Investigation of coal gasification hydrogen and electricity co-production plant with three-reactors chemical looping process

This paper analyzes a novel process for producing hydrogen and electricity from coal, based on chemical looping combustion (CLC) and gas turbine combined cycle, allowing for intrinsic capture of carbon dioxide. The core of the process consists of a three-reactors CLC system, where iron oxide particles are circulated to: (i) oxidize syngas in the fuel reactor (FR) providing a CO₂ stream ready for sequestration after cooling and steam vapor condensation, (ii) reduce steam in the steam reactor (SR) to produce hydrogen, (iii) consume oxygen in the air reactor (AR) from air releasing heat to sustain the thermal balance of the CLC system and to generate electricity. A compacted fluidized bed, composed of two fuel reactors, is proposed here for full conversion of fuel gases in FR. The gasification CLC combined cycle plant for hydrogen and electricity cogeneration with Fe₂O₃/FeAl₂O₄ oxygen carriers was simulated using ASPEN^® PLUS software. The plant consists of a supplementary firing reactor operating up to 1350 °C and three-reactors SR at 815 °C, FR at 900 °C and AR at 1000 °C. The results show that the electricity and hydrogen efficiencies are 14.46% and 36.93%, respectively, including hydrogen compression to 60 bar, CO₂ compression to 121 bar, The CO₂ capture efficiency is 89.62% with a CO₂ emission of 238.9 g/kWh. The system has an electricity efficiency of 10.13% and a hydrogen efficiency of 41.51% without CO₂ emission when supplementary firing is not used. The plant performance is attractive because of high energy conversion efficiency and low CO₂ emission. Key parameters that affect the system performance are also discussed, including the conversion of steam to hydrogen in SR, supplementary firing temperature of the oxygen depleted air from AR, AR operation temperature, the flow of oxygen carriers, and the addition of inert support material to the oxygen carrier.     

Oxygen-carrier selection and thermal analysis of the chemical-looping process for hydrogen production

The three-reactor chemical-looping process (TRCL) for the production of hydrogen from natural gas is quite attractive for both CO₂ capture and hydrogen production. The TRCL process consists of a fuel reactor, a steam reactor and an air reactor. In the fuel reactor, natural gas is oxidized to CO₂ and H₂O by the lattice oxygen of the oxygen carrier. In the steam reactor, the steam is reduced to hydrogen through oxidation of the reduced oxygen carrier. In the air reactor, the oxygen carrier is fully oxidized by air. In this process, the oxygen carrier is recirculated among the three reactors, which avoids direct contact between fuel, steam and air. In this study, various candidate materials were proposed for the oxygen carrier and support, and a thermal analysis of the process was performed. The oxygen carrier for the process must have the ability to split water into hydrogen in its reduced state, which is a different chemical property from that of the chemical-looping combustion medium. The selection of the oxygen carrier and support require careful consideration of their physical and chemical properties. Fe₂O₃, WO₃ and CeO₂ were selected as oxygen carriers. Thermal analysis indicated an expected hydrogen production of 2.64 mol H₂ per mol CH₄ under thermoneutral process conditions. The results indicated that hydrogen production was affected mainly by the steam-conversion rate. The solid-circulation rate and temperature drop in the fuel reactor were calculated for the selected oxygen carriers with different metal oxide contents and solid-conversion rates.     

Chemical looping gasification of biomass char for hydrogen-rich syngas production via Mn-doped Fe2O3 oxygen carrier

Because of its low cost, an iron-based oxygen carrier is a promising candidate for hydrogen-rich syngas production from the chemical looping gasification of biomass. However, it needs modification from a reactivity point of view. In this study effect of Mn doping on Fe₂O₃ has been investigated for hydrogen-rich syngas production from biomass char at different temperatures (700–900 °C) and steam flow rates (60–100 μL/min). Several techniques (XRD, XPS, BET, and TPR-H₂) have been utilized to characterize fresh and spent oxygen carriers. The result demonstrated Mn-doing boosted the redox activity and the amount of oxygen vacancies, which increased hydrogen gas generation. Hydrogen production displayed different behavior across temperatures due to detecting Fe₂O₃ and MnFeO₃ phases for spent oxygen carriers. For the Fe₂O₃ oxygen carrier hydrogen gas yield is 1.67 Nm³/kg which is due to reduction of Fe₂O₃ phase to Fe₃O₄. However, the MnFe₂O₄ spinel phase detected in the spent MnFeO₃ oxygen carrier is a reason for improving hydrogen gas yield to 1.84 Nm³/kg. Change reaction temperature from 900 °C to 850 °C reduced hydrogen gas yield from 1.84 Nm³/kg to 1.83 Nm³/kg for with MnFeO₃ oxygen carrier. Regarding different steam flows, the proper flow rates that can maintain the formed phases and obtained best hydrogen gas yield are 80 and 90 μL/min, respectively. Meanwhile, the best hydrogen gas yield (2.21Nm³/kg) are obtained with MnFeO₃ oxygen carrier at optimum conditions (850 °C and 90 μL/min).     

Experimental investigation of chemical-looping hydrogen generation using Al2O3 or TiO2-supported iron oxides in a batch fluidized bed

Chemical-looping hydrogen generation (CLHG) is a novel technology for hydrogen production with inherent separation of CO₂. Three oxygen carriers Fe₂O₃ using inert materials Al₂O₃ or TiO₂ as support were prepared by mechanical-mixing method, i.e., Fe90Al10 (90%Fe₂O₃ + 10%Al₂O₃), Fe60Al40 (60%Fe₂O₃ + 40%Al₂O₃) and Fe60Ti40 (60%Fe₂O₃ + 40%Al₂O₃). Reactivity of the three oxygen carriers was first determined under CO reduction, steam oxidation and air oxidation atmospheres at 900 °C in a thermogravimetric analyzer. Then experiments to simulate the CLHG process were carried out in a batch fluidized bed. In the fluidized bed, all of the three oxygen carriers showed good reactivity over the multi-cycle experiments at 900 °C, and Fe60Al40 had the highest hydrogen yield. The reactivity of the oxygen carrier supported on Al₂O₃ was higher than that on TiO₂, which interacted with iron oxide forming FeTiO₃. The reactivity of Fe60Al40 was better than that of Fe90Al10. No deterioration of the oxygen carrier occurred after the multiple cycles, but for Fe90Al10 some agglomeration was detected. At 600-900 °C, higher temperature favored deeper reduction of iron oxide and increased the hydrogen production, while carbon deposition in the reduction period was suppressed with the rise of temperature. In the reduction, the conversion of fuel gas was constrained by thermodynamics in a single-stage reactor, and a compact fuel reactor was proposed for a full conversion of gaseous fuels.     

A strategy of mid-temperature natural gas based chemical looping reforming for hydrogen production

Steam methane reforming (SMR) needs the reaction heat at a temperature above 800 °C provided by the combustion of natural gas and suffers from adverse environmental impact and the hydrogen separated from other chemicals needs extra energy penalty. In order to avoid the expensive cost and high power consumption caused by capturing CO₂ after combustion in SMR, natural gas Chemical Looping Reforming (CLR) is proposed, where the chemical looping combustion of metal oxides replaced the direct combustion of NG to convert natural gas to hydrogen and carbon dioxide. Although CO₂ can be separated with less energy penalty when combustion, CLR still require higher temperature heat for the hydrogen production and cause the poor sintering of oxygen carriers (OC). Here, we report a high-rate hydrogen production and low-energy penalty of strategy by natural gas chemical-looping process with both metallic oxide reduction and metal oxidation coupled with steam. Fe₃O₄ is employed as an oxygen carrier. Different from the common chemical looping reforming, the double side reactions of both the reduction and oxidization enable to provide the hydrogen in the range of 500–600 °C under the atmospheric pressure. Furthermore, the CO₂ is absorbed and captured with reduction reaction simultaneously.Through the thermodynamic analysis and irreversibility analysis of hydrogen production by natural gas via chemical looping reforming at atmospheric pressure, we provide a possibility of hydrogen production from methane at moderate temperature. The reported results in this paper should be viewed as optimistic due to several idealized assumptions: Considering that the chemical looping reaction is carried out at the equilibrium temperature of 500 °C, and complete CO₂ capture can be achieved. It is assumed that the unreacted methane and hydrogen are completely separated by physical adsorption. This paper may have the potential of saving the natural gas consumption required to produce 1 m³ H₂ and reducing the cost of hydrogen production.     

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.     

Use of heavy fraction of bio-oil as fuel for hydrogen production in iron-based chemical looping process

Chemical looping hydrogen (CLH) process with renewable energy sources as fuel shows the potential of producing pure hydrogen with inherent capture of CO₂ in a low-cost and sustainable way. The heavy fraction (HF) of bio-oil, derived from the fast pyrolysis of biomass and characterized as an energy carrier with difficulty in upgrading itself to bio-fuel or chemicals, was used in this study to generate H₂. Four low-cost iron-based oxygen carriers including an ilmenite and three iron ores were initially evaluated with respect to their reducibility and the ability to minimize carbon or iron carbide (Fe₃C) formation in a thermogravimetric analyzer (TGA). The reactivity and cyclic performance of the selected best candidate was then assessed in a laboratory scale fixed-bed reactor with HF bio-oil as fuel. The screening test in TGA showed that ilmenite was superior over the three iron ores in terms of promoting CO conversion and minimizing carbon or Fe₃C formation. Ilmenite could maintain its increasing reducibility with the increase of surrounding CO concentration, in contrast with the iron ores that were deactivated seriously by the formed carbon or Fe₃C. Subsequent CLH test with ilmenite and HF bio-oil showed that the reducibility and H₂ production capacity of ilmenite were strongly dependent on the operating temperature. The steam oxidation step at 950 °C yielded H₂ concentration and hydrogen yield exceeding all of those observed at the other investigated temperatures because of the deepest reduction degree of ilmenite at 950 °C. The decrease in the reducibility and H₂ production capacity of ilmenite in the cyclic test could be ascribed to the poorer physical structure of ilmenite with cycles.     

Chemical looping steam reforming of bio-oil for hydrogen-rich syngas production: Effect of doping on LaNi0.8Fe0.2O3 perovskite

Chemical looping steam reforming of bio-oil is novel conversion technology utilizing waste energy, which is an advantage to reduce cost and improve environmental. However, complex reaction process between oxygen carrier and bio-oil constrain its development. In this study, perovskite based La_0.8M_0.2Ni_0.8Fe_0.2O₃ (M = Ca, Ce and Zr) were investigated as an oxygen carrier for chemical looping steam reforming of bio-oil model reaction. The perovskites were prepared via sol-gel method and the effect of doping for reforming of acetic acid as bio-oil model compound is also investigated. Among all the perovskite tested, Ce doped La_0.8Ce_0.2Ni_0.8Fe_0.2O₃ oxygen carrier gave superior and stable catalytic performance for 1440 min at 600 °C and steam/carbon mole ratio (S/C = 2). The fresh and spent oxygen carriers were characterized using XRD, H₂-TPR, CO₂-TPD, TG-DTG, Dielectric constant, Raman, XPS and XANES. Doping with base metal generally, improved coke resistance ability of the perovskite. CO₂-TPD and XPS analysis reveal that the highest carbon resistance for La_0.8Ce_0.2Ni_0.8Fe_0.2O₃ perovskite is due to enhanced stronger surface basicity and oxygen adsorption. From DFT simulation and Dielectric constant results, the better activity for La_0.8Ce_0.2Ni_0.8Fe_0.2O₃ is attributed to its adsorption ability of reactants, oxygen and electron transfer from sub-surface to surface of the perovskite.     

Parametric study of chemical looping combustion for tri‐generation of hydrogen,heat, and electrical power with CO2 capture

In this article, a novel cycle configuration has been studied, termed the extended chemical looping combustion integrated in a steam‐injected gas turbine cycle. The products of this system are hydrogen, heat, and electrical power. Furthermore, the system inherently separates the CO₂ and hydrogen that is produced during the combustion. The core process is an extended chemical looping combustion (exCLC) process which is based on classical chemical looping combustion (CLC). In classical CLC, a solid oxygen carrier circulates between two fluidized bed reactors and transports oxygen from the combustion air to the fuel; thus, the fuel is not mixed with air and an inherent CO₂ separation occurs. In exCLC the oxygen carrier circulates along with a carbon carrier between three fluidized bed reactors, one to oxidize the oxygen carrier, one to produces and separate the hydrogen, and one to regenerate the carbon carrier. The impacts of process parameters, such as flowrates and temperatures have been studied on the efficiencies of producing electrical power, hydrogen, and district heating and on the degree of capturing CO₂. The result shows that this process has the potential to achieve a thermal efficiency of 54% while 96% of the CO₂ is captured and compressed to 110 bar. Copyright © 2005 John Wiley & Sons, Ltd.     

Characteristics of biomass gasification using chemical looping with iron ore as an oxygen carrier

Experiments regarding to biomass gasification using chemical looping (BGCL) were carried out in a fluidized bed reactor under argon atmosphere. Iron ore (natural hematite) was used as an oxygen carrier in the study. Similar to steam, a performance of oxygen carrier which provided oxygen source for biomass gasification by acting as a gasifying medium was found. An optimum Fe₂O₃/C molar ratio of 0.23 was determined with the aim of obtaining maximum gas yield of 1.06 Nm³/kg and gasification efficiency of 83.31%. The oxygen carrier was gradually deactivated with reduction time increasing, inhibiting the carbon and hydrogen in biomass from being converted into synthesis gas. The fraction of Fe²⁺ increased from 0 to 47.12% after reduction time of 45 min, which implied that active lattice oxygen of 49.75% was consumed. The oxygen carrier of fresh and reacted was analyzed by a series of characterization methods, such as X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDX).     

Characteristics of microalgae gasification through chemical looping in the presence of steam

As a novel gasification technology, chemical looping gasification (CLG) was considered as a promising technology in solid fuel gasification. In this work, CLG was applied into microalgae, and the characteristics of syngas production and oxygen carrier in the presence of steam were obtained through experiments in a fixed bed reactor. The results showed that the partial oxidation of oxygen carrier improved the gasification efficiency from 61.65% to 81.64%, with the combustible gas yield of 1.05 Nm³/kg, and this promotion effect mainly occurred at char gasification stage. Also, an optimal Fe₂O₃/C molar ratio of 0.25 was determined for the maximum gasification efficiency. 800 °C was needed for the gasification efficiency over 70%, but excess temperature caused the formation of dense layer on oxygen carrier particle surface. Steam as gasification agent promoted syngas production, but excess steam decreased the gasification efficiency. Steam also enhanced the hydrogen production by the conversion of Fe/FeO into Fe₃O₄, avoiding the intensive reduction of oxygen carrier. The Fe₂O₃ oxygen carrier maintained a good reactivity in 10th cycle while used for microalgae CLG. The results indicated that CLG provided a potential route for producing combustible gas from microalgae.     

Continuous hydrogen production via the steam–iron reaction by chemical looping in a circulating fluidized-bed reactor

The steam–iron reaction was examined in a two-compartment fluidized-bed reactor at 800–900 °C and atmospheric pressure. In the fuel reactor compartment, freeze-granulated oxygen carrier particles consisting of Fe₃O₄ supported on inert MgAl₂O₄ were reduced to FeO with carbon monoxide or synthesis gas. The reduced particles were transferred to a steam reactor compartment, where they were oxidized back to Fe₃O₄ by steam, while at the same time producing H₂. The process was operated continuously and the particles were transferred between the reactor compartments in a cyclic manner. In total, 12 h of experiments were conducted of which 9 h involved H₂ generation. The reactivity of the oxygen carrier particles with carbon monoxide and synthesis gas was high, providing gas concentrations reasonably close to thermodynamic equilibrium, especially at lower fuel flows. The amount of H₂ produced in the steam reactor was found to correspond well with the amount of fuel oxidized in the fuel reactor, which suggests that all FeO that was formed were also re-oxidized. Despite reduction of the oxygen carrier to FeO, defluidization or stops in the solid circulation were not experienced. Used oxygen carrier particles exhibited decreased BET specific surface area, increased bulk density and decreased particle size compared to fresh. This indicates that the particles were subject to densification during operation, likely due to thermal sintering. However, stable operation, low attrition and absence of defluidization were still achieved, which suggest that the overall behaviour of the oxygen carrier particles were satisfactory.     

Reactivity investigation on biomass chemical looping conversion for syngas production

Chemical looping gasification (CLG) is regarded as an innovative and promising technology for producing syngas. In this work, CLG of straw was conducted in a fixed bed reactor with Fe₂O₃ as the oxygen carrier, whose results led to conclusions that Fe₂O₃, the oxygen carrier, proved advantageous to the secondary gasification reaction and the formation of CO and CO₂. It was also found that CO was further oxidized to CO₂ at high Fe₂O₃/C molar ratio, which resulted in a decreased gasification efficiency and low heat value of syngas. Therefore, a conclusion was drawn that the most optimized Fe₂O₃/C molar ratio was 0.2. In addition, the alkali metals in the biomass evaporated as chlorine salts into gas phase and retained as alkali metal oxide at high temperature, resulting in coking, slagging and heating surface corrosion. In the mean time, the oxygen carrier mainly converted to Fe and sintering phenomenon was serious at high temperature despite the fact that high temperature promoted gas yield, carbon conversion efficiency and gasification efficiency. Therefore, the most optimized temperature was set to 800 °C in order to maximize gas yield and gasification efficiency.     

Design and comparisons of three biomass based hydrogen generation systems with chemical looping process

The technology of hydrogen generation from biomass has attracted more and more attentions nowadays. In this work, three biomass-based chemical looping hydrogen generation systems, Systems A, B and C, are comprehensively studied. System A is mainly composed of biomass hydrogasification, methane reformation and the calcium-looping based CO₂ absorption. System B is mainly composed of biomass steam gasification and Fe₂O₃/FeO-looping based hydrogen generation circulation. System C is mainly composed of biomass steam gasification and Fe₃O₄/FeO-looping based hydrogen generation circulation. The three systems are modeled and their characteristics are analyzed and compared thermodynamically. System A has the highest cold gas efficiency (CGE) which is 72%; System B has the lowest CGE of 54% but it can generate additional nitrogen as byproduct; System C has the highest hydrogen generation ratio and its CGE is moderate and is 60%. The carbon dioxide sequestration rates of the three systems are all above 90%.     

The role of Al2O3, MgO and CeO2 addition on steam iron process stability to produce pure and renewable hydrogen

Steam iron process represents a technology for H₂ production based on iron redox cycles. Fe_xO_y are reduced by syngas/carbon to iron, which is subsequently oxidized by steam to produce pure H₂. However, the system shows low stability.In this work, the effect of promoters (Al₂O₃, MgO and CeO₂) on Fe_xO_y stability is investigated (10 consecutive redox cycles). Bioethanol is used as a reducing agent. The particles are synthesized by coprecipitation method, analysed by BET, XRD, SEM and tested in a fixed bed reactor (675 °C, 1 bar). Pure H₂ is obtained controlling the Fe_xO_y reduction degree feeding different amounts of ethanol (4.56–1.14 mmol) until no CO is detected in oxidation. The results show that the promoters not only improve the thermal stability of Fe_xO_y but also affect its redox activity and react with iron forming spinel structures. MgO led to the highest activity and cyclability (H₂ = 0.15 NL; E = 35%).     

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.     

Reactivity of iron oxide as an oxygen carrier for chemical-looping hydrogen production

The three-reactor chemical-looping (TRCL) process is a three-step water-splitting cycle for production of hydrogen with intrinsic CO₂ separation. Iron oxide (Fe₂O₃), a metal oxide acting as an oxygen carrier, is a strong reducing agent for steam circulating through reactors in the TRCL process.     

Chemical looping steam methane reforming using Al doped LaMnO3+δ perovskites as oxygen carriers

Chemical looping steam methane reforming (CLSMR) is capable of co-production of high-quality syngas and pure hydrogen, and it is important to develop appropriate oxygen carriers for this process. In this work, LaMn_1-xAl_xO_3+δ (x = 0, 0.1, 0.3, 0.5, 0.7) perovskites were investigated as oxygen carriers for CLSMR by means of characterizations and fixed-bed tests. The characterization and test results suggested that the substitution of Al leaded to more surface active sites and higher symmetry of crystal structure, which facilitates the activation of methane molecule on the surface and the formation of the oxygen vacancy in the bulk of the oxygen carrier particles, increasing the release rate of selective oxygen and the yield of syngas. The yield of CO₂ declined with the Al doped proportion due to the decrease of the mount of Mn⁴⁺ and surface absorbed oxygen. The substitution of Al cations could stabilize the crystal structure and prevent the destruction of perovskite structure. No carbon formed on LaMn_1-xAl_xO_3+δ with x from 0 to 0.5 and a long period of partial oxidation was achieved to produce high-quality syngas with the H₂/CO ratio of 2 and pure hydrogen, while carbon deposition occurred on the LaMn_0.3Al_0.7O_3+δ oxygen carrier. LaMn_0.5Al_0.5O_3+δ possessed the best performance with CO selectivity of 96.4%, the CO yield of 1.70 mmol·g⁻¹, the H₂ yield of 3.32 mmol·g⁻¹ in the reduction stage and the H₂ yield of 1.98 mmol·g⁻¹ in the oxidation stage on average in 20 cyclic redox tests. LaMn_0.5Al_0.5O_3+δ exhibited good thermal stability and cyclic performance. It can be deduced that LaMn_0.5Al_0.5O_3+δ perovskite is a potential oxygen carrier for cyclic CLSMR.     

Modeling a counter-current moving bed for fuel and steam reactors in the TRCL process

A mathematical model for the moving bed is developed to simulate the fuel and steam reactor in the TRCL (Three-Reactor Chemical-Looping) process. An ideal plug flow of the solid and gas is assumed in modeling the fuel and steam reactor in the TRCL process. The model considered the mass, heat balances, equilibrium, physical properties, such as the heat capacity and viscosity, and kinetics. From this model, the temperature, gas conversion and solid conversion profiles can be predicted for fuel and steam reactors. The oxygen carrier inventory (the mass of the oxygen carrier) in the fuel and steam reactor was calculated with variation of the solid inlet temperature, solid conversion, Fe₂O₃ content and steam feed rate. The temperature of the oxygen carrier to the reactor was the most sensitive parameter for determining the required inventory of the oxygen carrier. An increase in the solid inlet temperature was predicted to decrease the required inventory of the oxygen carrier. In the steam reactor, a solid inlet temperature increase over 1150 K will cause an increase in the inventory of the oxygen carrier due to the equilibrium conversion. An excessively low or high active material content will require a larger inventory of the oxygen carrier in the fuel reactor. In this study, approximately 20 wt.% of the Fe₂O₃ content was suitable for reducing the inventory of the oxygen carrier while achieving a solid conversion of 0.9 in the fuel reactor.     

Effect of different gasifying agents (steam,H2O2, oxygen,CO2, and air) on gasification parameters

Two sensitivity analyses were performed in an Aspen simulation of fluidized bed gasification for five different gasifying agents such as steam, hydrogen peroxide (H₂O₂), pure oxygen (O₂), carbon dioxide (CO₂), and air. In the first sensitivity analysis, the modified equivalence ratio (MER) was varied (0.22-0.36). For the varied modified equivalence ratio (MER), %hydrogen, H₂/CO molar ratio, and hydrogen yield were the highest in steam-gasification, but %carbon monoxide, %methane, CO yield, and the lower heating values (LHV) were the highest in CO₂-gasification. In the second sensitivity analysis, the freeboard temperature was varied (500-900 °C). With increasing freeboard temperature, %hydrogen and %carbon monoxide increased while %carbon dioxide and %methane decreased for all the gasifying agents. Also, with increasing freeboard temperature, the LHV decreased and the hydrogen yield, CO yield, and the gas production rate increased for all the gasifying agents, but the H₂/CO molar ratio increased only in oxygen, air, and CO₂-gasification.