Natural minerals as oxygen carriers for chemical looping combustion in a dual circulating fluidized bed system

Progress in Energy and Combustion Science

Garcı́a-Labiano

et al. 2012

1,999

1,614

This work is a comprehensive review of the Chemical-Looping Combustion (CLC) and Chemical-Looping Reforming (CLR) processes reporting the main advances in these technologies up to 2010. These processes are based on the transfer of the oxygen from air to the fuel by means of a solid oxygen-carrier avoiding direct contact between fuel and air for different final purposes. CLC has arisen during last years as a very promising combustion technology for power plants and industrial applications with inherent CO 2 capture which avoids the energetic penalty present in other competing technologies.CLR uses the chemical looping cycles for H 2 production with additional advantages if CO 2 capture is also considered.The review compiles the main milestones reached during last years in the development of these technologies regarding the use of gaseous or solid fuels, the oxygen-carrier development, the continuous operation experience, and modelling at several scales. Up to 2010, more than 700 different materials based on Ni, Cu, Fe, Mn, Co, as well as other mixed oxides and low cost materials, have been compiled. Especial emphasis has been done in those oxygen-carriers tested under continuous operation in Chemical-Looping 2 prototypes. The total time of operational experience (≈ 3500 h) in different CLC units in the size range 0.3-120 kW th , has allowed to demonstrate the technology and to gain in maturity. To help in the design, optimization, and scale-up of the CLC process, modelling work is also reviewed. Different levels of modelling have been accomplished, including fundamentals of the gas-solid reactions in the oxygen-carriers, modelling of the air-and fuel-reactors, and integration of the CLC systems in the power plant. Considering the great advances reached up to date in a very short period of time, it can be said that CLC and CLR are very promising technologies within the framework of the CO 2 capture options.

Section: Low Cost Materials As Oxygen-carriersmentioning

confidence: 98%

Progress in Chemical-Looping Combustion and Reforming technologies

Adánez

Progress in Energy and Combustion Science

Garcı́a-Labiano

et al. 2012

1,999

1,614

“…The ilmenite used is a concentrate from a natural ore. Fresh particles have been exposed to thermal pre-treatment at 950ºC in air during 24 hours, since it improves its performance as oxygen-carrier [30,31]. [34].…”

Section: Oxygen-carrier Materialsmentioning

confidence: 99%

“…Leion et al [29,30] analyzed the reactivity of ilmenite in a batch fluidized-bed and ilmenite gave high conversion of H 2 and CO but moderate conversion of CH 4 . This carrier has been already used in both gaseous and solid fuels [24][25][26][27]31]. Ilmenite is mainly composed of FeTiO 3 (FeO·TiO 2 ), where iron oxide is the active phase that behaves as the oxygen-carrier.…”

Section: Introductionmentioning

confidence: 99%

Behavior of ilmenite as oxygen carrier in chemical-looping combustion

Cuadrat

Fuel Processing Technology

Adánez

et al. 2012

225

147

For a future scenery where will exist limitation for CO 2 emissions, Chemical-Looping Combustion (CLC) has been identified as a promising technology to reduce the cost related to CO 2 capture from power plants. In CLC a solid oxygen-carrier transfers oxygen from the air to the fuel in a cyclic manner, avoiding direct contact between them. CO 2 is inherently obtained in a separate stream. For this process the oxygen-carrier circulates between two interconnected fluidized-bed reactors. To adapt CLC for solid fuels the oxygen-carrier reacts with the gas proceeding from the solid fuel gasification, which is carried out right in the fuelreactor. Ilmenite, a natural mineral composed of FeTiO 3 , is a low cost and promising material for its use on a large scale in CLC.The aim of this study is to analyze the behavior of ilmenite as oxygen-carrier in CLC.Particular attention was put on the variation of chemical and physical characteristics of ilmenite particles during consecutive redox cycles in a batch fluidized-bed reactor using CH 4 , H 2 and CO as reducing gases. Reaction with H 2 was faster than with CO, and near full H 2 2 conversion was obtained in the fluidized-bed. Lower reactivity was found for CH 4 . Ilmenite increased its reactivity with the number of cycles, especially for CH 4 . The structural changes of ilmenite, as well as the variations in its behavior with a high number of cycles were also evaluated with a 100 cycle test using a CO+H 2 syngas mixture. Tests with different H 2 :CO ratios were also made in order to see the reciprocal influence of both reducing gases and it turned out that the reaction rate is the sum of the individual reaction rates of H 2 and CO. The oxidation reaction of ilmenite was also investigated. An activation process for the oxidation reaction was observed and two steps for the reaction development were differenced. The oxidation reaction was fast and complete oxidation could be reached after every cycle. Low attrition values were found and no defluidization was observed during fluidized-bed operation. During activation process, the porosity of particles increased from low porosity values up to values of 27.5%. The appearance of an external shell in the particle was observed, which is Fe enriched. The segregation of Fe from TiO 2 causes that the oxygen transport capacity, R OC , decreases from the initial R OC = 4.0% to 2.1% after 100 redox cycles.

“…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].…”

Section: Introductionmentioning

confidence: 99%

“…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].…”

Section: Introductionmentioning

confidence: 99%

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

Cabello

Chemical Engineering Journal

Garcı́a-Labiano

et al. 2014

114

The objective of this work was to determine the kinetic parameters for reduction and oxidation reactions of a highly reactive Fe-based oxygen carrier for use in chemical looping combustion (CLC) of gaseous fuels containing CH 4 , CO and/or H 2 , e.g. natural gas, syngas and PSA-off gas. The oxygen carrier was prepared by impregnation of iron on alumina. The effect of both the temperature and gas concentration was analysed in a thermogravimetric analyser (TGA).The grain model with uniform conversion in the particle and reaction in grains following the shrinking core model (SCM) was used for kinetics determination. It was 2 assumed that the reduction reactions were controlled by two different resistances: the reaction rate was controlled by chemical reaction in a first step, whereas the mechanism that controlled the reactions at higher conversion values was diffusion through the product layer around the grains. Furthermore, it was found that the reduction reaction mechanism was based on the interaction of Fe 2 O 3 with Al 2 O 3 in presence of the reacting gases to form FeAl 2 O 4 as the only stable Fe-based phase. The reaction order values found for the reducing gases were 0.25, 0.3 and 0.6 for CH 4 , H 2 and CO, respectively, and the activation energy took values of between 8 kJ mol -1 (for H 2 ) and 66 kJ mol -1 (for CH 4 ). With regard to oxidation kinetics, the reacting model assumed a reaction rate that was only controlled by chemical reaction. Values of 0.9 and 23 kJ mol -1 were found for reaction order and activation energy, respectively.Finally, the solids inventory needed in a CLC system was also estimated by considering kinetic parameters. The total solids inventory in the CLC unit took a minimum value of 150 kg MW -1 for CH 4 combustion, which is a low value when compared to those of other Fe-based materials found in the literature.