U.S. patent number 3,708,956 [Application Number 05/092,991] was granted by the patent office on 1973-01-09 for regenerative drier for air to be conditioned.
This patent grant is currently assigned to Carl Georg Munters. Invention is credited to Per Gunnar Norback.
United States Patent |
3,708,956 |
Norback |
January 9, 1973 |
REGENERATIVE DRIER FOR AIR TO BE CONDITIONED
Abstract
A regenerative drier primarily intended for air to be
conditioned compressed to superatmospheric pressure and comprising
a drying rotor containing a moisture absorbing mass and mounted for
rotation between two air passageways thru which one is passed by
the air to be conditioned and the second by regenerating air for
the moisture absorbing mass, said second air housing a heater the
supply of heat to which is controlled by a hygrostat disposed in
said second passage at the outlet side as it passes from the rotor.
When the regenerating air is circulated in a closed circuit, a
portion of said circuit is constituted by said first passage so
that the dehumidification of the regenerating air is partially
effected within said rotor.
Inventors: |
Norback; Per Gunnar (Lidingo,
SW) |
Assignee: |
Carl Georg Munters (Stocksund,
SW)
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Family
ID: |
20302331 |
Appl.
No.: |
05/092,991 |
Filed: |
November 27, 1970 |
Foreign Application Priority Data
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Dec 1, 1969 [SW] |
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16493/69 |
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Current U.S.
Class: |
95/10; 95/113;
95/124; 96/111; 96/125 |
Current CPC
Class: |
B01D
53/06 (20130101); B01D 53/0454 (20130101); B01D
53/261 (20130101); F24F 3/1423 (20130101); F24F
2203/1032 (20130101); F24F 2203/1068 (20130101); B01D
2259/40096 (20130101); B01D 2259/40081 (20130101); F24F
2203/1056 (20130101); B01D 2253/25 (20130101); B01D
2251/302 (20130101); B01D 2257/80 (20130101); B01D
2251/60 (20130101); B01D 2259/4009 (20130101); F24F
2203/1084 (20130101) |
Current International
Class: |
B01D
53/06 (20060101); B01d 053/06 () |
Field of
Search: |
;55/163,20,23,34,35,208,51 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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166,920 |
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Apr 1959 |
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SW |
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212,794 |
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May 1967 |
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SW |
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Primary Examiner: Adee; John
Claims
What is claimed is:
1. In a regenerative drying system for compressed air having a
compressor, a rotary moisture absorber having moisture absorbing
material distributed thereon, said absorber being mounted to pass
in rotation between a drying section and a regenerating section
defined by dual compressed air streams continuously passed
therethrough as said moisture absorber rotates, means for cooling
the compressed air to remove moisture therefrom, duct means
defining a first air stream passing the cooled compressed air from
said cooling means to the drying section of said rotary dryer,
there being dried to less than 10 percent relative humidity, duct
means passing said cooled dried air emitted from the drying section
of said rotor for use as dry compressed air, duct means defining a
second air stream passing compressed regeneration air to the said
regenerating section of said rotary moisture absorber for removing
moisture therefrom, means for heating said compressed regeneration
second air stream before it enters said absorber regeneration
section and outlet duct means conveying said second moisture laden
regeneration air stream from the regeneration section of said
rotary moisture absorber, the improvement comprising mounting a
hygrostat in said outlet second air stream duct means withdrawing
moisture-laden air from the said regeneration section to sense the
moisture content thereof, and means controlled by said hygrostat
responsive to a pre-set moisture content of said moisture-laden
outlet second stream air to activate said heating means, whereby to
accelerate the moisture regeneration by raising the temperature of
said regeneration gas as it enters said regeneration section
responsive to the moisture content of the regeneration gas
evolved.
2. The regenerative drying system for compressed air as defined in
claim 1 wherein the duct means conveying regeneration gas passed
into said regeneration section is connected by duct means to the
dry air stream withdrawn from said drying section as a regeneration
gas source, whereby the regeneration gas comprises a portion of the
first stream air dried in the drying section and recycled by the
said duct means to said regeneration section as said second air
stream.
3. The regenerative drying system for compressed air as defined in
claim 1 wherein the said second stream moisture-laden regeneration
gas outlet comprises duct means interconnected with said cooling
means and, after cooling, then with duct means passing the cooled
outlet regeneration gas to the air drying section of said rotary
dryer.
4. The regenerative drying system for compressed air as defined in
claim 1 wherein the total duct means forms in part a continuous
cycling system, withdrawing some of the compressed dry air of said
first stream from the dried compressed air outlet of the rotary
dryer and passing a portion as compressed regeneration inlet air as
the regeneration gas source, the duct means further returning the
moisture-laden regeneration air from said second stream as
compressed moisture-laden air to said first stream before cooling
to deposit moisture therefrom.
5. The method of operating a regenerative drying system for
compressed air with a rotary moisture absorber having a moisture
absorbing desiccant therein, mounted to rotate between a compressed
air stream to be dried and a compressed regeneration air stream to
regenerate the rotary dryer, comprising compressing air in a first
air stream, passing the compressed air to a cooler to cool and
condense some moisture from the compressed air stream, passing the
cooled stream through the drying section of said moisture absorbent
dryer as it rotates to dry the compressed air to less that 10%
relative humidity, and then passing the first compressed dry air
stream to storage or to a means for using said dry compressed air
stream; simultaneously passing a second heated compressed
regeneration air stream through a separate regeneration section of
said rotary dryer, said second stream being heated to variable
degrees by heating means as it enters the regeneration section of
said rotary dryer, expelling moisture as a heating and scavenging
gas as it passes through the rotating dryer, mounting a hygrostat
in the outlet stream to sense the moisture content of the
moisture-laden compressed air as it leaves the said regenera-tion
section, said hygrostat being connected to activate the heating
means for the second compressed air stream as it enters said
regeneration section, variably heating said entering gas responsive
to a selected pre-set moisture content of the outlet gas from said
regeneration section as sensed by said hygrostat.
6. The method as defined in claim 5 wherein the said compressed
regeneration air is supplied as a recycled portion of the first
compressed dry air stream dried in said air drying section.
7. The method as defined in claim 5 wherein the compressed outlet
air stream from said regeneration section is cooled to remove
moisture therefrom and recycled for further drying in said air
drying section.
8. The method as defined in claim 5 wherein the compressed air
outlet stream from said regeneration section and from said
compressor are cooled as a single combined stream and to remove
moisture therefrom, and passed thence for further drying to said
air drying section.
Description
BACKGROUND OF THE INVENTION
This invention relates to a regenerative drier for air to be
conditioned.
More particularly this invention relates to an improvement in a
regenerative drier primarily for air to be conditioned, which is
compressed to superatmospheric pressure. The drier has a drying
rotor containing a moisture absorbing mass and is rotated between
two passages connected to a surrounding casing. A first passage of
said passages is passed by the air to be conditioned for the
purpose of becoming dehumidified, and a second passage by
regenerating air preferably circulating in a closed circuit and
dehydrates said mass. A heater is provided in said second passage
at the side thereof opening towards the rotor. The moisture content
of the air to be conditioned is controlled by a hygrostat. The most
important field of application of the invention is constituted by
driers or dehumidifiers for air which has been compressed to a
superatmospheric pressure of e.g. 7 kgs/cm.sup.2, and the invention
will be described hereinafter in connection with said type of
driers.
In connection with the compression in a compressor, the air will
contain a greater quantity of humidity which must be removed, as it
otherwise would cause serious difficulties, e.g. by enhancing
corrosion of those metal surfaces with which it establishes contact
or on which humidity is de-posited in the state of water or ice
e.g. in feed pipes or in tools operated by compressed air, or
deteriorate the operative properties of said tools. Normally, a
first precipitation of humidity is effected in a condenser by means
of water or air acting as cooling agent. However, in many cases
this drying operation is not sufficient to lower the moisture
content to a required degree and for this reason when very dry air
is required a drier assembly or unit is interposed following the
precooler in which assembly the main part of the remaining humidity
is removed. The lowest and most uniform drying is attained with
apparatus of the sorption type the sorption agent of which is
continuously regenerated. It has been proposed in order to control
that a desired dry content of the conditioned air be attained under
different conditions of operation while maintaining good working
economy, to control also the regeneration of the drier by means of
a hygrostat which is located in the way of the air to be
conditioned, when it is discharged from the drier and its humidity
content has been lowered to one or several few per cents of
relative moisture content. It has proved, however, this method has
several drawbacks. It is difficult to have the hygrostat to
maintain its reliability constant at such low values of the
relative humidity. The calibration hygrostat changes as time
passes, and it requires adjustments. In addition, it may occur in
connection with partial loads that those portions of the moisture
absorbing mass which are the first to be met by the air saturated
with humidity when leaving the compressor, may become
supersaturated without activating the hygrostat to emit an impulse.
When the absorbing agent is a salt such as lithium chloride, such
excess of saturation may result in so much liquid being taken up by
the salt that it is dissolved into a free solution within the
drying mass which can be displaced within the rotor and even be
carried along by the air and thus escape from the rotor, whereby
the capacity of said rotor is impaired to a corresponding
degree.
SUMMARY OF THE INVENTION
One main object of the invention is to eliminate said drawbacks.
According to one main feature of the invention the hygrostat
controlling the supply of heat to the heater is disposed in the
second passage at the outlet side thereof from the rotor. During
passage through the regenerating sector of the rotor the
regenerating air absorbs gradually more and more moisture so that
its relative moisture content when leaving the rotor amounts to
e.g. 50 to 60 and up to about 90 percent. At such high percent
values the hygrostat reacts highly sensitively so that it can start
the heater in time and thereby intensify the regeneration so that
the moisture content in the rotor is maintained below the critical
values. In addition, the hygrostat retains its calibration at so
high relative moisture values over very long periods of time for
which reason interruptions for adjusting said hygrostat need not be
made but only at very long intervals. Further, in the practice of
the invention the consumption of energy such as electric current,
for the heater is maintained within favorable economical limits.
Due to the fact that the circulation of the regenerating air in the
closed circuit is continuous, the degree of saturation of the rotor
is scanned continuously and the heater is thus switched in only
when the hygrostat indicates that the quantity of moisture in the
rotor has partially exceeded permissible values.
SHORT DESCRIPTION OF THE DRAWINGS
Further objects and advantages of the invention will become
apparent from the following description, considered in connection
with the accompanying drawing which forms part of a specification
and which shows one embodiment of the invention and of which:
FIG. 1 is a diagrammatic view of a drying apparatus embodying the
invention and FIG. 2 is an axial view of the rotor forming part of
said drying apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawing, reference numeral 10 denotes a
compressor of a type known per se, such as a compressor of the
two-stage type in which atmospheric air is compressed to
superatmospheric pressure of 7 atmospheres excess pressure, for
example. By the compression the air is imparted a considerably
increased temperature, such as 120.degree.C and more. The hot
compressed air is conducted through a condenser 12, the cooling
agent of which may be water, the air being cooled down to
approximately the temperature prevailing in the surrounding
atmosphere, e.g. down to about 5 to 40.degree.C depending on the
season. The compressed air has now a relative moisture content of
about 100 percent or even higher, if also the water particles
floating in the air are taken into account. The air is conducted
via a conduit 14 through the larger drying zone or sector 16 of the
cylindrical rotor 18 of a drying apparatus. The rotor contains a
mass which is moisture absorbing due to impregnation with a
hygroscopic salt such as lithium chloride. The rotor may be built
up as is disclosed in the U.S. Pats. Nos. 3,231,409 and 3,307,617,
e.g. it is composed by alternate flat thin sheets 20 and corrugated
thin sheets 22 of a fibrous material, such as asbestos, impregnated
with the hygroscopic salt. The thin sheets form a very great number
of narrow passages extending form end to end in parallel to the
axis 24 of the rotor. The spacing between two adjacent flat sheets
20 may be less than 3 millimeters.
The drying sector or zone 16 may occupy more than half of the
circumference of the rotor, such as three fourths thereof. The
remaining sector or zone 26 is passed by the regenerating air which
preferably is taken from the compressed air after that said air has
passed through the drying zone 16 and has been dried to a very low
both absolute and relative moisture content. The relative moisture
content may amount to at the utmost one or several few per cents.
Extending from the outlet conduit 28 which communicates with the
place of consumption of the compressed or conditioned air, is a
branch conduit 30 for regenerating air which passes first through a
heater 32 and then streams through the sector 26 of the rotor 18
counter-current to the flow direction of the air being conditioned
in passage through the other side of the rotor. The regenerating
air leaves the sector 26 through a conduit 34 which houses a fan 36
and which is connected to the conduit 14. Provided in the conduit
34 may be a condenser 37 which is cooled by e.g. available water
and which may be identical with the condenser 12.
It is assumed that the rotor 18 rotates as is indicated by the
arrow 38 in FIG. 2. The rotational speed is low, such as only few
revolutions per hour. The relative moisture content of the air to
be conditioned which initially was 100 percent is during the
passage gradually lowered to a predetermined low value, such as
e.g. 1 to 5 to 10 percent. The impregnated mass of the sheets in
the rotor picks up this moisture and transfers it to the sector 26
passed by the regenerating air. The relative moisture content of
said air will increase so that it when leaving the rotor may amount
to between 50 and 90 percent, depending on the temperature to which
it is heated by the heater 32. The relative moisture content of the
air leaving the regenerating sector varies also over the
cross-sectional area in such a manner that it increases gradually
from that part of the cross-sectional area where the rotor is on
its way from the regenerating sector to the drying sector to that
part where the rotor enters the regenerating sector from the drying
sector. According to the invention a hygrostat 40 is disposed in
the conduit 34, This hygrostat in turn through a control device 42
and conductors 44 controls the supply of heat to the heater 32 so
that the relative moisture content of the regenerating air when
leaving the apparatus does not exceed a predetermied value which in
turn determines the moisture content in the drying zone 16 of the
rotor 18.
Most suitably, the hygrostat 40 is caused to react on the air which
leaves the rotor at the place indicated by the cross 46 set out in
FIG. 2. At this point the mass of the rotor has the highest
moisture at the start of regeneration, the rotor having just passed
the rotor sector 16 and under said passage during the whole time
picked up air from the inlet side for the compressed air and where
the emitted regenerating air, has the greatest relative moisture
content. When the object is to obtain an even better working
economy, the quantity of regenerating air may be lower while at the
same time managing the supply of heat to become unnecessary, e.g.
by reducing the number of revolutions of the fan 36 whereby the
consumption of energy required for the circulation of the
regenerating air is reduced. This is the reason why the cross 46 is
located adjacent the partition wall 48 between the two sectors.
The circulation of the regenerating air in the closed circuit
formed by the two sectors or zones 16, 26 of the rotor and the
conduits 14, 28, 30 and 34 connected thereto may be brought about
by an ejector utilizing a pressure drop created in the circulation
circuit. The closed circulation circuit for the regenerating air
need not necessarily pass through the drying sector 16 of the
rotor, but may be located laterally thereof, the required drying of
the regenerating air then being effected by means of a particular
cooling condenser.
The invention is with advantage applicable also in the drying of
air under normal atmospheric pressure, in particular in such cases
of operation where a precooling is effected in a cooler assembly
and where the air to be conditioned enters the drier while having a
very high relative moisture content. In this connection the
regenerating air instead of being returned to the conditioned air
may be discharged into the surrounding atmosphere via the
condenser.
While one more or less specific embodiment of the invention has
been shown and described, it is to be understood that this is for
purpose of illustration only and that the invention is not to be
limited thereby, but its scope is to be determined by the appended
claims.
* * * * *