Energy and exergy analysis of hydrogen production by solid oxide steam electrolyzer plant

Energy and exergy analysis has been conducted to investigate the thermodynamic–electrochemical characteristics of hydrogen production by a solid oxide steam electrolyzer (SOSE) plant. All overpotentials involved in the SOSE cell have been included in the thermodynamic model. The waste heat in the gas stream of the SOSE outlet is recovered to preheat the H₂O stream by a heat exchanger. The heat production by the SOSE cell due to irreversible losses has been investigated and compared with the SOSE cell's thermal energy demand. It is found that the SOSE cell normally operates in an endothermic mode at a high temperature while it is more likely to operate in an exothermic mode at a low temperature as the heat production due to overpotentials exceeds the thermal energy demand. A diagram of energy and exergy flows in the SOSE plant helps to identify the sources and quantify the energy and exergy losses. The exergy analysis reveals that the SOSE cell is the major source of exergy destruction. The energy analysis shows that the energy loss is mainly caused by inefficiency of the heat exchangers. The effects of some important operating parameters, such as temperature, current density, and H₂O flow rate, on the plant efficiency have been studied. Optimization of these parameters can achieve maximum energy and exergy efficiencies. The findings show that the difference between energy efficiency and exergy efficiency is small as the high-temperature thermal energy input is only a small fraction of the total energy input. In addition, the high-temperature waste heat is of high quality and can be recovered. In contrast, for a low-temperature electrolysis plant, the difference between the energy and exergy efficiencies is more apparent because considerable amount of low-temperature waste heat contains little exergy and cannot be recovered effectively. This study provides a better understanding of the energy and exergy flows in SOSE hydrogen production and demonstrates the importance of exergy analysis for identifying and quantifying the exergy destruction. The findings of the present study can further be applied to perform process optimization to maximize the cost-effectiveness of SOSE hydrogen production.     

Electrochemical modeling of hydrogen production by proton-conducting solid oxide steam electrolyzer

An electrochemical model was developed to study the J–V characteristics of a solid oxide steam electrolyzer based on proton-conducting electrolyte (H-SOSE) for hydrogen production. All important overpotentials, namely, activation, concentration, and ohmic overpotentials, were considered in the model. The model was validated as the simulation results agreed well with experimental data from literature. It was found that the optimal designs of H-SOSE and conventional SOSE based on oxygen ion-conducting electrolyte (O-SOSE) are totally different. For conventional O-SOSE, the anode-supported configuration has been identified as the most favorable design for high energy conversion efficiency. However, in the present study, it was found that the cathode-supported configuration was the most favorable design for H-SOSE. The electrochemical performance of the H-SOSE can be further enhanced by operating the cell at high temperature or high steam molar fraction. The electrochemical modeling analyses provide a better understanding of the working principles of H-SOSE and can serve as an effective tool for design optimization.     

Theoretical analysis of reversible solid oxide fuel cell based on proton-conducting electrolyte

A single reversible solid oxide fuel cell (RSOFC) can accomplish two functions: (1) as a solid oxide steam electrolyzer (SOSE) for hydrogen production and (2) as a solid oxide fuel cell (SOFC) for power generation. An electrochemical model was developed to study the performance of an RSOFC based on a proton-conducting electrolyte (RSOFC-H). In both SOSE and SOFC modes, the hydrogen electrode-supported configuration was identified as the most favorable design to achieve high energy conversion efficiency of RSOFC-H. For comparison, in a previous study on conventional RSOFC based on an oxygen ion-conducting electrolyte (RSOFC-O), the hydrogen electrode-supported configuration was found to be favorable in the SOFC mode but such configuration would cause high concentration overpotential in the SOSE mode. Thus, the oxygen electrode-supported configuration was desirable for RSOFC-O operating in the SOSE mode. The results obtained in this study show that RSOFC-H has a natural advantage over RSOFC-O in terms of structural design. The modeling study signifies the difference between RSOFC-H and RSOFC-O and can serve as a useful tool for further design optimization.     

Configuration design and performance optimum analysis of a solar-driven high temperature steam electrolysis system for hydrogen production

A new solar-driven high temperature steam electrolysis system for hydrogen production is presented, in which the main energy consumption processes such as steam electrolysis processes, heat transfer processes, and product compression processes are included. The detailed thermodynamic-electrochemical modeling of the solid oxide steam electrolysis (SOSE) is carried out, and consequently, the electrical and thermal energy required by every energy consumption process are determined. The efficiency of the system is derived, from which the effects of some of the important parameters such as the operating temperature, component thickness of the SOSE, leakage resistance, effectiveness of heat exchangers, and inlet rate of water on the performance of the system are discussed. It is found that the efficiency attains its maximum when a proper current density is chosen. The ratio of the required electric energy to the total energy input of the system is calculated, and consequently, the problem how to rationally operate the solar concentrating beam splitting device is investigated. The results obtained will be helpful for further understanding the optimal design and performance improvement of a practical solar-driven high temperature steam electrolysis system for hydrogen production.     

Hydrogen production through steam electrolysis: Model-based steady state performance of a cathode-supported intermediate temperature solid oxide electrolysis cell

Hydrogen production via steam electrolysis may involve less electrical energy consumption than conventional low temperature water electrolysis, reflecting the improved thermodynamics and kinetics at elevated temperatures. The present paper reports on the development of a one-dimensional dynamic model of a cathode-supported planar intermediate temperature solid oxide electrolysis cell (SOEC) stack. The model, which consists of an electrochemical model, a mass balance, and four energy balances, is here employed to study the steady state behaviour of an SOEC stack at different current densities and temperatures. The simulations found that activation overpotentials provide the largest contributions to irreversible losses while concentration overpotentials remained negligible throughout the stack. For an average current density of 7000 A m⁻² and an inlet steam temperature of 1023 K, the predicted electrical energy consumption of the stack is around 3 kW h per normal m³ of hydrogen, significantly smaller than those of low temperature stacks commercially available today. However, the dependence of the stack temperature distribution on the average current density calls for strict temperature control, especially during dynamic operation.     

Methanol fuel processor and PEM fuel cell modeling for mobile application

The use of hydrocarbon fed fuel cell systems including a fuel processor can be an entry market for this emerging technology avoiding the problem of hydrogen infrastructure. This article presents a 1 kW low temperature PEM fuel cell system with fuel processor, the system is fueled by a mixture of methanol and water that is converted into hydrogen rich gas using a steam reformer. A complete system model including a fluidic fuel processor model containing evaporation, steam reformer, hydrogen filter, combustion, as well as a multi-domain fuel cell model is introduced. Experiments are performed with an IDATECH FCS1200™ fuel cell system. The results of modeling and experimentation show good results, namely with regard to fuel cell current and voltage as well as hydrogen production and pressure. The system is auto sufficient and shows an efficiency of 25.12%. The presented work is a step towards a complete system model, needed to develop a well adapted system control assuring optimized system efficiency.     

Performance evaluation of a solarized gas turbine system integrated to a high temperature electrolyzer for hydrogen production

In this paper, the performance of a solar gas turbine (SGT) system integrated to a high temperature electrolyzer (HTE) to generate hybrid electrical power and hydrogen fuel is analyzed. The idea behind this design is to mitigate the losses in the electrical power transmission and use the enthalpy of exhaust gases released from the gas turbine (GT) to make steam for the HTE. In this context, a GT system is coupled with a solar tower including heliostat solar field and central receiver to generate electrical power. To make steam for the HTE, a flameless boiler is integrated to the SGT system applying the SGT extremely high temperature exhaust gases as the oxidizer. The results indicate that by increasing the solar receiver outlet temperature from 800 K to 1300 K, the solar share increases from 22.1% to 42.38% and the overall fuel consumption of the plant reduces from 7 kg/s to 2.7 kg/s. Furthermore, flameless mode is achievable in the boiler while the turbine inlet temperature (TIT) is maintained at the temperatures higher than 1314 K. Using constant amounts of the SGT electrical power, the HTE voltage decreases by enhancing the HTE steam temperature which result in the augmentation of the overall hydrogen production. To increase the HTE steam temperature from 950 K to 1350 K, the rate of fuel consumption in the flameless boiler increases from 0.1 m/s to 0.8 m/s; however, since the HTE hydrogen production increases from 4.24 mol/s to 16 mol/s it can be interpreted that the higher steam temperatures would be affordable. The presented hybrid system in this paper can be employed to perform more thermochemical analyses to achieve insightful understanding of the hybrid electrical power-hydrogen production systems.     

Asymmetric behavior of solid oxide cells between fuel cell and electrolyzer operations

The electrochemical performance of solid oxide cells (SOCs) is investigated under both fuel cell and electrolyzer operations to understand their asymmetric behavior between the two operation modes. The current–voltage and electrochemical impedance characteristics of a hydrogen-electrode-supported cell are experimentally analyzed. Also, a numerical model is developed to reproduce the cell performance and to understand the internal resistances of the cell. Partial pressures of supplied gas and load current are varied to evaluate their effects on the cell performance. The gas partial pressures of hydrogen and steam supplied to the hydrogen electrode are kept equivalent so that the cell performance can be fairly compared between the two operation modes when the same current is applied. It is found that the origin of the asymmetry is mostly from the hydrogen electrode; both activation and concentration overpotentials show asymmetric behavior particularly at high current densities. A numerical experiment is also conducted by deliberately changing parameters in the model. Asymmetry in the activation overpotential is found to be originated from the non-identical charge-transfer coefficients in the Butler–Volmer equation and also from the non-uniform gas concentration formed in the hydrogen electrode under current-biased conditions. On the other hand, asymmetry in the concentration overpotential is associated with the non-equimolar counter diffusion of hydrogen and steam caused by the effect of Knudsen diffusion. Therefore, enhancing gas transport in the hydrogen electrode and reducing the contribution of Knudsen diffusion are effective approaches to reduce asymmetry not only in the concentration overpotential but also in the activation overpotential.     

Analysis of pressurized operation of 10 layer solid oxide electrolysis stacks

High temperature steam electrolysis using solid oxide electrolysis cell (SOEC) technology can provide hydrogen as fuel for transport or as base chemical for chemical or pharmaceutical industry. SOECs offer a great potential for high efficiencies due to low overpotentials and the possibility for waste heat use for water evaporation. For many industrial applications hydrogen has to be pressurized before being used or stored. Pressurized operation of SOECs can provide benefits on both cell and system level, due to enhanced electrode kinetics and downstream process requirements. Experimental results of water electrolysis in a pressurized SOEC stack consisting of 10 electrolyte supported cells are presented in this paper. The pressure ranges from 1.4 to 8 bar. Steady-state and dynamically recorded U(i)-curves as well as electrochemical impedance spectroscopy (EIS) were carried out to evaluate the performance of the stack under pressurized conditions. Furthermore a long-term test over 1000 h at 1.4 bar was performed to evaluate the degradation in exothermic steam electrolysis mode. It was observed that the open circuit voltage increases with higher pressure due to well-known thermodynamic relations. No increase of the limiting current density was observed with elevated pressure for the ESC-stacks (electrolyte supported cell) that were investigated in this study. The overall and the activation impedance were found to decrease slightly with higher pressure. Within the impedance studies, the ohmic resistance was found to be the most dominant part of the entire cell resistance of the studied electrolyte supported cells of the stack. A constant current degradation test over 1000 h at 1.4 bar with a second stack showed a voltage degradation rate of 0.56%/kh.     

High temperature water electrolysis in solid oxide cells

Hydrogen production via high temperature steam electrolysis is a promising technology as it involves less electrical energy consumption compared to conventional low temperature water electrolysis, as consequence of the more favourable thermodynamic and electrochemical kinetic conditions for the reaction. This paper reports on the Solid Oxide Electrolyser Cell (SOEC) performance as function of the operating parameters temperature, humidity and current density. Current–voltage measurements are coupled with impedance spectroscopy, in order to identify the different loss terms in the cell behaviour coming from the electrolyte resistance and the electrode processes. Remarkably high electrical-to-hydrogen energy conversion efficiencies are achieved (e.g., cell voltages of 1.0 and 1.25 V at −1 A cm⁻² and 900 and 800 °C, respectively). Results obtained, moreover, show that an important limitation for the electrolysis reaction, at least at moderate absolute humidity values below about 70 vol.% can be the steam diffusion in the hydrogen/steam electrode.     

Decentralized generation of electricity from biomass with proton exchange membrane fuel cell

Biomass can be applied as the primary source for the production of hydrogen in the future. The biomass is converted in an atmospheric fluidized bed gasification process using steam as the gasifying agent. The producer gas needs further cleaning and processing before the hydrogen can be converted in a fuel cell; it is assumed that the gas cleaning processes are able to meet the requirements for a PEM-FC. The compressed hydrogen is supplied to a hydrogen grid and can be used in small-scale decentralized CHP units. In this study it is assumed that the CHP units are based on low temperature PEM fuel cells. For the evaluation of alternative technologies the whole chain of centralized hydrogen production from biomass up to and including decentralized electricity production in PEM fuel cells is considered.Two models for the production of hydrogen from biomass and three models for the combined production of electricity and heat with PEM fuel cells are built using the computer program Cycle-Tempo. Two different levels of hydrogen purity are considered in this evaluation: 60% and 99.99% pure hydrogen. The purity of the hydrogen affects both the efficiencies of the hydrogen production as well as the PEM-FC systems. The electrical exergy efficiency of the PEM-FC system without additional heat production is calculated to be 27.66% in the case of 60% hydrogen and 29.06% in the case of 99.99% pure hydrogen. The electrical exergy efficiencies of the whole conversion chain appear to be 21.68% and 18.74%, respectively. The high losses during purification of the hydrogen gas result in a higher efficiency for the case with low purity hydrogen. The removal of the last impurities strongly increases the overall exergy losses of the conversion chain.     

Electrochemical study of a planar solid oxide fuel cell: Role of support structures

This paper presents a performance analysis of a planar solid oxide fuel cell (SOFC) with different support structures, i.e., electrode (anode and cathode) and electrolyte supports. An electrochemical model, taking into account structural and operational parameters and gas diffusion at the electrodes, is used to analyze the characteristics of the planar SOFC. Simulation results demonstrate that under cell operation at an intermediate temperature (1073 K), an anode-supported SOFC is superior to an electrolyte- and cathode-supported SOFC. Analysis of individual cell voltage loss indicates that ohmic loss dominates the performance of an electrolyte-supported SOFC whereas activation and ohmic overpotentials constitute the major loss in an electrode-supported counterpart. Sensitivity analyses of the anode-supported SOFC show that decreasing the electrolyte and anode thickness can improve cell performance. A decrease in operating temperature causes the cell to operate at a lower range of current density due to an increase in ohmic and activation overpotentials. Further, increasing the operating pressure and degree of pre-reforming reduces the concentration overpotential and thereby enhances cell performance.     

Thermo-fluid dynamics modelling of steam electrolysis in fully-assembled tubular high-temperature proton-conducting cells

Electrolysis based on renewable energies offers a promising carbon-free solution for hydrogen generation and storage. The recent developments of proton ceramic electrolysis cells operating at intermediate temperatures bear promise of superior energy efficiency compared to oxide ion conducting electrolytes. Here, a proton ceramic Single Engineering Unit (SEU) design is optimized for steam electrolysis using a computational fluid dynamics (CFD) model implemented in a COMSOL Multiphysics software. The SEU is an all-in-one tubular cell arrangement that constitutes the smallest electrolysis unit and enables efficient, adaptable pressurized hydrogen generation. The parametrical modelling study is conducted for two adiabatic operation scenarios with distinct steam conversion rates and tested for multiple key parameters, namely internal and external chamber pressures and inlet stream temperature. The modelling results show that low steam conversions enable operation at higher current densities and that the thermoneutral voltage for a fixed steam conversion is highly sensitive to the process conditions and operation modes. The increment of the pressure of the generated hydrogen implies a reduced production rate at thermoneutral voltage, although it can be compensated with an enhanced steam pressure or a reduced inlet temperature. Additionally, the introduction of a porous medium as the SEU current collector in the steam chamber enhances heat transport within this chamber. The area specific resistance of the system determines the current density, enforcing an adaption of the area of the electrolyser to satisfy the target hydrogen production and energy efficiency. The resulting proposed SEU design and adapted operational parameters allow effective delivery of pressurized dry hydrogen for a wide range of conditions and applications.     

Electrochemical high temperature technology for hydrogen production or direct electricity generation

Solid oxide electrolyte cells have been developed for hydrogen production from water vapour with high overall efficiency. On the basis of experimental data plant concepts have been designed for autothermal electrolysis operation with low temperature (∼150°C) steam input at a mean cell voltage of ∼1.3 V. The production of modules of series connected cells is under way in order to demonstrate the vapour electrolysis in a small, but complete plant for ∼3.5 kW hydrogen output. The actual state of the art of this technology will be described. It has been demonstrated that the solid oxide cells can be operated also in the reverse mode acting as fuel cells for hydrogen as well as for carbon monoxide. Calculations of overall performance of high temperature fuel cell plants show that, e.g. for electricity generation from natural gas, efficiencies of about 60% can be achieved with the additional advantage of extremely low NO_x emission.     

Equivalent electrical model for a proton exchange membrane (PEM) electrolyser

In this work, an electrical equivalent model for a proton exchange membrane (PEM) electrolyser has been developed. Through experimental analysis, the input current–voltage (I–V) characteristic for a single PEM electrolyser cell has been modelled under steady-state conditions. It has been developed by using electrical equivalent circuit topology in which the useful power conversion and losses have been taken into account. Electrolytic hydrogen production rates of PEM electrolyser cell have been calculated with respect to the input current and power. The developed model has been tested with experiments results at the nominal operating temperature. The experimental results have been verified with the developed model results and the relative errors between them are around 1–2%. It has been observed that the electrolytic hydrogen production rate increases with the input current in a linear fashion. But the variation of electrolytic hydrogen production rate with the input electrical power is non-linear (i.e. logarithmic). These characteristics are verified by using the developed electrical equivalent model of PEM electrolyser cell. The parameters of the developed model can also be defined by taking into account of temperature and pressure effects. The equivalent electrical model of PEM electrolyser is very useful for analysing the electrical energy system behaviour in which the energy is stored in the form of electrolytic hydrogen.     

Performance analysis of a solid oxide fuel cell with reformed natural gas fuel

In the present study a two‐dimensional model of a tubular solid oxide fuel cell operating in a stack is presented. The model analyzes electrochemistry, momentum, heat and mass transfers inside the cell. Internal steam reforming of the reformed natural gas is considered for hydrogen production and Gibbs energy minimization method is used to calculate the fuel equilibrium species concentrations. The conservation equations for energy, mass, momentum and voltage are solved simultaneously using appropriate numerical techniques. The heat radiation between the preheater and cathode surface is incorporated into the model and local heat transfer coefficients are determined throughout the anode and cathode channels. The developed model has been compared with the experimental and numerical data available in literature. The model is used to study the effect of various operating parameters such as excess air, operating pressure and air inlet temperature and the results are discussed in detail. The results show that a more uniform temperature distribution can be achieved along the cell at higher air‐flow rates and operating pressures and the cell output voltage is enhanced. It is expected that the proposed model can be used as a design tool for SOFC stack in practical applications. Copyright © 2009 John Wiley & Sons, Ltd.     

Technological development of hydrogen production by solid oxide electrolyzer cell (SOEC)

High-temperature solid oxide electrolyzer cell (SOEC) has great potential for efficient and economical production of hydrogen fuel. In this paper, the state-of-the-art SOEC technologies are reviewed. The developments of the important steam electrolyzer components, such as the ionic conducting electrolyte and the electrodes, are summarized and discussed. YSZ and LSGM are promising electrolyte materials for SOEC working at high and intermediate temperatures, respectively. When co-doping or a blocking layer is applied, SDC or GDC are possible electrolyte materials for intermediate-temperature SOEC. Ni–YSZ remains to be the optimal cathode material. Although LSM–YSZ is widely used as SOEC anode, other materials, such as LSF–YSZ, may be better choices and need to be further studied. Considering the cell configuration, planar SOECs are preferred due to their better manufacturability and better electrochemical performance than tubular cells. Anode depolarization is an effective method to reduce the electrical energy consumption of SOEC hydrogen production. Although some electrochemical models and fluid flow models are available, the present literature is lacking detailed modeling analyses of the coupled heat/mass transfer and electrochemical reaction phenomena of the SOEC. Mathematical modeling studies of SOEC with novel structures and anode depolarization processes will be fruitful for the development of SOEC. More works, both experimental and theoretical, are needed to further develop SOEC technology to produce hydrogen more economically and efficiently for the coming hydrogen economy.     

Effect of the vacancy close to heat exchange wall on the heat transfer performance of the solid particles steam generator using waste heat in a methanol steam reforming hydrogen production system

With the massive consumption of fossil fuels and it resulted in significant carbon emissions, it is urgent to find an alternative clean energy source. Hydrogen has been regarded as one of the most promising energy candidates for the next generation. It is a great approach that methane steam reforming for hydrogen production by rational utilization of industrial waste heat, which significantly minimizes carbon emissions and develops methanol steam reforming technology. A solid particle steam generator based on the primary heat exchange method has been proposed, which can provide the heat and steam in the methanol steam reforming hydrogen production system. The quasi-two-dimensional packing heat transfer model of solid particles steam generator was set up.The effect of distance change between the vacancy and the cold wall and distance change between vacancies on heat transfer performance of the steam generator and hydrogen production capacity were studied. As the distance between the vacancy and the wall increases, the heat transfer performance of the steam generator gradually deteriorates, so the steam production of the steam generator decreases, and the system's hydrogen production capacity is reduced, the maximum of the heat flux and the minimum of the apparent thermal resistance are 34.67 kW/m² and 12.02 K/W, respectively. As the distance between vacancies increases, the heat transfer performance of the steam generator is gradually optimized slightly. To maintain the hydrogen production capacity, vacancies should be avoided to appear 2 layers of particles away from the heat exchange wall in the particles steam generator. From the results of the study, the farther the distance between vacancies, the better the steam production and hydrogen production capacity.     

Performance of an anode-supported solid oxide fuel cell with direct-internal reforming of ethanol

A theoretical study of a solid oxide fuel cell (SOFC) fed by ethanol is presented in this study. The previous studies mostly investigated the performance of ethanol-fuelled fuel cells based on a thermodynamic analysis and neglected the presence of actual losses encountered in a real SOFC operation. Therefore, the real performance of an anode-supported SOFC with direct-internal reforming operation is investigated here using a one-dimensional isothermal model coupled with a detailed electrochemical model for computing ohmic, activation, and concentration overpotentials. Effects of design and operating parameters, i.e., anode thickness, temperature, pressure, and degree of ethanol pre-reforming, on fuel cell performance are analyzed. The simulation results show that when SOFC is operated at the standard conditions (V = 0.65 V, T = 1023 K, and P = 1 atm), the average power density of 0.51 W cm⁻² is obtained and the activation overpotentials represent a major loss in the fuel cell, followed by the ohmic and concentration losses. An increase in the thickness of anode decreases fuel cell efficiency due to increased anode concentration overpotential. The performance of the anode-supported SOFC fuelled by ethanol can be improved by either increasing temperature, pressure, degree of pre-reforming of ethanol, and steam to ethanol molar ratio or decreasing the anode thickness and fuel flow rate at inlet. It is suggested that the anode thickness and operating conditions should be carefully determined to optimize fuel cell efficiency and fuel utilization.     

Modeling the effect of non-linear process parameters on the prediction of hydrogen production by steam reforming of bio-oil and glycerol using artificial neural network

Biomass-derived substrates such as bio-oil and glycerol are gaining wide acceptability as feedstocks to produce hydrogen using a steam reforming process. The wide acceptability can be attributed to a huge amount of glycerol and bio-oil obtained as by-products of biodiesel production and pyrolysis processes. Several parameters have been reported to affect the production of hydrogen by biomass steam reforming. This study investigates the effect of non-linear process parameters on the prediction of hydrogen production by biomass (bio-oil and glycerol) steam reforming using artificial neural network (ANN) modeling technique. Twenty different multilayer ANN model architectures were tested using datasets obtained from the bio-oil and glycerol steam reforming. Two algorithms namely Levenberg-Marquardt and Bayesian regularization were employed for the training of the ANNs. An optimized network configuration consisting of 3 input layer 14 hidden neurons, 1 output layer, and 3 input layer, 5 hidden neurons, and 1 output layer were obtained for the Levenberg-Marquardt and Bayesian regularization trained network, respectively for hydrogen production by bio-oil steam reforming. While an optimized network configuration consisting of 5 input nodes, 9 hidden neurons, 1 output node, and 5 input nodes, 8 hidden neurons, and 1 output node were obtained for Levenberg-Marquardt and Bayesian regularization trained network, respectively for hydrogen production by glycerol steam reforming. Based on the optimized network, the predicted hydrogen production from the bio-oil and glycerol steam agreed with the actual values with the coefficient of determination (R²) > 0.9. A low mean square error of 3.024 × 10⁻²⁴ and 6.22 × 10⁻¹⁵ for the optimized for Levenberg-Marquardt and Bayesian regularization-trained ANN, respectively. The neural network analyses of the two processes showed that reaction temperature and glycerol-to-water molar ratio were the most relevant factors that influenced the production of hydrogen by bio-oil and glycerol steam reforming, respectively. This study has demonstrated the robustness of the ANN as a technique for investigating the effect of non-linear process parameters on hydrogen production by bio-oil and glycerol steam reforming.