Method of and apparatus for fluidization

A fluid is introduced into a bed of a material to be fluidized along the bottom surface thereof at a pulsating velocity which is by an order of magnitude greater than the velocity of fluidization. Such method can be carried out in a fluidization apparatus having a per se known distributor the orifices of which are overlapped by reeds which vibrate when a pressure fluid is introduced into a bed above the distributor.

BACKGROUND OF THE INVENTION 
This invention relates to a method of and apparatus for fluidization and 
more particularly for drying bulk material. 
Fluidization is employed extensively for contacting gaseous materials with 
solids since contacting takes place on relatively much larger surfaces 
when contacted solids are fluidized. Fluidization is employed for 
conveying purposes as well because in their fluidized state solids behave 
as liquids and, thus, can more easily be advanced. 
Fluidization is generally obtained by having a bed of the material to be 
fluidized traversed by a fluidizing gaseous medium or fluid. However, 
various difficulties may be met with in the course of fluidization. Gas 
velocities needed for obtaining and maintaining fluidization are difficult 
to conform to values required for technological reasons as in case of 
drying, absorbing, chemical reactions, conveying and the like. Powder-like 
or minute particles of fluidized solids may deposit or flow back into 
inlet areas of fluidizing fluids at shut down periods and cause start-up 
problems. Channels may be formed in fluidized beds particles of which may 
be transported in the stream of withdrawing fluidizing fluids. Fluidized 
beds may have uneven surfaces and variable porosities both of which have 
adverse effects on start-ups. Homogeneous gas distribution in fluidized 
beds could only be obtained with beds of limited breadths. 
Such difficulties could partly be overcome by fluidization methods where a 
fluidizing fluid of pulsating flow velocity is employed and is introduced 
at a plurality of level locations simultaneously. The fluidizing fluid 
enters through tuyeres in orifices of a distributor wherefrom it withdraws 
substantially transversely of the bed. 
The present invention is thought to be an improvement over such methods in 
that a more uniform fluidization is permitted and, thereby, considerably 
broader beds are rendered possible without backflowing at shut-downs and 
start-up problems at refluidizations. 
SUMMARY OF THE INVENTION 
The invention relates to an improved method of fluidization and more 
particularly of drying bulk material. A fluidizing fluid is introduced at 
the bottom of a bed to be fluidized at a velocity which is by at least one 
order of magnitude greater than the velocity of fluidization. The flow 
direction of the fluidizing fluid which issues from the orifices of a 
distributor is parallel to the bottom of the bed. It has been found that 
such inflow direction and velocity in connection with the pulsation of the 
latter and the employment of a plurality of level inlets results in 
vigorous circulating currents or fluxes throughout the bed by which the 
entire material of the later is set into uniform bubbling motion. Thus, a 
homogeneous loose bed can be obtained in an unusually broad band of 
velocities. In addition, no particles will deposit in the inlets of the 
fluidizing fluid since they would be unable to proceed against a 
horizontal flow of high speed gaseous medium. 
The flow velocity of the fluidizing fluid will preferably be pulsated by 
permitting a resilient variation of its inflow cross-sectional areas. Such 
resilient variation results in an automatic interdependence between flow 
velocity and penetration depth of a fluid jet so that flow velocities can 
be selected at which circulating fluxes die just at the surface of the 
bed. This means that the whole mass of the bed is bubbling, yet no 
particles are transported in the stream of the fluid. 
Fluidization in the above described manner will preferably be carried out 
by apparatus of the type having a first passage which serves for receiving 
the material to be fluidized in the form of a bed. A second passage is 
separated from the first passage by a distributor and is destined to 
conduct a fluidizing fluid to the aforesaid distributor. Rows of orifices 
in the distributor permit the fluid to penetrate into the bed. 
The present invention suggests to improve such known apparatus by providing 
reeds on the outlet sides of the orifices in the distributor. Reeds having 
the nature of resilient tongues located above the orifices are liable to 
be raised by the inflowing fluid and then snap back into their rest 
positions. Thereby, the reeds abruptly and periodically interrupt the 
fluid flow through the respective orifices. Thus, a pulsating flow 
velocity is automatically obtained. Obviously, in their rest positions 
each reed has to overlap its associated orifice so that no particles of 
the bed may have access to the passage beneath the distributor. 
Oscillation frequencies and amplitudes of the reed movements are determined 
by the material and sizes of the reed as well as by the flow velocity of 
the fluid, and the consistency and thickness of the bed. 
Automatic oscillation of the reeds permits working with beds which are 
composed of grains of different sizes or of sticky materials.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates the working principle of the invention. 
Reference character 20 designates a distributor which, as is known, serves 
for introducing a gaseous fluidising fluid 22 to a bed 24 of solid 
material to be fluidized. While the flow direction of the fluid 22 is 
indicated by continuous arrows 26, dotted arrows 28 suggest movements of 
the bed material. Orifices in the distributor 20 known per se are referred 
to by reference numeral 30. 
The present invention provides resilient transverse passageways 32 above 
each orifice 30 which deflect the fluid flow in a direction parallel to 
the bottom surface of the bed 24 as suggested by arrows 26a. Resiliency of 
the passageways 32 means that their cross-sectional flow areas vary under 
mutual influence of various factors such as flow velocity, bed thickness 
and consistency, nature and size of constructional material etc. as will 
be more apparent hereinafter in the course of detailed description. 
As the fluid 22, through an orifice 30, enters a passageway 32 its pressure 
causes an expansion of the latter with consequent changes of gas pressure 
and velocity. As the gas pressure decreases, the resilient passageway 32 
resumes its initial position whereupon the whole cycle starts anew. Thus, 
the resilient passageways 32 periodically vary their cross-sectional areas 
and, thereby, render the flow velocity of the fluid automatically 
pulsating. 
Jets of the fluid 22 leaving the passageways 32 along the bottom of the bed 
24 meet each other and become mutually deflected in the direction of 
arrows 26b upwardly so that they penetrate into and through the bed 24. 
Bed particles are thereby seized by the initial strong jets and carried 
upwards. As flow velocity decreases due to spreading of the fluid in the 
bed, upwardly travelling bed particles lose their upward momentum and, by 
gravity, begin to descend substantially in regions above the orifices 30. 
Thus, the whole mass of the bed 24 is set into motion while flow velocity 
of the fluid 22 is slowed down to a value at which it leaves the bed 24 in 
the direction of arrows 26c into an ambiency 34 without carrying away any 
bed particles so that a quiet and even bed surface is obtained. 
The above described fluid supply results, as it seems, in forming 
circulating fluxes of pairwise opposite rotational directions indicated by 
dotted arrows 28a and 28b which set the whole bed material into vigorous 
bubbling and, thus, into a well fluidized state. 
Although such method may be used for fluidizing stationary beds it is 
particularly suitable for continuous operation. This will now be described 
by reference to FIG. 2. 
With continuous operation, material to be fluidized is constantly supplied 
onto a distributor 20, and fluidized material is constantly withdrawn 
therefrom as will hereinafter be described in greater detail. Due to such 
material supply and withdrawal the bed proceeds on the distributor from an 
inlet towards an outlet as indicated by arrow 28. Meanwhile, circulating 
fluxes 28a and 28b described above are formed which, in the course of 
proceeding, become sort of helicoids. Thus, it will be a suitably 
fluidized bubbling mass which arrives at the outlet referred to above. As 
far as orifices 30 with resilient passageways 32 are provided, the bed 24 
will be exempt of quiescent areas so that a very efficient fluidization 
will be obtained along the whole perforated distributor surface the width 
of which is thus practically unlimited. 
The method according to the invention may, e.g., in case of drying, be 
carried out in an apparatus shown, by way of example, in FIGS. 3 to 7. 
The interior of a casing 40 is subdivided by a distributor 20 into a 
passage 44 for receiving a bed 24 consisting of wet solid material 42 to 
be dried, and into a passage 46 for conducting a gaseous medium such as 
fluid 22 for introducing it by means of the distributor 20 into the bed 
24. 
Details of the distributor 20 are shown in FIGS. 5 and 6. In the instant 
case, the orifices 30 interconnecting the passages 44 and 46 constitute 
longitudinal slits which lie parallel to the flow direction 28 of the bed 
24. On the upper side of the distributor 20 facing the passage 44 the 
orifices 30 are overlapped each by a reed 48. Overlapping is referred to 
by reference characters a, b, and c, in FIG. 5. In the represented 
embodiment, the reeds 48 are formed by teeth 50 of a metal plate incised 
in the manner of a rake. Such expedient is preferable from a plurality of 
points of view such as simple manufacture, reliable overlapping and the 
forming of slits of small resistance and considerable specific 
circumference (circumference versus surface area). 
Likewise, in the instant case, on its lower side facing the passage 46 the 
distributor 20 is provided with a lock plate 52 arranged for adjusting the 
cross-sectional flow area of the orifices 30. Thereby, the operation of 
the apparatus may be adapted to operational conditions of drying since 
higher moisture contents require relatively more air while in case of 
materials of lower moisture content less air will be needed to obtain a 
certain degree of dryness. Adjustments may be effected also during 
operation by displacing the lock plate 52 in one of the directions 
designated by arrows 54 and 56. Thereby, efficiency may greatly be 
enhanced. The lock plate 52 is guided either on the distributor 20, or on 
side walls 58 and 60 of the casing 40 in a manner known per se, e.g., by 
slide rails which are, for the sake of clarity, not represented in the 
drawing. 
In the instant case, on its upper side the distributor 20 carries sluices 
62 arranged transversely as regards the flow direction 28 of the bed 24. 
Height of the slucies 62 may be adjusted by means of sluice valves 64 in a 
manner known per se. Such arrangement permits simple flow control and 
prevention of back flows. 
As illustrated, the sluices 62 may comprise orifices 66 the cross-sectional 
flow area of which can likewise be adjusted by the sluice valves 64. Such 
expedient permits adjusting the flow rate without altering the thickness 
of the bed 24. Larger particles at the bottom of the bed are permitted to 
proceed as well. Thereby, any tendencies to segregation may be obviated 
which is very important in case of continuous operation as will be clear 
to any skilled art worker. 
With the represented embodiment, the sluices 62 are arranged on the 
distributor 20 so that they pairwise enclose a row of orifices 30 as can 
be seen particularly in FIG. 4. The sluices 62 extend to longitudinally 
arranged baffle plates 68 and 70 which are shorter than the passage 44 and 
serve to recirculate a portion of the bed material to the inlet extremity 
of the distributor 20, the flow path of which is extended thereby. By such 
recirculation even substances difficult to fluidize can be rendered 
accessible to fluidization. For instance, particles of granular metals may 
be coated with a paste which helps to fluidize such materials. 
The lower side facing the fluid passage 46 of the distributor 20 is 
provided with conditioning compartments 72 arranged one behind the other 
as regards the flow direction 26 of the fluid 22. The compartments 72 
comprise, in the instant case, each a throttle valve 74 which permit an 
adjustment of their cross-sectional flow area. Furthermore, the 
compartments 72 register each with a row of orifices 30 between a pair of 
sluices 62 although other arrangements might be selected as well, if 
necessary. 
The employment of compartments 72 as described above furthers adaptation of 
operational conditions to requirements of drying since each compartment 72 
may have different thermal and/or humidity conditions established therein. 
A chute 76 serves for supplying wet material 42 to be dried onto the 
distributor 20 at one of its extremities and comprises an inlet thereto. A 
feed rotor 78 ensures uniformity of supply as is known per se. 
A discharge shaft 80 constituting an outlet is provided at the other 
extremity of the distributor 20 and is provided with a feed rotor 82 which 
ensures a uniform discharge likewise in a manner known per se. 
The passage 44 itself opens into a vortex chamber or cyclone 84 which, in 
turn, opens into the ambiency 34. At its lower extremity the cyclone 84 is 
connected with the discharge shaft 80. 
Reference numeral 86 designates a gate by which inflow cross-sectional 
areas of the fluid 22 may be adjusted according to operational 
requirements. Steam may be supplied to the system at 88. Precipitations or 
deposits may be discharged at 90. Reference numeral 92 designates a 
distribution hopper while reference numeral 93 refers to a steam calorifer 
connected with the steam supply means 88. 
In operation, wet solid material 42 to be dried is supplied through the 
chute 76 by means of feed roller 78 onto the distributor 20 as indicated 
by arrow 28. At the same time, air will be introduced through gate 86 into 
distribution hopper 92 as indicated by arrows 26 wherefrom it flows into 
the passage 46 and through the compartments 72 into orifices 30 of the 
distributor 20. 
In each compartment 72 there prevail individually selected temperature 
and/or moisture conditions so that the air jets entering the passage 44 
through the orifices 30 are conditioned in accordance with the temperature 
and/or moisture conditions prevailing between the sluices 62. 
More particularly, the air as fluidizing fluid 22 flows from compartments 
72 into orifices 30 of the distributor 20 and raises the reeds 48 from 
under which it penetrates into the bed 24 as indicated by arrows 26a (FIG. 
1). Raising of the reeds 48 creates resilient passageways 32 by which the 
inflowing air is caused to discharge along the bottom side of the bed 24 
as has been explained in connection with FIG. 1. Meanwhile the flow 
velocity of air suddenly increases while decreasing pressure permits the 
reeds 48 to resume their initial position where they overlap their 
associated orifices 30 as shown in FIG. 5 at a, b and c. 
Closed reeds 48 are again exposed to the pressure of the inflowing fluid 22 
so that they rise anew and the whole cycle of reed movements and air flow 
is started again. This is the way in which the reeds 48 carry out 
vibrational motions and thereby automatically ensure the building up of 
circulating fluxes and bubbling as has been described in detail in 
connection with FIGS. 1 and 2. It means that a flow pattern as shown in 
FIG. 1 will appear between each pair of sluices 62 as indicated by arrows 
26b and 28b in FIGS. 1 and 2, respectively. 
The air leaves the bed 24 in the direction of arrows 26c after having been 
in close contact with particles of the fluidized wet solid material 42 and 
having taken over their moisture content to a desired degree. The wet air 
flows into the cyclone 84 where transported solid particles will 
precipitate so that it will be pure air which leaves the cyclone 84 into 
the ambiency 34. Precipitated solid particles drop from the cylone 84 into 
discharge shaft 80 wherefrom they leave together with dry solid material 
79 in the direction of dotted arrow 28 in a manner known per se to a place 
of processing. 
FIGS. 7 and 8 show an exemplified embodiment of a distributor provided with 
a pair of toothed plates 98 and 100 the teeth of which engage each other 
in the manner of a toothed joint. It will be apparent from FIG. 8 that by 
such arrangement of reed fluidization will be more even than with 
unidirected reeds since the reeds will act symmetrically across the spaces 
between pairs of sluices 62. 
The exemplified embodiment of the apparatus shown in FIG. 9 differs from 
the previous one in that it is provided with a plurality of distributors 
20a, 20b and 20c of various levels in cascade arrangement between an inlet 
and an outlet of the type described in connection with the embodiment 
shown in FIGS. 3 to 6. The distributors 20a, 20b and 20c are separated 
from one another by partitions 104a and 104b, respectively. It will be 
seen that the reeds of this exemplified embodiment are of the type shown 
in FIGS. 7 and 8. 
In operation, fluidization may be carried out on the various distributors 
20a, 20b and 20c under substantially different operational conditions. It 
is important that backflow is effectively impeded by the step arrangment 
of the distributors by which efficiency is considerably increased. 
Efficiency of the fluidization method according to the invention will be 
apparent from the following tables I and II. Table I identifies materials 
and their characteristics chosen for comparison while table II comprises 
drying characteristics of the materials set forth in table I, the data 
being grouped according to the apparatus employed for fluidization. 
Table I 
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Materials and their characteristics 
Average Initial moisture 
grain size 
Density content 
milli- gram/cubic 
(H.sub.2 O+ solvent) 
No. Material meter centimeter 
% 
______________________________________ 
1 K-asparagin- 
0.68 0.71 27 
ate granular 
material 
2 Mg-asparagin- 
1.06 0.81 8 
ate granular 
material 
3 phenyl buta- 
0.65 0.34 31 
zone crystal- 
line material 
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Table II 
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Drying characteristics 
Heat exploitation 
Air consumption 
Average operational 
Kilogram/steam 
Cubic meter air/ 
velocity of air 
Kilogram evaporated 
Kilogram evaporated 
No. 
Material Type of drier 
meter/secundum 
liquid liquid 
__________________________________________________________________________ 
1. K-asparaginate 
I 0.42 28.00 580.0 
II 0.40 9.00 110.0 
III 0.12 1.12 38.0 
2 Mg-asparaginate 
I 0.48 16.00 640.0 
II 0.41 10.00 190.0 
III 0.13 1.15 50.0 
3. Phenyl butazone 
I 0.22 6.20 300.0 
II 0.21 5.00 120.0 
III 0.08 1.10 55.0 
__________________________________________________________________________ 
Type I: Fluidization drying apparatus known per se 
Type II: Mixed bed fluidization drier known per se 
Type III: Drying apparatus in accordance with the invention. 
It will be seen that in case of a method and apparatus according to the 
invention average operation air velocity, steam and air consumptions 
amount likewise to a fraction of corresponding parameters of known methods 
and apparatus, respectively. Distributors as described above might be 
employed, e.g., multistep and overflow columns where bubble plates consist 
each of distributors and of reed overlapping orifices thereof as described 
above. Flow patterns of fluidizing fluid and fluidized bed, respectively, 
are similar to those shown in FIGS. 1 and 2. The material to be fluidized 
proceeds from upper levels through overflows onto bubble plates at lower 
levels. Such arrangement permits to erecting multistage heat and/or mass 
transfer apparatus of relatively small surface area. 
It has been found that beds fluidized in accordance with the present 
invention are substantially homogeneous. At the same time, operational 
fluidization velocities are relatively low. Operational gas velocities and 
gas consumptions are likewise relatively low which means, in addition to 
energy savings, a simple solvent recovery and permits thereby carrying out 
sorption operations at relatively low costs. 
Obviously, distributors and reeds may be of other than horizontal 
arrangement. For instance, the distributor might define a curved surface 
or an oblique plane. The essence is that it should be provided with reeds 
which overlap the orifices of the distributor whatever its form may be.