WO2009066004A1

WO2009066004A1 - Method for feeding material flows from a preheating furnace to a smelting furnace and a preheating system

Info

Publication number: WO2009066004A1
Application number: PCT/FI2008/050654
Authority: WO
Inventors: Janne Ollila
Original assignee: Outotec Oyj
Current assignee: Metso Corp
Priority date: 2007-11-21
Filing date: 2008-11-13
Publication date: 2009-05-28
Anticipated expiration: 2010-05-21
Also published as: ZA201003205B; EA201000655A1; CN101878407B; BRPI0820318A2; FI20075824A0; EA019835B1; FI20075824L; FI20075824A7; CN101878407A

Abstract

In a method for feeding material flows from a preheating furnace (1) to a smelting furnace (2), there is provided a preheating furnace (1) having at least two sub-silos, including a first sub-silo (3) with a first outlet pipe (4) for conducting material to a first inlet conduit (5) of the smelting furnace (2), said inlet conduit (5) being located in the upper part of the smelting furnace, at a distance from the furnace center; and a second sub-silo (6) with a second outlet pipe (7) for conducting material to a second inlet conduit (8) of the smelting furnace, said inlet conduit (8) being located in the upper part of the smelting furnace, in the vicinity of the furnace center. Material is heated in the sub-silos (3, 6) by conducting into both sub-silos an essentially same amount of thermal energy in relation to the volume flow discharged from said silo. A first material flow is conducted to the first inlet conduit with a first volume flow, which is defined from the material downward- flowing rate at said point of the smelting furnace. A second material flow is conducted to the second inlet conduit with a second volume flow, which is defined downwardly from the material flowing rate at said point of the furnace and is larger than the first volume flow. The residence time of a volume unit of the material flow in the second sub-silo (6) is arranged to be higher than in the first sub-silo (3), so that the temperatures of the first and second material flow are rendered essentially equally high.

Description

METHOD FOR FEEDING MATERIAL FLOWS FROM A PREHEATING FURNACE TO A SMELTING FURNACE AND A PREHEATING SYSTEM

FIELD OF THE INVENTION The invention relates to a method defined in the preamble of claim 1. The invention also relates to a preheating system defined in the preamble of claim 3.

BACKGROUND OF THE INVENTION In the prior art there is known the pretreatment of mineral alloy material, prior to feeding the material into an electric furnace, through a preheating arrangement, so that the feed mixture is heated in a separate preheating silo, where granular or lump-like (for example pelletized) feed mixture is heated and dried. Preheating is necessary in order to reduce the amount of energy needed for smelting the material in the electric furnace proper, and in order to volatilize certain impurities before feeding the material into an electric furnace. Preheated feed material also stabilises the operation of the furnace. It is a well-known practice to use one or several preheating furnaces per each electric furnace. The material to be heated is fed in batches through a feed silo, by means of a distributor device, to the preheating furnace, where the material is heated by a hot gas flow. Typically the hot gas mixture is fed into the preheating furnace through the bottom part thereof, so that it is distributed evenly inside the material bed. The preheating furnace is connected to the smelting furnace in a known fashion by separate pipe arrangements that extend through the ceiling of the smelting furnace to the interior of the electric smelting furnace, thus feeding the preheated material for smelting. Various preheating furnace arrangements are described for example in the publications FI 842577 A, FI 105236 B and FI 71088 B.

In the known method for feeding flows of material from a preheating furnace to a smelting furnace, there is provided a preheating furnace including at least two sub-silos. The sub-silos include a first sub-silo having a first outlet pipe for conducting the material to a first inlet conduit of the smelting furnace, which inlet conduit is located in the upper part of the smelting furnace, at a distance from the furnace center. Further, the preheating furnace includes a second sub-silo provided with a second outlet pipe for conducting the material to a second inlet conduit of the smelting furnace, which inlet conduit is located in the upper part of the smelting furnace, in the vicinity of the furnace center. In the first and second sub-silos, the material is heated and flows then downwards to a first outlet pipe and respectively to a second outlet pipe, when essentially the same amount of thermal energy, in relation to the volume flow discharged from said silo, is conducted to each sub-silo. The first flow of preheated material is conducted from the first sub-silo along a first outlet pipe to a first inlet conduit of the smelting furnace with a first volume flow, which is defined from the downward-flowing rate of the material at said point of the smelting furnace. A second flow of preheated material is conducted from the second sub-silo along a second outlet pipe to a second inlet conduit of the smelting furnace with a second volume flow, which is defined from the downward-flowing rate of the material at said point of the smelting furnace, said second volume flow being larger than the first volume flow.

Respectively, the known preheating system includes a preheating furnace provided with at least two sub- silos, a first sub-silo having a first outlet pipe for conducting the material to the first inlet conduit of the smelting furnace, said first inlet conduit being located in the upper part of the smelting furnace, at a distance from the furnace center. Moreover, the preheating furnace has a second sub-silo having a second outlet pipe for conducting the material to the second inlet conduit of the smelting furnace, said second inlet conduit being located in the upper part of the smelting furnace, in the vicinity of the furnace center.

In the prior art, the sub-silos are equally large in volume. The volume flow of the feed material to the smelting furnace varies at different points of the furnace, so that the volume flow is larger in the vicinity of the furnace center than in the periphery, at a distance from the center. Therefore the flowing rate and volume flow of the material arriving in the vicinity of the center is larger than that of the material arriving near the periphery. In equally large sub-silos, where the flowing rates of the material flowing out of the sub-silo are different, also the material residence times are different, and therefore the temperatures of the material flows arriving from the sub-silos at different points of the furnace likewise become different. This is disadvantageous with respect to an optimal operation of the smelting furnace .

OBJECT OF THE INVENTION

The object of the invention is to eliminate the above mentioned drawbacks .

A particular object of the invention is to introduce a method and preheating system by means of which the temperatures of material flows arriving at different points of a smelting furnace are made essentially equally high.

It is a further object of the invention to introduce a method and preheating system that ensure an optimal operation for a smelting furnace.

SUMMARY OP THE INVENTION

The method according to the invention is characterized by what is set forth in claim 1. Moreover, the system according to the invention is characterised by what is set forth in claim 3.

According to the invention, in the method the residence time of a volume unit of the material flow in the second sub-siIo is arranged to be longer than in the first sub-silo, so that the temperatures of the first and second material flows are rendered essentially equally high.

According to the invention, in the preheating system the volume of the second sub-silo is larger than the volume of the first sub-silo.

An advantage of the invention is that the temperatures of the material flows entering the smelting furnace are equally high irrespective of the different feed points through which they are fed into the smelting furnace. This enhances an optimal operation of the smelting furnace.

In an embodiment of the method, the volume of the second sub-silo is arranged to be larger than the volume of the first sub-silo, in which case the residence time of a volume unit of the material flow in the second sub-silo is longer than in the first sub-silo . In an embodiment of the system, the number of first sub-silos included in the preheating furnace is larger than the number of second sub-silos.

In an embodiment of the system, the preheating furnace is divided into three sub-silos, including two first sub-silos and one second sub-silo. Now there are provided three preheating furnaces per one smelting furnace.

In an embodiment of the system, the preheating furnace is divided into nine sub-silos, including six first sub-silos and three second sub-silos. Thus there is provided one preheating furnace per one smelting furnace .

DRAWINGS

The invention is described in more detail below by means of examples of its embodiments and with reference to the appended drawings, where

Figure 1 illustrates an embodiment in principle of a preheating system according to the invention, seen in a scherαatical cross-section,

Figure 2 illustrates a preheating furnace belonging to an embodiment of the preheating system according to the invention, seen axonometrically in a slanted view from the top, Figure 3 illustrates the preheating furnace of Figure 2, seen in a slanted view from below,

Figure 4 illustrates a section IV-IV of Figure 2, and Figure 5 illustrates a corresponding section as seen in Figure 4 of a preheating furnace belonging to another embodiment of the preheating system according to the invention. DETAILED DESCRIPTION OF THE INVENTION

Figure 1 is a simplified illustration of a preheating system for feeding material flows from a preheating furnace 1 to a smelting furnace 2. The preheating furnace 1 is arranged to preheat the loose material in order to further feed said material into the smelting furnace 2. In this kind of an application, the loose material can contain for example sintered pellets, lump ore, lump coke, lump carbon and lump quartzite.

The feed material is fed into the preheating furnace 1 from a storage silo (not illustrated) . The storage silo serves as a gas seal for the furnace. A distributor device 9 arranged in the upper part of the preheating furnace distributes the feed material into sub-silos 3, 6 that are arranged inside the preheating furnace. From these sub-silos 3, 6, the material flows downwards to the outlet pipes 4, 7 and therethrough to the smelting furnace 2. The distributor device 9 rotates and stops automatically at the furnace sub- silos 3, 6, one after the other. The filling level of the material in the sub-silos is controlled by continuous level measurements. If the material level in one of the sub-silos falls down to an alert level, the distributor device 9 automatically turns to fill said sub-silo first. The material distribution is monitored, and control automatics take care that each outlet pipe is all the time full of' material, and that carbon monoxide has no access to the preheating furnace through the outlet pipes from the smelting furnace. The heating of material in the sub-silos is carried out by a gas mixture fed therein through gas ducts 10.

In Figure 1, the preheating furnace 1 comprises a first sub-silo 3 and a second sub-silo 6. The first sub-silo 3 has a first outlet pipe 4 for conducting the material to a first inlet conduit 5 of the smelting furnace 2, which conduit 5 is located in the upper part of the smelting furnace, at a distance from the center of the smelting furnace.

The second sub-silo 6 has a second outlet pipe 7 for conducting the material to a second inlet conduit 8 of the smelting furnace, which inlet conduit 8 is placed in the upper part of the smelting furnace, in the vicinity of the furnace center.

In both sub-silos 3, 6, material is heated, so that it flows further downwards to the first outlet pipe 4 and respectively to the second outlet pipe 7, by conducting to each sub-silo essentially the same amount of thermal energy in relation to the volume flow discharged from said silo. The first flow of preheated matex'ial is conducted from the first sub- silo 3 along the first outlet pipe 4 to the first inlet conduit 5 of the smelting furnace with a first volume flow, the size of which is defined from the material downward-flowing rate, inside the smelting furnace at the point in question, because also the smelting furnace is full of material. The second flow of preheated material is conducted from the second sub-silo β along the second outlet pipe 7 to the second inlet conduit 8 of the smelting furnace with a second volume flow that is defined from the material downward-flowing rate at said point of the smelting furnace, and is thus larger than the first volume flow, because the material in the preheating furnace is settled slower in the periphery, at a distance from the center, than in the vicinity of the center. The volume of the second sub-silo 6 is larger than the volume of the first sub-silo 3, in which case a longer residence time is obtained for the material in the second sub-silo 6, and the temperatures of the first and second material flows are rendered essentially equally high.

Figures 2 - 5 illustrate two embodiments of the preheating furnace 1, both of which embodiments include a larger number of first sub-silos 3 than second sub-silos 6, which are larger in size.

In the embodiment of Figures 2 - 4 , the preheating furnace 1 is by sectors divided into three sub-silos, including two first sub-silos 3, their sector angle β being 110 ^s, and one second sub-silo 6, its sector angle α being 140². The system can include three preheating furnaces 1 according to Figures 2 - 4 per one smelting furnace 2.

Figure 5 illustrates a preheating furnace 1 that is by sectors divided into nine sub-silos, including six first sub-silos 3 and three second sub-silos 6. The sector angle β of the first sub-silos 3 is 35^a. The sector angle α of the second sub-silos is 50². Per one smelting furnace 2, there can be provided one preheating furnace 1 according to Figure 5.

The invention is not restricted to the above described embodiments only, but many modifications are possible within the scope of the inventive idea defined in the appended claims.

Claims

1. A method for feeding material flows from a preheating furnace (1) to a smelting furnace (2), where - there is provided a preheating furnace (1) comprising at least two sub-silos, including a first sub-silo (3) having a first outlet pipe (4) for conducting material into a first inlet conduit (5) of the smelting furnace (2), said inlet conduit (5) being located in the upper part of the smelting furnace, at a distance from the furnace center; and a second sub- silo (6) having a second outlet pipe (7) for conducting material into a second inlet conduit (8) of the smelting furnace, said inlet conduit (8) being located in the upper part of the smelting furnace, in the vicinity of the furnace center,

- material is heated in the first sub-silo (3) and in the second sub-silo (β), the material flowing downwards to the first outlet pipe (4) and respectively to the second outlet pipe (7), by conducting to each sub-silo essentially the same amount of thermal energy in relation to the volume flow discharged from said silo,

- a first material flow of preheated material is conducted from the first sub-silo along the first outlet pipe to the first inlet conduit of the smelting furnace with a first volume flow, which is defined from the material downward-flowing rate at said point of the smelting furnace, a second material flow of preheated material is conducted from the second sub-silo along a second outlet pipe to the second inlet conduit of the smelting furnace with a second volume flow, which is defined from the material downward-flowing rate at said point of the smelting furnace and is larger than the first volume flow, charac t er i z ed in that the residence time of a volume unit of the material flow in the second sub-silo (6) is arranged to be larger than in the first sub-silo (3), so that the temperatures of the first and second material flows are rendered essentially equally high.

2. A method according to claim 1, charac t eri z ed in that the volume of the second sub-silo (6) is arranged to be larger than the volume of the first sub-silo (3), in which case the residence time of a volume unit of the material flow in the second sub-silo is longer than in the first sub-siIo .

3. A preheating system comprising a preheating furnace (1) with at least two sub-silos, a first sub-silo (3) having a first outlet pipe (4) for conducting material to a first inlet conduit (5) of a smelting furnace

(2), said inlet conduit (5) being located in the upper part of the smelting furnace, at a distance from the furnace center; and a second sub-silo (6) having a second outlet pipe (7) for conducting material to a second inlet conduit (8) of the smelting furnace, said inlet conduit (8) being located in the upper part of the smelting furnace in the vicinity of the furnace center, charac teri zed in that the volume of the second sub-silo (6) is larger than the volume of the first sub-silo (3) .

4. A system according to claim 3, charac teri z ed in that the number of first sub-silos (3) included in the preheating furnace (1) is larger than the number of second sub-silos (6) .

5. A system according to claim 4, charac teri z ed in that the preheating furnace

(1) is divided into three sub-silos, including two first sub-silos (3) and one second sub-silo (6), and that there are arranged three preheating furnaces (1) per one smelting furnace (2) .

6. A system according to claim 4, charac t er i z ed in that the preheating furnace (1) is divided into nine sub-silos, including six first sub-silos (3) and three second sub-silos (6), and that there is arranged one preheating furnace (1) per one smelting furnace (2) .