WO2015068132A1

WO2015068132A1 - Single loop induction furnace

Info

Publication number: WO2015068132A1
Application number: PCT/IB2014/065874
Authority: WO
Inventors: Louis Johannes Fourie
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-11-07
Filing date: 2014-11-07
Publication date: 2015-05-14
Anticipated expiration: 2016-05-07

Abstract

The invention relates to a single loop channel type induction furnace comprising a shell lined with refractory material, and having a floor and a wall extending from the floor to form a hearth, at least one single loop channel type induction heater associated with the furnace and in fluid communication with the hearth by means of a throat in the floor, the throat including two throat passages each of which is in fluid communication with the induction heater channel (1), the throat passages including an inlet passage (2) for flow of metal from the hearth to the induction heater channel (1) and an outlet passage (3) for flow of metal from the induction heater channel (1) to the hearth, with the inlet passage (2) having a larger cross sectional area than the outlet passage (3).

Description

SINGLE LOOP INDUCTION FURNACE

FIELD OF THE INVENTION

This invention relates to channel type induction furnaces used in the melting or smelting of metals and particularly to induction furnaces used in smelting particulate materials floating on the surface of metal and slag in a furnace hearth.

BACKGROUND TO THE INVENTION

Similar to conventional double loop inductors, single loop inductors are connected to the metal bath of an induction heated furnace for heating it by one single large opening or throat. Heated metal from the inductor rises through the throat opening while cooler metal from the bath flows down to the inductor. This arrangement leads to local overheating when a shallow metal bath with large surface area is used. A large surface area and shallow bath is required for best efficiency when particulate material which floats on the metal bath surface is being melted.

The problem was overcome for double loop inductors, as disclosed in PCT patent application WO20121 17355, through the use of two separate passages for flow of heated metal from the inductors and a single passage for flow of metal from the bath to the inductor. The heated metal is introduced back to the metal bath through a trench in a raised portion of the hearth floor.

Single loop inductors offer advantages of lower energy losses, simpler construction and lower refractory and fabrication costs, but conventionally cannot be used with a shallow and large bath surface area.

OBJECT OF THE INVENTION

It is an object of the invention to provide a single loop channel type induction furnace which at least partly overcomes the abovementioned problem. SUMMARY OF THE INVENTION

In accordance with this invention there is provided a single loop channel type induction furnace comprising a shell lined with refractory material, and having a floor and a wall extending from the floor to form a hearth, at least one single loop channel type induction heater associated with the furnace and in fluid communication with the hearth by means of a throat in the floor, the throat including two throat passages each of which is in fluid communication with the induction heater channel, the throat passages including an inlet passage for flow of metal from the hearth to the induction heater channel and an outlet passage for flow of metal from the induction heater channel to the hearth, with the inlet passage having a larger cross sectional area than the outlet passage.

There is further provided for at least the inlet passage, and preferably also for the outlet passage, to be configured to connect tangentially with the induction heater channel.

According to a further feature of the invention there is provided for the furnace to be provided with a plurality of single loop channel type induction heaters, and for the induction heater channels to be arranged in line or at right angles to each other, alternatively circumferentially spaced around the wall of the furnace.

There is also provided for the outlet passage to be directed away from the inlet passage, and preferably for the inlet passage to be formed to extend substantially vertically between the hearth and the induction heater channel, and for the outlet passage to extend at least for part of its length, preferably including the part of its length that includes the termination thereof at the floor, at an angle away from the inlet passage.

These and other features of the invention are described in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described by way of example only and with reference to the accompanying graphical representations in which:

Figure 1 is an end view of a channel and throat passage assembly of a furnace according to the invention; is an end view of an assembly as shown in Figure 1 which also includes a starter passage, in a rectangular furnace, with all refractory material transparent;

is a perspective end view of the furnace of Figure 2 from the opposing end side with the end wall removed for clarity;

a top view of the furnace of Figure 2;

is a side view of the furnace of Figure 2;

is a side view of a rectangular furnace with two channel and throat passage assemblies according to the invention, with all refractory material transparent; is a top perspective view of a circular furnace with a channel and throat passage assembly according to the invention, with all refractory material transparent;

is a top perspective view of a circular furnace with three circumferentially spaced apart channel and throat passage assemblies according to the invention, with all refractory material transparent;

is an end view of a drum furnace with a channel and throat passage assembly according to the invention, with all refractory material transparent; is a side view of the furnace of Figure 9;

is an end view of another drum furnace with a channel and throat passage assembly according to the invention, with all refractory material transparent; and

is a side view of the furnace of Figure 1 1 .

DETAILED DESCRIPTION OF THE INVENTION

The invention provides for a single loop induction heated furnace that includes a shell lined with refractory material, and having a floor and a wall extending from the floor to form a hearth. The furnace includes at least one single loop channel type induction heater associated with it and this induction heater is in fluid communicating with the hearth by means of a throat in the floor.

The throat comprises two throat passages each of which is in communication with the induction heater channel. The throat passages include an inlet passage for flow of metal from the hearth to the induction heater channel and an outlet passage for flow of metal from the induction heater channel to the hearth, with the inlet passage having a larger cross sectional area than the outlet passage. The general arrangement of the channel (1 ) and the throat passages (2, 3) of a furnace according to the invention is shown in Figure 1 . The channel (1 ) comprises a circular coil with a circular cross-section that acts as a secondary coil for the induction heater. The primary coil (not shown) is located coaxially within the coil in known manner. This arrangement is described at first with reference to Figure 1 which relates to an induction furnace in general terms, and then in more detail with reference to Figures 2 to 12 with various specific embodiments of the furnace shape and heating arrangement. A person skilled in the art will appreciate that the channel (1 , 1 1 , 17) and the portions of the passages (2, 3, 17), that extend below the furnace are formed within a bulk of refractory material. For the sake of clarity, this refractory material below the furnace is not shown in any of the drawings. As mentioned, the throat comprises two passages, namely the inlet passage (2) and the outlet passage (3). The inlet passage (2) commences at floor level (4) in the hearth and extends substantially vertical down from the floor to the channel (1 ), to which it is tangentially connected (5). The outlet passage extends from the channel (1 ), also tangentially (6), and terminates in a raised portion of the floor (7). It has a first section (8) that is arranged substantially vertical, and a longer second section (9) that is angled away from the inlet passage (2). The outlet passage (3) terminates in the floor of the furnace, on a higher level than the inlet passage (2), on a raised portion (34) of the floor. This difference in height is not per se crucial for the functioning of the furnace, but it is beneficial for the prevention of short- circuiting of metal flow in the furnace.

Crucially, the inlet passage (2) has a larger cross sectional area compared to the outlet passage (3).

In use the hearth of the furnace is filled with liquid metal which circulates through the induction heater for heating. Cooler metal is drawn into the channel (1 ) via the inlet passage (2). Heated metal flows from the channel (1 ) to the hearth via the outlet passage (3).

When the power is switched off at any stage, there is no movement of metal in the passages (2, 3). When power is switched on, heat is exchanged between the channel (1 ) and the metal in the ends of the passages (2, 3) where they connect (5, 6) with the channel (1 ). Since there is a greater volume of metal contained in the larger inlet passage (2), more heat is required to heat metal in the inlet passage (2) than what is required to heat the metal in the smaller outlet passage (3). At some stage the metal in the outlet passage (3) reaches a higher temperature than the metal in the inlet passage (2). The density of metal generally decreases with an increase in it temperature. The higher density of the metal in the inlet passage (2) causes it to displace metal via the channel (1 ) loop to the outlet passage (3). Initially the flow rate is extremely low, but once it is started, the effect is enhanced by cool metal being drawn into the inlet passage (2), heated in the channel (1 ) and passed on into the outlet passage (3). By having separate inlet (2) and outlet (3) passages it is possible to direct the flow of metal from the outlet passage (3). In particular, it is possible to direct the flow of heated metal away from the inlet passage (2) to avoid short circuiting of metal flow. In a conventional single loop induction heated furnace short circuiting is possible, and usually expected, when the bath level is low in the hearth. This could lead to local overheating with well-known negative effects.

By directing flow of metal away from the inlet, it is possible even with very low bath levels to avoid short circuiting. It is possible to use the arrangement described above in several different combinations and adaptations, and with some modifications. It is for example to include a starter passage (10) as shown in Figures 2 to 6. The starter passage (10) allows communication between outlet passage (12) and inlet passage (1 1 ) for use during start-up of the furnace, in cases such as in this embodiment where the outlet passage (12) terminates on a higher level (34) in the floor than the level at which the inlet passage (1 1 ) commences. In this embodiment, flow becomes possible when the bath level reaches the level of the starter passage (10).

Once the bath level has reached the level of the outlet passage (12), metal flows preferentially through the outlet passage (12) instead of through the starter passage (10), due to the additional driving force caused by the difference in height and to the required change in direction for metal to flow through the starter passage (10) which is not required when metal flows through the outlet passage (12).

It is possible to install a heater and passage arrangement in a rectangular furnace (14, 15) as shown in Figures 2 to 6. As shown in Figure 6, it is possible to install a heater and passage arrangement (16) at the ends of such a furnace (15). In this instance the channels of the heater and passage arrangement (16) are arranged coaxially.

It is also possible to install a single heater and passage arrangement (17) in the base of a vertical circular cylindrically shaped furnace (18), as shown in Figure 7, with the outlet passage (19) terminating in a position in the floor of the furnace, remote from the inlet passage (20) and vertically higher than it. The inlet passage (20) commences proximate the side of the furnace (18). As shown in Figure 8 it is also possible to include three spaced apart heater and passage arrangements (21 ) in the base of a vertical circular cylindrically shaped furnace (22), with their outlet passages (23) directed to exit around the inner circumference of the hearth (25). In this instance, the floor of the furnace (22) is provided with a trench (26) for each outlet passage (22) that extends circumferentially away from each outlet passage (23), and each trench (26) terminates in a ramp (27). This controls the flow of metal in front of each outlet passage (23) and directs it away from its inlet passage (24).

It is also possible to install one or more heater and passage arrangements in a horizontal drum type furnace. The heater and passage arrangement (28) may be installed with the central axis of the induction heater channel (29) aligned with the longitudinal central axis of the drum furnace (30), as shown in Figures 9 and 10. The heater and passage arrangement (31 ) may also be installed with the central axis of the induction heater channel (32) transverse with the longitudinal central axis of the drum furnace (33), as shown in Figures 1 1 and 12.

It will be appreciated that the embodiments described above are given by way of example and are not intended to the limit the scope of the invention. It is possible to include further modifications without departing from the essence of the invention. The channel (1 ) may for example comprise a coil with a non-circular cross-section, for example oval, rectangular and so forth.

Claims

A single loop channel type induction furnace comprising a shell lined with refractory material, and having a floor and a wall extending from the floor to form a hearth, at least one single loop channel type induction heater associated with the furnace and in fluid communication with the hearth by means of a throat in the floor, the throat including two throat passages each of which is in fluid communication with the induction heater channel, the throat passages including an inlet passage for flow of metal from the hearth to the induction heater channel and an outlet passage for flow of metal from the induction heater channel to the hearth, with the inlet passage having a larger cross sectional area than the outlet passage.

A furnace as claimed in claim 1 in which the inlet passage is configured to connect tangentially with the induction heater channel.

A furnace as claimed in claim 2 in which the outlet passage is configured to connect tangentially with the induction heater channel.

A furnace as claimed in any one of claims 1 to 3 which is provided with a plurality of single loop channel type induction heaters.

A furnace as claimed in any one of claims 1 to 4 in which the plurality of induction heater channels are arranged in a line or at right angles to each other, alternatively circumferentially spaced apart around the wall of the furnace.

A furnace as claimed in any one of claims 1 to 5 in which the outlet passage is directed away from the inlet passage and the outlet passage extends at least for part of its length at an angle away from the inlet passage.

A furnace as claimed in claim 6 in which the part of the outlet passage that extends at an angle away from the inlet passage includes an upper portion of the outlet passage opening in the floor.

8. A furnace as claimed in any one of claims 1 to 7 in which the inlet passage is formed to extend substantially vertically between the hearth and the induction heater channel.