Oxygen polishing of chemical looping combustion flue gases

Abstract

Chemical looping combustion has arisen as an attractive possible option for carbon capture and storage. With coal as our most abundant fuel type it is of great interest to include it in the process. Chemical looping combustion of solid fuels faces some difficulties, one being unconverted fuel, CO, CH4 and H2 leaving the reactor with the flue gas. A possible measure to increase the total efficiency is to oxidize the remaining fuel with pure oxygen in a post oxidation chamber. The aim of this work is to evaluate the performance of such a chamber and to provide recommendations regarding operating conditions. The project is based on gas reaction modelling in the software CHEMKIN where a thorough simulation setup is established. The importance of operating temperature and mixing of oxygen is analyzed and a sensitivity analysis investigating the importance of different process parameters on the performance is also conducted. In addition to combustion performance a limited study on the fate of NOx and SOx in the post oxidation chamber is also performed. The results from the simulations show that the POC should have a temperature above 800°C and be designed to allow for good mixing with the added oxygen. The vast majority of the remaining fuel from the fuel reactor will be oxidized in the POC but complete oxidation is impossible at stoichiometric conditions. The outlet concentration of oxygen will not be able to meet the guidelines of 100 ppm even at an air to fuel ratio below unity.