Note: Descriptions are shown in the official language in which they were submitted.
WO 91/tO508 2 ~ PCI/US91/002t6
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1ETHt)_) FOR RE(~ENERA~ING F'~RTICULATE ADSORBENTS
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' ' TCHNIC L_FIELD
lhls lnventlon concerns an lmproved method for regeneratlng
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partlculate adsorbent and part~cularly tor reqeneratlng
, actlvated carbon adsorbent.
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8ACK_OUNO ART
~ Act1vated c:ar~on 1S a wlde~y-usea aasor~ent ~or removlng
: ~, orqanlc contamlnants from qas streams and llquld streams,
~, herelnafter referreà to collectlvely as ~luld s~reams
Actlvated carbon 15 partlcularly useful ~or ré'movlng orqanlc
contamlnants ~rom fluld streams ln WhlCh the organlc
contamlnants constltute a mlnor portlon ~less than 1~) o~ a
~1 fluld stream. For example: removlng palnt solvents ~rom
,~ ventllatlon ~ases exhausted from palnt spray operatlons;
, ~ recoverlna ~asollne vapors ~rom alr; removlng coo~lnq odor~
; .'.......... causlng lngredlsnts from exhaust aases from ~ltchens;
~ recoverlllg prlntlny ln~ solvents ~rom exhaust ~ases o~
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prlntlnq plants; recoverlng tugltlve or~anlc contamlnants from
.~. the exhaust alr at tan~ farms and transfer pumps ln
strlbutlon termlnals: removlng oraanlc contamlnants from the
exhaust qase~ at coatlng and calenderlng shops Other
~ partlculate a~sorbents are slllca q~el. actlvated alumlna and
.~:. molecular 51 eves.
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WO 91/10508 ~ 7 PCI/US91/~)0216
~11 of these clean-up treatments lnvolve a gas (usually alr~
stream contalnlng varylng amount~, but often less than one
percent by volume of the or~anlc con~amlnant. The
contamlnated gas stream lS dellvered thl-ough a ~ed of
actlvated carbon whlch-adsorbs the organlc contamlnant The
treated gas (usually alr) normally can be dlscharged lnto the
atmosphere or recycled as a strealn contalnlng less than the
prescrlbed quan~lty of the contamlnant Many of the same
types o~ organlc materlals can be removed from waste ~ater or
grouna water Wl th actlvated carbon.
Whlle the expresslon contamlnant lS employed ln thls
speclflcatlon, there are lnstances ln wnlch the adsorbate lS a
valuable materlal to be recovered. The expresslon
contamlnant 1S lntended to refer to the lngredlent whlch lS
present ln the Fluld materlal ~n small quantltles and lS
recovared on the aotlvated carbon as the a~sorbate.
Customarlly the actlvated carbon 1S provlded ln several
vessels whlch cycle through ~a) a wor~lng stage (durlng whlc~
contamlnants are adsorbed on the actlvated carbon) and (b) a
regeneratlon stage (durlng wh ch the adsorbed contamlnants are
removed from the actlvated carbon and the ablllty of the
actlvated carbon to adsorb more contamlnants lS restored). If
the servlce llfe of the actlvated carbon ~s su~flclently long,
the spent actlvated carbon may ~e removed perlodlcally for
reactlvatlon elsewhere, or perhaps dlscarded and replaced.
Vlrgln aotlvated carbon 15 customarlly provlded as screened
partlclec, usually 1~8 lnch to 3~8 lnch slze, or as pellets of
slmllar slze ~ctlvated carbon lntended ~or use Wlth llqulds
~s usually smaller, e g ~ 1.0 to 1.5 mm dlameter. The vlrgln
actlvated car~on has a larye surface area per unl~ welght.
Thls surface area lS avallable for adsorblng organlc
con~amlnants. ~s the organlc contamlnants are adsorbed on the
actlvated carbon, the remalnlng surface area avallable for
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WO91/10508 ~ r~ ,~ 7 PCT/US91/00216
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turtner aasorptlon decreases and the effectlveness of the
actlvated car~on lS reduced The spent actlvated carbon lS
regenerated or replaced when lts effectlveness has reac~ed a
pre-determlned mlnlmum acceptable value. The mlnlmum
accepta~le value wlll be determlned by the requlrements of the
nstallatlon, e.g , the allowablP contamlnan~ content of the
scharged gas.
There are several commerclal rsgeneratlon procedures. In some
lns~allatlons the spent actlvatea carbon lS removed from the
vessel and lS replaced wlth vlrsln actlvated carbon or Wl t~
off-slte regenerated actlvated carbon or Wlth a mlxture of
~ot~. Replacement wlth vlrgln actlvated c~rbon lS costly bUt
may be Justlfled ~f substantlalIy total contamlnant removal lS
requlred. Movement of the actlvated carbon off-slte results
ln transportatlon costs, labor costs and partlcIe a~raslon and
degradatlon, producln~ flnes whlch must ~e screened from the
regenerated actlvated carbon. Regeneratlon off-slte lS
usually accompllshed by heatlng the spent actlvated carbon ln
a Furnace or ~lln, wlth steam belng lntroduced to create a
sultable atmosphere. 7he regeneratlon gases burn some of the
adsorbed contamlnants, and also burn some of the actlvated
carbon wlth the result that there lS less actlvated car~on
and7 more lmportantly, the resldual actlvated car~on commonly
has a lower adsorptlon capaclty ~nd lS a less e,fflclent
adsorbent than vlrgln actlvated carbon, and may be un~eslrabIy
soft and dusty. There are also ~nown l n-~ tu regenerat1on
procedures uslng steam and/or hOt gases to devolatlll~e
adsorbate.
DISCLOSURE OF THE INVENTlON
~ccordlng to the preferred embodlment, the regeneratlon l S
carrled out ~n Sl tU, 1.e , ln the same vessel, WlthOUt
removlng the spent actlvated carbon Thls preferred
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embodlment lS partlcularly useful when the duty cycle of tne
unlts lS short, e~g., 30 mlnutes to several wee~s.
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In general the regenerated actlvated carbon never achleves the
adsorblng capaclty and effectlveness of the vlrgln actlvated
car~on because there lS some resldual aasorbate whlch reslsts
separatlon from the actlvated carbon regardless of the
regeneratlon procedure. Thls lS eSpeClally common Wlth lJ7
sltu steam-regenerated actlvated carbon, where practlcal
conslderatlons usually demand that steamlng the actlvated
carbon be curtalled before the resldual adsorbed substances
(those ~n the nlghest adsorptlon energy portlons of tne
adsorbent structure) are removed.
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In many actlvated carbon treatment processes, t~e regenerated
actlvated carbon has ltS effectlveness reduced to such a level
that the system cannot satlsfy demandlng contamlnant removal
requlrements ln suhsequent cycles, and thus regenerated
actlVated carbon cannot meet the requlrement at all or can
meet the requlrement for only uneconomlcally brlef cycles.
~ novel apparatus and method for regeneratlng actlvate~ carbon
employs a heatlng stage and a vacuum stage as essentlal stages
n the regeneratlon process for actlvated carbon Flrst: A
bed of spent actlvated carbon lS heated ln a vessel to
ncrease the temperature and cause substantlal desorptlon of
adsorbate (generally organlc materlals) through adsorbate
volatlllzatlon. A flow of lnert gas (l.e , free of oxl~ants~
lS malntalned through the ~ed of actlvated carbon durlng the
heatlng stage to avold combustlon of the adsorbate and to
avold com~ustlon o~ the actlvated carbon. The lnert gas
car-rles out the volatlllzed adsorbate for separate recovery.
Ihe lnert gas contalnlng the volatlllzed adsorbate lS chllled
below the aew polnt Of the adsorbates and the resultlng
condensed adsorbates are recovered as a llquld phase ~rom the
chllled lnert gas Secona: ~fter a slgnlflcan~ portlon of the
a~sorbed adsor~ate lS desorbed ln the heatlng stage, the
vessel lS sealed and evacuated~ The reduced pressure wlthln
the vessel causes further desorptlon as the vapor pressure of
the adsorbed adsorbate approaches or exceeds the reducad
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pressure wlthln the vessel. The wltndrawn lnert gas
contalnlng desorbed adsorbate lS chllled and the contamlnants
are recovered as a llqu d. Durlng the second stage, the
heated actlvated carbon becomes cooled as the adsorba~es are
desorbed and volatlllzed Coolln~ results from the heat of
vaporlzatlon requlred by the volatlllzed materlal Because
reheatlng the bed to supply la~ent heat lS a relatlvely qulc~
procedure, and re-evacuatlon of the bed 1S a relatlvely qulc~
procedure, the desorptlon stages may ~e repeated lf requlred
by the nature of the a~sor~ates
The resultlng regenerated actlvated carbon lS restored to a
greater adsorblng capac~ty and efflclency ~han regenerated
actlvated carbon obtalned by other types of regeneratlon,
Because the regenerated actlvated carbon has greater adsorblng
efflclency, the system can satlsfy more aeman~lng adsorbate
separatlon requlrements. By uslng multlple parallel vessels
contalnlng actlYated carbon, lt lS feaslble, wlth the present
regeneratlon method1 to malntaln a nlgh level of adsorptlon
efflclency by regeneratlng the actlvated carbon before lts
adsorptlon efflclency lS serlously dlmlnlshed.
The adsorbate may ~e collectea as a llquld for recovery or for
dlsposal. ~lternatlvely, a gas stream contalnlng an lncreased
concentratlon of the desorbed adsorbate may be,wlthdrawn from
the system for flarlng or burnlng or other alsposal or
recovery as a gas stream.
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The two-stage regeneratlon process also can be employed ln
off-slte or moblle regeneratlon of spent'actlvated oarbon.
Off-slte or moblle regeneratlon can be consldered when the
duty cycle of the system 1S relatlvely long, e.g.; from
several days to several months
~he regeneratlon lnven~lon can be applled to processes for
treatlng gas streams Wlth actlvated carbon and also for
treatlng llquld streams wlth actlvated carbon. ~he term
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fluld lS employed ln thls speclflcatlon and clalms to
. lndlcate a gas or a llquld Wlth llquld treatment
, lnstallatlons, the actlvated carbon should be drled before
-~ commenclng regeneratlon
T~e regenerat on system iS of especlal lnterest wlth actlvated
carbon as the aasorbent However the method and operatlon are
useful for regeneratlng other partlculate adsorbents such as
: slllca gel, actlvated alumlna and molecular sleves.
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DESCRIPTION OF THE DRAWINGS
:. Flgure I 1S a schematlc lllustratlon of three vessels
contalnlng granular actlvated carbon for use ln
removlng organlc contamlnan~s from a gas stream.
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, Flgure 2 lS a schematlc lllustratlo~ of one of the vessels
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from Flgure 1 showlng perlpheral apparatus For
regeneratlng spent actlvate~ carbon.
FlgUre 3 lS a schematlc vlew of an alternatlve embodlment of
the perlpheral apparatus of Flgure 2.
Flgures 4 and 5 are schematlc lllustratlons of al~ernatlve
. , embodlments of an actlvated carbon vessel of
the type lllustrated ln Flgure 1.
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i ' F19Ure 6 lS a graphlcal presentatlon showlng the adsorptlon
:~ j capaclty (welght percent) of actlvated carbon For
, ;.! acetone accordlng to the partlal pressure of acetone
n the vessel at three temperatures.
, . ~ F19Ure 7 lS a graphlcal presentatlon, slmllar to Flgure 6,
for Freon-ll.
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- BEST MODE OF C~RRYING OUT THE INVENTION
Referrlng to Flgure 1, there lS lllustrated a contamlnated gas
source 10 and three vessels 11,12,13, each contalnlng a bed of
partlculate actlvated carbon Contamlnated gas from the
source 10 lS dellvered through one (or more) o~ the vessels
11712,13. Clean, low contamlnant content gas 15 exhausted
from the vessels 11,12,13 through an exhaust condult 14 ln
one em~odlment, one of the vessels (e g., vessel 1~) s on-
s~ream and connected to the gas source 10 and the exhaust
condult 14; the other two vessels (12,13) are experlenclng
- regeneratlon. In another embodlment, two of the v0ssels
(e.g., vessels 11,12) may be on-stream and connected to the
gas source 10 ln parallel and to t~e exhaust condult 14, whlle
the thlrd vessel 13 lS experlenclng regeneratlon. In a stllI
further em~odlment, two of the vessels ~e.g., vessels 11,12
may be connected ln serles whereby the gas from source 10
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passes through a flrst YesSel (e.g., vessel 11) and tnence
through a seoond vessel (e.g., vessel 12) and thence to the
exhaust condult 14, whlle the remalnlng vessel 13 lS
experlenclng regeneratlon.
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Three vessels have ~een lllustrated ln Flgure 1 ln an
lnctallatlon The deslgn of a commerclal lnstallatlon may use
a slngle vessel or multlples of vessels. Where a slngle
vessel lS employed, gas treatment lS termlnated whlle the
51 ngle vessel lS regenerate~.
~he three vesselst 11,12,13 of Flgure 1 are each connected to
the contamlnated gas source 10 by means af condults 15,16,17
havlng valves 18,19,20 respectlvely. Each vessel 11,12,13 }s
.
connected to the gas exhaust condult 14 through condu~ts
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21r22,23, each contalnlng a valve 24,25,26 respectlvely Each
outlet condult Zl,22,23 has a by-pass condult 27,28,29
respectlvely whlch accommodates serlal operatlon of the
vessels llv12,13. For example, the vessel 11 may nave lts
dlscharge stream aellvered through t~e condult 27 and a
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WO91/10508 PCT/US91/Oa216
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condult 30 lnto the con~ult 1~ to the vessel 12; alternatlvely
the dlscharge ~rom the vessel 11 may be dellvered through the
condUlt 27 ana a condult 31 lnto the condult 17 to the vessel
13 ~he exha~st gas from the vessel 12 may be dellvered
through the condult 28 and a condult 32 lnto the condult 15 to
the vessel 11; alternatlvely the exhaust gas ~rom vessel 12
may be dellvered through condult 28 and a condul~ 33 lnto the
condult 17 to the vessel 13 Slmllarly the exhaust gas from
the vessel 13 may be dellvered $hrough con~ult 23 ana condult
29 to a con~ult 34 1nto condult 16 to vessel 12; alternatlvely
the exhaust gas from vessel 13 may be dellverea through
condult 23 and condult Z9 to a condult 35 lnto condult 15 to
the vessel 11 It should be notea that approprlate valves
30a,31a,32a,33a,3~a and 35a are provlded ln the conaults
30,31,32,33,34 and 35 respectlvely
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Regeneratlon condults 36,37,38 are oonneoted to the vessel
oondults 21,22,Z3 respeotlvely and through valves 36a,37a and
3~a respectlvely to a gas oondult ~ whlch 15 more fully
explalned ln flgure 2 Slmllarly regeneratlon condults 39,40
and 41 are connected to the vessel condults 15,16,17
respectlvely and are also connected through valves 39a,40a,41a
respectlvely to a regeneratlon condult B whlOh lS more fully
explalned ln Flgure 2.
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ONE ~ESSEL ON-STRE~M
I~ vessel 12 lS on-stream, the valves 19 and 25 wlll be open
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,; and valves 30a,32a,33a,34a,37a and 40a wlll be olosed.
Conourrently, wlth respect to vessel 11 w~lch lS eXperlenCln9
regeneratlon, the valves 18,24,30a,31a,32a and 35a wlll be
- closed and the valves 36a,39a wlll be open Slmllarly ~or the
vessel 13 whloh lS experlenclng regeneratlon, the valves
20,26,31a,33a,34a and 35a wlll be closed and the valves
;~; 38a,~1a wlll be open.
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WO91/10508 ~ PCT/US91/00216
PARALLEL OPER~TIONIf the Yessels 12rl3 are operatlng on-stream ln parallel, the
valves 19~20,25,26 wlll be open The valves
18724,30a,31a,32a,33a,34a,37a,38a,40a and 41a wlll be closed.
SERI~L OPERATI ON
If the vessels 11, 13 are operatlng serlally Wlth ~he
contamlnated gas flowlng lnltlally through the vessel 11, the
valves 18,31a and 26 wlll be open The valves
19~20,24,25,30a,32a,33a,34a,35a,36a,3~a,39a and 41a wlll be
closed ln thls embodlment, the contamlnated gas ~rom source
10 wlll ~low through conault 15, vessel 11, condult 21,
condult 27, condult 31, condult 17, vessel 13, condult 23 and
e~haust gas condult 14.
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REGENERATION
ln Flgure 2 the vessel 11 lS lllustrated as experlenolng
regenerat~on. The valves 36a,39a are open and all of the
other valves are olos~d, namely, 18,Z4,30a,31a,32a, and 35a.
Thus the vessel 11 1S oonnected to the regeneratlon apparatus
ndlcated generally by the numeral 42 whlch connects to
re9eneratlOn COnaUlts f~.i ,E3; . f~S lndloated by the t>ro~en llnes
43A,43b, the regeneratlon oondults A and ~; are conneoted.
The regenerat~on equlpment 42 lncludes a neat sxchanger 43, a
vaouum pump 44, a gas pu~p 45, a source 46 of inert gas, a
chliler/conaenser 47, a llqula oondensate oollectlon tan~ 48
and a source 49 of hOt lnert gas whlch may be flue gas1 steam
or oombUstlon gases.
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i ST~GE I
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The vessel 11, prlor to regeneratlon, oontalns a ~ed of
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;~ aotlvated oarbon havlng aasorbed thereon slgnlflcant
quantltles of adsorbate, usually a 'contamlnant . The gas
pressure ln vessel 11 15 reduced by operat~ng the vacuum pump
4 Gas and desor~ed contamlnants are drawn through condults
B, Bi and the chlller/condenser 47. Contamlnants are
con~ensed and recovered through condult 51 and collected ln
.
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WO91/10508 ~ r~ti PCT/US91/00216
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tan~ 48. Non-condensed gas lS vented through the vacuum pump
44 and an exhaust condult 44a Thls prellmlnary stage removes
alr tlf any~ from the vessel ll prlor to the heatlng state.
Durlng the heatlng stage of the regeneratlon cycle lnert gases
from an lnert gas source 46 or 49 are dellvered through a
COnaUlt 55 and a heat exchanger 43 to the regeneratlon condult
A; and tnence through the regeneratlon condult ~ lnto the
vesse~ ll where the lnert hot gases lncrease the temperature
of the vessel contents and cause desorptlon of the
contamlnants through devolatlll~atlon Hot lnert gases
contalnlng volatlllzed contamlnants are drawn from the vessel
ll throu~h the conaults 15,39,B and 8; by the gas pump 45
The hOt lnert gases contalnlng contamlnants are drawn through
the chlller/condenser 47 whlch lowers the temperature of the
nert gas pre~erably below the dew polnt of the contalned
contamlnants. The chllled contamlnants condense wlthln the
chlller~condenser 47 and oan be co~lected as a condensed
qu~d through a condult Sl ln' the conaensate oollectlon tank
48. Chllled gases, substantlally ~ree of the contamlnants,
are recovered from the chlller/condenser 47 through a conau
52 and dellvered alternatlvely to a recycle pump 4S or to a
vacuum pump 44 through condults 53,54 respectlvely. Valves
S~a,54a are provlaed ln condults 53,54 respectlvely. Durlng
the heatlng stage, the valve 53a lS open, the valve 54a lS
closed and the vacuum pump 44 lS not ln servlce. rhe vacuum
pump 44 may be connected to other regeneratlng vessels, not
shown ln Flgure 2. The chllled lnert gas lS dellvered through
the recycle pump 45 through a condult 55 to the heat exchanger
43. The reoycled lnert gas lS heated ln the heat exchanger 4
to a deslred temperature and recycled through regeneratlon
condults A',A to the vessel ll to contlnue heatlng or to
malntaln the selected regeneratlon temperature ln the vessel
ll. Some of the chllled recycle gas may be exhausted through
the conault 54 and valv~- 54a Corresponalng ma~e-up lnert gas
may ~e added to the recycle gas stream from the gas source 49
through the condult 50 and valve SOa. ~ddltlonal ma~e-up
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WO 91/10508 2 ~ ?~ ~ PCI/US91/00216
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lnert gas from a source 46 may ~e lntroduced lnto the recycle
stream condult 55 through a condult 56 and valve 56a. Thermal
energy may be trans~erred ~etween heat exchangers, e.g., the
chlller/condenser 47 and the heat exchanger 43 to pre-heat or
to pre-chl11 gases for overall energy conservatlon.
The descrlbed heatlng and movement o~ recycled lnert gas
through tne vessel 11 contlnues untll t~e deslre~ temperature
lS achleved and malntalned wlthln the vessel 11. Typlcally
the actlvated carbon bed ln the vessel 11 wlll be heated to a
selected temperature ln the range of 100-~00 Fahrenhelt.
The exact temperature w~ epend upon the aeslre~ level o~
regeneratlon and the speclf lC adsorbates on the actlvated
carbon. Two typlcal adsorptlon capaclty charts are provld~d
as log-log plots ln Flgure 6 and 7. Flgure 6 shows the
adsorptlon capaclty of acetone on actlvatsd car~on~ It wlll
be seen that actlvated carbon contalnlng ~!0 percent by welght
acetone at 100F presents a partlal pressure of 0.25 pSl
~polnt ~, Flgure 6). I~ the temperature lncreases at the same
pressure to 300F, the acetone wllI constltute only about 1.3
welght percent o~ the actlvated carbon (polnt B, Flgure 6).
~t 200F at tne same pressure, the acetone wlll comprlse about
7 percent of ~he welght of the actlvated carbon (polnt C,
Flgure 6). Thus lt can be seen that elevatlng the temperature
of the actlvated carbon bed wlll cause substantlal desorptlon
of acetone. The same prlnclple appl es to other adsorbates.
Note that for Freon-ll, Flgure 7, at 70F, actlvated carbon
contalnlng 30 percent by welght Freon-ll, exhlblts (polnt D,
Flgure 7) a partlal pressure of 0.09 p51. I~ the temperature
lS lncreased at the same pressure to 170F, the adsorbed
Freon-ll wlll drop to 14 percent by welght (polnt E, Flgure
7).
V~CUU~ STAGE
~ter the vessel 11 Flgure 2, has achleved the deslred
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tempera~ure for the deslred tlme, the heatlng stage lS
- termlnated and the vacuum stage commences. The valves
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36a,50a,53a and 56a are closed The valves 54a and 39a are
opened The vessel 11 thus lS connected dlrectly to ~he
vacuum pump 44 through the condults 15,39,B, and B'~ the
chlller/condenser ~7, condu}ts 52 anà 54. The gases from the
lnterlor of the vessel 11 are chllled ln ~he chlller/condenser
47 causlng t~e contamlnant to condense for collectlon ln the
condensate collector vessel 48 The contamlnant-depleted
nert gas from the chlller/condenser 47 passes through the
condults 52,54 ana lS exhausted through tne vacuum pump 44 and
exhaust condult 44a. The vacuum stage contlnues untll the
sub-atmospherlc pressure wlthln the vessel 11 achleves a pre-
determlned level ~s the aasorbate lS volatlllzed aurlng the
vacuum stage, the latent heat for adsorbate volatlllzatlon lS
supplled from the sensl~le heat of the actlvated carbon
causlng the bed temperature to drop.
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The reduced pressure ln the vessel 11 aurlng the vacuum stage
lowers the amount of a~sorbed contamlnant ln the actlvated
oarbon be~. For acetone, the amount of acetone at 0.01 pSl
partlal pressure and 300F lS 0 46~ (polnt F, Flgure 6) ~t
0.001 pSl partlal pressure and 200F, the amount of aoetone lS
0 68% ~po~nt G~ Flgure 6). Slmllarly, Wlth Freon~ll as
adsorbate, the aasor~ed Freon-ll at 0 001 pSl partlal pressure
and 170F lS 2 4% (polnt H7 Flgure 7) At the same 0 001 pSl
partlal pressure at 70F, the adsorbed Freon-ll 'lS 7.8% ~pOlnt
I, Flgure 7~
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It should be noted that by constantly encouraglng removal of
vaporlzed adsorbate from the adsorbent, the vacuUm pump 44
performs a ~unctlon whlch s slmllar a large flow of purge
gas That 1S, the vaouum pump depletes the absolute pressure
of the vaporous materlals and thus promotes su~stantlal
adaltlonal aasorbate vaporlzatlon by unbalanclng the ratlo of
adsorbed:~esorbed adsorbate In addltlon, when compared wlth
the use of steam or other purge gas for regeneratlon, the
vacuum pump 44 offers a substantlal beneflt by removlng the
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adsor~ate ln an undlluted form ln a gaseous stream o~
comparatlvely small volume
The vacuum stage lS ended wnen the regeneratlon has proceed&d
to the deslred extent 7he resultlng rsgenerated actlvated
carbon may not be as e~flclent as vlrgln actlvated carbon and
may not have the full adsorptlon capaclty o~ vlrgln actlvated
carbon, bu~ lS superlor to regenerated actlvated carbon
resultlng fro~ prlor art regeneratlon proceaures Repeated
cycllng thro~gh a heatlng stage and a vacuum stage can restore
the actlvated carbon to near-vlrgln quallty
:',.
preferred lnstallatlon lS lllustrated ln Flgure 1 lncludlng
three vessels 11,12,13. The lncomlng gas stream from the
source 10 passes sequentlally through two of the vessels,
e.g., vessel 11 an~ then vessel 12. Substantlally
contamlnant-~ree exhaust gas lS reoovered from the exhaust gas
oon~ult 14. The lnltlal vessel 11 Wlll approach adsorptlon
; capaclty lnltlally ~ecaUse the actlvated carbon ln the lnltlal
vessel 11 wlll adsorb most of the contamlnants from ~he source
10, l.e.~ the gas stream ln condults 21,27~30~16 wlll have a
slgnlflcantly lower contamlnant content than the contamlnated
gas from the source 10. When the actlvated carbon ln the
- vessel 11 reaches the establlshed capaclty, the gas stream
flow 1S shlfted to vessel 12 as the lnltlal vessel and to
vessel 13 as the sequentlal vessel. The vessel 13 oontalns
regenerated actlvatqd carbon of near-vlrgln quallty. ~t thls
; tlme the vessel 11 lS su~ected tv the regeneratlon stage.
When the vessel lZ reaohes lts establlshed capaclty, another
cycle lS oommenoed wlth the gases from the source 10 passlng
.
nltlally t~rough the vessel 13 and thereafter through the
vessel 11, whlch then oontalns regenerated actlvated carbon of
near-vlrgln quallty. Durlng thls cycle, the vessel 12 lS ln
the regeneratlon stage.
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The duratlon of each cycle wlll depend upon the slze of the
actlvated carbon ~eds ln vessels 11,12,13 and upon the
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concentratlon of the contamlnants }n the gas source lO. Tha
present system lS lntended for use Wlth low contamlnant
streams such as streams contalnlng about one percent or less
of the organlc contamlnant (by volume~ whlch lS to be removed
ln the sequentlal treatment7 the gas stream exlts from the r
system through a vessel whlch has been most recently
regenerated and whlch contalns actlvated carbon of near-vlrgln
quallty so that the adsorptlon efflclency of tl-e actlvated
car~on lS hlgh
A varlety of means ~or heatlng the actlva~ed carbon bed durlng
regeneratlon are avallable. ~s shown ln Flgure 2, the
recycled gases may be heated ln a heat exchanger 43 whlch
typlcally wlll contaln steam, flue gas, hot water, hot oll or
electrlcally-heated COllS as a souroe of hsat The hot gases
n t~e regeneratlon con~ult A' surrsnder thelr senslble hsat
to ths aotlvated oarbon bed ln the vessel ll. ~lternatlve
embodlmen~s ln Flgures 3,4,S ellmlnate the heat exohanger (43
o~ Flgure 2) and lnstead provlde for lnternal heatlng of the
aotlvated carbon bed. In Flgure 3 one or more electrloal
reslstance heatlng elements 58 are mounted wlthln the vessel
. The electrlcal heatlng elements 58 are connecte~ to a
trans~ormer 59 by electrlcal conductors 60. In order to ~eat
the contents of the vessel 11, the transformer 59 lS actlvated
and electrlcal energy lS converte~ to heat lnside the vessel
ll. The vessel ll should contaln lnert gas durlng the heatlng
phase to avold oxldatlon and posslble exploslon. The lnert
gas may be recyoled contlnuously through the chlller 47 and
recycle pump 45. ~lternatlvely the lnert gas may be
malntalne~ wlthln the vessel ll untll the daslrea temperature
has been achleved. Thereafter the lnert gas may be recycled
through the vessel ll, chlller 47 and recycle pump 45
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Flgure 4 lllustrates an embo~lment of the lnventlon requlrlng
a speclal actlvated carbon materlal whlch contalns
slectrlcally conductlve materlals such as lron flllngs, lron
., oxlde or other metals whlch conduct electrlclty, ana whlch are
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dlspersed throughout the actlvated carbon bed The conductorsmay be dlscrete partlcles, dlstlnct from the actlvated carbon
partlc1es ~lternatlvely the actlvated carbon may contaln as
a homogeneoUs dlsperslon wlthln each actlvated carbon par~lcle
an approprlate quantlty of the electrlcally con~uctlve
materla1 In the embodlment of Flgure 4, the electrlcal
energy can be dell~ered through the actlvated carbon bed
~etween a palr of electrodes 61 whlch are connected to a
transformer 59 by means of conauctors 60 Thls embodlment
uses the eleCtrlCal reslstlvlty of the bed to generate t~e
necessary heat. ~ hlS form of lnalrect heatlng avolds the nesd
for multlple electrlcal reslstance heaters of the type
ustrated ln Flgure 3 as elements 58~
ln Flgure 5 a mlcrowave generator 62 provldes electromagnetlc
waves whlch can be dellvered to the vessel 11 tnrough an
approprlate wave gulde 63. The contents of tne vessel 11 are
thUs heated by mlorowave energy. Procedures for mlorowave
heatlng materlals are d~scrlbe~ ln U.S. Patent 4,103,~31.
Throughout the speclflcatlon, the term "lnert gas" lS lntenaed
to ldentlfy any gas stream whlch lS substantlally free of
oxlaants and substantlally free of any gaseous lngre~lents
WhlCh wlll chemlcally react Wlth actlvated carbon or the
materlals whlch are adsorbed on the actlvated carbon or the
materlals of constructlon of the vessels, condults and other
processlng components. A preferred lnert gas lS nltrogen
whlch can be supplled from gas tan~s, e.g., the tank 46
11ustrated ln Flgure 2. Alternatlvely the lnert gas may be
carbon dloxlde. Flue gases from combustlon lnsta11atlons suc~
as furnaces or ~urners are acceptable lnert gas and may he
supplled from a source 49 as hot gas~
OPERATION WITH LIQUIDS
Whlle ~he examples ln thls speclflcatlon have ll1ustrated the
treatment of gases to remove contamlnants, the regeneratlon
procedure lS effectlve for treatlng spent actlvated carbon,
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regardless of whether the re~oval system treats llqulds or
gases The spent carQon should be drled by passlng ~arm gas
through the wet bed prlor to commenclng the regeneratlon
cycle,
EX~PLE
~ssume a gac~ stream contalnlng 3,000 ppm ben~ene aS a
temperature of lOO~F The total benzene content lS 1230
pounds per day Two vessels, each contalnlng about 3000
pounds of actlvated car~on can accompllsh t~e recovery
requlrement
In order to regenerate a ~essel, a vacuum lS applled to remove
alr from the system for about one-half hour. The system lS
refllled wlth nltrogen gas, approxlmately 400 CU~lC f~et. The
nltrogen gas lS heated to 325F and recycled through the unlt
for a~out one-and-one-half hours untll the unlt reaches a
temperature of aboUt 225F. The nltrogen recycle rate lS
approxlmately 1500 oublc ~eet psr mlnute or about 80 pounds
nltrogen gas per mlnute.
A c~ er lS operated to condense the benzene for abcut one-
half hour. Thereafter the gases are evacuated whlle the
chlller contlnues to operate for about one-half hour The
total regeneratlon procedure requlres about 3.25 to 4 hours.
OFF-SITE ~PER~TION
The examples lllustrate regeneratlQn on-slte. Under some
clrcumstances~ lt may be deslrable to alsOonnect a vessel
whlch requlres regeneratlon and to transport the vessel or the
spent actlvated carQon to an off-slte locatlon contalnlng the
eqUlpmellt lllustrated ln Fl9Ure 2. Af ter regeneratlonJ the
vessel 15 returned to the operatlng slte. Thls procedure lS
of especlal value when the adsorptlon cycle lS long, e~g.,
more than about a wee~.
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