Heat transfer in circulating fluidized beds

Wirth, Karl‐Ernst

doi:10.1016/0009-2509(95)00025-z

Cited by 32 publications

(6 citation statements)

References 7 publications

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“…Figure 5 shows the relation between solids concentration from 1.1 to 8.03 m (splash zone and freeboard) and the heat transfer coefficient α CL . It is shown, that α CL strongly depends on the solids concentration in this area, which is consistent with the findings in literature also for large CFB boilers (Wu et al, 1987;Molerus and Mattmann, 1992;Wirth, 1995;Grace et al, 1997;Molerus and Wirth, 1997;Breitholtz et al, 2001;Oka, 2003;Dutta and Basu, 2004). As the entrainment increases, more particles get in contact with the heat exchanger surfaces.…”

Section: Heat Transfer Coefficientsupporting

confidence: 91%

Acceleration of Load Changes by Controlling the Operating Parameters in CFB Co-Combustion

et al. 2021

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The integration of intermittent renewable energy sources into the electricity market requires flexible and efficient technologies that compensate for the fluctuating electricity demand. A circulating fluidized bed (CFB) boiler is a suitable solution due to its fuel flexibility, but the thermal inertia of the fluidized bed can have negative effects on the load following capabilities. This study investigates the influence of the operating parameters of the fire side on the speed of load changes on the waterside. Co-combustion of lignite, straw, and refuse derived fuel (RDF) was carried out. In a 1 MWth pilot CFB combustor fifteen load changes were performed with a varying step input of the primary air, the secondary air, and the fuel mass flow. The step input of the primary air had a large influence on the load ramps, as it strongly affects the solids concentration in the upper furnace. The step size of the fuel mass flow had a positive effect on the load change rate. Based on the results, concepts were developed to accelerate load ramping by controlling the hydrodynamic conditions and the temperature on the fireside.

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Section: Heat Transfer Coefficientsupporting

confidence: 91%

Acceleration of Load Changes by Controlling the Operating Parameters in CFB Co-Combustion

et al. 2021

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“…for Re i > 10 and Ar > 500 (38) where, d a and d i are the diameter of the active particle and inert particle, respectively. The theory was validated against previous experimental data on combustion of a single carbon particle in a fluidized bed and also against the napthalene sublimation data reported in [45].…”

Section: Convective Mass Transfer Modelsmentioning

confidence: 99%

“…Wirth [38] presented a simple correlation for gas convective heat transfer coefficient, h gc , in a circulating fluidized bed as:…”

Section: Empirical Modelsmentioning

confidence: 99%

Convective Heat and Mass Transfer Modeling in Gas-Fluidized Beds

Yusuf¹,

Melaaen

Mathiesen

2005

Chem. Eng. Technol.

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This review examines selected mechanistic and empirical models reported in the literature to predict convective heat and mass transfer coefficients in gas-fluidized beds. The role of hydrodynamics in heat and mass transfer is briefly outlined before embarking on the modeling approaches. Both bed to wall and interphase heat transfer, are considered. In bed to wall heat transfer, the main focus of the review is the modeling of particle convective components, based on surface renewal. The concepts of transient and local heat transfer models are also discussed briefly. In the case of mass transfer, only interphase transfer is considered. Emphasis is placed on models based on combustion where mass transfer is seen to occur from a few active particles contained in a fluidized bed of inert particles.

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“…Few research articles are reported on experimental investigations on heat transfer in a PCFB unit. Molerus (1993) and Wirth (1995) conducted some experimental investigations in a 190 mm internal diameter and 1000 mm height pilot scale PCFB unit and the heat transfer results were presented in non-dimensional numbers. Shen et al (1991) reported the bed-to-wall convective heat transfer in a PCFB for different solid concentrations, system pressures and superficial gas velocities.…”

Section: Introductionmentioning

confidence: 99%

Effect of pressure on thermal aspects in the riser column of a pressurized circulating fluidized bed

Gupta

Reddy

2006

Int. J. Energy Res.

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SUMMARYIn the present paper the effect of pressure on bed-to-wall heat transfer in the riser column of a pressurized circulating fluidized bed (PCFB) unit is estimated through a modified mechanistic model. Gas-solid flow structure and average cross-sectional solids concentration play a dominant role in better understanding of bed-to-wall heat transfer mechanism in the riser column of a PCFB. The effect of pressure on average solids concentration fraction 'c' in the riser column is analysed from the experimental investigations. The basic cluster renewal model of an atmospheric circulating fluidized bed has been modified to consider the effect of pressure on different model parameters such as cluster properties, gas layer thickness, cluster, particle, gas phase, radiation and bed-to-wall heat transfer coefficients, respectively. The cluster thermal conductivity increases with system pressure as well as with bed temperature due to higher cluster thermal properties. The increased operating pressure enhances the particle and dispersed phase heat transfer components. The bed-to-wall heat transfer coefficient increases with operating pressure, because of increased particle concentration. The predicted results from the model are compared with the experimentally measured values as well as with the published literature, and a good agreement has been observed. The bed-to-wall heat transfer coefficient variation along the riser height is also reported for different operating pressures.

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Heat transfer in circulating fluidized beds

Cited by 32 publications

References 7 publications

Acceleration of Load Changes by Controlling the Operating Parameters in CFB Co-Combustion

Acceleration of Load Changes by Controlling the Operating Parameters in CFB Co-Combustion

Convective Heat and Mass Transfer Modeling in Gas-Fluidized Beds

Effect of pressure on thermal aspects in the riser column of a pressurized circulating fluidized bed

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