CA2050927A1 - Method for regenerating particulate adsorbents - Google Patents

Abstract

Method and apparatus for in-situ regeneration of particulate adsorbent in a vessel (11) including: heating the adsorbent, passing inert gas (57) through heated adsorbent to collect vaporized adsorbate (52), chilling the inert gas (47) to condense adsorbate (48), thereafter lowering the pressure within the vessel, collecting withdrawn gases containing volatilized adsorbate (52), and chilling the withdrawn gases (47) to condense adsorbate (48).

Description

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 ;,, 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 SlJ8STlTlJTE SHEET

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WO91/10508 ~ r~ ,~ 7 PCT/US91/00216 :

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 i ' 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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WO 91/10508 r PCI/US91/00216 2 ~

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 SUBSTITUTE SHEET

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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.
'''',' 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.
'' ' ' 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 .. ~
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 .. . .
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 ., 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 2 ~ ~ d;~

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 , 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 i ,; 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 :
;~ 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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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 SUBSTITUTE SHEE~T

, WO 91/10508 2 ~ ?~ ~ PCI/US91/00216 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 . .
tempera~ure for the deslred tlme, the heatlng stage lS
- termlnated and the vacuum stage commences. The valves SUBSTITUTE SHEE~
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WO 91/10508 ~f i~ ! PCI'/US91/00216 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.
, 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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WO 91/10~08 ~ rl ,~ ~' P~/US91/00216 . . 13 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 SUBSTITUTE SH~ET
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, WO91/10508 '~J'~ ;! PCT/US91/00216 14 <.
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 ,", .................................. .
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 i ' ':.-.,, . ~,, SUBSTITUTE SHEET
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;, W0 91/10508 ~ ~ '3 ~ PCI/US91/00216 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, SUBST~TUTE~ SHEET

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W091tlO5~8 ~ 7 PCT/US91/00216 .J ~ `.t ;! ~

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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~.

~E;UBSTITOTE SH~ET
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Claims (7)

1. The method for regenerating a static bed of particulate adsorbent in a container (11) having an inlet conduit (21) and an outlet conduit (15) said particulate adsorbent having adsorbed thereon an adsorbate which lowers the adsorbing efficiency of said particulate adsorbent, comprising:

A. Heating said bed by passing hot inert gas through said bed to an elevated temperature at which said adsorbate has a vapor pressure which is greater than the adsorbate vapor pressure of said adsorbate at ambient temperature;

B. Continuing to pass heated inert gas through said heated bed to entrain volatilized adsorbate;
recovering a first gaseous mixture from said container through said outlet conduit (15) including said inert gas and said volatilized adsorbate;

C. Chilling said first gaseous mixture in a chiller/condenser (47) whereby the said adsorbate is separated from said inert gas;

D While the said bed is at an elevated temperature and when the concentration of said adsorbate in said gaseous mixture indicates a substantially reduced rate of adsorbate desorption, closing said inlet conduit (21) and connecting said outlet conduit (15) through said chiller/condenser (47) to a vacuum source (44) and withdrawing through said outlet conduit (15) a second gaseous mixture containing residual inert gas and devolatilized adsorbate;

E. Passing said second gaseous mixture through said chiller/condenser (47) to separate adsorbate as a liquid from chilled residual inert gas;

F. Continuing to withdraw said second gaseous mixture until the residual adsorbate content of said bed 15 less than a pre-established content and said bed has developed a lowered temperature as a result of the cooling achieved by volatilization of adsorbate from said bed

2. The method of Claim 1 wherein the said particulate adsorbent is activated carbon particles.

3. The method of Claim 1 wherein at least a portion of said inert gas from said first gaseous mixture is recycled through said container.

4. The method of Claim 1 wherein said hot gases are at least in part heated recycled inert gas from said first gaseous stream.

5. The method of Claim 1 wherein said bed is heated by directing electric current through resistance heating elements (61) in said bed.

6. The method of Claim 5 wherein said resistance heating elements are particles of electric-conducting material within said bed.

7. The method of Claim 1 wherein said bed is heated, in part, by introducing microwave energy from a microwave source (62) into said bed.