Note: Descriptions are shown in the official language in which they were submitted.
`` 1073432
FIELD OF THE INVENTION:
The present invention relates to an advantageous
method of regenerating used active carbon, and more particularly,
it pertains to a novel method which lncludes heating the used
active carbon by applying an electric current thereto.
BACKGROU_D OF THE INVENTION:
In order to regenerate or reclaim used active carbon,
it is known to heat the active carbon by passing an electric
current therethrough, since the active carbon i8 electrically
conductive. In prior art processes utilizing direct heating,
the heat treatment has been carried out usually by one of three
methods. The first method involves gradually accumulating the
used active carbon betwéen two vertical electrode plates
arranged face to face and then applying an electric current
thereto (Accumulation Method). The second method involves ~ -
continuously passing the particles between the two electrode
pla~es whilst maintaining the spac-e between the plates filled
with the particles and at the same time applying an electric
current thereto (Method Using A Particle-Moving Layer). The
20 third method involves providing several further vertical --
electrodes in a horizontal section of the particle-flow passage.
These prior art processes have several disadvantages.
- For example, in the Accumulation Method, the only possible
operation is a batch type operation, which is unsuitable for
continuous cyclic use of the active carbon. Additionally, the
desorption of the materials adsorbed onto the active carbon is
accompanied by a complicated procedure in which the applied
voltage must be controlled, because the electric resistance of
the particles suffers a change as the material is desorbed.
The Accumulation Method has the further drawback that it is
difficult to establish a voltage control system capable of
2 ~
` ~07343Z
coping with the fluctuations in the amount of materials adsorbed
onto the used active carbon and the fluctuations in the amount
of carbon to be treated.
The above-mentioned Method Using A Particle-Moving
Layer is suitable for continuous cyclic use of the active carbon,
but it has the drawback that the electric current is applied at
right angles to the direction of flow of the particles, which
results in non-uniform application of the current to the
particles present between the electrode plates. This is due
to the fact that the electric resistance of the particles under-
goes a change during the course of desorption of the adsorbed
materials. To explain this in more detail, the apparent
electrical resistance of the adsorbed material-containing
particles in the moving layer of the active carbon has a higher
value than that of the particles containing no adsorbed
materials or of the regenerated active carbon. Therefore, the
ele~ctrical resistance distribution in the layer of particles i
of carbon between the two electrode plates has a high value on
the upper side of the electrode plate and a low value on the
lower side. When voltage is applied to the electrode plates,
therefore, the electric current is biased towards the particles
low iQ resistance on the lower side of the electrode plate.
As a reeult, heat generatioQ takes place only OQ the lower
side of the electrode plates so that effective heat transfer is
only produced w thin a narrow range. Therefore, iQ order to
uniformly desorb the adsorbed carbon, the electrode plates
must be of a considerable length and for this reason, the
apparatus must be increased iQ size. This is why this method
is not considered to be very useful in prastice.
Finally, the method for heating the used active
carbon by providing a plurality of further vertical electrodes
...
107343Z
in a horizontal section of the particle-flow passage and then
applying an electric current to the particles passing among
these electrodes, is often effective when a small experimen-
tal device sufficient to uniformly heat the whole sectional
area is used. This is because the particle-flow passage has
} a comparatively narrow sectional area, but as previously
explained, this method has the defect that the flow of elec-
? tric current becomes non-uniform and unstable, and the same
phenomenon as in the previous method is observed.
10 SUMMARY OF THE INVENTION:
An object of the present invention is to provide a method
for advantageously reclaiming and treating used active carbon.
According to one aspect of the invention, there is pro-
vided a method for regenerating used active carbon which
comprises: (a) providing a generally vertical column
containing at least two generally horizontal, vertically
spaced electrodes, said electrodes having a plurality of
- holes large enough to allow passage of the used active carbon
particles therethrough and the total open area of said holes
20 in said electrodes being at least 25% of the total surface
area defined by said electrodes; (b) introducing the used
active carbon into the top of said column above the upper -
electrode and allowing the used activated carbon to flow
downwardly through said electrodes; and (c) applying a
voltage between said electrodes to cause an electric current
to flow through the carbon particles thereby heating said
carbon to effect desorption of adsorped materials.
According to another aspect of the invention, there
is provided apparatus for regenerating used active carbon
30 particles, comprising a generally vertical hollow column
containing at least two generally horizontal, vertically
~ _ 4 _
C
- . , .. : ~;- .. :.
` 1073432
- spaced electrodes, said electrodes having a plurality of holes large enough to allow passage of the used active
carbon therethrough, the total open area of said holes in
said electrodes being at least 25% of the total surface
area defined by said electrodes.
,
'
- 4a -
.r~,
107343~
The invention is based on the finding that,
when electrodes are provided at the top and bottom of a
perpendicular column and the space between these electrode
plates is charged with used active carbon and a voltage is
applied; then the flow of electric current through the carbon
is uniform.
The term "used active carbon" as used in the present
invention means active carbon which has lost its activity
through use and is synonymous with the so-called "adsorbed
carbor." i.e. carbon having materials adsorbed thereon.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION:
The primary feature of one embodiment of the method
of the present invention is that the problem of heat generation
resulting from a biased flow of electric current, which is a
disadvantage of the above-mentioned prior art processes, has
been solved by applying an electric current parallel to the
flow direction of the moving layer of used active carbon
particles.
The used active carbon particles are introduced into
a perpendicular column having a pair of upper and lo~er
electrode plates provided in the entrance and exit, respec-
tively, of the column. The electrode plates have holes large
enough to let the particles of the adsorbed carbon pass there-
through, the holes being uniformly distributed over the
surface of each plate. When a voltage is applied to the
electrode plates, an electric current flows through the carbon
and produces direct heating as the carbon flows do-~n through
the column. Advantageously, the total open area of the
electrode plates should account for at least 25 % of the total
;~
- . . ~ .
" 107343Z
surface area of the plates, and the holes may be of any
sectional shape.
The reason why heat is generated in the particies of
carbon when an electric current is applied directly thereto is
that Joule effect heat is generated by electrical resistance
mainly at the contact points between the particles. According-
ly, in order to obtain stable heat generation, it is necessary
not only to maintain contact between the particles and elec-
trode plates, but also to maintain contact between the
particles themselves. Further, in order to let the particles
flow down through the perpendicular column whilst fully
retaining these contacts, the total area of the holes in the
electrode plates made at right angles thereto should be at
least 25 % and preferably more than 40 % of the total surface
area of the electrode plates, and furthermore, it is preferred
that the holes be uniformly arranged in the electrode plates.
If ~he electrode plates have a lower percentage hole area than
25 %, a cone-like cavity may form which corresponds to the
angle of repose of the particles, so that there become in-
sufficient contacts between the particles and the electrodeplates, which causes non-uniform heat generation to take place
in the particles. On the other hand, if the holes are too
large, sometimes no electric current flows in a part of the
particle layer, whereby the heat generation in the particles
also becomes non-uniform. Further, such a tendency is
conspicuously observed if the distance between the two elec-
trode plates is too shor,. Such defects can largely be
improved, for example, by making the lower part (i.e. the exit
side) of the holes in a tapered shape having a wider angle of
elevation than the angle of repose of the particles to avoid
formation of the cone-like cavity. Alternatively, instead of
-- 6 --
1073432
providing a pair of upper and lower electrode plates of ldentical
~hape in a completely symmetrical position, the pl~tes may be
provided in slightly different positions from the symmetrical
position to improve uniformity of current flow. Basically,
however, these defects can be remedied by using flat plate-like
electrodes in which the holes are large enough for the particles
of the used active carbon to pass therethrough and are uniformly
arranged over the surfaces of the electrode plates, the total
area of the openings of the holes being at least 25 % of the
total surface area of the electrode plates.
By using electrode plates having the above-mentioned
construction features, a stable process for continuously heating
ehe used active carbon particles can be provided which is free
from the defects of prior art processes. That is, a very
efficient procesæ for heating used active carbon by continuously
applying an electric current thereto can be provided, wherein
the above-mentioned electrode plates are positioned at the
upper and lower ends of a perpendicular column through which
the used active carbon flows. Voltage is applied to the
electrode plates, and an electric current flows parallel to
the cirection of movement of the particles, whereby the
electric current is uniformly applied over the whole of the
:` moving passage to cause uniform heating of the moving particles.
This method of heating used active carbon is par-
ticularly effective when it is applied to used carbon particles
; of spherical shape. In the case of spherical particles, the
apparent electric resistance of the particles in a dense layer
shows a fixed value with good reproducibility which is main-
tained even when pressure is applied to the layer because the
number of contact points among the particles, more specifically
the contact point density, is constant. On the other hand,
7 --
1073432
.
the apparent electric resistance of crushed carbon, or the like,
suffers a comparatively great change, because the contact
point density varies according to the manner of filling the
column with the particles. Therefore, the reproducibility
becomes poor. Spherical particles, however, have stable
resistance `to electric current, stably flow down the column
and show less change in the charged condition. From the
technical and economical view-points, therefore, it is advan-
tageous to use spherical particles in the present invention.
The electrical heat treatment of the used active
carbon may be carried out in two heating stages: i.e. a pre-
heating stage and a desorption heating stage. Alternatively,
when several kinds of materials having different desorption
temperatures are separately to be desorbed and recovered from
the used active carbon, these materials may be recovered by
controlling the voltage applied to a plurality of electrode
plates distributed in several stages.
According to one embodiment of the present invention,
a very efficient compact apparatus can be obtained as a
reclamation unit, ior example, for use in the gas treatment
apparatuses or the like that use active carbon continuously.
In the drawings which illustrate this invention:
FIG. 1 is a schematic explanatory diagram illustrating
one example of a vertical column for reclaiming used active carbon
according to the present invention;
FIG. 2 is a plan view illustrating one preferred embodi-
ment of perforated electrode suitable for use in the invention;
FIG. 3 is a similar plan view to FIG. 2 but illustra-
ting another preferred perforated electrode;
In FIG. 1, reference numeral 1 indicates a vertical
column, 2 indicates used active carbon, 3 indicates an electrode
' .
,
.. . . . .
`` 107343Z
and 4 a hole in said electrode. The shape of the electrode 3
is not important but the electrode may be, for example, rectangu-
lar or circular as shown in FIG. 2 or FIG. 3. In F~IG. 2, 5
denotes a rectangular electrode and 6 a hole in said electrode.
In FIG. 3, 7 denotes a circular electrode and 8 a hole in said
electrode.
The present invention will be explained below in ~
more detail by way of example, bu~ the present invention shall
not be limited to the example.
EXAMPLE
A carbon electrode plate having a thickness of 5 mm, -
a length of 96 mm and a width of 96 mm was installed at the
lower end of a square column made of hard glass. The carbon -`
` plate was provided with 61 holes each having a diameter of 8
mm arranged uniformly over the surfaceiof the plate. The
square column had a height of 300 mm and an inner section side
length of 100 mm. Another similar electrode plate was installed
at a position 90 mm from the top of the lower electrode plate.
The column had a bottom portion having the shape of a converse
~ 20 pyramid type funnel. Particles (having an average grain size of
650 ~) of used spherical active carbon containing carbon
tetrachloride adsorbed in an amount of 500 grams per kg of
active carbon were fed into the top of the column at a velocity
of 5 kg/hr. An alternating current of 100 V was applied to the
above-mentioned electrode plates and when the temperature in
- the center of the column reached 130C, a valve provided at the
bottom portion of the column was opened to let the particles
flow down and at the same time, air heated to 80C was fed into
the column from a nozzle provided at the bottom portion. The
`30 air served as a carrier stream for transportation of desorbed
- components.
.
_ g _
~' ' -
, .~ . , .
107343Z
The amount of undesorbed carbon tetrachloride in the
reclaimed active carbon discharged from the column bottom was
examined. The examination showed that the amount was 30 g, or
below, per kg of reclaimed carbon.
For comparison, the same electrodes as used above
were installed in two opposite walls inside the square column.
A voltage of 100 V was applied to these electrodes to heat the
particles at right angles to their direction of movement. The
amount of undesorbed carbon tetrachloride in the resulting
reclaimed carbon was 80 g or more per kg of active carbon. In
this case, the temperature in the center of the column was
105C to 120C. It was observed that a reduction in desorption
efficiency was caused by a decline in temperature.
-- 10 --
~, 1
;. . .
1073432
SUPPLEMENTARY DISCLOSURE
. _
The principal disclosure relates to the application
of an electric current to used active carbon particles in the
direction of movement of said particles through the space
between two or more perforated electrodes. In this supple-
mentary disclosure, further information is provided about
the perforated electrodes and specific electrode types are
described in connection with the accompanying drawings, in which:
FIG. 4 is a sectional view of one type of perforated
electrode, illustrating the shapes of the holes therein;
FIG. 5 is a similar view to FIG. 4 but illustrating
holes of different shape; and
FIG. 6 is a similar view to FIG. 4 but illustrating
in addition to holes, a number of hollow legs in communication
with the holes.
In FIG. 4, 9 denotes an electrode and 10 a hole
therein having taper 11 at the upper part thereof. In FIG. 5,
12 denotes an electrode plate and 13 a hole therein having
a taper 14 and a taper 15 at the upper and lower parts thereof,
respectively. If desired, only the lower parts of the
holes may be tapered outwardly towards the lower electrode
surface.
The electrodes may have a number of hollow legs ~
or tubular extensions on the undersides thereof in communication
with the holes therein, as shown in FIG. 6. Each of the
legs ordinarily has a length in the order of 300 mm. In
FIG. 6, 16 denotes an electrode and 17 denotes a leg in
communication with a hole in the electrode. The electrodes
having a number of hollo~ legs on the undersides thereof
are preferred in the present invention, because the mobility
of the used active carbon flowing through the holes in the
electrodes can be increased when such electrodes are used.
--11--
