Abstrict A method of and apparatus for drying products with a gas stream
passing the product to extract moisture therefrom and a contacting
device producing at least one desiccant liquid layer in the vicinity
of the product to be dried, which liquid layer removes moisture
from the gas. The gas stream is bubbled through a substantially
horizontal liquid layer or can pass between liquid film conducting
elements. The desiccant liquid is continuously regenerated. By means
of several partial gas streams and a contacting device having more
separated liquid film modules, a counter-current type of drying
is possible. The product to be dried can be heated to a predetermined
temperature by the desiccant liquid through the drying gas stream.
Claims What is claimed is:
1. In a method of drying products comprising the steps of introducing
the product to be dried into a drying compartment; continuously
circulating a drying gas stream in a closed cycle so as to cause
it to pass the product to be dried; contacting the drying gas stream
with a desiccant liquid to remove moisture from the gas; and regenerating
the desiccant liquid by circulating at least a part of it through
regenerating means which remove moisture therefrom; and improvement
comprising producing at least one continuous layer of the desiccant
liquid in the drying compartment, and conducting said contacting
so that said at least one continuous desiccant liquid layer is substantially
perpendicular to the direction of the flow of the drying gas stream
in the drying compartment.
2. The method according to claim 1 in which said at least one
desiccant liquid layer is a substantially horizontal liquid layer,
and said drying gas stream is bubbled through said substantially
horizontal liquid layer.
3. The method according to claim 1 in which said at least one
desiccant liquid layer is produced by causing the desiccant liquid
to flow on liquid film conducting elements arranged in at least
one plane at the boundary of or within the drying compartment, and
said contacting is performed by causing said drying gas stream to
pass between said liquid film conducting elements.
4. The method according to claim 1 in which said desiccant liquid
is a desiccant solution; said regenerating is performed by a multi-effect
evaporation of the desiccant solution; and the steam evaporated
from the desiccant solution is at least partly condensed by the
desiccant solution to be regenerated.
5. The method according to claim 4 in which the steam evaporated
during the first boiling of the desiccant solution is at least partly
condensed by the incoming desiccant solution to be regenerated.
6. The method according to claim 4 in which the steam evaporated
during the last boiling of the desiccant solution is at least partly
condensed by the incoming desiccant solution to be regenerated.
7. The method according to claim 1 in which said desiccant liquid
is a desiccant solution, and said regenerating is performed by multi-stage
flashing.
8. The method according to claim 4 further comprising the step
of cooling the desiccant solution after said contacting and before
said regenerating in dependence of the cooling of the desiccant
solution during said contacting so that the incoming desiccant solution
to be regenerated is of a predetermined temperature.
9. The method according to claim 1 in which said continuous circulation
of the drying gas stream is performed by conducting the drying gas
stream in a path section between the product to be dried and the
desiccant liquid so that in said path section the ratio of the maximum
and minimum velocity of the drying gas stream is smaller than five
to one and the alteration of the direction of flow of the drying
gas stream is less than 30 degrees.
10. The method according to claim 9 in which said drying gas stream
is conducted between the product to be dried and the desiccant liquid
substantially without any alteration of velocity and direction.
11. The method according to claim 7 in which said desiccant solution
is an aqueous solution of calcium chloride, and the drying gas is
air.
12. In a method of drying products comprising the steps of moving
the product to be dried through a drying compartment; continuously
circulating a drying gas stream in a closed cycle so as to cause
it to pass the product to be dried; contacting the drying gas stream
with a desiccant liquid to remove moisture from the gas; and regenerating
the desiccant liquid by circulating at least a part of it through
regenerating means which remove moisture therefrom; the improvement
comprising producing at least one layer of the desiccant liquid
and bringing about a continuous heat exchange between the desiccant
liquid layer and the product to be dried by heating the desiccant
liquid in the course of said regenerating and then contacting the
desiccant liquid with said drying gas to cool the desiccant liquid
and heat the drying gas to at least 40.degree. C. in the course
of said contacting.
13. The method according to claim 12 further comprising the step
of producing said at least one layer of the desiccant liquid in
the vicinity of the product being in the drying compartment so that
said at least one desiccant liquid layer is disposed substantially
perpendicularly to the direction of flow of the drying gas stream
in the drying compartment.
14. In an apparatus for drying products comprising at least one
drying compartment for the product to be dried; at least one contacting
device for contacting a drying gas stream with a desiccant liquid
to remove moisture from the gas; gas conducting means for conducting
the drying gas stream in a substantially closed path through said
drying compartment and said contacting device; gas circulating means
to cause the drying gas stream to circulate along said closed path;
regenerating means for removing moisture from the desiccant liquid;
and liquid circulating means for circulating at least part of the
desiccant liquid through said regenerating means and said contacting
device; the improvement in which said contacting device (43) includes
means (13 58) for producing at least one continuous layer (1 41)
of the desiccant liquid to be contacted with the drying gas stream;
said contacting device (43) being located at the boundary of or
within said drying compartment (25 40) and said at least one continuous
layer being disposed substantially perpendicularly to said path
for conducting said drying gas stream in said drying compartment
(25 40).
15. The apparatus according to claim 14 in which said contacting
device comprises a vessel (13) for producing a substantially horizontal
desiccant liquid layer (1), said vessel (13) having on its wall
bubbling caps (20) for bubbling the drying gas stream through said
liquid layer (1), said vessel (13) being connected to said liquid
circulating means (36) so as to cause the desiccant liquid to flow
along said vessel, and said drying compartment (25) is located above
or below said vessel (13).
16. The apparatus according to claim 15 in which said drying compartment
(25) comprises a device (4) for transporting the product (2) to
be dried through said drying compartment, said transporting device
(4) having openings (5) for letting through the drying gas stream,
but not letting the product (2) to be dried drop.
17. The apparatus according to claim 16 in which said transporting
device is an endless belt conveyor (4), and said gas circulating
means are ventilators (17A, 17B, 17C, 17D) placed side by side along
said belt conveyor (4).
18. The apparatus according to claim 14 in which said contacting
device (43) comprises liquid film conducting elements (58) being
placed so that the drying gas stream is passing between said liquid
film conducting elements (58), said liquid film conducting elements
(58) being arranged in at least one substantially vertical plane
at the boundary of or within said drying compartment (40), said
vertical plane being substantially perpendicular to the direction
of the flow of the drying gas stream.
19. The apparatus according to claim 18 in which said contacting
device (43) further comprises a receptacle (55) for receiving and
holding the incoming desiccant liquid, at least one pile lock (56)
to guide in film form the liquid out of said receptacle (55), liquid
distributing means having at least one distributing surface (57)
connected to said at least one pile lock (56) and facing downwards,
and liquid outlet means (62), wherein said film conducting elements
(58) are connected between said liquid distributing surface (57)
and said liquid outlet means (62) so that they conduct liquid films
(41) from said surface (57) into said outlet means (62).
20. The apparatus according to claim 18 in which said contacting
device (43) consists of at least two liquid film modules (48A, 48B,
48C) placed side by side, each liquid film module (e.g. 48A) has
its own liquid film conducting elements (e.g. 58A) and own liquid
circulating device (e.g. 60A, 61A) providing a liquid circulation
to form the liquid films on said own conducting elements, and said
liquid film modules (48A, 48B, 48C) are provided with a common liquid
channel (62) interconnecting said liquid circulating devices, said
common liquid channel (62) being connected to said liquid circulating
means (e.g. 36), and said gas circulating means (66 66'; 17A, 17B,
17B, 17C, 17D) being adapted for circulating at least two parallel
partial gas streams.
21. The apparatus according to claim 14 in which the ratio of
any two flow cross sections of said gas conducting means (37 38
49 54) between said drying compartment (40) and said contacting
device (43) is between 0.2 and 5; and said contacting device (43)
is located at said drying compartment (40) so that the drying gas
stream is flowing between the product (50) to be dried and said
contacting device (43) with a directional change of less than 30
degrees.
22. The apparatus according to claim 21 in which said flow cross
section ratio is between 0.5 and 2 and said directional change
is substantially zero degree.
23. The apparatus according to claim 21 in which the distance
between said drying compartment (40) and said contacting device
(43) is less than the hydraulic diameter of said gas conducting
means (37 38 49 54) between them.
24. The apparatus according to claim 14 in which said regenerating
means (150) comprises a multi-effect evaporator (e.g. 70 to 84).
25. The apparatus according to claim 14 in which said regenerating
means (150) comprises a multi-stage flash evaporator (151).
26. In an apparatus for drying products comprising at least one
drying compartment for the product to be dried; at least one contacting
device for contacting a drying gas stream with a desiccant liquid
to remove moisture from the gas; gas conducting means for conducting
the drying gas stream in a substantially closed path through said
drying compartment and said contacting device; gas circulating means
to cause the drying gas stream to circulate along said closed path;
regenerating means for removing moisture from the desiccant liquid;
and liquid circulating means for circulating at least a part of
the desiccant liquid through said regenerating means and said contacting
device; the improvement comprising a basement (49), a shell-roof
(65), and a false roof (54) provided with openings (47 47A) for
letting through the drying gas stream and located between said basement
(49) and said shell-roof (65); said drying compartment (40) being
located between said basement (49) and said false roof (54); said
gas circulating means (66 66') being placed between said false
roof (54) and said shell-roof (65); said contacting device (43)
comprising liquid film conducting elements (58A, 58B, 58C); said
contacting device (43) being placed at said drying compartment (40)
so that said liquid film conducting elements (58A, 58B, 58C) are
arranged in at least one substantially vertical plane, said plane
being substantially perpendicular to the direction of flow of the
drying gas stream and extending between said basement (49) and said
false roof (54).
27. The apparatus according to claim 26 in which said contacting
device (43) consists of at least two liquid film modules (48A, 48B,
48C) placed side by side, each liquid film module (e.g. 48A) has
its own liquid film conducting elements (e.g. (58A) and own liquid
circulating device (e.g. 60A, 61A) providing a liquid circulation
to form the liquid films on said own conducting elements, and said
liquid film modules (48A, 48B, 48C) are provided with a common liquid
channel (62) interconnecting said liquid circulating devices, said
common liquid channel (62) being connected to said liquid circulating
means (e.g. 36), and said gas circulating means (66 66'; 17A, 17B,
17C, 17D) being adapted for circulating at least two parallel partial
gas streams.
28. The apparatus according to claim 26 in which said regenerating
means (150) comprises a multi-effect evaporator (e.g. 70 to 84).
29. The apparatus according to claim 26 in which said regenerating
means (150) comprises a multi-stage flash evaporator (151).
30. In a method of drying products comprising the steps of moving
the product to be dried through a drying compartment; continuously
circulating a drying gas stream so as to cause it to pass the product
to be dried; contacting the drying gas stream with a desiccant liquid
to remove moisture from the gas; and regenerating the desiccant
liquid by circulating at least a part of it through regenerating
means which remove moisture therefrom; the improvement wherein said
drying gas stream consists of at least two parallel partial gas
streams; the product to be dried is moved acress said partial gas
streams; and each of said partial gas streams is contacted with
a desiccant liquid of different specific concentration and temperature;
each of said partial gas streams being contacted with a more concentrated
desiccant liquid than the desiccant liquid contacting the previous
partial gas stream with respect to the direction of movement of
the product to be dried; producing at least two separated groups
of desiccant liquid films of different concentration; placing said
groups of desiccant liquid films side by side in a way of said partial
gas streams so that each of said partial gas streams is contacted
with its own at least one group of desiccant liquid films; each
of said groups of desiccant liquid films being provided with its
own liquid circuit; the liquid circuit of the last group with respect
to the direction of movement of the product to be dried being fed
with the regenerated desiccant liquid coming from said regenerating
means; the circuit of each preceding group being fed with the overflow
of the circuit of the subsequent group; and the overflow of the
circuit of the first group being conducted into said regenerating
means.
Description This invention relates to a method and an apparatus for drying
products with a closed gas stream and with a desiccant (sorption)
liquid diminishing the moisture content of the gas stream.
A well-known method for drying products is that the material to
be dried is brought into direct contact with some gas, in most cases
with air unsaturated with moisture, this way the material gets drier,
the gas more and more saturated with moisture. Drying apparatuses
in common use at present--especially the ones serving for drying
a relatively big amount of products--usually dry with heated air
of small relative humidity, which is released into the atmosphere
after the drying had taken place. This open gas stream drying is
accompanied by a significant loss of thermal energy, and it is unsatisfactory
also because in some cases the products to be dried are heat-sensitive.
It can also be disadvantageous because of producing air-pollution.
It was precisely the heat-sensitivity of special products (medicines,
gelatine, foodstuffs, etc.) which made drying with low (e.g. environment
or under environment) temperature gas necessary. The small relative
humidity of low temperature gas, which is a prerequisite of effective
drying of these kinds of products, can be achieved through diminishing
the absolute humidity of the gas. Therefore it has been suggested
e.g. in U.S. Pat. No. 3257737 that the drying gas should be contacted
with solid adsorbents which extract the moisture content of the
gas. It has also been suggested e.g. in Austrian Pat. No. 317857
and in British Pat. No. 1152440 to use desiccant (hygroscopic)
liquids (e.g. aqueous solution of lithium chloride or ethylene glycol)
to remove the moisture from a gas. A continuous regeneration of
the drying gas in this manner makes a closed gas stream also applicable.
The suggested solutions utilizing a desiccant liquid cause the liquid
to contact with the gas stream in sprayed or pulverized form, and
the liquid particles carried away by gas stream are held back by
a drip separator. Such a system from the point of view of energetics
is theoretically more favourable than the one working with heated
air essentially because thermal loss caused by the releasing of
the air into the atmosphere is omitted. Still, up till now, closed
gas circulation systems have only been used in case of special drying
problems, and whenever it was possible with regard to the characteristics
of the products to be dried, the open air stream method with heated
air was applied. The reason for this is that the traditional type
of closed gas circulating driers makes a costly investment, the
circulation of very much gas is extremely energy-consuming, and
the desiccant liquid used for regeneration is expensive; these latters
result in high operating expenses.
It is the main object of the invention to provide a closed gas
stream drier which as far as expenses are concerned is more favourable
than the previous closed gas stream dryers, and is competitive with
the known open air steam dryers, even in case of a big amount of
products to be dried.
The invention is based on the following basic ideas:
(1) Contact between the gas stream and the desiccant liquid should
not be brought about by spraying or pulverization of the liquid
but with the aid of a gas-liquid contacting device placed in the
path of the gas stream which allows the separation of drying space
and contacting space as used until now to be eliminated.
(2) In a closed air stream circulation system the amount of air
to be used for a particular purpose is a multiple of that used in
an open system. For this reason, the gas contacting device using
desiccant liquid and the product to be dried must be placed close
to one another and in such a way that the air stream should suffer
the least possible alteration in velocity and in direction in the
course of the circulation.
(3) Drying must be carried out not with low but with such high
temperature gas stream as is allowed by the character of the product
at all. To do this it is expedient to heat the circulated gas stream
by the desiccant liquid.
(4) When regenerating the desiccant liquid the evaporation heat
of the steam eliminated from the liquid must be recuperated into
the liquid to be regenerated with regard also to the heating needed
during the regeneration.
(5) The desiccant liquid gas contacting device must be of a structure
that can also be modularly arranged, and permit the application
of the per se known principle of counter-current at the drying of
continually moving products.
Hence, one subject matter of the invention is a method of drying
products with a closed gas stream and a desiccant liquid wherein
the following steps are performed: introducing the product to be
dried into a drying compartment; continuously circulating a drying
gas stream so as to cause it to pass the product to be dried; contacting
the drying gas stream with a desiccant liquid to remove moisture
from the gas; and regenerating the desiccant liquid by circulating
at least a part of it through regenerating means which remove moisture
therefrom. The essence of this method consists in producing at least
one layer of the desiccant liquid in the vicinity of the product
being in the drying compartment, and contacting the drying gas stream
with said at least one desiccant liquid layer.
The application of a liquid layer according to the invention is
advantageous in several respects. First, it renders unnecessary
the drip separator applied in the systems known, all the same it
prevents radically pollution of the gas stream by the liquid-drops,
and thus it diminishes the loss of the desiccant liquid, too. Second,
the coefficient of the mass transfer between the liquid and the
gas is more favourable here than with liquid particles; this allows
compact structure accompanied by a smaller pressure drop of the
gas stream. Third, it does not demand a contacting space separated
from the drying compartment; the liquid layer can be established
quite close to the product to be dried. Another advantage is that
bringing about a liquid layer is less delicate an operation that
spraying as known from the previous solutions, because the danger
of a block up is much less, and so is the need for maintenance.
This latter factor is of particular significance as the gas stream
often transports dust and other pollution beside moisture into the
desiccant liquid, which block up the holes in the spray nozzles.
An advantageous implementation of the method according to the invention
is to produce a substantially horizontal desiccant liquid layer,
and bubbling the gas stream through said horizontal liquid layer.
By this it is possible to dry bulk goods, for instance transported
on a belt conveyor which is conducted under or above the horizontal
liquid layer.
It is another extremely advantageous implementation of the method
wherein at least one desiccant liquid layer is produced by causing
the desiccant liquid to flow on liquid film conducting elements,
and said contacting is performed by causing said drying gas stream
to pass between said liquid film conducting elements. The liquid
film conducting elements can be applied to form a curtain-like arrangement
which may for example border the drying compartment.
Another subject matter of the invention is a method of drying product
wherein the following steps are performed: introducing the product
to be dried into a drying compartment; continuously circulating
a drying gas stream so as to cause it to pass the product to be
dried; contacting the drying gas stream with a desiccant liquid
to remove moisture from the gas; and regenerating the desiccant
liquid by circulating at least a part of it through regenerating
means which remove moisture therefrom. The essence of this method
consists in bringing about a heat exchange between the desiccant
liquid and the product to be dried so that the heat is transmitted
by the drying gas stream between the desiccant liquid and the product
to be dried.
It is practical to raise the temperature of the desiccant liquid
during regeneration to such a degree that while contacting the desiccant
liquid with the drying gas stream the temperature of the gas is
raised to a predetermined temperature, preferably over 40.degree.
C., for heating up the product to the degree required. This method
provides for the possibility of diminishing the quantity and velocity
of the gas to be circulated because at a higher temperature the
quantity of moisture extractable with 1 kg air is increasing, and
allows an efficient recuperation of the evaporation heat of the
steam evaporated from the desiccant liquid during the regeneration
into the desiccant liquid to be regenerated. A further advantage
is the omission of cooling applied in the previous gas-liquid contactors:
this results in a simpler construction of the gas-liquid contacting
device.
According to a particular execution of this method the desiccant
liquid is a desiccant solution; said regenerating is performed by
evaporating the desiccant solution; and the steam evaporated from
the desiccant solution is at least partly condensed by the desiccant
solution to be regenerated. This permits highly economic regeneration
during which energy requirement of regeneration can be reduced at
a great extent by applying a multi-effect boiling or a multi-stage
flash evaporation. Compared to the previous solutions where the
evaporation heat of the evaporated steam is used for heating the
air which is to predry the product it is an advantage that the steam
condensation with a liquid requires a smaller and cheaper device
than that working with air.
It is practical to boil the desiccant solution to be regenerated
with the steam evaporated from the solution during regeneration.
Energy requirement can be reduced through concentrating the desiccant
solution by multi-effect boiling, and using the incoming solution
to be evaporated for condensing at least partly the steam evaporated
during the first or during the last boiling process of the regeneration.
Regeneration can be executed by heating the desiccant solution
to be regenerated without making it to boil, with the steam evaporated
from the solution. In this case it is particularly advantageous
to regenerate the desiccant solution with a multi-stage flash evaporator.
According to a very advantageous implementation of the method of
the invention, the desiccant solution is to be cooled before regeneration
as a function of the cooling down of the desiccant solution during
the drying process so that the desiccant solution to be regenerated
is of a predetermined temperature. The cooling suggested here is
vital for the control of the cycle of the desiccant solution, and
is meant to complement the cooling down which occurs in the desiccant
solution at contact with the drying gas stream. The degree of cooling
must be altered for instance according to the season. The cooling
is preferably done during regeneration.
According to another advantageous implementation of the method
the continuous circulation of the drying gas stream is performed
by conducting the drying gas stream in a path section between the
product to be dried and the desiccant liquid so that in said path
section the ratio of the maximum and minimum velocity of the drying
gas stream is smaller than five to one and the alteration of the
direction of the drying gas stream is less than 30 degrees. This
measure results in a relatively small demand for ventilation power;
this is an important point in the economy of the whole drying procedure.
The ventilation power can be further diminished if the drying gas
stream is conducted between the product to be dried and the desiccant
liquid substantially without any alteration of velocity and direction.
It is practical to use air as drying gas and aqueous solution of
calcium chloride as a desiccant solution. The calcium chloride solution
is particularly profitable owing to it cheapness. The method according
to the invention is applicable not only for eliminating the moisture
of water but also for drying materials which contain a different
kind of moisture by using an appropriate desiccant liquid. It is
possible, for instance, to apply the present method for drying materials
containing alcoholic moisture using closed air stream and petrol
as desiccant liquid.
According to a further implementation of the method the drying
gas stream consists of at least two parallel partial gas streams;
the product to be dried is moved across said partial gas streams;
and each of said partial gas streams is contacted with a desiccant
liquid of specific concentration and temperature. In this way the
drying program for the product to be dried can be extremely varied.
For instance, according to a highly expedient implementation of
the method, each of said partial gas streams is contacted with a
more concentrated desiccant liquid than the desiccant liquid contacting
the previous partial gas stream with respect to the direction of
movement of the product to be dried. This results in a counter-current
between the product to be dried and the desiccant liquid.
The method according to the invention can be implemented also by
producing at least two separated groups of desiccant liquid films
of different concentration; placing said groups of desiccant liquid
films side by side in the way of said partial gas streams so that
each of said gas streams is contacted with its own at least one
group of desiccant liquid films. It is an advantageous implementation
wherein each of said groups of desiccant liquid films is provided
with own liquid circulation; the liquid circulation of the last
group with respect to the direction of movement of the product to
be dried is fed with the regenerated desiccant liquid coming from
said regenerating means; the circulation of each preceding group
is fed with the overflow of the circulation of the subsequent group;
and the overflow of the circulation of the first group is conducted
into said regenerating means. In this way counter-current is attained
between the desiccant liquid and the product to be dried.
It is also possible to move the product to be dried across the
partial gas streams and alter the temperature of the product in
a prescribed manner through controlling the temperature of the desiccant
liquid separately in each individual group of desiccant liquid films.
In this manner the drying temperature also in case of continuous
drying can easily be programmed for each phase of drying.
A further subject matter of the invention is an apparatus for drying
products with a closed gas stream and desiccant liquid wherein the
apparatus comprises at least one drying compartment for the product
to be dried; at least one contacting device for contacting a drying
gas stream with a desiccant liquid to remove moisture from the gas;
gas conducting means for conducting the drying gas stream in a substantially
closed path through said drying compartment and said contacting
device; gas circulating means to cause the drying gas stream to
circulate along said closed path; regenerating means for removing
moisture from the desiccant liquid; and liquid circulating means
for circulating at least a part of the desiccant liquid through
said regenerating means and said contacting device. The apparatus
is characterized by that said contacting device includes means for
producing at least one layer of the desiccant liquid to be contacted
with the drying gas stream; said at least one desiccant liquid layer
is located in the vicinity of the product being in said drying compartment.
In an embodiment of the apparatus according to the invention the
contacting device comprises a vessel for producing a substantially
horizontal desiccant liquid layer, said vessel having on its wall
bubbling caps for bubbling the drying gas stream through said liquid
layer, said vessel being connected to said liquid circulating means
so as to cause the desiccant liquid to flow along said vessel, and
said drying compartment is located above or below said vessel. Preferably
the drying compartment comprises a device for transporting the product
to be dried through said drying compartment, said transporting device
having openings for letting through the drying gas stream but not
letting the product to be dried drop. Advantageously the transporting
device is an endless belt conveyor, and said gas circulating means
are ventilators placed side by side along said belt conveyor.
According to another embodiment of the apparatus the contacting
device comprises liquid film conducting elements being placed so
that the drying gas stream is passing between said liquid film conducting
elements. A high degree of operational safety and simple structure
can be achieved if the contacting device further comprises a receptacle
for receiving and holding the incoming desiccant liquid, at least
one pile lock to guide in film form the liquid out of said receptacle,
liquid distributing means having at least one distributing surface
connected to said at least one pile lock and facing downwards, and
liquid outlet means, wherein said film conducting elements are connected
between said liquid distributing surface and said liquid outlet
means so that they conduct liquid films from said surface into said
outlet means. This embodiment is not very sensitive to the pollution
which might get into the desiccant liquid from the drying gas stream.
It is practical to arrange the liquid film conducting elements--preferably
strips or fibres--into at least one substantially vertical plain.
There is an excellent heat--and mass-transfer between the desiccant
liquid films created on the thin fibres and the drying gas stream.
The strips or fibres can be made of a metal resistant to the desiccant
liquid or of a plastic material which tolerates the highest possible
temperature of the desiccant liquid.
One possible embodiment of the drying apparatus according to the
invention is applicable for products as wood. This embodiment comprises
a basement, a shell-roof, and a false roof provided with openings
for letting through the drying gas stream and located between said
basement and said shell-roof, wherein said drying compartment is
located between said basement and said false roof, said gas circulating
means are ventilators placed between said false roof and said shell-roof,
and said contacting device is placed at said drying compartment
so that said at least one vertical plain formed by said liquid film
conducting elements is substantially perpendicular to the drying
gas stream and extends between said basement and said false roof.
In such an arrangement the liquid film gas contacting device is
placed at a boundary surface or a cross-section of the drying compartment,
said surface or cross-section being substantially perpendicular
to the direction of the gas stream. This arrangement guarantees
little pressure drop for the gas stream which results in a low energy
consumption due to the ventilation.
A very advantageous embodiment of the apparatus according to the
invention is wherein the contacting device consists of at least
two liquid film modules placed side by side, each liquid film module
has its own liquid film conducting elements and own liquid circulating
device providing a liquid circulation to form the liquid films on
said own conducting elements, and said liquid film modules are provided
with a common liquid channel interconnecting said liquid circulating
devices, said common liquid channel being connected to said liquid
circulating means. Thus the apparatus has one single regenerating
means belonging to it, still each liquid film module gets a desiccant
liquid whose activity is different from that of the others.
According to a further embodiment the ratio of any two flow sections
of said gas conducting means between said drying compartment and
said contacting device is between 0.2 and 5; and said contacting
device is located at said drying compartment so that the drying
gas stream is flowing between the product to be dried and said contacting
device with a directional change of less than 30 degrees. It is
very advantageous if said flow cross section ratio is between 0.5
and 2 and said directional change is substantially zero degree,
and the distance between said drying compartment and said contacting
device is less than the hydraulic diameter of said gas-conducting
means between them.
According to a highly profitable embodiment of the apparatus the
desiccant regenerating means contain a multi-effect evaporator a
multi-stage flash evaporator. It is the latter which is more expedient
with regard to its simple operation. This embodiment guarantees
very economical regeneration also from the point of view of energy
consumption.
A further subject matter of this invention is, as an article of
manufacture, the product prepared according to the present method.
Further details of the invention will be described by taking reference
to the accompanying drawings which show, by way of example, embodiments
of the apparatus according to the invention, and in which:
FIG. 1 is a schematic illustration of a first embodiment of a drying
apparatus according to the invention;
FIG. 2 is a sectional view of a second embodiment of the drying
apparatus, taken along the line B--B of FIG. 4;
FIG. 3 is another sectional view of the second embodiment, taken
along the line A--A of FIG. 4;
FIG. 4 is a top view of the second embodiment of the drying apparatus
shown in FIGS. 2 and 3;
FIG. 5 is a sectional perspective view of a third embodiment of
the drying apparatus;
FIG. 6 is a sectional top view of the third embodiment, taken along
the line C--C of FIG. 5;
FIG. 7 is a circuit diagram of the desiccant liquid regenerator
of the second embodiment as shown in FIGS. 2 to 4;
FIGS. 8 and 9 are circuit diagrams of two other desiccant liquid
regenerators applicable in the drying apparatus according to the
invention;
FIG. 10 is a circuit diagram of a multi-stage flash evaporator
applicable as a desiccant liquid regenerator in the drying apparatus
according to the invention.
Same reference characters refer to same or similar elements throughout
the drawings.
In FIG. 1 a casing 42 of a drying apparatus is shown schematically.
In the apparatus a gas stream e.g. an air stream which dries product
50 e.g. bulk goods as shown in the figure, circulates in a closed
cycle in the direction of arrow 64. Circulation is forced by a ventilator
66 which is driven by an electric motor 46 placed above a false
roof 54 shown schematically, without its holding means in the figure.
The false roof 54 has openings 47 in it which the air stream can
get through. The product 50 is situated in a drying compartment
40 under the false roof 54. After flowing through the product 50
the now wet air stream gets into a contacting device 43 which causes
the air stream to contact liquid films 41 of a desiccant liquid.
The desiccant liquid is circulated by a pump 141 in a regenerator
150. The active and hot desiccant liquid comes into the contacting
device 43 from a pipeline 44 above, it flows into a pot-shape receptacle
55 from there over a pile lock 56 to a liquid distributing surface
57 facing downwards. From the liquid distributing surface 57 it
flows down-a-long liquid film conducting elements 58 e.g. fibres,
said elements conduct it to a liquid outlet channel 62 from there
it departs through a pipeline 45.
The desiccant liquid diluted and cooled by the contact with the
air stream flows into the regenerator 150 through the pipeline 45.
The regenerator 150 displayed in the drawing as an example contains
a multi-stage flash evaporator 151 a liquid circulating pump 141
a pump 142 for removing the distillate of the multi-stage flash
evaporator 151 through a pipe end 149 and a heat-exchanger 143
which is fed with cooling water through pipe ends 144. Cooling in
the heat-exchanger 143 is essential for the appropriate operation
of the multi-stage flash evaporator 151. The active liquid leaving
regenerator 150 warms up while going through condenser 145 then
gets back to the contacting device 43. The condenser 145 gets the
heating steam through a pipe end 146 and the condensate is carried
away by a pump 147 through a pipe end 148. Elements of the regenerator
150 and the heating after the regeneration are well-known in themselves,
so their detailed description is unnecessary.
The embodiment according to FIG. 1 is particularly advantageous
when drying products with high heat tolerance e.g. bricks, as in
this arrangement the temperature of the desiccant liquid which has
returned from the contacting device 43 and has been "cooled"
there is still enough for eliminating the moisture during the flashing
process.
Application of the multi-stage flash evaporator 151 shown in FIG.
1 is particularly advantageous in the apparatus according to the
invention because it is from the point of view of control, operation
and reliability more favourable then other multi-effect evaporators
of the same energetic efficiency. Here the evaporation does not
take place along heat transfer surfaces, so it is less sensitive
to encrustation and corrosion, and its construction does not become
complicated even if energetic effectivity is improved. Naturally,
an evaporator of different arrangement or construction per se known
can equally be applied for the regeneration.
Similarly, to use the contacting device 43 as shown in FIG. 1 in
the apparatus according to the invention is very profitale. This
construction is not sensitive to the pollution getting into the
liquid from the air stream, and guarantees the contact between the
liquid and the air stream to have a good heat- and mass-transfer
coefficient.
In the apparatus according to the invention the drying compartment
can be constructed and the product 50 to be dried can be placed
in many ways (suspended, fluid-bedded, geyser, chamber, tunnel or
anything else). The product can be moved during the drying process
and the drying gas can equally meat the products in counter-, cross-
or direct-current.
FIGS. 2 3 and 4 show such an embodiment of the drying apparatus
according to the invention which operates with a substantially horizontally
moving liquid layer 1 and with also horizontally moving product
2 above the liquid layer. The product 2 e.g. soybean through a throat
3 gets onto a transporting device, in the drawing a belt conveyor.
The belt 4 has air transmitting openings 5 in it which let the air
through but prevent the product 2 from falling off. The belt 4 is
held by two wheels 6 which are constructed to be capable of stretching
and driving the belt, for this purpose e.g. they can be indented
or rubberized. One of the wheels 6 is driven by an electric motor
8 through a driving gear 7. The loaded belt 4 of the belt conveyor
transports the product 2 from the throat 3 through the drying compartment
25 which is situated in the casing 9 of the drying apparatus, then
through gate 10 transports it to a collector 11 from where the dried
product is transported to the place of storing or utilization by
a belt conveyor or a pulley not shown in the figure. The empty strand
of the belt conveyor passes under the casing 9.
In the bottom part of the casing 9 under the loaded strand of
the belt conveyor there is a lower air collecting space 12 and
above this but under the loaded strand of the belt conveyor there
is a liquid vessel 13. In the liquid vessel 13 a desiccant liquid
flows in the direction of arrow 14 opposite to the product 2 which
moves in the direction of arrow 15. Above the loaded strand of the
belt conveyor, in the upper part of the casing 9 there is an upper
air collecting space 16. Four ventilators 17A, 17B, 17C and 17D
driven by electric motors 23A, 23B, 23C and 23D, respectively suck
the air from the upper air collecting space 16 through suction ports
22A, 22B, 22C and 22D, and force it through pressure tubes 18A,
18B, 18C and 18D and through openings 19A, 19B, 19C and 19D to the
lower air collecting space 12. From here the air bubbles through
bubbling caps 20 situated in the wall of the liquid vessel 13--one
of the caps 20 is shown in a magnified form in FIG. 2--into the
desiccant liquid layer 1 in the direction of arrow 21 then, leaving
the liquid layer 1 through the openings 5 of the belt gets into
the layer formed by the product 2 to be dried, and after going through
it the air gets back to the upper air collecting space 16 thus
the air circle is closed. The liquid vessel 13 which is provided
with bubbling caps 20 in this embodiment functions as a contacting
device 43 which brings about contact between the air stream and
the desiccant liquid.
The four ventilators 17A, 17B, 17C and 17D bring about four closedly
circulating partial air streams. The first partial air stream goes
through suction port 22D and meets the arriving wet product 2. The
second one goes through suction port 22C, the third through suction
port 22B and the fourth through suction port 22A, and this last
one extracts from product 2 the last part of moisture to be extracted.
The desiccant liquid gets into the liquid vessel 13 through pipe-joint
26 and departs through pipe-joint 27. The arriving hot and active
liquid is bubbled through by the air of the last partial air stream,
and the departing, cooled and diluted liquid is bubbled through
by the first partial air stream.
Using several partial air streams brought about by several ventilators
17A, 17B, 17C and 17D is not only advantageous with respect to stream
conditions but also because of ensuring counter-current dyring with
the product 2 and the desiccant liquid 1 moving opposite to one
another. It is obvious that if there were only one single air stream
circulated by one ventilator, there would be no counter-current
drying in spite of the product 2 and the desiccant liquid 1 moving
in opposite directions. The counter-current effect would have an
optimum efficiency if there were an endless number of partial air
streams circulating side by side. In this respect it is expedient
to use as many partial air streams as possible at drying according
to the invention.
It can be seen in FIGS. 2 to 4 that drying compartment 25 and the
contacting device 43 are placed immediately above one another quasi
forming two "floors" of the casing 9.
Another embodiment of the same type of arrangement, different from
the embodiment shown in FIGS. 2 to 4 is that the liquid vessel
13 is placed above the loaded strand of the belt conveyor. This
is advantageous when the product 2 contains such little particles
as would fall into the liquid vessel 13 through openings 5 of the
belt 4 and would pollute the desiccant liquid at an unfavourable
degree. In such an embodiment the air stream entering through openings
19A, 19B, 19C and 19D would first go through the product 2 then
through the liquid layer 1. Another advantage of this embodiment
is that particles of the product 2 fallen through openings 5 of
the belt 4 can be collected on the bottom of the casing 9 and from
there can be transported away as dried product from time to time
or continually. It is also advantageous that liquid drops which
might have been carried away from the liquid layer 1 by the air
stream, do not get onto product 2 but having gone through ventilators
17A, 17B, 17C and 17D can be collected in pots or in channel formed
in the bottom of tubes 18A, 18B, 18C and 18D, and from there can
be fed back to the liquid circle.
In the embodiment displayed in FIGS. 2 to 4 the pollution which
had got into the liquid layer 1 e.g. from the product 2 through
openings 5 can be eliminated with the help of a separating tank
well known in itself, which is inserted into the desiccant liquid
circle preferably after pipe-joint 27 in such a way for example,
that the liquid pouring into the separating tank can only depart
through openings placed at half-way to the full height of the liquid
level in the tank. Naturally, the tank must be cleaned appropriately,
the fluid must be skimmed, and deposits must be removed.
The diluted desiccant liquid, in this embodiment a desiccant solution,
gets into the regenerator, in case of the embodiment shown in FIGS.
3 and 4 into a solution-condenser, which consists of a liquid circulating
pump 28 a vapor condenser 29 which is cooled by the arriving diluted
solution, a pump 30 for removing the distillate, a steam-heated
evaporator 31 and a pump 36. The pump 28 pumps the diluted solution
through condenser 29 as a cooling medium, from there the solution
gets into the evaporator 31 through pipeline 32. The evaporator
31 is heated by steam through pipe-joint 33 and the condensate of
the heating steam departs through pipe-joint 34. The steam evaporated
from the solution gets to the condenser 29 from the evaporator 31
through a pipeline 35 there it gets condensed and the distillate
is removed by the pump 30. The system of the pump 30 is such that
together with the distillate it is capable of removing the non-condensable
gases, too. From the evaporator 31 the condensed, active solution
is pumped by a pump 36 through a pipeline 24 to the pipe-joint 26
through which it gets back to the liquid vessel 13. This desiccant
solution regenerator is also shown by circuit diagram on FIG. 7
for the sake of better understanding.
In the interest of lucidity FIGS. 2 to 4 show such a simplest possible
evaporator, which uses only the arriving solution to be regenerated
as cooling medium for condensing the steam evaporated from the solution
during the regeneration. However, according to the invention, it
is more practical to use instead a multi-effect evaporator whose
energetic efficiency is higher, for example as shown in FIG. 8 or
9 or a multi-stage flash evaporator, for example as shown in FIG.
1 or 10.
Naturally in place of the belt conveyor some other transporting
device can equally be applied, and the product 2 can be taken through
the drying compartment 25 not only horizontally but also askew.
The cross-section of the liquid vessel 13 is much bigger than that
of pipe-joints 26 and 27 for this reason it is practical for ensuring
an even streaming picture to let the desiccant solution stream in
and out of the liquid vessel 13 not only through a single incoming
and outgoing pipe-joint but through many ones along the width of
the vessel 13.
FIGS. 5 and 6 show another embodiment which works with horizontally
moving product 50 and a contacting device 43 placed beside the product
50 bringing about a vertical liquid film 41 of a desiccant liquid.
The product 50 sawn wood on the drawing, is put onto carriages
51 with wheels supported in bearings on axle 52 and moves very
slowly forward on basement 49 in the direction of arrow 53. Above
the top of the product 50 the drying compartment 40 is closed by
a false roof 54.
The whole drying apparatus is closed from above by a shell-roof
65 which the false roof 54 is connected to by suspending columns
65A. The shell-roof 65 is closed on two sides by walls 37 and 38
respectively, the walls have gates 39 in them for the product 50.
The air stream circulates in the direction of arrows 64 as an effect
of ventilators 66 and 66' driven by electric motors 46 and 46' respectively,
built into a separation wall 69. Leaving the ventilators 66 and
66' the air stream proceeds between the shell-roof 65 and the false
roof 54 then through an opening 47 of the false roof 54 it goes
over into the drying compartment 40 between the basement 49 and
the false roof 54 from there it gets to liquid films 41 of the
contacting device 43 then through another opening 47A between the
shell-roof 65 and the false roof 54 back to the ventilators 66 and
66'. As in the embodiment shown there are two ventilators 66 and
66', two parallel partial air streams are going to come about.
The contacting device 43 in this embodiments as shown in FIGS.
5 and 6 consists of three liquid film modules 48A, 48B and 48C placed
immediately side by side. Each module has an individual liquid circulation
and all modules have a common lower liquid outlet channel 62 through
which they are connected to a regenerator not shown here with pipe-joints
67 and 68. The active hot desiccant liquid coming from the regenerator
enters through the pipe-joint 67 then gets more and more diluted
by circulation in liquid film modules 48A, 48B and 48C as it passes
the channel 62 in the direction of arrow 63 then through the pipe-joint
68 it gets into the regenerator.
The regenerator can be like the ones shown in FIG. 1 or FIG. 4
but multi-effect evaporators shown in FIGS. 8 and 9 are also suitable,
and so is multi-stage flash evaporator of FIG. 10.
The liquid film modules 48A, 48B and 48C are similarly constructed,
for this reason we describe the liquid film module 48A, only. An
upper receptacle 55A is placed under false roof 54 and is bordered
by a pile lock 56A. To the pile lock 56A a downwards directed liquid
distributing surface 57A is connected. From the liquid distributing
surface 57A there are liquid film conducting elements 58A, e.g.
fibres as shown in the drawing, going down. Along the periphery
of each of the elements 58A a liquid film comes about, all the elements
58A belonging to the liquid film module 48A together make up a liquid
film group whose characteristic feature is that all the elements
in the group conduct a desiccant liquid of the same concentration.
The elements 58A reach down to the lower collecting channel 62 placed
beneath. A suction pipe 59A starts from the bottom of the channel
62 thus conducts the desiccant liquid to a liquid circulating pump
60A. The pump 60A circulates the liquid through a tube 61A into
the upper receptacle 55A, from there through the pile lock 56A it
gets to the liquid distributing surface 57A, and then, along the
elements 58A into the lower collecting channel 62.
The upper receptacle 55A is separated from the upper receptacle
of the neighbouring liquid film module 48B, but the common lower
channel 62 makes it possible that the liquid circulating circles
belonging to tubes 61A, 61B and 61C give liquid to one another through
it. Sections of lower channel 62 which belong to liquid film modules
48A, 48B and 48C, respectively are separated from one another by
separating elements 162 provided with openings, so that the liquid
stream is always flowing in the direction of arrow 63 without a
mixing effect backward. Starting in the direction of arrow 63 the
first liquid circulating circle belonging to the first liquid film
module 48C gets the hot and active liquid from the regenerator.
This is diluted by the air stream coming from the drying compartment
40 so the liquid delivered to the second liquid circulating circle
belonging to the liquid film module 48B in the form of overflow
of the first liquid circulating circle is somewhat diluted. It is
the overflow of the last--in the drawing the third--liquid circulating
circle which gets back as diluted and cold desiccant liquid to the
regenerator, said liquid containing all the moisture which had been
extracted from the product 50 by the air stream.
The two ventilators 66 and 66' bring about two parallel partial
air streams. The velocity of each of the partial air streams should
be of a value, that the liquid films along the conducting elements
58A, 58B and 58C are not disturbed by the air stream, i.e. the air
stream does not carry off liquid particles from the film. A velocity
of 1 to 5 m/sec is suitable. The embodiment shown in FIGS. 5 and
6--similarly to that shown in FIGS. 2 to 4--carries out a counter-current
drying, as the product 50 moving slowly in the direction of arrow
53 while going through the drying compartment 40 meets air streams
which had been contacted with more and more active desiccant liquid.
A prerequisite of said counter-current drying here, too is to have
at least two partial air streams. It is expedient to have one partial
air stream belonging to each liquid film module 48A, 48B and 48C
that is, the number of ventilators is equal to that of the liquid
film modules.
The concentration of the desiccant liquids circulated in the liquid
film modules 48A, 48B and 48C can be increased in a sequence different
from that of the modules in space. The sequence can be arranged
as seems best with appropriate joining of individual sections of
the channel 62 belonging to individual modules. For instance, from
the section of the channel 62 belonging to liquid film module 48C
the desiccant liquid can get into the section belonging to liquid
film module 48A instead of the one belonging to liquid film module
48B through the separating element 162 and from there into the
section belonging to liquid film module 48B. In such a way the apparatus
according to the invention can be programmed with regard to the
drying prescriptions of the product 50 going through the drying
compartment 40.
In the embodiment shown the contacting device 43 borders the drying
compartment 40 on the left hand side quasi forming a "liquid
curtain". As the liquid film 41 brought about according to
the invention is essentially dropless, the contacting device 43
can also be placed on the right hand side of the drying compartment
40 moreover it can be placed in such a way that it divides the
drying compartment 40 into two parts, e.g. between the two stacks
of wood shown in FIG. 5. According to the invention, the only thing
important is that the closed air stream goes through the contacting
device 43 during recirculation, and the contacting device 43 and
the drying compartment 40 are arranged and placed in such a way
that the air stream suffers the least possible alteration of velocity
and direction when going from one to the other. It is obvious that
these conditions are fulfilled in all the embodiments mentioned.
The type of the contacting device 43 shown in FIG. 5 is the same
as that of the one shown in FIG. 1 but it can also be made in a
different way. Several contacting devices applicable in the apparatus
according to the invention are described in U.S. Pat. Nos. 3857911
and 4009229 in Hungarian Pat. No. 168451 and in British Pat.
No. 1363523. In the apparatus according to the invention it is
highly advantageous to apply aqueous solution of calcium chloride
in the concentration of 40 to 50% as a desiccant liquid. The pollution
getting into the desiccant solution can be eliminated with a tank
in the same way as the one described in connection to the embodiments
shown in FIGS. 2 to 4.
In FIGS. 5 and 6 we do not show a regenerator as it can be the
same as that in any of FIGS. 1 4 8 9 and 10. With the appropriate
selection of regeneration it is also possible to ensure for the
active solution arriving through pipe-joint 67 to be as hot as is
needed so that it can heat the air stream and through it the product
50. With the help of liquid film modules 48A, 48B and 48C it is
possible to set a temperature program for the product 50 going through
the drying compartment 40.
FIGS. 7 8 9 and 10 show various solutions for the regenerator.
Having considered that the regenerator comes about from different
connecting of devices per se known, the various regenerators to
be applied in the invention are shown in FIGS. 7 8 9 and 10 only
with circuit diagrams. For the sake of lucidity we marked each operation
with a separate schematic sign in the circuit diagrams but the invention
can be realized also in such a way that, for instance, more than
one device is placed into one casing.
FIG. 7 represents the circuit diagram of the regenerator shown
in FIGS. 2 to 4 and described in relation to these figures in detail.
FIG. 8 represents a regenerator which uses the steam evaporated
from the desiccant liquid for making to boil the liquid to be regenerated,
and the steam coming of the departing active liquid heats the incoming
diluted liquid. This regenerator is a multi-effect evaporator.
The diluted liquid is pumped by a pump 70 into a condenser 71
there it serves as cooling medium for the condenser 71 then while
cooling the liquid evaporating in heat exchangers 72 and 73 it gets
warmed further, finally it gets into an evaporator 75 through a
pipeline 74. This evaporator 75 is heated from the outside with
heat taken in. For instance, according to the embodiment shown,
steam is taken in through a pipe-joint 76 this gets condensed,
and the condensate departs through a pipeline 77. Of course, flue
gas, radiant heat, solar energy or something else can also be used
for heating. From here through a heat exchanger 73 and a throttle
78 the liquid gets into an evaporator 79 where it is further boiled
by the steam produced in the evaporator 75. From here a pump 83
pumps the liquid through the heat exchanger 72 to a pipe-joint 80
which is connected to a pipe-joint conducting the active liquid
in the dryer body itself, e.g. to the pipe-joint 67 in FIG. 6. The
steam produced in the evaporator 79 through a pipeline 84 and the
condensate of the steam heating the evaporator 79 through a throttle
81 get in the condenser 71 and both heat there the diluted, incoming
desiccant liquid. The condensed distillate and the non-condensable
gases are removed by a pump 82.
FIG. 9 shows the circuit diagram of an embodiment of the regenerator
which is also a multi-effect evaporator and uses the steam evaporated
from the diluted liquid for heating the incoming diluted liquid
to be regenerated.
The diluted liquid is pumped to a condenser 91 by a pump 90 as
cooling medium, there it warms up, then cooling the departing already
condensed liquid in the heat exchanger 92 it goes on warming and
gets into an evaporator 93. From here a pump 94 takes it through
a heat exchanger 95 where cooling the active liquid it gets warmed,
further to an evaporator 96. Here it is evaporated with heat taken
in from outside, for example with steam taken in through a pipe-joint
97. The condensate of the steam departs through a pipe-joint 98.
The steam which had come about in the evaporator 96 boils the diluted
liquid in the evaporator 93. The condensed, active liquid through
a pipeline 99 gets into the heat exchanger 95 then into the heat
exchanger 92 and departs through a pipe-joint 100 towards the dryer
body e.g. to the pipe-joint 67 in FIG. 6. The steam produced in
the evaporator 93 gets into the condenser 91 through a pipeline
101 condensate of the steam heating the evaporator 93 gets into
the same place through a throttle 102 there it heats the diluted
liquid, then the distillate produced by condensing and the gases
not condensable are carried away by a pump 103.
FIG. 10 shows the circuit diagram of a further embodiment of the
regenerator in which the heat released during condensing the steam
evaporated from the liquid by flash only warms the liquid to be
regenerated but does not evaporate it. This regenerator is a multi-stage
flash evaporator.
The diluted liquid is driven through condensers 112 113 and 114
by a pump 111. On leaving the condenser 114 the liquid goes through
a throttle 115. The pump 111 and the throttle 115 are arranged in
such a way that the pressure of the liquid when going through condensers
112 113 and 114 is bigger than the saturation pressure all the
way through, so vaporization does not occur anywhere. The temperature
of the diluted liquid serving as cooling liquid in condensers 112
113 and 114 is increasing. After the throttle 115 in an evaporator
116 steam is released from the liquid without heat transfer. This
steam gets condensed in the condenser 113. The liquid goes on to
an evaporator 117 where more steam is released from it which gets
condensed in the condenser 112. The condensed active liquid that
is left is carried back to the drying body by a pump 118 e.g. in
FIG. 6 to the pipe-joint 67. The distillate condensed in the condenser
113 through a pipeline 119 gets to the condenser 112 where it flashes.
The distillate and the non-condensable gases are pumped away by
a pump 120.
In the condenser 114 the diluted liquid to be regenerated should
be heated by heat taken in from outside, for example with steam
taken in through a pipe-joint 121 the condensate of the steam departs
through a pipe-joint 122.
With respect to the control of equipments of the regenerator it
is expedient to alter the embodiments described above in such a
way that only a part of the diluted desiccant liquid gets concentrated
and the other part is mixed with the concentrated part. It is this
mixture which has to be used as active desiccant liquid in the drying
body.
For the sake of simpler description in the embodiment above we
showed two evaporators i.e. two stages only, but of course it is
possible and advisable in the interest of increasing the energetic
efficiency to apply more stages.
In FIG. 10 it is shown that when the surplus heat produced by the
regenerator cannot be utilized in the drying body or when the heat
loss of the drying body is little (e.g. in summer) the desiccant
liquid regenerating system should be balanced. In FIG. 10 there
are two expedient solutions applicable separately but also together.
As to the first solution the condenser 112 must be provided with
cooling medium from the outside e.g. cooling water and coolable
subsidiary surface e.g. coil pipe. This latter can be placed in
a separate casing, in such a case the steam spaces must be connected
with pipelines. Cooling water can for example enter the heat exchanger
through a pipe-joint 123 and leave it through a pipe-joint 124.
According to the second solution the diluted liquid entering the
condenser 112 is pre-cooled in a heat exchanger 127 which is cooled
by a medium e.g. water entering through a pipe-joint 125 and leaving
through a pipe-joint 126.
In the embodiments according to FIGS. 7 8 and 9 these two solutions
are also applicable. In this respect an equivalent of the condenser
112 cooled additionally in FIG. 10 is the condenser 29 in FIG. 7
the condenser 71 in FIG. 8 and the condenser 91 in FIG. 9. The heat
exchanger 127 shown in FIG. 10 must be inserted between the condensers
29 71 and 91 and the pumps 28 70 and 90 of FIGS. 7 8 and 9 respectively
situated before said condensers.
As various changes might be made in the embodiments herein disclosed
without departing from the spirt of the invention, it is understood
that all matter herein shown or described should be deemed illustrative
and not by way of limitation. |