Vacuum air lock for a closed perimeter solvent conservation system

A vacuum air lock assembly for transferring an article into an enclosure for treating the article with a solvent, the enclosure including a door for admitting the article into or out of the enclosure, the assembly including a chamber mounted on the enclosure and having an outer door, the chamber being sealed to the enclosure for transferring the article from the chamber through the enclosure door into the enclosure, a vacuum pump for drawing a vacuum in the chamber and discharging the air to atmosphere, the chamber being connected to the enclosure to break the vacuum in the chamber with solvent vapor from the enclosure, the article is transferred into the enclosure through the enclosure door for treatment and returned to the chamber after treatment, and the solvent vapor in the chamber is returned to the enclosure chamber through the vacuum pump and the vacuum in the chamber is broken to atmosphere.

FIELD OF THE INVENTION 
The present invention relates generally to an emission control system for 
minimizing the atmospheric introduction of volatile constituents from 
fluid compositions used to treat articles as part of or incident to a 
manufacturing procedure. 
BACKGROUND OF THE INVENTION 
U.S. Pat. No. 5,106,404, issued Apr.21, 1992, assigned to the same 
assignee, a system for minimizing the escape of volatile compositions to 
the atmosphere is described wherein an article to be treated is placed in 
a chamber capable of maintaining both pressure and an effective vacuum, 
evacuating the chamber to remove virtually all gases, introducing into the 
chamber a fluid composition comprised of volatile constituents such as a 
solvent for treating the article, recovering the fluid and vapor 
components of the solvent composition following the treatment step and 
subsequently removing residual liquid by flushing the chamber with a 
drying fluid. The drying fluid is derived from the residual charge of 
noncondensable gas and solvent vapor within a closed loop system. The 
chamber is evacuated and the chamber then opened to the atmosphere for 
removal of the article. 
In a closed perimeter system of the type contemplated herein a vapor 
barrier or perimeter is used to form an enclosure around a solvent 
consuming process to thereby prevent solvent emission and air entry into 
the process. The closed perimeter system is applicable to 
cleaning/flushing, drying, coating, degreasing/defluxing solvent cooled 
machining, etc. It was early recognized that the secret to avoiding 
solvent emission is to prevent the solvent from coming into contact with 
air. If allowed to mix with air inevitably some solvent will be lost to 
the atmosphere. 
Since pressure within the enclosure is maintained at essentially room 
pressure, the enclosure can be very lightweight and can be as simple as a 
frame covered with film or as complex as a sealed skin enclosure. There is 
flexibility as to where the enclosure is placed to make necessary operator 
or maintenance access easier. 
At startup the enclosure is filled with air, as solvent vapor is added due 
to loss from the process, gas volume increases. The solvent vapor is 
passed through a stripper and the gas is stored in a pressure controlling 
accumulator. When the volume limit of the accumulator is reached, venting 
from the system occurs. Gas from the exit of the stripper, having the 
lowest solvent vapor concentration in the system, is vented. Recovery of 
this small vapor loss by a carbon absorber may be used, or the solvent 
vapor may be destroyed to prevent its emission to the atmosphere. Gas from 
the enclosure is circulated to the stripper and back to the enclosure, 
thus forming a closed loop of circulating gas. As solvent relative 
humidity (SRH) rises within the closed loop its dew point decreases. The 
solvent dew point decreases to the temperature of the stripper (about 
-20.degree. F.). Any further additional solvent added by the process to 
the circulating gas will result in condensation of solvent to maintain a 
constant 90% SRH at the discharge of the stripper. 
The closed perimeter system, CPS, provides a practical and relatively low 
cost way to significantly reduce solvent emissions. When the CPS is 
applied to or retrofitted to an existing solvent process such as cleaning, 
little, if any, process development is needed since the process will run 
essentially the same after application of the enclosure as before. The 
closed perimeter system is tolerant of process deficiencies within the 
enclosure. Load slugs are no problem and in some cases increase production 
through put and decreased solvent emission are available simultaneously. 
However, solvent emission from the closed loop and air entry into the 
closed loop does occur on introduction and removal of the article from the 
enclosure. 
SUMMARY OF THE PRESENT INVENTION 
The present invention relates to an air lock assembly which in combination 
with the closed perimeter system provides a system for introducing a 
product into and removal of the product from the closed perimeter 
enclosure without introducing air or allowing solvent vapor to escape. The 
air lock assembly provides a basic vacuum to vacuum process for 
introducing and removing a product from the closed perimeter enclosure. 
The air lock assembly generally includes a chamber and a vacuum pump. The 
chamber being connected to the enclosure and to the vacuum pump. 
The process includes the steps of isolating the air lock chamber from the 
rest of the closed perimeter system. Opening the chamber to introduce the 
product, closing the chamber, removing the air from the chamber by a 
vacuum pump, discharging the air from the vacuum pump outside the system, 
breaking the vacuum in the chamber with gas from inside the enclosure, 
opening the enclosure door and moving the product into the enclosure, 
processing the product, replacing the product in the air lock chamber, 
closing the enclosure door to isolate the chamber from the enclosure, 
evacuating the chamber air by the vacuum pump and discharging the chamber 
air back to the enclosure, breaking the vacuum in the chamber with air 
from the room and opening the air lock chamber door to remove the product. 
The advantage of applying the air lock to the closed perimeter system is 
that the product can be put into and removed from the closed perimeter 
system without introducing air into the system or allowing solvent vapor 
to escape from the system. The closed perimeter system in combination with 
the vacuum air lock assembly makes it possible to retrofit existing open 
type vapor degreasers with a low cost easy to install effective retrofit 
package and to reduce solvent emissions by more than 99%. 
Other principal features and advantages of the invention will become 
apparent to those skilled in the art upon review of the following 
drawings, the detailed description and the appended claims.

Before explaining at least one embodiment of the invention in detail it is 
to be understood that the invention is not limited in its application to 
the details of construction and the arrangement of the components set 
forth in the following description or illustrated in the drawings. The 
invention is capable of other embodiments or being practiced or carried 
out in various ways. Also, it is to be understood that the phraseology and 
terminology employed herein is for the purpose of description and should 
not be regarded as limiting. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention relates generally to a process for cleaning a product 
with a solvent vapor either in a continuous or a batch process. The 
practical application of the closed perimeter system depends on the 
configuration of the type of process. The closed perimeter system includes 
an enclosure 12 which is used to keep solvent vapor inside the system 
during a cleaning process and a closed loop 17 which recirculates the 
solvent vapor back to the enclosure. The closed loop 17 consists of the 
following components in order of circulation: a degreaser 10 which is the 
source of solvent vapor, the enclosure 12 which is sealed to the 
degreaser, conduit 20 connecting the enclosure to a stripper 18, conduit 
21 connecting the stripper 18 to a circulating blower 22, conduit 40 
connecting the blower 22 to a venting valve 38 and conduit 42 connecting 
the venting valve 38 to a conduit 48 which connects an accumulator 46 to 
an enclosure 12. Since pressure within the closed loop 17 is maintained at 
essentially room pressure, the enclosure 12 can be very lightweight. It 
can be as simple as a frame covered with film or as complex as a sealed 
skin enclosure. 
The concentration of solvent vapor in the air contained within the closed 
loop 17 at startup will rise as solvent vapor is lost from the process. 
The vapor stripper 18 is used to maintain the "solvent relative humidity" 
(SRH) at a low level. If SRH is controlled at 20% within the enclosure 12, 
the drying performance of the process functions much as it did before the 
enclosure was installed. In many cases the recovered distilled solvent 
liquid from the stripper 18 may be recycled through conduit 32, valve 30 
and conduit 34, back to the enclosure 12 without additional processing. 
Liquid solvent can also be directed by valve 30 and conduit 39 to 
reservoir 36. 
Of the several types of strippers 18 direct temperature swing recovery is 
recommended. The stripper is small, relatively inexpensive and easy to 
operate. Gas recirculation rate is low. Low solvent relative humidity 
(SRH) gas returning to the enclosure with or without added heat may be 
used to enhance product drying. Water within the closed loop 17 is 
captured in the stripper as ice and is removed in a defrost cycle. The 
volume of gas within the closed loop 17 will increase during startup as 
solvent vapor is added to the air within the closed loop 17. Once SRH 
equilibrium is reached the volume of the gas will be essentially constant 
for a continuous process or will swing through a small range for a 
cyclical process. The air within the closed loop 17 is used to transport 
solvent vapor to the stripper 18 for recovery. It transports the solvent 
vapor but does not allow the solvent to pass outside the enclosure. 
The slack sided accumulator 46 is used to accommodate gas volume swings, 
maintain internal pressure in the closed loop 17 at room level and with 
instrumentation to control venting. Venting may be necessary to expel 
excess air on startup and to accommodate the ingestion of air during 
operation, e.g., air entering with the product. Air at the exit of blower 
22, with the lowest vapor concentration in the closed loop, is vented 
through valve 38 and conduit 44. 
In accordance with the present invention an air lock system 14 is added to 
the enclosure 12. The air lock system 14 is used to transfer the product 
into and out of the enclosure 12 without entry of air or loss of solvent 
vapor. The design of the air lock system will vary depending on the 
product. An air lock system for a web product is relatively simple. An air 
lock system for baskets may be manual or automated and needs careful 
attention. An air lock system for an in line defluxer, processing several 
different circuit boards, is more sophisticated. 
A representative closed perimeter system 12 as shown in FIG. 1 generally 
includes a commercial degreaser 10 having an enclosure 12 mounted thereon. 
The degreaser 10 is a standard system with the enclosure 12 sealed to the 
top of the commercial degreaser. The enclosure 12 provides the vapor 
barrier. The enclosure 12 may include hand holes 16 for performing the 
cleaning function. A vapor stripper 18 is connected to the enclosure 12 by 
a tube or pipe 20. A chiller and circulating pump assembly 24 is connected 
to the stripper 18 by pipes or tubes 26 and 28. The exit of stripper 18 is 
connected by tube or pipe 21 to blower 22 which draws solvent vapor from 
enclosure 12 through stripper 18 where excess solvent is condensed and the 
low SRH gas enters blower 22. The blower 22 runs continuously. The 
stripper 18 is connected to a two way valve 30 by a pipe 32. The two way 
valve 30 is connected to the degreaser 10 by a tube 34 or to a storage 
tank 36 by a tube 39. Solvent collected in the stripper 18 may be returned 
to the degreaser 10 through the valve 30 or to the solvent storage tank 36 
through tube 39. The blower 22 is connected to a three way valve 38 by a 
tube 40. The valve 38 is connected to the enclosure 12 by a tube 42 or 
vented to atmosphere through a tube 44. Low solvent humidity gas from the 
stripper 18 may be returned to the enclosure 12 or vented to atmosphere 
through valve 38. A slack sided accumulator 46 is connected to the 
enclosure 12 by a tube 48. The accumulator 46 is used to accommodate gas 
volume swings to maintain the internal pressure which the enclosure at 
room level and, with instrumentation, to control venting. Venting may be 
necessary to expel excess air on startup and to accommodate the ingestion 
of air during operation. The air with the lowest vapor concentration is 
vented through valve 38 as noted above. 
The air lock system 14 includes an air lock chamber 50 having an access 
door 52. A transfer door 54 is provided on the enclosure for opening the 
enclosure to chamber 50. The chamber 50 is connected to a three way valve 
56 by a tube 58. The valve 56 is connected to a vacuum pump 60 by a tube 
62 and to a second three way valve 64 by a tube 66. The vacuum pump 60 is 
connected to a three way valve 70 by a tube 68. The valve 70 is connected 
to the enclosure by a tube 72 and vented to atmosphere by tube 74. The 
valve 64 is connected to the enclosure 12 by a tube 76 and vented to 
atmosphere by a tube 78. 
At startup the enclosure 12 is filled with air. As solvent vapor 
accumulates in the enclosure 12 during the processing of the article, the 
enclosure 12 is vented to the slack sided accumulator 46 through tube 48. 
When the volume limit of the accumulator 46 is reached, gas from the exit 
of the stripper 18 which has the lowest solvent concentration of the 
system is vented through blower 22 and valve 38 to tube 44. This small 
vapor loss may be recovered by a carbon absorber provided at the end of 
tube 44 or may be destroyed by chemical, thermal or other processes. 
Gas from the enclosure 12 is circulated to the stripper 18 by the 
circulation blower 22. As the solvent relative humidity within the closed 
loop 17 rises, it will reach a level where the solvent dew point is 
reduced to the temperature of the stripper heat exchanger (-20.degree. 
F.). Further addition of solvent vapor will result in condensation of 
solvent in the stripper 18 to maintain a constant 9% relative humidity at 
the discharge of the stripper. This will produce a solvent relative 
humidity within the enclosure chamber 12 of 10%-20% in a fully loaded 
machine. During idle solvent relative humidity in the enclosure 12 is 
reduced by vapor recovery from full load level of about 20% to idle level 
of 9%-10%. Recovered solvent of distilled solvent quality may be returned 
directly to the degreaser through line 34. At shut down solvent gas stored 
in the accumulator 46 is returned to the enclosure 12. 
In accordance with the invention the air lock system 14 provides the means 
to access the enclosure 12 without release of solvent to the atmosphere. 
The air lock chamber 50 shown is one of many possible configurations that 
may be applied to a closed barrier system for exiting or new open type 
vapor degreasers or other solvent processing systems. 
In operation a basic vacuum to vacuum process is utilized. This involves 
isolating the air lock chamber 50 from the rest of the closed solvent 
processing system. An access door 52 is opened and the product to be 
cleaned is introduced into the chamber 50. The access door 52 is closed, 
valve 56 is opened and the air evacuated from the chamber by the vacuum 
pump 60. The air from the vacuum pump is vented to atmosphere through the 
valve 70 and tube 74. When the air chamber 50 has been completely 
evacuated, the vacuum pump 60 is turned off, valve 56 is closed to the 
vacuum pump 60, and opened to the valve 64 which is opened to the closed 
loop 17 through tube 76. The vacuum in the air lock chamber 50 draws gas 
from inside the closed loop 17 so that the air lock chamber 50 is of the 
same air/solvent/vapor composition as inside the enclosure chamber 19. 
The transfer door 54 is opened to transfer the product to the enclosure 12 
for degreasing. After degreasing the product is replaced in the air lock 
chamber 50 and the transfer door 54 closed to isolate the air lock chamber 
54 from the enclosure 12. The air lock chamber 50 is again evacuated by 
the vacuum pump 60 and the contents discharged through the valve 70 back 
to the closed loop 17 through pipe 72. The vacuum in the air lock chamber 
50 is broken by opening valves 56 and 64 to return the air lock chamber 50 
to room pressure. The access door 52 is then opened to remove the product. 
Referring to FIG. 3 an alternate embodiment of the air lock system 80 is 
shown which can be used with a manually operated open top type degreaser. 
The air lock system 80 includes a housing or bell 84 which is suspended 
above the top 86 of the enclosure 12 by means of a rope or cable assembly 
88. An opening 90 is provided in the top 86 of the degreaser enclosure 12 
through which the product 92 to be cleaned is inserted or removed from the 
enclosure 12 and degreaser 10. The housing or bell 84 is open at the 
bottom and has an outer circumference larger than the opening 90 in the 
top 86 of the enclosure 12. A door 94 is pivotally mounted on the inside 
of the top 86 to open and close the opening 90. Means are provided around 
the perimeter of the door opening 90 to hermetically seal the housing or 
bell to the top of the degreaser. 
In this regard, an adapter ring 95 is mounted on the top of the enclosure 
around opening 90 and secured thereto by any appropriate means. The ring 
95 is also sealed to the top of the enclosure 12. A containment ring 97 is 
mounted on the outer edge of the top of the adapter ring 95 and an 0-ring 
seal 96 is positioned on the top of the adapter ring 95 inside of the 
containment ring 97. The 0-ring seal 96 is retained in place by a spacer 
ring 99 mounted on the outside of the bell 84 which is guided into 
position on the adapter ring 95 by the containment ring 97 and sealed 
therein by 0-ring 96. The door 94 is sealed to the inside of the top of 
the enclosure by means of a gasket 98 secured to the inside of the top of 
the enclosure. 
The product 92 to be cleaned is supported in a basket 100 suspended in the 
housing or bell by a hook assembly 102. In this regard, hook assembly 102 
includes a double acting piston and cylinder assembly 104 having a 
cylinder 106 mounted on the top of housing 84. A piston 108 is provided in 
the cylinder 106 and includes a rod 110 which depends from the cylinder 
106 into the housing 84. A hook 112 is connected to the end of the rod 110 
for supporting the basket 100 in which the product 92 to be cleaned is 
placed. 
In operation, the housing or bell 84 is suspended above the enclosure with 
the piston rod 110 extended downwardly below the housing 84. The product 
or products to be cleaned are placed in the basket 100 and the basket 100 
attached to the hook 112. Air is introduced into the lower end 115 of the 
cylinder 100 to raise the piston rod 110 into the cylinder and the basket 
into the housing or bell 84. The housing or bell 84 is pulled down to seat 
the bell 84 on the seal 96 in the top of the enclosure and the door 94 
closed against gasket 98. The air is evacuated from the bell 84 through an 
opening 114 in the adapter ring 94 which is connected by tube 58 to the 
vacuum pump 60 for discharge to atmosphere as described above. The vacuum 
in bell 84 is broken by opening valves 64 and 56 to fill the bell with 
solvent vapor from the closed loop 17. The door 94 is opened and the 
piston and cylinder assembly 102 actuated by introducing air into the 
upper end 117 of the cylinder to lower the basket into the degreaser. 
After the product has been cleaned, the product is placed in the basket 
100 which is then mounted on the hook 112. The piston and cylinder 
assembly is reversed to lift the basket 100 into the bell 84. The door is 
closed and the valve 56 opened to pump 60 to draw the solvent gas from the 
bell 84 and return it to the closed loop 17 through valve 70 and tube 72. 
The vacuum in bell 84 is broken by opening valves 56 and 64 to the 
atmosphere. The bell 84 is then lifted off the adapter ring 95 and the 
basket 102 lowered to remove the solvent cleaned product. 
Thus, it should be apparent that there has been provided in accordance with 
the present invention a vacuum air lock for a closed perimeter solvent 
conservation system that fully satisfies the objectives and advantages set 
forth above. Although the invention has been described in conjunction with 
specific embodiments thereof, it is evident that many alternatives, 
modifications and variations will be apparent to those skilled in the art. 
Accordingly, it is intended to embrace all such alternatives, 
modifications and variations that fall within the spirit and broad scope 
of the appended claims.