Our research focuses on CO2 emission reduction of energy conversion systems in terms of exergy engineering.

In chemical absorption method, a large quantity of regeneration energy is required for stripping CO2 and regeneration of solution and needed to be reduced. Solid-liquid phase separation process using high concentration 2-Amino-2-methyl-1-propanol (AMP) solution can reduce sensible heat by separating and sending precipitated carbonate with absorption of CO2 to stripper. In conventional phase separation process, sensible heat was decreased by 50%, however increasing the amount of precipitated carbonate can be expected to reduce energy further. In this study, precipitation conditions of AMP solution were explored by experimentation and precipitation method was changed to secondary nucleation in metastable zone width (MSZW) to control of the amount of carbonate. MSZW of AMP solution was defined 33-44 degree by the measurement of solubility and supersolubility. The heat exchanger and jacket type precipitation container were designed based on results of testing to cool the solution to the temperature of precipitation and keep it warm. The regeneration energy was evaluated by CO2 capture and recovery tests using the improved apparatus. As a result, separation rate of solid phase increased and regeneration heat was decreased compared to the conventional process.

Among CO2 capture technologies, chemical absorption method by aqueous amine solutions is the most technically mature and have a wide range of applications for its practicability and maneuverability on the traditional energy-intensive industries. One of the critical issues preventing the rapid deployment of chemical absorption method is the degradation of amine-based absorption solution over the long-term operation. Various undesired compounds which affect the solution composition are generated from amine degradation and result in alteration in solution properties and the deterioration of capture process performance. The total acidity and alkalinity are relevant to the type and the concentration of degradation products and reflect the change of the solution composition.
A holistic approach quantifying the total acidity/alkalinity without the identification of all degradation compounds by titration was proposed in this research. A degraded solution of aqueous monoethanolamine (MEA) solution was made by 750 hours continuous operation of a bench-scale, 10kg/day CO2 capture apparatus in the laboratory. The simulated degraded solution which has a same acidity/alkalinity with the real degraded solution was prepared according to the titration results. The CO2 capture experiments for these degraded solutions were performed under the same conditions to experimentally investigate the effect of total acidity/alkalinity on solution properties and understand the mechanisms leading to the variation in operating characteristics.
As a result, it was confirmed that total acidity/alkalinity is the dominant influencing factor in vapor-liquid equilibrium characteristics of the solution based on the good reproducibility of CO2 loading profile in the absorber. Besides, the simulated degraded solution accurately simulated the real degraded solution from the perspectives of CO2 capture rate and the vapor pressure at the outlet of the stripper.

In recent years, global warming has become one of the most serious problems around the world, so various measures are developed to reduce greenhouse gas emissions. Considering the sustainability for environment and economy, CO2 capture and utilization (CCU) technology applied to the iron making process (iACRES) is being promoted. From the perspective of energy saving, Lithium ortho-silicate (Li4SiO4, LS) is the optimal CO2 absorbent for application in iACRES. It is desirable to design a practical honeycomb type which balances absorption rate, pressure loss and absorption capacity. In this study, we analyzed the CCU system for iACRES and designed the application of honeycomb type LS to experimental equipment. Since the calorific value of the blast furnace gas (BFG) is low, 30% of combusted BFG can be branched and operated with a recovery rate of about 80% in the absorption tower to make the absorption heat during the regeneration process self-supporting. Assuming switched in 40 minutes, it can be predicted that the required LS amount is 259t in a full-scale 5,000 m3 blast furnace, and the CO2 recovery amount is 92t / 40min. This reaction tower has a diameter of 4.9 m, a height of 15 m, an internal volume of 261 m3, and the space velocity is about 3128 h-1 at a packing ratio of 75%. Matching the space velocity, the absorption behavior during the experiment was predicted with the honeycomb type LS which is suitable for the experimental space on campus.

Solid Oxide Fuel Cells (SOFC) are high efficiency power sources and expected to be distributed power sources. However, to accelerate the penetration of SOFC, it is important to reduce the material and manufacturing cost by increasing the single cell power density. Unlike the other heat engines, SOFC can convert the chemical energy of fuel into electricity directly. Since the electrochemical reaction of SOFC occurs only at the triple phase boundary (TPB), composed of the electrode as the electron path, the electrolyte as the oxide ion path and the pore for the fuel flow. In order to increase the TPB density, this research aimed to make a multilayered cross-hatched microscale geometry. The structure is produced by squeegeeing the electrode and electrolyte slurry and removing negative step by step. It is called nega-posi method. The negative is made of polyvinyl alcohol (PVA) which is water soluble resin and polylactic acid (PLA) which is thermoplastic resin by using fuse deposition modeling 3D printer. Water insoluble electrode slurry is composed of NiO, N-methylpyrrolidone (NMP) and polyvinyl butyral (PVB). Electrolyte slurry which squeegeed after water dissolve is composed of yttria stabilized zirconia (YSZ), pure water and polyvinylpyrrolidone (PVP) + YB-132A. Addition rate of the binder is determined to be 10wt%. It is achieved 84.6% filling rate by squeegeeing with high concentration (82.8wt%) and high viscosity (13800 Pa･s when shear velocity is 1 /s) slurry. The sintering is successfully produced by the heating process considering the oxidation and heating reaction of the resin. Finally, we have succeeded to make the cross-hatched structure made of electrode and electrolyte..

An electric vehicle does not emit carbon dioxide while driving. However, there is a problem that the energy density of the secondary battery is low. A lithium-air battery is attracting attention because they have a theoretical capacity about 10 times that of lithium-ion batteries. However, the diffusion of oxygen in the electrolytic solution is rate-determining, and it has not been put into practical use.
In this study, we conducted a discharge experiment of a lithium-air battery, fitted it with a one-dimensional model, and then investigated the oxygen transport resistance due to the structure of the positive electrode. As a result, it was found that the tortuosity has a great influence on oxygen transport. Therefore, when constructing a three-dimensional model and examining a structure with a small tortuosity , a structure in which electrodes were arranged parallel to the direction of the separator from the air source to secure an oxygen transport path had a low tortuosity and oxygen transport resistance. When a new structure was constructed based on the above and the discharge capacity was fitted with a one-dimensional model, it was found that the tortuosity of the new structure was smaller than that of the positive electrode used in the discharge experiment. In addition, focusing on the fact that the transport in the gas phase is faster than that in the liquid phase, we devised a structure in which the transport path of the gas phase was inserted in the positive electrode, and calculated the conditions for achieving the theoretical capacity under the experiment conditions of this study.

In the basic energy plan announced by the government, nuclear power is positioned as an important base load power source from the viewpoint of 3E+S strategy (Energy Security, Economic Efficiency, and Environment + Safety). Hydrogen countermeasures in the event of a severe accident are one of the important issues to ensure the safety of nuclear power plant. In the hydrogen treatment system using CuO(Ⅱ), there is an induction period at the beginning of the reaction. In this study, we focused on the changes in the surface structure of CuO(Ⅱ) and the crystal structure peculiar to the surface, which are considered to be the causes of the induction period and compared and evaluated the experimental values and the calculation model for the effects of these on the induction period. Changes in the surface structure were measured by SEM image analysis on the CuO(Ⅱ) surface before and after the reduction reaction. As a result of evaluation by a numerical calculation model incorporating the change of the surface structure, it was found this was not the main factor of the induction period. The crystal structure peculiar to the surface was analyzed by using TEM and XPS on the CuO(Ⅱ) surface. Two types of binding energies, 933 eV and 931 eV, were measured before and after the reduction reaction, and it was presumed that the latter was a crystal structure peculiar to the surface, and different correction terms were given to the reaction rate equation for hydrogen adsorption before and after the induction period. The calculation results generally simulated the behavior of the unsteady reduction reaction including the induction period and proved that the influence of the site that is poor at adsorbing hydrogen is dominant during the induction period.

In Tanegashima, a sugar mill burns sugarcane bagasse as biomass fuel and exhausts a lot of unused heat about 200 oC during sugar milling period. On the other hand, many factories in the island require process steam about 120 oC through a year and now obtain this steam by burning imported heavy oil. Thermochemical energy storage and transport system utilizing zeolite steam adsorption and desorption cycle can overcome this spatial and seasonal heat mismatch. This system is divided into three processes: heat storage of zeolite at a sugar mill, transportation to heat demand factories, and heat output at there. This study focused on the heat output process of the system, and “zeolite boiler” employing moving bed and indirect heat exchanging process was devised as a pressurized steam generator. A cleaning factory in the industrial department and a hotel in the consumer / business department was assumed as heat demand areas, and parameters of the full-scale zeolite boiler installed in these areas was decided.
A rectangular zeolite boiler with a plate-fin-tube heat exchanger was devised as a full-scale zeolite boiler. the performance of this zeolite boiler was predicted by constructed 2D numerical model. As a result, the difference between the 2D analysis and the 1D analysis was only 0.4% in the heat increase rate. From the above, the 1D model has been adopted as a design tool of the rectangular zeolite boiler.
The 1D unsteady numerical model was constructed by modifying the 1D steady model. The validity of this model was confirmed by comparing the analysis results with the test results. When the performance of the full-scale zeolite boiler was predicted by this model, it was found that the temperature distribution at the start of the zeolite boiler had almost no effect on the fuel reduction.
Based on unsteady numerical analysis, the parameters of the full-scale zeolite boiler installed in a cleaning factory and a hotel was decided, and the fuel reduction by installing the zeolite boiler was predicted. As a result, an annual fuel reduction of about 8.6 kL in the cleaning factory and 49 kL in the hotel is expected.
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Combined production system of sugarcane byproducts which are ethanol production from molasses, excess electricity using surplus bagasse and heat demand of unused heat in sugar mill is focused in recent years. Sugar and ethanol combined production system is operated already in the world, and it is researched in Tanegashima. On the other hand, in Tanegashima heat charging process of thermochemical energy storage and transport system utilizing zeolite steam adsorption and desorption cycle is proposed to resolve spatial and seasonal thermal mismatch between unused heat source exhausted from a sugar mill operating winter to spring and heat demand in vicinal industry consuming imported fossil fuel all year around, too. Also, changing cultivated variety of sugarcane on the large scale to 2050 is planned in Tanegashima. In this study, I conducted design of sugar and byproducts from sugarcane combined production system of some sugarcane varieties.
Conducted sugarcane varieties are NiF8 which is major variety in Tanegashima and other three varieties which are high yielding, high yielding of ratooning and early high sugar. Furthermore, I considered two types of milled sugarcane flow which are conventional operation and high loading operation in other three varieties. Available steam to byproducts production process of each case calculated. First, in ethanol production process from molasses, about 73% input energy is for distillation process and supply of steam is necessary for this process. Second, this study is focused on distillation process and it was calculated about 3.7 kg-Ethanol/kg-steam by process flow diagram aimed at distillation process. Also, additional power generation for electricity using surplus bagasse puts additional steam to steam turbine in sugar mill. The additional generating electricity possible quantity calculated 150-400 kW in cases. Third, in heat charging process, blower power consumption for heat charging, fuel saving of heat discharging and some design parameters in the heat discharging device named “Zeolite Boiler” and the heat charging device named “Heat Charger”.
In combined production system, because the profit of ethanol production and additional power generation increases to supply steam flow, the system profit of each process is maximized to supply maximum steam flow to each process. On the other hand, the more the profit of the fuel saving increases involved steam supply in ZB, the more the cost of blower power consumption increases in HC. So, the system profit of combined production system is maximized to supply 1) maximum steam flow of ethanol production and additional power generation and 2) steam adjusted cost balance between fuel saving and blower power consumption of surplus steam to heat charging process in all cases of four sugarcane varieties and two operation types.