Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
-- 2100768
8TR~ NG ~OD AND APPA~Aq~S
FIELD OF INV~TION
The present invention relates to a rlovel form of
stripping op-ration for the removal of dissolved gasss
from liquid solvents or absorb-nts therefor
_ C=~
In pr-viously iJsu-d Unit-d States Pat-nt~ No~
4,865,817, 4,963,329 and 5,023,064 as w~ll as
concurr-ntly p-nding UnitQd States patent applications
8ial Nofi 646,197, 672,021 and 754,643, all a~ign-d
to the assign-e her-of and th- di-clo~ur-s o~ which are
incorporat-d h-rein by ref~r-nce, th-re $8 disclo~ed the
ub~tance of a gas r-actinq apparatus and ~thod for
th w t ~a-~ transfer of ~olut- ga--~ fro~ or a g~-
~tr-a~ to a liguid reacting ~ediu~ capabl- of
ch~i-orption of th ~olute ga~es ~rom or contain-d in
` th ga~ ~ts-a~
- 20 Th ba-i- Or the above patents and applicat~on~ and
~, al~o why th unique approach to gas ab~orption d--crib-d
th~r-in work~ ~o efrectively relate~ to the
xc ptionally large ~urface ar-a of liquid absorption
~iu~ in tho ~orm Or ~ry ~all droplots Or the liquid
2S ~b orptlon ~d~ g n-rat-d in-duct with two-pha~e
nto~izing nozzl-- or c-rtain hydraulic nozzl--
Accordingly, th-r- h~v- b -n d-velop-d co~cial
~pplle~tion- or ueh t-chnology ror the r~oval Or
nol~llo g~-J~ uch ~- 802, H~8, C12, C102, NOX, HCl, HF,
803, te u-lng a v~ri-ty Or ab~orption ~edia In ~o~t
Or th--- ~ppllc~tion, the ab-orptlon m dia ch~ically
r~ct ~rlth th ~cidlc g~ o~eti~es to oxidize it or
- r~uc- it or oth~i~e to rorm ~ ~tabl- r-action
~uct, th~t ~y b di-po~-d Or or oth-rwi~- tr-at-d
3~ ror dl~po ~l Apparatu~ ~odying ~uch t-chniqu-- i-
lcnown by our --i,gn-- a- th- "Wat-rloo Scrub~r"
2 1 ~
In some cases of such solute gas absorption
process, the absorption ~edia can be regenerated
Often, the regeneration step is accomplished by stea~
stripping in more or less conventional tray or packed
s columns This steam stripping regeneration procedure is
an industrial process step that is widely used
throughout the chemical industry for many differing
desorbing or separating reguirements, and not simply for
the reg-neration of ab~orption media u~-d to r-move
olute gas-~ by the procQdur-s describQd in the above
pat-nt~ and applications
The stea~ which is used in such stripping
operations usually is generated in a reboiler located at
the base of the conventional tray or packed column and
rises in counter-current flow to the load-d liquid
~b~orption ~edium, which normally is fed to the middle
of the coluon and pa~ses tray-to-tray or over th
packing down the column Overhead product reflux
g n ally i- mploy-d to further purify the ov-rh-ad
product The ~t-am (gas)-liquid contact in uch
op ation~ i- confined to the interfacial ar-a g-nerat-d
~8 the bubbl-~ of steam pass through the ~hallow lay
of liquid ab-orption medium covering each tray in the
colu~n In nor~al practice, each eguilibrium ~tage
r pr nts a nu~b r of trays ~he number of equilibrium
tag ~ requir-d to effect ~-paration of th absorb-d
oo pon nt v~ri-s and is d-p-ndent on th~ particular
~y-t ~ und con~id-ration
~'~ ~
~h un~qu- f-atur-~ that have nabl-d th- Wat-rloo
8crubb r to b- -p-ci~lly effici-nt at absorption al-o
~r- mploy d to r-v r-e the absorption st-p in a
d orption or t aD--tripping operation Accordingly,
t~- pr - nt inv ntion r-lat-~ to th- r-moval o~ ab~orb-d
3S gn~ roo ~b orbing m-dia th-r-for In vi-w of th-
larg- nu~b-r of more-or-le-~ conv-ntional ~t-~m
- 21~76~
stripping operations carried out in the chemical
industry, the apparatus and process described below and
provided in accordance with this invention is considered
to have broad applications in this industrial segment as
well as other industrial segments wherein steam stripping
is carried out
Accordingly, in one aspect, the present invention
provides a method for the removal of a solute gas from a
solute gas-laden aqueous absorbing medium, which
comprises
(a) passing a flowing gas stream comprising steam
through an elongate conduit having an inlet thereto and
an outlet therefrom,
(b) injecting said absorbing medium directly into
said flowing gas stream to form at least one spray
pattern of said absorbing medium in said conduit
containing liquid droplets ranging in size from about 5
to about 100 micron~,
(c) desorbing dissolved solute gas from said liquid
droplets Or absorbing medium into said flowing gas
stream,
(d) agglomerating said liguid droplets at said
downstream end of said conduit to remove entrained liguid
droplets from said gas stream to form an at least
partially regenerated aqueous absorbing modium, and
(e) dlscharging a gaseous mixture comprising solute
ga- and steam from ~aid downstream end Or said conduit
and r-coverlng aid solute gas rrOm said gaseous mixture
Pigur- 1 iJ a schematic flow sheet of an S~-
ab~orblng oporation;
Figure 2 is a fichematic flow ~heet of an S~-
strlpping oporation efrected in accordance with one
mbodlment Or th- present invention, the two operation~
21~076~
being interacted to provide a cycle absorption-
desorption operation; and
Figure 3 is a schematic flow sheet of an
alternative stripping operation to that illustrated in
Figure 2, provided in accordance with another embodiment
of the invention
GENERAL DESCRIPTION OF INVENTION
For a solvent or other liqui~ absorbing medium
~loadQd with S02 or other gas) that can be reversably
str$pped by heating of the solvent by steam or other
means to attain the desired temperature, one or more
steps of adiabatic flashing coupled with some degree of
heat stripping, where exceptionally large surface areas
of liquid absorbing medium are produced according to the
invention, may be incorporated into very compact
eguipment and effect optimal separation of the S02 or
other dissolved gas from the solvent in a minim~l number
of stages, in contrast to conventional tray columns
One class of absorption media of interest in th-
pre~ent invention is water-soluble single salts of
~econdary and tertiary di-amines, as described in U S
Patent No 5,019,361, and water-soluble members of the
hydroxyalkyl 2-piperazinone family, as described in
published EP 303,501, both of which represent stable,
high boiling chemical compounds useful as absorbing
media for the removal of sulfur dioxide from gas strsams
uslng the technigues described above Th-~e latter
compounds are characterized with an esp-cially high
d-gr-- or ~ ctivity for the chemisorption of S02 from
indu-tri~l ga- ~tr-am~ at t-mperatures below about 100C
and normally at the adiabatic dewpoint of the gas stream
or, pr-f-rably, at lower or at ambient temperatures
Wlth the-e organic solvents, the chemisorption proc-ss
which r-mov s the S02 from the gas str-am can readily be
3S r-v r--d at some higher temperature to errect de~orpt~on
Or the S02 and regeneration o~ the absorption medi~
21~76~
s
In conventional practice, steam distillation is
employed to reverse the absorption process and regenerate
the absorption media In such instances, the off-gas
stream from the regeneration step contains only S02 and
steam After condensation by cooling of the steam and
removal of the resulting water, a clean flow of S02 can
be produced, which, after drying, is the pure product of
the cyclic absorption-desorption operation The same
result is achieved by the process of the invention In
this way, a furnace or process off-gas stream containing
S02 may be contacted by absorption media to remove S02
contaminant and any particulate present prior to venting
the clean gas stream to a suitable stack and the
absorption medium may be regenerated for reuse while
recovering the S02 as a pure gas stream The S02-free
absorption medium resulting from the regeneration
operation is recycled to the absorption step ~he by-
product pure S02 stream can be used or sold as such or
can be easily converted to sulfuric acid or, where
~pecific reductant~ are available, be reduced to
elemental sulfur
In U S Patent No 4,963,329, referred to above,
Figure 7 presents a two-stage scrubber concept where
fresh or regenerated reagent (absorption medium) is
employed in the second absorption stage of the solute gas
absorption scrubber in a recycle mode, wherein the
ab-orption medium contacts an So2-containing gas stream
containing le~ser amount~ of S02 To obtain a mass
balanc- on th- scrubbing reagent, the amount of fresh or
r-g-n-rat-d ~olvent entering the second absorption stage
mu-t be balanc-d by an eguivalent amount of reagent
collected from the second absorption stage passing on to
the fir~t ab-orption stage where it contacts a higher
1QV 1 Of S~ in the entering ga~ stream, thereby en~uring
that the absorption medium removed from this
21~7~8
first stage may be completely loaded with absorbed So2,
depending on the L/G ratio employed and characteristics
of the sorbent system
It now has been found that certain specific
reagents are much better than others, in that the
kinetics in the absorption syste~s described in the
above-mentioned patents and applications utilizing the
Waterloo Serubber is very fast so tbat equilibrium is
vory quickly aehieved
Nozzles employed in the duct to aehieve formation
of the sprays of very fine liquid droplets preferably
are of the dual-fluid type wherein atomizing g~s and
liquid to be sprayed are combined into a gas-liquid
mixture whieh is ejeeted from the nozzle Prefer~bly,
the nozzles are cluster nozzles, which result in a
plurality of sprays being obtained from a single nozzle,
as de~cribed in U S Patent No 4,893,752, a~sign-d to
the a~ignee hereof, and U S Patent applieation S-rial
No 753,404 ~iled August 30, 1991, the di~elosures oS
whieh are incorporated herein by referenee ~owever,
any nozzle teehnology or desiqn whieh is eapable of
generating Sine sprays with the characteristics of
droplet ~ize distribution and surfaee area may be used
In most instances, only two such absorption stages
re r-quir-d to aehieve 98S re~oval of the S02 in the
ent~ring gas str-am By varying the liguid-to-gas (L/G)
r~tio (-xpr--~-d in US gallons Or liquor fiprayod/~tago
y-r 1000 rt3 o~ gas b-lng scrubbod), hig~er or low r
p~re-nt r-moval Or the S02 can roadily be aehieved
N-v-rth-l--~, mor- than two solute gas absorption ~tages
ray b- u~-d a8 th- n--d arisos
~ he xeoll-nt kin-ties obs-rved in this proprietary
~pproach to ~b~orption o~ S02 and oth-r solut- ga--
~rrom o~-ga~ troa~s doponds on two raetOr-, n~moly,
Sir~t, th- prop-rti-~ of the speei~ic liquid absorption
r-agent omployod and seeond, the amount of sur~aee ~ro~
7 ~ ~
of reagent generated by the spray nozzles within the
ducts which comprise the Waterloo Scrubber
With the countercurrent or co-current flow of liquid
absorption medium and solute gas-containing stream, the
first and second stages of absorption are preferably
separated to avoid completely-loaded liquor from passing
from the first stage to the second stage While there
are many ways of achieving such separation, the preferred
method enploys banks of special chevron-type mist
eliminators located between the two stages, as described
in the aforementioned U S Patent application Serial No
646,197 These mist eliminators have been found to be
most suitable for the purposes at hand, because 100%
removal of the loaded reagent is not essential while
greater than about 99% removal is readily achievable
Such interstage mist eliminators are not required when
the absorbing medium is fed in parallel to two or more
stages of solute gas removal, as described in U K Patent
application No 9123999 6 filed November 12, 1991
All of these design features, coupled with
kinetically-aggressive reagent molecules in the
absorption medium, enable S02 or other solute gas removal
from a gas stream to be effected at duct space velocities
of up to as high as about 40 to 50 feet per second
The deoorption and regeneration operation of the
pre~ent invention employs similar technigues to those
u~ed to remove solute gases from gas streams described
above and in more detail in th- aforementioned patents
and applications, except that desorption of dissolved
oluta ga~ fr-ct-d in at least one stage by spraying
h-at-d olut- ga--load-d liquid ab~orption medium at an
l-vated t-mperature as fine liquid droplets of large
surface area u~ing steam as the atomizing gas into a duct
through which passes a purge
3S
~100'~
steam stream into which is desorbed the solute gas.
Although it is preferred herein to effect the formation
of the fine liquid droplets of solute-loaded absorption
medium using steam as the atomizing medium, any other
convenient procedure may be employed. In such spray
pattern of fine liquid droplets, the droplets have a size
ranging from about S to about 100 microns, preferably
about 5 to about 30 microns. The loaded liquid
absorption medium is sprayed into the duct through which
the purge steam passes at an elevated temperature to
facilitate mass transfer of solute gas from the liquid
droplets to the gaseous phase. The temperature employed
varies with the particular absorption medium and may vary
generally from about 170 to about 270F (about 75 to
15 about 135C).
However, simply because fine liquid droplets of
liquid absorbing medium are very effective in removing
solute ga6es from gas streams does not mean that a
somewhat analogous technique is effective for
regeneratinq an absorption medium and, in fact, it is
surprising that the regeneration procedure provided
herein is so effective.
The regeneration operation may be effected by
passing the loaded absorption medium first to a second
stage of steam stripping, removing partially-regenerated
solvent from the downstream end of the second stage,
forwarding the partially-regenerated solvent to a first
~tage of steam stripping and rocovering the regenerated
~olv-nt rOr recycle to the solute gas absorption
op-ration.
An alternative regeneration procedure involves
r~ooval o~ a percentage of the volume of partially-
r~generated solvent from the downstream end of the second
regeneration stage and rorwarding the same to the first
3S ~tage Or the ab~orber scrubber for reloading, whilo the
renaining volume o~ partially-regenerated
- 21 ~a7~
solvent is forwarded to a second stage of stripping, to
recover a much leaner sorbent for application to the
second or third stage of the absorber
The desorbed sulfur dioxide or other solute gas,
which may be, for example, C12, HCl, S03, or VOCs, is
removed from the downstream end of the duct following
removal of the partially regenerated solvent by suitablo
coalescing means, such as a mist eliminator, in a stream
of water vapor Following cooling and condensation of
water of the gas stream followed by drying, a pure
stream of S02 or other solute gas is recovered, and may
be further processed, as desired
DESCRIPTION OF PREFERRED EHBODI~ENT
Referring to the drawings, Figures 1 and 2
illustrate an integrated absorption-desorption
operation for removing S02 from a gas stream containing
the same using a suitable regenerable solv nt, with the
absorption stag- sp-cirically b ing illu~trat-d in
Figure 1 and tbe d-sorption stage sp-cifically b ing
illu-trat-d in Figure 2 While this sp-ciSic mbodim-nt
is d-scrib d with respect to the removal of the S02 from
~lue gas or other waste and off-gas streams, the
invention has broad application to the removal of any
solute g~s from a gas stream containing the s~me in any
2S r g-n-rabl- liquid absorbing medium and the subs-quent
r-g neration o~ the absorbing medium for r-u~e in the
ab-orption tage and Sor r-covery oS pure ~olut- ga~
On- xample of ~uch a proo-ss is the r-moval of H2S from
~-our~ n~tural ga~ streams by using a liquid ~min-
~b orb nt and th- ~Ubs-quent st-am stripping ~t-p
wh r-by th- N2S is r-cov r-d in relatively pure form Sor
Surth r proc-ssing The recovery of C02 from gas
~tr-am~ by ~imilar t-chniqu-s r-pr-sent~ anoth-r
x~pl-.
3S In Figur- 1, there is illu~trat-d a olut- ga-
r-~ov~l apparatus 10 Thi~ apparatus 10 and its
210~768
operation are generally described in the aforementioned
US patent application Serial No 646,197 The
apparatus lo comprises a generally horizontal duct 12
having an inlet end 14 for receipt of a sulfur dioxide-
containing off-gas stream from which the SO2 is to be
removed prior to venting to atmosphere The duct 12
also may be arranged vertically, if desired ~he ga~
stream also may contain particulate m~tter, which iB
r-mov-d along with the SO2 in the duct 12 Heavily
particulate-cont~minated gas stre~m first ~ay be
subjected to a particulate removal operation prior to
pas~age to the duct 12, such as described in the
aforementioned US Patent No 5,023,064
A pair of mist eliminators 16 and 18 of any
convenient construction, such as the chevron type, to
effect coalescence of gas stream borne liquid droplets
passing therethrough is provided, defining in the
interior of the duct 12 two gas absorption st~ges or
cha~bQrs 20 and 22, separated by the mist eliminator 16
A pair of dual-fluid nozzles 24 and 26 is locat-d one in
each of the gas ab~orption stages 20 and 22 The dual-
tluid nozzles 24 and 26 are constructed to produce ~
fipray of very fine liguid droplets of high surface area
of regonerable liguid abQorbing medium in the duct 12
and preferably compri~e cluster nozzles, such as tbo-e
d-scrib-d in the aforem-ntion-d V S Pat-nt No
4,893,7S2 and USSN 753,404, although any nozzl- capable
of g-n rating imil~r fine droplet sprays may b- u--d
~h- noz21-- 24 ~nd 26 are illustrat-d a8 ~praying
tb- ~b orbing ~ dium count-rcurrent to the dir-ction of
~low of tb- SO2-containing gas stream tbrouqh tbe duct,
inc- thi~ ori-ntation is tbe most convenient to obtain
hiqh rat- of gas-liguid transfer How-ver, co-curr-nt
~pr~ying oS ~b~orbing m-dium into the duct 12 from both
or on- of th- nozzl-~ 24 or 26 c~n be rr-ct-d
2100r
ll
The downstream end 28 of the duct 12 is connected
to an I D fan 30, which maintains the flow of gas
through the du~t 12 and discharges the purified gas
stream, now So2- and particulate-free by duct 32 to a
discharge stack 34 An 52 analyzer 36 may be provided
in association with the discharge stack 34 to monitor
S2 content of the discharged gas stream to ensure that
the ultimate discharge is within allowable limits or
meets any other level as desir-d
At the immediate downstream end 28 of the duct 12
i~ a further mist eliminator 38 which serves, in
conjunction with hot water sprays 39, to scavenge any
re~idual entrained droplets of ab~orbing medium from the
purified gas stream Liquid collected in the mist
eli~inator 38 is returned by line 41 to the water tank
42, from which it is pumped to the sprays 39 by line 43
Any liguid droplets coalesced by the fan blades in the
I D fan 30 are returned by line 40 to the w~sh wat-r
- t~nk 42
A liquid rog-nerable solvent or sorbent for ~ulrur
dioxid-, such as an aqueous solution of an aliphatic,
alicyclic or heterocyclic amine, is fed to the dual-
- fluid pray nozzle 26 in chamber 22 Such ~olvent is
~-d by line 44 to the nozzle 26 and comprises make-up
quantities of ~resh ~olvent in an amount r-guired to
make up 1088e~ and regenerated solv-nt produo-d
ploying the proc-dure of Figure 2 deacrib d b low
Atocizing air or other gas is r-d to the nozzle 26 by
lin 46 Th- atomizing air g-nerally i~ appli-d to th-
du~ luld Jpray nozzle~ 24, 26 at a pr-ssure Or about
20 to ~bout 100 p-i, pr-2erably about 20 to about 70 p8i
~nd more pr-f rably about 25 to about 75 psi
Th air and liquid ~olvent ~orm an intim~te mixture
in th- nozzl- 26 which is ~prayed as a ma~- 48 Or rine
liguid dropl-ts Or high ~urr~ce area into th~ duct 12,
whlch cont~ct the gas stream rlowing through chamk~r 22
21007~,
12
Such liquid droplets range in size from about 5 to
about 100 microns, preferably about 5 to about 30
microns
The liquid solvent is low in dissolved SO2
5 concentration (or contains no So2, depending on the
efficiency of removal of So2 in the stripping operation)
while the gas stream is depleted in S02 contont as a
result of an initial removal in chamber 20
Accordingly, the S02 is rapidly and substantially
10 completely dissolved in the liquid droplets
The entrained liquid droplets in the flowing gas
~tream in chamber 22 are removed and coalesced by the
mist eliminator 18 and partially-loaded solvent pa~Bes
by line 50 from the mist eliminator 18 to a tank 52
15 The S02-free gas passes through the mist eliminator 38,
through the outlet 28 to the fan 30 and then to the vent
stack 34
The partially-loaded solvent is forwarded by lin~
54 to the dual-fluid nozzle 24 located in chamber 20
20 Ato~izing air also is fed to the nozzle 24 by line 56
The air and liquid solvent form an intimate mixture in
the nozzle 24 which is sprayed as a mass 58 of fine
liquid droplets of high surface area, which contact the
ga~ stream flowing through chamber 20 The fine liguid
;25 droplets range in size from about 5 to about 100
imicrons, pr~ferably about 5 to about 30 microns
The partially-load-d liguid ~olvent contact~ a hlgh
-conc-ntration of ~ulfur dioxide in the ga- str-am
pa-~lng through the duct 12 Sulfur dioxide is rapidly
J30 ch-nl~orb-d ln the llquid droplets, up to ~aturat-d
loa~lng o~ th- olv-nt by S02
The ntrain-d liquid droplets in the flowing gas
tream in chamber 20 are r-mov d and coalesced by mi~t
llminator 16 and fully-loaded olvent is r-mov-d from
35 tb ~i~t ll~lnator 16 by lin- 60 Th- partlally
d pl-t d S02-containing ga- tr-am th-n pa~ rom th-
2~ 0~ ~g
13
mist eliminator 16 into chamber 22 for r~moval of the
remainder of the So2 in the manner described above
In place of the countercurrent flow of gas stream
and absorbing medium employed in the embodiment of
Figure 1, with an intermediate mist eliminator 16, there
may be employed a parallel flow of liquid absorbing
medium to the two dual-fluid nozzles 24 and 26 with no
mist eliminator 16, as described in our afor~mentioned
UR patent application No 9123999 6
While two stages of gas-liquid contact are
illu~trated in Figure 1, additional ~tages may be
employed, as desired, depending on the concentration of
~olute gas present in the gas stream, the degree of
removal required, the L/G ratio employed, and the nature
of the solvent employed
Referring now to Figure 2, there is illustrated
therein a loaded absorbing medium regeneration apparatus
llO which comprises a horizontal duct 112 having an
inlet end 114 for receipt of a low pressure steam purg-
~tream Tho duct 112 may be arranged vertically, ifd--ired The duct 112 is provided with an outer h-ating
~acket 116 to heat the duct sufficiently to avo$d
condensation of steam therein The duct 112 may have a
; ~light ~e g about 1) incline towards its downstream
end to facilitate removal of any condensate from the
walls of the duct 112
A pair of mist eliminators 118 and 120 o~ any
conv ni-nt con-truction to ~rect coale-c-nc- of llquid
dropl-t- pa--ing th-rethrough is provid-d, d-fining in
th- int-rior Or th- duct 112 two de~orption ~tag-~ or
cba~b r- 122 ~nd 124, -parated by the mist eliminator
118 A pair of dual fluid nozzl-s 126 and 128 is
provid-d on- in each of the gas desorption chambers 122
and 124 Tbe dual-tluid nozzles 126 and 128 are
con truct-d to produce v-ry fine liguid dropl~t- o~ higb
~urtac- ~r-~ ot tb- b-at-d load-d liquid ~b~orbing
210~
14
medium and preferably comprise cluster nozzles, such as
those ~escribed in the aforementioned US Patent No
4,893,752 and USSN 7S3,404, although any other suitable
nozzle may be employed
The atomizing gas used in the desorption process is
steam employed at a pressure necessary to generate a
proper droplet size distribution The entire system,
however, is maintained at approximately 100C regardless
of steam temperature and liguid temperature, since the
excess heat is rapidly spent in evaporating water from
the amine solution and expelling some of the S02 In
cases where the sorbent employed cannot withstand
temperatures of 100C, the system must be operated at a
reduced pressure to maintain the desired temperature
The nozzles '26 and 128 are illustrated as spraying
the absorbing medium countercurrent to the direction of
flow of purge steam gas stream through the duct 112,
although co-current flow may be preferred Thus, co-
current spraying of absorbing medium and purge gas
steam into the duct 112 from both or one of the nozzles
126 and 128 can be effected
The downstr~am end 130 of the duct 112 is connected
by line 131 to a cooler-condenser 132 of any convenient
construction wherein steam is condensed and removed as
water in line 134, resulting in a clean saturated flow
of pure S02 in line 136 This by-product pure S02 gas
~tream may be used as such, may be converted into oth-r
u~-ful ch-nicals, such as sul~uric acid, may b- r-duced
to l-o-ntal sulfur, or otherwise proces~e~ ~ solvQnt
analyz-r 138 ~y be provid-d between the downstream nd
130 of th- duct 112 and the coolQr-condQnsQr 132 to
monitor solv-nt content of the gas stream to ensure the
ab--nce of uch material from the gas stream exiting the
duct 112
3S At the i~n-diate-down~tream nd 130 of th- duct 112
i- a furth r mi-t eliminator 140 which -rve~, in
21~7~
combination with hot water sprays 142 to scavenge any
residual entrained droplets of absorbing medium from the
gas stream exiting the duct 112 Liguid collected in
the mist eliminator 140 is returned by line 144 to a hot
water tank 146, from which it is pumped by line 146 to
the sprayers 142
The loaded liguid solvent in line 60 (Figure l) i8
forwarded to a heated solvent holding tank 152 and then
i8 forwarded by line 154 and pump 155 to the nozzle 128
located in tbe chamber 124 Atomizing steam also is
forwarded to the nozzle 128 by line 156 via a solvent
beater 150 The atomizing steam generally is applied to
the dual-fluid spray nozzles 126, 128 at a pressure of
about 20 to about loO psi, preferably about 20 to about
70 psi and more preferably about 25 to about 75 psi
- The steam and loaded liquid solvent form an
intimate saturated mixture in nozzle 128 which is
spray-d as a mass 158 of fine liguid dropl-ts of high
~urfac- are~ into the duct 112 in contact with the purg-
gas str-am passing therethrough The liguid dropl-ts
g~nerally are sized from about 5 to about 100 microns,
pref-rably about 5 to about 30 microns The high
~urfac~ ar-a of liguid droplets contain-d in th- flowing
hot purge gas stream in the chamber 124 and the
r-latively high t-mperature of the droplets r-sults in a
rapid ma~s transfer of S02 gas to th- gas pha--,
; r-~ulting in partial reg-neration of th- liquid
~b orb nt m dium
lh ntrain-d liquid droplets in the flowing purg-
g~ ~tr-~ in chu~b-r 124 ~r- r mov d and coal--c-d by
ml-t liminator 120 Th- r-Julting partially
r-g n rat-d olvent passes by line 160 fro~ the mist
li~ln tor 120 to a tank 162 The solv-nt-fr-- gas
tr-~o xits th- downstream ond 130 of th- duct 112 by
3S lin- 131 ~nd p~-~-s through the solv-nt analyz-r 138 and
an optional vacuum pump 164 to the cooler-cond-ns-r 132
210~7~
16
The vacuum pump 164 may be employed to maintain the duct
112 under a reduced pressure, to enable operation at a
lower temperature to be effected
The partially-regenerated solvent is forwarded by
s line 166 to the dual-fluid nozzle 126 located in chamber
122 via a second solvent heater 167 Atomizing steam is
fed to the dual-fluid nozzle i26 by line 168 The ste~m
and partially-stripped solvent form an intimate mixture
within the nozzle 126 which is sprayed into the chambor
122 as a mass 170 of fine liquid droplets of high
surface area in the purge gas stream flowing through
chamber 122 The liquid droplets generally are siz~d
from about 5 to about loo microns, preferably about 5 to
about 30 microns The high surface area of t~e liquid
droplets and the relatively high temperature of the
droplets results in a rapid mass transfer of S02 gas to
the hot purge gas stream, resulting in further
- r-gen-ration of the liquid absorbent medium
The ntrained liquid dropl-ts in the flowing gas
tr-am ar- r-oov-d and coal-sc-d by mi~t eliminator 118
and r-g-nerat-d ~olvent is removed from the mist
liminator 118 by line 172 and passes to a regenerat-d
solv~nt holding tank 174 The reg-nsrated solvent,
after cooling by heat exchanger 176, may be passed by
line 178 to regenerat-d solvent feed lin- 44 in Figure
1 Energy r-covered from the r-generat-d solv-nt by
h-at xchang-r 176 may be us-d to provid- at l-ast part
of th- h-at r-quir m nts of solv-nt h-at-r lS0
Altbough th- procedure of Figur- 2 i~ describ-d
Witb r -p ot to oount-rourrent flow of load-d solv-nt
~nd purq- ga- wlth an intermediat- mist liminator 118,
th r- may be ~ploy-d a parallel flow of loaded solvent
to th- dual-fluid nozzles 126, 128 with no mist
~ inator 118, in analogou~ manner to that de~crib-d in
the for-- ntion-d UX pat-nt application No 9123999 ~
for ab orblng th- ~olut- ga~ ~n uch op-ratlon, th-
210~rJ6~
17
duct or ducts in which the regeneration is effected may
be vertical rather than horizontal and the spray nozzles
may be oriented to effect spraying countercurrent to or
co-current with the direction of flow of the gas stream
While two stages of steam stripping are illustrated
in Figure 2, additional stages may be employed, as
desired, depending on the concentration of dissolved gas
in the loaded absorbing medium, the nature of the
absorbing medium, and the degree of r~generation
required
In a closed cycle (absorption-desorption)
operation combining the operations of Figures 1 and 2,
it may be preferred to strip less than 100% of the
absorbed 52 during the regeneration operation from the
absorbing medium as long as this does not have a
deleterious effect on the effectiveness of the absorbing
medium to remove S02 to the desired level from the
incoming gas stream The choice of action may be more a
Sunction oS the absorbing medium, so each situation mu-t
be handl-d as appropriate
In describing the above approach ~pplied
specifically to in-duct scrubbing to remove S02 from
various emitting sources, as depicted schematically in
Figure 1, those skilled in the art can readily perceive
that such an approach results in relativ-ly smaller
equipment than any conventional absorption proc-~s can
adopt Thi~ re~ult infers signiricant advantag-~ wher-
r-troSit applications xi~t a~ w-ll as much mall-r
c~p~t~l n--d- Sor a vari-ty of purposes In addition,
th- liquid-to-ga- ratio u~ed to achieve high removal
SSici-ncy oS the S02 as shown in the absorption
procedure oS Ex~mple 1 is consistently much lower than
; pr-viou-ly Sound in any other system
~he ~ct th~t ~n in-duct absorption proce~ i8 ~o
~ucco~Sul oncourag-d U5 to inve~tigat- th~ u-- o~
imilar t-chnology to perform the Jtripping step which,
21Ql~r~5~
18
in effect, reverses the absorption step ~he basis of
this approach, according to the invention, depends again
on the creation of a very large liquid surface area,
found to be as high as 50,000 ft2 per gallon of liguid
sprayed, in the duct 112 of the desorption apparatus
110 Such generation of a large surface area is coupled
with heating the loaded absorbing medium by steam to a
temperature where the vapour pressure of S02 over the
solvent is sufficient to completely release the S02
under the dynamic conditions of the operation into the
purge stream but below a temperature that would be
deleterious to the absorbing medium The temperature
required to achieve the release of S02 or other solute
gas from the absorbing medium varies be with the
specific reagent used and the solute gas removed and is
limited solely by the stability of the absorbent medium
used This efficient stripping of S02 or other solute
gas from the sorbent medium is effected at relatively
lower steam consumption, shorter exposure time to
l-vated temperature, with consequQnt decreased chemical
oxidation or degradation of the solvent, increased inlet
temperature of sorbent and steam than in conventional
steam stripping operations
In the desorption system of Figure 2, low gas
velocities are employed, equivalent to the amount of S02
generated per unit time plus the amount of low pressure
st-a~ introduced to purge the system plus the amount of
st-a~ ~ploy-d in the dual-fluid nozzl-s to ff-ct
~to~ization Of the loaded and h-ated solvent
A~¢ordinqly, th- ~ize of the stripping equipment (duct
112) can be much smaller than the size of the related
absorption equipment (duct 12) since the total gas flow
through the duct 112 is considerably smaller than that
~lowing through the duct 12
Sp cific solvents may r-quir- more than one stag-
to ff-ct the d-gr-- of r-g-n-ration ~d--orption)
2100r
19
desired in the procedure of Figure 2 While one ~ay
consider employing a higher temperature t~ achieve
better stage-wise separation (desorption), the ability
to proceed in this manner also depends on the stability
of the specific reagent to elevated temperature, as this
relates to oxidation and/or disproportionation of the
solvent or to the formation of heat-stable salts in the
solvent, which must be rQmoved to retain th- ab~orption
capability of the solvent system
In Figure 3, there is illustrated an alternative
and currently preferred stripping operation to that
described with respect to Figure 2, comprising multiple
~erial stages of stripping with multiple spr~y stages in
p~rallel within each stage of stripping This stripping
operation may be integrated with a solute gas removal
operation, such as that described above with respect to
Figure 1
as seen in Figure 3, a stripping apparatus 210
co~prir-- thr-e ~eparate stripping ~tag-s 212, 214, 216
E~ch ~tripping ~tage 21Z, 214, 216 comprising ~n
elongate duct 218 having an inlet 220 for a stea~ purge
stre~J at one end and a mist elimin~tor 222 for removal
and coal-~cence of droplets ~rom the gaseous phase at
the oppo~ite end In the illustrated embodiment, the
ducts 218 ~re oriented horizontally and m~y h~ve a
slight (e g ~bout 1~ downw~rd incline towards the
down~tr-~m nd to f~cilit~te r-mov~l of cond-n-~te from
; th duct 218 How v-r, ~ch or one or more of the duct-
218 ~y b provld-d in ~ vertic~l orient~tion
Withln ~oh duct 218 ~re loc~ted thr-e du~l-fluid
pray nozzl-- 224, 226, 228, which ~re fed in parallel
by ~olv nt g~s lo~ded absorption medium, as well as
t ~o, to for~ spr~ys 230 of very fine liguid dropl-ts
count rcurrent or co-current to t~e flow of the ~to~m
- 35 purg- through the duct 218 One or mor- of th- ~pr~y
nozzl-~ 224, 226, 228 m~y be ~ploy-d p-r ~t~g-,
210~7~
depending on the system requirements The liquid
droplets in such sprays may be sized from about 5 to
about 100 microns, preferably about 5 to about 30
microns The spray nozzles 224, 226, 228 are
illustrated oriented to spray absorption medium
countercurrent to the flow of the purge gas stream in
each duct 218 One or more of such groups of nozzles or
individual members of the groups of nozzles may be
oriented to spray co-current with the flow of the purge
gas stream
Solute gas-loaded solvent is passed from a holding
tank 232 by line 234 through a steam heater 236 and via
line 238 to the series of spray nozzles 224, 226, 228
and into the duct 218 of the first stripping s~age 212
Steam is fed to the dual-fluid spray nozzles 224, 226,
228 in the duct 218 of the first stripping stage 212 by
line 240 At the downstream end of the first stripping
stage 212, the liquid droplets in the gas stream are
coale~ced in the mist eliminator 222 and the resulting
partially-stripped absorbing modium is forwarded by line
242 through heater 244 to parallel feed 246 to the dual-
~luid spray nozzles 224, 226, 228 in duct 218 of the
second stripping stage 214 Steam also is fed to the
nozzles 224, 226, 228 in stripping stage 214 by line
248
Further partially-stripped absorbing medium
collected from mist eliminator 222 at the downstream end
of tho ~-cond stripping stage 214 is p~ssed by line 250
via ~t-am h-at-r 252 to parallel foed 254 to the dual-
fluid pr~y nozzles 224, 226, 228 in duot 218 of the
third ~tripping st~ge 218 Steam is fed to those
nozzlo~ by line 256
The l-~n regenerated solvent is removed by line 258
~rom mi~t eliminator 222 at the downstream end of the
3S third ~tripping stage 216 and p~ssed through ~ cool-r
260 to provide in line 262 a fin~l disch~rge Or cooled
21 Q~76~
21
lean regenerated solvent for utilization in an
absorption operation
The gas exiting the mist eliminators 222 at the
downstream ends of the ducts 218 of the three stripping
stages, comprising steam and S02, passes through ducting
264 to a further mist eliminator 266, which is fed with
hot water showers 268, to ensure that any residual
solvent is removed from the gas stream Liquid removed
from the gases by the mist eliminator 266 passes by line
268 to storage tank 270 for recycle to the showers 268
by line 272
The gas stream exiting the mist eliminator 266
passes by line 274 to a cooler-condenser 276, wherein
the steam component of gas stream is condensed out,
leaving a pure saturated 52 gas stream in line 278 for
recovery The condensed water is removed from the
cooler-condenser 276 by line 280 and normally is added
back to regenerated sorbent to maintain a water balance
EXA~LES
An experimental stripping unit was set up with a
single stage of stripping to test the feasibility of the
stripping procedure and to test the effect of various
parameters on the efficiency of stripping of absorbed
S2 from two agueous amine absorbents, namely
triethanolamine (TEA) and a proprietary amine (PA),
which was a proprietary blend consisting prim~rily of an
aqu-ous ~mine salt solution
In the xperiment~, a single dual-~luid spray
nozzl- wa~ axially located in an insulated, j~cketed
horizontal duct of 12 inches I D and a length of 12
f--t to ~pray co-current with the direction o~ flow of
the purge stream and a chevron-type demister was located
i at the downstream end to remove entrained partially
stripp-d liquid droplets A steam purge stre~m was
3S pa~-d through the duct from the upstre~m ~nd to the
21~Q~- 6~
22
downstream end. Steam also was fed to the dual-fluid
spray nozzle.
The data which has been obtained is set forth in
- the following Table I:
.1
..
, ~ ~
2 ~ 8
~ii-- n i
3 ~ 3 ~ D 3 . .
_ ~i ~ ~ ~ 8888 ____~
_ ~ .... ~ ~io~
~1 ~ R ~ R R r~ ~ R R .~
o ~ o ~ o ~ ~ ~ ~o o~ ~ ~o ~l
~ i ~1~ E~2~ 8-~0~ 2 ~ #
J l ~ tit;tit
_ _ .~ .. ~ .0 .~ .. 0. 0 - ~ e i~ _
2~75~
24
As may be seen from this data, the best single
stripping efficiency obtained was that in Example lo of
50% Attaining this degree of stripping in a single
stage of stripping indicates that substantially complete
stripping is attainable using multiple stripping stages
It is also considered that improved single-stage
stripping can be achieved via an optimization process
From this data, several conclusions can be drawn
with respect to the effect of various variables on the
stripping operation For example, at higher steam
pressures to the nozzles, smaller droplets are produced
and a higher surface area is generated per unit of flow
~his operation improves the efficiency of S02 stripping
at any one temperature large volume nozzles -spraying
high liquid flows use large volumes of steam and may
eliminate or significantly decrease the need for a steam
purge Upon stripping, the highest S02 concentration
occurs approximately 1 to 2 feet downstream from the
nozzle M ans may be provided to rapidly dilute and
disper-e the S02 and thereby decrease the potential for
rQadsorption If steam is employed as this means,
further stripping of the amine is quite likely In
addition, the greater the volume of steam purge, the
greater is the efficiency
A relationship appears to exist between amine
; concentration and S02 loading At any amine
conc-ntr~tion, a higher S02 loading provid-s a more
a-ily tripp d olution and for each solvent there is a
low-r tripping limit which is approach-d
a-y~o trically
~ARY OF ~ISCLOS~RE
In summary of this disclosure, the present
inv ntion provides a novel r-g-neration procedure for
~- ~olut- ga~-load-d liquid absorption media which i-
~mpl- and fS-ctiv- and of low capital cost a~ compar-d
to conv-ntional column-type steam strippers
~Q0~5~
Modifications are possible within the scope of this
invention.
