Experiments on chemical looping combustion of coal with a NiO based oxygen carrier

A chemical looping combustion process for coal using interconnected fluidized beds with inherent separation of CO₂ is proposed in this paper. The configuration comprises a high velocity fluidized bed as an air reactor, a cyclone, and a spout-fluid bed as a fuel reactor. The high velocity fluidized bed is directly connected to the spout-fluid bed through the cyclone. Gas composition of both fuel reactor and air reactor, carbon content of fly ash in the fuel reactor, carbon conversion efficiency and CO₂ capture efficiency were investigated experimentally. The results showed that coal gasification was the main factor which controlled the contents of CO and CH₄ concentrations in the flue gas of the fuel reactor, carbon conversion efficiency in the process of chemical looping combustion of coal with NiO-based oxygen carrier in the interconnected fluidized beds. Carbon conversion efficiency reached only 92.8% even when the fuel reactor temperature was high up to 970 °C. There was an inherent carbon loss in the process of chemical looping combustion of coal in the interconnected fluidized beds. The inherent carbon loss was due to an easy elutriation of fine char particles from the freeboard of the spout-fluid bed, which was inevitable in this kind of fluidized bed reactor. Further improvement of carbon conversion efficiency could be achieved by means of a circulation of fine particles elutriation into the spout-fluid bed or the high velocity fluidized bed. CO₂ capture efficiency reached to its equilibrium of 80% at the fuel reactor temperature of 960 °C. The inherent loss of CO₂ capture efficiency was due to bypassing of gases from the fuel reactor to the air reactor, and the product of residual char burnt with air in the air reactor. Further experiments should be performed for a relatively long-time period to investigate the effects of ash and sulfur in coal on the reactivity of nickel-based oxygen carrier in the continuous CLC reactor.     

基于钾盐修饰Fe基载氧体的化学链燃烧研究

采用典型的钾盐和惰性载体对Fe基载氧体进行修饰,在热重和小型流化床反应器上,采用CO/N2对其还原活性和化学链燃烧特性进行测试,考察了钾盐种类、反应温度对和惰性载体种类的影响。结果表明：钾盐修饰（KCl、K2SO4和K2CO3）能提高载氧体还原反应速率,并以K2CO3效果最好,最大还原反应速率提高约30%,载氧体完全还原时间由50 min缩短到25 min,主要归因于K2CO3修饰促进形成高活性的Fe-K-O化合物及发达的孔隙结构;对于K2CO3修饰Fe基载氧体,SiO2和高岭土载体易与K2CO3发生烧结,造成活性下降,TiO2与载氧体反应生成复杂的化合物,其氧化过程变慢,影响整个进程,而Al2O3载体展现了最好的反应活性,随着反应循环的增加其活性略有下降并趋于稳定,9个循环后CO2捕集效率高达98.0%     

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

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

Comparison of CuO and NiO as oxygen carrier in chemical looping combustion of a Victorian brown coal

Chemical looping combustion (CLC) is a novel process where an oxygen carrier, preferably oxides of metal, is used to transfer oxygen from the combustion air to the fuel. The outlet gas from the process reactor consists of CO₂ and H₂O, and concentrated stream of CO₂ is obtained for sequestration when water vapour is condensed. Chemical looping has been widely studied for combustion of natural gas; however its application to solid fuels, such as coal, is being studied relatively recently; no work has been done using Victorian brown coal which represents a very large resource, over 500 years at current consumption rate. In this study we carried out an experimental investigation pertaining to CLC of a Victorian brown coal from Loy Yang mine using NiO and CuO as oxygen carrier. The experiments were conducted using a thermogravimetric analyser (TGA) under CO₂ gasification environment with NiO and CuO. The reduction and re-oxidation of NiO in five repeated cycle operations were performed at 950 °C. However, the same cyclic operation for CuO was performed at 800 °C, as it was observed that at 950 °C CuO could not be re-oxidized to its original state due to sintering, which significantly altered the morphology. The extent of coal combustion and re-oxidation of metal oxides resulted in a 4.4-7.5% weight loss of NiO per cycle. No such weight loss was observed in case of CuO at 800 °C. The high reactivity of CuO was observed as compared to NiO during cyclic operation. The percentage of combustion at the end of the 5th cycle with CuO was 96% as compared to 67% with NiO. Fresh oxide particles and solid residues are characterized using SEM to understand surface morphological changes due to combustion. The energy dispersive X-rays (EDX) helped to get surface elemental information, albeit qualitative, of fresh and used metal oxide particles. The current study, for the first time, has generated practical information on the temperature range, approximate time, and percent combustion that can be achieved while using NiO and CuO as oxygen carriers during CLC with Loy Yang brown coal. Based on these results the ongoing work includes long duration experiments with Loy Yang and other Victorian brown coals.     

Comparison of metallic oxide,natural ore and synthetic oxygen carrier in chemical looping combustion process

As one of clean coal combustion ways, chemical looping combustion (CLC) showed high CO₂ capture efficiency with lower energy penalty. But these processes were limited by the low reaction rate between oxygen carriers (OCs) with coal char. This study evaluated the performances of Cu-based OCs with coal in in-situ gasification chemical-looping combustion (iG-CLC) and chemical-looping with oxygen uncoupling (CLOU) process. CuO modified by iron ore and chrysotile were employed as OCs which the addition of chrysolite improved the char gasification and iron ore enhanced the stability of CuO at high temperature. Results showed that CuO supported by ores (chrysolite and iron ore) had better H₂ and CO conversion under H₂O atmosphere than CuO and iron ore. Chrysolite decorated CuO can convert almost all H₂ to H₂O at 850 °C. Synthetic OCs showed better stability and high temperature tolerance during 10 redox cycles.     

A mechanistic investigation of a calcium-based oxygen carrier for chemical looping combustion

Chemical looping combustion (CLC) has been suggested as an energy-efficient method for the capture of carbon dioxide from combustion. It is indirect combustion by the use of an oxygen carrier, which can be used for CO₂ capture in power-generating processes. The possibility of CLC using a calcium-based oxygen carrier is investigated in this paper. In the air reactor air is supplied to oxidize CaS to CaSO₄, where oxygen is transferred from air to the oxygen carrier; the reduction of CaSO₄ to CaS takes place in the fuel reactor. The exit gas from the fuel reactor is CO₂ and H₂O. After condensation of water, almost pure CO₂ could be obtained. The thermodynamic and kinetic problem of the reduction reactions of CaSO₄ with CO and H₂ and the oxidization reactions of CaS with O₂ is discussed in the paper to investigate the technique possibility. To prevent SO₂ release from the process of chemical looping combustion using a calcium-based oxygen carrier, thermochemical CaSO₄ reduction and CaS oxidation are discussed. Thermal simulation experiments are carried out using a thermogravimetric analyzer (TGA). The properties of the products are characterized by Fourier transform infrared (FT-IR) spectroscopy and X-ray diffractometry (XRD), and the optimal reaction parameters are evaluated. The effects of reaction temperature, reductive gas mixture, and oxygen partial pressure on the composition of flue gas are discussed. The suitable temperature of the air reactor is between 1050 and 1150 °C and the optimal temperature of the fuel reactor between 900 and 950 °C.     

Chemical looping combustion of Victorian brown coal using NiO oxygen carrier

This study is part of a program assessing the suitability of chemical looping for direct combustion of Victorian brown coal. The performance of NiO as an oxygen carrier in presence of a dried Victorian brown coal was assessed during five alternating cycles of reduction and oxidation in a CO₂ environment using a TGA. The experiments indicate a 4.4-7.5% weight loss of the oxygen carrier per cycle. Preliminary SEM-EDX and FACTSAGE predictions also indicate weight loss, but not to the same extent. The percentage of combustion of coal achieved at the 5th cycle was approximately 67%. Cycle 2 showed maximum reactivity (during reduction) with a decreasing trend during the subsequent cycles. These initial experiments did not reveal much agglomeration between ash and NiO although longer duration experiments are required to explore this issue further.     

基于铁矿石载氧体的生物质化学链气化机理研究

在单批次进料小型流化床上,以稻壳为生物质燃料,研究了床料、气化温度、水蒸气体积分数以及载氧体载氧量与生物质含碳量的摩尔比(O/C)对生物质化学链气化反应特性的影响,并考察了铁矿石的长期交替氧化还原过程中的反应特性,分析了在小型流化床,水蒸气气氛气化条件下,铁矿石载氧体在反应过程中主要的反应以及反应后的铁矿石的床料变化。研究表明:在载氧体条件下,生物质的碳转化率显著增大,随着反应温度的升高,合成气中的H_2和CO的体积分数也相应升高。在温度不变情况下,随着水蒸气比例的升高,CO_2和H_2的体积分数显著上升。伴随着O/C摩尔比的升高,CO和H_2均显著下降。因此,在不同的反应条件下,铁矿石在生物质化学链气化过程中对反应速度、合成气比例等均有明显的作用,对研究生物质的综合利用具有一定的意义。     

Effect of steam reforming on methane-fueled chemical looping combustion with Cu-based oxygen carrier

The reduction characteristics of Cu-based oxygen carrier with H₂, CO and CH₄ were investigated using a fixed bed reactor, TPR and TGA. Results showed that temperatures for the complete reduction of Cu-based oxygen carrier with H₂ and CO are 300 °C and 225 °C, respectively, while the corresponding temperature with CH₄ is 650 °C. The carbon deposition from CH₄ occurred at over 550 °C. CO-chemisorption experiments were also conducted on the oxygen carrier, and it was indicated that Cu-based oxygen carrier sinter seriously at 700 °C. In order to lower the required reduction temperature of oxygen carriers, a new chemical looping combustion (CLC) process with CH₄ steam reforming has been presented in this paper. The basic feasibility of the process was illustrated using CuO–SiO₂. The new CLC process has the potential to replace the conventional gas-fired middle- and low-pressure steam and hot water boilers.     

Utilization of laterite ore as an oxygen carrier in chemical looping reforming of methane for syngas production

Growing energy demands in various sectors have resulted in overusing fossil fuel sources and rise in greenhouse gases in the atmosphere. This necessitates the need for reducing greenhouse gases and shifting to cleaner, renewable energy sources like H₂. Chemical looping is one such renewable method to produce clean H₂. The efficiency of this process depends on the oxygen carrier. Generally, oxygen carriers (OC) are transition metal oxides (Fe₂O₃ or NiO) or some complex metal oxides like spinel or perovskites, but usage of these OCs are restricted due to their availability and redox performance. One solution for selecting OCs can be using industrial waste like slag or low-grade ores because of their composition, which consists of metal oxides. One such low-grade ore is Ni-laterite ore or chromite overburden, a mining waste found in the chromite mines of Sukinda (India). In this work, we have focused on utilizing this laterite ore as an OC for the chemical looping reforming of methane to produce syngas. The reactivity analysis of laterite ore with CH₄ was performed in DSC-TG and the reaction products were analyzed in gas chromatography along with microscopy and spectroscopic techniques. Results showed the formation of H₂ and CO gases along with reduced metallic phases. The total H₂ yield at 750 °C is determined to 53.67 (±1.09) ml/g of OC which is comparable or even higher than existing CeO₂ based OCs. Further, thermodynamic calculations are presented to calculate the theoretical yield for our process and compared with the experimental H₂ yield. This study effectively demonstrates the performance of laterite ore as an OC for generating clean and renewable energy through chemical looping technique.     

Characterization of chemical looping combustion of coal in a 1 kWth reactor with a nickel-based oxygen carrier

Chemical looping combustion is a novel technology that can be used to meet the demand on energy production without CO₂ emission. To improve CO₂ capture efficiency in the process of chemical looping combustion of coal, a prototype configuration for chemical looping combustion of coal is made in this study. It comprises a fast fluidized bed as an air reactor, a cyclone, a spout-fluid bed as a fuel reactor and a loop-seal. The loop-seal connects the spout-fluid bed with the fast fluidized bed and is fluidized by steam to prevent the contamination of the flue gas between the two reactors. The performance of chemical looping combustion of coal is experimentally investigated with a NiO/Al₂O₃ oxygen carrier in a 1 kW_th prototype. The experimental results show that the configuration can minimize the amount of residual char entering into the air reactor from the fuel reactor with the external circulation of oxygen carrier particles giving up to 95% of CO₂ capture efficiency at a fuel reactor temperature of 985 °C. The effect of the fuel reactor temperature on the release of gaseous products of sulfur species in the air and fuel reactors is carried out. The fraction of gaseous sulfur product released in the fuel reactor increases with the fuel reactor temperature, whereas the one in the air reactor decreases correspondingly. The high fuel reactor temperature results in more SO₂ formation, and H₂S abatement in the fuel reactor. The increase of SO₂ in the fuel reactor accelerates the reaction of SO₂ with CO to form COS, and COS concentration in the fuel reactor exit gas increases with the fuel reactor temperature. The SO₂ in the air reactor exit gas is composed of the product of sulfur in residual char burnt with air and that of nickel sulfide oxidization with air in the air reactor. Due to the evident decrease of residual char in the fuel reactor with increasing fuel reactor temperature, it results in the decrease of residual char entering the air reactor from the fuel reactor, and the decrease of SO₂ from sulfur in the residual char burnt with air in the air reactor.     

基于草木灰修饰Fe基载氧体的化学链燃烧实验

采用草木灰对Fe基载氧体进行修饰,并在流化床反应器上进行了气体燃料化学链燃烧实验。研究了草木灰修饰对提高Fe基载氧体还原活性的可行性,讨论了草木灰种类、草木灰的无机组分对载氧体活性的影响。结果表明,草木灰修饰能有效提高Fe载氧体的反应活性,载氧体的反应活性由草木灰中K和Si的含量共同决定。随着修饰草木灰中的K含量提高,载氧体的活性逐渐提高;但在Fe3O4/FeO的转化阶段中,同时存在碱金属K对还原反应的催化作用和低熔点碱金属硅酸盐对还原反应的抑制作用。循环实验表明,草木灰中碱金属K对载氧体活性的提高效果始终明显,载氧体中负载的K在循环过程中出现了流失现象,而生成的碱金属硅酸盐类化合物,可抑制碱金属K的流失。     

Research of coal-direct chemical looping hydrogen generation with iron-based oxygen carrier modified by potassium

Coal-direct chemical looping hydrogen generation (CLHG) is a promising process for hydrogen production with high coal conversion efficiency and low carbon footprint. In this work, experiments on coal-direct CLHG process were carried out using K₂CO₃ modified Fe₂O₃/ZrO₂ as oxygen carrier (OC) and Shenmu (SM) char as fuel in a fixed-bed reactor. The effect of char/OC mass ratio on CO₂/CO volume ratio, H₂ production and phase transformation was investigated. Multicycle tests with SM char and deashed SM char were conducted to investigate the activity stability of OC and the reason for the deactivation of OC. The results confirm the feasibility of coal-direct CLHG process. Higher char/OC mass ratio could enhance the H₂ production and decrease the CO₂/CO volume ratio and oxidation state of iron oxides in OC. In the multicycle tests with SM char, carbon conversion and H₂ production remained almost constant during the first 2 redox cycles and then decreased abruptly in the 3rd cycle. During the 3 cycles, the phases of OC residues remained unchanged and no detectable surface sintering was observed. Furthermore, the K contents of residues decreased slightly. In the multicycle tests with deashed SM char, the carbon conversion and accumulation H₂ production were stable during the first 10 cycles and then decreased slowly. Some morphology features changes appeared during the 11 cycles, but no obvious surface sintering was observed. The K contents of residues declined by 2/3 after the 10th cycle.     

基于草木灰修饰铁矿石载氧体的串行流化床化学链燃烧实验

采用草木灰对铁矿石载氧体进行修饰,在1kWth串行流化床反应器上,以合成气（CO H2 CH4）为燃料进行了化学链实验,对其反应活性进行测试。结果表明：生物质灰修饰铁矿石载氧体在1 kWth串行流化床上表现出较高的反应活性,且反应温度越高,反应活性越好;燃料反应器出口CO和CH4体积百分数显著降低,930 ℃下分别为0.12%和2.63%,与采用纯铁矿石相比分别降低了97.3%和16.0%,CO2捕集效率提升明显,最大值达89.38%;SEM分析表明,反应后的铁矿石颗粒表面出现了晶粒熔融粘接的现象,但生物质灰修饰铁矿石的孔隙结构仍较为明显;EDS分析表明生物质灰修饰铁矿石中K的负载情况较为稳定,没有出现明显的流失现象。     

Investigation on gasification performance of sewage sludge using chemical looping gasification with iron ore oxygen carrier

Chemical looping gasification (CLG), with inherent characteristic of low pollutant emissions can realize the treatment and disposal principle of sewage sludge of harmlessness, reduction, stabilization and reutilization. This work attempted to investigate the feasibility of CLG of sewage sludge with hematite oxygen carrier. The role of hematite in CLG was firstly determined and it was used as gasification agent to provide the required oxygen for sludge conversion. Subsequently, the effect of various operating parameters on sludge CLG was discussed. An optimal mass ratio of sludge to hematite oxygen carrier was determined at 0.33 to achieve the high-efficient conversion of sludge. The reaction temperature of sludge gasification was set at 900 °C to avoid the excessive reduction of hematite. Suitable steam content was assigned to at 19.52%, where the sludge conversion attained the maximum. Ash deposited caused the decrease of specific surface area of hematite, but the accumulated mineral elements in sludge ash can improve the reactivity of oxygen carrier. Additionally, the ash accumulation also can prolong the gas mean residence time. Hence, the sludge conversion showed a slight uptrend with the cycle numbers. The phosphorus element of sludge was formed of CaH₂P₂O₇ and CaHPO₄ during the CLG. Although some sludge ash deposited on the surface of hematite particles, the new compounds were not observed in the reacted oxygen carrier. Additionally, sludge ash has a relatively high resistance trend for bed agglomeration and deposit formation due to the high content of Ca/Al elements. Consequently, the accumulation of sludge ash only reveals physical effects rather than chemical effects on the hematite particles. Thus, it is easy to separate the sludge ash from hematite particles according to the differences in density and size.     

结构化载氧体颗粒化学链燃烧内扩散影响模拟分析

采用有限速率模型对CuO/Al_2O_3结构化载氧体颗粒化学链燃烧进行了数值模拟,考察了不同结构化载氧体颗粒模型和进气速度对载氧体化学反应内扩散的影响。结果表明,相比于球形载氧体,环形结构拉西环载氧体内扩散更为容易,反应快,温升高;相比于全活性载氧体,1/4活性和半活性载氧体气体扩散到活性物质距离短,反应更快;增加进气速度能够加速颗粒内扩散,改善反应速率。     

Investigation of Coal Fueled Chemical Looping Combustion Using Fe_3O_4 as Oxygen Carrier：Influence of Variables

Chemical-looping combustion (CLC) is a novel combustion technique with inherent CO2 separation.Magnetite (Fe3O4) was selected as the oxygen carrier.Shenhua coal (Inner Mongolia,China),straw coke and natural coke were used as fuels for this study.Influences of operation temperatures,coal to Fe3O4 mass ratios,and different kinds of fuels on the reduction characteristics of the oxygen carrier were investigated using an atmosphere thermogravimetric analyzer (TGA).Scanning electron microscopy (SEM) was used to analyse the characteristic of the solid residues.Experimental results shown that the reaction between the coal and the oxygen carrier become strong at a temperature of higher than 800℃.As the operation temperature rises,the reduction conversion rate increases.At the temperatures of 850oС,900℃,and 950℃,the reduction conversion rates were 37.1%,46.5%,and 54.1% respectively.However,SEM images show that at the temperature of higher than 950℃,the iron oxides become melted and sintered.The possible operation temperature should be kept around 900℃.When the mass ratios of coal to Fe3O4 were 5/95,10/90,15/85,and 20/80,the reduction conversion rates were 29.5%,40.8%,46.5%,and 46.6% respectively.With the increase of coal,the conversion rate goes up.But there exist an optimal ratio around 15/85.Comparisons based on different kinds of fuels show that the solid fuel with a higher volatile and a more developed pore structure is conducive to the reduction reactivity of the oxygen carrier.     

Bauxite waste with low Fe2O3 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.     

Evaluation of calcined copper slag as an oxygen carrier for chemical looping gasification of sewage sludge

Chemical looping gasification (CLG) of sewage sludge (SS) using calcined copper slag as an oxygen carrier (OC) represents a novel approach for achieving the comprehensive use of two wastes (SS and copper slag), where the SS is converted into syngas through the oxidation of calcined copper slag. The effect of the calcined temperature on the reactivity of copper slag was first studied. The results show that the copper slag calcined at 1100 °C (1100CS) exhibits excellent performance for SS gasification. Using 1100CS as an OC, the effect of the mass ratio of OC and SS (OC/SS), steam content, oxygen source and cycle number on the SS CLG were investigated in detail in a fixed bed reactor. OC/SS and steam content are determined at 5 and 33.33% for obtaining a relatively high carbon conversion and an acceptable energy recovery during the SS CLG, respectively. The 1100CS is similar to steam, which can provide an oxygen source for SS conversion, and it can catalyze the cracking of tar. The conversion of SS undergoes a slight increase with the cycle number due to the prolongation of the gas-solid mean residence time (R_t) and the deposition of alkali or alkaline earth metals on the surface of the OC particles. Phosphorus eventually appears in the form of water-soluble phosphate during the SS CLG, benefiting its recovery. Thus, CLG with 1100CS as an OC is one of good option for sludge treatment.     

Pressurized chemical-looping combustion of coal with an iron ore-based oxygen carrier

Chemical-looping combustion (CLC) is a new combustion technology with inherent separation of CO₂. Most of the previous investigations on CLC of solid fuels were conducted under atmospheric pressure. A pressurized CLC combined cycle (PCLC-CC) system is proposed as a promising coal combustion technology with potential higher system efficiency, higher fuel conversion, and lower cost for CO₂ sequestration. In this study pressurized CLC of coal with Companhia Valedo Rio Doce (CVRD) iron ore was investigated in a laboratory fixed bed reactor. CVRD iron ore particles were exposed alternately to reduction by 0.4 g of Chinese Xuzhou bituminous coal gasified with 87.2% steam/N₂ mixture and oxidation with 5% O₂ in N₂ at 970 °C. The operating pressure was varied between 0.1 MPa and 0.6 MPa. First, control experiments of steam coal gasification over quartz sand were performed. H₂ and CO₂ are the major components of the gasification products, and the operating pressure influences the gas composition. Higher concentrations of CO₂ and lower fractions of CO, CH₄, and H₂ during the reduction process with CVRD iron ore was achieved under higher pressures. The effects of pressure on the coal gasification rate in the presence of the oxygen carrier were different for pyrolysis and char gasification. The pressurized condition suppresses the initial coal pyrolysis process while it also enhances coal char gasification and reduction with iron ore in steam, and thus improves the overall reaction rate of CLC. The oxidation rates and variation of oxygen carrier conversion are higher at elevated pressures reflecting higher reduction level in the previous reduction period. Scanning electron microscope and energy-dispersive X-ray spectroscopy (SEM-EDX) analyses show that particles become porous after experiments but maintain structure and size after several cycles. Agglomeration was not observed in this study. An EDX analysis demonstrates that there is very little coal ash deposited on the oxygen carrier particles but no appreciable crystalline phases change as verified by X-ray diffraction (XRD) analysis. Overall, the limited pressurized CLC experiments carried out in the present work suggest that PCLC of coal is promising and further investigations are necessary.