62
3 A Structuring Regime to Control Bubbling Beds
with chaotic dynamics by trying to provide some “structures” into flows. Conventional approaches entail the use of internals via baffles and heat exchanger tubes.
These are used as a way to force certain flow paths but do not show any flexibility and
suffer from additional costs in energy, pressure drop and other disadvantages, such
as particle attrition. Besides, the improvement associated with internals is dependent
on the specific particle type, operating conditions and the specific unit design, which
makes it very difficult to obtain a universally valid standard across all scales.
Alternatively, external pulsation excels as a non-intrusive way to modify system
hydrodynamics. The previous study has applied this principle and demonstrated,
at specific conditions, that pulsating the gas in a relatively deep, quasi-2D bed can
suppress instabilities within fluidised systems and create fully regular and predictable
macroscopic flow structures. In these structures, bubbles self-organise dynamically
in arrays of triangular lattices, with a determined wavelength and angle [2, 6]. This
pattern formation suggests a solution to stabilise inherently chaotic fluidised systems.
Such structured flows manifest great potential to facilitate the engineering design
and control of fluidised bed systems. As discussed in Chaps. 1 and 2, modulated
pulsation of the inlet gas flow leads to various fluidisation regimes, showing the
ability to effectively manipulate bubble properties, such as size and separation.
Apart from this, the features associated with structuring are not yet properly identified. This chapter focuses on analysing the use of such dynamic self-organisation
as a method to structure the flow behaviour. The impacts of operating conditions
on the self-organisation process and its reproducibility are quantified using pattern
recognition tools, which characterise each experimental flow structure with specific
attributes, such as pattern intensity, wavelength and lattice angle, and relate them
to controlled bubbling properties. An operating window of highly structured flows
is then constructed and correlated to the flow properties experimentally, through
the comparison of flow patterns across various experimental conditions. The results
demonstrate that structured flows manifest different levels of control over size, residence time and motion of bubbles, which are directly associated with the oscillatory
flow applied. As a result of structuring, the overall hydrodynamics can be manipulated tightly in a controllable manner. These features would be highly desirable in
solids processing units, as they would allow for bypassing some of the challenges in
conventional units, such as flow misdistribution, non-uniform contact, and geometry
dependence, but also decouple conflicting design objectives.
3.2 Experimental Implementation
and Analysis Methodology
The same experimental setup and image analysis described in Sect. 2.2 are employed
to create pulsed flows and analyse properties of bubbles. In addition, the flow structures created in various static bed heights are studied. Besides, the same type of
Geldart B glass beads is used in order to mitigate the impacts of size distribution and
3 A Structuring Regime to Control Bubbling Beds
with chaotic dynamics by trying to provide some “structures” into flows. Conventional approaches entail the use of internals via baffles and heat exchanger tubes.
These are used as a way to force certain flow paths but do not show any flexibility and
suffer from additional costs in energy, pressure drop and other disadvantages, such
as particle attrition. Besides, the improvement associated with internals is dependent
on the specific particle type, operating conditions and the specific unit design, which
makes it very difficult to obtain a universally valid standard across all scales.
Alternatively, external pulsation excels as a non-intrusive way to modify system
hydrodynamics. The previous study has applied this principle and demonstrated,
at specific conditions, that pulsating the gas in a relatively deep, quasi-2D bed can
suppress instabilities within fluidised systems and create fully regular and predictable
macroscopic flow structures. In these structures, bubbles self-organise dynamically
in arrays of triangular lattices, with a determined wavelength and angle [2, 6]. This
pattern formation suggests a solution to stabilise inherently chaotic fluidised systems.
Such structured flows manifest great potential to facilitate the engineering design
and control of fluidised bed systems. As discussed in Chaps. 1 and 2, modulated
pulsation of the inlet gas flow leads to various fluidisation regimes, showing the
ability to effectively manipulate bubble properties, such as size and separation.
Apart from this, the features associated with structuring are not yet properly identified. This chapter focuses on analysing the use of such dynamic self-organisation
as a method to structure the flow behaviour. The impacts of operating conditions
on the self-organisation process and its reproducibility are quantified using pattern
recognition tools, which characterise each experimental flow structure with specific
attributes, such as pattern intensity, wavelength and lattice angle, and relate them
to controlled bubbling properties. An operating window of highly structured flows
is then constructed and correlated to the flow properties experimentally, through
the comparison of flow patterns across various experimental conditions. The results
demonstrate that structured flows manifest different levels of control over size, residence time and motion of bubbles, which are directly associated with the oscillatory
flow applied. As a result of structuring, the overall hydrodynamics can be manipulated tightly in a controllable manner. These features would be highly desirable in
solids processing units, as they would allow for bypassing some of the challenges in
conventional units, such as flow misdistribution, non-uniform contact, and geometry
dependence, but also decouple conflicting design objectives.
3.2 Experimental Implementation
and Analysis Methodology
The same experimental setup and image analysis described in Sect. 2.2 are employed
to create pulsed flows and analyse properties of bubbles. In addition, the flow structures created in various static bed heights are studied. Besides, the same type of
Geldart B glass beads is used in order to mitigate the impacts of size distribution and