Chemical-Looping Combustion of Coal with Metal Oxide Oxygen Carriers

Abstract

The combustion and reoxidation properties of direct coal chemical-looping combustion (CLC) over CuO, Fe2O3, Co3O4, NiO, and Mn2O3 were investigated using thermogravimetric analysis (TGA) and bench-scale fixed-bed flow reactor studies. When coal is heated in either nitrogen or carbon dioxide (CO2), 50% of weight loss was observed because of partial pyrolysis, consistent with the proximate analysis. Among various metal oxides evaluated, CuO showed the best reaction properties: CuO can initiate the reduction reaction as low as 500 °C and complete the full combustion at 700 °C. In addition, the reduced copper can be fully reoxidized by air at 700 °C. The combustion products formed during the CLC reaction of the coal/metal oxide mixture are CO2 and water, while no carbon monoxide was observed. Multicycle TGA tests and bench-scale fixed-bed flow reactor tests strongly supported the feasibility of CLC of coal by using CuO as an oxygen carrier. Scanning electron microscopy (SEM) images of solid reaction products indicated some changes in the surface morphology of a CuO−coal sample after reduction/oxidation reactions at 800 °C. However, significant surface sintering was not observed. The interactions of fly ash with metal oxides were investigated by X-ray diffraction and thermodynamic analysis. Overall, the results indicated that it is feasible to develop CLC with coal by metal oxides as oxygen carriers.

Feasible utility of inorganic remains from potable water purification process in chemical looping combustion studied in TG

“…The similar observation for bi-metallic Fe-Cu-based oxides with higher amount of Fe was reported elsewhere [12]. The bi-metallic oxygen carriers were more ashresistant compared with these oxygen carriers that are based on mono-metallic Ni, or Cu oxides carriers [27]. Therefore, the Fe-based sediment from water purification process has a great potential to be the excellent candidates for application for direct coal combustion process, since no interaction with Janina coal ash was observed.…”

“…during the CLC reaction. Our data showed that to obtain full combustion at an appreciable reaction rate, a reaction temperature within an approximate temperature range from 800 to 910°C that is lower than shown in [27], would be required for the Fe 2 O 3 oxygen carrier/coal system based on sediments from potable water.…”

“…For the sediments from the potable water purification process that were also run separately in TG under the same experimental conditions as for the mixtures, almost constant mass was observed within the TG measurements (not shown). Siriwardane et al [27] showed that for an Fe 2 O 3 /Illinois #6 coal system, the maximum combustion rate occurred over a temperature range from 973 to 977°C. They reported that approximately 95 % combustion could be attained using pure, synthetic Fe 2 O 3 .…”

“…For practical power generation in a real CLC system, the other solution for small reaction rates of solid fuel with Fe species might be applied, i.e., by replacing the coal/biomass with, for example, coal/biomass steam gasification syngas. Some examples of that option were also recommended elsewhere [11,23,27].…”

Progress in Chemical-Looping Combustion and Reforming technologies

“…The use of particles consisting of pure manganese oxide has shown low reactivity with methane or coal [227,230]. Several inert compounds have been tested as supporting material for the particle preparation of Mn-based oxygen-carrier to improve its performance.…”