Note: Descriptions are shown in the official language in which they were submitted.
CONTINUOUS-FLOW DRYER FOR DRYING A MATERIAL BY MEANS OF HOT
AIR, COMPRISING AT LEAST TWO SECTIONS
Background of the Invention
The invention relates to a continuous-flow dryer for drying
a material by means of hot air, comprising a first and a
second section, which in a transport direction are
successively passed through by the material, in which dryer
a fresh air supply device for supplying fresh air as first
supply air into the first section is provided, an exhaust
air recirculation device for removing exhaust air from the
second section and for recirculating exhaust air as second
supply air back into the second section is provided, and a
first heat exchanger is provided, through which fresh air
on the one hand and exhaust air on the other hand are led,
for transferring waste heat of the exhaust air into the
fresh air.
A continuous-flow dryer is a dryer, in which material to be
dried is transported continuously or in batches through the
dryer. Such a dryer is in particular a belt dryer which
conveys the material to be dried through the continuous-
flow dyer by means of a belt. The material to be dried, for
example sewage sludge, wood chips, hogged wood, RDF
(refuse-derived fuel), SSW (solid shredded waste), MSW
(municipal solid waste), household waste, grass or
agricultural products and by-products such as sugar beet
pulp, is here at first damp or wet. The material is dried,
moisture being removed from it by means of hot air. The hot
air is separately produced by heating in particular air
1
CA 2986740 2017-11-27
from the surroundings of the continuous-flow dryer. On
heating the air, the relative air moisture of this air
decreases, the air becomes "drier". This hot air with low
relative air moisture then flows through or around the
constituents to be dried in the continuous-flow dryer. The
material to be dried is at the same time conveyed in a
transport direction through the continuous-flow dryer and
in so doing runs through at least two sections. The
individual sections divide the continuous-flow dryer
spatially. The sections are for this purpose largely
separated from one another in terms of air flow. Different
air flows are thus possible in the sections, which can each
have different relative air moistures and different
temperatures. For heating the air to hot air, energy is of
course needed. This energy is lost when the hot air
generated is discharged into the surroundings after the
drying of the material. First steps for circulating the hot
are therefore known.
Object of the Invention
The object on which the invention is based is to provide a
continuous-flow dryer for drying a material by means of hot
air which makes possible a further energy saving compared
with known continuous-flow dryers.
Solution According to the Invention
This object is achieved according to the invention with a
continuous-flow dryer for drying a material by means of hot
air, comprising a first and a second section, which in a
transport direction are successively passed through by the
2
CA 2986740 2017-11-27
material. According to the invention, in this case a fresh
air supply device for supplying fresh air as first supply
air into the first section is provided, an exhaust air
recirculation device for removing exhaust air from the
second section and for recirculating exhaust air as second
supply air back into the second section is provided, and a
first heat exchanger is provided, through which the fresh
air on the one hand and the exhaust air on the other hand
are led, for transferring waste heat of the exhaust air
into the fresh air. According to the invention, furthermore
a line arrangement is provided, by means of which the
exhaust air is led from the second section through the
first heat exchanger and then into the first section.
In the continuous-flow dryer according to the invention, a
fresh air supply device is provided, which supplies
generally dry fresh air, removed from the surroundings, to
the continuous-flow dryer as first supply air. At the
continuous-flow dryer furthermore an exhaust air
recirculation device removes exhaust air from a drying
process from the second section. This exhaust air is at
least partly recirculated into the second section of the
continuous-flow dryer.
Furthermore, according to the invention, part of the
exhaust air is led to at least a first heat exchanger, at
which thermal energy or waste heat from the exhaust air is
transferred to the first supply air likewise flowing
through the heat exchanger. The two flows of exhaust air
and first supply air are in this case separated from one
another at the first heat exchanger, in particular by means
of a separating surface. At the separating surface, on one
3
CA 2986740 2017-11-27
side the exhaust air and on the other side the first supply
air then flow along. Heat energy of the exhaust air is
discharged to the fresh air through the separating surface.
The waste heat of the exhaust air thus heats the fresh air
supplied to the continuous-flow dryer and heat energy from
the exhaust air is recovered. At the same time, the air
flows of exhaust air and first supply air are separated
from one another in terms of moisture. The moisture
contained in the exhaust air cannot therefore pass over
into the first supply air.
By means of a line arrangement, according to the invention
the exhaust air led through the first heat exchanger which
comes from the second section is led into the first
section. This first section serves for the first drying of
the material to be dried. The material to be dried
therefore has itself in this first section a comparatively
high moisture content. Accordingly, by means of the
recirculated exhaust air from the second section,
nevertheless moisture can be withdrawn in an energy-
efficient manner from the material in the first section.
Advantageously, the first heat exchanger according to the
invention is dimensioned such that moisture condenses out
on it from the exhaust air. Moisture condenses out when the
relative air moisture of the respectively relevant air has
reached 100% (in words: one hundred percent. The relative
air moisture in air increases when the air, as in this case
the hot exhaust air, cools. On the other hand, the relative
air moisture decreases when the air is heated. These
physical effects of the increase and decrease of the air
moisture are shown in the Mollier h,x-diagram. The
4
CA 2986740 2017-11-27
condensing-out sought according to the invention is
preferably achieved by the moisture condensing out on the
separating surface of the heat exchanger. For this the
exhaust air releases so much thermal energy to the
separating surface that the relative air moisture in the
exhaust air reaches 100% (in words: one hundred percent).
The first heat exchanger according to the invention thus
advantageously has three functions. The first function is
the dehumidifying of the exhaust air which flows through
the first heat exchanger. The second function is the
heating of the supplied fresh air. The third function is
the reducing of relative air moisture of the supplied fresh
air, caused by the heating of this fresh air.
According to the invention, preferably at least one second
heat exchanger is further provided, through which likewise
on the one hand fresh air and on the other hand exhaust air
are led, for transferring waste heat of the exhaust air
into the fresh air, the fresh air heated in so doing being
led into the second section. By means of the second heat
exchanger, further residual heat can be withdrawn from the
exhaust air led through it. At the same time, this residual
heat can advantageously be used to heat up fresh air which
has a comparatively low moisture content and is then led
into the second section. In the second section the finished
drying-out of the material to be dried takes place.
Accordingly, in this second section it is particularly
advantageous if air with only low moisture content is led
into this section for drying. With the second heat
exchanger according to the invention, it is achieved that
not, for instance, the exhaust air cooled down at the first
heat exchanger but at the same time still completely
5
CA 2986740 2017-11-27
saturated, is led back into the second section, but instead
heated-up fresh air which has a comparatively lower
moisture content.
The second heat exchanger is advantageously likewise
dimensioned such that water from the exhaust air condenses
out on it. The second heat exchanger thus likewise utilises
the heat and moisture absorption from the exhaust air
resulting from condensing out.
With regard to the flow direction of the exhaust air, the
second heat exchanger is preferably arranged before the
first heat exchanger. Owing to such a sequence of a
plurality of separate heat exchangers separated in
particular also spatially and/or in terms of control, a
thermodynamically advantageous overall arrangement is
created, in which the existing temperature and moisture
differences can be utilised particularly advantageously.
Preferably, control means are further provided, in
particular in the form of supply lines equipped with air
flaps, by means of which a transmission of fresh air
through the first heat exchanger and/or the second heat
exchanger are to be separately controlled. The two heat
exchangers according to the invention can thus be
separately adapted to existing conditions during the
operation of the continuous-flow dryer according to the
invention.
According to the invention, preferably a first heater is
further provided, by means of which the first supply air
before being supplied into the first section, and the
6
CA 2986740 2017-11-27
exhaust air from the second section led through the heat
exchanger before being supplied into the first section, are
to be heated up. A heater heats air by means of energy
supply. The heater is, for example, a hot-water heat
exchanger, a steam heat exchanger, an electric heating
device or a heating burner. On heating the air with the
heater the relative air moisture of this supply air
decreases as already mentioned above. A low air moisture on
drying is advantageous, since such supply air can then
absorb more water again. Warmer supply air can therefore
absorb more water than colder supply air. According to the
invention, the first supply air is supplied to the first
section. In this first section the moisture of the material
to be dried is still at its greatest in relation to its
conveying direction. Therefore, it is particularly
advantageous if at this first section the exhaust air from
the second section, which exhaust air is removed from the
second section and dehumidified at the heat exchanger or
heat exchangers according to the invention, is heated up
before being led into the first section. Owing to the fact
that this heating-up of exhaust air together with the
supplied fresh air takes place by means of a common heater,
additional components can be saved.
Advantageously, a second heater is further provided, by
means of which the second supply air before being
recirculated into the second section and fresh air led
through the second heat exchanger before being supplied
into the second section are to be heated up. As already
described the relative air moisture of air decreases when
it is heated. A second heater, which heats up the
recirculated supply air and the fresh air newly supplied
7
CA 2986740 2017-11-27
into the second section as second supply air, thus reduces
the relative air moisture in this second supply air. A low
relative air moisture in the second supply air is
particularly advantageous when comparatively low residual
moisture has to be removed from the material to be dried in
the second section.
Preferably, the exhaust air recirculation device is further
provided with a recirculation line which serves for the
direct recirculation of exhaust air from the second section
as recirculation air back into the second section. The
exhaust air recirculation device recirculates, by means of
the recirculation line, exhaust air from the second section
directly into the second section. The directly recirculated
exhaust air from the second section is mixed with the
supplied fresh air which has accordingly the consequence
that a mixture of treated supply air and untreated exhaust
air flows into the second section. This mixture has a
mixing temperature and a mixing air moisture. Thus, the
supply air is colder and drier and the exhaust air warmer
and more most. Advantageously, the supply air can be very
cold and very dry because it is heated directly by the
albeit moist but warm portion of the recirculated exhaust
air. Furthermore, a particularly simple control of the
moisture and the temperature of the air in the second
section is also possible with this direct recirculation.
According to the invention, preferably at least two regions
or subsections largely separate in terms of air flow are
provided in the second section and the exhaust air of the
two regions is led collectively through the heat exchanger.
The second section is in this way for its part further
8
CA 2986740 2017-11-27
divided, precisely into at least a first and a second
region. These regions are connected sequentially in the
transport direction in series. The respective region
generally has its own temperature and its own relative air
moisture of the air flow within this region.
Advantageously, this temperature and relative air moisture
is adjusted to the prevailing moisture conditions of the
material to be dried there in each case. Exhaust air to be
removed from the respective regions is brought together and
jointly led to the heat exchanger. Advantageously, an
exhaust air mixture is formed with the collection of the
exhaust air. The exhaust air mixture has a largely uniform,
common relative air moisture and a mixing temperature. It
is particularly advantageous here that a separate heat
exchanger does not have to be provided for each individual
region, but that in particular a single heat exchanger is
sufficient for the entire exhaust air to be removed from
the plurality of regions.
Advantageously, in at least one of the sections and/or
regions, there is further provided an exhaust air sensor by
means of which in the exhaust air its moisture is to be
determined. Such an air sensor determines in particular the
relative air moisture and/or the temperature of the air
flowing against or around it. Advantageously, the relative
air moisture of the exhaust air is thus to be determined by
means of the exhaust air sensor. When the relative air
moisture of the exhaust air is known, it is possible by
means of a control to define whether this exhaust air is to
be dehumidified or whether this air is to be supplied
directly to the respective section or the respective region
again.
9
CA 2986740 2017-11-27
Alternatively or additionally, a supply air sensor is
further provided, by means of which in the supply air its
moisture is to be determined. The supply air sensor
determines the relative air moisture of the flowing-against
supply air. It is thus advantageous to determine the
relative air moisture with which the supply air flows into
the respective section. It is thus particularly
advantageous also to determine whether and by how many
degrees Celsius the supply air is to be additionally heated
by a heater to achieve a desired relative air moisture in
the supply air.
In a preferred manner, for transporting the material
through the continuous-flow dryer two belts are further
provided, which are assigned in particular to the first
section and the second section. Such a two-part belt in a
continuous-flow dryer makes it possible for each of the two
sections to have their own belt. Thus, the two sections can
also be arranged spatially separated from each other, in
particular above each other.
According to the invention the transport direction is
preferably directed from the second section to the first
section. Such a transport direction is thus not aligned
from the first section to the second section, but vice
versa. Such a transport direction in "the opposite
direction" makes it possible for the material to be dried
last with supplied fresh air. This is particularly
advantageous when the material is to be dried last with
particularly clean air. As a further advantage, in this
transport direction the second heater for heating the
CA 2986740 2017-11-27
second supply air can be of small design. Particularly
advantageously this heater can be omitted.
Further, preferably also a regulating device is provided,
by means of which the moisture in the exhaust air is to be
measured and an air guide in the exhaust air recirculation
device, in the first heat exchanger and/or in the second
heat exchanger is to be regulated. A regulating device or
control evaluates inputs of the regulating device and
regulates or controls by means of logic of the regulating
device its outputs. Electrical signals of sensors of
different type, such as for example a temperature sensor or
a moisture sensor, serve as inputs here. Mostly switches or
electrical signals, for example for controlling the heater,
serve as outputs. By means of the regulating device,
advantageously the air guide, in particular by means of
ventilation, in the exhaust air recirculation device is to
be adapted to the respectively prevailing relative air
moisture of the exhaust air.
According to the invention, further a method for operating
a continuous-flow dryer for drying a material by means of
hot air is provided, wherein a first and a second section
are successively passed through by the material in a
transport direction, fresh air is supplied as first supply
air into the first section, exhaust air is removed from the
second section and is recirculated as second supply air
back into the second section, and also fresh air on the one
hand and exhaust air on the other hand are led through a
first heat exchanger, for transferring waste heat of the
exhaust air into the fresh air. According to the invention,
11
CA 2986740 2017-11-27
the exhaust air is led from the second section through the
first heat exchanger and then into the first section.
Brief Description of the Drawings
An exemplary embodiment of the solution according to the
invention is explained in more detail below with the aid of
the appended schematic drawings, in which:
Fig. 1 shows a highly simplified longitudinal section of a
continuous-flow dryer according to the prior art
and
Fig. 2 shows a highly simplified longitudinal section of a
continuous-flow dryer according to the invention.
Detailed Description of the Exemplary Embodiment
In Figs. 1 and 2 there is each shown a continuous-flow
dryer 10 in the form of a belt dryer. The continuous-flow
dryer 10 has a housing 12, through which the initially
moist or wet material 14 is to be transported by means of a
belt 16 in a transport direction 18 through the continuous-
flow dryer 10.
During transport, the material 14 passes firstly through a
first section 20 and after that a second section 22. The
two sections 20 and 22 divide the housing 12 spatially. In
the transport direction they are largely separated from one
another in terms of air flow, if necessary, by means of
dividing walls. Within the housing 12 there is hot air 24
which withdraws moisture (not shown) from the material 14
12
CA 2986740 2017-11-27
to be dried. With the withdrawing of moisture from the
material 14, the material 14 becomes drier, it is dried.
Fig. 2 illustrates how the hot air 24 is produced in the
exemplary embodiment there. For this, fresh air 26 flows
from outside the housing 12, conveyed by a fresh air supply
device 28, into the housing 12. The fresh air 26 flows
through a first heater 30 which heats the fresh air 26 on
its way through the heater 30. With the heating of the
fresh air 26, the relative air moisture of the fresh air 26
decreases, the fresh air 26 becomes "drier". The heater 30
may optionally advantageously also be completely omitted.
Surprisingly, the efficiency of the entire plant can
thereby be increased. Alternatively, the heater 30 is
intentionally operated only in a throttled manner, whereby
the specific energy consumption of the entire plant
(consumed amount of energy per amount of evaporated water)
can be optimised.
This fresh air 26, after the heating, is referred to as the
first supply air 32. The first supply air 32 flows into the
first section 20 and there flows around the individual
particles of the material 14 or flows through the layer of
the material 14 on the belt 16. On this flowing around the
particles of the material 14, the first supply air 32 takes
up moisture from the material 14. The relative air moisture
of the first supply air 32 increases, the first supply air
32 becomes "more moist". The moistened supply air 32 is
subsequently discharged from the housing 12 into
surroundings thereof from the first section 20 as first
exhaust air 34 by means of an exhaust air outlet 35 with a
fan. This exhaust air thus constitutes outgoing air.
13
CA 2986740 2017-11-27
After the first section 20 the material 14 passes through
the second section 22. This second section 22 is in turn
divided into two regions 36, 38. The two regions 36, 38 are
connected in series and, in terms of air flow, are largely
separated from each other. As an alternative to the
illustrated exemplary embodiments, the second section 22
and/or the first section 20 may also be divided altogether
into a plurality of regions, in particular into two, three,
four or more regions.
At both regions 36, 38, respectively at the bottom, second
exhaust air 40 is discharged and, respectively at the top,
second supply air 42 is supplied. The second exhaust air 40
is recirculated by means of respectively one exhaust air
recirculation device 44, partly directly as second supply
air 42, into the respective region. The exhaust air
recirculation device 44 has, for this purpose, a respective
recirculation line 46, in which a fan 49 for sucking-off
the second exhaust air 40 is provided. Before supplying the
second supply air 42 into the respective region 36, 38, a
respective second heater 46 is provided. The second heater
46 in this case heats the second supply air 42, whereby the
relative air moisture of the second supply air 42
decreases.
The recirculation lines 46 have a respective branch 50, to
which a line 52 is connected. At the branch 50, part of the
exhaust air 40 is branched off from the recirculation line
46 and led into a collecting line 54 by means of the line
52. For this purpose, a sucking fan 55 to be separately
14
CA 2986740 2017-11-27
regulated can be optionally arranged in the collecting line
54.
The collecting line 54 leads the branched-off exhaust air
to a heat exchanger 57, through it and further into a
continuation 56.
The heat exchanger 57 has a separating surface 58 at which,
on one side, the exhaust air 40 thus branched off and, on
the other side, fresh air 26 is led along. At the
separating surface 58, heat therefore changes from the
exhaust air 40 as waste heat 59 to the fresh air. At the
same time, water 60 condenses out of the exhaust air 40 at
the separating surface 58 with the cooling of the exhaust
air 40 in this way.
The fresh air 26 is led by means of a supply air feed 61
and an air flap, provided there and to be separately
controlled, through the heat exchanger 57 and then to a
discharge line 62. By means of the discharge line 62 the
fresh air 26 heated at the heat exchanger 57 is led to the
second section 22. For this purpose, a sucking fan 63 can
be optionally provided in the discharge line 62. A
respective continuation 64 leads from the discharge line 62
to a junction 65 with the recirculation line 46, in order
thus to lead the heated fresh air 26 into the second
section 22. The fresh air 26 thus led in then likewise
passes through the heater 48 respectively assigned to the
recirculation line 46.
The exhaust air 40 led through the heat exchanger 57
passes, by means of the continuation 56 of the collecting
CA 2986740 2017-11-27
line 54, on to a heat exchanger 66 and through the latter.
The heat exchanger 66 likewise has a separating surface 67
for cooling the exhaust air 40 and for heating fresh air 26
guided along it. With the heating, further waste heat 68 of
the exhaust air 40 changes to fresh air 26, and at the same
time further water 69 condenses out from the exhaust air
40.
For leading the fresh air 26 through the heat exchanger 66,
a supply air feed 70 with air flap to be separately
controlled is provided. The heated supply air 26 is then
led by means of a discharge line 71 from the heat exchanger
66 to the heater 30, in order to be further heated at the
latter as explained above.
By means of a continuation 73 of the collecting line 54 the
exhaust air 40 thus further cooled at the heat exchanger 66
and coming from the second section 22 is likewise led to
the heater 30 and further into the first section 20.
Fig. 2 further illustrates that at the second section 22
optionally in the region of the exhaust air recirculation
device 44 supply air feeds 74 for supplying further fresh
air 26 from outside and also exhaust air discharges 75 for
discharging exhaust air 40 to the outside can be provided
with respective air flaps to be separately controlled.
Furthermore, a control 76 is schematically illustrated,
which serves for controlling the fans and air flaps
mentioned and which is in this case functionally coupled in
particular to associated sensors (not shown).
16
CA 2986740 2017-11-27
In conclusion, it should be noted that all the features
which have been mentioned in the application documents and
in particular in the dependent claims, despite their formal
dependence on one or more specific claims, should also be
accorded independent protection individually or in an any
arbitrary combination.
17
CA 2986740 2017-11-27
List of reference symbols
continuous-flow dryer
12 housing
5 14 material
16 belt
18 transport direction
section
22 section
10 24 hot air
26 fresh air
28 fresh air supply device
heater
32 supply air
15 34 exhaust air
exhaust air outlet
36 region
38 region
exhaust air
20 42 supply air
44 exhaust air recirculation device
46 recirculation line
48 heater
49 fan
25 50 branch
52 line
54 collecting line
55 fan
56 continuation of the collecting line
30 57 heat exchanger
58 separating surface
59 waste heat
18
CA 2986740 2017-11-27
60 water
61 supply air feed
62 discharge line
63 fan
64 continuation of the discharge line
65 junction
66 heat exchanger
67 separating surface
68 waste heat
69 water
70 supply air feed
71 discharge line
73 continuation of the collecting line
74 supply air feed
75 exhaust air discharge
76 control
19
CA 2986740 2017-11-27
