Kinetic study of fast pyrolysis of sawdust in a conical spouted bed reactor in the range 400–500 °C

An original reactor (a conical spouted bed reactor) is used for the kinetic study of Pinus insignis sawdust pyrolysis in the range 400–500 °C under the usual conditions of this reactor for pyrolysis in a continuous regime. The equipment meets the requirements for pyrolysis kinetic study (bed isothermality, high mass and heat transfer between phases and short residence time of gaseous products). The results of yield of products are evidence of the good performance of the conical spouted bed reactor for obtaining a liquid product, with a maximum yield of 70 wt% in the range 440–460 °C. © 2001 Society of Chemical Industry     

Cold flow experimental study and computer simulations of a compact spouted bed reactor

Spouted beds are a very interesting class of gas–solid contactors that possess excellent heat transfer and mixing characteristics, while they are particularly suited to process coarse particles. Proper design of such beds requires the prediction of various hydrodynamic characteristics, such as the minimum spouting velocity and maximum spoutable height. Contrary to their typical initial applications, spouted beds have been finding recently more frequent use on the one hand at endothermic processes and on the other hand using much finer particle sizes. In the current work, the hydrodynamic characteristics of a laboratory scale spouted bed of 0.05 m diameter have been investigated via cold flow studies using olivine particles of 3.55–5.00 × 10⁻⁴ m size. Hydrodynamic parameters have been measured at this compact geometry and fine particle size and were compared with common literature correlations. An empirical correlation was derived to predict the fountain height for the studied fine particle spouted bed. Computer simulations have been further used to investigate the heat transfer characteristics of the bed under endothermic reactive conditions, using methane reforming as a case study. Given sufficient external heat supply, a spouted bed operating at a well-mixed regime can efficiently drive even highly endothermic reactions.     

Hydrodynamic and thermal experimentation on square‐based spouted beds for polymer upgrading and unit scale‐up

This paper presents the results from an extensive experimentation on polyester chips heating, crystallization and upgrading in three different size spouted bed units: a cylindrical 0.15 m diameter × 1.3 m tall, a 0.35 m square‐based × 2.1 m tall parallelepiped and a sextuple multi‐spouting 0.7 × 1.05 m² demonstration reactor for solid state post‐polymerization. The first apparatus was finalized to measuring several process operating variables (maximum gas temperature at the inlet, overall heat transfer coefficient and particle agglomeration tendency); the second unit provided the hydrodynamical data necessary to scale‐up the system, insert into a PET upgrading process of 30 ton/day operating capacity and partially replace a bubbling fluidized bed heating/crystallizing unit. The ultimate goal of the project consisted in intensifying the process design by saving gas compression and thermal energy. The hydrodynamical findings of the squared modular unit were compared against several existing correlations: Manurung's equations for the maximum pressure drop and the pressure drop at stable spouting required a minimal alteration; Mathur and Gishler's equation properly fitted the experimental minimum spouting velocity. The continuously operating multiple spouting apparatus showed that regulating the solids level was an issue mainly due to the very large particle throughput, if related to the mixing efficiency of each module; reciprocal interference between spouted bed cells was manifested.     

Methane steam reforming in large pore catalyst

In this work we have studied the performance of catalyst extrudates of Ni-Al₂O₃ promoted with potassium for steam methane reforming. The most interesting property of this catalyst is the presence of large pores (average diameter of 8×10^?4 m) to reduce diffusional limitations. We have determined the true kinetics using catalyst powder in the temperature range covering 757–804 K. Furthermore, experiments using a fixed bed filled with extrudates were performed in the temperature range covering 701–800 K at constant methane/steam ratio for different feed flowrates.In the true kinetic experiments using catalyst powder it was observed that this catalyst has a very high CO₂ selectivity against CO. The conversion of the catalyst is smaller than other commercial materials due to the smaller content of Ni (10%).Experiments using catalyst extrudates showed that the reaction suffers from strong mass and heat limitations: diffusion of reactants/products and heat transfer in the gas/solid interface. The presence of large pores has an important contribution in decreasing the resistance to mass transfer in particles with 1.1×10^?2 m diameter. At 800 K and 2 bar the effectiveness factor was about 0.43 for the steam methane reforming reaction and 0.41 for the global reaction.     

Spouted bed and microwave-assisted spouted bed drying of parboiled wheat

The effect of spouted bed and microwave-assisted spouted bed drying on drying rates of parboiled wheat was investigated. In addition, the effective moisture diffusivities of parboiled wheat were calculated. The drying experiments were performed using 200 g of parboiled wheat, at three different air temperatures (50, 70, 90 °C) and at two different microwave powers (3.5 W/g (db), 7.5 W/g (db)). Microwave-assisted spouted bed drying at microwave power of 3.5 W/g and 7.5 W/g reduced drying time by at least 60% and 85%, respectively compared to spouted bed drying. The effective diffusivity values were in the range of 1.44 × 10^?10–3.32 × 10^?10 in spouted bed drying while they were between 5.06 × 10^?10 and 11.3 × 10^?10 in microwave-assisted spouted bed drying at different experimental conditions.     

Char‐formation kinetics in the pyrolysis of sawdust in a conical spouted bed reactor

Both the generation of a microporous structure and char formation kinetics have been studied in the pyrolysis of sawdust of Pinus insignis in a conical spouted bed reactor, in the range 350–700 °C. The BET surface area (representative of the physical evolution of the solid) and the C/H ratio of the solid (representative of the chemical structural change) have been taken as conversion indices. From the measurement of the C/H ratio of the solid (the more significant variable), it has been determined that the reaction order is 0.5 and that the kinetic constant is between 0.18 min⁻¹ at 350 °C and 1.26 min⁻¹ at 700 °C. However the value of the constant is almost independent of temperature, at 1 min⁻¹ in the range 500–700 °C. © 2000 Society of Chemical Industry     

Kinetics of the thermal dissociation of ZnO exposed to concentrated solar irradiation using a solar‐driven thermogravimeter in the 1800–2100 K range

The two‐step H₂O‐splitting thermochemical cycle based on the Zn/ZnO redox reactions is considered for solar H₂ production, comprising the endothermal dissociation of ZnO followed by the exothermal hydrolysis of Zn. A solar‐driven thermogravimeter, in which a packed‐bed of ZnO particles is directly exposed to concentrated solar radiation at a peak solar concentration ratio of 2400 suns while its weight loss is continuously monitored, was applied to measure the thermal dissociation rate in a set‐up closely approximating the heat and mass transfer characteristics of solar reactors. Isothermal thermogravimetric runs were performed in the range 1834–2109 K and fitted to a zero‐order Arrhenius rate law with apparent activation energy 361 ± 53 kJ mol^?1 K^?1 and frequency factor 14.03 × 10⁶ ± 2.73 × 10⁶ kg m^?2 s^?1. Application of L‘vov’s kinetic expression for solid decomposition along with a convective mass transport correlation yielded kinetic parameters in close agreement with those derived from experimental data. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Usage of solar-assisted spouted bed drier in drying of pea

The main objective of this study is to evaluate the effects of solar-assisted spouted bed and open sun drying on the drying rate and quality parameters of pea. Color, shrinkage, bulk and apparent densities, internal and bulk porosities, rehydration capacity and microstructure were the quality parameters investigated in dried product.Drying rate for solar-assisted spouted bed was about 3.5 times of drying rate for open sun drying. Air temperature changed between 20 °C and 27.4 °C during open sun drying while temperature of air at the inlet of solar-assisted spouted bed dryer varied between 35.3 °C and 65.5 °C during the experiments. Effective diffusivities were found to be 0.64 × 10^?10 and 3.27 × 10^?10 m²/s for open sun and solar-assisted spouted bed drying of pea, respectively. In color analysis, it was observed that a* value increased while b* value decreased for both drying methods. Bulk density and apparent density of peas dried under open sun was higher than that in solar-assisted spouted bed drier. In both drying methods, internal and bulk porosities decreased. Shrinkage was more for open sun dried samples. Rehydration capacity for solar-assisted spouted bed dried sample was higher than the one for open sun dried.     

Investigations on heat transfer and hydrodynamics under pyrolysis conditions of a pilot-plant draft tube conical spouted bed reactor

This paper describes the hydrodynamic and heat transfer performance of a pilot-plant scale conical spouted bed reactor designed for the pyrolysis of biomass wastes. The spouted bed reactor is the core of a fast pyrolysis pilot plant with continuous biomass feed of up to 25 kg/h, located at the Ikerlan-IK4 facilities.The aim of this paper is to obtain a deeper understanding of the spouted bed reactor performance at pyrolysis temperatures, in order to operate under stable conditions, improve the heat transfer rate in the reactor and minimize energy requirements. The influence of temperature on conical spouted bed hydrodynamics has been studied and wall-to-bed and bed-to-surface heat transfer coefficients have been determined.     

Modelling wood combustion under fixed bed conditions

A computer model describing the conversion of wood under packed-bed conditions is presented. The packed bed is considered to be an arrangement of a finite number of particles, typically sized between 5 and 25 mm, with a void space left between them. Each particle is undergoing a thermal conversion process, which is described by a one-dimensional and transient model.Within the single-particle model, heating, drying, pyrolysis, gasification and combustion are considered, whereby each particle exchanges energy due to conduction and radiation with its neighbours. Because of the one-dimensional discretization of the particles, heat transfer and mass transfer is taken into account explicitly. Therefore, no macrokinetic data are needed within the model. For ease of implementation and access, kinetic data and property data are stored in a database. The global conversion of the packed bed is represented by the contributions of single particles, where each particle is coupled to the surrounding gas phase by heat and mass transfer. For gas phase flow through the porous bed, the conservation equations for mass, momentum and energy are solved on a Cartesian mesh by a Finite Volume method.Experiments have been performed to validate the single particle model for the conversion of beech wood during pyrolysis and char combustion. Agreement between experimental and predictions obtained by the model is very satisfactory. However, for wet wood, changes in structure seem to enhance the heat transfer to the solid which is not yet covered in the model.     

The Gas-to-Particle Heat Transfer and Hydrodynamics in Spouted Bed Drying of Sawdust

Abstract

This article presents experimental results for spouted bed drying of sawdust, carried out in a full-scale as well as in a laboratory-scale dryer using air as well as steam as drying media. The aim is to present design parameters for a spouted-bed sawdust dryer that can be used by the industry in designing full-scale dryers. A hydrodynamically stable spouted jet spouted bed was obtained. The heat transfer characteristics of the bed were represented in terms of a volumetric heat transfer coefficient (VHC). When sawdust is dried in a spouted bed, the mean VHC is increasing up to fiber saturation level (20–25% wb) from 40 to 110 W/m³ K. The VHC decreases with the residence time and with an increased static bed height. Gas temperature profiles are also presented for the bottom part of the drying chamber.     

Hydrodynamic characteristics of cold-bed circulating fluidized beds for the methanol to olefins process

The effects of the riser inlet velocity (2.2–3.9 m/s), seal-pot inlet velocity (2.4–7.1 U _mf ), aeration flow rate (2.5×10^?7–3.7×10^?6 m³/s) in seal-pot, and solid inventory (0.15–0.2 kg) on the hydrodynamic characteristics of a 9 mm-ID×1.9 m-high cold-bed circulating fluidized bed for methanol to olefins (MTO) process were investigated. FCC (Engelhard; 82.4 μm) particles were used as bed particles. Most of the experimental flow regimes were observed in fast fluidization and pneumatic transport regimes. The axial solid holdup in a riser increased with increasing solid mass flux and solid inventory. Solid mass flux increased proportionally until reaching a maximum value and then decreased with increasing seal-pot inlet velocity. The obtained hydrodynamic characteristics in the cold-bed circulating fluidized beds were compared with previous results.     

Pyrolytic characteristics of Jatropha seedshell cake in thermobalance and fluidized bed reactors

Pyrolytic kinetic parameters of Jatropha seedshell cake (JSC) were determined based on reaction mechanism approach under isothermal condition in a thermobalance reactor. Avrami-Erofeev reaction model represents the pyrolysis conversion of JSC waste well with activation energy of 36.4 kJ mol^?1 and frequency factor of 9.18 s^?1. The effects of reaction temperature, gas flow rate and feedstock particle size on the products distribution have been determined in a bubbling fluidized bed reactor. Pyrolytic bio-oil yield increases up to 42 wt% at 500 °C with the mean particle size of 1.7 mm and gas flow rate higher than 3U _mf , where the maximum heating value of bio-oil was obtained. The pyrolytic bio-oil is characterized by more oxygen, lower HHVs, less sulfur and more nitrogen than petroleum fuel oils. The pyrolytic oil showed plateaus around 360 °C in distribution of components’ boiling point due to high yields of fatty acid and glycerides.     

Microkinetic model for the pyrolysis of methyl esters: From model compound to industrial biodiesel

A tool for the generation of decomposition schemes of large molecules has been developed. These decomposition schemes contain radicals which can be eliminated from the model equations if both the μ‐hypothesis and the pseudosteady‐state approximation are valid. The reaction rate coefficients and thermodynamic parameters have been calculated by incorporating a comprehensive group additive framework. A microkinetic model for the pyrolysis of methyl esters with a carbon number of up to 19 has been generated using this tool. It is validated by comparing calculated and experimental yields of the pyrolysis of methyl decanoate and novel rapeseed methyl ester pyrolysis data in the temperature range from 800 to 1100 K and methyl ester partial pressure range from 1 × 10^?3 to 1 × 10^?2 MPa. This modeling frame work allows to not only assess the use of methyl ester mixtures as potential feedstock for olefin production but also their effect as blend‐in or trace impurity. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4309–4322, 2015     

Ash-agglomerating gasification of coal in a spouted bed reactor

Australian bituminous coal (Hoskisson) was gasified with oxygen and steam in a 0.4m diameter spouted bed reactor at atmospheric pressure and temperatures of 1050–1170 °C to produce medium calorific value gas. High-ash agglomerates fell through the throat of the spouted bed under restricted gasification conditions, with no simultaneous loss of coal. The effects of temperature, steam-oxygen ratio, coal feed rate and coal size on carbon conversion, production of ash agglomerates, gas composition and decompsition of steam were established.     

Effect of particle size on thermal decomposition and devolatilization kinetics of melon seed shell

Thermogravimetric analysis (TGA) and devolatilization kinetics of melon seed shell (MSS) at different particle sizes (150?µm and 500?µm) and at different heating rates (10, 15, 20, and 25?°C/min) were investigated with the aid of TGA. The results of the TGA analysis show that the TGA curves corresponding to the first and third stages for 150?µm particle sizes exhibited some bumps that developed at the first and third stages of pyrolysis. It was also observed that at constant heating rate, the maximum peak temperature increases as the particle sizes increase from 150 to 500?µm, whereas 500?µm particle sizes exhibited higher peak temperatures compared to 150?µm particle sizes. The resulting TGA data were applied to the Kissinger (K), Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods and kinetic parameters (activation energy, E and frequency factor, A) were determined. The E and A obtained using K method were 74.27?kJ mol^?1 and 3.84?×?10⁵?min^?1 for 150?µm particle size, whereas for 500?µm particle size were 97.12?kJ mol^?1 and 3.74?×?10⁷?min^?1, respectively. However, the average E and A obtained using KAS and FWO methods were 82.35?kJ mol^?1, 1.29?×?10⁷?min^?1, and 88.50?kJ mol^?1, 1.32?×?10⁷?min^?1 for 150?µm particle sizes. While for 500?µm particle sizes, the E and A were 108.46?kJ mol^?1, 3.14?×?10⁹?min^?1, and 113.05?kJ mol^?1, 7.56?×?10⁹?min^?1, respectively. It was observed that E and A calculated from FWO and KAS methods were very close and higher than that obtained by K method. It was observed that the minimum heat required for the cracking of MSS particles into products is reached later at higher peak temperatures since the heat transfer is less effective as they are at lower peak temperatures.     

Simultaneous heat and mass transfer in spouted beds

The results of a fluid-particle heat and mass transfer study in air spouted beds of silica gel and activated coal particles, using a 9 cm I.D. column with a 30° and 90° conical base, are reported. The effects of gas velocity, particle size, bed depth and cone angle on the heat and mass transfer coefficients are discussed. Equations correlating heat and mass transfer coefficients have been established. The ratio (jn)_s/(j_D)₈ has been found to be dependent on the Reynolds number and the system of spouting.     

Kinetic and thermodynamic study of methanolysis of poly(ethylene terephthalate) waste powder

Depolymerization of poly(ethylene terephthalate) waste (PETW) was carried out by methanolysis using zinc acetate in the presence of lead acetate as the catalyst at 120–140 °C in a closed batch reactor. The particle size ranging from 50 to 512.5 µm and the reaction time 60 to 150 min required for methanolysis of PETW were optimized. Optimal percentage conversion of PETW into dimethyl terephthalate (DMT) and ethylene glycol (EG) was 97.8% (at 120 °C) and 100% (at 130 and 140 °C) for the optimal reaction time of 120 min. Yields of DMT and EG were almost equal to PET conversion. EG and DMT were analyzed qualitatively and quantitatively. To avoid oxidation/carbonization during the reaction, methanolysis reactions were carried out below 150 °C. A kinetic model is developed and the experimental data show good agreement with the kinetic model. Rate constants, equilibrium constant, Gibbs free energy, enthalpy and entropy of reaction are also evaluated at 120, 130 and 140 °C. The methanolysis rate constant of the reaction at 140 °C (10.3 atm) was 1.4 × 10^?3 g PET mol^?1 min^?1. The activation energy and the frequency factor for methanolysis of PETW were 95.31 kJ mol^?1 and 107.1 g PET mol^?1 min^?1, respectively. © 2003 Society of Chemical Industry     

Investigation into the viability of a liquid-film three-phase spouted bed biofilter

A variety of technologies exist for the treatment of malodorous air streams, including adsorption, absorption, catalytic combustion, biofiltration and bioscrubbing. Conventional packed bed biofiltration of malodorous substances from waste gas streams has the disadvantages of large unit surface area and relatively uncontrolled design principles. The large bed surface area leads to difficulties in maintaining even moisture and temperature profiles. In addition, the control of such biologically important parameters as pH is difficult. Novel fluidized/spouted beds were studied for biological treatment of gases because of their high specific gas flowrate and vigorous mixing which facilitates enhanced gas–biomass contact. Trials of a range of fluidized and spouted beds, with gas loadings of up to 14000 m³-gas m⁻²-bed h⁻¹, were carried out on various biofilm support media including glass ballotini, rice hulls, plastic discs and granules, silica gel, molecular sieves, vermiculite, perlite, activated carbon, cork, polystyrene and expanded clay. Severe aggregation and wall adhesion restricted the operational range of the reactors. Particle suitability was based on a combination of shape, density, size, porosity and wettability, with large, heavy clay particles performing best. Limited gas-phase bacterial studies on selected media with ammonia- and nitrite-oxidizing bacteria demonstrated the potential of fluidized/spouted beds for efficient biofiltration of ammonia (20–40 mg dm⁻³). © 1998 Society of Chemical Industry     

Experimental studies on pyrolysis of Datong coal with solid heat carrier in a fixed bed

An experimental apparatus was set up for batch simulation of coal pyrolysis with solid heat carrier in a fixed bed. Quartz sand as heat carrier preheated to about 700–800°C was mixed with Datong bituminous coal by an agitator. The thermal history of the coal particle has been followed by a K-type thermocouple. The effects of particle size, pyrolysis time and temperature on the gas yield during pyrolysis of coal with solid heat carrier were examined for different conditions. The experimental results showed that a dominant percentage of the gas product is produced during the first 1–3 min, although gas evolution would last for as long as 10 min. The total gas yield, insensitive to particle size of the heat carrier, depends on carrier temperature and coal particle size under tested conditions. The contact heat transfer of cold and hot particles was analyzed.