Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1 2064799
IMPRO'JEMENT IN OR RELATING TO BURNERS
This invention relates to improvements in or relating to
burners more particularly of a type known in the art as a
"Matrix burner".
Matrix burner: are versatile in application and can be
used both in domesi;ic and in industrial plants or
installations. Re=Latively large numbers of these burners may
be employed in industrial furnaces and can be used to burn off
waste gases with the potential of recycling the energy back
into the processing plant.
Therefore, the efficient and continued operation of
burners employed in such conditions is of the utmost
importance because the task of repairing or replacing burners
deployed on such a large scale would be expensive and highly
inconvenient in de7_aying the processing operations of the
plant.
Thus, any improvements in the design of the matrix
burners leading to a more efficient or versatile operation or
extended lifespan are of very considerable importance in this
field. The applicant owns several patents in this field,
including British Patent Specification Nos. 1325443 and
1548388.
C
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With the design of matrix burner as shown in Patent
Specification No. 1548388 problems have been encountered where the
burners have undergone heavy and continued usage for a long period
of time (for example 7 years or so) more particularly where the
burners have been employed in the petrochemical field. These
problems involve the degree of corrosion of the metal of the burner
head, which head comprises two parallel plate portions provided with
a number of apertures for combustion gases. This corrosion has taken
the form of a chemical attack causing the burners to fail. Since the
cost of the burners for a petrochemical plant may be of the order of
~250,000 or so the advantages in providing a longer lasting burner
should be readily apparent.
Therefore, there tends to be a problem with matrix burners in
that corrosion can take place despite the previous work done in the
burner design field and there tend to be additional problems
encountered where such burners may be utilised in a dual fuel, e.g.,
gas/liquid, situation.
Accordingly, it is an object of the present invention to at
least alleviate one or more of the aforementioned, or other,
problems associated with matrix burners or their application.
According to a first aspect of the present invention there is
provided a burner having a head provided with an array or matrix of
combustion air apertures, said burner head having spaced plate
portions defining a fuel supply gallery or passageway to said
apertures, said plate portions including an aperture ring which
closely follows an outer boundary of the burner head, and which is
adjacent to said boundary to thereby prevent or restrict localised
regions of the plate portions, at least near
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said boundary, becoming subject to temperatures which are higher
than any other region of the plate or becoming subject to a
corrosion or deterioration rate higher than any other region of the
plate portions and/or to prevent or restrain substantially anomalous
flow patterns of the fuel supply in the gallery at least around said
aperture ring and adjacent said boundary.
Preferably, the matrix of apertures is configured to prevent or
restrict any anomalous high temperature or high corrosion regions
occurring on the plate portions by giving substantially the same
freedom of access of the fuel supply in the gallery to each of the
apertures. The plate portions may be spaced from one another by
spacers and, accordingly, the aperture matrix may be configured to
allow for substantially even flow characteristics of the fuel supply
through the gallery around said spacers.
Preferably, the aperture ring comprises a series of combustion
air apertures, at least half or the majority of which are spaced at
a distance from said boundary by an amount which is less than or
equal to the spacings between one another.
One embodiment of the burner of the present invention has a head
with circular shaped plate portions and said aperture ring consists
of a circle of apertures spaced closely to one another and close to
said boundary. The apertures in the circular ring are, preferably,
spaced equidistantly from one another and are preferably of circular
form. Preferably each aperture is spaced from the boundary by a
distance not more than two (and preferably not more than three)
times the distance in between each aperture. Preferably, the burner
head has second and third aperture rings arranged radially inwardly
of the first aperture ring and each of the
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second and third aperture rings may consist of a series of circular
apertures. Preferably the third, innermost aperture ring comprises
a series of circular apertures which are arranged concentrically
with the first outermost aperture ring so that each of the apertures
in the innermost ring is radially aligned with respective apertures
in the outermost ring, said innermost and outermost ring apertures
being concentrically aligned with the circular plate portions of the
burner head. The second aperture ring may comprise a series of
circular apertures which are displaced circumferentially relative to
the outer and innermost aperture rings and preferably such that the
aperture configuration results in an array of substantially
triangular shaped sector regions extending around the circumference
of the plate portions with spacers being provided in between the
triangular shaped sectors. It is believed that such an aperture
matrix substantially eliminates anomalous hot spots on the plate
portions and indeed test results have confirmed this and a much more
equal fuel distribution to the apertures is provided. Preferably the
burner is provided with radial ports at said boundary for radial
discharge of the fuel and many other advantageous features of the
burner will be apparent from the following description and drawings.
The radial ports may be spaced equally around said boundary in
between said apertures in the outer ring.
Corrosion problems have occurred with previous designs of
burners as aforementioned and the burner plates are generally made
from an austenitic chromium alloy steel. It has been realised that
at operating temperatures in excess of 500°C, when burning carbon
based gases, corrosion occurs from the inside of the burner plate
portions by carbon from the fuel gas penetrating into the metal
material of the burner plates.
206479.9 .,
The structure of t:he plate metal is granular and the carbon
penetrates into th~= grain boundaries and reacts with the
chromium in the alloy, causing individual grains of the
material to be loo;aened and to eventually drop away from the
metal. Consequently, it has been realized that the degree of
corrosion is greater where the size of the grains is large and
the degree of corrosion could be reduced by using a fine grain
material. The app:Licant presently manufactures burners from a
high nickel/chromium fine grain material reference NSU No.
800800 (referred to as alloy 800).
However, for high temperature applications and in order
to extend the burner-life expectancy the applicant has
realized the import=ance of developing the burner out of
"higher grade" materials (i.e. materials which re less prone
to physical and chemical attack under various operating
condit ions ) .
Therefore, according to a second aspect of the present
invention there is provided a burner having a head with an
array or matrix of apertures for combustion air, and said head
comprising two plate portions defining a gallery or passageway
to said apertures, said plate portions being constructed from
one or more of the following materials:
a. InconelTM 600, NicroferTM 7216, HaynesTM 750
b. Inconel 601, PJicrofer 6023, (UNS 06601)
c. Inconel 617, (UNS 06617)
d. Inconel 625, PJicrofer 6020hM0, Haynes 625 (UNS 06625)
e. Haynes 214
f. Haynes 230
g. Alloy RA 330 (UNS 08330)
and preferably in which the plate portions are
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constructed from one of the following:
1. UNS 06617
2. UNS 06625
3. UNS 08330
The manufacture of the plate portions from any one of the alloys
referred to above should give a more equal fuel flow distribution to
the burner apertures and reduce the temperature. The plate portions
will normally be of 16 gauge metal.
According to a further aspect of the present invention there is
provided a dual fuel burner having a burner head with an array or
matrix of combustion air apertures and plate portions defining a
gallery or passageway therebetween for a main fuel supply to be fed
to said apertures, the arrangement being such that the burner can be
run on the first or main fuel supplied along the gallery to said
apertures and may alternatively be operated on a second fuel mixed
with combustion air supplied through said apertures.
The burner may be operated on a mixture of the first main fuel
and the secondary fuel.
The need for a convenient, efficient dual fuel burner has been
recognised by the Applicant and once again has substantial
applications in the petrochemical field geared to the least wastage
of energy. It may be convenient, for example, to begin the plant
processing on natural gas and as more waste carbon dioxide and
hydrogen is produced the natural gas could be reduced and recycled
carbon dioxide and hydrogen used as a fuel for the burner. Sometimes
processing plants produce oil by-products (Naphthalene) and
therefore, a dual fuel process
CA 02064799 1999-10-18
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which could utilise oil as a second fuel for the burner is also
desirable.
It should also be noted that use of a burner in a dual fuel
capacity should also reduce the corrosion effects already explained
since a large contributory facto to said corrosion is attributed to
the use of carbon based gases, which use would be avoided whilst
running on a secondary fuel such as oil.
In a preferred embodiment of the dual fuel burner the secondary
fuel is introduced into the burner by way of a supply line arranged
within the supply line of the main fuel supply. The secondary fuel
may be oil and accordingly an oil lance may be inserted in the main
fuel supply line toe the burner. Thus the oil lance may have a tip
which extends beyond said plate portions in order to spray fuel oil
above said plate portions for mixing with combustion air drawn
through said apertures for ignition at the burner, preferably by a
spark ignitor. The amount by which the lance tip extends beyond the
burner head is, preferably, adjustable. Preferably, separate
controls are provided for delivery of either or both fuels to the
burner.
Advantageously, the same burner may be employed in a single fuel
situation or in a double fuel situation, an inner pipe (e. g., guide
pipe for the oil lance where applicable) being used for the
secondary supply merely being closed off where the burner is to be
used in a single fuel application only.
An advantage of such a dual fuel system is the production of a
desirable and controllable flame shape which is most important in a
furnace application, e.g. a hydrocarbon cracking process in the
petrochemical
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industry, where, for example, ~500,000 worth of ceramic tube
equipment may be needed to constrain the flame production by the
burners.
Further advantageous features of the dual fuel burner will be
apparent from the following description and drawings.
An embodiment of a matrix burner in accordance with the present
invention and of a dual fuel burner in accordance with the present
invention will now be described by way of example only with
reference to the accompanying simplified drawings in which:
FIGURE 1 is a plan view of a burner head of the matrix burner;
FIGURE 2 is a diametrical section of the burner head shown in
FIGURE 1, and taken on line II-II;
FIGURE 3 shows a part sectional side view of a dual fuel burner
assembly;
FIGURE 4 shows a section view taken on line IV-IV of FIGURE 3;
FIGURES 5 and 6 show views similar to 1 and 2 of a burner
adapted for dual fuel operation; and
FIGURE 7 shows a plan view of an alternative burner head for
dual fuel application.
Referring to FIGURES 1 and 2 of the drawings a matrix burner
head 1, suitable for use in a furnace, or for example a
petrochemical plant, has an upper circular metal plate portion 2
joined to a lower circular metal plate portion 3 at the
circumferential boundary wall 4, for example by welding. Boundary
wall 4 provides an outer boundary of the burner head 1. The upper
and lower plate portions 2 and 3 are spaced apart from one another
by spacers 5 in a generally known manner in order to
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provide a gallery or passageway G in between the plate portions 2
and 3 leading to individual apertures 6a, 7a, 8a, of outer 6, middle
7, and inner 8 aperture rings. In use a gaseous fuel is conveyed
down the central fuel pipe 9 and flows through the gallery G to the
apertures 6a, 7a, 8a where it mixes with combustion air being drawn
up through the centre of said apertures 6a, 7a, 8a providing a
mixture for burning. In this instance, the apertures 6a, 7a and 8a
are of the broached or pierced type in which small holes or ports P
(see FIGURE 1) are provided around the circumference of the
individual apertures 6a, 7a, 8a to allow fuel gas to flow
therethrough into the apertures. The apertures 6a, 7a, 8a are formed
by a downwardly depending tubular portion a of the upper plate 2
snugly overlapping with an upwardly depending tubular portion b of
the lower plate as shown best in FIGURE 2. The present invention is
not confined to the apertures 6a, 7a, 8a being of the broached type
and could instead be of the "annular gap" form in which the gas
escapes from the gallery G into the apertures via an annular gap
left in between the overlapping tube portions a,b of the upper and
lower plates, which overlapping tube portions form the individual
apertures. Both the broached and annular gap type apertures are
known generally. In this embodiment the burner 1 is also provided
with radial ports P' around the circumference or boundary 4 between
the two plate portions 2,3. The radial ports P' are formed on the
upper plate portion and allow a radial discharge of gaseous fuel
around the boundary of the burner head 1.
The outer aperture ring 6 consists of a series (in this case 24)
of apertures 6a of the same size and spaced equiangularly around the
centre of the burner and following the boundary 4 and arranged
closely adjacent thereto. The array of apertures 6a, 7a, 8a, form a
matrix
CA 02064799 1999-10-18
which has been produced in order to seemingly optimise fuel flow
characteristics within the gallery G to the individual apertures,
whilst also taking into account the resistance to flow afforded by
the spacers 5. The aperture matrix is configured in order to
substantially eliminate anomalous hot spots which could ultimately
give rise to corrosion in the burner, as well as to equalise flow
distribution to the apertures 6a, 7a, 8a.
The benefits of this matrix design are considerable and:
a. provides much greater temperature uniformity and energy/release
across the burner is greatly improved,
b. a lower burner heat operating temperature can be achieved under
similar operating conditions with prior art burners, by virtue
of the improved combustion air distribution system of the
burner,
c. areas of high metal content at the periphery of the burner have
been minimized as far as can reasonably be envisaged,
d. a lower burner heat operating temperature combined with
reduction areas of high metal content, more particularly around
the outer periphery of the burner should considerably reduce
corrosion rates and extend the life expectancy of the burner
accordingly,
e. an improved flame profile is provided by this type of burner,
f. general combustion characteristics and performance of the burner
are also improved.
It is envisaged that at least four basic sizes of burner will
be provided namely with diameters of 26 cm, 22.4 cm, 17.7 cm and 14
cm. The thermal output from the burners can, advantageously be
suitably varied and is
CA 02064799 1999-10-18
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largely a function of the gaseous fuels and air pressures available,
burners can be individually designed to meet specific site
requirements.
It is an important feature of the design that lower burner head
operating temperatures achievable may enable manufacture of the
burner to be of a "lower grade" cheaper material, hence reducing
manufacturing costs, where higher operating temperatures are not
required. However, where higher temperature applications are
required or where extended burner life expectancy is of primary
importance it is proposed that the burner will be manufactured from
higher grade materials less prone to physical and chemical attack.
A list of these materials has been given earlier on in the Patent
Specification.
An important aspect of the design is the fuel flow distribution
throughout the gallery G and as previously stated the apertures 6a,
7a, 8a have been developed selectively for the particular burner as
shown with its spacer configuration 5 in order to seemingly optimize
flow characteristics.
It is possible that differently sized apertures could be
provided to the ones as shown and indeed the design may incorporate
two or three or more sets of differently sized apertures. However,
in this particular design the aperture matrix comprises 8
circumferentially spaced triangular sector regions (one of these
regions is outlined by a chain dotted line X) consisting of 6
individual apertures, one aperture Sa being from the innermost ring
8, two apertures 7a being from the middle ring and three apertures
6a being from the outer ring 6. Spacers 5 are provided inbetween the
triangular sectors and alternate from the provision of two spacers
to one spacer on a circumferential path around the burner. The
CA 02064799 1999-10-18
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more equal distribution of fuel flow to the apertures 6a, 7a, 8a
itself brings with it a reduction in temperature of the burner plate
portions 2,3. These type of burners are very versatile and can be
run for example to produce 2 million B.T.U.'s per hour or 100
B.T.U.'s per hour. As shown in this embodiment the apertures 6a are
positioned very close to the boundary line and indeed are closer to
the boundary wall 4 than they are to one another. Each aperture 8a
aligns radially with the centre aperture 6a of the arcuate line of
3 apertures of a particular triangular shaped sector X. The centre
of the upper plate portion 2 may be slightly dished (not shown here)
as is known in this type of burner. This design of burner head 1
seeks to obviate any anomalous flow patterns or resistances to flow
which could substantially affect the equal distribution of fuel to
the individual apertures 6a, 7a, and 8a to thereby provide a more
even temperature distribution and extend the burner life.
FIGURES 3 and 4 show a dual fuel burner assembly 100 for use in
a furnace (not shown). The burner assembly 100 may be utilised to
burn a main, gaseous fuel and/or a secondary fuel in the form of oil
or oil by-products produced by processing plant incorporating a
plurality of such burner assemblies. In this way the efficiency of
the processing plant can be upgraded by the utilisation of the oil
by-products.
The burner assembly 100 has a burner head B which may or may not
be identical or similar to the burner head 1 shown in FIGURES 1 and
2 of this specification. The overall layout of the assembly 100 is
generally known in the provision of a gas inlet to the burner head
which is surrounded by a refractory quarl. As shown in FIGURE 3 the
assembly 100 has a gas inlet 103 leading to a central main fuel
supply delivery tube or pipe 104 positioned
CA 02064799 1999-10-18
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centrally of the burner head B. The main fuel supply passes up this
pipe 104 to the gallery system of the burner head B and to the
matrix of apertures as previously discussed in relation to FIGURES
1 and 2 of the drawings. The assembly 100 further includes an air
inlet 105, a windbox 106 with windbox top plate 107 and generally
cylindrical refractory quarl 108 surrounding the burner head B. As
shown, an oil lance 109 is positioned centrally and coaxially with
the gas supply pipe 104. The oil burner tip 110 has a conical end
which extends beyond the front plate portion f of the burner B and
joins the oil burner station pipe 111 at the other end thereof.
Provision may be made to adjust the position of the oil lance
longitudinally of the supply pipe 104 in order to attempt to
optimise flame profile above the burner head B and the oil lance
will be received in a guide tube . T (not shown in FIGURE 3 - see
FIGURES 5 and 6) running along the length of gas pipe 104. FIGURE 4
shows the location of the U.V. detector mounting tube 112, view port
113 and igniter tube and cap 114, the operation of which should be
readily apparent; 115 (see FIGURE 3) designates the purge interlock
safety valve of the fuel oil lance 109.
In use of the burner assembly 100, a main gaseous fuel supply
is delivered by the gas inlet 103 and flows upwardly (in use)
through the gas pipe 104, through the annular space provided
inbetween the guide tube T and wall of the pipe 104. Since the
assembly 100 incorporates a fuel lance 109 running along the axis of
the burner B the width of the pipe 104 is subsequently greater than
required for single fuel burners because of the physical space taken
up in the pipe 104 by the lance 109. Thus the gaseous fuel is
delivered to the gallery system of the burner head B in a similar
manner as in a single fuel burner and is delivered to the aperture
CA 02064799 1999-10-18
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matrix through the gallery system either in a generally known manner
or in the manner as previously described in relation to FIGURES 1
and 2 of the Specification.
Additionally, or alternatively, a secondary fuel oil is
delivered from the station pipe 111 along the fuel lance 109 to the
oil burner tip 110 which sprays oil above the upper burner plate f
for ignition thereabove by an igniter which is of a form generally
known per se. Thus the burner may run on a main gaseous fuel alone,
or on the oil alone, or alternatively on a mixture of both. The
position of the oil lance 109 can be varied along the length of the
gas supply pipe 104 in order to optimize the flame profile produced
when the burner is operating on both fuels or on oil alone. The
burner head B in this instance is 22.4 ~m rliamatr~r mhc
aforedescribed dual fuel burner allows the shape of the flame and
control of the flame to be determined fairly critically.
FIGURES 5 and 6 show more detailed views of a burner head 1~ of
a dual fuel supply type. In this instance the burner head 1~ has
plate portions 2~,3~ showing the same matrix configuration of
apertures as in FIGURE 1 of this specification. However, the
apertures 6~a, 7~a, 8~a are formed from downwardly depending
portions a' and upwardly depending portions b' which overlap one
another to leave an annular gap g for fuel gas to enter the aperture
6a, 7a, 8a, rather than being provided with ports as in FIGURE 1.
Either design may be used in the dual fuel application. The central
gas supply pipe 104 has a central guide tube T (not shown in FIGURES
3 and 4) for the fuel lance 109. Item C represents a locating collar
for the guide tube T and the pipe 104 is much wider than in prior
art arrangements in order to allow the main gaseous fuel to enter
the gallery G whilst also providing a housing for the oil lance 109.
The burner head
CA 02064799 1999-10-18
aperture matrix 6a, 7a, 8a may be modified to that shown to take
into account the wider pipe 104, for example by omission of the
inner aperture ring 8a. The dual fuel burner could be provided in a
single gaseous fuel application in which case the open end of the
tube T protruding from the burner head 1' would be blocked off. To
assemble the burner head 1 ~ the inlet pipe 104 and guide tube T
comprises a subassembly and the burner head 1~ is screwed to the
pipe 104, after lock nut N is fitted with guide tube T entering
locating collar C. The burner head is screwed down until
approximately 2mm of guide tube protrudes from the upper plate when
it is locked tightly with locking nut N. A circular stabiliser plate
Y is shown positioned on top of the upper plate portion 2.
The dual fuel burner assembly may be provided with any
convenient burner head design and accordingly FIGURE 7 shows a
burner head 1' corresponding more closely with prior art designs of
the applicant. The arrangement of combustion air apertures follows
a general hexagonal shape which is known (and which burner head
design has at least some of the disadvantages outlined at the
beginning of the specification) but the apertures A (shown in chain
dotted lines) which are present in a single fuel application are
omitted in the dual fuel application. The stabilizing plate is
hexagonal and weld lines are shown in this view.
The Applicant has carried out test analysis of a prior art
burner head of hexagonal matrix pattern and a burner head in
accordance with the present invention (circular matrix pattern) in
order to illustrate the dramatic reduction in temperature of the
plate portions near the boundary of the burner head.
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This test analysis is shown in FIGURES 8 to 16 in which:
FIGURE 8 shows a hexagonal matrix burner head and thermocouple
locations in conjunction with a lower view showing graphical data in
relation to the thermocouples;
FIGURES 9 to 11 shown burner performance test results for the
hexagonal burner head shown in FIGURE 8;
FIGURE 12 shows a burner head in accordance with the present
invention (circular matrix) indicating thermocouple positions
identical with those in FIGURE 8 and additionally graphical data in
relation to those thermocouples; and
FIGURES 13 to 15 shown burner performance test results for the
burner head shown in FIGURE 12.
As will be seen from FIGURES 8 to 15 and more particularly from
FIGURES 8 and 12, thermocouples 1 to 4 were located to measure the
temperature occurring in different regions of the plate portions.
Thermocouple 1 was located in the centre of the burner head,
thermocouples 2 and 3 in mid regions of the plate portions with
thermocouple 3 being located at one of the inner spacers and
thermocouple 4 located at the outer boundary region of the plate.
It should be stressed that the burner test results whilst
meaningful in showing the general pattern of temperature
distribution between the prior art burner head design and the burner
head design of the present invention are not identical to operating
conditions in the field. For example, due to the presence of the
refractory quarl as well as other factors, the temperature at the
boundary of the burner head is significantly increased to that shown
in the test results.
WO 91/19942 PCT/GB91/00973
17
Referrin~~ specifically to the graphical data in
FIGURE 12, it: will be seen that after some minutes the
temperature registered by thermocouple 1 has reached the
value of about 800°C (see upper part of trace 1), whilst
the temperature of thermocouple 4 is also at about the
same level i.e. the temperature at the centre of the
burner is in the same order as the temperature at the
boundary. This indicates that in the field the
temperature of the boundary area that will be registered
by thermocouple 4 would be very significantly higher (for
example 150 to 200°C or more higher). The difference
would be enough for the centre region to be emitting
effectively a black heat radiation with the outer
boundaries emitting a dull red radiation. The temperature
measured by thermocouple 2 is the lowest at about 660°C
(see upper part of trace 2).
Comparing this data to the data given in FIGURE 15
shows that 'the temperature at the boundary regions
(measured by thermocouple 4).has dramatically dropped to
about 660°C (aee upper part of trace 4) and there is also
a slightly lower operating temperature at the middle of
the burner which is measured by thermocouple 1. Thus the
temperature at the boundary has been lowered to within
about 30° of the temperature measured by thermocouple 2
and the temperature measured by thermocouple 2 has also
been lowered 1~y about 30° or so.
Thus, ii: can be seen that under like for like
conditions, i~he overall operating temperature of the
burner head has been lowered but most significantly the
temperature has been reduced very significantly at the
boundary regi~~ns so that in the field the temperature of
the middle of the burner and of the boundary will be of
the same order. It should be remembered that even where
the temperature of the boundary regions is the same as
WO 91/19942 PCT/GB91/00973
18
the temperature of the centre of the burner head, the
centre of the burner may in some circumstances not be
subject to an accelerated corrosion rate because of the
speed of gas flow through to the apertures, whereas the
corrosion rate is accelerated abnormally at elevated
temperatures where there is a lingering presence of the
gas i.e. particularly inbetween the hexagonal matrix
configuration termination and the boundary of the burner
(i.e. in the segmental regions of the hexagonal shape
burner head).
Furthermore, in comparing the burner performance
test results it will be seen that improved combustion
characteristics are apparent from the burner head in
accordance with the present. invention, this being
indicated by the generally lower carbon monoxide and
higher nitrous-oxide emissions at 1~, 2~ and 3g oxygen at
comparable furnace temperatures (flue temperatures).
?p Thus, it can be seen that even under the test
conditions the temperature of the boundary region is not
substantially higher than any other region of the plate
portion (as shown in FIGURE 12 the temperature of the
boundary region is only approximately 30° higher than the
region of the plate detected by thermocouple 2).
It has been found by way of experiment on prior art
burner heads having a matrix configuration as shown in
FIGURE 7 of this specification that high temperatures)
may exist over portions of the burner head top plates
during operation. During tests on burners operating on a
furnace at approximately 1000°C in flue it has been
observed that temperatures may range from 800-850°C in
the central regions of the plate and at the periphery of
the burner in areas of higher metal content. In the
field, often temperatures result in the majority of the
WO 91/19942 PGT/GB91/00973
19
20~1~~J
burner emitting a black heat radiation whils~: dull red
heat radiation is emitted from areas near the periphery,
said areas being defined between the periphery of the
burner and th.e aperture matrix ( refer FIGURE 7 ) . It is
at temperatures of 700°C or above that the corrosion rate
of the plate portions, subjected to that heat, is very
significantly accelerated (particularly where gas flow is
restricted) i..e. decarbonisation of the plate material
may be dramatically increased.
Test experiments with burner heads of the present
invention (e,.g. see FIGURE 1) illustrate significant
temperature variation between boundary regions of the
plate and middle or central regions i.e. a very
significant reduction in temperature of ~ the boundary
regions (reduction of approximately 150°C). This
indicates that the boundary temperature in the field will
be substantially lower than with the prior art hexagonal
burner configuration. This is due to improved gas and
air cooling achieved by the burner in accordance with the
present invention. Thus, the matrix array adopted in
accordance with the present invention effectively
prevents any part of the burner plate reaching an
elevated temperature which would result in excess
corrosion when compared with any other area of the plate.
The burner of hexagonal matrix design and the
circular matrix burner were tested under identical
conditions on the same test furnace and conditions were
3p maintained under very close tolerances throughout the
duration of the tests.
To summarise as will be seen from the "Burner
Performance Tc~st Data", major benefits have been obtained
from the burner head in accordance with the present
invention as c;mbodied in FIGURE 1 and FIGURE 12, namely:-
WO 91/19942 PCT/GB91/00973
2C
1. Substantially improved air and gas flow patterns and
mixing characteristics as a direct result of the
redesign and distribution of the matrix system
resulting in a lower temperature operating burner
head.
2. Areas of higher metal content namely at the
periphery of the prior art burner based on a
hexagonal design matrix have been eliminated which,
combined with lower temperatures of operation,
dramatically reduce potential corrosion of the
burner head and by virtue of this can considerably
extend life expectancy.
3. Due to the symmetrical arrangement of the circular
matrix design the flame shape has also been improved
resulting in a shorter compact and- more precise
flame profile (flame profile is approximately 15$
smaller). This new compact/precise flame profile
provides clear advantages in certain process
applications.
4~ Combustion characteristics have also been
considerably enhanced by virtue of the improved
intimate mixing patterns of the air and gas mediums,
resulting in slightly higher outputs being achieved
from the same size burner head combined with higher
turn down ratios before instability occurs. This
improved combustion performance is clearly indicated
on the burner performance test results illustrated.
5. The redistribution of burner ports in accordance
with FIGURES 1 and 12 facilitates a larger centre to
the burner on a "like for like" basis. This larger
area at the centre of the burner provides an
additional benefit in the formation of a "Dual-Fuel"
version of the burner in which an oil lance is
located straight through the centre of the burner
27 via a sealed guide tube (see FIGURE S).
WO 91/19942 PCT/GB91/00973
21
6. As outlined in 5 above, the design of the circular
matrix burner facilitates a larger area free of
discharge ports at the centre of the burner enabling
a fuel oil lance to be located at this point . The
gas supply pipe diameter can be increased without
adversely affecting the gas distribution/flow to
individual discharge ports. This is not the case
with then original hexagonal design matrix burner
head.
7. The oil lance providing the second fuel source is
also centrally and symmetrically located relative to
the main matrix system and thereby enhances the
overall symmetrical/radial arrangement of the burner
assembly. The less combustible fuel is located at
the centre of the flame and therefore affords
g= ~ter flame stability.
8. The Dual.-Fuel burner is designed to enable either
gaseous or liquid fuels to be burnt together or
independently in varying percentages.
g. The fuel oil lance can also be withdrawn or
relocated whilst the gas burner remains in
operation .
The central and symmetrical location of these two
burner elements combined with adjustability in itself
seems to provide major improvement.
In the burner according to the present invention,
gas in the burner head develops pressure as its velocity
reduced. As the gas glows outwards, radially, its
velocity reduces due to an expanding flow area. The flow
through the ~~as ports is proportional to the pressure
developed at 'the port. Hence to achieve even flow of gas
per port, all ports must be at the same position relative
to the source of supply. With a single ring of ports gas
flow will be wen from port to port.
WO 91/19942 ~ PGT/GB91/00973
22
If a second ring of ports is added in order to
increase the gas/air flow in and through the burner head,
then the geometry of the inner ring of ports also becomes
important.
As a result of detailed test and development work,
the spacing between these ports (which creates the
gallery) has been carefully selected to allow the correct
flow of gas past the inner rings of ports for the supply
to the outer ring. This proportioning of gas flow
applies at full fire (maximum gas flow). At lower gas
flows, the gallery offers less resistance and hence the
gas is transmitted to the outer areas of the burner head
and discharged at the outer ports.
The hexagonal matrix port spacing does not totally
meet this criteria as port positions vary radially and
the port spacing (gallery size) is not optimum for the
sharing of gas between inner and outer ports.
The burner head in accordance with the present
invention has many beneficial aspects on burner
performance and application, a number of which are listed
below:-
1. The optimised flow arrangement provides increased
burner output for a given burner size.
2. The flame profile (gases released) across the burner
head is uniform resulting in a shorter more compact
flame thus widening its field of application.
3. Under low fire conditions, the design achieves:-
3.1. Improved and more intimate mixing with
combustion air.
3.2 Gas flow is maintained to the outside of the
burner head providing "gas cooling" and
avoiding the development of "hot spots" and
WO 91/19942 PCT/GB91/00973
23
re:aultant corrosion.
3.3. Higher turn down ratio as the concentration of
ra:~ at the outer ports permits smaller gas
flows before flame instability occurs.
4. Substantially reduced potential corrosion.
On the burner head of hexagonal matrix arrangement,
the gas flow does not properly reach and hence cool
the outer periphery of the burner head, particularly
in areas of higher metal content. This can result
in "hot spots" that lead to metal failure due to
excessive carbonisation. The burner head avoids
this by providing gas flow and hence "gas cooling"
to all p~~rts of the burner head.
5. Combustion characteristics are improved as a direct
result of a better and more even air/gas mixing
system ( reference is made to the burner performance
test results).
6. Increased turn down ratios, the circular matrix
burner also exhibits greater flame stability under
all oper2:ting conditions .
7. The radial arrangement of discharge ports gives more
space/are:a at the centre of the burner. This allows
the gas supply pipe diameter to be increased without
affecting the gas distribution within the burner
gallery system. Gas being evenly distributed to
each discharge port. This is not possible on the
burner head of hexagonal matrix design.
This larger area at the centre of the burner enables
jp the production of a "Dual-Fuel" burner head, in
which an oil lance can be fitted through its centre.
Hoth gaseous and liquid fuels can be burnt either
separately or together in varying percentages in a
uniform and symmetrical formation. The less
combustible fuel (ie oil being placed at the centre
of the burner surrounded by an air and gaseous
WO 91/19942 PGT/GB91/00973
24
medium) thus ensuring efficient combustion.
Still further according to the present invention
there is provided a burner element as claimed in Claim 1
of U.K. Patent Specification No. 1325443 in which a ring
of said combustion air apertures closely follows an outer
boundary of the burner head.
It is to be understood that the scope of the present
invention is not to be unduly limited to the particular
choice of terminology and that a specific term may be
replaced by any equivalent or generic term where
sensible. Further it is to be understood that individual
features, methods, uses or functions related to the
burner head or parts of the burner assembly might be
individually patentably inventive. The singular may
include the plural where sensible. Additionally, any
range mentioned herein for any variable or parameter
shall be taken to include a disclosure of any derivable
sub-range within that range or of any particular value of
the variable or parameter arranged within, or at an end
of, the range of sub-range.
30
