Note: Descriptions are shown in the official language in which they were submitted.
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"Q method of cleaning humid air contaminated with vapor".
TIE PRESENT INVENTION rotates to a method of cleaning air, which may
be humid air, which is contaminated with vapor, such as oil vapor. The
invention also relates to an apparatus for carrying out such a method.
It if often necessary to clean air which is contaminated with vapors,
and that air will have a certain humidity, depending upon the ambient
atmospheric humidity at the time.
In n rolling mill In which steel is rolled or converted, the rollers
which come into contact with the hot ingots or metal billets to be rolled
have to be cooled. This cooling is often carried out by spraying an oil-based
liquid onto the rollers. Large quantities of oil are evaporated during the
cooling process as result of absorbing heat from the rollers or even from the
ingots or metal billets, and the resultant vapor is entrained in the
I ventilating air. For environmental reasons, this air has to be cleaned to a
certain maximum acceptable level of contamination before it is released to
the atmosphere or reused. The quantities of air involved can be very large,
for example or the order of 50000 cubic metros per hour.
It is Jo be understood that the contaminated air contains, in addition
to the oil vapor mentioned above, a quantity of water in the form of
atmospheric humidity. The quantity of water contained in the air at any one
time depends upon the ambient level of atmospheric humidity
If an attempt is made to glean the air simply by cooling the air so as
to condense the oil vapor, it has been found that large quantities of water
will also condense, for example of the order of 40 cubic metros per 24 hours
when Lowe cubic metros per hour of air is treated. The reason for this is
that the air has to be cooled to a comparatively low temperature in order to
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condense a substantial proportion of the oil or vapor in the air, and of
course a substantial proportion of the oil vapor must be condensed to
obtain de-contaminated air that is suitable for release into the atmosphere.
Thus, the result of the substantial cooling of the air is condensation of a
mixture of oil and water. While a large proportion of the condensed oil can
be separated comparatively easily from the water for reuse, a certain
quantity of the condensed oil will remain in suspension in the condensed
water. It is very expensive and time consuming to separate the oil
completely from the water. The quantity of oil that remains in the water
after an economically satisfactory separation of the oil and water has been
carried out is so large that the water is not suitable for release into a
municipal sewer without further cleaning of the water.
It will be appreciated, therefore, -what the cleaning of substantial
quantities of humid air contaminated with oil vapor presents a severe
problem that is difficult to solve in an economically satisfactory way.
Whilst the prior art process provides air thaw is suitably de-contaminated,
the prior art method produces large quantities of water that are con-
laminated and that must therefore be disposed off appropriately.
The present invention seeks to reduce or overcome the above-
described difficulties of the prior art.
According to one aspect of this invention there is provided a method
of cleaning humid air contaminated with vapor, said method comprising the
step of cooling the air in one or more stages to a temperature below the
condensation temperature of the contaminating vapor in the air and below
the dew point of water to effect condensation of the vapor and water and
collecting the condensate in such a way that the condensed vapor is
3û substantially separated from the condensed water, and subsequently no-
introducing the water, which may stiff be contaminated with a small portion
of the condensed vapor, to the air to remodify the air.
Preferably the cooling is effected by cooling the air initially to a
temperature below the condensation point of the vapor but above the dew
point of water, so that substantially only the vapor is condensed, and
subsequently cooling the air to a temperature below the dew point of water,
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so that water and further quantities of the contaminating vapor condensed.
Conveniently the condensate obtained during the said subsequent
cooling stage is allowed to separate into an aqueous fraction and a
condensed vapor fraction, and the aqueous fraction is the water that is no-
introduced to the air.
Advantageously the ventilating air is cooled to at least about -10
degrees centigrade during the cooling process.
Preferably the cleaned air is heated before the water is reintroduced
to the air.
Conveniently heat pumps or the like are utilized initially to cool the
air by extracting heat from the air, and then to heat the air by no-
introducing that heat to the air.
According to another aspic t of the invention there is provided an
apparatus for cleaning humid air contaminated with vapor, said apparatus
comprising one or more cooling stages adapted to cool the air to a
temperature below the condensation temperature of the contaminating
vapor in the air and below the dew point of water to effect condensation of
the vapor and water, means for collecting the condensate formed in the
said stage or stages in such a way that the condensed vapor is substantially
separated from the condensed water, and means for subsequently no-
introducing the water, which may be contaminated with a small proportion
of the condensed vapor, to the air to remodify the air.
Preferably the apparatus comprises at least two successive cooling
I stages, a first cooling stage or stages being adapted to cool the air to a
temperature below the condensation point of said vapor and above the dew
point of water, a subsequent cooling stage or stages being adapted to cool
the air to a temperature below the dew point of water.
Conveniently said means for collecting the condensate comprise
means for collecting the condensate from said first stage or stages and
directing thaw condensate to a first receptacle and means for collecting the
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condensate from said subsequent stage or stages and directing thaw con-
dentate to a second receptacle.
In one embodiment the second receptacle comprises a receptacle
having a relatively large volume such that the condensate directed to the
vessel only flows slowly through the vessel to enable the condensate to
separate into an aqueous fraction and a condensed vapor fraction.
Preferably said receptacle is divided into two compartments by
means of a vertical partition, the compartments communicating in the
lowermost region of the receptacle the means supplying condensate to the
receptacle terminating in a first said compartment, there being an overflow
outlet from the second said compartment to permit the flow of the aqueous
phase to a further receptacle.
Conveniently means are provided for detecting the level of fluid
within said further receptacle, and a control device is provided, responsive
to the level of fluid within the receptacle, for controlling a pump, said pump
being provided in a circuit to pump fluid from said further receptacle to a
2û moistener or humidifier which may operate to return the moisture to the air
before it leaves the apparatus.
Preferably said cooling stage or at least one of said cooling stages is
provided with coolant from a refrigeration plant, heat pump or the like.
Conveniently heating means are provided for heating the air after it
has been cooled and before the water is returned to the air.
Advantageously said heating means incorporate at least one heating
stage which is provided with heclt from said refrigeration plant, heat pump
or the like.
Preferably means are provided for controlling the quantity of heat
supplied to said heating stage in response to the level of fluid within said
further receptacle.
Conveniently said cooling stage or stages and said heating means
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comprise at least one cooling heat exchanger and at least one heating heat
exchanger, and means for pumping heat exchange medium between the said
heat exchangers, the arrangement being such that the hoe t exchange
medium is utilized in the cooling heat exchange or exchangers to cool the air
initially, the heat exchange medium thus being heated, and tile heated heat
exchange medium is then transferred to the heating heat exchanger which
subsequently heats the air with a consequent cooling of the heat exchange
medium the then cooled heat exchange medium being returned to the
cooling heat exchanger or exchangers.
In order that the invention may be more readily understood, and so
that further features thereof may be appreciated, the invention will now be
described by way of example with reference to the accompanying drawing
which is a flow diagram of an apparatus for carrying out a method in
IS accordance with the present invention.
In the apparatus illustrated in the accompanying drawing a plurality
of heat exchangers 11, 12, 13, I 15 and 16 are arranged serially along a
conduit defining a flow path that is followed by a stream of air that is to be
de-contaminated. The inlet part 17 of the conduit is shown at the left hand
side of the drawing, and the outlet part 18 of the conduit is shown at the
right hand side of the drawing
The apparatus effectively comprises four cooling stages l-IV which
cool the air flowing from the inlet 17 towards the outlet 18 and two heating
stages V-VI which subsequently heat the air before it passes to the outlet 18.
A closed circuit is provided for the flow of a heat exchange medium
from the heat exchanger I I, through a pump (indicated by a circle
containing an arrow head, which is the conventiollal sign for a pump uiilsed
throughout the accompanying drawing) to the heat exchanger 15. The heat
exchanging medium passes from the heat exchanger 15 to the heat ox-
changer 12, and then back to the heat exchanger 11. A refrigeration plant
or heat pump 19 is provided to supply a cooling heat exchange fluid to the
heat exchangers 13 and 14. The main outlet of the refrigeration plant 19
supplies a flow of coolant directly to the heat exchanger 14, and part of the
heat exchange fluid emerging from that heat exchanger is returned directly
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to the refrigeration plant 19, whilst another part of that flow is directed
through the heat exchanger 13. The refrigeration plant or heat pump 19 is
also associated with a heated heat exchange fluid circuit which causes
heated heat exchange fluid to flow through the heat exchanger 16.
The portions of the conduit between the heat exchangers 11 end 12,
and 12 and 13 each have their lower regions configured to form a funnel, and
the lowermost parts of the funnels extend into drain conduits which combine
and terminate within a receptacle 20. The receptacle 20 is divided into two
interior chambers 21, 22 by means of a whir and the drain conduit
terminates within the chamber 21~ A float arrangement is associated with
the chamber 22 and is adapted to control a valve such that when the level of
the fluid within the chamber 22 reaches a predetermined level the valve
may be opened to permit the fluid to flow away through a drain conduit 23.
A valve controlled outlet is provided at the base of the chamber 21, and a
sight glass is provided on the exterior of the receptacle 20 to enable the
nature of the contents of the chamber 21 to be observed.
The conduit portions between the heat exchangers Andy 14, and 15
and 16 also have lower regions defining funnels which are connected two
downwardly extending conduits which combine to form a single drain conduit
that enters into a second relatively large receptacle I The receptacle 24
has a downwardly extending partition so that the receptacle is divided into
two compartments 25, 26 that communicate adjacent the base of the
receptacle 24. The single drain conduit enters into the compartment 25
mentioned above. An overflow outlet is provided extending -from the
compartment 25 to q further receptacle 27. This further receptacle 27 is
provided with a sight glass and has a valve controlled towel outlet and a
valve controlled outlet located at an intermediate level.
An overflow outlet 28 is also provided` from the compartment 26
which extends to a further receptacle 29. A float actuated control is
associated with the receptacle 29 which is adapted to actuate a pump to
pump fluid from the receptacle 29 through a conduit 31 to an evaporator
aye located within the conduit through which the air flows, after the last
heat exchanger. A return conduit 32 is also provided. The float actuated
control also actuates valves present in the heated heat exchange medium
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circuit located between the refrigeration plant or heat pump 19 and the heat
exchanger 16.
The lowermost part of the conduit portion between the heat
exchangers 15 and 16 is also shaped like a funnel" the outlet of which is
connected to the single drain conduit mentioned above.
In operation of the device air, which may be humid, which is
contaminated with oil vapor or some other vapor is caused to flow through
the conduit that defines said flow path and enters the apparatus through the
inlet 17 in the direction indicated by the arrow. The air typically has a
temperature of ~35 degrees centigrade. The air passes through the first
heat exchanger i I, and the air is cooled to approximately 20 degrees
centigrade. The heat from the air is transferred to the heat exchange
medium flowing through the heat exchanger 11 and the thus heated heat
exchange medium is driven by the pump to the heat exchanger 15. The air
then passes through the second heat exchanger 12, where it is further cooled
to a temperature of + 13 degrees centigrade. The heat exchanger 12
receives its heat exchange medium at a very tow temperature from the heat
exchanger 15 as will be described hereinafter, and the heat exchange
medium flows from the heat exchanger 12 to the heat exchanger 11.
The temperatures of 20 degrees centigrade and 13 degrees centigrade
are below the condensing point of the oil vapor that is contaminating the
air, but these temperatures are above the dew point of water. Thus, in the
first two cooling stages I and 11 substantially only oil is condensed. The
condensing oil droplets fall into the funnels defined in the lower regions of
the conduit and flow downwardly through the pipes into the chamber 21 at
the right hand side of the receptacle 20. When this chamber has been filled
up the oil will flow over the whir into the chamber 22. When the level of
the oil within the chamber 22, as detected by the float, is sufficient the
valve is opened and the oil is drained off through the conduit 23 for reuse.
If any water is condensed within the first two cooling stages I and 11, the
water will collect at the lower part of the chamber 21. If any water is seen
within this chamber through the sight glass the water can be drained out
approprkltely and such water may, for example, be introduced to the
receptacle 29.
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The air then passes through the heat exchangers 13 and 14 which
further cool the air in two stages to a temperature of I degree centigrade
and then to a temperature of -10 degrees centigrade. These temperatures
are below the dew point of water, and in these stages water will be
condensed. However, these low temperatures ensure that substantially all
the oil vapor present in the air is condensed and thus, as the air leaves the
cooling stage IV, the air is substantially pure, containing, -for example, only
60 my of oil per cubic moire. The condensed water and oil flows
downwardly into the compartment 25 of the receptacle 24. The receptacle
lo has a very large volume relative to the flow of water so that, within the
receptacle 24, there are only very slow flow rates. Consequently there will
be a period of time during which the oil and water may separate out. Thus,
in the compartment 25 the water will tend to gravitate to the lower part of
the compartment, whereas the lighter oil will remain in the upper part of
the compartment. The water in the lower part of the compartment flows
underneath the partition into the compartment 26 whilst the oil flows
through the overflow conduit into the receptacle 27. If any water is still
entrained with the oil, the water will be given an opportunity to settle out in
the receptacle 27 and if any water is observed in the sight glass the water
2û may be drained out through the lowermost drain in the receptacle 27, that
water being returned, for example, to the receptacle 29. When a sufficient
level of oil has accumulated within the receptacle 27, as seen through the
sight glass, the oil may be drained out through the intermediate level outlet
and may be returned to the rolling mill for reuse.
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the air passes through the heat exchanger 15, which is supplied, as
has been mentioned, with heated heat exchange medium From the heat
exchanger I I . The air is thus heated to + 12 degrees centigrade and the heat
exchange medium is cooled to a very low temperature. It is this very tow
temperature heat exchange medium that is supplied to the heat exchange
aye and then to the heat exchanger 11. Any fluid droplets still in the air
may fall into the funnel before the air enters the heat exchanger 16 where it
is raised to a temperature of +32 degrees centigrade. The droplets in the
funnel are drained into compartment 25 of the receptacle 24.
Meanwhile, within the receptacle 24, the water flowing into the
compartment 26 may still contain a certain quantity of oil, for example of
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the order of 50 grams per cubic moire. Thus this water is not suitable for
direct release into a municipal sewage disposal system. The water is thus
drained off through the overflow drain 28 into the receptacle 29, and, under
the control of the float operated control device 30, the fluid from the
receptacle 29 is pumped up to the humidifier aye, where the water with the
small amount of oil entrained therein is absorbed by the dry clean
ventilating air which has been heated by the heat exchanger 16 to a
temperature of ~32 degrees centigrade. Thus the air flowing to the outlet
18 has approximately the same relative humidity as the air initially
introduced to the described apparatus through the inlet 17, and the air
flowing through the outlet 18 stiff has entrained therein a small quantity of
oil vapor, this being the oil vapor reintroduced to the air at the
humidifier aye, together with the oil that remained in the air throughout
the entire cleaning process. However this small quantity of oil vapor is not
detrimental to the environment and is thus quite acceptable.
It should be mentioned that the float operated control device 30
associated with the receptacle 29 detects the level of water in the
receptacle and controls the heat supply to the heat exchanger 16 in such a
way that the heat supply increases when the level of water in the receptacle
29 is rising, so that the moisture absorbing capacity of the air increases.
Equally the heat supply to the heat exchanger 16 decreases when the water
level in the receptacle 29 is falling. This ensures, in an easy way, that the
condensed water will always be absorbed by the air leaving the described
apparatus with a minimum wastage of heat.
The present invention provides significantly improved results when
compared with the prior art discussed above. If air containing oil vapor is
cooled to a temperature of 10 degrees centigrade the air may still contain
about 25û milligram oil per cubic moire. Even if, in the prior art
arrangement, the temperature have been lowered to 0 degree centigrade,
the air would still contain about 130 degree my of oil per cubic moire.
However, in utilizing the present invention and cooling the air to a
temperature of -10 degrees centigrade the ventilating air subsequently only
contains about 60 my of oil per cubic moire, which is a very low value.
admittedly this value is increased slightly when oil is reintroduced to the
air stream at the humidifier aye, but the final figure is still very low when
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compared with the prior art.
It is to be appreciated trot the apparatus described above wilt
operate with a minimum consumption of power, since the apparatus is
internally efficient. Effectively a refrigeration plant or heat pump is
utilized to extract heat from the air as it enters the apparatus and to no-
introduce that heat to the air before it leaves the apparatus. Thus the
refrigeration plant or heat pump must merely transfer heat from one part of
the apparatus to another part of the apparatus, although, due to heat loss
lo and the inevitable slight inefficiency of the apparatus, some make-up heat
will have to be provided.
Whilst only one embodiment of an apparatus according to the
invention and only one specific example of the application of the apparatus
have been described it is to be understood that many modifications may be
effected without departing from the scope of the invention.
The cooling stage IV in which the temperature reduced to -10 degrees
centigrade may be constituted by two identical cooling stages mounted in
parallel. The reason for this is that, at a temperature of -lo degrees
centigrade, ice may form within the cooling stage, thus restricting the flow
of air. If there are two identical cooling stages connected in parallel, one
cooling stage may be utiiised while the ice in the other cooling stage melts
and drains away or while the ice is physically removed, and then the flow of
air, and coolant, may be switched over to the other stage.
It is to be understood that the cooling temperatures specified with
regard to the various cooling stages can be modified depending upon the
specific nature of the air to be purifies and the available cooling power. It isalso to be understood that the separation of oil or any other cooling or
lubricating liquid from the water can be performed in many different ways
so that, for example, only owns cooling stage will be needed. It is, however,
very convenient to use at least two cooling stages having different
temperatures so that the great proportion of the cooling or lubricating liquid
can be condensed in one stage (or a group of stages) and the water can be
condensed in a second stage (or a group of stages) as described above,
because this will considerably facilitate the recovery of the cooling or
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Lubricating liquid.
It is to be understood that the supply of cooling and heating power,
respectively to the separate stages, may also be provided in many ways. In
S this connection, heat pumps may be used to take up the waste heat
appearing in the system. The number of cooling and heating stages may also
be varied within wide limits, as required. During the winter months it has
been found that only one heating stage is normally required, and this stage
can be supplied with heat from any of the preceding stages. In the summer,
however, normally a second heating stage is required which must be supplied
with external heat, to make it possible for the ventilating air leaving the
apparatus to absorb the water from the humidifier 1 aye.
