Condensation free nozzle

A nozzle which includes a nozzle body, a central tube contained within the nozzle body for a flow of gas at a temperature less than the temperature of the nozzle body, and an annular passage, located between the nozzle body and central tube, for a flow of gas at a velocity less than the flow of gas in the central tube and less than about 100 ft/sec. enabling the nozzle to operate at elevated temperatures and avoid condensation thereon of vapors from the surrounding gas environment.

FIELD OF THE INVENTION 
The present invention relates generally to nozzles, more particularly to 
nozzles useful for the injection of gases into a combustion zone. 
BACKGROUND ART 
Advances in combustion technology have employed the use of high velocity 
gas injection into a combustion zone to carry out combustion with reduced 
nitrogen oxides (NO.sub.x) generation. Nozzles with relatively small 
diameters are employed in order to achieve the high velocities. The high 
gas velocities cause furnace gases to be aspirated or entrained into the 
high velocity gas which has a dampening effect on NO.sub.x generation. 
A problem with high velocity gas injection into a combustion zone is that 
the furnace gases, which may comprise particulate matter and condensable 
vapors, cause the nozzles, which have small openings to begin with, to 
foul, plug or corrode easily as the furnace gases are aspirated or 
entrained into the high velocity gas exiting the nozzle. The furnace gases 
also tend to be quite hot, on the order of 1000.degree. F., or more, which 
exacerbates the fouling and corrosion problem. This problem becomes 
particularly severe when the furnace temperature exceeds 2200.degree. F. 
The maximum service temperatures of common high temperature alloys are 
generally less than 2200.degree. F., for fuel-fired furnace atmospheres. 
Some noble metals such as platinum can withstand higher temperatures, but 
the cost becomes excessive. 
One way of dealing with this problem has been to provide a large amount of 
water cooling to the nozzle so as to prevent high temperature corrosion or 
melting. However, a water cooling system is complex to operate, costly, 
and does not address the fouling problem where the furnace atmosphere has 
a high particulate content. Moreover, water cooling can escalate the 
corrosion and fouling problems when the furnace atmosphere contains 
condensable vapors. 
Ceramic lances have been proposed as a solution to the fouling problem in 
high velocity gas injection. However, presently available ceramic lances 
are not suitable for industrial scale operations because of corrosion and 
cracking due to thermal and other stresses. 
It is known that temperature effects on a nozzle may be ameliorated by 
recessing the nozzle in a cavity communicating with a combustion zone. 
However, a relatively large recess is required to achieve a significant 
beneficial effect. With high velocity gas injection, such a large recess 
may be detrimental because a large amount of corrosive furnace gas may be 
drawn into the cavity. Furthermore, this results in a reduction in the gas 
jet velocity. Thus, while the nozzle avoids temperature induced damage, 
this is offset by increased damage caused by contact with corrosive 
furnace gas drawn into the cavity. 
A recurring problem in refractory tipped oxygen or fuel injectors in glass 
furnaces can be the accumulation of condensed materials on the tip of the 
nozzle which form a narrow tube-like structure around the jet extending 
into the furnace. These growths, over time, can distort the jet and cause 
undesirable combustion conditions to exist in the furnace which, in turn, 
can damage the furnace refractory, cause off ratio burner operation, or 
upset the glass quality. 
One previous approach, described in U.S. Pat. No. 5,266,025, purged the 
area around the nozzle with clean gas, e.g. oxygen. This usually required 
passing a large percentage of the gas (30%-50%) around the nozzle to 
prevent the furnace atmosphere from contacting the nozzle. In practice, 
however, because the concentricity of the nozzle within the annulus is 
important to achieve this protection, it is generally difficult to 
achieve. Also, by shifting a large percentage of gas to the annulus, the 
NO.sub.x performance of the burner may be compromised (i.e., high NO.sub.x 
can form) or higher oxygen pressure may be required to increase the 
velocity of the center jet. 
Another previous approach involved building the nozzle from a porous 
material to have clean gas emanating from any surface which could possibly 
accumulate deposits. The design of such a nozzle, however, is fairly 
complicated, its life in the furnace is questionable, and it produces 
slightly higher NO.sub.x than a conventional refractory-tipped nozzle. 
A further approach involved lengthening the refractory section of the 
nozzle to elevate the surface temperature of the nozzle. Also, along these 
lines, the existing nozzles were inserted further into the furnace 
resulting in higher surface temperatures on the nozzle. These techniques 
alleviated the problem, but did not eliminate it, or created other 
problems such as overheating of the metallic components of the lance. 
In light of the foregoing, there is a need for a nozzle that overcomes the 
disadvantages of the related art. 
SUMMARY OF THE INVENTION 
Accordingly, the present invention is directed to a nozzle which may be 
employed in a high velocity gas injection system and substantially 
obviates one or more of the problems due to the limitations and 
disadvantages of the related art. 
An additional object of the present invention is to prevent condensation on 
nozzle surfaces, for instance by preventing cold nozzle surfaces from 
occurring instead of altering the conditions around the nozzle (i.e., 
shrouding, purging, etc.). 
Additional features and advantages of the present invention will be set 
forth in part in the description which follows, and in part will be 
apparent from the description, or may be learned by practice of the 
present invention. The objectives and other advantages of the present 
invention will be realized and attained by means of the elements and 
combinations particularly pointed out in the written description and 
appended claims. 
To achieve these and other advantages and in accordance with the purpose of 
the present invention, as embodied and broadly described herein, the 
nozzle of the present invention has a nozzle body, a central tube, and an 
annular passage. The central tube is contained within the nozzle body and 
is for a flow of a gas. The annular passage, located between the nozzle 
body and the central tube, is substantially flush with the end of the 
central tube, and is also for a flow of a gas. The velocity of the gas 
flowing through this passage is less than the velocity of the gas flowing 
through the central tube and is less than about 100 ft/sec. The wall 
thickness of the central tube is less than or equal to the radial width of 
the annular passage (i.e., gap of the annulus). 
Another aspect of the present invention is a gas injection system 
comprising a cavity within a wall of a combustion zone and having an 
opening communicating with the combustion zone and the above-described 
nozzle in the cavity. 
An additional aspect of the present invention is a nozzle for injecting gas 
into a combustion chamber. The nozzle has an annular body having a central 
bore with an inlet end and an outlet end. The nozzle also has a tubular 
member positioned in the central bore for receiving a first gas at the 
inlet end and ejecting the first gas at an outlet end. The tubular member 
has an outer surface defining an annular passage extending between the 
inlet and outlet ends for passing a second gas received at the inlet end. 
Also, the nozzle has means for reducing the transfer of heat in the radial 
direction between the annular body and the first gas contained in the 
tubular member. The first gas and second gas can be from the same or 
different gas sources. 
A further aspect of the present invention is a method of minimizing or 
preventing condensation on a nozzle surface of a nozzle used for injecting 
gas into a combustion chamber. The method includes passing a first gas at 
a first rate of flow through a tubular member located within a nozzle body 
and forming an annular passage, and passing a second gas at a second flow 
rate through the annular passage that is substantially flush with the end 
of the tubular member. The second rate of flow of the second gas is 
substantially less than the first rate of flow and less than about 100 
ft/sec. The tubular member has a thickness less than or equal to the 
radial width of the annular passage, and along with the second rate of 
flow, impedes the transfer of heat between the nozzle and the gas at the 
first flow rate. 
It is to be understood that both the foregoing general description and the 
following detailed description are exemplary and explanatory only and are 
intended to provide further explanation of the present invention, as 
claimed.

DETAILED DESCRIPTION 
As used herein, the term "nozzle" means a device through which either 
gaseous oxidant or gaseous combustible matter or a premixed mixture of 
oxidant and fuel is injected into a cavity or a combustion zone. 
As used herein, the term "ceramic" means a non-metallic material which can 
withstand a temperature greater than 2200.degree. F. Ceramics typically 
are refractory materials comprising oxides, carbides, or nitrides. 
The present invention minimizes or prevents condensation on a surface of a 
nozzle, for instance, used for injecting gas into a combustion chamber. 
This is primarily accomplished by passing a first gas at a first rate of 
flow through a tubular member located within a nozzle body and forming an 
annular passage, and also passing a second gas at a second rate of flow 
through the annular passage. The tubular member has a thickness less than 
or equal to the radial width of the annular passage. The second gas 
through the annular passage is at a second rate of flow substantially less 
than the first rate of flow and less than about 100 ft/sec. This 
difference in flow rate impedes the transfer of heat in the radial 
direction. Or, in other words, it impedes the transfer of heat between the 
nozzle and the gas at the first flow rate. The first and second gas can be 
from the same or different gas source. 
Referring to FIGS. 1, 2A and 2B, refractory wall 2 borders combustion zone 
3 wherein there is contained a furnace atmosphere comprising furnace gases 
such as, for example, carbon dioxide, water vapor, nitrogen and/or oxygen. 
The furnace atmosphere is generally at an elevated temperature typically 
exceeding 2000.degree. F., and usually within the range of from 
2000.degree. to 3500.degree. F. The furnace atmosphere may also contain 
particulate matter, such as glass batch materials or ash from coal 
combustion, and/or condensable vapors such as sodium species or acid 
vapors. 
Within refractory wall 2 there is provided cavity 11 which communicates 
with combustion zone 3 at opening 4. Generally, opening 4 will have a 
diameter, denominated in FIG. 1 as D.sub.c, within the range of from 1.0 
to 10 inches. 
In accordance with the present invention, the nozzle for injecting a gas 
has an annular body. This annular body has a central bore having an inlet 
end and an outlet end. A tubular member 9 is positioned in the central 
bore and has an outer surface 10 defining an annular passage 13 (i.e., 
annulus). This annular passage 13 extends between the inlet and outlet 
ends and is substantially flush with the outlet end of the annular body 
and the tubular member 9. The nozzle also contains means for reducing the 
transfer of heat in the radial direction between the annular body and the 
gas contained in the tubular member. The presence of the low velocity gas 
in the annular passage limits the heat transfer. 
In more detail, the nozzle has a nozzle body 6, 7 that contains a central 
tube 9 and an annular passage 13 (i.e., an annular body having a central 
bore and a tubular member, having an outer surface defining an annular 
passage, positioned in the central bore). The central tube 9 is for a flow 
of a gas. The temperature of the gas flowing through the central tube 9 is 
less than the temperature of the nozzle body. 
Further, the annular passage 13 (i.e., annulus) is located between the 
nozzle body 6, 7 and the central tube 9. The annular passage 13 is for a 
flow of gas having a velocity less than the velocity of the gas flowing 
through the central tube and has a velocity less than about 100 ft/sec. 
The nozzle body 6, 7 can be fabricated from any material commonly used in 
combustion technology which is able to withstand elevated temperatures, 
which typically exceed 2000.degree. F. Preferably the nozzle body is a 
composite piece. The nozzle body can have a 11/2" inner diameter and an 
outer diameter of 27/8". 
Preferably, the nozzle body is constructed of a heavy nozzle wall. The 
thickness of the nozzle body from a point beginning at the outer edge of 
the annular passage to the edge of the nozzle body is preferably about 
1/21" to about 11/2", more preferably from about 3/4" to about 1". This 
preferred heavier nozzle wall protects the central tube from damage by 
impact during the insertion or removal of the nozzle in a furnace. The 
heavier nozzle wall also reduces the susceptibility to thermal shock. 
Furthermore, any adjustments necessary to the nozzle can be made without 
any fear of damage to the parts of the nozzle. 
The nozzle body preferably has a back piece and a front piece and has an 
axial length denominated in FIG. 1 by L. The L/D.sub.n can be from 0.75 to 
2.5, wherein D.sub.n is the diameter of the nozzle body. Back piece 6 can 
comprise from about 10 to about 60% of the nozzle axial length and front 
piece 7 comprises from about 40 to about 90% of the nozzle axial length 
measured on the outer side of the nozzle body. Preferably, the nozzle will 
have an axial length within the range of from 0.5 to 2 times the diameter 
of opening 4. Generally, this will result in a nozzle having an axial 
length within the range of from 1 to 5 inches. Also, the opening in the 
cavity is usually minimized so that D.sub.c =D.sub.n +0.25". 
Back piece 6 preferably comprises a metal such as stainless steel, cast 
iron, other steels and other high temperature alloys having maximum 
surface temperatures, preferably within the range of from 1500.degree. F. 
to about 2200.degree. F. Other suitable materials can be used. 
Front piece 7 preferably comprises a ceramic such as refractory materials 
comprising alumina, silica, zirconium, magnesium, or silicon carbide. The 
preferred ceramic material for glass furnace applications is 
alumina-zirconia-silicate refractory. 
The maximum surface temperatures of ceramics are typically between 
2000.degree. F. and 4000.degree. F. A ceramic material normally used for 
the hot side of a furnace wall will generally be useful in the practice of 
this invention. 
The central tube (or tubular member) 9 can be made of the same material as 
the front piece of the nozzle body, but is preferably a ceramic tube. As 
an example, the ceramic tube can have an inner diameter of 1" and an outer 
diameter of 11/4". Preferably, besides being a ceramic tube, the central 
tube is a thin walled tube. The thickness of the central tube is less than 
or equal to the radial width of the annular passage or gap. Generally, the 
thickness of the ceramic tube wall is preferably from about 1/16" to about 
3/8", more preferably from about 1/8" to about 3/16". The material of the 
central tube can be any high temperature refractory material that is 
compatible with the temperature levels in a furnace and the gases being 
injected into a furnace. A preferred material is an alumina tube. Other 
materials that can be used for the central tube include, but are not 
limited to, mullite, quartz, silicon carbide, or molybdenum disilicide. 
Typically, the length of the central tube is from about 1.5 d to about 4 d, 
more preferably from about 1.5 d to about 1.6 d, wherein d is the inner 
diameter of the central tube. This preferred length minimizes the pressure 
drop of the gas emanating from the nozzle and entering the combustion 
zone. 
The difference between the outer diameter of the central tube 9 and the 
inner diameter at 12 of the nozzle body opening generally forming the 
nozzle body defines twice the radial width of the annular passage or the 
annulus gap 13. Preferably, this gap is less than 3/8"; more preferably 
from about 1/8" to about 3/8", most preferably is about 1/8" in thickness. 
When a gas enters the central tube and annular passage, the central tube's 
diameter preferably permits the flow of gas at a volume greater than the 
volume of gas flowing through the annular passage. 
Though not necessary, generally the gas entering the central tube and the 
gas entering the annular passage are from the same gas source or supply. 
Generally, this gas-supply may be an oxidant such as oxygen, 
oxygen-enriched air, or technically pure oxygen, or may be fuel which is 
any gas which contains combustibles and which may combust in the 
combustion zone, or may be a premixture of oxidants and fuel. Such fuels 
include, but are not limited to, natural gas, vaporized liquid fuel, coke 
oven gas, propane, hydrogen, and methane. 
The present invention will find particular utility with high velocity gases 
wherein the gas is ejected out the central tube and annular passage 
wherein the velocity of the gas exiting the central tube preferably 
exceeds about 150 feet per second and can reach velocities up to 1000 feet 
per second or more. More preferably, the velocity of the gas exiting the 
central tube is from about 185 feet/second to about 400 feet/second. The 
velocity of the gas exiting the annular passage is typically from about 10 
feet/second to about 50 feet/second. 
In general, the majority of the gas supplied to the nozzle enters the 
central tube and the remaining amount of gas enters the annular passage. 
Preferably, from about 80% by volume to about 95% by volume of the gas 
entering the nozzle from the gas source enters the central tube, more 
preferably about 90% by volume of the gas enters the central tube while 
the remaining amount, preferably about 10% by volume, enters the annular 
passage from the gas source. 
Back piece 6 communicates with a gas supply tube (shown in FIG. 3 as 25). 
In particular, the annular passage and central tube communicate with an 
inlet section 14. As shown in FIG. 2B, this inlet section has a central 
opening 15 and a plurality of openings 16 surrounding the central opening 
15. The central opening communicates with the central tube and the 
plurality of openings communicates with the annular passage. Generally, 
the plurality of openings is from about 4 to about 24 equally spaced 
openings, each having a diameter such that the total cross-sectional area 
of all the openings is from about 5 to 15 percent, preferably about 10% of 
the total area of the openings plus the central tube opening. The 
plurality of openings enable the attainment of the requisite low velocity, 
especially from the same gas source as that of the central tube fluid, 
which cannot be attained with a conventional thin annular opening while 
still maintaining the defined low relative gas flow. 
Generally, the annular passage has a length sufficient so that the velocity 
of the gas entering from the inlet section through the plurality of 
openings obtains a substantial uniform velocity in the annular passage 
prior to exiting the passage and entering the combustion zone. Preferably, 
the length of the annular passage is from about 1" to about 3". 
As shown in FIG. 1, the inlet section 14 also communicates with the inner 
diameter of the back piece 6. Preferably, the inlet section 14 is 
comprised of a pipe and is attached to the nozzle body as shown in FIG. 1 
by welding, brazing, or threading. Back piece 6 to front piece 7 can be 
adjoined by means of a reverse taper joint. Fiber ceramic gaskets 21 are 
used against the back piece and front piece to allow the front piece room 
to expand into the reverse taper joint. A reverse taper joint-gap 20 is 
filled with refractory ceramic cement similar to the way brick mortar 
fills the gap between two bricks. Small holes can be used to deliver 
refractory ceramic cement to joint-gap 20 which is circumferential. Other 
means of adjoining the front piece to the back piece include mechanical 
locking. 
Referring to FIG. 3, the annular flow 28 provides a shielding between the 
central tube which may be cold and the furnace gases 26 in addition to its 
heat transfer effects. These effects are especially seen when the central 
tube is of a thin walled construction since thin walls do not require as 
much gas to blanket their edges and hence can tolerate being slightly 
eccentric in the hole. Also, due to the entrainment of gas 26 into gas jet 
27 exiting the central tube, gas 28 flowing through the annulus, being of 
low momentum, will be preferentially pulled into jet 27 thus ensuring 
adequate blanketing of the central tube. Preferably, the nozzle of the 
present invention is either flush with the internal wall of the furnace 29 
or slightly recessed (i.e., recessed about 1/2D, where D is the diameter 
of the opening of the cavity in the furnace wall). However, if recessed in 
a cavity, other surfaces in the cavity may be low enough in temperature to 
nucleate condensation. Thus, if the nozzle of the present invention is 
recessed, bulk cavity purging techniques could be required especially if 
the nozzle is significantly recessed in the cavity. 
Preferably, the flow of the gas through the central tube and the flow of 
the gas through the annular passage are essentially parallel, i.e. 
coaxial. However, it is within the bounds of the present invention to 
configure the nozzle such that the flow of the gas through the annular 
passage converges into the flow of the gas through the central tube. 
The subject invention uses the annular flow to minimize the heat transfer 
between the cold gas flowing through the nozzle and the nozzle itself. 
This results in elevated nozzle temperatures and hence no condensation 
onto the nozzle. Although extending the length of the nozzle also creates 
elevated nozzle temperatures, it only addresses the axial flow of heat and 
not the more important radial flow of heat from the nozzle inside diameter 
to the cold jet. The fact that the deposits on the nozzle form as long 
tubes attached at the nozzle exit shows that the surface adjacent to the 
gas flow is the coldest section and the nucleation point of the 
condensation. 
The present invention minimizes the heat transfer from the hole or orifice 
from which the gas is exiting. Heat transfer analysis provides an example 
of the potential effectiveness of the present invention. The convective 
heat transfer coefficient in a pipe is a function of velocity of the gas. 
Keeping all other parameters constant, changing the velocity of the gas by 
a factor of 5, from 250 feet/second to 50 feet/second, would drop the 
convective heat transfer coefficient by 3.62. Using a heat balance 
equation in which the heat radiated from the furnace to the nozzle equals 
what is convected away by the flowing gas, the change in nozzle 
temperature resulting from this invention can be approximated: 
EQU Qrad=Qconv===&gt;A.delta.(T.sup.4.sub.furn -T.sup.4.sub.nozz)=hA(T.sub.nozz 
-T.sub.gas) 
After combining constants, the two equations become: 
EQU Co(T.sup.4.sub.furn -T.sup.4.sub.nozz)=h(T.sub.nozz -T.sub.gas) 
wherein T.sub.furn is the temperature in the furnace; T.sub.nozz is the 
temperature of the nozzle adjacent the furnace; and T.sub.gas is the 
temperature of the gas flowing through the nozzle, h is the convective 
heat transfer coefficient, and Co is a constant. 
By selecting initial conditions of temperature and heat transfer 
coefficient, the constant Co can be determined (e.g., at T.sub.furn 
=2800.degree. F., T.sub.gas =80.degree. F. and T.sub.nozz =1200.degree. 
F., and h=3.62 the constant Co becomes 4.times.10.sup.-11). By changing 
the heat transfer coefficient to 1 (equivalent to reducing the velocity by 
a factor of 5), a new nozzle temperature (T.sub.nozz) is calculated as 
2274.degree. F. This calculation demonstrates the utility of the present 
invention by showing the magnitude of the achievable temperature 
difference with the nozzle of the present invention. 
Another factor contributing to the success of the present invention is the 
small volume of gas flowing through the annular passage that has a small 
heat capacity. Thus, this gas in the annular passage increases in 
temperature more readily than the larger volume of gas in the central 
tube. This warmer gas in the annular passage again minimizes the heat 
transfer from the wall of the nozzle body to the gas by decreasing the 
temperature difference between adjacent materials. 
The present invention will be further clarified by the following examples, 
which are intended to be purely exemplary of the invention. 
A gas injection system was constructed using nozzles of the present 
invention using the preferred embodiments described earlier and 
illustrated in FIG. 1. In particular, the nozzle comprised a central 
refractory tube which carried 90% of the oxygen generally at a high 
velocity of about 250-400 ft/sec. The tube was located within the 
refractory tip nozzle such that an annulus was formed between the 
refractory central tube and the nozzle body. The remaining ten percent of 
the oxygen was passed through this cavity at a velocity of about 10-50 
ft/sec. The flow split between the two cavities was achieved by the 
difference in area between the inlet sections of the two passages. The 
annular passage, supplied by 12 holes, had enough length to ensure that 
velocity in that passage was uniform when it reached the exit of the 
passage. The ceramic tube had an outer diameter of 11/4" and an inner 
diameter of 1" and was placed in a 11/2" diameter ceramic nozzle. This 
produced a 1/8" annulus gap. The outer diameter of the nozzle was 27/8". 
When operated at 4230 scfh, the velocity of the main jet was 194 ft/sec 
and that of the annulus was 31 ft/sec. After six weeks of combustion being 
carried out within the combustion zone of an operating glass furnace, no 
fouling of the nozzle occurred. 
Other embodiments of the present invention will be apparent to those 
skilled in the art from consideration of the specification and practice of 
the present invention disclosed herein. It is intended that the 
specification and examples be considered as exemplary only, with a true 
scope and spirit of the present invention being indicated by the following 
claims.