CA1103607A - Exhaust gas recirculation jet - Google Patents
Exhaust gas recirculation jetInfo
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- CA1103607A CA1103607A CA303,613A CA303613A CA1103607A CA 1103607 A CA1103607 A CA 1103607A CA 303613 A CA303613 A CA 303613A CA 1103607 A CA1103607 A CA 1103607A
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- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10B—DESTRUCTIVE DISTILLATION OF CARBONACEOUS MATERIALS FOR PRODUCTION OF GAS, COKE, TAR, OR SIMILAR MATERIALS
- C10B21/00—Heating of coke ovens with combustible gases
- C10B21/10—Regulating and controlling the combustion
- C10B21/18—Recirculating the flue gases
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Combustion & Propulsion (AREA)
- Materials Engineering (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Organic Chemistry (AREA)
- Coke Industry (AREA)
- Combustion Of Fluid Fuel (AREA)
- Gas Burners (AREA)
Abstract
ABSTRACT
An ejector style exhaust gas recirculation jet is disclosed, for use in the underjet firing system of a coke oven battery, wherein a long throat of conventional diameter is combined with a non-tapered, reduced radius inlet trumpet and a straight nozzle positioned out of the entry flow path of hot exhaust gases. The present invention reduces deterioration of the nozzle from hot gas bombardment and at the same time stabilizes flow rate and pressure differentials in the entry and exit flues connected to the ejector resulting in more reliable and precise controlability of the coke oven combustion system.
An ejector style exhaust gas recirculation jet is disclosed, for use in the underjet firing system of a coke oven battery, wherein a long throat of conventional diameter is combined with a non-tapered, reduced radius inlet trumpet and a straight nozzle positioned out of the entry flow path of hot exhaust gases. The present invention reduces deterioration of the nozzle from hot gas bombardment and at the same time stabilizes flow rate and pressure differentials in the entry and exit flues connected to the ejector resulting in more reliable and precise controlability of the coke oven combustion system.
Description
1~36~7 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, ~336~7 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 6~7 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 6~7 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, ;}6~7 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.
6~7 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 - 5a -36'~7 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 ~1936~7 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
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, ~336~7 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 6~7 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 6~7 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, ;}6~7 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.
6~7 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 - 5a -36'~7 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 ~1936~7 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 6`~P7 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
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.
~lQ;~6~7 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 6~a7 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.
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 ~lQ36`~7 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 6~!7 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.
lists the results of the tests run on Mod. 2.
~lQ;~6~7 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 6~a7 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.
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 ~lQ36`~7 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 6~!7 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.
Claims (8)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An exhaust gas recirculation jet for use in the underjet firing system of a coke oven battery comprising:
a) a suction chamber member having a cylindrical internal cavity of height equal to diameter, b) a riser member, forming the first end of said cylindrical internal cavity of such suction chamber member, having a cylindrical internal cavity the central axis of which forms a continuation of the central axis of said cylindrical internal cavity of said suction chamber member, but having a smaller diameter than the diameter of said cylindrical internal cavity of said suction chamber member, said cylindrical internal cavity of said riser member forming a stepped entry into said cylindrical internal cavity of said suction chamber member, c) a nozzle of conventional external and internal dimension centrally mounted within said cylindrical internal cavity of said riser member, the tip of said nozzle being recessed within said riser member away from said stepped entry, d) a suction chamber inlet section having a cylindrical internal cavity, equal in diameter to said cylindrical internal cavity of said suction chamber member, positioned to form a side entry into said cylindrical internal cavity of said suction chamber member, the central axis of which is perpendicular to the central axis of said cylindrical internal cavity of said suction chamber member, e) a flare section forming the second end of said cylindrical internal cavity of said suction chamber member, having a cir-cular aperture aligned about the central axis of said cylin-drical internal cavity of said suction chamber member, said circular aperture having a trumpet-mouth shaped side view cross-sectional configuration formed of a 90° arc, the larger diameter of which forms an exit from said cylindrical internal cavity of said suction chamber member, the smaller diameter being remote fro said exit;
f) a throat section, having an internal cylindrical cavity equal in diameter to the smaller diameter of said circular aperture of said flare section, the first end of said throat section being fixed to said flare section and positioned, the central axis of said internal cylindrical cavity of said throat section commencing at and running perpendicular from the center of said circular aperture of said flare section, such that said circular aperture of said flare section forms a transition from said internal cylindrical cavity of said suction chamber member into said internal cylindrical cavity of said throat section, the length of said internal cylindrical cavity of said throat section being about equal to about one to two throat diameters, g) a secondary diffuser having an internal cavity in the shape of a conical section, the smaller diameter of said conical section being equal to the diameter of said internal cylindrical cavity of said throat section, the smaller diameter of said conical section forming the egress from said internal cylindrical cavity of said throat section, the central axis of said conical section being an extension of said central axis of said internal cylindrical cavity of said throat section, such that said conical section forms a transition of said diameter of said internal cylindrical cavity of said throat section into a larger diameter.
a) a suction chamber member having a cylindrical internal cavity of height equal to diameter, b) a riser member, forming the first end of said cylindrical internal cavity of such suction chamber member, having a cylindrical internal cavity the central axis of which forms a continuation of the central axis of said cylindrical internal cavity of said suction chamber member, but having a smaller diameter than the diameter of said cylindrical internal cavity of said suction chamber member, said cylindrical internal cavity of said riser member forming a stepped entry into said cylindrical internal cavity of said suction chamber member, c) a nozzle of conventional external and internal dimension centrally mounted within said cylindrical internal cavity of said riser member, the tip of said nozzle being recessed within said riser member away from said stepped entry, d) a suction chamber inlet section having a cylindrical internal cavity, equal in diameter to said cylindrical internal cavity of said suction chamber member, positioned to form a side entry into said cylindrical internal cavity of said suction chamber member, the central axis of which is perpendicular to the central axis of said cylindrical internal cavity of said suction chamber member, e) a flare section forming the second end of said cylindrical internal cavity of said suction chamber member, having a cir-cular aperture aligned about the central axis of said cylin-drical internal cavity of said suction chamber member, said circular aperture having a trumpet-mouth shaped side view cross-sectional configuration formed of a 90° arc, the larger diameter of which forms an exit from said cylindrical internal cavity of said suction chamber member, the smaller diameter being remote fro said exit;
f) a throat section, having an internal cylindrical cavity equal in diameter to the smaller diameter of said circular aperture of said flare section, the first end of said throat section being fixed to said flare section and positioned, the central axis of said internal cylindrical cavity of said throat section commencing at and running perpendicular from the center of said circular aperture of said flare section, such that said circular aperture of said flare section forms a transition from said internal cylindrical cavity of said suction chamber member into said internal cylindrical cavity of said throat section, the length of said internal cylindrical cavity of said throat section being about equal to about one to two throat diameters, g) a secondary diffuser having an internal cavity in the shape of a conical section, the smaller diameter of said conical section being equal to the diameter of said internal cylindrical cavity of said throat section, the smaller diameter of said conical section forming the egress from said internal cylindrical cavity of said throat section, the central axis of said conical section being an extension of said central axis of said internal cylindrical cavity of said throat section, such that said conical section forms a transition of said diameter of said internal cylindrical cavity of said throat section into a larger diameter.
2. An exhaust gas recirculation jet as recited in claim 1, in which said suction chamber member, said riser member, said suction chamber inlet section, said flare section, said throat section and said secondary diffuser are composed of conventional refractory material.
3. An exhaust gas recirculation jet as recited in claim 1 wherein said central axis of said internal cylindrical cavity of said suction chamber member is vertical.
4. An exhaust gas recirculation jet as recited in claim 1 wherein said 90° arc of said circular aperture of said flare section has a radius dimension of less than 1 inch.
5. An exhaust gas recirculation jet as recited in claim 1 wherein said nozzle tip is positioned between 1 inch and 2 inches distant, within said riser member, from said stepped entry.
6. An exhaust gas recirculation jet as recited in claim 1 wherein the diameter dimension of said internal cylindrical cavity of said throat section is within the range of 2 inches and 3 inches, inclusive.
7. An exhaust gas recirculation jet as recited in claim 1 wherein the length dimension of said internal cylindrical cavity of said throat section is within the range of 2-1/2 inches and 5 inches, inclusive.
8. An exhaust gas recirculation jet as recited in claim 1 wherein the distance between said nozzle tip and said smaller diameter of said circular aperture of said flare section is within the range of 2-1/2 inches and 5 inches, inclusive.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US83215277A | 1977-09-12 | 1977-09-12 | |
| US832,152 | 1977-09-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1103607A true CA1103607A (en) | 1981-06-23 |
Family
ID=25260837
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA303,613A Expired CA1103607A (en) | 1977-09-12 | 1978-05-18 | Exhaust gas recirculation jet |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS5453101A (en) |
| CA (1) | CA1103607A (en) |
| DE (1) | DE2834803A1 (en) |
| FR (1) | FR2402833A1 (en) |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR454172A (en) * | 1912-08-31 | 1913-06-27 | Dr C Otto & Comp Ges Mit Beschraenkter Haftung | Coke oven for heating alternately with lean gas, rich gas, or a mixture of the two |
| FR1179237A (en) * | 1955-10-03 | 1959-05-21 | Koppers Co Inc | Coke oven structure |
-
1978
- 1978-05-18 CA CA303,613A patent/CA1103607A/en not_active Expired
- 1978-08-09 DE DE19782834803 patent/DE2834803A1/en not_active Withdrawn
- 1978-08-23 FR FR7824506A patent/FR2402833A1/en active Granted
- 1978-09-12 JP JP11216778A patent/JPS5453101A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| DE2834803A1 (en) | 1979-03-15 |
| FR2402833A1 (en) | 1979-04-06 |
| JPS5453101A (en) | 1979-04-26 |
| FR2402833B1 (en) | 1982-07-02 |
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