Continuous pyrolysis of waste tyres in a conical spouted bed reactor

Continuous pyrolysis of scrap tyres has been carried out in a conical spouted bed reactor and the results (yields, composition of the volatile fraction and carbon black properties) have been compared with those obtained operating in batch mode in a previous study. Continuous operation in the 425-600 °C range gives way to a yield of 1.8-6.8 wt.% of gases, 44.5-55.0 wt.% of liquid fraction (C₅-C₁₀ range hydrocarbons, with a maximum yield of limonene of 19.3 wt.% at 425 °C), 9.2-11.5 wt.% of tar and 33.9-35.8 wt.% of char. The main differences between the continuous and batch processes are in the yield of light aromatics, which is higher in the continuous process, and in that of the heavy liquid fraction or tar, which is higher in the batch process. These are the advantages of the continuous process, although hydrogenation of the liquid fraction is required even in this case in order to use it as fuel. The high yield of limonene, the flexibility in the operating conditions and the capacity for a continuous removal of the residual carbon black from the reactor are the advantages of conical spouted bed technology. The excellent performance of the conical spouted bed reactor for the tyre pyrolysis process is due to the solid cyclic movement, the good contact between phases, the high heating rate and the reduced residence time of the volatile products.     

Minimum spouting velocity for the pyrolysis of scrap tyres with sand in conical spouted beds

The effect of temperature (in the 298-973 K range) on minimum spouting velocity has been studied in conical spouted beds made up of mixtures of tyre and sand particles, for different sizes of tyre particles and for different tyre/sand ratios. The good fit to the experimental results confirms the validity of the correlations already proposed by Olazar et al. [M. Olazar, M.J. San José, A.T. Aguayo, J.M. Arandes, J. Bilbao, Stable operation conditions for gas-solid contact regimes in conical spouted beds, Ind. Eng. Chem. Res. 31 (1992) 1784-1791] for room temperature, which is due to the fact that they take into account the density and viscosity of the gas. For fine particles, the effect of density prevails on the effect of viscosity and the equations proposed by Bai et al. [D. Bai, Y. Masuda, N. Nakagawa, K. Kato, Hydrodynamic behavior of a binary solids fluidized bed, J. Chem. Eng. Jpn. 29 (1996) 211-216] are suitable for the calculation of the average particle size and density, in order for them to be used in the calculation of minimum spouting velocity. For coarse particles, the effect of gas viscosity is insignificant compared to the effect of density and the equation of Goossens et al. [W.R.A. Goossens, G.L. Dumont, G.L. Spaepen, Fluidization of binary mixtures in the laminar flow region, Chem. Eng. Prog. Symp. Ser. 67 (1971) 38-45] is suitable for the calculation of the average particle size required for ascertaining minimum spouting velocity.     

Simulation of a spouted bed reactor for solid catalyst alkylation

A process simulator was developed to afford a better understanding of the performance of a butene-isobutane alkylation plant that uses a three-phase spouted bed reactor and a super acid solid catalyst. The mass and energy balances were numerically solved using lump of reactions and kinetic expressions previously developed. The results indicate the strong influence of the gas linear velocity and temperature in the riser and downcomer behavior that affects the activity, selectivity, and stability of the catalytic systems that cannot be predicted otherwise. The optimal operating conditions were determined for a particular catalyst and set of costs. The impacts of the recycling alkylate and isobutane to the reactor as well as the presence of hydrogen to control the coke formation are analyzed.     

Modelling batch drying of sand in a draft-tube conical spouted bed

A model has been built to predict the evolution of sand drying in a conical spouted bed with a non-porous draft tube. Three regions have been considered in the model, i.e., spout, annulus and fountain, and unsteady-state mass balances have been written for water in the solid and gaseous phases. The model has been validated by comparing its results with the experimental ones obtained in a previous study and it allows predicting the moisture content evolution of both the air and the sand during the drying process.     

Sustainable hydrogen production via reforming of ethylene glycol using a novel spouted bed reactor

Hydrogen produced from renewable energy sources is of great interest as an alternative to fossil fuels and as a means for clean power generation via fuel cells. The aqueous fraction of bio-oil can be effectively reformed to hydrogen rich streams in the presence of active catalytic materials. In this paper we present the experimental work carried out in a novel spouted bed reactor for the reforming of bio-oil. The use of a specially designed injection nozzle in combination with the particular hydrodynamic characteristics of the spouted bed resulted in efficient processing of the organic feed. The known problem of coking was notably avoided regardless of the loading material of the reactor. The effect of reaction temperature and steam to carbon ratio in the feed was investigated in the presence of various catalytic and non-catalytic particles. Runs were conducted with ethylene glycol as a representative model compound of the aqueous phase of bio-oil. Olivine, when associated with nickel, proved to be a very suitable catalytic material for the process combining high activity in reforming, anti-coking characteristics combined with exceptional mechanical strength.     

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     

Analysis of conical spouted bed fluid dynamics using carton mixtures

The pyrolysis has risen as an important alternative technology for generating value from waste. Among the modern solid wastes, the post-consumer carton packaging highlights due to the high value-added of the primary products obtained from pyrolysis. In an attempt to use conical spouted beds (CSBs) as a pyrolysis reactor for processing cartons, this present research aims at analyzing experimentally the air–carton mixtures flow dynamics in CSBs and stating comparisons with characteristic fluid dynamics obtained by using CFD technique. The flow behavior of air–carton disk is experimentally investigated by analyzing data of bed pressure drop, air velocity and fountain height. For the carton disk and polyethylene mixtures up to 50% cartons (in mass), and carton disks and sand mixtures comprising 5 and 10% cartons (in mass), the analysis of the experimental data shows that the stable spouted regimes are achieved. Furthermore, the simulated results demonstrate that the Eulerian approach using the Syamlal drag model is able to predict qualitatively the flow behavior in conical spouted beds comprising non-spherical particle mixtures.     

Mathematical modeling of polyethylene terephthalate pyrolysis in a spouted bed

A model has been developed for pyrolysis of polyethylene terephthalate (PET) in a spouted bed reactor based on the conservation equations for heat, mass, and momentum transports. A spouted bed has been constructed and the kinetic parameters have been obtained within the temperature range of 723–833 K, using two particle size ranges, (0.1–1.0) × 10^?3 and (1.0–3.0) × 10^?3 m. The model' predictions for the radial distributions of temperature and concentration confirm the excellent mixing of particles. Thus, spouted beds are appropriate equipments for performing kinetic studies of PET pyrolysis. The inlet gas temperature and the mass of PET highly affect PET conversion. The amount of inert particles has a negligible effect on the conversion and it can be reduced as far as a stable spouting is preserved. The gas flow suffices to eliminate the external heat and mass‐transfer limitations. It can be reduced to the minimum value to decrease the energy consumption. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1900–1911, 2015     

Deposition of SiC/Si coatings in a microwave plasma-assisted spouted bed reactor

Silicon carbide (SiC) layers were deposited onto alumina particles in a microwave plasma-assisted spouted bed reactor using methyltrichlorosilane (MTS) and hydrogen mixtures, in argon, as precursor gas feed. The operating parameters studied were enthalpy, gas composition, and pressure. Microwaves were guided from a generator, operating at 2.45 GHz, along a rectangular waveguide intersecting a quartz tube, acting as the reaction zone. A graphite nozzle at the bottom of the tube facilitated the spouting action. Growth rates varied from 50 to 140 μm/h. Overall results indicate that the optimal region for SiC deposition requires relatively high enthalpy (～5 MJ/kg) and pressure (>?60 kPa) conditions, with hydrogen-to-MTS ratios ～5:1. The quality (i.e. crystallinity, particle size, Si/C ratios) of the layers improve at these conditions, at the cost of decreased deposition rates. Characterisation was done by XRD, FTIR, XPS, SEM, TEM and EDX, which assisted in developing colour and morphological charts to indicate the changes as a function of changing operating parameters. A microwave plasma spouted bed reactor is demonstrated to be a viable alternative technique for SiC layer deposition onto microspheres.     

Feasibility study of a spouted bed gasification plant

We have studied the feasibility of building a biomass gasification plant with an innovative spouted bed reactor for distributed energy production. The process was simulated using a thermodynamic approach (concentrated parameter model) using LIBPF, a C++ process modelling library. A nominal size of about 100 kW total thermal power was chosen.     

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.     

Co-pyrolysis characteristics of typical components of waste plastics in a falling film pyrolysis reactor

Waste plastics mainly come from MSW and usually exist in the form of mixed plastics. During the co-pyrolysis process of mixed plastics, various plastic components have different physicochemical properties and reaction mechanisms. Considering the high viscosity and low thermal conductivity of molten plastics, a falling film pyrolysis reactor was selected to explore the rapid co-pyrolysis process of typical plastic components (PP, PE and PS). The oil and gas yields and the compositions of pyrolysis products of the three components under different ratios at pyrolysis temperatures were analyzed to explore the co-pyrolysis characteristics of PP, PE, and PS. The study is of great significance to the recycling of waste plastics.     

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     

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.     

Effect of operating conditions on the drying of fine and ultrafine sand in a fountain confined conical spouted bed

Abstract

A study has been carried out on the influence process conditions and design parameters have on the drying in a conical spouted bed. Optimum parameters have been determined for the draft tube and the fountain confiner. Drying time is reduced when the spout region is enlarged. A distance between the bed surface and the lower end of the confiner in the 0.10–0.15 m range and a confiner of 0.5–0.9 m length minimize the drying time. Longer distances do not avoid entrainment, and shorter distances lead to higher pressure drop and minimum spouting velocity. Longer fountain confiners do not reduce significantly the drying time. Draft tubes with a reduced aperture ratio lead to longer drying times due to their adverse effect on the gas–solid contact. Aperture ratios above 60% cause a decrease in the efficiency of the process due to the higher gas flow rates required to achieve spouting regime.     

循环喷动流化床颗粒抛射高度的计算

通过对循环喷动流化床顶部封闭空间气体射流及气固运动的理论分析 ,得出了循环喷动流化床中颗粒出循环管后抛射高度的计算方法 ,所得计算结果与实测结果误差小于 8% ,为循环喷动流化床的设计提供理论依据     

A comparative hydrodynamic study of two types of spouted bed reactor designs

In order to properly design and scale up spouted beds, one needs to predict the minimum spouting velocity of specific systems having different bed dimensions, and properties of particle and spouting gas. Because of inherent complexity of predicting minimum spouting velocity, the prevailing approach has been to use empirical correlations, a number of which are available in the literature. Central jet distributors are commonly used in the experimental studies reported in the literature. Circular slit distributor is a new concept in which air is supplied to the bed of particles through a circular slit. This paper presents results of an experimental study on the hydrodynamics of central jet and circular slit distributors. In this paper a fully connected feed-forward neural network model was used to predict the minimum spouting velocity of central jet and circular slit spouted beds. A neural network model was also developed to predict minimum fluidization velocity. The actual experimental data obtained from published literature and from the experiments carried out in this study were used for training and validating the models. The minimum spouting and fluidization velocities predicted using the neural network models developed in this study show a better approximation to the actual experimental values than those obtained from correlations available in the open literature. The position of flow regime of circular slit spouted bed was also established relative to the flow regimes of central jet spouted bed and fluidized bed.     

Prediction of spouted bed reactor performance using kinetic models

The form of the equation governing the kinetic model of a reactor depends on the mixing regime of the reacting phases and the conversion kinetics. The formation of detached flow in a spouted-bed reactor results in backmixing of the solid material. Therefore, the processes in a spouted-bed reactor can be described by a diffusion (quasihomogeneous) model equation. The paper compares the values of the production capacity of a spouted-bed reactor calculated using the diffusion model with experimental values of the efficiency of green ultramarine oxidation (kinetic region), of oxidative calcination of some metal sulphides (mixed region), and of the ion exchange extraction of copper from solutions (diffusion region). The kinetics of the corresponding conversions are also described.     

Local porosity in conical spouted beds consisting of solids of varying density

Local bed voidage has been measured in conical spouted beds by means of an optical fibre, for different geometric factors of the contactor (angle and inlet diameter) and under different experimental conditions (height of the stagnant bed, particle diameter and air velocity). The study has been carried out with glass beads and materials of lower density (high- and low-density polyethylene, polypropylene and extruded and expanded polystyrene). From the results, a correlation has been proposed for calculation of the local bed voidage in the spout and annular zones. The effect of the experimental conditions on the bed voidage in the solid ascent (core) and descent (periphery) regions of the fountain has been studied and the fountain has been proven to be of greater importance in the design of conical spouted beds, as solid density and shape factor are lower.     

Characterization and CFD-modeling of the hydrodynamics of a prismatic spouted bed apparatus

Recently the importance of spouted bed technology has significantly increased in the context of drying processes as well as granulation, agglomeration or coating processes. However, the understanding of the complex interactions within and between the single phases is still low and needs further improvement. Several research groups apply both continuum as well as discrete element simulations to understand the hydrodynamics of the spouting process. This work focuses on the simulation of the hydrodynamic behavior of a prismatic spouted bed apparatus by applying the Euler/Euler continuum approach in the commercial computational fluid dynamics (CFD) software package FLUENT 6.2. The simulations are validated by experiments. Calculated and experimental (by PIV-measurements) obtained velocity vector maps, as well as measured and calculated gas phase pressure fluctuations over the entire bed are compared. The aim of this work is to improve the understanding of the hydrodynamics of the spouting process.