Testing of minerals and industrial by-products as oxygen carriers for chemical-looping combustion in a circulating fluidized-bed 300W laboratory reactor

Abstract

Chemical-looping combustion (CLC) is a promising technology for future energy production with inherent CO 2 separation. One approach is to use minerals or industrial by-products as oxygen carriers to reduce the costs of the process. This study focuses on the investigation of two iron-based oxygen carriers, which were examined under continuous operation in a 300 W laboratory reactor. Ilmenite is an iron-titanium oxide mineral, whereas iron oxide scale (IOS) is obtained as a by-product from the rolling of sheet steel. Syngas was used as a fuel -pure and with steam addition to suppress the formation of solid carbon.During the experiments the variables reactor temperature, fuel flow and air flow were changed. Furthermore the effect of steam addition to the fuel was investigated. Particle properties were compared over the span of 85 h of continuous operation for ilmenite and 37 h for IOS. The analysis is based on gas measurements from the actual CLC operation, but also on scanning electron microscopy, X-ray powder diffractometry and measurements of BET surface area and density.With ilmenite oxygen carrier it was possible to achieve full conversion of syngas up to about 190 W th fuel equivalent at 900°C. With design fuel flow of about 300 W th at 900°C the combustion efficiency was above 98 %. There was almost no visible difference in reactivity of fresh activated particles and those used for 85 h. Combustion efficiency up to 99 % was achieved with IOS oxygen carrier at 900°C and about 100 W th fuel equivalent. At 300 W th fuel equivalent and 900°C a combustion efficiency of only 90 % could be reached.Both oxygen carriers were operated for tens of hours, which allowed for a better understanding of lifetime behavior and other basic characteristics. Whereas ilmenite oxygen-carrier particles were mostly stable over the course of 85 h of experiments, a large fraction of IOS oxygen-carrier particles had disintegrated to fines after only 37 h of experiments. The gathered data indicates that both oxygen carriers could be an alternative to synthesized particles, though with more drawbacks for IOS than for ilmenite.

Using Low-Cost Iron-Based Materials as Oxygen Carriers for Chemical Looping Combustion

“…Leion et al have concluded that such materials are good candidates for converting solid fuels in chemical looping combustion [21] and Xiao et al have reported promising results using an iron ore to convert solid fuels in a fixed-bed reactor under pressurized conditions [26]. Moldenhauer has investigated the mineral ilmenite and an iron-based oxide scale, in a 300 W circulating chemical looping combustion unit fuelled by syngas, to improve the understanding of the lifetime behaviour and other basic characteristics of these oxygen carriers [29].…”

Kinetic determination of a highly reactive impregnated Fe2O3/Al2O3 oxygen carrier for use in gas-fueled Chemical Looping Combustion

“…Consequently, incomplete combustion of CH 4 occurred in different continuous CLC plants when Fe-based materials were used [21][22][23][24][25][26][27][28]. Among these materials there were synthetic oxygen carriers prepared by different methods [21][22][23], iron-containing minerals [24][25][26][27] and residues [27][28].…”

“…Among these materials there were synthetic oxygen carriers prepared by different methods [21][22][23], iron-containing minerals [24][25][26][27] and residues [27][28]. Our research group at Instituto de Carboquímica (ICB-CSIC) has recently developed a highly reactive Fe-based oxygen carrier prepared by the impregnation method [16].…”

Use of Spinel Nickel Aluminium Ferrite as Self-Supported Oxygen Carrier for Chemical Looping Hydrogen Generation Process

“…Outlet gases from the air reactor contain N 2 and unreacted oxygen gases. Thus, the primary benefit of CLHG process is combined CO 2 separation and H 2 generation without entailing any direct cost or energy penalty (Adánez et al, 2012;Moldenhauer et al, 2012 Therefore, redox behaviour of an oxygen carrier is a key issue for the use in CLHG process (Adánez et al, 2004;Cho et al, 2004;Hossain et al, 2008;Kang et al, 2010). In our previous study, nickel ferrite (NiFe 2 O 4 ) powder with a single spinel phase demonstrated higher redox behaviour than standard nickel oxide (NiO) and iron oxide (Fe 2 O 3 ) by a thermogravimetric analyzer (TGA).…”