Note: Descriptions are shown in the official language in which they were submitted.
10~5~16~
The present invention relates to the processing
and recovery of chemicals from the residual waste liquor
discharged from a Kraft paper pulp digestion process.
A common method of chemical recovery used in ~;
the Kraft Paper Pulping Process starts with the concentrat-
ing of what is known as the residual waste liquor. The re-
sidual waste liquor is that stream which results from the
washing of the pulp after the wood has been digested by ;
the cooking liquor. This stream is rich in valuable
chemicals which if recovered may be used to produce the
basic cooking liquor employed in the digester. This liquor
also contains organic material picked up in the digestion
. . .
process of the prepared woods. Generally this residual
waste li~uor is concentrated to approximately 65 per cent ~-
solids by weight and is sprayed or introduced into the
bottom portion of a chemical recovery furnace where the
organic portion of the liquor is gasified at temperatures ~-
~ . .: .~,: .,
in excess of 1800F and the inorganic portion becomes ~ ~
.
molten forming the smelt in the bottom of the furnace. ~-
In such a process, hydrogen sulfide ~ S and sulfur dioxide
S2 may be generated in amounts in excess of acceptable
emission standards. Other air born contaminants such as
vaporized sodium compounds in the form of a fine fume not
only aggravate the pollution problem, but can also con-
dense on the steam generating tubes causing fouling in
many cases and a reduction in heat transfer ability. The
smelt which is deposited in the bottom part of the furnace
can be hazardous. Should leaks develop in the water tubes~
the probability of an explosion from the contact of the
water and smelt is quite high. This flowing smelt will be
-- 2 --
.
-
... ~ .. . ,, . , ~ . . .. . . . .. . . .. . .. .
~08916Z
drawn off and treated so as to reconstitute the cooking liquorfor the digestion process.
In view of the foregoing, the desirability of alternate
approaches to the recovery problem becomes obvious.
The present invention seeks to overcome the disadvantages
of the presently used chemical recovery processes in Kraft
pulping processes by the use of low temperature treatment of
the residual waste liquor in a reactor so as to gasify the
organic portion of the liquor while allowing the inorganic
portion to remain in the solid phase. Such treatment eliminates
the formation of a smelt and thus eliminates the possibility of
a smelt water explosion while simultaneously doing away with the
fouling of the heat transfer tubes and the fume pollution
problem. The off gases from the gasification step are cooled
and are then contacted in an absorbing device with an absorbing
medium composed of a solution of the remaining inorganic solids
from which any residual carbon has been separated. In such
absorption, the H2S is removed from the gaseous phase. Any ;-
remaining H2S can be oxidized to SO2 and be subjected to
further treatment as necessary. The spent absorbing medium
can then be treated to form the cooking liquor which is returned
to the digestion process.
Thus, according to the present invention there is provided
in a kraft pulping process of cellulosic materials employing
compounds of sodium and sulfur in the coo~ing liquor, wherein
a residual waste liquor containing digested ceIlulosic organic ~ ~
and sodium bearing inorganic solids is formed, a method of ~ ;
recovering chemicals useful in forming a kraft cooking liquor
from the residual waste liquor while avoiding the hazard of
smelt-water explosion comprising introducing the residual
waste liquor into a lower section of a fluidized bed gasifying
unit; gasifying the digested cellulosic organic solids
- 3 -
IB
108916Z
contained in the residual waste liquor in the bed at a tempera-
ture not in excess of 1400F to produce a gas phase containing
hydrogen sulfide, while maintaining the sodium bearing
inorganic solids of the residual waste liquor in a solid state,
reducing in the bed at least a portion of the sodium bearing
inorganic solids to form sodium sulfide and sodium carbonate;
removing the sodium sulfide and sodium carbonate from the .
fluidized bed unit; and absorbing hydrogen sulfide from the gas
phase with aqueous absorbing media containing sodium sulfide ~:
and sodium carbonate. - ~-
BRIEF DESCRIPTION OF THE DRAWINGS ~ -
Figure 1 depicts the relevant part of a chemical recovery ~:.
process for a pulping process and shows ~ow the present ~;-
invention is integrated into this recovery process. This
figure also contains a legend so as to better enable one to
follow the various streams employed in using this :-~
,,'.'.. ~,;
'"'
':~
.
,B 3a -
,~, ,, ~ , . . . . . .
~ase 3980
~~`` ~0891~Z
procev~.
Fl~urc 2 depicts a cutaway view Or a fluldized
bed reactor which i5 employed in the preferred embodiment
of the present invention.
~ igure 3 depicts a multi-stage absorption system
and shows how the same fits into the present invention.
A more fully understandable description follows.
DESC~IPTION OF THE PREFERRED EMBODIMFNTS
Referring generally to Figures 1 and 2, wood,
having been prepared for pulping is fed into the digester
(not shown) to be digested by the cooking liquor. This
liquor is rich in the sulfur-bearing compounds that produce
the pulp by the delignification of the prepared wood. The
Kraft cooking li~uor generally contains NaOH, Na2S,
Na2C3, Na2S4, Na2S03 and Na2S203. This liquor will acquire ~
organic matter from its intimate contact with the wood in ~-
the digester. The contents of the digester are transferred ;
to a blow tank (not shown) wherein gaseous products are
~ ented to a condenser (not shown). The pulp and spent cook- -~~ 20 ing liquor move on to a pulp washer (not shown) where the
chemicals are washed ~rom the pulp. This operation usually
takes place in a multiple drum rotary type washer where the
chemicals are washed from the pulp. This operation usually
; takes place in a multiple drum rotary type washer where the
fl~w of the pulp 1s counter-current to the flow of the wash
water. The pulp and the wash liquor are now separated and
the pulp goes on for further processing to make paper and
other products. The wash liquor~ which is basically a dilute
solution of the spent cook~ing liquor containing organic rem-
0 nants of the wood moves on for chemical recovery. Because of
the color o~ this wash liquor, it is referred to as the black
liquor.
' .. ':
- -4- : ~
,,~ ,, . , . . . ,, ~ , . . .
10l~16Z c~ 39~0
The black liquor is introduced into a concentration
system. qhis systern is usually in the form of a multlple
effect evaporator 10. Such a system can have as many as 5
or 6 effects. A vacuum is usually applied to the evaporator
wherein water is driven off by the counter-current flow of
steam through the tubes thus concentrating the black liquor
to about 50-55 per cent solids by weight. A further concen-
tration step may be added though it is not necessary. In ;~
the present invention, black liquor concentrated in the range
of 40-70 per cent by weight solids may be employed but better
operating economy will be experienced with the use of at
least a 50 per cent solids stre~m. It is preferable that the ;~
black liquor be concentrated in the range of 50-60 per cent
by weight. The present lnvention can be operative with the
solids in a completely dry form if they are so available.
These solidscontain the organic matter ~rom the wood and the
sodillm salts of the spent cooking liquor.
In Figurel, the black liquor, stream 12 having been
suitably`concentrated is discharged from the multiple ef~ect
evaporator 10 and is now ready for the gasification step.
Salt cake Na2S04 may be added to stream 12 i~ so desired~
This would increase the concentration o~ the stream and pro- .
vlde additional recovery benefits. Such addition may be
made in a mix tank (not shown). The gasification step will
result in the organic content of the concentrated black
liquor stream 12 being driven off in a gaseous state. The
~ ~ .
procedure is carried out so as to allow the inorganic con-
stituents of stream 12 to remain in thé solid phase. In the
preferred embodiment of thepresent invention, this gasification ``
step is carried out in a ~luid bed reactor 16 at a temperature
of 1300-1400F. Reference to Figure 2 will aid in understand-
ing the method of practlcing this step of the invention. The
,.. ,. ' `' ``
108916Z case 39~0
flui.d bed rcactor 16 baslcally conslsks of a brick-lined
housin~ 17 (brick-lining not shown~ containing a bed of
material 18 supportcd on a plate 28 with perforations 29.
The bed of material 18 can be composed of inert materials
or inor~anic chemicals useful in the pulping process. Thus,
bed 18 can be composed of sodiwn carbonate Na2C03, sodium
sulfide Na2S, sodium sulfate Na2S04 and hot char. In the
preferred method of practice of this invention, the black
llquor stream 12 will be introduced into the lower region
~0 20 of this bed 18. Stream 12 will be introduced by nozzle
means 22. In the actual practice of the invention a number ~ ~'
of nozzle means 22 will be placed about the perimeter of -~ '
reactor 16. Nozzle means 22 may all be connected to a header
pipe 24 which can surround reactor 16 and will distribute
stream 12 to the various nozzle means 22. The nozzle means
22 should be arranged so as to introduce and to give even
distribution of stream 12 over the cross section of the lower
.. .
region 20 of bed 18. In practicing this invention stream 12
ahould be dispersed and atomized by nozzle means 22 so as to
generate droplets of a size in the 500~1000 micron range.
Air a'nd gas, stream 53 is introduced into reactor 16 beneath '~
- support plate 28 and passed upwardly through perforations 29.
' It is desirable to minimize the amount of air used ~or gasi~
~; ri'cation so às to restrict the forma;tlon of C02. The C02 ' -
interferës with the absorption'of the H2S. ;As such, it will
` ;~ be found beneficiai to limit the ~ontent'of stream 53 so
tha~ it contains 1-2 lbs. dry air per lb o~ dry solid in
stream 12; The air portion may be preheated to approxlmately ~ -
. .
300-600F as shown ln Figure 1. Stream 53 provides the
fluidiæing medium for bed 18 and conveys the thermal energy
required for the gasification step. Fuel, stream 14 is
combusted in a conventional type fuel burner (not shown)
to pr~vide the he~t content necess~ry to ca-ly out the
6-
10~il91~Z cAse 39~o
gasification. l'he u~lard velocity of strcam 53 through
bed 1~ i~ in the ordcr Or 1-10 f`eet per second depending
on the size Or the dropleks generated by noz~le means 22.
Bed 18 should be of sufricient hei.ght to allow the required
residence time for the liquid droplets so as to bring
about the gasification of the organic material and allow
the sodium sulfur-bearing compounds, including sodium
sulfate Na2S04 to be reduced to sodium sulfide Na2S. The
residence time of the liquid dropiets is estimated to be ~ -
of the order of 30 minutes per 1 foot of bed height. Such
residence time may vary depending on the concentration of ':.
stream 12 and the quantity of stream 53 relative to stream
. 12. ~ -
. As mentioned before, the fluidized b'ed 18 is
; operated at a temperature of 1300-1400F. Such an operat-
ing temperature range is essential to the practice of this
.,
invention when processing residual waste li~uors from a Kraft . ' .
process since the lowest melting point of the sodium salts .'
~orm'ed is approximately 1400F. If higher temperatures are ~ :
20 ' used, a molten phase and the attendant vapors may.form re- ;
sulting in the formation of sodium fumes. If the fluid bed
reactor 16 is operated under increased pressure.s one can '~
expect increased treatmént capàcity. Accordingly, other
ad~ustments to the system.will.be''réqui'red shouid.this ''
. . mode of operation be practiced. . :~
~ . . . . .
While the organic portion of stream 12 has been
gasified, the inorganic portion has remained in the solid
. phase in the form of a particulate. This particulate .. -
. would typically contain sodium carbonate Na2C03 at about
3 90 per cent by weight, sodium sulfide Na2S at about 9 per
cent, sodium sulfate Na2S04 at Iess than 1 per cent and ~:
unburned carbon at less than 1 per cent Such materials
' .
~7- :
., .
cas e 39~0
1089162
can be use~ to rorm ~cd 18. There will be extra particulate
in the form of a~glomerate, which will be removed by down-
comer means (not shown), and fines which will be carried
over in stream ~2 and separated in the cyclone 36. Removed
particulate is sent to the dissolving tankll4 but the
agglomerate may contain substantial unburned carbon,therefore
it may be recycled to the feed liquor 12. Preferably, this
recycled portion is passed through a comminuting device such
as a crusher (not shown) prior to its introduction into
stream 12. '
Stream 53,having passed through bed 18,will pass
into a free board area 19 located within reactor 16 above
bed 18 and then be exhausted through exhaust opening 30.
This exhaust stream which is now indicated in the drawings
as stream 32 is expected to have the following approximate
composition by volume due to the reactions having taken
place in reactor 16: C0 - 9~; C02 ~ ; H20 - 23%;
H2 - 21%; N2 - 35% and H2S - 0 2 - o. 8~. Stream 32 will
also contain an amount o~ particulate matter (i.e. the fines
20 ' mentioned above) which has been picked up from the bed 18.
The upper portion of housing l~ may be enlarged in cross
~ sectional area so as to lower the upward velocity below '
` ~ the conveying velocity o~ the particulate causing part o*
the entrained solids to fall out.''The stream 32 temperature
w1ll b~ somewhat less than 1400F. The'exhaust stream 32 '~
is ducted to a gas cleaning device 36 which is preferably ~-
' a dry type cyclone. A multiclone or high efficiency
cyclone is pre~erred but such e**iciency req~irements are
llOt necessary for the practice of ~his invention. The
particulate matter collected in and discharged from gas
cleaning device 36 can be processed further along wlth
~hat portion of stream 33 not recycled to black liquor
.~, . .
..
Case 3980
'~08gl6Z
stream 12. Strc~m 34 on the drawines is thc result if
such comblnation is desired. Stream 34 delivcrs the parti-
culate which consists of mainly the inorganic components
of stream 12 to a dissolving tankll4 wherefrom a portion
of the later described absorbing solution may be drawn.
Exhaust stream 32, having been cleaned of
particulate matter by air cleaning device 36,is exhausted
from device 36 and is designated as stream 38. The thermal
content of stream 38 is quite high and part of this may be
recovered by a heat recovery unit 40. Conventional steam
generating units or waste heat bo~lers can be used for this
purpose, wherein part of the thermal content o~ stream 38
is transferred by pre~erably indirect means to a liquid
phase 42 to gene,rate a steam or vapor phase 44. This re~
c~vered thermal value may be employed in other parts of
~he pulping process or the plant. It will be of interest -~
that due ~o the elimination of the sodium ~ume, the heat
.
trans~er surfaces (not shown) of heat recovery unit 40
will require less maintenance since no fume can ~ondense
on the transfer surfaces. The exhaust o~ the heat re~
covery unit, stream 46, has been cooled to 400-700F by
the use of conventional heat recovery equipment 40 and may
still be rich in thermal content. Such thermal content~ ;
may~ be recovered by a heat exchange device 4O Such device ;~
48 may be an air heater wherèin ambient air 50 may be
heated to 300-600F. Such heated-air indicated as stream
52 may ultimately be used to form stream 53 which is
introduced into a lower area 26 beneath support plate 28
~` in reactor I6. Again the~heat exchange process is pre-
~erably an ~ndirect one and should pre~erably cool ex-
haust gas stream 46 to a temperature o~ about 350-400F.~ -
is ~as str~am~indicated as stream 56 in the drawings
,, . . . ~, .- ~ :
.10~91~;2 case 39~30
i8 no~l rcady I'or the a~sorptlon process more ~ully herein-
after described.
The absorption step is concerned with removal
of the hydrogen sulfide ~2S gas from exhaust stream 56.
As indïcated by the above approximate flue gas analysis,
the H2S contaminant will usually be present in an amount
less than or equal to one (1) per cent by volume. Loss
of the sul~ur-bearing cornpound is undesirable from the
point o~ view of chemical recovery as well as air pollution
conslderations. The gas stream leaves absorption system
58 as gas stream 60 and may go on for further treatment.
As shown in Figure 1, stream 60 enters condenser 68 wherein
stream 60, which was at approximately 140-170F, and is
expected to have the following approximate composition on '~ -
a Yolume basis: C0-9%; CC~-10%; E~20-25%; H2~21%; N2-35~ ,~
and H2S-002-.06% may then be cooled to approximately 100F
using an indirect heat trans~er mechanism. The cooling
M u1d is cold water stream 70 which results in hot water
stream 72- and condensate stream 740 The gas stream exits
20 , condenser 68 as stream 76 and will have a considerably ' , -~
lower moisture content. Stream 76 may then be introduced
lnto gas boiler 78 where, by the combustion of fuel 80
with air 82, the C0 will oxidize to C02, H2 to H20 and H2S
to S02. I~ater, 84 may be used for thermal rec~very re~
~, ~ sulting in stream 86. The gas 88 may then be ven~ed to ,~
~; atmosphere. ,~
~; ~ ' Most of the inorganic solids retrieved from
reactor 16 have been,led to dissolving tank 114 wherein
.
the inorganic solids preY~ously mentioned are dissolved in
, 3o ~ an aqueous solukion along with make-up chemicals 110 and
make-up water 111. The effluent liquld stream 116 (which
is re~erred to as the green liquor)is led to a clarifier
, It is here that any re~ain~na carbon and insolubLe
:, .
-10- :.
. . . . ....... ,., :.: . --
: , : ... : . ~ . . .
iO891~2 Case 39~0
wood ~sh 322 ~rc scparatcd from stream llG producing
clarified strcam 120. Stream 120 enters storage tank
- 124 from which may bc drawn as necessary, stream 126~
which contributes to the formation of the absorbent 62.
Absorption system 58 c~mprises a multi-stage
contacting arrangement. It is to be understood that the
term contacting stage refers to a zone wherein the gas ~-
phase containing H2S contacts a liquid phase~ the result
being mass transfer of the H2S from the gas to the con-
tacting liquid phase. A typical arrangement of the
absorption system and a corresponding liquid circuit is ~;
shown in Figure 3 ~or a multi-contacting stage approach. ~ ~ -
Of course, it will be understood that the present invention ~ -
can be practiced with more than two contacting stages but
for convenience and simplicity of description, only two
such stages are depicted in Figure 3
In Figure 1, stream 56 is ducted to the absorption ;
system 58, and liquid stream 62 is piped to the absorption ^~
system 58 wherein the two phases will be brought into
intimate contact so as to allow the mass trans~er phenomenon
, . ,
to proceed. The scrubbed gas stream emerges from absorption
system ~8 as gas stream 60. The spent absorbing medium
contalning primarily Na2C03, Na2S and NaHS exits the
absorption system as stream 66 and is split into stream
66A which is piped to storage tank 67 and stream 66B which
~is~piped to storage tank 124. The liquid from tank 67
shown as stream 67A is piped to causticizer 90 wherein
slaked lime 9? is added to form white liquor and CaC03. The
whi~te liquor contains NaOH, Na2S-and Na2C03~ Part of the
Na2C03 has been converted to NaOH which has converted a
~portion of the NaHS to Na2S. Stream 94 is transferred to
filter drum 96 wherein the filtered solution 98 is
.
10891~;Z c~g~ 39~0
scpa.rated from the CaC03 solids. A portion of stream 98
is rcturncd via stream 100 and piped to storage tank 67
~la stream lOOA for odor control purposes and to storage
tank 124 via stream lOOB wherein it combines with NaHS to
produce additional Na2S. The remaining portion of stream 98
is ~ sedonfor disposal. Slurry 102 from filter drum 96
goes to a second filter drum 104 where the CaC03 is washed
with water 106. The offcoming liquid phase 108 is known as
weak wash and may be reused in the process. Accordingly,
it is piped via stream108A to dissolving tank 114 and via
stream 108B to storage tank 124. The CaC03, 112, is returned
to the lime kiln (not shown) wherein lime CaO, is regenerated -~
for use in causticizer 90. ;~
Figure 3 depicts the preferable arrangement of ~ ~
absorption system 58 as being one with two (2) contacting ~ ~ ;
stages. It has been fou~ld that such a two-stage contact~
ing absorption system is most beneficial in the practice
of this invention. It has been further found that Venturi-
like contacting stages give greater effectiveness. It will
be understood that the present invention may be practiced
using other conventional mass transfer equipment in the
absorption sy~tem. Such substitutions may include a
packed or plate tower or cyclonic scrubbers. While in many
absorption devices, the direction of flow of the absorb-
ing medium is concurrent with that of the gas stream, `~
the present invention may be practiced USillg either con-
current or counter-current flow. In employing a multi-
stage arrangement as depicted in Figure 3, it is desirable
to employ a counter-current flow pattern. It also should ~;
be understood that while two distinctly separate contact
stages are depicted in Figure 3, a single piece of equip-
ment which houses the two stages may or may not
-12-
.. ... . . .
case 39~0
10891~Z
separa~! the two stages by a distinctly defined separationzone, may be used for the practice o~ the invention.
In Figure 3, ~as stream 56 enters the first
absorption stage 58A wherein lt is accelerated and brought
into intirnate contact with stream 62A which preferably
has been shattercd into liquid droplets either by stream
56 shattering a liquid film or by nozzle means (not shown).
Stream 56 is cooled and picks up liquid droplets which can
be separated from the gas stream in separating device 58B.
This separating device 58B may employ a cyclonic effect or
a baffled gas path to separate the droplets from the gas.
The collected liquor exits the separator device 58B and
is referred to as 65 in Figure 3. Gas stream 56 exits
the separator 58B as stream 56A and is ducted to the
second absorption stage 58C which may be substantially
identical to 58A. Contact is made with absorbing medium
62 whereby an additional amount o~ HzS is absorbed. Gas
stream 56A then passes into separating device 58D which
may be substantially identical to 58B. The separated liquid
exits separating device 58D as stream 64. It should be
pointed out that substitution of a wet cyclone or cyclonic
scrubber for separator 58B will prodùce substantially the
same results as the system described above. Those familiar
with the Art will recognize that slight modifications of
the liquid circuit will be necessitated in the event that
such substitution is made.
Although the absorption stages 58A and 58C may be
substantially identical as regards the actual equipment,
each~sta~e will operate somewhat di~ferently in that the
second stage 58C will be expected to remove the H2S at a
greatly reduced concentration in comparison with that as
seen by absorption stage 58A. As such, in the preferable
~, ... . . . . . .
- : , . , ". ..
c~s~ 39~0
~08~6Z
mode Or practl(c, cach stagc will bc operated somewhat
dlfferently, th~ rnaln dif`fcrence being in the relative
amounts of the constituents in the absorbing media 62
and 62A.
~ s previously indicated, gas stream 56 will contain
approximately 1~ H2S by volume or 10,000 ppm. It is well
known to those skilled in the art that scrubbing such a
stream ~lith alkaline green liquor, which is available from
storage tank 124 will give respectable absorption e~cierAcies
and can reduce the H2S concentration down to about 1000 ppm
(.1%). As indicated by Figure 3, a portion of stream 126,
126B will combine with stream 64B to form 126C which will
unite ~ith 65A to form absorbing medium 62A. Such com~
bination will give a partial recycle effect as well as a
counter-current flow effect so as to use the recovered ~-
chemicals most efficiently. A portion of the spent
absorbing medium 65,which contains Na2C03, Na2S and NaHS
will be returned to storage tanks 67 and 124 via stream
66 which splits into 66A and 66B respectively. Exposure
to white liquor will convert NaHS to Na2S.
Gas stream 56A will contain H2S at approximately
.1% by volume. Absorption of H2S at~such low concentrations
has proven to be a formidable problem when C02 is present.
~- Fortunately, a practical solution to the problem is avail~
able in the teachings of Markant et al in U.S. Patent
No. 3,471,249, A System for Absorbing H2S Gases. Markant
points out that critical ratios of certain constituents
~: .
of the absorbing media and the H2S in the gas must be
malntained to bring about the desired resu-l~s. l!he
30 absorbent medi~ml should contain sodium sulfide Na2S, some
sodium hydrosul~ide NaHS, and sodium carbonate Na2C03.
10~91~2 Case 3980
The flo~l ratio of the absorbing medium to the gas contain-
ing ~l2S shou]~ be in the range o~ 6-10, on a weight basis.
Na2S should be present in such amounts so that the welght
ration I~a2S/H2S is 35 or greater. Furthermore, Na2C03
should be controlled so that the weight ratio Na2C03/
H2S is 30 or greater. Also, the'molar concentration of
Na2S is to be greater than 0.1 of the molar concentration
of sodium hydrosulfide NaHS. Such ratios can be established
and maintained by the intermixing and control of various
streams of the recovery process. To further aid in main-
taining'these ratios~ part or all of the makeup chemicals
required by the rnill can be added to the absorber feed streams.
Markant recommends that the makeup chemicals such as MaOH, ~'
Na2S or Na2C03 be added at the inlet side of the recirculation
pump (not shown) and so may be the practice here. However,
a separate mixing tank 130 may be provided whereby these
constituents are added to maintain the critical ratios
mentioned ab'ove, or one may employ dissolving tank 114 for
such purpose. Na2C03 may be introduced into the system by
addition to the causticizer 90. Absorbing med~m 62 having
been contacted with gas stream 56A, leaves separator 58D as
stream 64. A portion will be a recycle stream 64A, a
portion 64B will combine with stream 65A and the remainder,
which combines with 66B will return to storage tank 124.
The recycle stream 64A will unite with stream 126A to form
stream 128. In the preferabIe form of the invention, stream
128 enters mix tank 130 wherein chemical additions ~32 are
made tQ achieve the Markant ratios thus forming absorbing
medium 62. As will be apparent to those skilled in the Art,
proper employment of automatic or manual means for control
and mixing of the varlous streams in various amounts will re-
sult ln form~n~ nbsorbin~'medium 62 with mai.ntenance of the
-15-
c~se 3980
108~1~;Z
proper ratios.
~ hi.le ln accordance with the provisions of th~
statutes there is :;llustrated and described herein a
specific embodlment of` the invention, those skilled in the
Art will understand that changes may be made in the form : :
of the invention covered by the claims, and that certain
features of the invention may sometimes be used to .
advantage ~lithout a corresponding use of the other features.
,
,'
~ , ~
' ' ' ' ~; '':
,~
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