Hydrogen-rich syngas production and carbon dioxide formation using aqueous urea solution in biogas steam reforming by thermodynamic analysis

Biogas is a renewable biofuel that contains a lot of CH₄ and CO₂. Biogas can be used to produce heat and electric power while reducing CH₄, one of greenhouse gas emissions. As a result, it has been getting increasing academic attention. There are some application ways of biogas; biogas can produce hydrogen to feed a fuel cell by reforming process. Urea is also a hydrogen carrier and could produce hydrogen by steam reforming. This study then employes steam reforming of biogas and compares hydrogen-rich syngas production and carbon dioxide with various methane concentrations using steam and aqueous urea solution (AUS) by Thermodynamic analysis. The results show that the utilization of AUS as a replacement for steam enriches the production of H₂ and CO and has a slight CO₂ rise compared with pure biogas steam reforming at a temperature higher than 800 °C. However, CO₂ formation is less than the initial CO₂ in biogas. At the reaction temperature of 700 °C, carbon formation does not occur in the reforming process for steam/biogas ratios higher than 2. These conditions led to the highest H₂, CO production, and reforming efficiency (about 125%). The results can be used as operation data for systems that combine biogas reforming and applied to solid oxide fuel cell (SOFC), which usually operates between 700 °C to 900 °C to generate electric power in the future.     

System optimization for effective hydrogen production via anaerobic digestion and biogas steam reforming

To construct a system for the effective hydrogen production from food waste, the conditions of anaerobic digestion and biogas reforming have been investigated and optimized. The type of agitator and reactor shape affect the performance of anaerobic digestion reactors. Reactors with a cubical shape and hydrofoil agitator exhibit high performance due to the enhanced axial flow and turbulence as confirmed by simulation of computational fluid dynamics. The stability of an optimized anaerobic digestion reactor has been tested for 60 days. As a result, 84 L of biogas is produced from 1 kg of food waste. Reaction conditions, such as reaction temperature and steam/methane ratio, affect the biogas steam reforming reaction. The reactant conversions, product yields, and hydrogen production are influenced by reaction conditions. The optimized reaction conditions include a reaction temperature of 700 °C and H₂O/CH₄ ratio of 1.0. Under these conditions, hydrogen can be produced via steam reforming of biogas generated from a two-stage anaerobic digestion reactor for 25 h without significant deactivation and fluctuation.     

Economic analysis of hydrogen production from wastewater and wood for municipal bus system

The levelized cost of hydrogen for municipal fuel cell buses has been determined using the DOE H2A model for steam methane reforming (SMR), molten carbonate fuel cell reforming (MCFC), and wood gasification using wastewater biogas and willow wood chips as energy feedstocks. 300 kg H₂/day was chosen as the design capacity. Greenhouse gas emissions were calculated for each for the three processes and compared to diesel bus emissions in order to assess environmental impact. The levelized cost per kilogram for SMR, MCFC, and gasification is $5.12, $8.59, and $10.62, respectively. SMR provided the lowest sensitivity to feedstock price, and lowest levelized cost at various scales, with competitive cost to diesel on a cost/km basis. All three technologies provide a reduction in total greenhouse gases compared to diesel bus emissions, with MCFC providing the largest reduction. These results provide preliminary evidence that small scale distributed hydrogen production for public transportation can be relatively cost-effective and have minimal environmental impact.     

Simulation of steam reforming of biogas in an industrial reformer for hydrogen production

The paper aims to investigate the steam reforming of biogas in an industrial-scale reformer for hydrogen production. A non-isothermal one dimensional reactor model has been constituted by using mass, momentum and energy balances. The model equations have been solved using MATLAB software. The developed model has been validated with the available modeling studies on industrial steam reforming of methane as well as with the those on lab-scale steam reforming of biogas. It demonstrates excellent agreement with them. Effect of change in biogas compositions on the performance of industrial steam reformer has been investigated in terms of methane conversion, yields of hydrogen and carbon monoxide, product gas compositions, reactor temperature and total pressure. For this, compositions of biogas (CH₄/CO₂ = 40/60 to 80/20), S/C ratio, reformer feed temperature and heat flux have been varied. Preferable feed conditions to the reformer are total molar feed rate of 21 kmol/h, steam to methane ratio of 4.0, temperature of 973 K and pressure of 25 bar. Under these conditions, industrial reformer fed with biogas, provides methane conversion (93.08–85.65%) and hydrogen yield (1.02–2.28), that are close to thermodynamic equilibrium condition.     

Iron oxide ores as carriers for the production of high purity hydrogen from biogas by steam–iron process

Production of high purity hydrogen (<50 ppm CO) by steam–iron process (SIP) from a synthetic sweetened biogas has been investigated making use of a natural iron ore containing up to 81 wt% of hematite (Fe₂O₃) as oxygen carrier. The presence of a lab-made catalyst (NiAl₂O₄ with NiO excess above its stoichiometric composition) was required to carry out the significant transformation of mixtures of methane and carbon dioxide in hydrogen and carbon monoxide by methane dry reforming reaction. Three consecutive sub-stages have been identified along the reduction stage that comprise A) the combustion of CH₄ by lattice oxygen of NiO and Fe₂O₃, B) catalyzed methane dry reforming and C) G–G equilibrium described by the Water-Gas-Shift reaction. Oxidation stages were carried out with steam completing the cycle. Oxidation temperature was always kept constant at 500 °C regardless of the temperature used in the previous reduction to minimize the gasification of eventual carbon deposits formed along the previous reduction stage. The presence of other oxides different from hematite in minor proportions (SiO₂, Al₂O₃, CaO and MgO to name the most significant) confers it an increased thermal resistance against sintering respecting pure hematite at the expense of slowing down the reduction and oxidation rates. A “tailor made” hematite with additives (Al₂O₃ and CeO₂) in minor proportions (2 wt%) has been used to stablish comparisons in performance between natural and synthetic iron oxides. It has been investigated the effect of the reduction temperature, the proportion of methane to carbon dioxide in the feed (CH₄:CO₂ ratio) and the number of repetitive redox cycles.     

Catalytic steam co-gasification of biomass and coal in a dual loop gasification system with olivine catalysts

A dual loop gasification system (DLG) has been previously proposed to facilitate tar destruction and H₂-rich gas production in steam gasification of biomass. To sustain the process auto-thermal, however, additional fuel with higher carbon content has to be supplied. Co-gasification of biomass in conjunction with coal is a preferred option. Herein, the heat balance of the steam co-gasification of pine sawdust and Shenmu bituminous coal in the DLG has been analyzed to verify the feasibility of the process with the help of Aspen Plus. Upon which, the co-gasification experiments in the DLG have been investigated with olivine as both solid heat carriers and in-situ tar destruction catalysts. The simulation results show that the self-heating of the DLG in the co-gasification is achieved at the coal blending ratio of 28%, gasification circulation ratio of 19 and reforming circulation ratio of 20 when the gasifier temperature 800 °C, reforming temperature 850 °C, combustor temperature 920 °C and S/C 1.1. The co-gasification experiments indicate that the tar is efficiently destructed in the DLG at the optimized reformer temperature and with olivine catalysts.     

Biogas to high purity hydrogen by methane dry reforming in TZFBR+MB and exhaustion by Steam-Iron Process. Techno–economic assessment

A techno-economic study has been carried out with the aim of analyzing the performance (product distribution and energy yields) and estimating the production costs of high purity hydrogen obtained from biogas. For such purpose and taking advantage of empirical data developed in our laboratory, it has been proposed a system consisting of a two-zone fluidized bed reactor aided by a system of permselective (Pd/Ag) metallic membranes inserted in the fluidized bed (TZFBR+MB), and a battery of several fixed bed reactors operating cycles of reduction and oxidation (Steam-Iron Process -SIP-). The feed has always been an equimolar mixture of CH₄ and CO₂ simulating a sweetened biogas. The first reactor (TZFBR+MB) can produce a stream of pure hydrogen (i.e. PEMFC quality) as permeated flow through the MB, and a retentate stream rich in all species resulting from the methane dry reforming reaction (MDR) and the water gas shift equilibrium (WGS). The singularity of this kind of complex reactors is that regeneration of the catalyst is performed in the same reactor and simultaneously to the MDR reaction because of the two-zone. Due to the reductive behavior of the retentate stream, it can be fed to a bed of solid where up to two different oxygen carriers (iron oxide with additives and cobalt ferrite) can be reduced to their metallic state. Once the solid has been completely reduced, it can be reoxidized with steam releasing a high purity hydrogen stream. Both reactors (i.e. TZFBR+MB and SIP) have been coupled in different degrees. A performance (hydrogen and energy yields) as well as costs analysis (fixed assets and operating costs) have been performed with the aid of Aspen HYSYS v9.0, used for dimensioning the equipment needed to process up to 1350 kg/h of biogas. On this way, the integrated process enhances the efficiencies of every single process allowing pure hydrogen yields up to 68% at 575 °C in the TZFBR+MB and an overall energy efficiency greater than 45%. Production costs have been found to be in the range from 4 to 15 €/kg, still high but not so far away from the target of DOE fixed in 2 $/kg by 2020.     

Experimental study on biomass steam gasification for hydrogen-rich gas in double-bed reactor

Based on Response Surface Methodology, the experiments of biomass catalytic gasification designed by Design-Expert software were carried out in steam atmosphere and double-bed reactor. The response surface was set up with three parameters (gasification temperature, the content of K-based catalyst in gasification bed and the content of Ni-based catalyst in reforming bed) for biomass gasification performance of carbon conversion efficiency and hydrogen yield to make analysis and optimization about the reaction characteristics and gasification conditions. Results showed that gasification temperature and the content of K-based catalyst in gasification bed had significant influence on carbon conversion efficiency and hydrogen yield, whilst the content of Ni-based catalyst in reforming bed affected the gasification reactions to a large extent. Furthermore, appropriate conditions of biomass steam gasification were 800 °C for gasification temperature, 82% for the content of K-based catalyst in gasification bed and 74% for the content of Ni-based catalyst in reforming bed by the optimization model. In these conditions, the steam gasification experiments using wheat straw showed that carbon conversion efficiency was 96.9% while hydrogen yield reached 64.5 mol/kg, which was in good agreement with the model prediction. The role of the reforming bed was also analyzed and evaluated, which provided important insight that the employment of reforming bed made carbon conversion efficiency raised by 4.8%, while hydrogen yield achieved a relative growth of 50.5%.     

Production of hydrogen enriched syngas from municipal solid waste gasification with waste marble powder as a catalyst

Marble processing leads to the production of high amount of waste marble powder (WMP) as a byproduct, which can be a potential health risk and has hazardous impacts on the surrounding environment. However, marble is composed of calcite making it suitable for the calcium-based catalyst. Moreover, no study has been carried out to utilize this WMP in municipal solid waste (MSW) gasification process. Therefore, there is a need to address its utilization as a potential catalyst/sorbent in the gasification of municipal solid waste (MSW). A laboratory scale batch-type fixed bed reactor was used to study the effect of WMP addition on the CO₂ adsorption, steam reforming capability and char gasification in the presence of steam. Produced gas composition, gas yield, carbon conversion efficiency and tar yield were examined at different WMP to MSW ratios. Effect of temperature and steam rate varying from 700 to 900 °C and 2.5–10 ml/min respectively were also considered in this study. WMP showed a good capacity towards hydrogen enriched syngas production as well as CO₂ adsorption and tar reforming. The H₂ concentration increased significantly with an increase in the WMP to MSW mass ratio, while CO₂ decreased. A significant effect of temperature and steam rate was also observed on the produced gas composition, gas yield, and tar content. This study helps us to understand the effect of WMP addition in MSW gasification process and thus assists in the industrial application.     

Exergy analysis of biomass staged-gasification for hydrogen-rich syngas

Using Aspen Plus simulations, exergy analyses of hydrogen-rich syngas production via biomass staged-gasification are carried out for three configurations, namely, staged-gasification with pyrolysis gas combustion and char gasification (C-1), staged-gasification with pyrolysis gas reforming and char gasification (C-2), and staged-gasification with pyrolysis gas reforming and char combustion (C-3). The results show that, for the gasification and reforming processes, the exergy loss of pyrolysis gas with tar reforming is less than that of char gasification. As for the system, it is conducive to generating hydrogen by making full use of the hydrogen element (H) in biomass instead of the H in water. The benefits of C-1 are that it removes tar and produces higher yield and concentration of hydrogen. However, C-2 is capable of obtaining higher exergy efficiency and lower exergy loss per mole of H₂ production. C-3 theoretically has greater process performances, but it has disadvantages in tar conversion in practical applications. The appropriate gasification temperature (T_G) are in the range of 700–750 °C and the appropriate mass ratio of steam to biomass (S/B) are in the range of 0.6–0.8 for C-1 and C-3; the corresponding parameters for C-2 are in the ranges of 650–700 °C and 0.7–0.8, respectively.     

Heat integration modeling of hydrogen production from date seeds via steam gasification

The purpose of the current study is to identify the potential of energy-efficient hydrogen (H₂) production from date seeds as biomass via steam gasification process along with heat integration in Gulf countries. A reaction kinetics model has been established for steam gasification with in-situ carbon dioxide (CO₂) capture of date seeds using MATLAB software. The kinetics of reactions involved in the gasification process was calculated using the optimization parameters fitting approach. The heat integration model has been developed via mixed integer nonlinear programming (MINLP) in MATLAB. In the parametric study, temperature and steam/biomass ratio considered their impact on syngas composition and energy recovery. Results showed that both variables have a strong positive effect on H₂ production and depicted maximum production of 68 mol% at a temperature of 750 °C with steam/biomass ratio of 1.2. Methane (CH₄) and CO₂ production were low in the product gas, which showed the activity of water gas shift reaction, methanation reaction, and carbonation reaction. Utilization of waste heat via process heat integration within the system reduced system's external heat load. More than 70% of energy recovered, which could be utilized for gasification and steam production. Energy analysis and process heat integration proved a prospective approach for energy-efficient and sustainable hydrogen production from date seeds.     

Coke formation in the co-production of hydrogen and phenols from pyrolysis-reforming of lignin

The phenolics derived from pyrolysis of lignin are important fractions of bio-oil, which could be reformed to generate hydrogen. Nevertheless, some phenolics are value-added chemicals and they might not have to be utilized as source of hydrogen. In this study, we have explored the concept of co-production of hydrogen and phenolics via a pyrolysis-reforming process at the low to medium temperatures of 450–650 °C over Ni/Al₂O₃ catalyst. The results indicated that, below 500 °C, pyrolysis of lignin was almost the exclusive reaction route to form phenolics of varied side chains. The effective reforming of the phenolics initiated at 600 °C and became remarkable at 650 °C. Meanwhile, cracking of the methoxy group and other side chains of the phenolics was also intense at these higher temperatures, producing phenol as the main phenolic compound. Polymerization of the phenolics on Ni/Al₂O₃ catalyst occurred from 450 to 650 °C, while the gasification of the precursors of coke accelerated at 650 °C, forming remarkably lower amount of coke together with enhanced yield of hydrogen. The coke formed from the phenolics was generally the polymeric type with abundant aliphatic structures like C–O–C, –OH and -C-H, low thermal stability, low carbon crystallinity, hydrophilic surface and amorphous morphology at 450–650 °C. The polymerization or cracking of the phenolics could form multiple carbon layers in the vicinity of nickel species, and also on alumina.     

Thermodynamics research on hydrogen production from biomass and coal co-gasification with catalyst

A model comprises two sub-models, i.e. combustion and gasification models, is developed to simulate a single fluidized bed two-step gasification process and to predict H₂ production under different conditions. The combustion sub-model which consists of volatile precipitation and char combustion sub-models. The combustion sub-model is used to forecast residual char. The gasification sub-model, based on the mass and energy balance, is used to examine thermodynamically the effect on the hydrogen production of calcium oxide as the catalyst. Moreover, the effects of the operational conditions on the hydrogen production such as biomass/coal (mass ratio), temperature, steam/coke, and calcium/coke, are simulated. The results indicate that the addition of calcium oxide at certain conditions can significantly improve hydrogen production and lower the required temperature for gasification. The model predicts that the maximum hydrogen production of 60% can be achieved under the conditions of temperature in the range of 800-850 °C, calcium/coke, steam/coke, and coal/biomass (mass ratio) are 0.5, 1.8, and 1/4, respectively. The model predictions are in good agreement with the experimental data.     

Biogas dry reforming over Ni-Al catalyst: Suppression of carbon deposition by catalyst preparation and activation

Biogas dry reforming is as an alternative renewable route for the hydrogen production. However, the major drawback of this process is the catalyst deactivation by carbon deposition and sintering. In this work, Ni-Al catalysts were studied aiming to suppress the carbon deposition in the dry reforming of biogas. The catalysts were prepared by coprecipitation and evaluated the washing step. The reactions were carried out with unreduced and reduced catalysts in a fixed bed tubular reactor using a synthetic biogas (60% CH₄ and 40% CO₂). The washing and activation steps influenced the characteristics of the catalysts and the catalytic properties in the biogas reforming. The unwashed sample resulted in an oxide containing potassium nickelate with high basicity and low surface area. Both washed samples, reduced and unreduced, showed a high amount of carbon formation, whereas no carbon formation was observed in the unwashed samples for the reactions in the temperature range of 500–750 °C. The unwashed and unreduced sample was the only one that maintained the activity during all the reaction time at 700 °C (40% CH₄ conversion and 75% CO₂ conversion), low coke amount and no evidence of sintering, which was confirmed by XRD, TPO, and SEM analyses. The carbon suppression was related to the nickelate phase and to the Ni carbide formation in the unwashed and unreduced catalyst. In summary, the carbon deposition in biogas dry reforming was completely controlled between 600 and 750 °C using the unwashed and unreduced Ni-Al catalyst.     

Refuse derived fuel hydrogasification coupled with methane steam reforming

The hydrogasification of Refuse Derived Fuel (RDF) consisting of non-recyclable plastic polymers was combined with methane steam reforming in a “hydrogen self-sustained” loop configuration. The hydrogasification unit fed by 1000 kg/h of RDF was initially modeled by Aspen plus to define best operating conditions, namely temperature, pressure and hydrogen feed flow rate. After the simulations, the temperature of the hydrogasification process has been fixed at 300 °C, the pressure at 10 bar and the hydrogen feed flow rate at 140 kg/h. The steam reforming unit operates at 850 °C while the water-gas shift is conducted at 350 °C. When all the methane produced by hydrogasification is used to feed the steam reformer, which yields H₂ that is recycled back to the hydrogasifier, the net hydrogen production is 222 kg/h with an amount of CO₂ released of 2265 kg/h. For the different process configurations adopted, the energy efficiency of the process ranges 84–89%.     

Hydrogen generation from 2,2,4-trimethyl pentane reforming over molybdenum carbide at low steam-to-carbon ratios

Because of the need for an efficient and inexpensive reforming catalyst, the objective of this work is to determine the feasibility of employing Mo₂C catalyst for the steam reforming and oxy-steam reforming of the higher hydrocarbons typical of transportation fuels such as gasoline. It is shown that bulk Mo₂C catalysts can successfully reform 2,2,4-trimethyl pentane (isooctane) to generate H₂, CO and CO₂ at very low steam/carbon ratios, without coke formation, eliminating the need for pre-reforming. Maximum hydrogen generation was observed at a S/C ratio of 1.3 and 1000 °C during SR reactions and S/C of 0.71, O₂/C of 0.12 at 900 °C during oxidative steam reforming reactions.     

Hydrogen production from acetic acid steam reforming over nickel-based catalyst synthesized via MOF process

In our earlier work, we have reported that Ni supported on γ-Al₂O₃–La₂O₃–CeO₂ (ALC) catalyst prepared via metal organic framework (MOF) was more active for acetic acid steam reforming (AASR) [1]. Here we report detailed study on the performance of this catalyst for AASR. Effects of operating conditions such as temperatures (400–650 °C), steam to carbon molar ratio (S/C) and feed flow rate (1.5–5.5 mL/h) were evaluated and optimized. Results showed an excellent activity for AASR at the molar ratio S/C = 6.5, feed flow rate = 2.5 mL/h and, at 600 °C with almost total conversion and more than 90% of H₂ yield. The ordered porous structure of embedded nickel supported catalyst promotes excellent steam reforming activity and water gas shift reaction even at low temperatures, which leads to the good stable behaviour up to 36 h of TOS. The coke formation was also significantly suppressed by ALC support. Catalyst regenerated by passing oxygen at 500 °C and followed by reduction in hydrogen also show a good activity. Catalysts were characterized by DT-TGA, XRD, TEM, H₂-TPR and N₂-adsorption-desorption to understand the micro structure and coke deposition behaviour.     

Simulation and optimization of hydrogen production by steam reforming of natural gas for refining and petrochemical demands in Lebanon

Steam reforming of natural gas produces the majority of the world's hydrogen (H₂) and it is considered as a cost-effective method from a product yield and energy consumption point of view. In this work, we present a simulation and an optimization study of an industrial natural gas steam reforming process by using Aspen HYSYS and MATLAB software. All the parameters were optimized to successfully run a complete process including the hydrogen production zone units (reformer reactor, high temperature gas shift reactor HTS and low temperature gas shift reactor LTS) and the purification zone units (absorber and methanator). Optimum production of hydrogen (87,404 MT/year) was obtained by fixing the temperatures in the reformer and the gas shift reactors (HTS & LTS) at 900 °C, 500 °C and 200 °C respectively while maintaining a pressure of 7 atm, and a steam to carbon ratio (S/C) of 4. Moreover, ~99% of the undesired CO₂ and CO gases were removed in the purification zone and a reduction of energy consumption of 77.5% was reached in the heating and cooling units of the process.     

Deactivation and in-situ regeneration of Dy-doped Ni/SiO2 catalyst in CO2 reforming of methanol

The self-regeneration of Ni-based catalysts has been considered as a promising approach to maintain not only a continuous but also economical process. However, the effect of catalyst nature, operating temperature, amount and types of carbon deposits on the effectiveness of the in-situ regeneration is still not well-investigated. Therefore, in this work, the self-regeneration ability of the undoped and Dy-doped Ni/SiO₂ catalysts, which were prepared by the same impregnation method, were examined in the dry reforming of methanol. The physicochemical properties of the fresh and spent catalysts were analyzed by various techniques such as X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR), oxygen temperature-programmed desorption (O₂-TPD), transmission electron microscopy (TEM), N₂-BET isothermal adsorption. The nature and chemical reactivity of coke deposits formed during dry reforming at various temperatures (550, 600, and 650 °C) and the regeneration possibility of used catalysts through CO₂ gasification at these temperatures were investigated by the in-situ temperature-programmed gasification by CO₂ (TPCO₂). The Dy additive significantly improves the dispersion of the nickel active sites of Ni/SiO₂ catalyst, as demonstrated by the decreased Ni crystal size as well as the increased specific surface area and reduction degree of the catalyst. Furthermore, Dy promotion increases the quantity of oxygen vacancies and the nature of oxygen species, thereby improving the catalyst activity and stability. Specifically, methanol conversion dropped from 93% to 96%–61% and 31% for undoped Ni/SiO₂ at 600 °C and 650 °C, respectively and from about 99% to 87% (at 600 °C) and 52% (at 650 °C) for Dy-doped catalyst.     

Hydrogen production from biomass and plastic mixtures by pyrolysis-gasification

The addition of plastics to the steam pyrolysis/gasification of wood sawdust with and without a Ni/Al₂O₃ catalyst was investigated in order to increase the production of hydrogen in the gaseous stream. To study the influence of the biomass/plastic ratio in the initial feedstock, 5, 10 and 20 wt.% of polypropylene was introduced with the wood in the pyrolysis reactor. To investigate the effect of plastic type, a blend of 80 wt.% of biomass and 20 wt.% of either polypropylene, high density polyethylene, polystyrene or a mixture of real world plastics was fed into the reactor. The results showed that a higher gas yield (56.9 wt.%) and a higher hydrogen concentration and production (36.1 vol.% and 10.98 mmol H₂ g⁻¹ sample, respectively) were obtained in the gaseous fraction when 20 wt.% of polypropylene was mixed with the biomass. This significant improvement in gas and hydrogen yield was attributed to synergetic effects between intermediate species generated via co-pyrolysis. The Ni/Al₂O₃ catalyst dramatically improved the gas yield as well as the hydrogen concentration and production due to the enhancement of water gas shift and steam reforming reactions. Very low amounts of coke (less than 1 wt.% in all cases) were formed on the catalyst during reaction, with the deposited carbonaceous material being of the filamentous type. The Ni/Al₂O₃ catalyst was shown to be effective for hydrogen production in the co-pyrolysis/gasification process of wood sawdust and plastics.