Use of CaMn_0.875Ti_0.125O₃as Oxygen Carrier in Chemical-Looping with Oxygen Uncoupling

Abstract

Chemical-looping with oxygen uncoupling (CLOU) is a novel method to burn fuels in gas-phase oxygen without the need for an energy-intensive air separation unit. The carbon dioxide from the combustion is obtained separated from the nitrogen in the combustion air. The technique is based on chemical-looping combustion (CLC) but does not involve any direct reaction between the fuel and oxygen carrier. Instead, the CLOU process uses three steps in two reactors, one air reactor where a metal oxide captures oxygen from the combustion air (step 1), and a fuel reactor where the metal oxide releases oxygen (step 2) and where this oxygen reacts with a fuel (step 3). This means that the fuel burns directly with gaseous O2. In this work CaMn0.875Ti0.125O3 will be used as oxygen carrier. Experiments were first performed with a thermogravimetric analyzer (TGA). Here the sintering temperature, and thereby the porosity, for the produced granulates was varied and optimized. The substitution of Ti on Mn sites in CaMnO3 was chosen since this material showed no coke formation even in dry CH4 at high temperatures. This was followed by fluidized bed experiments with both methane and petroleum coke as fuel. The CaMn0.875Ti0.125O3 particles showed promising results both for the tests performed in TGA and in fluidized bed experiments. CaMn0.875Ti0.125O3 released O2 both in inert and reducing atmosphere, making it a possible candidate as oxygen carrier in CLOU.