Syngas combustion in a chemical-looping combustion system using an impregnated Ni-based oxygen carrier

Progress in Energy and Combustion Science

Garcı́a-Labiano

et al. 2012

Self Cite

1,997

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: Carbon Depositionmentioning

confidence: 99%

Section: Ni-based Oxygen-carriersmentioning

confidence: 99%

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Progress in Chemical-Looping Combustion and Reforming technologies

Adánez

Progress in Energy and Combustion Science

Garcı́a-Labiano

et al. 2012

Self Cite

1,997

1,614

“…Several oxygen-carriers based on Ni, Cu, Fe and Mn oxides have shown good reactivity with syngas components, i.e. H 2 and CO [15,16], and the use of syngas in a CLC system has been successfully accomplished in 300-500 W th continuously operated reactors [17][18][19][20][21].…”

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.

“…NiO18-Al oxygen carrier had been previously used successfully in CLC with different fuels [45][46] even in the presence of impurities, such as sulphur [47] and light hydrocarbons [48]. Both NiO18-Al and NiO21-Al particles were also tested in CLR experiments in a continuous plant [49] and at pressurized conditions in a batch reactor [50].…”

Section: Introductionmentioning

confidence: 99%

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

Dueso

Ortiz

Chemical Engineering Journal

et al. 2012

Self Cite

168

114

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. 