Burner for coal slurry

A burner (10) is provided for supplying coal-liquid slurry and combustion air to a furnace (2). The burner housing (12) is mounted about the burner throat opening (6) and interconnected to a combustion air supply duct (8). A coal slurry gun (14) is disposed coaxially within the housing for spraying the coal-liquid slurry into the furnace. A first conduit means (20) is disposed coaxially about the coal slurry gun to define a primary air flow passage (22) surrounding the slurry gun. Additionally, a second conduit means (30) is disposed coaxially about the first conduit means (20) to define a secondary air flow passage (32) between the first and second conduit means and a tertiary air flow passage (34) between the second conduit means and the burner throat (4). Independently controllable dampers 41, 42 and 43 are provided in the air inlets to the primary, secondary and tertiary air flow passages to permit independent control of air flow velocity. A diffuser means (50) is slidably mounted about the coal slurry gun so as to be translatable from a position adjacent the furnace at low loads to a position remote therefrom at high loads. Further, an annular sleeve (60) is mounted about the first conduit means (20) and translatable therealong for selective postioning relative to the diffuser means (50) for controlling the flow area (33) of the outlet of the secondary air flow passage (32).

BACKGROUND OF THE INVENTION 
The present invention relates to a burner for supplying liquid fuel and air 
to a furnace and, more particularly, to a burner for supplying coal slurry 
fuel and air to a furnace. 
One type of burner commonly utilized on industrial and certain utility 
furnaces firing liquid fuel, such as oil, is known as a round burner. In 
such a burner, a fuel supply pipe is disposed coaxially within an outer 
air supply conduit which comprises the outer housing of the burner. The 
fuel supply pipe opens into the furnace for spraying the liquid fuel into 
the furnace. One or more annular flow passages are defined coaxially about 
the fuel supply plate through which combustion air is passed into the 
furnace so as to annularly surround the liquid fuel sprayed into the 
furnace. One particular embodiment of this type of burner is disclosed is 
U.S. Pat. No. 3,743,471. 
In recent years, interest has generated in the utilization of coal as a 
replacement fuel for more costly and less available fuel oil. One scenario 
for using coal as a replacement fuel for oil comprises burning the coal as 
a liquid by forming a mixture of coal and water which has the properties 
of a liquid slurry. However, experience has shown that coal-water 
mixtures, although liquid slurries, cannot be directly substituted for 
fuel oil on typical industrial and utility furnaces. Combustion 
characteristics of coal-water mixtures are not the same as the combustion 
characteristics of typical fuel oil. Additionally, the combustion 
characteristics of a coal-water mixture depend directly upon the coal 
being utilized in the mixture. Therefore, as coals vary substantially in 
their combustion characteristics, the burning equipment utilized on a 
furnace firing coal-water slurry must be capable of handling liquid fuels 
having a wide range of combustion characteristics as one cannot be assured 
of always having available a coal-water slurry made from a particular 
coal. 
Accordingly, it is an object of the present invention to provide a burner 
for supplying a coal-water mixture and combustion air to a furnace which 
is uniquely designed to be capable of adjustment to handle a wide range of 
coal-water mixtures. 
Additionally, it is an object of the present invention to provide such a 
coal-water slurry burner which is capable of operating with a high 
turndown. 
SUMMARY OF THE INVENTION 
The burner of the present invention comprises a slurry gun with atomizer 
disposed coaxially within a refractory-lined, divergent throat which is 
mountable in an opening in the wall of the furnace associated with the 
burner. First conduit means are disposed coaxially about the slurry gun in 
spaced relationship therewith between the slurry gun and the burner throat 
so as to divide the annular region therebetween into a primary air conduit 
surrounding the slurry supply gun and a auxiliary air conduit in the 
annular space between the burner throat and the first conduit means. 
Preferably, a swirler is disposed about the slurry gun so as to impart a 
swirl to the primary air passing through the first conduit means in order 
to stabilize the burner flame. Additionally, a second conduit means is 
disposed in spaced relationship between the burner throat and the first 
conduit means so as to divide the annular auxiliary air passage into a 
secondary air flow passage between the first and second conduit means and 
a separate tertiary air passage between the second conduit means and the 
burner throat. 
In accordance with the present invention, a conically flared diffuser cone 
is slidably mounted about the first conduit means so as to be retractable 
within the secondary air passage from a position adjacent the burner 
outlet to a fully retracted position within the burner housing at a 
location remote from the burner outlet. Additionally, an annular sleeve is 
slidably mounted to the second conduit means so as to be retractable from 
a position adjacent the burner outlet to a second position within the 
burner housing remote from the burner outlet. Further, independently 
adjustable damper means are positioned in the inlet of each of the 
primary, secondary and tertiary air flow passages so as to independently 
control the pressure drop experienced by the air flowing through each of 
these passages. 
By selectively positioning the diffuser cone at the outlet of the burner, 
combustion stability can be increased at low loads by the deflection of 
the secondary air outwardly as it passes from the secondary air flow 
passage around the diffuser cone and through the burner throat into the 
furnace. A recirculation pattern is established by the secondary air 
flowing around the diffuser cone which leads to flame stabilization at low 
loads. At high loads, the diffuser cone will be retracted fully within the 
housing so that the secondary air can enter the furnace in an axial 
direction to provide a difussion-type flame rather than being deflected 
outward to form the strong recirculation zone. 
Further, with the diffuser cone positioned at the outlet of the burner, the 
area of the secondary air flow passage may be adjusted as to control air 
flow by selectively positioning the annular sleeve surrounding the 
secondary air conduit with respect to the diffuser cone. As the annular 
sleeve is slid along the second conduit means towards the diffuser cone, 
the secondary air flow passage area is decreased. Conversely, as the 
annular sleeve is retracted away from the diffuser cone, the secondary air 
flow passage is increased.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawing, there is depicted therein a burner 10 for 
burning a slurry fuel such as pulverized coal mixed in water. The burner 
10 is shown mounted to a furnace wall 2 in the typical well-known manner. 
The refractory-lined burner throat 4 is inserted through the wall of the 
furnace 2 and defines a throat opening 6 through which the coal slurry and 
streams of supporting combustion air pass into the furnace. 
As depicted in the drawings, the burner 10 comprises a housing 12 mounted 
to the burner throat 4 so as to surround the throat opening 6 in the 
burner throat 4 and extend therefrom away from the furnace 2 along a 
longitudinal axis. The end of the housing 12 surrounding the throat 4 
opens directly into the furnace through the throat opening 6, while the 
opposite end of the housing 12 is closed. A combustion air supply duct 8 
opens into the side wall of the housing 12 to provide combustion air to 
the interior of the housing 12. A coal slurry gun 14 is disposed within 
the burner housing 12 along the longitudinal axis thereof so as to extend 
coaxially through the housing. The end of the coal slurry gun 14 adjacent 
the furnace 2 is equipped with an atomizer tip 16 through which the coal 
slurry passing through the coal slurry gun 14 is sprayed into the furnace 
2. 
A first conduit means 20 is disposed coaxially about the coal slurry supply 
gun in spaced relationship therewith and intermediate the coal slurry 
supply gun and the throat means 4 so as to define a primary air flow 
passage 22 surrounding the coal slurry supply gun and opening into the 
furnace 2 through the throat opening 6 for directing a first stream of 
combustion air, termed primary air, into the furnace. A first inlet 
passage 44 opening into the primary air flow passage 22 is provided within 
the housing 12 for directing combustion air into the primary air flow 
passage 22 within the first conduit means 20 from the combustion air 
supply duct 8. Preferably, swirler means 24, shown as a spinner vane 
assembly, is disposed about the coal slurry supply pipe 14 within the 
first conduit means 20 so as to impart a swirling motion to the combustion 
air passing through the primary air flow passage 22 as a means of 
stabilizing the flame and increasing combustion efficiency. 
Additionally, a second conduit means 30 is disposed coaxially about the 
first conduit means 20 in spaced relationship therewith intermediate 
between the first conduit means 20 and the burner throat means 4. The 
second conduit means 30 defines an annular secondary air flow passageway 
32 between the first conduit means 20 and the second conduit means 30 and 
also defines an annular tertiary air flow passage 34 between the burner 
throat means 4 and the second conduit means 30. The annular secondary air 
flow passage 32 opens to the furnace 2 through the burner throat opening 6 
in an annular circumferential ring about the primary air flow passage 22. 
A second air inlet 36 is provided within the housing 12 to open directly 
into the secondary air passage 32 for passing a flow of secondary air from 
the air supply duct 8 directly into the furnace 2 through the secondary 
air flow passage 32. The tertiary air flow passage 34 opens into the 
furnace 2 through the burner throat opening 6 in a second an annular 
circumferential ring disposed about the secondary air flow passage 32. A 
third air inlet passage 38 is provided within the housing 12 communicating 
with the tertiary air flow passage 34 for directing combustion air from 
the air supply duct 8 directly to the furnace 2 through the tertiary air 
flow passage 34. 
First damper means 41, second damper means 42 and third damper means 43 are 
disposed respectively in the first air inlet 44 to the primary air flow 
passage 22, the second air inlet 36 to the secondary air passage 32, and 
the third air inlet 38 to the tertiary air passage 34 for controlling the 
gas pressure drop through the air inlets. Each of the first, second and 
third damper means is selectively positionable within its associated air 
inlet for independently controlling the gas pressure drop therethrough in 
accordance with the present invention. By independently positioning each 
of the damper means 41, 42 and 43 within the air inlets 44, 36 and 38, the 
combustion air passing into the burner housing through the supply duct 8 
will experience an independently selected pressure drop in passing through 
each of the independent air inlets 44, 36 and 38. In this manner, the 
operator of the burner can vary the pressure differential in any of the 
three air streams independent of the others so as to independently control 
the velocity of each of the primary, secondary and tertiary air streams in 
response to load changes or to variations in the combustion 
characteristics of the coal slurry being burned. 
Further in accordance with the present invention, diffuser means 50 is 
disposed about the first conduit means 20 and is slidably translatable 
therealong in an axial direction by means of positioning means 70 from a 
first position adjacent the furnace 2 within throat opening 6 as shown in 
FIGS. 1 and 2 to a position remote from the furnace 2 at the opposite ends 
of the burner housing 12 as shown in FIG. 3. Preferably, the diffuser 
means 50 comprises a support sleeve 52 disposed about and slidably 
translatable along the first conduit means 20 and an annular truncated 
cone-like ring 54 mounted to the end of the support sleeve 52 adjacent the 
furnace and extending outwardly therefrom towards the furnace into the 
burner throat opening 6. The diffuser means serves to deflect the 
secondary air radially outward through the divergent opening 6 defined by 
the throat means 4 whereby a strong recirculation pattern is established 
in the furnace downstream of the diffuser 50 thereby providing stability 
to the flame both aerodynamically and thermally. 
Further in accordance with the present invention, an air flow adjustment 
sleeve 60 is disposed adjacent the second conduit means 30 and is slidably 
translatable therealong in an axial direction by means of positioning 
means 80. The air flow adjustment sleeve 60 is selectively adjustable with 
respect to the diffuser means 50 so as to cooperate together to close the 
flow area 33 of the opening of the secondary air flow passage 32 to the 
furnace 2. By translating the annular air flow adjustment sleeve 60 along 
the second conduit means 30 in a direction away from the diffuser 50, the 
flow area 33 at the outlet of the secondary air flow passage 32 between 
the diffuser 50 and the air flow adjustment sleeve 60 is increased. 
Conversely, by translating the annular air flow adjustment sleeve 60 along 
the second conduit means 30 in a direction toward the diffuser 50, the 
flow area 33 at the outlet of the secondary air flow passage 32 between 
the diffuser 50 and the air flow adjustment sleeve 60 can be decreased. As 
best seen in FIG. 2, by positioning the annular air flow adjustment sleeve 
in a fully forward position so as to contact or nearly contact the 
diffuser 50, the flow area 33 at the outlet of the secondary air flow 
passage 32 is closed or nearly closed off so as to preclude all but 
leakage air flow through the secondary air flow passage. 
A burner design in accordance with the present invention provides the 
operator with a multiplicity of adjustments which can be made to control 
the flow of combustion air so as to provide good turndown capability in 
response to load changes and also so as to permit optimization of 
combustion efficiency for a wide variety of coal slurry composition. By 
selectively adjusting the damper means 41, 42 and 43 in conjunction with 
controlling the flow area 33 at the outlet of the secondary air flow 
passage 32, the operator may control the distribution of the combustion 
air amongst the primary, secondary and tertiary air streams for 
simultaneously controlling the velocity of these air streams. 
Additionally, the ability to respond to change in load is greatly enhanced 
by providing the translatable diffuser 50 which may be fully retracted 
within the burner housing 12 for operation at full load or may be fully 
extended into the burner throat opening 6 at lower loads to increase mass 
recirculation and provide flow stabilization at low loads.