Chemical Looping Gasification Process Research Articles

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.

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.

Effect of reaction conditions on the agglomeration of the oxygen carrier in biomass chemical looping gasification

The oxygen carrier (OC) agglomeration is an important factor limiting the development of biomass chemical looping gasification (CLG) technology. However, the agglomeration behavior of OC is not clear under multiple perspectives of reaction conditions. In this study, we investigated the Fe-based OC agglomeration behavior during CLG from three perspectives of biomass species, reaction temperature and steam/biomass (S/B). The results showed that biomass with high ash and K content was easy to form more low melting point substances, causing a lower deformation temperature (DT) and more severe agglomeration of OC after CLG. Moreover, with the increase of reaction temperature from 700 °C to 900 °C, the DT of OC decreased by 6.8 %, while the average particle size and agglomeration degree of OC increased by 26.2 % and 209.5 %, respectively. Although high temperature was beneficial for improving reaction performance and shortening reaction time, the excessive temperature would cause severe agglomeration and inhibit CLG process. In addition, the higher the S/B was, the more severe the agglomeration became. With the increase of S/B from 0 to 1.8, the DT of OC decreased by 3.2 %, while the average particle size and agglomeration degree of OC increased by 28.2 % and 75.5 %, respectively. The excessive S/B would form more KOH and NaOH with lower melting point, exacerbating the OC agglomeration and inhibiting the gasification.

Multi-level optimization of biomass chemical looping gasification process based on composite oxygen carrier

Biomass chemical looping gasification (BCLG) is one of the essential technology to utilize renewable resources, but the current lack of in-depth research on BCLG makes it difficult for practical industrial applications. In this paper, the combination of quantum chemical calculation, ReaxFF molecular dynamic (ReaxFF MD) simulation, and process simulation is used to conduct an in-depth study of BCLG process. Firstly, three composite oxygen carriers (CuFe2O4, CoFe2O4, and Fe3O4) are selected by density functional theory (DFT), which finally indicates that CuFe2O4 is the best composite oxygen carrier for BCLG. Then, the reaction mechanism between syngas and oxygen carrier surface is studied at the microscopic level, which validates the high performance of CuFe2O4. After determining the oxygen carrier, the reaction mechanism of BCLG and the effect of temperature on the product distribution are studied by ReaxFF MD simulation. Finally, the process simulation of BCLG is constructed based on the results discussed above.

Hydrogen production from municipal solid waste via chemical looping gasification using CuFe2O4 spinel as oxygen carrier: An Aspen Plus modeling

Combined with carbon capture, chemical looping gasification (CLG) provides a clean and carbon-negative approach to converting municipal solid waste (MSW) into high-quality syngas without air separation units. An Aspen Plus simulation of the CLG process with continuous MSW feeding was constructed and investigated in this work. The CuFe2O4 spinel oxygen carrier (OC) was utilized to provide lattice oxygen. This model was validated using the experimental results from the literature to demonstrate its feasibility for CLG of MSW. The effects of gasification temperature, steam-to-municipal solid waste ratio (SMR) and OC mass flow (OCMF) on H2 selectivity were throughout investigated. Results demonstrated that at 750 °C, the H2 selectivity peaked at 51.44%. The H2 selectivity rose from 43.89% to 56.29% when SMR varied from 0.1 to 2.1. Lower OCMF availed H2 production. At 800 °C, SMR of 1.1 and OCMF of 100 kg h−1, 67.85% of the initially introduced H in the CLG process can be recovered as pure H2 by the end, resulting in an energy efficiency of 57.66% based on the low heat value (LHV) of MSW, the electricity consumption and H2. The process consumed 7.93 t/t H2 with a corresponding product cost of 2941.21 USD/t. Additionally, it contributes 66.90% and 66.73% to the overall global warming and acidification potentials of the entire process, respectively. The combined impact of temperature and SMR, while maintaining a constant OCMF, highlights that the temperature within the lower range primarily governs the H2 selectivity. Although both OC and steam can supply oxygen during CLG, their effects on gasification efficiency are diametrically opposed due to their varying oxidation capabilities. Notably, utilizing CuFe2O4 OC, the maximum H2 selectivity of 63.30% was achieved at 700 °C, SMR of 2.1 and OCMF of 100 kg h−1.

Understanding the structural changes on Fe2O3/Al2O3 oxygen carriers under chemical looping gasification conditions

Chemical Looping Gasification (CLG) has emerged recently as a promising technology for producing non N2-diluted syngas without the need for an external power supply or the expensive use of pure O2. Many studies have focused on development of oxygen carriers since they are considered a crucial factor in CLG processes. Fe2O3/Al2O3 (FeAl) oxygen carriers have been proposed due to previous experience in Chemical Looping Combustion (CLC). However, the aggressive conditions of gasification cause a decrease in the mechanical stability of the particles, which can be a challenge for their use in CLG. In this work, the operating conditions and Fe-content required to maintain the particle integrity of oxygen carrier particles during redox cycles in both CLC and CLG operations were determined. Long-term tests, consisting of 300 redox cycles, were conducted in a TGA to simulate the operation in a continuous unit and the results were compared with attrition data obtained from a 1.5 kWth CLG unit. Three oxygen carriers with varying Fe2O3-content (10, 20 and 25 wt%) were used, and three different solid conversions (0–25 %, 75–100 % and 0–100 %) were performed to emulate CLC or CLG atmospheres at three temperatures (850 °C, 900 °C and 950 °C). The evolution of the microstructure of particles was analyzed using a scanning electron microscope (SEM) and it was found that the lower the Fe2O3 content in the particles, the greater their stability in redox cycles, an increase in the reaction temperature led to a more rapid degradation of the oxygen carrier particles, and the solid conversion variation and degree of reduction/oxidation during redox cycles strongly influenced the evolution of the mechanical stability of the oxygen carrier particles.

Effect of alkali metals and alkaline earth metals on promotion and agglomeration of Fe-based oxygen carrier during chemical looping gasification

Alkali metals and alkaline earth metals (AAEMs) are the most abundant trace elements in biomass, which will provide different effects of catalytic or inhibitory at different time during chemical looping gasification (CLG). However, the role of AAEMs in the catalysis or agglomeration at different time remains unclear in biomass CLG. In this study, the promotion and agglomeration effects of AAEMs on CLG performance is studied under different time and different AAEMs. The results show that K plays a major role in promoting CLG before 20 min and inhibiting CLG at 30 min. Moreover, K promotes the conversion from Fe3+ to Fe2+ and the earlier existence of more FeAl2O4 and Fe2Al4Si5O18, causing obvious agglomeration. Na and Mg provide obvious catalytic and promotional effects after the excitation. Further, more FeO is converted from Fe3+ at 3–8 min in Na-AH, leading to the earlier formation of Fe2Al4Si5O18 and agglomeration between particles. Ca obviously promotes the whole CLG process. Furthermore, Ca helps to promote the conversion of Fe2O3 to Fe3O4, but delay the conversion to FeO and a slower generation of FeAl2O4, resulting in less adhesion and obvious inhibition of agglomeration. Mg slightly slows down the conversion of Fe2O3 to Fe3O4, but earlier generates FeO with a lower strength than other samples, leading to low FeAl2O4 and slight agglomeration. In addition, the effect of Mg on reducing agglomeration is weaker than that of Ca, but better than that of K and Na.

Analysis of hydrogen-rich syngas generation in chemical looping gasification of lignite: Application of carbide slag as the oxygen carrier, hydrogen carrier, and in-situ carbon capture agent

Chemical looping gasification (CLG) has become a popular method for producing hydrogen-rich syngas due to its environment-friendliness. Recently, a method of using industrial solid waste carbide slag as an oxygen carrier, hydrogen carrier, and in-situ carbon capture agent in the CLG process has been proposed. However, the actual experiment was affected by heat and mass transfer, and the detailed reaction pathway of the carbide slag was not fully understood. In the present study, the process of the CLG process for producing hydrogen-rich syngas with lignite and carbide slag was analyzed using tube furnace experiments, FactSage calculations, and joint characteristic experiment of carbide slag. The result showed that to achieve a gas phase product with a hydrogen concentration exceeding 90 vol% (with dry N2 excluded), a molar ratio of lignite to carbide slag of greater than 1:5 and a reaction temperature of 923 K should be maintained. In terms of the reaction pathway of carbide slag in the CLG process, it was revealed that calcium hydroxide, the primary component of carbide slag, directly participated in the reaction at temperatures of less than 773 K. Overall, this work provides a novel idea for the preparation of hydrogen-rich syngas during CLG process.

Design and control concept of a 1 MWth chemical looping gasifier allowing for efficient autothermal syngas production

Chemical looping gasification (CLG) is a novel gasification concept, allowing for the efficient production of a high calorific, N₂-free syngas with low tar content. Previous studies showed that the inherent process characteristics require a dedicated process control concept in order to allow for sufficient solid and thus heat transport between the two reactors (air and fuel reactor) of the gasification unit, while at the same time being able to accurately tailor the air-to-fuel equivalence ratio (λ), thus obtaining stable gasification conditions. To demonstrate its viability, a suitable control concept was implemented in the 1 MWth modular pilot plant located at the Technical University Darmstadt. In this paper, results obtained during the first ever autothermal CLG operation, achieved in this unit using biomass pellets as the feedstock, are presented, highlighting important process fundamentals. It is demonstrated that the novel process control concept allows for an accurate control of λ in semi-industrial scale, while at the same time guaranteeing stable hydrodynamics and thus solid and heat transport between the air and fuel reactor, making it a suitable control concept for large-scale implementation. Moreover, it is demonstrated that the underlying phenomena of the CLG process lead to substantial system inertia, as the solid bed inventory of the gasifier acts as an oxygen storage during transient periods, evoked by changes in the air-to-fuel equivalence ratio.

Chemical looping reforming of toluene as bio-oil model compound via NiFe2O4@SBA-15 for hydrogen-rich syngas production

Hydrogen-rich syngas was a clean energy and an important industrial material. Based on the decoupling strategy of biomass chemical looping gasification process, this paper proposed a strategy of metal oxides embedded into molecular sieves to prepare highly dispersed and nanosized oxygen carriers for producing hydrogen-rich syngas. NiO@SBA-15, Fe2O3@SBA-15, and NiFe2O4@SBA-15 were prepared by the impregnation method, and the reaction conditions on the chemical looping reforming of toluene were investigated. The results showed that NiFe2O4@SBA-15 had the highest toluene conversion rate of 93.4% and a relatively high CO selectivity rate of 80.7%. It was confirmed that the embedding strategy can effectively enhance the nanocrystallization and dispersion of metal oxides in oxygen carriers, which could effectively reduce sintering. The inverse spinel structure of NiFe2O4 made the oxygen carrier have more metal adsorption sites and a closer reaction distance, which were beneficial to the adsorption and reaction of the fuel. After testing, the optimum reaction temperature was 750 °C, and the optimum weight hourly space velocity was 1.168 h−1. In the 10 cycles of testing of 20 NiFe2O4@SBA-15, the average conversion rate of toluene was 95.34%, the moderate selectivity of CO in the gaseous product was 94.83%, the average H/C ratio was 1.97, which indicated that the cycle stability is good. It provided a reference for developing and designing future oxygen carriers of biomass chemical looping reforming.

Process modelling integrated with interpretable machine learning for predicting hydrogen and char yield during chemical looping gasification

Chemical looping gasification (CLG) is a promising thermochemical process for the production of H2. CLG process is mainly based on oxygen transfer from an air reactor to a gasification reactor using solid metal oxides (also called oxygen carriers, (OC)) as oxidants. The unique oxygen separation system of CLG makes it an advanced process with a smaller carbon footprint compared to the conventional gasification process. The other advantages of CLG includes increased efficiency, reduced greenhouse gas emissions, and improved process stability compared to conventional biomass gasification. Although CLG is a promising technology, it still faces several challenges such as high capital cost, OC durability, complex reaction mechanism and scalability issues. Some of these challenges can be addressed by understanding the impact of various process conditions on H2 yield and char formation during CLG. The present study proposes a novel integrated process simulation and experimental studies to generate large dataset used for interpretable machine learning (ML) analysis. Three different ML models including support vector machine (SVM), random forest (RF), and gradient boost regression (GBR) were used to develop models for predicting the H2 and char yield during CLG. The GBR outperformed other models for the prediction of H2 and char yield during CLG with R2 value > 0.9. Among the experimental conditions, the temperature (T) and steam to biomass ratio (SBR) were the most relevant parameters affecting H2 and char production. Biomass ash, C, volatile matter (VM) and H content also influenced H2 and char formation. Overall, a combination of SHAP and partial dependence plot helped address the black box challenges of ML models.

An innovative Cu-Al oxygen carrier for the biomass chemical looping gasification process

Biomass chemical looping gasification (BCLG) is a novel technology that enables the production of renewable syngas without the need for an external supply of energy or power while achieving negative carbon emissions. In this work, the behavior of a synthetic Cu-based (14 wt% CuO) oxygen carrier, Cu14Al_ICB, was tested for 45 h in a 1.5 kWth continuous unit using pine sawdust as fuel. The effect of the oxygen-to-fuel ratio (λ) and gasification temperature on syngas composition and gasification parameters, including fuel conversion, carbon capture, cold gas efficiency, and syngas yield, was studied. A decrease in the oxygen-to-fuel ratio increased molar flows of H2 and CO in the syngas, while an increase in gasification temperature mainly improved char gasification, also enhancing H2 and CO generation. High amounts of syngas with low CH4 molar flows (∼2.3 mol CH4/kg of dry biomass) were obtained under any conditions due to the catalytic effect of metallic copper on CH4 reforming reactions. Syngas yield values were achieved approximating those obtained with Ni-based solids. The oxygen carrier also had a very positive effect on tar removal, reaching tar concentration values similar to those obtained by operating under chemical looping combustion conditions. The attrition rate measured with this oxygen carrier was the lowest obtained to date for any oxygen carrier operating under BCLG conditions. In addition, the mechanical properties, reactivity, and oxygen transport capacity of the oxygen carrier were maintained throughout the campaign. Therefore, the Cu14Al_ICB oxygen carrier has proved to be an excellent material for the BCLG process.

Coal-fueled chemical looping gasification: A CFD-DEM study

Chemical looping gasification (CLG) is an emerging technology for reducing greenhouse gas emissions, yet the complex physical-thermal-chemical behaviour in the CLG unit has not been well understood. This work developed a high-fidelity computational fluid dynamics-discrete element method (CFD-DEM) reactive model considering four heat transfer modes (e.g., conduction, convection, radiation, and reaction heat) and complex heterogeneous and homogeneous reactions. The hydrodynamics and thermochemical characteristics in a CLG unit operating under several key operating parameters are numerically studied. The contribution from each heat transfer mode is quantified and the relationship between particle-scale behaviour and mesoscale bubble structures is quantitatively illuminated. The results show that the solids vertical dispersion coefficient is one order of magnitude larger than the horizontal one. At a low solid holdup, the interphase drag force plays a dominant role and particles in the bubble phase have higher vertical slip velocities. The ratio of particle-averaged heating rates for char particles through conduction, convection, radiation, and reaction take 5.41%, 14.91%, 14.39%, and 65.29%, and that for oxygen carriers take 7.77%, 23.46%, 20.33%, and 48.44%, respectively. For char particle and oxygen carriers, the reaction heat dominates the heat transfer process. Increasing gas inlet velocity promotes particle mixing, alleviates dead zone, and finally increases gas products while increasing the char to oxygen carrier mass ratio decreases gas products. The present work provides a cost-effective tool for the in-depth understanding of heat and mass transfer mechanisms in the CLG process.

Microscopic mechanism study and process optimization of dimethyl carbonate production coupled biomass chemical looping gasification system

Biomass chemical looping gasification technology is one of the essential ways to utilize abundant biomass resources. At the same time, dimethyl carbonate can replace phosgene as an environment-friendly organic material for the synthesis of polycarbonate. In this paper, a novel system coupling biomass chemical looping gasification with dimethyl carbonate synthesis with methanol as an intermediate is designed through microscopic mechanism analysis and process optimization. Firstly, reactive force field molecular dynamics simulation is performed to explore the reaction mechanism of biomass chemical looping gasification to determine the optimal gasification temperature range. Secondly, steady-state simulations of the process based on molecular dynamics simulation results are carried out to investigate the effects of temperature, steam to biomass ratio, and oxygen carrier to biomass ratio on the syngas yield and compositions. In addition, the main energy indicators of biomass chemical looping gasification process including lower heating value and cold gas efficiency are analyzed based on the above optimum parameters. Then, two synthesis stages are simulated and optimized with the following results obtained: the optimal temperature and pressure of methanol synthesis stage are 150 °C and 4 MPa; the optimal temperature and pressure of dimethyl carbonate synthesis stage are 140 °C and 0.3 MPa. Finally, the pre-separation-extraction-decantation process separates the mixture of dimethyl carbonate and methanol generated in the synthesis stage with 99.11% purity of dimethyl carbonate. Above results verify the feasibility of producing dimethyl carbonate from the perspective of multi-scale simulation and realize the multi-level utilization of biomass resources.

Performance Evaluation of Torrefaction Coupled with a Chemical Looping Gasification Process under Autothermal Conditions: Flexible Syngas Production from Biomass

Herein, a coupled biomass torrefaction and chemical looping gasification (BTCLG) process was proposed, and process simulations were performed under autothermal conditions. The effects of operational parameters on product distribution with torrefaction temperatures from 240 to 300 °C, gasification temperatures from 700 to 880 °C, and steam/biomass (S/B) ratios from 0.5 to 1.5 were explored. The results showed that the process could stably operate under autothermal conditions. Torrefaction increased the syngas yield, heating value, and cold gas efficiency by 12.44, 5.11, and 36.73%, respectively. Moreover, it reduced the bed material circulation rate required for autothermal operation by 59.03%. At the torrefaction temperature of 240 °C, the syngas yield reached a maximum value of 0.78 Nm3/kg. Increases in the gasification temperature also positively impacted syngas production. However, the optimal gasification temperature was 810 °C based on the bed material circulation rate constraint. The syngas H2/CO ratio could be flexibly adjusted from 1.62 to 3.34 by changing the S/B ratio to meet downstream demands. Overall, the simulation results support the technical viability and demonstrate the excellent performance of the BTCLG process compared to the biomass CLG process.

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.