Performance of a bauxite waste as oxygen-carrier for chemical-looping combustion using coal as fuel

Abstract

In the recently developed Chemical-Looping Combustion (CLC) technology, the oxygen needed for the oxidation of the fuel is provided by an oxygen-carrier. Today, there is an increasing interest on CLC application to solid fuels, especially coal. One of the possibilities to process coal in a CLC system is the in situ gasification and subsequent combustion of the product gases (iG-CLC). Potential CLC oxygen-carriers should comply with some chemical and mechanical requirements but it would be interesting that the carrier is as inexpensive as possible, as some losses are expected accompanying the coal ashes. In the present work, a residue from alumina production mainly constituted by Fe 2 O 3 has been tested as oxygencarrier in CLC of coal. Batch experiments were carried out in a fluidized-bed reactor using a bituminous coal as fuel. The effect of operating conditions, such as temperature and gasification agent on the char conversion and combustion efficiency of gasification products were evaluated. Several H 2 O/CO 2 mixtures were tested as gasifying agents. After 50 hours of cycling operation in a batch fluidized bed, no defluidization or agglomeration problems were observed. A gain in the reactivity of the bauxite waste was observed with the number of redox cycles. The carrier showed high combustion efficiencies at all temperatures tested meaning that the bauxite waste was capable of burning the gases generated during the gasification of the char. The percentage of CO 2 in the feeding should be limited in order to maintain high gasification rates and combustion efficiencies. The present results indicate that this bauxite waste is a promising oxygen-carrier for the iG-CLC of coal.

Release of pollutant components in CLC of lignite

“…The release of sulphur from lignite during pyrolysis and gasification processes under conditions similar to those in the fuel reactor of the CLC unit was analyzed in a batch fluidized bed reactor. Details about the fluidized reactor can be found elsewhere (Mendiara et al, 2013). The reactor was loaded with 300 g of silica sand (+200-300 µm) which act as an inert.…”

“…This can be done by means of a carbon separation unit located between fuel and air reactors. The effect of the efficiency of the carbon separation unit (η CSS ) on carbon capture has been described before (Mendiara et al, 2013). This time the effect of its incorporation on pollutant emissions in the air reactor will be investigated.…”

“…This time the effect of its incorporation on pollutant emissions in the air reactor will be investigated. For that purpose, a simple model based on carbon balances to the fuel reactor and carbon separation unit was used to estimate the emission levels reached for different efficiencies of the carbon separation unit (Mendiara et al, 2013). The model considers the char gasification rate at the corresponding temperatures and using that value, first the char conversion and then the carbon capture efficiency are calculated for different η CSS values.…”

Characteristics of a CaSO4 oxygen carrier for chemical-looping combustion: reaction with polyvinylchloride pyrolysis gases in a two-stage reactor

“…10 The outlet stream from the oxidizer, which contains nitrogen and unreacted oxygen, can be safely emitted to the atmosphere. Because the conversion of air and fuel takes place in separate reactors, a concentrated CO 2 stream is obtained from the reducer aer the condensation of the water vapor.…”

On a Highly Reactive Fe2O3/Al2O3 Oxygen Carrier for in Situ Gasification Chemical Looping Combustion

“…This fact has been observed in previous works. 15,46,47 Reactivity does not have a direct effect on the char gasification rate, as the solid−solid reaction between oxygen carrier and carbon in char particles has little influence on char gasification in a fluidized bed reactor. 48 Hence, the effect was due to the actual H 2 concentration in the reacting atmosphere, as described above.…”