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[Display omitted] • Agglomeration is affected by OC preparation of methods, carriers and Al:Fe ratios. • Co-precipitation method has better dispersion and lower agglomeration degree. • The carrier plays a role in dispersing active metals and supporting the OC structure. • Fe content will influence the active sites and the metal-carrier interaction. • Excessive Fe content causes serious agglomeration and lower performance. 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 Al 2 O 3 carrier exhibited 36.18 % lower agglomeration degree and 25.15 % smaller particle size than that of CeO 2 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. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • High ash content in biomass is easy to cause lower DT and severe agglomeration. • High K content in biomass with similar ash content induces more agglomeration. • The higher the temperature is, the more severe the agglomeration becomes. • High S/B causes larger average particle size and lower DT of oxygen carrier. • The excessive S/B will exacerbate the agglomeration and inhibit the gasification. [ABSTRACT FROM AUTHOR]

• CaMn 0.5 Ti 0.375 Fe 0.125 O 3-δ perovskite prepared by spray drying granulation method. • FB-TGA was used to evaluate the characteristics of the OC. • After several redox cycles the crystal phase of perovskite was distorted. • The OC reacted with the air distribution plate and quartz tube wall in redox cycle. • The high oxygen transfer capacity is the root cause of particles agglomeration. The development of oxygen carrier particles that can be prepared on an industrial scale with good cycling stability remains a challenge in the field of chemical looping. In this work, a perovskite oxygen carrier (CaMn 0.5 Ti 0.375 Fe 0.125 O 3-δ) was prepared by an industrial-scale spray drying granulation and tested on a fluidized bed thermogravimetric analyzer for long-term chemical looping combustion. The results showed that the attrition of oxygen carrier particles originated from irregular parts of the fresh particle surface early in the cycle, and the chemical stress on particles gradually increased with the number of redox cycles, increasing the attrition and sintering of the particles. In addition, as the cycle proceeds, the perovskite structure was destroyed and the oxygen carrier reacted chemically with the quartz tube wall and the air distribution plate leading to bonding. The deep redox cycling reactions indicated that agglomeration of particles occurred mainly in the reduction stage, with the bed entering repeated periods of defluidization during the 37th-43rd and 47th-55th cycles due to the changes in particle bonding and bed pressure. Fixed bed experiment showed that particle activation came from an increase in the active area of the particles during the cycle, independent of whether they were fluidized or not. In addition, agglomeration started at the contact surface between the air distribution plate and the particles, resulting in blocked oxidation of the particles and deepening agglomeration due to excessive reduction of the particles. [ABSTRACT FROM AUTHOR]

[Display omitted] • Composite hematite and copper ore OC prepared by spray drying granulation method. • FB-TGA was used to evaluate the characteristics of the OC. • Copper and iron migrate to the particle surface after several cycles. • The high temperature is the direct factor leading to the sintering of OC particles. • The high oxygen transfer capacity is the root cause of particles agglomeration. A single natural ore oxygen carrier (OC) has a limited industrial application due to its weak reactivity and cyclic stability. For the composite hematite and copper ore OC prepared by spray drying granulation, long-term chemical looping combustion (CLC) cycle tests were performed on a fluidized bed thermogravimetric analyzer (FB-TGA). The results showed that a substantial mechanical stress and the presence of partially enriched fine particles on the surface of new OC particles caused a high attrition rate of OC at the early stage of fluidization. After 6 min, the attrition rate of the particle was stabilized at 0.28 %/h. The OC was subjected to chemical and thermal stresses during the redox cycle reaction, which decreased the mechanical strength and increased particle attrition and sintering. The particle sintering also hindered the oxidation stage, which led to a deep reduction of OC to a lower valence state, which drove particle agglomeration and eventual defluidization. Therefore, lowering the oxygen transfer capacity and residence time in the fuel reactor is beneficial for the safe operation of OC in industry. [ABSTRACT FROM AUTHOR]

[Display omitted] • Temperature greatly influences the formation of agglomeration. • Mechanisms, detection methods and countermeasures of agglomeration were reviewed. • The agglomeration mechanism of chemical looping technology was speculated. • The directional design can improve the sintering resistance of OC. • Coating-induced and melt-induced together lead to the ash-related agglomeration. This review discusses the influence of three key factors on agglomeration of chemical looping technology from the aspects of reaction conditions, the oxygen carrier and biomass composition. In addition, the existing agglomeration mechanisms are extended, and the technologies of detection and prevention of the agglomeration is reviewed. In the process of chemical looping reaction, high reaction temperature, the oxygen carrier materials with poor anti-sintering ability and the reaction system containing more alkali metals and silicon-based materials will easily cause agglomeration. Previous literatures have summarized the agglomeration produced by two mechanisms, and both of them pointed out that the alkali metal in the biomass ash is the main component to induce the agglomeration. For the SiO 2 -based oxygen carrier material, it is speculated that the alkali metal will react with the support to inactivate the active metal component through the inclusion of the molten material. However, the oxygen carrier without SiO 2 -based material is mainly produced through the mechanism of melt-induced, but not the coating-induced agglomeration. The predication of agglomeration focuses on the biomass ash test before the reaction and the monitoring of some variables during the reaction process, such as temperature and pressure analysis. Moreover, the agglomeration can be prevented or controlled by condition adjustment, reactor design, oxygen carrier design and biomass pretreatment. In addition, the use of additives is also a reliable method to reduce the agglomeration. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ca in biomass can significantly improve the CLG performance. • The excessive Ca will cause obvious agglomeration and sintering. • Ca reduces the activation energy of CLG under the reasonable concentration. • The improvement of (CH 3 COO) 2 Ca is better than that of CaCl 2. • Gasification efficiency increases by 45.61% after adding 6% (CH 3 COO) 2 Ca. As the most abundant trace element in agricultural wastes, Ca can improve the reaction performance, but aggravate the agglomeration and sintering of reaction materials at high temperature during the process of thermochemical conversion. In this paper, the effect of Ca in rice husk was studied in chemical looping gasification (CLG) under different conditions of Ca concentration, Ca solution, temperature and steam/carbon (S/C). The results indicated that Ca would significantly improve the CLG performance, but cause obvious agglomeration and sintering phenomenon at high Ca concentration. Furthermore, the improvement for CLG performance of (CH 3 COO) 2 Ca was greater than that of CaCl 2. After adding 6% (CH 3 COO) 2 Ca, gas yield, carbon conversion efficiency and gasification efficiency increased by 53.30%, 47.06% and 45.61%, respectively. By contrast, they respectively increased by 28.11%, 17.27% and 26.79% after adding CaCl 2. Thermogravimetric analysis showed that the presence of Ca was beneficial to reduce the activation energy of the reaction. In the pyrolysis stage, the maximum reduction of activation energy was 37.43%, while in the gasification stage, the maximum reduction of activation energy was 65.36% after adding Ca in the rice husk. Compared with CaCl 2 , (CH 3 COO) 2 Ca decreased more activation energy of CLG process. Moreover, with the increase of temperature and S/C, the CLG performance increased firstly and then decreased after adding 6% (CH 3 COO) 2 Ca by impregnation on the pickling rice husk. 800℃ and 6.9 was the optimal temperature and S/C to achieve the best gasification efficiency of 65.03% and gas yield of 0.69 Nm3/kg in the CLG process. [ABSTRACT FROM AUTHOR]