Heat transfer in the splash zone of a bubbling fluidized bed

Dyrness, Albert; Glicksman, Leon R.; Yule, Thomas

doi:10.1016/0017-9310(92)90252-n

Cited by 12 publications

(5 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…To clarify this point, the present authors carried out separate heat transfer measurements according to the technique described by Prins et al , It appeared that the heat transfer coefficient from a spherical, 10 mm diameter particle in the splash zone of the fluid bed is just slightly lower than that in the dense phase (475 versus 400 W/m 2 ·K for the relevant conditions). This is further confirmed by the literature − concerning heat transfer from the fluid bed splash zone to a cooling tube. For instance, Pidwerbecki et al measured a value of 230 W/m 2 ·K in the splash zone against a value of 273 W/m 2 ·K in the dense phase, for a vigorously fluidized bed of 1.1 mm particles (silica/alumina mixture), and a cooling tube of 51 mm outside diameter.…”

Section: Resultssupporting

confidence: 84%

See 1 more Smart Citation

Biomass Pyrolysis in a Fluidized Bed Reactor. Part 2: Experimental Validation of Model Results

Wang

Kersten

Prins

et al. 2005

Ind. Eng. Chem. Res.

187

164

View full text Add to dashboard Cite

Various types of cylindrical biomass particles (pine, beech, bamboo, demolition wood) have been pyrolyzed in a batch-wise operated fluid bed laboratory setup. Conversion times, product yields, and product compositions were measured as a function of the particle size (0.7-17 mm), the vapor's residence time (0.25-6 s), the position of the biomass particles in the bed (dense bed or splash zone), and the fluid bed temperature (250-800 °C). For pyrolysis temperatures between 450 and 550 °C, the bio-oil yield appeared to be maximal (in this work: about 65 wt %), while the water content of the bio-oil is minimal. The position of the biomass particles in the fluid bed, either in the dense bed or in the splash zone, does not affect the conversion time and product yields to a large extent during pyrolysis at 500 °C. In the small fluid bed used for this work, with a char hold-up of up to 5 vol % (or 0.7 wt %), the residence time of the pyrolysis vapors is not that critical. At typical fast pyrolysis temperatures of around 500 °C, it appeared sufficient to keep this residence time below 5 s to prevent significant secondary cracking of the produced vapors to noncondensable gas. Up to a diameter of 17 mm, the particle size has only a minor effect on the total liquid yield. However, for particles larger than 3 mm, the water content of the produced bio-oil increases significantly. The experimental results are further compared with predictions from a one-dimensional (1D) and a two-dimensional (2D) single-particle pyrolysis model. Such models appeared to have a limited predictive power due to large uncertainties in the kinetics and selectivity of the biomass decomposition. Moreover, the product quality cannot be predicted at all.

show abstract

Section: Resultssupporting

confidence: 84%

“…It appeared to be in the order of 1 s, which is at least 20 times shorter than the pyrolysis times observed experimentally (see Figure 3). (7) The furnace is switched off and left to cool. ( 8) The condensers, the paper filter, and the cotton filter are weighed again to determine the accumulated liquids.…”

Section: Experimental Equipment and Proceduresmentioning

confidence: 99%

Biomass Pyrolysis in a Fluidized Bed Reactor. Part 2: Experimental Validation of Model Results

Wang

Kersten

Prins

et al. 2005

Ind. Eng. Chem. Res.

187

164

View full text Add to dashboard Cite

show abstract

“…They may vary along the bed height. Nevertheless, global heat transfer coefficients in a fluidized bed commonly range from 200 to 800 W·m −2 ·K −1 . − Moreover, due to efficient mixing and intensive heat transfer between particles, the material temperature can be considered as practically uniform in the whole fluidized bed volume. Assuming a material bed temperature of about 1120 K, the available heat flux density at the biomass particle surface during pyrolysis can be considered as ranging from about 0.2 to 0.8 MW·m −2 .…”

Section: Methodsmentioning

confidence: 99%

Wood Fast Pyrolysis: Comparison of Lagrangian and Eulerian Modeling Approaches with Experimental Measurements

Authier

Ferrer

Mauviel

et al. 2009

Ind. Eng. Chem. Res.

View full text Add to dashboard Cite

International audienceThe aim of the present paper is to validate Lagrangian and Eulerian modeling approaches of biomass fast pyrolysis from comparison with experimental measurements. Wood samples are submitted during measured times to a controlled and concentrated radiation delivered by an image furnace. The heat flux densities are close to those encountered when wood is surrounded by hot bed particles in a dual fluidized bed (DFB) gasifier. In the image furnace, the sample is placed inside a transparent quartz reactor fed by a cold carrier gas. The volatile matter (condensable vapors and gases) released by the solid is quenched inside the reactor. It is hence possible to selectively study primary pyrolysis phenomena occurring at the solid level. All the pyrolysis products (char, vapors, and gases) are recovered, and their masses are measured as a function of the flash time allowing the assessment of mass balances. The yield of vapors does not significantly depend on the available heat flux density, unlike the gases and char yields. The experimental results are compared to data derived from two different modeling approaches. Their basic assumptions are discussed from characteristic time values which reveal the controlling phenomena. Mass transfer limitations are neglected in comparison with heat transfer and chemical phenomena. The first type of pyrolysis model relies on an original Lagrangian approach where mathematical equations of heat and mass balances are written with the assumptions that wood and char form two distinct layers. In the second one, a classical Eulerian approach is considered: equations are directly written at the whole particle level. The results of the two models as well as the experimental data (sample mass losses and product yields) are in quite good agreement

show abstract

“…The heat transfer is represented by a simple convection equation (Eq. 1) and uses global heat transfer coefficient h. Typically, this coefficientvaries between 200 and 1000 Wm -2 K -1 in fluidized beds [25,26,27,28]. It is intended to compare the experimental surface temperature evolution of char with the theoretical evolution which would be encountered in a fluidized bed gasifier (bed temperature T r = 1123 K).The global heat transfer coefficient his assumed to be constant and equal to 500 Wm -2 K -1 .Other numerical data are reported in table 2.…”

Section: Theoretical Modelmentioning

confidence: 99%

Novel vertical image furnace for fast pyrolysis studies

Christodoulou

Mauviel

Lédé

et al. 2013

Journal of Analytical and Applied Pyrolysis

View full text Add to dashboard Cite

International audienceThe image furnace is used to mimic experimentally heating conditions representative of a fluidized bed biomass gasifier. The aim of this paper is to demonstrate the feasibility of heat flux density modulation with a new improved vertical image furnace which is based on the former horizontal setup. This is achieved through the comparison of the experimental and theoretical surfaces temperatures evolutions. A numerical model is solved in order to estimate the theoretical surface temperature evolution of a char particle immersed in a fluidized bed at 1123 K. The goal of the experiments performed with char samples is to reproduce the same temperature evolutions. The surface temperatures profiles are measured by pyrometry in different conditions (constant heat flux density, variation of the heat flux density over time) and compared to the modelling results. The experiments at constant heat flux density show poor agreement with the model, in comparison with experiments made with variable heat flux density. The best agreement is obtained when the heat flux density is decreased from 560 kW m-2 to 250 kW m-2 in 1 s after a period of 500 ms

show abstract

Heat transfer in the splash zone of a bubbling fluidized bed

Cited by 12 publications

References 7 publications

Biomass Pyrolysis in a Fluidized Bed Reactor. Part 2: Experimental Validation of Model Results

Biomass Pyrolysis in a Fluidized Bed Reactor. Part 2: Experimental Validation of Model Results

Wood Fast Pyrolysis: Comparison of Lagrangian and Eulerian Modeling Approaches with Experimental Measurements

Novel vertical image furnace for fast pyrolysis studies

Contact Info

Product

Resources

About