Fluctuations and waves in fluidized bed systems: The influence of the air-supply system

A general model of the response of a fluidized bed to disturbances is formulated, and the information provided by the model with respect to the dynamics of the bed, the bed plus the air-plenum and the bed plus the entire air-supply system, is investigated. Expressions given in literature on the fundamental frequency of the bed-plenum system are analyzed, and it is shown that they are a special case of the general model. In order to simulate various types of interaction between the bed and the rest of the system, experiments were performed in a cold fluidized bed unit operated under both non-circulating and circulating conditions. At low velocity, three regimes were identified: the multiple bubble regime with almost no interaction between bed and air-plenum, the single bubble regime with the interaction between bed and air-plenum only, and a regime with numerous irregular bubbles, where the bed interacted with the entire air-supply system. At high fluidization velocity, the exploding bubble regime was identified, with the same dominant frequency as that of the single bubble regime (the interaction with the air-supply system remains at that frequency). The models investigated correctly reproduce the dynamics when the bed is independent of the other parts of the system, or when the bed interacts only with the air-plenum. However, the models are only partially applicable when the bed interacts with the entire air-supply system. The reasons for this are investigated. In the case of system interaction, pressure waves, generated in the bed, interact with pressure pulsations from the air-supply system. This results in a coupled system, which is not covered by the models. Pressure waves resulting from events in the bed, are recognized as the coherent part of the cross power spectra of pressure fluctuations measured in the bed and the air-plenum.     

Exit effect on hydrodynamics of the internal circulating fluidized bed riser

This is the first time an extensive investigation has been carried out regarding the effects of riser exit geometry on pressure drop and solid behaviour inside the Internal Circulating Fluidized Bed (ICFB) riser, using different riser exit geometries at several operating conditions.The Radioactive Particle-Tracking (RPT) technique was used for solid concentration measurements and solid residence time distribution at the exit zone. Experiments were conducted using Geldart B particles, in the gas superficial velocity range of 4 to 10 m/s. Axial solid hold-up, solid residence time distribution in the exit zone, and the reflux ratio factor k_m, (defined earlier by [E.H. Van der Meer, R.B. Thorpe, J.F. Davidson, Flow patterns in the square cross-section riser of a circulating fluidized bed and the effect of riser exit design, Chem. Eng. Sc. 55 (19) (2000) 4079-4099]), were the main criteria used to investigate the impact of gas-solid separator devices implemented at the ICFB riser exit.Solid residence time distribution results and axial solid hold-up profiles provided clear evidence that the separator device at the riser exit strongly influences the hydrodynamic structure of the ICFB riser. The V-shaped riser exit geometry was found to be the optimum of all the configurations studied.     

Simultaneous sulfide and acetate oxidation under denitrifying conditions using an inverse fluidized bed reactor

BACKGROUND: Simultaneous removal of sulfur, nitrogen and carbon compounds from wastewaters is a commercially important biological process. The objective was to evaluate the influence of the CH₃COO^?/NO₃^? molar ratio on the sulfide oxidation process using an inverse fluidized bed reactor (IFBR). RESULTS: Three molar ratios of CH₃COO^?/NO₃^? (0.85, 0.72 and 0.62) with a constant S^2?/NO₃^? molar ratio of 0.13 were evaluated. At a CH₃COO^?/NO₃^? molar ratio of 0.85, the nitrate, acetate and sulfide removal efficiencies were approximately 100%. The N₂ yield (g N₂ g^?1 NO₃^?‐N consumed) was 0.81. Acetate was mineralized, resulting in a yield of 0.65 g inorganic‐C g^?1 CH₃COO^?‐C consumed. Sulfide was partially oxidized to S⁰, and 71% of the S^2? consumed was recovered as elemental sulfur by a settler installed in the IFBR. At a CH₃COO^?/NO₃^? molar ratio of 0.72, the efficiencies of nitrate, acetate and sulfide consumption were of 100%, with N₂ and inorganic‐C yields of 0.84 and 0.69, respectively. The sulfide was recovered as sulfate instead of S⁰, with a yield of 0.92 g SO₄^2?‐S g^?1 S^2? consumed. CONCLUSIONS: The CH₃COO^?/NO₃^? molar ratio was shown to be an important parameter that can be used to control the fate of sulfide oxidation to either S⁰ or sulfate. In this study, the potential of denitrification for the simultaneous removal of organic matter, sulfide and nitrate from wastewaters was demonstrated, obtaining CO₂, S⁰ and N₂ as the major end products. Copyright © 2008 Society of Chemical Industry     

2,4,6‐Trichlorophenol and phenol removal in methanogenic and partially‐aerated methanogenic conditions in a fluidized bed bioreactor

A fluidized bed bioreactor (FBBR) was operated for more than 575 days to remove 2,4,6‐trichlorophenol (TCP) and phenol (Phe) from a synthetic toxic wastewater containing 80 mg L^?1 of TCP and 20 mg L^?1 of Phe under two regimes: Methanogenic (M) and Partially‐Aerated Methanogenic (PAM). The mesophilic, laboratory‐scale FBBR consisted of a glass column (3 L capacity) loaded with 1 L of 1 mm diameter granular activated carbon colonized by an anaerobic consortium. Sucrose (1 g COD L^?1) was used as co‐substrate in the two conditions. The hydraulic residence time was kept constant at 1 day. Both conditions showed similar TCP and Phe removal (99.9 + %); nevertheless, in the Methanogenic regime, the accumulation of 4‐chlorophenol (4CP) up to 16 mg L^?1 and phenol up to 4 mg L^?1 was observed, whereas in PAM conditions 4CP and other intermediates were not detected. The specific methanogenic activity of biomass decreased from 1.01 ± 0.14 in M conditions to 0.19 ± 0.06 mmolCH₄ h^?1 gTKN^?1 in PAM conditions whereas the specific oxygen uptake rate increased from 0.039 ± 0.008 in M conditions to 0.054 ± 0.012 mmolO₂ h^?1 gTKN^?1, which suggested the co‐existence of both methanogenic archaea and aerobic bacteria in the undefined consortium. The advantage of the PAM condition over the M regime is that it provides for the thorough removal of less‐substituted chlorophenols produced by the reductive dehalogenation of TCP rather than the removal of the parent compound itself. Copyright © 2005 Society of Chemical Industry     

工业聚合反应装置 Ⅴ.流化床气相聚合反应器

简介了流化床气相聚合反应器的原理和6种典型的聚合装置。     

硫铁矿沸腾炉内蒸发管组防磨技术的探讨

为减少磨损,沸腾炉内蒸发管采用加焊半圆形钢板防磨.探讨了沸腾炉内蒸发管加焊半圆形钢板的防磨机理.实际使用情况表明,加焊半圆形钢板防磨大大降低了维修费用,显著提高了防磨效果.     

Feedback linearizing control of a fluidized bed reactor

The design of an adaptive nonlinear controller for the control of a fluidized bed reactor is derived by using exact linearization techniques. Reset action and parameter adaptation are used to make more robust the precise compensation of nonlinear terms, which is called for in the linearization technique. A nonlinear antiwindup mechanism is introduced to handle reset windup problem and to provide fast response without large overshoot. Simulation results show that the proposed adaptive controller guarantees good setpoint tracking. The developed estimation algorithm allows accurate estimation of the parameters for which the regressor component is not zero.     

多孔挡板流化床还原UO3反应器模型的研究

针对ＵＯ＿３的Ｎ＿２还原反应建立了多孔挡板流化床反应器模型。将多孔挡板床的每一级视为具有相似的流动状态，每一级的上、下段称为稀、密相段，分别用鼓泡床和活塞流模型描述。该模型的计算值与￠６３ｍｍ的多孔挡板床Ｈ＿２还原ＵＯ＿３的热态实验值能较好的吻合。还预计了还原温度、操作气速和挡板结构参数对固相转化率的影响，为该类反应器的工业设计、放大和优化提供了依据。     

DRYING OF GRANULAR PARTICLES IN A MULTISTAGE INCLINED FLUIDIZED BED WITH MECHANICAL VIBRATION

A mathematical model for the drying rate of granular particles in a multistage inclined fluidized bed(IFB) is presented from the standpoint of simultaneous heat and mass transfer, with taking the effect of mechanical vibration added vertically into consideration.

Steady-state distributions for the temperatures and concentrations of the particles and the heating gas, and for the moisture content of the particles are numerically calculated based on the present model. The calculated results show fairly good agreement with the experimental data, which were obtained from the drying experiments of brick particles in a three-stage IFB using comparatively low temperature air(40-60°C) as the heating gas.

It has been found within the range of the experimental conditions employed that, the mechanical vibration added vertically enhances the over-all drying rate of the particles and its effect can be considered equivalent to an increase in the air velocity.     

应用底饲回燃循环流化床技术改造东锅DG35/3.82-7型流化床锅炉

采用飞灰循环底饲回燃技术改造西南合成制药总厂热电分厂、天府矿务局磨心坡发电厂2台东方DG35/3.82-7型低倍率循环流化床锅炉。改造后运行结果表明,锅炉可长期、稳定运行,尾部飞灰可燃物含量大幅度降低,锅炉蒸发量提高20％左右,节煤效果明显。为燃用贫煤、无烟煤和煤矸石等劣质燃料且锅炉炉膛高度较低的电站技改,提供了一种切实可行的方法。