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Fonts I.,Centro Universitario Of La Defensa Of Zaragoza | Fonts I.,Aragon Institute of Engineering Research | Gea G.,Aragon Institute of Engineering Research | Azuara M.,Aragon Institute of Engineering Research | And 2 more authors.
Renewable and Sustainable Energy Reviews | Year: 2012

The high output of sewage sludge, which is increasing during recent years, and the limitations of the existing means of disposing sewage sludge highlight the need to find alternative routes to manage this waste. Biomass and residues like sewage sludge are the only renewable energy sources that can provide C and H, thus it is interesting to process them by means of treatments that enable to obtain chemically valuable products like fuels and not only heat and power; pyrolysis can be one of these treatments. The main objective of this review is to provide an account of the state of the art of sewage sludge pyrolysis for liquid production, which is under study during recent years. This process yields around 50 wt% (daf) of liquid. Typically, this liquid is heterogeneous and it usually separates into two or three phases. Some of these organic phases have very high gross heating values, even similar to those of petroleum-based fuels. The only industrial sewage sludge pyrolysis plant operated to date is currently closed due to some technical challenges and problems of economic viability. © 2012 Elsevier Ltd. All rights reserved.

Fernandez J.R.,CSIC - National Coal Institute | Abanades J.C.,CSIC - National Coal Institute | Murillo R.,CSIC - Institute of Carbochemistry
Applied Energy | Year: 2014

A dynamic model was developed to describe the oxidation of Cu in a large-scale Cu/CuO chemical looping process performed in adiabatic fixed-bed reactors at high pressure. An ideal plug flow pattern without axial dispersion or radial gradients and with negligible intra-particle concentrations and temperature gradients on the scale of millimeters were assumed. Cu oxidation is favoured at high pressure and therefore fast reaction rates and total oxygen conversion were achieved, even with low contents of oxygen in the feed (around 4-6%). Short breakthrough periods were achieved, which is highly favorable in operations carried out in alternative fixed-bed reactors. In order to maximize energy efficiency, the oxidation needs to be carried out at the highest allowable temperature, but CuO tends to decompose and agglomerate at relatively low temperatures (over 1223K). Also the high exothermicity of Cu oxidation can generate hot spots in the reaction front. The use of a large recycle of nitrogen (previously cooled down) so that it mixes with regulates the temperature in the reaction front. At these conditions, the gas-solid heat exchange front advances faster than the reaction front and the oxidized bed is finally left at a lower temperature (as the cooled N2 recycle), which is insufficient to initiate the subsequent reduction of CuO to Cu. Therefore, an additional stage is introduced to carry out a gas-solid heat exchange between the hot N2 rich recycled gas and the oxidized bed. The bed is then ready for the next reaction step that involves the exothermic reduction of CuO. Operating parameters, such as the recirculation ratio (content of O2 in the feed) and the proportion of Cu in the solid bed, which have a substantial effect on Cu oxidation and CO2 capture efficiency, were also evaluated. Recirculation ratios higher than 0.75 and inlet gas temperatures of around 423K limit the maximum temperature to reasonable values (generally below 1200K). A trade-off between the O2 content in the feed (4-6%) and the amount of Cu in the bed (20-33%) leads to high energy efficiencies in CLC processes and minimal CaCO3 calcination in the case of the Ca-Cu looping process. © 2013 Elsevier Ltd.

Alonso M.,CSIC - National Coal Institute | Criado Y.A.,CSIC - National Coal Institute | Abanades J.C.,CSIC - National Coal Institute | Grasa G.,CSIC - Institute of Carbochemistry
Fuel | Year: 2014

Calcium looping CO2 capture systems use CaO as a reversible sorbent of CO2. Therefore, the evolution of the CO2 carrying capacity of CaO-materials at increasing number of carbonation- calcination needs to be determined to assess sorbent performance. Thermogravimetric analyzers (TGA) are commonly used for this purpose, by simulating around a small batch of material the average cyclic conditions expected in the real system. Many variables have been reported to influence the results and we review in this paper the main observations and trends, which can at times be conflicting when diffusional effects are not ruled out from the experiments. Furthermore, in a selected number of tests on a typical limestone using four different TG equipment, we have detected that some design characteristics of the TGA apparatus can strongly affect the determination of the CO2 carrying capacities of the material. In particular, we note that the decay in CO2 carrying capacity is accelerated as the power density of the TGA oven increases. This effect is most pronounced in the first calcination cycle, and it seems to be linked to an additional shrinking of the particles taking place in the TG apparatus with the highest heating rates. The use of larger sample masses and/or larger particle sizes tends to reduce the error in the determination of CO2 carrying capacity curves at the expense of departing from differential conditions that are required to obtain kinetic information on the sample. ©2013 Elsevier Ltd. All rights reserved.

Arias B.,CSIC - National Coal Institute | Grasa G.S.,CSIC - Institute of Carbochemistry | Alonso M.,CSIC - National Coal Institute | Abanades J.C.,CSIC - National Coal Institute
Energy and Environmental Science | Year: 2012

This paper presents a novel sorbent regeneration technique for post-combustion calcium looping CO2 capture systems. The advantage of this technique is that it can drastically reduce the consumption of limestone in the plant without affecting its efficiency and without the need for additional reagents. The method is based on the re-carbonation of carbonated particles circulating from the carbonator using pure CO2 obtained from the gas stream generated in the calciner. The aim is to maintain the CO2 carrying capacity of the sorbent close to optimum values for CaL post-combustion systems (around 0.2). This is achieved by placing a small regeneration reactor between the carbonator and the calciner. This reactor increases slightly the conversion of CaO to carbonate so that it exceeds the so-called maximum CO2 carrying capacity of the sorbent. This increase compensates for the loss of CO2 carrying capacity that the solids undergo in the next calcination-carbonation cycle. Two series of experiments carried out in a thermogravimetric analyzer over 100 cycles of carbonation-recarbonation-calcination show that the inclusion of this recarbonation step is responsible for an increase in the residual CO2 carrying capacity from 0.07 to 0.16. A conceptual design of the resulting capture system shows that a limestone make-up flow designed specifically for a CO2 capture system can approach zero, when the solid sorbents purged from the CaL system are re-used to desulfurize the flue gas in the existing power plant. This journal is © 2012 The Royal Society of Chemistry.

Fernandez J.R.,CSIC - National Coal Institute | Abanades J.C.,CSIC - National Coal Institute | Murillo R.,CSIC - Institute of Carbochemistry | Grasa G.,CSIC - Institute of Carbochemistry
International Journal of Greenhouse Gas Control | Year: 2012

This work presents a conceptual design of a novel method to obtain hydrogen and/or electricity from natural gas and a concentrated stream of CO 2 suitable for permanent geological storage. The method is based on the well known Sorption Enhanced Reforming (SER) principles for H 2 production using a CaO/CaCO 3 chemical loop. A second chemical loop of Cu/CuO is employed to solve the problem of endothermic CaCO 3 calcination in order to regenerate the sorbent and release the concentrated CO 2. The reduction reaction of CuO with natural gas, CO or H 2 is shown to be feasible for providing the necessary heat for calcination. A preliminary design of the process has been carried out based on the principles of fixed bed operation and high temperature PSA, making use of the information offered by the literature to define the operating best conditions for the key gas-solid reaction steps and assuming ideal plug flow behaviour in all the reactors during the chemical reactions and gas-solid heat transfer. This makes it possible to define the precise operating windows for the process, so that the reactors can operate close to neutrally thermal conditions. Special material properties (particularly the Ca/inert and Cu/inert ratios) are required, but these are shown to be within the limits of what have been reported in the literature for other gas/solid reaction processes using the same reactions. The conclusion is that there is a great potential for achieving a high degree of energy efficiency with the proposed process by means of a sequence of reactions under the conditions described in this work. © 2011 Elsevier Ltd.

Arias B.,CSIC - National Coal Institute | Grasa G.S.,CSIC - Institute of Carbochemistry | Abanades J.C.,CSIC - National Coal Institute
Chemical Engineering Journal | Year: 2010

It is well known that the solid sorbents used in calcium looping CO2 capture systems experience a reduction in carrying capacity with the number of cycles. Several sorbent reactivation schemes have been proposed as means of overcoming this deactivation process. This work analyzes the integration of a reactivation process in a Ca-looping cycle by means of a hydration reactor. The mass balances involved in this three-reactor systems must then be solved in order to evaluate the effect of the different variables on the average activity of the sorbent. The positive impact of reactivation by hydration (i.e. average increase in activity of the sorbent arriving at the carbonator) is discussed in conjunction with the negative impacts on the overall operation of the system (e.g. steam consumption, etc.) and on the large reactivation reactors. Two different scenarios employing different degrees of hydration have been evaluated. The results obtained show that steam is used more efficiently when only a small fraction of the circulating solids is hydrated to a high degree. Moreover, the performance of the sorbent reactivation step is better when low make up flows of limestone are used. © 2010 Elsevier B.V.

Anson-Casaos A.,CSIC - Institute of Carbochemistry | Gonzalez-Dominguez J.M.,CSIC - Institute of Carbochemistry | Martinez M.T.,CSIC - Institute of Carbochemistry
Carbon | Year: 2010

Electric arc single-walled carbon nanotubes (SWCNTs) can be separated from their graphitic impurities by a single centrifugation process in a surfactant or in polymer solutions. The purity of SWCNT dispersions, evaluated from near infrared (NIR) spectroscopy measurements, substantially increased after centrifugation at a moderate speed. The supernatant NIR purity was affected by the surfactant choice, following the sequence: sodium cholate ∼ Pluronic F68 > sodium dodecylbenzene sulfonate > Pluronic F127 > sodium dodecyl sulfate. NIR purity was also influenced by the centrifugation speed and the pristine SWCNT concentration in the starting dispersion, but not by the surfactant concentration. SWCNT enrichment was not observed in a pure organic solvent (N,N′-dimethylformamide) under identical centrifugation conditions. X-ray diffraction analysis demonstrated that graphitic impurities were mostly eliminated from SWCNTs during the centrifugation process in a surfactant or in polymer solutions. Thermogravimetric analysis under CO 2 showed that metallic impurities were substantially reduced during the centrifugation process. © 2010 Elsevier Ltd. All rights reserved.

Cano M.,CSIC - Institute of Carbochemistry | Benito A.,CSIC - Institute of Carbochemistry | Maser W.K.,CSIC - Institute of Carbochemistry | Urriolabeitia E.P.,ICMA CSIC UZ
Carbon | Year: 2011

A fast and easy one-step linker-free approach for the synthesis of palladium nanoparticle/multiwall carbon nanotube (Pd-NP/MWCNT) hybrid materials is described using microwave irradiation for the effective decomposition of Pd 2dba 3 complex in the presence of MWCNTs. High loadings of Pd nanoparticles (up to 40 wt.%) having sizes between 3 and 5 nm are deposited on the surface of MWCNTs within a time of only 2 min. The Pd-NP/MWCNT materials serve as efficient catalysts in C-C coupling as well as in hydrogenation reactions, all characterized by high conversion rates using a small amount of catalysts, high turnover frequency values and good recyclability. © 2010 Elsevier Ltd. All rights reserved.

Martinez De Yuso A.,San Jorge University | Rubio B.,CSIC - Institute of Carbochemistry | Izquierdo M.T.,CSIC - Institute of Carbochemistry
Fuel Processing Technology | Year: 2014

The aim of this work was to compare the effect of different activating atmospheres on the final properties and adsorption performance of activated carbons. Almond shell based activated carbons have been obtained by chemical activation with phosphoric acid. Two sets of activated carbons were prepared. First set was prepared under inert atmosphere at different impregnation ratios, temperatures and times of activation. Second set of activated carbons was prepared at the same activating conditions except the activating atmosphere using an oxidant one. Activated carbons prepared under both activation atmospheres were characterized by elemental analysis (EA), thermogravimetry (TGA), temperature programmed desorption (TPD), point zero charge (PZC), Boehm titration and N2 physisorption. To study the adsorption performance of the activated carbons toluene adsorption-desorption isotherms were determined gravimetrically. The results obtained confirm that the activating atmosphere has a strong influence on the final characteristics of the activated carbons. Activated carbons with higher oxygen content and more negative surface charge have been obtained by changing the activating atmosphere by an oxidant one. Surface area is also higher for activated carbons prepared under oxidant atmosphere. However toluene adsorption capacity is lower for activated carbons prepared under oxidant atmosphere due to their surface chemistry. © 2013 Elsevier B.V.

Mayoral M.C.,CSIC - Institute of Carbochemistry | Andres J.M.,CSIC - Institute of Carbochemistry | Gimeno M.P.,CSIC - Institute of Carbochemistry
Fuel | Year: 2013

Mineral carbonation is one of the alternatives considered for CO 2 sequestration. This consists of inducing the artificial weathering of alkaline minerals to produce stable carbonate solids. This work presents the wet carbonation of lime-rich ashes from the fluidized bed combustion of two different fuels: a Spanish sulfur-rich lignite, with calcium carbonate and quartz as main mineral constituents, and the waste produced during the extraction of the coal. The novelty of the work is its experimental approach, which explores all the variables (pH, temperature, time, liquid to solid ratio, NaCl ratio) from a statistical survey centered on finding optimized conditions that maximize the degree of carbonation. CO2 uptake is determined by direct thermogravimetric tests. The results indicate that high carbonation efficiency (78% efficiency) is achieved for both solids at basic pH and moderate treatment times. Those conditions cause anhydrite to dissolve, increasing the availability of Ca2+ for reprecipitation as carbonate and hydroxide. At neutral pH, 72% conversion efficiency is equivalent to a capture of 8% of the CO2 theoretically emitted in the combustion of coal wastes. The proposed conditions for fly ash carbonation enables rapid CO2 capture that is applicable for upscaling and industrial use. © 2012 Elsevier Ltd. All rights reserved.

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