Hidefumi Araki

Evaluation of energy storage method using liquid air

An energy storage system using liquid air for high storage efficiency is studied. Liquid air is produced by off-peak power and can be stored at atmospheric pressure in a large tank. When on-peak power is needed, the stored liquid air is pumped to high pressure and fed to the combustor of a gas turbine. Then, power generation is more than doubled from that of a system with an ordinary air compressor. Furthermore, energy storage efficiency of this system is significantly increased above that of a pumping-up power plant when low-temperature liquid air is used to produce new liquid air.

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

The advanced humid air turbine (AHAT) 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 (1, 3.2, 10, 32, and 100 MW) 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 1 m for the lowest pressure ratio case, and 6 m for the highest pressure ratio case.

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

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

An Evaluation of Advanced Humid Air Turbine System With Water Recovery

The AHAT (Advanced HAT) system can be used for single shaft gas turbines without redesigning them and it gives a similar effect as intercooling by using suction air atomization. In this paper, two basic experiments with a spray nozzle, simplified humidifier and water recovery were carried out. A compact heat exchanger for humidified gas turbines could be realized by using the spray nozzle without significant pressure loss. In addition, a big effect was found in the efficiency improvement when water atomization into the compressor was combined with the regenerative cycle. The AHAT system had high efficiency, 5% higher compared with the mid-size combined cycle.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

An Experimental and Analytical Study on the Advanced Humid Air Turbine System

The Advanced Humid Air Turbine (AHAT) is a regenerative cycle using high-humidity air. This system improves the gas turbine thermal efficiency by using high-humidity air without needing high firing temperature and pressure ratio. It is estimated AHAT cycle thermal efficiency exceeds that of combined cycle if it is designed by the optimum conditions, and the efficiency difference grows especially by the small and medium-size gas turbine. To verify the system concept and cycle performance of AHAT system, AHAT verification plant construction began in April 2005 and completed in September 2006. The plant that consists of a gas turbine with a two-stage radial compressor (pressure ratio of 8), a two-stage axial turbine, a reverse-flow type of single-can combustor, a recuperator, a humidification tower, a water recovery tower, an economizer, and other components. It is planned to validate performance and reliability of the AHAT system. Expected performance is: rated output 3.6 MW, efficiency 43% (LHV), and NOx emissions less than 10 ppm at 16% O2. This paper describes the system verification plant constructed, a news flash of integrated test results, and so on.

Test Results of 40MW-Class Advanced Humid Air Turbine and Exhaust Gas Water Recovery 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 advanced humid air turbine (AHAT) system has been studied to improve operational flexibility and thermal efficiency of gas turbine power generation systems. A 40MW-class AHAT test facility was built and the rated output was achieved. Through operations at the facility, it has been verified for the first time that the key components of the medium-class gas turbines, such as an axial compressor and multi-can combustor, can be applied to the AHAT system. The cold start-up time from ignition to rated power was about 60 min, which is approximately one-third that of a conventional gas turbine combined cycle (GTCC) plant. NOx emissions were 24ppm (at 16% O2) when the humidity of combustion air was approximately a half that of present commercial AHAT plants, and NOx emissions in a future commercial AHAT system were thought to be less than 10ppm. A water recovery system which recovers water from a part of the exhaust gas of the 40MW-class test facility was built and test operations were made from June 2013. In this paper, water recovery test results as well as the 40MW-class gas turbine test results are shown.Copyright

Progress of the 40MW-Class Advanced Humid Air Turbine Tests

A 40MW-class test facility has been constructed to verify practicability of applying the advanced humid air turbine (AHAT) system to a heavy-duty gas turbine. Verification tests have been carried out from January 2012, and interaction effects between the key components were established.First, water atomization cooling (WAC) was confirmed to contribute to both increased mass flow rate and pressure ratio for the axial flow compressor. The good agreement between measured and calculated temperatures at the compressor discharge was also confirmed. These results demonstrated the accuracy of the developed prediction model for the WAC.Second, a control method which realized both flame stability and low NOx emissions was verified. Although the power output and air humidity were lower than the rated values, NOx concentration was about 10 ppm.Finally, a hybrid nozzle cooling system, which utilized both compressor discharged air and humid air, was developed and tested. The metal surface temperatures of the first stage nozzles were measured, and they were kept under the permissible metal temperature. The measured temperatures on the metal surface reasonably corresponded with calculation results.Copyright

Study of Humid Air Gas Turbine System by Experiment and Analysis

Humid air gas turbine systems that are regenerative cycle using humidified air can achieve higher thermal efficiency than gas turbine combined cycle power plant (GTCC) even though they do not require a steam turbine, a high combustion temperature, or a high pressure ratio. In particular, the advanced humid air gas turbine (AHAT) system appears to be highly suitable for practical use because its composition is simpler than that of other systems. Moreover, the difference in thermal efficiency between AHAT and GTCC is greater for small and medium-size gas turbines. To verify the system concept and the cycle performance of the AHAT system, a 3MW-class pilot plant was constructed that consists of a gas turbine with a two-stage centrifugal compressor, a two-stage axial turbine, a reverse-flow-type single-can combustor, a recuperator, a humidification tower, a water recovery tower, and other components. As a result of an operation test, the planned power output of 3.6MW was achieved, so that it has been confirmed the feasibility of the AHAT as a power-generating system. In this study, running tests on the AHAT pilot plant is carried out over one year, and various characteristics such as the effect of changes in ambient temperature, part-load characteristics, and start-up characteristics were clarified by analyzing the data obtained from the running tests.Copyright