Redox reactions and energy analysis in chemical looping using hematite as an oxygen carrier: A thermodynamic approach

Abstract

Chemical looping is a promise technology in carbon dioxide capture and storage which is an almost less energy and provide heat during the process This technology can get pure carbon dioxide by condense the water vapor of the outlet gas depend on what fuel and oxygen carriers (OCs) used there will be different syngas and outlet gas release OCs is an import role in chemical looping because it can transfer oxygen to the fuel and recycle between reduction and oxidation two reactors Generally the reactor is fluidized bed or move bed two kind since the basic concept of the chemical looping is redox reaction in the reactor so that thermodynamic analysis is helpful reference to operator reactor This study use hematite as oxygen carrier (OC) with chemical looping process methane as reduction gas and air as oxidation gas at 900 °C Five different M/H ratio (1/15 1/12 1/10 1/8 and 1/5) and O/H ratio (1 5 0 3 0 2 0 18 and 0 15) on iron oxide redox reaction were examined In addition a redox degree of the reactors was defined The results showed that higher M/H ratio needed more cycles to achieve equilibrium state and O/H ratio also show that it is significantly relate to cycle number The maximum CO2 and H2O yield was located at M/H=1/15 but the yield of these two compounds decreased with an increase of M/H ratio The demonstrate species would be Fe3O4 at lower M/H ratio the further reduced stage iron oxides will show with higher M/H ratio but accompany CO and H2 generated The O2 consumption in the air reactor was decreased with increasing M/H ratio The overall CH4 conversion of the five M/H ratio almost remained at 100% revealing that the conversion did not relate to M/H ratio and O/H ratio Carbon formation is also presented in this study the yield of carbon deposition is direct proportion to M/H ratio Under five O/H ratios with M/H=1/12 the maximum CO2 and H2O yield are achieved in O/H?0 8 similar with M/H ratio result the gas yield is decrease when O/H is reduced Our results showed that the less oxygen input to the reactor the more carbon formation The enthalpy of the reactors reveals that the behavior of reactors was endothermic (expect M/H=1/5) To find the optimal parameters the redox degree was introduced in this study and the results showed that reactor should be controlled at M/H=1/12 and O/H=0 18 where temperature is 900 °C the enthalpy of this condition showed endothermic behavior at both reactor

Date of Award	2020
Original language	English
Supervisor	Chih-Hua Chang (Supervisor)