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Modelling of Catalytical Bubbling Fluidized Bed on Pilot Scale  [PDF]
Amir Farshi,Saeed Hassan Boroojerdi
Petroleum and Coal , 2005,
Abstract: Crystalline melamine is a raw material for synthesizing of formaldehyde melamine resin. Formaldehyde melamine resin has been widely used in the industry. The simulation of fluidized reactor is a requirement of reactor design. To simulate the fluidized bed reactor is required that kinetic parameters (e.g. rate constant, k and reaction degree, n) and thermodynamic parameters (e.g. height, and minimum fluidization rate) to be known. The quantity of these parameters must be determine to synthesise melamine from urea (For both fixed bed reactor and fluidized bed reactor). They have been determined for both fixed bed and fluidized bed reactor in a pilot scale . Farshi (2002) has corrected these quantities for a two phases hydrodynamic model to simulate fluidized bed reactor. The results of these simulation and their comparison with the resulting experimental data from literature has been indicated that the results from the two phases model more properly matched with experimental data. Thus the two phases model is an appropriate model for simulation of gas-solid bubbling fluidized bed reactor.The two phases model with some correction and the bubbles with the medium diameter that their diameter have been calculated using Mori and Wen equation (1975) are used in this paper.
Eulerian-Lagrangian simulation of a bubbling fluidized bed reactor: Assessment of drag force correlations  [PDF]
Ku Xiao-Ke,Li Tian,Lovas Terese
Thermal Science , 2012, DOI: 10.2298/tsci1205442k
Abstract: An Eulerian-Lagrangian approach is developed within the OpenFOAM framework to investigate the effects of three well-known inter-phase drag force correlations on the fluidization behavior in a bubbling fluidized bed reactor. The results show a strong dependency on the restitution coefficient and the friction coefficient and no occurrence of bubbling and slugging for the ideal-collision case. The mean pressure drops predicted by the three models agree quite well with each other.
Mixing Behavior of Binary Polymer Particles in Bubbling Fluidized Bed
S.M. Tasirin,S.K. Kamarudin,A.M.A. Hweage
Journal of Physical Science , 2008,
Abstract: Fluidized bed mixer offers the most efficient and economical process compared to other mixers. However, less effort has been devoted to understand the local behavior of the solids in fluidized bed, partly due to the lack of reliable experimental methods. Thus, the objective of this paper was to view the local mixing behavior and property of a free flow polymer binary mixture in bubbling fluidized bed. In this work, an experimental study of mixing process of free flowing polymers binary mixtures at different densities and colors in bubbling fluidized were investigated. The mixing properties were studied by analyzing the variation of the proportions of the marked particles with time and position in the bed. The variation of mixture composition based on the samples incorporated into Lacey mixing index that describes the degree of mixing of the particle at particular time. This method enables the assessment of the overall mixing behavior in terms of the rate of mixing (through estimation of the time required for the mixing index to increase from zero to a certain value) and with the degree of mixing at the mixing equilibrium stage. Finally, the parameters were optimized. Results showed that gas velocity and bed depth were important parameters influencing the solids mixing in the bubbling fluidized bed. From the results, complete mixing of binary polymer particles was attained at a bed depth of 17 cm and gas velocity of 1.38 Umf in the fluidized bed.
Effect of Operating Conditions on Catalytic Gasification of Bamboo in a Fluidized Bed  [PDF]
Thanasit Wongsiriamnuay,Nattakarn Kannang,Nakorn Tippayawong
International Journal of Chemical Engineering , 2013, DOI: 10.1155/2013/297941
Abstract: Catalytic gasification of bamboo in a laboratory-scale, fluidized bed reactor was investigated. Experiments were performed to determine the effects of reactor temperature (400, 500, and 600°C), gasifying medium (air and air/steam), and catalyst to biomass ratio (0?:?1, 1?:?1, and 1.5?:?1) on product gas composition, H2/CO ratio, carbon conversion efficiency, heating value, and tar conversion. From the results obtained, it was shown that at 400°C with air/steam gasification, maximum hydrogen content of 16.5%?v/v, carbon conversion efficiency of 98.5%, and tar conversion of 80% were obtained. The presence of catalyst was found to promote the tar reforming reaction and resulted in improvement of heating value, carbon conversion efficiency, and gas yield due to increases in H2, CO, and CH4. The presence of steam and dolomite had an effect on the increasing of tar conversion. 1. Introduction Energy demand has been growing for the past several decades due to rapid industrial and urban development in industry, but fossil fuel reserves have been in decline [1]. Renewable energy has been very popular as an obvious candidate to substitute fossil fuels. Biomass is one of the renewable fuel sources that can claim to have significant environmental benefits with regards to neutral carbon emissions and reduction in global warming [2, 3]. There are many biomass materials that can be utilized for energy [4]. Fast growing plants, which do not compete with food crops, may be used as sustainable energy resources [5, 6] for developed and developing countries. Biomass can be converted to biofuels via several pathways such as biochemical or thermochemical conversion. Gasification process is one of the promising technologies to produce syngas from solid feedstock [2, 7–9]. Producer gas containing simple molecular gas can be used, instead of fossil fuels, in combustion engines. Gas production is dependent on input streams, operating conditions, and gas output conditioning. Input of gasification process is referred to by type and components of feedstock materials and type and flow of gasifying agent. Gas output conditioning is a process involved in cooling and disposing particulate matter and tar in the gas product. Gasification reactions are controlled by operation conditions such as temperature, pressure, and residence time. Reaction temperature is one of the most influential parameters for the gasification operation. Gasification temperature is normally classified into three ranges; low (400–600°C), medium (600–900°C), and high (>900°C). Increasing temperature tends to result
High temperature degradation by erosion-corrosion in bubbling fluidized bed combustors
Hou, Peggy;MacAdam, Stuart;Niu, Yan;Stringer, John;
Materials Research , 2004, DOI: 10.1590/S1516-14392004000100011
Abstract: heat-exchanger tubes in fluidized bed combustors (fbcs) often suffer material loss due to combined corrosion and erosion. most severe damage is believed to be caused by the impact of dense packets of bed material on the lower parts of the tubes. in order to understand this phenomenon, a unique laboratory test rig at berkeley was designed to simulate the particle hammering interactions between in-bed particles and tubes in bubbling fluidized bed combustors. in this design, a rod shaped specimen is actuated a short distance within a partially fluidized bed. the downward specimen motion is controlled to produce similar frequencies, velocities and impact forces as those experienced by the impacting particle aggregates in practical systems. room temperature studies have shown that the degradation mechanism is a three-body abrasion process. this paper describes the characteristics of this test rig, reviews results at elevated temperatures and compares them to field experience. at higher temperatures, deposits of the bed material on tube surfaces can act as a protective layer. the deposition depended strongly on the type of bed material, the degree of tube surface oxidation and the tube and bed temperatures. with hcl present in the bed, wastage was increased due to enhanced oxidation and reduced oxide scale adherence.
High temperature degradation by erosion-corrosion in bubbling fluidized bed combustors
Hou Peggy,MacAdam Stuart,Niu Yan,Stringer John
Materials Research , 2004,
Abstract: Heat-exchanger tubes in fluidized bed combustors (FBCs) often suffer material loss due to combined corrosion and erosion. Most severe damage is believed to be caused by the impact of dense packets of bed material on the lower parts of the tubes. In order to understand this phenomenon, a unique laboratory test rig at Berkeley was designed to simulate the particle hammering interactions between in-bed particles and tubes in bubbling fluidized bed combustors. In this design, a rod shaped specimen is actuated a short distance within a partially fluidized bed. The downward specimen motion is controlled to produce similar frequencies, velocities and impact forces as those experienced by the impacting particle aggregates in practical systems. Room temperature studies have shown that the degradation mechanism is a three-body abrasion process. This paper describes the characteristics of this test rig, reviews results at elevated temperatures and compares them to field experience. At higher temperatures, deposits of the bed material on tube surfaces can act as a protective layer. The deposition depended strongly on the type of bed material, the degree of tube surface oxidation and the tube and bed temperatures. With HCl present in the bed, wastage was increased due to enhanced oxidation and reduced oxide scale adherence.
Removal of SO2 with particles of dolomite limestone powder in a binary fluidized bed reactor with bubbling fluidization
Pisani Jr., R.;Moraes Jr., D.;
Brazilian Journal of Chemical Engineering , 2003, DOI: 10.1590/S0104-66322003000200002
Abstract: in this work, so2 was treated by reaction with dolomite limestone (24 μm) in a fluidized bed reactor composed of 500-590 μm sand particles. the influence of operating temperature (500, 600, 700 and 800oc), superficial gas velocity (0.8, 1.0 and 1.2 m/s) and ca/s molar ratio (1, 2 and 3) on so2 removal efficiency for an inlet concentration of 1000 ppm was examined. removal of the pollutant was found to be dependent on temperature and ca/s molar ratio, particularly at 700 and 800oc. a maximum removal of 76% was achieved at a velocity of 0.8 m/s, a temperature of 800°c and a ca/s of 3. the main residence time of the powder particles was determined by integrating normalized gas concentration curves as a function of time; the values found ranged from 4.1 to 14.4 min. it was concluded that the reactor operated in bubbling fluidization under every operational condition.
Removal of SO2 with particles of dolomite limestone powder in a binary fluidized bed reactor with bubbling fluidization  [cached]
Pisani Jr. R.,Moraes Jr. D.
Brazilian Journal of Chemical Engineering , 2003,
Abstract: In this work, SO2 was treated by reaction with dolomite limestone (24 μm) in a fluidized bed reactor composed of 500-590 μm sand particles. The influence of operating temperature (500, 600, 700 and 800masculineC), superficial gas velocity (0.8, 1.0 and 1.2 m/s) and Ca/S molar ratio (1, 2 and 3) on SO2 removal efficiency for an inlet concentration of 1000 ppm was examined. Removal of the pollutant was found to be dependent on temperature and Ca/S molar ratio, particularly at 700 and 800masculineC. A maximum removal of 76% was achieved at a velocity of 0.8 m/s, a temperature of 800degreesC and a Ca/S of 3. The main residence time of the powder particles was determined by integrating normalized gas concentration curves as a function of time; the values found ranged from 4.1 to 14.4 min. It was concluded that the reactor operated in bubbling fluidization under every operational condition.
Hydrodynamic study on gasification of biomass in a fluidized bed gasifier  [PDF]
S.BASKARA SETHUPATHY,E. NATARAJAN
International Journal of Engineering Science and Technology , 2012,
Abstract: Current scenario of energy insecurity urges us to realize the importance of alternate energy sources. In country with variety of vegetation like India, Biomass finds its place of which fluidized bed gasification of biomass could be more effective. This paper emphasizes the importance of a fluidized bed gasifier for energy conversion of agro-residues for useful purposes. Coconut Shell and Ground nut shell of gross calorific value 19.43MJ/kg and 14.91 MJ/kg respectively are taken for the study. The particle size is restricted not to exceed 3mm. Various empirical correlations involved in fluidization are studied and their interdependence is detailed. From various published data, importance of inert materials and their relative proportions with biomass fuels are studied and optimum biomass to sand ratio is fixed as 10 to 15% by mass. Equations for predicting the minimum fluidization velocities of these mixtures are also discussed. Variations of Fluidization parameters such asminimum fluidization velocity, bubble rise velocity, expanded bed height with respect to temperature, equivalence ratio, particle size is studied and their quantification is analyzed. A 108 mm internal diameter and 1400 mm high FBG is used for the study. Fuel is fed through screw feeder and air is supplied through blower. In the down stream side cyclone separator is placed after which the sampling and burner lines are connected. A regression model is developed and the feasibility of gasifying coconut shell and groundnut shell are discussed. Earlier and present work of coconut shell gasification proves fluidized bed gasification is more appropriate for agro residues.
Model Development for Hydrodynamic Study of Fluidized Bed Gasifier for Biomass Gasification  [PDF]
Athirah Mohd Tamidi,Ku Zilati Ku Shaari,Suzana Yusup,Lau Kok Keong
Journal of Applied Sciences , 2011,
Abstract: Fluidized beds are widely employed in industrial operation due to their excellent solid mixing, heat and mass transfer properties. Deeper knowledge of the fluidized bed hydrodynamics would provide the base for development of a fully predictive model. This study highlights the model development for hydrodynamic study and the effect of particle size to the solid fluidization in fluidized bed gasifier using Eulerian-Eulerian multiphase model coupled with kinetic granular theory in CFD software, Ansys Fluent v6.3. The result obtained has been compared with literature data and had proven that the model is capable of accurately model the hydrodynamic of fluidized bed gasifier. Different particle size will give different hydrodynamic flow in the gasifier and particle size in the range of 250-300 m is observed to give the best solid fluidization behavior in the gasifier. This model can be used further to study the effect of other parameters such as steam inlet velocity and solid initial bed height on the hydrodynamic of the fluidized bed reactor.
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