EFFECTS OF PARTICLE CHARACTERISTICS ON THE PERFORMANCE OF A FAST FLUIDIZED BED REACTOR

A heterogeneous model for the fast fluidized bed reactor which carries out a gas-solid non catalytic reaction is presented. The hydrodynamics of the fast fluidized bed is characterized by the model of Kwauk et al. (1985) which assumes the existence of two phases; a dense phase and a dilute pneumatic transport phase. For a given solid flowrate, the length of the reactor occupied by each phase depends on gas velocity, particle diameter and density and average voidage within the reactor. The gas-solid reaction is assumed to follow the shrinking core model. The solids are assumed to be completely backmixed in the dense phase and move in plug How in the dilute pneumatic transport phase. The gas phase is assumed to be in plug flow in both phases

For given gas and solid flowrates, the transition from the dense phase flow to the fast fluidized bed (containing two regions) as functions of particle size and density is determined using the model of Kwauk et al. (1985). The numerical solution of the governing mass balance equations show that for given solid and gas flowrates, (and average voidage) the gas phase conversion shows an unusual behavior with respect to particle diameter and density. Such behavior is resulted from the effects of particle diameter and density on the reactor volume occupied by each phase and the effect of particle diameter on the apparent reaction rate. The numerical results show that a fast fluidized bed gives the best conversion at large particle density and for the particle diameter which results the fast fluidized bed to be operated near the pure dense phase flow.     

三相流化床中磷石膏分解渣碳酸化反应研究

通过对磷石膏分解渣在三相流化床中碳酸化反应的实验研究,探讨了不同因素对磷石膏分解渣中CaS转化的影响。实验结果表明:增大CO2气体流量和增加反应时间有利于CaS的转化,随着液固比的增大,CaS的转化率首先是增大然后趋于平缓,而升高反应温度对CaS的转化有微弱抑制作用。得到磷石膏分解渣碳酸化反应的最佳反应条件:CO2气体流量为300 mL/min、反应时间为40 min、液固比(体积质量比)为6 mL/g、反应温度为(25±2)℃。在最佳反应条件下,三相流化床中CaS的转化率为97.34%,釜式反应器中CaS的转化率为86.32%,相差了11%。与釜式反应器相比,三相流化床反应器更有利于磷石膏分解渣的碳酸化反应。     

Gasification characteristics of combustible wastes in a 5 ton/day fixed bed gasifier

The gasification characteristics of combustible wastes were determined in a 5 ton/day fixed bed gasifier (1.2 m I.D. and 2.8m high). The fixed bed gasifier consisted of air compressor, oxygen tank, MFC, fixed bed gasifier, cyclone, heat exchanger, solid/gas separator, water fluidized bed reactor and blower. To capture soot or unburned carbon from the gasification reaction, solid/gas separator and water fluidized bed were used. The experiments with 10–50 hours of operation were carried out to determine the effects of bed temperature, solid/oxygen ratio and oxidant on the gas composition, calorific value and carbon conversion. The calorific values of the produced gas decreased with an increase of bed temperature because combustion reaction happened more actively. The gas composition of partial oxidation of woodchip is CO: 34.4%, H₂: 10.7%, CH₄: 6.0%, CO₂: 48.9% and that of RPF is CO: 33.9%, H₂: 26.1%, CH₄: 10.7%, CO₂: 29.2%. The average calorific values of produced gas were about 1,933 kcal/Nm³, 2,863 kcal/Nm³, respectively. The maximum calorific values were 3,100 kcal/Nm³ at RPF/oxygen ratio: 7     

Autothermal CO2 reforming of methane over NiO–MgO solid solution catalysts under pressurized condition: Effect of fluidized bed reactor and its promoting mechanism

The effect of fluidized bed reactor in autothermal CO₂ reforming of methane over NiO–MgO solid solution catalysts was investigated by comparing with fixed bed reactor. Methane conversion to syngas was drastically enhanced by using a fluidized bed reactor. The catalyst was reduced and oxidized repeatedly in fluidized bed reactor during the reaction. The enhancement of methane conversion is related to the catalyst reducibility.     

Residence times in fluidized beds with secondary gas injection

Experiments were carried out to determine the effects of secondary gas injection on the gas residence time and macromixing characteristics in a bubbling fluidized bed. Primary gas is introduced via a bottom distributor plate, while secondary gas is introduced via a fractal injector submerged in the bed. Results indicate that the average residence time decreases only slightly. Calculated overall reactor Péclet numbers indicate that the gas experiences less back-mixing with secondary gas injection. The bubble size was observed to decrease by up to 70%, indicating improved gas–solid contact. Taking this improved contact and plug flow behavior into account, the conversion in a fluidized bed with secondary gas injection is expected to increase significantly, particularly for mass-transfer limited reactions.     

Convective heat transfer and solid conversion of reacting particles in a copper(II) chloride fluidized bed

This paper develops a predictive model of convective heat transfer and conversion of cupric chloride particles in a fluidized bed reactor of a copper–chlorine (Cu–Cl) cycle of thermochemical hydrogen production. The hydrolysis reaction of particles in the fluidized bed is endothermic and it requires excess steam for complete conversion of cupric chloride solid. The excess steam supply may be used for partial heat supply to the endothermic reaction, and also to avoid defluidization in the bed. To avoid defluidization, the change of gas flow in the bed due to the reaction should be minimized at a given operating condition. The model predicts the maximum possible steam inlet temperature, steam conversion, amount of partial heat supply, and also gas flow rates through the bed to avoid defluidization. The new model presents significant new insight by analyzing the hydrodynamic and mass transport processes, considering the equilibrium limitation on the conversion of cupric chloride solid. The model results indicate that the chemical reaction requires a high mole ratio of steam for complete conversion of cupric chloride particles. The maximum steam conversion is limited by temperature, pressure, and the presence of hydrogen chloride gas. The maximum conversion of steam at 400 °C is 3.75% and it requires excess steam of 12.8 moles per unit mole of cupric chloride solid for complete conversion of solid. The heat supply by steam for the reaction, as well as raising the solid feed to the reaction temperature, varies with reaction temperature. The paper also adds significant new insight by analyzing the steam flow requirement in terms of temperature, conversion rate, and quality of fluidization. Additional new results are presented and applications discussed for the Cu–Cl cycle of nuclear hydrogen production.     

NOx removal by selective noncatalytic reduction with urea solution in a fluidized bed reactor

A fluidized bed reactor has been developed to overcome the plugging problem of urea injection by employing a sparger rather than nozzles in the SNCR process for simultaneous removal of SO₂ and NO_x. In a developed fluidized bed reactor, the optimum temperature to remove NO_x is shifted to lower values, the reaction temperature window is widened with the presence of CO in flue gas, and NO conversion is higher than that in a flow reactor. The optimum amount of urea injection in the reactor is found to be above 1.2 based on the normalized stoichiometric molar ratio (NSR) with respect to NO conversion. In the simultaneous removal of SO₂/NO, conversions of SO₂ and NO reach 80–90%, nearly the same values for the individual removal of SO₂ and NO above 850 ‡C.     

THE ROLE OF GAS DISTRIBUTION IN FLUIDIZED BED CHEMICAL REACTOR DESIGN†

The design of fluid bed gas distributors may have a marked influence on the performance of a fluid bed reactor. The primary physical reason for this influence is that the distributor design influences the hydrodynamics and thus the gas/solid contacting pattern in the fluidized bed.

In the paper presented here the influence of distributor design on mass transfer and chemical reaction has been investigated systematically in fluid bed reactors with diameters of 0.2 and 1.0 meter. Coefficients of mass transfer between the bubble phase and the suspension phase were determined from chemical conversion and tracer gas residence time distribution measurements. In the experimental program the height of the fluidized bed was varied between 0.3 m and 0.9 m with superficial gas velocities in the range of 0.06 m/s to 0.30 m/s.

The comparison of the experimental results with a suitably modified and extended two-phase model yields quantitative relationships which allow to account for the influence of the gas distributor in the design of fluid bed chemical reactors.     

THE ROLE OF GAS DISTRIBUTION IN FLUIDIZED BED CHEMICAL REACTOR DESIGN†

Abstract

The design of fluid bed gas distributors may have a marked influence on the performance of a fluid bed reactor. The primary physical reason for this influence is that the distributor design influences the hydrodynamics and thus the gas/solid contacting pattern in the fluidized bed.

In the paper presented here the influence of distributor design on mass transfer and chemical reaction has been investigated systematically in fluid bed reactors with diameters of 0.2 and 1.0 meter. Coefficients of mass transfer between the bubble phase and the suspension phase were determined from chemical conversion and tracer gas residence time distribution measurements. In the experimental program the height of the fluidized bed was varied between 0.3 m and 0.9 m with superficial gas velocities in the range of 0.06 m/s to 0.30 m/s.

The comparison of the experimental results with a suitably modified and extended two-phase model yields quantitative relationships which allow to account for the influence of the gas distributor in the design of fluid bed chemical reactors.     

Elimination d'anhydride sulfureux par réaction sur l'oxyde de cuivre en couche fluidisée

Reaction between cupric oxide, oxygen, and sulphur dioxide has been studied in a fluidized bed reactor continuously fed with solid reactant. The effect of bed temperature, solid flow rate, gas flow rate and the hight at minimum fluidization conditions has been investigated. Experimental conversions are between 20 to 60%. Olcutt and Davidson's fluidized bed reactor model slightly modified for our particular reactor has been compared with experimental data. The assumption of plug flow of gas in the dense phase is good for the height of 5 cm, on the contrary, the assumption of perfect mixing of gas in the dense phase is better for the deepest bed.     

Methanation in a fluidized bed reactor with high initial CO partial pressure: Part I—Experimental investigation of hydrodynamics, mass transfer effects, and carbon deposition

An extensive experimental study on the methanation reaction was carried out in a gas–solid fluidized bed reactor at 320 °C with a stoichiometric ratio of H₂/CO=3. By means of spatially resolved measurements of the axial gas species concentration and temperatures along the fluid bed the effects of different catalyst loadings, gas velocities and dilution rates were observed and analyzed. By applying this technique, it was found that most of the reaction (CO and H₂ conversion) proceeds in the first 20 mm of the bed depending on the experimental conditions. For a few cases, the temperature increases by up to 80 °C from 320 to 400 °C within the first 3 mm of the bed. By increasing the inlet volume flow only by a factor of 1.4, the temperature hotspot diminishes and isothermal behavior develops. For all experiments, a CO conversion of practically 100% was achieved. The experimental data indicate that the dense phase of the fluidized bed is probed and that mass transfer between bubble and dense phase is dominating in the upper part of the bed. It could be shown that both hydrodynamic and chemical boundary conditions influence the methanation reaction inside the fluidized bed reactor.     

Wirbelschicht-Prozesse für die Chemieund Hütten-Industrie,die Energieumwandlung und den Umweltschutz

Fluidized bed processes for the chemical and metallurgical industries, energy conversion, and pollution control . This article presents a review of, and selection criteria for, gas/solids reactors with the aid of examples of industrially operating fluidized bed processes. The choice of optimum reactor design with regard to flow and reaction conditions, heat and mass transfer, grain size, and retention time of solids and gas is considered. In conclusion, various processes are described in terms of several process flowsheets.     

丙烯催化氧化制丙烯酸的两段流化床工艺

分别在一段和两段流化床反应器中对丙烯催化氧化制备丙烯酸过程进行了研究. 主要考察了温度、丙烯空速和氧/烯比等操作条件对丙烯氧化制备丙烯醛的第一步反应中丙烯转化率和液相收率的影响. 结果表明,在两段流化床反应器中,由于能够有效抑制气体和固体的返混及催化剂床层中气泡的增长,第一步反应中丙烯转化率和液相收率可以分别大幅度提高到94.2%和74.4%. 得到第一步反应的优化条件为：丙烯空速20~21 L/(h·kg),操作温度360~365℃,氧/烯摩尔比1.6~1.8,在此条件下,考察了连续两步反应中的丙烯转化率和液相收率.     

Fluidized‐bed reactor modeling for polyethylene production

Gas‐phase technology for polyethylene production has been widely used by industries around the world. A good model for the reactor fluid dynamics is essential to properly set the operating conditions of the fluidized‐bed reactor. The fluidized‐bed model developed in this work is based on a steady‐state model, incorporating interactions between separate bubble, emulsion gas phase, and emulsion solid polymer particles. The model is capable not only of computing temperature and concentration gradients for bubble and emulsion phases, calculating polymer particle mean diameter throughout the bed and polyethylene production rate, but also of pinpointing the appearance of hot spots and polymer meltdown. The model differs from conventional well‐mixed fluidized‐bed models by assuming that the particles segregate within the bed according to size and weight differences. The model was validated using literature and patent data, presenting good representation of the behavior of the fluidized‐bed reactor used in ethylene polymerization. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 321–332, 2001     

A simplified mathematical modeling for thermo-catalytic decomposition of methane over carbon black catalyst in a fluidized bed reactor

A mathematical model for thermo-catalytic decomposition of methane over carbon black catalysts in a fluidized bed was proposed. The simplified isothermal, uniform flow model was considered and implemented into a computer code to predict the reactor performance. The experiment of methane decomposition into hydrogen and carbon was carried out in a fluidized bed of I.D of 0.055 m and height of 1.0 m. The range of reaction temperature was 850–900 °C, gas velocity was 1.0–3.0 U _mf , and catalyst loading was 50–200 g. The reaction parameters for model equation were determined from the curve fittings and the comparison of experimental data with simulation results showed good agreement for fluidized bed reactor system. From the simulation results, the fluidized bed performance with different operating conditions were obtained, and this simple model can be used to predict the performance of a larger scale fluidized bed reactor and also in determining the optimum operating conditions.     

Group C+ particles: Efficiency augmentation of fluidized bed reactor through nano-modulation

Group C⁺ particles, Group C particles after nano-modulation, with extremely large specific surface area, have been shown to exhibit extraordinarily good fluidization quality with superiorly high bed expansion, significantly increasing gas holdup in the bed. As a first attempt, Group C⁺ particles were used as catalysts in a fluidized bed reactor (C-plus FBR) to evaluate the reaction performance and were compared to that using Group A particles. C-plus FBR could achieve a much higher reaction conversion, up to 235% of that using Group A particles. The contact efficiency for Group C⁺ particles is much higher, being 330% more than that for Group A particles. The greater contact efficiency is due to both larger specific surface area and higher bed expansion, providing larger gas–solid interfacial area and longer gas residence time. Conclusively, Group C⁺ particles with superior fluidization quality and reaction performance do have huge potential in gas-phase catalytic reactions.     

A novel induction heating fluidized bed reactor: Its design and applications in high temperature screening tests with solid feedstocks and prediction of defluidization state

A novel mini induction heating fluidized bed reactor (IHFBR) is introduced which was developed to carry out screening tests of high temperature reactions up to 1500°C particularly for solid feedstocks. Despite conventional mini reactors, this reactor mimics real scenario of solid feeding in industrial reactors: cold feedstock is injected within 1 s from a lift tube, then particles reach reaction temperature in less than 5 s in a reaction zone. The lift tube (9.5 cm diameter) is also the gas distributor of the fluidized bed (2.5 cm diameter) so that the bed is completely fluidized with uniform gas distribution. Beside facilities to perform tests in a fluidized bed, another important feature of this reactor is prediction of the defluidization state in the bed. Not only reproducible data are generated, but also many tests can be conveniently carried out, that is, one test per hour. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1507–1523, 2015     

Analysis of a fluidized bed membrane reactor for butane partial oxidation to maleic anhydride: 2D modelling

The partial oxidation of butane to maleic anhydride in a membrane reactor with improved heat transfer through the wall has been studied in this work. The reactor consisted of a catalytic fixed bed with sintered metal membrane wall that allows the gradual feed of air from the external fluidized bed. The influence of the most important design and operation variables (reactor length, gas flow rate, inlet temperature, butane inlet concentration, and air gas flow rate) on butane conversion and maleic anhydride selectivity has been studied by means of computer simulations using an experimentally-validated detailed 2D model. The performance of this reactor was systematically compared to the corresponding conventional fixed bed reactor. The membrane reactor has been found to provide slightly higher selectivity than the fixed bed reactor. Moreover, in the membrane reactor, the mixing of butane and air takes place through the wall directly inside the catalytic bed. Since solid beds avoid flame propagation, the process can be operated with higher butane inlet concentrations under safety conditions. Hence, the fluidized bed membrane reactor represents an interesting alternative for industrial-scale operation.     

一氧化碳等温变换技术进展

对现代合成氨CO变换技术中发展起来的不同种类的固定床等温反应器进行了比较 ,从转化率、操作稳定性、结构复杂程度及发展前景等方面进行了论述。特别分析了另一类等温反应器———流化床反应器的特点 ,并结合其在传热、传质、处理量及操作等方面的优势和流态化技术的发展。流化床反应器在CO变换过程中的工业化应用很有前景     

Conditions determining explosion hazards of catalytic oxidation reactors

Conditions have been determined which exclude flame propagation in the processes and which employ reaction media within their explosiveness region. The possibility has been considered of using worked-out catalysts of carbon dioxide conversion STK-1 and catalyst of exhaust gases purification of nitrogen oxides APK-2 as flame arresters and fire quenching elements instead of an inert nozzle, which allow not only localizing the flame but quenching it as well. The equation has been obtained which relates the major parameters of the gas mixture, fluidized bed, and the kinetic characteristics of the catalytic oxidation reaction with flame propagation into the fluidized bed of the catalyst. The proposed model allows for determining the minimal height of the fluidized bed which provides flame quenching in the flame arrester or excludes its propagation in the reactor up to 700°C.