centrifugal Compressor Stage

Design parameters for a suction channel of process centrifugal compressors were investigated, and an optimizing method to improve efficiency by using the new design parameters was proposed. Both pressure loss and circumferential flow distortion in the suction channel were evaluated by using computational fluid dynamics (CFD). The main dimensions, which had a large influence on pressure loss and circumferential flow distortion, were identified by using design of experiments (DOE). Next, the passage sectional area ratios Ac /Ae , Ae /As , and Ac /As were found to be the dominant design parameters for the pressure loss and circumferential flow distortion, where Ac , Ae and As are passage sectional areas for the casing upstream side, casing entrance and impeller eye, respectively. Then the shape of the suction channel was optimized using Ac /Ae , Ae /As , and Ac /As . Finally, to evaluate the improvement effect of optimizing the values of Ac /Ae , Ae /As , and Ac /As on compressor stage performance, a base suction channel and an optimized type of suction channel were manufactured and tested. The design suction flow coefficient was 0.1 and the peripheral Mach number was 0.78. Test results showed that the optimized suction channel achieved 3.8% higher stage efficiency than the base one while maintaining the overall operating range from surge to choke. The method for optimizing suction channels by using the three described design parameters was concluded to be very effective for improving the stage efficiency.Copyright

Performance Improvement of a Centrifugal Compressor Stage by Increasing Degree of Reaction and Optimizing Blade Loading of a 3D-Impeller

Performance improvement of 3D impellers in a high specific speed range was investigated using computational fluid dynamics (CFD) analyses and experimental tests. In order to reduce the loss production within the stator passages, the backsweep angle of the impellers was increased. At the same time, the inlet-to-exit relative velocity diffusion ratio was also increased by increasing impeller exit width to prevent the reduction in pressure ratio. Moreover, the blade loading distribution at the impeller shroud side was optimized to suppress the surge margin reduction caused by the increased relative velocity diffusion ratio. Five types of unshrouded impellers were designed, manufactured and tested to evaluate the effects of blade loading, backsweep angle and relative velocity diffusion ratio on compressor performance. The design suction flow coefficient was 0.125 and the machine Mach number was 0.87. Test results showed that compressor stage efficiency was increased by 5% compared to the base design without reducing the pressure coefficient and surge margin. It was concluded that an increased relative velocity diffusion ratio coupled with large backsweep angle was a very effective way to improve compressor stage efficiency. An appropriate blade loading distribution was also important in order to achieve a wide operating range as well as high efficiency.Copyright

Verification of Performance and Operating Characteristics of High Pressure Gas Injection Centrifugal Compressor

The development process of a 70-MPa high pressure compressor for oil and gas applications is presented in this paper. Great attention was paid to any relevant technical challenges due to the high design pressures, such as the material selection, deformation casing structure, stability of the rotordynamics, and the aerodynamic performance. Among the technical considerations, some technical findings for the operational tests are proposed in this paper as well.Copyright

Starting Characteristic Analysis of a Radial Inflow Turbine for the Regenerative Brayton Cycle

Microturbines have been developed as compact gas turbines to be applied in the regenerative Brayton cycle. A typical microturbine is composed of a centrifugal compressor and a radial inflow turbine. As such, the microturbine has a starting characteristic peculiar to radial inflow turbines. An idling state known as the windage point for mass flow rate can be formed because of improper inlet flow conditions for turbine expansion flow. The present study looked at the relationships between the radius ratio of the radial inflow turbine to the centrifugal compressor and the starting characteristic and at the effects of turbine inlet flow conditions on the starting characteristic. Fundamental equations for the relationships between the radius ratio and the starting characteristic were obtained. Effectiveness of the equations was compared with experiment results obtained with a 150 kW class prototype microturbine.

Effects of Return Channel With Splitter Vanes on Performance of Multistage Centrifugal Compressor

The effects of a return channel with splitter vanes on the performance of a multistage centrifugal compressor were investigated. As a preliminary study, the optimum location of the splitter vanes was numerically examined with the aim of achieving high overall efficiency. The results indicated that the optimum location was the 30% of the normalized pitchwise distance from the suction side of the main vane, with the leading-edge located at a radius ratio to the main vane trailing-edge of 1.77. To investigate the effects of the return channel with and without the optimum splitter vanes on the overall performance, performance tests were carried out using a one-and-half-stage test rig. Three pre-swirl vanes, whose vane angles from the tangential direction at the trailing-edge were 20, 30 and 40° were used to simulate three operating conditions with low, design and high flow coefficients, respectively. The design flow coefficient of the downstream impeller was 0.073 and the peripheral Mach number was 0.87. The test results showed that the return channel with the optimum splitter vanes achieved 11.8% higher overall efficiency at the high flow coefficient with respect to the case without the splitter vanes while maintaining the same efficiency at both low and design flow coefficients. The return channel with the optimum splitter vanes was concluded to be effective for improving the efficiency of a multistage centrifugal compressor.Copyright

Evaluation of Axial Compressor Characteristics Under Overspray Condition

An axial compressor was developed for an industrial gas turbine equipped with a water atomization cooling (WAC) system, which is a kind of inlet fogging technique with overspray. The compressor performance was evaluated using a 40MW-class test facility for the advanced humid air turbine system. A prediction method to estimate the effect of WAC was developed for the design of the compressor. The method was based on a streamline curvature (SLC) method implementing a droplet evaporation model. Four test runs with WAC have been conducted since February 2012. The maximum water mass flow rate was 1.2% of the inlet mass flow rate at the 4th test run, while the design value was 2.0%. The results showed that the WAC decreased the inlet and outlet temperatures compared with the DRY (no fogging) case. These decreases changed the matching point of the gas turbine, and increased the mass flow rate and the pressure ratio by 1.8% and 1.1%, respectively. Since prediction results agreed with the results of the test run qualitatively, the compressor performance improvement by WAC was confirmed both experimentally and analytically. The test run with the design water mass flow rate is going to be conducted in the near future.Copyright