Improvement of coal and Petroleum coke combustion in a fluidized bed by using ilmenite ore as bed material

Abstract

Oxygen carrier-aided combustion (OCAC) is an innovative technology that adopts the reactive oxygen carrier (OC) particles as bed materials instead of inert ones, which improves the uniformity of temporal and spatial oxygen distribution in the fluidized bed combustor. However, the existing research of OCAC mainly focuses on high-volatile fuels, less attention has been paid to high-ash and low-volatile fuels (such as coal), which are widely used in the world. In this work, three kinds of solid fuels have been comprehensively evaluated in a lab-scale fluidized bed reactor. Results show that compared to quartz sands as bed material, the OC as bed material shows an apparent “oxygen buffering capacity”, improving combustion stability and reducing the unburnt gas. The promotion effect of OCAC increases with the increase of volatile content in fuel, which indicates that OCAC mainly improves combustion through the redox reaction between volatile and OC particles. The solid-solid reaction between OC and char was negligible. The OCAC experiment was carried out for more than 20 h and found that due to the abrasion of the OC surface, the generated fly ash has a significantly higher Fe content than that using quartz sand as bed material at the initial stage of the experiment, and the abrasion of OC decreases with the increase of experimental time. Interestingly, during a 20-h continuous operation, the reactivity of ilmenite ore increased gradually, which was attributed to the development of pore structure and Fe diffusion of ilmenite ore. In addition, the content of unburnt carbon in the fly ash is similar regardless of the bed materials.