Search

The oxidative fast pyrolysis of plastics was studied in a conical spouted bed reactor with a fountain confiner and draft tube. An inexpensive fluid catalytic cracking (FCC) spent catalyst was proposed for in situ catalytic cracking in order to narrow the product distribution obtained in thermal pyrolysis. Suitable equivalence ratio (ER) values required to attain autothermal operation were assessed in this study, i.e., 0.0, 0.1, and 0.2. The experiments were carried out in continuous regime at 550 degrees C and using a space-time of 15 gcatalyst min gHDPE -1. The influence of an oxygen presence in the pyrolysis reactor was analyzed in detail, with special focus on product yields and their compositions. Operation under oxidative pyrolysis conditions remarkably improved the FCC catalyst performance, as it enhanced the production of gaseous products, especially light olefins, whose yields increased from 18% under conventional pyrolysis (ER = 0) to 30% under oxidative conditions (ER = 0.1 and 0.2). Thus, conventional catalytic pyrolysis led mainly to the gasoline fraction, whereas light olefins were the prevailing products in oxidative pyrolysis. Moreover, the oxygen presence in the pyrolysis reactor contributed to reducing the heavy oil fraction yield by 46%. The proposed strategy is of great relevance for the development of this process, given that, on one hand, oxygen cofeeding allows solving the heat supply to the reactor, and on the other hand, product distribution and reactor throughput are improved. This work was carried out with financial support from Spain's ministries of Science, Innovation and Universities RTI2018-101678-BI00 (MCIU/AEI/FEDER, UE) and RTI2018-098283-JI00 (MCIU/AEI/FEDER, UE) and Science and Innovation PID2019-107357RB-I00 (MCI/AEI/FEDER, UE) and TED2021-132056B-I00 (MCI/AEI/FEDER, UE), the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 823745, and the Basque Government IT1645-22.

The present study evaluates elastic and inelastic contact forces in predicting the fluidization characteristics of irregularly shaped Titania nanoparticle agglomerates in a bench-scale conical fluidized bed. At first, experiments were performed to identify the mutual effects of gas velocity and agglomerate size on the instantaneous pressure, bed pressure drop and bed expansion ratio. Rigid complex-agglomerates (∼100−200 μm) were mainly formed in the partially fluidized regime, while soft simple-agglomerates (∼20−70 μm) were primarily formed in the spouting regime. The simulations were performed through the CFD-DEM approach. The error analysis of results in the partially fluidized regime revealed that the combination of Hertz-Mindlin and Johnson-Kendall-Roberts (HM + JKR) model led to a better prediction of the bed pressure drop and bed expansion ratio than the spring-dashpot (LSD) model. In the transition flow regime, the Hysteretic model led to better results of the instantaneous pressure values than those proposed for other flow regimes. In the spouting flow regime, the HM and Thornton models led to over-estimation of bed pressure drop when compared to the LSD model. The comparative results of this study provide promising new insights into the collision mechanism of polydisperse agglomerates in different flow regimes for industrial aspects.

Spouted bed stability and operation is greatly affected by particle features. Accordingly, the hydrodynamic behaviour of conical spouted beds has been studied for fine particles differing in size and density in a wide range of inlet air flow rates. This knowledge is essential for a successful scaling up and industrial implementation of the spouted bed. Therefore, the effect air velocity and solid properties (density and size) have on local solid velocity has been ascertained in a fountain confined conical spouted bed using a borescope technique (Particle Tracking Velocimetry, P T V ) applied to several bed configurations. The results show a close relationship between the inlet air velocity and the local solid velocity, with the gas-solid contact being especially vigorous in the configurations without draft tube and with the open-sided draft tube. The solid circulation flow rate is lowest when a nonporous draft tube is used due to the low solid vertical velocities in the annulus, even at high air flow rates. Nevertheless, vertical velocities in the annular zone increase when particle size and density are increased, although these velocities are lower in the spout and fountain regions due to the higher momentum exchange required for their acceleration.

Pressure fluctuation analysis has been used to identify different flow regimes in spouted beds. Although this is a promising cost-effective tool for process control and design purposes, it has hardly been used in spouted beds operating with fine and irregular particles. Therefore, the aim of this paper is to apply pressure fluctuation analysis to spouted beds operating with fine and irregular particles, either without tube or equipped with draft tube. The minimum spouting velocities estimated by the spectral analysis in systems without tubes differ from those obtained based on the characteristic curves in the range from 10.60% (sand) to 3.50% (glass beads). Thus, the main novelty of this study lies in the application of pressure fluctuation and spectral analyses in spouted beds operating with fine and irregular particles by considering the influence of the internal devices. Therefore, the methodology proposed based on both hydrodynamic and spectral analyses is a feasible and promising alternative for delimiting the minimum spouting velocity and stable operating conditions in industrial processes, especially when the aim is process control and scaling up.

The effect the solid inlet design has on the continuous drying of sand in a conical spouted bed has been studied. Five designs have been tried, four feeding the solid from the top and the fifth one...

The catalytic cracking of 2-methoxy-4-methylphenol (MMP) and of a mixture of this compound (20 wt%) with n-hexadecane (C16) has been conducted in a CREC Riser Simulator Reactor at 400-550 °C using ...

The flow and mixing behavior of two miscible liquids has been studied in an innovative static mixer by using CFD, with Reynolds numbers ranging from 20 to 160. The performance of the new mixer is compared with those of Kenics, SMX, and Komax static mixers. The pressure drop ratio (Z-factor), coefficient of variation (CoV), and extensional efficiency (α) features have been used to evaluate power consumption, distributive mixing, and dispersive mixing performances, respectively, in all mixers. The model is firstly validated based on experimental data measured for the pressure drop ratio and the coefficient of variation. CFD results are consistent with measured data and those obtained by available correlations in the literature. The new mixer shows a superior mixing performance compared to the other mixers.

Biomass gasification is a promising and sustainable process to produce renewable and CO2-neutral syngas (H2 and CO). However, the contamination of syngas with tar is one of the major challenges to limit the deployment of biomass gasification on a commercial scale. Here, we propose a hybrid plasma-catalytic system for steam reforming of tar compounds over honeycombbased catalysts in a gliding arc discharge (GAD) reactor. The reaction performances were evaluated using the blank substrate and coated catalytic materials (gamma-Al2O3 and Ni/gamma-Al2O3). Compared with the plasma alone process, introducing the honeycomb materials in GAD prolonged the residence time of reactant molecules for collision with plasma reactive species to promote their conversions. The presence of Ni/gamma-Al2O3 gave the best performance with the high conversion of toluene (86.3%) and naphthalene (75.5%) and yield of H2 (35.0%) and CO (49.1%), while greatly inhibiting the formation of byproducts. The corresponding highest overall energy efficiency of 50.9 g/kWh was achieved, which was 35.4% higher than that in the plasma alone process. Characterization of the used catalyst and long-term running indicated that the honeycomb material coated with Ni/gamma-Al2O3 had strong carbon resistance and excellent stability. The superior catalytic performance of Ni/gamma-Al2O3 can be mainly ascribed to the large specific surface area and the in situ reduction of nickel oxide species in the reaction process, which promoted the interaction between plasma reactive species and catalysts and generated the plasma-catalysis synergy., National Natural Science Foundation of China [51907087]; Natural Science Foundation of Jiangsu Province [BK20190675]; Postdoctoral Science Foundation of China [2020M671289]; Natural Science Foundation for Colleges in Jiangsu Province [19KJB470005]; European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement [823745]; Royal Society Newton Advanced Fellowship [NAF/R1180230]; British Council [623389161]; Scientific and Technological Research Council of Turkey (TUBITAK Project) [219M123], The support of this work by the National Natural Science Foundation of China (no. 51907087), the Natural Science Foundation of Jiangsu Province (no. BK20190675), the Postdoctoral Science Foundation of China (no. 2020M671289), and the Natural Science Foundation for Colleges in Jiangsu Province (no. 19KJB470005) is gratefully acknowledged. The authors acknowledge the funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement (no. 823745). X.T. thanks the support of the Royal Society Newton Advanced Fellowship (NAF/R1180230) and the British Council (No. 623389161). J.Y. acknowledges funding from the Scientific and Technological Research Council of Turkey (TUBITAK Project Contract No. 219M123).

A methodology based on the borescopic technique has been developed and validated for tracking solid movement within a conical spouted bed. The procedure developed and fine-tuned allows monitoring the descending and ascending optical flow of both spherical and irregular particles in the annulus (dense zone) and spout (dilute zone) in the bed. A high speed camera (up to 16,000 fps) fitted with a fiber optic continuous light source was used for recording, and an image treatment algorithm modified and adapted to account for differences in particle shape and bed density (dilute or dense) was applied to the registered data. The procedure allows gathering information on the velocity of particles in a wide range of sizes, from a few millimeters ( d p ¯ = 7 mm) to micrometers ( d p ¯ = 93 μm).

A novel strategy has been proposed for the rigorous kinetic modeling of tyre pyrolysis in a conical spouted bed reactor. A kinetic model coupled with a gas flow model was used in the fitting of experimental results obtained in a bench scale unit in the 425–610 °C range. A gas flow model should be incorporated to account for the delay and mixing phenomena observed in tracer experiments, as these phenomena cause remarkable deviations in the assessment of the kinetic parameters. The gas flow pattern from the reactor to the measuring device was modeled using two different approaches based on ideal flow reactors. Furthermore, two kinetic schemes considering lumped products have been proposed; the first one is based on four parallel independent reactions accounting for the volatile products (gas, liquid, aromatics and tar). The second one considers an additional secondary reaction of aromatic formation from the liquid. The strategy proposed for coupling the kinetics and the flow model led to a suitable fitting of the experimental results, with the performance of the model considering a secondary reaction being slightly better than the simple one.

A study has been conducted on the joint influence of the fountain confiner and draft tube on the solid circulation in a conical spouted bed made up of sawdust. Knowledge of the performance of these...

The minimum spouting velocity, Ums, is a critical topic, and an exact prediction of this parameter certainly can be useful in design and scale-up of the conical spouted beds. In the present study, a number of intelligence methods was applied to predict Ums in conical spouted beds equipped with non-porous draft tube. Six dimensionless moduli comprising the essential operating and geometric parameters, namely, the gas density, the gas viscosity, the particle diameter, the particle density, the cone angle, the nozzle diameter, the static bed height, the length of the tube, the entrainment height, and the tube diameter were taken as models inputs. The total number of data samples is 1004 that includes 572 data points to train the smart models and 432 data points to test those models. The self-organizing map (SOM) was used to examine the effect of inputs correlation on the performance of the chosen smart models. Among the different models, a multi-layer perceptron (MLP) trained by Bayesian Regulation (BR) incorporating SOM i.e. (MLP-BR-SOM) predicted the best results with mean relative error of 9.71 and 12.45% for train and test data, respectively. In addition, sensitivity analysis (SA) of the proposed model was performed and it was shown the Ar, DT/D0, and H0/D0 have most influential parameters in prediction of Ums.

One of the most important parameters for the design, selection, and operation of a microhydrocyclone is pressure drop. Although there are certain correlations in the literature for determining micr...

A full 3D model of a conical spouted bed equipped with an open-sided draft tube was simulated using CFD-DEM embedded in a commercial CFD code ANSYS-FLUENT. The dense discrete phase model (DDPM) with DEM closure for particle–particle interaction available in the FLUENT was used for the particulate phase. The dispersed k-e turbulent model was used in the computational model for the gas phase. The geometry used in the simulation for both the contactor and the open-sided draft tube was identical to that of a pilot plant in which the hydrodynamic studies were carried out. The influence of the open-sided draft tube was studied by using two configurations, one flushed with the bed surface and the other one protruding above the bed surface. The CFD-DEM results indicated that the accuracy of model predictions significantly depends on the modification in the Gidaspow drag function. The predicted pressure drops and fountain heights were consistent with the experimental data. New aspects of particle flow pattern, axial solid velocity, solid volume fraction in the bed, and power spectral density have also been discussed.

A study has been carried out on the applicability of the correlations proposed in the literature for calculating peak and spouting pressure drops to biomass materials. These parameters are essential for estimating energy consumption in spouted beds and depend on the contactor geometry, operating conditions and the type of particles. Five biomass materials have been studied based on their suitability for energy production by combustion and their different size, density and shape factor. Both peak and spouting pressure drops increase as particle size and density are increased and shape factor is decreased. Correlations have been proposed based on those already reported in the literature for regular materials. The influence of particle size and density is more pronounced in these irregular biomass materials than in regular ones, especially in the peak pressure drop. Shape factor is also highly influential, which is reflected on the greater influence of the static bed height for irregular materials, especially for the spouting pressure drop.

A multilayer perceptron with back-propagation learning algorithm is developed to predict the minimum spouting velocity (ums) in draft tube conical spouted beds. Six dimensionless variables involving ten essential geometric and operating parameters of the beds were taken as model inputs. To compare the model results with both experimental data and those predicted by the limited existing empirical equations, the root mean square error and the mean relative error are utilized. Although there is a complex relationship between the input variables and ums, and despite the huge number of data available, the steps of training and testing show good agreement with the corresponding experimental values. This demonstrates that an artificial neural network is a useful approach to predict ums, especially when the relationship between the geometric and operating parameters and ums is complex and difficult to define.

A correlation has been proposed for predicting local bed-to-surface heat transfer coefficients in conical spouted beds based on an experimental study conducted using beds made up of sand, sawdust, and their mixtures under various operating conditions, namely, different static bed heights and gas velocities over minimum spouting. A comparison of the results with those obtained using the correlations in the literature proved that they provide very poor predictions and, furthermore, they are not able to predict local coefficients in the bed. Based on a statistical analysis, the significant moduli have been identified in the relevant literature correlations and two new moduli related to the radial and longitudinal positions have been contemplated. The analysis identified two groups of heat transfer coefficients: those within the bed and those on its surface. The correlation proposed is specifically suitable for ascertaining the best location of heat transfer devices within the annulus of the spouted beds.

A continuous process has been developed consisting in the flash pyrolysis (500 °C) of high density polyethylene (HDPE) in a conical spouted bed reactor (CSBR) followed by steam reforming in a fluidized bed reactor (Ni commercial catalyst). The effect reforming temperature in the 600–700 °C range, space time from 2.1 to 20.8 g cat min g HDPE −1 and steam/plastic ratio between 3 and 5 have on product yields and gas composition has been studied. The continuous pyrolysis-reforming process performs well, with no operational problems and attaining complete HDPE conversion. Under the optimum conditions, i.e., 700 °C, space time 16.7 g cat min g HDPE −1 and steam/plastic of ratio 5, the H 2 yield was 92.5% of that corresponding to stoichometry, which accounts for a H 2 production of 38.1 g per 100 g of HDPE in the feed.

Spouted beds are an interesting alternative for the treatment of biomass for energy purposes, given that the insertion of a draft-tube allows large-scale handling of solids with a wide range of sizes and diverse properties. The hydrodynamic correlations proposed in the literature have not been validated with particles of low density and shape factor. Therefore, a detailed experimental study has been conducted using five types of biomasses and different combinations of the contactor geometric factors. The correlations in the literature for plain conical spouted beds and for those provided with nonporous and open-sided draft-tubes have been taken as a starting point and, based on the experimental results, they have been modified in order to account for the properties of the solids. Two strategies have been considered in the methodology for modifying the coefficients in the literature correlations. Both are based on the introduction of coefficients one by one based on a hypothesis test. Accordingly, new correlations based on existing ones have been proposed, with the number of coefficients modified being minimum.

The continuous fast pyrolysis (500 °C) of pine wood sawdust has been studied in a conical spouted bed reactor (CSBR) followed by in-line steam reforming of the pyrolysis vapours in a fluidised bed reactor on a Ni commercial catalyst. An analysis has been carried out on the effect reforming temperature in the 550–700 °C range, space time from 2.5 to 30 gcat min gvolatiles−1 and steam/biomass ratio between 2 and 5 have on the pyrolysis volatile conversion, H2 yield and gaseous stream composition. The continuous pyrolysis-reforming process has shown great potential for H2 production from biomass, with no operational problems and allowing for full conversion of pyrolysis vapours. Thus, a maximum H2 yield of 117 g per kg of biomass was obtained at 600 °C, at the highest space time studied (30 gcat min gvolatiles−1) and for a S/B ratio of 4. This yield is higher than those obtained by other alternatives, such as direct steam gasification or bio-oil reforming. Moreover, the char produced in the pyrolysis step has been continuously removed from the conical spouted bed reactor in order to be upgraded following promising valorisation alternatives.

A mathematical model and molecular dynamics simulation were applied to study the integrated process consisting of industrial methane steam reforming and pressure-swing adsorption (PSA) to produce pure hydrogen. The process was highly endothermic with an outlet temperature of 1190 K. It was found that the industrial plant suffers from high coke filament formation by the methane cracking reaction with the maximum affinity of 3. Moreover, the output H2/CO ratio of 3.27 was obtained for the industrial case under study. Relevant adsorption isotherms of the components and molecular dynamic simulations showed that hydrogen is not adsorbed on the zeolite 5A, while carbon dioxide and methane compete to adsorb on the zeolite. Results of a dual-bed PSA process showed that pure hydrogen (>99%) is produced during the process, and the results were compared to the available data reported in the literature for each step.

The design factors of fountain confined conical spouted beds have been assessed in order to determine their best combination for scaling up and enhancing fine particle retention. The results evidence that the length of the confiner and the height of the draft tube entrainment zone are the key design factors, causing the highest entrainment reduction. Thus, the optimum confiner length is within the range of 2-3 times the bed surface diameter and the desirable height of the entrainment zone is approximately 1-2 times the tube diameter. This study also concludes that the best system for attaining high stability with minimum elutriation is the one equipped with an open-sided draft tube with an aperture ratio of around 20%.

[EN]This work pursues the validation of a new reactor for the evaluation of char gasification kinetics. This novel reactor allows continuous gas flow through the fixed bed sample and accurately monitoring the mass loss throughout the reaction. Accordingly, this thermogravimetric flow reactor has a great potential for the analysis of different thermochemical processes, such as pyrolysis and gasification of solid feedstocks. In this paper, the gasification of pine sawdust char was carried out and the effect carbon dioxide concentration (10 and 100 vol%) and temperature (800, 850 and 900 °C) have on char gasification kinetics was assessed. The experimental results were fitted to five different kinetic equations, i.e., homogeneous model (VM), shrinking core model (SCM), nth order model, random pore model (RPM) and modified random pore model (MRPM), and the best-fit parameters (frequency factor, activation energy, adjustable parameters and fitting error) were obtained for each model. The modified random pore model provides the best fit to the experimental data. The new thermogravimetric flow reactor allows obtaining rigorous kinetic results, which is clear evidence that the reactor is suitable for studying char gasification kinetics under CO2 atmosphere. This work was carried out with financial support from the Spain’s Ministries of Economy and Competitiveness (CTQ2016-75535-R (AEI/FEDER, UE)) and Science, Innovation and Universities (RTI2018-098283-J-I00 (MINECO/FEDER, UE)), the Basque Government (IT1218-19), and the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 823745. Maria Cortazar also thanks the Basque Government for her research training grant.

The spouted bed regime is an alternative to fixed and fluidized beds due to the excellent gas-solid contact and the high reduction in operating pressure drop. Nevertheless, the most important limitation of this technology lies in its scaling up, since the inlet diameter/particle diameter ratio must be below 20–30 to avoid bed instability. In order to overcome this limitation, a new internal device called fountain confiner has been developed, which stabilises the system and allows operating with fine particles even without any type of draft tube. Runs have been carried out using the fountain confiner in order to analyse the stability of beds composed of very fine particles and the characteristic hydrodynamic curves (pressure drop vs. air velocity) have been obtained. The use of this new device allows attaining highly stable operation regimes, widening the operational range to 4 times that of plain spouted beds, and increasing the inlet diameter/particle diameter ratio from 20–30 to 1000. Moreover, the optimum distance between the bed surface and the lower end of the confiner has been delimited for the range of operating conditions studied, 0.06 - 0.08 m (between 1 / 2 and 1 / 3 the confiner diameter), since it is a key parameter for system stability. Finally, the effect of several geometric factors and the scaling up of this technology has been analysed for fine particles of different size and density.

A study has been carried out on the influence the draft-tube configuration has on the solid circulation in conical spouted beds made up of sawdust. Knowledge on the performance of these fine particles of low density and irregular texture is required for the pyrolysis, gasification or combustion of this waste materials in conical spouted beds. Accordingly, particle cycle times have been monitored for contactors of different geometry (angle and gas inlet diameter) provided with draft-tubes of different configuration (nonporous and open-sided tubes). The study has been carried out according to a factorial design of experiments. Particle cycle times follow an almost exponential distribution for both types of tubes and are highly dependent on the type of draft tube and contactor angle, especially in the range from 36° to 45°. On average, cycles times are twice to triple longer when nonporous tubes are used. Therefore, the open-sided internal device provides stability and ensures high turbulence to beds made up of fine and irregular particles, with their behaviour being similar to stable beds made up of coarse particles in which no draft-tube is required.

Steam gasification (900 °C) of high density polyethylene (HDPE) in a conical spouted bed reactor (CSBR) followed by steam reforming in a fixed bed reactor (Ni commercial catalyst) has been carried out. The effect reforming temperature in the 600–700 °C range has on product yields and gas composition as well as on the amount and nature of the coke deposited on the catalyst has been studied. The reforming leads to a full transformation of C2+ hydrocarbons and tar. The maximum H2 yield is obtained at 700 °C (36 wt % by mass unit of HDPE in the feed, which accounts for 83 wt % of the maximum H2 yield according to stoichiometry), with CH4 conversion being 94% and the coke amount deposited on the Ni catalyst being minimum (3.3 wt % by mass unit of HDPE in the feed). The syngas obtained by reforming at 700 °C has a H2/CO volumetric ratio of 6 and is suitable for hydrogenation reactions and further valorization to produce H2.

Sewage sludge valorization by flash pyrolysis has been carried out in a conical spouted bed reactor with continuous biomass feed and char removal. The effect of temperature on product yields and composition has been studied in the 450–600 °C range and a maximum liquid yield of 77 wt.% daf (dry and ash free basis) has been obtained at 500 °C. The liquid collected has a water content of 23–27 wt.% and is mainly composed of oxygen-containing compounds (phenols, ketones and acids amongst others), whose yield decreases with temperature, and nitrogen-containing compounds, such as amides and pyrroles. In addition, the importance of an efficient char removal system has been assessed by operating with and without char accumulation in the bed. The char fraction retains most of the heavy metals contained in the sludge and they may have applications in agriculture or as adsorbent.

A study has been performed on the production of high quality activated carbon from rice husk char obtained by flash pyrolysis in a conical spouted bed reactor. In order to enhance both the quality of the adsorbents obtained and the economy of the process, the amorphous silica contained in the char has been recovered with Na2CO3. Subsequently, the resulting carbonaceous material has been subjected to physical activation at 800 °C using steam and carbon dioxide as activating agents. Although the maximum BET surface areas obtained with carbon dioxide and steam are similar, 1514 and 1365 m2 g–1, respectively, significant differences are observed in the performance of the two oxidizers. Thus, steam gasification kinetics is faster than that of carbon dioxide. The carbons produced by activation using both steam and carbon dioxide have a wide pore size distribution, with microporous structure being more developed when the latter is used.

Principal Component Analysis (PCA) has been used to process the data obtained from the batch pyrolysis of high density polyethylene (HDPE) in order to recognize trends in the formation rates of the large number of components in the product stream. Two different criteria for component grouping have been compared, i.e., according to molecular size, and the nature of C C bond. The choice of the suitable criterion is crucial in order to establish the kinetic scheme, and PCA has proven to be a very helpful tool. The multivariate analysis applied to the lumps obtained according to the molecular size of the components provides very useful information, which allows proposing similar kinetic schemes to those in the literature, but with significant details involved in the definition of the lumps and their distribution between primary and secondary reactions. Furthermore, although there are substantial differences in the formation rate of single-ring aromatics (which are particularly affected by temperature), PCA carried out by grouping the products according to the nature of their C C bond does not provide relevant information concerning differences in the performance of the main products (aliphatic hydrocarbons).

Continuous catalytic pyrolysis of high density polyethylene has been carried out for obtaining light olefins in a two step reaction system: (i) thermal pyrolysis in a conical spouted bed at 500 °C; (ii) cracking of the volatiles (mainly waxes, C21+) formed in the first step, in a fixed bed reactor using a catalyst based on HZSM-5 zeolite. A kinetic model based on lumps including catalyst deactivation by coke deposition has been established to quantify the product distribution obtained in the second step and its evolution with time on stream. Experimental data have been obtained at 400, 450 and 500 °C, with space-times of 0, 1, 2, 4, 6 and 8 gcat min gHDPE−1 and for 5 h time on stream. The discrimination of kinetic models has been carried out based on statistics calculated for Fischer distribution (stepwise procedure), and the best fits have been obtained for a model considering six steps: cracking of waxes to produce non-aromatic C5–C11 compounds, single-ring aromatics, light alkanes and light olefins; cracking of non-aromatic C5–C11 compounds to yield light olefins and light olefin condensation reactions to produce single-ring aromatic compounds. The deactivation kinetic equation considers waxes as main coke precursors, whose deposition rate decreases with time on stream.

The transformation of 1-butene was studied in order to intensify propylene production on catalysts prepared based on HZSM-5 zeolites of different SiO 2 /Al 2 O 3 ratio modified as follows: (i) by incorporating K or P (1–5 wt.%) and (ii) subject to mild in situ steaming. The effect of zeolite modifications on the catalyst physical and acid properties and on their kinetic performance was analyzed, given that they are two key factors for selectively re-routing oligomerization–cracking reactions to propylene production and for minimizing coke formation. Experiments were carried out under the following operating conditions: 500 °C; space time, up to 1.6 (g of catalyst) h (mol of CH 2 ) −1 ; time on stream, 5 h. The following criteria were used for assessing catalyst performance: (i) conversion; (ii) product yield and selectivity of each lump of reaction products (CH 4 , C 2 H 4 , C 3 H 6 , C 2 C 3 paraffins, C 4 H 10 , C 5+ aliphatics and BTX), with the aim of maximizing propylene, and (iii) deactivation by coke deposition. Although catalytic performance was improved by selecting a high SiO 2 /Al 2 O 3 ratio, as well as by incorporating 1 wt.% P and mild in situ steaming, the incorporation of 1 wt.% K was the most effective treatment for maximizing propylene yield and minimizing coke formation, which is explained by the considerable attenuation of the acid strength of the zeolite sites. A steady propylene yield of 30% and a selectivity of 40%, for a conversion of 1-butene higher than 70%, have been obtained with a catalyst prepared by agglomerating (with bentonite and alumina) 1 wt.% K modified HZSM-5 zeolite with SiO 2 /Al 2 O 3 = 280.

The hydrodynamics of a cylindrical spouted bed with a draft tube were studied using the two-fluid model (TFM) incorporating the kinetic theory of granular flow. The effect of some essential parameters, namely, particle–wall restitution coefficient (ew), specularity coefficient ( φ ), and minimum frictional solid volume fraction ( α s , min ), was examined. Different values of ew and φ were evaluated in the draft tube. The CFD results show that the accuracy of model predictions depends on the proper evaluation of the frictional stress as well as on the values chosen for ew and φ . In particular, model predictions for particle behavior through the draft tube are sensitive to the values of these parameters. A series of CFD simulations for gas–solid flow in spouted beds were performed. Particular attention was given to the solid-phase boundary condition on the draft tube. The model proposed was found to be in close quantitative agreement with the experimental measurements in a wide range of gas flow rates and values of design parameters, such as draft tube diameter and entrainment height.

A genetic programming (GP) algorithm is developed to estimate the minimum spouting velocity (Ums) in the spouted beds with a cone base. In order to have a general model, five dimensionless variables including seven critical geometric and operating parameters of spouted beds, namely, column diameter, spout nozzle diameter, base angle, static bed height, particle diameter, particle density, and gas density, have been taken as model inputs. A general correlation including nearly all fundamental and operating variables has been obtained based on the GP approach. The Ums values predicted by the GP are in fair agreement with those obtained by experiments, with a root-mean-square error of 0.1329 m/s. The model results show that GP can be used as an effective tool to provide relatively accurate information on minimum spouting velocity in conical spouted beds.

A kinetic model of eight lumps (methane, ethylene, propylene, C2–3 paraffins, butanes, C5+ hydrocarbons (aliphatic hydrocarbons of five or more carbon atoms), and aromatics (benzene, toluene, and xylenes, BTX)) has been established for the transformation of 1-butene over a 1 wt % K modified HZSM-5 zeolite (SiO2/Al2O3 = 280) catalyst (of moderate acidity). The kinetic model allows quantifying product distribution at zero time on stream, and particularly propylene production, which has an increasing demand in petrochemical industry. The experimental data have been obtained in an isothermal fixed-bed reactor in the 400–600 °C range and under a wide range of experimental conditions: space time up to 1.6 (gcatalyst h) (molCH2)−1 and 1-butene partial pressure between 0.375 and 1.35 bar. It has been proven that a simplified kinetic model of five lumps (ethylene, propylene, butenes, C1–4 paraffins and C5+ hydrocarbons (aliphatics and aromatics)) is also suitable. Both models predict a product distribution that fi...

A study has been conducted on the steam reforming of ethanol on different Ni and Co catalysts synthesized on several supports (SiO2, ZnO and α-Al2O3 undoped and doped with La2O3) in a fluidized bed reactor (to ensure bed isothermicity). The results allow analysing the effect of both temperature (in the 300–700 °C range) and the type of metal and support on the reaction indices [ethanol conversion and yields and selectivities of H2 and by-products (CO2, CO, CH4 and C2H4O)]. Catalyst stability has been specifically studied by comparing the evolution with time on stream of the reaction indices at 500 °C (minimum CO production) and at 700 °C (insignificant deactivation by coke). A slightly higher H2 yield is obtained on Co catalysts than on Ni ones in the 500–600 °C range. Nevertheless, the highest H2 yield at 700 °C is obtained with a highly stable performance on Ni catalysts over α-Al2O3 support.

The effect operating conditions have in the selective transformation of 1-butene into propylene has been studied on a catalyst of HZSM-5 zeolite (SiO2/Al2O3 = 280) modified with 1 wt % K (of moderate acid strength) and agglomerated with bentonite and alumina. The kinetic runs have been performed in a fixed bed reactor under the following operating conditions: 400–600 °C; space time, up to 1.6 (gcatalyst·h) (molC)−1; and butene partial pressure, 0.375–1.35 bar. The kinetic performance has been evaluated at zero time and throughout time on stream in order to find the suitable conditions to maximize propylene yield and selectivity and minimize deactivation by coke. A region of optimum propylene yield (>30%) and propylene selectivity (>50%) has been established for temperatures above 500 °C and space time values depending on the reaction temperature. Furthermore, cofeeding 50% of inert gas is highly recommended in order to attenuate coke deactivation.

Principal component analysis is used as a pattern recognition method to find criteria for grouping into lumps the compounds formed in the thermal and catalytic pyrolysis of waste tyres. This information is the stating point for the proposal of simple kinetic schemes that efficiently describe the complex reactions that occur in the pyrolysis process. It has been proven that the kinetic scheme must consider a depolymerization step of the waste to give isoprene and styrene monomers and the dimer of the former (limonene), the formation of primary products (char, tar and gas) by thermal cracking of the original high molecular weight compounds, and the subsequent secondary reactions by thermal cracking of heavy primary fractions (tar) to form lighter fractions (gas, gasoline and C10− aromatics). The use of a catalyst prepared based on a HY zeolite selectively enhances the reactions of condensation and alkylation of limonene and gasoline to aromatics, whereas the one based on a HZSM-5 zeolite selectively enhances the cracking of tar to lighter fractions (gas and C10− aromatics), limonene cracking to isoprene and C5–C10 hydrocarbons or even the cracking of the latter to C1–C4 gases.

This paper studies the effect of operating conditions in dimethyl ether (DME) steam reforming on a bifunctional catalyst synthesized with CuO–ZnO–Al2O3 metallic function and a HZSM-5 zeolite treated with NaOH to moderate acidity. The experimentation has been carried out in a fluidized bed reactor in the 225–325 °C range, with space time between 0.1 and 2.2 gcatalyst h/gDME, steam/DME molar ratio between 3 and 6, and DME partial pressure between 0.08 and 0.25 bar. The 275–300 °C range is suitable for obtaining high values of DME conversion and H2 yield with minimum CO formation and deactivation by coke and avoiding hydrocarbon formation. Stable values of DME conversion (0.85), H2 yield (0.81), and H2 production rate (180 mmolH2/(gcatalyst h)) are obtained during 48 h at 300 °C with a steam/DME ratio of 4 and space time of 0.60 gcatalyst h/gDME. The main cause of deactivation is coke deposition on the metallic function.

Pinewood sawdust has been gasified by using steam as gasifying agent in a conical spouted bed reactor operating in continuous regime. A study has been made of the effect of temperature (in the 800–900 °C range), steam/biomass ratio (between 0 and 2) and sawdust particle size (0.3–1, 1–2 and 2–4 mm ranges) on the distribution of products (gas, tar and char) and their composition has been studied. Temperature has a positive effect on the gas composition by increasing H 2 content and reducing that of CO. Furthermore, the tar and char yields are reduced as gasification temperature is higher. An increase in steam/biomass ratio from 0 to 1 has a positive effect on hydrogen concentration, char gasification and tar reforming, and a further increase in this parameter from 1 to 2 gives way to only a limited improvement in the results. Sawdust particle diameter plays a minor role in the gasification process in the temperature range studied, which must be attributed to the high heat transfer rate in the bed. Thus, this technology allows operating with coarse sawdust particles without reducing the syngas yield. However, the reduced gas residence time gives way to a high tar yield.

Operating and peak pressure drops have been studied in conical spouted beds equipped with draft tubes of different configuration using materials of different size. The draft tubes used are nonporous and open-sided ones. Based on an experimental design, the factors of greater influence on both pressure drops have been determined and general correlations valid for fine and coarse materials have been proposed for predicting the operating pressure drop and peak pressure drop with each type of draft tube. The results show that conical spouted beds equipped with draft tubes give way to lower operating and peak pressure drops than those without draft tube. A comparison of draft tube systems reveals that nonporous tubes give way to the lowest values of both pressure drops, but the solid circulation rates and the gas–solid contact efficiency are poorer than those with open-sided draft tube systems.

The pyrolysis behaviour and kinetics of forest shrub wastes (Cytisus multiflorus, Spartium junceum, Acacia dealbata and Pterospartum tridentatum) from the Portuguese Central Inland Region have been studied in a thermobalance, as a previous step for their valorization by pyrolysis in order to obtain fuels and chemicals within the framework of the BioREFINA-Ter project. The kinetic model consists of a multi-component mechanism that describes the volatile formation involving three independent and parallel reaction networks corresponding to the decomposition of the three main biomass pseudo-components: hemicellulose, cellulose and lignin. The thermogravimetric curves and kinetic parameters have been compared with those obtained for other materials, and the chemical features of the biomasses have been determined. Although the samples are highly heterogeneous because of their bark and leaf content, the degradation of these shrubby biomasses is similar to other lignocellulosic materials, evidencing that their valorization by pyrolysis is feasible.

Particle cycle times (average, maximum, and minimum) have been measured in draft tube conical spouted beds for different geometric factors of the contactor (angle and gas inlet diameter), draft tubes (diameter, height of the entrainment zone, and width of the faces) and under different operating conditions (particle density). On the basis of the results, the effects of the type of draft tube and different factors of the contactor/draft tube/particle system have been studied, and those of greater influence have been determined. The results show that particle cycle times and solid circulation rates are highly dependent on the type of draft tube, solid density, and contactor angle. Open-sided draft tubes are the ones with the highest solid circulation rate with stable spouting performance. Therefore, this internal device is a suitable option for scaling up spouted beds with a hydrodynamic performance similar to those without tubes.

High density polyethylene (HDPE) cracking has been carried out in a thermal-catalytic two-step unit for the selective production of light olefins. Continuous pyrolysis of HDPE has been conducted in a conical spouted bed reactor at 500 °C, and the volatiles formed (mainly waxes) have been transformed in a downstream fixed bed catalytic reactor at 500 °C. The effect of catalyst acidity on product yield and composition has been studied by using three catalysts based on HZSM-5 zeolites with a SiO2/Al2O3 ratio of 30, 80, and 280. The maximum light olefin yield (58 wt %) has been obtained using the most acidic catalyst (SiO2/Al2O3 ratio of 30), with the individual yields of ethylene, propylene, and butenes being 9.5, 32, and 16.5 wt %, respectively. The results are a clear evidence of the higher efficiency of the two-step reaction system compared to the in situ catalytic pyrolysis (single-step), which is explained by the suitable combination of operating conditions in each one of the steps.

The fluidization characteristics of nanoparticle agglomerates have been experimentally and numerically studied in a fluidized bed. The experimental studies were carried out in a bed containing silver oxide dry powder belonging to group B of Geldart’s classification with a primary particle size of 30 nm. Pressure drop measurements using an optical fiber technique allowed the effects of particle loading and inlet gas velocity on the fluidization characteristics of the particles to be determined. Interparticle adhesion forces between silver oxide nanoparticles give rise to the formation of agglomerates with a wide size distribution. Furthermore, a considerable number of bubbles are formed in the bed with agglomerate bubbling fluidization and low bed expansion. Numerical simulations were also performed to evaluate the sensitivity of gas–solid drag models. An Eulerian multiphase model was used with different drag models. A mean particle size of 175 μm was chosen for the numerical simulations, and the results o...

The hydrodynamics and the influence of the geometric and operating factors on the minimum spouting velocity have been studied in draft tube conical spouted beds with materials of different size and density. Two draft tube configurations have been used: nonporous and open-sided tubes. Based on an experimental design, the factors of greater influence have been extracted and the general correlations valid for fine and coarse materials have been proposed for predicting the minimum spouting velocity for each type of draft tube. A comparison of the velocities with and without a tube reveals that the nonporous draft tube requires the lowest minimum spouting velocity. Nevertheless, the solid circulation rate and the gas–solid contact efficiency of the open-sided draft tube outperform any other spouted bed configuration, especially for fine particles. Consequently, open-sided draft tubes allow stable operation with fine particles and high solid circulation rates in conical spouted beds.

A two-step process has been used for the selective production of light olefins by the thermal cracking of high-density polyethylene. The plastic has been continuously fed into a conical spouted-bed reactor (CSBR) operating at 500 °C, which yields 93 wt % of waxes (C21+) and C12–C21 hydrocarbons. The volatile product stream has been cracked downstream in a multitubular (quartz tubes) reactor in the 800–950 °C range, with short residence times (0.016–0.032 s). A yield of 77 wt % of light olefins (C2–C4) has been obtained by operating at 900 °C in the second step. The maximum yields of ethylene, propylene, and butenes are 40.4, 19.5, and 17.5 wt %, respectively. Given the short residence time of the products in the reactor, the yield of aromatics is only 6.2 wt %. The high light olefin yield is due to the excellent performance of both steps. The CSBR allows maximizing the yield of waxes and avoiding defluidization problems. The operating conditions in the multitubular reactor (low concentration of the compou...

The catalytic cracking of HDPE (high density polyethylene) at 500 °C using a spent FCC catalyst agglomerated with bentonite (50 wt %) has been studied in a conical spouted bed reactor. The reaction is carried out in continuous regime (1 g min–1 of HDPE is fed) with no bed defluidization problems. The results obtained, namely, total conversion, and high yields of gasoline (C5–C11 fraction) (50 wt %) and C2–C4 olefins (28 wt %), are explained by favorable reactor conditions and good catalyst properties. These results are compared with those for a catalyst prepared in the laboratory by agglomerating a commercial HY zeolite (SiO2/Al2O3 = 5.2). The conical spouted bed is a suitable reactor for enhancing the physical steps of melting the polymer and coating the catalyst with the melted polymer. Furthermore, high heat and mass transfer rates promote devolatilization, and short residence times minimize secondary reactions from olefins by enhancing primary cracking products. The meso- and macroporous structure of ...