The use of mineral materials as oxygen carriers for Chemical Looping Combustion (CLC) is an attractive option due to their low cost. This paper reports an experimental study of four manganese minerals as potential oxygen carriers focusing on the behaviour in CLC as well as in Chemical Looping with Oxygen Uncoupling (CLOU). Experiments were carried out in a thermogravimetric apparatus (TGA) and a fluidized-bed reactor. Repeated tests with all the minerals showed no sufficient CLOU properties. Then, they can only be used in CLC applications involving the redox pairs Mn 3 O 4 /MnO and Fe 2 O 3 /Fe 3 O 4. Oxygen transport capacity and reactivity to the main fuel gases (H 2 , CO and CH 4) were determined in a TGA with gaseous fuels. Manganese minerals were also tested during 35-54h in a fluidized-bed reactor to evaluate the evolution of reactivity to H 2 , CO and CH 4, as well as their attrition rate and mechanical strength. The reactivity of the materials decreased in the first 10 cycles with CH 4 and then became quite stable for the rest of the cycles performed with CH 4 , CO and H 2. In comparison to previously tested Fe-based minerals, lower reactivity with CH 4 was found for the manganese minerals. However, in terms of CO and H 2 combustion, their reactivity was adequately high. During the tests, agglomeration and de-fluidization were never found for any material. Mechanical crushing strength of the particles decreased with cycles, which led to the increase of attrition rate of some materials above acceptable levels. Nevertheless, materials with adequate crushing strength and low attrition were identified. Combining the reactivity

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Iron ore is a cheap and nontoxic oxygen carrier in chemical looping combustion (CLC) systems. However, iron ore exhibits low reactivity with solid fuels. In this work, hematite decorated with Cu via impregnation was used as an oxygen carrier. Experiments were conducted in a batch fluidized bed reactor using Shenhua (SH) bituminous coal and Gaoping (GP) anthracite as fuels. The effects of Cu loading in the hematite, reaction temperature, supply oxygen coefficient, and coal type on the CLC performance of coal were investigated. It was found that hematite loaded with 6% Cu (6CuHem) had better reactivity with the gasification products (CO and H 2 ) of coal than hematite (Hem) alone. Furthermore, 6CuHem was found to accelerate the gasification rate of GP anthracite char. A reaction temperature higher than 900 °C was conducive to fast and complete conversion of carbon in coal. As the supply oxygen coefficient was increased, the rate of carbon conversion and the combustion efficiency of coal increased. Multiple redox cycles were performed to study the stability of these oxygen carriers. It was found that the reactivity of 6CuHem was mostly stable after three redox cycles. SEM-EDX analysis revealed a shell enriched with copper on the outside of fresh 6CuHem particles. After 29 cycles, the shell nearly disappeared, and the copper content on particle's surface was decreased due to surface abrasion and migration of copper toward the internal part of the particle.

Chemical looping with oxygen uncoupling (CLOU) without the coal gasification that limits the efficiency in ordinary chemical looping combustion (CLC) is a very promising approach for CO 2 capture in the combustion of solid fuels. In the present work, the sol−gel-derived CuO/CuAl 2 O 4 oxygen carrier was evaluated in terms of its ability to release gaseous oxygen in an oxygen-deficient atmosphere and its reactivity with coal in a laboratory-scaled fluidized-bed reactor at 850, 885, 900, 925, and 950 °C. Three typical Chinese coals of different coal ranks, GP coal (anthracite), FG coal (bituminous), and SL coal (lignite), were used as fuels in the CLOU experiments. The effects of the fuel-reactor temperature and coal rank on the carbon conversion rate, combustion efficiency, and CO 2 yield were investigated. Nearly complete conversion of coals was attained. The conversion from carbon to CO 2 can be enhanced if the temperature increases. Meanwhile, the combustion efficiency would be reduced because of the loss of partially unconverted products, such as H 2 and CO, in the reduction process at a higher temperature. Experimental results also suggest that a higher reaction rate but lower combustion efficiency can be attained when the coal of a lower rank is used.

Calcium sulfate (CaSO4) has attracted a great amount of attention as a potential oxygen carrier (OC) to be applied in chemical looping combustion (CLC) due to its high oxygen transfer capacity, wide distribution, and easy accessibility, but its low reactivity and sulfur emission from side reactions of CaSO4 should be well resolved. In this research, the CaSO4–CuO mixed OC was prepared using the template method combined with the sol–gel combustion synthesis (SGCS). Its reaction characteristics with a selected lignite (designated as YN) were investigated and the greatly enhanced reactivity of this mixed OC was confirmed relative to the single CaSO4 and CuO. Meanwhile, the comprehensive heat effect showed the desired exothermic characteristics for this mixed OC reaction with YN when the mass ratio of CaSO4 to CuO was fixed as 6:4. Furthermore, morphological analysis indicated that the solid products from YN reaction with the CaSO4–CuO mixed OC were porous without discernible sintering, mainly because the CaSO4 included not only provided the lattice oxygen involved for oxidation of YN coal, but also acted as the temporary inert support to improve the resistance of the reduced Cu to sintering. Finally, the gaseous and solid products formed were systematically investigated and clearly indicated that the gaseous sulfur species formed from the side reactions of CaSO4 were effectively fixed with solid Cu2S formation; as such the potential harms incurred could be eliminated. Overall, this preliminary research revealed the greatly enhanced reactivity of this mixed OC as well as its good fixation capacity for sulfur emitted from the side reaction of CaSO4, which is much desired in the real CLC system.