Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The most prevalent and widely used design for coke oven batteries is
classified as the underjet fired horizontal coke oven. In this design coal
is placed into a horizontal oven chamber. Vertical combustion flues run
along the sides of the oven chamber, separated from that chamber by heat
resistant refractory material. It is in these flues that combustion occurs.
Under the oven chambers are refractory heat exchangers called
regenerators. Their purpose is to preheat the air used in the combustion
flues to obtain a high ~emperature level and more efficient combustion.
But to preheat air, the regenerators must first be heated. This is
accomplished by first channelling hot exhaust gases from combustion in the
combustion flues on the opposite side of the oven chamber, across the top of
that oven chamber, down through the non-burning combustion flues on the
opposite side of the oven chamber. From there the hot exhaust gases continue
down through the regenerator to heat the refractory. The exhaust gases
then exit the bottom of the regenerator into a waste gas flue which delivers
the waste gases to the battery stack and ~hen to the atmosphere. In an
alternate underjet battery design the heating flues of each heating wall are
arranged in pairs, called hairpins, wherein combustion occurs in one flue of
each pair and the waste gases are delivered to the regenerators by flowing
them down~ard through the second flue of each pair. In both battery
designs the functions of the burning and non-burning flues are periodically
reversed in order to restore the temperature conditions of the regenerators.
For optimum operation of underjet coke oven batteries, it has been
found historically to be beneficial to dilute the rich fuel gas with recircu-
lated waste gas prior to combustion. This dilution serves two very useful
purposes. Due to the oxygen content of the recirculated waste gas, its
- addition to the rich fuel gas avoids the accumulation of carbon deposits
formed by high temperature cracking of hydrocarbons in the fuel. Secondly,
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dilution of the fuel gas with recirculated waste gas slows down the
combustion of the rich fuel gas causing a longer flame and more uniform
vertical heat distribution in the vertical heating flues. Past experience
has shown that a concentration of waste gas of about 50% or greater in
the fuel gas-waste gas mixture gives good results.
In practice, the quantity of waste gases needed for recirculation
has been withdrawn from near the bottom of the non-burning flue through the
fuel gas riser. This riser is interconnected by a recirculation duct with
the fuel gas riser of a burning flue of the companion wall, or companion flue
of a hairpin. The motive force which induces the flow of recirculated waste
gas comes from the jet of rich fuel gas being fed into the riser of the
burning flue. This rich fuel gas jet is discharged at high velocity into
the throat of a venturi type ejector which serves to aspirate the waste gases
from the non-burning flue and to mix the rich fuel gas and recirculated waste
gases to form the combination mixture. This combustion mixture passes up
through the fuel gas riser bf the burning flue into the combustion flues
where it is burned. As this cycle continues, the near side regenerator
decreases in temperature and the opposite side regenerator is increased in
temperature. At a given point of relative temperature gradation, valves
operate to rechannel the gases into an opposite direction of flow. Now
combustion occurs in the opposite side combustion flue with the exhaust gases
descending through the near side combustion flue to the near side regenerator.
The present invention relates to the area of the coke oven where a
portion of the hot exhaust gases are mixed with rich fuel gas prior to
ascending into the burning flues. In this area, the exhaust gas is entrained
in a stream of rich fuel gas by a device known, alternately, as an ejector or
a jet.
. Description of the Prior Art.
~ Conventional jets are composed of several eleme~ts. A rich fuel gas
nozzle is placed at the bottom of a suction chamber. This nozzle has a
straight bore which , in operation, produces a conical pattern of pressurized
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gas exiting from it. This gas is called the motive gas. The included angle
of the cone has been found to be about 20, varying slightly as gas pressure
through the nozzle varies.
The suction chamber has a single inlet positioned on the side of
the suction chamber. The recirculated waste gas, termed as the induced gas,
enters the jet through this inlet.
Directly opposite the nozzle, on the top of the suction chamber,
is a primary diffuser. This primary diffuser is in the form of a conical
section, the large end of which provides the exit from the suction chamber.
Accumulated design data indicates that the included angle of the primary
diffuser should be in the range of 25 for best results, the theory being
that it must be greater than the naeural 20 angle of pressurized motive gas
emanating from the nozzle to eliminate turbulence, shock and eddy losses.
The small end of the conical section of the primary diffuser
provides the entry into a throat. The throat is simply a cylindrical form
with straight smooth walls, all sides being parallel. The diameter of the
throat is quite critical in that small changes in this dimension change
the pressure loss of the system and also greatly chan~e the
amount of induced gas entrained by the motive gas. Under the conditions
operable in an underjet firing system, a diameter of 2-1/4 inches has been
determined by extensive testing to be suitable for batteries having large
capacity ovens. Another throat dimension must also be considered. That is
the length of the throat. In practice this dimension i5 short in relation
to the throat diameter, being only about 1/4 inch, and providing a ratio
of about 9 to 1.
At the upper end of the throat is placed a second conical
diffuser, called the secondary diffuser, the conical section being opposite
in projection to the primary diffuser. The smaller diameter of this
conical section mates with the top of the throat while the larger diameter
exits into the fuel gas riser.
Previous designs of jets for coke oven application placed the
nozzle adjacent to or within the largest diameter of the conical sectlon of
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the primary diffuser. ~ater tests showed that as nozzle gas pressure
increased, the nozzle could be retracted away from the diffuser. It was
learned that the key factor was the distance between the nozzle tip and
the throat entry, this being a direct function of nozzle gas pressure. The
l~wer the pressure, the closer the nozzle tip needed to be to the throat
entry.
The principle upon which a jet operates is one of combining gas
velocity with rapid pressure drop. Motive gas is ejected under pressure
from the nozzle. As lt escapes it expands due to lowered pressure. This
expanding jet entrains the surrounding gases, in this case recirculated
waste gas, and some of the kinetic energy of the motive gas is imparted to
the entrained recirculated waste gases. Entrainment of the waste gases
creates a low pressure zone in the suction chamber and the entrained gases
are replaced by additional waste gases from the non-burning flue. The
velocity of the motive gas carries the induced gas with it into the throat
where the combination is constricted, decreasing the velocity and raising
the pressure. As the combination of gases exits the throat, it again expands,
increasing in velocity and decreasing in pressure, which tends to enhance
the direction of flow through the jet.
However, several problems have become apparent in the application
of iets to coke ovens. The first is that, due to the volume of exhaust gas
required to be entrained with rich fuel gas, to attain acceptable combustion
characteristics, the inlet to the suction chamber must be relatively large.
To effect this, the suction chamber must also be relatively large. The rich
fuel gas pressure must be kept relatively low for safety reasons, therefore
the nozzle is placed up into the suction chamber to position it at a proper
distance from the throat entry. Thus, it is placed directly into the flow
path of the hot exhaust gases. The heat attacks the nozzle causing
- corrosion and erosion, necessitating frequent nozzle changes.
A second problem is that, due to the short throat length of the
e~ector and other dimensional relationships which have been used in the past,
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the flow rate of entrained waste gases at times is erratic, unstable and
highly sensitive to prevailing process conditions and jet orientation. As
a result, optimum fuel gas-waste gas mixtures might not always be realized.
Brief Description of the Drawings
Fig. 1 is a schematic representation of the test apparatus
used to develop the present invention.
Fig. 2 is a schematic representation of the standard jet
configuration in use in conventional underfired coke oven batteries as used
in the test apparatus.
Fig. 3 is a schematic representation of a modification of jet
configuration (Mod. 1) as used in the test apparatus.
Fig. 4 is a schematic representation of a modification of jet
configuration (Mod. 2.) as used ln the test apparatus.
Fig. 5 is a side cross section view of a jet for use in an
underfired coke oven battery, corresponding to Mod. 2, as illustrated in
Fig. 4.
Summary of the Invention
The present invention is directed primarily to improvements in
mixing jets ~n underfired coke oven batteries in which the jet is used to
mix rich fuel gas with hot recirculated exhaust gases. A conventional sized
suction chamber is utilized along with its attendant conventional sized
suction chamber inlet~ A rich fuel gas nozzle is recessed into a riser in
the bottom of the suction chamber of an ejector such that the nozzle tip is
positioned out of the flow of hot exhaust gases entering the suction chamber.
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At the top of the suction chamber no entrance cone to the ejector is used.
A cylindrical throat of conventional diameter runs vertically from the top
of the suction chamber to a transition point. At the transition point the
smaller end of a conical secondary diffuser begins. The large end of the
conical secondary diffuser opens into the fuel gas riser leading to the
base of the heating flue.
The connection of the end of the throat to the suction chamber
is formed by a small radius or flare rather than a 90 angle. The flare
eliminates turbulence created by the otherwise abrupt change in volumetric
configuration.
Tests have indicated that the nozzle position in relation to
the leading edge of the throat is critical. Of equally critical importance
is the length of the throat. Best results are attained, using a conven-
tional 2-1/4" throat diameter, when the distance from the nozzle tip to the
leading edge of the throat is equal to 2-1/3 diameters or approximately
5-1/4".
A full scale model was constructed to test various factors
critical to coke oven operation as affected by a jet. The model was
constructed from clear plastic and was operated cold. Air was used as a
gaseous medium rather than rich fuel gas and hot exhaust gases. The plastic
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was molded to simulate the actual refractory shapes and surface textures as
are in use in conventional coke oven batteries. The duct work leading to
and from the jet was a duplication of an actual installation now in operation
in terms of size, shape and configuration. Fig. 1 is a schematic
representation of the arrangement of the test apparatus including all
dimensions and the placement of all measuring equipment.
Referring to Fig. 1, a metering orifice was provided at
point B to measure the induced air flow rate and, concurrently, to impose
a pressure drop in the system to simulate the total normal pressure drop
found in existing coke oven batteries. The pressure differential imposed
by the metering orifice was measured by a micromanometer having a range
of 0 to -2 inches of water column and a professed accuracy and repeatability
of within +.0005 inch of water column.
The nozzle mounting was equipped with 0-ring seals within a
riser to provide adjustability of the distance between the nozzle tip and
the throat. A pressure indicator was inserted into the riser, well below
the turbulent zone of the suction chamber, to measure static pressure within
the suction chamber.
Air from a standard compressor was supplied tG the nozzle, as
illustrated in Fig. 1, through a filter, a pressure regulator, and a flow
meter (a device to measure volume of gas per interval of time, such as in
cubic feet per minute, CFM). Pressure indicators (Pl) were inserted, one on
each side of the flow meter, to permit correction of the flow meter reading
for the prevailing static pressure in the flow meter.
The nozzle port diameter (I.D. of the nozzle) used was
0.4688 inch, this being a typical nozzle diameter actually used in operating
coke oven batteries. Likewise, to simulate actual operating practice, the
nozzle port length (the length of the internal bore of the nozzle) was
maintained at 1 inch.
The motive air rate through the nozæle was maintained at
9 43 cubic feet per minute, to give the motive stream momentum equivalent
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to the fuel gas momentum rate used in the coke oven battery from which the
test apparatus was patterned.
The object of the test was to determine the ratio of the
volume of induced gas entering through the suction inlet to the volume
of motive air entering through the nozzle, as related to various arrangements
of jet elements. Five different throat and diffuser arrangements were
tested. For all five, the position of the nozzle tip was altered from
4 inches below its normal position to 4 inches above its normal position in
1/2 inch increments Tables I, II and III show comparable results of
tests with the standard jet configuration and with two preferred jet
configurations and nozzle tip positions. At each increment the ratio of
induced gas to motive gas was calculated. Fig. 2 is a schematic representa-
tion of the standard jet configuration as currently used in coke oven
batteries. Figs. 3 and 4 are schematic representations of the two preferred
modifications, hereinafter termed as Mod. 1 and Mod. 2 respectively.
Table I lists the results of the tests run on the standard jet configuration.
TABLE I
Nozzle position relative to Induced Gas Flow
Distance Below (-) or Ratio:Motive Gas Flow
Above (+) the Design Position
- 3 1.05
- 2-1/2" .97
- 2" .98
- 1-1/2 " 1.00
- 1" 1.05
- 1/2" 1.59
1.64
+ 1/2" 1.67
+ 1" 1.67
+ 1-112" 1.64
+ 2" 1.60
+ 2-1/2" 1.59
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The concept of Mod. 1, as illustrated in Fig. 3, was to
completely eliminate the diffuser. Mod. 1 incorporates a 4-5/8 inch throat
length with a 1/8 inch radius flare at the point of connection with the
suction box. The test was repeated for this modification. Table II lists
the results of the tests run on Mod. 1.
TABLE II
Nozzle Position Relative to Induced Gas Flow
Distance Below (-) or Ratio:
Above (+) the Design Position Motive Gas Flow
~ 4" 1.16
- 3-172" 1.26
_ 3~ 1.58
- 2-1/2" 1.66
- 2" 1.70
- 1-1/2" 1.73
- 1" 1.73
- 1/2" 1.71
o 1.71
+ 1/2" 1.68
+ 1" 1.~5
+ 1-1/2" 1.63
+ 2" 1.59
+ 2-1/2" 1.54
Mod. 2 as illustrated in Fig. 4 differs from Mod. 1, as
illus~rated in Fig. 3 in that the radius of the flare is increased fr3m
1/8 inch to 11/16 inch and the throat length is reduced from 4-5/8 inches
to 3-7/8 inches. The test was repeated for this modiication. Table III
lists the results of the tests run on Mod. 2.
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TABLE III
Nozzle Position Relative to Induced Gas flow
Distance Below (-) or Ratio:
Above (+) the Design Position Motive Gas flow
- 3-1/2" 1.31
- 3" 1.59
- 2-112" 1.57
- 2" 1.~8
- 1-1/2" 1.70
- 1" 1.73
- 1/2" 1.72
0 1.73
+ 1/2" 1.73
+ 1" 1.71
+ 1-112" 1.69
+ 2" 1.65
+ 2-1/2" 1.72
It should be noted that the ratios recorded in Table I
between the -1-1/2 lnch nozzle position and the +1 inch nozzle position,
inclusive, are average figures. The induced air flows recorded on the standard
arrangement fluctuated in an unstable manner. Therefore multiple values
were recorded for each of the nozzle positions in these three arrangements
within the above mentioned control range of nozzle positions. To get a
usable figure the recorded figures were averaged. ~o fluctuations were
recorded or noted for the arrangements in Mod. 1 and Moa. 2.
The conclusions to be drawn from the test data are that by
utilizing Mod. 1 or Mod. 2 the nozzle tip can be recessed into the riser, out
of the path of flow of the induced gas fl~w (hot exhaust gas in a coke oven
battery), and the fluctuations in the mixture of gases, induced and motive
~the combustion gas in a coke oven battery), can be eliminated. But these
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conclusions are only tentative until a determination is made concerning
the pressure differential that would, in practice, occur between the
downflow of hot exhaust gas in the opposite fuel gas riser, reversing
the direction of flow through the inactive jet, and the crossover inlet
pipe leading into the near side suction chamber. Unless this pressure
differential is within an acceptable range, the active jet will be unable
to pump the required amount of waste gases needed to provide optimum
dilution.
The normal pressure differential through the waste gas
recirculating system between the base of a pair of burning and non-burning
flues of a coke oven battery is in the range of 5 mm of Water Column
(0.197 inch). Referring to Fig. 1, a micromanometer measured the pressure
drop from G to C. The test revealed that at operating conditions the
increase in pressure differential in a real battery for Mod. 1, as
illustrated in Fig. 3, would be about 0.336 mm of Water Column while the
increase in pressure differential for Mod. 2, as illustrated in Fig. 4,
would be about 0.132 mm of Water Column, both considered with an
acceptable range with Mod. 2 being preferred. Therefore the early
conclusion has its tentative condition removed.
Accordingly, one of the principal features of the present
invention is to provide a means by which the nozzle can be positioned
outside of the flow of the hot exhaust gas mixture.
Another feature of the present invention is to provide a
means by which the ratio of induced gas to motive gas can be stabilized
and controlled in an underfired coke oven battery jet.
Another feature of the present invention is to provide
a means by which the downflow pressure differential in the idle jet is
maintained within acceptable limits concurrent with the above features.
These and other features of the present invention will be
more completely disclosed and described in the following specification, the
accompanying drawing and the appended claims.
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Detailed Description
Referring to the drawings, specifically Fig. 5, there is
illustrated an exhaust gas recirculation jet generally designated by the
numeral 11 that includes a nozzle 12 of conventional shape and size as used
in existing underjet coke oven batteries. The nozzle 12 is positioned
centrally in a riser section 13 such that the nozzle tip 14 is recessed
from the top edge 15 of the riser 13 a distance of 1-1/2 inches. The riser
13 is cylindrical in configuration and of sufficient diameter to allow easy
placement and replacement of the nozzle for maintenance purposes, notl~_nally
2-1/2 inches in diameter.
Positioned above the riser section 13 is a vertically cylindrical
suction chamber section 16. A horizontally cylindrical suction chamber
inlet 17 is connected to the side of the suction chamber section 16. The
height and diameter of the suction chamber section 16 are dictated by
the diameter of the suction chamber inlet section 17 which in turn is
dictate~ by the volume of gas at a given pressure to be flowed through the
jet 11. Nominally this diameter is approximately 3-1/2 inches. The suction
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chamber section 16 is centrally positioned about the nozzle 12. Directly
opposite the nozzle 12 and the riser 13, at the top of the suction chamber
section 16, is a flare section 18 formed of a radiused dimetrical section
as illustrated in the drawings. The cross-sectional radius dimension is
11/16 inch, the bottom diameter of the flare section 18 being 3-3/8 inches
and the top diameter being 2-1/4 inches. Thus, the height of the flare
section is also 11/16 inch.
Centrally positioned directly above the flare section 18 is a
throat section 19. The throat section 19 is a cylindrical shape, the
internal dimensions being 2-1/4 inches in diameter and 3-7/8 inches height,
Thus a smooth transition is made from the top of the flare section 18
into the throat section 19.
Centrally positioned above the throat section 19 is a secondary
diffuser 20 of conventional size and configuration. Nominally, the
secondary diffuser 20 is internally formed of a conical section, the smaller
diameter conforming to the throat section's 19 internal diameter, a height
of 7 inches and a 17 included angle. The larger internal diameter of the
secondary diffuser 20 forms the fuel gas riser entry section 21.
The riser section 13, suction chamber section 16, suction
chamber inlet section 17, flare section 18, throat 19, secondary diffuser 20,
and the fuel gas riser entry section 21 are all composed of conventional
refractory material.
The motive gas, rich fuel gas, enters the jet 11 through the
nozzle 12 under pressure. Nominally the pressure is in the range of about
125 mm W.C. The nozzle 12 expels the motive gas vertically into the suction
chamber section 16 where the motive gas expands from its initial pressure
to a pressure less than that of the induced gas, hot exhaust gas, already
in the suction chamber section 16. In the process of being expanded, the
motive gas is accelerated from its initial entrance velocity to a
relatively high velocity, generally directed upward but fannin~ outward to
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form a conical flGw path with an in(luded angle of approximately 20 . The
result is a region, within the suction chamber section 16, of low pressure,
high velocity flow which causes the induced gas of higher pressure to
become entrained with the motive gas, moving with it. Additional induced
gas is drawn into the suction chamber section 16 through the suction
chamber inlet section 17. During this entrainment, the motive gas is
decelerated and the induced gas is accelerated in velocity. As the
mixture of motive and induced gas enters the throat section 19 it is
compressed by the reduction in cross-sectional area of the throat section 19.
This compression reduces the velocity of the gas mixture. The flare
section 18 serves to eliminate the otherwise abrupt transition from the
suction chamber section 16 into the throat section 19. The mixture, at the
increased pressure and reduced velocity, is then expelled ~rom the throat
section 19 into the secondary diffuser 20 at a relatively stabile condition
of velocity and pressure. In the secondary diffusel 20 the gas mixture
decreases slightly in pressure and increases slightly in velocity directed
upwardly through the fuel gas riser entry section 21 into the fuel gas
riser to the burning flue above.
According to the provisions of the patent statute, the principal,
2Q preferred construction and mode of operation of the present invention have
been illustrated and its best embodiment has been described. However, it
is ~o be understood that, within the scope of the appended claims, the
invention may be practiced otherwise than as specifically illustrated and
descr~bed.
