U.S. patent application number 13/822455 was filed with the patent office on 2013-07-11 for plant for fluorine production and a process using it.
This patent application is currently assigned to SOLVAY SA. The applicant listed for this patent is Oliviero Diana, Francis Feys, Alain Fobelets, Joachim Lange, Philippe Morelle, Maurizio Paganin, Holger Pernice, Peter M. Predikant. Invention is credited to Oliviero Diana, Francis Feys, Alain Fobelets, Joachim Lange, Philippe Morelle, Maurizio Paganin, Holger Pernice, Peter M. Predikant.
Application Number | 20130175161 13/822455 |
Document ID | / |
Family ID | 45831030 |
Filed Date | 2013-07-11 |
United States Patent
Application |
20130175161 |
Kind Code |
A1 |
Morelle; Philippe ; et
al. |
July 11, 2013 |
Plant for fluorine production and a process using it
Abstract
A fluorine gas manufacturing plant wherein F.sub.2 is
manufactured by the electrolysis of KF/HF compositions. The plant
comprises skid modules for: HF storage, the electrolytic cells,
storage and purification of the manufactured F.sub.2 raw gas, for
fluorine gas delivery including a single buffer tank or multiple
storage units, scrubbers to provide purified waste gas, for
providing cooling water circuits, analysis, electrical rectifiers,
an electrical sub-station with transformers and emergency supply,
and for utilities including a control room with laboratory and a
rest room for the personnel. The advantage of the skids is that
they can be separately manufactured in workshops, tested,
transported to the facility and assembled there. A great advantage
is the safety aspect, a reliable F.sub.2 production for 24 hours
and 7 days a week of high purity F.sub.2.
Inventors: |
Morelle; Philippe;
(Alsemberg, BE) ; Diana; Oliviero; (Vilvoorde,
BE) ; Predikant; Peter M.; (Hannover, DE) ;
Lange; Joachim; (Tervuren, BE) ; Pernice; Holger;
(Schwanewede, DE) ; Feys; Francis; (Hannover,
DE) ; Fobelets; Alain; (Brussels, BE) ;
Paganin; Maurizio; (Brussels, BE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Morelle; Philippe
Diana; Oliviero
Predikant; Peter M.
Lange; Joachim
Pernice; Holger
Feys; Francis
Fobelets; Alain
Paganin; Maurizio |
Alsemberg
Vilvoorde
Hannover
Tervuren
Schwanewede
Hannover
Brussels
Brussels |
|
BE
BE
DE
BE
DE
DE
BE
BE |
|
|
Assignee: |
SOLVAY SA
Brussels
BE
|
Family ID: |
45831030 |
Appl. No.: |
13/822455 |
Filed: |
September 12, 2011 |
PCT Filed: |
September 12, 2011 |
PCT NO: |
PCT/EP2011/065773 |
371 Date: |
March 12, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61383204 |
Sep 15, 2010 |
|
|
|
61383533 |
Sep 16, 2010 |
|
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Current U.S.
Class: |
204/241 ;
204/194; 204/230.6; 204/232; 204/267; 204/271 |
Current CPC
Class: |
B01D 53/68 20130101;
C25B 1/245 20130101; Y02C 20/30 20130101; C25B 15/02 20130101; C25B
15/08 20130101; C01B 7/20 20130101 |
Class at
Publication: |
204/241 ;
204/194; 204/271; 204/267; 204/230.6; 204/232 |
International
Class: |
C25B 1/24 20060101
C25B001/24 |
Claims
1. A plant for fluorine gas production comprising at least one skid
mounted module selected from the group consisting of a skid mounted
module comprising at least one storage tank for HF, denoted as skid
1, a skid mounted module comprising at least one electrolytic cell
to produce F.sub.2, denoted as skid 2, a skid mounted module
comprising purification means for purifying F.sub.2, denoted as
skid 3, a skid mounted module comprising means to deliver fluorine
gas to the point of use, denoted as skid 4, a skid mounted module
comprising cooling water circuits, denoted as skid 5, a skid
mounted module comprising means to treat waste gas, denoted as skid
6, a skid mounted module comprising means for the analysis of
F.sub.2, denoted as skid 7, and a skid mounted module comprising
means to operate the electrolysis cells, denoted as skid 8.
2. The plant of claim 1, further comprising a skid module 9 which
is an electrical sub-station to transform medium voltage to low
voltage.
3. The plant of claim 1, comprising skid 1, and wherein the at
least one storage tank for HF in skid 1 has an internal volume of
from 1 to 2 m.sup.3.
4. The plant according to claim 1, comprising skid 2, wherein said
skid 2 comprises at least 4 electrolytic cells, each of which is
allocated to at least one separate rectifier.
5. The plant according to claim 1, comprising skid 3, and wherein
said skid 3 comprises an HF washer for contacting raw F.sub.2 gas
with liquid HF, a condenser to remove HF from the F.sub.2, and at
least one absorber column to absorb HF from the F.sub.2.
6. The plant according to claim 1, comprising skid 4, and wherein
said skid 4 comprises a multitude of hollow bodies for fluorine gas
storage.
7. The plant according to claim 6, wherein each hollow body is shut
off from the plant separately.
8. The plant according to claim 1, comprising skid 5, and wherein
said skid 5 comprises at least 2 cooling water circuits and heating
and cooling means for the cooling water.
9. The plant according to claim 1, comprising skid 6, and wherein
said skid 6 comprises a sub-skid 6A comprising an emergency
scrubber, and a sub-skid 6B comprising scrubbers for F.sub.2 and
H.sub.2.
10. The plant according to claim 1, comprising skid 7, and wherein
said skid 7 comprises a multi-cell FT-IR spectrometer and
optionally a UV spectrometer.
11. The plant according to claim 1, comprising skid 8, and wherein
said skid 8 comprises a multitude of rectifiers wherein the number
of rectifiers corresponds to the number of anodes, or wherein said
skid 8 comprises a multitude of dual rectifiers wherein each of the
dual rectifiers provides current to 2 anodes.
12. The plant according to claim 2, wherein said skid 9 comprises
sub-skids 9A housing the medium voltage cells for incoming,
outgoing and bypassing current, and further comprises skid 9B
housing low voltage switchgears, an emergency generator, and a
battery charger station.
13. The plant according to claim 18, wherein said skid 10 comprises
sub-skid 10A housing a control room including a laboratory, and
sub-skid 10B housing a rest room.
14. The plant according to claim 1 wherein at least one emergency
button is present in each skid.
15. The plant according to claim 1 further comprising a
seismometer.
16. The plant of claim 15, wherein the seismometer is a strong
motion seismometer.
17. The plant of claim 15, wherein the seismometer is connected to
a control board and triggers a shutdown of the plant.
18. The plant of claim 1, further comprising a skid module 10 which
houses utilities and amenities.
19. The plant according to claim 1, comprising skid 2, wherein said
skid 2 comprises at least 4 electrolytic cells with a multitude of
anodes, and wherein each of a multitude of rectifiers is allocated
to a single anode, or wherein each of a multitude of dual
rectifiers is allocated to two anodes.
20. The plant according to claim 1, comprising skid 4, and wherein
said skid 4 comprises a single cell FT-IR for final analysis of the
fluorine.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a U.S. national stage entry under
35 U.S.C. .sctn.371 of International Application No.
PCT/EP2011/065773 filed Sep. 12, 2011, which claims priority to
U.S. provisional patent applications No. 61/383,204 filed Sep. 15,
2010 and N.degree. 61/383,533 filed Sep. 16, 2010, the whole
content of each of these applications being incorporated herein by
reference for all purposes.
TECHNICAL FIELD OF THE INVENTION
[0002] The present application concerns a plant for fluorine
production in the form of assembled skids and a process wherein it
is applied.
BACKGROUND
[0003] During the manufacture of semiconductors, photovoltaic
cells, thin film transistor (TFT) liquid crystal displays, and
micro-electromechanical systems (MEMS), often consecutive steps of
deposition of material and etching of the respective items are
performed in suitable chambers; these processes are often
plasma-assisted. During the deposition step, deposits are often not
only formed on the item, but also on the walls and other interior
parts of the chamber. It was observed that elemental fluorine is a
very effective agent both for etching and for cleaning the chambers
to remove undesired deposits. Processes of this kind are for
example described in WO 2007/116033 (which describes the use of
fluorine and certain mixtures as etchant and chamber cleaning
agent), WO 2009/080615 (which describes the manufacture of MEMS),
WO 2009/092453 (which describes the manufacture of solar cells),
and in unpublished EP patent application 09174034.0 which concerns
the manufacture of TFTs.
[0004] US patent application publication describes the generation
and distribution of fluorine within a fabrication facility.
Providing fluorine on-site reduces the risk connected to the
transport of fluorine from a facility where it is generated to the
point of use.
[0005] There are still problems to be solved in connection with the
apparatus used in the on-site concept, for example, the destruction
of greater amounts of pure fluorine (F.sub.2) and of HF in case of
leakages, or the breakdown of equipment.
SUMMARY OF THE INVENTION
[0006] The present invention provides an improved plant suitable to
produce fluorine on-site especially for the use as etchant and
chamber cleaning agent in the manufacture of semiconductors,
photovoltaic cells, thin film transistor liquid crystal displays
and micro-electromechanical systems.
[0007] The plant of the present invention provides fluorine gas to
a tool which applies fluorine gas as reactant to perform chemistry
in this tool which apparatus comprises skid mounted modules
including at least one skid mounted module selected from the group
consisting of [0008] a skid mounted module comprising at least one
storage tank for HF, denoted as skid 1, [0009] a skid mounted
module comprising at least one electrolytic cell to produce
F.sub.2, denoted as skid 2, [0010] a skid mounted module comprising
purification means for purifying F.sub.2, denoted as skid 3, [0011]
a skid mounted module comprising means to deliver fluorine gas to
the point of use, denoted as skid 4, [0012] a skid mounted module
comprising cooling water circuits, denoted as skid 5, [0013] a skid
mounted module comprising means to treat waste gas, denoted as skid
6, [0014] a skid mounted module comprising means for the analysis
of F.sub.2, denoted as skid 7, and [0015] a skid mounted module
comprising means to operate the electrolysis cells, denoted as skid
8.
BRIEF DESCRIPTION OF THE DRAWING
[0016] FIG. 1 shows an embodiment of the plant according to the
invention with a useful arrangement of the skids.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The preferred plant of the present invention provides
fluorine gas to a tool which applies fluorine gas as reactant to
perform chemistry in this tool which apparatus comprises skid
mounted modules including [0018] a skid mounted module comprising
at least one storage tank for HF, denoted as skid 1, [0019] a skid
mounted module comprising at least one electrolytic cell to produce
F.sub.2, denoted as skid 2, [0020] a skid mounted module comprising
purification means for purifying F.sub.2, denoted as skid 3, [0021]
a skid mounted module comprising means to deliver fluorine gas to
the point of use, denoted as skid 4, [0022] a skid mounted module
comprising cooling water circuits, denoted as skid 5, [0023] a skid
mounted module comprising means to treat waste gas, denoted as skid
6, [0024] a skid mounted module comprising means for the analysis
of F.sub.2, denoted as skid 7, and [0025] a skid mounted module
comprising means to operate the electrolysis cells, denoted as skid
8.
[0026] The plant preferably also comprises skid modules which may
be located close to the skid modules 1 to 8 but may be separated
from them, namely [0027] a skid module 9 which is an electrical
sub-station mainly to transform medium voltage to low voltage,
and/or [0028] a skid module 10 which houses utilities (control
room, laboratory, rest room).
[0029] Further, the apparatus may comprise means to supply inert
gas, e.g., means to supply liquid and gaseous nitrogen; means to
supply compressed air and water; and ancillaries and amenities. At
least, skids 1, 2, 3, 4, and 7, preferably all skids, comprise
housings for safety reasons.
[0030] In the context of the present invention, the term "fluorine
gas" denotes in particular molecular fluorine (F.sub.2) and
mixtures thereof, in particular with inert gases. Inert gases are
preferably selected for example from argon, nitrogen, oxygen and
N.sub.2O. A preferred fluorine gas consists or consists essentially
from F.sub.2.
[0031] In the following, a preferred plant as shown in FIG. 1 is
described in detail.
[0032] FIG. 1 shows a plant P according to the present invention.
The size is 39 m by 23 m. Reference sign 1 in FIG. 1 indicates skid
1 comprising HF storage and evaporation. Reference sign 2 indicates
skid 2 indicated by a dotted line, comprising the electrolytic
cells; it is located in the basement of the plant underneath
modules 5 and 7. Reference sign 3 of the figure refers skid 3
comprising purification means to purify the produced F.sub.2.
Reference sign 4 of FIG. 1 indicates skid 4 comprising the storage
means for fluorine gas. Skid 4 may also comprise, according to one
embodiment, a single cell FT-IR for final analysis of the purified
F.sub.2 ready for use or final storage. Reference sign 5 of FIG. 1
indicates skid 5 housing the cooling water means. It is located
above skid 2. Reference sign 6A in FIG. 1 refers to skid 6A which
contains the emergency response scrubber ERS, and reference sign 6B
indicates skid 6B with F.sub.2 scrubbers and H.sub.2 scrubbers.
Reference sign 7 in FIG. 1 indicates skid 7 which includes optional
means for analysis of F.sub.2 (it may, for example, contain an
FT-IR and/or a UV spectrometer). Reference sign 8 in FIG. 1 refers
to the rectifier cabinets in skid 8. Reference signs 9A and 9B
refer to the medium voltage electricity sub-skid 9A and the low
voltage electricity sub-skid 9B. Reference sign 10A indicates the
skid 10A comprising a laboratory and a control room, and reference
sign 10B refers to skid 10B with amenities like rest room and
gowning. Reference signs 11a and 11b indicate escalators and
platforms for walking to arrive at skids in the upper floor,
especially skids 5 and 7. Reference sign 12 shows a fork lift in
action. Reference sign 13 indicates a storage place for KOH
solution and other chemicals needed, and reference sign 14 refers
to an emergency shower. If desired, the plant can be fenced in as
indicated by the black lines in FIG. 1. A fenced-in plant has
advantages because workers not foreseen to operate the F.sub.2
producing plant are kept from entering it, thus reducing the risk
for such workers. In this case, the fluorine gas plant may be built
on-site of the fluorine gas consuming semiconductor manufacturing
plant, and delivery of fluorine gas occurs over the fence.
[0033] Such a plant comprising parts assembled in several skids has
many advantages. For example, the skids can be pre-assembled and
tested in a factory; thus, they are a kind of "off-shelf" product,
and need only be mounted on-site. This saves time. It is also much
easier to dismount specific skids for maintenance, repair or
substitution by skids comprising parts with the same function but
improved performance, or with lower or higher output. There are
also improvements in safety: for example, as explained above, skid
2 comprises at least one electrolytic cell; preferably, all
electrolytic cells are already filled with the electrolyte and then
delivered to the site for being assembled in skid 2. Thus, the
filling can be performed under respective safety considerations and
must not be performed on a local site where such safety precautions
may not be available. The capacity of the plant can be expanded by
adding modules. Preferably, the skids have sea container size thus
allowing for the easy transport of modules. A great advantage is a
reliable production for 24 hours and 7 days a week of high purity
F.sub.2.
[0034] The skids will now be explained in detail.
[0035] It is generally preferred that the cells are blocked and
connected to the structure to avoid movements, e.g., as a seismic
protection. It is also preferred that the plant comprises means
which detect earthquakes and send a signal to the control room
which causes the plant to shut down automatically or personnel to
shut it down manually. Preferably, the plant includes at least one
seismometer, e.g., a strong motion seismometer (accelerometer)
which can detect vibration acceleration of the plant and, if a
certain level is reached, e.g., 0.5 G, send a respective signal
which triggers an alarm and/or an automatic shutdown of the
plant.
[0036] All pipes connecting the cells and connected to the cells
must be electrically isolated, e.g., by means of spacers between
flanges. The floor must be electrically isolating, too.
[0037] Preferably, all process skids (skids 1 to 8) are comprised
in an enclosed space.
[0038] Skid 1: The skid module for HF storage (skid 1) comprises at
least one HF (hydrogen fluoride) storage tank which serves to store
HF and to deliver it to the electrolytic cells. The storage tanks
for HF are generally hollow bodies which optionally can be mounted
on wheels or which can be transported e.g., by a forklift.
Preferably, the skid comprises several storage tanks, more
preferably, 2, 3, 4, 5, or 6 storage tanks. Preferably, the HF is
stored in liquid form in the tank. Skid 1 is connectable to a tank
comprising pressurized N.sub.2. The liquid HF is pressurized with
N.sub.2 and delivered to an evaporator where it is evaporated. The
resulting gaseous phase containing HF is delivered to the
electrolytic cell or cells. If desired, for each electrolysis cell
an evaporator can be installed.
[0039] The evaporator preferably contains a heating, e.g., an
electrical heating or a heat exchanger using the heat of hot
cooling water, to generate the evaporated HF. More preferably the
HF storage containers can be isolated from the HF supply line by
double isolation valves having a closed isolation space. In that
case, skid 1 suitably further comprises at least one interspace
vent valve in connection with one or more closed isolation space.
The interspace vent valve is generally operable to remove
optionally present hydrogen fluoride from the closed isolation
space. Removal can be carried out, for example, by applying vacuum.
In another aspect, removal can be carried out, for example, by
flushing the closed isolation space with an inert gas and/or a
pressurized purging gas such as for example anhydrous air or,
preferably, nitrogen.
[0040] In one aspect, the removal is carried out continuously.
[0041] Preferably, the removal is carried out discontinuously, in
particular when an HF storage container is connected to and/or
disconnected from the supply line. Gases recovered from the closed
isolation space are suitably vented to an HF destruction unit, for
example a scrubber in skid 6.
[0042] In the plant according to the invention, parts thereof which
are supposed to be in contact with gas such as e.g., if
appropriate, hollow bodies, valves and lines for charging and/or
discharging gas are suitably made of or coated with material
resistant to molecular fluorine. Examples of such materials include
Monel metal, stainless steel, copper, and, preferably, nickel.
[0043] In a preferred aspect of skid 1, the hydrogen fluoride
storage containers are contained in an enclosed space having at
least a closeable gate allowing for entering into or removing from
the enclosed space a hydrogen fluoride storage container. In one
embodiment of this aspect the enclosed space contains the hydrogen
fluoride storage containers and the connections to the hydrogen
fluoride supply line. In another embodiment, the enclosed space
contains in addition an evaporator for evaporation of liquid HF. In
this preferred aspect and its embodiments, the enclosed space
suitably comprises an HF sensor capable to trigger connection of
the enclosed space to a scrubber described below.
[0044] Skid 1 generally has at least a liquid line and a gas line.
In that case, the liquid line can be connected, if appropriate to
the hydrogen fluoride supply line, for example by means of a flange
connection. The gas line can additionally be connected to an inert
gas (e.g., anhydrous air, nitrogen, etc.) supply line which allows
to pressurize the hydrogen fluoride storage containers.
[0045] In skid 1, each hydrogen fluoride storage container has
generally a capacity of from 10 to 5000 liters, often from 500
liters to 4000 liters, preferably from 500 to 3000 liters.
Particular examples of hydrogen fluoride storage containers are
tanks approved by RID/ADR-IMDG--of UN T22 or, preferably, UN T20
type. Such tanks are commercially available.
[0046] Each HF storage container in skid 1 can be suitably
connected to the hydrogen fluoride supply line through a
manifold.
[0047] Each HF storage container in skid 1 is preferably
individually isolatable from the hydrogen fluoride supply line.
[0048] The HF storage containers in skid 1 can generally be
isolated from the hydrogen fluoride supply line by a remotely
controlled device, preferably a remotely controlled valve. More
preferably each storage container is equipped with a remotely
controlled device, preferably a remotely controlled valve, allowing
isolating that container from the hydrogen fluoride supply
line.
[0049] When remotely controlled valves are present, manual valves
are suitably installed in addition. The remotely controlled valves
allow for example to operate the HF-storage-containers from a
remote control-room.
[0050] In a preferred embodiment, the HF storage containers
comprise an automatic HF level sensor. In particular the HF storage
containers can be installed on weighing scales. In that case,
preferably, a process control system, in particular an automatic
process control system is operable to closes the remotely
controlled valve of a first, empty HF container and to open the
remotely controlled valve of another second HF-containing hydrogen
fluoride storage container. This embodiment is particularly
effective to avoid manual handling of HF valves and to ensure a
continuous HF supply.
[0051] In a preferred aspect, the valves are operable to close
automatically in case of abnormal operation state, such as for
example a process-interruption in a process-equipment connected to
the HF supply line.
[0052] In another preferred aspect, the valves are operable to
close automatically in case of an HF leakage in skid 1. Such HF
leakage can for example be caused by a leakage of optional
flange-connections inside the HF storage-container there is the
possibility to close these valves via remote control. This avoids
in particular the necessity to approach the hydrogen fluoride
supply unit in this case.
[0053] The skid also contains valves to shut down the supply of HF
and nitrogen. Preferably, skid 1 comprises from 3 to 10 HF
containers; especially preferably, it comprises 4, 5, 6, 7, or 8
containers. 4 HF containers are suitable for a productivity of 150
tons F.sub.2/year. Tanks with smaller size, especially, if they can
be closed via valves separately, improve the safety of the plants.
The tanks must be made from or at least lined with material
resistant to HF. The walls should be sufficiently thick;
preferably, they have a 10 mm IMDG code (international maritime
dangerous goods code) equivalent thickness.
[0054] In a particular embodiment, skid 1 comprises, preferably
permanently, at least one HF emergency container. Such HF emergency
container is preferably an empty HF storage container as described
herein which is preferably connected to the HF supply line. The HF
emergency container is generally operable to receive HF from a
leaking HF storage container. The HF emergency container is
suitably kept under pressure of an inert gas or under vacuum.
[0055] The tanks are preferably portable so that they can be
transported by trucks and/or can be handled by a fork lift.
[0056] Skid 1 comprises a ventilation system, and the ambient air
is preferably permanently ventilated to a scrubber, especially the
ERS scrubber for HF and F.sub.2 removal (as described below).
[0057] Skid 2: The skid comprising the electrolytic cell or 2 or
more cells (skid 2) is now described in detail. It contains at
least one electrolytic cell. Preferably, it contains at least two
electrolytic cells. More preferably, it contains at least 6
electrolytic cells. A skid 2 with 8 electrolytic cells is very
suitable. The skid preferably is constructed such that if desired,
additional electrolytic cells can be added if the demand for
fluorine gas is rising. The cells comprise jackets through which
cooling water can be circulated. If desired, skid 2 can be provided
in the form of separate sub-skids 2A, 2B and so on. In these
sub-skids, a certain number of electrolytic cells are assembled.
The separate sub-skids 2A and 2B (and any other sub-skids) are
attached together to form one cell room. Often, the cell room will
contain 4, 6 or more cells, for example, 8 cells or even more. The
advantage of providing several electrolytic cells is that the
shut-off of one or even more cells for maintenance or repair can be
compensated by raising the output other cells. To assemble several
sub-skids has the advantage that dimensions can be kept within
permissible maximum dimensions for usual road transport. The
electrolytic cells are connected to collectors for the F.sub.2 and
the H.sub.2 produced. It has to be noted that each cell may
comprise 1 or more anodes. Typically, each cell comprises 20 to 30
anodes. In other embodiments, the number of anodes in each of the
electrolytic cells may be greater than 30; each cell may, for
example, have more than 60 anodes, up to 70 or even up to 80
anodes. A cable connects each of the anodes with the rectifier.
Each cell cathode is connected through one copper or aluminium bus
bar to the rectifier. One rectifier can supply current to one or
more cells. It is preferred to apply one rectifier per anode. The
advantage is that the intensity at each individual anode can be
fine tuned depending on the specific anode characteristics,
abnormal situations at a specific anode (e.g., overvoltage,
short-circuit, or broken anode) can be immediately detected
allowing the automatic shutdown of the faulty anode while all other
anodes and cells continue to produce F.sub.2. Accordingly, skid 2
preferably comprises at least 4 electrolytic cells with a multitude
of anodes wherein each of a multitude of rectifiers in skid 8 is
allocated to a single anode, or wherein each of a multitude of dual
rectifiers in skid 8 is allocated to two anodes.
[0058] Skid 2 includes a cooling water circuit (fed by or connected
to cooling water circuits of skid 5) supplying cooling water to the
jackets of the cells.
[0059] Skid 2 also comprises settling boxes; preferably, a settling
box for F.sub.2 and a settling box for H.sub.2 are connected with
each of the cells. The settling boxes serve to reduce the gas
velocity of the F.sub.2 and H.sub.2 produced in the cell to avoid
electrolyte dust to be carried over. Preferably, the settling boxes
comprise a vibrator and a heating to melt the separated electrolyte
dust for easy removal.
[0060] The collectors collecting the produced F.sub.2 are connected
by a pipe with skid 3, the collectors for produced H.sub.2 are
connected by a pipe with a scrubber for H.sub.2 in skid 6B (this
will be described in detail below). In a preferred embodiment, skid
2 also comprises a ventilation system to treat accidental releases
of F.sub.2 and/or H.sub.2.
[0061] The ambient air of skid 2 is ventilated to a scrubber,
especially the ERS scrubber for safety reasons (the scrubber is
described below).
[0062] Skid 3: it comprises means for the purification of the
produced F.sub.2. It comprises a cooler wherein the F.sub.2 is
pre-cooled. Skid 3 also comprises an HF washer wherein the
pre-cooled F.sub.2 is contacted with HF which is kept at a very low
temperature. The HF washer contains a cooling jacket through which
a coolant is circulating. Skid 3 further comprises a buffer tank, a
compressor, e.g., a diaphragm compressor, an HF condenser operated
at low temperature and at least one HF absorber column, preferably
containing NaF as absorbent for HF. Preferably, at least two
absorber columns are contained in the skid 3. If desired, the
absorber columns are redundant so that one set is in absorption
mode, the other set can be regenerated. The absorber columns
comprise a heating. If desired, a further set of absorber columns
may be present in skid 3 or on the site for reloading of absorbent.
The HF condenser is connected via pipes to the electrolysis skid 2.
Preferably, at least one set of columns is mounted on a wheeled
trolley to keep them (re-)movable from the skid.
[0063] The HF condenser may be cooled to a temperature where HF
condenses to form a liquid or even a solid. It is preferred if it
is condensed to form liquid HF. Cooling the trap to a temperature
of -60.degree. C. to -80.degree. C., preferably to about
-70.degree. is very suitable. As cooling medium, well-known cooling
liquids operable at the desired low temperature are suitable. It is
preferred to apply a N.sub.2 gas which was obtained by mixing
liquid N.sub.2 and gaseous N.sub.2 in appropriate amounts. This way
of cooling is very reliable. Thus, skid 3 comprises lines to
deliver and to withdraw cooling medium.
[0064] The ambient air of skid 3 is ventilated to a scrubber,
especially the ERS scrubber (described below) for safety
reasons.
[0065] Skid 4: this skid serves for storage of fluorine gas and the
delivery of fluorine gas to the point of use. Skid 4 comprises
filters to remove any remaining entrained solids. For example, the
F.sub.2 produced in the electrolytic cells may comprise entrained
solid electrolyte from the cell, usually, adducts of KF and HF. The
filter is preferably constructed from material resistant to HF and
fluorine; stainless steel, copper, Monel metal and especially
nickel are especially suitable. Filters made from sintered
particles of these metals comprising a pore diameter in the
nanometer range to provide semiconductor grade F.sub.2, e.g., with
a pore diameter of equal to or less than 5 nm, and more preferably,
with a pore diameter of equal to or smaller than 3 nm, are very
suitable.
[0066] If desired, skid 4 comprises a pre-filter to remove from the
F.sub.2 coarser particles with a pore diameter of equal to or less
than 1 .mu.m.
[0067] Skid 4 may also comprise a single-cell FT-IR. In this
single-cell FT-IR, the purified F.sub.2 which is ready for storage
or delivery to the point of use, may be analyzed. In this case, it
is not necessary to provide the UV spectrometer and/or the
multi-cell FT-IR in skid 7.
[0068] Skid 4 preferably comprises means for the storage of
fluorine gas. It may, for example, contain a buffer tank for
fluorine gas.
[0069] Additionally to, but preferably instead of the buffer tank,
skid 4 may comprise a permanent or temporary fluorine gas storage
unit in the form of a plurality of hollow bodies to store the
F.sub.2. The storage unit is connectable to other skids.
[0070] "Permanent fluorine gas storage unit" is understood to
denote in particular a fluorine gas storage unit which is
integrated into the fluorine plant. For example, the fluorine gas
storage unit can be a transportable or preferably fixed unit which
is present in skid 4 throughout operation of the fluorine plant.
Preferably, the permanent fluorine gas storage unit is designed to
contain more than 90 wt % more preferably more than 95 wt %, most
preferably about 100 wt % of the fluorine gas relative to the total
weight of fluorine gas stored in the plant.
[0071] Skid 4 is further able to convey fluorine gas from skid 2 to
the point of use. Possible components of skid 4 include but are not
limited to supply lines, compressors, mixers and buffer tanks.
[0072] "Connectable" is understood to denote in particular that the
permanent fluorine gas storage unit is equipped to be able to be
connected to a component of skid 4. Preferably, the permanent
fluorine gas storage unit is equipped to be able to be connected to
a fluorine gas supply line. In a preferred aspect, the fluorine gas
storage unit is connected to a component of skid 4, in particular a
fluorine gas supply line throughout operation of the fluorine gas
plant. In a further preferred aspect, the fluorine gas storage unit
is directly connected to a component of skid 4.
[0073] Suitable equipment for connecting the fluorine gas storage
unit connected to a component of skid 4 includes a manifold
connected to each hollow body of the fluorine gas storage unit
through a line and preferably having a shut-off valve in each line
allowing to individually isolate each hollow body and said manifold
is further connected to a component of skid 4.
[0074] Skid 4 preferably comprises from 4 to 25 hollow bodies, more
preferably from 5 to 8 hollow bodies. The hollow bodies are
preferably of substantially identical shape and dimensions.
Cylindrically shaped hollow bodies (tubes) are preferred. Each
hollow body of the fluorine gas storage has preferably a shut-off
valve.
[0075] The hollow bodies of the fluorine gas storage unit can be
suitably fixed together by means of an appropriate frame.
Particular frame geometries include triangular, square, and
rectangular geometries.
[0076] In the fluorine gas plant according to the invention, the
fluorine gas storage means are generally able to contain or
contains fluorine gas at a pressure of at least 25 psig (about 1.72
barg). Often this pressure is equal to or greater than 35 psig
(about 2.4 barg), preferably equal to or greater than 40 psig
(about 2.8 barg). In the plant according to the invention, the
fluorine gas storage means is generally able to contain or contains
fluorine gas at a pressure of at most 400 psig (about 27.6 barg),
preferably, equal to less than 75 psig (about 5.2 barg). Often,
this pressure is equal to or lower than 65 psig (about 4.5 barg),
preferably equal to or lower than 60 psig (about 4.1 barg). It is
understood that the hollow bodies of the fluorine gas storage unit
are generally able to contain or contain fluorine gas at the
aforesaid pressures. It is particularly preferred that the hollow
bodies contain fluorine gas at the aforesaid pressures.
[0077] In the fluorine gas plant according to the invention the
ratio of the molecular F.sub.2 stored in the fluorine storage means
to the daily molecular F.sub.2 producing capacity of the fluorine
gas plant is generally from 0.1 to 1, preferably from 0.1 to
0.25.
[0078] Preferably, each of the hollow bodies can be shut off from
the plant separately; this improves safety. The fluorine leaving
skid 4 is transported preferably through double-walled pipes to the
point of use. Fluorine gas is transported in the inner tube; the
outer double wall envelope comprises nitrogen. The piping contains
a pressure sensor to analyze the nitrogen pressure in the outer
double wall envelope. Preferably, the walls of the pipes are
thicker than commonly used for transporting gases, i.e. preferably,
they are thicker than 1 mm, preferably, thicker than 4 mm; a wall
thickness of equal to or greater than 5 mm is especially preferred;
pipes classified as "schedule 80" are very suitable. This serves to
improve the safety. Welded piping with radiographic inspection is
very suitable.
[0079] The storage container or containers can be mounted on wheels
or are transportable by a forklift.
[0080] The ambient air of skid 4 is ventilated to a scrubber,
especially the ERS scrubber described below (for safety
reasons).
[0081] In the fluorine gas plant according to the invention, the
point of use can be connected to a further manufacturing plant, for
example a chemical plant or, in particular, a plant using fluorine
gas for surface treatment. The point of use is often connected to a
semiconductor manufacturing plant, preferably a manufacture of
photovoltaic devices or flat panel displays.
[0082] In a preferred embodiment of the fluorine gas plant
according to the invention, skid 4 comprising the fluorine gas
storage unit is an enclosed space. The enclosed space generally
comprises a fluorine sensor capable to trigger connection of the
enclosed space to skid 6. Suitably, the enclosed space is connected
to skid 6 through a suction line connected to a fan which is
operable to transport gas from the enclosed space of skid 4 to skid
6.
[0083] In a further embodiment, the fluorine gas plant according to
the invention further comprises a mixer, preferably a static mixer,
said mixer being preferably capable to receive fluorine from skid 4
and to receive inert gas, such as preferably argon and/or nitrogen,
from an inert gas supply line.
[0084] In an optional embodiment, a pressure control loop adjusts,
generally reduces the pressure of fluorine gas supplied to the
point of use to a desired value.
[0085] Skid 5 provides for cooling or heating of parts of the plant
by means of cooling water. It is preferably located close to the
electrolytic skid 2 or sub-skids 2A and 2B or any additional
sub-skids 2X, more preferably, it is located above the skids. Skid
5 comprises at least one circuit which serves to heat the
electrolyte cells to melt the electrolyte salt when the reaction is
started, and to cool the cells when the reaction is running. The
circuit is filled with cooling water which may be tap water or
distilled water. The circuit includes a buffer tank, a pump which
is preferably redundant, and a dry cooler with fans with variable
speed drives. The cooling water, during operation, is preferably
kept at 75 to 95.degree. C. to avoid solidification of the
electrolyte in the cells.
[0086] Another circuit comprised in skid 5 serves to cool other
heat exchangers of the apparatus. It contains a cooling liquid,
preferably a mixture of water and ethylene glycol, more preferably,
water comprising 40% by weight of ethylene glycol. Also this
circuit comprises a buffer, a pump which preferably is redundant,
and a dry cooler. The cooling circuits include detectors to measure
the temperature of the cooling water, means to heat the cooling
water, e.g., electric heating, heat exchangers to cool the
circulating liquids. Optionally, the plant comprises a steam
generator to provide steam or hot cleaning water. The steam
generator may be a portable one. The hot steam may be, for example,
used to provide hot water in which electrolyte salt may be
dissolved, if necessary. Consequently, skid 5 preferably contains
at least two cooling water circuits.
[0087] Skid 6 comprises at least one scrubber each for F.sub.2 and
H.sub.2. Preferably, the scrubber pumps are redundant. The skids of
the plant (especially skids 1, 2, 3, 4, and 7) include a
ventilation system to ventilate the ambient air of the skid
enclosures permanently through scrubbers in skid 6.
[0088] Preferably, skid 6 comprises an F.sub.2 scrubber for
destruction of any F.sub.2 or HF vent required for safety reasons
or maintenance operations. F.sub.2 and HF from the ventilated air
from the skids are treated in a scrubber for emergency response
(ERS). The scrubbers are preferably jet scrubbers and provide the
suction. The scrubbers may be mounted on sub-skids, e.g., a
sub-skid 6A which comprises at least one scrubber for emergency
response (ERS), a sub-skid 6B which serves to scrub produced
H.sub.2 with the purpose to remove HF entrained therein, and a
scrubber to remove HF and/or F.sub.2 in waste gas originating from
ventilating the ambient atmosphere from skids as explained
below.
[0089] The capacity of the regular F.sub.2 scrubber (optionally
mounted in sub-skid 6B) corresponds at least to the expected amount
of F.sub.2 to be removed during regular operation. F.sub.2 is
removed by contact with an abatement solution. This scrubber
preferably comprises a jet scrubber and a packed column to provide
a high contact area between the abatement solution and F.sub.2.
Preferably, the gas leaving the regular F.sub.2 scrubber is passed
through the back-up scrubber of the ERS scrubber.
[0090] The ERS scrubber serves as back-up of the regular F.sub.2
scrubber used for removal of F.sub.2 or HF from ventilated air, and
for the emergency treatment of ventilated air which contains HF
and/or F.sub.2 after a leakage. The capacity of the ERS scrubber
(optionally mounted in sub-skid 6A) corresponds preferably at least
to the amount of fluorine and HF to be removed in cases for
emergency, for example, in the very improbably case of pipe
breaking, an accident with one of the tubes containing fluorine or
an HF storage tank. It is advisable to select the capacity of the
ERS scrubber according to a worst-case scenario; for example, if HF
tanks with 2 m.sup.3 capacity and F.sub.2 storage tubes with a
capacity of 8 kg F.sub.2 are present, the ERS should be able to
abate the respective amounts of HF and F.sub.2 and the
plant-holdup. Preferably, the ERS scrubber comprises 2 units for
scrubbing to achieve a high destruction and removal efficiency;
redundant pumps are fed by normal and emergency power supply. It
preferably comprises a jet scrubber and a packed column to achieve
a good contact between the gas to be treated and the abatement
solution. The other unit serving for emergency treatment may
comprise a packed column, but preferably, it comprises two jet
scrubbers in series. The F.sub.2 removal can be performed with
agents known to remove F.sub.2. Preferably, a KOH solution or NaOH
optionally comprising an alkali metal thiosulfate, e.g., sodium
thiosulfate or potassium thiosulfate is used as abatement solution
and is pumped through the scrubber or scrubbers and the column, if
present, as decomposing agent for F.sub.2. A cooler may be foreseen
to cool the KOH solution. Of course, it is an advantage of the
concept that one emergency scrubber serves to treat HF and
F.sub.2.
[0091] The scrubber of skid 6 serving for the HF abatement of the
H.sub.2 gas stream may be mounted in sub-skid 6B. Sub-skid 6B
includes preferably a jet scrubber operated with aqueous HF
solution to reduce the content of HF in the H.sub.2. The
concentration of HF may be in a range between 1 and 10% by weight.
The scrubber further comprises a packed column wherein fresh water
is given on top of the column to reduce the HF content. Skid 6B
also includes a line which allows the dilution of H.sub.2 by
nitrogen which was used as cooling medium in skid 3.
[0092] The reliability of the scrubbers in skid 6, or in skids 6A
and 6B respectively, is very important. Thus, essential parts like
fans or pumps to circulate the abatement solution through the
scrubbers may be redundant. From time to time, fresh abatement
agent, for example, KOH solution, and/or thiosulfate or its
solution, e.g., provided by a truck, is added to the circulating
abatement solution.
[0093] Skid 6 preferably comprises also one or more retention pits
for liquid in case of accidental leakages.
[0094] Skid 7 concerns the apparatus used for the analysis of the
produced F.sub.2. It is preferably installed near skids 2A and 2B;
very preferably, it is located above the skids 2A and 2B. Skid 7
is, for example, an analyzer shelter. The ambient atmosphere around
it is preferably ventilated to the ERS. The analyzer contains
analyzing means suitable to determine the content of the main
impurities of the produced F.sub.2.
[0095] In one embodiment, a UV spectrometer (which analyses the UV
spectrum) and multi-input, multi-cell FT-IR spectrometer
(Fourier-Transform Infra-Red spectrum) analyzers are very suitable.
Preferably, both raw F.sub.2 taken from the cells and purified
F.sub.2 may be sent to a single-cell FT-IR or a multi-cell FT-IR.
In a multi-cell FT-IR, one channel is analyzed at a given time. The
amount of HF, CF.sub.4, C.sub.2F.sub.6 and COF.sub.2 can, for
example, be measured by FT-IR while the content of F.sub.2 is
analyzed by UV. It has been found that UV spectroscopy can be used
as a direct measurement tool for fluorine which shows a sharp
decrease in fluorine concentration when an anode burn occurs; an
enormous increase of CF.sub.4 is observed at the same time in the
FT-IR. Therefore the burn can be detected easily by the sharp
decrease of the F.sub.2 concentration during the burn, during which
impurities are formed (mainly CF.sub.4 and C.sub.2F.sub.6). The
result of this burn (the produced F.sub.2 contains more CF.sub.4,
C.sub.2F.sub.6, COF.sub.2, HF than when working regularly) is not
only the alteration of impurities' contents but also a sharp
decrease in the content of fluorine monitored by a detector system,
especially, in the present invention, by UV spectroscopy. During
the measurements using UV spectroscopy, the whole UV spectrum can
be used. Preferably, not the whole spectrum but only the absorption
at this particular wavelength, particular UV spectroscopy between
200 and 400 nm, more preferred between 250 and 330 nm, most
preferred between 270 to 290 nm, even at about 280 nm is used for
measuring, because it is more or less the maximum of the UV
absorption of F.sub.2. The FTIR and UV measurements are also used
to control the purity of the purified F.sub.2. Thus, the analysis
serves to detect anode burns by measuring the raw F.sub.2 by UV and
CF.sub.4 by FT-IR and to document and control the purity of the
purified F.sub.2.
[0096] The raw F.sub.2 of all cells and the purified F.sub.2 are
continuously sampled and analyzed. Current FT-IR can accept up to 9
samples. Thus, the purified F.sub.2 and the raw F.sub.2 of up to 8
electrolysis cells can be analyzed with one multi-cell FTIR of the
current generation of apparatus.
[0097] According to another embodiment, the analysis of the
fluorine produced is performed only with a single-cell FT-IR; a UV
spectrometer is not applied. The single-cell FT-IR is used for the
analysis of the purified F.sub.2 (final analysis).
[0098] Skid 8 contains the rectifiers, the BPCS (basic process
control system), the ESD (emergency shutdown system), the F&G
(fire and gas system) panel which registers fire alarms and gas
alarms, small motor starters, lighting distribution and other means
to provide electricity and to control electric means of the plant.
Skid 8 is installed near skids 2A and 2B; preferably, it is located
above them. Each electrolytic cell, as mentioned above, usually has
at least one, but often a multitude of anodes, e.g., 26 anodes. The
term "multitude of anodes" may denote any figure which is equal to
or greater than 2. The number of anodes is limited only by
practical considerations, e.g., the cell or cell unit (constituted
of several cells) should not be unreasonably large. Often, the
number of anodes is equal to or lower than 80, preferably, equal to
or lower than 70. One rectifier could provide current to one, two
or more anodes. Preferably, each anode is supplied by a rectifier.
Rectifiers are available on the market which can provide current
separately to several anodes. For example, if 26 anodes are present
in a cell, it is preferred to provide 26 rectifiers or 13 dual
rectifiers which separately provide current to 2 anodes. The
rectifiers are preferably assembled in rectifier cabinets installed
in air-conditioned enclosure.
[0099] It is preferred to provide a slight overpressure in this
skid 8 to protect from gas ingress. All cables and cathode bus bars
should be carefully sealed.
[0100] It is preferred that the rectifier cabinets are bolted on a
fixed frame for seismic protection.
[0101] Skid 8 comprises walls and a roof. It includes preferably
also a fire detection system, especially a VESDA (very early smoke
detection apparatus) and a fire extinguishing system operating,
e.g., with HFC-227ea or with Inergen.RTM., a mixture of inert gases
(nitrogen, argon, and carbon dioxide).
[0102] Skid 9 is preferably a pre-fabricated room with concrete
walls or similar to a container, made from metal shields. It
contains means for connection to electric current and to transform
it from medium to low voltage. Preferably, it contains the
"electric sub-stations" sub-skids 9A and 9B. Skid 9A preferably
contains the MV (medium voltage) cells for incoming and outgoing
current and bypass current and the transformers to transform the
medium voltage current into low voltage current. It is adaptable to
the local network; for example, the transformers are selected such
that they fit to the local voltage which may, for example, be 380 V
or 400 V (50 Hz) or 440 V (60 Hz). Skid 9 includes preferably also
a fire detection system, especially a VESDA (very early smoke
detection apparatus) and a fire extinguishing system operating,
e.g., with HFC-227ea or with Inergen.RTM., a mixture of inert gases
(nitrogen, argon, and carbon dioxide).
[0103] Skid 9B also is preferably a pre-fabricated concrete room
having walls and a roof. This substation houses the low voltage
switchgears (LVCS) and a diesel generator. It is interconnected by
cables to the skids which need a low voltage power supply, e.g.,
via a cable trench. It includes preferably also a fire detection
system, especially a VESDA (very early smoke detection apparatus)
and a fire extinguishing system operating, e.g., with HFC-227ea or
with Inergen.RTM., a mixture of inert gases (nitrogen, argon, and
carbon dioxide).
[0104] Skid 9B preferably also comprises a battery charger station
for a forklift.
[0105] Skid 9B must be interconnected to the process skids,
especially with the rectifiers in skid 8.
[0106] Skid 10 comprises utilities for the personal, for example, a
control room, a laboratory, and a rest room. Preferably, it is
divided into sub-skid 10A and sub-skid 10B. Sub-skid 10A contains
the control room and the laboratory. The laboratory which may be
small includes a fume hood with good ventilation, e.g., up to 500
m.sup.3/h and even more, which hood is preferably made from
acid-resistant materials and can be used for analytical titrations,
a safety cabinet for reagents and samples, a wash basin and a
chemical sink wherein chemical waste can be collected, preferably
in a drum made from acid resistant material. The laboratory
preferably has a gas detector installed in a fresh air intake and a
closing mechanism which closes the air intake in case of a gas
alarm. Sub-skid 10A preferably is kept under a slight overpressure
to prevent gas ingress. Skid 10A preferably comprises
air-conditioning.
[0107] The control board of the control room is preferably
connected online to a remote control board which may be located on
another facility. This allows operating several fluorine gas
production plants remotely from one single control room.
[0108] Sub-skid 10B contains the rest room. It contains
installations useful for the control room personal. It preferably
includes lockers, a changing room, a toilet, a shower, and cabinets
for chemical gowning (gloves, capes etc). The plant safety shower
includes eye-shower systems and is preferably located close to the
outside of sub-skid 10B because it must be fed with warm potable
water. Skid 10 preferably comprises ventilation and heating.
[0109] The plant will include further equipment useful to operate
it.
[0110] Compressors are needed to provide pressurized fluorine gas.
They must be resistant to fluorine gas. Compressors which are used
for fluorine gas handling in the nuclear industry are very
suitable. They are preferably diaphragm type compressors.
[0111] Such compressors are available on the market. The diaphragms
are made from F.sub.2 resistant material, especially from Monel
metal, stainless steel, copper or nickel. The membranes are 3-layer
membranes so in case of a membrane break the break will be detected
by pressure measurement, and no F.sub.2 will leave the compressor
membrane to the outside area.
[0112] The plant also will need instruments and valves for
operation.
[0113] For example, if a mixer is present to provide mixtures of
F.sub.2 and inert gases or other gases, the process step of mixing
the gases includes mass flow meters for F.sub.2 and the gas or
gases to be mixed with it, installed control valves with dedicated
programmed control loops and interlocks to ensure an appropriate
and safe mixing of the gases, e.g., the inert gas or inert gases,
with F.sub.2.
[0114] The plant, as described above, has means to analyze certain
parameters (e.g., mass flow control of fluorine gas or inert gas)
for its operation. For this purpose, mass flow controllers are
preferably used. With such mass flow controllers, the amount of
fluorine gas can be controlled which passes through lines carrying
it for example, to the FTIR and UV analyzers. The mass flow
controllers ought to be "low .DELTA.P type" controllers causing
only a low pressure drop. Such flow meters, as well as tubes,
pipes, and fittings used to transport gas to the analyzers which
must be suitable for fluorine gas transport, are also available on
the market. Valves should be bellow sealed heavy duty valves. A PLC
(programmable logic controller) manages the movements of the FTIR
mirrors, collects malfunction alarms and transmits results to the
BPRS (basic process control system). To analyze pure F.sub.2,
windows made from AgCl are preferably applied, for the analysis of
raw F.sub.2, e.g., raw F.sub.2 from the sampling lines of the
electrolytic cells, Al.sub.2O.sub.3 windows can be applied.
[0115] From the description above, it becomes clear that several
alternatives can be applied concerning the analysis of F.sub.2.
[0116] According to a first alternative, a single cell FT-IR is
located in skid 4. It serves to perform a final analysis of the
F.sub.2.
[0117] According to a second alternative, a multi-cell FT-IR and
optionally, a UV analyzer is located in skid 7.
[0118] According to a third alternative, a single-cell FT-IR is
located in skid 4, and a multi-cell FT-IR and optionally, a UV
analyzer is located in skid 7.
[0119] The first alternative is the cheapest solution. The second
alternative is more expensive than the first alternative; but it
allows a quick reaction if the F.sub.2 production in one or more
cells is disturbed. It also allows to identify the cell operating
irregularly. The third alternative is the most expensive one; it
allows, at the same time, a quick reaction and to identify faulty
cells, and it allows to check the purity of the final F.sub.2.
[0120] Which alternatives are chosen depends on the expectations or
demands of the customer, the experience of personnel, the
inclination of the plant to run into faulty conditions etc. It
would also be possible to provide analyzers in skid 4 and 7 but to
operate one of them or both not continuously, but
intermittently.
[0121] Safety equipment: It is well known that especially F.sub.2
and HF are compounds which need cautious handling. H.sub.2 is, of
course, flammable. Accordingly, the plant includes safety
installations. For example, the plant comprises a safety panel with
switches for an emergency shutdown (ESD), for alarms, and for
overriding automatic processing.
[0122] Detectors for F.sub.2, HF and, where appropriate, H.sub.2,
are installed, for example, in ventilation ducts to the ERS
scrubber and at the emission points. Gas alarm signals are sent to
the ESD for safety functions. The plant includes warning lights
which are activated, i.e., if gas alarm signals are sent to the
ESD. The alarms must also be detectable in the control room of skid
10. Gas measurements must be given in the control room, e.g., in
ppm. It is very advantageous if the plant comprises a Fire &
Gas panel in the control room of skid 10 to show all fire and gas
alarms, and failure of ventilation.
[0123] As mentioned above, the plant includes smoke detectors and
VESDA detectors. Especially the process skids, e.g., skids 1, 2, 3,
4, and 7, comprise means to stop the F.sub.2 production manually,
e.g., emergency push buttons, and/or to actuate fire extinction
apparatus. CC TV (closed circuit television) can be used to
supervise the plant. It can be used to monitor access to the plant,
unloading of materials (e.g., of HF portable tanks or KOH
solution).
[0124] Safety Instrument Systems (SIS) comprising sensors, ESD
system and safety actuators are included in this plant. The SIS are
designed to achieve a Safety Integrity Level "2". In particular,
where electrical motors or electrical loads were needed to be
included as a part of a safety instrumented function, alternate and
independent means of tripping these motors/loads are considered,
e.g., by tripping the upstream breaker if the contactor or circuit
breaker dedicated to the motor/electric load fails to open.
[0125] An emergency generator, preferably a diesel generator
supplying 100 kVA is preferably contained in the plant if external
power supply is interrupted.
[0126] It is also preferred if the control room comprises a "dead
man" detection for the operator working alone.
[0127] Further, it is preferred that the control room provides data
for wind direction and wind speed.
[0128] The footprint of the assembled process skids for a plant
with a capacity of 150 t/year is 30 m by 9.2 m. With skids for
utilities, personnel areas and access clearance for maintenance and
servicing, the overall size is about 39 m by 23 m. The height of
the skids may be higher than standard (standard height is 64
inches). Skid 6A comprising the emergency scrubber has often not
the standard footprint but must be adapted to the specific need of
the respective plant.
[0129] Often, the skid structure is a painted steel frame on which
all equipments are fixed; they are designed for outdoor
installation. Panels, doors and roofs, if fixed on the external
structure of the skid, imply that the external skid dimensions
exceed the standard sea container dimensions. If necessary, such
skids are prefabricated and panels, doors and the roof,
respectively, are assembled to the skids on site. The skids are
anchored on an existing concrete slab or by or on specific
foundations.
[0130] The advantage of skids is, for example, that they are
manufactured, piped, wired and assembled together before shop
testing. It is preferred if they are constructed such that the
interfaces between the skids are minimized and that all parts in
the respective skid are accessible as easily as possible for
maintenance, inspection or repair.
[0131] The advantage of the skids is the safety aspect, a reliable
F.sub.2 production for 24 hours and 7 days a week of high purity
F.sub.2.
[0132] In the following, the assembly and operation of a plant
constructed of skids is described.
[0133] The skids as described above are assembled in a workshop; in
one embodiment, the electrolytic cells of skid 2 already are
supplied filled with the electrolyte salt. This improves safety.
The skids are preliminarily tested in the workshop and then shipped
to the facility where the F.sub.2 produced by them is needed. On
the facility, it is preferred if a concrete slab had been built
sufficiently beforehand upon which the F.sub.2 production plant can
be erected.
[0134] The skids are assembled and connected. Skid 2 comprises 6
electrolytic cells forming one cell room. Each electrolytic cell,
in this case, comprises 26 anodes; other multitudes, e.g., up to 80
anodes and even more, would be possible, if desired.
[0135] Before connection or thereafter, they are blocked to the
ground as an earth quake or bad weather precaution measure.
[0136] Skid 13 serves as storage room for chemicals needed, e.g.,
thiosulfate, hydroxide and/or electrolyte salt.
[0137] Operability of the built-in parts is preferably tested
then.
[0138] The operation of the plant is now described in detail.
[0139] A plant with 6 cells is provided. The nominal capacity of
this plant, if run 24 hours for 7 days a week, is about 100
tons/year of pure F.sub.2 (12 kg/h, peak 20 kg/h). The capacity
could be expanded by adding two further electrolysis cells and
rectifiers or rectifier racks. The expansion of capacity to 300
t/year would be possible by adding further skids (additional cell
room and rectifiers, additional cooling skid, additional
analyzers). Tanks, preferably with an inner volume of from 1 to 20
m.sup.3, most preferably in a size of from 1 to 3 m.sup.3, filled
with HF, are assembled in skid 1 and connected to the electrolytic
cells. Electrolyte salt of the rough composition KF.2HF had already
been filled into the cells before the final assembly of the plant.
The content of the electrolytic cells is heated to about
80-120.degree. C. to be molten therein. HF coming from the
evaporator from skid 1 is fed into the electrolytic cell. From skid
9A, medium voltage is supplied to skid 9B, transformed to low
voltage direct current with a voltage in the range of from 8 to 12
V, and current is passed through the molten composition of HF and
the molten electrolyte salt which is kept in a temperature range
between 80 and 120.degree. C. One rectifier may be allocated to
each cell; preferably, one rectifier is allocated to each anode. It
is especially preferred to apply dual rectifiers; such a dual
rectifier can serve two anodes. If 26 anodes are present in each
cell, then 13 dual rectifiers may be applied to provide electric
current to the anodes. The cells are operated at as pressure higher
than ambient pressure (e.g., at 7 to 10 mbarg). Elemental fluorine
(F.sub.2) and elemental hydrogen (H.sub.2) form in the respective
electrode compartments in skid 2.
[0140] HF is advantageously supplied such that the level of
electrolyte salt and HF in the respective cell does not exceed
specific upper and lower levels. Preferably, the skid containing
the electrolytic cell or cells also includes sensors which
determine the temperature in the cell, the level of liquid in the
cell or cells, the pressures and pressure differences, the anode
currents and voltages and gas temperatures. The cells are cooled
with cooling water having a temperature of about 75 to 95.degree.
C., preferably from 75 to 85.degree. C.
[0141] H.sub.2 formed is passed to skid 6B and is contacted in a
jet scrubber with an aqueous solution comprising 0 up to about 5%
by weight of HF in water. Gas leaving the scrubber is passed to the
bottom of a packed column and contacted therein with fresh water
sprayed on top of the column. Gas leaving the packed column is
diluted with nitrogen and passed into the atmosphere.
[0142] The plant produces about 415 kg/day of F.sub.2.
[0143] F.sub.2 produced in the cells is first pre-purified by
removing particles (mainly, entrained re-solidified electrolyte
salt). The stream of raw F.sub.2 is then cooled down whereby a part
of entrained HF condenses and can be removed. Then, the raw F.sub.2
is compressed with a diaphragm compressor to a pressure of about
3.5 barg. The redundant pairs of NaF towers are installed on
trolleys to keep them movable, especially for the case that the NaF
pellets need to be exchanged completely (when further regeneration
is not possible any longer). The compressed F.sub.2 is then passed
through a trap and cooled therein to about -70.degree. C. by means
of evaporated liquid N.sub.2 and gaseous N.sub.2. Residual HF is
removed in this trap by condensation. Any remaining traces of HF
are then removed by passing the F.sub.2 through one line of two
lines of two absorption towers containing NaF pellets; the lines
are redundant because from time to time, the NaF towers are heated
to about 350 to 400.degree. C., and N.sub.2 is passed through them
to remove absorbed HF and to regenerate the respective towers. The
pressure in the NaF towers in absorption mode is about 3.5 barg.
The F.sub.2 gas stream leaving the two NaF towers is passed through
two filters to remove any solids, especially NaF; the filters are
preferably made from Monel metal, and the second filter has a pore
diameter of 3 nm. The temperature of the first tower is about
100.degree. C., the temperature of the second tower is about
30-40.degree. C. The purified F.sub.2 is continuously sampled.
[0144] According to one embodiment, samples are sent to a
multi-cell FT-IR and to a UV analyzer, as described above.
According to another embodiment, a single-cell FT-IR is applied for
the analysis selectively of the purified F.sub.2. Analytical data
are sent online to a control board in the control room in skid
10A.
[0145] If the analysis of the samples shows that one or more of the
cells produces F.sub.2 too impure to be useful for semiconductor
manufacturing purposes, for example, containing too much CF.sub.4
or higher homologues which indicates a cell failure, the respective
sample or samples and the F.sub.2 produced by the electrolytic cell
are passed to the F.sub.2 scrubber in skid 5 and the emergency
scrubber for destruction by means of a KOH solution including
sodium thiosulfate. Alternatively, the impure F.sub.2 could be
collected to be used for purposes for which the degree of purity is
sufficient. If the samples show that the F.sub.2 produced
corresponds to the desired purity, the samples are returned to the
F.sub.2 product line. The F.sub.2 is then passed to a storage means
which includes 6 identically shaped containers each having an
internal volume of 1.3 m.sup.3. Each of the cylinders can be opened
and shut off individually by shut-off valves. Alternatively, the
pressure of the produced F.sub.2 is lowered to about 1.5 barg by a
pressure control loop and is then passed to the point of use, a
flat panel display manufacturing plant using F.sub.2 for chamber
cleaning. A double-walled pipe is used, wherein the space between
the inner and the outer tube contains nitrogen, and the F.sub.2 is
passed through the inner tube of it.
[0146] In normal operation, the shut-off valves are open and the
pressure difference between the F.sub.2 storage unit and the point
of use provides a buffer allowing a smooth control of the delivered
fluorine gas flow, even for variable consumption patterns at the
point of use or during interruption of the production of the
F.sub.2 generating unit.
[0147] Should the disclosure of any patents, patent applications,
and publications which are incorporated herein by reference
conflict with the description of the present application to the
extent that it may render a term unclear, the present description
shall take precedence.
* * * * *