CA1195257A - Method and apparatus for purifying a gas stream in a sorption filter - Google Patents
Method and apparatus for purifying a gas stream in a sorption filterInfo
- Publication number
- CA1195257A CA1195257A CA000435474A CA435474A CA1195257A CA 1195257 A CA1195257 A CA 1195257A CA 000435474 A CA000435474 A CA 000435474A CA 435474 A CA435474 A CA 435474A CA 1195257 A CA1195257 A CA 1195257A
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- Prior art keywords
- gas
- purified
- sorption
- circulating
- loop
- Prior art date
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Classifications
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- 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
- B01D53/02—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 adsorption, e.g. preparative gas chromatography
- B01D53/04—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 adsorption, e.g. preparative gas chromatography with stationary adsorbents
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2257/00—Components to be removed
- B01D2257/70—Organic compounds not provided for in groups B01D2257/00 - B01D2257/602
- B01D2257/702—Hydrocarbons
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2257/00—Components to be removed
- B01D2257/70—Organic compounds not provided for in groups B01D2257/00 - B01D2257/602
- B01D2257/708—Volatile organic compounds V.O.C.'s
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2259/00—Type of treatment
- B01D2259/40—Further details for adsorption processes and devices
- B01D2259/402—Further details for adsorption processes and devices using two beds
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2259/00—Type of treatment
- B01D2259/40—Further details for adsorption processes and devices
- B01D2259/414—Further details for adsorption processes and devices using different types of adsorbents
- B01D2259/4141—Further details for adsorption processes and devices using different types of adsorbents within a single bed
- B01D2259/4145—Further details for adsorption processes and devices using different types of adsorbents within a single bed arranged in series
- B01D2259/4148—Multiple layers positioned apart from each other
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Analytical Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Separation Of Gases By Adsorption (AREA)
- Treating Waste Gases (AREA)
- Physical Or Chemical Processes And Apparatus (AREA)
Abstract
Abstract of the Disclosure Method for the purification of a gas stream loaded with organic gases or vapors, especially up to near the saturation limit, in a sorption filter, in which the gas stream loaded with organic gases or vapors is mixed with a gas conducted in a loop, and together with the latter is conducted through the sorption medium layer of the sorption filter, the volumetric flow of the circulating gas being larger than the volumetric flow of the gas to be purified. After the mixed gas stream is conducted through the sorption medium layer, a partial stream of the now purified gas is branched off and removed, where the volumetric flow of the branched-off gas corresponds to the volumetric flow of the gas to be purified and where the remainder of the purified gas is returned to the mixing point as circulating gas and is mixed there again with the gas to be purified.
Description
R-647 ~S~7 METHOD AND APPARATUS FOR PURIFYING A GAS STREAM
IN A SORPTION FILTER
Background of the Inventlon Field of the Invention The invention relates to a method for purifying a gas stream loaded with organic gases or vapors especially to near the saturation limit in a sorption filte.r~ as well as to an ar-rangement for carrying out this method.
Description of the Prior Art In gas-purifying technology, vaporous organic su~stances are separated in many cases from the gas stream to be purified by adsorption in a sorption medium, preferably activate~ carbon For this purpose, the gas stream is conducted through a layer of granular sorption medium and during its travel t~rough the layer turbulence and diffusion transport the molecules to be separated into the activated carbon, where they are retained by adsorption and capillary condensa-tion. In the process, adsorption heat is released, which heats up the sorption medium and the gas stream to be purified. This temperatur~ rise which is substantially determined only by the concentration, reaches such values at high concentrations of the substances t~ be separated that the separation is impeded thereby because the attainable equilibrium loadings drop with increasing tempera-ture. Thereby, the concentrations of organic impurities in ~he gas subjected to purification in the sorption medium remain relatively high. In addition, the danger o~ ignition or more s~
generally, thè danger of undesired chemical reactions is increased by the temperature rise. In order to decrease ~he temperature rise, an amount of atmospheric air is fre~uently admixed to the gas stream to be purified to r~duce ~he concen-tration of the substances to be separated to desirable low values before entering the sorption medium bed. Howe~er~ with the increase of the gas stre~m to be purified~ the power requirements of the blowers and in many cases also the size of the sorption ilters increase. In particular~ however~ the product of the emission from the sorption *ilter has a concen-tration and a gas flow which remains high even ~hough the concentration is lowered by addition of air, because ~he gas stream is increased at the same timeO
German Published Non-Prosecuted Application ~o. DE-OS 3a 20 656 attempts to avoid these disadvantag2s by ~wo measures: Instead of one activated-carbon bed, several are connected in series, and the gas stream to be purifi~d is always conaucted o~er a cooler between two beds and thereby cooled. Through these intermediate cooling operations, it i5 possible to remove the adsorption heat. A still present high concentr~ltion of or~nic substances in the gas can be eliminated by post-combustion according to the proposal of DE-OS 30 20 656. In order to obt~in, according to this proposal, the desired or required low emission values, an elaborate struc~ure of the sorption fi~ter with intermediate coolers inserted between a multiplicity of ~35~
sorption medium stages and optionally, additi~nal post-combustion may be necessary~ Thus, not only ~ust th~
equipment expense be taken into account but the power consump~
tion for the intermediate cooling and maint~nance of the post-combustion must also be taken into cons.ideration~
Summary_of the Inven-tion An object of the invention is to provide a simple and ef~icien~
method and an arrangement by means of which a gas stream can be purified to obtain and maintain the desired or specified emission values.
With the foregoing and other objects in view, there is provided in accordance with the invention a method for the purifica~ion of a gas stream loaded with organic gases or ~apors, especially up to near the saturation limit, in a sorp~ion fi.lter, which comprises circulating a gas in a loop through a sor~tion medium layer, introducing a gas stream containing organic impurities into.the circulating gas stream at a point in the loop prior t~
passage through the soxption medium layer t mainta}ning a volumetric flow of the circulating gas which is larger tha~ the volumetric flow of the gas to be purifie~ introduce~ into the circulating gas stream, passing the mixture of circulating gas and gas containing organic impurities through the sorption medium layer to remove organic impurities, withdrawing. a portion of said purified mixture of gases after passage through ~.9~7 the sorption medium layer, maintaining a ~olumetric flow oE
said portion of gases which substantially corresponds to the volumetric flow of khe gas to be puxified, and continuing the circulation of the remainder of the purified mixture o~ gases as circulating gas to the mixing point to be ~ixed with gas to be purified and this mixture of gases circulated ~o the sorption medium layer.
In accordance with the invention, there is provided an appara-tus for the purification of a gas stream loade~ with organic gases or vapors comprising a gas loop with a circulatory blawer and connecting pipes connected to a container of a sorption filter, a feedline for the gas to be purified opening into the loop on the suction side of the blower, said ~ontainer of the sorption filter having at least two sorption medium layers which are separated from each oth~r to provide a space therebetween, said loop having its return line from the con-tainer opening into said space between the two ~ayers, and a purified gas outlet in the container above the sorption me~ium layer above said space for the discharge of purifiea gas, Other features which are considered as characteristic ~or the invention are set forth in the appended claims.
Although the invention is illus~rated and descri~ed herein as embodied in a method and apparatus for purifyin~ a gas stream ~95;2~7 in a sorption filter, it is nevertheless not intended to be limited to the details shown, since VariQUs modifications may be made therein without departing from the spir}t of the invention and within the scope and range of equivalents of the claims.
Brief Descri tion of the Drawing The invention, however, toyether with additional objects and advantages thereof will be best unders tood from the following description when read in connection with the accompanying drawing which diagrammatically illustrates apparatus for carrying the method of the operation. Gas is circulated in a loop by a blower, through a cooler intv a sorption filter~
through a sorption medium layer therein, then out of the filter back to the blower. Gas to be purified is introduced into t~e loop at the suction side of the blower in a volumetric flow less than the circulating gas and the mixture recirculated. A
portion of the purified gas in a volumetric fl~w substantially equal to the feed-in of gas to be purified passes from the top of the sorption medium layer to another sorption medium layer spaced above it and is then discharged from the sorption filter. The remainder of the purified ga~s is recircul~ted for further mixing with gas to be purified and this mixture sent by the blower to the sorption filter.
Detailed Description of the Invention , . . .
In the purification of a gas stream loadea with organic gases or vapors, especially up to near the saturation limit, in sorption filters, adsorption heat is released which depends on the concentration of the substances to be separated an~ can heat the sorption media and the gas stream to be pur;fie~ until the separation is impeded. To reduce the tempera~ure increase, the gas stream to be purified is mixed wit~ circulating gas and is conducted, together with the latter, through the sorption medium layer of the sorption ilter, where the ~o~umetric flow of the circulating gas exceeds the volumetric fl~w o~ the gas to be purified. The circulating gas can be cooled in the process and a sorptive post-purification o~ the ~asically purified gas which flows out of the loop can be provided~ The apparatus for carrying out the method contains a gas loop with a circulating blower and connecting pipelines, which is con-nected to the container of the sorption filter~ The gas to ~e purified is fed via the feedline into the loop in the vicinity of the line on the suction side. In the container o~ the sorption filter, separated sorption medium layers are pro~idea arranged at a distance from each other. The loop return is connected to the space between the two layers and the pu-rified-gas discharge to the space following the second layer.
According to the invention, the gas stream loaded with orga~ic gases or vapors is mixed with gas conducte~ in a closed circuit and is conducted, together with the l~tter, through the ~ 9~2S~
sorption medium layer of the sorption ilter, where t~e volumetric flow of the circulating gas is larger than th~
volumetric flow of the gas to be purified. After the mixed-gas stream is conducted through the sorption me~ium layer, a partial stream of the now purified gas is branche~-o~ an~
discharged. The volumetric flow of the branched-o~f gas corresponds to the volumetric flow of the gas to be puri~ie~
The remainder of the purified gas is returne~ to the mixing point with incoming gas to be purified as circulati~g gas ana is mixed there with the incoming gas to be purifie~. Since the concentration of the substances to be separated ~s reduced i~
the ratio of the volumetric flow of the gas to ~e purifie~ t~
the volumetric flow of the circulating gas, a~d ~ince the volumetric flow of the circulating gas is larger than ~he volumetric flow of the gas to be purified, the concentration of the substances to be separated is lowered tv a value less than half the value of the entry concentration.
In general, a reduction by one order of magnitude is sufficient in case of very high concentrations of organic substances in gas such as occur in the displacement gas of tanks which ar~
filled with organic substances, especially if their charge consists of highly volatile hydrocarbons. For this latter purpose, the volumetric flow of the irculating gas shoul~
desirably have a magnitude which exceeds the volumetric flow of the displacement gas to be purifiea by a factor of about 5 to 20.
~52~'7 In a fur~her embodim~nt of the method, the circulatin~ gas is co~led, preerably after flowing throuyh the circulati~ blower transporting the circulating gas. Heat is thereby r~moved from `the circulating gas beyond t~e heat remo~al by ~he tra~ferre~
purified gas and by the sur~aces of the parts of the 3pparat~s forming the gas loop. Thereby, the dissipation heat o~ t~e circulating blower, in addition tQ the a~sorption hea~, ca~ he compensated in a simple manner.
The partial stream of the branched-off purified gas may ~e conducted through a further sorption material layer before it is discharged. The gas stream fed to this further s~p~ian medium layer has a volumetric flow which corresponds to the volumetric flow of the gas to be purifie~ The concentratlQn of the substances to be separated is extremely low in the gaS
stream fed to the further sorption me~iu~. The concentration in this gas stream may increase if the sorption medium layer connected into the loop has reached its breakthrough, i.e., it~
maximum loading. The separation in this ~urther sorption medium layer ensures that the outflowing ~as i5 pr~tically free of impurities to be separated. This flow of the ~as stream to the further sorption medium is maintained sven if the sorption medium layer connected into the loop is loaded to maximum saturation and an increase of the substance~ to be separated in the circulating gas indicates that this saturatlon has been reached. It goes without saying that the sorp~ion filter should be regenerated when this loading stat~ is reached.
An arrangement for carrying out the method, according t~ the invention, is characterized by the features: that a gas loop with a circulating blower and connecting pipelines is connecte~
to the container of the sorption filter, an~ the feed line for the gas to be purified leads into the loop in the ~icini~y ~
the line on the suction side of the circulating blower; that the container of the sorption filter has sorption ~edium ~ayers which are separated from each other, the return li~e nf ~he loop is connected in the region of tha space between two sorption medium layers and the filter container has a con-nection for the purified-gas discharge line followin~ the second sorption medium layer. In addition, the circulat1ng blower is followed by a cooler. With this arrangement~ the method can be carried out in a simple manner. The desi~ o~
the circulating blower is determined here by the desired mixing ratio which is to be maintained, as well as by the pressure difference which the volumetric flow of the circulatihg ~as must overcome. In view of the expect:ed released adsorption heat and of the dissipation heat of the circulating blower, the surfaces of containers of the sorption filter and p;pelines are designed to effect considerable heat removal. The insertion of a cooler into the loop, according to the embodimentO permits removal of heat going beyond the removal o:E adsorption heat a~
well as of dissipation heat of the blower.
In addition, a shut-off valve is provided in each of t~e ~oop lines leading to the container of the sorption ~ilter. These shut-off valves permit one to cut off the loop ~rom the sorption filter, for instance for the purpose o~ regenexa~ing the sorption filter. The regeneration ca~ be carriea out by known means, for instance, with superheate~ steam or wïth heated inert gas, wherein the desorption medium is aavanta~
geously fed into the sorption filter through the line previous-ly used for discharging the purified gas ancl the desorptio~
medium flows through the sorption filter in a dir~ction counter to that of the ~low of the gas to be puri~ied. The desorption medium loaded with desorbate is discharged from the line which previously fed the circulating gas into the sorption filter~
In a further embodiment, a second sorption filter i5 pro~idec~
in which the blower can be connected alternatingly, ~hrough shut-off valves in association with the first sorption filter or the second sorption filter. In thi~ ~ual arrangement it goes without saying, that other similar multiple arrangements may be employed, continuous operation may be carried out. One of the connected sorption filters can be in ~he operating phase "regenerationl', while the other one is switched to ~gas puri-fication".
Desirably, a check valve 13 which prevents ~low-back is provided in the feedline for the gas to be purified. This check valve prevents flow-back from the loop into the feed line, if an increased underpressure should occur there for whatever reason.
A further embodiment is characterized by the feature that the feedline is provided with flashback protection 14. In handling flammable vapors and gases, ignition can never be pre-cluded with ultimate certainty. Even with supposedly well inertized adsorbers, there is always the danger that locally confined overheated "nests" are formed. Such "nests", if oxygen is present or is supplied, can be the starting poin-t of fires, the flashing-back of which via the connected gas feedline is prevented by the flashback protection.
The drawing shows a schematic flow diagram for an installation with two sorption filters 1 and 2. The air stream to be purified, generally tank exhaust air loaded with organic impurities is conducted via the connecting line 10 to a mixing point 8 located on the suction side of a circulating blower 6 and is mixed there into the circulating-a:ir stream conducted through lines 7.41. The line 7.41 connects at the mixing point with the line 7.1 going to the blower 6. The blower 6 is connected via the line 7.2 to the cooler 5, the outlet of which leads to the two lines 7.31 and 7.32. Line 7.31 and line 7.32, lead to respective sorption fil.ters 1 and 2, and lines 7.31 and . .
~s~
~7 line 7032 hàve respec-tive shllt-off valves 11 1 an~ 11.2 to permit feeding the air to only one of the two sorptio~ fil~ers.
The circulation flow goes through the sorpkion medium layer 3 of the sorption filter 1 pu-t in operation and leaves ~he sorption filter 1 through open valve 12.1 and line 7.41, back to the mixing point 8. Similarly, if the sorption ~ilter 2 is inserted into the loop by closing valves 11 1 and 12~1 and opening the valves 11.2 and 12~2~ the circul~ting gas i5 conducted through open valve 12.2 and line 7~42 ~ack to the mi.xing point 8~ A second sorption medium layer 4 in the sorption filter 1 can take up residual traces of impurities which have possibly not been separated in the ~o~ption mediu~
layer 3 and the so purified gas, the volumetric fl~w o~ which corresponds to the volumetric flow of the gas to be puri~ied~
leaves the system through the connection stub g.l. As a balanced system, only as much gas is discharged through the stubs 9.1 and 9.2 as is fed into the system throug~ the feedline 10. ("Breathing" of the loop due to temperature changes is ignored here) The following example illustrates the present inventio~:
During filling a storage tank with benze~e, maximally 300 m3/h of "displacement air" are discharged fr~m the tank. This discharged air contains 330 g/m3 gaseous benæene according to the saturation concentration at ambient temperature. This g2s stream ~. . . . .
~g52S7 (displacement air) is to be purified to reduce the resiclual concentration of benzene vapor to a value below the existing limit o 20 mg/m3. This is accomplished by the me~hod an~
plant in accordance with the drawing~ Two adsorbers 1 an~ 2 alternatingly take over the purification of the ~isplacemen~
air". While the one is switched to "purificati~n~, ~he other one is regenerated in known manner with steam or wit~ iner~
gas. The sorption medium layers 3 of the two adsor~ers an~ 2 which purify the circulating gas each contains 2~0~0kg acti~a~-ed carbon and the safety layers 4 purifying the outflowing pure gas contain l,OOOkg activated caxbon each~ The blowex 6 transports a circulating flow of 5,000 m3lh, to which the "displacement air" of maximally 300 m3/~ is admixea~ The water-cooled gas cooler 5 generates a temperature ~ifference in the circulating gas of 2 to 8 K which is sufficlent to remo~e the adsorption heat of the benzene release~ in the adsorbing sorption medium layer and the dissipation los~ of the ~lower.
The loading process of the sorption filter swi~chea to adsorption is terminated if the benzene concentration in the returning circulating gas has reached appro~imately ~ g~m3. At this point in time, the benzene concen~ration after the sorption medium layer acting as the safety filter 4 is actually still below 1 mg/m3. This is more tha~ one order of magnit~e less than the limit of 20 mg/m3.
. . .
~, i;257 The foregoing is a description corresponding, in substance, to German application No. P 32 32 138.4, dated August 28, 1982t international priori-ty o~ which is being claimed for the instant application, and which is hereby made part of th~s application. Any material discrepancies bet~een the fore~oing specification and the ~pecification of the ~orementioned corresponding German application are to be resolve~ ~n ~vor of the latter.
IN A SORPTION FILTER
Background of the Inventlon Field of the Invention The invention relates to a method for purifying a gas stream loaded with organic gases or vapors especially to near the saturation limit in a sorption filte.r~ as well as to an ar-rangement for carrying out this method.
Description of the Prior Art In gas-purifying technology, vaporous organic su~stances are separated in many cases from the gas stream to be purified by adsorption in a sorption medium, preferably activate~ carbon For this purpose, the gas stream is conducted through a layer of granular sorption medium and during its travel t~rough the layer turbulence and diffusion transport the molecules to be separated into the activated carbon, where they are retained by adsorption and capillary condensa-tion. In the process, adsorption heat is released, which heats up the sorption medium and the gas stream to be purified. This temperatur~ rise which is substantially determined only by the concentration, reaches such values at high concentrations of the substances t~ be separated that the separation is impeded thereby because the attainable equilibrium loadings drop with increasing tempera-ture. Thereby, the concentrations of organic impurities in ~he gas subjected to purification in the sorption medium remain relatively high. In addition, the danger o~ ignition or more s~
generally, thè danger of undesired chemical reactions is increased by the temperature rise. In order to decrease ~he temperature rise, an amount of atmospheric air is fre~uently admixed to the gas stream to be purified to r~duce ~he concen-tration of the substances to be separated to desirable low values before entering the sorption medium bed. Howe~er~ with the increase of the gas stre~m to be purified~ the power requirements of the blowers and in many cases also the size of the sorption ilters increase. In particular~ however~ the product of the emission from the sorption *ilter has a concen-tration and a gas flow which remains high even ~hough the concentration is lowered by addition of air, because ~he gas stream is increased at the same timeO
German Published Non-Prosecuted Application ~o. DE-OS 3a 20 656 attempts to avoid these disadvantag2s by ~wo measures: Instead of one activated-carbon bed, several are connected in series, and the gas stream to be purifi~d is always conaucted o~er a cooler between two beds and thereby cooled. Through these intermediate cooling operations, it i5 possible to remove the adsorption heat. A still present high concentr~ltion of or~nic substances in the gas can be eliminated by post-combustion according to the proposal of DE-OS 30 20 656. In order to obt~in, according to this proposal, the desired or required low emission values, an elaborate struc~ure of the sorption fi~ter with intermediate coolers inserted between a multiplicity of ~35~
sorption medium stages and optionally, additi~nal post-combustion may be necessary~ Thus, not only ~ust th~
equipment expense be taken into account but the power consump~
tion for the intermediate cooling and maint~nance of the post-combustion must also be taken into cons.ideration~
Summary_of the Inven-tion An object of the invention is to provide a simple and ef~icien~
method and an arrangement by means of which a gas stream can be purified to obtain and maintain the desired or specified emission values.
With the foregoing and other objects in view, there is provided in accordance with the invention a method for the purifica~ion of a gas stream loaded with organic gases or ~apors, especially up to near the saturation limit, in a sorp~ion fi.lter, which comprises circulating a gas in a loop through a sor~tion medium layer, introducing a gas stream containing organic impurities into.the circulating gas stream at a point in the loop prior t~
passage through the soxption medium layer t mainta}ning a volumetric flow of the circulating gas which is larger tha~ the volumetric flow of the gas to be purifie~ introduce~ into the circulating gas stream, passing the mixture of circulating gas and gas containing organic impurities through the sorption medium layer to remove organic impurities, withdrawing. a portion of said purified mixture of gases after passage through ~.9~7 the sorption medium layer, maintaining a ~olumetric flow oE
said portion of gases which substantially corresponds to the volumetric flow of khe gas to be puxified, and continuing the circulation of the remainder of the purified mixture o~ gases as circulating gas to the mixing point to be ~ixed with gas to be purified and this mixture of gases circulated ~o the sorption medium layer.
In accordance with the invention, there is provided an appara-tus for the purification of a gas stream loade~ with organic gases or vapors comprising a gas loop with a circulatory blawer and connecting pipes connected to a container of a sorption filter, a feedline for the gas to be purified opening into the loop on the suction side of the blower, said ~ontainer of the sorption filter having at least two sorption medium layers which are separated from each oth~r to provide a space therebetween, said loop having its return line from the con-tainer opening into said space between the two ~ayers, and a purified gas outlet in the container above the sorption me~ium layer above said space for the discharge of purifiea gas, Other features which are considered as characteristic ~or the invention are set forth in the appended claims.
Although the invention is illus~rated and descri~ed herein as embodied in a method and apparatus for purifyin~ a gas stream ~95;2~7 in a sorption filter, it is nevertheless not intended to be limited to the details shown, since VariQUs modifications may be made therein without departing from the spir}t of the invention and within the scope and range of equivalents of the claims.
Brief Descri tion of the Drawing The invention, however, toyether with additional objects and advantages thereof will be best unders tood from the following description when read in connection with the accompanying drawing which diagrammatically illustrates apparatus for carrying the method of the operation. Gas is circulated in a loop by a blower, through a cooler intv a sorption filter~
through a sorption medium layer therein, then out of the filter back to the blower. Gas to be purified is introduced into t~e loop at the suction side of the blower in a volumetric flow less than the circulating gas and the mixture recirculated. A
portion of the purified gas in a volumetric fl~w substantially equal to the feed-in of gas to be purified passes from the top of the sorption medium layer to another sorption medium layer spaced above it and is then discharged from the sorption filter. The remainder of the purified ga~s is recircul~ted for further mixing with gas to be purified and this mixture sent by the blower to the sorption filter.
Detailed Description of the Invention , . . .
In the purification of a gas stream loadea with organic gases or vapors, especially up to near the saturation limit, in sorption filters, adsorption heat is released which depends on the concentration of the substances to be separated an~ can heat the sorption media and the gas stream to be pur;fie~ until the separation is impeded. To reduce the tempera~ure increase, the gas stream to be purified is mixed wit~ circulating gas and is conducted, together with the latter, through the sorption medium layer of the sorption ilter, where the ~o~umetric flow of the circulating gas exceeds the volumetric fl~w o~ the gas to be purified. The circulating gas can be cooled in the process and a sorptive post-purification o~ the ~asically purified gas which flows out of the loop can be provided~ The apparatus for carrying out the method contains a gas loop with a circulating blower and connecting pipelines, which is con-nected to the container of the sorption filter~ The gas to ~e purified is fed via the feedline into the loop in the vicinity of the line on the suction side. In the container o~ the sorption filter, separated sorption medium layers are pro~idea arranged at a distance from each other. The loop return is connected to the space between the two layers and the pu-rified-gas discharge to the space following the second layer.
According to the invention, the gas stream loaded with orga~ic gases or vapors is mixed with gas conducte~ in a closed circuit and is conducted, together with the l~tter, through the ~ 9~2S~
sorption medium layer of the sorption ilter, where t~e volumetric flow of the circulating gas is larger than th~
volumetric flow of the gas to be purified. After the mixed-gas stream is conducted through the sorption me~ium layer, a partial stream of the now purified gas is branche~-o~ an~
discharged. The volumetric flow of the branched-o~f gas corresponds to the volumetric flow of the gas to be puri~ie~
The remainder of the purified gas is returne~ to the mixing point with incoming gas to be purified as circulati~g gas ana is mixed there with the incoming gas to be purifie~. Since the concentration of the substances to be separated ~s reduced i~
the ratio of the volumetric flow of the gas to ~e purifie~ t~
the volumetric flow of the circulating gas, a~d ~ince the volumetric flow of the circulating gas is larger than ~he volumetric flow of the gas to be purified, the concentration of the substances to be separated is lowered tv a value less than half the value of the entry concentration.
In general, a reduction by one order of magnitude is sufficient in case of very high concentrations of organic substances in gas such as occur in the displacement gas of tanks which ar~
filled with organic substances, especially if their charge consists of highly volatile hydrocarbons. For this latter purpose, the volumetric flow of the irculating gas shoul~
desirably have a magnitude which exceeds the volumetric flow of the displacement gas to be purifiea by a factor of about 5 to 20.
~52~'7 In a fur~her embodim~nt of the method, the circulatin~ gas is co~led, preerably after flowing throuyh the circulati~ blower transporting the circulating gas. Heat is thereby r~moved from `the circulating gas beyond t~e heat remo~al by ~he tra~ferre~
purified gas and by the sur~aces of the parts of the 3pparat~s forming the gas loop. Thereby, the dissipation heat o~ t~e circulating blower, in addition tQ the a~sorption hea~, ca~ he compensated in a simple manner.
The partial stream of the branched-off purified gas may ~e conducted through a further sorption material layer before it is discharged. The gas stream fed to this further s~p~ian medium layer has a volumetric flow which corresponds to the volumetric flow of the gas to be purifie~ The concentratlQn of the substances to be separated is extremely low in the gaS
stream fed to the further sorption me~iu~. The concentration in this gas stream may increase if the sorption medium layer connected into the loop has reached its breakthrough, i.e., it~
maximum loading. The separation in this ~urther sorption medium layer ensures that the outflowing ~as i5 pr~tically free of impurities to be separated. This flow of the ~as stream to the further sorption medium is maintained sven if the sorption medium layer connected into the loop is loaded to maximum saturation and an increase of the substance~ to be separated in the circulating gas indicates that this saturatlon has been reached. It goes without saying that the sorp~ion filter should be regenerated when this loading stat~ is reached.
An arrangement for carrying out the method, according t~ the invention, is characterized by the features: that a gas loop with a circulating blower and connecting pipelines is connecte~
to the container of the sorption filter, an~ the feed line for the gas to be purified leads into the loop in the ~icini~y ~
the line on the suction side of the circulating blower; that the container of the sorption filter has sorption ~edium ~ayers which are separated from each other, the return li~e nf ~he loop is connected in the region of tha space between two sorption medium layers and the filter container has a con-nection for the purified-gas discharge line followin~ the second sorption medium layer. In addition, the circulat1ng blower is followed by a cooler. With this arrangement~ the method can be carried out in a simple manner. The desi~ o~
the circulating blower is determined here by the desired mixing ratio which is to be maintained, as well as by the pressure difference which the volumetric flow of the circulatihg ~as must overcome. In view of the expect:ed released adsorption heat and of the dissipation heat of the circulating blower, the surfaces of containers of the sorption filter and p;pelines are designed to effect considerable heat removal. The insertion of a cooler into the loop, according to the embodimentO permits removal of heat going beyond the removal o:E adsorption heat a~
well as of dissipation heat of the blower.
In addition, a shut-off valve is provided in each of t~e ~oop lines leading to the container of the sorption ~ilter. These shut-off valves permit one to cut off the loop ~rom the sorption filter, for instance for the purpose o~ regenexa~ing the sorption filter. The regeneration ca~ be carriea out by known means, for instance, with superheate~ steam or wïth heated inert gas, wherein the desorption medium is aavanta~
geously fed into the sorption filter through the line previous-ly used for discharging the purified gas ancl the desorptio~
medium flows through the sorption filter in a dir~ction counter to that of the ~low of the gas to be puri~ied. The desorption medium loaded with desorbate is discharged from the line which previously fed the circulating gas into the sorption filter~
In a further embodiment, a second sorption filter i5 pro~idec~
in which the blower can be connected alternatingly, ~hrough shut-off valves in association with the first sorption filter or the second sorption filter. In thi~ ~ual arrangement it goes without saying, that other similar multiple arrangements may be employed, continuous operation may be carried out. One of the connected sorption filters can be in ~he operating phase "regenerationl', while the other one is switched to ~gas puri-fication".
Desirably, a check valve 13 which prevents ~low-back is provided in the feedline for the gas to be purified. This check valve prevents flow-back from the loop into the feed line, if an increased underpressure should occur there for whatever reason.
A further embodiment is characterized by the feature that the feedline is provided with flashback protection 14. In handling flammable vapors and gases, ignition can never be pre-cluded with ultimate certainty. Even with supposedly well inertized adsorbers, there is always the danger that locally confined overheated "nests" are formed. Such "nests", if oxygen is present or is supplied, can be the starting poin-t of fires, the flashing-back of which via the connected gas feedline is prevented by the flashback protection.
The drawing shows a schematic flow diagram for an installation with two sorption filters 1 and 2. The air stream to be purified, generally tank exhaust air loaded with organic impurities is conducted via the connecting line 10 to a mixing point 8 located on the suction side of a circulating blower 6 and is mixed there into the circulating-a:ir stream conducted through lines 7.41. The line 7.41 connects at the mixing point with the line 7.1 going to the blower 6. The blower 6 is connected via the line 7.2 to the cooler 5, the outlet of which leads to the two lines 7.31 and 7.32. Line 7.31 and line 7.32, lead to respective sorption fil.ters 1 and 2, and lines 7.31 and . .
~s~
~7 line 7032 hàve respec-tive shllt-off valves 11 1 an~ 11.2 to permit feeding the air to only one of the two sorptio~ fil~ers.
The circulation flow goes through the sorpkion medium layer 3 of the sorption filter 1 pu-t in operation and leaves ~he sorption filter 1 through open valve 12.1 and line 7.41, back to the mixing point 8. Similarly, if the sorption ~ilter 2 is inserted into the loop by closing valves 11 1 and 12~1 and opening the valves 11.2 and 12~2~ the circul~ting gas i5 conducted through open valve 12.2 and line 7~42 ~ack to the mi.xing point 8~ A second sorption medium layer 4 in the sorption filter 1 can take up residual traces of impurities which have possibly not been separated in the ~o~ption mediu~
layer 3 and the so purified gas, the volumetric fl~w o~ which corresponds to the volumetric flow of the gas to be puri~ied~
leaves the system through the connection stub g.l. As a balanced system, only as much gas is discharged through the stubs 9.1 and 9.2 as is fed into the system throug~ the feedline 10. ("Breathing" of the loop due to temperature changes is ignored here) The following example illustrates the present inventio~:
During filling a storage tank with benze~e, maximally 300 m3/h of "displacement air" are discharged fr~m the tank. This discharged air contains 330 g/m3 gaseous benæene according to the saturation concentration at ambient temperature. This g2s stream ~. . . . .
~g52S7 (displacement air) is to be purified to reduce the resiclual concentration of benzene vapor to a value below the existing limit o 20 mg/m3. This is accomplished by the me~hod an~
plant in accordance with the drawing~ Two adsorbers 1 an~ 2 alternatingly take over the purification of the ~isplacemen~
air". While the one is switched to "purificati~n~, ~he other one is regenerated in known manner with steam or wit~ iner~
gas. The sorption medium layers 3 of the two adsor~ers an~ 2 which purify the circulating gas each contains 2~0~0kg acti~a~-ed carbon and the safety layers 4 purifying the outflowing pure gas contain l,OOOkg activated caxbon each~ The blowex 6 transports a circulating flow of 5,000 m3lh, to which the "displacement air" of maximally 300 m3/~ is admixea~ The water-cooled gas cooler 5 generates a temperature ~ifference in the circulating gas of 2 to 8 K which is sufficlent to remo~e the adsorption heat of the benzene release~ in the adsorbing sorption medium layer and the dissipation los~ of the ~lower.
The loading process of the sorption filter swi~chea to adsorption is terminated if the benzene concentration in the returning circulating gas has reached appro~imately ~ g~m3. At this point in time, the benzene concen~ration after the sorption medium layer acting as the safety filter 4 is actually still below 1 mg/m3. This is more tha~ one order of magnit~e less than the limit of 20 mg/m3.
. . .
~, i;257 The foregoing is a description corresponding, in substance, to German application No. P 32 32 138.4, dated August 28, 1982t international priori-ty o~ which is being claimed for the instant application, and which is hereby made part of th~s application. Any material discrepancies bet~een the fore~oing specification and the ~pecification of the ~orementioned corresponding German application are to be resolve~ ~n ~vor of the latter.
Claims (14)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Method for the purification by adsorption in a sorption medium of a gas stream loaded with organic gases or vapors, especially up to near the saturation limit, in a sorption filter, which comprises circulating a gas in a loop through a sorption medium layer, introducing a gas stream to be purified containing organic impurities from a source outside of the loop into the circulating gas stream at a point in the loop prior to passage through the sorption medium layer, maintaining a volumetric flow of the circulating gas which is larger than the volumetric flow of the gas to be purified introduced into the circulating gas stream, passing the mixture of circulating gas and gas containing organic impurities through the sorption medium layer to remove organic impurities, withdrawing a portion of said purified mix-ture of gases after passage through the sorption medium layer, maintaining a volumetric flow of said portion of gases which substantially corresponds to the volumetric flow of the gas to be purified, and continuing the circulation of the remainder of the purified mixture of gases as circulating gas to the mixing point to be mixed with gas to be purified and circulating this mixture of gases to the sorption medium layer.
2. Method according to claim 1, wherein the circulating gas is cooled to effect removal of adsorption heat.
3. Method according to claim 2, wherein cooling is effected after the circulating gas flows through a circulating blower in the loop which transports the circulating gas.
4. Method according to claim 1, wherein the withdrawn portion of purified gas is conducted through a further sorption medium layer before it is discharged.
5. Method according to claim 2, wherein the withdrawn portion of purified gas is conducted through a further sorption medium layer before it is discharged.
6. Apparatus for the purification of a gas stream loaded with organic gases or vapors comprising a gas loop with a circulatory blower and connecting pipes connected to a contain-er of a sorption filter, a feedline for the gas to be purified opening into the loop on the suction side of the blower, said container of the sorption filter having at least two sorption medium layers which are separated from each other to provide a space therebetween said loop having its return line from the container opening into said space between the two layers, and a purified gas outlet in the container above the sorption medium layer above said space for the discharge of purified gas.
7. Apparatus according to claim 6, wherein the circulating blower is followed by a cooler.
8. Apparatus according to claim 6, wherein in each of the loop lines leading to and from the container of the sorption filter a valve for shutting-off the flow of gas through the loop lines is provided.
9. Apparatus according to claim 7, wherein in each of the loop lines leading to and from the container of the sorption filter a valve for shutting-off the flow of gas through the loop lines is provided.
10. Apparatus according to claim 8, wherein a second sorption filter is provided, wherein the blower can be connected alter-natingly to the first sorption filter and to the second sorption filter by means of shut-off valves in inlet and outlet loop lines which are associated in pairs with each sorption filter and can be actuated in pairs.
11. Apparatus according to claim 6, wherein a check valve which prevents backward flow is inserted in the feedline for the gas to be purified.
12. Apparatus according to claim 6, wherein the feedline is equipped with flame flashback protection.
13. Method according to claim 1, wherein the volumetric flow of the circulating gas exceeds the volumetric flow of the gas to be purified introduced into the circulating gas stream by a factor of about 5 to 20.
14. Method according to claim 4, wherein the volumetric flow of the circulating gas exceeds the volumetric flow of the gas to be purified introduced into the circulating gas stream by a factor of about 5 to 20.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP3232138.4 | 1982-08-28 | ||
| DE19823232138 DE3232138C2 (en) | 1982-08-28 | 1982-08-28 | Method and device for cleaning a gas flow in a sorption filter |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1195257A true CA1195257A (en) | 1985-10-15 |
Family
ID=6171992
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000435474A Expired CA1195257A (en) | 1982-08-28 | 1983-08-26 | Method and apparatus for purifying a gas stream in a sorption filter |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5987017A (en) |
| CA (1) | CA1195257A (en) |
| DE (1) | DE3232138C2 (en) |
| FR (1) | FR2532187B1 (en) |
| GB (1) | GB2126917B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19532279C2 (en) * | 1995-09-01 | 1998-07-23 | Cs Halbleiter Solartech | Device for cleaning gases which contain ozone-depleting and / or climate-effective halogenated compounds |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE843544C (en) * | 1950-10-12 | 1952-07-10 | Metallgesellschaft Ag | Process for the production of adsorbable substances from gases or vapors or gas vapor mixtures |
| DE1442904A1 (en) * | 1964-05-08 | 1968-11-28 | Schilde Ag | Method and device for catalytic detoxification and deodorization of industrial and heating exhaust gases |
| DE2231640B2 (en) * | 1972-06-28 | 1977-09-15 | Ceagfilter Und Entstaubungstechnik Gmbh, 4600 Dortmund | METHOD FOR SEPARATING STEAM OR GASEOUS IMPURITIES FROM AN AIR OR GAS STREAM |
-
1982
- 1982-08-28 DE DE19823232138 patent/DE3232138C2/en not_active Expired
-
1983
- 1983-08-17 FR FR8313405A patent/FR2532187B1/en not_active Expired
- 1983-08-26 GB GB08323005A patent/GB2126917B/en not_active Expired
- 1983-08-26 CA CA000435474A patent/CA1195257A/en not_active Expired
- 1983-08-26 JP JP58155131A patent/JPS5987017A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| GB2126917A (en) | 1984-04-04 |
| GB8323005D0 (en) | 1983-09-28 |
| FR2532187B1 (en) | 1987-01-30 |
| DE3232138A1 (en) | 1984-03-01 |
| FR2532187A1 (en) | 1984-03-02 |
| JPS5987017A (en) | 1984-05-19 |
| DE3232138C2 (en) | 1989-05-18 |
| GB2126917B (en) | 1986-08-28 |
| JPH0330409B2 (en) | 1991-04-30 |
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