Multiple coherent jet lance

A system for establishing a plurality of coherent gas jets proximate one another using a single lance wherein plurality of gas jets are ejected from a corresponding plurality of nozzles in a lance and a flame envelope is established around the plurality of gas jets, and the jets remain distinct and do not coalesce for their length.

TECHNICAL FIELD
 This invention relates generally to the flow of gas. The invention enables
 the flow of more than one gas stream from a single lance such that the gas
 streams flow proximate to one another for an extended distance while
 remaining distinct.
 BACKGROUND ART
 It is often desired to establish a flow of gas. For example, a flow of gas
 may be injected into a liquid for one or more of several reasons. A
 reactive gas may be injected into a liquid to react with one or more
 components of the liquid, such as, for example, the injection of oxygen
 into molten iron to react with carbon within the molten iron to
 decarburize the iron and to provide heat to the molten iron. Oxygen may be
 injected into other molten metals such as copper, lead and zinc for
 smelting or refining purposes or into an aqueous liquid or hydrocarbon
 liquid to carry out an oxidation reaction. A non-oxidizing gas, such as an
 inert gas, may be injected into a liquid to stir the liquid in order to
 promote, for example, better temperature distribution or better component
 distribution throughout the liquid.
 Sometimes it is desirable to have the gas stream flow for an extended
 distance at a high velocity such as a supersonic velocity. This can be
 done by surrounding the gas stream in a flame envelope. The flame envelope
 keeps ambient gas from aspirating into the gas stream and this leads to
 the establishment of a coherent gas stream which can flow for an extended
 distance without any significant decrease in the gas stream velocity or
 significant increase in the diameter of the gas stream.
 It is often desirable to use more than one gas stream in an operation. The
 gas could be the same for all the gas streams, or different gases could be
 used for one or more of the gas streams. For example, in electric arc
 furnace practice or basic oxygen furnace practice it is sometimes
 preferable to inject oxygen into the molten metal at two or more locations
 rather than at a single location. Moreover, in electric arc furnace
 practice it may be desirable to use one or more gas streams for gas
 injection into the molten metal and, in addition, one or more gas streams
 to provide oxygen into the head space of the furnace vessel for post
 combustion.
 When in such multiple gas stream practice it is desired that the gas
 streams also be coherent, this has heretofore been accomplished by using a
 separate injection lance for each gas stream whereby the gas streams and
 the fluids for the corresponding flame envelopes for each of the gas
 streams are provided. While such a system using multiple lances
 effectively provides multiple coherent gas streams, it is costly and
 difficult to use. These problems increase as the number of individual
 lances increases.
 Accordingly, it is an object of this invention to provide a system for
 establishing multiple coherent jets wherein only a single injection lance
 is required.
 SUMMARY OF THE INVENTION
 The above and other objects, which will become apparent to one skilled in
 the art upon a reading of this disclosure, are attained by the present
 invention, one aspect of which is:
 A method for establishing multiple coherent gas jets from a single lance
 comprising:
 (A) providing a lance having an end with a plurality of nozzles, each of
 said nozzles having an output opening for ejecting gas from the nozzle;
 (B) passing gas in a jet out from each nozzle output opening and forming a
 plurality of gas jets, each gas jet flowing from a nozzle output opening;
 (C) passing fuel and oxidant in at least one stream out from the lance end
 and combusting the said fuel with the said oxidant to form a flame
 envelope around the plurality of gas jets; and
 (D) maintaining the flow of each gas jet distinct for the length of said
 gas jet.
 Another aspect of the invention is:
 A lance for establishing multiple coherent gas jets comprising:
 (A) a lance having an end with a plurality of nozzles, each said nozzle
 having an input opening and an output opening;
 (B) each said nozzle input opening communicating with a source of gas, and
 each said nozzle output opening disposed on the face of the lance end;
 (C) at least one ejection means at the lance end face around the plurality
 of nozzle output openings; and
 (D) an extension extending from the lance end face forming a volume with
 which each of the plurality of nozzle output openings and the ejection
 mean(s) communicates.
 Another aspect of the invention is:
 A method for establishing multiple coherent gas jets from a single lance
 comprising:
 (A) providing a lance having an end with a plurality of nozzles, each of
 said nozzles having an output opening for ejecting gas from the nozzle;
 (B) passing gas in a jet out from each nozzle output opening and forming a
 plurality of gas jets, each gas jet flowing from a nozzle output opening;
 (C) passing fuel in at least one stream out from the lance end around the
 plurality of gas jets and combusting the said fuel with air entrained into
 the fuel stream(s) to form a flame envelope around the plurality of gas
 jets; and
 (D) maintaining the flow of each gas jet distinct for the length of said
 gas jet.
 As used herein the term "annular" means in the form of a ring.
 As used herein the term "flame envelope" means a combusting stream
 coaxially around at least one other gas stream.
 As used herein the term "length" when referring to a gas jet means the
 distance from the nozzle from which the gas is ejected to the intended
 impact point of the gas jet.
 As used herein the term "distinct" when referring to a gas jet means
 without significantly interacting with another gas jet.
 As used herein the term "contained oxygen flowrate" means the oxidant
 flowrate times the percent oxygen in the oxidant divided by 100. For
 example, 10,000 CFH pure oxygen has 10,000 CFH contained oxygen and 10,000
 CFH air has about 2,100 CFH contained oxygen.

The numerals in the drawings are the same for the common elements.
 DETAILED DESCRIPTION
 The invention will be described in detail with reference to the Drawings.
 Referring now to FIGS. 1 and 2, lance 1 has an end or tip section 2
 housing a plurality of nozzles 3. FIG. 1 illustrates a preferred
 embodiment of the invention wherein the nozzles are each
 converging/diverging nozzles. Each of the nozzles 3 has an input opening 4
 and an output opening 5. Preferably, as illustrated in the Figures, the
 nozzle output openings are circular, although other shapes, such as
 elliptical nozzle openings, may be used. The input openings 4 each
 communicate with a source of gas. In the embodiment illustrated in FIG. 1
 all of the input openings 4 communicate with the same source of gas, that
 source being gas passageway 6 within lance 1. Alternatively one or more of
 the input openings 4 could communicate with another gas source. Gas having
 the same composition could be provided to all of the nozzles, or different
 gases could be provided to one or more of the nozzles. Indeed, a different
 gas could be provided to each of the nozzles. Among the gases which could
 be used in the practice of this invention for ejection from a nozzle one
 can name air, oxygen, nitrogen, argon, carbon dioxide, hydrogen, helium,
 gaseous hydrocarbons, other gaseous fuels and mixtures comprising one or
 more thereof.
 The gas jets may come off at any angle upon ejection from the lance. The
 Figures illustrate certain preferred embodiments of the invention.
 Referring to FIGS. 1-3, the nozzles may be oriented in the lance end with
 their centerlines parallel with the centerline of the lance. As
 illustrated in FIG. 1, the nozzles are oriented in the lance end with
 their centerlines at an outward angle A to the centerline of the lance.
 Angle A may be up to 60 degrees or more and preferably is in the range of
 from 0 to 30 degrees, most preferably within the range of from 0 to 15
 degrees. Preferably the throat diameter of the nozzles is within the range
 of from 0.25 to 3 inches and the diameter of output openings 5 is within
 the range of from 0.3 to 4 inches. Preferably the nozzle centerlines form
 a circle on the face 7 of lance end 2 having a diameter D. Preferably D is
 at least 0.4 inch and no more than 10 inches and most preferably is within
 the range of from 0.5 to 8 inches.
 If desired, the nozzles may be oriented so that one or more jets are
 ejected from the lance at an inward angle to the lance centerline.
 Gas is ejected out from each of the nozzle output openings 5, preferably at
 a supersonic velocity and generally within the range of from 500 to 10,000
 feet per second (fps), to form a plurality of gas jets, each gas jet
 flowing outwardly from a nozzle output opening.
 The lance end also has at least one ejection means, preferably an annular
 ejection means, for passing at least one gas stream out from the nozzle,
 preferably concentrically around the plurality of gas jets. The gas stream
 or streams passed out from the ejection means can be in any effective
 shape and need not go completely around the plurality of gas jets. When
 one annular ejection means is employed the concentric gas stream
 preferably comprises a mixture of fuel and oxidant. In one embodiment of
 the invention the injection means may provide only fuel, and the oxidant
 needed for the combustion with the fuel to form the flame envelope may
 come from air entrained into the fuel stream or streams. Preferably, as
 illustrated in FIGS. 1 and 2, the lance end has a first annular ejection
 means 8 and a second annular ejection means 9 for passing respectively
 fuel and oxidant out from the lance in two concentric streams. The fuel
 may be any fluid fuel such as methane, propane, butylene, natural gas,
 hydrogen, coke oven gas, or oil. The oxidant may be air or a fluid having
 an oxygen concentration which exceeds that of air. Preferably the oxidant
 is a fluid having an oxygen concentration of at least 30 mole percent,
 most preferably at least 50 mole percent. Preferably the fuel is provided
 through the first annular ejection means and the oxidant is provided
 through the second annular ejection means when oxygen is the gas ejected
 from the nozzles. When an inert gas is ejected from the nozzles,
 preferably the oxidant is provided through the first annular ejection
 means and the fuel is provided through the second annular ejection means.
 If desired, the fuel and oxidant may be provided using three annular
 ejection means with the oxidant provided from the inner and outer annular
 ejection means and the fuel provided from the middle annular ejection
 means. Although one or both of the annular ejection means may form a
 continuous ring opening on lance face 7 from which the fuel or oxidant is
 ejected, preferably, as illustrated in FIG. 2, both the first and second
 annular ejection means form a series of discrete openings, e.g. circular
 holes, from which the two concentric streams of fuel and oxidant are
 ejected. The ejection means need not provide fuel and oxidant completely
 around the gas jets.
 The first annular ejection means at the lance end face forms a ring around
 the plurality of nozzle output openings and the second annular ejection
 means at the lance end face forms a ring around the first annular ejection
 means. The fuel and oxidant passed out of the first and second annular
 ejection means combust to form a flame envelope around the plurality of
 gas jets. If the environment into which the fuel and oxidant is injected
 is not hot enough to auto ignite the mixture, a separate ignition source
 will be required to initiate the combustion. Preferably the flame envelope
 is moving at a velocity less than that of each of the gas jets and
 generally at a velocity within the range of from 100 to 1000 fps.
 FIG. 3 illustrates in cross section the flame envelope around the coherent
 jets 20. Near the lance face there will be a single flame envelope with
 all of the coherent jets contained within the flame envelope as
 illustrated by flame envelope 21 in FIG. 3. Depending upon the lance
 design and the operating conditions, further downstream of the lance face
 there may be observed a single flame envelope with all of the coherent
 jets contained within that flame envelope and/or individual flame
 envelopes around each of the coherent jets. In FIG. 3 for illustrative
 purposes there is shown such individual flame envelopes represented by
 combusting streams 21 and 22.
 Preferably, as illustrated in FIG. 1, extension 10, having a length
 generally within the range of from 0.5 to 6 inches, extends from lance end
 face 7 forming a volume 11 with which each of the plurality of nozzle
 output openings 5, the first annular ejection means 8 and the second
 annular ejection means 9 communicates, and within which each of the
 plurality of gas jets and the flame envelope around the plurality of gas
 jets initially form. Volume 11 formed by extension 10 establishes a
 protective zone which serves to protect the gas streams and the fuel and
 oxidant immediately upon their outflow from lance end 2 thus helping to
 achieve coherency for each gas jet. The protective zone induces
 recirculation of the fuel and oxidant around the gas jets and in some
 cases around each individual gas jet. Thus, even though fuel and oxidant
 may not be provided initially into the volume 11 completely around the gas
 jets, the recirculation of the fuel and oxidant within the protective zone
 serves to ensure that one or more effective flame envelopes are formed so
 as to establish coherency for each gas jet.
 The flow of each gas jet remains distinct from the flow of all the other
 gas jets passed out from the nozzle openings of lance 1 for the entire
 length of such gas jet until the gas jet reaches its target. Such a target
 may be, for example, the surface of a pool of liquid such as molten metal
 or an aqueous liquid, or may be a solid or a gaseous target such as with
 another gas jet with which the gas jet interacts. This is in contrast to
 what happens when conventional gas jets are ejected from the same lance.
 With such conventional gas jets, the jets quickly merge or flow together
 to form a single gas jet. The gas jets remain distinct for a distance of
 at least 10 nozzle exit diameters, typically at least 20 nozzle exit
 diameters, and generally for a distance within the range of from 20 to 100
 nozzle exit diameters.
 It has been found that as the total flowrate of the gas jets passed out
 from the nozzles increases, the total flowrate of the fuel and oxidant
 passed out from the ejection means to form the flame envelope also
 increases but at a lesser rate than the increase for the gas jet flowrate.
 When the total flowrate of the gas jets passed out from the nozzles is
 within the range of from 20,000 to 100,000 CFH, the total flowrate of the
 fuel forming the flame envelope is preferably within the range of from 2
 to 15 million BTU per hour (MMBTU/hr) and the total flowrate of the
 contained oxygen in the oxidant forming the flame envelope is preferably
 within the range of from 2,000 to 15,000 CFH. When the total flowrate of
 the gas jets passed out from the nozzles is within the range of from
 400,000 to 2,000,000 CFH, the total flowrate of the fuel forming the flame
 envelope is preferably within the range of from 10 to 70 MMBTU/hr and the
 total flowrate of the contained oxygen in the oxidant forming the flame
 envelope is preferably within the range of from 10,000 to 70,000 CFH.
 Tests were carried out to demonstrate the effectiveness of the invention,
 using embodiments of the invention similar to those illustrated in FIGS.
 1-3 and using oxygen as the gas passed from the nozzles, and the tests and
 results are discussed below and shown in FIG. 4 along with the results of
 a comparative test. These tests are reported for illustrative or
 comparative purposes and are not intended to be limiting.
 Four nozzles were set around a circle surrounding a lance axis. Each nozzle
 was a converging/diverging nozzle with throat and exit diameters of 0.27
 and 0.39 inches respectively. The circle diameter (D) was 3/4". The angle
 (A) between the coherent jets and the lance axis was 0 degrees and the
 perimeter of each jet was spaced 0.14 inch from the perimeters of adjacent
 jets. Natural gas and oxidant for the flame envelope were supplied through
 two rings of holes: the inner ring (16 holes, 0.154" diameter, on a 2"
 diameter circle) for natural gas; and the outer ring (16 holes, 0.199"
 diameter on a 23/4" diameter circle) for the oxidant which, in this case,
 was commercially pure oxygen having an oxygen concentration of about 99.5
 mole percent. An extension (31/2" diameter, 2" long) was attached to the
 end of the lance to provide gas recirculation to stabilize the flames.
 Tests were run with a supply pressure of 150 pounds per square inch gauge
 (psig) for the main oxygen passed out from the nozzles. At that pressure
 just upstream of the nozzle, the flow rate of oxygen through each nozzle
 was 10,000 cubic feet per hour (CFH) for a total flow of 40,000 CFH for
 all four nozzles. The calculated exit temperature, velocity and Mach
 Number for the coherent jets at the nozzle exits were -193.degree. F.,
 1700 fps and Mach 2.23 respectively. The natural gas and oxygen flow rates
 to the inner and outer rings of holes were 5,000 and 6,000 CFH
 respectively.
 Four distinct coherent jets were visually observed and there was no
 apparent interaction between the jets. Velocities, calculated from pitot
 tube measurements in plane B--B as shown in FIG. 2 taken at 18, 24 and 30
 inches from the nozzle face, are shown as curves A, B, and C in FIG. 4.
 For normal jets in close proximity, entrainment draws the jets together to
 form a single jet as is shown by curve D in FIG. 4 which shows the results
 obtained when the above described test was repeated but without the flame
 envelope around the four jets. The pitot tube measurements shown in Curve
 D were taken at 10.25 inches from the nozzle face. This entrainment did
 not occur for the tests of the invention described herein even though the
 coherent jets were very close together. This was very striking
 particularly with the four coherent jets parallel to the lance axis and
 the perimeter of each jet being less than 1/4" from the perimeter of the
 adjacent jets. Each jet acted as if it were a single jet in free space
 remaining coherent for a considerable distance from the nozzle face. A
 very effective means of providing flame envelopes for multiple coherent
 jets is through two rings of holes (for natural gas and oxygen)
 surrounding all of the coherent jets. This arrangement, along with an
 extension to bring about gas recirculation near the nozzle, results in
 uniform flames around each coherent jet.
 FIG. 5 illustrates the results obtained with another embodiment of the
 invention, similar to that illustrated in FIG. 1 except that this
 embodiment employed only two nozzles. Each nozzle opening was oriented at
 an outward angle of 5 degrees from the lance axis and the distance between
 the centerlines of the nozzle openings was 0.875 inch. Oxygen at a
 flowrate of 20,000 CFH passed through each nozzle and at the nozzle exits
 the separation between the perimeters of the nozzle exits was 0.32 inch.
 The natural gas and secondary oxygen flowed from the two annular rings of
 holes at 5,000 CFH and 4,000 CFH respectively. Two distinct coherent jets
 were formed and velocity profiles at 18 inches (curve E) and 24 inches
 (curve F) are shown in FIG. 5. There was no interference between the two
 jets and each jet acted as if it were a single jet in free space.
 FIG. 6 illustrates the results obtained with another embodiment of the
 invention illustrated in cross section in FIG. 7. In this embodiment the
 lance end had two nozzles with two holes or output openings with the
 distance between the centerlines of the holes being 0.725 inch. The first
 nozzle was designed for 30,000 CFH oxygen with the axis parallel to the
 lance axis. The second nozzle was designed for 10,000 CFH oxygen with the
 axis angled out 5 degrees from the lance axis. At the exits the separation
 between the perimeters of adjacent holes was 0.20 inch. The natural gas
 and secondary oxygen to the rings of holes (not shown) were 5,000 and
 4,000 CFH respectively. The flow rates through the two
 converging-diverging nozzles differed by a factor of three. Velocity
 profiles at 30, 34 and 38 inches from the lance face are shown in FIG. 6,
 as curves G, H, and I. For the high flow jet (30,000 CFH oxygen), the
 profile remained essentially the same over the range of distances from the
 nozzle face. The coherent jet remained parallel to the lance axis. As
 expected, the low flow jet (10,000 CFH oxygen) started to lose its
 coherency beyond 30 inches from the lance face. The location of the peaks
 indicate that the jet angled out about 5.5 degrees from the lance axis.
 This was close in value to the 5 degree angle at the lance face. There was
 no apparent interference between the two jets. These results illustrate
 the flexibility that is possible with multiple hole coherent jet lances.
 For example, oxygen for both lancing and post combustion would be possible
 with a single multiple nozzle lance. One jet could be directed towards the
 molten bath for lancing while the smaller jet could be directed above the
 bath for post combustion. This could all be accomplished with a multiple
 coherent jet lance.
 In one particularly preferred embodiment of the invention which is employed
 in the operation of a basic oxygen furnace, there is employed from 3 to 6
 gas jets each at a diverging angle to the other and each at a supersonic
 velocity wherein each jet has the same gas composition and the flame
 envelope is formed using two concentric streams of fuel and oxidant around
 the plurality of gas jets.
 Although the invention has been described in detail with reference to
 certain preferred embodiments, those skilled in the art will recognize
 that there are other embodiments of the invention within the spirit and
 the scope of the claims.