Note: Descriptions are shown in the official language in which they were submitted.
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PPcOCESS AND APPARATlJS FOR THE ADSORPTION,/CElEl~ISOR~rION
OF GASEOUS COMPONENTS _OF A~ GAS STREAM
This invention relates to a process and an
apparatus for the adsorption or chemisorption of gaseous
materials from a raw gas stream through the addition of
essentially dry adsorbents, possibly with the
characteristics of adsorbents which enter into a
chemical reaction with the adsorbed gaseous components
in which the reacted adsorbent together with the
adsorbent that has not been reacted are separatsd out in
a cloth filter and partly carried back to the
adsorption process.
In the past a number of processes, mostly in
connection with the protection of the environment, have
been known, all of which have as their object the
adsorption of harmful gas components from a pollution-
laden gas stream, by the addition of finely divided
adsorbents. In most cases there is additionally a
chemical reaction with the adsorbent, in which the
harmful gas components are combined permanently with the
adsorbent. In this case there is a combination o~
adsorption and chemical reaction, the so-called
chemisorption. Often in these cas~s it is essential
either to have steam in the gas, or to have a particular
degree of dampness in the adsorbent, especially when
the chemical reaction of the harmful material with the
adsorbent has, as a prerequisite, the preliminary
dissolution of the adsorbed component in water.
By contrast with the wet process (for example flue
gas washing by the use of slaked slime or susp~nded
lime-stone) or the semi-dry process (for example
absorption processes in spray dryers with tha addition
of an alkali suspension, however with a dry endproduct),
these drying processes have the disadvantage that,
because of the slow rate of reaction, a long contact
time between the adsorbent and the gas to be cleaned is
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required. If the dwel:L time is not long enough, a large
part of the adsorbent, having not taken part in this
reaction, is expelled from the process unused together
with the endproduct, and is thus lost. From an economic
point o~ view, this loss is acceptable only within
certain limits.
The degree to which the adsorbent is used is
normally expressed in terms of the "molar ratio". A
; molar ratio of 1.0 signifies the complete utilization of
the adsorbent, whereas a higher molar ratio indicates
the loss of unreacted adsorbent in terms of the extent
to which the number exits unity.
In the drying-chemi~orption processes tor
adsorption processes) here considered, the molar ratios
of the typical process combinations are at least 2.5.
However it is also known that this number can
substantially exceed ~Ø From an economic point of
view the costs associated with such processes are not
; acceptable. Moreover, high storage costs are created.
All known processes attempt to increass the
utilization of the adsorbent by ensuring that the
separated-out dust which has only partially been reacted
is to a greater or lesser degree recirculated back to
the raw stream. Recirculation factors of 5 - lO times,
relative to the added fresh adsorbent, are normal, but
even so a molar ratio of less than 2.5 is not known.
Apparatus for recycling the partly utilized adsorbent
represents a substantial portion of the investment
costs, gives rise to additisnal expenditures for
measuring and control devices, and generally requires
substantial space.
While some o~ these processes simply use the feed
conduits to khe dust separator as the reaction space,
other processes use an additional reaction chamber of
considerable size, in order to increase the contact time
hetween the adsor~ent and the gas. In this case the
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recirculated material is sent to the reaction chamber.
However with this installation as well, only a limited
r~circulation quantity can be attained at justifiable
expenditures, so that even in this case no satisfactory
utilization of the adsorbent is possible.
It is an object of one aspect of the invention to
greatly increase the degree of utilization o~ the
adsorbent in a dry process, with the smallest possible
investment expenditure, and-in such a way as to avoid
complicated and costly apparatus for recycling dust.
This object is attained by carrying out the recycling of
the dust within a cloth filter, the process being
adjustable within wide limits, and such that
simultaneously a recirculation o~ gas takes place in
order to increase the mixing of adsorbent and gas, this
being substantially independent oP the recycled quantity
of dust and also being adjustable within wide limits.
In a particular form of the invention, the raw gas and
the fresh adsorbent are fed to a cloth filter which is
constructed as a bag filter. There a portion o~ the gas
is maintained in circulation by means o~ a trap tube in
combination with a nozzle, wherein separated dust takes
part in the circulation after separation~
By this means, the recirculation of dust takes
place within the bag filter which serves as a dust
separator, virtually without requiring additional space.
By virtue of the geometric formation o~ the inner space,
a flow condition is reached which promotes an intensive
mixing of the recirculated dust with the polluted gas.
In accordan~e with the invention, the raw gas with the
fresh adsorbent is led to the trap tube through an
adjustable nozzle section. Further, the raw yas with
the adsorbent and the separated dust is led to the trap
tube through an adjustable gap during the inner
recycling. In this manner the raw gas with the
adsorbent, and the circulating gas with the dust
2 ~
components, are brought together and mixed before
entering the trap tube.
It is important to the invention that the cross-
section of the nozzle and of the gap be adjustable in
such a way that the pressure recovery in the trap tube
compensates the loss of recirculation of the gas-dust-
mixture outside of the trap tube.
The inner space of the bag filter is so arranged
that not only does the already separated dust circulate
within wide limits, but also a multiple of the entering
raw gas stream is recirculated, adjustable by alteration
of the geometric form. The process offers dust
recirculation without additional expense (for
transportation elements and storage facilitie~),
simultaneously with a contact time of adsorbent with gas
which is adjustable within wide limits.
The process in accordance with the invention
therefore combines the process steps of dust
recirculation~ gas recirculation and dust separation in
a single apparatus in which the recirculated quantity of
dust and the recirculated quantity of gas can be
adjusted independently of each other and within wide
limits.
The internal racirculation of dust influences the
degree of utilization ~the molar ratio) of the
adsorbent, and also the degree of separation, whereas
the recycled quantity of gas contributes to an
intensification of the mixture of gas and dust~
A~cordingly, the process and apparatus offer not only a
better utilization of the adsorbent, but also the
attainment of a greater degree of separation for the
pollutants to be adsorbed. The essence of the invention
resides in that both the recirculatèd gas quantity and
the recycled dust quantity are so adjusted with respect
to each other (through an appropriate combination of
nozzle cross-saction and gap) that the degree of
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utilization and the cleanness of ~he yas correspond to
the requiremsnts set forth.
Further it is proposed that the raw gas and/or the
adsorbent and/or the mixture of raw gas and adsorbent
S be moistened, such that the temperatures are re~ulated
in such a way that the gas does not ~all below its dew
point. In this way, the fresh adsorbent can be added
to the gas stream in its most finely divided ~orm. The
moisture can be provided by water, by a corresponding
solution, or by steam. Depending upon the operating
sequence of the process, the moisture and/or steam can
be added to the raw gas stream, to the fresh adsorbent,
or to the recirculating gas stream. It is also
conceivable to add the moisture during the fine
grinding of the adsorbent.
More particularly, this invention provides a
process ~or the adsorption or chemisorption of gaseous
materials from a raw gas str~-am utilizing the addition
of essentially dry adsorbent, possibly with
characteristics of adsorbents which have a chemical
reaction with the adsorbed gas components, whereby the
reacted adsorbent, together with the unreacted
adsorbent, are separated in a cloth filter in the form
of dust, whereupon they are led back to the adsorption
process,
charactsrized in that
the dust recycling takes place within a cloth
~lter and is adjustable witAin wide limits, in which
simultaneously a recycling o~ the gas takes place in
order to intensify the mixing of the adsorbent and gas,
the gas recycling being largely independent of the
recycled guantity of dust, and also being adjustable
within wide limits.
An example embodiment of the invention is
illustrated in the drawings, and will be described more
fully below. In the drawings:
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5a
Figure 1 is a section through an apparatus in
accordance with the invention;
Figure 2 is a view, to a larger scale, of the
entry region of the trap tube;
Figure 3 is a view of a portion of Figure 2, to a
larger scale;
Figure 3a shows a variant of one portion of the
structure seen in Figure 3; and
Figure 4 illustrates a further embodiment of the
invention.
Figure 1 shows a cloth filter illustrated as a bag
filter 1 of the standard construction. A large number
of such bag filters can be provided within a separator
installation. In this example embodiment, the bag
filter consists of a rectanguIar housing 2 with an
upper bulkhead 3, in which the ~ilter bags 8 are
suspended. Within a total filter installation, the
housings 2 are also described as chambers. Above the
bulkhead 3 is a
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clean gas chamber 4 provided with a clean gas conduit 5
through which the clean gas exists. At the lower end
there is a dust collecting bunker 6 provided with an
outlet valve 7. The filter bags 8 are disposed around a
central free space 20 in which a rectangular trap tube 9
is located. The latter has its upper end 10 located at
a predetermined distance from the upper ~ilter bulkhead
3. The lower end 11 of the trap tube 9, which extends
further downwardly than the filter bags, has an outer
lo rounded portion 21, thus defining a chamber in which
dust 22 collects (Fig. 3). Fig. 3a shows a further
shock losæ reducing shape 21a for the lower end 11 of
the trap tube 9. Spaced from the lower end 11 of the
trap tube 9 are angulated dust-directing plates 12,
which are attached to the housing 2 of the filt~r at
hinges 13. They are so arranged as to define an inner
opening 23 on the one hand, and on the other to define,
with the lower edge 11 of the trap tube 9, a gap 24. By
changing the slope angle alpha of the dust directing
plates 12, the gap 24 can be changed. Below the
opening 23 there i5 provided a nozzle 15 in which the
nozzle cross-section can be changed by adjusting the
upper nozzle walls 16. To this end the nozzle walls 16
are provided with hinges 17. At the lower portion of
the nozzle 15 is connected a raw gas conduit 1~ into
which the absorbant can be introduced along a conduit 19
in a fineIy divided condition.
The raw gas, along with the adsorbent which it
contains, passes through the nozzle 15 and the trap tube
g to reach the upper region of the filter bags 8. The
gas is passed through the filter bags, and is
substantially freed of dust.- In this manner, a dust
layer of increasing thickness forms on the outer surface
of the bags 8. According to known methods the dust
layer is removed at preset time intervals, this being
done automatically utilizing differential pressure. The
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clean gas, largely freed from dust and impurities,
leaves the. filter 1 through the clean gas chamber 4 and
the clean gas pipe 5. In the example embodiment, the
quantity o~ fresh absorbant required for the process is
mixed with the raw gas stream by appropriate apparatus
immediately before the entry into the ~ilter chamber.
It is conceivable to introduce the adsorbent also at
other appropriate locations in the system, for example
downstream of the nozzle 15~ From the raw gas conduit
18, which can taper in the direction of the stream, the
dust-laden gas exists upwardly through a slot of width
25, and is formed into a directed jet by the lateral
limit walls 16. By virtue of the hinges 17, the walls
16 can be changed in angulation, as is shown in broXen
lines in Figure 3, so that (for example under partial
load) the gas outlet from the nozzle 15 can be changed
from the origin21 width 25 to the narrower width 26. By
this means the impulse of the existing gas stream can be
increased, so that, even under partial load, the below-
described recirculation can be maintained to the desiredextent.
The spacing of the nozzle 15 from the lower end 11
of the trap tube 9 is determined in accordance with
generally known methods. The spacing 27 between the
walls of the trap tube 9 is greater than the spacing 25
of the walls of the nozzle 15. In this region the gas
stream exiting from the nozzle 15 widens and at the same
tim~ is mixed with dust-laden gas in the region of the
gap 24, the latter gas being drawn in laterally due to
the lower pressure at the nozzle exit. In this manner
there is created an overlapping gas stream circulating
around the trap tube 9. This brings about an intense
mixing of gas and recycled dust, and in this mannPr
gives rise to a better material transport factor. By
changing the angle alpha and thereby altering the slope
of the dust-directing plates 12, the size of the gap 24
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for the recycled gas stream can be selected, whereby the
quantity of recycled gas can ba changed. The adjustment
of the angle alpha can be done during operation by
appropriate apparatus.
The dust which falls downwardly during cleaning of
the bags is partly taken into the recycled gas stream,
and partly removed from the inner recycle system by
adjustable openings or slits 28 in the dust-directing
plates 12, whereupon it collects in the bunker 6 of the
Eilter 1 and is withdrawn through the valve 7.
A further portion of the separated dust runs along
the dust-directing plates 12, falling over the forward
edges thereof into the gas stxeam exiting from the
nozzle 15, the gas stream recycling this portion of the
dust into the system due to mixing with the gas. The
dust-directing plates 12 consist of two parts which are
provided at their ends with slotted holes. After
adjustment the plates are fixed with the help of a
threaded fastener 1~. By altering the length 29, an
additional portion of the dust (i~ the length is
shortened) can be removed from the recirculation system
and passed into the bunker 6.
Using the appropriate gap 2~, any desired recycling
condition Por gas and dust can be set, provided that the
impulse o~ the gas exiting from the nozzle lS is
sufficient to accelerate the dust and recycled gas up to
the exit velocity at the top end of the widening of the
stream inside the trap apparatus (having regard to the
total exit pressure-loss). When the dust-directing
plates 12 hang vertically (angle alpha = 0), only an
extremely small amount of dust is recycled, while the
recycled gas quantity reaches its maximum, assuming an
unchanging exit impulse from the nozzle 15, because the
pressure loss in the gap 24 reaches its smallest value.
Conversely the recycled gas can go to zero if the angle
alpha is selected to be large enough that the gap 24 is
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only sufficient to allow the collected dust to pass
through. At the same time this constitutes the
condition in which the largest possible dust
recirculation is achieved, assuming an appropriate
selection of the length 29 of the dust-directing plates
12.
Since the quantity of recirculated gas and the
quantity of recirculated dust exhibit opposing
tendencies when adjustments are made, the concentration
of dust in the upwardly flowing gas stream can be
selected within wide limits, can be altered, and is
restricted only in terms of the impulse or energy
balance-of the system. An additional degree of freedom
consists in the adjustment of the exit impulse by
altering the opening 26 of the nozzle 15, so long as
allowance is made for the associated pressure loss.
The degree of separation, apart from other
parameters, is dependent upon the sur~ace area which the
adsor~ent offers per unit vslume of gas. Since, with a
specific granular size, the sum of the surface of all
particles is proportional to the dust loading of the gas
stream, the separated amount per unit time, in each
volume element of the system, is proportional to the
solids content of the gas~ The degree of separation is
also proportionately influenced by the adsorbent content
of the ga~ stream and the recirculated quantity of dust
per unit volume.
The influence of the recirculating quantity of gas
arises virtually exclusively from the effe~t of an
increase of the mixing of gas and dust, and leads to
advantageous material transfer conditions in the system.
The dwell time of the gas in the system is strictly
determined by the size of the chamber, and cannot be
in~luenced - as with any other process utilizing a
reaction chamber. By contrast, the contact time
relative to the dust can be influenced within wide
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limits by altering the dust concentration, and is
directly proportional thereto. In this way the molar
ratio tutilization factor) of the adsorbent is
immediately influenced. In contrast to the systems
described earlier representing the state of the art, the
process according to the invention, despite lower
apparatus cost (elimination of devices for
transportation, storage and dosing o~ the recirculated
material), allows the recirculation of 20 to 80 times
the introduced fresh material. The following
conditions are apparent:
The pressure recovery in the trapped tube
compensates for the 105s of recirculation of the dust-
gas-mixture outside the trap tube.
With a correspondingly higher speed in the nozzle
15 (from a physical poin of view the speed of sound
establishes a limit here), the quantity of recirculated
dust can be still further increased~ However in the
practical case, the actual limit for recirculation is
established in terms of the economically replaceable
expenditure of energy.
This expenditure of energy is influenced in an
important way by the configuration of the no2zle exit 26
and the entrance 11 to the trap tube ~. While the exit
26 from the nozzle 15 must be made as sharp-edged as
possible and cannot diverge, since this would lead to a
decrease of the exit impulse, the lower edge 11 of the
trap ube 9 mu~t be carefully rounded, such that the
angle beta must be substantially greater than 0, in
order to eliminate shock losses during deflection.
Further achieved by this configuration is the fact that
the downwardly falling dust, as seen in cross-hatch in
Figure 3, will continue to be stored until it reaches
its usual angle of repose 22. The dust which becomes
hardened over the course of time leads to a practically
ideal stream flow. With dust that flows well tie. with
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a small angle of repose), the desired stream flow can
also be achieved by a corresponding configuration for
the plate 21a, as illustrated in Figure 3a. In
accordance with Figure 4, a mill 30 is connected to the
; S adsorbent conduit 19, the mill 30 having a delivery
conduit l9a for fresh adsorbent. Steam delivery
conduits are identified with the numeral 31, including a
conduit 31a ~or the mill 30, a conduit 31b into the
adsorbent conduit 19, a conduit 31c into the filter
space under the filter bags 8, and a conduit 31d into
ths raw gas conduit 18.
