Central Research Institute Of Electric Power Industry Research Articles

Evaluation of coal ammonia flames using a non-adiabatic three mixture fraction flamelet progress variable approach

A highly resolved large eddy simulation (LES) modeling of the co-firing of ammonia with pulverized coal in a single-burner test furnace of the Central Research Institute of Electric Power Industry (CRIEPI) has been performed using a non-adiabatic three mixture fraction flamelet/progress variable (3Z-FPV) approach. To parametrize the thermochemical space, a six-dimensional tabulation method based on non-premixed flamelets is introduced, which uses three mixture fractions, for ammonia, coal volatiles, and char-off gases, respectively, as well as variance of mixture fraction, reaction progress variable, and total enthalpy. The accuracy of non-adiabatic model has been tested by comparing it with experimental data and previously computed adiabatic FPV results for two different ammonia injection cases. The results show that the non-adiabatic FPV model accurately predicted the peak temperature and its location, while the peak NO, overpredicted by approximately 150 % in the adiabatic FPV model, is slightly underpredicted in the non-adiabatic FPV model. Ammonia injection in the primary reaction zone lowered NO concentrations in both cases, primarily due to dominant NO reduction reactions with ammonia under the reducing environment. Reactive conditions and higher temperature caused NH3 dissociation, increasing H2 and H2O concentrations near burner exit in burner ammonia injection case.

Fuel Melting Simulation with FRAPCON/FRAPTRAN Codes for the Power-to-Melt-and-Maneuverability Simulation Exercise and Consideration of Model Modifications

This paper presents simulation results of earlier fuel melting tests (xM3 and HBC4) performed under the power-to-melt-and-maneuverability (P2M) simulation exercise organized within the Organisation for Economic Co-operation and Development (OECD)/Nuclear Energy Agency (NEA) framework for irradiation experiments. The simulations were performed using the single-rod performance analysis code FRAPCON/FRAPTRAN as a contribution of the Central Research Institute of Electric Power Industry (CRIEPI) to the P2M simulation exercise. To this end, the base irradiation of each sample was simulated using FRAPCON software, and the calculated result was used to define the initial state of the transient simulations; the xM3 and HBC4 ramp tests were simulated using FRAPTRAN. Fuel melting was not predicted for xM3, and the melting radius was underestimated for HBC4 using the original version of FRAPTRAN. The value of the fuel/cladding gap conductance was modified to obtain results that satisfy the experimental measurement of the melting radius. In this paper, the simulation results are compared with experimental results, and the causes for discrepancy between the simulation and experiment results are discussed. The necessary improvements for FRAPTRAN to achieve a better simulation of fuel melting are also discussed. These results can help calibrate codes against high-temperature behavior and improve fuel melting modeling toward the planned P2M power ramp tests.

Degradation Analysis of SOFC Performance for Long-Term Operation with High Fuel Utilization (2)

Solid oxide fuel cells (SOFCs) are a power generation technology with its high efficiency and low environmental impact, and the most important issue for SOFC for practical use is to improve reliability as well as high efficiency. A national project on SOFC development in Japan, “Development of advanced evaluation and analysis technologies for the durability of Solid Oxide Fuel Cells stacks (2020-),” has been initiated as a NEDO project in order to clarify their long-term durability and find dominant degradation factor for each SOFC stacks. Central Research Institute of Electric Power Industry (CRIEPI) has operated three kinds of different SOFC cell/stacks (flat-tubular and two kinds of planer) for durability under NEDO’s project, which have been developed by KYOCERA, MORIMURA SOFC Technology, and DENSO.Long-term durability tests of 20,000 hours have been conducted under high fuel utilization of 80% and 85%, which is close to the operating limit of each SOFC cell/stack for high efficiency, to evaluate the effects on the performance and degradation behavior of the cell/stack. In previous projects, we have developed an electrode polarization model that can accurately represent SOFC performance, including cell voltage and each overvoltage, under a variety of conditions. The degradation factors for durability of each SOFC cell/stack have been analyzed by using this model. The analysis revealed that the dominant degradation factors were increased cathode overvoltage and IR loss, similar to the SOFC cell/stacks that were modified from the previous project to improve their long-term durability. On the other hand, the degradation rate of cell voltage was higher at 85% than at 80% fuel utilization in one cell/stack, and the performance degradation factor analysis revealed that this difference was due to an increase in anode overvoltage at 85% than at 80% fuel utilization, where anode overvoltage was not the primary degradation factor.This work has been carried out under the projects (JPNP13001 and JPNP20003) of the New Energy and Industrial Technology Development Organization (NEDO), Japan as contract research. We would like to express our gratitude to NEDO, many SOFC developers, as well as to university partners and National Institute of Advanced Industrial Science and Technology (AIST).

A particle-size dependent smoothing scheme for polydisperse Euler-Lagrange simulations

In Euler-Lagrange models for particulate systems, the information exchange of multiphase coupling terms, i.e. drag force, heat transfer, or mass transfer, is often smoothed from particles' location to nearby computational cells when the cell and particle sizes are comparable. The diffusion-based smoothing is among the most popular approach. However, when it comes to polydisperse systems, the state-of-the-art constant diffusivity approach does not consider variation in particle sizes, resulting in an even smoothing of exchanged information across all particles with different sizes.In this paper, a particle-size dependent smoothing scheme named “non-constant diffusivity approach” is proposed. This approach distributes the exchanged information based on the local Sauter diameter d32 such that the area of influence per particle varies by size. The one-dimensional analytical solution of the non-constant diffusivity approach is first derived and two control parameters L⁎ and S are identified, where L⁎ determines the characteristic length of the diffusivity and S determines the magnitude of the diffusivity. Together they control the characteristic length scale ℓ˜c of the smoothing operation. In the one-dimensional study, it is found that the proposed smoothing method is most suitable for the dilute particulate regime. The investigation is extended to a three-dimensional dilute particle flow based on the experiment of the CRIEPI (Central Research Institute of Electric Power Industry) pulverized coal burner. It is shown that using the non-constant diffusivity smoothing, the prediction of the O2 concentration is more accurate than when using the constant diffusivity smoothing approach, which assumes a universal smoothing length for all sizes of particles. The findings suggest that when it comes to polydisperse particulate systems, the area of influence per particle on the fluid depends on the particle size. The proposed non-constant diffusivity approach can describe that with the benefits of cheap computational cost, conservation of exchanged quantities, and easy-to-implement.

Development of SOEC Performance Model Based on Cell Performance

Central Research Institute of electric Power Industry (CRCIEPI) has developed original SOFC performance evaluation method and applied to a wide variety of cells. Based on the SOFC performance evaluation method, a new SOEC performance evaluation method has been developed this time. By this evaluation method, the difference between the open circuit voltage and the cell voltage can be expressed by the internal resistance loss (measured value), the fuel electrode overvoltage, the oxygen electrode overvoltage, and the Nernst loss.In this study, cell performance before and after the CO2 direct electrolysis test was compared by SOFC and SOEC evaluation methods and clarification of cell degradation factor by CO2 direct electrolysis.

Evaluation of ammonia co-firing in the CRIEPI coal jet flame using a three mixture fraction FPV-LES

Highly resolved Large Eddy Simulations (LES) are performed to investigate co-firing of coal and ammonia in a burner experiment conducted by the Central Research Institute of Electric Power Industry (CRIEPI) in Japan. The coaxial burner with a hydrogen supported pulverized coal flame is modeled using the in-house code PsiPhi. A three mixture fraction flamelet/progress variable (FPV) approach is employed to simulate coal particle conversion due to devolatilization, hydrogen combustion, and ammonia combustion. Three cases are investigated and compared to each other: 1) a coal combustion case, injecting air and coal particles, 2) an ammonia combustion case, injecting a mixture of ammonia and air, and 3) a co-firing combustion case, injecting a mixture of coal, ammonia and air in the center tube. Two mechanisms are used to build the chemistry table and are compared against each other: a reduced CRECK mechanism with 120 reaction species and 1551 elementary reactions, originally reduced for coal combustion modeling, and a newly introduced reduced CRECK mechanism with 129 reaction species and 1644 elementary reactions, including the detailed NH3 reaction paths in addition to the coal chemistry. Species are compared for the coal case and temperature fields are compared for both the coal and co-firing case. Normalized LIF signals for OH and NH are presented for all three cases. The gas composition profiles are in good agreement with the experiment and the temperature fields are consistent with previous results for the pure coal flames. For pure ammonia and for ammonia co-firing, the new mechanism shows an improved prediction of the reaction zone.

Incorporation of flamelets generated manifold method in coarse-grained Euler-Lagrange simulations of pulverized coal combustion

Large Eddy Simulations (LES) combined with the Flamelet Generated Manifold (FGM) approach has become popular for modeling turbulent flame/combustion of pulverized coal or biomass. In this paper, we incorporate a coarse-graining discrete element method (CG-DEM) with the FGM-LES for cost-effective Euler–Lagrange (EL) simulations of turbulent coal combustion. This developed method significantly reduces the computational burden in both Eulerian phase (via FGM) and Lagrangian phase (via CG) compared to conventional reactive EL simulations. The study is based on the experiment of the CRIEPI (Central Research Institute of Electric Power Industry) burner, which has been extensively used for model validation in literature. It is shown that the developed model can effectively reduce the computing cost while maintaining a good accuracy in predicting the pulverized coal flow dynamics as well as combustion performance. For this particular case, an optimal coarse-graining factor, the size ratio of coarse-grained parcels to original particles, of 2 is determined. A larger coarse-graining factor will create local concentrated regions of fuel and consequently lead to different combustion behavior.

Engineering geological investigations for designs of excavation method and support system of diversion tunnel at Bulango Ulu Dam, Indonesia

This paper presents engineering geological investigations for designs of excavation method and support system of a diversion tunnel at Bulango Ulu Dam, Indonesia. Evaluation of drill cores along the tunnel was carried out to determine the geological engineering conditions. Classifications of rock masses were carried out based on the Central Research Institute of Electric Power Industry (CRIEPI) and Rock Mass Rating (RMR) to analyze the excavation method and support system. The rock masses along the tunnel were classified into D, CL, and CM classes based on the CRIEPI and poor, fair, and good quality based on the RMR. The tunnel portals consisted of poor quality rock masses, while the main tunnel section consisted of good quality rock masses. The excavation method of full-face was proposed for the main tunnel section, while top heading and bench were proposed for the tunnel portals and main tunnel section having fair quality rock masses. The support system recommended for tunnel portals were 4-5 m long, 1-1.5 m spaced systematic bolts, 100-150 mm thick shotcrete, and 1.5 m spaced steel ribs. Meanwhile, the support system proposed for the main tunnel section was 3 m long, 2.5m spaced bolts, and 50mm thick shotcrete in the crown.

Degradation Analysis of SOFC Performance for Long-Term Operation with High Fuel Utilization

A national project in Japan for SOFC development has been initiated from FY2020 to FY2024 in NEDO’s project in order to establish the method for degradation diagnosis of SOFC stacks with durability and reliability for 130,000 hours or the method for evaluation of expanding application. Central Research Institute of Electric Power Industry (CRIEPI) has operated three types of SOFC stacks, which are developed by KYOCERA, MORIMUA SOFC TECHNOLOGY, and DENSO and investigated their long-term durability in this project. We have developed the electrode polarization model for SOFC performance which is able to express the SOFC performance such as Nernst loss, cathode overvoltage, anode overvoltage, and internal resistance (IR) loss under various conditions with high prediction accuracy. Each SOFC stack has been operated with high fuel utilization (Uf = 80% and 85%) as a severe condition for high efficiency towards 20,000-hours operation, and degradation factors for SOFC durability has been analyzed by using our electrode polarization model. Analysis results until now showed that dominant degradation factors for both Uf = 80% and 85% were increase of cathode overvoltage or IR loss as same as that of the SOFC stacks in the previous term [1]. Although anode overvoltage was a minor degradation factor, increase rate of anode overvoltage under Uf = 85% was relatively larger than that under Uf = 80%. In addition, thermal property testing will be conducted for each SOFC stack in order to include temperature term into our electrode polarization model. This new model can predict SOFC performance more accurately under various operating conditions. This work has been carried out under the project of the New Energy and Industrial Technology Development Organization (NEDO), Japan as a contract research. We would like to express our gratitude to NEDO, KYOCERA, MORIMUA SOFC TECHNOLOGY, Denso as well as to university partners and National Institute of Advanced Industrial Science and Technology (AIST).Reference[1] A. Ido et al., ECS Transactions, 91(1), 801-808 (2019).

Degradation Analysis of SOFC Performance for Long-Term Operation with High Fuel Utilization

In a NEDO’s project from FY2020 to FY2024, Central Research Institute of Electric Power Industry (CRIEPI) has operated three types of SOFC stacks, which are developed by KYOCERA, MORIMURA SOFC TECHNOLOGY (MST), and DENSO in order to clarify the technical issues for high efficiency and toughness of SOFC stacks and establish the method for degradation diagnosis of SOFC stacks. Each SOFC stack has been operated with the high fuel utilization (Uf = 80 and 85%) as a severe condition for high-efficiency and degradation factors for SOFC durability have been analyzed by using the electrode polarization model which we have developed. Analysis results until now showed that dominant degradation factor was increase of cathode overvoltage or IR loss as same as that in the previous term. Moreover, thermal property testing has been conducted to apply the effect of temperature to our polarization model. It was clarified that internal resistance and electrode resistance coefficients can be expressed by Arrhenius equation.

Development of a human reliability analysis (HRA) guide for qualitative analysis with emphasis on narratives and models for tasks in extreme conditions

Probabilistic risk assessment (PRA) has improved its elemental technologies used for assessing external events since the Fukushima Daiichi Nuclear Power Station Accident in 2011. HRA needs to be improved for analyzing tasks performed under extreme conditions (e.g., different actors responding to external events or performing operations using portable mitigation equipment). To make these improvements, it is essential to understand plant-specific and scenario-specific conditions that affect human performance.The Nuclear Risk Research Center (NRRC) of the Central Research Institute of Electric Power Industry (CRIEPI) has developed an HRA guide that compiles qualitative analysis methods for collecting plant-specific and scenario-specific conditions that affect human performance into “narratives,” reflecting the latest research trends, and models for analysis of tasks under extreme conditions.

Root-Mean Square Model of Three-Phase Photovoltaic Inverter for Unbalanced Fault

The feed-in tariff, introduced in 2012, led to a significant increase in Photovoltaics (PVs) throughout Japan. About half of PVs are three-phase PVs that are connected to low voltage or medium voltage networks. Central Research Institute of Electric Power Industry (CRIEPI) has developed root-mean square-based time-domain power system analysis tools used by all the Japanese utilities for dynamic studies following balanced and unbalanced faults for over the last thirty years. Two 10 kW three-phase PV inverter were tested in the CRIEPI's test lab reproducing various levels of the voltage dips that come from three-phase balanced and unbalanced faults with various fault duration. The PV model was developed and validated, comparing measured responses obtained in the test lab with simulated responses obtained by the time-domain simulation tool. Sensitivities of identified parameters to the model error are carefully examined, which proves that the same model parameters may be used for balanced and unbalanced faults. Derived model parameters are further verified, comparing the simulated response of the combined two PV outputs with the measured response. The excellent match of those responses demonstrates that individually identified parameters for the two single PV inverters are also adequate for representing the combined PV dynamics.

Degradation Analysis of SOFC Performance (1) — Severe Operation with High Fuel Utilization

Central Research Institute of Electric Power Industry (CRIEPI) has operated four types of SOFC stacks, which are developed by Kyocera, NGK SPARK PLUG (NTK), NGK INSULATORS (NGK), and Denso in a NEDO’s project since FY2018 to FY2019 in order to clarify the technical issues for high-efficiency and toughness of SOFC stacks or make a concept for the high-efficient stacks. Each SOFC stack has been operated with the high fuel utilization (Uf = 80%) as a severe condition for high-efficiency for more than 3,000 hours, and degradation factors for SOFC durability have been analyzed by using the electrode polarization model which we have developed. Analysis results until now showed that dominant degradation factor was increase of cathode overvoltage or IR loss as same as that of the SOFC stacks which were modified for improving long-term durability in the previous term.

Degradation Analysis of SOFC Performance (2) - Severe Operation with an Instantaneous Load Fluctuation

Central Research Institute of Electric Power Industry (CRIEPI) has operated four types of SOFC stacks, which are developed by KYOCERA, NGK SPARK PLUG (NTK), NGK INSULATORS (NGK), and DENSO under NEDO’s project on high efficiency and toughness of SOFC cell-stacks (FY2018-FY2019). In order to evaluate the applicability of SOFC for an instantaneous load fluctuation, the load-fluctuation tests in this project have been carried out. It was determined as a test protocol that the periodic current fluctuations which are the waveform of triangular wave with the periods of time for 0.02-20 sec are applied to SOFC cell-stacks as a severe operating condition with the instantaneous load fluctuation. The durability with instantaneous load fluctuation for 2,000 h applying this test protocol was evaluated. As a result, the instantaneous response of cell voltage and power density, and the voltage decay rates of cell voltage of each SOFC cell-stack during the load fluctuation tests were clarified.

Prediction of soot formation characteristics in a pulverized-coal combustion field by large eddy simulations with the TDP model

In this study, the soot formation characteristics in a pulverized-coal combustion field formed by a 4 kW Central Research Institute of Electric Power Industry (CRIEPI) jet burner were predicted by large eddy simulation (LES) employing a tabulated-devolatilization-process model (TDP model) [N. Hashimoto et al., Combust. Flame 159 (2012) 353–366]. This model enables to take into account the effect of coal particle heating rate on coal pyrolysis. The coal-derived soot formation model proposed by Brown and Fletcher [A. L. Brown and T. H. Fletcher, Energy Fuels 12 (1998) 745–757] was employed in the LES. A comparison between the data predicted by LES and the soot volume fraction distribution data measured by laser induced incandescence confirmed that the soot formation characteristics in the coal combustion field of the CRIEPI burner can be accurately predicted by LES. A detailed analysis of the data predicted by LES showed that the soot particle distribution in this burner is narrow because the net soot formation rate is negative on both sides of the base of the soot volume fraction. At these positions, soot particles diffused from the peak position of soot volume fraction are oxidized due to a relatively high oxygen concentration. Finally, the effect of soot radiation on the predicted gas temperature distribution was examined by comparing the simulation results obtained with and without soot radiation. This comparison showed that the maximum gas temperature predicted by the simulation performed with soot radiation was over 100 K lower than that predicted by the simulation performed without soot radiation. From result strongly suggests the importance of considering a soot formation model for performing numerical simulations of a pulverized-coal combustion filed.

Degradation Analysis of SOFC Stack Performance: Investigation of Cathode Sulfur Poisoning Due to Contamination in Air

Central Research Institute of Electric power Industry (CRIEPI) has operated seven types of SOFC stacks, which are developed by MITSUBISHI HITACHI POWER SYSTEMS (MHPS), KYOCERA, TOTO, NGK SPARK PLUG (NTK), NGK INSULATORS (NGK), MURATA Manufacturing (Murata), and Denso in order to investigate their durability and find dominant degradation factor for each SOFC stacks under NEDO’s project. In the first half of period, remarkable feature of durability tests was large cathode degradation in KYOCERA’s, NGK’s, and Murata’s cells which were examined at CRIEPI site. Because sulfur was detected on their cathodes from post analyses done by AIST with SIMS, in the last half of period, these stacks were reexamined by adopting sophisticated chemical filter for SO2 removal. Results become more acceptable. On the other hands, SO2 concentration in air at CRIEPI site was less than 3 ppbv. The amount of sulfur detected on cathode is significantly larger than that of calculated sulfur from supplied air, another sulfur sources might be considered.

Degradation Analysis of SOFC Stack Performance: Investigation of Cathode Sulfur Poisoning Due to Contamination in Air

Central Research Institute of Electric power Industry (CRIEPI) has tested on seven types of SOFC stacks, which are developed by MITSUBISHI HITACHI POWER SYSTEMS (MHPS), KYOCERA, TOTO, NGK SPARK PLUG, NGK INSULATORS, MURATA, and Denso in order to reveal their durability and find dominant degradation factor for each SOFC stacks under NEDO’s project. Large degradation behaviors arising from SO2 in air have been observed in our site for the stacks of Kyocera’s, TOTO’s, NGK’s, and Murata’s. Therefore, the stacks were reexamined by adopting sophisticated chemical filter for SO2 removal, and a concentration of the sulfur in supplied air was measured. As results, acceptable degradation data have been obtained under the operation with chemical filter. Moreover, it was found that organic sulfur compound such as dimethyl sulfide almost comes through the physical filter and fed to their stack. In this study, we report our recent results on the durability and the change of degradation behaviors with chemical filter.

Degradation Analysis of SOFC Stack Performance-Durability Test and Verification of Improved SOFCs-

Central Research Institute of Electric power Industry (CRIEPI) has operated six types of SOFC stacks, which are developed by MITSUBISHI HITACHI POWER SYSTEMS (MHPS), KYOCERA, TOTO, NGK SPARK PLUG (NTK), NGK INSULATORS (NGK), and MURATA Manufacturing (Murata), in order to investigate their durability and find dominant degradation factor for each SOFC stacks under NEDO’s project. The MHPS’s stack which was operated until 18,000 hours, showed better stability and no further degradation factor has been identified. On the other hand, peculiar behaviors of cathode overvoltage degradation have been observed in some stacks at CRIEPI site. From post analyses, sulfur was detected on their cathode in some stacks. The large cathode degradation therefore seems to be caused by the sulfur impurity in air despite SO2 concentration in the suppling air is less than 2 ppbv. Therefore, the stacks which have been observed peculiar behavior were reexamined by adopting sophisticated chemical filter for SO2 removal, and acceptable data have been obtained.

Degradation Analysis of SOFC Stack Performance-Durability Test and Verification of Improved SOFCs-

Central Research Institute of Electric power Industry (CRIEPI) has operated six types of SOFC stacks, which are developed by MITSUBISHI HITACHI POWER SYSTEMS (MHPS), KYOCERA, TOTO, NGK SPARK PLUG, NGK INSULATORS, and MURATA, to reveal their durability and find dominant degradation factor for each SOFC stack under NEDO’s project. The target of this NEDO durability project is set at 0.11%/1,000hr. In order to evaluate a performance degradation of the SOFC quantitatively and in order to quantify a performance change with time, the performance factor analysis method is required. We have been developed the electrode polarization models which is able to express SOFC performance factors such as Nernst loss (ηne), anode polarization (ηa), cathode polarization (ηc), and internal resistance IR drop (ηiR) with high prediction accuracy for six types of SOFCs. This gives us enable to make detail comparison among different type of SOFCs with the same performance analysis method inside the NEDO project. The MHPS’s stack which was operated until 16,000 hours, showed better stability and no further degradation factor has been identified. On the other hand, peculiar degradation behaviors arising from some impurities in air have been observed in our test for the stacks of Kyocera’s, TOTO’s, NTK’s, NGK’s, and Murata’s. For example, performance test exibited a rapid voltage drop within initial operation period for flattened tubular segment-in-series stack. The factor of this rapid voltage drop was increment of cathode overvoltage from a performance factor analysis result. One of possible reason for the negative effect to cathode overvoltage is sulfur contamination in the supply air from air compressor or thermal insulating foam on furnace. In this study, we report our recent activities on the durability and the dominant performance factors, and the peculiar degradation behaviors.

Observation of lightning strikes at Tokyo skytree [News From Japan

More than 260 years have passed since the famous experiment on lightning carried out by Benjamin Franklin in 1752. Everybody knows that lightning is an electromagnetic phenomenon. However, scientific observation of lightning strikes and lightning currents is still of prime importance to achieve more complete lightning protection. Researchers in the Central Research Institute of Electric Power Industry (CRIEPI) and the University of Tokyo are observing lightning strikes and measuring lightning currents at Tokyo Skytree, one of the tallest freestanding towers in the world.