U.S. patent application number 13/505149 was filed with the patent office on 2012-08-30 for method of combusting particulate solid fuel with a burner.
This patent application is currently assigned to L'Air Liquide Societe Anonyme Pour L'Etude Et L'Exploitation Des Procedes Georges Claude. Invention is credited to Brenice Belasse, Jacques Mulon, Faustine Panier, Xavier Paubel, Remi Tsiava.
Application Number | 20120216730 13/505149 |
Document ID | / |
Family ID | 42040366 |
Filed Date | 2012-08-30 |
United States Patent
Application |
20120216730 |
Kind Code |
A1 |
Belasse; Brenice ; et
al. |
August 30, 2012 |
Method of Combusting Particulate Solid Fuel with a Burner
Abstract
A method of combining oxygen and fuel in a burner to produce a
flame whereby an outer oxidant flow is discharged through an outer
oxidant outlet of the burner; a flow of conveyor-gas propelled
particulate solid fuel is discharged with a fuel discharge velocity
through a fuel outlet of the burner arranged coaxially with respect
to the outer oxidant outlet and spaced radially inwardly therefrom;
and a first inner oxidant flow is discharged with an inner oxidant
discharge velocity, which differs from the fuel discharge velocity,
through an inner oxidant end outlet of the burner arranged
coaxially with respect to said fuel outlet and spaced radially
inwardly therefrom; and whereby a second inner oxidant flow, having
a higher oxygen concentration than the conveyor gas is injected
into the fuel-conducting passage and mixed with the fuel flow
inside said fuel-conducting passage so as to obtain, upstream of
the fuel outlet and upstream of the inner oxidant end outlet, an
oxygen-enriched conveyor-gas propelled particulate solid fuel flow
having an oxygen content of at least 21% vol O.sub.2.
Inventors: |
Belasse; Brenice;
(Maintenon, FR) ; Mulon; Jacques; (Massy, FR)
; Panier; Faustine; (Jouy En Josas, FR) ; Paubel;
Xavier; (Chatenay Malabry, FR) ; Tsiava; Remi;
(Saint Germain-Les-Corbell, FR) |
Assignee: |
L'Air Liquide Societe Anonyme Pour
L'Etude Et L'Exploitation Des Procedes Georges Claude
Paris
FR
|
Family ID: |
42040366 |
Appl. No.: |
13/505149 |
Filed: |
October 29, 2010 |
PCT Filed: |
October 29, 2010 |
PCT NO: |
PCT/EP2010/066500 |
371 Date: |
April 30, 2012 |
Current U.S.
Class: |
110/347 ;
431/12 |
Current CPC
Class: |
F23D 1/00 20130101; Y02E
20/344 20130101; F23L 7/007 20130101; Y02E 20/34 20130101 |
Class at
Publication: |
110/347 ;
431/12 |
International
Class: |
F23L 7/00 20060101
F23L007/00; F23D 1/00 20060101 F23D001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 30, 2009 |
EP |
09174635.4 |
Claims
1-15. (canceled)
16. A method of combining oxygen and fuel in a burner to produce a
flame, said method comprising: supplying an outer flow of
oxygen-containing oxidant to an outer oxidant-conducting passage of
the burner, conducting said outer oxidant flow through said outer
oxidant-conducting passage and discharging said outer oxidant flow
with an outer oxidant discharge velocity from said outer
oxidant-conducting passage through an outer oxidant outlet of the
burner, supplying a fuel flow to a fuel-conducting passage of the
burner, conducting said fuel flow through said fuel-conducting
passage and discharging said fuel flow with a fuel discharge
velocity from said fuel-conducting passage through a fuel outlet of
the burner arranged coaxially with respect to the outer oxidant
outlet and spaced radially inwardly therefrom, supplying a first
inner flow of oxygen-containing oxidant to an inner
oxidant-conducting passage of the burner, conducting said first
inner oxidant flow through said inner oxidant-conducting passage
and discharging said first inner oxidant flow with an inner oxidant
discharge velocity from said inner oxidant-conducting passage
through an inner oxidant end outlet of the burner arranged
coaxially with respect to said fuel outlet and spaced radially
inwardly therefrom, characterized in that: the fuel flow is a flow
of conveyor-gas propelled particulate solid fuel, a second inner
oxidant flow, having a higher oxygen concentration than the
conveyor gas, is supplied to the burner and is injected into the
fuel-conducting passage and mixed with the fuel flow inside said
fuel-conducting passage so as to obtain, upstream of the fuel
outlet and upstream of the inner oxidant end outlet, an
oxygen-enriched conveyor-gas propelled particulate solid fuel flow
having an oxygen content of at least 21% vol O.sub.2, the fuel
discharge velocity differs from the inner oxidant discharge
velocity so as to promote mixing between the fuel flow and the
inner oxidant flow downstream of the inner oxidant end outlet.
17. The method of claim 16, whereby, at the fuel outlet, the
oxygen-enriched conveyor gas has an oxygen content of at least 28%
vol O.sub.2, preferably of at least 32% vol O.sub.2.
18. The method of claim 16, wherein each of said first and second
inner oxidant flows has an oxygen content of at least 50% vol
O.sub.2, preferably of at least 80% vol O.sub.2 and more preferably
of at least 90% vol O.sub.2.
19. The method of claim 16, wherein the outer oxidant flow is an
air flow.
20. The method of claim 16, wherein the outer oxidant flow has an
oxygen content of at least 50% vol O.sub.2, preferably of at least
80% vol O.sub.2 and more preferably of at least 90% vol
O.sub.2.
21. The method of claim 16, whereby the conveyor gas is air.
22. The method of claim 16, whereby the conveyor gas contains
combustion effluent gas, steam and/or CO.sub.2.
23. The method of claim 16, whereby the particulate solid fuel is
selected from pulverized coal, pet coke, particulate biomass and
mixtures thereof.
24. The method of claim 16, whereby the second inner oxidant flow
is injected into the fuel-conducting passage at multiple points of
injection along the length of the fuel-conducting passage of the
burner.
25. The method of claim 16, wherein the fuel flow is mixed with the
first inner oxidant flow before being mixed the said outer oxidant
flow.
26. The method of claim 16, wherein at least 35%, preferably at
least 50% and more preferably at least 65% of the total oxygen
supply to the burner is supplied to the burner through the outer
oxidant flow.
27. The method of claim 16, wherein the first inner oxidant
discharge velocity is equal to or greater than the outer oxidant
discharge velocity.
28. The method of claim 16 to produce heat in a combustion zone of
a furnace.
29. The method of claim 28, wherein the furnace is select from the
group consisting of: tunnel kilns and furnaces, passage kilns,
boilers, rotary kilns and furnaces and tunnel furnaces.
30. The method of claim 28 in the production of hydraulically
setting binder.
Description
[0001] The present invention relates to an improved method of
combusting particulate solid fuel, such as pulverized coal.
[0002] From the applicant's earlier patent application
EP-A-0763692, it is known to burn gaseous fuel in an oxy-fuel
burner, whereby: [0003] an outer oxidant flow is conducted through
an outer oxidant-conducting passage and discharged through an outer
oxidant outlet; [0004] a gaseous fuel flow is conducted through a
fuel-conducting passage and is discharged through a fuel outlet
arranged coaxially with respect to the outer oxidant outlet and
spaced radially inwardly therefrom; and [0005] an inner oxidant
flow is conducted through an inner oxidant-conducting passage and
is discharged through an inner oxidant outlet arranged coaxially
with respect to the fuel outlet and spaced radially inwardly
therefrom, whereby each of the outer and inner oxidant flows
preferably contains at least 80% oxygen.
[0006] This known method as developed by the applicant enables
various characteristics of the flame to be effectively controlled
by changing the relative flow rates of the gaseous fuel and oxidant
flows. For example, by decreasing the inner oxidant flow, the
length and luminosity of the flame can be increased, and the flame
momentum can be decreased without any mechanical modification of
the burner. An important advantage of said method is that it is
possible to maintain an optimum flame length when varying the
firing rate of the burner. Furthermore, the control of the relative
flow rates can be used to change the luminosity of the flame. These
properties make this known method for combusting gaseous fuel
highly desirable.
[0007] However, coal is more abundantly available than gaseous
fuel.
[0008] It would therefore be desirable to provide a method having
advantageous properties similar to those of the known process, but
which is applicable to the combustion of a solid fuel such as coal
at an industrial level.
[0009] It is a goal of the present invention to provide such a
method.
[0010] It is known in the art to supply coal for combustion to a
burner in the form of conveyor-gas propelled pulverized coal. This
enables the particulate solid fuel to be supplied to the burner and
from the burner to the combustion zone in a manner similar to the
supply of gaseous fuel.
[0011] Nevertheless, tests conducted by the applicant with
different known conveyor-gas propelled particulate solid fuels have
shown that the method known from EP-A-0763692 is not as such
suitable for the combustion of conveyor-gas propelled particulate
solid fuel. It is speculated that this is due to the fundamental
differences between the mechanism of combusting gaseous fuels and
the multi-step mechanism of combusting solid fuels, which includes,
for example, a devolatilisation step. In particular, the phenomena
observed by the applicant during these tests were incomplete fuel
combustion, flame detachment and flame instability, all of which
are highly detrimental to the efficiency of industrial combustion
processes.
[0012] It is a further goal of the present invention to provide a
method for combusting conveyor-gas propelled particulate solid fuel
by means of a burner, having similar advantages as those obtained
with the method according to EP-A-0763692, and whereby the observed
problems of incomplete combustion, flame instability and flame
detachment can be overcome.
[0013] In accordance with the present method, there is provided a
new method of combining oxygen and conveyor-gas propelled
particulate solid fuel in a burner to produce a flame. The method
comprises the steps of: [0014] supplying an outer flow of
oxygen-containing oxidant to an outer oxidant-conducting passage of
the burner, conducting said outer oxidant flow through said outer
oxidant-conducting passage and discharging said outer oxidant flow
from said outer oxidant-conducting passage through an outer oxidant
outlet of the burner, [0015] supplying a fuel flow to a
fuel-conducting passage of the burner, conducting said fuel flow
through said fuel-conducting passage and discharging said fuel flow
with a fuel discharge velocity from said fuel-conducting passage
through a fuel outlet arranged of the burner coaxially with respect
to said outer oxidant outlet and spaced radially inwardly
therefrom, and [0016] supplying a first inner flow of
oxygen-containing oxidant to an inner oxidant-conducting passage of
the burner, conducting said first inner oxidant flow through said
inner oxidant-conducting passage and discharging said first inner
oxidant flow with an inner oxidant discharge velocity from said
inner oxidant-conducting passage through an inner oxidant end
outlet of the burner arranged coaxially with respect to
[0017] said fuel outlet and spaced radially inwardly therefrom, the
fuel flow being a flow of conveyor-gas propelled particulate solid
fuel.
[0018] It is a specific characteristic of the present invention
that a second inner oxidant flow is supplied to the burner. Said
second inner oxidant flow, which has a higher oxygen concentration
than the conveyor gas, is injected into the fuel-conducting passage
and is thus mixed with the fuel flow inside said fuel-conducting
passage so as to obtain, upstream of the fuel outlet and upstream
of the inner oxidant end outlet, an oxygen-enriched conveyor-gas
propelled particulate solid fuel flow having an oxygen content of
at least 21% vol O.sub.2.
[0019] It is a further aspect of the invention, that the fuel flow,
in the form of the oxygen-enriched conveyor-gas propelled
particulate solid fuel flow, is discharged from the fuel-conducting
passage with a fuel discharge velocity which differs from the inner
oxidant discharge velocity with which the first inner oxidant flow
is discharged from the inner oxidant-conducting passage so as to
promote mixing between the fuel flow and the first inner oxidant
flow downstream of the inner oxidant end outlet.
[0020] Preferably, the second inner oxidant flow is injected into
the fuel-conducting passage so as to obtain, upstream of the fuel
outlet and upstream of the inner oxidant end outlet, an
oxygen-enriched conveyor-gas propelled particulate solid fuel flow
having an oxygen content of at least 28% vol, and more preferably
of at least 32% vol. Thereto, the second inner oxidant flow
advantageously has an oxygen content of at least 50% vol O.sub.2,
preferably of at least 80% vol O.sub.2 and more preferably of at
least 90% vol O.sub.2. Usefully, both the first and second inner
oxidant flows have an oxygen content of at least 50% vol O.sub.2,
preferably of at least 80% vol O.sub.2 and more preferably of at
least 90% vol O.sub.2. On a practical level, it is interesting for
the first and second inner oxidant flows to have the same oxidant
content, in which case they can easily be supplied by a single
oxidant source.
[0021] The outer oxidant flow may have the same oxidant content as
one or both of the first and second inner oxidant flows or may have
a different oxidant content. The oxidant content of the outer
oxidant flow may be lower than the oxidant content of the first and
second inner oxidant flows. The outer oxidant may in particular be
air or synthetic air obtained by mixing oxygen with a gas which is
generally inert to combustion. Such synthetic air advantageously
contains a mixture of oxygen and one or more of combustion gases
(i.e. combustion fumes), CO.sub.2 and water vapour and can, for
example, have an oxygen content of about 21% vol O.sub.2. When an
outer oxidant flow with a lower oxygen content, e.g. an oxygen
content of about 21% vol O.sub.2, such as air, is used, a more
diffuse flame and larger volume of combustion gases are obtained,
as may be advantageous in some industrial combustion processes.
When, on the other hand, an outer oxidant flow with a higher oxygen
content is used, such as an outer oxidant having an oxygen content
of at least 50% vol O.sub.2, of at least 80% vol O.sub.2, or even
of at least 90% vol O.sub.2, a more intense flame and smaller
volumes of combustion gases are obtained, which may be preferable
for other industrial combustion processes. It also enables lower
NOx emissions. In particular, the outer, the first inner and the
second inner oxidant flows may all have the same oxygen content, in
which case they may be supplied by a single oxidant source.
[0022] The conveyor gas, which propels the particulate solid fuel
to and through the fuel-conducting passage may be air. The conveyor
gas may also be or contain combustion gas, CO.sub.2 and/or water
vapour. It will be understood that, when the conveyor gas has an
oxygen content of 21% vol O.sub.2, the oxygen-enriched conveyor-gas
propelled particulate solid fuel flow will have an oxygen content
higher than 21% vol O.sub.2, which is generally preferred. High
oxygen contents in the conveyor gas upstream of the fuel-conducting
passage of the burner are to be avoided, in view of the risks of
premature ignition and explosion.
[0023] The method of the invention is useful for a wide range of
particulate solid fuels, including pulverized coal, pet coke,
particulate biomass and mixtures thereof. It is particularly useful
for the combustion of pulverized coal, including low-grade
pulverized coal which has been shown to be difficult to combust
efficiently with known particulate fuel burners.
[0024] The burner used in the method of the invention
advantageously comprises a burner block with a through passage into
which the outer oxidant-conducting passage, the fuel-conducting
passage and the inner oxidant-conducting passage are mounted. The
outlets of the respective gas conducting passages (the inner
oxidant-conducting passage, the fuel-conducting passage and the
outer oxidant-conducting passage) are then preferably set back from
the outlet opening of the through passage in the burner block,
which outlet faces the combustion chamber of the furnace.
[0025] According to a preferred embodiment of the present
invention, the second inner oxidant flow is injected into the
fuel-conducting passage at multiple points of injection along the
length of the fuel-conducting passage. In this manner, the
conveyor-gas propelled particulate solid fuel flow is progressively
enriched with oxygen towards the fuel outlet. This embodiment
presents a number of advantages such as a lower risk of premature
ignition or explosion. Multiple-point injection of the second inner
oxidant flow into the fuel-conducting passage also lowers the risk
of inhomogeneous distribution of the particulate solid fuel in the
conveyor gas, such as particle settling, roping, etc. A
particularly suited burner for use in the present invention is
described in European patent application 09174622.2 filed on 30
Oct. 2009 and incorporated herein by reference, more specifically
the embodiments of said burner with a central oxygen lance. The
present invention therefore also relates to the use of such a
burner in the present method.
[0026] Oxygen enrichments of the conveyor-gas propelled particulate
solid fuel flows up to an oxygen content of 35% vol O.sub.2 and of
60% vol O.sub.2 and even more were achieved with the method
according to the invention without premature ignition or explosion.
In practice, the upper limit for the oxygen enrichment of the
conveyor-gas propelled particulate solid fuel flow is determined by
the properties, and in particular the flammability, of the
particulate solid fuel and, to a lesser extent, by the properties
of the conveyor gas. In practice, said oxygen content may for
example reach levels of upto 60% vol, preferably upto 80% vol.
[0027] The fuel flow, in the form of the oxygen-enriched
conveyor-gas propelled particulate solid fuel flow, is preferably
mixed with the first inner oxidant flow before being mixed with
said outer oxidant flow. This can be achieved by having the inner
oxidant end outlet upstream of the fuel outlet. In this manner
increased flame stability and attachment is achieved. The
combustion is then a staged combustion, with the first inner
oxidant flow acting as a primary oxidant flow and the outer oxidant
flow acting as a secondary oxidant flow.
[0028] The total oxygen supply to the burner typically corresponds
to the stoichiometrically required amount of combustion oxygen or a
minor excess thereof (for example, a total oxygen supply of upto
115% of the stoichiometrically required amount).
[0029] The total oxygen supply to the burner may also be less than
the stoichiometrically required amount of combustion oxygen, in
particular when the method includes a separate supply of additional
oxygen, which is injected separately from the burner.
[0030] The total supply of oxygen to the burner is the sum of the
oxygen supplied through the outer oxidant flow and through the
first and second inner oxidant flows, as well as any oxygen that
may be supplied as part of the conveyor gas, for example when the
conveyor gas is air. According to a useful embodiment, at least 35%
of the total oxygen supply to the burner is supplied through the
outer oxidant flow, preferably at least 50% and more preferably at
least 60%.
[0031] The sum of the oxygen supplied through the first and second
inner oxidant flows usefully corresponds to at least 22% of the
total oxygen supply to the burner, preferably at least 25%, and not
more than 65%, preferably not more than 50%.
[0032] Similarly, the sum of the oxygen supplied through the first
and second inner oxidant flows is preferably at least 22% and more
preferably at least 25% of the stoichiometrically required amount
of oxygen, and not more than 65%, preferably not more than 50%.
[0033] The first inner oxidant discharge velocity can
advantageously be equal to or greater than the outer oxidant
discharge velocity, and is preferably in the range of from about 10
to 200 m/s. The fuel discharge velocity can notably be in the range
of from 10 to 80 m/s, whereas the outer oxidant discharge velocity
is suitably in the range of 10 to 50 m/s. It is, however, a
particular advantage of the present invention, that efficient
combustion of particulate solid fuel can be achieved at fuel
discharge velocities as low as 5 m/s. Consequently, the present
invention also includes methods, as described above, for combining
oxygen and fuel in a burner to produce a flame, whereby the fuel
discharge velocity is within the range of 5 to 80 m/s, preferably
between from 5 to 40 m/s and more preferably from 5 to 25 m/s.
[0034] According to a preferred embodiment of the present
invention, the outer oxidant flow, the fuel flow and the inner
oxidant flow are discharged through respectively the outer oxidant
outlet, the fuel outlet and the inner oxidant end outlet into a
wider precombustion section upstream of the combustion zone of the
furnace. This provides for an improved stability and/or attachment
of the flame. The wider precombustion section can be integrated in
the burner block of the burner. Alternatively, the precombustion
section can be integrated in a wall of the combustion chamber of
the furnace when the burner is mounted in said wall in a recessed
position with respect to said combustion chamber. The length to
diameter ratio of said precombustion section is preferably between
0.6 and 1.0, more preferably between 0.7 and 0.9.
[0035] The present invention also relates to the use of the method
to produce heat in a combustion zone of the furnace, whereby the
furnace can in particular be a tunnel kiln or furnace, a passage
kiln, a boiler, a rotary kiln or furnace or a tunnel furnace, the
particulate solid fuel preferably being preferably pulverized
coal.
[0036] The method of the invention can in particular be
advantageously used in a furnace for the production of
hydraulically setting binder, such as cement lime or plaster.
[0037] The invention is illustrated in the example hereafter,
reference being made to FIGS. 1 to 4, whereby:
[0038] FIG. 1 is a schematic representation of a cross-section of a
burner suitable for use in the invention,
[0039] FIG. 2 is a schematic representation of a cross section of
the injector assembly thereof, and
[0040] FIGS. 3 and 4 are schematic representations in cross section
of the type of flame obtained with said burner in accordance with
the example.
EXAMPLE
[0041] Tests were conducted with different ratios of first to
second inner oxidant flows.
[0042] A particulate solid fuel burner with a central oxygen lance
as described in European patent application 09174622.2 filed on 30
Oct. 2009was mounted in the side wall of a combustion furnace and
illustrated in FIGS. 1 and 2.
[0043] The illustrated burner comprises a burner block 100 and an
injector assembly 200. The burner block 100 has an inlet face 110
and an outlet face 120. The block further presents an injector
passage 130 extending through the burner block from the inlet face
110 to the outlet face 120.
[0044] The injector passage 130 has a passage inlet 131 in the
inlet face 110 and a passage outlet 132 in the outlet face 120.
[0045] In use, the burner block 100 is mounted or incorporated in
the walls of a combustion chamber, so that the outlet face 120
faces the combustion zone inside the combustion chamber whereas the
inlet face 110 faces outwards of the furnace and is generally
accessible from outside the combustion chamber for burner control,
maintenance and repair.
[0046] The burner block 100 is made of refractory material.
[0047] In the illustrated embodiment, the injector passage 130
comprises a wider precombustion section 135 in the vicinity of the
passage outlet 132.
[0048] In the illustrated embodiment, the burner block 100 is an
assembly of two parts of refractory material 136 and 137. Inlet
face 110 comprises several facets 110a, 110b and 110c. The length
of the precombustion section (in longitudinal direction D1) is
determined by the relative position of the two parts 136, 137 of
refractory material.
[0049] The injector assembly 200 comprises an inner oxygen supply
pipe 210, a fuel injector 220 and an oxygen injector 230.
[0050] The downstream ends 211, 221 and 231 of respectively the
inner oxidant supply pipe 210, the fuel injector 220 and the
oxidant injector 230 are all positioned within the injector passage
130 of the burner block 100. Fuel injector 220 has a fuel injection
nozzle 222 at its downstream end 221 and surrounds the inner
oxidant supply pipe 210 at least in the vicinity of the downstream
end 211 of said inner oxidant supply pipe so as to create a flow of
particulate solid fuel propelled by a conveyor gas around the inner
oxygen supply pipe 210 and directed towards the passage outlet 132
for injection therefrom into the combustion zone.
[0051] In the illustrated embodiment fuel injection nozzle 222 is a
separate piece mounted on the downstream end 221 of the fuel
injector 220.
[0052] A swirler 229 is mounted in fuel injector 220 near its
downstream end 221. Said swirler 229 surrounds the inner oxidant
supply pipe 210.
[0053] Oxidant injector 230 has an outer oxidant nozzle 232 at its
downstream end 231 for the injection of the outer oxidant. The
oxidant injector 230 surrounds the fuel injector 220, at least in
the vicinity of the downstream end 231 of the oxidant injector
230.
[0054] In use, the oxidant injector 230 thus provides a flow of
outer oxidant around the fuel injector 220 and towards the passage
outlet 132 for injection therefrom into the combustion zone.
[0055] In the illustrated embodiment, the downstream end 231 of the
oxidant injector 230 is positioned further away from the passage
outlet 132 than the downstream end 211 and 221 of respectively the
inner oxidant supply pipe 210 and the fuel injector 220.
[0056] In the vicinity of its downstream end 211, the inner oxidant
supply pipe 210 is positioned centrally within fuel injector
220.
[0057] A number of lateral inner oxidant nozzles 212 are mounted on
the lateral surface of inner oxidant supply pipe 210, by means of
perforations 215 in said lateral surface. These lateral inner
oxidant nozzles and the corresponding perforations 215 are
positioned at different distances from the downstream end 211 of
the inner oxidant supply pipe 210.
[0058] In use, these lateral second inner oxidant nozzles 212
inject second inner oxidant into the fuel injector body thereby
progressively enriching the conveyor gas as it projects the
particulate solid fuel towards the fuel injection nozzle 222 and
the passage outlet 132.
[0059] The lateral inner oxidant nozzles 212 have an injection
opening orientated so as to inject second inner oxidant into fuel
injector 220 with an injection direction towards the passage outlet
132, substantially tangential to the lateral surface of the oxygen
supply pipe and forming an angle .alpha. with the longitudinal
direction D1 of the injector passage 130.
[0060] In the illustrated embodiment, the inner oxidant supply pipe
210 further comprises a central oxidant lance 213 which terminates
in a terminal primary oxidant nozzle 216.
[0061] The terminal nozzle 216 of the central oxidant lance 213
injects first inner oxidant in the longitudinal direction D1 of the
injector passage towards the passage outlet.
[0062] An annular passage 214, surrounding the central oxidant
lance 213 is formed between the oxidant lance and the lateral
surface of the inner oxidant supply pipe 210, the lateral inner
oxidant nozzles 212 being in fluid communication with said annular
passage 214 via perforations 215.
[0063] The fuel injector 220 is in fluid connection with a fuel
supply line comprising an elbow 223 upstream of the fuel injector
220. Branch pipe 224 is mounted on the fuel supply line at said
elbow 223 and extends in line with the fuel injector 220.
[0064] Inner oxidant supply pipe 210 extends from said branch pipe
224 into the fuel injector 220.
[0065] Oxidant distributor 240 is positioned at the upstream end of
the inner oxidant supply pipe 210. The oxidant distributor 240
comprises an inlet chamber 241 and two outlet chambers 242, 243. In
use, the inlet chamber 241 is connected to a source of inner
oxidant via inlet opening 246. The first outlet chamber 242 is in
fluid connection with the surrounding annular passage 214 of the
inner oxidant supply pipe 210. The second outlet chamber 243 is in
fluid connection with the central oxidant lance 213. The inlet
chamber 241 communicates with the first outlet chamber 242 via
first passage 247. The inlet chamber 241 communicates with the
second outlet chamber 243 via second passage 248. The oxygen
distributor 240 further comprises first and second means 247a and
248a for restricting the flow of inner oxidant through respectively
the first and second passage 247 and 248 into respectively the
first and second outlet chamber 242 and 243 and consequently for
restricting the flow of inner oxidant to respectively the
surrounding annular passage 214 and the central oxygen lance 213.
Flow restriction can in particular be achieved by manually or
automatically restricting the free cross section area of the first,
respectively second passage. In the particularly resilient
illustrated embodiment first screw 247a and second screw 248a are
used as respectively the first and second means for restricting the
flow of inner oxidant.
[0066] In use, inner oxidant flows from a source of inner oxidant
into the inlet chamber 241 of oxidant distributor 240 via inlet
opening 246. Said flow of inner oxidant is then divided over the
first and second outlet chambers 242 and 243 at a ratio determined
by the settings of the first and second means for restricting the
flow of inner oxidant. Thereafter, the inner oxidant flows from the
first outlet chamber 242 to the central oxygen lance 213, and then
to the terminal nozzle 216 and from the second outlet chamber 243
to the surrounding annular passage 214 and then to the lateral
inner oxidant nozzles 212.
[0067] An auxiliary gaseous fuel burner was used to preheat the
furnace to a temperature of 900.degree. C., before starting up
above-described the particulate solid fuel burner.
[0068] The particulate solid fuel was a standard pulverized coal
with a particle size (diameter) in the range of 75 to 120
.mu.m.
[0069] The conveyor gas was recycled combustion gas. Analogous
results were obtained with air as the conveyor gas.
[0070] The conveyor gas was supplied to the burner at a rate of
17.6 Nm3/h. It propelled pulverized coal to the burner at a rate of
30 kg/h.
[0071] The outer oxidant was supplied to the burner at a rate of 33
Nm3/h. The total inner oxidant supply to the burner (first and
second inner oxidants) was 13 Nm3/h.
[0072] The same oxidant with an oxygen content of 90% vol O.sub.2
was used for the outer, for the first inner and for the second
inner oxidant.
[0073] The total oxygen supply to the furnace corresponded to 113%
of the stoichiometrically required amount of combustion oxygen.
[0074] In other words, the outer oxidant supply to the burner
corresponded to 71.74% of the total supply to the burner and to
68.07% of the stoichiometrically required amount of oxygen. The
total inner oxidant supply to the burner corresponded to 28.26% of
the total oxygen supply to the burner and to 31.93% of the
stoichiometrically required amount of oxygen.
[0075] The inner oxidant discharge velocity was higher than the
fuel discharge velocity.
[0076] The oxygen-enriched fuel flow mixed with the first inner
oxidant flow before mixing with the outer oxidant flow.
[0077] The results of said tests are presented in the table below,
with reference to the enclosed FIGS. 1 and 2, which are schematic
representations in cross section of the type of flame obtained.
TABLE-US-00001 first inner oxidant flow [m3/h]/second inner oxygen
flow [m3/h] observations Figure 1.5/11.5 The flame is unstable and
detached 1a from the burner front. 3.0/10.0 The flame is in part
attached to and in 1b part detached from the burner front, with a
small improvement in flame stability. 3.5/9.5 Flame detached from
burner front 1c at burner startup, but becomes attached to the
burner front shortly thereafter and becomes slightly recessed into
the glory hole. 4.0/9.0 Flame stable and attached to burner, 1e
recessed into glory hole. 5.2/7.8 Flame stable and attached to
burner, 2a recessed into glory hole. 6.5/6.5 Long stable flame
stable attached to 2b burner, recessed into glory hole. 7.5/5.5
Flame no longer recessed in glory 2c hole, getting at times
detached from burner. Shorter flame. 9.5/3.5 Flame no longer
recessed in glory 2e hole. Flame even shorter. 11.5/1.5 Unstable
(pulsating) short flame 2f detached from burner.
[0078] A more complete combustion of the particulate solid fuel and
better flame stability and flame attachment to the burner front
were observed using the method according to the present invention
than is generally the case with known solid particulate fuel
combustion methods when using similar total oxidant and fuel
flows.
[0079] The bests results were obtained with first to second inner
oxidant flow ratios between 4.0/9.0 and 7.5/5.5.
* * * * *