The combustion of carbon monoxide in a two-zone fluidized bed

Hayhurst, A.N.; Tucker, R.F.

doi:10.1016/0010-2180(90)90042-p

Cited by 73 publications

(31 citation statements)

References 4 publications

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“…The possibility of CO oxidation in the emulsion phase has been studied by Hayhurst (Hayhurst, 1990). He concluded that CO will not burn in the dense phase of a fluidized bed at temperatures below 1273 K due to inhibition of the gas phase oxidation reaction by the presence of the bed particles.…”

Section: Introductionmentioning

confidence: 99%

Modeling of single char combustion, including CO oxidation in its boundary layer

Lee¹,

Longwell²,

Sarofim³

1994

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AbstractsA model incorporating intrinsic surface reaction, internal pore diffusion, and external mass transfer was developed to predict a transient temperature profile during a single char particle combustion. This model provides useful information for particle ignition, burning temperature profile, combustion time, and carbon consumption rate.A gas phase reaction model incorporating the full set of 28 elementary C/H/O reactions was developed. This model calculated the gas phase CO oxidation reaction in the boundary layer at particle temperatures of 1250K and 2500K by using the carbon consumption rate and the burning temperature at the pseudo-steady state calculated from the temperature profile model, but the transient heating was not included. This gas phase model can predict the gas species and the temperature distributions in the boundary layer, the CO2/CO ratio, and the location of CO oxidation.These models were applied to the ignition temperature profile and the CO 2 /CO ratio obtained by Tognotti (Tognotti et al., 1990) in an electrodynamic balance for 180 gm Spherocarb particles and to the combustion rate data measured by Tullin (Tullin et al., 1993) in a fluidized bed combustor for 4 mm Newlands char particles.The temperature profile model reproduced the experimental measurement of Spherocarb combustion temperatures in an electrodynamic balance, including the dependence of particle ignition on the oxygen partial pressure. Increasing the oxygen partial pressure reduces the combustion time and increases the maximum temperature. The internal diffusion limitation could be treated by using macropore surface area. The particle diameter does not have a large impact on the maximum temperature rise, but has a considerable effect on the combustion time. The addition of mineral catalyst promotes heterogeneous CO 2 formation and raises the particle temperature.A gas phase reaction model was used to calculate the CO2/CO ratio measured by Tognotti. Different water vapor concentrations at low and high particle surface temperatures (1250K and 2500K) were used to see the effect of hydrogen containing species on CO oxidation in the gas phase. The particle diameter was 180 gm. The bulk gas was a mixture of 100% oxygen and water vapor.At a temperature of 1250K, there was no significant CO oxidation in the gas phase even with 3.5% water vapor due to the small size of the particle and the steep temperature gradient. Estimates of gas phase reaction in the macropore could not account for the high CO 2 /CO ratio indicating that the presence of water vapor may enhance the rate of heterogeneous oxidation of CO.At a high temperature of 2500K, without hydrogen containing molecules the gas phase oxidation of CO is negligible. The effect of the hydrogen containing component on 2 the CO oxidation was significant. Spherocarb particles have 0.74% of 'H' internally. This internal hydrogen source was enough to explain the observed CO2/CO ratio.A mechanistic heat and mass transfer model was added to the temperature profile model to predict ...

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Section: Introductionmentioning

confidence: 99%

Modeling of single char combustion, including CO oxidation in its boundary layer

Lee¹,

Longwell²,

Sarofim³

1994

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“…Thus, the volumetric fiow-rate that crosses the bed as bubbles increases, while the volumetric fiow-rate in the particulate phase decreases. It is plausible to assume that, in a fiuidized bed, the kinetic mechanism of the combustion of a mixture proceeds within the bubbles and that in the particulate phase the same mechanism is quenched by the sand through radical-wall collision reactions (Dennis et ai., 1982;Hayhurst, 1991;Ribeiro and Pinho, 1998;Hesketh and Davidson, 1991;Hayhurst and Tucker, 1990). Therefore, as the fiow-rate of bubbles crossing the bed increases with the temperature of the bed, the mole fraction of CO2 will also increase.…”

Section: Type I Curvesmentioning

confidence: 99%

“…The temperature of the fluidized bed at which combustion takes place when the bubbles reach the free surface of the bed is known as the critical temperature. For a bed which is above critical temperature (Dennis et aI., 1982;Hayhurst, 1991;Ribeiro and Pinho, 1998;Hayhurst and Tucker, 1990), the bubbles burn inside the bed, while below the critical temperature the bubbles burn over the bed. Bulewicz et a!.…”

Section: Introductionmentioning

confidence: 99%

Generic Behaviour of Propane Combustion in Fluidized Beds

Ribeiro

Pinho²

2004

Chemical Engineering Research and Design

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“…Recent studies [25][26][27][28] show that the oxidation of CO occurs either inside the ascending bubbles or at the top of the fluidized bed; according to Hayhurst [28] this reaction does not normally occur in the dense phase, because it is quenched by free radicals recombining on the inert particles, if the bed is below about 1173 K. As there is oxygen consumption inside the bubbles, the model described above must be reanalyzed. This is done in Appendix I, considering that the oxidation of all the CO takes place inside the bubbles; the resulting equation is: …”

Section: Transfer Rate During Bubble Formationmentioning

confidence: 99%