CA2100768A1 - Stripping and method and apparatus - Google Patents
Stripping and method and apparatusInfo
- Publication number
- CA2100768A1 CA2100768A1 CA002100768A CA2100768A CA2100768A1 CA 2100768 A1 CA2100768 A1 CA 2100768A1 CA 002100768 A CA002100768 A CA 002100768A CA 2100768 A CA2100768 A CA 2100768A CA 2100768 A1 CA2100768 A1 CA 2100768A1
- Authority
- CA
- Canada
- Prior art keywords
- conduit
- gas
- gas stream
- solute
- liquid droplets
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
- B01D53/1425—Regeneration of liquid absorbents
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B17/00—Sulfur; Compounds thereof
- C01B17/48—Sulfur dioxide; Sulfurous acid
- C01B17/50—Preparation of sulfur dioxide
- C01B17/60—Isolation of sulfur dioxide from gases
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Analytical Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Health & Medical Sciences (AREA)
- Environmental & Geological Engineering (AREA)
- Inorganic Chemistry (AREA)
- Biomedical Technology (AREA)
- Gas Separation By Absorption (AREA)
- Treating Waste Gases (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Solute gas-rich absorbing media formed in scrubbing a solute gas from an off-gas stream prior to discharge of the same are regenerated to solute-lean absorbing medium for recycle to the scrubbing operation. Hot rich absorbing media is formed into one or more spray patterns of very small liquid droplets in a flowing purge steam stream in an elongate conduit into which the solute gas is desorbed from the droplets. The droplets are coalesced to form a regenerated absorption medium, the solute gas-containing gas stream is cooled to condense out the steam and a pure solute gas stream is recovered. The operation may be effected in multiple stripping stages, which may comprise countercurrent flow of solute gas laden absorbing medium and purge steam within a single conduit or in multiple conduits.
Multiple stripping steps may be effected within a single stripping stage.
Solute gas-rich absorbing media formed in scrubbing a solute gas from an off-gas stream prior to discharge of the same are regenerated to solute-lean absorbing medium for recycle to the scrubbing operation. Hot rich absorbing media is formed into one or more spray patterns of very small liquid droplets in a flowing purge steam stream in an elongate conduit into which the solute gas is desorbed from the droplets. The droplets are coalesced to form a regenerated absorption medium, the solute gas-containing gas stream is cooled to condense out the steam and a pure solute gas stream is recovered. The operation may be effected in multiple stripping stages, which may comprise countercurrent flow of solute gas laden absorbing medium and purge steam within a single conduit or in multiple conduits.
Multiple stripping steps may be effected within a single stripping stage.
Description
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"
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 ~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~, 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 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~
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~
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~
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~
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 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 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~
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~
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~
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.
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 ~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~, 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 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~
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~
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~
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~
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 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 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~
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~
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~
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.
Claims (18)
1. 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 microns, (c) desorbing dissolved solute gas from said liquid droplets of absorbing medium into said flowing gas stream, (d) agglomerating said liquid droplets at said downstream end of said conduit to remove entrained liquid droplets from said gas stream to form an at least partially regenerated aqueous absorbing medium, and (e) discharging a gaseous mixture comprising solute gas and steam from said downstream end of said conduit and recovering said solute gas from said gaseous mixture.
(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 microns, (c) desorbing dissolved solute gas from said liquid droplets of absorbing medium into said flowing gas stream, (d) agglomerating said liquid droplets at said downstream end of said conduit to remove entrained liquid droplets from said gas stream to form an at least partially regenerated aqueous absorbing medium, and (e) discharging a gaseous mixture comprising solute gas and steam from said downstream end of said conduit and recovering said solute gas from said gaseous mixture.
2. The method of claim 1, wherein said absorbing medium is injected into said conduit from at least one dual-fluid spray nozzle disposed in said conduit and to which steam is fed to effect atomization of said absorbing medium to form said spray pattern.
3. The method of claim 2, wherein said absorbing medium is injected directly into said flowing gas stream to form a plurality of said spray patterns in said conduit which do not substantially overlap one another.
4. The method of claim 2 which is effected to form a partially-regenerated aqueous absorbing medium, and including:
(i) injecting said partially-regenerated aqueous absorbing medium into a further elongate conduit through which passes a flowing gas stream comprising steam, by atomization from a dual-fluid nozzle in said further conduit using steam to form a spray pattern of the partially-regenerated aqueous absorbing medium in said further conduit containing liquid droplets ranging in size from about 5 to about 100 microns, (ii) desorbing dissolved solute gas from said liquid droplets of partially-regenerated absorbing medium into said flowing gas stream, (iii) agglomerating said liquid droplets at said downstream end of said further conduit to remove entrained liquid droplets from said gas stream to form a regenerated aqueous absorbing medium, and (iv) discharging a gaseous mixture comprising solute gas and steam from said downstream end of said further conduit and recovering said solute gas from said from gaseous mixture.
(i) injecting said partially-regenerated aqueous absorbing medium into a further elongate conduit through which passes a flowing gas stream comprising steam, by atomization from a dual-fluid nozzle in said further conduit using steam to form a spray pattern of the partially-regenerated aqueous absorbing medium in said further conduit containing liquid droplets ranging in size from about 5 to about 100 microns, (ii) desorbing dissolved solute gas from said liquid droplets of partially-regenerated absorbing medium into said flowing gas stream, (iii) agglomerating said liquid droplets at said downstream end of said further conduit to remove entrained liquid droplets from said gas stream to form a regenerated aqueous absorbing medium, and (iv) discharging a gaseous mixture comprising solute gas and steam from said downstream end of said further conduit and recovering said solute gas from said from gaseous mixture.
5. The method of claim 4 wherein said conduit and said further conduit comprise a single contiguous conduit with said further conduit being located upstream of said conduit with respect to said flowing gas stream, and said flowing gas stream passes from the upstream end of said further conduit to the downstream end of said conduit.
6. The method of claim 2 which is effected to form a partially-regenerated aqueous absorbing medium, and including:
(i) injecting said partially-regenerated aqueous absorbing medium into a further elongate conduit through which passes a flowing gas stream comprising steam, by atomization from at least one dual-fluid nozzle in said further conduit using steam to form a spray pattern of the partially-regenerated aqueous absorbing medium in said further conduit which contains liquid droplets ranging in size from about 5 to about 100 microns, (ii) desorbing dissolved solute gas from said liquid droplets of partially-regenerated aqueous absorbing medium in said spray pattern into said flowing gas stream, (iii) agglomerating said liquid droplets at said downstream end of said further conduit to remove entrained liquid droplets from said gas stream to form a further partially-regenerated absorbing medium, and (iv) discharging a gaseous mixture comprising solute gas and steam from said downstream end of said further conduit and recovering said solute gas from said gaseous mixture.
(i) injecting said partially-regenerated aqueous absorbing medium into a further elongate conduit through which passes a flowing gas stream comprising steam, by atomization from at least one dual-fluid nozzle in said further conduit using steam to form a spray pattern of the partially-regenerated aqueous absorbing medium in said further conduit which contains liquid droplets ranging in size from about 5 to about 100 microns, (ii) desorbing dissolved solute gas from said liquid droplets of partially-regenerated aqueous absorbing medium in said spray pattern into said flowing gas stream, (iii) agglomerating said liquid droplets at said downstream end of said further conduit to remove entrained liquid droplets from said gas stream to form a further partially-regenerated absorbing medium, and (iv) discharging a gaseous mixture comprising solute gas and steam from said downstream end of said further conduit and recovering said solute gas from said gaseous mixture.
7. The method of claim 6 which is effected to form a further partially-regenerated absorbing medium and wherein said further partially-regenerated absorbing medium is subjected to steps (i), (ii), (iii) and (iv) of claim 6 in a yet further conduit to form a regenerated absorbing medium.
8. The method of claim 1 wherein said solute gas is sulfur dioxide and said absorbing medium is an aqueous amine solution or aqueous amine salt solution.
9. The method of claim 2 wherein said liquid droplets in said pray pattern are sized from about 5 to about 30 microns.
10. The method of claim 2 wherein said atomizing is effected at a pressure of about 20 to about 100 psi.
11. The method of claim 10 wherein said atomizing is effected at a pressure of about 20 to about 70 psi.
12. The method of claim 11 wherein said atomizing is effected at a pressure of about 25 to about 75 psi.
13. The method of claim 1 wherein said absorbing medium has a temperature of about 170° to about 270°F (about 75°
to about 135°C) when injected into said conduit.
to about 135°C) when injected into said conduit.
14. The method of claim 1 wherein said solute gas-laden aqueous absorbing medium is formed in a solute gas-removal process for removing solute gas from an off-gas stream prior to venting the same using said absorbing medium.
15. A method for the removal of a solute gas from a gas stream containing the same using a regenerable aqueous solvent for said solute gas, which comprises:
A. effecting removal of solute gas from said gas stream to form a purified gas stream by the steps of:
(i) passing said gas stream through an elongate conduit having an inlet thereto and an outlet therefrom, (ii) injecting said regenerable aqueous solvent directly into said gas stream from at least two dual-fluid spray nozzles located in longitudinally spaced-apart relationship in said conduit by atomizing gas to form a spray pattern of said regenerable aqueous solvent in said conduit from each said nozzle and containing liquid droplets ranging in size from about 5 to about 100 microns, (iii) absorbing solute gas from said gas stream into said liquid droplets at a first temperature, (iv) agglomerating said liquid droplets contained in said conduit to remove entrained liquid droplets from said gas stream to form a solute gas-laden aqueous solvent, and (v) discharging said purified gas stream from said downstream end of said conduit;
B. effecting regeneration of aid solute gas-laden aqueous solvent to remove and recover dissolved solute gas and regenerate the solvent for recycle to step A for use as said regenerable aqueous solvent therein by steps of:
(i) passing a flowing gas stream comprising steam through a further elongate conduit having an inlet thereto and an outlet therefrom, (ii) injecting said solute gas-laden aqueous solvent directly into said flowing gas stream from at least one dual-fluid spray nozzle located in said further conduit by atomizing steam to form a spray pattern of said solute gas-laden liquid solvent in said further conduit from each said nozzle and containing liquid droplets ranging in size from about 5 to about 100 microns, (iii) desorbing dissolved solute gas from said liquid droplets of solute gas-laden liquid solvent into said flowing gas stream at a second temperature greater than said first temperature, (iv) agglomerating said liquid droplets contained in said further conduit to remove entrained liquid droplets from said flowing gas stream to form a regenerated aqueous solvent, and (v) discharging a gaseous mixture comprising solute gas and steam from said downstream end of said further conduit and recovering said solute gas from said aqueous mixture; and C. recycling said regenerated aqueous solvent to step A as said regenerable aqueous solvent
A. effecting removal of solute gas from said gas stream to form a purified gas stream by the steps of:
(i) passing said gas stream through an elongate conduit having an inlet thereto and an outlet therefrom, (ii) injecting said regenerable aqueous solvent directly into said gas stream from at least two dual-fluid spray nozzles located in longitudinally spaced-apart relationship in said conduit by atomizing gas to form a spray pattern of said regenerable aqueous solvent in said conduit from each said nozzle and containing liquid droplets ranging in size from about 5 to about 100 microns, (iii) absorbing solute gas from said gas stream into said liquid droplets at a first temperature, (iv) agglomerating said liquid droplets contained in said conduit to remove entrained liquid droplets from said gas stream to form a solute gas-laden aqueous solvent, and (v) discharging said purified gas stream from said downstream end of said conduit;
B. effecting regeneration of aid solute gas-laden aqueous solvent to remove and recover dissolved solute gas and regenerate the solvent for recycle to step A for use as said regenerable aqueous solvent therein by steps of:
(i) passing a flowing gas stream comprising steam through a further elongate conduit having an inlet thereto and an outlet therefrom, (ii) injecting said solute gas-laden aqueous solvent directly into said flowing gas stream from at least one dual-fluid spray nozzle located in said further conduit by atomizing steam to form a spray pattern of said solute gas-laden liquid solvent in said further conduit from each said nozzle and containing liquid droplets ranging in size from about 5 to about 100 microns, (iii) desorbing dissolved solute gas from said liquid droplets of solute gas-laden liquid solvent into said flowing gas stream at a second temperature greater than said first temperature, (iv) agglomerating said liquid droplets contained in said further conduit to remove entrained liquid droplets from said flowing gas stream to form a regenerated aqueous solvent, and (v) discharging a gaseous mixture comprising solute gas and steam from said downstream end of said further conduit and recovering said solute gas from said aqueous mixture; and C. recycling said regenerated aqueous solvent to step A as said regenerable aqueous solvent
16. The method of claim 15 wherein steps A (ii) to (iv) include:
(a) agglomerating said liquid droplets contained in said conduit to remove entrained liquid droplets from said gas stream at a location intermediate between said dual-fluid spray nozzles to form said solute gas-laden aqueous solvent, (b) agglomerating liquid droplets contained in said conduit to remove entrained liquid droplets from said gas stream at said downstream end of said conduit to form a partially solute gas-laden aqueous solvent, (c) injecting said regenerable aqueous solvent only from said dual-fluid spray nozzle immediately upstream of said downstream end of said conduit, and (d) injecting said partially solute gas-laden aqueous solvent from said dual-fluid spray nozzle immediately downstream of said upstream end of said conduit
(a) agglomerating said liquid droplets contained in said conduit to remove entrained liquid droplets from said gas stream at a location intermediate between said dual-fluid spray nozzles to form said solute gas-laden aqueous solvent, (b) agglomerating liquid droplets contained in said conduit to remove entrained liquid droplets from said gas stream at said downstream end of said conduit to form a partially solute gas-laden aqueous solvent, (c) injecting said regenerable aqueous solvent only from said dual-fluid spray nozzle immediately upstream of said downstream end of said conduit, and (d) injecting said partially solute gas-laden aqueous solvent from said dual-fluid spray nozzle immediately downstream of said upstream end of said conduit
17. The method of claim 15 wherein steps B (ii) to (iv) include:
(a) injecting said solute gas-laden aqueous solvent directly into said flowing gas stream from at least two dual-fluid spray nozzles located in longitudinally spaced-apart relationship in said further conduit and each forming a spray pattern in said further conduit;
(b) agglomerating said liquid droplets contained in said further conduit to remove entrained liquid droplets from said flowing gas stream to form at a location intermediate between said dual-fluid spray nozzles said regenerated aqueous solvent, (c) agglomerating liquid droplets contained in said further conduit to remove entrained liquid droplets from said flowing gas stream at said downstream end of said further conduit to form a partially regenerated aqueous solvent, (d) injecting said solute gas-laden aqueous solvent only from said dual-fluid spray nozzle immediately upstream of said downstream end of said further conduit, and (e) injecting said partially regenerated aqueous medium from said dual-fluid spray nozzle immediately downstream of said upstream end of said further conduit.
(a) injecting said solute gas-laden aqueous solvent directly into said flowing gas stream from at least two dual-fluid spray nozzles located in longitudinally spaced-apart relationship in said further conduit and each forming a spray pattern in said further conduit;
(b) agglomerating said liquid droplets contained in said further conduit to remove entrained liquid droplets from said flowing gas stream to form at a location intermediate between said dual-fluid spray nozzles said regenerated aqueous solvent, (c) agglomerating liquid droplets contained in said further conduit to remove entrained liquid droplets from said flowing gas stream at said downstream end of said further conduit to form a partially regenerated aqueous solvent, (d) injecting said solute gas-laden aqueous solvent only from said dual-fluid spray nozzle immediately upstream of said downstream end of said further conduit, and (e) injecting said partially regenerated aqueous medium from said dual-fluid spray nozzle immediately downstream of said upstream end of said further conduit.
18. The method of claim 15 wherein said solute gas is sulfur dioxide and said absorbing medium is an aqueous amine solution.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9101336.7 | 1991-01-22 | ||
| GB919101336A GB9101336D0 (en) | 1991-01-22 | 1991-01-22 | Stripping method and apparatus |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2100768A1 true CA2100768A1 (en) | 1992-07-23 |
Family
ID=10688790
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002100768A Abandoned CA2100768A1 (en) | 1991-01-22 | 1992-01-22 | Stripping and method and apparatus |
Country Status (6)
| Country | Link |
|---|---|
| AU (1) | AU1180192A (en) |
| CA (1) | CA2100768A1 (en) |
| GB (1) | GB9101336D0 (en) |
| IE (1) | IE920185A1 (en) |
| WO (1) | WO1992012786A1 (en) |
| ZA (1) | ZA92455B (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5648048A (en) * | 1993-04-09 | 1997-07-15 | Babcock-Hitachi Kabushiki Kaisha | Wet-type flue gas desulfurization plant |
| US5474235A (en) * | 1994-04-13 | 1995-12-12 | Wheelabrator Technologies, Inc. | Spray nozzle insert and method for reducing wear in spray nozzles |
| GB9413714D0 (en) * | 1994-07-07 | 1994-08-24 | Turbotak Technologies Inc | Regenerative process for removal and recovery of volatile organic compounds (VOCs) from effluent gases |
| JPH09262432A (en) * | 1996-03-29 | 1997-10-07 | Kansai Electric Power Co Inc:The | Method for recovering basic amine compound in waste gas of decarboxylation column |
| WO2012092982A1 (en) * | 2011-01-07 | 2012-07-12 | Statoil Petroleum As | Method and apparatus for co2 capture |
| FI125659B (en) | 2012-06-04 | 2015-12-31 | Outotec Oyj | Remover, method for modifying an existing wet type gas washer and wet type gas washer |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3633339A (en) * | 1968-11-18 | 1972-01-11 | Freeport Minerals Co | Recovery of sulfur dioxide from a sulfur dioxide-containing aqueous ammonium phosphate solution |
| US4374653A (en) * | 1976-11-05 | 1983-02-22 | Shell Oil Company | Process control |
| WO1985002787A1 (en) * | 1983-12-19 | 1985-07-04 | The Dow Chemical Company | Use of nucleating agents for enhancement of efficiency of acid gas scrubbing processes |
| US4957715A (en) * | 1988-04-15 | 1990-09-18 | Uop | Gas treatment process |
-
1991
- 1991-01-22 GB GB919101336A patent/GB9101336D0/en active Pending
-
1992
- 1992-01-22 AU AU11801/92A patent/AU1180192A/en not_active Abandoned
- 1992-01-22 WO PCT/CA1992/000025 patent/WO1992012786A1/en active Application Filing
- 1992-01-22 CA CA002100768A patent/CA2100768A1/en not_active Abandoned
- 1992-01-22 IE IE018592A patent/IE920185A1/en not_active Application Discontinuation
- 1992-01-22 ZA ZA92455A patent/ZA92455B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| GB9101336D0 (en) | 1991-03-06 |
| WO1992012786A1 (en) | 1992-08-06 |
| ZA92455B (en) | 1993-01-27 |
| AU1180192A (en) | 1992-08-27 |
| IE920185A1 (en) | 1992-07-29 |
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