U.S. patent application number 13/932746 was filed with the patent office on 2014-01-09 for heating device and method for its operations.
The applicant listed for this patent is Schwank GmbH. Invention is credited to Bernd H. Schwank, Konrad Weber.
Application Number | 20140011140 13/932746 |
Document ID | / |
Family ID | 36088366 |
Filed Date | 2014-01-09 |
United States Patent
Application |
20140011140 |
Kind Code |
A1 |
Schwank; Bernd H. ; et
al. |
January 9, 2014 |
HEATING DEVICE AND METHOD FOR ITS OPERATIONS
Abstract
This invention relates to a heating device consisting of at
least one burner for the combustion especially of a gaseous fuel,
at least one radiant tube connecting to the burner, at least one
fan generating a negative pressure or an excess pressure in the
radiant tube, and at least one exhaust gas recirculation system
with at least one exhaust gas recirculation passage through which
an exhaust gas produced during the combustion of the primary fuel
can be recirculated from the radiant tube to a transition zone from
the burner into the radiant tube. In order to further develop a
heating device of this type as well as a method for its operation
the burner is adapted for being operated in at least two power
stages and the exhaust gas recirculation system is controlled in
dependence of the power stages of the burner in such a way that the
volume flow of the recirculated exhaust gas is reduced with an
increasing power stage of the burner.
Inventors: |
Schwank; Bernd H.; (Cologne,
DE) ; Weber; Konrad; (Burscheid, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Schwank GmbH |
Cologne |
|
DE |
|
|
Family ID: |
36088366 |
Appl. No.: |
13/932746 |
Filed: |
July 1, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11637620 |
Dec 12, 2006 |
8475163 |
|
|
13932746 |
|
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Current U.S.
Class: |
431/12 ; 126/89;
126/91A; 431/115 |
Current CPC
Class: |
F23C 3/002 20130101;
F24H 9/0068 20130101; F23D 14/12 20130101; F24H 3/006 20130101;
F23C 9/00 20130101; F24H 9/2085 20130101 |
Class at
Publication: |
431/12 ;
126/91.A; 126/89; 431/115 |
International
Class: |
F24H 9/00 20060101
F24H009/00; F23D 14/12 20060101 F23D014/12; F24H 9/20 20060101
F24H009/20; F24H 3/00 20060101 F24H003/00; F23C 9/00 20060101
F23C009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 13, 2005 |
EP |
05/027165.9 |
Claims
1. A heating device comprising at least two radiant tubes opposed
to each other and each including a burner capable for combustion of
a gaseous fuel, at least one fan generating a negative pressure or
an excess pressure in the radiant tubes, each radiant tube having
at least one exhaust gas recirculation system through which an
exhaust gas that is produced during the combustion of the primary
fuel can be recirculated from the radiant tube to a transition zone
from the burner into the radiant tube, characterized in that the
burners can be operated in at least two power stages and that the
exhaust gas recirculation systems can be controlled in dependence
of the power stages of the burners in such a way that the volume
flow of the recirculated exhaust gas is reduced with an increasing
power stage of the burner.
2. The heating device of claim 1, wherein the radiant tubes are
mutually parallel aligned.
3. The heating device of claim 1, wherein the burners are arranged
on the opposite ends of the opposed radiant tubes.
4. The heating device of claim 1, wherein the exhaust gas
recirculation systems can be controlled in dependence of the output
of the burner of the radiant tube.
5. The heating device of claim 1, wherein the exhaust gas
recirculation systems of the radiant tubes can be controlled
independently of each other.
6. A method for operating a heating device in which a gaseous fuel
is burned in at least one burner and in at least one radiant tube
connecting to the burner a flame is produced which heats up the
radiant tube, wherein a negative pressure or an excess pressure is
generated in the at least one radiant tube through a fan, and
wherein exhaust gas produced during the combustion of the fuel is
recirculated from the radiant tube to a transition zone from the
burner into the radiant tube through at least one exhaust gas
recirculation system including at least one exhaust gas
recirculation passage, characterized in that the burner is operated
in at least two power stages and that the exhaust gas recirculation
system is controlled in dependence of the power stages of the
burner in such a way that the volume flow of the recirculated
exhaust gas is reduced with an increasing power stage of the
burner.
7. The method of claim 6, wherein the burner is operated in a
modulating fashion in power stages.
8. The method of claim 6, wherein through the exhaust gas
recirculation system a volume flow regulator for the volume flow of
the recirculated exhaust gas is controlled.
9. The method of claim 8, wherein through the volume flow regulator
the output and the speed of the fan is controlled.
10. The method of claim 8, wherein through the volume flow
regulator a flap and/or sliding valve is controlled which is
arranged in the exhaust gas recirculation passage and which is
closed at a determined output of the burner.
11. The method of claim 6, wherein the burner is operated in two
power stages and that the exhaust gas recirculation system is
activated in one power stage.
12. The method of claim 6, wherein exhaust gases from a first
radiant tube including a first burner are introduced through an
exhaust gas recirculation system in an opposed second radiant tube
which includes a second burner, whereas exhaust gases from the
opposed second radiant tube are introduced in the first radiant
tube through an exhaust gas recirculation system.
13. The method of claim 12, wherein the exhaust gas recirculation
systems are controlled in dependence of the output of the burners
of the opposed radiant tubes.
14. The method of claim 12, wherein the exhaust gas recirculation
systems of the opposed radiant tubes are controlled independently
of each other.
15. The method of claim 6, wherein the exhaust gas recirculation
systems are controlled through a measuring element by temperature,
exhaust gas values, volume flow and the like are measured.
16. The method of claim 8, wherein the volume flow regulator is
electrically and/or thermally controlled.
17. The method of claim 8, wherein the volume flow regulator is
controlled simultaneously with an output regulator of the
burner.
18. The method of claim 6, wherein the power stages of the burner
are controlled through a magnetic valve which has a number of
switching steps corresponding to the number of power stages.
19. The method of claim 6, wherein the switching steps of the
magnetic valve are controlled through a temperature regulator.
20. The method of claim 6, wherein the exhaust gas is conveyed by
pressure differences between the end-side end of the radiant tube
and the transition zone between the burner and the radiant
tube.
21. The method of claim 6, wherein in a first, higher power stage
of the burner 0 to 30% by volume of the exhaust gas are
recirculated into the transition zone between the burner and the
radiant tube.
22. The method of claim 6, wherein in a second, lower power stage
of the burner from 20 to 60% by volume of the exhaust gas are
recirculated into the transition zone between the burner and the
radiant tube.
Description
[0001] This application is a divisional application of U.S. patent
application Ser. No. 11/637,620, filed on Dec. 12, 2006.
[0002] This invention relates to a heating device which consists of
at least one burner for the combustion especially of a gaseous
fuel, at least one radiant tube connecting to the burner, at least
one fan which generates a negative pressure or an excess pressure
within said radiant tube, and at least one exhaust gas
recirculation system which includes at least one exhaust gas
recirculation passage through which exhaust gas that is produced
during the combustion of the primary fuel can be recirculated from
the radiant tube to a transition zone from the burner into the
radiant tube. The invention further relates to a method for the
operation of a heating device, in which method especially a gaseous
fuel is burnt in at least one burner and a flame which heats up the
radiant tube is produced in at least one radiant tube connecting to
the burner, and a negative pressure or an excess pressure are
generated through a fan in said at least one radiant tube, and
exhaust gas which is produced during the combustion of the fuel is
recirculated through at least one exhaust gas recirculation system
including at least one exhaust gas recirculation passage from the
radiant tube to a transition zone from the burner into the radiant
tube.
[0003] Heating devices having a construction as described above and
among others also referred to as dark radiators are heat generators
which are operated with gaseous or liquid fuels and are preferably
used for heating bigger rooms like industrial halls or factories.
These heating devices normally consist of a radiant tube to which a
burner and a fan are connected. The fan can be arranged on the
input side of the burner, so that the fan works as a pressure-type
fan. Alternatively, the fan can be arranged on the output side of
the radiant tube, the output side of the radiant tube being the end
of the radiant tube which is directed away from the burner. In this
alternative the fan works as an extraction fan sucking off the
exhaust gases that are introduced in the radiant tube during the
combustion of the gaseous or liquid fuels.
[0004] The radiant tube can be formed in a linear or curved shape
or with one or several knees and can consist of several segments,
and the radiant tube normally includes a reflector housing which
directs heat to be radiated from the radiant tube in a
predetermined direction. At the normal use of a heating device of
the kind described, where the heating device is installed under the
ceiling of a building, the reflector housing is arranged on an
upper side of the radiant tube so as to be facing the ceiling, in
order to direct radiation heat specifically to a lower part of a
room, for instance to the zone where people, animals and/or plants
are.
[0005] In a heating device of the kind described above and to be
referred to as a dark radiator the transfer of heat to a room to be
heated takes place primarily through infrared radiation. During its
operation the burner produces inside the radiant tube a long flame
which may be several meters long, depending on the fuel and load.
The exhaust gases produced during the combustion are conveyed by
the fan through the radiant tube and are finally supplied to an
exhaust passage which is normally connected to the end of the
radiant tube which is directed away from the burner. Through the
exhaust passage exhaust gases are removed from an upper part of the
building close to the ceiling directly or indirectly together with
the aeration of the room.
[0006] By a special formation of the flame a temperature
distribution as uniform as possible is obtained over the
longitudinal axis of the radiant tube. The radiant tube which is
heated through the flame and through the heat of the exhaust gases
emits a heat radiation of a particular wave length range which as
electromagnetic waves penetrates the room almost lossfree and is
converted in sensible heat only after meeting against absorbing
surfaces like parts of a building, for instance walls and floors,
pieces of furniture, human beings, animals, plants. For this
reason, a heating device of this type in the form of a dark
radiator works particularly energy-saving in big rooms.
[0007] From the document DE 44 30 860 A1 there is known for example
a heating device which is formed as a radiant element and which
includes a gas-fired burner, a radiant tube connected to it and an
extraction fan in a housing. The radiant tube is formed as a closed
tube system and has a U-shaped configuration. The extraction fan
generates within the housing a negative pressure which is intended
for producing a flame that passes through the interior of the
radiant tube smoothly and uniformly and enables the removal of the
exhaust gases.
[0008] Furthermore, the document EP 0 282 838 B1 discloses a
gas-fired heating radiator including a radiant tube as a combustion
space and including a burner which is connected to one end of the
radiant tube. On the opposite end of the radiant tube a fan is
connected sucking exhaust gases off the radiant tube. The radiant
tube is U-Shaped and is arranged in a housing.
[0009] A further heating device is known from the document DE 91 03
004 U1 which includes a radiant tube that is connected to a
pressure and mixing chamber housing. On one side the radiant tube
is connected to a backflow chamber with a fan and on the other side
to a mixing chamber with a flame tube surrounding a burner. The
pressure and mixing chamber housing has a twin-screw shape, with
two cylinder-like parts forming the housing and with a front and a
back plate having the twin-screw shape. Between the backflow
chamber and the mixing chamber a flap is arranged, of which the
position can be regulated. By means of this flap the amount of air
and the pressure ratios are adjusted for the different lengths of
the radiant tube. The fan includes an impeller with adjustable
speed, in order to adjust the volume flow of the sucked-off waste
gases for different lengths of the radiant tube. Accordingly, this
pre-known heating device can be readily adapted to differently long
radiant tubes without requiring structural modifications of the
heat generating elements such as the burner.
[0010] A gas-fired heating device of the type as described above is
further known from the document DE 92 07 513 U1 and includes a
U-shaped radiant tube having arranged an upstream burner on its
part on the inflow side and having arranged an extraction fan on
its part on the outflow side. On its outflow side the extraction
fan includes a bypass passage which is connected to the radiant
tube on the inflow side and through which a part of the exhaust
gases is introduced in the inflow-side part of the radiant tube,
with a flame being produced by the burner in the inflow-side part
of the radiant tube. In this heating device it is provided that 15
to 30% by volume of the exhaust gases are passed via the bypass
passage and that the bypass passage can be throttled, in order to
adjust the amount of exhaust gases so as to suit the construction
of the heating device, particularly the length of the radiant tube,
so that differently designed heating devices and particularly
heating devices with a variable length of the radiant tube can be
formed and operated with the required efficiency, independently of
the burner.
[0011] Heating devices of the above-described construction are
predominantly operated in an ON/OFF mode, in which the burner is
either switched on or switched off, so that either a preset power
or no power is delivered. The operation of this heating device is
particularly determined by the heat distribution provided in the
room to be heated and by the pollutant concentration of the exhaust
gases.
[0012] Since normally the heating device is set for the maximum
heat consumption of the room to be heated at lowest outside
temperatures, the result is an intermittent operation of the
heating device at temperature variations during an annual heating
period. The consequences are less convenience due to fluctuations
in the room temperature and as a result energy losses of the
building which as a rule have to be compensated by an expensive
insulation. Due to the intermittent operation with frequent warming
up and cooling down processes the heating device and its components
are subject to a relatively high load and accordingly to an
increased wear of its components.
[0013] Because of the narrow physical limits it is not easily
possible to make an adaptive control of the power output by a
multi-step or continuously modulated operation of the heating
device. If for instance the gas load is reduced without
adapting/adjusting the blower output, the amounts of excess air
will be too high, accompanied by a tendency of higher exhaust gas
losses of the heating device. Also, the flame length will be
considerably reduced at a high amount of excess air, resulting in a
reduced heat distribution within the radiant tube and accordingly
in a less favorable distribution of radiation in the room to be
heated.
[0014] If on the other hand the blower output is reduced with the
gas load, the large heat transfer areas and the high heat
capacities of the heating device will result in an undesired
condensation. In addition, the construction of the required air
deficiency safety device is more complicated.
[0015] Starting from the above-described prior art and the
drawbacks involved in this prior art, the invention is based on the
problem of further developing a heating device of the described
type as well as a method for its operation to an extent that an
adaptation of the power output of the heating device is possible
with a simple construction and without the aforementioned
drawbacks, while obtaining in each power range an optimum heat
distribution at small losses of exhaust gas and consequently a high
thermal comfort in rooms to be heated, with small energy losses and
with clearly reduced pollutant concentrations of the exhaust gases
and at the same time avoiding condensation effects, so that the
service life of the heating device according to the invention is
clearly increased.
[0016] In a heating device according to the invention the solution
of this problem is obtained by the burner being adapted for
operation in at least two power stages and by the exhaust gas
recirculation system being adapted to be controlled in dependence
of the power stages of the burner in such a way that the volume
flow of the recirculated exhaust gas is reduced with an increasing
power stage of the burner.
[0017] On part of the method according to the invention for
operating a heating device it is provided as a solution that the
burner is operated in at least two power stages and that the
exhaust gas recirculation system is controlled in dependence of the
power stages of the burner in such a way that the volume flow of
the recirculated exhaust gas is reduced with an increasing power
stage of the burner.
[0018] Further features and advantages of the invention will become
apparent from the dependent claims and from the following
description of embodiments and further developments of the heating
device and the method according to the invention.
[0019] Accordingly, in the heating device according to the
invention it is provided that at the same time as the power output
is reduced by reducing the gas load a part of the exhaust gas is
introduced in the fresh air which is taken in or in the radiant
tube subsequent to the burner and recirculates in the radiant tube.
The volume flow of the recirculated exhaust gases can be regulated
for instance by means of a control element which is formed as a
volume flow regulator which is provided in an exhaust gas
recirculation system between a fresh air passage with a normally
low pressure level and an exhaust gas passage with a normally
higher pressure level that is arranged on the end of the radiant
tube directed away from the burner. The control element can be
driven for instance electrically and simultaneously with a signal
for reducing the power output of the burner. Therefore, any
additional driving means for conveying the recirculated exhaust gas
is not necessarily required.
[0020] In a preferred embodiment of the invention the fan is
arranged on the input side of the burner, so that both the fresh
air required for the combustion and recirculating exhaust gases are
forced into the burner and hence into the down-stream radiant tube.
On the input side of the fan an intake passage is arranged for the
intake of fresh air from the room or from outside via a passage
through the roof. In the intake passage a small negative pressure
exists compared to the atmosphere.
[0021] The exhaust passage which is arranged on the end of the
radiant tube serves to discharge exhaust gases for instance through
the roof of the building to be heated. In this exhaust passage a
small excess pressure exists as compared to the atmosphere. Between
the intake passage and the exhaust passage a short
temperature-resistant connecting passage is arranged which includes
as a control element for instance an exhaust gas flap that is
driven by an electric motor and that is thermally controlled for
example.
[0022] The gas-operated burner includes in the preferred embodiment
a two or multi-step magnetic valve for fuel supply, the steps of
the valve being selected by a room temperature regulator in
dependence of the required heat.
[0023] In a high power stage of the heating device an elongate
flame is produced by the burner in the radiant tube which leads to
a favorable heat distribution. In this power stage no exhaust gas
or only a small amount of exhaust gas, for example 0 to 30% by
volume of the available exhaust gas are recirculated to the radiant
tube through the exhaust gas recirculation system for instance via
the fresh air passage of the burner. Due to the special flame
formation, the emission of nitrogen oxides which are thermally
produced during the combustion and which are harmful to the
environment is determined in this condition by the flame length
(sojourn time) and flame temperature. The flame temperature
necessarily is relatively high, in order to produce a high
temperature in the radiant tube.
[0024] In a lower power stage a larger volume flow of the exhaust
gases, for instance 20 to 60% by volume of the available exhaust
gas are recirculated to the radiant tube for example via the fresh
air passage of the burner and are mixed with fresh air in the fan
and are supplied to the burner and/or radiant tube, by opening the
volume flow regulator, for example the exhaust gas flap in the
exhaust gas recirculation system. Without adding the exhaust gases
the flame length in the low power stage would be drastically
reduced due to the high amount of excess air, so that in the
radiant tube the heat distribution would become worse and higher
exhaust gas losses would be produced. By the output-related exhaust
gas recirculation according to the present invention the flame is
extended at a reduced flame temperature and a very favorable heat
distribution is attained at a reduced radiation power due to the
locally smaller amount of oxygen offered, through the addition of
exhaust gas.
[0025] Further, by the exhaust gas recirculation in the lower power
stage the exhaust gas losses of the burner are kept constant and
are even further reduced compared to the higher power stage. A
further advantage of the invention is that the amount of exhausted
nitrogen oxides of the burner is clearly reduced in the lower power
stage due to the reduced combustion temperature and the low oxygen
partial pressure in the flame. It is possible to reduce the amount
of the contaminant transport over a whole heating period up to 50%,
depending on the exhaust gas addition rate.
[0026] Besides the above-described operation of the burner in two
power stages it is also possible to operate the burner in a
modulating fashion in power stages. Accordingly, the possibility
exists that the burner output is continuously varied, and at the
same time the recirculating exhaust gas is supplied to the radiant
tube corresponding to the power stage, while simultaneously
effecting in turn a control of the burner and the exhaust gas
recirculation system.
[0027] The exhaust gas recirculation system preferably includes a
volume flow regulator for the volume flow of the recirculated
exhaust gas. The volume flow regulator can be formed for instance
as a bypass valve which is inserted in an exhaust gas recirculation
passage and which can be controlled with regard to its opening. It
is also possible for the volume flow regulator to control the
output and particularly the speed of the fan, so that for example
by increasing the speed of the fan a larger volume flow of exhaust
gas is taken in and supplied to the radiant tube. A further
alternative provides that that volume flow regulator includes a
flap and/or sliding valve which is arranged in the exhaust gas
recirculation passage and which closes when a certain output of the
burner is reached. The above-mentioned volume flow regulators can
be provided also in a combination, and a combination of a speed
regulation of the fan and a volume flow regulation system in the
form of a bypass valve or a flap and/or a sliding valve turned out
to be advantageous.
[0028] As far as the burner has two power stages, it turned out to
be advantageous that the exhaust gas recirculation system is
activated in one power stage and is deactivated in a further power
stage. As a rule, the exhaust gas recirculation system is
deactivated in the higher one of the two power stages of the
burner, while it is activated in the lower one of the two power
stages of the burner, in order to return a predetermined volume
flow of exhaust gas to the radiant tube.
[0029] As it has been already discussed above, the fan can be
arranged both on an end of the radiant tube opposite to the burner
or together with the burner on one end of the radiant tube. If the
fan is arranged on an end of the radiant tube opposite the burner,
the fan generates a negative pressure in the radiant tube, so that
the exhaust gases are sucked off and are in case supplied again to
the radiant tube in the region of the end of the radiant tube
including the burner. If the fan together with the burner is
arranged on one end of the radiant tube, the fan generates an
excess pressure in the region of the radiant tube, in which case
the fan is provided both for supplying fresh air and for supplying
the exhaust gas to be recirculated. Of course, it is also possible
to form the heating device according to the invention with two
fans, provided that the radiant tubes have a corresponding length,
one fan being arranged on an end of the radiant tube opposite the
burner and one fan together with the burner being arranged on one
end of the radiant tube.
[0030] In a preferred embodiment of the invention it is provided
that at least two radiant tubes are arranged oppositely to each
other, each of which having a burner, and that each of the radiant
tubes has an exhaust gas recirculation system through which the
exhaust gases are introduced in the respective oppositely arranged
radiant tube. In this embodiment of the invention the radiant tubes
are normally formed in a linear fashion, and the two burners are
arranged on diametrically opposite ends of the radiant tubes, so
that the free end of the first radiant tube is arranged in the
region of that end of the second radiant tube to which the burner
is mounted in the second radiant tube. On the end of the first
radiant tube the exhaust gas recirculation system of the first
radiant tube is arranged, through which the exhaust gas produced by
the burner of the first radiant tube is introduced in the region
between the burner and the second radiant tube. This also applies
for the end of the second radiant tube which is arranged in the
region of the first radiant tube including the burner and which
also has an exhaust gas recirculation system through which the
exhaust gas of the second radiant tube is introduced in the first
radiant tube, in the region between the burner and the first
radiant tube.
[0031] Normally, this embodiment of a heating device is able to
operate also without an output-related introduction of the exhaust
gases in the corresponding radiant tubes. But it turned out that
also with this construction of the heating device an output-related
recirculation of the exhaust gases is advantageous.
[0032] A further development of this heating device provides that
the radiant tubes are oriented in a mutually parallel extending
fashion. Preferably, the two radiant tubes are arranged in a common
housing, so that both radiant tubes directionally convey the
thermal energy to the room to be heated through a common reflector.
Of course, it is also possible to arrange the two mutually parallel
aligned radiant tubes in different housings, each of which having a
reflector, and the reflectors can have different orientations, to
make it possible for the two radiant tubes to convey heat
selectively to different areas.
[0033] A further form of this advantageous embodiment of the
heating device according to the invention provides that the exhaust
gas recirculation systems are controllable in dependence of the
output of the burner of the oppositely directed radiant tube.
Preferably, a further development provides that the exhaust gas
recirculation devices of the mutually oppositely directed radiant
tubes are controllable independently of each other.
[0034] According to a further feature of the invention it is
provided that the exhaust gas recirculation system includes a
measuring element, by means of which parameters like temperature,
exhaust gas values, volume flow or the like are measured and used
for the control of the exhaust gas recirculation system. If for
instance an inadmissible exhaust gas value is measured by such a
measuring element, the exhaust gas recirculation systems can be
influenced for a short time independently of the power stage, in
order to bring the required parameters like temperature, exhaust
gas values, volume flow or the like to the preset range which
enables an optimum operation of the heating device according to the
invention.
[0035] A further development of the heating device according to the
invention provides that the volume flow regulator can be driven
electrically and/or thermally. An electrical drive of the volume
flow regulator results in a simple construction of the exhaust gas
recirculation system and enables the simultaneous selection of the
power stages of the burner and the exhaust gas recirculation
system. In addition to a thermal switching element time-delayed
circuits can be provided which are triggered only upon reaching a
predetermined temperature in the exhaust gas flow or in the radiant
tube. Preferably, the volume flow regulator can be driven
simultaneously with an output regulator of the burner.
[0036] The above-described advantages of the heating device
according to the invention substantially apply also for the method
according to the invention, so that concerning the embodiment of
the method according to the invention reference may be made to the
above-described advantages of the heating device according to the
invention.
[0037] Further features and advantages of the invention will become
apparent from the following description of the attached drawings
showing a preferred embodiment of the heating device according to
the invention. In the drawings it is shown by:
[0038] FIG. 1 a perspective view of a first embodiment of a heating
device;
[0039] FIG. 2 a perspective view of a part of a second embodiment
of the heating device;
[0040] FIG. 3 a perspective view of a part of a third embodiment of
a heating device;
[0041] FIG. 4 a perspective view of a fourth embodiment of a
heating device;
[0042] FIG. 5 a perspective view of a fifth embodiment of a heating
device; and
[0043] FIG. 6 a perspective view of a sixth embodiment of a heating
device.
[0044] In FIG. 1 a first embodiment of a heating device is shown in
a perspective view. The heating device consists of a burner 1 for
the combustion especially of a gaseous fuel. The burner 1 is
flanged on its end to a radiant tube 2 and produces a flame within
the radiant tube 2 during the combustion of the fuel, which flame
extends into the radiant tube 2. The linear radiant tube 2 is
arranged in a housing 3 which has a trapezoidal cross section and
which includes an opening through which heat radiation produced by
the radiant tube 2 can exit. On its inner surface (not further
shown) the housing 3 includes a reflector which supports the
dissipation of heat radiation.
[0045] On its second end 4 arranged oppositely to the burner 1 the
radiant tube 2 includes an exhaust passage 5 which runs parallel to
the radiant tube 2 outside 110 the housing and which opens into a
chimney 6 through which the exhaust gas produced during the
combustion of the fuel is discharged.
[0046] The burner 1 has an upstream fan 7 which is formed as a
radial fan in the illustrated embodiment. Through the fan 7 fresh
air for the combustion in the radiant tube 2 is drawn into the
radiant tube 2 by the burner 1, and the fan 7 is connected to a
fresh air passage 8.
[0047] Between the exhaust passage 5 and the fresh air passage 8 an
exhaust gas recirculation system 9 is arranged which consists of an
exhaust gas recirculation passage 10 and a volume flow regulator
11.
[0048] The volume flow regulator 11 includes an electric motor 12
through which a flap (not further shown) can be moved that is
arranged in the exhaust gas recirculation passage 10.
[0049] In the embodiment of the heating device illustrated in FIG.
1 the burner 1 can be operated in two power stages, and the exhaust
gas recirculation system 9 can be controlled in dependence of the
selected power stage of the burner 1. The flap (not further shown)
which is arranged in the exhaust gas recirculation system 9 is
closed during the operation of the burner 1 in the higher one of
the two power stages, so that the exhaust gas carried via the
exhaust gas passage is completely discharged through the chimney 6.
If the burner 1 is switched to the lower one of the power stages,
the flap (not further shown) which is arranged in the exhaust gas
passage 10 is pivoted by the electric motor 12, so that a part of
the exhaust gas from the exhaust gas passage 5 is admixed to the
fresh air in the fresh air passage 8 through the exhaust gas
recirculation passage 10 and is blown into the burner 1 and the
radiant tube 2 through the fan 7.
[0050] In FIG. 2 a second embodiment of a heating device is
illustrated which substantially corresponds to the embodiment
according to FIG. 1, so that identical parts carry identical
reference numbers. Differently from the embodiment according to
FIG. 1 the heating device according to FIG. 2 includes a U-shaped
radiant tube 2 having two mutually parallel extending tube portions
within the housing 3 which are interconnected by a U-shaped
connecting element. Consequently, in the embodiment according to
FIG. 2 also the residual heat of the exhaust gas within the radiant
tube 2 is utilized, and the exhaust passage 5 is formed much
shorter compared to the embodiment according to FIG. 1.
[0051] Moreover, FIG. 2 shows the flap 13 which has been explained
in conjunction with the embodiment according to FIG. 1 but has not
been further illustrated there. The flap 13 is arranged in the
exhaust gas recirculation passage 10 and can be driven through the
electric motor 12.
[0052] A third embodiment of a heating device is illustrated in
FIG. 3. This embodiment substantially corresponds to the embodiment
according to FIG. 2, so that here, too identical reference numbers
are used for identical components.
[0053] The difference between the embodiments according to the
FIGS. 2 and 3 resides in the fan 7 being arranged upstream of the
burner 1 in the embodiment according to FIG. 2, so that the fan
forces the fresh air and in case the recirculated exhaust gas into
the burner 1 and the radiant tube 2, whereas the fan 7 of the
embodiment according to FIG. 3 is arranged on the end 4 of the
radiant tube 2, so that a negative pressure is produced in the
radiant tube 2 through the fan 7.
[0054] In FIG. 4 a fourth embodiment of a heating device is shown
which differently form the embodiments of the heating device shown
in the FIGS. 1 to 3 includes two mutually parallel extending
radiant tubes 2 in a common housing 3. On opposite ends the two
radiant tubes 2 each have a burner 1, so that the flames produced
by these burners 1 extend in opposite directions within the
parallel radiant tubes 2.
[0055] On their ends the two radiant tubes 2 are each connected to
an exhaust passage 5 through which the exhaust gases produced by
the combustion in the burners 1 are supplied to chimneys 6.
[0056] Furthermore, each burner 1 includes a fresh air passage 8
through which the respective one of the burners 1 is supplied with
fresh air for the combustion. The fresh air passage 8 is
respectively connected to the fan 7 which is arranged upstream of
the respective burner 1.
[0057] In FIG. 4 it can be further seen that between each exhaust
passage 5 of a radiant tube 2 and the fresh air passage 8 of the
adjacent radiant tube 2 an exhaust gas recirculation system 9
corresponding to the embodiment according to the FIGS. 1 to 3 is
provided. Through these exhaust gas recirculation systems 9 the
exhaust gas form a radiant tube 2 is supplied to the fan 7 of the
second radiant tube 2 extending parallel to it.
[0058] Normally the operation of the heating device according to
FIG. 4 corresponds to the operation of the heating devices
according to the FIGS. 1 to 3. This results in a heating device
with a high efficiency, because heat losses which are due to long
exhaust passages are avoided.
[0059] A further embodiment of a heating device according to the
invention is shown in FIG. 5. Differently from the above-described
embodiments according to the FIGS. 1 to 4 this embodiment according
to FIG. 5 includes a second fan 7 which is arranged in the exhaust
passage 5 and is formed as a radial fan. The output of this fan 7
in the exhaust passage 5 is variable in dependence of the power
stage of the burner 1, so that the fan 7 in the exhaust passage 5
blows a high portion of exhaust gas into the burner 1 and the
downstream radiant tube 2, so far as the burner 1 is operated in
the lower one of the two power stages. When the burner 1 is
switched to the higher one of the two power stages, the output of
the fan 7 in the exhaust passage 5 is reduced or cut off, so that
the exhaust gas supplied to the fan 7 through the exhaust passage 5
can escape through the chimney 6.
[0060] A further embodiment of the heating device according to the
invention is illustrated in FIG. 6. This embodiment substantially
corresponds to the embodiment according to FIG. 5 or to the
embodiments according to the FIGS. 2 and 3. Differently from the
above-described embodiments according to the FIGS. 2, 3 and 5 the
embodiment according to FIG. 6 includes an electromagnetically
controlled flap, so that the volume flow regulator 11 has an
electromagnet, by means of which the flap can be adjusted in
dependence of the power stages of the burner 1.
[0061] Besides the embodiments of the heating device according to
the invention described above and illustrated in the FIGS. 1 to 6
further embodiments are conceivable which for instance include in
the volume flow regulator 11 a bypass valve which can be driven in
dependence of the power stage of the burner 1. Of course, it is
also possible to combine a number of the above-described control
elements of the volume flow regulator 11. It turned out as
particularly advantageous to combine the second fan 7 in the
exhaust passage according to FIG. 5 with a further control element
in the volume flow regulator 11.
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