Reactivity Of Oxygen Carrier Research Articles

Reaction Characteristics of Hydrogen-Rich Syngas Production by Sludge/Coal Cogasification Based on the Iron-Based Oxygen Carriers

With the acceleration of industrialization and urbanization in China, wastewater treatment is increasing yearly. As a by-product of wastewater treatment, the gasification of sludge with coal in chemical looping process is a clean and efficient conversion technology. To explore the reaction behavior of cogasification of sludge and coal with iron-based oxygen carriers (OCs) for producing hydrogen-rich syngas, the experiment of cogasification using Fe2O3/Al2O3 as OC in a fluidized bed reactor was conducted. The result showed that the volume percentage of hydrogen (H2) and syngas yield is proportional to the amount of sludge added. The optimal operation conditions were: temperature at 900 °C, the mass ratio of OC to coal at 5.80 and mass ratio of sludge to coal at 0.2. Under this operating condition, the volume percentage of H2 and syngas yield in the flue gas was 75.6 vol% and 97.5 L·min-1·kg-1, respectively. Besides, the OC showed a stable reactivity in the sixth redox cycle with added sludge. However, the reactivity of OC significantly declined in the seventh and eighth redox cycles. It was recovered when the ash was separated. The decrease in the specific surface area of the OC caused by ash deposition is the main reason for the decline in its reactivity. The kinetic analysis showed that the random pore model describes the reaction mechanism of sludge/coal chemical looping gasification (CLG). The addition of sludge can reduce the activation energy of coal CLG reaction, accelerate the gasification reaction rate and increase the carbon conversion.

Influences of reaction and thermal conditions on microstructural evolutions of ilmenite oxygen carriers for chemical looping combustion

Ilmenite ore has been widely accepted to be a cost-effective oxygen carrier (OC) of Chemical Looping Combustion (CLC) for CO2 capture. The focus of this study is to investigate into the influences of chemical impact, thermal variation and ageing effect on microstructure and performance evolutions of ilmenite OCs. Iron element migration, crystallinity and morphology alterations, and irreversible change of chemical composition were identified to be the major aspects responsible for gradual microstructural evolutions of Ilmenite OCs. Iron element migration from bulk materials to particle surface, occurring during the oxidation step of redox cycles, was of temperature- and O2 concentration- dependences. A schematic diagram was developed to explain the pathways of irreversible iron migration and alteration of chemical composition in redox cycle reactions. By lowering phase interaction between Fe2TiO5 and TiO2, the cycled thermal shock (due to reaction and processing in CLC) promotes the iron element concentration on OC particle surface and the ilmenite OC reactivity. Long-term ageing at elevated temperature, as one of typical severe conditions in CLC, exhibits activation effects for ilmenite OCs, even though it causes increased crystallinity, denser particle structure and redistribution of Fe2TiO5-TiO2 phase

Coal and biomass combustion with CO2 capture by CLOU process using a magnetic Fe-Mn-supported CuO oxygen carrier

The Chemical Looping with Oxygen Uncoupling (CLOU) process is a derivative technology of the Chemical Looping Combustion (CLC) process for the combustion of both renewable and non-renewable solid fuels. The present work studies the combustion and CO2 capture efficiency of burning coal or biomass using a single Cu-based oxygen carrier with magnetic properties as an oxygen carrier. The combustion of two different coals and three different biomasses was performed in a 1.5 kWth CLOU continuously operated unit for 36 h. The magnetic properties of the oxygen carrier were also studied after combustion and its separation from the ashes. Complete combustion of the fuel to CO2 and H2O was achieved in all cases. For both coals, CO2 capture efficiency increased with fuel reactor temperature, with both reaching values of 97% at 900 °C. The same increase was obtained with the biomasses. The highest CO2 capture efficiency for a biomass was obtained with pine sawdust, which achieved a value of 93%, followed by almond shell (86%) and olive stone (80%) at 900 °C. Oxygen carrier reactivity remained constant after use in the continuous unit with one small increase in the attrition jet index (AJI) value. The used particles were found to still be as magnetic as the fresh particles, and the fines were also highly magnetic. Values higher than 99% were achieved with separation from the fines reached. It was therefore proven that the elutriated oxygen carrier from the plant was still magnetic and could be easily separated from the elutriated ash.

Spatial evolution characteristics of active components of copper-iron based oxygen carrier in chemical looping combustion

Reactivity of oxygen carriers (OCs) is a key issue in chemical looping technology. Exploring spatial evolution characteristics of active components and lattice oxygen migration during reduction reaction is of great importance in improving the reactivity of OCs. In this study, thermogravimetric analyzer (TGA) is used to control the reduction degree of OCs. Oxygen migration to the surface of CuFe2O4 (100) and CuO (111) is studied based on density functional theory (DFT). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) are used to investigate phase change and valence evolution of active components of the oxygen carriers. The results show that the ratios of lattice oxygen, chemical adsorbed oxygen and physical adsorbed oxygen at three points are very close in OCfresh. As the reduction reaction progresses, lattice oxygen is gradually consumed and the content of Cu0 and Fe2+ is increased. The closer to the edge point, the more lattice oxygen is consumed and the larger ratio of Cu0 and Fe2+. Moreover, there is no Fe0 in sample OC6.24% or OC9.19%, which is caused by the rapid migration and replenishment of lattice oxygen. The calculation results show that bulk oxygen migration to the surfaces of the OCs is exothermic and has a certain energy barrier.

Effect of preparation conditions on the performance of K-decorated Fe2O3/Al2O3 oxygen carrier (OC) in chemical looping conversion of coal process with deep OC reduction

Chemical looping conversion of coal (CLCC), an innovative technology, is an efficient and clean way for the utilization of coal. Oxygen carrier (OC) reduction by the coal is the rate-limiting process for the CLCC with deep OC reduction. K-decorated Fe2O3/Al2O3 OC, found to be a promising OC, can increase the reaction rate of OC and char. Unfortunately, due to the complexity of the OC the preparation conditions on the performance of this composite OC were not clear. In this study, the effect of Al2O3 content and calcination temperature on the activity and stability of Fe-based OC were investigated by thermogravimetric analysis (TGA), H2 temperature-programmed reduction (TPR), N2 adsorption analyzer, X-ray diffraction (XRD) and scanning electron microscope (SEM). The impact of K2CO3 loadings on the reactivity and stability of OC was also studied in a fix-bed reactor. In addition, optimal preparation conditions were screened out. The results showed that Al2O3 could increase the specific surface area of OC and anti-sintering ability. However, the Al2O3 had an adverse impact on the mechanical strength and reactivity of OC. The increase of calcination temperature of OC could increase the mechanical strength but decrease the reactivity of OC. The loading of K2CO3 could significantly improve the reactivity of OC, and K2CO3 was favorable for the redox stability of OC. The optimal preparation conditions of the composite OC are as follows: the addition amount of Al2O3 was 30%, the addition amount of K2CO3 was 5%, and the calcination temperature of OC was 1030 °C.

Sulfur release and migration characteristics in chemical looping combustion of high-sulfur coal

Chemical looping combustion of coal has attracted great attention due to its advantage in carbon capture. Sulfur in coal may have negative impacts on this process including deteriorating the reactivity of oxygen carrier and generating gaseous sulfur species. In this research, the release and migration characteristics of sulfur in the chemical looping combustion of Xinzhou coal with two synthetic oxygen carriers, CuO/SiO2 and NiO/Al2O3, were investigated by experiments and thermodynamic simulation. The thermodynamic analysis showed that sulfur in coal mainly migrated to metal sulfides at lower temperatures and peroxide coefficients, but the formation of SO2 was favored at higher temperatures and peroxide coefficients. Experimental results showed that the sulfur conversion efficiencies (XS,g) during the reduction stage reached 62.34 % and 61.25 % under Cu- and Ni-based oxygen carriers, respectively, and XS,g during the reoxidation stage were 6.25 % and 7.44 %, respectively. For both oxygen carriers, the share of H2S and SO2 in the sulfurous gases exceeded 96 % during the reduction stage, while SO2 was the only sulfurous gas when air was introduced. Even though the metal sulfides (Cu2S, Ni3S2 and NiS) were observed in the reduced samples, those two oxygen carriers showed satisfactory regeneration performance after one redox process.

Development of CuO-based oxygen carriers supported on diatomite and kaolin for chemical looping combustion

Chemical Looping Combustion (CLC) technology has emerged as a promising alternative capable of restricting the effects of global warming due to anthropogenic gas emissions, especially CO2, through its inherent capture. This study aims to synthesize and evaluate Cu-based oxygen carriers supported on natural materials such as diatomite and kaolin, through the incipient wet impregnation method for CLC process applications. Oxygen carriers were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), and scanning electron microscopy with surface energy dispersive x-ray spectroscopy (SEM-EDS). The mechanical strength of the two oxygen carrier particles was determined after the sintering procedure resulting in high crushing force. Reactivity of oxygen carriers was evaluated in a thermobalance with CH4 and H2 gases. Different reaction pathways were attempted when undergoing the redox cycles: total direct reduction of CuO to Cu0 for Cu-K and partial reduction of CuO to Cu2O and CuO to Cu-D. However, the highest reactivity and reaction rate was achieved in Cu-D due to the pore structure of diatomite, the chemical composition and the resulting interaction between CuO and the support. H2 gas reactivity tests showed a higher conversion rate and greater stability between cycles for both oxygen carriers. Thus, the reducible CuO content present in Cu-Diatomite during the reactivity test with H2 as the fuel gas was ideal for achieving high solids conversion, tendency for greater stability and a higher reaction rate.

Cu-Mn oxygen carrier with improved mechanical resistance: Analyzing performance under CLC and CLOU environments

Chemical Looping Combustion process allows combustion of gaseous, liquid or solid fuels with CO2 capture. The oxygen necessary for combustion can be supplied using lattice oxygen (CLC) or oxygen uncoupling (CLOU) mechanisms. The present work studies the effects of kaolin addition on CuMn oxygen carrier behavior for CLC and CLOU processes. CuMn oxygen carrier was prepared by granulation with a composition: 27.2 wt% CuO, 52.8 wt% Mn3O4 and 20 wt% kaolin. Oxygen release rates and fluidization behavior were analyzed by TGA and batch fluidized bed reactor. The oxygen carrier was studied for CH4 and synthetic biogas combustion in a 500 Wth CLC continuous unit for 50 h of combustion at temperatures up to 930 °C. No agglomeration problems were observed. Results found during biogas combustion were similar to methane combustion. The addition of 20 wt% kaolin changed the mixed oxide chemical composition generating Cu1.2Mn1.8O4 and improved significantly the oxygen carrier mechanical resistance, increasing the extrapolated lifetime to 19,000 h, 3.6 times over the value found for any Cu based oxygen carrier in CLC. However, the oxygen carrier reactivity had an important decrease with respect to a similar oxygen carrier without kaolin addition, whose fraction in oxygen carrier must be optimized.

Preparation of Metal Oxide‐based Oxygen Carriers Supported with CeO2 and γ‐Al2O3 for Chemical Looping Combustion

AbstractThe development of efficient oxygen carriers (OCs) in chemical looping combustion (CLC) exhibited tremendous achievement considering inherent CO2 capture. The selectivity of CO2 in the CLC process depends on the performance of employed OCs during multiple redox cycles. Different types of OCs were prepared, including 5wt%Ni/5wt%Ce/γ‐Al2O3, 5wt%La/5wt%Ce/γ‐Al2O3, and 5wt%Pr/5wt%Ce/γ‐Al2O3, using the wet impregnation method and characterized by scanning electron microscopy/energy‐dispersive X‐ray spectroscopy, temperature‐programmed reduction, and thermogravimetric analysis (TGA). The redox reactivity of OCs was investigated through TGA and tubular furnace reactor. The as‐prepared OCs revealed higher thermal stability along with excellent oxygen capacity. Pr/Ce/γ‐Al2O3‐based OCs showed moderate oxygen capacity, which may increase by the addition of active metals.

A comparative study on clean ammonia production using chemical looping based technology

A comparative assessment of NH3 production using a chemical looping based process is carried out for 500,000 tons per year with inherently integrated CO2 separation using natural gas as feedstock. The chemical looping process, with dynamically operated packed bed reactors, has been modelled, designed and simulated to accomplish steady-state operation and the results are used to carry out the full-scale energy analysis and costing. Two process heat management strategies have been considered on the basis of the oxygen carrier reactivity. With respect to the commercial process for natural gas-to-ammonia, the chemical looping based process replaces the syngas generation and purification units while the NH3 synthesis and purification units remain unvaried. The chemical looping plants show a yield of 1.54–1.63 kgNH3/kgNG. The overall primary energy consumption to separate CO2 is 0.78–2.32 MJLHV/kgCO2 to achieve a carbon capture rate >99% compared to 73% achieved by the reference plant with integrated carbon capture and storage. The final cost of NH3 production is slightly lower than the reference technologies because of a decreased plant cost (19% lower) in particular for the reforming unit and CO2 separation. As a result, by using chemical looping the cost of CO2 avoidance is negative (−1 to −5 $/tonCO2) and strongly dependent on the cost of the oxygen carriers and chemical looping reactors.

Predictive screening and validation on chemical looping oxygen carrier activation by tuning electronic structures via transition metal dopants

Owing to its high fuel conversion efficiency and in-situ CO2 capture capability, chemical looping is a promising and versatile platform for fossil fuel utilization. Through the circulation of oxygen carriers (OCs), which are usually metal oxides, the carbonaceous fuels are oxidized into power/heat and/or value-added chemicals by lattice oxygen of OC in the fuel reactor. The reactivity of OC towards the carbonaceous fuels is crucial to the success of chemical looping processes. Incorporating low-percentage dopants into OC is a promising strategy to improve their reactivity while maintaining the recyclability. Consequently, a systematic screening strategy in dopant selection with a solid physical foundation is highly desired. Using hematite (α-Fe2O3) as the model OC material, density functional theory calculations were conducted herein to exemplify the impact of transition metal dopants on the surface reactivity with CO and CH4, the two most common C1 reducing agents in fossil fuels. We found that the amount of electrons accumulated on the lattice oxygen that bound with dopants is a key descriptor to evaluating the surface reactivity in the Mars-van Krevelen type reactions, which can be tailored by dopants with different electronegativities. Cu and Ni were predicted to be the most effective dopants, and such theoretical predictions were validated in temperature-programmed reduction and cyclic redox experiments, where a significant reactivity enhancement was observed using only 1% atomic ratio of effective dopants. The proposed screening strategy is expected to facilitate new OC designs and modifications in an energy and cost effective manner, thus significantly expedites the development of chemical looping technologies.

Chemical looping combustion with nanosize oxygen carrier: a review

This paper reports latest advancement on oxygen carriers (OCs) and effect of particle size from micro- to nanoscale in chemical looping combustion (CLC). CLC is basically a carbon capture and storage technology with the objective to reduce carbon dioxide emission from fossil fuel-based power plants, and it has the potential to reduce the global warming. Attention has been drawn toward utilization of nanosize-based oxygen carrier for bulk application. CLC is a novel technology for combustion of fossil fuels that avoids dilution of carbon dioxide (CO2) with flue gases. Performance of CLC system depends upon redox reactivity and stability of oxygen carrier particles at high operating temperature. Oxides of metals like nickel, iron, copper, and mixed metals have also been discussed. Tendency of discussed nano-OC to agglomerate and stability at high temperature can be addressed by the use of suitable inert support materials. Reactivity of oxygen carrier increases with decreasing particle sizes from micro- to nanosize. Recent developments in nanosized oxygen carriers can be exploited for application. The challenges associated with nanosize oxygen carriers are stabilization and agglomeration at temperature above 600 °C. Different techniques have been proposed and investigated to overcome challenges. Various metal/metal oxide pair has been evaluated for its oxygen bearing capacity, stability, and resistance to agglomeration. Stability and agglomeration of nanosize oxygen carrier at temperature above 700 °C is an open issue.

Earth abundant spinel for hydrogen production in a chemical looping scheme at 550 °C

Operating chemical looping process at mid-temperatures (550–750 °C) presents exciting potential for the stable production of hydrogen. However, the reactivity of oxygen carriers is compromised by the detrimental effect of the relatively low temperatures on the redox kinetics. Although the reactivity at mid-temperature can be improved by the addition of noble metals, the high cost of these noble metal containing materials significantly hindered their scalable applications. In the current work, we propose to incorporate earth-abundant metals into the iron-based spinel for hydrogen production in a chemical looping scheme at mid-temperatures. Mn0.2Co0.4Fe2.4O4 shows a high hydrogen production performance at the average rate of ∼0.62 mmol g−1 min−1 and a hydrogen yield of ∼9.29 mmol g−1 with satisfactory stability over 20 cycles at 550 °C. The mechanism studies manifest that the enhanced hydrogen production performance is a result of the improved oxygen-ion conductivity to enhance reduction reaction and high reactivity of reduced samples with steam. The performance of the oxygen carriers in this work is comparable to those noble-metal containing materials, enabling their potential for industrial applications.

Interaction of coal ashes with potassium-decorated Fe2O3/Al2O3 oxygen carrier in coal-direct chemical looping hydrogen generation (CLHG)

Coal-direct CLHG is a novel hydrogen production technology with inherent CO2 capture. Potassium-decorated Fe2O3/Al2O3 oxygen carrier (OC) has been proved to be a potential OC for the technology. However, the ash in the coal could influence the OC performance. In this work, the effect of ash addition on the reactivity, the morphology structure and phase composition of OC, and the potassium migration in the reduction stage were investigated. Furthermore, the effect of OC on the ash fusion temperature was discussed. Results indicated that the OC reactivity had no significant change when SM (Shenmu) ash addition was less than 1% in the reduction stage and decreased when the addition was more than 2%. In the steam oxidation stage, the H2 yield varied between 5.80–5.57 mmol/g when the SM ash addition was less than 10% and decreased to 4.31 mmol/g when the addition was 40%. FeO could react with SiO2 deriving from coal ash to form Fe2SiO4, which could cause the loss of Fe and the OC sintering; K2CO3 could react with silicon-aluminum minerals which could cause the potassium loss. The ash with high CaO content had a less negative effect on the OC reactivity. With the increase of SM ash addition, the potassium in OC decreased, the potassium in char increased and the volatile potassium decreased after the reduction stage. After the OC addition, the deformation temperature decreased from 1242 °C to 1114 °C in the weak reduction atmosphere while increased from 1162 °C to 1300 °C in the air atmosphere.

Bauxite waste with low Fe 2 O 3 and high Na concentration as a promising oxygen carrier in chemical looping combustion

Development of a cost-effective oxygen carrier (OC) for chemical looping combustion (CLC) technology remains an important task to be accomplished. Bauxite waste red mud from the United States has shown promise as an OC, but bauxite waste from China has not been evaluated extensively although huge quantities of it exists. In comparison, the Chinese bauxite waste usually contains low Fe2O3 and high Na concentration. Hence, the purpose of this study was to evaluate a typical red mud (from Zibo, China) with low Fe2O3/Na mass ratio for its potential as a cost-effective OC during CLC processing. Parametric reactor testing was accomplished with a focus on OC reactivity during CLC, and evaluations were accomplished of morphologies, elemental concentrations, and mechanical strengths before and after reaction testing; special attention was paid to the stability of Na. These results showed that Zibo red mud (a) used as an OC during CLC had satisfactory reactivity particularly after pre-calcination at 1250°C, (b) had high contents of Na that were stable and uniformly distributed during reaction testing and formed NaAlSiO4 during sample calcination and reaction testing, and (c) showed high mechanical strengths that were similar to those of other oxygen carriers. Considering that huge amounts of this inexpensive Zibo red mud are located within areas near aluminum processing plants, it may become a promising material as an OC for CLC processing.

The role of CuO modified La0·7Sr0·3FeO3 perovskite on intermediate-temperature partial oxidation of methane via chemical looping scheme

Synthesis gas production via chemical-looping partial oxidation (CLPO) of methane reduces operating cost and likely avoids carbon dioxide emissions. Previous studies exhibit La0·7Sr0·3FeO3 (LSF) a good high-temperature oxygen carrier, but not being applicable in intermediate-temperature CLPO processes. This work proposes a CuO modified LSF (xCuO/LSF, x = 2,5,10,15) for enhancing the reactivity of oxygen carriers at relatively low temperatures. Characterization methods, including N2 physisorption, ICP-OES, H2-TPR, XRD and XPS, are implemented to determine properties of xCuO/LSF. Fixed-bed experiments determine the best candidate under 750 °C is 10CuO/LSF. The methane conversion rate of 10CuO/LSF is more than 3 times compared to that of unmodified LSF and the concentration of syngas increases by 375% with the H2/CO molar ratio of about 2.5. The regenerability of 10CuO/LSF proves to be good. This study provides a promising and simple way to lower the operating temperature of the CLPO process, likely leading a considerable energy saving.

Measuring the fast oxidation kinetics of a manganese oxygen carrier using microfluidized bed thermogravimetric analysis

Oxygen carriers play critical roles in chemical looping combustion. A key task in investigating the oxygen carrier reactivity is to measure the redox kinetics in the fluidization state. However, this is still a challenge because one must perform the redox kinetics measurement in a fluidizing environment in order to simulate the strong mass and heat transfer occurring in a practical fluidized bed reactor. Herein, we report a new method, called the microfluidized bed thermogravimetric analysis (MFB-TGA), to measure the kinetics of the redox reactions, specifically the fast oxidation reaction of a manganese ore oxygen carrier. MFB-TGA is based on a real-time mass measurement of a solid sample inside a fluidized bed. The experimental data measured by MFB-TGA are interpreted with a K-L two-phase fluidized bed model to incorporate the effect of the gas concentration change in the emulsion phase. We conclude that the oxidation kinetics of this manganese ore are much faster than those of other oxygen carriers in the published works. Based on the measured oxidation reaction kinetics, the reaction time required in the air reactor is only 2.3–4 s. Therefore, a new design concept for CLC where the air reactor is operated under a dilute-phase transport regime is put forward. The new design of the air reactor has the potential to reduce cost and avoid the hot pot problem, which is a promising choice for future CLC application. In brief, this MFB-TGA method can be applied to measure the fast gas–solid reaction kinetics of any type of oxygen carriers, and thus contributes to providing reliable redox kinetics for chemical looping combustion.

Chemical looping reforming of CH4 in the presence of CO2 using ilmenite ore and NiO-modified ilmenite ore oxygen carriers

In this paper, a naturally occurring ilmenite ore and the same ore modified with NiO were employed as oxygen carriers for chemical looping reforming of CH4 for syngas production. The reactivity of the oxygen carriers and the syngas selectivity with CH4-based feedstocks were quantitatively examined in a fixed-bed reactor in the presence of CO2. The results showed that calcined ilmenite ore partially oxidizes CH4 to syngas and the reactivity of the calcined ilmenite can be greatly improved by a redox activation treatment. With the reaction of CH4 and calcined ilmenite, there is an initial period in which CH4 is fully oxidized via the reduction of Fe3+ to Fe2+ containing species; while subsequently, CH4 is partially oxidized leading to the reduction of Fe2+ to Fe0 containing species. However, the presence of CO2 in the feedstock stops any iron-containing species reduction beyond Fe2+, which is a critical reaction for syngas production. In order to permit syngas production in the presence of CO2, a NiO-modified ilmenite ore oxygen carrier was developed and evaluated, largely eliminating the negative effect of CO2. Consequently, syngas was successfully produced through partial CH4 oxidation in the presence of CO2. We have attributed this phenomenon to the catalytic effect of the metallic Ni or FeNi alloys generated during oxygen carrier reduction by CH4, which converted CO2 and CH4 into CO and H2via dry-reforming. Additionally, the incorporation of NiO within ilmenite ore significantly improved the reactivity of the ilmenite-based oxygen carrier. We believe that this dual-function catalyst-modified oxygen carrier will enable CH4-based syngas generation through both chemical looping reforming and dry-reforming processes simultaneously, ultimately allowing for syngas production in combination with CO2 utilization.

Application of Mn–Fe Composite Oxides Loaded on Alumina as Oxygen Carrier for Chemical Looping Gasification

The reactivity of oxygen carriers is curial for biomass chemical looping gasification (CLG) process. In this work, Mn–Fe composite oxides were loaded on Al2O3 through sol–gel combustion synthesis to improve their reactivity. The feasibility of these composite oxygen carriers for straw CLG process was proved in a thermogravimetric analyzer and better recyclability was found from oxygen carriers with Al2O3. Fixed-bed tests showed that the addition of Al2O3 could enhance the stability at relatively high temperature but decrease the oxygen transfer ability when temperature was low. Mn–Fe composite oxide with 60 wt% Al2O3 was chosen as the ideal oxygen carrier and the optimum condition was temperature at 850 °C, steam flow of 0.0432 g/min and OC/C mole ratio of 0.2. Under these parameters, gasification efficiency and carbon conversion efficiency reached 92.93% and 94.52% respectively. Moreover, cyclic experiments indicated that Al2O3 enhanced the stability of Mn–Fe composite oxides and gasification efficiency was decreased by 1.96% after 10 cycles. It was contributed to the porous structure supported by Al2O3, which could improve the sintering resistance and lattice oxygen transmission ability.

Development of iron ore oxygen carrier modified with biomass ash for chemical looping combustion

Natural iron ore as oxygen carrier for Chemical looping combustion (CLC) for CO2 capture has attracted increasing attention. However, the major challenge of iron ore is the relatively low reactivity. In this paper, the iron ore was combined with biomass ash to promote its performance. The reduction reactivity of the combined iron ore was determined using CO in TGA and fluidized bed. Afterwards, sewage sludge CLC in a 1 kW continuous reactor was conducted using the optimal oxygen carrier. The effect of several factors on the oxygen carrier performance was discussed, including ash type, ash content and reaction temperature. The results indicate that the iron ore performance was significantly affected by ash type. The biomass ashes in iron ore promoted the reactivity of oxygen carrier except for the Si-rich rice stalk ash which caused serious particle sintering. The rape stalk ash (RSA) exhibited the best performance, but the ash content should be lower than 20% to prevent reactivity deterioration because of serious sintering. The 20% RSA combined iron ore 20RSAIO exhibited excellent fluidization characteristic and promoted reactivity stability during continuous sludge CLC process. The interaction between sludge ash and the 20RSAIO did not cause serious reactivity deterioration.