Iron-based oxygen carriers in chemical looping conversions:A review

A solid oxygen carrier is usually applied in a chemical looping conversion process to transfer oxygen from the gaseous oxygen source to the fuel,which can avoid the direct contact of these two reactants and hence decrease the energy penalty of separation.Among the solid oxygen carriers,iron-based oxygen carrier is an attractive option due to its inherent properties of low cost and environmentally-friendly.Several processes such as chemical looping combustion(CLC),chemical looping gasification(CLG),chemical looping reforming(CLR),and chemical looping hydrogen generation(CLHG)have been proposed and investigated based on the iron-based oxygen carrier.In this review,the relevant researches on the iron-based oxygen carrier are summarized,which include the characteristics of iron oxides,the preparations of the iron-based oxygen carrier based on the iron ores and some other low-cost iron contained materials,and their applications in the continuous operated chemical looping conversion processes.It is expected to provide a better understanding for the development and utilization of iron-based oxygen carrier in the practical chemical looping processes.

Effect of pressure on gasification reactivity of three Chinese coals with different ranks

The gasification reactivities of three kinds of different coal ranks(Huolinhe lignite,Shenmu bituminous coal,and Jincheng anthracite)with CO_(2) and H_(2)O was carried out on a self-made pressurized fixed-bed reactor at increased pressures(up to 1.0 MPa).The physicochemical characteristics of the chars at various levels of carbon conversion were studied via scanning electron microscopy(SEM),X-ray diffraction(XRD),and BET surface area.Results show that the char gasification reactivity increases with increasing partial pressure.The gasification reaction is controlled by pore diffusion,the rate decreases with increasing total system pressure,and under chemical kinetic control there is no pressure dependence.In general,gasification rates decrease for coals of progressively higher rank.The experimental results could be well described by the shrinking core model for three chars during steam and CO_(2) gasification.The values of reaction order n with steam were 0.49,0.46,0.43,respectively.Meanwhile,the values of reaction order n with CO_(2) were 0.31,0.28,0.26,respectively.With the coal rank increasing,the pressure order m is higher,the activation energies increase slightly with steam,and the activation energy with CO_(2) increases noticeably.As the carbon conversion increases,the degree of graphitization is enhanced.The surface area of the gasified char increases rapidly with the progress of gasification and peaks at about 40%of char gasification.