CA1144873A

CA1144873A - Solvent recovery installation

Info

Publication number: CA1144873A
Application number: CA000350163A
Authority: CA
Inventors: Hubert Mugrauer
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1979-04-20
Filing date: 1980-04-18
Publication date: 1983-04-19
Also published as: DE2916095C2; ATE3186T1; EP0018478B1; JPS55142524A; EP0018478A1; DE2916095A1

Abstract

ABSTRACT OF THE DISCLOSURE
A solvent recovery system is disclosed with at least two adsorbers and a condenser. A first gas which is enriched with solvent vapor is guided for adsorbtion over the first ad-sorber. Simultaneously, a second gas is guided for the pickup of solvent vapor which has been released by the second adsorber previously charged with solvent vapor so as to discharge it while being heated. The second gas which is charged with sol-vent vapor is guided over the condenser in which the solvent precipitates out of the second gas. Following this, the second gas which for the most part is free of solvent is guided add-itionally over the first adsorber in order to attain a complete cleaning of the gas. After charging of the first adsorber the first gas is switched over to the second adsorber and the first adsorber is discharged. The switchover proceeds with the help of a multi-path valve which can connect an input conduit with the first adsorber and the second adsorber. Additionally, the multi-path valve for the discharging of the adsorbers can con-nect with the condenser. As gas, air is used both for the charging and discharging of the adsorbers.

Description

8~7~

BACKGROUND OF THE INVENTICN
me inventlon concerns a solvent recovery system with at least two adsorbers and a condenser. In the system a first gas en-riched with solvent vapor is conducted over the first adsorber for adsorption; a second gas for the adsorption of the released solvent vapor is guided over the second adsorber in order to discharge it while being heated and the second adsorber is sub~e3uently cooled;
the charged second gas is conducted through the condenser where the solvent is deposited (or precipitated) out of the second gas; and after charging the first adsorber, the first gas is diverted to the second adsorber and the first adsorber is discharged.
The adsorption of solvent vapors with the help of ad-sorbers is known ("Activated Gharcoal And Its Industrial Use" by Dr. Bailleul, Dr. Bratzler, Dr. ~lerbert, Obering. Vollmer, 4th Edition, 1962, Ferdinand Enke-Verlag, Stuttgart, pages 9, 38, 39, 46-49). Accordingly, what i5 understo3d by adsorption is the auto-matically occurring condensation of a medium (desorbent) on the sur-face of another medium (adsorbent). It is further known to use special activated charcoals for the adsorption. This has the advant-age that they can almost completely adsorb vapors from gas even in the case of very low concentrations and thereby can be ex*ra-ordinarily highly charged or loaded. The activated charcoal further has the advantage that it can be very easily dischc~rged or unloacled again. For this purpose, in the case of the prior art, water vapor is used which is blown through the activated c~larcoal and thereby ., ,,~
' picks up the solvent vapor.
It is also known from the literature selection which was cited (pages 46-49) what type of method must be employed in order to remove a solvent vapor from a gas, for example, air.
The air with the solvent vapor contained in it is, for example, blown from below upward through the activated charcoal. Thereby, solvent vapors are adsorbed by the activated charcoal and the air exits freed of solvent vapors from the adsorbent. When the activated charcoal is charged with solvent vapor, water vapor is guided in a counter~flow, for example, from above downward, through the activated charcoal. Thereby, the activated charcoal is freed of solvent vapors and is guided with the water vapor flow to a condenser and there is precipitated with cold water.
Following this, the activated charcoal which had been heated by the water vapor is again cooled. Large scale plants thereby function as a rule with at least two adsorbers. The air which contains the solvent vapor is first guided through the first ad-sorber. After charging of the first adsorber is completed, the air is switched over from the first to the second adsorber. The charged first adsorber is, following this, steamed out from above downward with the help of water vapor for the purpose of expul-sion of the solvent vapors which were picked up. The mixture of water vapor and solvent vapors which arises thereby is guided to a condenser for condensation. There, the solvent separates out of the water vapor.
The known installations are used on a large scale es-pecially in chemistry for the elimination of solvent vapors in '.' 4~3 the air in the case of chemical processes. These conventional large scale plants thereby require water vapor generators or ;
superheated steam connections. In the case of installations wlth which only very small solvent vapor quantities in the air are to be recovered~ an expense typical for the large plants cannot be undertaken. Such a situation exists in copying or printing de~
vices which function according to the electrostatic principle.
There, toner images of the symbols to be printed are produced upon a recording means, for example, a web of paper. The toner ~lO images must be fixed to the recording medium for the purpose of ~; a permanent bond. For this it is known to guide the web~of paper wl~h the toner images through a fixing station. In the fixing station, solvent vapor is guided over the web of paper having the toner images. ~he~solvent vapor dlssolves the toner so that ~; this can penetrate into the web of paper. In order to~prevent the solvent vapor from penetrating into the air surrounding the ;
fixing station, a solvent recovery~installation can be provided ~
; for the fixing statlon over~which the air that surrounds the flx-ing station is guided and in which the solvent vapor is comp~letely 20~ ~removed from the air. In the case of a device of this sort, how-~e~er, only relatively small quantlties of air need be fre~ed~of s~olvent vapor. The large scale plants cited above are not suit~
able for this.
SUMMARY OF THE~IN~ENTION
It is an ob;ect of the invention to provide a solvent recovery installation whtch;is low ln expense, economlcal, and with which smaller air~quantitles which contain small traces~of ~ 3 ~

. . . ~ .... ~ . . . : :: . . . ~
, ~ ~ , : ' ' ' ' ' solvent vapor can be cleaned. With the solvent recovery instal-lation of the type cited above~ in accordance with the invention, behind the condenser a first conduit is provided for a second gas which, via a valve, is connected with conduits for the first gas which lead to the adsorber such that the gas which is released from the condenser passes through that adsorber which is then being charged.
It is practical to provide an input conduit for the supply of the first gas which ends at a multi-path valve. From the multi-path valve, a second conduit leads to the first adsorb-er, a third conduit to the second adsorber, and a fourth conduit to the condenser. The first conduit thereby connects the con-denser with the input conduit.
For the transport of quantities of air through the in-stallation, a blower is arranged in the input conduit. Accord-ingly, it is advantageous that the blower is arranged between the discharge of the first conduit into the input conduit and the multi-path valve. Accordingly, for the transport of the second gas through the condenser, no blower of its own need be provided.
In order to free the charged adsorber of solvent vapor, it is practical to arrange heaters in the adsorber.
Both the condenser as well as the adsorber must be eooled from time to time. It is thus advantageous to provide a cooling device with a cooling liquid container. The cooling de-vice is thereby connected direetly with the condenser, whereas the cooling liquid container is connected with cooling coils ., ~ .

. , .

which are arranged in the adsorber.
Both the first gas and the second gas can consist of air. It is thus no longer necessary to use water vapor for the discharging of the adsorber.
For the controlling of the gas flows in the system, be-sides the multi-path valve there can be provided a first valve in the first conduit, a second valve at the cutput of the first ad-sorber, and a third valve at the output of the second adsorber.
With the help of the three valves and of the multi-path valve~
then the gas flows can be controlled in the system.
The operation of the system is such that the multi-path valve is set in a manner that the input conduit is connected with the second conduit and the third conduit with the condenser. The second valve is opened so that the first adsorber is charged by the first gas. Further~ the third and the first valves are opened so that by means of the suction force of the blower, the second gas is guided via the third valve, the second adsorber, the con-denser, and the blower to the first adsorber. Thereby, the sec-ond adsorber is unloaded. After the discharging of the second adsorber~ the first valve and the third valve are again closed and the cooling is connected for the second adsorber. After the charging of the second adsorber, the multi-path valve is switched over so that the input conduit is connected with the third conduit to the second adsorber and the second conduit is connected with the condenser. The valves are now controlled such that the first gas runs through the second adsorber while the second gas dis-charges or unloads the first adsorber and following this is guided over the condenser. The solvent recovery installation is provided such that it can recover solvent consumption quantities smaller than 0.5 Kg per hour. It is constructed in simple fashion as is well-known in the art and can be manufactured inexpensively.
Additional gases are not required for the discharging of the ad-sorbent.
BRIEF DESCRIPTION OF THE DRAWI'NGS
The drawing illustrates in schematic form the solvent recovery installation of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The solvent recovery installation consists of a first adsorber ADl, a second adsorber AD2, a condenser KD, a blower ~E, a cooling device ~R and the conduits connecting the individual components, in which conduit valves are arranged.
A gas, for example, air, which is enriched with solvent vapor, is provided to an input conduit EL at the input E. It is sucked in with the help of the blower which is arranged in the input conduit EL and is transported to a multi-path valve MV at the end of the input conduit EL. The multi-path valve MV can be a four-way valve. The multi-path valve MV can be adjusted such that the air flow with the solvent vapor is diverted from the in-put conduit EL to a conduit L2, which leads to the first adsorber AD]. This is shown in the Figure. The air flow thus passes through the first adsorber ADl and charges or loads the activated charcoal which is contained in the first adsorber ADl. In order to make possible the transport of the air flow through the first adsor'ber ADl, a valve V2 which is arranged at the output of the adsorber ADl in the conduit is opened.
It is assumed that the second adsorber AD2 is already charged with solvent vapor. It is discharged during the time in which the first adsorber ADl is charged. ~or this purpose, the multi-path valve MV is ad~justed such ~hat a conduit L3 which leads from the multi-path valve MV to the second adsorber AD2 is con-nected with the condenser KD. Simultaneously, a valve V3 which lies at the output of the second adsorber AD2 in the conduit is opened and a heater HZ2 which is arranged in the second adsorber AD2 is connected. A further conduit Ll leads from the condenser KD to the input conduit EL in such a manner that the blower GE is positioned between the discharge mouth of the conduit Ll and the multi-path valve MV.
If the valve Vl whlch is positioned in the conduit Ll is then also opened, an air flow is then sucked in by the blower GE which can flow via the valve V3, the second adsorber AD2, the condenser KD, the conduit Ll and the valve Vl to the conduit EL;
and from there can flow via the blower GE, the multi-path valve MV together with the remaining air flow from the input E to the first adsorber ADl. Since the heater HZ2 in the second adsorber AD2 is connected, the solvent vapors separate at a temperature of approximately 90C from the activated charcoal in the second ad-sorber AD2 and are carried along by the air flow. They proceed together with the air flow via the conduit L3 into the condenser KD. The condenser KD in known manner can be cooled by the cooling device VR (constructed in known manner) directly to a temperature of -15C, for example. Thereby, the solvent separates from the air and flows into a container BH. The air behind the container 3~7~

BH now contains only very low quantities of solvent vapor. Thismixture is supplied via the conduit L1, the valve Vl to the input conduit L and flows together with the air flow from the input E
to the first adsorber AD1. The solvent vapors which are still contained in the alr behind the condenser KD are then completely adsorbed in the first adsorber ADl.
If the second adsorber AD2 is discharged, then the heater HZ2 is disconnected and the valves V2 and V3 are closed.
Following this, the adsorber AD2 is cooled. For this purpose, cooling coils KS are contained in the adsorber AD2, which are connected with the cooling device VR.
It is thereby practical to provide a cooling liquid con-tainer S0 in the cooling device V~, the content of which is con-stantly cooled by a refrigerator. Then it is not necessary that the refrigerator itself has to be designed to directly cool the cooling coils in the adsorber ADl and AD2 besides the condenser KD. The cooling of the second adsorber AD2 is necessary because it is to be ready for discharging use again as soon as possible.
For the setting of different gas quantity flows in the conduits, in a practical manner valves can be used. In particular, the valves V2 and V3 can be adjusted such that the second gas flow is smaller than the first gas flow.
If the first adsorber ADl is charged with solvent vapor, then the air flow is switched over from the input E of the input conduit EL from the first adsorber ADl to the second adsorber AD2.
The multi-path valve ~V is adjllsted correspondingly. The air flow from the input E is thus diverted from the input conduit EL via .

the conduit L3 to the second adsorber AD2. For this procedure the valve V3 is opened. Simultaneously, care is taken that the conduit L2 which leads to the first adsorber ADl is switched over by means of the multi-path valve MV to the condenser KD.
Thus, the first adsor~er ADl is connected via the conduit 1,2 with the condenser KD. Now the first adsorber ADl is discharged with the help of the condenser KD in ~he manner cited above.
~or this purpose the valves Vl and V3 are opened and an air flow opposite to the air flow during the loading is guided through the first adsorber ADl. Simultaneously, a heater HZl is connected. After the discharging of the first adsorber ADl, the valves Vl and V3 are again closed and cooling coils KS in the adsorber ADl are connected with the cooling liquid container S0 in the cooling device VR. The process continues then in the ; manner described above.
Although various minor modifications may be suggested by those versed in the art, it should be understood that I wish to embody within the scope of the patent warranted hereon, all such embodiments as reasonably and properly come within the scope of my contribution to the art.

_ g_ ~ ' .

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A solvent recovery system, comprising: at least a first and a second adsorber means each having a heater and for being charged by a solvent vapor when a gas containing the same is passed therethrough and discharged to release the solvent vapor when heated; a first gas input/output leading to the first adsorber means and a second gas input/output leading to the second adsorber means; a condenser means for precipitating solvent from a gas being guided therethrough; a gas input;
means for conveying gas from the condenser means after precip-itation of the solvent so as to combine with gas at the gas input; and switching means for first selectively guiding the gas from the gas input and gas from the condenser means to the first adsorber means while gas from the second input/output is guided through the second adsorber means with the heater being energized to the condenser means so as to discharge the second adsorber means while the first adsorber means is charging, and in a second position for guiding gas from the gas input and gas from the condenser means through the second adsorber means while gas from the first input/output is guided through the first ad-sorber means with the heater being energized to the condenser means so as to discharge the first adsorber means while the second adsorber means is charging.

2. A system according to claim 1 wherein an input conduit feeds the gas from the gas input to the switching means compris-ing a multi-path valve; from the multi-path valve a second con-duit connects to the first adsorber means, a third conduit to the second adsorber means, and a fourth conduit to the condenser means; and a first conduit connects an output of the condenser means with the input conduit.

3. A system according to claim 2 wherein between a dis-charge of the first conduit into the input conduit and the multi-path valve a blower is arranged.

4. A system according to claim 1 wherein a heater element and a cooler element is arranged in each of the first and second adsorber means.

5. A system according to claim 1 wherein a cooling device with a cooling liquid container is provided, the cooling device being connected directly with the condenser means, while the cooling liquid container is connected with cooling coils arranged in each of the first and second adsorber means.

6. A system according to claim 1 wherein the gas in all cases is air.

7. A system according to claim 2 wherein for the control-ling of the gas flows, besides the multi-path valve, a first valve is arranged in the first conduit, a second valve at an output of the first adsorber means, and a third valve is ar-ranged at an output of the second adsorber means.

8. A system according to claim 7 wherein each of the valves has adjusting means for determining different gas quant-ities in the conduits.

9. A solvent recovery system, comprising: at least first and second adsorber means each having a heater connected there-with and for being charged by a solvent vapor in a gas passing through the adsorber and being discharged when the heater is energized so as to release the solvent vapor to a gas passing therethrough; condenser means having a cooler attached thereto for precipitating out solvent when a gas is passed therethrough;
a gas input; a first gas input/output connected to the first adsorber means; a second gas input/output connected to the second adsorber means; a conduit connecting an output of the condenser means so as to combine gas output therefrom with gas at the input; and a multi-path switchable valve means which in a first position directs gas from the input to the first adsorber means at an end thereof opposite the first input/output while directing gas from the second adsorber means entering at the second input/output to an input of the condenser means, and in a second position directing gas from the input to the second ad-sorber means at an end opposite the second input/output and di-recting gas from the first adsorber means entering at the first input/output to an input of the condenser means; whereby in the first position the first adsorber means is charged while the second adsorber means is discharged and in the second position the first adsorber means is discharged while the second adsorber means is charged.

10. A system according to claim 9 wherein a blower is ar-ranged between the discharge of the gas from the condenser means which combines with the gas at the input and the multi-path valve means whereby this blower provides air movement for both the first adsorber means and the second adsorber means along with the condenser means.

11. A method for operating a solvent recovery system, com-prising the steps of: providing first and second adsorbers which are charged when a gas passes therethrough with solvent vapor and which are discharged when the adsorbers are heated so as to release the solvent vapor to a gas passing therethrough;
providing a condenser for precipitating out solvent when a gas passes therethrough; providing a gas switching system; in a first mode of the switching system directing gas through the first adsorber to charge it, directing gas through the second adsorber while it is heated to discharge it, and feeding gas from an output of the second adsorber through the condenser and then combining it with the gas passing through the first ad-sorber; in a second operating mode of the switching system feeding gas through the second adsorber so as to charge the same, feeding gas through the first adsorber while it is heated to discharge the same, and feed gas from an output of first adsorber through the condenser for precipitation of solvent and then combining it with the gas passing through the second adsorber.

12. The method of claim 11 including the steps of cooling the first adsorber during the first mode when charging occurs and cooling the second adsorber during the second mode when charging occurs, and wherein the condenser is cooled during both modes.