Sanyo Takahashi

Development of Anode Gas Recycle System Using Ejector for 1 KW Solid Oxide Fuel Cell

An anode gas recycle system using an ejector for 1 kW solid oxide fuel cells (SOFCs) was developed to increase the electrical efficiency of combined power generation. We call this an AGR-SOFC (anode gas recycle-solid oxide fuel cell). The effects of recirculation ratio, externally steam feed rate, and fuel utilization were determined experimentally on the AGR-SOFC performance (i.e., output power, stack temperature and gas composition) using a variable flow ejector and a recirculation ratio of 0.55–0.62, overall fuel utilization of 0.72–0.84, and steam feed rate of 0–1.5 g/min. A quadrupole mass spectrometer was used to identify the recirculation ratio, the gas composition of reformed gas at the AGR-SOFC inlet, and that of the recycle gas at the outlet. Compared to one-path SOFC systems i.e. without an anode gas recycle, the AGR-SOFC was stable and generated about 15 W more electricity when the overall fuel utilization was 0.84 and the recirculation ratio was 0.622 with no steam supply. This improved performance was due to the reduced H2O concentration in the anodic gas. In addition, although the recirculation ratio did not affect the AGR-SOFC performance, a high recirculation ratio can provide steam produced via the electrochemical reaction to the injected fuel for the steam reforming process.Copyright

Development of Anode Gas Recycle System Using Ejector for 1 kW Solid Oxide Fuel Cell

An anode gas recycle (AGR) system using an ejector for 1 kW solid oxide fuel cells (SOFCs) was developed to increase the electrical efficiency of combined power generation. We call this an AGR–SOFC. The effects of recirculation ratio, externally steam feed rate, and fuel utilization were determined experimentally on the AGR–SOFC performance (i.e., output power, stack temperature, and gas composition) using a variable flow ejector and a recirculation ratio of 0.55–0.62, overall fuel utilization of 0.720–84, and steam feed rate of 0–1.5 g/min. A quadrupole mass spectrometer was used to identify the recirculation ratio, the gas composition of reformed gas at the AGR–SOFC inlet, and that of the recycle gas at the outlet. Compared to one-path SOFC systems, i.e., without an AGR, the AGR–SOFC was stable and generated about 15 W more electricity when the overall fuel utilization was 0.84 and the recirculation ratio was 0.622 with no steam supply. This improved performance was due to the reduced H2O concentration in the anodic gas. In addition, although the recirculation ratio did not affect the AGR–SOFC performance, a high recirculation ratio can provide steam produced via the electrochemical reaction to the injected fuel for the steam reforming process.

Conceptual Investigation of a Small Reheat Gas Turbine System

The mirror gas turbine proposed by Tsujikawa and Fujii extends the applications of turbo machinery. The characteristic component of a mirror gas turbine is a thermal generator, which is a kind of “inverted Brayton cycle”. The operating sequence of the thermal generator is reverse that of an ordinary gas turbine, namely, the hot working fluid is first expanded, and then cooled, compressed, and finally exhausted. In this work, we investigated the theoretical feasibility of inserting a thermal generator to a small reheat gas turbine of 30–100kW classes. Using process simulator software, we calculated and compared the thermal efficiency of this reheat gas turbine to that of a micro gas turbine under several conditions, turbine inlet temperature. This comparison showed that the performances of the both gas turbines are significantly influenced by the performance of the heat exchanger used for the recuperator. The efficiency of the micro gas turbine is also improved by using water injection into the compressor to cool the inlet gas. The resulting thermal efficiency of this reheat gas turbine is about 7% higher than that of a micro gas turbine with the same power unit.Copyright

Potential of a Reheat Gas Turbine System Using Inverted Brayton cycle

The concept of a small reheat gas turbine system is proposed and discussed. This reheat gas turbine consists positive-pressure part (Brayton cycle), negative-pressure part (inverted Brayton cycle) and heat exchangers. The system components are interchangeable with the micro gas turbine. This system can supply hot water and steam. This paper describes that the introduction of reheat and an inverted cycle to a fixed Brayton cycle is explored from various views. The thermal efficiency of electric power output (EFFEP ) has a peak and thermal efficiency of heat output of hot water 1 (EFFQHW1 ) decrease with increase of the pressure ratio of Vacuum Turbine (PRVT ). The thermal efficiency of heat output of hot water 2 (EFFQHW2 ) increases monotonously with PRVT . The overall efficiency of the improved cycle for cogeneration increases with PRVT although the overall efficiency of the original cycle decreases monotonously with PRVT . The PURPA efficiency of improved cycle has the peak around PRVT = 4. In the type2 cycle EFFEP has a weak peak of 31.4% when the inlet pressure of combustor 2 (Pcomb2 ) is 0.14MPa. The overall efficiency increases with Pcomb2 . PURPA efficiency has a weak peak at Pcomb2 = 0.16MPa. Two axes system is examined. EFFEP reaches to 30.2% at the maximum. EFFQHW1 decreases slightly with increase of PRVT . EFFQHW2 increases with PRVT . The overall efficiency increases with PRVT . The PURPA efficiency also increases with PRVT .Copyright

Influence of Radiation Reabsorption on Laminar Burning Velocity of Methane Premixed Flame Composed With Steam and Carbon Dioxide

Replacing the Nitrogen with another kind of inert gas such as steam and Carbon dioxide is effective for both reducing NOx and enhancing system efficiency in gas turbine combustor. But the flame properties of such radiative mixture are complicated because of the third body effect and radiation reabsorption. So, we made detailed chemical kinetic calculations including the effect of radiation reabsorption to clarify the premixed laminar flame speed of such mixture as one of the most important properties for controlling the combustion. The concentrations of mixture are varied, and addition of other species such as Carbon monoxide and Hydrogen are also calculated to simulate the utilization of reforming gas and partially oxidized gas. And the pressure was varied up to 5.0 MPa to simulate the 1700 °C class combined gas turbine system. The results show remarkable incensement of laminar burning velocity by considering the radiation reabsorption. Laminar burning velocities were accelerated up to 150% in cases of Methane–Oxygen and steam or Carbon dioxide mixture. It was found that preheating of upstream-unburned mixture caused this acceleration. And the influence of radiation reabsorption was much larger in case of lower pressure.Copyright

Performance of a Small Reheat Gas Turbine System as a Cogeneration System

We proposed the concept of a small reheat gas turbine system. This reheat gas turbine consists positive-pressure part (Brayton cycle), negative-pressure part (inverted Brayton cycle) and heat exchangers. The system components are interchangeable with the micro gas turbine. This system can supply hot water and steam. However, we focused on the electric efficiency in the previous paper. This paper describes the performance of a small reheat gas turbine system from a point of view as a cogeneration system. The efficiency of electric power output is over 32% and the efficiency of heat output is only 15–20%. So overall, efficiency is about 50%. Therefore, we improved the heat recovery system of a small reheat gas turbine system. As a result, the overall efficiency becomes over 60% and consumption of cooling water reduces extremely. PURPA is over 50% when TIT is over 1573K.Copyright

Expermiental Study of Gas Combustion Fluidized Bed and Radiation Contribution toHeat Transfer inside the Bed.

Radiation contribution to the total heat transfer at the immersed surface in high-temperature fluidized beds has been a controversial subject. Some investigators have reported that it is significant, and others say it is not. The controversy has resulted from the ambiguity of the specification of the temperatures of the beds and heat transferring surfaces. Most experiments were conducted in a combustion fluidized bed with water-cooled tubes immersed in the beds. Radiation effects might not appear when the surface temperatures are low, even if the bed temperatures are high. In this report, a gas-cooled thin tube was immersed in a gas combustion fluidized bed, in order to keep both the bed and tube temperatures high enough to observe the radiation effects. The results show that the radiation contribution to total heat transfer becomes significant as both the tube and bed temperatures increase. The transient temperature profiles and the characteristics of the exhaust gas of the gas combustion fluidized bed are also reported.

Ammonia concentration measurement using oxidizing catalyst.

With the aim of application to the measurement of ammonia concentration, an ammonia converter was constructed using commercially available platinum catalyst. The dependences of the ammonia converter efficiency on reaction temperature and ammonia concentration were investigated by measuring the concentration of the converted nitric oxide. The results have shown that the catalyst used almost completely oxidizes ammonia into nitric oxide at temperatures above 600°C in the tested range of ammonia concentration. In addition, the combination of the ammonia converter and a chemiluminescent NOx analyzer was found to be able to measure ammonia concentration in an ammonia-nitric oxide mixture with a precision within 3% by making a correction due to oxygen concentration.