Investigation into Decomposition Behavior of CaSO4 in Chemical-Looping Combustion

Chemical-looping combustion (CLC) is a promising technology to combine the energy-use situation in China and CO2 zero emission in situ, which allows for CO2 sequestration by efficient ways and without nitrogen oxide (NOx) formation. An oxygen carrier with good performance is one of the key issues of the CLC process. Calcium sulfate has proven to be a kind of new oxygen carrier with sufficient reactivities in reduction and oxidation reactions, with enough ability for carrying oxygen and no secondary pollution. The decomposition mechanism of calcium sulfate with an average particle size of 8.934 mu m in a different simulated atmosphere in CLC is investigated using a simultaneous thermal analyzer at five different heating rates. In an inert atmosphere, the relationship between activation energy and conversion fraction of calcium sulfate is obtained without the introduction of the reaction mechanism function. The values of activation energy, frequency factor, and linear factor corresponding to 5 different heating rates and 30 different common reaction mechanism functions, respectively, are calculated using an accurate kinetics integral expression and a temperature integral approximation with high precision. Kinetic parameters of the decomposition reaction without any disturbance of other reactions, including E-beta -> 0 and In A(beta -> 0), are determined by extrapolating the heating rate to zero. Additionally, the relationship between the activation energy of decomposition and conversion rate is found using the double-extrapolated method. The activation energy at the start of the decomposition reaction, E-alpha -> 0, is also evaluated by extrapolating the conversion rate to zero. Whe E-beta -> 0 and E-alpha -> 0 are compared, the most likely mechanism function in the decomposition process is characterized by the Avrami-Erofeev equation and the reaction is dominated by the nucleation rate. The Avrami-Erofeev equation is also evaluated on the basis of the most likely mechanism function by the Popescu method.