Flame flashes when bubbles explode during the combustion of gaseous mixtures in a bubbling fluidized bed

Bulewicz, E.M.; Żukowski, Witold; Kandefer, Stanisław; Pilawska, M.

doi:10.1016/s0010-2180(02)00466-2

Cited by 22 publications

(20 citation statements)

References 6 publications

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“…This was typical, but bubbles could occasionally still reach the surface to release gases to burn for several milliseconds in a luminous flame (see also Fig. 1, frame D, in [10]). …”

Section: The Video Resultsmentioning

confidence: 91%

“…When the residence time of bubbles in the bed is too short for thermal ignition to occur, the gases in a bubble can ignite from surface flames or from a neighbouring bubble. In both cases the presence of chemically active regions is signalled by the characteristic blue emission [10]. It is a matter of speculation whether the reaction is started by a sudden thermal impulse or the penetration of the bubble by active free radicals, produced in the flame or explosion in above equilibrium concentrations (the presence of free radicals under fluidised bed conditions is well documented [24][25][26][27]).…”

Section: The Video Resultsmentioning

confidence: 99%

“…The quartz sand is opaque and behaves like a grey body, but photographs taken through the walls of the quartz reactor demonstrated that light flashes occur in the bed, with strong components in the blue and green, superimposed on grey-body emission from the sand, (mainly orange to red) [10]. Blue and green chemiluminescent emission in the flashes is characteristic of all hydrocarbon flames and is particularly strong with premixed gases [11].…”

Section: Introductionmentioning

confidence: 99%

“…Optical recording is much simpler and suitable video cameras are readily available. Observations in the visible and near infra red, through the quartz walls of a laboratory reactor, can yield much useful information (subject to limitations due to radiation from the reactor walls) [10,15]. A fast video camera was used to record images of the phenomena observed when propane-air was burned in a bubbling fluidised bed of quartz sand.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Propagation of Reaction Between Bubbles with a Gas Burning in a Fluidised Bed

Baron

Bulewicz

Zabagło

et al. 2011

Flow Turbulence Combust

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A bubbling fluidised bed reactor has been used for investigating how combustion propagates between bubbles of premixed fuel + air, rising from the distributor towards the surface. Earlier work has shown that when the temperature of the sand gradually rises, the gases first burn in flames above the bed, regime A, then combustion moves under its surface, to occur in bubbles travelling up the bed, under regime B. Above a certain temperature, characteristic of the gas mixture composition, combustion descends towards the bottom of the bed. Ignition then occurs in small bubbles near the distributor, under the stable regime C. The kinetic model, used to calculate the delay for thermal ignition inside gas bubbles rising through the bed, gives correct predictions for regimes A and C but not for B. Under regime B, bubbles of the mixture begin to ignite under the bed's surface while their residence time in the bed is remains shorter than the delay times for thermal ignition derived from the kinetic model. As the temperature rises, the ignition delay rapidly decreases, and regime C is reached, in accordance with the model. In this work attention was focused on regime B. A laboratory reactor of quartz glass was used, with a bed of quartz sand. Fast video recording was employed to capture ignition phenomena as the bed's temperature was raised or lowered. Records of freeboard concentrations of O 2 , CO and of total hydrocarbons, VOCs, were obtained, confirming the specific aerodynamic and chemical character of regime B. It has been shown that combustion spreads from the surface to bubbles near the bed's surface and then to other bubbles close by. Such transfer of the reaction stabilizes combustion inside the bed, at temperatures appreciably lower than that for the thermal ignition of the mixture, given by the kinetic model. This is consistent with earlier findings, which have shown that the combustion of gaseous mixtures in bubbling fluidised beds is controlled by gas phase processes, as in flames.

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“…This was typical, but bubbles could occasionally still reach the surface to release gases to burn for several milliseconds in a luminous flame (see also Fig. 1, frame D, in [10]). …”

Section: The Video Resultsmentioning

confidence: 91%

Section: The Video Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Propagation of Reaction Between Bubbles with a Gas Burning in a Fluidised Bed

Baron

Bulewicz

Zabagło

et al. 2011

Flow Turbulence Combust

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“…Exploding bubbles, in the bed but near the reactor walls and at its top surface can be directly observed [20]. The observations can be also supply quantitative information and be employed to measure local, transient temperatures in small elements of the bed.…”

Section: Introductionmentioning

confidence: 99%

An optical method of measuring the temperature in a fluidised bed combustor

Żukowski

Baron

Bulewicz

et al. 2009

Combustion and Flame

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Premixed LPG + Air Combustion in a Bubbling FBC with Variable Content of Solid Particles in the Bubbles

Baron

Żukowski

Migas

2018

Flow Turbulence Combust

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This paper presents the results of studies on the combustion of gaseous LPG in a bubbling fluidized bed. Relationships between the temperature, the bed mass and the location of the combustion zone and the NOx and CO concentrations in exhaust gases are described. The concentrations of both gases increase with rising temperature and then quickly decline. It has been shown that despite the increase in average bed temperature the drop in the emission of nitrogen oxides is connected with lower temperatures inside the exploding bubbles. These temperatures strongly depend on the quantity of solid contained in them. The paper also presents the results of modeling the combustion process in a fuel-air bubble. The modeling carried out has shown that above the temperature at which bubble self-ignition becomes possible inside the bed, with further bed temperature rise there is an increase in the solids content inside the bubbles at the moment of explosion. As a result, the maximum temperature inside the bubbles falls and the emission of nitrogen oxides is reduced. In turn, the emission of CO is linked to the propagation of combustion between bubbles when self-ignition cannot take place inside them. Graphical AbstractComparison of experimental and calculated NOx concentration, as a function of the fluidised bed temperature Highlights1.A gaseous fuel burns in a bubbling fluidized bed2.The combustion is intermittent and takes place inside bubbles, the combustion process starts in the toroidal part of the bubble3.The NO concentration is linked to the bubble temperature, not to the bed temperature4.The solids inside a bubble affect its thermal capacity5.Consequently NO concentration falls with rising bed temperature

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Flame flashes when bubbles explode during the combustion of gaseous mixtures in a bubbling fluidized bed

Cited by 22 publications

References 6 publications

Propagation of Reaction Between Bubbles with a Gas Burning in a Fluidised Bed

Propagation of Reaction Between Bubbles with a Gas Burning in a Fluidised Bed

An optical method of measuring the temperature in a fluidised bed combustor

Premixed LPG + Air Combustion in a Bubbling FBC with Variable Content of Solid Particles in the Bubbles

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