Note: Descriptions are shown in the official language in which they were submitted.
~ ~ 7~ 0 ~
A key factor in the new process is that the re liquefied
ammonia, instead of being sent directly back to the process, is
directed into the desuperheater vessel9 there being combined with
the condensed process ef~luent. The combined solution, cont~ining
a minor fraction of condensed residual water is then fed back to
the process. In this manner9 the to~al water ~raction in the pro-
cess solution may be kept a satisfactorily low level3 typically
on the order of two or three percent maximum) under extreme process
conditions, and desirably much lower than tha~ under more favarable
process conditions.
This application also is related to and constitutes an
improvement over the subject màtter o~ the Briley et al patent
No. 3~721,097, assigned to Cluett, Peabody ~ Co. a Inc., the
assignee of this inventîon.
..
Back~round and Summary o the Xnvention
Fabrics constructed at least in part of celluloslc mate-
rials can be processed advantageously~by exposure to liquid ammonia,
to achieve improvement in shrinkage resistance and to provide
greater affinity of the fabric to other process chemicals, In
accordance with known liquid ammonia treating techniques, ~he
fabric may be exposed briefly to liquid ammonia solution~ as by
immersion in a bath o~ the liquid. After a predetermined reaction
time~ advantageously leSs than about nine seconds, the fabric is
heated, to vaporize and drive off the ammonia and tenminate the
~ ~ 7 ~
reactions at a desired level J
In a typical liquid ammonia process, only a smaLl per-
centage 9 (for example~ about 5%) of the ammonla is actually con~
sumed in the process reactions, or otherwlse lost. The baLance
is in the fonm of ammonia vapor~ Because of th~ potentially
hazardous and unpleasant nature of ammonia vapors, and also ~or
obvious economical reasons, it is important ln a pract~cal liquid
ammonia processing operation to recover9 for reliquefaction and
reuse, the spent ammonia vapors~ Broadly speaking, this can be
accomplished by withdrawlng the ammonia vapors from the fabric
treatment chamber and compressing and condensing such vapors4 The
condensed vapors are returned to a liquid ammonia storage tank
for eventual reuse in the ~ystemO
One advantageous system for the recovery ~nd reusè of
ammonia vapors is reflected in the aforementloned Briley et al
patent No. 3972190970 In the system of the~Briley et:al patent~
the hot vapors from the proces~ing chamber are directed to a de-
superheating vessel9 in which the vapors bubble through a bath
of liquid ammonia, which may be at a ~emperature around ~28Fo
The desuperheated gases are ~hen directed through appropriate
compressing and condensing stages9 and the resulting liquefied
ammonia is returned to a storage tank for ultimate reuse in the
process~
~ hile ~he system of the Briley et al patent NoO 3~7219097,
constituted an important advance in the art of ammonia reoovery,
overall operating efficiencies are partially limite~ by gradual
accumulation of water in the system~ Because water is h7ghly
8~
condensable m relation to the ammonia9 it is difficult to sepa~
rate from the liquid ammonia~ That is 9 ;n a high speed continuous
processing lineg large quantities of treating medium in the fonm
of anhydrous liquid ammonia are utilized and to a large extent
must be continuously recycled~ Because the system inherently will
accumulate water9 it must also be accomodated either on a batch
basis requiring shutting down the line9 or on a con~inuou~ basisO
However, because the properties of ammonia and water are closely
related their separation is difficult in ~he environment of a
continuously operating processing line9 as opposed to conventional
laboratory separation procedures. These water accumulations have
necessitated the extraction and discarding from the process of
water-diluted liquid ammonia from time to time~ Where circum~
stances permit9 such extractions can be used in fertilizer appli-
cations. Otherwise, the mat~rial must be incinerated or otherwise
properly disposed ofO
In accordance with the present invention, a unlque, high~
ly simplified, yet wholly effective procedure is provlded for con-
tinuously eliminating water accumulations from the liquld ammonia
recovery system without requiring the destruction or low grade
utilization of significant quantities o~ liquid ammonia~ The
procedure of the invention involves 9 in a liquid ammonia recovery
system of the general type described in the Briley et al patent~
the unique procedure of deriv~ng.the liquld ammonia make~up flow
to the treatment chamber from the retained Liquid body in the
desuperheating vessel which receives the spent process vapors in
cluding the residual water-fraction in the first place~ In a con~
tinuously operating process, this continuous outflow of condensed
water in the make-up liquid prevents signifi~ant arcumulations of
~ ~ 7 ~
water in the desuperheatlng vessel and maintains the percentage
of wa~er at a level Ofg for example9 2-3% under ~he most extreme
process conditions and much less under more favorable conditions.
At those levels the water constitutes a relatively insignificant
impurity.
In conjunctlon with the forego~ngg the fabric trea~ment
process ideally is carried ou~ ln such a manner tha~9 when ~he
fabric is heated after contact with the liquid ammonia, to term-
inate ~he ammonia reactions~ the ammonia is vaporized 9 bu~ the
water content of the fabric substantially remalns~ Thus, fabric
emerging from the treatment chamber carries with it an increment
of additional moisture9 which is thus permanently removed from the
ammonia recovery system.
In some commercial applications of the process 9 it is
not always practicable to control the process so as to avoid diso
tilling off slgnificant percentages of the residual mois~ure con~
tent of the fabric. In such cases, the gaseous process effluent
may carry excessively high percentages o~ moistureO Pursuan~ to
another specific aspect of the invention~ such a gaseous process
effluent, prior to being discharged into direct heat exchange con
tact with liquid ammonia in the desuperheating vessel? is pre
chilled by non contact heat exchange~ desirably utilizing liquid
ammonia as the heat exchange medium~ With a heat exchange un~t
of practical proportions, this can serve to precondense residual
moisture out of the gaseous effluent d3wn to the two or three per-
cent level.
Reg~rdless of the procedure utilized tv extract excess
~ ~7~
water from the continuous process system9 whether by mechanically
conveying it out with the fabric and/or by condensing a portion
of it and/or by utilizing some other technique, such as desi~cants,
no practical technique for water removal will be 100% effective,
Such being the case9 with conventional procedures, water will
gradually accumulate ~n the desuperheater vessel~ either rapidly
or slowly depending on the efficiency of the w~er extraction
techniques, to the point where the desuperheating vesæel will be
operating at greatly reduced ef~iciençy. However, pursuant to
the invention, the liquid content o~ the desuperheater vessel,
including condensed residual water, is continually fed back to
the process chamber, and recycled through the various~water re-
moval stages. The re-liquefied ammonia from the recovery system,
ins~ead of being fed directly back to the processing chamber from
its storage vessel7 is fed to the desuperheating vessel as make-
up for the extracted watercontainingOsolution. Accordingly, the
water content of the desuperheater-vessel is easily maintained
at an adequately low level on a s~eady-s~ate basis~
A secondary, but nevertheless significant, advantagç of
feeding re-l~quefied ammonia to the desuperheating vessel is that
it is thereby simultaneously pre-chilled to its operating tempera-
ture of -28F. (-33G) at a convenient location upstream of
the processing chæmber without requiring a separate procedure for
that purpose. As compared to feeding the re-liquefied ammonia
directly tG the processing chamber where ~he eLevated temperature
must be accommodated, the pre-chilling significantly reduces the
energy requirements of ~he systPmO Thus, the procedure of the
invention not only effectively eliminates accumulating water on
a continuous, steady-state basis, but simultaneously achieves
~L~713~9
significant e~iciency improvements in the ammonia recovery system.
For a better understanding of the above and o~her fea-
tures and advantages, reference should be made to the following
detailed description and ~o the accompanying drawings.
Descri~tion of the_Drawings
Fig. l is a simplified schematic rapresentation of a
typical fonm of liquld ammonia ~abric processing system, lncorpo-
rating an ammonia recovery syst.em in accordance with the invention.
Fig. 2 ~s a simplified schema~ic represen~ation of prin-
cipaL components of an ammonia recovery liquefaction system ac-
cording to the invention~
~ ,.
RefPrring now to the drawin~s~.and initial~y ~o Fig~ 1
thereo~, there is shown schematically an advantageous system for
carrying.out a liquid~ammonia trea~men~ of a ~abric or yarn, for
ex~mple. For purposes of this deseription, i~ will be assumed
that.the material being pro~essed is a fabric web) comprised sub-
stantially of ~ellulosic ~aterials. However, apart from the
ability of ~he treated material to optimize process efficiencies
by receiving and carrying away small quantities of water,~the
specific nature of the ma~erial being ~reated is not signlfican~
~o the present i~ventionO
In Fig. L, a ~abrir web 10~ ~rom a suitable supply (not
shown) passes over tension r-ontrol rollers 11 and is then direct-
-ed about one or more heated rollers 12, consti~u~in~ a pre~drying
~ - 7 -
~,
1 ~ 7 ~ ~ 9
section, Passing over the series of pre drying rollers L2~ the
fabric is heated sufficiently to drive of ~ excess moisture~ In
this respect, incoming fabric typically may contain as much as
7-10% (by weight of the fabric) of moisture. The amount of mois-
ture in the fabric may unduly inhibit the desired reactions o
the liquid ammonia process, which nonmally should be carried out
in a liquid ammonia solu~ion containing not more than about 10%
water. Although the weight of ammonia in relation to the weight
of abric during the reactlon phase may vary wldely, a relation-
ship o~ one-to~one (e~g,, one part by weight of thP ammonia solu-
tion to one part by wêight of fabric) i9 not untypical. In such
- 7a ~
:1078~C~9
cases, if -the incomin~ Eabric carries as much as 10% water, that
amount of water will be present at the reaction site, and will
constitute approxima~ely 10% of the ammonia solution. This is an
undesirably high level, particularly where the ammonia solution
itself may contain some water, as contemplated in the present
invention. Accordingly, the pre-drying stage typical~y is con-
trolled to drive off enouyh moisture from the fabric to leave a
residual moisture content on the order of 3-5~ by weight of the
fabric. Of course, if the incoming ~abric is sufficiently dry
to be~in with, the pre-drying stage may be omitted.
Fabric leaving the pre-drying stage will be at an un- ~`
desirably elevated temperature and is thus cooled prior to enter-
ing the liquid ammonia treatment chamber 13. Typically, suitable ;
fan or blower means 14 is disposed downstream of the pre-drying
section, to direct streams of cooling air on the fabric and
return it to near ambient temperature levels.
The pre-dried and cooled fabric, after passing over
additional tension control rollers 15, enters the treatment cham- -
ber 13 through a sealed opening 16. An advantageous form of seal
for such opening is described and claimed in U.S. Patent
3,939,576 of Jackson Lawrence, for "Low Friction Pressure Seal ~
For Fabric Processing Chamber". Typically, the interior of -
the chamber is maintained at a slightly negative pressure, rela-
tive to ambient, and the entrance opening 16 is provided
with a double seal. An intermediate chamber, between the
double seals, is maintained at a slightly more negative
pressure than the interior of the chamber, so that inevitable
slight leakage of the seals will ~end to be directed
-- 8 --
.. . . ..
~ 7 ~
into the intermediate ~hamberO This minimizes leakage of ammonia
vapors from the treatment chamber into the atmosphere. In a typo
ical process, the main treatment chamber may be operated at a
negative pressure of about 0.5" H20 while the intermediate cham-
ber may be kept at a negative pressure of about 0.75" H20.
In the simpLified arrangement illustrated in ~ig L~ a
processlng trough 17 is provided in the treatment chamber 13.
This trough, through appropriate controls (not shown, and forming
no part of the invention) is supplied wlth liquid ammonia process-
ing solution through an infeed line 18. The controls o~ thLs may
include a float valve (not shown), for maintaining the processing
liquid at an appropriate level in the trough
After entering the processing chamber, the ~abric is
guided into the trough L7 and thus immersed in the liquid ammonia
solution which is at a temperature of about 28F. It is then
directed through padding rollers 19, ~or extractian of excess
processing solution~ then about a series of adjustable timing
rollers 20. After a predetermined reaction time, the fabric is
brought into contact with a source of heat9 which flash~s off the
liquid ammoniaO In the illustrated system, a pair of Palmer~type
dryer units 21, 22 are provided. These include large heated
drums 23 about which a confining blanket 24 is trained. For
practical purposes, the ammonia react~ons are substantially
diminished soon after thc initial contact between the fabric and
the first dryer drum. To advantage3 the time interval between
initial immersion in the liquid ammonia and initial contact with
the first dryer drum is controlled to be within the range of
0 6 seconds to 9 secondsO This can be effectlvely controlled by
~ 9 ~
:~71 3~9
regulation of the length o~ travel between the trough 17 and the
first dryer unit ~19 as by adjustment of the rollers 20 to lengthen
or shorten the path of the web9 as may be appropriate, However,
except as relates to the control of water in the ~abric and in
the processing solution and as relates to the controL of the
operation of ~he dryer units 21, 229 specific process condi~ions
do not fonm a part of this invention.
A~ter leaving ~he second dryer stage 22, the fabric
leaves the main treatment chamber 13 through a discharge opening
25, This opening9 like the entrance opening 169 advantageously
is provided with a double seal with an intenmediate chamber main~
tained at a slightly more negative pressure than the treatmen~
chamber itseLfO
Fabric leaving the ma~n treatment chamber 139 advantage~
ously may be directed through a steam chamber 269 after which the
fabric may be conveyed away to a folder or batcher9 for example.
In ~he processing of fabric in the main treatment chamber
13~ only about 5% of the liquid ~mmonia supplied to the trough 15
is actually consumed~ The remainder is flashed off as ammonia
vapor. These vapors are not only potentially hazardous9 but the
re-use thereof is economically important in a continuous commercial
pro~ess~ Heretofore9 recovery of the ammonia vapors has been
carried out by withdrawing vapors from the treatment chamber9 and
compressing and condensing the vapors~ Considerable amounts of
air are normally contained in the withdrawn gases9 but air is
easily separated from the ammonia because of the relative non-
condensability of air~ The withdrawn gases also include:quantities
- 10 ~ ',
~ ~ 7 ~ ~ O ~
o~ water, which continuaLly enter the process because of the
basic moisture content of the fabric and also of the incoming air
which, notwithstand;ng the efficiencies of the entrance and exit
sealsg is present in certain amounts in the interstices of the
fabrlc and en~ers with the fabricO Such amounts of wa~er have9 in
the past9 proven difficult to remove as noted ~bove9 necessitating
occasional discarding of quantities of the diLuted liquld ammonia9
or its use as a low grade materlal such as in fertilizer appl~
cations~ The process of the present invention is directed to the
recovery of the spent ammonia in a manner that enables the water
to be easily and effectively removed on a continuous basis a SO
that the process react~ons are not inhibited by excessive water
in solution with the otherwise relatively pure anhydrous liquid
ammonia, and so that maximum utilization of the liquid ammonia
in the processing operation may be real~zed.
In the simplified schematic representatlon of Figo 1~ a
surtion line 27 Leads from the main treatment chamber 13 for
effecting eontinual withdrawal of gases from the interior of the
chamber. These gases are dire¢ted initlaLly to a recovery sec~
tion, generally designated by the numeral 28 in Fig. l, in which
the gases are processed to compress and condense the liquid ~mmonia
and to separate airO A liquid ammonia storage vessel 29 is pro~
vided for temporary contai~ment of the reco~ered liquid ammonia.
As will be~described in greater detail with respect to Figs~ 2 9
the infeed line 189 through wh~ch the processing trough 17 is
supplied, is not dir~ctly connected wi~h ~he storage vessel 299
but rather leads from the recovery section ~8~ The stored liquld
ammonia is first directed ~rom the vessel 29 back into the re
covery system9 where ~t is utilized in a manner to be described~
and then is directed to ~he processing trough 17 along with an
increment of water extracted from the recovered gases~
In accordance w;th conventional practice9 air separated
from the recovery system is direct to an incinerator or other
disposal facility 300 Likewise ? the mixture of air and steam
from the steam chamber 269 containing some residual ammonia gas,
is directed through a suction lirle 31 to the disposal ~acllity.
Because of the relatively small amoun~s o ammonia ln these gases,
it is considered uneconomical to attempt to recover lto
Referring now ~o ~he schematic diagram of Fig. 2a the
suction line 27 is shown to lead from the treatment chamber 13 to
a non~contact heat exchanger 32 which may be of a shell and tube
type. The withdrawn gases, comprising.predominantly amm~nia gas9
but also containing quantities of air and water vapor, may be
passed throu~h the shell side of the exchanger9 while cooling
medi~m ib-flowed in the tube side of the exchanger~
To advantage9 the non~contact heat exchanger-32 has two
heat exchange stages constituting cooling and chilling stages~
In the cooling.stage, water may be u~ilized as the heat exchange
medium, being flowed through lines 33~ 34~ In this stage3 gas~s
leaving the treatment chamber 13 at a temperature of 9 typically9
about 150F., are pre-cooled in the wa~er section of the exchanger
to about:90F7 In the second stage of the heat exchanger9 liquid
ammonia desirably is u~ilized as the non-contact heat exchange
medi~m. The liquid ammonia is supplied through l mes 33a9 34a9
being supplied at a temperatur~ of around ~8F~ a~d serving to
chill the effluent process gases from the .~re~cooled temperature
12
~78~119
of 90 to9 say9 about ~21F!
Pursuant to one aspect of the mvention9 the low tempera-
ture chilling of the effluent gases in the second stage of the
heat exchanger 32 serves to condense out of the gas a substantlal
fraction of the residual moisture contentO ThLs condensed wa~er
fraction can be drained of~ at 32a and collected for ~urther pro-
cesslng or low grade utilization~
Because of ~he extremely high affinity of ~mmonia for
water, the water fraction condensed in the heat exchanger 32 will
inevitably absorb some ammonia, so that the condensate extracted
at 32a typically is around a fifty percent mixture of water and
ammonia. The overall amounts of collected cond~nsate are gener-
ally quite small. Thus, in a typical commer~;al process handling,
say, 3000 pounds o~ fabric per kour and thus requiring a process
feed of liquid ammonia solution of around 2500 to 3000 pounds per
hour3 the outtake of condensate may be on the order of eight to
ten gallons per hour, approximately half of which is ammonia~
Insofar as the outtake quantity of ammonia At this stage may be~
come economically significant in a proeess of sufficiently high
overall volume, at least somP of the ammonia content of the con- :
densate could be recovered without great diffieulty~
The chilled gases from the heat exchanger 32~ are di~
rected into a desuperhea~ing vessel 36 conta m ing a body 37 of
liquid ammonia9 In the process of the invention9 the de~uper~
heating:vessel is maintained at a sl~ghtly negative pressure9 and
thus the,-body 37 of liquid ammonla therein is maintained at a
temperature on the order o~ ~28F., (or slightly higherg depend~
- 13-~
7~
ing primarily on the total water fraction)~ The incoming process
gases can be discharged directly into the lower portion of the de-
superheating vessel 36 and bubbled upward through the cold liquid
ammonia~ Alternatively, the process gases may be sprayed with
liquid ammonia. In either case, the direct contact heat exchange
serves to remove superheat from the ammonla gases 9 with the cooled
gases acc~mulating in the upper portion 38 of the vessel, along
with additional gases which are 1ashed o~f from the liquid itself,
in order to maintain its low temperature and liquid phase.
A suction line 39 connect~ the upper portion.of the de
superheating vessel 36 with the suction side of a compressor 40
driven by a motor 41~ In the compressor~ the gases comprising
principally desuperheated ammonia gas together with alr~ may be
compressed to a pressure o~, for exampleg about 180 psigO The
compressed gases are heated substantially by the compression and
leave the compressor through a high pressure llne 42g at a tempera
ture of about 100F O The high pressure l me 42 leads to the shell
side of a shell and tube condenser~heat ex~hanger 43~ cooled by
water supplied to the tube side by inlet and outlet lines 449 45
Liquid ammonia condensate from the condenser 43~ now
at a temperature of about 95F~, is flowed throu~h a high pressure
line 46 into the storage and retention vesseL 29u Uncondensed
vapors.from the condenseroheat ~xchanger 439 are taken off through
a line 47 and directed into a pur~ing vessel 489 in which the un-
condensed vapors are fLowed in non-contact heat ex~hange relation-
ship with liquid ammonia at Low temperature (typi~ally ~28Fo)
and caused to condense~ The condensed material from the purge
v~ssel 48, is flowed through a:.llne 49 into the desuperheating
~ ~4 ~
1~78~'3
vessel 36, where the liquid fraction of such mater~al adds to the
body of liquid ammonia9 and the contained gaseous fraction, if
any, is bubbled through the liquid ammonia and recycled~
Liquid ammonia ~or cooling the purge vessel 48 is drawn
from the retention vessel 299 passed throu~h a suitable expanslon
valve 50 and directed into the tube side of ~he purge vessel,
which typically is a sheLl and tube type heat exchange vessel~
After passing through the tube side o~ the purge vessel 489 the
liquid ammonia may be directed through an outlet line Sl and
combined with the condensate flowing in the line 499 to the de~
superheating vessel.
In accordance with a significant aspect of the i~ventlon,
the liquid ammonia requirements of the process are supplied to th~
main treatment chamber 139 entirely or in subst~ntial part through
a l~ne 18 which leads, not directly from the storage vessel 299
but rather from the de~upe~heating vessel 36 whi~h received the
efflu~nt in the first place. To this end9 the vessel 36 has an
outlet line 52~ leading to the intake side of a suitable pump 53
which dischar~es through a ~ontrol valve means 54 into the line
18a connected to the processing trough 17. To advantage9 the de~
superheating vessel 36 may be provided wi~h appropriate liquid
level sensing elements 55, 56, establishing upper and L~wer limits
for the level of liquid ammonia thereln. A valve 579 in a liquid
ammonia supply line 58 from the high pressure suppLy ve~sel 29,
may be controlled by the sensors 559 569 to admit liquid ammonia
into the desuperheater vessel, as necessary9 to maintain the de~
sired level thereinO
As will be understood~ ~he fresh9 relatively pure an~
hydrous liquid
~ 15
~ ~ 7 ~
ammonia admitted into the desuperheating vessel 36 from the
storage vessel 29 perfonms several functions. First, the liquid
may be directed to the desuperheating vessel 36 while still at a
relatively high temperature of around 95F~ for example, and at
a relatively high pressure of around 180 psig~ Since the liquid
body within the desuperheating vesseL i5 in equilLbrium at a
slightly negative pressure and at a temperature o~ around -28F.
a certain amount of the incoming, ~resh liquid ammonia is initi-
ally 1ashed of to provide sel~-cooling to the equilibrium con-
ditions. In a typical process~ as much as 25% by weight of the
liquid ammonia rom the storage vessel is flashed off as gas in
order to effect self-cooling to -28F~ of the remaining 75%O
Significant advantages are realized, in the process of
the invention, by effecting self~cooling of the re~liquefied
ammonia at the desuperheater stage~ rather than in the treatment
chamber 13, as would be the case if the re~liquefied ammonia were
taken directly from the storage vessel 29 to ~he treatment chamber.
As will be appreciated, large volumes of ammonia are required for
the self-coollng action and, where sueh volum~s are released with~
in the treatment chamber 13, as in the past, this serves to in~
crease the energy requiremen~s of the heating section of the pro-
cessing chamber and correspondingly to increase the cooling re-
quirements of the ammonia recovery system~
In the operation of the system of Fig. 29 liquid ammonia,
rontaining a mlnor fraction of water, is directed through the
lines 52, 18 into the processing chamber 13, and is supplied
direc~ly to the trough 17. The fabric web 10 is continuously
advanced in~o and through the processing chamber at a predetanmined
~ 16 -
1~7~3~L09
speed. As the fabric en~ers the chamber, it is immersed in ~he
trough 17 and becomes saturated with the liquid ammonia solution.
When the processing equipment is in a steady-state condition, the
chamber 13 is fully saturated with ammonia vapors so that, when
the fabric emerges from the trough 17 and travels to the point o
its initial contact wlth the dryer unit 21~ lt remains e~fectively
saturated with the liquid ammonia. During thl~ ln~erval, the
principal desired reactLons between the ammonla and the ~abric
occur Soon after the ~abric is flashed o~f to substantialLy
tenminate the reaction, and the balance is substantially removed
as the fabric travels over the dryer units 21, 22.
Although the relationship of fabric processed to ammonia
solution utilized may vary widely with different fabrics, a reW
lationship of one pound liquid ~mmonia infeed to one;pound of
fabric infeed is not untypical and will be assumed for the pur-
poses of illustration herein. Thusg for each pound of fabric
e~tering the chamber, a pound of the liquid ammonia solu~ion is
~bsorbed ~rom the trough 17 and carried away with the moving
fabric, wi~h approximately 95% of tha~ ~mount being 1ashed by
the dryer units 21, 22. Thus, for each pound of fabric processed,
nearly a pound of spent gases must be withdrawn from the chamber
13.
Because the incoming fabric conveys trappe~ air within
its interstices, and because that air inherently will contain
som moisture, the atmQsphere within the chamber 13 necessarily
will become partly dilu~ed wi~h air and its mois~ureO This will
occur regar~less of the ef~ica~y of the seals at the entrance
and exit openings. When this ammonia~rich mixture of gases is
withdra~ from the chamber and bubbled through the desuperheating
vessel 36, the moisture fraction in the gases readily condenses
in the body 37 of liquid ammonia, which is at approximately -28F.
In addition, for some processing operations, an additional mois-
ture fraction may be driven off of the fabric by the heat of the
dryers 21,22. Unless properly dealt with, these water fractions
will accumulate in the vessel 36, causing the temperature in the
bath 37 eo progressively rise until it is no longer serving its
intended function, and must be e~tracted and discarded an/or
used in low grade application. In accordance with the invention,
however, the water-containing liquid ammonia in the desuperheating
vessel 36, is constantly extracted through the line 52 and uti~
lized as the make-up feed to the impregnating trough 17.
As an integral part of the process of the invention, pro-
vision is made for the constant removal of water from the process,
on a convenient and economical basis. Although the particular
technique utilized for water extraction is not critical to the basic
process of the invention) it is of~rourse critical that some means
be provided for water removal. To greatest advantage, and as one
of the specific aspects of the in~ention, water is most convenient-
ly removed by a combination of techniques, including mechanically
conveying a water fraction out with the processed fabrics, where
practicable and condensing a water fraction out of the hot ef-
fluent gases extracted from the treatment chamber~ Thus, where
processing conditions permit, it is advantageous to so control
the time-temperature relationships of the heating section as to
drive off primarily the ammonia fraction while substantially re-
training the wa~er fraction in the fabric. By this means, the -
fabric can be caused to leave the process with a slightly gxeater
~'
-18-
:.
7 ~ ~ g
moisture content than when it enters, resulting in a net out~ake
of water from the processing system.
Since not all fabrics and not all proc~ssing conditions
admit of optimum control of the heating sec~ions, secondary pro-
vision is made for pre-cooling and then chiLli~g ~he hot ef~luent
gases from the process, in order to condense out at least part
of the water fraction in the spent gasesO By pre-chilling the
spent gases down to about -21F., for example, which ls readily
accomplished in a non-contact heat exchanger of practical propor-
tiQns, using available liquid ammonia as the chilling agent, the
water fraction may easily be reduced down to 2~3%. By thus pro-
viding for alternative water removal by fabric conveyance or by
condensation from the hot effluent gas, optimum process efficien-
cies may be realized. Where the nature of the fabric-and the
particular procesaing admits, the heating stage may be oo~trolled
to ach~eve a net outflow of water on the fabric itself. H~wever,
where the process cannot be operated in this ideal manner, the
resulting high moisture content of ~he hot effLuent gases will be
significantLy reduced by chilling in the non-contact heat ex-
changer 32
The system of the invention is uniquely effe tive in
eliminating the build-up of undesired quantities of water in the
systPm and~ at the same t~me, ~ignificantly improving the thenmo-
dynamic efficien~y of the system, by drawing upon the ~ody o~
water-containing liquid ammonia solut~on in the desuperheating
vessel for ~he supply o~ process solution. By feeding this solu-
tion back ~nto the process, the water fraction, which is inherent-
ly going to be present in ~he recovexed process gases, ls
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~ ~ ~ 8~ ~ 9
prevented from accumulating to an undesired level and can be re-
moved at a convenien~ stage of the process.
Under ideal condi~ions of process operation, the steady-
state residual water content in the desuperhea~er vessel may be
maintained at ex~remely low level. Even under adverse conditions,
the water content of the desuperheating vessel may be easily kept
at levels (2-3% or less) which enabLes both the primary treating
process itself, and also the recovery sys~em, ~o be operated at
highly efficient levels.
One of ~he signiflcant dditional advantages of the uni-
que process is the improved thenmodynamic efficiency which results
from feeding the re-liquefied ammonia into the desuperheating ves-
sel, rather than directly into the process chamber 13~ Thus, the
re-liquefied ammonia in the starage vessel 29 is both at high
pressure and at a relatlvely elevated temperatureO At the time
of use, the liquid ammonia must be brought to equilibrium at sub-
stantially atmospheric pressure (actually slLghtly below atmos-
pheric) and at an equilibrium temperature of about -28F~ In
order to achieve this equilibrium ~tate, substantial percentages
of the re-liquefied ammonia are flashed off as gas9 When this
is caused to occur at the desuperheating vessel~ these substantial
quantities o~ flash~d-o~f gases are simply recycled throu~l the
recovery s~stem, compressed and re-liquefied~ I~, on the other
hand~ the gases are flashed off in the treatment chamber 13, as
according to prior practice, the flashed-off gases are returned
to the recovery system only after being exposed to substantial
heat within the treatment chamber~ As will be appre~iated, the
heat which goPs mto elevating the temperature of that fraction
- 20 ~-
~ ~ 8 1 ~ ~
of gas which is flashed off merely to bring the liquid ~mmonia
to an equilibrium condition represents a waste of heat energy in
the he~ting section of the processu Likewise, in order to re~
quefy and recover this gas~ the heat ~ust be removed therefrom,
which serves to increase the working lo~d on the compressor~ Thus,
in the new process, by deriving the process ~eed ~rom ~he desuper-
heating vessel, and ~tilizlng the re-lique~ied ammonia as make~up
feed to the vessel and not directly to the process chamber, not
only is the water conten~ o the system stabilized at an appropri-
ate equilibrium level, bu~ significant energy efficiencies are
realized.
The system of the invent10n is uniqueLy effective in
eliminating undesired water from the recir~ulating ammonia system~
This is of criti~al importance~ ~n a practical, commercial system9
because there is almost a twenty~to~one ratio between the amounts
of æmmonia recycled and the ~amount basically consumed ~n the pro-
cess, such that effective reclaiming te~hniq~es are vitalq Here-
tofore, such reclaiming techniques have been severely limited by
the practical difficulties ln ridding:the~system of water which
unavoidably en~ers the system.
The process and system of the present invention, operate
on the ba~is of condensing out the water frac~ion a~.an early
stage in the recovery processJ by dire~t GOntaCt with a body cf
cold liquid ammonia,.with or-without a prior non contact conden~
sation stage, to provide the make~up supply to ~he processl The
condensed water in the desuperheating vessel is thus fed dirçctly
back into the process as qui~kly as it enters~.enabling a steady
stae ~evel to be rea hed which~ experience ha$ shown7 is
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~7~1~g
suficiently low as to ha~e insignificant effects upon the process
reactions. Thus, while as much as LO% moisture in th~ liquid
ammonia solution may substantially inhibit the desired reactions,
the water fraction introduced into the processing solutio~ by the
system of the invention, represents a rela~ively insignificant
increment. In any case, prov~slon may be made ~or predrying the
incoming fabric, not only ~o minimize incoming moisture content,
but aLso, under some conditions, enabling a water fraction to be
removed by the fabric. Thus, in An ldeal process 9 fabrlc may
enter the process with a mois~ure content on the order of 5%, be
subjected to the desired liquid ~mmonia reactions, and leave the
process with a moisture content on the order, for example, 5.1%~
By this means, the fabric itself serves as a continuous means of
extracting water from the ammon~a reco~ry system, permitting the
system to operate on an ex~remely efficient basis~ with a minimum
wastage or low grad~ utilization of the recovered material. Where
such ideal conditions are not realizeable, other means, s~ch as
non-contact condensation of spent gases~are utilized to extract
a water fraction.
It should be understood, of course, that the form of
the invention herein illustrated and described is ~nte~ded to be
representative only, as certain changes may be made therein with-
out departing~from the clear teachings of the disclosure. Ac-
cordingly, reference should be made to the following appended
claims in detenmining the full srope of the invention.
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