467048 Characterization of Ilmenite As Oxygen Carrier during Chemical Looping Combustion and Reforming

Monday, November 14, 2016: 3:15 PM
Union Square 21 (Hilton San Francisco Union Square)
Dennis Lu, Zhenkun Sun, Firas Ridha and Robin Hughes, CanmetENERGY, Natural Resources Canada, Ottawa, ON, Canada

<span" roman"="Roman"" new="New"> Fossil fuel usage is considered a major source of CO2 emissions, the major contributor to greenhouse effect. Carbon capture and storage (CCS) is considered a promising approach to mitigate CO2 emissions from such industrial facilities. CCS involves separation of carbon dioxide from the flue gas, transportation to a storage location and subsequent long-term storage. Among these steps, CO2 capture is the major challenge due to issues relating to the technical feasibility and cost. One of these technologies is chemical looping process (CLP). In the CLP process, an oxygen carrier (a metal oxide) is circulated between two fluidized-bed reactors; a fuel reactor where the oxygen carrier is reduced according to equation (1) and (2), and an air reactor where the reduced oxygen carrier is oxidized according to equation (3). The main advantage with CLP, compared to other conversional conversion processes, is that CO2 is inherently separated from the other flue gas components, and therefore reducing the economic cost of CO2separation.

<span" roman"="Roman"" new="New">CH4  + 4MexOy → CO2 + 2H2O + 4MexOy-1(1)

<span" roman"="Roman"" new="New">CH4  + MexOy → CO + 2H2 + MexOy-1(2)

<span" roman"="Roman"" new="New">MexOy-1 + 1/2O2 → MexOy(3)

<span" roman"="Roman"" new="New"> CanmetENERGY has two on-going research programs on CLP, one is pressurized chemical looping combustion (PCLC) for the production of power and steam, the other one is pressurized chemical looping reforming (PCLR) for hydrogen production. High reactivity and proper flow behaviour of the oxygen carrier are crucial in developing both PCLC and PCLR technologies. Among all the low-cost materials including ores and industrial residues, ilmenite, a nature-occurring mineral material, has been paid much more attentions for their potential in CLP due to its desired thermodynamical properties resulting in 100 % theoretical combustion efficiency. Crushed ilmenite ore, henceforth referred to as ilmenite, is considered a leading candidate for oxygen carrying in CanmetENERGY’s pressurized chemical looping (PCL) processes since it is relatively inexpensive and possesses good physical attributes. However, as an iron-based oxygen carrier, the reactivity of ilmenite is lower than Mn-, Co-, Ni- and Cu-based ones. Lower reactivity will result in large bed inventory (8-10 times that required for the synthetic Fe-based oxygen carriers) and high pressure drop when used in CFB, and unconverted gas fuels in the outflow of fuel reactor. In addition, there is evidence of attrition, sintering and agglomeration of ilmenite in certain CLP conditions, which negatively impact its reactivity and operating behaviour. This study focuses on introducing nonporous (or mesoporous) dopants of CeO2, ZrO2, NiO or Al2O3into the ilmenite (mainly immobilized on their surface) to improve the reactivity of the ilmenite-based OCs towards methane combustion and reforming. On the other hand, when mesoporous dopants are employed, the agglomeration of ilmenite particles could be eased.

<span" roman"="Roman"" new="New"> A pressurized thermogravimetric analyzer (PTGA) and a pressurized fixed-bed reactor (PFBR) are used for testing the doped ilmenite particles at various temperatures (850-1050°C), gas compositions, pressures, and cycle stages. These particles are then analyzed by X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). The results from the measurements and discussion on the OC performance are outlined in this paper.

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