[0001] The invention relates to a method for the drying and combustion of water-containing
material containing combustible components, such as dehydrated waste water sludge,
according to the preamble of claim 1 wherein the following steps are carried out:
(1) introduction of water-containing material into a direct dryer,
(2) drying of the material introduced into the dryer by the introduction of atmospheric
air as drying air into the dryer,
(3) introduction of the dried material into a furnace and combustion of the material
therein,
(4) introduction into the furnace of at least a portion of the drying air after the
dryer as combustion air,
(5) preheating of the drying air intended for the drying of the material, by utilization
of the heat contained in the hot flue gas discharged from the furnace.
[0002] For instance in the biological purification of waste water, a residual product consisting
of water and organic matter is produced. The organic matter possesses a sufficiently
high heating value which makes it attractive to use it as a fuel with a view to exploiting
the energy bound therein. Prior to using the organic matter as fuel, however, it should
be dried to a degree of dryness that allows it to burn. This may be done by mechanical
dehydration of the sludge, for instance by means of centrifuges, strain belt presses
or chamber filter presses, in order to subsequently introduce this dehydrated sludge
into a dryer, e.g. a direct dryer, where the dehydrated sludge is dried by the introduction
of drying air into the dryer. The drying air is usually heated either in a heat exchanger
which utilizes hot flue gas as a heating medium, or by means of direct heating.
[0003] The introduction of the drying air into the furnace as combustion air following drying
means that smelling inconveniences are avoided since the foul-smelling substances
released from the sludge to the drying air are burnt off. If the drying air is not
burnt off in the furnace, it is to be purified in a separate purification plant. In
order to avoid these odour inconveniences associated with the flue gas, the furnace
temperature should be maintained at about 800-900°C.
[0004] It is difficult with mechanical dehydration of sludge from state-of-the-art purification
plants with nitrogen and phosphorus removal to obtain a high dry matter content.
[0005] With centrifuges and strain belt presses it is typically possible to obtain 17-18%
of dry matter by dehydration of biological/chemical sludge.
[0006] With chamber filter presses it is typically possible to obtain 22-25%, of dry matter
by sludge dehydration.
[0007] It is impossible to dehydrate the sludge at very high pressures to increase the dry
matter contents since the sludge forms a filter skin under high pressures which is
impervious to water.
[0008] Moreover, in case of high pressures there is a risk of blowing the cells in the sludge
thereby releasing substances whose recycling to the purification plant is undesirable.
GB 2190178 teaches a system for drying sludge. In this system the sludge is fed through
a preheater and led into a dryer where it is heated by means of superheated steam.
[0009] In the thus known methods for the treatment of sludge, it is difficult to obtain
a sufficiently high degree of sludge dryness to allow it to burn without auxiliary
fuelling, e.g. fossile fuels. The exercise of the known sludge treatment methods thus
involves considerable costs for auxiliary fuelling.
[0010] It is thus the object of the present invention to provide a method wherein it is
possible to incinerate sludge without auxiliary fuelling, said sludge being introduced
into the dryer with an increased water content compared to the known methods.
[0011] This is obtained with a method of the type described in the introductory part for
the treatment of water-containing material which contains combustible components,
such as dehydrated waste water sludge, and wherein the following steps are carried
out:
(6) addition of water to the atmospheric air in the preheater, whereby the water evaporates,
and is superheated,
and
(7) reduction of the water content in the drying air following the dryer in a condenser
prior to its introduction as combustion air into the furnace.
[0012] The addition of water to the drying air provides a more effective heat transfer in
the heat exchanger, and the enthalpy of the drying air is increased. The enthalpy
increase is obtained simultaneously with a reduced temperature increase in the drying
air. The increased enthalpy of the drying air enables a more effective drying of the
sludge introduced into the dryer, and the reduced temperature ensures that the drying
may be effected at a reduced risk of pyrolysis of the sludge in connection with the
drying. Following discharge of the drying air from the dryer and prior to utilization
of this air as combustion air, the water content of the drying air is reduced since
this water content would otherwise presuppose a large amount of energy to obtain the
required high furnace temperature. Thus, since the method according to the invention
eliminates the need for auxiliary fuelling to the same extent by the burning of the
sludge, an overall improved operational economy is obtained.
[0013] Advantageously at least a portion, preferably all of the drying air/combustion air
is preheated in a heat exchanger following discharge from the dryer and prior to its
introduction into the furnace. This enables the introduction of material having a
higher water content than usual, since the combustion air has a higher heat content
which serves to evaporate the water.
[0014] The means for preheating the drying air may be divided into several heat exchanges.
Examples of such means include a first heat exchanger, wherein the air is evaporated
to a certain extent, and wherein the water added is evaporated following which the
air is conveyed to a second heat exchanger, where the air is preheated to the temperature
required for the drying. Hereby the flue gas may be used as heating medium in both
heat exchangers since the discharge side for the heating medium in the one heat exchanger
is in communication with the supply side in the second heat exchanger. Moreover, it
is an option that only the one heat exchanger is in contact with the flue gas, since
the drying air still contains much heat following discharge from the dryer, and therefore
it may be used as heating medium in the first heat exchanger.
[0015] Moreover it is possible to preheat the dehydrated material prior to its introduction
into the dryer. Preheating of the material reduces the amount of thermal energy required
from the drying air to evaporate the requisite amount of water.
[0016] The supply of water to the atmospheric air is advantageously controlled in accordance
with a desired temperature of the drying air supplied to the dryer. This control is
utilized for regulating the drying process whereby the dried material becomes exactly
auto-combustible.
[0017] The addition of water to the drying air may be effected in the form of a separate
addition of water, in the form of a condensate from the flue gas in instances where
the latter is conveyed through a condensing heat exchanger, or in the form of a condensate
of the drying air discharged after the dryer. Moreover it is possible to utilize vapour-
or water-containing drying air after the dryer as water supply to the drying air.
Thus, the drying air is recycled.
[0018] Moreover the invention relates to a plant for carrying out the method described above
and comprising means for preheating the drying air, a direct dryer for drying material,
a combustion furnace for the combustion of dried material, a conduit for connecting
the preheating means to the dryer, and a conduit for conveying dried material from
the dryer to the furnace. The plant is characterised in comprising a device for the
introduction of water into the drying air, said device being so arranged that the
preheating of the drying air in the preheating means causes the formation of hot vapour-containing
air for introduction into the dryer, and in having a condenser in connection with
a conduit that connects the dryer to the furnace.
[0019] Advantageously such plant may comprise means for preheating the drying air after
the latter has left the dryer and prior to its introduction into the furnace.
[0020] Since a condenser is used for the condensing of the water content in the drying air/the
combustion air, such condenser may conveniently be coupled to a district heating plant
whereby the energy released in the condensing may be utilized for heating purposes.
[0021] The invention will now be described in further detail with reference to the drawings,
wherein
Figure 1 shows a first plant for exercising the method according to the invention,
Figure 2 shows a second plant for exercising the method according to the invention,
and
Figure 3 shows a third plant for exercising the method according to the invention.
[0022] Figure 1 is a schematical view of a plant wherein drying air/combustion air is introduced
into a heat exchanger 1 where the air is heated and the water evaporated prior to
the air being introduced into a direct dryer 2, and into which the dehydrated waste
water sludge is also introduced.
[0023] Following drying of the dehydrated waste water sludge, the air which now contains
water is conveyed to a condenser 3 where a part of the water contained in the air
is condensed by the introduction of water to cool the air. After the condenser, the
air is introduced into a heat exchanger 4 where it is heated prior to its introduction
into a furnace 5. Moreover, the dehydrated and dried waste water sludge from the dryer
2 is introduced into the furnace. The waste water sludge is incinerated off in the
furnace 5 and hereby residual products in the form of ashes are produced which are
discharged from the furnace, and flue gas which is also discharged from the furnace
and conveyed in part to the second heat exchanger 4 and then to the first heat exchanger
1. The flue gas is subsequently discharged. In the first heat exchanger means for
the supply of water to the drying air are provided. Condensing operation of the flue
gas side of the heat exchanger allows the use of a portion of the condensate as water
supply to the drying air side. It is possible to recycle a portion of the air after
the dryer 2 to the first heat exchanger since the air still contains a substantial
amount of water after the dryer.
[0024] Figure 2 illustrates a plant which differs from the plant shown in figure 1 in that
no heat exchanger is provided after the condenser, and wherein the heat exchanger
before the dryer is divided into two heat exchangers 1,4. This division into two heat
exchangers is particularly advantageous in case of condensing operation of the latter
heat exchanger since condensing operation makes substantial demands to the material.
The second heat exchanger 4 may thus be less resistant to corrosion that the first
1.
[0025] Figure 3 illustrates a plant where air is introduced into a first heat exchanger
1 with water supply for subsequent transfer to a second heat exchanger 4. From the
second heat exchanger the air is conveyed to the dryer 2, and from the dryer the air
which now contains water is recycled through the first heat exchanger 1 where a portion
thereof may optionally be condensed, and from here to a condenser where further vapour
in the air is condensed prior to introduction of the air into the furnace 5. The dehydrated
waste water sludge is first introduced through a third heat exchanger 6 prior to being
introduced into the dryer 2 and then into the furnace 5. The flue gas from the furnace
is first used as a heating medium in the second heat exchanger 4 and then as a heating
medium in the third heat exchanger 6. Like in connection with the plants shown in
Figures 1 and 2, the option is available of utilizing the condensate from the condensed
operation as water supply to the drying air in connection with the first heat exchanger
1.
[0026] In connection with the three plants shown in Figures 1 through 3, the option is also
available of introducing auxiliary fuel into the furnace. This is necessary in connection
with the starting up of such plant but not necessary provided the degree of dryness
of the waste water sludge introduced into the furnace is sufficient for it to be burnt
without auxiliary fuelling which will be the normal situation.
[0027] In the following, examples of treatment of the waste water sludge in the three plants
are shown schematically in Figures 1 through 3. Comparative data are shown for drying
and combustion without and drying and combustion with water supply to the drying air,
respectively.
CONDITIONS
[0028] Waste water sludge of the following composition of the combustible portion of the
waste water sludge (water- and ash-free sample) is treated:
C |
% |
56.6 |
H |
% |
7.4 |
N |
% |
4.6 |
S |
% |
1.4 |
O |
% |
30.0 |
[0029] The combustible portion of the dry matter is 65%. The remaining portion 35% is ashes.
This yields the following thermal values for the water- and ash-free sample:
Upper heating value |
24,400 kJ/kg |
Lower heating value |
22,800 kJ/kg |
[0030] The following operating conditions remain unchanged in all examples:
T flue gas, furnace |
850°C |
Lambda (excess air count) |
1.4 |
x represents the water contents of the respective gas (kg water/kg dry gas).
EXAMPLE 1 (a plant corresponding to Figure 1)
[0031] In order to burn without auxiliary fuelling the waste water sludge introduced into
the furnace must have a dry matter content of 26.1%.
|
|
Water added |
No water added |
Dehydrated waste |
|
|
|
water sludge: |
kg/h |
1327 |
1327 |
Combustible dry matter |
kg/h |
169 |
197 |
Ashes |
kg/h |
91 |
106 |
Water |
kg/h |
1067 |
1024 |
|
Furnace: |
|
|
|
Airin: |
|
|
|
Amount, dry |
kg/h |
1846 |
2148 |
x-air |
kg/kg |
0.028 |
0.028 |
Temperature |
°C |
600 |
600 |
|
Gasout: |
|
|
|
Amount, dry |
kg/h |
1904 |
2215 |
x-gas |
kg/kg |
0.473 |
0.473 |
|
Heat Exchanger 1: |
|
|
|
Airin: |
|
|
|
x-air |
kg/kg |
0.004 |
0.004 |
Temperature |
°C |
20 |
20 |
|
Airout: |
|
|
|
x-air |
kg/h |
0.412 |
0.004 |
Temperature |
°C |
450 |
450 |
Evaporated water |
kg/h |
754 |
0 |
|
Gasin: |
|
|
|
x-gas |
kg/kg |
0.473 |
0.473 |
Temperature |
°C |
575 |
575 |
|
Gasout: |
|
|
|
x-gas |
kg/kg |
0.155 |
0.473 |
Temperature |
°C |
60 |
366 |
Condensed water: |
kg/h |
606 |
0 |
|
Heat Exchanger 2: |
|
|
|
Airin: |
|
|
|
x-air |
kg/kg |
0.028 |
0.028 |
Temperature |
°C |
30 |
30 |
Airout: |
|
|
|
Temperature |
°C |
600 |
600 |
Gasin: |
|
|
|
Temperature |
°C |
850 |
850 |
Gasout: |
|
|
|
Temperature |
°C |
575 |
575 |
|
Dryer: |
|
|
|
Waste water |
|
|
|
sludgein: |
|
|
|
Dry matter |
kg/h |
260 |
303 |
DM |
% |
19.6 |
22.8 |
Temperature |
°C |
10 |
10 |
|
Waste water |
|
|
|
sludgeout: |
|
|
|
DM |
% |
26.1 |
26.1 |
Temperature |
°C |
95 |
95 |
|
|
Airin: |
|
|
|
x-air |
kg/kg |
0.412 |
0.004 |
Temperature |
°C |
450 |
450 |
|
Airout: |
|
|
|
x-air |
kg/kg |
0.591 |
0.085 |
Temperature |
°C |
95 |
95 |
|
Condenser: |
|
|
|
Necessary cooling: |
kw |
773 |
128 |
[0032] Comparison of the data relating to the example without addition of water to the drying
air with the example with addition of water will show that in order to obtain the
dry matter content of 26.1% necessary for combustion without addition of water, the
initial waste water sludge material must have a dry matter content of 22.8%. With
addition of water, a waste water sludge material with a dry matter content of 19.6%
may be introduced into the dryer to obtain the requisite 26.1% of dry matter. Thus,
in the given operational conditions for the method according to the invention, a dry
matter content is allowed which, relative to the total amount of waste water sludge,
is 3.2 percent points less that in the method known today. This corresponds to a reduction
of the requirement to the dry matter content in the waste water sludge of 14.0% compared
to the known method.
EXAMPLE 2 (a plant corresponding to Figure 2)
[0033] In order to burn without auxiliary fuelling the waste water sludge introduced into
the furnace must have a dry matter content of 37.4%.
|
|
Water added |
No water added |
Dehydrated waste |
|
|
|
water sludge: |
kg/h |
1327 |
1327 |
Combustible dry matter |
kg/h |
172 |
208 |
Ashes |
kg/h |
93 |
112 |
Water |
kg/h |
1062 |
1007 |
|
Furnace: |
|
|
|
Airin: Amount, dry |
kg/h |
1884 |
2270 |
x-air |
kg/kg |
0.028 |
0.028 |
Temperature |
°C |
30 |
30 |
|
Gasout: |
|
|
|
Amount, dry |
kg/h |
1943 |
2341 |
x-gas |
kg/kg |
0.315 |
0.315 |
|
Heat Exchanger 1 + 2: |
|
|
|
Airin: |
|
|
|
x-air |
kg/kg |
0.004 |
0.004 |
Temperature |
°C |
20 |
20 |
|
Airout: |
|
|
|
x-air |
kg/h |
0.278 |
0.004 |
Temperature |
°C |
700 |
700 |
Evaporated water |
kg/h |
515 |
0 |
|
Gasin: |
|
|
|
x-gas |
kg/kg |
0.315 |
0.315 |
Temperature |
°C |
850 |
850 |
|
Gasout: |
|
|
|
x-gas |
kg/kg |
0.155 |
0.315 |
Temperature |
°C |
60 |
463 |
Condensed water: |
kg/h |
311 |
0 |
|
Waste water sludge dryer: |
|
|
|
Waste water |
|
|
|
sludgein: |
|
|
|
Dry matter |
kg/h |
265 |
320 |
DM |
% |
20.0 |
24.1 |
Temperature |
°C |
10 |
10 |
|
Waste water |
|
|
|
sludgeout: |
|
|
|
DM |
% |
37.4 |
37.4 |
Temperature |
°C |
95 |
95 |
|
Airin: |
|
|
|
x-air |
kg/kg |
0.278 |
0.004 |
Temperature |
°C |
700 |
700 |
|
Airout: |
|
|
|
x-air |
kg/kg |
0.608 |
0.212 |
Temperature |
°C |
95 |
95 |
|
Condenser: |
|
|
|
|
Necessary cooling: |
kw |
811 |
340 |
[0034] Comparison of the data relating to the example without addition of water to the drying
air with the example with addition of water will show that in order to obtain the
dry matter content of 37.4% necessary for combustion without addition of water, the
initial waste water sludge material must have a dry matter content of 24.1%. With
addition of water, a waste water sludge material with a dry matter content of 20.0%
may be introduced into the dryer to obtain the requisite 37.4% of dry matter. Thus,
in the given operational conditions for the method according to the invention, a dry
matter content is allowed which, relative to the total amount of waste water sludge,
is 4.1 percent points less that in the method known today. This corresponds to a reduction
of the requirement to the dry matter content in the waste water sludge of 17.0% compared
to the known method.
EXAMPLE 3 (a plant corresponding to Figure 3)
[0035] In order to burn without auxiliary fuelling, the waste water sludge introduced into
the furnace must have a dry matter content of 37.4%.
|
|
Water added |
No water added |
Dehydrated waste |
|
|
|
water sludge: |
kg/h |
1327 |
1327 |
Combustible dry matter |
kg/h |
138 |
198 |
Ashes |
kg/h |
74 |
107 |
Water |
kg/h |
1115 |
1022 |
|
Furnace: |
|
|
|
|
Airin: Amount, dry |
kg/h |
1507 |
2167 |
x-air |
kg/kg |
0.028 |
0.028 |
Temperature |
°C |
30 |
30 |
|
Gasout: |
|
|
|
Amount, dry |
kg/h |
1554 |
2234 |
x-gas |
kg/kg |
0.315 |
0.315 |
|
Heat Exchanger 1: |
|
|
|
Fresh air |
|
|
|
Airin: |
|
|
|
x-air |
kg/kg |
0.004 |
0.004 |
Temperature |
°C |
20 |
20 |
|
Airout: |
|
|
|
x-air |
kg/h |
0.609 |
0.004 |
Temperature |
°C |
85 |
85 |
Evaporated water |
kg/h |
912 |
0 |
|
Drying air |
|
|
|
Airin: |
|
|
|
x-air |
kg/kg |
1.129 |
0.253 |
Temperature |
°C |
95 |
95 |
|
Airout: |
|
|
|
x-air |
kg/kg |
0.480 |
0.253 |
Temperature |
°C |
78 |
68 |
Condensed water: |
kg/h |
978 |
0 |
|
Heat Exchanger 2: |
|
|
|
Airin: |
|
|
|
x-air |
kg/kg |
0.609 |
0.004 |
Temperature |
°C |
85 |
85 |
Airout: |
|
|
|
Temperature |
°C |
650 |
650 |
Gasin: |
|
|
|
Temperature |
°C |
850 |
850 |
Gasout: |
|
|
|
Temperature |
°C |
127 |
530 |
|
Heat Exchanger 3: |
|
|
|
Waste water |
|
|
|
sludgein: |
|
|
|
Temperature |
°C |
10 |
10 |
|
Waste water |
|
|
|
sludgeout: |
|
|
|
Temperature |
°C |
85 |
85 |
|
Gasin: |
|
|
|
x-gas |
kg/kg |
0.315 |
0.315 |
Temperature |
°C |
127 |
530 |
|
Gasout: |
|
|
|
x-gas |
kg/kg |
0.250 |
0.315 |
Temperature |
°C |
68 |
362 |
|
Condensed water: |
kg/h |
101 |
0 |
|
Dryer: |
|
|
|
Waste water |
|
|
|
sludgein: |
|
|
|
Dry matter |
kg/h |
212 |
305 |
DM |
% |
16.0 |
23.0 |
Temperature |
°C |
85 |
85 |
|
Waste water |
|
|
|
sludgeout: |
|
|
|
DM |
% |
37.4 |
37.4 |
Temperature |
°C |
95 |
95 |
|
Airin: |
|
|
|
x-air |
kg/kg |
0.609 |
0.004 |
Temperature |
°C |
650 |
650 |
|
Airout: |
|
|
|
x-air |
kg/kg |
1.129 |
0.253 |
Temperature |
°C |
95 |
95 |
|
Condenser: |
|
|
|
|
Necessary cooling: |
kW |
1205 |
387 |
[0036] Comparison of the data relating to the example without addition of water to the drying
air with the example with addition of water will show that in order to obtain the
dry matter content of 37.4% necessary for combustion without addition of water, the
initial waste water sludge material must have a dry matter content of 23.0%. With
addition of water, a waste water sludge material with a dry matter content of 16.0%
may be introduced into the dryer to obtain the requisite 37.4% of dry matter. Thus,
in the given operational conditions for the method according to the invention, a dry
matter content is allowed which, relative to the total amount of waste water sludge,
is 7.0 percent points less that in the method known today. This corresponds to a reduction
of the requirement to the dry matter content in the waste water sludge of 30.4% compared
to the known method.
Reference numerals:
[0037]
- 1
- Heat exchanger 1
- 2
- Dryer
- 3
- Condenser
- 4
- Heat exchanger 2
- 5
- Furnace
- 6
- Heat exchanger 3
1. A method for the drying and combustion of water-containing material containing combustible
components, such as dehydrated waste water sludge, and wherein the following steps
are carried out:
(1) introduction of water-containing material into a direct dryer (2),
(2) drying of the material introduced into the dryer (2) by the introduction of atmospheric
air as drying air into the dryer (2),
(3) introduction of the dried material into a furnace (5) and combustion of the material
therein,
(4) introduction into the furnace (5) of at least a portion of the drying air after
the dryer (2) as combustion air,
(5) preheating of the drying air intended for the drying of the material, by utilization
of the heat contained in the hot flue gas discharged from the furnace (5),
characterized in the
(6) addition of water to the atmospheric air in the preheater (2), whereby the water
evaporates, and is superheated,
and
(7) reduction of the water content in the drying air following the dryer (2) in a
condenser (3) prior to the introduction as combustion air into the furnace (5).
2. A method according to claim 1, characterized in that at least a portion of the drying air is preheated in a heat exchanger (4)
after the dryer (2) and condenser (3) and prior to its introduction into the furnace
(5).
3. A method according to claim 1 or 2, characterized in that at least a portion of the drying air is further preheated in a heat exchanger
(4) where the heating medium is flue gas from the furnace, after the evaporation of
the water and prior to its introduction into the dryer (2).
4. A method according to claims 1-3, characterized in that, after removal from the dryer (2), at least a portion of the drying air is
utilized as heating medium in a heat exchanger (4) for preheating the drying air and
evaporating the water added.
5. A method according to claims 1-4, characterized in that at least a portion of the water-containing material is preheated in a heat
exchanger (4) prior to its introduction into the dryer.
6. A method according to claims 1-5, characterized in that the water added to the drying air is a condensate of the flue gas or a condensate
of the drying air discharged after the dryer (2).
7. A method according to claims 1-6, characterized in that the water added to the drying air is vapour or water-containing drying air
discharged after the dryer (2).
8. A method according to claims 1-7, characterized in that water is added to the drying air in an amount determined by the fact that
the temperature and volume flow of drying air through the dryer (2) relative to the
temperature, water content and volume flow of the water-containing material will produce
a dried material which is exactly auto-combustible.
9. A plant for exercising the method according to claims 1-8 and comprising means (1)
for preheating drying air, a dryer (2) for drying material to be burnt, a furnace
(5) for burning dried material, a conduit for connecting the preheating means to the
dryer and a conduit for conveying dried material from the dryer to the furnace, characterized in comprising a device for the introduction of water into the drying air, where said
device is so arranged that the preheating of the drying air in the preheating means
causes the formation of air containing superheated steam for introduction into the
dryer, and in that a condenser (3) is provided in connection with a conduit connecting
the dryer to the furnace.
10. A plant according to claim 9, wherein at least a portion of the drying air is used
as combustion air, characterized in comprising means (4) for preheating the drying air after it has left the dryer
(2) and the condenser (3) and prior to introduction of this air into the furnace.
1. Verfahren zum Trocknen und Verbrennen von wasserhaltigem Material mit brennbaren Komponenten,
wie entwässertem Klärschlamm, wobei die folgenden Schritte ausgeführt werden:
(1) Einleiten von wasserhaltigem Material in einen direkten Trockner (2),
(2) Trocknen des in den Trockner (2) eingeleiteten Materials durch das Einleiten von
Umgebungsluft als Trocknungsluft in den Trockner (2),
(3) Einleiten des getrockneten Materials in einen Verbrennungsofen (5) und Verbrennung
des Materials daselbst,
(4) Einleiten von mindestens einem Teil der Trocknungsluft aus dem Trockner (2) als
Verbrennungsluft in den Verbrennungsofen (5),
(5) Vorheizen der zum Trocknen des Materials vorgesehenen Trocknungsluft unter Verwendung
der im heissen, vom Verbrennungsofen (5) abgegebenen Abgas enthaltenen Wärme,
gekennzeichnet durch die
(6) Zugabe von Wasser zur Umgebungsluft im Vorheizer (2), wobei das Wasser verdampft
und überhitzt wird,
und
(7) die Reduktion des Wassergehalts in der Trocknungsluft in einem Kondensator (3)
nach dem Durchlauf durch den Trockner (2) und vor dem Einleiten als Verbrennungsluft
in den Verbrennungsofen (5).
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass mindestens ein Teil der Trocknungsluft
in einem Wärmeaustauscher (4) nach dem Trockner (2) und dem Kondensator (3) und vor
ihrem Einleiten in den Verbrennungsofen vorgeheizt wird
3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass mindestens ein Teil
der Trocknungsluft nach dem Verdampfen des Wassers und vor ihrem Einleiten in den
Trockner (2) weiter in einem Wärmeaustauscher (4) vorgeheizt wird, wobei das Heizmedium
ein Abgas aus dem Verbrennungsofen ist.
4. Verfahren nach den Ansprüchen 1-3, dadurch gekennzeichnet, dass mindestens ein Teil
der Trocknungsluft nach dem Entfernen aus dem Trockner (2) als Heizmedium in einem
Wärmeaustauscher (4) zum Vorheizen der Trocknungsluft und zum Verdampfen des hinzugefügten
Wassers verwendet wird.
5. Verfahren nach den Ansprüchen 1-4, dadurch gekennzeichnet, dass mindestens ein Teil
des wasserhaltigen Materials in einem Wärmeaustauscher (4) vorgeheizt wird, bevor
es in den Trockner eingeführt wird.
6. Verfahren nach den Ansprüchen 1-5, dadurch gekennzeichnet, dass das zur Trocknungsluft
hinzugefügte Wasser ein Kondensat aus dem Abgas oder ein Kondensat aus der vom Trockner
(2) abgegebenen Trocknungsluft ist.
7. Verfahren nach den Ansprüchen 1-6, dadurch gekennzeichnet, dass das zur Trocknungsluft
hinzugefügte Wasser Dampf oder wasserhaltige Trocknungsluft ist, der bzw. die vom
Trockner (2) abgegeben worden ist.
8. Verfahren nach den Ansprüchen 1-7, dadurch gekennzeichnet, dass Wasser in einer derart
festgelegten Menge zur Trocknungsluft hinzugefügt wird, dass die Temperatur und der
Volumendurchfluss der Trocknungsluft durch den Trockner (2) relativ zu Temperatur,
Wassergehalt und Volumenfluss des wasserhaltigen Materials getrocknetes Material erzeugen,
das gerade selbstbrennbar ist.
9. Anlage zur Ausübung des Verfahrens nach den Ansprüchen 1-8, die Mittel (1), um die
Trocknungsluft vorzuheizen, einen Trockner (2) zum Trocknen der zu verbrennenden Materials,
einen Verbrennungsofen (5) zum Verbrennen von getrocknetem Material, eine Leitung
zum Verbinden der Vorheizmittel mit dem Trockner und eine Leitung zum Fördern des
getrockneten Materials vom Trockner zum Verbrennungsofen aufweist, dadurch gekennzeichnet,
dass sie eine Vorrichtung zum Einleiten von Wasser in die Trocknungsluft enthält,
wobei die genannte Vorrichtung so ausgebildet ist, dass das Vorheizen der Trocknungsluft
in den Vorheizmitteln die Bildung von überhitzten Dampf enthaltender Luft zum Einleiten
in den Trockner bewirkt, und dass ein Kondensator (3) vorhanden ist, der mit einer
Leitung verbunden ist, die den Trockner mit dem Verbrennungsofen verbindet.
10. Anlage nach Anspruch 9, wobei mindestens ein Teil der Trocknungsluft als Verbrennungsluft
benutzt wird, gekennzeichnet durch Mittel (4), Trocknungsluft vorzuheizen, nachdem
sie den Trockner (2) und den Kondensator (3) verlassen hat und bevor diese Luft in
den Verbrennungsofen eingeführt wird.
1. Procédé pour sécher et brûler une matière contenant de l'eau contenant des constituants
combustibles, comme boues de curage déshydratées, les pas suivants étant exécutés
:
(1) introduction de matière contenant de l'eau dans un sécheur direct (2),
(2) séchage de la matière introduite dans le sécheur (2) par l'introduction de l'air
atmosphérique comme air séchant dans le sécheur(2),
(3) introduction de la matière séchée dans un four (5) et combustion de la matière
là-dedans,
(4) introduction dans le four (5) de au moins une part de l'air séchant après le sécheur
(2) comme air de combustion,
(5) préchauffage de l'air séchant déstiné à sécher la matière en utilisant de la chaleur
contenue dans les gaz de la combustion chauds émis du four (5),
caractérisé par
(6) l'addition de l'eau à l'air atmosphérique au préchauffeur (2), l'eau se vaporisant
et étant surchauffée,
et
(7) la réduction de la teneur en eau dans l'air séchant après le sécheur (2) dans
un condenseur (3) avant l'introduction comme air de combustion dans le four (5).
2. Procédé selon la revendication 1, caractérisé en ce qu'au moins une part de l'air
séchant est préchauffée dans un échangeur de chaleur (4) après le sécheur (2) et le
condenseur (3) et avant son introduction dans le four (5).
3. Procédé selon la revendication 1 ou 2, caractérisé en ce qu'au moins une part de l'air
séchant est préchauffé encore dans un échangeur de chaleur (4) où le milieu chauffant
sont des gaz de la combustion du four après la vaporisation de l'eau et avant son
introduction dans le sécheur (2).
4. Procédé selon les revendications 1-3, caractérisé en se qu'après son écartement du
sécheur (2), au moins une part de l'air séchant et utilisé comme milieu chauffant
dans un échangeur de chaleur (4) pour préchauffer l'air séchant et pour vaporiser
l'eau ajouté.
5. Procédé selon les revendications 1-4, caractérisé en ce qu' au moins une part de la
matière contenant de l'eau est préchauffée dans un échangeur de chaleur (4) avant
son introduction dans le sécheur.
6. Procédé selon les revendications 1-5, caractérisé en ce que l'eau ajouté à l'air séchant
est un condensé des gaz d'échappement ou un condensé de l'air séchant émis après le
sécheur (2).
7. Procédé selon les revendications 1-6, caractérisé en ce que l'eau ajouté à l'air sécheur
est du vapeur ou de l'air sécheur émis après le sécheur (2) et contenant de l'eau.
8. Procédé selon les revendications 1-7, caractérisé en ce que de l'eau est ajoutée à
l'air séchant en une quantité déterminée de manière que la température et le flux
de volume de l'air séchant à travers le sécheur (2) en relation à la température,
la teneur en eau et le flux de volume de la matière contenant de l'eau produisent
une matière séchée qui est exactement auto-combustible.
9. Installation pour exercer le procédé selon les revendications 1-8 et comprenant des
moyens (1) pour préchauffer de l'air séchant, un sécheur (2) pour sécher la matière
à être brûlée, un four (5) pour brûler de la matière séchée, une conduit pour la connexion
des moyens de préchauffage avec le sécheur et un conduit pour le transport de la matière
séchée du sécheur au four, par un appareil pour l'introduction de l'eau dans l'air
séchant, cet appareil étant tellement arrangé que le préchauffage de l'air séchant
dans les moyens de préchauffage cause la formation de l'air contenant de la vapeur
surchauffée pour l'introduction dans le sécheur, et en ce qu' un condenseur (3) est
pourvu en connexion avec un conduit connectant le sécheur avec le four.
10. Installation selon la revendication 9, au moins une part de l'air séchant étant utilisée
comme air de combustion, caractérisé par des moyens (4) pour préchauffer l'air séchant
après qu'il a quitté le sécheur (2) et le condenseur (3) et avant l'introduction de
cet air dans le four.