The present invention relates to a burner-lance and combustion method
for heating surfaces that are susceptible to oxidation or reduction in industrial
Combustion processes are often used to heat oxidation sensitive materials
in furnaces. For example, burners are used to preheat the scrap steel feed in electric
arc furnace steelmaking processes. Practical considerations often require that the
burner be placed at a distance from the material to be heated that is much greater
than the optimum distance preferred from a purely heat transfer viewpoint. In addition,
heating oxidation sensitive materials requires either control of the oxidation potential
at the surface or a subsequent reduction step.
U.S. Patent No. 6,250,915 seeks to address this problem for gaseous
fuels by disclosing use of parallel fuel-rich and fuel-lean gaseous jets. Impingement
of the parallel fuel-rich and fuel-lean jets on a surface initiates combustion reactions
in close proximity to the surface, which substantially increases the heat transfer
rate and efficiency. The jet array can be adjusted to maintain appropriate fuel-rich
or fuel-lean atmosphere in contact with the surface. In one embodiment, the use
of a low velocity coherent jet consisting of an array of parallel fuel-rich and
fuel-lean zones provides efficient heat transfer and reasonable control of the oxidation
potential of the melting zone. This technique increases the heat transfer rate to
the surface and the ability to control surface oxidation. This technique is effective
when the fuel-rich and fuel-jets have similar densities, which in turn requires
gaseous fuels and oxidants.
There are, however, many industrial processes where gaseous fuels
or oxidants are not used because solid fuels, oxidants, and/or reagents are preferred;
for example, coal, carbon or coke are usually the preferred reducing agents and
fuels for most iron and steel production processes. By way of further example, metallurgical
processes typically require the injection of particulate reagents, e.g., lime.
U.S. Patent No. 6,254,379 seeks to address particulate injection by
having a reagent containing carrier gas pass through a flame envelope. The flame
envelope forms a fluid shield or barrier around the gas jet to minimize ingression
of gas into the jet and maintain a coherent jet. The flame envelope has a velocity
that is less than the velocity of the jet. As the jet exits the flame envelope,
the rate of gas entrainment increases and the jet loses its coherency and delivers
the reagent to a diffuse reaction zone as a turbulent jet. In contrast, the heating
method disclosed in U.S. Patent No. 6,250,915 teaches that the jet coherency be
maintained, to the maximum extent possible, until the jet impacts the surface in
order to provide a well-defined reaction zone and increase heat and mass transfer
efficiency to the surface. Metallurgical processes typically require significant
heat input coincident with solids injection.
U.S. Patent No. 5,954,855 discloses techniques to use direct flame
impingement, high velocity oxygen jets, and carbonaceous fuel injection jets to
melt steel in electric arc furnaces. High efficiency melting requires the simultaneous
feeding of oxygen and a carbonaceous jet to the melting zone. However, it is very
difficult to precisely feed oxygen and carbon from separate lances, with different
characteristics, to a melting zone that is a constantly moving melting steel surface.
Despite the above teachings, there is no process disclosed for condensed
phase fuels, reducing, or oxidizing agents. Therefore, there is still a need for
a system to generate a coherent jet having a fuel-rich zone, a fuel-lean zone, and
a condensed phase fuel or reagent to efficiently heat and treat surfaces. It would
also be desirable to have a system whereby troublesome by-product iron oxide fines
from metallurgical processes could be recycled using an efficient particulate injection
and heating method.
A method of heating a surface susceptible to oxidation or reduction
is provided, comprising:
BRIEF DESCRIPTION OF THE DRAWINGS
- a) generating a central, generally cylindrical, fuel-rich particulate jet, and
a coaxial, annular, supersonic velocity, oxidant-rich jet having an auto-thermal
ignition temperature greater than the temperature of the fuel-rich particulate jet,
directed toward the surface to be heated, wherein the velocity of the fuel-rich
particulate jet is less than the velocity of the oxidant-rich jet;
- b) allowing the supersonic oxidant-rich jet and the fuel-rich particulate jet
to coact to form a coherent particulate fuel-rich and fuel-lean jet having a central
particulate fuel-rich region and a coaxial annular fuel-lean region;
- c) impinging the coherent particulate fuel-rich and fuel-lean jet upon the surface
to be heated for forming a turbulent reaction zone at the surface; and
- d) optionally controlling oxidation and reduction reactions at the turbulent
reaction zone by adjusting at least one property of at least one of the supersonic
oxidant-rich jet and the fuel-rich particulate jet.
For a more complete understanding of the present invention, reference
may be had to the detailed description taken in conjunction with the following drawings,
- Figure 1 is a cross-section of a burner to produce parallel fuel-rich and fuel-lean
jets with at least one non-gaseous feed.
- Figures 1A and 1 B are cross sections of the burner taken along corresponding
section views 1A-1A and 1B-1B of Figure 1.
- Figure 2 is a schematic representation of an arrangement of parallel fuel-rich
and fuel lean jets to heat a surface.
- Figures 2A and 2B are cross sections of the fuel jets taken along corresponding
section views 2A-2A and 2B-2B of Figure 2.
- Figures 3A and 3B are schematic representations of alternate systems to improve
the performance of a lance and provided feed streams.
- Figure 3C is a schematic representation of a method of producing a motive gas.
- Figure 4 is a photograph of the various regions providing a coherent particulate
fuel-rich and fuel-lean jet.
The burner lance and combustion method of the present invention produces
and uses coherent jets. The coherent jets have an annular fuel-lean gas jet and
a coaxial cylindrical fuel-rich jet that contains a condensed fuel or reagent. These
coaxial jets are used to transport particles and to heat surfaces by direct impingement
upon such surfaces, and in certain embodiments, to simultaneously transport the
particles for heating.
Combustion gases are used to efficiently transport condensed phase
fuels or reagents to a surface to be heated. The higher temperature of a flame increases
its viscosity, helping to maintain the coherent particulate containing jet. A coherent,
higher temperature supersonic annular flame jet is therefore produced to confine
and direct a lower velocity and coaxial jet containing the particles. Thus, the
particles in the jet tend to move toward the lower shear and lower temperature region
along an axis of the jet, due to its lower velocity gradient and viscosity. These
powerful forces produce a very compact particulate jet along, in particular, the
axis of the jet.
The formation of this compact particulate jet substantially reduces
interaction between any particulate fuel and the hotter, higher velocity oxidizing
annular gaseous shroud gas. This limited interaction between the fuel-rich particle
jet and the annular fuel-lean gas shroud having a greater temperature and velocity,
produces a combustion gas shroud region around the central fuel-rich particulate
In addition, the lower temperature of the fuel-rich particulate jet
decreases the overall heat lost to the walls of the industrial furnace prior to
impingement of the coherent jet with the surface to be heated. This advantage results
from the fact that solids have much higher emissivities than the fuel-lean shroud
gas. When the aforementioned coherent jet impinges the surface to be heated, the
adjacent fuel-lean and fuel-rich regions burn, in close contact with the surface
to be heated, to achieve unusually efficient heat transfer and good control of combustion
stoichiometry. Thus, significant advantages are provided by generating coaxially
parallel fuel-rich and fuel-lean jets utilizing non-gaseous fuel for heating surfaces.
With reference to Figure 1, a burner-lance according to the present
invention and shown generally at 50 includes an annular hot oxidant-lance 1 and
central fuel-lance 2. The central fuel-lance 2 provides for a lower velocity jet
as discussed below and accordingly, the fuel-lance 2 may also be referred to as
the lower velocity central fuel-lance 2. The annular hot oxidant-lance 1 and lower
velocity central fuel-lance 2 may comprise a single unit or separate units as shown
in Figure 1. Since the lower velocity central fuel-lance 2 is usually inspected,
repaired and replaced more often than the annular hot oxidant-lance 1, the fuel-lance
2 may be removably mountable with respect to the oxidant-lance 1 as a separate element
to be easily removed, inspected and repaired.
The annular hot oxidant-lance 1 is preferably constructed using high
strength steel, copper, nickel or copper-nickel alloys, and is preferably equipped
with cooling channels (not shown) to limit its rate of surface oxidation. Ceramic
materials are also appropriate materials of construction for the hot oxidant-lance
1. The central fuel-lance 2 may also contain cooling channels (not shown) and similar
materials of construction may be used. However, the temperature and composition
of gas in contact with the annular hot oxidant-lance 1 may determine the most appropriate
materials of construction.
The oxidant-lance 1 has a gaseous oxidant feed 3; fuel feed 4; and,
an optional inert containing gas feed 5. The oxidant feed 3 may be air, oxygen (O2)
enriched air, substantially pure oxygen, chlorine containing gas or fluorine containing
gas. Substantially pure oxygen may be greater than 0.7 molar fraction O2,
in other embodiments greater than 0.9 molar fraction O2, and in still
other embodiments, greater than 0.95 molar fraction O2.
Provided to the oxidant-lance 1, is an appropriate fuel for the oxidants.
For example, hydrocarbons, elemental sulfur and metal hydrides are appropriate fuels
for oxygen, chlorine, and fluorine oxidants. With a fluorine containing oxidant,
many gases, e.g. steam, are also potential gaseous fuels. The oxidant feed 3 and
fuel 4 are transported to an oxidation reactor 6. Products of the oxidation reaction
are fed to an annular converging-diverging nozzle 7 to produce an annular supersonic
oxidant-rich jet 8 around the axis X-X. Appropriate gaseous fuels include natural
gas, petroleum distillate vapor, coal tar distillate vapor, and carbon monoxide
and hydrogen-rich gaseous products from partial oxidation processes. Liquid fuel
could be used with an appropriate atomizer. Appropriate liquid fuels include petroleum
and coal distillate and residual liquid fuels.
An inert gas feed 5, such as nitrogen, may be used to protect the
surface of the annular converging-diverging nozzle 7 from the products of the oxidation
reaction. The use of an inert gas feed 5, such as to envelope the oxidant feed and
oxidation products, becomes progressively more important as a more powerful gaseous
oxidant feed 3 is used. The inert gas feed 5 is more necessary with fluorine containing
Generally, the gaseous oxidant feed 3 and annular hot oxidant-lance
gaseous fuel 4 properties, such as flow rates and pressures, and the converging-diverging
nozzle Ac1/A2 area ratio may be adjusted by trial and error
to achieve the desired annular supersonic oxidant-rich jet temperature and velocity.
Ac1 is the minimum nozzle cross-sectional area at the throat of the nozzle
7 and A2 is the nozzle maximum downstream cross-sectional area.
In certain embodiments, the velocity of the annular supersonic oxidant-rich
jet 8 may typically be greater than 1.25 times the sonic velocity (Mach 1.25) in
the throat of the nozzle 7. In other embodiments, the velocity of the annular supersonic
oxidant-rich jet 8 may typically be greater than about 1.5 times the sonic velocity
(Mach 1.5) in the throat of the nozzle 7.
The temperature of the annular supersonic oxidant-rich jet 8 should
typically be greater than the auto-thermal ignition temperature of the lower velocity
fuel rich jet 9 produced by the central fuel-lance 2 to ensure stable operation.
Excessive temperatures of the annular supersonic oxidant-rich jet
8 should be avoided in order to maintain reliable operation of the annular converging-diverging
As shown in Figure 1, the central fuel-lance 2 is a pipe that functions
as a conduit for a lower velocity, particulate, fuel-rich feed 10. The feed 10 enters
the central fuel-lance 2 at a proximal end of the fuel lance 2 and exits at a distal
end of the fuel lance 2 as a lower velocity, cylindrical, and fuel-rich particulate
jet 9. The particulate, fuel-rich feed 10 contains particles.
A particle is defined as a non-gaseous fuel or reagent. A non-gaseous
substance can be a solid or a liquid at the feed temperature and pressure. A reagent
is a substance that interacts with the surface to be heated. A fuel is a substance
that can be rapidly oxidized by the annular supersonic oxidant-rich jet. There are
situations where particles can be both a fuel and reagent. For example, carbon can
be rapidly oxidized or injected into a molten iron bath by the annular supersonic
oxidant-rich jet 8. In the latter situation, the carbon can interact with the iron
bath and be dissolved by the molten iron.
The lower velocity, cylindrical, fuel-rich particulate jet 9 can also
contain gaseous fuels or inert components. For example, either natural gas (a fuel)
or argon (usually an inert) could be used to facilitate particulate transport. In
addition, a particulate substance could be used to facilitate transport of another
particulate component. For example, a liquid fuel oil could be used to facilitate
transport for coal particles.
Figure 2 illustrates how the annular supersonic oxidant-rich jet 8
and lower velocity, cylindrical, fuel-rich particulate jet 9 are used to efficiently
heat a surface and optionally add reagents to a surface 18. In various embodiments,
the fuel-rich jet 9 velocity is less than 90% of the oxidant-rich jet 8 velocity,
or less than 75% of the oxidant-rich jet 8 velocity, or less than 50% of the oxidant-rich
jet 8 velocity (Figure 2A). The higher velocity of the supersonic oxidant-rich jet
8 results in entrainment and acceleration of the lower velocity fuel-rich jet 9
within a turbulent mixing region 11 forming coherent jet 20 having a central, lower
shear, fuel rich region 13 and an outer, higher shear, fuel lean region 15. In certain
embodiments, the supersonic oxidant-rich jet and the fuel-rich particulate jet coact
over a distance of about 0.5 meters.
As shown in Figure 2B, as the velocity of the particulate matter in
the fuel-rich jet approaches the velocity of the gaseous oxidant, particles flow
(arrow 16) radially toward an axis X-X of the coherent jet 20 in a short formation
zone 12 and away from the coherent jet outer, higher shear, fuel-lean region 15,
toward the coherent jet central, lower shear, fuel-rich region 13. The fuel rich
fuel gas flows (arrow 17) radially away from the axis X-X of the coherent jet 20
and the coherent jet central, lower shear, fuel-rich region 13 in the formation
zone 12, toward the coherent jet outer, higher shear, fuel-lean (or oxidant-rich)
region 15, which produces a coherent jet intermediate combustion gas shroud 14.
The gas shroud 14 limits the interaction between the fuel-rich region 13 and the
fuel-lean region 15 until the coherent jet 20 impinges the surface 18 to be heated.
A turbulent reaction zone 19 is formed by impingement of the coherent
particulate fuel-rich and fuel-lean jet 20 with the surface 18. Maximum process
efficiency is observed in the coherent jet 20 that is perpendicular to the surface
to be heated 18. The relative amounts of oxidant and fuel in the turbulent reaction
zone 19 can be controlled in certain embodiments by controlling oxidant and fuel
properties such as feed rates to the supersonic annular hot oxidant-lance 1 and
the lower velocity central fuel-lance 2.
Refractory furnace walls, such as shown generally at furnace wall
21, are advantageously used to minimize heat losses.
This burner and combustion method are useful for iron and steel production.
Coal is a particularly useful component of the particulate, fuel-rich feed 10 for
iron and steel melting. The coal volatile matter is evolved as the coal particles
are heated in the central fuel-rich region 13, which helps to form the intermediate
gas shroud 14. The gas shroud 14 protects the coal char particles in the fuel-rich
region 13 from further oxidation. Upon impact with the surface 18, the coal char
dissolves in the molten iron to decrease the rate of iron oxidation, or to chemically
reduce iron oxide, thereby increasing the iron yield of the melting process. Lime
(CaO) can be advantageously added to the particulate, fuel-rich feed 10 to decrease
the viscosity of the iron oxide rich phase in contact with the turbulent reaction
zone 19 and increase the rate of the iron oxide-carbon reduction reaction. By-product
iron oxide fines from metallurgical processes can also be recycled and injected
in the particulate, fuel-rich feed.
Figures 3A and 3B illustrate a plurality of approaches to improve
the performance of the lower velocity central fuel-lance 2. Figure 3A shows the
lower velocity central fuel-lance 2 of Figure 1. Figure 3B shows a higher velocity
central fuel-lance 22 using a central fuel-lance motive gas 23 introduced at feed
23a for the fuel-lance 22 to substantially increase the velocity of the lower velocity,
cylindrical, fuel-rich particulate jet 9, (although less than the velocity of the
supersonic oxidant-rich jet). The higher velocity central fuel-lance 22 includes
lower velocity central fuel-lance 2, a central fuel lance motive gas conduit 24,
and a central fuel-lance converge-divergent nozzle 25. The motive gas 23 may be
an inert gas, e.g. argon, typically for use in steel making; or a fuel, e.g. natural
gas, vaporized petroleum or coal derived liquids, and carbon monoxide and hydrogen-rich
streams from partial oxidation processes. The nozzle 25 is positioned at the distal
end of the fuel-lance 2. The gas conduit 24 directs the motive gas 23 such that
the particulate, fuel-rich feed 9 exiting the distal end of the fuel-lance 2 does
not contact the converge-divergent nozzle 25. The velocity of the higher velocity
central fuel-lance 22 should be selected so as to avoid excessive erosion of the
central fuel-lance converge-divergent nozzle 25, in relation to the velocity of
the lower velocity, cylindrical, fuel-rich particulate jet 9 and the particulate,
fuel-rich feed 10 rate, as well as the particulate and gaseous compositions desired
to be used.
Figure 3C shows alternative embodiments for producing the feed streams.
The solid particulate feed 26 for the particulate, fuel-rich feed 10 could be stored
in a solid particulate feed hopper 27. The particulate feed 26 is periodically transferred
from the hopper 27 to a solid particulate feed lock hopper 28. The lock hopper 28
may be pressurized with either a non-fluidizing motive fluid feed 32 or a separate
lock hopper pressurizing gas 29. The motive fluid 30 and pressurizing gas 29 may
be an inert gas (e.g., argon or nitrogen), a gaseous fuel (e.g., natural gas) or
liquid fuel (e.g., petroleum derived fuel oil). The pressurizing gas 29 is typically
used with the motive fluid 30.
Once the lock hopper 28 is pressurized, a fluidizing motive fluid
feed 31 is used to increase the mobility of the particulate feed 26 in the bottom
of the feed lock hopper 28. The fluidizing motive fluid may comprise the same composition
as the pressurizing gas 29 or motive fluid 30. A similar quantity of material 33
is withdrawn from the lock hopper 28 and may be either vented or recycled. The rate
of the fluidizing motive fluid feed 31 can be used to control the ratio of the particulate
feed 26 to the motive fluid 30 in the particulate, fuel-rich feed 10. A flow rate
of the non-fluidizing motive fluid feed 32 can be used to control the overall feed
rate of the particulate, fuel-rich feed 10.
As discussed above, the motive gas 23 may be a pressurized gaseous
fuel. Figure 3C shows alternative methods to produce the motive gas 23. A distillate
fuel feed pump 35 can cost-effectively increase the pressure of a liquid distillate
fuel 34. Then, a distillate fuel vaporizer 36 can produce the motive gas 23 and
annular hot oxidant lance gaseous fuel 4. This approach can avoid the capital and
operating cost associated with compressing gaseous fuel to the annular converging-diverging
nozzle 7 inlet pressure. In addition, this approach increases the range of potential
Figure 4 shows, in an electric arc furnace steel making process, a
coherent jet produced by a high velocity central fuel-lance using nitrogen as the
central fuel-lance motive gas for a coal particulate feed, and an annular supersonic
oxidant-rich jet at Mach 1.5, using methane (natural gas) as the annular hot oxidant-lance
gaseous fuel and substantially pure oxygen as the oxidant. These operating conditions
provided a short turbulent mixing region 11, a short coherent jet formation zone
12, and a long coherent particulate fuel-rich and fuel-lean jet 20.
It will be understood that the embodiments described herein are merely
exemplary and that a person skilled in the art may make many variations and modifications
without departing from spirit and scope of the invention. The various embodiments
may be practiced in the alternative, or in combination, as appropriate. All such
modifications and variations are intended to be included within the scope of the
invention as defined in the appended claims.