Suchergebnisse

The use of mineral materials as oxygen carriers for Chemical Looping Combustion (CLC) is an attractive option due to their low cost. This paper reports an experimental study of four manganese minerals as potential oxygen carriers focusing on the behavior in CLC as well as in Chemical Looping with Oxygen Uncoupling (CLOU). Experiments were carried out in a thermogravimetric apparatus (TGA) and a fluidized-bed reactor. Repeated tests with all the minerals showed no sufficient CLOU properties. Then, they can only be used in CLC applications involving the redox pairs Mn3O4/MnO and Fe2O3/Fe3O4. Oxygen transport capacity and reactivity to the main fuel gases (H2, CO, and CH4) were determined in a TGA. Manganese minerals were also tested during 35–54 h in a fluidized-bed reactor to evaluate the evolution of reactivity to H2, CO, and CH4 as well as their attrition rate and mechanical strength. The reactivity of the materials decreased in the first 10 cycles with CH4 and then became quite stable for the rest of the cycles performed with CH4, CO, and H2. In comparison to previously tested Fe-based minerals, lower reactivity with CH4 was found for the manganese minerals. However, in terms of CO and H2 combustion, their reactivity was adequately high. During the tests, agglomeration and defluidization were never found for any material. Mechanical crushing strength of the particles decreased with cycles, which led to the increase of attrition rate of some materials above acceptable levels. Nevertheless, materials with adequate crushing strength and low attrition were identified. Combining the reactivity and attrition resistance, the manganese minerals MnSA and MnGBHNE from South Africa and Gabon, respectively, can be suggested as promising materials for CLC with coal. ; This work was supported by the Spanish Ministry of Economy and Competitiveness (project ENE 2013-45454-R), by the European Regional Development Fund (ERDF), by the CSIC (project 2014-80E101) and by the Government of Aragón (Spain, Ref. T06). T. Mendiara thanks for the ''Ramón y Cajal'' post-doctoral contract awarded by the Spanish Ministry of Economy and Competitiveness. D. Mei is grateful for the support provided by the China Scholarship Council (CSC201306160054). The authors also thank Hidro Nitro Española S.A. for providing MnSA and MnGBHNE materials and Leopoldo Alcázar (CT-GAS) for providing the MnBR material. ; Peer reviewed

The autothermal Chemical-Looping Reforming (a-CLR) is a process where syngas is produced with two main advantages; there are captured CO2 emissions and the heat required for the syngas production is generated by the process itself. A Ni-based material is used as oxygen carrier circulating between two fluidized bed reactors: the fuel and air reactors. In this work, the auto-thermal conditions in a global H2 production process, integrated by the a-CLR process and a Water Gas Shift reactor, using different liquid fossil fuels were theoretically determined. The hydrogen production per mol of carbon in the fuel was similar for all fossil fuels, taking a value of 2.2 at the optimal operating temperature (700 °C). In addition, the possibility of working at low temperature for a maximum H2 production was experimentally demonstrated in a continuous 1 kWth a-CLR unit. ; This work is partially supported by the Spanish Ministry for Science and Innovation (MICINN project ENE2011-26354), by European Regional Development Fund (ERDF) and by the Government of Aragón (Spain, DGA ref. T06). ; Peer reviewed

13 páginas,8 figuras.-Available online 12 August 2013 ; The chemical looping combustion of solid fuels by in situ gasification (i G-CLC) has great potential to reduce the economical and energetic cost of CO2 capture for generating energy from coal. Previous studies have highlighted that a high CO2 capture rate can be reached, but incomplete combustion is predicted by theoretical models or obtained during experimental work. In this paper, a mathematical model for the fuel reactor and carbon stripper, validated through experimental results, is adapted to evaluate the relevance of several technological improvements in order to increase the combustion efficiency of the iG-CLC process. The technological options evaluated include increasing the gas–solid contact in the fuel reactor, incorporating a secondary fuel reactor, re-circulating exhaust gases to the fuel reactor or the carbon stripper, or feeding coal into the carbon stripper instead in the fuel reactor. Model simulations showed that the use of a secondary fuel reactor has the major impact by reducing the unburnt compounds in the CO2 stream. The origin of the unburnt compounds is determined from a thorough analysis of the results obtained during the evaluation of these technological options. Thus, a new arrangement of the iG-CLC reactors is proposed, one which would minimise the presence of unburnt compounds. In this concept, exhaust gases from the fuel reactor are sent to the carbon stripper. The oxygen demand for this concept is predicted to be XT= 0.9%. 2013 Elsevier B.V. All rights reserved. ; This paper was partially supported by the European Commission, under the RFCS program (ACCLAIM Project, Contract RFCP-CT-2012-00006), the Government of Aragon and La Caixa (2012-GA-LC-076 project) and the Spanish Ministry for Science and Innovation via the ENE2010-19550 project. ; Peer reviewed

6 pages, 5 figures, 4 tables.--Published on Web 07/20/2007 ; Waste management generated from a Chemical-Looping Combustion (CLC) plant using copper-based materials is analyzed by two ways: the recovery and recycling of the used material and the disposal of the waste. A copper recovery process coupled to the CLC plant is proposed to avoid the loss of active material generated by elutriation from the system. Solid residues obtained from a 10 kWth CLC prototype operated during 100 h with a CUO-Al2O3 oxygen carrier prepared by impregnation were used as raw material in the recovery process. Recovering efficiencies of ∼80% were obtained in the process, where the final products were an eluate of Cu(NO3) 2 and a solid. The eluate was used for preparation of new oxygen carriers by impregnation, which exhibited high reactivity for reduction and oxidation reactions as well as adequate physical and chemical properties to be used in a CLC plant. The proposed recovery process largely decreases the amount of natural resources (Cu and Al2O3) employed in a CLC power plant as well as the waste generated in the process. To determine the stability of the different solid streams during deposition in a landfill, these were characterized with respect to their leaching behavior according to the European Union normative. The solid residue finally obtained in the CLC plant coupled to the recovery process (composed by Al2O3 and CuAl2O4) can be classified as a stable nonreactive hazardous waste acceptable at landfills for nonhazardous wastes. © 2007 American Chemical Society. ; This research was carried out with financial support from the Spanish Ministry of Education and Science (Projects PPQ-2001-2111, CTQ-2004-04034) and from the Diputación General de Aragón (Project PIP023/2005). C.R.F. thanks UNIZAR-BSCH for the predoctoral fellowship. ; Peer Reviewed

CO2 emissions to the atmosphere became an important environmental problem because of the effect on the global warming and consequently, the climate change. The climate change challenge demands a commitment of combined strategies between global institutions, governments and citizens. To reach the objectives set in the Paris Agreement (2015), greenhouse gas emissions need to be reduced. No technology is currently able to achieve the necessary reductions in greenhouse gas emissions on its own. Biomass represents an interesting alternative fuel for heat and power production as a carbon dioxide-neutral fuel. Moreover, if the CO2 generated during biomass combustion process is captured then negative-CO2 emissions would be reached and these are named bioenergy with Carbon Capture and Storage (BECCS) technologies. Chemical Looping Combustion (CLC) came up as one of the most promising CO2 capture technologies thanks to the low energy penalty of the CO2 separation and therefore, low-cost. CLC technologies are based in two interconnected fluidized bed reactors without gas mixing. The combustion takes place in the fuel reactor where the oxygen is supplied by a solid oxygen carrier, normally metal oxides. After being reduced, the oxygen carrier goes to the air reactor without gas mixing between reactors where it is oxidized again in air, and it is able for a new redox cycle starts. The main objective of this thesis is to evaluate the biomass combustion with CLC technologies (bioCLC). The research plan covers studies different at different scales, starting at lab scale, through a 1 kWth pilot plant, to the continuous operation in a 20 kWth plant to demonstrate the viability and optimizing the operation range for different low-cost oxygen carriers and different types of biomass residues. Iron based ores as well as manganese ores has been pointed as promising oxygen carriers because of their reactivity and low cost. Under In Situ Gasification Chemical Looping Combustion (iG-CLC) mode, the performance of the process was studied ...

8 pages, 2 figures, 2 tbles.-Available online 3 July 2013 ; The Chemical Looping with Oxygen Uncoupling (CLOU) process is a type of Chemical Looping Combustion (CLC) technology that allows the combustion of solid fuels with air, as with conventional combustion, through the use of oxygen carriers that release gaseous oxygen inside the fuel reactor. The aim of this work was to study the behaviour of the sulphur present in fuel during CLOU combustion. Experiments using lignite as fuel were carried out in a continuously operated 1.5kWth CLOU unit during more than 15h. Particles containing 60wt.% CuO on MgAl2O4, prepared by spray drying, were used as the oxygen carrier in the CLOU process. The temperature in the fuel reactor varied between 900 and 935°C. CO2 capture, combustion efficiency and the sulphur split between fuel and air reactor streams in the process were analysed. Complete combustion of the fuel to CO2 and H2O was found in all experiments. Most of the sulphur introduced with the fuel exited as SO2 at the fuel reactor outlet, although a small amount of SO2 was measured at the air reactor outlet. The SO2 concentration in the air reactor exit flow decreased as the temperature in the fuel reactor increased. A carbon capture efficiency of 97.6% was achieved at 935°C, with 87.9wt.% of the total sulphur exiting as SO2 in the fuel reactor. Both the reactivity and oxygen transport capacity of the oxygen carrier were unaffected during operation with a high sulphur content fuel, and agglomeration problems did not occur. Predictions were calculated regarding the use of a carbon separation system in the CLOU process in order to reduce sulphur emissions. Coals with high sulphur content, such as lignite and anthracite, would require a carbon separation system in order to comply with legislation governing sulphur-limits. In conclusion, coals with a high sulphur content can be burnt in a CLOU process using Cu-based material to obtain high carbon capture efficiencies. © 2013 Elsevier Ltd. ; This work was carried out with financial support from the European Commission, under the RFCS programme (ECLAIR Project, Contract RFCP-CT-2008-0008), ALSTOM Power Boilers (France), the Spanish Ministry of Science and Innovation (PN, ENE2010- 19550), and Government of Aragón and La Caixa (Project 2012- GA-LC-076). I. Adánez-Rubio thanks CSIC for the JAE fellowship co-financed by the European Social Fund. ; Peer Reviewed

Chemical-Looping with Oxygen Uncoupling (CLOU) is an alternative Chemical Looping process for the combustion of solid fuels with inherent CO2 capture. The CLOU process needs a material as oxygen carrier with the ability to give gaseous O2 at suitable temperatures for solid fuel combustion, e.g. copper oxide and manganese oxide. In this work, treated commercial Carulite 300® was evaluated as oxygen carrier for CLOU. Carulite 300® is a hopcalite material composed of 29.2 wt.% CuO and 67.4 wt.% Mn2O3. Oxygen release rate and the fluidization behavior, regarding agglomeration and attrition rate, were analyzed in a TGA and in a batch fluidized bed respectively. Experiments in a batch fluidized bed reactor were carried out at temperatures ranging from 800 to 930 ºC with a medium volatile bituminous coal from South Africa and its char as fuels. The hopcalite derived oxygen carrier showed high O2 release rate, no unburnt products at low oxygen carrier to fuel mass ratios and very high oxygen transference rate by gas-solid reaction. This material has the capacity to generate gaseous oxygen at lower temperatures than Cu-based oxygen carriers, which suggest this material is suitable to work at lower temperatures in the fuel reactor without the presence of unburnt products; however its low mechanical resistance after redox cycles makes necessary an improvement of its physical properties for being use as an oxygen carrier. ; This work was partially supported by the Spanish Ministry of Economy and Competitiveness (MINECO Project: ENE2013- 45454-R) and the European Union FEDER funds. Special thanks to Carus Corporation (Illinois, EEUU) for suppling the Carulite 300 material. ; Peer reviewed