Assessment of the improvement of chemical looping combustion of coal by using a manganese ore as oxygen carrier

Abstract

Finding suitable low-cost materials to be used as oxygen carrier in Chemical Looping Combustion (CLC) of coal is a key issue to achieve the CO 2 capture at low economic cost. Recently, a Mn-ore from Gabon has been identified as an alternative to the state of the art of oxygen carriers based on minerals or wastes with high iron content. This Mn-ore showed a high reactivity and a long particle lifetime during batch characterization to be considered as a suitable oxygen carrier. To evaluate the potential of this material in CLC, this work analyses the behaviour of the Mn-ore during continuous combustion of a bituminous coal in a 0.5 kW th CLC unit. The CLC process was evaluated and the effect of the main operating variablessuch as fluidizing medium, oxygen carrier circulation rate, temperature, and solids inventory in the fuel reactor-on the combustion efficiency and CO 2 capture was investigated. A direct relation between the char conversion rate and the CO 2 capture is given, being mainly affected by the mean residence time of solids and temperature in the fuel reactor. The use of a carbon separation system with separation efficiency above 90 % would be required to achieve CO 2 capture rates higher than 95 %. Total oxygen demand values as low as 4.5 % were found when optimal operating conditions were selected, mainly being related to oxygen carrier to fuel ration higher than  > 3. At these conditions, the Mn-ore material showed similar combustion efficiencies than other Fe-based low-cost materials previously tested, but with higher CO 2 capture rates.

Developing Oxygen Carriers for Chemical Looping Biomass Processing: Challenges and Opportunities

“…Oxygen transfer capacity of Cu-, Fe-, Mn-, Ni, and Co-based OCs versus their respective theoretical capacities. Most experimental OTCs were obtained by TGA measurements with gaseous reactants, [39,41,62,[75][76][77][78][79][80][81][82][83][84] except the case of "oxidized LD slag," whose OTC was calculated from the conversion of syngas in the batch reactor. [77] TPR of NiFe 2 O 4 in 5 vol% CO (N 2 balance) shows two reduction peaks around 800 °C, which are assigned to the reduction of NiFe 2 O 4 spinel and FeO, respectively.…”

“…On average, Ni-based OCs exhibit higher surface areas than the other OCs, probably owing to the fact that NiO is often loaded on high surface area supports. [23,94] For Mn, Fe, and Cu based oxygen carriers, there is a tendency to use low porosity Mn, [62] Fe, [95,96] and Cu [39,97] containing natural ores and minerals as the oxygen carrires for CLBP applications. Nevertheless, Mn, Fe, and Cu-based OCs with high surface area comparable to that of Ni-based OCs can also be obtained through material synthesis.…”

“…NiAl 2 O 4 , CuAl 2 O 4 and MnAl 2 O 4 will significantly reduce lattice oxygen activities of the active metal oxides, for example, NiO, CuO, and Mn 3 O 4 , and must therefore be inhibited. [62,117,165] Perovskites: Perovskite structured oxygen carriers have a general formula ABO 3-δ , where the A sites are occupied by large cations (e.g., alkali earth metals and rare earth metals), and the B sites are occupied by smaller, often transition metal cations (e.g., Mn, Co, Fe, etc.). [115] Perovskite structured oxides have received increasing attentions as oxygen carriers because of their outstanding redox activities.…”

“…Data were adapted from refs. [ 35,38,43,44,52,54,62 ] ), (b) Equilibrium product mole fraction during steam gasification of carbon at 1 atm total pressure; the black line represents the fraction of solid carbon at equilibrium.…”

“…a) A statistical analysis of the compositions of the gas products from selected studies (%) (The straight lines represent the line of best fit. Data were adapted from refs [35,38,43,44,52,54,62]…”