Abstract
ABSTRACT Hematite supported on alumina or alumina/titania was fabricated to serve as an oxygen carrier in the chemical looping combustion (CLC) of charcoal. The reduction rate of Fe2O3/Al2O3 and Fe2O3/Al2O3/TiO2 particles increased with the reactor inlet’s CO concentration and displayed a slight effect from elevated operating temperatures. Applying the shrinking core model, the mass transfer coefficients (kg) for the reduction of Fe2O3/Al2O3 and Fe2O3/Al2O3/TiO2 by CO were found to be 0.16 and 0.22 mm s–1, respectively, and using the Fe2O3/Al2O3 and Fe2O3/Al2O3/TiO2 to combust charcoal resulted in carbon conversion rates of approximately 61.8% and 47.2%, respectively, when the inlet steam flow rate was set to 221.4 mmol min–1. Significantly, a higher inlet steam flow rate may not be advantageous when employing iron-based oxygen carriers. More heat was released during combustion with the Fe2O3/Al2O3 than with the Fe2O3/Al2O3/TiO2 due to a high flow rate for the former being used. When Fe2O3/Al2O3/TiO2 was used as the oxygen carrier, the particles, which contained a large percentage of Fe2O3, exhibited high reactivity to syngas (CO/H2); thus, less Fe2O3/Al2O3/TiO2 than Fe2O3/Al2O3 was required to combust the charcoal.
Highlights
Coal is the second most important energy source and distributed in many countries (WEC, 2016)
The combustible gases generated during the solid fuel gasification, and oxygen carrier was reduced by the gasified syngas (CO/H2)
The kinetic study of solid fuel gasification and oxygen carrier reduction should be simultaneously considered for chemical looping combustion (CLC) of solid fuel in order to preliminarily assess the performance of the prepared oxygen carrier for solid fuel combustion
Summary
Coal is the second most important energy source and distributed in many countries (WEC, 2016). Markström et al (2013) presented the design and operation of CLC with Colombian coal in a 100 kWth fluidized bed reactor with ilmenite and indicated that the highest gas conversion and CO2 capture efficiency of coal combustion reached about 84.1% and 96.4–99.5% for experiments conducted at 940– 980°C in the fuel reactor, respectively. Bayham et al (2013) indicated that the carbon conversions were confirmed more than 90% for the combustion of both sub-bituminous coal and lignite coal using a 25 kWth moving bed reactor operated with iron-based oxygen carriers, while CO2 concentration in the fuel reactor outlet stream was obtained to be 99.5 vol.%. The present study was aimed at applying the chemical looping process using the Fe2O3/Al2O3 and Fe2O3/Al2O3/TiO2 oxygen carriers to combust charcoal. The concentrations of hydrogen in the effluent streams were determined with a China Chromatography Model 2000 gas chromatograph (GC) equipped with a thermal conductivity detector
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