Chemical Looping Gasification Process Research Articles

Production of aviation fuel with negative emissions via chemical looping gasification of biogenic residues: Full chain process modelling and techno-economic analysis

The second-generation bio aviation fuel production via Chemical Looping Gasification (CLG) of biomass combined with downstream Fischer-Tropsch (FT) synthesis is a possible way to decarbonize aviation sector. The CLG process has the advantage of producing undiluted syngas without the use of an air-separation unit (ASU) and improved syngas yield compared to the conventional gasification processes. This study is based on modelling the full chain process of biomass to liquid fuel (BtL) with LD-slag and Ilmenite as oxygen carriers using Aspen Plus software, validating the model results with experimental studies and carrying out a techno-economic analysis of the process. For the gasifier load of 80 MW based on LHV of fuel entering the gasifier, the optimal model predicts that the clean syngas has an energy content of 8.68 MJ/Nm3 with a cold-gas efficiency of 77.86%. The optimized model also estimates an aviation fuel production of around 340 bbl/day with 155 k-tonne of CO2 captured every year and conversion efficiency of biomass to FT-crude of 38.98%. The calculated Levelized Cost of Fuel (LCOF) is 35.19 $ per GJ of FT crude, with an annual plant profit (cash inflow) of 11.09 M$ and a payback period of 11.56 years for the initial investment.

Simultaneous in-situ tar abatement and H2-enriched syngas production via heterogeneous doping of LaFeO3 during chemical looping gasification of microalgae

Chemical looping gasification (CLG) is an emerging environment-friendly technology for efficient and clean utilization of biomass, in which oxygen carrier (OC) is one of the key issues concerning the overall performance. As a rising-star material, perovskite with a tunable crystal structure shows great potential in syngas enrichment and tar decomposition during the CLG of biomass. In this study, the newly-developed LaNi0.5Fe0.5O3 (LN5F5) and La0.3Ba0.7FeO3 (L3B7F) perovskites through heterogeneous doping of LaFeO3 (LF) were evaluated as oxygen carriers with the purpose of simultaneous tar abatement and H2-enriched syngas production from microalgae. Silica sand (SS) and iron ore (IO) were used for comparison. Results showed that the CLG performance order of several materials was L3B7F > LN5F5 > LF > IO > SS at an oxygen carrier to biomass ratio (O/B) of 0.4, water injection rate of 0.3 mL/min and gasification temperature of 800 °C. The heterogeneous doping obviously improved the cyclic stability of perovskite during redox tests. In addition, possible tar conversion routes over L3B7F oxygen carrier were proposed. Results implied that heavy PAHs (4 rings or more) were first converted to light PAHs (1–3 rings) and n-hydrocarbon, which were finally transformed into micromolecular gases. The outstanding performance of L3B7F in microalgae CLG can be ascribed to the formation of oxygen vacancies and high-valence Fe4+ stimulated by the introduction of Ba2+, which were demonstrated by the XRD, H2-TPR and XPS results. These results evidence that the heterogeneous doped L3B7F is a good alternative for improving biomass availability in the CLG process.

Intensified effect of K adhering to hematite involved in the sulfurous chemical looping gasification

When sulfur in petroleum coke (petcoke) converts to H2S instead of SO2, it is the resource which can be recovered by Claus process. Chemical looping gasification (CLG) is capable of achieving petcoke conversion and sulfur recovery. To simultaneously overcome the obstacles of low gasification reactivity and improve H2 and H2S production, hematite modified by K as oxygen carrier (OC) was involved in the high-sulfur system to investigate the effect on sulfur conversion via batch fluidized bed in petcoke CLG process. K enhanced H2 generation beyond expectation because K not only improved the petcoke gasification but also enhanced the steam oxidation of deep reductive OC. Especially when using 10 % KNO3-hematite, H2 yield increased by 3.9 times as compared to 0 % K, with the carbon conversion efficiency of 99.92 % in the 22nd minute. The different K sources had a different H2 selectivity. The sulfur fate had been originally studied using K-modified hematite OC. H2S was the main phase of sulfur release and the high H2 yield also assisted H2S production. Introducing K contributed to in-situ sulfur capture forming K-Fe-S compounds in the OCs due to the deep reduction of Fe. 10 % KNO3-hematite exhibited excellent cyclic stability with a H2 volume fraction of more than 65 % in 21 cycles. Furthermore, the mechanism of hematite modified by K involved in sulfur-containing system was summarized in petcoke CLG process.

Solar-assisted biomass chemical looping gasification in an indirect coupling: Principle and application

A new configuration of solar-assisted biomass chemical looping gasification (CLG), in which solar heat is indirectly absorbed and stored in the form of sensible heat in solid particles (oxygen carrier and support material), was developed (i.e., indirect coupling). A steam Rankine cycle was integrated to further recuperate the thermal energy of the high-temperature solid particles at the outlet of the steam reactor. Compared with the direct solar energy utilization approach, the proposed configuration can circumvent the fluctuating working conditions of the CLG and downstream processes. Additionally, since the solar receiver and reactor are uncoupled, efficient thermal integration of the developed system is relatively easy to achieve. Thermodynamic analysis of the proposed configuration was conducted, and the indirect coupling of solar energy with CLG was investigated. A case study of methanol synthesis was conducted to compare the annual output of the proposed configuration with that of an auto-thermal CLG. Results indicate that the energy and exergy efficiencies of the present configuration were 66.16% and 77.68%, respectively. The optimal solar multiple was 2.8, which corresponds to the thermal energy storage and designed heliostat size of 10 h and 110.74 × 103 m2, respectively. The case study shows that the present configuration-based methanol synthesis route produced more methanol and electricity but emitted less carbon than the auto-thermal CLG-based method.

Chemical looping gasification characteristics and kinetic analysis of Chlorella and its organic components

Chemical looping gasification (CLG) characteristics and kinetic analysis of Chlorella (CHL), simulated Chlorella (V-CHL) and medium-chain triglycerides (MCT) were investigated using a thermogravimetric analyzer coupled with an online mass spectrometer. The apparent activation energy was obtained via Kissinger-Akahira-Sunose (KAS) method. In the result of the weightless behavior, the addition of oxygen carrier inhibited the decomposition of V-CHL at lower temperatures but promoted its decomposition at high temperatures. The values of chemical looping process characteristic parameters showed that a 10 wt% oxygen carrier would maximize the release of volatile products in the CLG of MCT, with 5.12 × 10−6 %·min−1·oC−3. Oxygen carriers also affected gaseous products. The LHV of gaseous products of CHL reached the largest when the oxygen carrier was 10 wt%, which was 8.13 MJ/m3. And the gaseous product of MCT had the largest LHV with 30 wt% oxygen carrier, which was 8.83 MJ/m3. According to the kinetic analysis, the minimum value of apparent activation energy of MCT chemical looping gasification was 89.54 kJ·mol−1 with the oxygen carrier of 30 wt%, which was 50% less than that of MCT pyrolysis. And the minimum value for V-CHL was obtained when the mass fraction of Fe2O3 was 50 wt%. This paper could provide a reference for the choice of algae, the design of reactors, and the targeted regulation of the gaseous product for the algae CLG process.

Reaction performance and mechanism of a NiO/Ca2Fe2O5 oxygen carrier in Chemical looping gasification of cellulose

Chemical looping gasification (CLG) is a novel technology created to realize the clean and efficient utilization of solid fuels, where the syngas product avoids dilution by N2 and the pollutants are inhibited by using metal oxide as oxygen carrier (OC) instead of molecular oxygen. Cellulose, as the main component of biomass-based solid waste, was evaluated in the CLG process with NiO/Ca2Fe2O5 prepared by the impregnation method. Reaction mechanism and morphology evolution of the OC as well as the influence of key reaction parameters were investigated by fixed-bed reactor and thermogravimetric analysis experiments coupled with various characterization techniques. The results indicated that the addition of Ni not only improved the oxygen release performance of Ca2Fe2O5 but also helped tar cracking and carbon conversion. On the other hand, the excellent activity in the solid–solid reaction of Ca2Fe2O5 promoted the performance of the Ni-based OC. The test results revealed that Ca2Fe2O5 was a better base than CaFe2O4, and the carbon conversion efficiency reached 98% with the OC sample at 850 °C. NiO markedly improved the reactivity of Ca2Fe2O5 after 10 cyclic reactions. The temperature notably affected activity below temperatures of 850 °C and slightly above. Due to the limited reduction of Ca2Fe2O5 below 800 °C and the redox behavior improvement being minor above 850 °C, the temperature of 850 °C was marked as the optimum for the studied process Addition of water inhibited OC inactivation in cyclic reactions, which was mainly attributed to the crystal separation and agglomeration of OC particles. However, water inhibited the deep reduction of metal on the surface, which reduced the activity on tar cracking and carbon conversion to a certain extent.

Process Analysis of Chemical Looping Gasification of Biomass for Fischer–Tropsch Crude Production with Net-Negative CO2 Emissions: Part 1

Large-scale biofuel production plants require an efficient gasification process that generates syngas of high quality (with minimal gas contaminants and inert gases) to minimize the extent of the syngas cleaning processes required for liquid biofuel production. This work presents process modeling of the chemical looping gasification (CLG) process for syngas production. The CLG process is integrated with a Fischer–Tropsch synthesis (FTS) process to produce Fischer–Tropsch (FT) crude with net-negative CO2 emissions, enabling process and system-level analyses of this novel biomass-to-liquid process. CLG resembles indirect gasification in an interconnected circulating fluidized bed reactor, where instead of inert bed material, a solid-oxygen carrier, such as mineral ores rich in iron or manganese oxides, is used. The oxygen carrier particles undergo oxidation and reduction in the air reactor and fuel reactor, respectively, thereby providing heat and oxygen for gasification. This work uses data from CLG experiments performed with steel converter slag as the oxygen carrier and investigates its potential when integrated with different downstream gas cleaning trains and the subsequent fuel synthesis process with the primary objective of quantifying and evaluating the performance of the integrated CLG–FT process plant. Syngas with a high energy content of 12 MJ/Nm3 (lower heating value basis) is predicted with a cold gas efficiency of 73%. CO2/CO ratios, higher than indirect biomass gasification, are also predicted in the raw syngas produced; thus, there exists an opportunity to capture biogenic CO2 with a relatively lower energy penalty in the subsequent gas cleaning stages. This work quantifies other key performance indicators, such as heat recovery potential, negative CO2 emission capacity, and FT crude production efficiency of the CLG–FT plant. A 100 MWth CLG plant produces roughly 677–696 barrels per day of FT crude, with net-negative emissions of roughly 180 kilotonnes of CO2 annually.

Influence of an Oxygen Carrier on the CH4 Reforming Reaction Linked to the Biomass Chemical Looping Gasification Process.

A major challenge in biomass chemical looping gasification (BCLG) is the conversion of CH4 and light hydrocarbons to syngas (CO + H2) when the goal is the use for bioliquid fuel production. In this work, tests were performed in a batch fluidized bed reactor to determine the catalytic effect on the CH4 reforming reaction of oxygen carriers used in the BCLG process. Three ores (ilmenite, MnGB, and Tierga), one waste (LD slag), and five synthetic materials (Fe10Al, Fe20Al, Fe25Al, Cu14Al, and Ni18Al) were analyzed. These results were compared to those obtained during ∼300 h of continuous biomass gasification operation in a 1.5 kWth BCLG unit. The low-cost materials (ores and waste) did not show any catalytic effect in the CH4 reforming reaction, and as a consequence, the CH4 concentration values measured in the syngas produced in the continuous prototype were high. The synthetic oxygen carriers showed a catalytic effect in the CH4 reforming reaction, increasing this effect with increasing temperature. With the exception of the Ni-based oxygen carrier (used as a reference), the Cu-based oxygen carrier, working at 940 °C, showed the best catalytic properties, in good agreement with the low CH4 concentration values measured in the syngas generated in the continuous unit. The tests performed in a batch fluidized bed reactor were demonstrated to be very useful in determining the catalytic capacity of oxygen carriers in the CH4 reforming reaction. This fact is highly relevant when a syngas with a low CH4 content is desired as a final product.

Comprehensive optimization of coal chemical looping gasification process for low CO2 emission based on multi-scale simulation coupled experiment

Carbon dioxide (CO2) emission reduction has become an urgent topic to be studied and solved with the in-depth understanding of global warming and frequent occurrence of extreme climate. At present, the application of chemical looping technology in coal gasification to produce high purity synthesis gas is an important way to achieve CO2 emission reduction, ensure energy security, and promote ecological civilization. In this paper, a new fusion research method combining multi-scale modeling and experimental testing is adopted to comprehensively optimize the coal chemical looping gasification (CCLG) process, aiming at ruducing CO2 emissions in the synthesis gas production of CCLG. In order to investigate the effect of main reaction conditions on CCLG process, the pyrolysis and gasification experiments of Meihuajing coal are carried out in a tubular furnace reactor with Fe2O3 and CuO as oxygen carriers respectively. Subsequently, the multi-scale simulation of CCLG process including molecular dynamics (MD) and computational fluid dynamics (CFD) simulations is performed to validate the experimental results and supplement important reaction kinetics data. Both of multi-scale modeling and experimental testing suggest that the optimum pyrolysis temperature range, gasification temperature range, char/oxygen carrier mass ratio (C/O), and steam flow are below 900 ℃, 900–950 ℃, 1:1.5, and 0.15 g/min respectively, providing an effective guidance for the optimal design of practical CCLG pilot plant.

Syngas production from cellulose solid waste by enhanced chemical looping gasification using Ca-Fe bimetallic oxygen carrier with porous structure

Chemical looping gasification (CLG) is a promising and innovative technology used to produce synthesis gases without the preparation of gasifying agents, which exhibits advantages in synthesis gas heating value, tar inhibition and production cost Metal Oxide as oxygen carrier (OC) transfers the oxygen and heat in CLG process to avoid product syngas to be mixed with nitrogen, which decides the efficiency and feasibility of CLG system. Ca-Fe bimetallic OCs are considered as the potential available OC for its excellent selectivity on CO and H2 and char conversion activity. However, the low activity presents great challenges in further application for Ca-Fe OCs. To improve the performance of OCs, Ca-Fe OC with porous structure were prepared with simple method and investigated in a fixed bed with cellulose as fuel combined with various analytical methods. The results reveal that the pore area and pore volume increased significantly with increasing sol pH. The OCs with pH adjustment improved the syngas yield by over 28% and the carbon conversion efficiency by over 10%. Using the sample with pH = 6 as OC, from 800 °C to 950 °C, the carbon conversion efficiency increased more than 25%, and O/B = 0.5 and S/B = 1.2 should be the most property conditions for cellulose CLG. After 10 redox cycles, the performance of OCs with pH adjustment was better than that without adjustment in steam atmosphere. The improvement of OCs might be due to the higher pore surface area increasing the efficiency of steam reforming and the inner redox cycle of OCs. Therefore, Ca-Fe bimetallic OCs with large surface areas could potentially be used as good candidate oxygen carriers for CLG of cellulose solid waste.

Process simulation of chemical looping gasification of biomass using Fe-based oxygen carrier: Effect of coupled parameters

Chemical looping gasification (CLG) of biomass is an efficient way to obtain high-quality syngas without the need of air separation. It offers a carbon-negative and clean way for the utilization of biomass while syngas is used combining with carbon capture. A simulation model of CLG process with continuous feedstock of pine sawdust is constructed and investigated in this work. The iron-based oxygen carrier (OC) is adopted to offer lattice oxygen. This model is validated using the experimental results from literature to demonstrate its feasibility for CLG of biomass. Then, the operating parameters of gasification temperature, amounts of steam and OC are changed to investigated their effects on the gasification performances. Results demonstrated that increasing the temperature, OC and steam flow is beneficial to intensify the carbon conversion efficiency. When the gasification temperature is 880 °C, carbon conversion efficiency and gasification efficiency reach 92.76% and 81.87%. The carbon conversion efficiency rises from 76.81% to 82.18% when OC mass flow is changed from 0 to 1.5 kg/h. Coupled effects of the amounts of reaction temperature, OC mass flow and steam molar flow are also investigated while two of them are changed simultaneously. The minimum and maximum values of gasification efficiencies are 62.13% and 77.73% when the amounts of steam and OC are (0 mol/h, 1.0 kg/h) and (1.0 mol/h, 0 kg/h), respectively. When both of them increases to 1.0 kg/h or 1.0 mol/h, the carbon conversion efficiency reaches the maximum value of 88.57%. The coupled effects of temperature and OC or steam amount demonstrate that the carbon conversion efficiency is mainly determined by temperature at lower-temperature range. Though both of OC and steam can offer oxygen in CLG, due to the different oxidation ability, their effects on gasification efficiency are opposite. Investigation on coupled effects of multiple parameters offers thorough information for the system performance evaluation, which can be used for further system optimization.

Chemical looping gasification of cotton stalk with Cu/Ni/olivine in a Micro-fluidized bed Reactor: Gaseous products distribution and kinetics

Gas releasing characteristics and kinetics of chemical looping gasification (CLG) of cotton stalk (CS) under isothermal conditions have been investigated in a micro-fluidized bed reactor analyzer (MFBRA). NiO and CuO supported on olivine (Cu/Ni/O) used as oxygen carriers (OCs). The kinetic parameters for the formation of the main gaseous products were analyzed by model fitting method. Results indicated that due to the synergistic effect of CuO and NiO, the carbon conversion has been reached to 97.2% for 9Cu/6Ni/O. The Shrinking core, Jander equation and Ginstling-Brounshtein equation with their higher fitting coefficients were selected to calculate the activation energy (Ea). Ea for CH4 and H2 decreased while Ea for CO2 increased with the presence of OCs. The Ea of CO generated from olivine were increased, while Ea of 15Cu/O, 15Ni/O and 9Cu/6Ni/O decreased. Further comparing the Ea, in the CLG process, the gasification effect of different OCs on the gas composition is different. The kinetics of CLG of CS with 15Cu/O, 15Ni/O and 9Cu/6Ni/O were calculated to be 81 ∼ 103 kJ/mol, 116 ∼ 147 kJ/mol and 99 ∼ 133 kJ/mol respectively, which indicate that the prepared bimetallic OC can be a more suitable OC for CLG both in terms of conversion effect and Ea due to synergistic effect of Ni and Cu.

Syngas production from lignite via chemical looping gasification with hematite oxygen carrier enhanced by exogenous metals

Chemical looping gasification (CLG) has revealed advantages in the preparation of high-quality syngas and reduction of carbon dioxide. Hematite oxygen carriers (OCs) enhanced by exogenous active metals were investigated in CLG process of lignite by using TG and fixed bed reactor with various analytical methods. The experimental results indicated that Fe2O3 in hematite reacts with different exogenous metals to generate mixed oxide such as CaFe2O5, NiFe2O4, CeFeO3 and CoFe2O4, increasing oxygen vacancy concentration, strengthening lattice oxygen transfer, and improving the conversion efficiency of lignite. The CaO exhibited the best reaction performance among exogenous metals in promoting lignite CLG process with a reactivity order of CaO > CeO2 > NiO > Co2O3. The CaO enhanced the CLG reaction through two pathways. The synergistic effect in CaFe2O5 reduce the Fe-O bonds intensities, promoting the migration of lattice oxygen in OCs. Carbonation of CaO sorbents shifts the CLG reaction equilibrium towards syngas, which are conductive to improvement of the syngas yield. Water molecular played an important role in promoting carbon conversion, regulating H2/CO ratio, and reducing calcium loss. Synthesis gas with H2 concentration 63.19%, heating value 9.20 MJ/m3 and H2/CO ratio 5.77 corresponding to carbon conversion efficiency 66.41% and syngas yield 2.56 m3/kg was achieved in CLG of lignite with water participation. The main reaction path of Fe2O3→CaFe2O5→CaFe3O5/Fe2.91O4→Fe2O3 was revealed for CaO modified hematite OCs in CLG process. The main crystal form and lattice oxygen of OCs were regenerated with the improvement of particle size and pore channels. The experimental results indicate a potential application of modified hematite OCs in the CLG of lignite.

Effect of Mg in rice husk on promoting reaction and causing agglomeration during chemical looping gasification

Mg is one of the most abundant trace elements in biomass, which plays a contradictory role in biomass conversion. However, the evolution behavior and mechanism of Mg in biomass chemical looping gasification (CLG) are still unclear. In this paper, the comprehensive influence of Mg on the CLG performance is investigated under different Mg-type solutions, Mg contents, temperatures and ratios of steam/biomass (S/B). The results show that Mg added on pickling rice husk (AH) can promote CLG reaction, but cause more agglomeration by forming MgSiO3 around particles at high Mg content. Moreover, the CLG performance of (CH3COO)2Mg-AH is better than that of MgCl2-AH. Compared with pickling rice husk, the gasification efficiency, gas yield and carbon conversion efficiency of 6% (CH3COO)2Mg-AH are increased by 28.15%, 33.77% and 26.20%, respectively. Meanwhile, the smaller particle size, grain size and agglomeration degree are achieved in the CLG on (CH3COO)2Mg-AH. Furthermore, Mg-addition will reduce the activation energy in CLG process. Compared with rice husk, the activation energy of 6% (CH3COO)2Mg-AH decreases by 21.88% in pyrolysis stage and 61.90% in gasification stage. In addition, the activation energy of (CH3COO)2Mg-AH is lower than that of MgCl2-AH, especially the gasification stage (20.89%). With the increase of temperature and S/B, the CLG performance increases first and then decreases. The highest gasification efficiency of 70.26% and gas yield of 0.72 Nm3/kg are achieved under the optimal temperature of 850℃ and S/B of 3 during the CLG on 6% (CH3COO)2Mg-AH.

Characteristics of steel slag as an oxygen carrier for chemical looping gasification of sewage sludge

A comprehensive study was conducted to assess the characteristics of basic oxygen furnace slag (BOFS) and electric arc furnace slag (EAFS) as oxygen carriers for chemical looping gasification (CLG) of sewage sludge (SS). The surface roughness and wear resistance of BOFS were found to be higher than those of EAFS. Further, the oxygen transport capacity of BOFS was higher than that of EAFS at 800 ° C and 900 ° C with the same redox cycles. As the mass ratio increased, the carbon conversion rate and CO2 concentration gradually increased, while the water conversion rate, cold gas efficiency, and H2 and CO concentrations initially increased and then decreased. Both BOFS and EAFS as oxygen carriers had the highest carbon conversion rate and cold gas efficiency when the steam flow rate was 0.15 g min−1. The cyclic reactivity of BOFS as an oxygen carrier in the CLG process decreased faster than that of EAFS. However, the content of combustible components of BOFS as an oxygen carrier was significantly higher than that of EAFS in each cycle. Overall, these results provide a theoretical basis for steel slag as an oxygen carrier for the CLG of SS.

Syngas Production by Chemical-Looping Gasification of Waste Activated Carbon with Iron-Based Oxygen Carrier

Waste Activated Carbon (WAC), as a typical solid waste, can be utilized by Chemical-Looping Gasification (CLG) technology with an iron-based Oxygen Carrier (OC) to produce valuable synthesis gas. A series of experiments on WAC of the CLG process has been performed in a fixed-bed reactor. The operation parameters and cyclic performance of the iron-based OC have been investigated during CLG reactions. Fresh and cyclic reaction OC samples have been analyzed by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). To obtain high-quality syngas with high carbon conversion, the optimal OC/WAC mole ratio, steam flow rate and reaction temperature are 0.1, 0.10 mL/min, and 950 °C, respectively. The iron-based OC exhibits a stable cyclic performance during multiple tests, following the reaction path of Fe2O3 to Fe0.98O in the individual reduction process. Moreover, the iron-based OC is oxidized to almost its initial state after 10 redox tests without obvious sintering and agglomeration phenomena. The WAC of CLG provides a new approach to the comprehensive usage of solid waste, especially with low volatile feedstock.

Biomass chemical looping gasification for syngas production using modified hematite as oxygen carriers

Syngas is a clean energy carrier and a major industrial feedstock. In this paper, syngas was produced via biomass chemical looping gasification (CLG) process. Hematite, the most common Fe-based oxygen carrier (OC), was modified with different metal oxides (CeO2, CaO and MgO) by the impregnation method. The hematite modified by CeO2, CaO and MgO was namely as CeO2-hematite (CeO2-H), CaO-hematite (CaO-H) and MgO-hematite (MgO-H), respectively. The introduction of CeO2, CaO and MgO enhanced the reactivity of lattice oxygen of hematite. The optimum condition for syngas production had been explored as the mass ratio of oxygen carrier to biomass (O/B) of 0.2, the mass ratio of steam to biomass (S/B) of 0.75 and temperature of 800°C in the biomass CLG process. The CeO2-H exhibited the most wonderful performance compared to that for CaO-H and MgO-H. The crystal composition of OC influenced greatly in the CLG process. CeFeO3 had a good oxygen mobility property and lattice oxygen releasing capacity due to the most oxygen vacancy distributed on the OC surface and the most active lattice oxygen, which is conducive to the biomass chemical looping gasification process for syngas production, leading to the highest gasification efficiency of 95.86% and gas yield of 1.20 m3/kg of the three. Cyclic test proved that CeO2-H had well sintering resistance and cyclic performance.

Variation of gas composition and energy utilization in biomass CLG process with Fe and Ca oxides through thermodynamic simulation

Chemical looping gasification (CLG) proves to be effective route for biomass thermal conversion for quality gas production. Fe2O3 and CaO were applied in sawdust thermal decomposition as oxygen carrier and CO2 absorption agent to improve syngas composition and yield. The CLG process was investigated based on experiment and process model simulation. Process model was developed based on thermodynamic equilibrium and kinetics of 22 representative reforming reactions in CLG, with the model applicability validated with experimental results. The effect of Fe2O3 and CaO addition on CLG process, including product distribution, gas composition, energy balance and exergy efficiency, was analyzed through extensive simulation under varied combination of reaction temperature(773 ∼ 1273 K), blending ratio of Fe2O3 (0 ∼ 2) and CaO (0 ∼ 2) conditions in order to clarify the effect of variables. Especially the interaction between Fe2O3 and CaO addition on process performance was discussed to discover the potential synergetic effect on mechanism. The blending of Fe2O3 or CaO changed the gas composition with improved oxidation and reforming reactions. Optimum syngas production with maximum H2 and CO yield 682 mL/g was achieved at 1073 K CLG process. And the blending ratio of oxidant was an important factor influencing the energy balance and exergy efficiency, with the equivalent point between CLG reaction heat and char combustion heat appeared at 0.4–0.45 Fe2O3 addition. The results achieved from process simulation would be informative for CLG process mechanism understanding and efficient syngas conversion.

Nitrogen migration in coal during the chemical looping gasification reduction process using a nickel-based oxygen carrier

The release of nitrogen from a chemical looping gasification (CLG) system has always been a great concern. In this work, the thermal reactivity of samples obtained from the Jinfeng district, which were involved in the CLG process, was investigated via thermogravimetric–mass spectrometric (TG–MS) analysis. The migration mechanism of gas-phase nitrogen was characterized online, and changes in solid-phase nitrogen were analyzed during different stages using X-ray photoelectron spectroscopy. Results showed that nitrogen mainly existed in the solid and gas phases during different temperature stages of CLG; however, its migration varied at different stages. During the low-temperature pyrolysis stage (320 °C–795 °C, without adding steam), the addition of a nickel-based oxygen carrier accelerated the decomposition of the aliphatic structure and increased the hydroxyl content in the sample. Further, the release of nitrogen precursors was promoted by the accelerated release of hydrogen-containing free radicals from the aliphatic structure. The interaction between the nitrogen precursor and hydroxyl structure induced NO release at 350 °C. During the high-temperature pyrolysis stage (795 °C–950 °C, without adding steam), the reaction between the oxygen carrier and char exposed protic pyridine (N-Q) in the macromolecular structure. Furthermore, during the gasification stage (670 °C–950 °C, with steam addition), the addition of the oxygen carrier decreased the degree of graphitization of char and enhanced its gasification performance. As the structural units of char became smaller, N-Q in its macromolecular structure underwent further decomposition. Thus, the addition of the oxygen carrier at high temperatures benefited N-Q decomposition.

Mechanism study on the high-performance BaFe2O4 during chemical looping gasification

As an attractive oxygen carrier, BaFe2O4 shows an outstanding chemical looping gasification (CLG) performance with a high CO yield, but the reaction mechanisms of BaFe2O4 during CLG process are still not clear. The present work aims to reveal the reaction mechanisms of BaFe2O4 with solid carbon (C) and carbon monoxide (CO) by means of experiments and computational methods based on the density functional theory (DFT). The performance of Fe2O3 was also investigated for comparison. Results of fixed-bed experiments show that BaFe2O4 has a better reactivity in solid–solid reaction with high CO yield, while Fe2O3 shows a better performance in solid–gas reaction with high CO2 yield. Components of Fe and FeO were detected in the products of BaFe2O4-C reaction, but not found in the products of Fe2O3-C reaction, indicating that BaFe2O4 is more active in the solid–solid reaction. Pure Fe and FeO phases in the products of Fe2O3-CO reaction suggest that Fe2O3 is more active in the solid–gas reaction. Combining the experimental and calculation results, it can be found that both the solid–solid reaction and the solid–gas reaction can be divided into the steps of C/CO adsorption, formation of CO*/CO2* complex, CO*/CO2* desorption and lattice oxygen migration. The rate-limiting-steps in solid–solid and solid–gas reactions are the formation of CO* and CO2* complex, respectively. The adsorption energy of C/CO on BaFe2O4 surface is lower than that on Fe2O3 surface, and there is a large amount of adsorbed CO on BaFe2O4 surface, indicating that BaFe2O4 surface is more active than Fe2O3 surface. The BaFe2O4-C reaction is more favorable with a lower energy barrier (0.545 eV) than that Fe2O3-C reaction (0.960 eV). In the solid–gas reaction, Fe2O3-CO reaction has a lower reaction energy barrier of 0.791 eV than BaFe2O4-CO reaction (0.997 eV). The large amount of Fe2+ ion in Fe2O3 bulk indicates the strong oxygen migration ability. Therefore, BaFe2O4 displays good potential in CLG process due to its relative stronger surface activity and weaker migration ability of lattice oxygen.