Smelting process and apparatus

Abstract

A smelting vessel includes a plurality of heat pipes (21) positioned in a refractory lining of at least a part of the hearth (9) for cooling at least a part of the refractory lining. At least one of the heat pipes includes (a) a liquid phase of a heat transfer fluid, typically water, in a lower section of the heat pipe and (b) a vapor phase of the heat transfer fluid, typically steam, in an upper section of the heat pipe. The heat pipe also includes a vent to allow vapour phase to escape from the heat pipe to reduce the pressure or the temperature within the heat pipe when the vapour pressure or the temperature in the heat pipe exceeds a predetermined threshold pressure or temperature.

Claims

1. A smelting vessel for producing molten metal including a refractory lined hearth that in use is in contact with molten slag or molten metal in the vessel, with the hearth including a plurality of heat pipes positioned in a refractory lining of at least a part of the hearth for cooling at least a part of the refractory lining, with at least one of the heat pipes including: a liquid phase of a heat transfer fluid, in a lower section of the heat pipe; a vapour phase of the heat transfer fluid, in an upper section above a first section of the heat pipe; and a snorkel extending into the heat pipe through a vent defined in the heat pipe, the snorkel comprising: an open end, that is inside the heat pipe and adapted to communicate with the vapour phase, and a closed end, that is outside the heat pipe, wherein, the closed end of the snorkel is in the form of a plug that opens or a fuse that melts or a crimped end that is configured to open when the vapour pressure or the temperature in the heat pipe exceeds a predetermined threshold pressure or temperature, to allow the vapour phase and not the liquid phase to escape from the heat pipe to reduce the pressure or the temperature within the heat pipe.

2. The vessel defined in claim 1, wherein the snorkel is adapted to allow vapour phase rather than the liquid phase to escape from the heat pipe and to retain the liquid phase in the heat pipe.

3. The vessel defined in claim 1, wherein the hearth includes an upper part that in use is in contact with molten slag in a slag zone in the vessel and a lower part that in use is in contact with molten metal in a metal zone in the vessel, with the heat pipes being positioned in the refractory lining of the upper part of the hearth for cooling the refractory lining.

4. The vessel defined in claim 1, wherein the heat pipes include lower sections that extend vertically in the refractory lining.

5. The vessel defined in claim 4, wherein the lower sections of the heat pipes are straight sections.

6. The vessel defined in claim 4, wherein the lower sections of the heat pipes are curved shaped, having regard to the geometry of the hearth.

7. The vessel defined in claim 1, further comprising a slag zone cooler positioned in the refractory lining of the hearth for cooling the refractory lining, with the heat pipes being positioned below the slag zone cooler, with upper sections of the heat pipes being in heat transfer relationship with the slag zone cooler for transferring heat from the heat pipes to the slag zone cooler.

8. An assembly of (a) a slag zone cooler element for cooling a part of a refractory lining of a hearth of a smelting vessel and (b) heat pipes in heat transfer relationship with the slag zone cooler for transferring heat from the heat pipes to the slag zone cooler, with at least one of the heat pipes adapted to include (i) a liquid phase of a heat transfer fluid, in a lower section of the heat pipe and (ii) a vapour phase of the heat transfer fluid, in an upper section of the heat pipe, and (iii) a snorkel extending into the heat pipe through a vent defined in the heat pipe, the snorkel comprising: an open end, that is inside the heat pipe, and a closed end, that is outside the heat pipe, wherein, the closed end of the snorkel is in the form of a plug that opens or a fuse that melts or a crimped end that is configured to open when the vapour pressure or the temperature in the heat pipe exceeds a predetermined threshold pressure or temperature, to allow the vapour phase to escape from the heat pipe to reduce the pressure or the temperature within the heat pipe.

9. A smelting vessel for producing molten metal including a refractory lined hearth having an upper part that in use is in contact with slag in a slag zone in the vessel and a lower part that in use is in contact with molten metal in a metal zone in the vessel, the hearth including (a) a slag zone cooler positioned in a refractory lining of the upper part of the hearth for cooling the refractory lining and (b) a plurality of heat pipes positioned in the refractory lining of the upper part of the hearth below the slag zone cooler for cooling the refractory lining, with upper sections of the heat pipes being in heat transfer relationship with the slag zone cooler for transferring heat from the heat pipes to the slag zone cooler and lower sections extending downwardly within the upper part of the hearth from the slag zone cooler, and with at least one of the heat pipes including (i) a liquid phase of a heat transfer fluid, in a lower section of the heat pipe and (ii) a vapour phase of the heat transfer fluid, in an upper section above the lower section of the heat pipe, and (iii) a snorkel extending into the heat pipe through a vent defined in the heat pipe, the snorkel comprising: an open end, that is inside the heat pipe in communication with the second section of the heat pipe, and a closed end, that is outside the heat pipe, wherein, the closed end of the snorkel in the form of a plug that opens or a fuse that melts or a crimped end that is configured to open when the vapour pressure or the temperature in the heat pipe exceeds a predetermined threshold pressure or temperature, to allow the vapour phase to escape from the heat pipe to reduce the pressure or the temperature within the heat pipe.

10. A process for smelting a metalliferous feed material comprising smelting the metalliferous feed material in a molten bath in the smelting vessel defined in claim 1.

11. The process defined in claim 10, further comprising (a) at least partially reducing and partially melting the metalliferous feed material in a smelt cyclone and (b) completely smelting the at least partially reduced/melted material in the molten bath of the smelting vessel.

12. A smelting apparatus for smelting metalliferous feed material, the smelting apparatus comprising: a smelting vessel for producing molten metal including a refractory lined hearth that in use is in contact with molten slag or molten metal in the vessel, with the hearth including a plurality of heat pipes positioned in a refractory lining of at least a part of the hearth for cooling at least a part of the refractory lining, with at least one of the heat pipes including: a liquid phase of a heat transfer fluid, in a lower section of the heat pipe; a vapour phase of the heat transfer fluid, in an upper section above a first section of the heat pipe; and a snorkel extending into the heat pipe through a vent defined in the heat pipe, the snorkel comprising: an open end, that is inside the heat pipe and adapted to communicate with the vapour phase, and a closed end, that is outside the heat pipe, wherein, the closed end of the snorkel is in the form of a plug that opens or a fuse that melts or a crimped end that is configured to open when the vapour pressure or the temperature in the heat pipe exceeds a predetermined threshold pressure or temperature, to allow the vapour phase and not the liquid phase to escape from the heat pipe to reduce the pressure or the temperature within the heat pipe.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is described further by way of example with reference to the accompanying drawings, of which:

(2) FIG. 1 is an enlargement of a lower section of part of an embodiment of a direct smelting vessel in accordance with the invention prior to the commencement of a direct smelting process in the vessel, with the Figure including the levels of molten metal and molten slag that would be in the vessel under steady state operation of the process, with the levels shown under quiescent, i.e. non-operating, conditions in the vessel;

(3) FIG. 2 is a schematic perspective view that illustrates a segment of an upper part of the hearth of the vessel shown in FIG. 1 with the refractory material removed to show the slag zone cooler and the heat pipes of the embodiment;

(4) FIG. 3 is an underside view of the arrangement shown in FIG. 2;

(5) FIG. 4 is an end view of the arrangement shown in FIG. 2; and

(6) FIG. 5 is a schematic cross-section though one of the heat pipes shown in FIGS. 1 to 4 which illustrates the vent of the heat pipe in detail.

DESCRIPTION OF EMBODIMENTS

(7) The invention is relevant to the direct smelting vessels that are used in HIsarna and HIsmelt plants. The invention is not confined to direct smelting vessels used in these plants and is relevant to any suitable direct smelting vessel that contains a molten bath that includes a molten metal layer and a molten slag layer and has a refractory material-lined hearth that requires cooling to maximise the operational life of the hearth, more specifically to reduce refractory wear of the refractory material of the hearth due to contact with molten material in the form of molten slag or molten metal.

(8) The Figures show a part of a direct smelting vessel 4 that is in accordance with an embodiment of the invention. The smelting vessel 4 is suitable for HIsarna and HIsmelt plants and is of the type disclosed in the above-mentioned International publication WO 2015/081376 in the name of the applicant. The smelting vessel 4 comprises a hearth generally identified by the numeral 9 in FIG. 1 that is formed of refractory material and side walls 11 extending upwardly from the sides of the hearth, with the side walls 11 including water cooled panels. The disclosure in the International publication is incorporated herein by cross-reference.

(9) FIG. 1 is an enlargement of a lower section of part of the smelting vessel 4 prior to the commencement of a direct smelting process in the vessel.

(10) With reference to FIG. 1, the hearth 9 has an upper part 25 that in use is in contact with molten slag in the slag zone 18 in the smelting vessel 4 and a lower part 26 that in use is in contact with molten metal in the metal zone 19 in the smelting vessel 4. The slag zone 18 and the metal zone 19 are shown under quiescent, i.e. non-operating, conditions. It is well understood that the slag and metal zones would be highly agitated under steady state operation of the HIsarna and HIsmelt processes and agitated to a lesser extent under steady state operation of other molten bath-based direct smelting processes.

(11) With further reference to FIG. 1, the hearth 9 includes a base 43 and sides 44 that include a refractory lining in the form of refractory bricks, a forehearth 27 for discharging molten metal continuously and a tap hole 28 for discharging molten slag. An upper annular surface 31 of the hearth tapers upwardly and outwardly to the side wall 11 of the smelting vessel 4. In use of the vessel, this part of the hearth is exposed to splashing with molten metal and slag.

(12) With further reference to FIG. 1, the hearth 9 includes:

(13) (a) a slag zone cooler 20 positioned in the refractory lining of the upper part of the hearth 9 for cooling the refractory lining in that part of the hearth; and

(14) (b) a plurality of heat pipes 21 positioned in the refractory lining of the upper part of the hearth below the slag zone cooler 20 for cooling the refractory lining in that part of the hearth.

(15) The slag zone cooler 20 is as described in International publication WO 2007/134382 in the name of the applicant and the disclosure in the International publication is incorporated herein by cross-reference. The slag zone cooler 20 is formed as a ring by a plurality of cooler elements 35, one of which is shown in FIGS. 2-4. Each cooler element 35 is shaped as a segment of the ring, with the side walls extending radially of the ring. Each cooler element 35 comprises a hollow open backed cast shell structure 41 having a bottom wall 69, a pair of side walls 64, a two-part front wall 65a, 65b, a bottom wall 49, and a top wall 63 formed integrally in the cast shell structure 41 and incorporating coolant flow passages in the form of tubes 48 (FIG. 1 only), for flow of coolant therethrough. The cast shell structure 41 is made from a metal or metal alloy of high thermal conductivity, such as copper or copper alloy. The coolant tubes are formed from copper or nickel.

(16) Each slag zone cooler element 35 and the associated heat pipes 21 in heat transfer relationship with the slag zone cooler element 35 may be formed as an assembly that can be installed as an assembly on-site. Alternatively, the slag zone cooler elements 35 and the heat pipes 21 may be separately installed on site.

(17) The refractory lining of the upper part 25 of the hearth is efficiently cooled and supported by the slag zone cooler 20. The slag zone cooler 20 significantly reduces the rate of wear of the refractory material in this part of the hearth. In particular, operation of the slag zone cooler 20 cools the refractory lining to below the solidus temperature of the molten slag in the region of the lining and causes slag to freeze onto its surface, and the frozen slag provides a barrier to further wearing of the refractory material.

(18) As is described in International publication WO 2015/081376 and in more detail below, in use, the heat pipes 21 significantly reduce refractory wear of the refractory material of the hearth 9 due to contact with molten material in the form of molten slag or molten metal and make it possible to use a wider range of refractory materials in the hearth 9 than was previously the case and obtain operational benefits as a consequence of the wider materials selection. The heat pipes 21 are positioned so that they do not extend out of the smelting vessel 4. Each heat pipe 21 includes a section that extends vertically. The result is an arrangement of parallel straight vertically extending pipe sections in the refractory lining.

(19) As can best be seen in FIG. 5, each heat pipe 21 is an elongate hollow tube that has a side wall 47, and upper end wall 49, and a lower end wall 51. The tube contains (a) mainly water 53 in a lower section of the tube and (b) mainly steam 55 in an upper section of the tube.

(20) The heat pipes 21 extend downwardly vertically and parallel to each other within the upper part of the hearth 9 from the slag zone cooler 20. In use, the heat pipes 21 cool the refractory lining of the upper part of the hearth that is below the slag zone cooler 20. The upper sections of the heat pipes 21 are in heat transfer relationship with the slag zone cooler 20 and transfer heat from the heat pipes 21 to the slag zone cooler 20. In use, there is vaporization of the water phase and condensation of the vapor phase in response to heat transfer from the refractory lining to the heat pipes 21 and heat transfer from the heat pipes 21 to the slag zone cooler 20. Each heat pipe 21 transfers heat without direct conduction as the main mechanism, with the water vaporizing at a hot lower end and condensing and forming water at a colder upper end. The condensation of the vapor releases heat which is transferred to the slag zone cooler 20. With reference to FIG. 5, the condensed water flows downwardly and returns to the hot lower end to close the internal cooling circuit. For example, the condensed water may form a film, typically a thin film, on the inside surface of side wall 47 that flows downwardly to the hot lower end. The thin film layer is identified by the numeral 67 in FIG. 5.

(21) Typically, the heat pipes 21 are positioned all of the way around the hearth. The heat pipes 21 are arranged in four radially-spaced apart rings in the embodiment shown in FIGS. 1 to 4. This arrangement can best be seen in FIG. 2. The heat pipes 21 in each ring are staggered circumferentially with respect to the heat pipes 21 in the radially inward and radially outward rings of heat pipes 21. The length of the heat pipes 21 increases with radial spacing of the heat pipes 21 from an inner surface of the upper part 25 of the hearth in which the heat pipes are located. The heat pipes 21 may be in any other suitable arrangement and orientation. By way of example, the invention is not confined to arrangements in which the heat pipes 21 are vertical. By way of further example, the invention is not confined to arrangements in which the heat pipes 21 are straight—the heat pipes 21 may include curved sections to accommodate structural features of the hearth. By way of further example, the invention is not confined to arrangements in which the length of the heat pipes 21 increases with radial spacing of the heat pipes 21 from the inner surface of the upper part 25 of the hearth.

(22) The heat pipes 21 may be of any suitable construction.

(23) Typically, the heat pipes 21 contain water. Any other suitable heat transfer fluid at the operating temperature of the process may be used, such as alcohol, acetone or even metal as sodium. The heat pipes 21 remove heat from the refractory material of the refractory lining and any protective solidified material (slag or metal) that forms on an inner surface of the refractory lining. The objective of the heat pipes 21 is to maintain as large as possible a volume of the refractory material of the refractory lining in which the heat pipes 21 are positioned below the solidus temperature of the slag in the region of the refractory lining to cause slag (or metal) to freeze onto the surface of the hearth and form a frozen slag (or metal) layer that acts as a barrier to wear.

(24) With reference to FIG. 5, at least one of the heat pipes 21 includes a vent generally identified by the numeral 63 that allows steam and not water to escape from the heat pipe 21 when the pressure or temperature in the heat pipe exceeds a predetermined threshold—which is an indication that the heat pipe 21 is no longer working effectively and there is a risk of uncontrolled failure of the heat pipe 21 with potential release of water from the heat pipe 21 into the molten metal or molten slag in the smelting vessel.

(25) With further reference to FIG. 5, the vent includes a snorkel 57 in the form of an elongate tube that extends into the heat pipe 21 through the lower end wall 51 and has an open end 59 that is inside the heat pipe 21 and communicates only with the steam 55 in the heat pipe 21 and a closed end 61 that is outside the heat pipe 21 and is located within the refractory lining of the hearth 9. The closed end 61 of the snorkel 57 is formed via a plug (fuse) 75 of suitable material that blocks the end. The closed end 61 is formed to open when the vapour pressure or the temperature in the heat pipe 21 exceeds a predetermined threshold pressure or temperature. When the snorkel 57 is open, steam can escape from the heat pipe 21 via the snorkel 57 to reduce the pressure and the temperature within the heat pipe 21 and thereby minimise the risk of uncontrolled failure of the heat pipe 21. Consequently, in this condition, the liquid water is initially retained in the heat pipe 21 until it gradually evaporates by the continuous incoming heat flow. The steam escapes via the snorkel 57 into the refractory lining of the hearth 9.

(26) With further reference to FIG. 5, it can be seen that the snorkel 57 includes a section within the heat pipe 21 and a section that is external to the heat pipe 21. The selection of these lengths of snorkel 57 inside and outside the heat pipe 21 and the selection of the inside diameter of the snorkel 57 is a function of a number of factors including the size of the heat pipe 21 and the amount of heat transfer fluid in the heat pipe 21 and the operational conditions in which the heat pipe 21 is located.

(27) The vent advantageously results in a reduced risk of liquid water escaping from the heat pipe 21 and producing sudden vapour volume. This is advantageous in terms of reducing the risk of water coming into contact with molten metal and molten slag in the smelting vessel, thereby creating an uncontrolled event in the smelting vessel 4, such as a problematic explosion or uncontrollable pressure excursion. The snorkel 57 allows vapour and not liquid to escape directly from the heat pipe 21 when the threshold pressure and temperature is exceeded.

(28) The threshold pressure and temperature may be any suitable value having regard to the construction of the heat pipe 21 and the operational conditions (including required heat loads) on the heat pipes 21. The predetermined threshold pressure or temperature may be the design limit of pressure and temperature for the heat pipe under standard operational conditions. The predetermined threshold pressure or temperature may be the design limit of pressure or temperature for the heat pipe plus a margin above the design limit. By way of example, in the case of an HIsmelt or an HIsarna process smelting metalliferous feed material in the form of iron ore, typically the construction of the heat pipe 21 is such that the heat pipe 21 will burst, i.e. fail in an uncontrolled way, at temperatures of ˜270° C. within the heat pipe 21. In this situation, the threshold temperature would be selected to be lower than 270° C. so that the snorkel 57 opens and allows steam to vent from the snorkel before the heat pipe reaches the failure temperature.

(29) The applicant has carried out laboratory testing of the invention. Specifically, two heat pipes with snorkel vents 57 of the type described in the Figures were fabricated, as follows and then tested as described below.

(30) Fabrication

(31) Heat pipes: ¾ outer diameter (OD) and 24.5″ length formed from monel containing 30 g (˜25% of internal volume) water as the heat transfer fluid. Snorkels: tube sizes of ⅛″ OD and 1/16″ OD, respectively, formed from copper and vacuum brazed to the heat pipes, with snorkel length of ˜22″ within the heat pipes and snorkel length of 6-7″ outside the heat pipes. The ends of the snorkels were closed by pinching the ends and cold welding the pinched ends.
Test Setup Description Heat was supplied to the bottom 3″ of the heat pipes. Heat was rejected from the heat pipes by natural convection and radiation over the exposed length of the heat pipes (˜21.5″). Thermocouples were spot welded to the heat pipe surfaces. Constant Heat Input Test: applied a constant 450 W to the heat pipes and monitored temperature at which snorkel released vapour. Temperature Soak Test: used a temperature controller to vary the operating temperature of the heat pipes in a step-wise manner. Maintained each temperature set point for ˜30 min to determine if snorkel release is time/temperature dependent.
Results Prior to cold-weld pinch failure, both heat pipes demonstrated proper heat pipe operation, indicated by isothermal temperatures across each pipe surface. For all tests, the water remained in the vapour (or steam) state while venting from the snorkels. The test results showed that the snorkels could vent the heat pipes safely with steam release only.

(32) Many modifications may be made to the embodiment of the process of the present invention described above without departing from the spirit and scope of the invention.

(33) By way of example, whilst the embodiments include vents in the form of snorkels 57 that allows steam and not water to escape from the heat pipes 21 when the pressure or temperature in the heat pipes exceeds a predetermined threshold, the present invention is not limited to snorkels and extends to any suitable vent construction.

(34) By way of example, whilst the embodiments include snorkels 57 having closed ends formed as a plug (fuse) 75 of suitable material that blocks the end, the present invention is not so limited and extends to any suitable option for closing the ends of snorkels. The requirement is to provide a closure that is responsive to the selected threshold pressure or temperature in the heat pipe. The threshold pressure or temperature is selected to cause the vent to open before there is uncontrolled failure of the heat pipe failure of the heat pipe.

(35) By way of example, whilst the embodiments include arrangements of heat pipes 21 in which the lengths of the heat pipes 21 increase with radial spacing of the heat pipes 21 from an inner surface of the upper part of the hearth in which the heat pipes are located, the present invention is not so limited and the heat pipes 21 may be of any suitable length.

(36) By way of example, whilst the embodiments include a slag zone cooler 20, the present invention is not so limited and extends to arrangements in which there are no slag zone coolers 20. It is noted that slag zone coolers 20 of the type shown in the embodiments are a convenient option to facilitate heat transfer from the heat pipes 21 to outside the vessel 4.

(37) By way of example, whilst the embodiments focus on contact of refractory linings with molten slag, the present invention is not so limited and also extends to situations where refractory linings are contacted by molten metal.