Comparison of co–gasification efficiencies of coal,lignocellulosic biomass and biomass hydrolysate for high yield hydrogen production

The diversity in the chemical composition of lignocellulosic feedstocks can affect the conversion technologies employed for hydrogen production. Gasification and co–gasification activities of lignocellulosic biomass, biomass hydrolysate, and coal were evaluated for hydrogen rich gas production. The hydrolysates of biomass materials showed the best performance for gasification. The results indicated that biomass hydrolysates obtained from lignocellulosic biomass were more sensitive to degradation and therefore, produced more hydrogen and gaseous products than that of lignocellulosic biomass. The effects of feed (kenaf and sorghum hydrolysate), flow rate (0.3–2.0 mL/min) and temperature (700–900 °C) on hydrogen production and gasification yields were investigated. It was observed that 0.5 mL/min the optimum feed flow rate for the maximum total gas and hydrogen production. Synergism effects were observed for co–gasification of coal/biomass and coal/biomass hydrolysate. In all co–gasification processes, the main component of the gas mixture was hydrogen (≥70%).     

Hydrogen production from steam gasification of biomass: Influence of process parameters on hydrogen yield – A review

Steam gasification is considered one of the most effective and efficient techniques of generating hydrogen from biomass. Of all the thermochemical processes, steam gasification offers the highest stoichiometric yield of hydrogen. There are several factors which influence the yield of hydrogen in steam gasification. Some of the prominent factors are: biomass type, biomass feed particle size, reaction temperature, steam to biomass ratio, addition of catalyst, sorbent to biomass ratio. This review article focuses on the hydrogen production from biomass via steam gasification and the influence of process parameters on hydrogen yield.     

Experimental study and development of an improved sulfur–iodine cycle integrated with HI electrolysis for hydrogen production

The sulfur–iodine (SI or IS) thermochemical cycle assembled with solar or nuclear energy has been proposed as a large-scale, clean and renewable hydrogen production method. In present work, an improved SI cycle integrated with HI electrolysis for hydrogen production was developed according to experiments and simulation. The mathematical models of HI electrolysis using proton exchange membrane (PEM) electrolytic cell was developed, and then the user-defined module of HI electrolysis was set up through Aspen Plus and verified by experimental data. After designing and simulating the new flowsheet of the SI cycle based on HI electrolysis, 10 L/h of H₂ and 5 L/h of O₂ were obtained. The theoretic thermal efficiency of flowsheet reached 25–42% in terms of the utilization of waste heat. An ideal thermal efficiency of 33.3% through the proper internal heat exchange in the flowsheet was determined. Sensitivity analyses of parameters in the system were conducted. Increasing proton transfer number of PEM electrolytic cell in HI section improved the thermal efficiency of SI cycle. The ratio of distillate to feed rate and the plate number of distillation column in H₂SO₄ section were the most sensitive factors to the heat duty of overall SI cycle. The proposed new flowsheet for SI cycle is competitive to the flowsheets previously proposed in the field of flowsheet simplification.     

Laminar-burning velocities of hydrogen–air and hydrogen–methane–air mixtures: An experimental study

The laminar burning velocities of hydrogen–air and hydrogen–methane–air mixtures are very important in designing and predicting the progress of combustion and performance of combustion systems where hydrogen is used as fuel. In this work, laminar flame velocities of hydrogen–air and different composition of hydrogen–methane–air mixtures (from 100% hydrogen to 100% methane) have been measured at ambient temperatures for variable equivalence ratios (ER=0.8–3.2$\mathrm{ER}=0.8–3.2$). A modified test rig has been developed from the former Cardiff University ‘Cloud Chamber’ for this experimental study. The rig comprises of a 250 mm length cylindrical stainless steel explosion bomb enclosed at one end with a stainless steel plug which houses an internal stirrer to allow mixing. The other end is sealed with a 120 mm diameter round quartz window. Optical access for filming flame propagation is afforded via two diametrically opposed quartz windows in both sides. Flame speeds are determined within the bomb using a high-speed Schlieren photographic technique. This method is an accurate way to determine the flame–speed and the burning velocities were then derived using a CHEMKIN computer model to provide the expansion ratio. The design of the test facility ensures the flame is laminar which results in a spherical flame which is not affected by buoyancy. The experimental study demonstrated that increasing the hydrogen percentage in the hydrogen–methane mixture brought about an increase in the resultant burning velocity and caused a widening of the flammability limits. This experiments also suggest that a hydrogen–methane mixture (i.e. 30% hydrogen+70% methane) could be a competitive alternative fuel for existing combustion plants.     

Biogas reforming for hydrogen production over a Ni–Co bimetallic catalyst: Effect of operating conditions

A Ni–Co bimetallic catalyst, Ni–Co/La₂O₃/Al₂O₃, was prepared by conventional incipient wetness impregnation. It shows a high level of activity and excellent stability for biogas reforming. This work examines how operating conditions, such as the reaction temperature, operating pressure, feed ratio, gas hourly space velocity (GHSV), and CO₂ excessive coefficient, affect the catalytic performances of the catalyst. The experimental biogas is simulated with CH₄ and CO₂ at a molar ratio of 1, without any dilute gas. The catalyst was also characterized by XRD, BET, TEM and TG-DSC. In a stability test of 510 h under the conditions of 800 °C, 1 atm, and a GHSV of 6000 ml g_cat⁻¹ h⁻¹, the average coking rate over the catalyst was only about 0.0374 mg g_cat⁻¹ h⁻¹. The experimental results also indicate that the dynamic equilibrium between the deposition and gasification of carbon deposited on the surface of the catalyst can be established during the reaction. The aggregation of metallic Ni/Co and the formation of filamentous carbon over the surface of the catalyst can be inhibited effectively. During the last 50 h of the 510 h stability test, the average conversion of CH₄ and CO₂, the selectivity to H₂ and CO, and ratio of H₂/CO were 95.2%, 96.7%, 95.0%, 98.3%, and 0.96, respectively.     

Feasibility study of hydrogen production for micro fuel cell from activated Al–In mixture in water

A safe and environmental-friendly method of hydrogen production from milled Al–In–Zn–salt mixture in water was proposed in this paper. The 10 h—milled Al–In–Zn–salt mixture had high reactivity and produced hydrogen in water at room temperature. Its improved reactivity came from that the additive Zn and salts facilitate to the negative shift of Al–In alloy and benefited the combination of Al, In and Zn in the milling process. Optimized the composition content, 1 g of 10 h—milled Al—5 wt%In—3 wt%Zn—2 wt%NaCl mixture had highest hydrogen yield of 1035 mL hydrogen/1 g Al in 4 min of hydrolysis reaction in water, corresponding to 9.21 wt% hydrogen (excluding water mass). Hydrogen supplying from milled Al–In–Zn–salt mixture was performed for micro fuel cell and 0.96 W was produced with the stable hydrogen supply rate. Therefore, the milled Al–In–Zn–salt mixture could be a feasible alternative for providing a source of CO₂ free hydrogen production to supply micro fuel cell.     

An optimization study on the finned tube heat exchanger used in hydride hydrogen storage system – analytical method and numerical simulation

Metal hydrides show great potential for hydrogen storage. However, for efficient hydrogen storage, thermal management is the technical barrier. Among the different heat exchangers proposed in the literature, finned tube heat exchangers are of great technological interest due to their adaptability to wide range of practical applications, high compactness and high heat transfer efficiency. In the present paper, the optimization of finned heat exchanger considering both enhanced heat transfer and vessel volume efficiency is conducted. A semi-analytical expression of heat transfer rate from a single fin is derived. The effects of fin dimension (fin thickness and radius) on the heat exchanger performance are studied. It was shown that the thermal resistance of the whole heat exchanger can be reduced by increasing the fin radius and decreasing the fin thickness, while the fin volume is kept fixed. In the second part of the study, a 2-D numerical simulation was performed in order to validate the results of the analytical study. The effects of two parameters (cooling tube diameter, the fin length) on the hydrogen charging time were highlighted. The increasing in the tube diameter from 2.5 mm to 5 mm results to 25% reduction of the charging time, which is very noticeable. On the other hand, given a reactor radius, increasing the length of fin reduces the overall thermal resistance of the reactor-heat exchanger. The results showed that the decreasing of the thermal resistance of 13% leads to a decreasing in charging time of 42%. Finally, it was found that the results of the numerical simulation agreed qualitatively with those of analytical study. Therefore, the analytical solution presented can be used for a quick assessment of the finned tube heat exchanger design without significant errors.     

A review on wind energy and wind–hydrogen production in Turkey: A case study of hydrogen production via electrolysis system supplied by wind energy conversion system in Central Anatolian Turkey

Studies about investigation of hydrogen production from wind energy and hydrogen production costs for a specific region were reviewed in this study and it was shown that these studies were rare in the world, especially in Turkey. Therefore, the costs of hydrogen, hydrogen production quantities using a wind energy conversion system were considered as a case study for 5 different locations of Nigde, Kirsehir, Develi, Sinop and Pinarbasi located in the Central Anatolia in Turkey. Annual wind energy productions and costs for different wind energy conversion systems were calculated for 50 m, 80 m and 100 m hub heights. According to wind energy costs calculations, the amounts and costs of hydrogen production were computed. Furthermore, three different scenarios were taken into account to produce much hydrogen. The results showed that the hydrogen production using a wind energy conversion system with 1300 kW rated power had a range from 1665.24 kgH₂/year in Nigde at 50 m hub height to 6288.59 kgH₂/year in Pinarbasi at 100 m hub height. Consequently, Pinarbasi and Sinop have remarkable wind potential and potential of hydrogen production using a wind–electrolyzer energy system.     

Experimental study of Ni/CeO2 catalytic properties and performance for hydrogen production in sulfur–iodine cycle

The Ni/CeO₂ catalysts with different calcination temperatures have been tested for hydrogen production in sulfur–iodine (SI or IS) cycle. TG-FTIR, BET, XRD, HRTEM and TPR were performed for catalyst characterization. It was found that the Ni²⁺ ions could be inserted into the ceria lattice. This brought about the strong interaction between Ni and CeO₂ and the generation of oxygen vacancies. Perfect crystallites were formed in the catalysts. It was evident that there was a change in particle size and morphology as the calcination temperature increased from 300 to 900 °C. The Ni/CeO₂ catalysts with different calcination temperatures showed better catalytic activity by comparison with blank yield, especially Ni/Ce700. A hypothetic mechanism of HI catalytic decomposition on Ni/CeO₂ has been constructed. The two important reactive sites were assumed for HI catalytic decomposition.     

Metallic and carbonaceous –based catalysts performance in the solar catalytic decomposition of methane for hydrogen and carbon production

Solar catalytic decomposition of methane (SCDM) was investigated in a solar furnace facility with different catalysts. The aim of this exploratory study was to investigate the potential of the catalytic methane decomposition approach providing the reaction heat via solar energy at different experimental conditions. All experiments conducted pointed out to the simultaneous production of a gas phase composed only by hydrogen and un-reacted methane with a solid product deposited into the catalyst particles varying upon the catalysts used: nanostructured carbons either in form of carbon nanofibers (CNF) or multi-walled carbon nanotubes (MWCNT) were obtained with the metallic catalyst whereas amorphous carbon was produced using a carbonaceous catalyst. The use of catalysts in the solar assisted methane decomposition present some advantages as compared to the high temperature non-catalytic solar methane decomposition route, mainly derived from the use of lower temperatures (600–950 °C): SCDM yields higher reaction rates, provides an enhancement in process efficiency, avoids the formation of other hydrocarbons (100% selectivity to H₂) and increases the quality of the carbonaceous product obtained, when compared to the non-catalytic route.     

Influence of the structural and surface characteristics of activated carbon on the catalytic decomposition of hydrogen iodide in the sulfur–iodine cycle for hydrogen production

Coal-based activated carbon (AC-COAL) catalysts subjected to acid treatment were tested to evaluate their performance on hydrogen-iodide (HI) decomposition for hydrogen production in sulfur-iodine (SI or IS) cycle. The effects of acid treatment on catalysts and the relations between sample properties and catalytic activities were discussed. The AC-COAL obtained by non-oxidative acid treatments had the best catalytic activity. However, the catalytic activity of AC-COAL decreased after the treatment of nitric acid. Higher surface area, higher carbon contents, lower ash contents and fewer surface oxidation groups contributed to the catalytic activity of ACs. HI decomposition on the AC surface itself may be due to high densities of unpaired electrons associated with structural defects and edge plane sites with similar structural ordering. Moreover, the oxygen-containing groups reduced the electron transfer capability associated with the basal plane sites.     

A comparative study on the performance of mesoporous SBA-15 supported Pd–Zn catalysts in partial oxidation and steam reforming of methanol for hydrogen production

Using mesoporous SBA-15 (Santa Barbara Amorphous No. 15, a mesoporous material) as support, Pd–Zn nanocatalysts with varying Pd and Zn content were tested for hydrogen production from methanol by partial oxidation and steam reforming reactions. The physico-chemical characteristics of the synthesized SBA-15 support were confirmed by XRD, N₂ adsorption, SEM and TEM analyses. The PdZn alloy formation during the reduction of Pd–Zn/SBA-15 was revealed by XRD and DRIFT study of adsorbed CO. Also, the correlation between Pd and Zn loadings and PdZn alloy formation was studied by XRD and TPR analyses. The metallic Pd surface area and total uptakes of CO and H₂ were measured by chemisorption at 35 °C. The metallic Pd surface area values are in linear proportion with the Pd loading. The formation of PdZn alloy during high temperature reduction was confirmed by a shift in absorption frequency of CO on Pd sites to lower frequency due to higher electron density at metal particles resulted from back-donation. The reduced Pd–Zn/SBA-15 catalysts were tested for partial oxidation of methanol at different temperatures and found that catalyst with 4.5 wt% Pd and 6.75 wt% Zn on SBA-15 showed better H₂ selectivity with suppressed CO formation due to the enhanced Pd dispersion as well as larger Pd metallic surface area. The O₂/CH₃OH ratio is found to play a significant role in CH₃OH conversion and H₂ selectivity. The performance of 4.5 wt% Pd–6.75 wt% Zn/SBA-15 catalyst in steam reforming of methanol was also tested. Comparatively, the H₂ selectivity is significantly higher than that in partial oxidation, even though the CH₃OH conversion is less. Finally, the long term stability of the catalyst was tested and the nature of PdZn alloy after the reactions was found to be stable as revealed from the XRD pattern of the spent catalysts.     

Stability of nickel catalyst supported by mesoporous alumina for hydrogen iodide decomposition and hybrid decomposer development in sulfur–iodine hydrogen production cycle

We propose a hybrid HI decomposer, which combines a high-temperature catalytic decomposition reactor with a dual bed temperature-swing decomposer. For the high temperature step, we screened and identified a catalyst that is stable above 700 °C by preparing nickel catalysts supported on mesoporous alumina and evaluating their activity toward the high-temperature catalytic decomposition reaction. The catalysts achieved HI decomposition yields up to 23% at 650 °C and maintained over 20% yield after 100 h of operation. For the temperature-swing process, we investigated the adsorption, desorption, and regeneration efficiency, and the optimal regeneration temperature of nickel catalysts supported on silica/alumina adsorbents. The optimal regeneration temperature was 400 °C. Based on these results, we propose hybrid HI decomposers in two configurations: 1) residual HI decomposer and 2) HI concentrator. The residual HI decomposer improves the overall conversion efficiency to levels above the thermodynamic limit, while the HI concentrator increases the concentration of HI by simple temperature control, even at below-azeotropic HI concentrations.     

Mechanism of hydrogen production in [Fe–Fe]-hydrogenases: A quantum mechanics/molecular mechanics study

[Fe–Fe]-hydrogenases are a class of metalloenzymes that catalyze the production of H₂ from two protons and two electrons. Crystal structures for [Fe–Fe]-hydrogenases found in two species – Clostridium pasteurianum (CpI) and Desulfovibrio desulfuricans (DdH) – show very similar active sites. However, the catalytic mechanism has not as yet been fully clarified. We employed density functional theory (DFT) within a QM/MM method to investigate proposed mechanisms of hydrogen production by DdH and CpI hydrogenases and their dependence on the protein environment of the active sites. For each mechanism investigated, we found only minor differences between the CpI and DdH hydrogenases in terms of the intermediate active site structures, although one mechanism follows a lower energy path for DdH hydrogenase, while the other mechanism follows a lower energy path for the CpI hydrogenase. We note, however, that the high activation energy we calculated for a step unique to one of the mechanisms might preclude it, making the energy-path comparison for the two mechanisms unnecessary.     

Multi-tube Pd–Ag membrane module for pure hydrogen production: Comparison of methane steam and oxidative reforming

The results of steam and oxidative reforming of methane carried out through a membrane system are being compared in this work. The capability of the experimental setup to produce ultra-pure hydrogen has been evaluated in terms of hydrogen yield under different operating conditions.     

Availability,supply technology and costs of residual forest biomass for energy – A case study in northern China

In theory, China has vast potential forest resources for production of energy, but utilization on an industrial scale has been negligible. We assessed the practical possibilities and barriers for a forest energy business in a case study in northern China. The specific objectives of the study were 1) to assess the availability of forest biomass for energy production, 2) to determine feasible supply chains, and 3) to estimate the biomass fuel supply costs. Based on the case study results, the stand-level removals of the intended feedstock were low and the supply costs were relatively high. Suggestions for increasing the raw material basis, lowering the costs and further research and development were given. We conclude that although the case study area may not be promising from the feedstock point of view, the development could be started with small steps and proven technology. In order to avoid expensive mistakes further research for transfer of know-how and technology is needed.     

Synthesis and optimization of Mo–Ni–Se@NiSe core-shell nanostructures as efficient and durable electrocatalyst for hydrogen evolution reaction in alkaline media

Synthesis conditions are among the most influential factors in the electrocatalytic properties of the samples studied for the hydrogen evolution reaction (HER). In this study, conditions of NiSe synthesis over a Mo–Ni–Se layer were optimized to create core-shell nanostructures with excellent electrocatalytic properties. To optimize the synthesis conditions, first, two electrodeposition techniques in constant potential and pulse potential conditions were investigated and then the optimal temperature for electrodeposition between 5, 25, 40, and 60 °C was found. The electrocatalytic activity of the synthesized samples was investigated using linear sweep voltammetry (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronopotentiometry tests in a 1 M KOH solution. Preliminary results showed that pulsed electrodeposition of NiSe could improve the electrocatalytic activity of Mo–Ni–Se by forming durable and suitable nanostructures, while electrodeposited NiSe at constant potential could reduce the electrocatalytic activity of the electrode by forming a dense structure. Then, to determine the appropriate temperature, electrodeposition at the optimal pulse potential at four temperatures of 5, 25, 40, and 60 °C was used to synthesize NiSe on Mo–Ni–Se. The final results showed that the sample synthesized at 60 °C with an electrochemically active surface area of 2870 cm² had the highest hydrogen production sites and required only an overpotential of 77 mV to achieve a current density of 10 mA cm^?2.     

Distributed Generation in an isolated grid: Methodology of case study for Lesvos – Greece

The purpose of this article is to evaluate the economic effects of Distributed Generation (DG) in isolated grids and in particular Lesvos island in Greece. DG penetration is expected to rise in the following years since the island’s wind potential is still not exploited at a satisfying level. The necessity to replace the existing oil-fired power plant together with the need to cut down on greenhouse gases makes DG, and in particular wind turbines quite a promising technology. The present study with the use of specific software simulates the current electricity production for a whole year looking at its technical and economic performance. The sensitivity analysis that is carried out shows the effects of a potential increase in renewable energy sources (RES) capacity. Different sensitivity factors are investigated such as diesel price and hub height. The results show the environmental benefits of increased RES capacity and the variation of the cost of electricity production which remains high compared to other interconnected areas in Greece.     

Multigeneration system exergy analysis and thermal management of an industrial glassmaking process linked with a Cu–Cl cycle for hydrogen production

A multigeneration system for hydrogen production linked with a glassmaking process via thermal management is examined in this study. The exhaust gas is interconnected with a Rankine cycle and the copper-chlorine (Cu–Cl) cycle for hydrogen production. The present system consists of a steam Rankine cycle, Cu–Cl cycle with multistage compression, double-stage organic Rankine cycle, and multi-effect desalination system. A Cu–Cl cycle based on the four-step model is employed with the proposed system. The useful system outputs are electricity, hydrogen, and fresh water. The simulation software packages utilized in the analysis and modeling are Engineering Equation Solver and Aspen Plus. The energy efficiency of the overall system is 36.5% while 38.1% is the exergy efficiency. The parametric studies are conducted to investigate the system performance. In addition, the effects of exhaust gas variables, such as flow rate, temperature, and pressure are examined to investigate the system performance.     

CFD analysis and experimental measurements of the liquid aluminum spray formation for an Al–H2O based hydrogen production system

The paper proposes a combined approach between numerical modeling and experimental measurements for the analysis of a cogeneration system based on the reaction of liquid aluminum and water steam. Scrap aluminum is used for hydrogen production and the primary one is employed as an energy carrier to transport the energy from the alumina reduction system to the site of the suggested plant. The analysis focuses on the liquid aluminum injection phase immediately downstream the nozzle.High frequency thermo-cameras are employed to qualitatively assess the thermal behaviour the liquid aluminum jet. Fast imaging techniques are used to capture the multiphase flow pattern of the liquid metal jet during the injection phase.The experimental results are used to validate a 2D multi-phase CFD approach. The computational fluid dynamics model of the injection phase is created and used to extend the measurements and deepen the understanding of the thermo-fluid dynamics behaviour of the system. In particular, the influence of different nozzles diameters and different injection pressures on the liquid aluminum jet is investigated.A modular approach is adopted for the domain subdivision in order to represent accurately all the geometrical features, while the volume of fluid approach is used to model the multi-phase flow distribution in the real geometry under actual operating conditions. Finally, a good agreement between the measurements and the calculations is found.