Effect of support on reactivity and selectivity of Ni-based oxygen carriers for chemical-looping combustion

Gayán, Pilar; Diego, Luis F. de; Garcı́a-Labiano, F.; Adánez, Juan; Dueso, Cristina

doi:10.1016/j.fuel.2008.02.016

Cited by 159 publications

(91 citation statements)

References 24 publications

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“…An additional advantage of the joint use of these Ni-based materials and bioethanol is the absence of deactivation processes by sulphur that normally happens when fossil fuels are used [26]. Germany GmbH) as support [27]. The NiO18-Al 2 O 3 was prepared by hot incipient wet impregnation [28], a modification of the method above mentioned, to increase the amount of NiO which could be introduced into the support in each impregnation stage.…”

Section: Methodsmentioning

confidence: 99%

Syngas/H2 production from bioethanol in a continuous chemical-looping reforming prototype

Garcı́a-Labiano

García-Díez

Diego

et al. 2015

Fuel Processing Technology

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Abstract:Chemical-looping reforming (CLR) allows H 2 production without CO 2 emissions into the atmosphere. The use of a renewable fuel, bioethanol, in an auto-thermal CLR process has the advantage to produce H 2 with negative CO 2 emissions. This work presents the experimental results obtained in a continuously operating CLR unit (1 kW th ) using ethanol as fuel. Two NiO-based oxygen carriers were used during more than 50 hours of operation. The influence of variables such as temperature, water-to-fuel 2 and oxygen-to-fuel molar ratios was analysed. Full conversion of ethanol was accomplished and carbon formation was easily avoided. A syngas composed by ≈61 vol.% H 2 , ≈32 vol.% CO, ≈5 vol.% CO 2 and ≈2 vol.% CH 4 was reached at auto-thermal conditions for both materials. Gas composition was closed to the given by the thermodynamic equilibrium. These results demonstrate the technical viability of H 2 /syngas production by using bioethanol in an auto-thermal CLR process.

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Section: Methodsmentioning

confidence: 99%

Syngas/H2 production from bioethanol in a continuous chemical-looping reforming prototype

Garcı́a-Labiano

García-Díez

Diego

et al. 2015

Fuel Processing Technology

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“…These materials were prepared using the incipient wet impregnation method [51]. Commercial -Al 2 O 3 particles (Puralox NWa-155, Sasol…”

Section: Methodsmentioning

confidence: 99%

“…There was a first period where the reduction rate was fast, attributed to the reaction of NiO with the fuel, and then a stage of low reactivity which corresponded to the reaction of the nickel aluminate with the fuel [18,53]. The use of -Al 2 O 3 as support allowed reducing the interaction support-active phase [51] minimizing the formation of nickel aluminate and part of the impregnated nickel remained in this case as free NiO, increasing the reactivity of the NiO18-Al oxygen carrier. Nevertheless, when NiO21-Al material was used, the initial fast stage did not exist in the first redox cycle due to the higher tendency of -Al 2 O 3 to form…”

Section: Kinetic Modelmentioning

confidence: 99%

Reduction and oxidation kinetics of nickel-based oxygen-carriers for chemical-looping combustion and chemical-looping reforming

Dueso

Ortiz

Abad

et al. 2012

Chemical Engineering Journal

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168

114

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The kinetics of reduction with CH 4 , H 2 and CO and oxidation with O 2 of two NiO-based oxygen carriers prepared by impregnation, NiO18-Al and NiO21-Al, for chemicallooping combustion (CLC) and chemical-looping reforming (CLR) was investigated in this work. The experimental tests were carried out in a thermogravimetric analyzer using different reacting gas concentrations (5-20 vol. % for CH 4 , 5-50 vol. % for H 2 and CO and 5-21 vol. % for O 2 ) and temperatures (1073-1223 K). The reduction stage using both materials proceeded in two steps: a first period of high reactivity attributed to the presence of free NiO and then a low reactivity period that corresponded to NiAl 2 O 4 reduction. Therefore, the kinetic parameters for NiO and NiAl 2 O 4 reduction were determined separately for each oxygen carrier and each reacting gas. An empirical linear model was developed to describe NiO reduction. The solid conversion was a function of the fuel concentration and NiO content in the solid. The effect of temperature was low (E a ~ 5 kJ mol -1 ) although a chemical reaction rate controlled by diffusional processes was dismissed. The shrinking core model for spherical grain 2 geometry was used to obtain the kinetic parameters of the NiAl 2 O 4 reduction working with both NiO-based oxygen carriers. Chemical reaction control was assumed for NiO18-Al whereas diffusion through product layer was also considered when NiO21-Al was used as oxygen carrier. 82-472 kJ mol -1 activation energies were obtained with NiO18-Al particles. The activation energies were 237 and 373 kJ mol -1 for the kinetic constant and 200-281 kJ mol -1 for the diffusion coefficient, respectively, in the case of NiO21-Al oxygen carrier. Reduction reaction of NiO21-Al with CO was extremely slow and the kinetic parameters were obtained for comparison purposes with chemical control of the reaction rate. In this case, the reaction order was 1 and the activation energy 89 kJ mol -1 . The combined model for consecutive reduction of NiO and NiAl 2 O 4 in the NiO18-Al particles with the kinetic parameters obtained in this work predicted adequately the experimental results. The oxidation step of both oxygen carriers was fast and complete until reaching the initial condition. An empiric linear model, which assumes a linear relation between time and conversion, was developed to determine the kinetics of Ni oxidation. The reaction order of oxidation was about 0.8 for NiO18-Al and NiO21-Al and the activation energies were low, 22 kJ mol -1 in both cases. 

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“…CaSO 4 was also used for transferring oxygen for methane combustion in fluidized bed reactors (Song et al, 2009 (Adanez et al, 2004). Fabrication techniques of composite oxygen carriers with suitable particle size and mechanical strength include mechanical mixing, co-precipitation, dissolution, freeze-granulation, impregnation and spray drying (de Deigo et al, 2005;Gayan et al, 2008;Hossain and de Lasa, 2008).…”

Section: Oxygen Carriers For Chemical Looping Processmentioning

confidence: 99%

Chemical Looping Process - A Novel Technology for Inherent CO2 Capture

Chiu

2012

Aerosol Air Qual. Res.

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Chemical looping is a novel energy technology that undertakes inherent CO 2 capture and has better energy efficiency than existing CO 2 capture technologies. Metal oxides (also known as oxygen carriers) are applied for the chemical looping process in place of air to offer oxygen for fuel combustion, thus enhancing CO 2 purity in the effluent stream. This article introduces the major aspects of chemical looping technology, including the oxygen carrier, reactor and fuel. Fe-, Ni-and Cu-based metal oxides were found to be suitable oxygen carriers for the chemical looping process based on the evaluation indexes of oxygen capacity, cost, reactivity, and mechanical strength. The modification of oxygen carriers by supporting materials is the typical research regime for enhancing mechanical strength and reactivity. The reactor systems currently used for the chemical looping process include fluidized and moving bed reactors. Fluidized bed reactors are well developed for gaseous fuel combustion applications, while moving bed reactors operated with a counter-flow mode between the solid fuel and oxygen carriers would enhance combustion efficiency, and reduce the operating solid inventory of oxygen carriers. Gaseous fuels, including natural gas and syngas gasified from coal, could achieve complete fuel conversion and high CO 2 yield for different combinations of oxygen carrier and reactor system. Gasification of solid fuels, including coal, petroleum coke and biomass in the fuel reactor, is a critical step that might reduce overall combustion efficiency. To improve solid fuel combustion and CO 2 yield, modification of the reactor design or operational conditions are necessary for the combustion of solid fuels by a chemical looping process.

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Effect of support on reactivity and selectivity of Ni-based oxygen carriers for chemical-looping combustion

Cited by 159 publications

References 24 publications

Syngas/H2 production from bioethanol in a continuous chemical-looping reforming prototype

Syngas/H2 production from bioethanol in a continuous chemical-looping reforming prototype

Reduction and oxidation kinetics of nickel-based oxygen-carriers for chemical-looping combustion and chemical-looping reforming

Chemical Looping Process - A Novel Technology for Inherent CO2 Capture

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