Dynamic modelling and sensitivity analysis of a tubular SOFC fuelled with NH3 as a possible replacement for H2

A dynamic model of an ammonia fed-tubular solid oxide fuel cell (NH 3-SOFC) is developed and presented. The model accounts for diffusion, inherent impedance, transport (heat and mass transfer), electrochemical reactions, activation and concentration polarizations of electrodes and the ammonia decomposition reaction. Sensitivity analyses are conducted upon the effects of design parameters on the fuel cell performance. Dynamic output voltage, fuel-cell-tube temperature and efficiency responses to step changes in the inlet fuel flow pressure with different values of design parameters are discussed. It is found that among the studied parameters, the inner cell tube diameter has the strongest effect on fuel cell efficiency. On the other hand, the influence of cathodic porosity on fuel cell performance and transient response is higher than that of the anodic porosity. The transient response with different sizes of micro and macro-structures is studied and it is observed that changing the fuel cell length has the most effect. Also NH 3-SOFC is compared with H 2-SOFC and it is found that the performance of the former is close to that of the latter thus signifying that ammonia is a suitable fuel for substituting in place of hydrogen

Neural network predictive control of a tubular solid oxide fuel cell

The dynamic behavior and control of a tubular solid oxide fuel cell will be studied in this paper. The effect of fuel/air temperature and pressure will be investigated. Controlling the average stack temperature is the final objective of this study due to a high operating temperature of the system. In this case, temperature fluctuation induces thermal stress in the electrodes and electrolyte ceramics; therefore, the cell temperature distribution should be kept as constant as possible. A mathematical modeling based on first principles is developed. The fuel cell is divided into five subsystems and the factors such as mass/energy/momentum transfer, diffusion through porous media, electrochemical reactions, and polarization losses inside the subsystems are presented. Dynamic fuel-cell-tube temperature responses of the cell to step changes in conditions of the feed streams will be presented. A neural network model predictive controller (NNMPC) is then implemented to control the cell-tube temperature through manipulation of the temperature of the inlet air stream. The results show that the control system can successfully reject unmeasured step changes (disturbances) in the load resistance

Modeling of a tubular-SOFC: the effect of the thermal radiation of fuel components and CO participating in the electrochemical process

A mathematical model based on first principles is developed to study the effect of heat and electrochemical phenomena on a tubul solid oxide fuel cell (SOFC). The model accounts fordiffusion, inherent impedance, transport (momentum, heat and mass transfer) processes, internal reforming/shifting reaction, electrochemical processes, and potential losses (activation, concentration, and ohmic losses). Thermal radiation of fuel gaseous components is considered in detail in this work in contrast to other reported work in the literature. The effect of thermal radiation on SOFC performance is shown by comparing with a model without this factor. Simulation results indicate that at higher inlet fuel flow pressures and also larger SOFC lengths the effect of thermal radiation on SOFC temperature becomes more significant. In this study, the H2 and CO oxidation is also studied and the effect of CO oxidation on SOFC performance is reported. The results show that the model which accounts for the electrochemical reaction ofCO results in better SOFC performance than other reported models. This work also reveals that at low inlet fuel flow pressures the CO and H2 electrochemical reactions are competitive and significantly dependent on the CO/H2 ratio inside the triple phase boundary. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA,Weinheim

Economic feasibility analysis of a solar energy and solid oxide fuel cell-based cogeneration system in Malaysia

The current study presents a concept of a cogeneration system integrated with solar energy and solid oxide fuel cell technology to supply electrical and thermal energy in Malaysia. To appraise the performance, the system is analysed with two case studies considering three modes of operation. For the case-1, typical per day average electricity and hot water demand for a single family have been considered to be 10.3 kWh and 235 l, respectively. For the case 2, electricity and hot water demand are considered for the 100 family members. Energy cost, payback period, future economic feasibility and the environmental impact of the system are analysed for both cases using an analytical approach. The overall system along with individual component efficiency has been evaluated, and the maximum efficiency of the overall system is found to be 48.64 % at the fuel cell operation mode. In the present study, the proposed system shows 42.4 % cost effectiveness at higher load. Energy costs for case-1 and case-2 have been found to be approximately $0.158 and$0.091 kWh-1, respectively, at present. Energy costs are expected to be $0.112 and$0.045 kWh-1 for the case-1 and case-2, respectively, considering future (i.e. for the year 2020) component cost

Mathematical modeling of solid oxide fuel cells: A review

This paper presents a review of studies on mathematical modeling of solid oxide fuel cells (SOFCs) with respect to the tubular and planar configurations. In this work, both configurations are divided into five subsystems and the factors such as mass/energy/momentum transfer, diffusion through porous media, electrochemical reactions with and without CO oxidation, shift and reforming reactions, and polarization losses inside the subsystems are discussed. Using variety of fuels fed to SOFCs is issued and their effect on the system is compared briefly. A short review of solid oxide fuel cell configurations and different flow manifolding are also presented in this study. Novel models based on statistical data-driven approach existing in the literatures are considered shortly. Although many studies on solid oxide fuel cells modeling have been done, still more research needs to be done to improve the models in order to predict the fuel cell behaviors more accurately. At the end of this paper the works and studies that can be done for improving the fuel cell models is suggested and pointed by the authors

Electrokinetic remediation of nickel from low permeability soil

Electrokinetic remediation of nickel from low permeability soil using titanium electrodes having inter-electrode spacing of 10 cm was carried out in a cylindrical reactor. The influences of current density, voltage gradient and electrolyte pH were investigated upon removal efficiency for 60 h experimental runs. Efficiency improved from 49.3 to 57.2 when the current density was increased from 4.36 mA/cm 2 to 13.1 mA/cm 2. Furthermore, an enhancement in efficiency from 38.5 to 54.3 was observed when voltage gradient increased from 1 V/cm to 2 V/cm (at 13.1 mA/cm 2). Further increase in voltage gradient to 2.5 V/cm improved efficiency during initial runs. However, an overall reduction of 3.2 was observed after 60 h of operation in comparison to that obtained at 2 V/cm. This may be attributed to precipitation and localized accumulation of metallic ions. An inverse relationship between efficiency and electrolyte pH was also observed (at 13.1 mA/cm 2 and 2 V/cm). Although a removal of 74.1 was achieved at pH = 4.5, the system required optimization as the nickel content in treated soil was above the maximum values given in international standards

On site electrochemical production of sodium hypochlorite disinfectant for a power plant utilizing seawater

This investigation deals with the application of electrochemical technology for the onsite generation of sodium hypochlorite (NaOCl) from seawater for utilization in the power industry. The interaction at different levels of several variables namely, the electrode type and their surface area ratio, current density, and inter-electrode spacing were monitored. A laboratory scale reactor having two electrodes was fabricated and implemented to achieve the objective. The highest production of NaOCl was obtained using a titanium electrode coated with a dimensionally stable anode (DSA) that gave high-current efficiency and superior durability. Maximum production was achieved using titanium under conditions of 72.4 mA/cm 2 current density, 7 cm inter-electrode spacing and a value of 1 for the anode to cathode surface area ratio. Although at higher surface area ratios, more NaOCl production was observed, the increase in its production was marginal for ratios above unity in comparison to ratios below unity. Hence, a ratio of unity was chosen as a practical value which also reduced the costs of the process. This was found to be similar to, if not better than, results reported in the literature. Optimization studies using design of experiments are recommended in the future

Application of carbon materials in redox flow batteries

The redox flow battery (RFB) has been the subject of state-of-the-art research by several groups around the world. Most work commonly involves the application of various low-cost carbon-polymer composites, carbon felts, cloth, paper and their different variations for the electrode materials of the RFB. Usually, the carbon-polymer composite electrode has relatively high bulk resistivity and can be easily corroded when the polarised potential on the anode is more positive than that of oxygen evolution and this kind of heterogeneous corrosion may lead to battery failure due to electrolyte leakage. Therefore, carbon electrodes with high electrical conductivity, acid-resistance and electrochemical stability are highly desirable. This review discusses such issues in depth and presents an overview on future research directions that may help commercialise RFB technology. A comprehensive discussion is provided on the advances made using nanotechnology and it is envisaged that if this is combined with ionic liquid technology, major advantages could be realised. In addition the identification of RFB failure mechanisms by means of X-ray computed nano tomography is expected to bring added benefits to the technology