Experimental measurements of combustion of simulated coal volatiles in a bubbling fluidized bed combustor

Stubington, John F.; Chan, Shu W.

doi:10.1016/0016-2361(90)90028-o

Cited by 6 publications

(3 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Both the location and number of the fuel entry ports as well as the bed fluid-dynamics influence the extent of the transversal segregation. 14,15 A major contribution to the study of radial segregation of volatile matter in FBC was provided by the work of Stubington and co-workers, [16][17][18][19] that led to the formulation of the so-called "multiple discrete diffusion flame model" for FBC of volatiles. 20,21 This mechanistic model of coal particle devolatilization and motion in a fluidized bed assumes that the volatiles are released during different stages (lift-up, residence at surface, and recirculation of the fuel particle) and predicts that a large fraction of volatiles may be directly released in the freeboard.…”

Section: Introductionmentioning

confidence: 99%

“…A major contribution to the study of radial segregation of volatile matter in FBC was provided by the work of Stubington and co-workers, − that led to the formulation of the so-called “multiple discrete diffusion flame model” for FBC of volatiles. , This mechanistic model of coal particle devolatilization and motion in a fluidized bed assumes that the volatiles are released during different stages (lift-up, residence at surface, and re-circulation of the fuel particle) and predicts that a large fraction of volatiles may be directly released in the freeboard. More recently, on the base of the theoretical analysis by Fiorentino et al, a model of a bubbling FBC operated with high-volatile solid fuel feedings was presented, accounting for volatile matter segregation and postcombustion above the bed.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

On the Relevance of Axial and Transversal Fuel Segregation during the FB Combustion of a Biomass

2004

View full text Add to dashboard Cite

The fluidized bed combustion of a typical Mediterranean biomass (pine-seed shells) was investigated in a pilot-scale bubbling FB combustor (200 kWth) at different operating conditions. Both over-and under-bed fuel feeding options were considered. The focus of the experiments was to study the extent of volatile matter mixing/segregation in the bed and the subsequent postcombustion in the splashing zone and freeboard. To this end, temperature profiles along the combustor axis as well as transversal gas concentration profiles above the bed surface were measured. Experiments highlighted that complete conversion of the fuel within the combustor was obtained, even if a significant volatiles postcombustion above the bed occurred. This results in an appreciable overheating of the freeboard. Both the fuel feeding option and the excess air affect the extent of volatiles postcombustion. Gas concentration profiles were not uniform along the combustor diameter because of the single-point fuel feeding and the incomplete fuel mixing in the bed. The measured carbon-containing gaseous species profiles along the bed diameter were used to estimate the fuel lateral dispersion coefficient in the fluidized bed, by means of a simplified dispersion/pyrolysis model. Comparison of experimental profiles with model results at over-and under-bed feeding conditions allowed us to evaluate both the fuel lateral dispersion coefficient inside the bed and on the bed surface, which were determined to be of the order of 0.01 m 2 /s and 0.1 m 2 /s, respectively.

show abstract

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

On the Relevance of Axial and Transversal Fuel Segregation during the FB Combustion of a Biomass

2004

View full text Add to dashboard Cite

show abstract

“…It consisted of a zirconia-based oxygen sensor and a differential pressure probe, used to detect the pressure gradient within a bubble or the particulate phase at the oxygen sensor (Sitnai et af., 1981;Sitnai, 1982). Stubington and Chan (1990a) used this combined oxgyen/bubble probe and a 'simulated coal particle' (Stubington and Chan, 1986), which releases combustible volatiles on heating but leaves behind an inert residual particle, to investigate the release and combustion process of these simulated volatiles within the bed, and determine the relationships between fuel and oxygen, and bubble and particulate phases. Cross-correlation of the bubble and oxygen signals showed that the high and low values of the oxygen partial pressure did not correspond to the bubble and particulate phases, as would be expected for operation in the unclouded (slow) bubble regime.…”

Section: Combined Oggen /Bubble Probementioning

confidence: 99%

Experimental investigation of the two-phase theory in a fluidized-bed combustor

Stubington

Cui

1995

Int. J. Energy Res.

View full text Add to dashboard Cite

Though the two‐phase theory of fluidization is well‐accepted, no direct experimental measurements of the different gas concentrations predicted to occur in bubble and particulate phases could be found in the literature. For the first time, theoretical predictions of these different gas concentrations have been validated experimentally, using a combined oxygen/bubble probe. Based on the two‐phase theory, a mathematical model was developed for the combustion of a batch of char particles in a fluidized‐bed combustor. The experimental oxygen concentration in the particulate phase as a function of time was well predicted by the model. Slight discrepancies for the bubble phase values were eliminated when low‐oxygen‐concentration bubbles were excluded from the data, attributed to some char combustion occurring in bubbles being contrary to the model assumption. The temperature difference between char and bed particles (ΔT) was the only adjustable parameter in the model. A value of 20°C fitted the burnoff times measured by visual observation of the top of the bed, for both 5 and 10 g char batch masses. Model predictions of the oxygen concentrations were not sensitive to ΔT during the first half of burnoff, when mass transfer controlled the combustion rate, so the mass transfer processes were predicted correctly by the model effectively with no adjustable parameter. The ΔT value of 20°C was significantly lower than experimental measurements of maximum burning char particle temperatures, reported to be 70°C for the small‐diameter bed particles used in this work. The discrepancy was attributed to two factors: (i) the decrease in char particle temperature towards the end of the burnoff, when kinetics significantly affected the combustion rate; and (ii) a lower char particle temperature in the particulate phase than in the bubble phase, with experimental char particle temperature measurements biased towards the higher bubble phase values. It was inferred: (i) that the maximum values of ΔT measured experimentally are too high for calculation of the char particle combustion rate during the kinetic‐controlled latter stage of burnoff and (ii) that reported values of the heat transfer coefficient from burning char particles to the particulate phase deduced from these particle temperature measurements may have been underestimated.

show abstract

Model of sulphur capture in fluidised-bed boilers under conditions changing between oxidising and reducing

Lyngfelt¹,

Leckner²

1993

Chemical Engineering Science

View full text Add to dashboard Cite

Experimental measurements of combustion of simulated coal volatiles in a bubbling fluidized bed combustor

Cited by 6 publications

References 8 publications

On the Relevance of Axial and Transversal Fuel Segregation during the FB Combustion of a Biomass

On the Relevance of Axial and Transversal Fuel Segregation during the FB Combustion of a Biomass

Experimental investigation of the two-phase theory in a fluidized-bed combustor

Model of sulphur capture in fluidised-bed boilers under conditions changing between oxidising and reducing

Contact Info

Product

Resources

About