Desarrollo de un transportador de oxígeno con propiedades magnéticas para la combustión de combustibles sólidos con captura de CO2

En este TFM se ha estudiado el efecto de añadir un soporte metálico basado en hierro y manganeso a un transportador de oxígeno que pueda operar en un ciclo CLOU (Chemical looping with oxygen uncoupling). El ciclo CLOU es útil para separar una corriente gaseosa de CO2 en un proceso de combustión. De esta forma se pretende evitar su emisión a la atmósfera, y contribuir a la lucha contra el cambio climático. El transportador que se ha preparado además cuenta con propiedades magnéticas para facilitar su separación de las cenizas y así reutilizarlo, favoreciendo la economía del proceso. De los transportadores, se ha estudiado el magnetismo, la dureza, su capacidad de transporte de oxígeno, el espectrograma de rayos X (XRD), se ha ensayado en termobalanza (TGA) y por último se ha experimentado con él en un pequeño reactor experimental.<br /

Hydrogen production by auto-thermal chemical-looping reforming in a pressurized fluidized bed reactor using Ni-based oxygen carriers

9 pages, 12 figures.This work presents the experimental results obtained during auto-thermal chemical-looping reforming (CLRa) in a semicontinuous pressurized fluidized bed reactor working with two Ni-based oxygen carriers and using methane as fuel. During operation the effect of the total pressure, reduction reaction temperature, and oxygen carrier-to-fuel molar ratio on CH4 conversion, gas outlet concentrations, and carbon formation was analyzed. In the range of pressures analyzed (up to 10 bars), it was found that an increase in the total operating pressure did not produce a negative effect on the gas product distribution obtained in the process. At all operating pressures the CH4 conversion was very high (>98%) and no carbon formation was detected. The most important variable affecting the gas product distribution was the solid circulation rate, that is, the oxygen carrier-to-fuel molar ratio (NiO/CH4). The oxygen carriers were physically and chemically characterized by several techniques before and after using in the pressurized fluidized bed reactor. Important changes in the surface texture and the solid structure of the oxygen carrier particles were not detected. These results suggest that these oxygen carriers could have a high durability, being suitable for use in a pressurized CLRa system. © 2009 Professor T. Nejat Veziroglu.This work was partially supported by the European Commission, under the 6th Framework Programme (CACHET Project, Contract no. 019972), from the CCP2 (CO2 Capture Project), a partnership of BP, Chevron, Conoco-Phillips, Eni Technology, Norsk Hydro, Shell, Suncor, and Petrobras and from the Spanish Ministry of Science and Innovation (CTQ2007-64400). M. Ortiz thanks Diputación General de Aragon for the F.P.I. fellowship.Peer Reviewe

Hydrogen production by chemical-looping reforming in a circulating fluidized bed reactor using Ni-based oxygen carriers

7 pages, 11 figures.This work presents the experimental results obtained during auto-thermal chemical-looping reforming (CLR) in a 900 Wth circulating fluidized bed reactor under continuous operation using methane as fuel. Two oxygen carriers based on NiO and supported on γ-Al2O3 and α-Al2O3 were used during more than 50 h of operation with each oxygen carrier. During operation the effect of different operating variables, like fuel reactor temperature, H2O/CH4 molar ratio and solid circulation rate, on CH4 conversion and gas product distribution was analyzed. It was found that in all operating conditions CH4 conversion was very high (>98%) and the most important variable affecting to the gas product distribution was the solid circulation rate, that is, NiO/CH4 molar ratio. Similar gas product distribution was obtained working with both oxygen carriers although at different NiO/CH4 molar ratios. The oxygen carrier of NiO on α-Al2O3 needed lower NiO/CH4 molar ratio to reach the same gas product composition than the oxygen carrier of NiO on γ-Al2O3. Working at optimal operating conditions, 2.5 moles of H2 per mol of CH4 could be obtained in this process. During operation the oxygen carrier particles maintained their physical and chemical properties. These results suggest that these oxygen carriers could have a high durability, being suitable oxygen carriers for a CLR system. © 2008 Elsevier B.V. All rights reserved.This work was partially supported by the European Commission, under the 6th Framework Programme (CACHET Project, Contract no. 019972), and from the CCP2 (CO2 Capture Project), a partnership of BP, Chevron, Conoco-Phillips, Eni Technology, Norsk Hydro, Shell, Suncor, and Petrobras. M. Ortiz thanks Diputación General de Aragon for the F.P.I. fellowship.Peer Reviewe

Operation of a 10 kWth chemical-looping combustor during 200 h with a CuO-Al2O3 oxygen carrier

Chemical-looping combustion (CLC) is an attractive technology to decrease greenhouse gas emissions affecting global warming, because it is a combustion process with inherent CO2 separation and therefore without needing extra equipment for CO2 separation and low penalty in energy demand. The CLC concept is based on the split of a conventional combustion of gas fuel into separate reduction and oxidation reactions. The oxygen transfer from air to fuel is accomplished by means of an oxygen carrier in the form of a metal oxide circulating between two interconnected reactors. A Cu-based material (Cu14Al) prepared by impregnation of γ-Al2O3 as support with two different particle sizes (0.1-0.3 mm, 0.2-0.5 mm) was used as an oxygen carrier for a chemical-looping combustion of methane. A 10 kWth CLC prototype composed of two interconnected bubbling fluidized bed reactors has been designed, built in and operated at 800 °C during 100 h for each particle size. In the reduction stage full conversion of CH4 to CO2 and H2O was achieved using oxygen carrier-to-fuel ratios above 1.5. Some CuO losses as the active phase of the CLC process were detected during the first 50 h of operation, mainly due to the erosion of the CuO present in external surface of the alumina particles. The high reactivity of the oxygen carrier maintained during the whole test, the low attrition rate detected after 100 h of operation, and the absence of any agglomeration problem revealed a good performance of these CuO-based materials as oxygen carriers in a CLC process. © 2006 Elsevier Ltd. All rights reserved.This research was carried out with financial support from the Spanish Ministry of Education and Science (Projects PPQ-2001-2111 and CTQ-2004-04034) and from the Diputación General de Aragón (Project PIP023/2005).Peer Reviewe

Optimization of hydrogen production by Chemical-Looping auto-thermal Reforming working with Ni-based oxygen-carriers

9 pages, 11 figures, nomenclature.Chemical-Looping auto-thermal Reforming (CLRa) is a new process for hydrogen production from natural gas that uses the same principles as Chemical-Looping Combustion (CLC). The main difference with CLC is that the desired product is syngas (H2 + CO) instead of CO2 + H2O. For that, in the CLRa process the air to fuel ratio is kept low to prevent the complete oxidation of the fuel. The major advantage of this technology is that the heat needed for converting CH4 to syngas is supplied without costly oxygen production and without mixing of air with carbon containing fuel gases. An important aspect to be considered in the design of a CLRa system is the heat balance. In this work, mass and heat balances were done to determine the auto-thermal operating conditions that maximize H2 production in a CLRa system working with Nibased oxygen-carriers. It was assumed that the product gas was in thermodynamic equilibrium at the exit of the air and fuel-reactors and the equilibrium gas compositions were obtained by using the method of minimization of the Gibbs free energy of the system. It was found that to reach auto-thermal conditions the oxygen-to-methane molar ratio should be higher than 1.20, which means that the maximum H2 yield is about 2.75 mol H2/mol CH4. The best option to control the oxygen-to-methane molar ratio is to control the air flow fed to the air-reactor because a lower air excess is needed to reach auto-thermal conditions.This work was partially supported by the Spanish Ministry of Science and Innovation (MICINN) (CTQ2007-64400) and the European Commission, under the 6th Framework Programme (CACHET Project, Contract no. 019972), and from the CCP2 (CO2 Capture Project), a partnership of BP, Chevron, Conoco-Phillips, Eni Technology, Norsk Hydro, Shell, Suncor, and Petrobras. M. Ortiz thanks Diputación General de Aragón for the F.P.I. fellowshipPeer Reviewe

Synthesis gas generation by chemical-looping reforming in a batch fluidized bed reactor using Ni-based oxygen carriers

13 Figures, 3 Tables.Chemical-looping reforming (CLR) utilizes the same basic principles as chemical-looping combustion (CLC), being the main difference that the wanted product in CLR is H2 and CO. Therefore, in the CLR process the air to fuel ratio is kept low to prevent the complete oxidation of the fuel to CO2 and H2O. Ni-based oxygen carriers prepared by impregnation on alumina have been studied in a thermogravimetric analyzer (TGA) and in a batch fluidized bed reactor in order to know its potential for CLR of CH4. In the TGA the reactivity of the oxygen carriers has been determined. In the batch fluidized bed the effect on the gas product distribution produced during reduction-oxidation cycles and on the carbon deposition of different operating conditions, as type of support, reaction temperature, H2O/CH4 molar ratio, and preparation method, has been tested and analyzed. It was found that the support (different types of alumina) used to prepare the oxygen carriers had an important effect on the reactivity of the oxygen carriers, on the gas product distribution, and on the carbon deposition. In addition, for all oxygen carriers prepared, an increase in the reaction temperature and/or in the H2O/CH4 molar ratio produced a decrease in the carbon deposition during the reduction period. Finally, it was observed that the oxygen carriers prepared by a deposition-precipitation method had higher tendency to increase the C deposition than the oxygen carriers prepared by dry impregnation.This work was partially supported by the European Commission, under the 6th Framework Programme (CACHET Project, Contract no. 019972), and from the CCP2 (CO2 Capture Project), a partnership of BP, Chevron, Conoco-Phillips, Eni Technollogy, Norsk Hydro, Shell, Suncor, and Petrobras. M. Ortiz thanks Diputación General de Aragon for the F.P.I. fellowship.Peer Reviewe

Developmen of Cu-based oxygen carriers for chemical-looping combustion

In a chemical-looping combustion (CLC) process, gas (natural gas, syngas, etc) is burnt in two reactors. In the first one, a metallic oxide that is used as oxygen source is reduced by the feeding gas to a lower oxidation state, being CO2 and steam the reaction products. In the second reactor, the reduced solid is regenerated with air to the fresh oxide, and the process can be repeated for many successive cycles. CO2 can be easily recovered from the outlet gas coming from the first reactor by simple steam condensation. Consequently, CLC is a clean process for the combustion of carbon containing fuels preventing the CO2 emissions to atmosphere. The main drawback of the overall process is that the carriers are subjected to strong chemical and thermal stresses in every cycle and the performance and mechanical strength can decay down to unacceptable levels after enough number of cycles in use. In this paper the behaviour of CuO as an oxygen carrier for a CLC process has been analysed in a thermogravimetric analyser (TGA). The effects of carrier composition and preparation method used have been investigated to develop Cu-based carriers exhibiting high reduction and oxidation rates without substantial changes in the chemical, structural and mechanical properties for a high number of oxidation-reduction cycles. It has been observed that the carriers prepared by mechanical mixing or by coprecipitation showed an excellent chemical stability in multicycle tests in thermobalance, however, the mechanical properties of these carriers were highly degraded to unacceptable levels. On the other hand, the carriers prepared by impregnation exhibited excellent chemical stability without substantial decay of the mechanical strength in multicycle testing. These results suggest that copper based carriers prepared by impregnation are good candidates for chemical-looping combustion process.This work was partially supported by the European Commission, under the RFCS program (ECLAIR Project, Contract RFCP-CT-2008-0008), ALSTOM Power Boilers (France) and by the Spanish Ministry of Science and Innovation (PN, ENE2010-19550). I. Adánez-Rubio thanks CSIC for the JAE fellowship co-fund by the Eurpean Social Fund.Peer reviewe

Fate of pollutant components during chemical looping combustion of coal

6 figures, 2 tables.-- Work presented at the 6th International Conference on Clean Coal Technologies, CCT2013 in Thessaloniki, Greece. 12-16 May 2013.The recently developed Chemical Looping Combustion technology (CLC) is nowadays considered an interesting option to capture CO2 at low cost in fossil fuelled power plants. In this technology, the oxygen needed for combustion is supplied by an oxygen carrier, normally a metal oxide, avoiding the mixture of the fuel and air. In the past years, significant advances have been achieved in the combustion of both gaseous and solid fuels. Nevertheless, pollutant emission from CLC systems has received little attention. This paper focuses on the study of sulphur and nitrogen emissions in the combustion of a lignite in a 500 Wth CLC unit. Ilmenite was used as oxygen carrier, as it is one of the most common materials used for CLC of solid fuels. Emissions from both fuel and air reactors were studied. The main sulphur species detected in the fuel reactor were H2S and SO2. The amount and proportion depended on the temperature of the fuel reactor. At high temperatures, low H2S/SO2 molar ratios were observed. Regarding nitrogen emissions, no NH3, HCN or N2O were registered in the fuel reactor. N2 was the major product from fuel-N originated in the fuel reactor, together with small amounts of NO and NO2. In the air reactor, sulphur and nitrogen were released from unconverted char as SO2 and NO, respectively.The authors thank the Spanish Ministry for Science and Innovation for the financial support via the ENE2010-19550 project. This work was also partially supported by the European Commission, under the RFCS program (ACCLAIM Project, Contract RFCP-CT-2012-406). T. Mendiara thanks for the “Juan de la Cierva” post-doctoral contract awarded by this Ministry.Peer reviewe

CO2 capture by Chemical Looping Processes using C-fuels

1 figure.-- Work presented at the Carbon 2018 ´"The World Conference of Carbon", Madrid (Spain), 01st-6th JulyAccording to the IPCC, warming of the climate system is unequivocal and this is mainly consequence of the increase in the CO2 concentration in the atmosphere. In addition, “Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse gases are the highest in history”. These emissions are mainly consequence of the burning of C-fuels, mostly fossil fuels, which result in a net increase in carbon concentration in the atmosphere, soil and oceans. In fact, the natural carbon cycle in the earth is being affected. Limiting climate change would require substantial and sustained reductions in greenhouse gas emissions. The measures considered for the reduction of CO2 emissions to the atmosphere include the improvement in the use and generation of energy, the use of nuclear energy, the boost of energy generation from renewable sources and the CO2 capture and storage (CCS).This work was supported by the Spanish Ministry of Economy, Industry and Competitiveness (projects ENE2014-56857-R, ENE2016-77982-R, and ENE2017-89473-R), by the European Regional Development Fund (ERDF), by the CSIC (201780E035), and by the Government of Aragón. T. Mendiara thanks for the “Ramón y Cajal” post-doctoral contract awarded by MINEICO

Effect of H2S on the behaviour of an impregnated NiO-based oxygen-carrier for chemical-looping combustion (CLC)

16 figures, 4 tablesGaseous fuels for chemical-looping combustion (CLC) process can contain sulphurcompounds which can affect the oxygen-carrier behaviour, especially if NiO is used as active phase. In this work several samples of a NiO-based oxygen-carrier prepared by impregnation, NiO18-Al, extracted from a CLC unit after continuous operation with CH4 containing 500 vppm of H2S were characterized. Part of the fed sulphur to the system was release as SO2 in the air-reactor during the CLC experiments while the rest remained in the solid particles. Mainly Ni3S2 was found in the oxygen-carrier extracted from the fuel-reactor, although small amounts of NiSO4 were also detected. On the contrary, NiSO4 was the main sulphur compound in the oxygen-carrier from the airreactor and only a low concentration of Ni3S2 was found. Despite the accumulated sulphur and the oxygen transport capacity loss during the operation, the oxygen-carrier was capable of recovering the initial reactivity for the CH4 combustion after a time without H2S feeding to the CLC system. In addition, a study about the possible regeneration of the oxygen-carrier in the air-reactor working at different temperatures and oxygen concentrations was performed. Independently of the operating conditions, *Manuscript Click here to view linked References 2 part of the sulphur remained in the solid and total regeneration was not possible. The analysis of the NiO18-Al oxygen-carrier after the CLC operation using TPR and XPS techniques revealed that sulphur reacted preferably with free NiO instead of NiAl2O4. Although Ni3S2 was the majority sulphide in the fuel-reactor, minor amounts of other sulphides such as NiS were detected. It also was found that sulphur was preferably concentrated in the outer surface of the particles. Taking into account all the results found, a previous desulphuration process of the fuel would be necessary when using NiO-based oxygen-carriers in the CLC system.This research was conducted with financial support from the European Commission, under the Sixth Framework Program, Contract no. 019800-CLC GAS POWER, by the CCP2 (CO2 Capture Project), a partnership of BP, Chevron, Conoco-Phillips, Eni Technology, Norsk Hydro, Shell, Suncor and Petrobras. The authors thank I. Fernández, N. Fernández and E. Ayllón their help with the XPS and TPR analyses of the samples.Peer reviewe