Note: Descriptions are shown in the official language in which they were submitted.
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Burner unit for steel making facilities
Introduction
The present invention relates to a burner unit for steel making facilities.
More
particularly, the present invention relates to an external burner unit of a
regenerative or recuperative heat generator. The regenerative heat generator
may e.g. be a hot blast stove of a blast furnace.
The preheating of air for blast furnaces is conventionally carried out in
adjacent
regenerative heat generators known as hot blast stoves. Such stoves generally
comprise a combustion chamber and a heat-retention shaft. In case of an
internal combustion chamber stove, the combustion chamber and the heat-
retention shaft are separated from one another by a wall constructed from
refractory bricks. A burner unit is generally located in a bottom section of
the
combustion chamber. Combustion air and combustible fuel, generally
combustible gases, are supplied to the burner unit and a mixture of the
combustion air and fuel is burned in the combustion chamber of the stove. The
flue gases emanating from the combustion rise upwards in the combustion
chamber, are diverted via a dome and then pass through the heat-retention
shaft filled with checker bricks. Heat from the flue gases is absorbed by the
checker bricks. The flue gasses which have now cooled down escape the stove
via an exhaust gas chamber and at least one discharge port.
Once the checker bricks have been heated to a sufficient temperature, the
supply of combustion air and fuel is discontinued and air is blown through the
stove in the opposite direction. The air is heated as it passes through the
heat-
retention shaft containing the hot checker bricks, diverted via a dome into
the
combustion chamber, where it leaves the stove via a hot blast outlet in the
shell
of the stove to be fed to the blast furnace.
Generally, the burner unit comprises a ceramic burner arranged within the
stove, i.e. in the bottom section of its combustion chamber. It is also
possible to
provide external burner units, which are installed outside the shell of the
stove.
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One or more such external burner units may be used instead of an internal
ceramic burner. Alternatively, such external burner units may be used as
additional heaters if used in conjunction with an internal ceramic burner.
One advantage of such external burner units is that they are easily
accessible,
i.e. for maintenance or regulation purposes. Indeed, it may be advantageous to
regulate the burner unit in order to achieve different temperatures or
different
flue gas compositions. This is of particular interest if the stove is used for
experimental purposes.
Object of the invention
Consequently, the object of the present invention is to provide an improved
burner unit for steel making facilities, in particular in connection with
regenerative or recuperative heat generators. This object is achieved by a
burner unit as claimed in claim 1.
General description of the invention
In order to achieve this object, the present invention proposes a burner unit
for
steel making facilities, in particular for use in connection with a
regenerative or
recuperative heat generator, wherein the burner unit comprises a mixing zone,
a plurality of fuel feed channels for feeding combustible fuel to the mixing
zone;
and a plurality of air feed channels for feeding combustion air to the mixing
zone. The burner unit comprises a primary burner with an annular feed
arrangement comprising circumferentially alternating fuel feed channels and
air
feed channels; a central channel through the annular feed arrangement and a
secondary burner arranged in the central channel of the burner unit, the
central
channel being coaxial with the annular feed arrangement.
The primary burner may be considered as main burner, dimensioned to
generally work like a conventional burner. The secondary burner may be
considered as auxiliary burner for carrying out additional tasks, such as e.g.
heating up the burner unit before the primary burner is switched on or aiding
the
combustion of the primary burner. Indeed, the secondary burner can be used as
Printed: 12-03-20.121 DESCPAMD' PCT/EP 2010/069 177
= 12. Mar. 2012 8:13 Office Freylinger S.A. No. 4728 P. 8
PCT/EP 2010/069 177 - 12-03-2012
P PWU-644/WO 3
post combustion burner for using up any excess combustible fuel or combustion
air from the primary burner, thereby altering the composition of the flue
gasses
exiting the burner unit. Whereas, in conventional burner units, only one type
of
combustible fuel and one type of combustion air can be used at any one time,
regulation of the flue gases composition may be difficult. A mixing of
different
types of combustible fuel or combustion air may be carried out before feeding
it
to the burner unit. This is however generally cumbersome and sometimes
dangerous. The present invention allows, through the use of the secondary
burner, to mix different types of combustible fuel or combustion air within
the
burner unit; i.e. two different types of combustible fuel or combustion air
may be
fed to the mixing zone, thereby altering the burning conditions and the flue
gas
temperature and/or composition. The burner unit according to the present
invention is therefore much more flexible, where operation modes are
concerned, than conventional burner units.
The burner unit may also be used to directly supply fumes of a particular
composition to the steel making facility to which it is connected.
It should be noted that the air feed channels may also be referred to as
oxygen
feed channels. Indeed, instead of combustion air, oxygen 02 may be fed
through the air feed channels to the mixing zone.
According to the invention, the burner unit further comprises auxiliary feed
channels for feeding combustible fuel and/or combustion air to the mixing
zone,
the auxiliary feed channels having a cross-section smaller than a cross-
section
of the fuel feed channels or air feed channels.
Advantageously, the auxiliary feed channels comprise auxiliary fuel feed
channels for feeding combustible fuel to the mixing zone, the auxiliary fuel
feed
channels having a cross-section smaller than a cross-section of the fuel feed
channels of the primary burner. Similarly, the auxiliary feed channels may
also
further comprise auxiliary air feed channels for feeding combustion air to the
mixing zone, the auxiliary air feed channels having a cross-section smaller
than
a cross-section of the air feed channels of the primary burner. Both the
auxiliary
fuel feed channels and the auxiliary air feed channels are thus preferably low
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flow rate channels whereas the fuel feed channels and the air feed channels
are
preferably high flow rate channels.
The auxiliary feed channels allow feeding additional combustible fuel and/or
combustion air to the mixing zone, thereby altering the combustion conditions
of
the primary burner.
The additional combustible fuel or combustion air may be of the same type than
that fed through the main fuel and air feed channels, thereby adjusting the
burning combustion conditions of the primary burner. Preferably however, the
additional combustible fuel or combustion air is of a different type than that
fed
through the main fuel and air feed channels, thereby also altering the
composition of the flue gasses. The additional combustible fuel or combustion
air may also provide the primary burner with a non-stoichiometric mixture,
whereby the primary burner only achieves a partial combustion of the mixture.
The secondary burner may then be used to complete the combustion of the
mixture.
The auxiliary feed channels thus contribute to the flexibility of the burner
unit.
The combustible fuel fed through the fuel feed channels may be blast furnace
gas and/or the combustion air fed through the air feed channels may be air or
low calorific gas.
The combustible fuel fed through the auxiliary fuel feed channels may be high
calorific gas, such as natural gas or coke oven gas and/or the combustion air
fed through the auxiliary air feed channels may be oxygen.
The secondary burner preferably comprises air and fuel feed lines, thereby
allowing the secondary burner to be used independently from the primary
burner. It should be noted however that it is not excluded to provide the
secondary burner with only one of the air and fuel feed lines. Indeed, the
secondary burner may be used as post combustion burner, receiving air or fuel
from the flue gasses from the primary burner.
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The secondary burner may be of any appropriate type, depending on the fuel to
be used. Such fuel may be chosen from the non-exhaustive list comprising oil,
coke oven gas, blast furnace gas or natural gas.
According to one embodiment of the invention, the auxiliary fuel feed channels
5 and/or the auxiliary air feed channels pass through a circumferential wall
of the
burner unit. Annular feed chambers may be arranged around an exterior wall of
the burner unit, the annular feed chambers being arranged for feeding
combustible fuel or combustion air to the auxiliary fuel feed channels and the
auxiliary air feed channels.
According to another embodiment of the invention, the auxiliary fuel feed
channels and/or the auxiliary air feed channels pass through a rear wall of
the
burner unit, the auxiliary fuel feed channels and/or the auxiliary air feed
channels being arranged parallel to the axis of the burner unit. The auxiliary
fuel
feed channels and/or the auxiliary air feed channels may be arranged between
the annular feed arrangement of the primary burner and the secondary burner.
Alternatively, the auxiliary fuel feed channels and/or the auxiliary air feed
channels may be arranged within the annular feed arrangement of the primary
burner.
The annular feed arrangement is preferably formed by an annular channel
comprising a plurality of inner channels therein, the inner channels dividing
the
annular channel into the circumferentially alternating fuel feed channels and
air
feed channels, wherein the annular channel is connected for conveying one of
the combustible fuel or the combustion air and the inner channels are used for
conveying the other one of the combustible fuel or the combustion air. By
providing inner channels arranged in the annular channel, a gastight
separation
can be formed between the fuel feed channels and the air feed channels,
thereby avoiding any leaks from one channel to the other within the annular
feed arrangement.
The air feed channels and fuel feed channels are preferably parallel to the
central axis if the burner unit. Other configurations should however not be
excluded. The air and fuel feed channels may e.g. be twisted around the
central
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axis, which may provide a swirling of the combustible fuel and the combustion
air when entering the mixing zone. Although generally not desired, in some
instances such a swirl may be advantageous. It should be noted that other
means for achieving a swirl may also be used.
It should be noted that, although the present application mainly describes a
burner unit in connection with a hot blast stove, the burner unit may also be
used in connection with other steel making facilities, such as e.g. pulverised
coal injection (PCI) installations or direct recuperative heat exchangers.
Brief description of the figures
The present invention will be more apparent from the following description of
a
not limiting embodiment with reference to the attached drawings. In these
drawings, wherein identical reference numerals are used to indicate identical
or
similar elements,
Fig.1: is a cut through a burner unit according to a first embodiment of the
present invention;
Fig.2: is a partial section view across the burner unit along line A-A of
Fig.1;
Fig.3: is a cut through a burner unit according to a second embodiment of the
present invention; and
Fig.4: is a partial section view across the burner unit along line B-B of
Fig.3.
Detailed description with respect to the figures
Fig.1 shows a cut through a burner unit 10 according to a first embodiment of
the present invention. The burner unit 10 comprises a front section 12 with a
combustion chamber 14 and a rear section 16 with feed lines for feeding
combustible fuel and combustion air to a mixing zone 18 of the combustion
chamber 14. The front section 12 comprises an opening 20 for feeding flue
gases from the burner unit 10 to a steel making facility such as e.g. a hot
blast
stove (not shown). The burner unit 10 is connected to the hot blast stove via
a
connection flange 22. In the front section 12, refractory material 24 is
applied
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against the inner surface 26 of the circumferential wall 28 to protect the
latter
from the heat generated in the combustion chamber 14.
The rear section 16, which comprises the feed lines, is more easily described
by
referring to both Fig.1 and Fig.2, the latter being a partial section view
along line
A-A of Fig.1. The rear section 16 comprises an annular feed arrangement 30
alternately comprising fuel feed channels 32 and air feed channels 34. The
fuel
and air feed channels 32, 34 are arranged circumferentially, in alternating
manner, preferably in regular sectors. The fuel feed channels 32 and air feed
channels 34 respectively lead combustible fuel and combustion air from a fuel
inlet 36 and an air inlet 38 to the mixing zone 18 of the combustion chamber
14.
In the mixing zone 18 the combustible fuel and combustion air meet and the
mixture thereof is ignited to form a first combustion, represented by flames
40.
The annular feed arrangement 30 with its fuel and air feed channels 32, 34
forms a primary burner 42 of the burner unit 10.
The annular feed arrangement 30 surrounds a central channel 44, which is
configured so as to receive a secondary burner 46 therein. The annular feed
arrangement 30 and central channel 44 are coaxial with a central axis 47 of
the
burner unit 10. The central channel 44 is lined with refractory material 48.
The
secondary burner 46 feeds combustible fuel and combustion air to the mixing
zone 18, where a mixture thereof ignites to form a second combustion,
represented by flame 50. The secondary burner 46 is inserted into the burner
unit 10 though a socket 52 in a rear wall 54 of the burner unit 10.
The construction of the annular feed arrangement 30 of the primary burner 42
can be more closely described by referring to Fig.2. The annular feed
arrangement 30 is formed by two coaxial pipes - an outer pipe 56 and an inner
pipe 58 - between which an annular channel 60 is formed. Within the annular
channel 60, a plurality of inner channels 61 are formed by inserting pipe-like
elements 62 connected to the inner pipe 58. The pipe-like elements 62 form a
gas tight separation wall between the inner channels 61 and the annular
channel 60, thereby forming the fuel feed channels 32 and air feed channels
34.
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Auxiliary fuel feed channels 64 and auxiliary air feed channels 66 may be
provided for feeding further combustible fuel and further combustion air to
the
mixing zone 18. Although, Fig.1 shows both the auxiliary fuel feed channels 64
and the auxiliary air feed channels 66, it should be noted that it is also
possible
to provide the burner unit 10 with only one of these auxiliary feed channels
64,
66.
The auxiliary fuel feed channels 64 are arranged so as to feed further
combustible fuel from an annular fuel feed chamber 68 connected to a fuel
inlet
70 through the circumferential wall 28 of the burner unit 10 into the mixing
zone
18. Similarly, the auxiliary air feed channels 66 are arranged so as to feed
further combustion air from an annular air feed chamber 72 connected to an air
inlet 74 through the circumferential wall 28 of the burner unit 10 into the
mixing
zone 18.
The auxiliary fuel and air feed channels 64, 66 are low flow rate channels
arranged so as to deliver high calorific gas, such as natural gas or coke oven
gas or oxygen to the mixing zone 18, thereby altering the combustion
conditions
of the primary burner 42. The further fuel and/or air fed to the mixing zone
18
may be in quantities such that the mixture in the mixing zone 18 is non-
stoichiometric, thereby only achieving a partial combustion with the primary
burner 42. Further combustion of the flue gases from the first combustion may
then be achieved with the aid of the secondary burner 46.
Figs 3 and 4 show a burner unit 10 according to a second embodiment of the
invention, wherein Fig.4 is a partial section view along line B-B of Fig.3.
This
burner unit is very similar to the one shown in Figs 1 and 2 and will
therefore not
be described herein in detail. Same reference numerals refer to identical
features in both embodiments. The burner unit of Fig. 2 and 3 differs from the
first embodiment in the location of the auxiliary feed channels.
An auxiliary air feed channel 76 is arranged between the fuel feed channels 32
and air feed channels 34 of the annular feed arrangement 30 and the refractory
material 48 of the central channel 44. At one end, the auxiliary air feed
channel
76 is connected to an air inlet 78 arranged in the rear wall 54 of the burner
unit
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10; at the opposite end, the auxiliary air feed channel 76 comprises a port 80
opening into the mixing zone 18 of the burner unit 10.
Although Fig.2 shows an auxiliary air feed channel 76 only, it should be noted
that it is also possible to provide the burner unit 10 with an auxiliary fuel
feed
channel in a similar manner.
During typical operation of the burner unit 10, combustible fuel and
combustion
air are generally fed through the fuel feed channels 32 and air feed channels
34, so as to form a combustible mixture in the mixing zone 18. The flue gases
from the combustion of this combustible mixture by the primary burner 42 is
then fed through the opening 20 into the hot blast stove.
The auxiliary fuel and air feed channels 64, 66 allow the introduction of
additional combustible fuel and combustion air into the mixing zone 18,
thereby
creating a combustible mixture potentially comprising two distinctive types of
combustible fuel and two distinctive types of combustion air. The flue gas
composition can therefore be altered without having to resort to a potentially
dangerous mixture upstream of the burner unit 10.
The secondary burner not only allows burning any excess component in the flue
gases from the primary burner, it also allows heating up the burner unit and
any
downstream equipment before the primary burner is switched on.
To adjust the temperature, flow rated or composition of the flue gases fed to
the
hot blast stove, numerous combinations of burners and combustion media are
available due to the innovative design of the present burner unit.
It should be noted that, in the context of the present invention, the
expressions
"high flow rate" and "low flow rate" of the fuel and air feed channels and
auxiliary fuel and air feed channels are relative to each other. The flow rate
or
section size of the feed channels will strongly depend on the combustion media
used. Purely for the purpose of providing an example, the high flow rate, fuel
and air feed channels 32, 34 may have a section in the region of 1500 cm2; and
the low flow rate, auxiliary fuel and air feed channels 64, 66 may have a
section
in the region of 200 cm2.
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A non-exhaustive list of examples for operation modes of the burner unit
according to the present invention is shown in Table 1.
Operation Combustion Combustible Further Further Secondary
mode air fuel combustion combustible burner
air fuel
Typical hot Air Blast --- Coke oven ---
blast stove furnace gas gas
operation
Typical hot Air Blast --- --- Post
blast stove furnace gas combustion
operation burner'
Hot blast --- --- --- --- Heating up
stove burner
heating-up
operation
Hot blast Air --- --- Natural gas ---
stove
temperature
maintenance
operation
Hot blast Air --- --- --- Heat
stove maintenance
temperature burner3
maintenance
operation
Hot blast --- Blast Oxygen --- ---
stove N2 furnace gas
free
operation
Hot blast Flue gas Blast Oxygen Natural gas Post
stove N2 furnace gas combustion
free burner4
operation
post combustion burner using coke oven gas and flue gas from primary burner
2 heating up burner using coke oven gas and air
3 heat maintenance burner using oil and air
4 post combustion burner using blast furnace gas and flue gas from primary
burner
Table 1
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Reference signs
burner unit 50 flame
12 front section 52 socket
14 combustion chamber 54 rear wall
16 rear section 56 outer pipe
18 mixing zone 58 inner pipe
opening 60 annular channel
22 connection flange 61 inner channels
24 refractory material 62 pipe-like elements
26 inner surface 64 auxiliary fuel feed channels
28 circumferential wall 66 auxiliary air feed channels
annular feed arrangement 68 annular fuel feed chamber
32 fuel feed channels 70 fuel inlet
34 air feed channels 72 annular air feed chamber
36 fuel inlet 74 air inlet
38 air inlet 76 auxiliary air feed channel
flames 78 air inlet
42 primary burner 80 port
44 central channel
46 secondary burner
