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.
Chemical looping with oxygen uncoupling (CLOU) is a promising technology due to its potential to reduce energy efficiency penalty and cost associated with CO 2 capture. In this work, a CuO/CuAl 2 O 4 oxygen carrier (OC) prepared by sol-gel was investigated in its oxygen release kinetics (4CuO ? 2Cu 2 O ? O 2 ). Based on several well-organized temperature-programmed reduction experiments which were conducted in a thermogravimetric analyzer, the activation energy E (343.7 kJ mol -1 ) and pre-exponential factor A (3.78 9 10 12 s -1 ) were determined and the Avrami-Erofeev random nucleation and subsequence growth model fitted well with the reduction experimental data. The enhancement of OC reduction rate in real fluidized bed CLOU reactor using different types of solid fuels (petroleum coke, anthracite, bituminous, and lignite) was identified in terms of the chemical kinetics and thermodynamics for the first time. It was found that the CuO reduction rate is more sensitive to the local temperature change than the oxygen concentration driving force. The results could contribute to the design, operation, and performance prediction of real CLOU reactors.
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