Chemical Looping Gasification Research Articles

Fe–Ni composite oxygen carrier for chemical looping gasification with diverse fuels to produce syngas

Coal-based chemical looping gasification (CCLG) has been proposed as an emergent type of coal gasification technology that produces high-quality syngas by using lattice oxygen from oxygen carrier instead of molecular oxygen. In this paper, the Fe–Ni composite oxygen carrier was synthetized using sol-gel method and the gasification performance of the prepared sample was analyzed by a fixed-bed reactor. The results indicated that the Fe–Ni composite oxygen carrier presented a high carbon conversion of fuel and syngas selectivity during the CCLG process. Additionally, the cycle stability test showed that the carbon conversion of fuel and syngas selectivity did not change significantly with the increase of cyclic frequency. To further study the influence of volatiles released from coal on the gasification performance of oxygen carrier, the interactions between the oxygen carrier samples and char obtained at different pyrolysis temperatures were investigated by a fixed-bed reactor and TG-MS, respectively. The results suggested that the gas products (H2, CO, CO2 and CH4) yields of char-oxygen carrier were significantly lower than those of coal-oxygen carrier. Besides, the pyrolysis temperature for preparing char had a great effect on the carbon conversion of fuel and syngas selectivity due to the distinction of volatiles released from solid fuel.

Fuel reactor simulation for coal chemical looping process: Effects of ash on flow behavior

Chemical looping gasification (CLG) is an environmentally friendly strategy for using coal that has significant promise for application in reality. Nevertheless, the process of generating and accumulating ash from coal presents obstacles to the advancement of this technology. To fully comprehend the effects of ash from coal on the internal flow properties of a fuel reactor (FR). The Computational Particle Fluid Dynamics (CPFD) approach was applied to predict the CLG with coal at the FR, uncovering distinctive flow properties of gas-solid reactions. This study investigated the effects of ash particles content, polydispersity and sphericity on the flow behavior within the bed. The simulation accurately predicted the motion of the bubbles within the FR, and the gas phase composition distribution at the outlet is closer to the experimental data. Introducing coal ash creates a reduction in the concentration of ilmenite, resulting in a drop in the rates of the related reactions. The narrow particles diameter distribution among coal ash facilitates the particles arrangement in the bed and improves the overall reaction. The addition of moderately irregular-shaped coal ash particles has a certain positive effect on improving the gas-solid contact.

Thermodynamic modeling and performance analysis of chemical looping gasification combined with steam reforming for municipal solid waste: An Aspen Plus approach

Chemical looping gasification combined with steam reforming (CLG-SR) holds great promise for improving energy efficiency and streamlining the production of renewable H2 and synthetic fuels. In this investigation, the process underwent simulation and analysis using Aspen Plus, offering valuable insights into product outcomes, environmental impacts, and economic performance. The accuracy of the model was validated against experimental results from the literature, yielding a root mean square (RMS) of 4.17 %, thereby demonstrating its high feasibility. The findings demonstrate that within the temperature range of 700–800 °C, H2 achieves notable selectivity, reaching 60.68 % selectivity at 700 °C. When the steam-to-municipal solid waste (MSW) ratio surpasses 0.9, H2 demonstrates elevated selectivity. Notably, it is crucial to observe that the selectivity of CO2 also escalates concurrently with that of H2. Specifically, at steam-to-MSW ratio (SMR) of 0.9, the selectivity of H2 attains 60.72 %, whereas the selectivity of CO2 attains 27.69 %. Under these parameter conditions, H2, purified through pressure swing adsorption (PSA), constitutes 68.59 % of the total input H elements, leading to an impressive energy efficiency of 47.76 %. The economic analysis, based on the model, discloses a material consumption of 7.40 tons per ton of H2, resulting in a total production cost of 2487.20 USD per ton of H2. The study bears paramount strategic significance for advancing the in-depth research and development of chemical looping gasification technology.

Performance evaluation of red mud-based oxygen carriers in the chemical looping gasification of wet sludge rich in iron

A high-performance and low-cost oxygen carrier (OC) is the key for industrialization of chemical looping gasification (CLG) technology for sludge treatment. In this work, four OCs (RM_15 %CuO, RM_10 %CuO, RM, RM_POC) were prepared in an industrial-scale granulation equipment. The red mud was composited by mixing with different amounts of CuO and MnO2, then subjecting to different calcination temperatures. Firstly, the oxygen decoupling and oxygen carrying capacities of the OCs were compared using 5% H2 as the reducing agent. RM_15%CuO and RM_POC showed excellent oxygen release capabilities, with oxygen release loss of −1.99 % for RM_15%CuO. The catalytic gasification performances of RM_15%CuO and RM_POC were evaluated in a lab-scale fluidized bed reactor with wet sludge as the feedstock. Both OCs were able to maintain the H2 concentration of over 44.6% and no less than 79.2% sludge gasification efficiency after 30 cycles. However, the H2 content was clearly higher in case of RM_POC. SEM-EDS was used to analyze the influence of sludge ash, rich in Fe, on the performance of two OCs after the fluidized bed operation. The results showed that the sludge ash sample with more than 20% Fe2O3 could transfer its lattice oxygen to assist OC and prevent the in-situ segregation of Fe phase in the POC surface. However, the inhibitory effect of RM_15%CuO was much lower. The degradation performance of RM_POC carrier was slower and thus the H2 content was higher. This performance evaluation provides a theoretical guide for chemical looping gasification of sludge in future with an idea of mixed ratio of recycling sludge ash to the RM_POC.

Decarbonized core-shell-like structure: Enhancing Fe-based oxygen carriers for superior hydrogen selectivity and stability

Fe-based oxygen carriers undergo deactivation due to repeated oxidation-reduction cycles in chemical looping gasification. The primary cause of deactivation lies in the agglomeration and phase separation behavior exhibited by Fe-based oxygen carriers. In this research, a core-shell-like structure was developed to strengthen the structural stability of the oxygen carrier. This was achieved by constraining the thermal motion dimensions of active sites and establishing two pathways for oxygen ion transport. Briefly, the core-shell-like structure was constructed with NiFe2O4 as the core and CaO as the shell. Through characterization analysis, it was found that the interaction between the core-shell-like structures resulted in lattice distortion, promoting the generation of oxygen vacancies and providing a prerequisite foundation for the rapid reaction of lattice oxygen. Furthermore, the protective mechanism of the core-shell-like structure on the active sites inhibited the agglomeration behavior of the oxygen carrier. Remarkably, a hydrogen yield of 70 % was achieved at a temperature of 600 °C, and the reaction characteristics remained stable over 20 cycles of experimentation. Density functional theory calculations revealed that C atoms present stronger electron transfer at the core-shell-like structure, which induces stronger adsorption energy.

Effect of Biomass Torrefaction on the Syngas Quality Produced by Chemical Looping Gasification at 20 kWth Scale.

The innovative Biomass Chemical Looping Gasification (BCLG) process uses two reactors (fuel and air reactors) to generate nitrogen-free syngas with low tar content under autothermal conditions. A solid oxygen carrier supplies the oxygen for partial oxidation of the fuel. This study investigated the BCLG process, conducted over 25 h of continuous operation at 20 kWth scale, using ilmenite as the oxygen carrier and wheat straw pellets as fuel (WSP). The effect of using torrefied wheat straw pellets (T-WSP) on the syngas quality was assessed. In addition, the impact of several operational variables on the overall process performance and syngas yield was analyzed. The primary factors influencing the syngas yield were the char conversion through gasification and the oxygen-to-fuel ratio. Higher temperatures, extended residence times of solids in the fuel reactor, and using a secondary gasifier led to increased char conversion, enhancing H2 and CO production. Optimizing the air reactor design could enhance the CO2 capture potential by inhibiting the combustion of bypassed char. While char conversion and syngas yield with T-WSP were lower than those with WSP at temperatures below 900 °C, T-WSP achieved a higher syngas yield under conditions favoring high char conversion. The presence of CH4 and light hydrocarbons showed minimal sensitivity to operating conditions variation, limiting the theoretical syngas yield. Overall, the CLG unit operated smoothly without any agglomeration issues.

Preparation and chemical-looping-gasification performance of waste-sawdust briquette particles

Compared with loose biomass (LB), biomass briquettes (BBs) with high energy density and convenient transportation characteristics are more suitable as solid feedstock for preparing low-tar-content syngas through chemical looping gasification (CLG). Herein, the effects of key briquetting parameters, such as temperature, pressure, moisture content, and particle size, on the briquetting density (ρ), relaxation ratio, and crash resistance of waste sawdust are investigated, and the CLG performance of the briquetted sawdust is examined. Results show that pressure is the most critical factor affecting ρ. Briquetting of waste sawdust promotes the resultant syngas yield in CLG. Compared to LB, BBs exhibit increases in H2 yield, syngas yield, H2/CO molar ratio, and maximum gasification rate. When ρ was 0.8–0.9 g/cm3, the briquetting feature and CLG performance were good, with the briquetting pressure being optimized to 10–15 MPa. Moreover, granular-shaped BBs exhibits the highest CO release strength and good CLG performance. This discovery provides favorable briquetting conditions for the effective application of BBs in the field of CLG.

CO2 capture by the slag from lignite's chemical looping gasification using carbide slag

Due to its large amount, solid waste used as an oxygen carrier in chemical looping gasification (CLG) is not generally recycled. In order not to turn solid waste into secondary solid waste, re-resourcing research of the slag from CLG is worth consideration. The slag from lignite's CLG mainly consists of CaCO3, CaO, and small amounts of Ca(OH)2. In order to further purify CaCO3 and to achieve reduction in carbon emissions, the present work proposed the use of slag from lignite's CLG to capture CO2 and obtain purer calcium carbonate. The reaction properties and the reaction mechanism of the slag from CLG for CO2 capture were investigated using thermodynamic simulations, tubular furnace experiments, thermogravimetric experiments and characterizations. After analyses, it was suggested that reaction temperature for CO2 capture using slag from CLG lied within the temperature range of 300–800 °C. Reaction mechanism of slag from CLG to capture CO2 was different at different reaction temperatures. When the reaction temperature lied within the range of 300–400 °C, <Ca(OH)2+CO2→CaCO3+H2O> and <CaO+CO2→CaCO3> were the main reactions. When the reaction temperature lied within the range of 400–800 °C, <CaO+CO2→CaCO3> was the main reaction. The present study provides a method to turn waste into treasure without the need of subsequent recycling during lignite's CLG, and promotes the realization of “International Double Carbon Policy".

Oxygen donation of alkali earth metal ferrites for biomass chemical looping gasification: A comparative study

This study objectives to compare the oxygen donation properties among a series of alkali earth metal (AEM) ferrites as oxygen carriers (OCs), including MgFe2O4, CaFe2O4, SrFe2O4 and BaFe2O4, in biomass chemical looping gasification (CLG), through fixed bed reactivity tests and several characterizations, including XRD, XPS, TPR and thermogravimetric analysis. It was found that BaFe2O4 possessed the best syngas production performance, owing to its highest reactivity with char and lowest reactivity with CO/H2. Thermogravimetry analysis and TPR tests show that heavier AEM ferrites exhibited higher reactivity with char and lower reactivity with syngas, except for the relationship between SrFe2O4 and CaFe2O4. Fixed bed tests show that the AEM ferrites could be ranked as BaFe2O4 > CaFe2O4 > SrFe2O4 > MgFe2O4 according to their syngas production performance. Other than reactivity, 20-cycle tests demonstrate that BaFe2O4 had the best stability on H2 production compared to other OCs. The advantage of BaFe2O4 may be related to its more sufficient oxygen vacancy and crystal structure. Therefore, BaFe2O4-based OCs were found the most suitable for biomass CLG. The current study filled the gap in screening of AEM ferrite OCs and provided guidance for future OC development, achieving cleaner biomass conversion and enhanced sustainability.

Enabling plastic waste gasification by autothermal chemical looping with > 90 % syngas purity for versatile feedstock handling

The chemical looping gasification of plastics (CLGP) is a process that offers an innovative solution for transforming post-consumer waste plastics into high-value products. The process utilizes a co-current moving bed reducer reactor with iron-titanium-based oxygen carriers to gasify plastic feed and generate syngas autothermally. Its distinguishing feature is its ability to operate over a wide range of feed loadings and co-injection of mixed plastic species without any performance losses. Isothermal bench-scale experiments reveal a syngas purity of ∼95 %, aligning with the thermodynamic simulations. The moving bed reactor facilitates a deeper reduction of the oxygen carriers to the Fe+FeTiO3 phase, leading to the high syngas purity, which is then verified with additional TGA, XRD, and SEM analysis. For an autothermal operation of CLGP process, an active material content of 20 % is found to be sufficient to satisfy the kinetic and thermodynamic constraints. Further integration with downstream production of H2 is presented and compared to a steam gasification process. The process integration simulations show that the CLGP process outperforms the steam gasification system in terms of Cold Gas Efficiency (CGE), Effective Thermal Efficiency (ETE), and H2 yield. CO2 emissions are impressively reduced by ∼30 % in the CLGP system over that in the steam gasification system due to its ability to autothermally operate the process, unlike the highly endothermic steam gasification process.

Mercury Adsorption and Oxidation Performance of an Iron-Based Oxygen Carrier during Coal Chemical Looping Process.

During chemical looping combustion (CLC) and chemical looping gasification (CLG) of coal, the release, migration, and speciation of mercury in coal are significantly influenced by oxygen-carrier materials; however, the underlying mechanism remains inadequately addressed. In this work, the effect of a typical iron-based oxygen carrier on the release behavior of mercury from a bituminous coal and a lignite was investigated based on the Ontario-Hydro method. It is found that the effect of the iron-based oxygen carrier is attributed to three aspects: the enhanced release rate of mercury from coal, the adsorption of the released mercury, and the oxidization of gaseous Hg0 into Hg2+. With the increasing temperature, the adsorbance of mercury by the iron-based oxygen carrier decreases, while the oxidation of mercury enhances. Even at 900 °C, the adsorbance of mercury by the oxygen carrier remained at 0.1687 g/g, with a relative content of Hg2+ at 22.55%. Additionally, it was observed that iron-based oxygen carriers can physically absorb both Hg0 and Hg2+, while chemisorption refers to complex-compound formation between the iron-based oxygen carrier and mercury.

Effect of Nickel-Modified Hematite on the Conversion of Volatile and Char during Chemical Looping Gasification of Wood-Based Panel Waste

Effect of Nickel-Modified Hematite on the Conversion of Volatile and Char during Chemical Looping Gasification of Wood-Based Panel Waste

Parametric modeling and performance assessment of a novel cogeneration system of biomass chemical looping gasification driven by solar energy

Parametric modeling and performance assessment of a novel cogeneration system of biomass chemical looping gasification driven by solar energy

Chemical looping reforming of the micromolecular component from biomass pyrolysis via Fe2O3@SBA-16

AbstractTo solve the problems of low gasification efficiency and high tar content caused by solid–solid contact between biomass and oxygen carrier in traditional biomass chemical looping gasification process. The decoupling strategy was adopted to decouple the biomass gasification process, and the composite oxygen carrier was prepared by embedding Fe2O3 in molecular sieve SBA-16 for the chemical looping reforming process of pyrolysis micromolecular model compound methane, which was expected to realize the directional reforming of pyrolysis volatiles to prepare hydrogen-rich syngas. Thermodynamic analysis of the reaction system was carried out based on the Gibbs free energy minimization method, and the reforming performance was evaluated by a fixed bed reactor, and the kinetic parameters were solved based on the gas–solid reaction model. Thermodynamic analysis verified the feasibility of the reaction and provided theoretical guidance for experimental design. The experimental results showed that the reaction performance of Fe2O3@SBA-16 was compared with that of pure Fe2O3 and Fe2O3@SBA-15, and the syngas yield was increased by 55.3% and 20.7% respectively, and it had good cycle stability. Kinetic analysis showed that the kinetic model changed from three-dimensional diffusion to first-order reaction with the increase of temperature. The activation energy was 192.79 kJ/mol by fitting. This paper provides basic data for the directional preparation of hydrogen-rich syngas from biomass and the design of oxygen carriers for pyrolysis of all-component chemical looping reforming.

Effects of B-site substitution of SrFe2O4 oxygen carrier on the biomass chemical looping gasification performance

Effects of B-site substitution of SrFe2O4 oxygen carrier on the biomass chemical looping gasification performance

Effect of preparation of iron-based oxygen carriers on its agglomeration behavior with application to biomass chemical looping gasification

Iron-based oxygen carrier (OC) plays a crucial role in biomass chemical looping gasification (BCLG) to produce high quality syngas. However, a significant challenge during BCLG is the OC deactivation due to agglomeration, which is an urgent problem to be solved. In this study, the agglomeration behavior of iron-based OC preparation during the application for BCLG was obtained under the investigation of different preparation methods, carriers and ratios of active metal to carrier. The results revealed that preparation method affected the dispersion, crystal structure and stability of OC, thereby affecting the agglomeration. Among four preparation methods, the OC prepared by co-precipitation method achieved a 58.57 % lower agglomeration degree and 38.38 % smaller particle size than that of mechanical mixing method. Moreover, the carrier played a role in structural support and lattice oxygen transport, affecting crystalline structure and the agglomeration. Among four carriers, the OC prepared with Al2O3 carrier exhibited 36.18 % lower agglomeration degree and 25.15 % smaller particle size than that of CeO2 carrier. In addition, higher Fe content would weaken the metal-carrier interaction and reduce the structural stability of OC, causing serious agglomeration. With the decrease of Al:Fe molar ratio, the average particle size and agglomeration degree of spent OC increased by 43.56 % and 78.26 %, respectively. With the increase of cycles, the average particle size and agglomeration degree of spent OC increased gradually, while the reaction performance decreased obviously.

Kinetics analysis of cellulose chemical-looping gasification using Ca–Fe oxygen carrier

Ca–Fe oxygen carrier (OC) is an effective material with high selectivity on H2 and CO to aid to the gasification of solid fuel materials such as organic solid waste or biomass in chemical-looping gasification (CLG). However, the reaction mechanism of raw materials with high volatiles such as cellulose remains unclear. Kinetics analysis is considered as the efficient method to investigate the reaction mode and mechanism. In this study, isothermal method was conducted and the tristate intermedia products were used as substrates to reveal the kinetics characteristic of cellulose conversion process in CLG. The results demonstrated that the reduction process of Ca–Fe OC could be divided into three stages, and the activation energies were 40.40 kJ/mol, 91.28 kJ/mol and 165.33 kJ/mol, respectively; this indicates that the lattice oxygen could be transferred easily in the first stage, but much more difficult in the later two stages. The weak oxidizing molecules such as CO2 could re-oxide the reduced OC quickly and the activation energy was 27.83 kJ/mol. The mechanism model on kinetic of tar cracking was similar to the reaction between H2 and OC, and the activation energy was 82.27 kJ/mol. The decomposition of char was recognized as the stochastic nuclear shrinkage process with an activation energy of 52.22 kJ/mol.

Review on high-value utilization of phosphogypsum: Utilization of calcium and oxygen resources present in phosphogypusm

The world's annual production of phosphogypsum (PG) is up to 200 million tons at present. It was found that 15 % of PG produced worldwide is recycled. Therefore, it is imperative to seek a new pathway to recycle PG. This work provides an overview of the state-of-the-art scheme for high-value utilization of PG. Compared with previously published works, this review focuses on the utilization of oxygen (O) and calcium (Ca) resources. The state-of-the-art technology of utilizing O in PG consists of lignite’s chemical looping gasification (CLG) with PG-based oxygen carrier. The state-of-the-art technology for utilizing Ca in PG is the low-temperature decomposition of PG for producing CaO and CaCO3 from the reductive decomposition of PG. The process and the reaction mechanism of state-of-the-art technology for application of O and Ca in PG are summarized. Based on current research status, it is suggested to apply two or more solid wastes in cement, bricks and other aspects of large-scale. When utilizing PG, the migration transformation of impurities in PG and their reaction mechanisms at the molecular level deserve to be focused on. The key to solving the problems caused by PG large consumption, high value-added utilization and the introduction of policies providing incentives to this end. This research provides guidance for new engineering techniques for PG to achieve high-value and efficient use of resources in the large-scale utilisation of PG.

Inhibition strategies for phase separation of iron-based oxygen carriers in chemical looping gasification- enhanced oxygen transport efficiency through oxide-support interactions

Chemical looping gasification partially oxidizes biomass to obtain high-quality syngas using oxygen carriers, emerging as a potential method to cope with energy shortages. However, the oxygen carriers were susceptible to deactivation due to phase separation caused by different migration rates between atoms. In this work, the phase deviation of the oxygen carrier is inhibited by enhancing the lattice oxygen activity. Typically, the NiFe-based oxygen carriers were used as active sites and Ce atoms were introduced to change the lattice structure of the oxygen carriers. Calculated by density functional theory (DFT), Ce atoms formed a strong bonding interaction (Ni-O-Ce) with Ni atoms, causing lattice distortion of NiFe oxygen carriers that promote the formation of oxygen vacancies. Therefore, the syngas yields were increased from 537 ml/g (NF) to 633 ml/g (NF@0.5Ce) and 615 ml/g (NF@1.5Ce) in the N2 atmosphere. The syngas yields were increased from 895 to 1101 ml/g (NF@0.5Ce) and 1186 ml/g (NF@1.5Ce) with steam atmosphere. During the 20-cycle experiments, the phase separation of NiFe-based oxygen carriers was effectively suppressed by the intervention of Ce atoms. Therefore, it is a feasible option to induce lattice distortion of active grains by introducing inert elements to suppress phase separation.

Attempts of B-site doped LaFeO3 oxygen carriers in high-moisture content biomass chemical looping gasification

With the rapid development of anaerobic digestion engineering, the disposal and utilization of digestate are urgently required. Chemical looping gasification (CLG) technology provides potential for eliminate digestate and convert it into high-quality syngas. However, the application of conventional CLG is hindered by the high-moisture content of digestate. In order to decrease the energy consumption of dehydration, this work aims to optimize the CLG process by developing new oxygen carrier (OC) to enhance the transition of self-moisture of digestate. LaFeO3 was employed as the basic OC and Cr, Co, Cu were further doped on the B-site to form LaB0.5Fe0.5O3 (B = Cr, Co, Cu). H2O-TPD, OH/FTIR, NH3-Drifts, Raman, and XPS were employed to analyze the adsorption and dissociation of H2O by different OCs. Results indicated that LaFeO3 and LaB0.5Fe0.5O3 exhibited a synergistic effect with H2O, enabling adsorption of H2O at low temperatures and dissociation at high temperatures. In this case, it allows OC to capture H2O in the initial drying stage, then release H2O and OH at higher temperatures to participate in subsequent reactions, thus significantly increase the gasification performance. Fixed-bed CLG experiments were conducted to corroborate the characterization results. LaCu0.5Fe0.5O3 showcased the best gasification effect, achieving 81.83 % efficiency at a digestate moisture content of 40 %, surpassing LaFeO3 CLG by 5 %. Moreover, LaCu0.5Fe0.5O3 exhibited a noticeable catalytic effect and lowered the activation energy (E). Kinetic analysis revealed a 16 % reduction in E for LaCu0.5Fe0.5O3 CLG in comparison to LaFeO3 CLG.