Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
FIELD OF THE INVENTION:
,The present invention relates to a method for the
purification of a gas containing gaseous pollutants.
BACKGROUND OF THE INVENTION:
Various industrial processes generate waste gases
containing gaseous pollutants such as organic solvents. In
order to be able to recover such so:Lvents and to prevent air
pollution, therefore, the waste gases must be freed of the
noxious pollutants before they are released into the atmosphere.
Various methods have been devised for effecting the
purification by adsorption of gases containing gaseous pollutants.
When the occasion requires, these prior methods involve the
recovery of the noxious pollutants removed from the gases.
Of these prior methods, the method which makes use of the
so-called fluidized-bed type adsorption system is popular,
w,herein a gas to be treated and adsorbent particles, such as
activated carbon, activated alumina or silica, are brought
into mutual contact tc form a fluidized bed of the adsorbent
particles. In the adsorption treatment of the gas by this
fluidized-bed method, it is common practice to effect the
gas treatment continuously by forming several fluidized beds
in a multiplicity of stages within a tower. Particles from
each fluidized bed can flow over a barrier or weir to fall
onto the next lower bed via downcommers. Particles from the
lowermost bed are then transferred to the uppermost bed via
a pipe so that the particles are recycled continuously
through the tower.
In the adsorption treatment of the gas by the
fluidized-bed method described above, successful stabilization
of the fluidized beds thus formed constitutes an essential
requirement for enabling the removal of the noxious gaseous
- 1- ~
8~
pollutants from the gas to be effected continuously at a high
removal efficiency over long periods of service. The stability
of such fluidized beds depends on the shape of the adsorbent
particles used, the strength, wear resistance and other physical
properties of the particles and the flow volume, flow velocity
and viscosity of the gas used for fluidizing the adsorbent
particles, and so on. It also depends on the extent of change
in weight of the adsorbent particles being recycled. When the
adsorption treatment of gas by the conventlonal fluidized-bed
type technique is reviewed from this point of view, it is noted
that the so-called coconut-shell activated carbon obtained from
coconut husks is popularly used to form the adsorbent particles.
The activated carbon of this type is made up of particles of
various, irregular shapes and this makes their transport
through the adsorption apparatus substantially difficult
Moreover, the adsorbent particles have poor physical properties
and, for this reason, are readily pulverized as by crushing
and attrition. Recyclic use of such irregularly shaped
activated carbon particles, therefore, involves numerous
difficulties. In the adsorption treatment of gas by the
fluidized-bed method, the adsorbent particles of such shapes
induce undesirable phenomena such as boiling, channeling and
slugging~ when fluidized by the upward flow of the gas under
treatment. They also cause similar phenomena while they are
moving downwardly via the downcommers by gravity, with the
result that the smooth flow of the particles inside the
downcommers is impeded. This impeded flow consequently
brings about a quantitative change in the weight of the
adsorbent particles belng transferred for recyclic service.
With a view to precludlng these disadvantageous phenomena,
the conventional techniques have attempted to lmprove the
~6~
structure of the downcommers for particle flow. It has been
suggested, for example, to incorporate orifices in the bottoms
of the downcommers or9 as disclosed by U.S. Patent No. 2,674,338,
to have bottom plates supported on springs on the bottoms of
the downcommers. These attempts at improvement of the structure
of downcommers, however, effectively complicate the system
itself and have the disadvantage that the activated carbon
particles vary their shapes gradually with the lapse of time.
Thus, all these attempts fail to some extent to attain the
preferred stabilization of the quantitative transport of
adsorbent particles. Because the adsorbent particles in use
are highly susceptible to pulverization and also because
stabilization of the transport of these adsorbent particles is
difficult to accomplish, the conventional techniques do not
easily achieve the desired obejct of stabilizing the fluidized
beds of the adsorbent particles.
SUMMARY 0~ THE INVENTION:
It is, therefore, a primary object of the present
invention to provide a novel method and apparatus for the
purification of a waste gas by the fluidized-bed principle,
which method, by recyclic use of activated carbon spheres,
is capable of continuously and effectively purging the gaseous
pollutants from the gas.
It has now been discovered that the stabilization of
the fluidized beds and the stabilization of the quantitative
transport of activated carbon particles are both easily attained
by using activated carbon spheres as the adsorbent particles
- and also using perforated plates of a specific shape as the
stePPed trays within the reaction tower.
According to one aspect of the present invention,
there is provided a method for the continuous purification of a
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~L~60~
waste gas containlng gaseous pollutants, which comprises:
(a) providing a tower having at least two substantially
horizontal, vertically spaced per'forated plates therein arranged
so that gas flowing upwardly through said tower passes through
each of said perforated plates in succession, each of said
perforated plates having a single, non-circular weir provided
on its upper surface dividing said surface into two portions,
a first of said portions having 80 to 95 % of the total surface
area and a second of said portions having 5 to 20 % of the
total surface area, the weirs on each of said plates being of
substantially the same height, and the plates being arranged
in such a manner that the second portion of each plate overlies
the first portion of the next lower plate; (b) continuously
passing said waste gas upwardly through said tower so that the
gas passes through said perforated plates and at the same time
continuously and recircularly eeding activated carbon spheres
downwardly through said tower so that the spheres form
fluidi~ed beds on said perforated plates; and (c) continuously
removing purified gas from the top of said tower.
According to another aspect of the invention there
is provided a chemical process column containing at least two
substantially horizontal, vertically spaced perforated plates
arranged so that gas flowing upwardly through said tower passes
through each of said perforated plates in succession, each of
said perforated plates having a single, non-circular weir
provided on its upper surface dividing said surface into two
portions, a first of said portions having 80 to 95 % of the
total surface area and a second of said portions having 5 to
20 % of the total surface area, the weirs on each of said
plates being of substantially the same height, and the plates
being arranged in such a manner that the second portion of each
plate overlies the flrst portion of the next lower plate.
BRIEF EXPL~ANATION OF THE DRAWINGS:
In the accompanying drawings:
Fig. 1 is a schematic explanatory diagram illustrating
one example of a known adsorption apparatus for the remova] of
gaseous pollutants by the fluidized-bed principle;
Fig. 2 is a plan view illustrating one preferred
embodiment of one of the perforated plates used in the present
invention~ which perforated plate has a weir formed on its upper
surface in such a way that the plate surface is divided into a
first portion accounting for 80 to 95% of the entire surface
area and a second portion accouting for 5 to 20% of the entire
surface area;
Fig. 3 is a plan ùiew illustrating a perforated plate
similar to the plate shown in Fig. 2 but arranged in a reversed
position, which perforated plate has a weir formed on its upper
surface in su&h a way that the plate surface is divided into a
portion accounting for 5 to 20% of the entire surface area and
another portion accounting for 80 to 95% of the entire surface
area;
Fig. 4 is a schematic diagram illustrating a multiplicity
of horizontal stepped trays comprising the perforated plates
of the type of Fig. 2 and those of the type of Fig. 3 alternately
disposed and vertically spaced inside a tower;
Fig. 5 is a schematic diagram illustrating a multiplicity
of horizontal stepped trays comprising alternative examples of
perforated plates of Fig. 2 and Fig. 3 alternately disposed
vertically spaced inside a tower;
Fig. 6 is a plan view illustrating one preferred
embodiment of another type of the perforated plate used in the
present invention, which perforated plate is divided into two
-" ~.V~ 38~
portions having surface areas oE Lhe same portion as in the
plate of Fig. 2;
Fig. 7 is a plan view illustrating a perforated plate
similar to the plate shown in Fig. 6 but arranged in a reversed
position, which perforated plate is divided into two portions
having surface areas of the same portions as the plate of Fig. 3;
Fig. 8 is a schematic diagram illustrating a multiplicity
of horizontal stepped trays comprising the perforated plates of
Fig. 6 and Fig. 7 alternately disposed and vertically spaced
inside a tower;
Figo 9 is a schematic diagram illus~rating a multiplicity
of horizontal stepped trays comprising alternative examples of
the perforated plates of Fig. 6 and Fig. 7 alternately disposed
and vertica~ly spaced inside a tower; and
Fig. 10 is a schematic diagram illustrating one
preferred embodiment of the present invention in which a gas
containing gaseous pollutants is treated continuously for the
removal of the gaseous pollutants.
DETAILED DESCRIPTION OF THE INVENTION:
In Fig. 1, 1 denotes a reaction tower. A gas
containing noxious gaseous pollutants to be removed is
introduced into the tower 1 through a nozzle 2 in the adsorption
section A. On entering the tower interior, the gas ascends
vertically and comes into contact with adsorbent particles
held inside the adsorption section A, causing the adsorbent
particles to form fluidized beds on the stepped trays 3, 3', 3",
etc. The adsorbent particles forming the fluidized beds adsorb
the gaseous pollutants from the gas. The gas which has thus
been freed of the noxious pollutants is released into the
atmosphere via a discharge outlet 4 at the top of the tower.
The adsorbent particles on the stepped trays 3, 3', 3", Ptc.,
-- 6 --
8~0
fall through the downcommers 5, 5', 5", etc. associated with the
trays and descend gradually downwardly by virtue of gravity,
while slmultaneously adsorbing the gaseous pollutants from the
gas. The particles then leave the adsorption section A and
accumulate in the space formed on a guide plate 6 and gradually
reach a regeneration section B which is located at the bottom
of the reaction tower 1. On entering the regeneration section
B, the adsorbent particles are heated by a heater 7, with the
result that the particles are regenerated as they are forced
by the heating to release the adsorbed pollutants. Subsequently,
the regenerated adsorbent particles reaching the bottom 8 of the
tower are transferred via a lifting pipe 9 to the top of the
tower for recyclic service. In the meantime, the pollutants
which have been desorbed from the adsorbent particles are
forced out of the system via a nozzle 10 by means of a carrier
gas introduced via a nozzle 11 disposed at the lower portion of
the regeneration section B. The discharged pollutants are
transferred to a desorbate treating section C composed of a
condenser, decanter and the like.
In the method of the present invention, activated
carbon spheres are used as the adsorbent particles. ~ecause of
their spherical shape, these activated carbon spheres usually
have the advantages of excellent fluidity, outstanding resistance
to friction and wear and high impact strength. For the purpose
of the present invention, the activated carbon spheres may be
of the type which are obtained by mixing a powdery carbon or
carbon precursor with a binding agent, subsequently molding the
resultant mixture in the shape of spheres and activating the
molded carbon spheres by an ordinary method (otherwise,
referred to generally as "activated carbon spheres from coking
coal"). It is, however, preferable to use the type of activated
8~6~
carbon spheres produced from a specific type of pitch as the
raw material by a specific method such as disclosed in U. S.
Patent No. 3,917,806, because the activated carbon spheres of
this type are excellent in terms of their spherical shape and
physical properties. The superiority of this type of activated
carbon spheres over various other types of activated carbon
particles is easily confirmed by subjecting samples of the
various types of activated carbon to a friction test, then
sifting the tested sample particles through a sieve of 200 mesh
~by the Tyler standard) and comparing the weights of the
corresponding sievings. To be specific3 this comparison can
be accomplished by using glass containers measuring 28mm in
diameter and 220mm in length9 placing 20 cm3 samples of the
various types of activated carbon particles into the individual
containers, rotating the containers and their contents at the
rate of 36 r.p.m. for a fixed length of time, sifting the
contents through a metal screen of 200 mesh and measuring the
weight of the portion of each sample passing through the screen.
The results of a typical experiment performed as described
above are shown in Table 1 below.
Table 1 Extent of attrition loss of particles
due to friction in dry state (wt%)
Length of friction test (in hours)
TYPe of activated carbon 10 20 30 40
Activated carbon spheres 0 0 0.05 0.05
disclosed in ~.S. Patent
No. 3,917,806
Activated carbon spheres 0.05 0.08 0.22 0.60
from coking coal
Coconut-shell activated 2.3 2.9 3.3 3.5
carbon
~OtiO8~0
For the purposes of the present invention, the activated
carbon s~heres preferably have a bulk density in the range
of from 0.4 to 0.7 g/cm3, a particle diameter distribution range
of from 0.2 to 2.0mm and an average particle diameter in the
range of from 0.4 to 1.2 mm. I the particle diameter distribu-
tion of these activated carbon spheres is excessively sharp,
then during the actual use of the activated carbon spheres, the
phenomenon known as channeling may be induced. If the particle
diameter distribution of the activated carbon spheres is exces-
sively broad, then the actual use of such activated carbon spheresdoes not encounter the disadvantage described above but can result
in an adverse situation wherein the spheres of larger diameters
and those of smaller diameters become suspended at different
positions in the bed. This leads to a condition wherein only
spheres of smaller diameters flow over the weirs on the trays
and descend down the interior of the tower. Such a partial
movement of the spheres is contrary to the requirement that the
spheres should be transferred stably in a constant weight. For
this reason, the activated carbon spheres preferably have
a particle diame.er distribution such that the standard deviation
of individual particle diameter distribution will fall in the
range of fro~ 0.05 to 0.20mm.
In one embodiment of the present invention the stepped
shelves or trays mentioned above are rectangular perforated
plates of a type having a weir on the upper surface. As
illustrated in Fig. 2 of the accompanying drawings, the surface
of the tray is divided by the weir into a first portion
accounting for ao to 95% of the total surface area and a
second portion accounting for 5 to 20% of the total surface
area. In Fig. 2, 21 denotes one such a rectangular perforated
plate. The upper surface of this rectangular perforated plate
~ ~Gos~
21 is divided by a weir 24 into a first portion 22 and a second
portion ~3. In Fig~ 3, 31 denotes a ~ectangular perforated
plate dentical to the plate ~hown in Fi~. 2 except that the
positions of the first and second portions are transposed.
The upper surface of this rectangular perforated plate 31 is
divided by a weir 34 into a first portion 32 and a second
portion 33. The first portions 22 of the plate of Fig. 2 and
33 of the plate of Fig. 3 are the tray portions above which
fluidized beds of activated carbon spheres are formed. The
second portions 23 of the plate of Fig. 2 and 32 of the plate
of Fig. 3 are the portisns through which the activated carbon
spheres descend to the next lower tray. The weir 24 and the
weir 34 are so disposed on their respective rectangular per
forated plates that the portion 22 equals the portion 33 and
the portion 23 equals the portion 32 respectively in surface
area. The rectangular perforated plates 21 and 31 shown
respectively in Fig. 2 and Fig. 3 are level along their entire
surfaces and they each have a multiplicity of perforations
formed at an aperture ratio in the range of from 5 to 25%.
The entire surfaces of the rectangular perforated plates 21
and 31 may be in one level plane as shown in Figs. 4 and 8.
Otherwise, the two portions of these plates may be in different
horizontal planes separated by a vertical distance of 10 to 20
mm as shown in Figs. 5 and 9. h~hen the plates are level
throughout their entire surface, the perforations bored in
the portions 22 and 33 preferably have a diameter in the range
of from 3 to 5 mm and those bored in the portions 23 and 32
preferably have a diameter about 1.1 to 3 times that of the
perforations in the portions 22 and 33. When the plates have
stepped horizontal surfaces, all the perforations bored therein
may have a fixed diameter falling in the approximate range of
-- 10 --
B~
from 3 to 5 mm, The heights of the weirs 24 and 34 are not
specific~lly limited and are preferably in the range of from
20 to 6U mm. Moreover, it is usually necessary to make the
weirs on the respective plates of equal height for the purpose
of stabilizing the fluidized beds of the activated carbon
spheres and also stabilizing the transportation rate of the
spheres. The superficial velocity of the gas in the tower is
preferably from the practical point of view, within the range
of 0.5 to 2.0 m/sec. when the inside diameter of the tower is
from 500 to 2,000 mm, which is the usual diameter range.
The rectangular perforated plates 21 and 31 are
alternately vertically disposed to form a multiplicity of
stepped trays inside a tower as shown in Fig. 4 or Fig. 5 and,
thus form an adsorption section into which the gas is intro-
duced for purification. In Fig. 4, 41 denotes a tower. Inside
this tower 41, rectangular perforated plates 45 with surfaces
divided by a weir 44 into a first portion 42 and a second
portion 43, and rectangular perforated plates 49 with surfaces
divided by a weir 48 into a first portion 47 and a second
portion 46,are alternately disposed to form a multiplicity of
stepped trays. In Fig. 5, 51 denotes a tower. Inside this
tower 51 are rectangular perforated plates 55 having surfaces
divided by a weir 54 into a first portion 52 and a second
portion 53. The surface portion 53 is located in a level plane
10 to 20 mm below the surface portion 52. Every alternate
tray in tower 51 is a rectangular perforated plate 59 divided
by a weir 58 into a first portion 56 and a second portion 57
located in a level plane 10 to 20 mm below the portion 56. The
vertical distance by which two ad~acent trays are separated
is generally expected to be approximately the sum of the height
of the weir plus 60 mm. To effect the purification of gas in
-- 11 --
~608~
the tower described above, one has only to feed the gas
- upwardly,into the tower from the bottom and cause the
introduced gas to come into counter-current contact with
activated carbon spheres being introduced downwardly from the
top, so that the activated carbon spheres are caused by the force
of the flow of gas to form fluidize~ beds on the stepped trays.
The activated carbon spheres which have thus formed the fluidized
beds on tray portions 42 and 47 are horizontally transferred in
the direction of portions 43 and 4~, and then descend by gravity
through the perforations in the portions 43 and 46 of the rectangu-
lar perforated plates 45 and 49 in the tower of Fig. 4 (or the
portions 53 and 57 of the rectangular perforated plates 55 and 59
in the tower of Fig. 5) as they adsorb tne gaseous pollutants of
the gas under treatment. After they have passed through the
adsorption section formed by the multiplicity of stepped trays,
they are regenerated in the desorption and regeneration section.
The regenerated activated carbon spheres are recycled, being
again introduced downwardly into the tower from the top. Before
the activated carbon spheres forming the fluidized beds descend
from one tray to another, the individual activated carbon spheres
on the stepped trays move horizontally on the respective trays.
To be more specific, the activated carbon spheres which have
fallen from the narrower portion (hereinafter referred to as
"portion II") of a given tray onto the wide portion (hereinafter
referred to as"portion I") of the next lower tray move to the por-
tion II of the lower tray as they form in situ a fluidized bed.
The activated carbon spheres fed cnto portion 42 of the
rectangular perforated plate 45 in the tower of Fig. 4, for
example, are horizontally transferred in the direction of the
portion 43 by the upward stream of the gas and gravitational
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attraction and then,descend through the perforations distributed
in the portion 43. ~ecause th~ perforated plates used in the
prese~t invention as st~pped trays are rectangular in shape and
they have their upper surfaces divided each by a weir into two
portions, the invention enjoys the advantages enumerated in (1)
through (4) below.
(l)' The perforated plates are simple in their structure
and therefor can be easily produced. For this reason, the plates
are useful for a gas-treating apparatus of large type.
(2) All the particles of activated carbon spheres
move horizontally on the respective stepped trays. This means
that the stabilization of the fluidized bed on each tray is not
disturbed by the movement of the activated carbon spheres
suspended on that tray.
(3~ The direction in'which the horizontal transfer of
individual activated carbon spheres occurs on the stepped trays
alternates from tray to tray and the heights of the fluidized
beds on the respective stepped trays are equal due to the weirs
being of equal height. These facts make it possible to have the
activated carbon spneres achieve steady transfer and uniform
contact with the gas under treatment.
(4) Each of the stepped trays is divided into a
portion for permitting downward flow of activated carbon spheres
~portion II) and a portion for forminq a fluidized bed of t,h~
spheres (portion I) and the area ratio of these two portions is
constant. Therefore, by fixing the total aperture area in the
portion I at a value falling in the range of from 4 to 20 times
the total aperture area in the portion II, the weight of the
spheres to be transferred can be stabilized with minimal
deviation.
The perforated plates to be used in the present
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~L06~)8~3
invention are not necessarily ~ectangular in shape in order
to satisfy the advantages of (1) through (4) described above.
They may be of a circular shape as shown in Fig. 6 and Fig. 7,
for example. When a large scale system is used, such as a
tower having an inside diameter exceeding 1,500 mm, in the
invention for some special reason, a slight inclination of the
stepped trays, of not more than 2 degrees, may possibly aid in
the horizontal movement of activated carbon spheres on the
stepped trays. If the inside diameter of the tower is small,
however, such an inclination may conversely result in an
increased variation in the volume of activated carbon spheres
transferred. The desirability of such an inclination, there-
fore, should be evaluated with due respect to the inside
diameter of the tower.
In view of the fact that activated carbon spheres
are used as the adsorbent particles and perforated plates of
a specific shape are used as stepped trays as described above,
the present invention enables the fluidized beds formed on the
stepped trays to be stabilized to a height equalling the height
of the weirs disposed on the stepped trays and, furthermore,
permits the variation in the weight of activated carbon spheres
being transferred to be limited within +10% by weight without
resorting to any auxiliary device. Thus, the invention, in
most cases, enables the purification of the waste gas to be
carried out continuously for a long period of time, e.g. more
than 200 hours, with the efficiency or removal of the gaseous
pollutants kept at a high level (usually far exceeding 80%).
The gas which has been purified can be released into the atmos-
phere without further treatment from the top portion of the
tower. The present invention also serves the purpose of
simplifying the system itself, because it obviates the necessity
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of providing the stepped trays with downcommers as in
conventional techniques.
The present invention wi:Ll now be described more
specifically below with reference to the following Examples.
It should be noted that the present invention is not limited
in any way to these Examples.
Example 1:
A number of rectangular perforated plates were each
fabricated by joining a rectangular perforated plate measuring
20cm x lOcm and containing perforations 5mm in diameter at an
aperture ratio of 17.9%, and a rectangular perforated plate
measuring 20cm x 90cm and containing perforations 4 mm in
diameter at an aperture ratio of 17.9% along their respective
20 cm sides and placing a weir in the form of a flat plate
20 mm in height along the joint-so that the respective portions
or zones had an aperture area ratio of 1 . 9. The zones
containing the perforations 5 mm in diameter formed zones II
for permitting downward flow of activated carbon spheres. A
~ box-type fluidized bed test apparatus was made by disposing
four of such trays in such a way that the horizontal direction
of the movement of activated carbon spheres would alternate as
the particles descended from tray to tray. Activated carbon
spheres were fed downwardly into the uppermost tray at a rate
of 40 kg/hour and dry air was introduced upwardly below the
lowermost tray at a superficial tower velocity of 1 m/sec. to
fluidize the spheres. The activated carbon spheres were of
the type having an average particle diameter of 0.7 mm and a
particle diameter distribution range of 0.2 mm to 2.0 mm.
During a total of two hours of continued operation, the weight
of activated carbon spheres which flowed out of the tower in
two minutes (corresponding to average retention time of
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~o~
activated carbon spheres per tray in the apparatus of the
present case) was measured at a total of ten randomly selected
points of time. The ten values thus obtained averaged 1.33 kg
and the difference between the lar~est and smallest of the ten
values was 0.12 kg.
For the purpose of comparison, a number of rectan-
gular perforated plates were each fabricated by joining a
square plate measuring 20 cm x 20 cm and containing perfor-
ations 5 mm in diameter at an aperture ratio of 24%, and a
rectangular plate measuring 20 cm x 80 cm and containing
perforations 4 mm in diameter at an aperture ratio of 17.9%
along their respective 20-cm sides and placing a weir in the
form of a flat plate 20 mm in height along the joint so that
the respective zones had an aperture area ratio of 1 : 3. The
square zones II permitted downward flow of activated carbon
spheres. A fluidized bed test apparatus was made by
disposing such trays in a total of four steps in the same way as
above. By using this apparatus, the experiment described above
was repeated under the same conditions. The average of the
~0 values per tray was 1.28 kg and the difference between the largest
and smallest of the values was 0.31 kg. The operation was further
continued, without alteration, and the weight of activated carbon
spheres which flowed out of the tower over a period of eight minutes
~corresponding to average retention time of activated carbon spheres
per tower in the apparatus of this case) was measured three times at
intervals of 20 minutes. The values were 5.8 kg, 5.4 kg and
6.7 kg, indicating that the rate of transport of the spheres was
not stable.
To adapt the above test apparatus for the present
invention, about half of the perforations contained in the zones
II, permitting downward flow of spheres, in all the perforated
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plates were closed with adhesive tape. The same operation was
repeated; The amount of activated carbon spheres which flowed
out of the tower over a fixed period of two minutes was measured
four times during a period of 30 minutes. In this case, the
difference between the largest and smallest o~ the values per
tray was 0.15 kg. In the continued operation, the amount of
spheres which flowed out over a fixed period of eight minutes
was measured three times at interyals of 30 minutes. The values
per tower were 5.3 kg, 5.4 kg and 5.1 kg, indicating that the
closure of half of ~he perforations served to stabilize the rate
of transport of spheres.
By following the procedure described above, the flow
amount of spheres for the average retention time (per tray) and
the flow amount of spheres for the average retention time (per
tower) were measured for various aperture area ratios. The
results were as shown in Table 2 below.
Table - 2
. . _
Aperture area ratio Flow amount during Flow amount during
between zone for retention time per retention time per
20downward flow and tray tower
zone for fluidized __ __
bed Average Difference Average Differenc
.. . __ __ . _ .
1/3 1.28 kg 0.31 6.0 kg 1.3
1/4 1.24 kg 0.27 5.~ kg 0.9
1/6 _ _ 5.3 kg 0.3
1/10 1.33 kg 0.12 _ _
1/10 1.33 kg 0.18 5.7 kg 0.2
1~12 1.25 kg 0.15 5.7 kg 0.9
1/12 _ _ 5.4 kg 0.3
1/18 1.31 kg 0.20 _ _
1/20 1.28 kg 0.15 5.3 kg 0.3
1/24 _ _ 5.0 kg 1.2
- 17 -
From the above results, it was concluded that the rate
of transport of activated carbon spheres could be stabilized to
within 10~ by weight where the aperture area of the zone I was in
~he range of from 4 to 20 times the aperture area of the zone II.
Example 2:
(1) In the test apparatus of Example 1 which had an
aperture area ratio of 9 : 1, an experiment was performed with
four superficial-tower gas velocities of 0.6 m/sec, 0.8 m/sec,
1.0 m/sec and 1.2 m/sec and three recirculation rates of 20
kg/hr, 40 kg/hr and 50 kg/hr to determine changes in the
pressure drop across the entire tower. It was found that
under all the conditions, the pressure drop remained constant
at a value of 40 mm of water. Under all the conditions, the
variation in the water level in the manometer was very slight,
on the order of about 5 mm.
(2) To permit sampling o spheres from each of the
stepped trays of this test apparatus, the zones of the plates
permitting downward flow of spheres were disposed at levels 20 mm
lower than those of the other zones supporting the fluidized
beds and were each provided with a sampling port. Colored
spheres prepared by spraying activated carbon spheres with a
white paint were fed for a moment into the tower. Then, samples
from the various trays were examined to determined the time-course
change of the density of colored spheres in the samples. In all
the trays, the intervals from the time the colored spheres were
introduced to the time the density of colored spheres in the
samples reached its peak were invariably in the range of from 90
to 100 seconds. This means that the average speed of movement of
spheres in the horizontal direction was equal for all trays and,
therefore, the fluidized beds of spheres were so stable as to
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have equal average retention times.
It was further observe~ that the downward flow of
spheres was extremely stable where the zones of the plates for
downward flow of spheres (zone II) were at levels lower than
those zones supportiihg the fluidized beds (zone I).
Example 3:
Vinyl chloride monomer (VCM) was removed and recovered
from an exhaust gas containing the VCM in accordance with the
method of the present invention b~ recirculating activated
carbon spheres measuring 0.8 mm in average diameter, with a
gas-treating apparatus as shown in Fig. lO.
In Fig. lO, 101 denotes the gas-treating apparatus
having a fluidized-bed adsorptlon section (D) consisting of the
six stepped trays formed by alternately disposing the rectangular
perforated plates as shown in Fig. 2 and Fig. 3. The zone II
on each tray is at level lower than the zone I as shown in Fig. 5.
The aperture area ratio of the zone I to the zone II
is 9 : l. Each of the rectangular perforated plates, which is
made from a stainless steel, measures 450 mm x 450 mm and
contains perforations 3.5 mm in diameter at an aperture ratio
of 17.5%. The weir on each surface of the rectangular perforated
plates is 40 mm in height. The distance between zone I and zone
II is 15 mm. The desorbing section (E) in the apparatus 101 is
connected witn the adsorption section (D) by means of flange 102
and is in the so-called shell-and-tube type structure consisting
of a preheating zone and a desorbing zone. The desorbing section
(E) is in the form of circular tower having an inner diameter of
690 mm and a height of about 3,000 mm. The adsorption section
(D) is in the form of rectangular tower having a height of 2,000
mm. Further, in Fig. 10, 103 stands for a preheating jacket and
104 for a decanter.
-- 19 -
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The operation conditions and the results in this
Example were as shown in Table 3 below.
Example 4:
VCM was removed and recovered from the exhaust gas by
the same procedure as in Example 3, with the same apparatus as
used in Example 3 except for using the circular perforated plates
as shown Fig. 6 and Fig. 7 in place of Lhe rectangular perforated
plates.
Each of the circular perforated plates, which is made
from a carbon-steel, measures S00 mm in diameter and contains
perforations 3.5 mm in diameter at an aperture ratio of 17.5%.
The aperture area ratio of the zone I to the zone II is 9 : 1.
The weir on each surface of the circular perforated plates is
40 mm in height. The zone II on each tray is at level lower
than the zone I as shown in Fig. 9. The distance between zone I
and zone II is 15 mm. The adsorption section (D) is in the form
of circular tower having a height of 2,000mm.
The operation conditions and the results in this
Example were as shown in Table 3 below.
It is clear from the results shown in Table 3 that
the circular perforated plates of Example 4 are substantially
little inferior in performance to the rectangular perforated
plates of Example 3.
- 20 -
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