Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to the storage of gases and
'~ ls particularly concerned with the storage for reuse of carbon
monoxide obtained as a reaction by-product in basic oxygen
steelmaking.
`,5 In a basic oxygen steelmaking process iron derived
--' from a blast furnace is refined by blowing oxygen i.nto the melt
~; contained in a suitable converter. During refining, some
impurities in the iron react with the bLown oxygen to form a
slag which floats to the top of the melt and which can subsequentLy
,-io be separated from the refined metal poured from the converter.
A predomlnant impurity in iron d~rived from a blast '
furnace is carbon which can be present in concentrations of
' up to 5% weight. During refining this contained carbon is
~, ox~dised by blown oxygen and the reaction product is evolved
`,'15 from the converter as carbon monoxide gas. During blowing
a proportion of the iron in the converter also is oxidised '
and is evolved as fine particulate iron oxide~ which is entrained
~, as fume in the carbon monoxide. -
," ~ In conventional BOS converters, the evolved iron
' oxide-carbon monoxide gas stream generally is discharged into
-~ a stack which terminates at its upper end in a suitable flare ¦ ,,
, at which the~gas stream is burnt in atmosphere. In order to i '~ ,
" avoid contamin,tion of the ambient, the gas strea~l from the
-- converter is cooled by bringing it into heat exchange
~25 relationship with water flowing in a cooling circuit and is
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subsequently water scrubbed to remove iron oxides.
The flaring of the carbon monoxide at the stack outlet
is recognized as representing a considerable loss of potentially
combustible gas which could be used as an energy source in
ot~er processes or in energy conversion for example to mechanical
or electrical powerO Generation of carbon monoxide in BOS is
however intermittent and a number of methods have been proposed
for storing the gas stream from the converter or reuse as and
when required.
Difficulties inherent in any storage scheme for
carbon monoxide gas arise from the highly explosive characteristics
of carbon monoxide when diluted with oxygen or with air, and
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- from the high level of toxicity of carbon monoxide to living
beings. It is accordingly an object of the present invention
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to produce a combustible gas storage and discharge system which
can be used inter alia with the gas reaction products of basic
oxygen steekmaking and in which the risks arising from leakage
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are reduced.
- The improved gas storage and discharge system accord-
` 20 lng to the present invention comprises a collapsible container
or holding a given quantity of gas suitable for storage; this
- container being sealed into a rigid chamber containing an
ambient gas. The system also comprises a conduit between a
source of gas suitable for storage, the collapsible container
',! and a discharge point. The system further comprises additional
j means operable independantly of the pressure of the gas suitable
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for storage in said source and conduit, to cause expansion
of the container so as to permit to the gas to be transferred
from the source for storage in the container, and subsequently
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to cause contraction of said container to enable stored gas
to be discharged from said container to the discharge point.
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. These additional means comprises blower means connected to said
,! rigid chamber to pump said ambient gas out of the same so as
to cause expansion of the container independenly of the pressure
- of the gas suitable for storage which is drawn or siphoned
from the source, or to pump ambient gas into the chamber so as
to cause contraction of the container and discharge of the stored
gas from said container _ `
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By the use of the invention, the controlled and
independent expansion of the container can produce gas storage
substantially at the pressure of the gas source; thus in the
case where the gas source comprises the st3ck of a BOS converter
in which gas pressure is substantially that of abmvsphere, gas
will be drawn from the stack also at substantially atmospheric
pressure and will be stored at this pressureO In the case
where the gas source is at a pressure above atmosphere, any
suitable means of pressure reduction, for example by the use
~: 10 of a controlled orifice of selected flow impedance can be used
The absence o a significant pressure differential
between the gas when stored and the oxygen containing ambien~
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;- will reduce to a minimum the risk of dilution of the gas or
of the ambient and accordingly will reduce the possibility of
an explosive mixture being formed. Here while in ideal
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cLrc~Qstances the gas pressure in the storage container is
: matched to that of the atmosphere, higher or preferably lower
preasures may be provlded according to clrcumstances.
In a preferred embodiment of the invention the
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: 20 collapsible container is sealed into a chamber from which
the air or other ambient for example an inert gas can be
:` exhausted at a selected rate to produce the required degree
of and rate of expansion for storage and înto whioh the air
- or ambient can be re-introduced to produce collapse with
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~.. 25 accompanying dl~charge of stored gas. Suitably the chamber
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can be exhausted and filled by way of a blower arranged
selectively to pump air into or out of the chamber. Suitable
valves are introduced into the system to ensure that during
expansion of the container gas is drawn only from the source
and that during collapse the gas is discharged only into a
suitable outlet.
Suitably the container comprises a large bag of
flexible sheet material which may be of rubber or a plastics
material such as polyvinyl chloride.
Gas analysis e~uipment preferably is provided to
sample gas drawn from the source and to provide an indication
when this is contaminated to an unacceptable level. Shut-off
with the collapsible container to prevent gas belng drawn
or storage if contamination rises above the level at which
an explosive mixture may be produced. The shut off valves
` may be arranged to operate automatically in response to a
signal from~the analyser or may be manually operatedO As an
additional safeguard a similar analyser may be provided in
the chamber to enable leakage from the container to be detected.
An embodiment of the invention will now be particularly
described by way of example with reference to the accompanying
I
drawings in which;
Figure 1 is a schematic diagram of a system for
storing carbon monoxide evolved from a basic oxygen steelmakLng
; 25 process, and
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Figure 2 illustr~tes an al~:erna~ive form of gas storage
vessel to that shown in Figure 1.
Referring to the drawing the storage ~ystem is adapted
to receive gas from a BOS converter which discharges through a
: 5 flare stack 2 terminating at its uppe~r end in a burner 4.
The lower end of the stack 2 receives cool scrubbed
gas from the converter by way of the conventional converter
hood ~not shown) and a flow rate measuring device 7 of the kind
well known in the art.
Evolved gas comprising carbon monoxide which normally
- ls burnt ~t the burner 4 is tapped for storage at the station
which is controlled by a shut-off valve 8 per~its gas flow
~` through conduit 10 into a common inlet/outlet 14 of a storage
cont~iner indicated generally at 15. A meter 12 monitors the
x~ 15 rate of gas flow into the container which comprises a
....
~` collapsible bag 16 of a suitable grade and gauge of polyvinyl
~, chloride or rubber or a suitable combination thereof. The open , I end of the bag is sealed into the base 18 of a rigid chamber 20
which enclosed the bag and which is of sufficient volume to
accomod~te the b2g when fully expanded. In its fully expanded
condit~on, a bag will be of sufficient volume to accomodate the
- quantity of carbon monoxide evolved during one refining operation
in a converter, and a bag of some 1 million cubic eet will be
., . sufficient to accomodate the carbon monoxide gas evolved from a
25: typical refining operation in a coverter of some 250 tons capacity.
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The common intlet/outlet 14 which also is provided with
a gas analyser 22 to monitor the onset of a potentially explosive
mixture of carbon monoxide with oxygen or air is connected
also to a duct~26 effective to discharge gas stored in the
container 16 by way of shut-off valve 28 and a flow meter 24.
Chamber 20 may be provided with wlndows so that the
movement and extent of expansion of the bag or balloon can be
observed together with any cracking or other failuxe of the
bag fabric.
A fan 30 selectively connected intc chamber 20 by way
of shut-off vaIves 32 - 38 is effective to evacuate the chamber
with valves 38 - 34 closed and valves 32 and 36 open so as to
cause container 15 to expand independently of internal gas
pressure and thereby to draw or syphon gas from the source
stack 2. Depending on the rate of expansion which is controlled
by the adjustable pumping rate of fan 30, gas drawn for storage
into the container will be substantially at atmospheric pressure.
A gas sample analyser 33 is provided to test air in the chamber
20 to ensure that no leakage has occurred from container 16.
Collapse of the container to discharge stored gas
through duct 26 is achieved with valves 34 and 38 open and
valves 32 and 36 closed, and valve 8 closed to pump air into `
the chamber 20.
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In use of the storage system valves 8 and 2~ ini-tially
are closed with the container 16 fully collapsed. At this
point which generally is imrnediately before the beginning of
an oxygen steel making blow, air i5 being drawn through the
cooler and scrubber associated with the stack 2 and is being
discharged to atmosphere by way of the flare 4.
As oxygen blowing commences the carbon monoxide
produced is sampled by the analyser 5 for oxygen, carbon monoxide
and carbon dioxide content. With gas flow established and
detected as being substantially free of oxygen or air, valve 8
is automatically or manually opened in response to an acceptable
reading from analyser 5 and flow meter.
At this stage fan 30 with valves 32 and 36 open and
valves 34 and 38 closed, draws air from the chamber 20 to
produce expansion of container 16; expansion accordingly draws
carbon monoxide from the flare stack 2 for storage ~y way of
duct 10 and continues until a prede-termined point before the end
- of the blow. The pumping rate of fan 30 is controlled so that
the gas withdraw rate as measured by meter 12 is slightly lower
than the ~low rate through the flare stack 2 measured by meter
7 to ensure that air is not drawn down the flare stack and into
the conduit 10.
At the predetermined point the fan 30 is opened to
atmosphere and valve 8 is closed. At this stage container 16
contains carbon monoxlde at substantially atmospheric pressure
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so that the pressure diferential acr~ss the container is
substantially zero and is effective to reduce to a minimum
any risk of leakage capable of producing a potentiall~ explosive
or toxic mixture. Moreover analyser 22 has monitored the quality
and possible contamination of the stored gas so that its accept-
ibility for reuse can be assessed before it is dlscharged through
the outlet duct 26.
In the case where the carbon monoxlde stored in
container 16 is found to be unacceptably contaminated it can
be discharged into stack 2 for combustion at the flare 4
together with the gas produced during a subsequent oxygen blow.
The rate of discharge is selected so that the overall
~" contamination at the flare 4 is below explosive level.
Discharge of acceptable gas for example for combustion
in a boiler or a gas turbine is achieved by opening valve 38
and 34 with valves 32 and 36 closed.
In the alternative embodiment of the invention illustrated
in Figure 2, the bag 16 of Figure 1 which is of corrugated wall
~ cylindrical form to assist collapse is replaced with a bag in
;~ 20 the form of an oblate spheroid. As with the cylinder of Figure 19
the spheroid of Figure 2 is shaped to permit optimum collapse
of the bag 16 so that in the collapsed condition the containe~l
vo~umeis reduced to a minimum pre erably substantially zero.
With the contained volume at collapse approaching substantialiy
zero, the risk of contamination of a stored charge by residue
from a charge stored in a previous-
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cycle is considerably reduced; moreover by ensuring that the
bag 16 can be expanded to the maximum extent permitted by the
container 20 any contaminated residue from a previously stored
cycle will be diluted as far as possible to further reduce
- 3 any risk from combustion.
~ It will be appreciated that the invention descrlbed
- possesses a number of advantages and avoids a number of the
`~ disadvantages inherent in gas storage systems for combustion I -
and potentlally explosive gases. Thus for example since d~ring
storage the pressure differential across the container 16 is
~i small and is dictated solely by the dead weight of the container,
-' the likelihood of leakage is small- Any leakage will be
detected by analyser 33. Moreover any leakages of stored gas
i at valve 8 will be carried away by the flare stack 4 so that
-"15 the closer the tap-off sta~ion is to the upper end of the ~ ~`
`- stack the better.
-~ The carbon mono~ide within container 16 and ducts 10
and 26 is always at a pressure virtually equal to the pressure
of air Ln chamber 20 which is controlled by fan 30 and associated l ,~
~'20 valves. The carbon monoxide pressure within container 16 is
therefore always under control and can be made greater than,
equal to, or less than ambient, at will.
~ In addition the storage system does not interfere
`l with the basic oxygeTI refining operation and in particular
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~'25 any fault in the gas collection system does not prevent
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continuation of steelmaking.
, It will be appreciated that while the invention has
been described wlth reference to one container 16 connected
to draw carbon monoxide from a single flare stack 2, a plurality
of containers can be provided and can be selectively inter-
connected to a number of flare stacks associated wLth
~:. different converters so that continuous storage facilities
are made available irrespective of the ~lowing programme.
It will be appreciated that the storage system of
the invention can be used for the retention of any gas whether
combustible toxic or not.
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