Characterization of spray-dried NiO oxygen carriers supported on alpha alumina

Abstract

An oxygen carrier in chemical looping combustion (CLC) transfers oxygen from air to fuel. The oxygen carrier is composed of active metal oxides and support. The performance of the oxygen carrier greatly varies with the support materials used. In this study, the physical properties and oxygen transfer reactivity of spray-dried NiO-based oxygen carriers supported on alpha alumina (α-Al2O3) added with or without MgO were investigated. NiO oxygen carriers were prepared using the starting raw materials composed of 70 wt% NiO for active component and 0, 4.2, and 8.4 wt% MgO balanced with α-Al2O3 for support materials. The mechanical strength measured by a three-hole air-jet attrition tester showed that the oxygen carriers supported on α-Al2O3 only required the calcination temperatures above 1,400°C to obtain sufficient mechanical strength stronger than that of a commercial fluid-catalytic-cracking (FCC) catalyst. The required calcination temperature increased to 1,500°C when MgO was added. Oxygen transfer reactivity was measured using a thermogravimetric analyzer at a reaction temperature of 950°C. Compared with the oxygen carrier supported on α-Al2O3 only, the oxygen carrier added with 4.2 wt% MgO showed slightly enhanced oxygen transfer performance in reduction. However, the oxygen carrier added with 8.4 wt% MgO showed much slower oxygen transfer rate. This indicates that the addition of too much MgO to α-Al2O3 as support leads a negative effect on the oxygen transfer performance of the spray-dried NiO oxygen carrier.