Gas separation: apparatus – Solid sorbent apparatus – With control means responsive to sensed condition
Reexamination Certificate
2000-07-13
2002-04-09
Simmons, David A. (Department: 1724)
Gas separation: apparatus
Solid sorbent apparatus
With control means responsive to sensed condition
C096S134000, C096S142000, C096S417000, C055S318000, C055S338000, C055S385200, C055S473000, C095S012000, C095S090000, C454S187000
Reexamination Certificate
active
06368393
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fan filter unit to be installed in cleanrooms of factories for manufacturing semiconductor devices, liquid-crystal panels, and films and more particularly, to a fan filter unit comprising a ventilation fan and dust and chemical filters incorporated into an enclosure, which removes efficiently dust and chemical substance existing in the atmosphere of a cleanroom by the chemical and dust filters and which enables energy saving of the fan and reduction of the air circulating space.
2. Description of the Related Art
To maintain the cleanliness of air in the cleanroom at a specific level, typically, cleanroom systems have been used. For example, whole laminar flow type cleanroom systems have been used for this purpose, which comprise fan filter units of this sort arranged on the whole ceiling surface of the cleanroom.
FIG. 1
schematically shows the configuration of an example of the prior-art cleanroom systems of this sort.
The prior-art cleanroom system
100
shown in
FIG. 1
comprises a cleanroom
140
, a ceiling chamber
147
formed over the cleanroom
140
, fan filter units
142
arranged in a matrix array on the whole ceiling surface
140
a
of the cleanroom
140
, an underfloor region
144
defined by floor panels
143
arranged on the floor of the cleanroom
140
, a cooling coil
145
for air-temperature control mounted in the region
144
, and an air circulation path
146
that connects the region
144
with the chamber
147
. Each of the fan filter units
142
includes a ventilation fan
148
and a dust filter
141
. Each of the floor panels
143
has a punched or perforated structure that allows the air to penetrate.
With the prior-art cleanroom system
100
shown in
FIG. 1
, the air existing in the ceiling chamber
147
is introduced into the inside of the fan filter units
142
by their fans
148
. The air thus introduced is passed through the filters
141
to be cleaned by the same. The air thus cleaned or filtered is emitted or blown to the inside of the cleanroom
140
. At this time, the cleaned air emitted from the units
142
form a vertical laminar flow of air that heads for the floor panel
143
from the ceiling surface
140
a
of the cleanroom
140
. The cleaned air thus emitted into the cleanroom
140
flows vertically into the underfloor region
144
through the floor panels
143
and then, returns to the ceiling chamber
147
through the cooling coil
145
and the circulation path
146
. Thereafter, the air thus returned to the chamber
147
is introduced into the cleanroom
140
again.
Through the above-described processes, the clean air is repeatedly circulated in the cleanroom system
100
. The cooling coil
145
serves to decrease the thermal load of the circulating air and therefore, the clean air with a fixed temperature is always supplied to the cleanroom
140
. Also, since the vertical laminar flow of the air is formed in the cleanroom
140
, the inside of the cleanroom
140
can be maintained at a specific high cleanliness level.
The Japanese Non-Examined Patent Publication No. 9-287791 published in November 1997 discloses a cleanroom system having approximately the same configuration as that shown in FIG.
1
.
Although the above-described cleanroom system
100
makes the cleanroom
140
highly clean, there is an anxiety that defects occur in the product due to contamination induced by chemical substance existing in the atmosphere in the leading-edge manufacturing processes for highly miniaturized products such as ultralarge-scale integrated circuits (ULSIs). To cope with the anxiety, fan filter units having chemical filters have been developed and used, an example of which is shown in FIG.
2
.
The prior-art fan filter unit
250
shown in
FIG. 2
comprises an enclosure or casing
252
having a first cylindrical part
252
a
and a second cylindrical part
252
b
that are coaxially connected together. The first part
252
a
is smaller in size than the second part
252
b
. The bottom end of the first part
252
a
is connected to the top end of the second part
252
b
. The inner space of the first part
252
a
communicates with the inner space of the second part
252
b.
An air inlet
252
c
is formed at the top end of the first part
252
a
. A ventilation fan
253
is mounted in the first part
252
a
. The fan
253
is driven by a motor (not shown) provided in the part
252
a
. An air outlet
252
d
is formed at the bottom end of the second part
252
b
. A dust filter
254
for removing dust or particles and a chemical filter
251
for removing chemical substance are mounted to be vertically apart from each other in the second part
252
b
. The dust filter
254
is fixed to the bottom end of the second part
252
b
so as to close the air outlet
252
d
. The chemical filter
251
is fixed to the inner wall of the second part
252
b
over the dust filter
254
at a specific distance. A partition plate
255
having holes
255
a
in its peripheral area is fixed to the inner wall of the second part
252
b
over the chemical filter
251
at a specific distance. The plate
255
divides the inner space of the enclosure
252
into upper and lower ones. The upper and lower spaces thus divided are connected to each other through the holes
255
a
of the plate
255
.
With the prior-art fan filter unit
250
shown in
FIG. 2
, the outside air
261
existing in the outside of the unit
250
is introduced into the enclosure
252
through the air inlet
252
c
, forming the air
262
. The air
262
thus introduced into the enclosure
252
flows to reach the chemical filter
251
through the holes
255
a
of the partition plate
255
. The chemical filter
251
removes chemical substances contained in the air
262
, forming the chemical-removed air
263
. The air
263
thus filtered further flows to the dust filter
254
and penetrates the same. The dust filter
254
removes dust or particles contained in the air
263
. As a result, the purified air
264
is emitted from the outlet
252
d
of the enclosure
252
to the outside of the unit
250
.
The prior-art unit
250
shown in
FIG. 2
can be used as the fan filter unit
142
of the prior-art cleanroom system
100
shown in FIG.
1
. In this case, the concentration of chemical substance existing in the atmosphere of the cleanroom
140
can be lowered, because the unit
250
includes the chemical filter
251
. To further decrease the concentration of chemical substance in the cleanroom
140
, there is the need to increase the flow rate of the purified air
264
emitted from the unit
250
, thereby raising the flow rate of the air
262
that penetrates the chemical filter
251
.
However, if the flow rate of the purified air
264
emitted from the unit
250
is increased, the overall amount of the circulating air within the cleanroom system
140
increases. This raises a problem that the air circulating space (i.e., the air circulation path
146
and the ceiling chamber
147
) needs to be expanded.
Also, to allow the increased circulating air to penetrate the path
146
and the air-cooling coil
145
, the fan
253
needs to provide higher static pressure. Thus, there is a problem that electric power consumption of the motor for driving the fan
253
is raised.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a fan filter unit that decreases efficiently the concentration of chemical substance existing in the atmosphere while the expansion of the air circulating space and the electric power consumption increase of the fan-driving motor are suppressed.
The above object together with others not specifically mentioned will become clear to those skilled in the art from the following description.
A fan filter unit according to the present invention comprises:
an enclosure having an air inlet through which an outside air is introduced into the enclosure and an air outlet through which a cleaned air is emitted or discharged from the enclosure;
a chemical filter mounted in the enclosure to remove chem
Simmons David A.
Young & Thompson
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