[Show abstract][Hide abstract] ABSTRACT: The high carbon contents and low toxicity levels of chars from coal and pine gasification provide an incentive to consider their use as precursors of porous carbons obtained by chemical activation with K2CO3. Given the chars characteristics, previous demineralization and thermal treatments were made, but no improvement on the solids properties was observed. The highest porosity development was obtained with the biomass derived char (Pi). This char sample produced porous materials with preparation yields near 50% along with high porosity development (ABET≈1500m(2)g(-1)). For calcinations at 800°C, the control of the experimental conditions allowed the preparation of samples with a micropore system formed almost exclusively by larger micropores. A mesopore network was developed only for samples calcined at 900°C. Kinetic and equilibrium acetaminophen and caffeine adsorption data, showed that the processes obey to a pseudo-second order kinetic equation and to the Langmuir model, respectively. The results of sample Pi/1:3/800/2 outperformed those of the commercial carbons. Acetaminophen adsorption process was ruled by the micropore size distribution of the carbons. The caffeine monolayer capacities suggest a very efficient packing of this molecule in samples presenting monomodal micropore size distribution. The surface chemistry seems to be the determinant factor that controls the affinity of caffeine towards the carbons.
Journal of Colloid and Interface Science 07/2014; 433C:94-103. DOI:10.1016/j.jcis.2014.06.043 · 3.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fly ash, a residue produced from pine gasification, was used as precursor of carbon-based materials assayed in acetaminophen adsorption. Materials prepared by activation with K2CO3, presented high porosity development (ABET ≈ 1200 m2 g−1) and samples calcined at 900 °C presented high volumes of large micropores and mesopores. Kinetic and equilibrium acetaminophen adsorption data showed that the process obeys to the pseudo-second order kinetic equation and Langmuir model, respectively. The rate of acetaminophen adsorption depends of the presence of larger micropores. For the lab-made samples monolayer adsorption capacities attained values similar to those of commercial carbons. The influence of the micropore size distribution of the carbons in the acetaminophen adsorption process justified the lower adsorption affinities of the lab-made carbons. The importance of pores of a specific dimension (0.7 nm) to enhance the affinity of the molecule towards the carbon surface was demonstrated. The increase of temperature lead to higher monolayer adsorption capacities, most likely due to the easier accessibility of the acetaminophen species to the narrowest micropores.
Chemical Engineering Journal 03/2014; 240:344–351. DOI:10.1016/j.cej.2013.11.067 · 4.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A thermodynamic model was applied to foresee the occurrence of fouling, slagging, and bed agglomeration
phenomena during fluidized bed monocombustion of three different types of biomass, namely straw pellets, olive cake, and wood pellets. The cocombustion effect in reducing the occurrence of deposits and agglomerates of blends of 5, 15, and 25% (wt.) biomass with coal was also assessed. Chemical fractionation was applied to evaluate the reactive and nonreactive fraction of elements in the fuels, which was used to estimate their partition between the freeboard and bottom zone of the boiler. Qualitative and semiquantitative analytical techniques, namely, X-ray diffraction and scanning electronic microscopy − energy dispersive spectroscopy were used to compare the results from the simulation with the mineralogical and morphological composition of ash and deposits formed during combustion. The thermodynamic modeling revealed to be a powerful tool in foreseeing the formation of melt and liquids salts, depending on the temperature and chemical composition of fuels. The main discrepancies observed between the experimental and simulated data were due to particularities of the combustion process, which are not incorporated in the software, namely, kinetic limitations of the reactions, possible occurrence of secondary reactions in the ashes, and elutriation effects of ash and silica sand particles.
Energy & Fuels 01/2014; 28(1):697-713. DOI:10.1021/ef4018114 · 2.79 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The main objective of this work was to predict the influence of experimental conditions on product yields formed by waste mixtures pyrolysis, using response surface methodology (RSM). Accurate prediction of liquid yields at different experimental conditions and pyrolysis optimisation was achieved. The waste mixture studied contained 10% of pine, 10% of scrap tyres and 80% recycled plastic, whose main components were polyethylene (PE), polypropylene (PP) and polystyrene (PS). Experiment Factorial Design was used for the optimisation of reaction time, temperature and initial pressure to maximise the yield and composition of liquid products for the waste mixture studied. Experimental yields of liquids were fitted with a linear and second order model by the method of least squares with good correlation and high statistical significance. According to the model, the production of total pyrolysis liquids (including those obtained by solvent extraction) was maximised when the following conditions were used: reaction temperature of 350 degrees C, reaction time of 30 min and initial pressure of 0.2 MPa, leading to liquid yield of 91.3% (w/w). The yield of only decanted liquids (not considering those obtained by solvent extraction) was maximised to the value of 54.9% at 426 degrees C, 28 min and 0.2 MPa. The total liquid production at these conditions was 79.1%. The results obtained also showed that the approach used may be suitable for optimizing the experimental conditions that favour the formation of chosen gaseous and liquid compounds.
[Show abstract][Hide abstract] ABSTRACT: The behavior of Cynara cardunculus L. was studied during fluidized-bed (FB) combustion and gasification. The Cynara had a low moisture content and considerable lower heating value (LHV). Cynara presented significant quantities of S, Cl, and ash, which contained high levels of Na, K, P, Ca, and Si. The fuel N conversion to NO x was high because of the large release of NH 3 and HCN during pyrolysis. The conversion of the fuel S to SO 2 was low because of S retention mainly as alkali sulfates. HCl emissions were higher than the usual legal limits imposed in European Union (EU) countries, although retentions of 40− 55% fuel Cl could be estimated. The co-combustion of Cynara with eucalyptus was tested with benefits regarding process conditions, pollutant emissions, and ash behavior, but still, the HCl concentration surpassed the legal limit. The tendency for bed agglomeration was also observed during the gasification of cardoon. Two strategies were carried out to minimize this adverse effect: (1) co-gasification of cardoon with eucalyptus and (2) addition of natural minerals to the gasification bed. The results of the first strategy caused a decrease in H 2 levels, while tar, hydrocarbon, and CO amounts were found to increase. On the other hand, the addition of natural minerals did not lead to any significant change in the major gas components, although some tar and hydrocarbon abatements were observed, with olivine being the most effective. Dolomite and ZnO gave rise to a greater reduction in HCl and sulfur compounds in the gas phase, respectively.
Energy & Fuels 11/2013; 27(11):6725-6737. DOI:10.1021/ef401246p · 2.79 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The study performed aimed at analysing possible routes for pyrolysis reaction mechanisms of polymeric materials namely RI (rubber tyre) and plastic wastes (PE (polyethylene), PP (polypropylene) and PS (polystyrene)). Consequently, and seeking sustainable transformation of waste streams into valuable chemicals and renewable liquid fuels, mixture of 30% RI, 20% PE, 30% PP and 20% PS was subjected to pyrolysis. Different kinetic models were studied using experimental data. None of the mechanisms found in literature led to a numerical adjustment and different pathways were investigated. Kinetic studies were performed aiming to evaluate direct conversions into new solid, liquid and gaseous products and if parallel reactions and/or reversible elementary steps should be included. Experiments were performed in batch system at different temperatures and reaction times. Kinetic models were evaluated and reaction pathways were proposed. Models reasonably fit experimental data, allow explaining wastes thermal degradation. Kinetic parameters were estimated for all temperatures and dependence of Ea and pre-exponential factor on temperature was evaluated. The rate constant of some reactions exhibited nonlinear temperature dependence on the logarithmic form of Arrhenius law. This fact strongly suggests that temperature has a significant effect on reaction mechanism of pyrolysis of mixtures of rubber tyre and plastic wastes. Published by Elsevier Ltd.
Energy 09/2013; 58:270-282. DOI:10.1016/j.energy.2013.06.033 · 4.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: It was found a strong correlation between PCDD/F
formation and the sulphur and chlorine content. Our results point to
an interesting empirical model which should be further tested with
more experimental data.
Additionally, the attained mathematical model can be used to adjust
fuel mixtures with appropriate sulphur and chlorine input in order to
maintain PCDD/F emissions below the legal limits.
1st International Congree on Bioenergy Portugal; 05/2013
[Show abstract][Hide abstract] ABSTRACT: The main objective of rapeseed oil hydrogenation tests was the production of liquid bio-chemicals to be used as renewable raw material for the production of several chemicals and in chemical synthesis to substitute petroleum derived stuff. As, hydrogenation of vegetable oils is already applied for the production of biofuels, the work done focused in producing aromatic compounds, due to their economic value. The effect of experimental conditions on rapeseed oil hydrogenation was studied, namely, reaction temperature and time with the aim of selecting the most favourable conditions to convert rapeseed oil into liquid valuable bio-chemicals. Rapeseed oil was hydrogenated at a hydrogen initial pressure of 1.10 MPa. Reaction temperature varied in the range from 200 degrees C to 400 degrees C, while reaction times between 6 and 180 min were tested. The performance of a commercial cobalt and molybdenum catalyst was also studied. The highest hydrocarbons yields were obtained at the highest temperature and reaction times tested. At a temperature of 400 degrees C and at the reaction time of 120 min hydrocarbons yield was about 92% in catalyst presence, while in the absence of the catalyst this value decreased to 85%. Hydrocarbons yield was even higher when the reaction time of 180 min was used in the presence of catalyst, as the yield of 97% was observed. At these conditions hydrocarbons formed had a high content of aromatic compounds, around 50%. For this reason, the viscosity values of hydrogenated oils were lower than that established by EN590, which together with hydrogenated liquids composition prevented its use as direct liquid fuel to substitute fossil gas oil for transport sector. However, hydrocarbons analysis showed the presence of several valuable compounds that encourages their use as a raw material for the production of several chemicals and in chemical synthesis. (c) 2012 Elsevier Ltd. All rights reserved.
Applied Energy 02/2013; 102:272-282. DOI:10.1016/j.apenergy.2012.04.008 · 5.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The purpose of the present study was the analysis of possible routes for the pyrolysis reaction mechanism of rubber tyre wastes (RT). For this purpose, an evaluation was performed integrating both experimental data and different kinetic models. As none of the mechanisms found in literature allowed the numerical adjustment to the experimental data, new pathways were tested. Rubber tyre wastes kinetic studies were performed in order to evaluate possible direct conversions into new products (solids, liquids and gaseous), parallel reactions and/or reversible elementary steps. All experiments were carried out in a microautoclave system and based on the results obtained, at different temperatures and reactions times, kinetics models were evaluated and reactions pathways were established. Furthermore, products composition were analysed and according to the experimental data different reaction mechanisms were proposed. Afterwards, the kinetic data was compared with the experimental data. The proposed models were found to fit with the experimental data, which has allowed several explanations for the thermal degradation of rubber tyre waste to be proposed. Kinetics parameters were estimated, the dependence of activation energy and pre-exponential factor on temperature were evaluated. It was found that the rate constant of a number of reactions exhibited nonlinear temperature dependence on the logarithmic form of Arrhenius law, which strongly suggest that reaction temperature has an effect on reaction mechanism of rubber tyre wastes pyrolysis.
[Show abstract][Hide abstract] ABSTRACT: Hydrogen separation from a syngas mixture with different compositions was studied by using a Pd–Ag membrane. The effect of temperature (from 300 °C to 600 °C) and of relative pressure (from 0.2 MPa to 0.5 MPa) was studied. In general, rises of both these parameters allowed increasing H2 permeate flux. The Pd–Ag membrane showed to have a great selectivity, as when inlet gas mixture contained different compositions of CO2, CO or CH4, these gases were never detected in membrane permeate side. However, when hydrogen content in inlet gas decreased, a significant reduction in H2 permeate flux was observed, especially when CO was present, probably due to the deposition of solid carbon in membrane surface by Boudouard reaction. It was also observed the formation of hydrocarbons, due to CO and H2 reactions. H2 permeances were calculated by application of Sieverts’ law and values between 4.9 × 10−4 and 1.5 × 10−3 mol m−2 s−1 Pa−0.5 were obtained. The highest value was obtained at 600 °C. H2 permeances at different temperature followed Arrhenius’ equation. Thus, activation energies values between 11.5 kJ mol−1 and 14.0 kJ mol−1 were calculated.
[Show abstract][Hide abstract] ABSTRACT: The release of H2S and NH3 into syngas during co-gasification of two coals (German and Polish) mixed with wastes (pine, olive bagasse and polyethylene) was studied. Sulphur and nitrogen contents in feedstock were found to have a great influence on H2S and NH3 concentrations in syngas, as the highest contents of these elements led to the highest releases. Air/steam or oxygen/steam mixtures were used in the gasification medium, keeping constant experimental conditions, including equivalent ratio. However, when air was added instead of oxygen, higher flow rates were used, due to the introduction of nitrogen and thus lower residence times were used. Different H2S and NH3 contents were obtained by changing the gasification medium. In presence of oxygen and steam higher H2S contents and lower NH3 concentrations were obtained than those produced in presence of air and steam. However, after syngas hot treatment in two fixed bed reactors, the first one with dolomite and the second one with a Ni-based catalyst (G-90 B 5) these differences lost significance. On the other hand, different final compositions of H2S and NH3 were obtained for different feedstocks. Those with highest sulphur and nitrogen contents led to the highest final H2S and NH3 contents in syngas.
[Show abstract][Hide abstract] ABSTRACT: Mass balances of ash and potassium for a fluidized bed combustor were performed incorporating measurement uncertainties. The total output mass of ash or a chemical element should be equal to the mass in the input fuel; however, this is not often achieved. A realistic estimation of recovery uncertainty can support the reliability of a mass balance. Estimation of uncertainty helps to establish a reliable evaluation of the recovery ratio of ash mass and elemental mass. This may clarify whether any apparent lack in closing the mass balance can be attributed to uncertainties. The evaluation of measurement uncertainty for different matrices, namely coal, biomass, sand and ashes from different streams was based on internal quality control data and external quality control data, namely analysis of samples from proficiency tests or use of a certified reference material. The evaluation of intermediate precision and trueness allowed the estimation of measurement uncertainty. Due to the different physic and chemical characteristics of the studied matrices, the uncertainty of precision was evaluated using R-charts of data obtained from the analysis of duplicates for the majority of samples. This allowed evaluating sample heterogeneity effects. The instrumental acceptance criterion was also considered and included in the combined uncertainty. The trueness was evaluated using data from several proficiency tests and from analysis of a certified reference material or sample spiking. Statistically significant bias was included.
[Show abstract][Hide abstract] ABSTRACT: Over the last decades, several indices based on ash chemistry and ash fusibility have been used to predict the ash behaviour during coal combustion, namely, its tendency for slagging and fouling. However, due to the physical–chemical differences between coals and biomass, in this work only the applicability of an ash fusibility index (AFI) to the combustion and co-combustion of three types of biomass (straw pellets, olive cake and wood pellets) with coals was evaluated. The AFI values were compared with the behaviour of ash during combustion in a pilot fluidized bed and a close agreement was observed between them. For a better understanding of the mechanisms associated with bed ash sintering, they were evaluated by SEM/EDS and the elements present on the melted ash were identified. Evidences of different sintering mechanisms were found out for the fruit biomass and herbaceous biomass tested, depending on the relative proportions of problematic elements. The particles deposited on a fouling probe inserted in the FBC were analyzed by XRD and the differences between the compounds identified allowed concluding that the studied biomasses present different tendencies for fouling. Identification of KCl and K2SO4 in the deposits confirmed the higher tendency for fouling of fruit biomass tested rather than wood pellets.
Biomass and Bioenergy 04/2012; 39:192–203. DOI:10.1016/j.biombioe.2012.01.010 · 3.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper presents the study of the combustion of char residues produced during co-gasification of coal with pine with the aim of characterizing them for their potential use for energy. These residues are generally rich in carbon with the presence of other elements, with particular concern for heavy metals and pollutant precursors, depending on the original fuel used. The evaluation of environmental toxicity of the char residues was performed through application of different leaching tests (EN12457-2, US EPA-1311 TCLP and EA NEN 7371:2004). The results showed that the residues present quite low toxicity for some of pollutants. However, depending on the fuel used, possible presence of other pollutants may bring environmental risks. The utilization of these char residues for energy was in this study evaluated, by burning them as a first step pre-treatment prior to landfilling. The thermo-gravimetric analysis and ash fusibility studies revealed an adequate thermochemical behavior, without presenting any major operational risks. Fluidized bed combustion was applied to char residues. Above 700°C, very high carbon conversion ratios were obtained and it seemed that the thermal oxidation of char residues was easier than that of the coals. It was found that the char tendency for releasing SO(2) during its oxidation was lower than for the parent coal, while for NO(X) emissions, the trend was observed to increase NO(X) formation. However, for both pollutants the same control techniques might be applied during char combustion, as for coal. Furthermore, the leachability of ashes resulting from the combustion of char residues appeared to be lower than those produced from direct coal combustion.
[Show abstract][Hide abstract] ABSTRACT: Under the framework of the European project named COPOWER, the possibility to partially substitute coal used in a 243 MW(th) Power Plant by biomass and non-hazardous wastes for the production of electricity and steam was assessed. Three combustion scenarios were studied, based on the combustion tests performed in a Power Plant located in Duisburg (Germany): Scenario 0 (Sc0) - combustion of coal; Scenario 1 (Sc1) - combustion of coal + sewage sludge (SS) + meat and bone meal (MBM); Scenario 2 (Sc2) coal +SS+ wood pellets (WP). An environmental and socio-economic assessment of these three scenarios was performed. In the environmental point of view, Sc0 was the worst scenario, mainly due to the emission of greenhouse gases (GHG). Sc1 was the best scenario, mainly due to the reduction of GHG emission, eutrophication chemical species and ozone depletion gases. In the socio-economic point of view, Sc0 was the worst scenario, mainly due to the absence of GHG abatement, and Sc1 was the best scenario due to the best cost of electricity production and negative cost of avoided emissions.
[Show abstract][Hide abstract] ABSTRACT: Two combustion tests were performed in a fluidized bed combustor of a thermo-electric power plant: (1) combustion of coal; (2) co-combustion of coal (68.7% w/w), sewage sludge (9.2% w/w) and meat and bone meal (MBM) (22.1% w/w). Three samples of ashes (bottom, circulating and fly ashes) were collected in each combustion test. The ashes were submitted to the following assays: (a) evaluation of the leaching behaviour; (b) stabilization/solidification of fly ashes and evaluation of the leaching behaviour of the stabilized/solidified (s/s) materials; (c) production of concrete from bottom and circulating ashes. The eluates of all materials were submitted to chemical and ecotoxicological characterizations. The crude ashes have shown similar chemical and ecotoxicological properties. The s/s materials have presented compressive strengths between 25 and 40 MPa, low emission levels of metals through leaching and were classified as non-hazardous materials. The formulations of concrete have presented compressive strengths between 12 and 24 MPa. According to the Dutch Building Materials Decree, some concrete formulations can be used in both scenarios of limited moistening and without insulation, and with permanent moistening and with insulation.
[Show abstract][Hide abstract] ABSTRACT: Syngas obtained by co-gasification of coal and wastes was hot cleaned in two catalytic reactors, which allowed destroying tar and gaseous hydrocarbons with more than one carbon atom. H2S and NH3 contents were also significantly reduced, but CH4 concentrations varying between 2% and 10% and small amounts of H2S (below 100ppmv) were still found in syngas, depending on coal type and waste composition. This paper studies the effect of experimental conditions on CH4 destruction by reforming reactions in absence and in presence of catalysts. The effect of experimental conditions (temperature, steam flow rate and syngas composition) on CH4 destruction and on CO conversion into CO2 in the absence of catalyst was studied first, using the Equilibrium Reactor model from CHEMKIN modelling software. The selected experimental conditions were then tested in a fixed bed reactor with and without catalyst and the results obtained were consistent with CHEMKIN Equilibrium Reactor model predictions. Commercial Ni-based catalysts were tested (G-90 B5 and G 56B from C&CS). These catalysts were capable of significantly reducing CH4 content, by promoting reforming reactions. At the experimental conditions used and in absence of steam, G 56B seems to be more effective in CH4 conversion, as lower CH4 contents were obtained. In presence of steam both catalysts were capable of completely destroying CH4. Both catalysts also promoted WGS (water gas shift) reaction to some extent, though they are not specific catalysts for this reaction. Thus, a high increase in H2 content was observed, due to its formation by both reforming and WGS reactions. For a complete conversion of CO into CO2 and H2 a specific catalyst for WGS reaction is still needed.
[Show abstract][Hide abstract] ABSTRACT: Three species of biomass origin (straw pellets, olive cake and wood pellets) and two coals from different countries (Coal Polish and Coal Colombian) have been studied to understand the fate of their ash forming matter during the combustion process and to investigate the influence of co-firing biomass with coal. Three different approaches to investigate the ash behaviour were employed: (1) chemical fractionation analysis to evaluate the association/reactivity of ash forming elements in the fuels as a prediction tool, (2) establishment of elements partitioning in ash streams produced in the combustion and co-combustion trials, and (3) evaluation of enrichment factors of elements in the ash streams. The chemical fractionation analysis was applied to all fuels used to evaluate how the association/reactivity of elements making up ash may influence their behaviour during combustion. Combustion tests were carried out on a pilot scale fluidized bed combustor (FBC). Four ash streams were obtained at different locations. The uncertainty of measurements was estimated allowing a critical evaluation of mass balances over the combustion system and the partitioning of elements in the ash streams. The enrichment factors of elements in the several ash streams were estimated, incorporating uncertainties associated with analytical measurements. Results obtained showed that for FBC the relation between the chemical fractionation and the experimental partitioning is strongly affected by elutriation of particles. The element enrichment factor estimated for each ash stream, using Al as a reference element, revealed better correlations with the elements reactivity obtained by chemical fractionation because it overcomes particles elutriation effects. Nevertheless, it was observed that the reactivity estimated by chemical fractionation could not be solely interpreted as tendency of the elements to volatilize on FBC system, as reaction in bed zone of boiler may also occur retaining reactive elements.