U.S. patent application number 09/739458 was filed with the patent office on 2002-06-20 for compact volatile organic compound removal system.
Invention is credited to Logan, Mark A., Wright, Lloyd F..
Application Number | 20020073715 09/739458 |
Document ID | / |
Family ID | 24972399 |
Filed Date | 2002-06-20 |
United States Patent
Application |
20020073715 |
Kind Code |
A1 |
Logan, Mark A. ; et
al. |
June 20, 2002 |
COMPACT VOLATILE ORGANIC COMPOUND REMOVAL SYSTEM
Abstract
A compact, volatile organic compound removal system is
presented. The system has a metal condensation plate and a cooling
source in intimate thermal contact with the metal condensation
plate. The metal condensation plate has a channel formed in the
plate, an inlet in the condensation plate for introducing a gas
carrying volatile organic compound vapors into the channel, a high
surface area metallic structure, such as foamed metal or metallic
fins, in intimate contact with the walls of the channel, an outlet
in the condensation plate for removing the gas from the channel and
a drain in the condensation plate for removing volatile organic
compound condensates from the channel. The cooling source cools the
channel walls and the high surface area metallic structure so that
the volatile organic compound vapors condense on the high surface
area metallic structure to be removed from the gas.
Inventors: |
Logan, Mark A.; (Pleasant
Valley, NY) ; Wright, Lloyd F.; (Hopewell Junction,
NY) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Family ID: |
24972399 |
Appl. No.: |
09/739458 |
Filed: |
December 15, 2000 |
Current U.S.
Class: |
62/3.4 ; 62/272;
62/85 |
Current CPC
Class: |
F25B 21/02 20130101;
B01D 5/0015 20130101; Y02A 50/20 20180101; Y02A 50/235 20180101;
F28F 3/025 20130101; F28F 3/12 20130101; F28F 2215/02 20130101;
F28F 13/003 20130101 |
Class at
Publication: |
62/3.4 ; 62/272;
62/85 |
International
Class: |
F25B 021/02; F25B
047/00; F25D 021/00 |
Claims
What is claimed is:
1. A compact, volatile organic compound removal system, comprising
a metal condensation plate having a channel formed with said plate,
said channel having walls; an inlet in said condensation plate for
introducing a gas carrying volatile organic compound vapors into
said channel; a high surface area metallic structure in intimate
contact with said channel walls; an outlet in said condensation
plate for removing said gas from said channel; a drain in said
condensation plate for removing volatile organic compound
condensates from said channel; and a cooling source in intimate
thermal contact with said metal condensation plate for cooling said
channel walls and said high surface area metallic structure so that
said volatile organic compound vapors condense on said high surface
area metallic structure to be removed from said gas.
2. The system of claim 1 wherein said high surface metallic
structure comprises foamed metal in said channel between said input
and said outlet.
3. The system of claim 2 wherein said foamed metal is brazed to
said channel walls.
4. The system of claim 2 wherein said foamed metal comprising a
first section toward said inlet, said first section having a first
pore density; and a second section toward said outlet, said second
section having a second pore density greater than said first pore
density.
5. The system of claim 4 wherein said first section has a first
pore density of 10 pores per inch.
6. The system of claim 5 wherein said second section has a second
pore density of 40 pores per inch.
7. The system of claim 1 wherein said channel has a plenum between
said foamed metal and said inlet.
8. The system of claim 1 wherein said high surface metallic
structure comprises metal fins.
9. The system of claim 8 wherein said metal fins are brazed to said
channel walls.
10. The system of claim 8 wherein said metal fins comprise a first
section toward said inlet, said first section having a first fin
density; and a second section toward said outlet, said second
section having a second fin density, said second fin density
greater than said first fin density.
11. The system of claim 1 wherein said at least one cooling source
comprises a first cold plate cooled by water; and a first plurality
of thermoelectric devices between, and in thermal intimate contact
with, said metal condensation plate and said first cold plate.
12. The system of claim 11 wherein said at least one cooling source
further comprises a second cold plate cooled by water, said second
cold plate opposite said first cold plate with respect to said
metal condensation plate; and a second plurality of thermoelectric
devices between, and in intimate thermal contact with, said metal
condensation plate and said second cold plate.
13. The system of claim 1 wherein said at least one cooling source
comprises a first cold plate cooled by a refrigerant, said first
cold plate in thermal intimate contact with said metal condensation
plate.
14. The system of claim 13 wherein said at least one cooling source
further comprises a second cold plate cooled by said refrigerant,
said second cold plate opposite said first cold plate with respect
to, and in intimate thermal contact with, said metal condensation
plate.
15. The system of claim 1 wherein said at least one cooling source
comprises a first metal tube cooled by a refrigerant, said first
metal tube fixed to, and in thermal contact with, said metal
condensation plate.
16. The system of claim 15 wherein said at least one cooling source
further comprises a second metal tube cooled by said refrigerant,
said second metal tube fixed to, and in thermal contact with, said
metal condensation plate, said second metal tube opposite said
first metal tube with respect to said metal condensation plate.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention is related to systems for removing
volatile organic compounds from effluents and, more particularly,
to systems for removing volatile organic compounds from the
effluents of a semiconductor fabrication facility.
[0002] Many processes used in the fabrication of semiconductor
devices require subsequent cleaning steps with organic solvents or
the use of an alcohol to dry the device by removing water and
producing a hydrophobic surface. Removal of these organic compounds
from a semiconductor wafer surface usually requires directing a
gas, such as nitrogen, to flow across the wafer surface. The
resulting effluent gas stream is laden with volatile organic
compounds (hereafter termed VOCs). If released into the atmosphere,
these volatile organic compounds can react with sunlight to produce
photochemical smog or can cause other environmentally detrimental
effects.
[0003] As a result, environmental regulations strictly limit the
amount of VOCs which may be released into the air. It is desirable,
then, to remove a high percentage of these VOCs prior to releasing
these effluent gas streams into the air. It is further desirable
that a VOC removal system be flexible in operation to allow a wide
range of inlet gas of flow rates and VOC concentrations, so the
cleaning or drying processes are not impaired nor compromised.
[0004] A previous VOC removal technique has been the use of an
absorption medium, such as activated carbon, to remove the VOCs.
However, this technique has the disadvantage of creating a solid
waste product which must then be disposed of at substantial
cost.
[0005] A better approach is to remove the VOC vapor by
condensation. It is much more desirable because the resulting
liquid may be recycled at much lower cost. However, the problem in
most condensation systems is the formation of fog, which consists
of very tiny droplets of the VOC. Such tiny droplets do not settle
out of gas streams, but remain suspended within it. The fog
droplets also flow with moving air streams and avoid contact with
solid surfaces. As a result, the removal of fog droplets is
notoriously difficult. Fog forms when a gas stream is cooled below
the dew point of its condensable vapor constituents. Fog formation
is common when a gas stream containing condensable vapors is cooled
in a condensing unit with a low surface area-to-volume ratio.
[0006] On the other hand, the present invention provides for a
volatile organic compound removal system which has an extremely
high surface area to volume ratio. The system also has good thermal
conductivity to assure that the surfaces are cooled appropriately
to condense the VOCs.
SUMMARY OF THE INVENTION
[0007] The present invention provides for a compact, volatile
organic compound removal system. The system comprises a metal
condensation plate and a cooling source in intimate thermal contact
with the metal condensation plate. The metal condensation plate has
a channel formed in the plate, an inlet in the condensation plate
for introducing a gas carrying volatile organic compound vapors
into the channel, a high surface area metallic structure in
intimate contact with the walls of the channel, an outlet in the
condensation plate for removing the gas from the channel and a
drain in the condensation plate for removing volatile organic
compound condensates from the channel. The cooling source cools the
channel walls and the high surface area metallic structure so that
the volatile organic compound vapors condense on the high surface
area metallic structure to be removed from the gas. Foamed metal
works effectively as the high surface area metallic structure.
Alternatively, metal fins can also work as the high surface area
metallic structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIGS. 1A and 1B are opposing perspective views of an
assembly of a volatile organic compound removal system, according
to one embodiment of the present invention;
[0009] FIG. 2 is an exploded view of the volatile organic compound
removal system of FIGS. 1A and 1B; and
[0010] FIG. 3A is a detailed view of the condensation plate in the
volatile organic compound removal system of FIGS. 1A and 1B; FIG.
3B is a detailed view of an alternate condensation plate in the
volatile organic compound removal system.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
[0011] One embodiment of the present invention is illustrated by
the assembly in FIG. 1. A condensation plate 31 which receives the
gas carrying the VOCs is fixed between two cold plates 32. A cold
plate or heat transfer plate, such as described in U.S. Pat. No.
6,032,726, which issued Mar. 7, 2000 and is assigned to the present
assignee, is typically a flat metal plate in contact with a flowing
fluid. The fluid, normally a liquid, carries heat from (or to) the
thermally conductive metal plate for cooling (or heating) purposes.
It should be noted that the cold plate illustrated in the cited
patent, which is incorporated by reference herein, is an example of
a cold plate which might be used in the described assembly. Other
cold plates may also be used.
[0012] In the assembly of FIGS. 1A and 1B, the two liquid cold
plates 32 are plumbed together with a U-tube 36 to simplify the
connection of cooling water to the cold plate inlet and outlet
connections 10. Snap disc thermostats 38 in the cold plates 32
protect against operation without the cooling water. As shown by
the exploded view in FIG. 2, between each cold plate 32 and the
condensation plate 31 are thermoelectric modules 14 which transfer
heat from the condensation plate 31 to each cold plate 32.
Electrical connections to the thermoelectric modules 14 are made
through electric connectors 37. The thermoelectric modules 14 cool
the condensation plate 31 from both sides and inject the heat from
the condensation plate 31 into the two liquid cold plates 32 for
removal from the system. The entire assembly is clamped together by
bolts 13 and Belleville disc springs (not shown in the drawings)
which are tightened to a specific torque to properly compress the
thermoelectric modules 14 to the condensation plate 31 and the
liquid cold plates 32. A thermally conductive grease or other
compound between the condensation plate 31 and liquid cold plates
32 ensures good thermal contact. Insulation 15 increases the
efficiency of the thermoelectric modules 14.
[0013] The condensation plate 31 has a gas inlet tube 33, a gas
outlet tube 34 and a drain tube 35. A gas stream containing the
VOCs enters the condensation plate 31 though the inlet tube 33 and
the gas stripped of the VOCs exits the condensation plate 31
through the outlet tube 34. The condensed VOCs drain out of the
condensation plate 31 through the drain tube 35. The condensation
tube 31 also has a temperature probe 11 (shown in FIG. 2) for the
gas stream exiting the condensation plate 31 to control or monitor
the exit gas temperature and thus the VOC dew point/concentration
in the condensation plate 31.
[0014] An alternate arrangement removes the thermoelectric modules
14. Rather than cooling water, a refrigerant is pumped through the
liquid cold plates 32 which are placed in direct contact with the
condensation plate 31. Still another arrangement does away with
cold plates. Instead, the refrigerant is pumped through metallic
tubes which are in intimate thermal contact to the outside surfaces
of the condensation plate 31.
[0015] A preferred embodiment of the condensation plate 31 is shown
in FIG. 3A. The plate 31 is formed by a metallic base plate 22 and
a cover plate 20 which are brazed together. The metallic base plate
22 has a machined cavity forming a channel 19, which holds two
sections 16 and 17 of foamed metal. The section 16 is fixed by
brazing in the machined channel 19 near the gas inlet tube 33 when
the metallic base plate 22 and the cover plate 20 are joined. The
space in the machined channel 19 opposite the gas inlet tube 33
forms a plenum 23 so that the incoming gas is distributed evenly
across the width of the foamed metal section 16. The bottom
boundary 18 of the plenum 23 is angled to remove the condensed
VOCs, as discussed below. The section 16 has a particular surface
area-to-volume ratio. In the case of foamed metal, the ratio is
determined by a pore per inch (ppi) density. A ppi of 10 has been
found work effectively for isopropyl alcohol as the VOC. The foamed
metal section 17 of higher surface area-to-volume is fixed in the
machined cavity 19 just above, and between, the foamed metal
section 16 and the opening to the gas outlet tube 34. The space in
the machined channel 19 opposite the gas outlet tube 34 forms a
manifold 23 so that the gas leaving the section 17 collects in the
manifold for exhaust through the gas outlet tube 34. For the
section 17, a ppi of 40 has been found to effectively with the
section 16 of 10 ppi in removing isopropyl alcohol.
[0016] The cover plate 20 is brazed to the periphery 25 of the
machined channel 19 and the foamed metal pieces of the sections 16
and 17. The inlet and outlet tubes 33 and 34, and the drain tube 35
are either brazed or welded to the appropriate openings in the
cover plate 20.
[0017] Operationally, a gas, typically nitrogen or air, laden with
VOCs, such as isopropyl alcohol, flows into the inlet tube 33 of
the condensation plate 31. The gas in the plenum 23 is distributed
across the 10 ppi foamed metal section 16. The thermoelectric
modules 14 cool the 10 ppi foamed metal section 16 to the desired
dew point, typically <-10.degree. C. Any fog droplets formed in
the section 16 are removed by contact with the smaller pore size
(and higher density) 40 ppi foamed metal section 17. The two
sections 16 and 17 form two parts of a high surface area metallic
structure. The section 16 which first encounters the VOC laden gas
is larger than the section 17, but has a lower surface area and
lower pressure drop across the section 16. High concentrations of
VOCs and fog droplets are removed here. The section 17 is smaller
than the section 16, but has the highest possible surface area and
pressure drop across section 16 to remove the lower concentrations
of VOCs and fog droplets. The condensed VOC liquid drains by
gravity down through the foamed metal sections 16 and 17 to the
sloped bottom 18 by which the condensed liquid flows out to the
drain tube 35.
[0018] Alternatively, the high surface area metallic structure of
the foamed metal sections 16 and 17 in the condensation plate can
be replaced by two sections of metal fins 26 and 27 which are
brazed to the metallic base 22 of the condensation plate 31, as
illustrated in FIG. 3B. Metal fin section 26 has a first fin
density and metal fin section 27 has a second fin density, greater
than that of section 26. Metal fin sections 26 and 27 perform the
same functions as foamed metal sections 16 and 17, respectively. In
one example, section 26 has wavy fins with parameters at 20 fins
per inch density, 0.375 inch amplitude and 0.006 inch thickness, or
lanced off-set fins with parameters at 20 fins per inch density,
0.125 off-set and 0.006 inch thickness. Section 27 has wavy fins at
42 fins per inch density, 0.375 inch amplitude, 0.006 inch
thickness, or with lanced off-set fins at 20 fins per inch density,
0.125 inch off-set, 0.006 inch thickness but rotated 90.degree. (so
as to be perpendicular to the gas flow). Such exemplary fin
sections have been found to be effective in removing isopropyl
alcohol from nitrogen.
[0019] Tests conducted with the foamed metal embodiment of the
present invention on a inlet stream of 50% isopropyl alcohol in a
nitrogen flow of 100-400 cubic feet per minute and using
thermoelectric devices as the source of cooling have achieved the
surprising results of outlet concentrations of 400 ppm IPA, or a
dew point of -30.degree. C. without fog formation, a concentration
previously unreachable without using an absorption media.
Furthermore, the assembly is compact with dimensions no more than
16 inches wide by 13 inches tall by 3 inches deep. Additionally, by
adjusting the pore per inch density and/or the relative dimensions
of the sections 16 and 17, the present invention is flexible in
operation in allowing a wide range of inlet gas flow rates and VOC
concentrations.
[0020] Therefore, while the description above provides a full and
complete disclosure of the preferred embodiments of the present
invention, various modifications, alternate constructions, and
equivalents will be obvious to those with skill in the art. For
example, metallic fins brazed to the sides of the machined channel
19 might be used in place of the foamed metal. The density of the
fins are used to define the surface area-to-volume ratio. Thus, the
scope of the present invention is limited solely by the metes and
bounds of the appended claims.
* * * * *