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

In order to combat global warming CO2 emission reduction from the iron and steel making industry is necessary. The Active Carbon Recycling Energy System for the iron making process (iACRES) has been developed as a technical option for substantial CO2 reduction. Lithium ortho-silicate (Li4SiO4, LS), which can separate high purity CO2 at high temperatures, is a suitable solid sorbent to capture CO2 from the iACRES process. In our previous studies, there was a problem that the absorption capacity of a cylindrical LS pellet decline to 80% in 5th cycle test. In this study, we clarified the cause of decline of absorption capacity and established new recipe of a cylindrical LS pellet. Our study showed the cause of the decline of absorption capacity was cellulose as a pore forming material. The picture by Fe-SEM shows the form of cellulose becomes elliptical in compression molding. Q-states Potts model that can simulate the time dependent porosity showed the time dependent change of elliptical pore was more urgent than that of spherical one. The structure of acetylene carbon black can stand pressure. As a result of using acetylene carbon black as a pore forming material, the absorption capacity was maintained above 95% in the 10th cycle test. However, acetylene carbon black is more expensive than cellulose. Therefore, the optimum addition amount of acetylene carbon black was determined by simulation incorporating dusty gas model. As a result, the optimum addition amount of acetylene carbon black was 7 wt% based on LS..

Solid oxide fuel cells (SOFC) are high-efficiency power generation systems, that are expected to be an important power source in the coming years. To increase the adoption of SOFC it is important to increase the power density and power generation efficiency while reducing the operating and materials costs. Electrode reaction of SOFC occurs only at effective Triple Phase Boundary (TPB) where network paths of electrons, oxide ions, and fuel gas meet uninterruptedly, and its formation state affects power generation performance. Therefore, in this study, we aimed to implement microstructure　expanding TPB between anode and electrolyte using Dimatix that is an inkjet 3D printer. In this fiscal year, we devised fabricable microstructure with Dimatix, and prepared anode ink. Acrylic particles were selected as pore forming material added to the anode ink in consideration of particle size and influence of viscosity. Parameters of microstructure were determined by numerical calculation of anode overvoltage. It was confirmed that defect free microstructure was produced by microscopic observation. A unit cell with microstructure demonstrated maximum power density of 302 mW/cm2 at 600oC under dry methane. Based on the above, we established manufacturing process of SOFC with microstructure.

While switching to an interactive system with a distributed power supply is required, fuel cell cogeneration systems capable of utilizing advanced energy are attracting attention. Among them, Solid Oxide Fuel Cells (SOFC) has high power generation efficiency and is expected as a promising power source. Cost reduction is indispensable for further dissemination of SOFC, and higher efficiency of power generation and High degradation resistance are cited to achieve this requirement. As for High degradation resistance, it is important to clarify performance degradation factors such as sintering and influence of impurities, but previous research have not led to quantitative discussion and model construction. In addition, since the experimental approach requires enormous number of trials and time, prediction of microstructure temporal change by numerical analysis is effective. Since it was inferred that the main factor of the change over time through literature research is "agglomeration of Ni particles", Using the Q - state POTTS model capable of simulating particle sintering in the solid phase, the factors of microstructure temporal change in the anode TPB were analyzed. As a result of sensitivity analysis of influential factors, it was suggested that a structure with Ni: GDC = 4: 6, particle size = 0.75 to 1.0 μm could maintain high structural characteristics in the long term, and this tendency was confirmed from the demonstration experiment.

In recent years, measures concerning electric vehicles have been announced around the world in response to the increasing global warming problem. Since the internal phenomenon of lithium ion batteries loaded in electric vehicles is complicated, there is no numerical analysis model capable of predicting battery performance. Therefore, the lithium ion battery is designed by repeating the battery trial manufacture and performance evaluation. However, since this method requires enormous cost and time to complete the battery, developing a numerical analysis model capable of predicting battery performance is required. To develop a numerical analysis model, it is necessary to clarify the rate limiting process inside the battery. Therefore, electron and material transport resistance of the particle interface (grain boundary resistance) not considered in the conventional model was interposed, and the influence was evaluated.
In the grain boundary resistance interposed model, it was possible to simulate the decrease of the discharge capacity retention rate. But a reasonable concentration gradient could not be obtained. From this fact, it was found that the grain boundary resistance is not the main cause of the decrease of the discharge capacity retention rate.
On the other hand, it was confirmed that the grain boundary resistance delays the relaxation of the cell voltage, which suggests that it is a factor of the relaxation delay.

To use the chemical absorption method, a large amount of the amine regeneration energy is needed. The amine regeneration energy consists of sensible heat, evaporation latent heat, heat of CO2 dissociation. Highly concentrated 2-amino-2-methyl-1-propanol (AMP) precipitates CO2 rich carbonate with a CO2 absorption reaction, thus sending the solid to stripper intensively can reduce sensible heat. However, the CO2 recovery remained 60-70% in conventional phase separation process, and solid separation was unstable. In this study, a precipitation characteristic was grasped by batch examination aiming to the cancellation of the process instability to be caused by phase transition. AMP+N-methyl-1,3-diaminopropane (MAPA) absorption liquid had high absorption rate, therefore it was used to a CO2 recovery experiment. In addition, it was predicted that the CO2 absorption quantity in the upper tower was increased by supplying CO2 semi-lean liquid after the centrifugal separation to absorber intermediate part. Hence, the middle injection process was simulated by using Aspen Plus. And the influence was confirmed experimentally. As a result, we found that regeneration energy was decreased and a CO2 recovery increased to 90% by the new process.

Carbon dioxide removal (CDR) at the scale of 10 GtCO2/y by the end of the century are necessary to achieve a 50% chance of meeting 2°C scenario. We present a profitable pathway from desalination waste brines to negative CO2 emissions. The method, termed ‘brine to bricks’ (BtB), mineralizes CO2 as nesquehonite (MgCO3˙3H2O) using the Mg content of brines. Fresh water, gypsum (CaSO4˙2H2O), halite (NaCl), mirabilite (Na2SO4･10H2O), sylvite (KCl), and hydrochloric acid are concurrently produced. To prevent ‘carbon leakage’, BtB does not rely on external chemicals, power, or captured CO2.
BtB selectively precipitates gypsum, halite, and mirabilite by evaporative concentration and temperature-control. The remaining Na+ and K+ ions are separated as halite and sylvite from a magnesium chloride slurry by hydrochloric acid-based precipitation. Super-azeotropic hydrochloric acid is regenerated from the slurry using a novel method: low hydration magnesium chloride addition. Purified magnesium chloride is decomposed to amorphous periclase (MgO) prior to reaction with CO2 in the ambient atmosphere.
The current CDR potential of BtB, including the CO2 emissions from desalination, is 136 MtCO2/y. In the current market, BtB can operate with a profit margin of $156-272/t-CO2, dependent primarily on the availability of waste heat and quality of renewable energy resources. Based on current desalination adoption projections, BtB could remove 0.343–1.783 GtCO2/y by 2050 while providing substantial increases in fresh water, construction materials, and chemicals that are of use to other CDR methods.
Testing validated perfect separation of magnesium from mock desalination brine at the flask scale. Thermal design of the system through pinch analysis was used to optimize heat utilization. The subsequent economic analysis showed that the installed cost of the evaporative concentration step was large, warranting further research.

The iron and steel industry accounts for approximately 48% of the CO2 emissions in the Japanese industrial sector, and therefore is investing in improvements to reduce the CO2 emissions. Meanwhile, the stock of scrap steel products is expected to increase in the future. Being already in the reduced state, such scrap can be regenerated to steel with lower CO2 emissions than iron ore. The "Packed bed type Partial Smelting Reduction furnace" (PSR), which concurrently smelts scrap and reduces iron ore, is a promising method to utilize scrap iron. This work evaluated the feasibility of combining PSR with top gas recycling, so-called the ‘SMART steelmaking system’. In the SMART system, CO2 derived from the PSR gas is reduced into CO or CH4 and recycled to the furnace as a reducing agent and heat source. The SMART furnace and other processes in the integrated steelworks were modelled in Aspen Plus. The model referencing the experimental value using a small furnace was developed into the industrial scale furnace for application to actual steelworks by modifying the Rist model. The CO2 emissions reduction and exergy analysis of the full-scale SMART furnace were performed. Increasing the scrap ratio by 5% consistently lead to a 4% reduction in CO2 emissions. Similarly, increasing the CO input rate by 100 kg/THM consistently resulted in a reduction of CO2 emissions of approximately 3%. The maximum CO2 emissions reduction of 22% was achieved at the condition of the operably highest scrap ratio and CO input rate.

In Tanegashima, milling of sugarcane is one of the main industries, and bagasse is burned at the bagasse boiler as biomass energy to generate steam for the sugar milling operation. However, bagasse is burned more than necessary due to management of the bagasse. Consequently, temperature of flue gas remains high and a large amount of unused heat around 200 oC is exhausted during raw sugar production period from winter to spring. On the other hand, many factories buy fossil fuel from outside the island to generate process steam around 120 oC by boilers throughout the year. In order to resolve this spatial and temporal thermal mismatch, we propose thermochemical energy storage and transport system using zeolite steam adsorption and regeneration cycle. We focused on the specific steam generator using zeolite adsorption heat which is called “zeolite boiler” was considered as the heat release equipment at the local heat demand. In this study, a zeolite boiler adapted to a cleaning factory was examined based on experiments and numerical calculations. In the small-scale demonstration test, superheated steam generation at 0.2 MPa at 125 oC was confirmed under conditions of a zeolite flow rate of 10 kg/h, an injection steam flow rate of 1.5 kg/h, and a produced steam flow rate of 1.68 kg/h, and the heat release rate was 10.5%. Moreover, the validity of the numerical calculation code was confirmed by comparing the temperature distribution of the zeolite bed, the outlet adsorption amount, and the heat release rate in the numerical calculation and experimental results. Performance prediction of a zeolite boiler that covers all heat demand of the cleaning plant based on numerical calculation code resulted in reduction of heavy oil of maximum 10 kL/y. In case economizer was introduced, the reduction of heavy oil increased about 2 kL/y.

Thermochemical energy storage and transport system using zeolite steam ad/desorption cycle is proposed to make up for a spatial and seasonal mismatch in terms of heat between sugar mill and heat demands in Tanegashima. Zeolite 13X was selected as a heat storage material considering minimum requirements like cost, accessibility to adsorbate, among other things. On the other hand, many heat storage materials with higher energy density than zeolite 13X have been studied. However, energy density depends on operation conditions of the heat discharging device (Zeolite Boiler) and the heat charging device (Heat Charger), therefore reported materials are not necessarily superior in this system. In this study, we conducted techno-economic analysis utilizing three types of zeolites with different ad/desorption characteristic and indicated design guidelines of materials by comparing the results.
As a base model, zeolite13X was applied to the system. Ad/desorption characteristic was obtained by experiments and literature data and embedded to the quasi-2D simulation code of Zeolite Boiler and Heat Charger. Each device was designed by parametric study, which could fix all capital expenditure (CAPEX) and operation expense (OPEX). The results of economic-analysis suggested that independent management of the system was difficult because OPEX was higher than revenue.
By utilizing the same scheme, techno-economic analysis of other zeolites was conducted. In this study, type Y (lower ad/desorption heat) and type LSX (higher ad/desorption heat, adsorption capacity) were selected. In type Y’s case, lower desorption heat contributed increasing mass flow rate of zeolite, however, total selling heat decreased because of lower adsorption heat and the profit decreased. In type LSX’s case, since dramatical increase of total selling heat due to higher adsorption heat overcame the effect of not charged well at charging station, the profit increased. Thus, materials with high ad/desorption heat and adsorption capacity is profitable in this system.