An ultrasonic measurement system was development as a method for inspecting inside the primary containment vessel (PCV), especially for identifying leakage points and determining fuel debris distribution in the decommissioning of Fukushima Dai-ichi nuclear power plant. This measurement system has a liner array sensor and enables the obtaining of both 2-D flow map and reconstructed image of echo intensity distributions at once using Ultrasonic Velocity Profiler (UVP) and aperture synthesis method respectively. In other words, the developed system can visualize flow behavior and determine object surface at the same time and therefore has possibility to carry out the inspection efficiently. Additionally, pulse compression method was incorporated to expand the measurement depth. To verify the practicality of the developed system, it was applied to an experimental situation as may be expected inside the PCVs. As a result, the location of a leakage point and shape of mock fuel debris were estimated from a 2-D flow map and reconstructed image using proposed method.

View full abstract

This paper introduces methods on estimating dynamic Liquified Natural Gas (LNG) volume and tank temperature on LNG vessel throughout the laden (full) and ballast (empty) voyage by calculating the overall heat leakage of the tank using heat transfer equations involving conductive and convective heat flow based on parametric approach. This study considers a simplified model consisting of 4 layer tank based on tanks used in an actual LNG vessel. The methods involve analyzing tank structure, determining thermal resistance of both steady conductive and convective heat flows through spherical tank, volume and temperature estimation formulation as function of time and performing data analysis on raw data to empirically determine the evaporation ratio of LNG sprays as function of LNG volume. The results produced based on a two week voyage of a five tank vessel are compared with actual raw data and the comparisons are analyzed in this paper.

View full abstract

Regarding the storage of fuel debris accompanying the decommissioning of the Fukushima Daiichi Nuclear Power Plant, management of hydrogen gas generated by water radiolysis is indispensable. For this reason, it is important to maintain the concentration of hydrogen in the sealed container below the explosion limit value in order to improve the safety of long-term waste storage containers. Then, it was considered that the generated hydrogen and oxygen are recombined with the passive autocatalytic recombiner installed in the storage container and returned to water. Preliminary numerical simulations were performed to confirm the effectiveness of the passive autocatalytic recombiner and hydrogen behavior in the storage container. The present study shows results of the preliminary simulations.

View full abstract

It is necessary to assess the quantity of ash deposition and frequency of ash dropping to prevent troubles caused by clinker ash in coal fired boilers. It is considered that the time trend of heat absorption shows how much ash is deposited and that the Fourier transformation of the trend shows frequency of ash dropping. Actually the analysis of the heat absorption in pendant superheater tubes indicated both of different two characteristics. When slag remover was used, the Fourier transform indicates that the frequency of ash dropping became high compared with the case in which it wasn't used.

View full abstract

Responses of premixed laminar Bunsen flame to transient change in fuel gas composition has been investigated experimentally. Mixture of methane, ethane, and propane is used as a model of natural gas. The volumetric fraction of methane was varied from 92 % to 76 % by 4 %, keeping ethane/propane ratio 5 constant. Transition time of the fuel composition was changed from 1 to 20 sec. The flow velocity at the exit of the burner was 0.8 m/s. The distance between the fuel mixing point and the air and fuel mixing point L was changed from 0 to 1500 mm. A flame motion was recorded by a high speed video camera at 60 fps, and variation of the flame height was measured The flame height temporarily exceeded or fell below the steady flame height during the transition even though the equivalence ratio of mixture before and after the transition set the same. When a density meter was set in the flow channel to detect the fuel composition variation, the temporary flame height be suppressed.

View full abstract

The radioactive aerosol removal equipment is used as one of the safety systems of nuclear reactors. In this equipment, aerosol particles remove through gas-liquid interfaces formed in two-phase flow. The mechanism related to the removal of small particles through the gas-liquid interface is not clear, a numerical evaluation method of performance of aerosol removal equipment is not realized. In this situation, we have started to construct a numerical simulation method to simulate aerosol removal through a gas-liquid interface in two-phase flow. In this simulation method, detailed two-phase flow simulation code TPFIT developed in JAEA is used. TPFIT adopts the advanced interface tracking method and can simulate interface movement and deformation directly. In addition, to simulate the movement of aerosol particles in twophase flow, the Lagrangian particle tracking method is incorporated in TPFIT. By using the advanced interface tracking method and the Lagrangian particle tracking method, the correlation between interfaces and aerosol particles can be simulated in detail. To solve the Lagrangian equations of particles, fluid properties are evaluated by considering the distance between interface and particle, to simulate particle movement near the interface and through an interface. In this report, outline and preliminary results of this simulation method are shown.

View full abstract

An aerosol particle collection by liquid droplets has been applied in many industries. One example of this is the radioactive aerosol removal system in the safety system of the nuclear reactor. However, the mechanism related to the removal of fine particles through the gas-liquid interface is not clear. In the present study, the direct observation of micro-scale aerosol particle behavior on gas-liquid interface was performed to clarify the aerosol particle capturing behavior by droplets. The experiment was performed under the condition simulating the relative velocity between the droplet and the aerosol particle by fixing the droplet to the tip of the syringe needle in order to observe micro-scale CsI aerosol particles with a high-speed video camera with objective lens. We confirmed three cases of the capturing behavior; “particle penetration into the drop”, "deposition on the droplet interface" and "deposition on the interface after moving to slide on the droplet interface". Especially, “particle penetration into the drop” and "deposition on the interface after moving to slide on the droplet interface" are new capturing behavior model which are not considered in previous studies.

View full abstract

In this study, SiO₂ nanoparticles formation in the premixed flame have been investigated. Hexamethyldisiloxane (HMDSO) was used as the precursor of nanoparticles. The average primary particle increased with the feed rate of HMDSO as also described in the previous studies by other researchers. When the feed rate of HMDSO was constant, it was difficult to evaluate the molar fraction of Oxygen in the premixed flame. The primary particle size decreased with the average velocity in taking account of adiabatic flame temperature and then approached a constant value at a constant HMDSO feed rate even if the molar fraction of Oxygen was changed. In other words, nanoparticle formation could depend strongly on the residence time in the flame.

View full abstract

The fluidized bed was dried under heating using acrylic particles to investigate the internal particles and particles attached to the wall surface. As a result of investigating the charge amount and adhesion amount of the particles adhering to the wall surface, the charge amount and the adhesion amount increased with the temperature rise, but it appeared that they decreased and aggregated near the softening point. In order to investigate this cohesion behavior, the internal particles were evaluated by the angle of repose and the degree of compression, and the particle diameter dependence of the particles attached to the wall surface was investigated. The average of angle of repose was smaller at 80 ° C, but depending on the angle to be compared, there was a case where the value at 20 ° C was smaller. Therefore, in order to further evaluate the inner particle state, compression degree was measured. As a result, the degree of compression at 80 ° C was lower than at 20 ° C. From this, it is considered that in fluidization at 80 ° C heating, particles agglutinate once due to preheating, but weak aggregates that collapse as vibration is applied.

View full abstract

Hydrogen for fuel-cell power plants is commonly manufactured from hydrogen-rich materials such as hydrocarbons and alcohols, using steam-reforming with catalysts. Recently, the authors have investigated the optimum conditions for efficient and endurable steam reforming. In the present study, the authors investigate the optimum conditions, especially focusing on both the influences of LHSV upon concentrations and the ethanol conversion. As a result, all the concentrations are close to the theory except for the case at low T_R and high LHSV. To settle the inconsistency of this exceptional case, the authors propose a new theory using some chemical reactions related with acetaldehyde.

View full abstract

In the decommissioning of nuclear power plants, the long-term management of radioactive waste of fuel debris is necessary. In the process, hydrogen which is the flammable gas is generated by the decomposition of water by radiation. Therefore, it is important to ensure the safety of the waste storage container to reduce the concentration of hydrogen gas. Then, a fundamental experiment to confirm the effectiveness of the waste storage container with the hydrogen concentration reduction mechanism using the passive autocatalytic recombiner (PAR) has been planned. The present study describes fundamental experimental plans and also preliminary experimental and analysis results.

View full abstract

A mathematical model for high temperature operation of PEMWE was developed and the reliability of the model was confirmed by comparing measured electrolysis voltage with the theoretical value based on the model. The electrolysis voltage could trace the measurement values. Especially, temperature dependence of electrolysis voltage had a good agreement between the theoretical and measured values. It was also found that the increase in gas saturation with increasing temperature reduces effective exchange current density and weakens the high temperature effect, which expects to reduce anode activation overvoltage under high temperature operation. Furthermore, it was found that the gas saturation should be less than 0.3 to use the high temperature effect and that pressurization is available to keep the saturation. Under this guideline, pressurization up to 0.21 MPa and 0.22 MPa can exert the high temperature effect even under high current density operation at 2 A/cm² and 3 A/cm², respectively.

View full abstract

Excessive water is generated when a polymer electrolyte fuel cell (PEFC) works in a high current density range. The excessive liquid water may cause clogging in the catalyst layer and gas diffusion layer (GDL), resulting in performance deterioration due to inhibition of supply of the reactant oxygen in the cathode (Flooding). As a measure to enhance the drainage of GDL, it is effective to apply a micro porous layer (MPL), which is made of carbon and water repellent PTFE (Polytetrafluoroethylene), to the GDL substrate. In this research, we focus on three dimensional porous structure analysis of the MPL by using the focused ion beam scanning electron microscope. Then, derived pore size distribution is employed to the pore network model (PNM) for convective air permeation and oxygen diffusion. Gas permeation measurements are also carried out to validate the model. The aim of this research is thereby to develop a reliable numerical model and clarify the effects of two-phase flow and water clogging on the oxygen transport in the MPL.

View full abstract

Recently, formic acid is expected as one of the energy career of renewable energy. Especially, A direct formic acid fuel cell, DFAFC, has received considerable attention since it can generate higher power density than the other direct liquid fuel cells and its power density is comparable to that of a polymer electrolyte fuel cell, PEFC, operated with hydrogen and oxygen at room temperature. However, CO₂ gas is generated in the anode reaction when a DFAFC is operating. If CO₂ bubbles stay in the anode gas diffusion layer, GDL, the mass transport resistance in a GDL increases and the generated power of a DFAFC decreases with the lapse of time. Furthermore, the gas-liquid two-phase flow behavior in a GDL, which is porous material, is not clear. In this study, we investigated the effect of Anode GDL configuration on power generation characteristics and bubbles behavior by visualizing CO₂ bubbles distribution using Xray CT.

View full abstract

Discharge performance of a single cell composed of Ni-GDC|ScSZ|LSM fueled with humidified methane is evaluated at the temperature between 973 K and 1173 K at 0.2 A/cm2. The terminal voltages were changed as a mixed wave of a square and a sawtooth wave regularly during the experiments. For analyzing the mechanisms of the alternation of the terminal voltages, the temperature dependency of the alternation was investigated. The range of voltage fluctuation was 0.15 V and almost constant with temperature, therefore the range of fluctuation was independent from operating temperature. The impedance before and after the discharge experiments were almost same: therefore, signitature of anode deterioration was not observed. The single cell was exposed to methane atmosphere in open circuit voltage condition for 24 hours. The voltage fluctuation is still observed. However, electrochemical degradation was also not detected before and after the experiment by impedance analysis. In the experiments conducted, only the experiment operated at 973 K and 0.2 A/cm2 could not be operated more than 5 hours.

View full abstract

Methane and ammonia are promising candidates as a fuel for solid oxide fuel cells (SOFCs). In this study, we experimentally investigated fundamental characteristics of methane-ammonia mixed gas as a fuel for SOFCs. The purpose of this study is to clarify the consumption of each gas by the steam reforming or decomposition reaction when methaneammonia mixed fuel was supplied to Ni-YSZ porous catalyst and its impact on the temperature distribution. The inlet gas composition and the amount of catalyst were varied. It was found that ammonia decomposition preferentially occurred in the upstream region followed by the steam methane reforming downstream when the mixed gas was supplied. It affected the temperature distribution showing the possibility to control the thermal field inside SOFCs by tuning the composition of the mixed gas at the inlet.

View full abstract

The effect of chromium poisoning in solid oxide fuel cell (SOFC) cathode on the stack performance and on the distribution of physicochemical quantities in the cells is investigated by numerical simulation. For the stack-level analysis, two-dimensional layers are used to model each SOFC component and stacked to form a quasi-three-dimensional SOFC model. A chromium poisoning model, which is compatible with the quasi-three-dimensional model, is also developed by assuming exponential distribution of charge-transfer current in the cathode. The effect of an asymmetric thermal boundary conditions on the progress of chromium poisoning is investigated.

View full abstract

La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ(LSCF) is a promising material of solid oxide fuel cell cathode for its high electrochemical reactivities. In this study, electrochemical performance evolutions of LSCF during discharge operations were evaluated based on the microstructural analysis and electrochemical simulations. After 100 hours discharge operations, increase in both polarization and ohmic resistances were observed. Sr segregation was found within LSCF phase after the operation at 800 ˚C. After 100 hours operation, no significant change was observed for double phase boundary density and triple phase boundary density, where the electrochemical reaction takes place, from the three-dimensional reconstruction of microstructures by focused ion beam – scanning electron microscopy (FIB-SEM). Result of electrochemical simulations suggests that the change in surface exchange coefficient can be the dominant factor for electrode performance degradation.

View full abstract

Recently, development of a small and high efficient heat exchanger, which is utilized in a fuel battery and a heat pump system for Carbon dioxide refrigerant and so on, is strongly required. In previous study, a prototype of stacked high-pressure resistance microchannel heat exchanger manufactured with diffusing bond technique has been proposed. It has been confirmed that it achieves miniaturization to one hundredth and a heat transfer rate equal to or higher than that of existing heat exchangers. In the present study, the objective is to reveal flow and heat transfer properties of this microchannel heat exchanger when water and vapor are employed as low- and high-temperature fluids, respectively. From experimental results, it was shown that the flow distribution in the flow path in the heat exchanger influences the performance of the heat exchanger

View full abstract

In an industrial washing process, using chemicals causes increase of an environmental load and processing costs. In this study, we focus on the ice jet washing technology with ice particles generated in a Venturi tube. The purpose is to improve efficiency of ice generation with a Venturi tube and to evaluate washing capability in this device. By visualization in the tube, we verified that shape of tubes was important factors to ice formation. Second, we constructed a numerical calculation system of quasi-one-dimensional stationary air single phase flow. In a converging-diverging nozzle like a Venturi tube, a supersonic flow is formed as the increase of the air flow rate and pressure and temperature are rapidly dropping in the diverging section. A similar pressure drop was observed from the pressure distribution measurement results and we indicated that a supersonic flow was formed in the tube. Furthermore, it was suggested that a reverse pressure gradient was appeared with the generation of pseudo-shock waves and cooling of water was promoted. Finally, for evaluating washing capacity of ice jet, we simulated fine particles dirt and conducted washing tests. Ice jet is verified having high washing capacity to fine particles dirt. Moreover, improvement of washing efficiency was expected by design of optimal nozzle to ice formation.

View full abstract

A steam injector (SI) works as a passive jet pump and has high heat-transfer performance due to direct contact condensation between steam flow and subcooled water jet. The objective of the present study is to clarify heat-transfer and flow characteristics of an ultra-micro steam injector (UMSI) with throat diameter of 1.0 mm. To this end, internal flow was visualized by a high-speed video camera. Pressure, temperature and flow behavior in the SI were measured simultaneously. The main parameters were inlet steam pressure, inlet water flow rate and inlet water temperature. As a result, the formation of the water jet, a feature at the time of SI’s operation, was confirmed under the high-temperature water condition. In addition, it was verified that the formation of the water jet even under the low-temperature water condition by increasing the inlet water flow rate.

View full abstract

In the previous study, the CHF was shown experimentally to be enhanced to more than double that of a plain surface in the saturated pool boiling of water using a honeycomb porous plate. The honeycomb porous plate attached to the heated surface enhances the liquid supply due to capillary action to the heated surface and the release of vapor through the vapor escape channel. In this paper, similar idea was applied to the rectangular narrow channel flow to enhance the CHF of a saturated forced convection boiling of water. As a result, the CHF was enhanced up to approximately 1.3 times compared to the plain surface.

View full abstract

The purpose of this study is to clarify the characteristics of decompression boiling generated in a two-phase flow nozzle using HFO-1234yf refrigerant. Three types of convergent divergent nozzles were manufactured. And the static pressure distributions in these nozzle were measured by varying the degree of subcooling at the nozzle inlet with constant inlet temperature. Experimental results confirmed that the experimental flow rate of HFO-1234yf refrigerant is close to the theoretical critical flow rate calculated from the IHE model as compared with other refrigerants. In addition, the degree of superheat at the nozzle throat representing the thermodynamic non-equilibrium state of the throat became smaller as the flow rate increased. Furthermore, reducing the divergent opening angle immediately after the nozzle throat, the degree of superheat at the nozzle throat becomes smaller. Since these experimental results are consistent with the past studies, it is considered that existing study results can be applied also to HFO-1234yf refrigerant.

View full abstract

This paper describes experiments in which visualization measurement and pressure measurement are performed in synchronization with propagation of pressure wave generated in a venturi tube. A pressure wave is generated under the condition how speed reaches at the throat. As the gas flow rate increases, the pressure wave becomes stronger, and the occurrence frequency decreases. When it is further increased, no pressure wave is generated. Also, as the bubble collapse position transits to the downstream side. A pressure wave is generated and propagated due to the bubble collapses. It is suggested that propagating pressure waves can be predicted using an adiabatic homogeneous flow model.

View full abstract

Microbubble emission boiling (MEB) has attracted attention because of high heat flux exceeding CHF. Even though the subcooling conditions the fine bubbles do not condense, which shows that the bubbles should be non-condensable gasses. Therefore, in this paper, we carried out the boiling experiment by using ultra pure water and distilled water to examine the effect of dissolved gasses. And we discussed on the heat transfer mechanism of MEB based on the boiling curves and the observation of bubbles behaviors with use of high-speed camera. In both cases, we observed the fine bubbles in the subcooled water with little difference.

View full abstract

In this paper, salt finger (SF) during neutralized chemical reaction has been investigated using a Hele-Shaw cell (HS) placed horizontally towards the gravity. In the acetic acid (CH3COOH) and sodium hydroxide (NaOH) system regular streaky salt finger was appeared at the reaction front while the reaction front had semicylindrical protuberances due to not only salt finger but also Rayleigh-Taylor instability using a HS placed vertically toward the gravity in our previous work. On the other hand, wave number of the salt finger in the hydrochloric acid – NaOH system was less than that in CH3COOH-NaOH system. Therefore it was found that salt finger formation during neutralized chemical reaction depended strongly on the kind of acid.

View full abstract

Controlling of the heat transfer rate during quenching of steels is in great demand to avoid quenching cracks. In this study, we examined influence of the presence of micro-bubbles on the heat transfer during quenching of a sphere made of Inconel 600. The diameter and the initial temperature of the sphere were 30 mm and 1173 K, respectively. The water temperature ranged from 293 K to 333 K. The temperature at the center of sphere was measured by a thermocouple during quenching in water with or without micro-bubbles. The heat flux and heat transfer coefficient were calculated from the time change in the temperature. As a result, micro-bubbles enhance the heat transfer coefficient in the nucleate boiling regime and the effect is stronger in the low wall superheat conditions than in the high wall superheat conditions. The quench temperature tends to increase due to the presence of micro-bubbles, whereas the effect of micro-bubbles on the heat transfer in the film boiling regime is weak.

View full abstract

As a low-temperature thermal cycle, a cycle using CO₂ and amine aqueous solution have been proposed. The amine aqueous solution is an absorbing solution used in carbon capture and storage medium that absorbs CO₂ in exhaust gas from thermal power plant. The basic configuration is the same as the water-ammonia based Kalina cycle. However, it is a feature of this cycle that it contains CO₂ and a large amount of water vapor in the generated gas. In our trial study, it was expected that this cycle can obtain the performance equal to or higher than that of the current ORC. Therefore, a principle verification test was carried out. Although it is compared with the water-steam cycle, it was confirmed that higher thermal efficiency can be obtained in the amine aqueous solution-CO₂ cycle.

View full abstract

Lately, in Japan, energy saving and renewable energy utilization are strongly required from view point of both global warming protection and energy security. But the amount of energy consumption in the building sector has remarkably increased. Therefore, the Building Energy Efficiency Act was enforced on April of 2016 in order to strengthen energy efficiency measures on building. The authors have started the measurement of energy consumption for experimental apartment house “NEXT21” in order to investigate feasibilities of energy saving and renewable energy introduction. In this report, the actual performances of coupling air conditioning system consist of hot water driven single effect absorption refrigerator and gas fired doubled effect absorption chiller was mainly investigated.

View full abstract

Meso-porous silica is one of the promising adsorbents that will enhance performances of energy-saving technologies, such as adsorption cooling, adsorption heat pump and adsorption thermal storage. Adsorption equilibrium and adsorptin kinetics are essential information to design as well as to predict the performance of the systems. The adsorption isotherm equation for meso-porous silica is, however, difficult to model accurately because of a large jump of adsorption uptake at a certain relative pressure and strong hysteresis. The study measured adsorption and desorption isotherms at 30℃, 50℃, and 70℃. The isotherms are modeled using a Henry and Sips type equation. The average errors between the measurement and the model are 4.10〜6.79 % for adsorption and 3.27〜8.70% for desorption.

View full abstract

Ejector refrigeration cycle (ERC) is an attractive alternative refrigeration system to conventional vapor compression refrigeration cycle due to its capability to use low temperature heat source. However, low energy efficiency is the major obstacles for its widespread use. Binary fluid ejector refrigeration cycle (BERC) is one approach to improve this low efficiency. In this research, entrainment ratio and COP of ERC and BERC is calculated respectively. Entrainment ratio is one of the parameters which indicate efficiency of the ejector. As a result, both entrainment ratio and COP increased in BERC.

View full abstract

The thermoacoustic engine that can be driven by cold exergy has been designed and constructed. It is composed of a looped tube, a straight tube, two heat exchangers, a regenerator, and a tank. The regenerator is sandwiched by the heat exchangers and is located in the looped tube. When the temperature ratio of the heat exchangers exceeds 1.7, the gas inside the engine spontaneously oscillates. The amplitude of the oscillation increases with increasing the temperature ratio, and the output power of the engine reaches 190 W.

View full abstract

From a viewpoint of stable equilibrium between energy demand and supply, the development of technologies for improving the efficiency of coal fired power generation is critical to alleviating the problem of global warming. If Advanced Ultra-Super Critical (A-USC) is realized the turbine efficiency will exceed 50% and a plant efficiency of 46% or more can be expected. Mitsubishi Hitachi Power Systems, Ltd. (MHPS) has carried out the technology development of the A-USC turbine by support of the Japanese National Project from 2008 to 2016. The commercialization of 700o C-class turbines required the breakthrough technologies for materials and fabrication. We have developed a mainly Ni-based alloy with high-temperature creep strength exceeding 100MPa at 700o C for 100,000 with the successful production of a large-scale forged rotor weighing more than 10 tons, as well as fabrication technology for dissimilar-material welded rotor using Ni based alloy with high Cr steel. We finally carried out a turbine rotational test to inspect these development technologies. This test condition is specified in a steam turbine having a dissimilar material welding rotor under high temperature more than 700o C at 3600rpm. This paper describes these development technologies.

View full abstract

Ni-base alloys has been considered as candidate structural materials in high temperature section in advanced ultra supercritical power generation. Oxidation behavior and its dependence on the pressure were clarified based on oxide film thickness formed on alloys 625 and 617. Oxidation tests were carried out in a supercritical water and a superheated steam environment at 750ºC for up to 500 hrs. Elemental distribution along the thickness of oxide film were analyzed by means of Auger electron spectroscopy. Two layer of the oxide film were formed in supercritical water environment, while a single layer of Cr₂O₃ were identified in a superheated steam environment. In both environment, it was clearly shown that thickness of oxide film were monotonically increase with oxidation time. Oxidation rate constants estimated from the thickness of oxide film indicated that apparent oxidation rate in supercritical water environment was smaller than the one in superheated steam environment in both alloys.

View full abstract

A high-efficiency coal-fired power plant, called an A-USC (Advanced ultra-supercritical) plant, is being developed. In high-temperature sections of the A-USC plant, Ni-base superalloys is one of the possible candidates to replace ferrite steels. On the other hand, renewable energies are being widely promoted, which vary power output depending on those sources. Therefore, the fossil power plants including the A-USC plant are expected to cover the needs of the adjustment of the power supply to satisfy electricity demand. However, it is suggested that the output adjustment would induce fatigue damage in which the oxidation of material interacts. Meanwhile, the dependence on the cyclic loading frequency was investigated to understand the fatigue and creep interaction in a steam environment. Therefore, with aiming to evaluate the dependence of oxidation behavior of Ni-base superalloy, alloy 617, the crack growth behavior in a steam environment at 750°C is evaluated under cyclic loading using a compact tension specimen. It was found that crack propagated along grain boundary under lower cyclic loading frequency. In addition, localized oxide formation was more significant under such condition.

View full abstract

Higher thermal efficiency and operational flexibility are required for next generation thermal plants to reduce CO2 emission and cope with the increase of renewable energy which is changeable depending on the weather. The Advanced Humid Air Gas Turbine (AHAT) system is expected to meet these requirements. The system concept and cycle performances of the AHAT system were verified by operation tests of a 3MW-class test plant and a 40MW-class pilot plant so far. However, operational flexibility of commercial scale system has not been clarified sufficiently by experiment or calculation. Therefore, we develop a dynamic simulation model of commercial scale system and analyze the startup characteristics in this paper.

View full abstract

As intermittent renewable energies are introduced into the power grid, Natural Gas-fired Gas Turbine Combined Cycle (NGCC) is expected to increase frequent start-up, frequent shut-down, and partial-load operation time to stabilize the frequency of the power grid. These transient operations of the NGCC significantly change the ratio of NO₂/NOx in the exhaust gas. Therefore, it is necessary to develop an efficient de-NOx system applicable across the range of potential NO₂/NOx ratios. In this study, a modification of the de-NOx reaction scheme of Nova et al. (2011) was established, eventually consisting of 8 elementary reactions including 7 chemical species, with the activation energies and the preexponential factors of the reaction rate equations. The two-dimensional unsteady state numerical simulation code was developed and fitted using experimental results obtained under elementary conditions with a honeycomb-shaped SCR catalyst commonly employed at actual NGCC power plants. The numerical simulation utilizing the modified scheme accurately predicted transient changes and equilibrium concentrations of NOx and NH₃ in the NGCC exhaust under transient operations with a wide range of NO₂/NOx ratios.

View full abstract

In order to reduce CO₂ emission from coal-fired boiler, it is expected that ammonia is used as a fuel which has no carbon content. In that case, it is concerned that NOX concentration in flue gas is increased because ammonia has more nitrogen content than coal. With 10 MWth test furnace, 20 % ammonia co-firing test in lower heating value base was conducted. In the case of ammonia co-firing with appropriate supplying method, NO_X concentration was as same as that of coal firing with reducing CO₂. These results show 20 % ammonia co-firing in actual coal-fired boiler gets closer to realization.

View full abstract

CO₂ adsorption simulation technique was built and implemented to clarify the performance determinant of PTSA CO₂ adsorber. In the simulation, a CO₂ adsorber was connected with a methanation reactor which converted CO₂ and H₂ to CH₄. Exothermal heat of this methanation reaction was recovered by oil and then used as the energy of temperature swing at the CO₂ adsorber. The CO₂ adsorber was composed of 4 towers; adsorption, preheating, desorption and cooling. Each tower featured shell and tube design that was high heat exchange performance. Configuration of tubes and amount of the energy used for depressurization were investigated using the simulation. The results showed that CO₂ recovery ratio was determined only by the average temperature at the end of the adsorption cycle and desorption cycle, as far as the input energy for depressurization was the same. CO₂ recovery ratio depended on the configuration of tubes, because the average temperature was varied. When the diameter was too small, desorption average temperature was low because the heat capacity of adsorbents was small compared with that of pipes. On the other hand, when the diameter was too large, adsorption average temperature was high because eliminating adsorption heat at the center of the tube was difficult. These tendencies rise with decreasing CO₂ recovery ratio.

View full abstract

This study explores CO₂ methanation in the autothermal conditions using a two-staged reactor, which features a stepwise H₂ feed and direct provision of heat-carrier oil from the first-stage reactor to the second-stage reactor. The emphasis is on quantitative clarification of CO₂ conversions and heat recovery rates that vary depending on the reactor control parameters of oil flow rates Q_oil and H₂ feed rate ratios of the first-stage reactor to an overall H₂ feed rate α. The heat recovery rates are defined as the ratios of heat quantities recovered by the heat-carrier oil to the product of the overall H₂ feed rate and the H₂ lower heating value. Operational pressure, space velocity and feed rate of CO₂ was set to be 3 atm, 10 kh-1 and 1.7 slm, respectively. The results show that as Q_oil decreased, CO₂ conversions increased while heat recovery rates decreased. At α = 80%, a CO₂ conversion reached 99.0% by adjusting Q_oil and the heat recovery rate then was 8.4 %, which corresponds to the energy efficiency of 90.5%. As α increased, CO₂ conversions increased till the reactivity in the second-stage reactor started decreasing. Meanwhile, heat recovery rates increased with increasing α till the heat recovery rate in the first-reactor stopped increasing and leveled off.

View full abstract

O₂/CO₂-blown gasification test were carried out with the 50ton per day bench-scale test facility to verify syngas composition and slag discharge for the Oxy-fuel IGCC system utilization with CO₂ capture. The main component, hydrocarbon and trace elements of the syngas were analyzed during the stable gasifier operation. The performance of the gasifier such as calorific value of the syngas and cold gas efficiency, were almost same as oxygen-blown gasification. Although the temperature of the gasifier fell with higher the partial pressure of CO₂ compared with the oxygen-blown, it was verified that stable discarge of the slag and reduction of the hydrocaron in syngas by optimizeing reductor/total coal ratio.

View full abstract

CRIEPI is developing a high thermal efficiency integrated coal gasification combined cycle power generation system. The thermal efficiency of the system is enhanced by an active utilization of steam injection into a gasifier, which is expected to promote the steam gasification. The previous survey research by CRIEPI showed the possibility of a higher cold gas efficiency and the expected problems of the system. In this report, a numerical simulation was conducted to investigate the steam enriched gasification characteristics and to find an advantageous condition for the steam injection. The simulation revealed that a larger steam supply achieved a higher cold gas efficiency in the 3t/d bench scale coal gasifier with keeping the temperature in the combustor.

View full abstract

As a method of stably discharging molten slag from slag holes, an Integrated coal Gasification Combined Cycle, IGCC process using slag taps has been studied. The flow state of the slag varies depending on the shape of the slag tap and the viscosity of the molten slag. In this study, flow simulations were conducted using the lattice Boltzmann method considering the temperature dependency of viscosity. As a result, it was revealed that stable slag discharging conditions and the difference in flow due to the influence of viscosity were observed.

View full abstract

This study investigated the potential of a method with self-traveling carrier roller to measure the resistance force of conveyor belt. The resistance force was substitutionary measured by a load cell with resultant force of the driven bogie traveling on the conveyor belt laid on the flat plate. Indentation load of the carrier roller is also applied to conveyor belt by four air cylinders through rods put between conveyor belt and other guide rollers. The diameter of carrier roller were 89.1 mm and 160 mm, respectively. The indentation rolling resistance was increased with increase of indentation load. The indentation rolling resistance was slightly decreased when diameter of the carrier roller was large. The hysteresis loss of conveyor belt was increased when large indentation load was applied to the conveyor belt, while the hysteresis loss was decreased when diameter of the carrier roller was large. The experimental data was explained by difference of hysteresis loss of the conveyor belt. This study confirmed that the proposed method with self-traveling carrier roller is effective to evaluate the resistance force of actual conveyor belt.

View full abstract

Stress corrosion cracking (SCC) is the major factor to reduce the reliability of aged reactor components. Laser Peening (LP) technology was developed and applied to reactor components in operating Boiling Water Reactors (BWR) and Pressurized Water Reactors (PWR). Bottom mounted nozzles are made from Alloy 600 tubing and attached with Alloy 82/182 welds, which are known to be susceptible to Primary Water Stress Corrosion Cracking (PWSCC). Ultra-compact laser peening systems, which integrates laser oscillator and positioning robotics into a unit, were developed and applied for both inside and outside surface of BMI nozzles in the U.S. Small irradiation head with aspherical mirror was attached to optical fiber in order to perform LP inside surface of BMI nozzles. On the other hand, mirror-delivery type of LP tool was employed for outside surface of BMI nozzles. Magnitude of compression induced by the LP process was verified prior to application at the plant using mockups of BMI nozzles and effectiveness were proved.

View full abstract

A development of advanced ultra-super critical (A-USC) power plant has been recently promoted for further reduction of CO₂emission. Alloy617 is one of the candidate materials for high temperature components of A-USC power plant such as boiler pipings and tubings. In this study, the change in small punch (SP) creep property due to creep damage was investigated to examine the applicability of SP creep testing technique to the remaining-life assessment of A-USC power plants. The small disk-type specimens were removed from several interrupted uniaxial creep test specimens with various degrees of damage, and they were subjected to the SP creep test at 700°C. The experimental results revealed that the uniaxial creep test changed the SP creep life or 10³ h SP creep rupture strength, but they were not in good agreement with the degree of preliminary damage. The cumulative damage model was applied to the SP creep test results to investigate its adaptability to the remaining-life assessment. As a result, the strain fraction rule seemed to be more suitable than the life fraction one.

View full abstract

The small punch (SP) testing technique was applied to five heats of Gr.91 steel, which had been actually used for boiler pipings in different USC power plants for long periods of time, to investigate the applicability of this testing technique to the assessment of heat-to-heat variation of creep property. The SP creep test was carried out at the temperature of 650°C and under the loads of 190, 230, 300 N using a small disk-type specimen (φ8×0.5 mm). The experimental results revealed that the SP creep rupture strength (rupture life) and the deformation rate were different depending on the heat. These differences were qualitatively in good agreement with those observed in the uniaxial creep test. The obtained results indicated that the SP creep testing technique could be a strong tool for the assessment of heat-to-heat variation of inservice boiler pipings. It was also revealed that the SP creep rupture test data were relatively well converted to the uniaxial creep ones using the F/σ obtained from the SP tests.

View full abstract

With Gr. 91 boiler piping base metals used for a long time in ultra-supercritical（USC）power plant as target, a small sample was taken using the electric discharge sampling equipment, and we investigated the affected layer thickness by the electric discharge processing method, the dimensional accuracy of the small sample , and processing after sampling of small samples. As a result, it was confirmed that the thickness of the processing influence layer by the electric discharge processing method is within about 30 µm for both the sample and the pipe side, the sampling accuracy in the thickness direction of the sample is about ± 0.2 mm. In addition, almost no processing influence layer after grinder molding was found.

View full abstract

In the evaluation of the creep property of piping base metals, an important consideration is from which region in the thickness direction small specimens are taken. We conducted microstructural observation, composition analysis, hardness measurement and the creep test to evaluate creep properties in the thickness direction of Gr.91 steel boiler piping base metals used for a long time in five ultra-supercritical (USC) power plants. In the microstructure near the outer surface, no affected layer was observed. Regarding hardness, a change in hardness was observed in the region of about 0.1 mm to 0.2 mm from the outer surface, but in all other regions, the hardness in the thickness direction was almost constant. The time to rupture of base metal of the pipes are same level in the thickness direction. Therefore, it is suggested that an effective portion of the sample taken from USC boiler pipes to consider heat-to-heat variations of the creep properties of base metals is the material excluding the area less than about 1.0 mm from the outer surface of the pipes.

View full abstract

In the analytical life assessment of creep strength enhanced ferritic (CSEF) steels, average creep properties are generally assumed, although there is a large amount of scatter in the creep properties of welded joints of the steels. It is important to estimate the individual creep properties of welded joints of materials used at power stations if analytical life assessment is quantitatively applied to the components of power stations. Thus, author has developed a new method of assessing the individual creep properties of welded portions of actual piping using small samples. This paper describes the concept of the assessment method for the Grade 91 steel, which has been used worldwide as a CSEF steel.

View full abstract