Fluidized Bed Temperature Research Articles

Preparation of Syngas via Catalytic Gasification of Biomass with a Nickel-based Catalyst

Biomass gasification to produce syngas was carried out in a fluidized bed reactor and a catalytic fixed bed reactor. The feedstock was sawdust and the cracking catalyst included the calcined dolomite, Ni/dolomite, Ni/modified dolomite, and reforming catalyst. The Ni/modified dolomite catalyst showed better performance and low cost. The optimum technological conditions were as follows: fluidized bed temperature, 1,073 K; catalytic fixed bed temperature, 1,073 K; the mass ratio of steam to biomass, 2.0.

Particle attrition with supersonic nozzles in a fluidized bed at high temperature

Fluidized beds are used for a variety of processes such as food, pharmaceutical, petrochemical and energy production. Supersonic gas injection nozzles are used to grind particles in fluidized beds. For example, in the Fluid Coking process, which uses thermal cracking reactions to upgrade heavy oil, supersonic nozzles inject steam to control coke particle size. Maintaining a high attrition rate with a lower steam flowrate would reduce energy consumption, increase reactor throughput, and reduce sour wastewater production. The purpose of the present research is to study particle attrition with supersonic convergent–divergent nozzles in a fluidized bed at high temperatures, under conditions such as those encountered in the Fluid Coking process. According to the experimental results, the grinding efficiency is significantly improved by increasing fluidized bed temperature, attrition gas properties, or nozzle size. The experimental data further suggest that particle fragmentation is the dominant attrition process when using supersonic nozzles in a hot fluidized bed.

Biomass Combustion in a Fluidized-Bed System: An Integrated Model for Dynamic Plant Simulations

A model that can be used for dynamic simulation of fluidized-bed biomass combustion plants is presented. The model combines spatially concentrated (well-mixed) approaches for the fluidized bed and the ash separation cyclone with a one-dimensional plug-flow representation of the freeboard section. Simulation results are compared with steady-state experimental data for wood combustion in a laboratory-scale facility. Computed flue gas compositions are in good agreement with measured values, whereas some deviation is observed in fluidized-bed temperature. The integrated model provides reasonable accuracy at a high computational speed. Hence, it is appropriate, after coupling with a thermodynamic cycle, for real-time monitoring and control of distribution nets and electric grids supplied by various regenerative power sources. Possible model extension by a population balance for the fuel particles is briefly outlined.

Experimental investigation of the effect of initial fuel particle shape, size and bed temperature on devolatilization of single wood particle in a hot fluidized bed

Considerable amount of investigation on the subject of devolatilization of wood is found in the open literature. However, a systematic study of the effect of initial particle size and shape, and bed temperature on devolatilization time and char yield of wood in a hot fluidized bed is still missing. This paper attempts to fill this gap through a systematic experimental investigation to determine the devolatilization time and char yield of a typical woody biomass, “ Casuarina equisetifolia” particles of different initial sizes and shapes at various fluidized bed temperatures. Experiments are conducted using 10, 15, 20, and 25 mm Casuarina wood particles of three shapes, namely, cube, cylinder, and sphere at bed temperatures of 1023, 1123, and 1223 K. It is found that the initial wood particle size has the strongest influence on devolatilization time followed by the shape of initial wood particle and the bed temperature. Correlation for devolatilization time ( τ d) as a function of initial wood particle size ( d eq), sphericity ( ϕ), and bed temperature ( T b), is developed using 573 experimental data points exhibiting a correlation coefficient of 0.96 and predictions falling well within a deviation band of ±20%. The predictions of the present correlation are compared with the predictions of the existing correlations in literature for conditions also out of the present study and the deviation is found to be ±30%. Char yield, defined as the ratio of the residual mass at the end of devolatilization process to the initial mass of the wood particle is found to be in the range of 9–14% for all sizes, shapes, and bed temperatures. Char yield does not depict any definite trend with the variation of initial particle size, shape and bed temperature.

Non-premixed fluidized bed combustion of C1–C4n-alkanes

The non-premixed combustion of C1–C4n-alkanes with air was investigated inside a bubbling fluidized bed of inert sand particles at intermediate temperatures: 923K⩽TB⩽1123K. For ethane, propane and n-butane, combustion occurred mainly in the freeboard region at bed temperatures below T1=923K. On the other hand, complete conversion occurred within 0.2m of the injector at: T2=1073K. For methane, the measured values of T1 and T2 were significantly higher at 1023K and above 1123K, respectively. The fluidized bed combustion was accurately modeled with first-order global kinetics and one PFR model to represent the main fluidized bed body. The measured global reaction rates for C2–C4n-alkanes were characterized by a uniform Arrhenius expression, while the global reaction rate for methane was significantly slower. Reactions in the injector region either led to significant conversion in that zone or an autoignition delay inside the main fluidized bed body. The conversion in the injector region increased with rising fluidized bed temperature and decreased with increasing jet velocity. To account for the promoting and inhibiting effects, an analogy was made with the concept of induction time: the PFR length (bi) of the injector region was correlated to the fluidized bed temperature and jet velocity using an Arrhenius expression. These results show that the conversion of C2–C4n-alkanes can be estimated with one set of critical bed temperatures and modeled with one Arrhenius kinetics expression.

Bioactive Antioxidants Regulate RAC-GTP Expression at the Leading Edge of Migrating Oral Fibroblasts

Blended fuel comprising 23 wt.% polyethyleneterephthalate (PET) and 77 wt.% brown coal was gasified in an atmospheric fluidized bed gasifier of laboratory-scale. The gasification agent was composed of 10 vol.% O2 in bulk of nitrogen. Thermal and texture analyses were carried out to determine the basic properties of the fuel components. The influence of experimental conditions, such as the fluidized bed and freeboard temperatures on major and minor gas components and tar content, as well as features of the blended fuel gasification in comparison with the single coal gasification, were studied. In the case of coal with PET gasification, only the fluidized bed temperature showed significant influence on CO, CO2, CH4 and H2 content in the producer gas, whereas the effect of the freeboard temperature was insignificant. In single coal gasification both temperatures had considerable and almost the same influence. The content of minor components, such as ethane, ethylene, acetylene and benzene, was found to be more dependent on the freeboard temperature than on the fluidized bed temperature. It was observed that the higher the freeboard temperatures get, the lower is the concentration of the minor components, with the exception of acetylene. The absolute contents of almost all minor and tar components were approximately three times higher in blended fuel gasification than that in single coal gasification. Finally, partition of carbon (char) and selected metals into bottom and cyclone ash in gasification of both fuels is discussed.

An investigation of the dependence of roasting characteristics of sulfide nickel concentrates in fluidized bed furnaces on various factors by the method of design imitation experiment

The dependence of the roasting characteristics (fluidized bed temperature, specific productivity of the furnace, specific blasting expenditure, etc.) of nickel sulfide concentrates on various factors (blasting surplus factor, concentrate humidity, oxygen content in blasting, etc.) was studied using the method of the design simulation experiment. Software in the form of a mathematical model of roasting, which includes the material and heat balances and regression equations, is suggested. The factors are ranged by their effect on the fluidized bed temperature.

EXPERIMENT AND NEURAL NETWORK MODEL OF PRIMARY FRAGMENTATION OF OIL SHALE IN FLUIDIZED BED

In this paper, the effect of fluidized bed temperature on primary fragmentation of Huadian oil shale was investigated experimentally in thermal state using a small-scale fluidized bed with N 2 as fluidizing gas. The fluidized-bed temperatures changed from 600 °C to 1000 °C. Experimental results indicate that the fluidized bed temperature is an important factor of primary fragmentation of oil shale, and that higher bed temperature results in severer fragmentation. The laminated structure and high ash content may contribute to the primary fragmentation characteristics of Huadian oil shale. The thermal stress fragmentation and devolatilization-induced fragmentation have little effect on small oil shale particles. Furthermore, the experimental data were treated by a neural network method, and a Back Propagation network model for primary fragmentation of oil shale was set up through network learning and validated by experimental data.

Combustion and heat transfer characteristics in a square internally circulating fluidized bed combustor with draft tube

The effects of bed temperature (800–950 °C) and gas velocity to the draft tube (0.26–0.37 m/s) on the heat transfer coefficient and the overall combustion efficiency have been determined in a square internally circulating fluidized bed combustor (0.28 m width × 2.6 m height) with an orifice-type square draft tube (0.1 m width × 0.9 m height). The overall combustion efficiency increases with increasing the excess air and the bed temperature. At a given aeration rate to the moving bed, the heat transfer coefficient goes through a maximum value with increasing gas velocity in the fluidized bed. The heat transfer coefficients in the moving bed and in the freeboard increase with increasing gas velocity to the fluidized bed and bed temperature.

Optimization of an Artificial Neural Network by Selecting the Training Function. Application to Olive Oil Mills Waste

This article describes the selection of the training algorithm of an artificial neural network (ANN) used to model the drying of olive oil mill waste in a fluidized-bed dryer. The ANN used was a three-layer perceptron that predicts the moisture value at time t + T from experimental data (solid moisture, input air, and fluidized-bed temperature) at t time; T is the sampling time. In this study, 14 training algorithms were tested. This selection was carried out by applying several statistical tests to the real and predicted moisture values. Afterward, an experimental design was carried out to analyze the influence of the training function parameters on the ANN performance. Finally, Polak−Ribiere conjugate gradient backpropagation was selected as the best training algorithm. The ANN trained with the selected algorithm predicted the moisture with a mean prediction error of 1.6% and a correlation coefficient of 0.998.

Effects of operational parameters on emission performance and combustion efficiency in small-scale CFBCs

A well-designed CFBC can burn coal with high efficiency and within acceptable levels of gaseous emissions. In this theoretical study effects of operational parameters on combustion efficiency and the pollutants emitted have been estimated using a developed dynamic 2D (two-dimensional) model for CFBCs. Model simulations have been carried out to examine the effect of different operational parameters such as excess air and gas inlet pressure and coal particle size on bed temperature, the overall CO, NO x and SO 2 emissions and combustion efficiency from a small-scale CFBC. It has been observed that increasing excess air ratio causes fluidized bed temperature decrease and CO emission increase. Coal particle size has more significant effect on CO emissions than the gas inlet pressure at the entrance to fluidized bed. Increasing excess air ratio leads to decreasing SO 2 and NO x emissions. The gas inlet pressure at the entrance to fluidized bed has a more significant effect on NO x emission than the coal particle size. Increasing excess air causes decreasing combustion efficiency. The gas inlet pressure has more pronounced effect on combustion efficiency than the coal particle size, particularly at higher excess air ratios. The developed model is also validated in terms of combustion efficiency with experimental literature data obtained from 300 kW laboratory scale test unit. The present theoretical study also confirms that CFB combustion allows clean and efficient combustion of coal.

Preparation of Hydrogen via Catalytic Gasification of Residues from Biomass Hydrolysis with a Novel High Strength Catalyst

Producing fuel alcohol via hydrolysis of lignocellulosic biomass leaves a considerable amount of residues waiting for treatment. A study was carried out on the preparation of hydrogen via catalytic gasification of residues from biomass hydrolysis with a novel Ni/modified dolomite binary catalyst, which was prepared by a two-step coprecipitation method and proved available for hydrogen production in terms of both activity and strength. The effects of four operation parameters, that is, the fluidized bed temperature, the catalytic fixed bed temperature, the particle size of the catalyst, and S/B (i.e., the mass ratio of steam to biomass material fed into the fluidized bed per unit time), on hydrogen yield were investigated. The results indicate that hydrogen yield increases with an increase in the temperature of either the fluidized bed or the downstream catalytic fixed bed or the S/B ratio or a reduction in the particle size of the catalyst. The optimum range for each of the four operation parameters from a comprehensive consideration is as follows: 800–850 °C for both the fluidized bed temperature and the catalytic fixed bed temperature, 1.5–2 for the S/B ratio, and 2.0–3.0 mm for the particle size of the catalyst. Furthermore, the gas product from catalytic gasification of residues from biomass hydrolysis contains less CO and CO2 and has a higher H2/CO ratio compared with that of the sawdust. The hydrogen yield of the former is also much higher than that of the latter. These suggest that residues from biomass hydrolysis are an even better gasification material than the original sawdust. This paper provides a novel effective method for modifying the calcined dolomite, which endows the catalyst with satisfactory strength while retaining high activity, and opens a new promising way for utilizing the residues from biomass hydrolysis.

Wave propagation and granular temperature in fluidized beds of nanoparticles

AbstractThe speeds of motion of compression waves through a fluidized bed of 10 nm silica particles were determined by measuring the times of arrival of compression zones using a light probe. A correlation for the modulus of elasticity was determined as a function of void fraction. Using a kinetic theory type equation of state for particles, this experimentally determined modulus gives a value for the granular temperature for 10 nm particles of approximately one (meter per second) squared. This value is close to that obtained by assuming the motion of the 10 nm particles to be due to collision with air molecules with no energy dissipation. The values of the granular temperature were also determined in a two‐dimensional (2‐D) fluidized bed by measuring the volume fraction distributions of 10 nm silica particles. Granular temperatures were deduced from a one‐dimensional particle momentum balance using an ideal equation of state for particles, which is similar to the barometric formula for gases. These granular temperatures agreed with the measurements obtained from wave propagation experiments. © 2007 American Institute of Chemical Engineers AIChE J, 2007

A Model of Coal Particle Drying in Fluidized Bed Combustion Reactor

Experimental and theoretical investigation on drying of a single coal particle in fluidized bed combustor is presented. Coal particle drying was considered via the moist shrinking core mechanism. The results of the drying test runs of low-rank Serbian coals were used for experimental verification of the model. The temperature of the coal particle center was measured, assuming that drying was completed when the temperature equalled 100°C. The influence of different parameters (thermal conductivity and specific heat capacity of coal, fluidized bed temperature, moisture content and superheating of steam) on drying time and temperature profile within the coal particle was analyzed by a parametric analysis. The experimentally obtained results confirmed that the moist shrinking core mechanism can be applied for the mathematical description of a coal particle drying, while dependence between drying time and coal particle radius, a square law relationship, implicates heat transfer control of the process and confirms the validity of assumptions used in modeling.

Numerical simulation of temperature and concentration distributions in fluidized beds with liquid injection

In this paper a numerical simulation study of dynamic behavior of a fluidized bed with liquid injection is presented. A continuum model has been developed taking into account the mass and energy balances of solid, gas as well as liquid to describe the temperature and concentration distributions in gas–solid-fluidized beds. The model considers the deposition efficiency of the liquid droplets as well as the influence of the spray nozzle region. For solving the non-linear partial differential equations with discrete boundary conditions a finite element method is used. Numerical computations have been done with two different schemes of time integration, a fully implicit and a semi implicit scheme. The complex correlations of mass and liquid flow rates, mass and heat transfer, drying, and transient two-dimensional air humidity, air temperature, particle wetting, liquid film temperature and particle temperature were simulated. The model was validated with transient measurements of the air temperature and air humidity at the outlet of a fluidized bed with water injection.

Thermal remediation of oil polluted sands from black tides: The fluidized bed option

Abstract Following the oil spills due to the accidents involving the oil tankers Erika and Prestige on the Atlantic coast, thermal remediation of oil polluted sands in a fluidized bed was studied. A thermal process is proposed as an alternative to the physico-chemical washing that has been carried out with the Erika wastes. The study consists of: choice of the polluted wastes; air fluidization behavior of oil polluted sands in a cold fluidized bed; depollution characterization in a hot fluidized bed; design and engineering of an industrial scale furnace and investment and operating cost evaluation of such a remediation unit. Polluted sands were prepared for different combinations of sand particle diameter, oil and water content. Fluidizability of oil polluted sands was checked in a cold model fluidized bed facility. Hot tests showed that combustion started as soon as the fluidized bed temperature was equal to or higher than 700 °C. The remediation of the polluted sand was good in all the cases with a remaining pollution in the sand of about 50 mg/kg. Flue gas emissions were within the regulatory limits. There was no danger of any ash fusion noticed even in the long duration tests. An industrial scale furnace was then designed based on the measured limits of fluidizability and the evaluated time necessary to get an almost complete remediation of the oil. Fluidized bed treatment costs were then evaluated and compared to the physico-chemical separation that has been used in the case of Erika oil spill and the thermal treatment in a rotating furnace. Fluidized bed combustion appeared to be one of the best options with a cost of only 80 €/t of polluted waste.

Gasification of coal and PET in fluidized bed reactor

Blended fuel comprising 23 wt.% polyethyleneterephthalate (PET) and 77 wt.% brown coal was gasified in an atmospheric fluidized bed gasifier of laboratory-scale. The gasification agent was composed of 10 vol.% O 2 in bulk of nitrogen. Thermal and texture analyses were carried out to determine the basic properties of the fuel components. The influence of experimental conditions, such as the fluidized bed and freeboard temperatures on major and minor gas components and tar content, as well as features of the blended fuel gasification in comparison with the single coal gasification, were studied. In the case of coal with PET gasification, only the fluidized bed temperature showed significant influence on CO, CO 2, CH 4 and H 2 content in the producer gas, whereas the effect of the freeboard temperature was insignificant. In single coal gasification both temperatures had considerable and almost the same influence. The content of minor components, such as ethane, ethylene, acetylene and benzene, was found to be more dependent on the freeboard temperature than on the fluidized bed temperature. It was observed that the higher the freeboard temperatures get, the lower is the concentration of the minor components, with the exception of acetylene. The absolute contents of almost all minor and tar components were approximately three times higher in blended fuel gasification than that in single coal gasification. Finally, partition of carbon (char) and selected metals into bottom and cyclone ash in gasification of both fuels is discussed.

An Experimental Study of Temperature of Burning Coal Particle in Fluidized Bed

The purpose of this study was to investigate the temperature of coal particle during combustion in fluidized bed (FB). It is necessary to know the coal particle temperature in order to predict kinetics of chemical reactions within and at the surface of coal particle, accurate NOx and SO2 emission, fragmentation, attrition, the possibility of ash melting, etc. The experimental investigations were conducted in order to obtain the reliable data on the temperature of particle burning in the FB. A method using thermocouple was developed and applied for measurements. Thermocouple was inserted in the center of the particle shaped into spherical form with various diameters: 5, 7, 8, and 10 mm. Two characteristic types of low-rank Serbian coals were investigated. Experiments were done at the FB temperature in the range of 590−710 °C. Two types of experiments were performed: (i) combustion using air as fluidization gas and (ii) devolatilization with N2 followed by combustion of obtained char in air. The temperatu...

Modeling the Drying of a High-Moisture Solid with an Artificial Neural Network

The byproduct so-called alperujo (a solid−liquid byproduct generated from olive oil extraction by two-phase centrifugation) is difficult to dry due to its high moisture content. An artificial neural network (ANN) was developed to model the drying of alperujo in fluidized bed dryers. The ANN, a three layer perceptron (3 inputs, 4 hidden nodes, and 1 output) with back-propagation updating, serves to predict the moisture of the output solid at a time t + T from known input data at time t. The input data are the actual values of the input air temperature, fluidized bed temperature, and output solid moisture. T is the sampling time. The ANN learning, topology optimization, and verification are described in this paper. The essential data to design the ANN were taken from runs in a bench-scale dryer, and the ANN validation was carried out by applying basic statistical criteria and the standard tests of Mann−Whitney, Kruscal−Wallis, and Kolmogorov−Smirnov. The results of these tests, which compare the real with predicted moisture data, demonstrate that the fluidized bed dryer is well-modeled by the ANN (prediction error of 4.5%).

Catalytic Decomposition of N2O over the Bed Material from Circulating Fluidized-Bed (CFB) Boilers Burning Biomass Fuels and Wastes

In this paper, the catalytic decomposition of N2O was studied over the bed materials sampled from the bottom bed of two industrial circulating fluidized-bed (CFB) boilers (a 12 MWth boiler and a 550 MWth boiler) burning biomass fuels and wastes, either alone or as a mixture. The catalytic activity of the bed materials were compared by measuring the conversion of N2O in a laboratory fixed-bed reactor in the temperature range of 600−910 °C. The composition and morphology of the bed material were characterized using X-ray fluorescence and scanning electron microscopy coupled with energy-dispersive X-ray analysis. The activity of bed material was observed to be affected by the sample heterogeneity and tendency to deactivate when exposed to fluidized-bed temperatures. The activity of the bed materials was also influenced by the type of fuel, for which the kinetic expressions are derived. For the bed-material samples from the 12 MWth CFB boiler, it was observed that the higher the amount of the catalytically active oxides (CaO + MgO + Fe2O3 + Al2O3), the higher the activity of the sample toward N2O decomposition. The elemental composition of the surface of the bed material particles changed according to the composition of the ash from the parent fuel. On the other hand, such correlations were not observed for the samples from the 550 MWth CFB boiler.