Lance for gas injection and static pressure measurement

Abstract

A lance (4) for gas injection into a liquid (3), the lance (4) comprising: an elongate outer tube (5) with an inlet (21) to receive a gas flow (11) and an outlet (15) for directing the gas flow into the liquid; a swirler (7) for inducing a rotational swirl (18) in the gas flow; and an impulse line (10) providing fluid communication between at least one static pressure tap (16) and a sensor (12) for measuring static pressure in the gas flow at the pressure tap; wherein, the swirler (7) has a tubular hub (8) with an outer surface supporting formations to induce the rotational swirl (18) in the gas flow (11), and an inner surface defining at least part (10) of the impulse line (13) between the pressure tap (16) and the sensor (12). As the hub of the swirler provides part of the impulse line to the pressure sensor, the hub does not need to accommodate a separate, dedicated conduit for that section of the impulse line. The diameter of the hub can be reduced commensurately, thereby increasing the transverse cross section of swirler available for the gas flow into the pyrometallurgical bath. A greater cross section for the gas flow path reduces the pressure drop between the blower above the furnace and outlet of the lance in the bath, to provide an energy saving. (Figure 2A)

Description

LANCE FOR GAS INJECTION AND STATIC PRESSUREMEASUREMENTFIELD

[0001] The invention relates to a lance for gas injection into a liquid. The invention is particularly suited to a lance for immersion in a pyrometallurgical bath but may also be suitable in other applications.BACKGROUND

[0002] Gas injection into a liquid is necessary in many industrial processes. Injecting gas through a lance into the liquid is one technique. One particular application of this technique is the injection of gas into a pyrometallurgical bath of molten metal, matte and / or slag. Pyrometallurgical processing is the extraction and purification of metals by the application of heat in processors such as roasting, smelting and refining.

[0003] Smelting typically requires fuel for heating and an oxidant or reductant to react with metal bearing feed. The three main methods are:• Side blown gas through openings (known as tuyeres) in the side of the furnace,• Top blown gas injection via a lance extending through the top of the furnace into the molten bath, and• Oxidant injection with finely divided solids into the furnace freeboard.

[0004] In top blown smelters, the lower end of the lance needs cooling to prevent it from quickly burning away upon immersion into the bath. Some lances use a device known as a “swirler” to induce a spin in the gas flow at the lower end immersed in the molten bath. The rotating gas flow on the interior surface of the lance draws away heat to cool the outer surface of the immersed section. The cooling effect causes a protective layer of slag to solidify on the outer surface thereby extending the operational life of the lance.

[0005] The depth of immersion of the lance into the bath is another important factor in the operational life of the lance. If the lance is immersed too deeply, the end burns away morequickly. The static gas pressure of the gas flow at the lower end of the lance is indicative of the depth of immersion. The static pressure in the gas flow indicates the hydrostatic pressure from the head of liquid above the outlet or lower end of the lance. The static pressure is typically measured with an impulse line (that is, a relatively thin fluid conduit) leading from one or more pressure taps (i.e., openings) near the swirler, up the lance to a sensor in the superstructure above the furnace. The pressure taps are openings oriented with respect to the direction of gas flow to reduce or avoid dynamic pressure effects.

[0006] Using the static pressure, the depth of the lance in the bath may be controlled to extend the operational life. While top blown furnaces are effective, widely used, and the smelting process is energy efficient, there are ongoing efforts to further reduce the fuel requirements. The generation of high velocity gas flow through the lance into the bath consumes energy to overcome pressure loss between the inlet and the outlet.SUMMARY OF INVENTION

[0007] With the above issues in mind, the present invention provides a lance for gas injection into a liquid, the lance comprising: an elongate outer tube with an inlet to receive a gas flow and an outlet for directing the gas flow into the liquid; a swirler for inducing a rotational swirl in the gas flow; and an impulse line providing fluid communication between at least one static pressure tap and a sensor for measuring static pressure in the gas flow at the pressure tap; wherein, the swirler has a tubular hub with an outer surface supporting formations to induce the rotational swirl in the gas flow, and an inner surface defining at least part of the impulse line between the pressure tap and the sensor.

[0008] In another aspect, the invention provides a swirler for a lance used to inject gas into a liquid, the lance having an elongate outer tube with an inlet to receive a gas flow and an outlet for directing the gas flow into the liquid, the swirler comprising: a hub with an outer surface supporting vanes configured to induce a rotational swirl in the gas flow; and at least one static pressure tap for fluid communication with a sensor via an impulse line to measure static pressure in the gas flow at the pressure tap; wherein,the hub has an inner surface configured to at least partially define the impulse line.

[0009] The gas flow pressure loss through the lance is at least partially dependent on the internal diameter of the lance. In a generalised form, the relationship between pressure loss and lance diameter is non-linear, with pressure loss increasing inversely with diameter to the fifth power. Configuring the hub of the swirler to provide a part of the impulse line to the pressure sensor, the hub does not need to accommodate a separate, dedicated conduit for that section of the impulse line. This allows the diameter of the hub to be reduced, thereby increasing the transverse cross section of swirler available for the gas flow into the pyrometallurgical bath. A greater cross section for the gas flow path reduces the pressure drop between the blower above the furnace and outlet of the lance in the bath. As the gas flow required is pressurised and high speed, reducing the pressure losses provides a significant energy saving.

[0010] Preferably, the static pressure tap is positioned at a downstream end of the swirler with respect to the gas flow.

[0011] The pressure taps can be positioned at the upstream end of the swirler, but changes in the flowrate before the swirler can adversely affect pressure measurements.

[0012] Preferably, the static pressure tap comprises at least one opening facing a direction generally orthogonal to the longitudinal axis of the elongate tube.

[0013] Preferably, the lance further comprises a support element extending longitudinally within the elongate tube for mounting the swirler at a predetermined position within the elongate tube.

[0014] Preferably, the support element is a support pipe extending generally along the longitudinal axis of the elongate tube, such that the support pipe and the inner surface of the hub define an annular fluid path extending to the at least one opening of the static pressure tap.

[0015] Preferably, the static pressure tap includes a plurality of the openings formed in a generally cylindrical extension of the hub, extending downstream of the swirler. In a further preferred form, the downstream end of the cylindrical extension is enclosed by an end wall with an aperture for the supporting pipe, the aperture being sized to provide a sliding fit with the supporting pipe.

[0016] Preferably, the lance is used to inject gas into a pyrometallurgical bath in a furnace within a smelting facility.

[0017] Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms a part of the common general knowledge in the field.

[0018] Unless the context clearly requires otherwise, throughout the description and claims, the words “comprise”, “comprising” and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say in the sense of “including, but not limited to”.

[0019] Terms such as “generally” and “about” should be construed by the skilled addressee having regard to normal tolerances in this field of technology.

[0020] The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and are not intended to exclude other embodiments from the scope of the invention.

[0021] It must also be noted that, as used in the specification and the appended claims, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.

[0022] Although example embodiments of the disclosed technology are explained in detail herein, it is to be understood that other embodiments are contemplated. Accordingly, it is not intended that their disclosed technology be limited in its scope to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings.

[0023] A feature in the claims stated in general terms will represent a principle of general application, where it is reasonable to expect (i.e., reasonable to predict) that the claimed invention will work with anything that falls within the general term. Such a feature defined in general terms may be a major part of the claim, or it may be a simple descriptive word. In any other case, a feature in the claims expressed in general terms will be sufficiently enabled if thedisclosure enables at least one form of, or one application of, a general principle in respect of the feature, and the person skilled in the art would reasonably expect the invention to work with anything that falls within the general term.

[0024] Broadly drafted claims may be considered enabled if, prima facie: a) the disclosure teaches a principal that the person skilled in the art would need to follow in order to achieve each and every embodiment falling within the claim; and b) the specification discloses at least one application of the principal and provides sufficient information for the person skilled in the art to perform alternative applications of the principal in that way, while not explicitly disclosed, would nevertheless be obvious to the person skilled in the art.BRIEF DESCRIPTION OF DRAWINGS

[0025] Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which:

[0026] Figure l is a schematic section view of a “top blown” smelting furnace;

[0027] Figure 2A is a schematic section view of a prior art lance for injecting gas into a pyrometallurgical bath;

[0028] Figure 2B is a schematic section view of a lance according to the present invention;

[0029] Figure 3 is a schematic section view of a swirler for a lance according to the invention; and

[0030] Figures 4 A and 4B are schematic transverse cross-sections of a lance according to the prior art and a lance according to the present invention with the cross-sectional area available for the top blown gas flow shown in cross hatching.DESCRIPTION OF EMBODIMENTS

[0031] Referring to Figure 1, the basic elements of the smelter (1) are shown. A generally upright furnace (2) holds the molten metal, matte and / or slag in a pyrometallurgical bath (3). A lance (4) extends through the top of the furnace (2) into the pyrometallurgical bath (3).Typically a gas comprising air supplied by a blower remote from the furnace, oxygen from a cryogenic oxygen plant or other source remote from the furnace, and either a gaseous, or liquid, or solid fuel, is supplied to the inlet (21) of the lance (4) inserted in the furnace (2). The gas flow through the lance is at high speeds and pressurised (typically in the range of 30 to 190 m / s and 110 to 200 kPa). It is injected into the molten material of the bath (3) through the outlet (15) immersed in the bath (3). The high-speed, -pressurised injection of the gas flow creates turbulence within the molten material in the bath (3) to promote thorough mixing and rapid reaction times. Offgas is drawn out of the furnace (2) while the molten product from the pyrometallurgical bath (3) is drawn away through the taps in the base of the furnace (2).

[0032] Figure 2A is a schematic section view of the lower portion of a prior art lance (4) with its outlet immersed in the molten material of the pyrometallurgical bath (3). The elongate outer tube (5) encloses a supporting pipe (9) used to position a swirler (7) at a predetermined position along the length of the lance (4). The swirler (7) is a device for receiving the high speed / pressurised gas flow (11) from the inlet (21) of the lance (4) and inducing a rotational swirl into the flow. The rotating gas flow (18) cools the interior surface of the outer tube (5). This cooling causes a layer of slag to solidify or “freeze” on the external surface of the outer tube (5) immersed in the bath (3). This layer of solidified slag forms a protective coating to insulate the end of the lance (4) from the extreme temperatures within the bath (3).

[0033] Despite the insulation provided by the solidified slag, the molten material in the bath (3) will quickly burn away the lance if it is immersed too deeply. The depth of immersion can be monitored using the static pressure of the gas flow (11) in the outer tube (5). The static pressure of the gas is indicative of the hydrostatic pressure caused by the molten material above the outlet (15). This head of pressure effectively provides an indication of the depth (H) that the outlet is immersed into the bath (3). An operator can use this to ensure the immersion is not too deep and effectively extend the operational life of the lance (4).

[0034] Measuring the static pressure requires a static pressure tap (16) in fluid communication with a pressure sensor (12) in the superstructure around the furnace, via an impulse line (13). Typically, the pressure tap is provided by one or more openings (16) in a conduit positioned around the supporting pipe (9) to provide an annular flow path (10) forming the initial portion of the impulse line (13) to the pressure sensor (12).

[0035] This dedicated conduit (6) for the static pressure taps (16) must be accommodated within the hub (8) of the swirler (7). The outward facing surface of the hub (8) supports vanes and other formations configured to induce the required swirl (18) in the gas flow (11). The specific configuration of the vanes will depend on a number of operational factors relating to the smelting process as will be readily understood by skilled workers in this field.

[0036] One particular type of swirler device is described in detail in Australian Patent AU 657131 in the name of CSIRO (an Australian quasi -government agency - Commonwealth Scientific and Industrial Research Organisation). This swirler is known in the field as a “SIROSMELT™” swirler and provides an enabling description of the features required for a swirler (7) in a lance (4) of the same general type used in the present invention. Accordingly, the entire contents of AU 657131 are incorporated herein by cross reference.

[0037] Figure 2B and Figure 3, respectively show a lance and swirler according to the present invention. The swirler (7) according to the invention is reconfigured to effectively replace the dedicated conduit (6) from the pressure tap (16) used in the prior art lance shown in Figure 2A. With careful redesign of the swirler (7), the inward facing surface of the hub (8) defines the initial portion of the impulse line (13) leading from the static pressure tap openings (16). The diameter of the hub (8) is reduced to effectively match the inner diameter of the dedicated conduit (6) it replaces.

[0038] As best shown in Figure 3, the hub (8) provides a cylindrical extension (20) at the downstream end of the swirler (7) for the openings (16) of the static pressure tap. To improve the pressure measurements and reduce the effects of any turbulence, the cylindrical extension (20) is enclosed at its lower end with an annular wall (17). The aperture in the end wall (17) fits over the supporting pipe (9) with a sliding fit to accommodate any issues with differential thermal expansion between the various components.

[0039] As with the prior art lance shown in Figure 2 A, the pressure tap openings (16) face normal to the axis (19) of the lance to reduce fluctuations from the dynamic pressure effects caused by the rotating flow (18). Similarly, the openings (16) are positioned downstream of the swirler to reduce the effects of gas flow pressure changes that would be present in the gas flow (11) immediately upstream of the swirler (7). Notwithstanding this, pressure tap openings positioned in the hub for an upstream end of the swirler would provide workable alternatives in particular circumstances.

[0040] With the reduction in diameter of the hub (8), the transverse cross-sectional area of the swirler (7) available for the gas flow (11) is increased. As schematically illustrated in Figures 4A and 4B, the hub (8) of the swirler (7) accommodating the dedicated conduit (6) in the prior art lance is larger than the hub (8) that replaces the dedicated conduit (6) as shown in Figure 4B. Accordingly, the transverse cross-sectional area B of a lance according to the present invention is greater than the cross-sectional area A of the equivalent prior art lances.

[0041] The increased cross-sectional area of the swirler (7) reduces the drop in gas pressure between the inlet (21) and the outlet (15). As the gas flow injected via the outlet (15) must be pressurised and a high velocity (typically in the range of 30 to 190 m / s and 110 to 200 kPa) for effective turbulent mixing, reducing the pressure drop through the lance provides a significant energy saving. This energy saving directly equates to a reduction in the ongoing greenhouse gas emissions for the smelting process.

[0042] The invention has been described herein by way of example only. Skilled workers in this field will readily recognise many variations and modifications which do not depart from the spirit and scope of the broad inventive concept. For example, skilled workers will readily appreciate the lance may have multiple swirlers and any or all of the swirlers may have a hub configured in accordance with the present invention. Likewise some forms of the lance provide one or more the pressure taps in different configurations. In particular, the pressure taps may be formed in a cap that is attachable to one or both longitudinal ends of the swirler hub. Some examples of this type of lance may extend an end of the hub and add a thread for engagement with a threaded cap having a pressure tap arrangement suited to a certain smelting application. These varaitions are useful for customising the lance to different requirements, and may all embody the present invention.

Claims

CLAIMS:

1. A lance for gas injection into a liquid, the lance comprising: an elongate outer tube with an inlet to receive a gas flow and an outlet for directing the gas flow into the liquid; a swirler for inducing a rotational swirl in the gas flow; and an impulse line providing fluid communication between at least one static pressure tap and a sensor for measuring static pressure in the gas flow at the pressure tap; wherein, the swirler has a tubular hub with an outer surface supporting formations to induce the rotational swirl in the gas flow, and an inner surface defining at least part of the impulse line between the pressure tap and the sensor.

2. The lance according to claim 1 wherein the static pressure tap is downstream of the swirler with respect to the gas flow.

3. The lance according to claim 1 or claim 2 wherein the static pressure tap comprises at least one opening facing a direction generally orthogonal to the longitudinal axis of the elongate tube.

4. The lance according to any one of claims 1 to 3 further comprising a support element extending longitudinally within the elongate tube for mounting the swirler at a predetermined position within the elongate tube.

5. The lance according to claim 4 wherein the static pressure tap includes a plurality of the openings formed in a generally cylindrical extension of the hub, extending downstream from the swirler.

6. The lance according to claim 5 wherein the downstream end of the cylindrical extension being enclosed by an end wall with an aperture for the supporting pipe, the aperture sized to provide a sliding fit with the supporting pipe.

7. A smelting facility using a lance according to any one of claims 1 to 6 for injecting gas into a pyrometallurgical bath.

8. A swirler for a lance used to inject gas into a liquid, the lance having an elongate outer tube with an inlet to receive a gas flow and an outlet for directing the gas flow into the liquid, the swirler comprising: a hub with an outer surface supporting vanes configured to induce a rotational swirl in the gas flow; and at least one static pressure tap for fluid communication with a sensor via an impulse line to measure static pressure in the gas flow at the pressure tap; wherein, the hub has an inner surface configured to at least partially define the impulse line.

9. The swirler according to claim 8 wherein the static pressure tap is downstream of the swirler with respect to the gas flow.

10. The swirler according to claim 8 or claim 9 wherein the static pressure tap comprises at least one opening facing a direction generally orthogonal to the longitudinal axis of the elongate tube.

11. The swirler according to claim 10 wherein the static pressure tap includes a plurality of the openings formed in a generally cylindrical extension of the hub, extending downstream from the swirler.

12. The swirler according to claim 10 wherein the static pressure tap includes a plurality of the openings formed in a cap configured for attachment to a longitudinal end of the hub.

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