WO2008087245A1

WO2008087245A1 - Method of and equipment for pretreating material that is fed into a smelting furnace

Info

Publication number: WO2008087245A1
Application number: PCT/FI2007/000293
Authority: WO
Inventors: Harri Louhelainen; Tom RÖNNBERG; Janne Ollila
Original assignee: Outotec Oyj
Current assignee: Metso Corp
Priority date: 2006-12-15
Filing date: 2007-12-13
Publication date: 2008-07-24
Anticipated expiration: 2009-06-15
Also published as: FI20061124A7; FI20061124A0; ZA200710681B; FI20061124L

Abstract

The invention relates to a method of and equipment for pre-treating material that is fed into a smelting furnace (2), such as an electric furnace, whereby the feed material is directed to a preheating system (1) comprising several separate preheating silos (3), each containing at least one feed pipe (6) that is connected to the smelting furnace and a means (12) for distributing the preheating gas in the preheating silo, whereby the exhaust gas (16) that is released from each preheating silo (3) of the preheating system is directed to common gas cleaning equipment (10), the gas pressure in each individual preheating silo being controlled by adjusting the amount of exhaust gas that is fed into the equipment.

Description

METHOD OF AND EQUIPMENT FOR PRETREATING MATERIAL THAT IS FED INTO A SMELTING FURNACE

The invention relates to a method of and equipment for pre-treating material before feeding it into a smelting furnace, such as an electric furnace. According to the invention, the pressure in a single preheating silo is adjusted in a preheating system comprising several preheating silos.

It is well known to feed raw material into the electric furnace through the pre- heating system so that the feed mixture is heated in a separate preheating silo, wherein the granular or lumpy feed mixture is heated and dried. In order not to need as much energy in the actual electric furnace for smelting the material, and to evaporate certain impurities before taking the material into the electric furnace, preheating in connection with the pre-treatment is required. It is well known to use one preheating silo, the material to be heated being fed into it in batches and the material being heated therein by means of a hot gas flow. As is well known, the preheating silo is connected to the smelting furnace by separate feed pipe arrangements, which pass through the roof of the smelting furnace and into the interior of the furnace, taking the preheated material to smelt- ing. It is well known to use a feeding silo that is formed by several sub-silos. There are limitations related to the use of one preheating silo, e.g., the limitations of space related to the size of the silo. It is also more difficult to control the preheated feed material, if only a single preheating silo is used.

Published application ZA 20012421 discloses a method of and equipment for pre-treating the feed material before smelting it in the smelting furnace. According to the publication, the feed material is fed into several feeding silos, each of them being connected to a preheating silo for heating the feed material. Each preheating silo is connected to the smelting furnace by means of a feed pipe. According to the invention, the gases that are released from smelting and preheating are cleaned and burnt in the presence of oxygen and used for heating the feed material bed in the preheating silo. However, the publication does not present a solution to controlling the gas pressure in a single preheating silo.

Publication US 6099301 discloses equipment for pre-treating the material that is fed into the smelting furnace, whereby the material is heated in several preheating units, which, at their lower parts, are connected to feeding channels that lead to the smelting furnace, several feeding channels being provided per preheating silo. In the arrangement according to the invention, a gas distribution cone is arranged inside the silo for an even distribution of the gas inside the silo.

When smelting material in a system that contains a plurality of preheating silos, the pressure control of an individual preheating silo should be taken into consideration. When controlling the pressure in the preheating silo, excessive oxy- gen content in the preheating gas is avoided. The excessive oxygen content causes coke to burn in the preheating silo, which causes an imbalance of the coke when smelting the material in the electric furnace. This further causes operational problems for the quality of the product. The Si content of the metal or the SiO₂ content of the slag may vary. Excessive under pressure in the preheat- ing silo should be avoided in order to manage the composition of the circulation gas that is removed. The composition of the circulation gas affects the industrial safety of the process and the uniformity of the operation. As the gas is hot and contains CO gas, an excessively high pressure in the preheating silo is also a security risk. When cleaning the exhaust gases of several preheating silos by one gas washing apparatus, the pressure of the gas space in the individual preheating silo cannot be controlled by a control system subsequent to the gas washing apparatus. This is a well-known method, when operating with individual preheating silos.

The purpose of the invention is to provide a new method of and equipment for pre-treating material, which is fed into the smelting furnace, in a preheating system containing several preheating silos. In particular, the purpose of the inven- tion is to control the gas pressure in each individual preheating silo in the system containing several preheating silos per one smelting furnace.

The invention is characterized in that which is sited in the claims.

The invention relates to a method of pre-treating material that is fed into the smelting furnace, such as an electric furnace, whereby the feed material is directed to the preheating system comprising several separate preheating silos, each one of them containing at least one feed pipe that is connected to the smelting furnace and a means for distributing the preheating gas in the preheating silo, whereby the exhaust gas releasing from each preheating silo is directed to a common gas cleaning equipment, and the gas pressure in each individual preheating silo is controlled by adjusting the amount of exhaust gas that is fed into the equipment. The invention is preferably used for adjusting the gas pressure in the individual preheating silo of the preheating system comprising several preheating silos. By adjusting the gas pressure in each individual preheating silo, the pre-treatment conditions of the material in each preheating silo are adjusted so that, in the preheating silo, ideal conditions prevail for feeding the material into the smelting furnace, and the disadvantages caused by the variations in the gas pressure in the smelting process previously mentioned are avoided. If an agglomeration is formed in the smelting furnace by the material that is fed into it, because of which the feeding must be disconnected at the particular spot, or the material flow is minor, it is important to control the pressure in the individual preheating silo and, further, the feeding to the smelting furnace.

According to a preferred embodiment of the invention, the exhaust gas is directed from the gas cleaning equipment to at least one gas heating unit. According to an embodiment of the invention, the amount of gas that is fed into the gas heating unit is controlled by means of circulation gas pumps. The exhaust gas that is released from the smelting furnace is washed and directed to at least one gas heating unit to heat the gas mixture that is fed into the preheat- ing silo. According to an embodiment of the invention, the amount of heating gas fed into each preheating silo is adjusted.

According to an embodiment of the invention, the temperature of the gas mix- ture that is fed into each individual preheating silo is controlled by directing, to the gas mixture that is heated in the gas heating unit, a sufficient amount of circulation gas before feeding the gas mixture into each preheating silo and into the material bed therein, which is to be heated. The circulation gas can be directed to the preheating silo-specific gas lines in question through adjustable circulation gas control equipment, such as valves. This can also be used for adjusting the temperature of the gas mixture in the individual preheating silo.

The invention also relates to equipment for pre-treating the material that is fed into the smelting furnace, such as an electric furnace, whereby the equipment includes a preheating system comprising several separate preheating silos for heating the feed material, each silo including at least one feed pipe that is connected to the smelting furnace and a means for distributing the preheating gas in the preheating silo, whereby common gas cleaning equipment is arranged for the preheating silos for washing the exhaust gases of the preheating silos, whereby a control unit for adjusting the amount of circulation gas is arranged in the exhaust gas line of each preheating silo. According to the invention, the pressure can be adjusted for the individual preheating silo in the preheating system containing several preheating silos by arranging control equipment, such as a valve, in the exhaust gas channel of each individual preheating silo. When using one gas cleaning equipment for several preheating silos, the investment and operating costs become lower and the need for space of the process is smaller.

According to a preferred embodiment of the invention, the gas cleaning equip- ment is a cascade scrubber. When using the cascade scrubber, the water consumption in gas cleaning is minor and the water pressure is low, whereby the washer does not require high-pressure pumps. According to a preferred em- bodiment of the invention, the gas cleaning equipment is a Venturi scrubber. If corrosive components evaporate from the preheated material, the large amount of water that is used in the Venturi scrubber will dilute the corrosive components. This reduces the corrosion of the gas and water pipe lines.

According to the invention, the control unit for adjusting the amount of circulation gas at least consists of valves. According to the invention, the gas line of the preheating system comprises at least one gas heating unit for heating the gas mixture that is fed into the preheating silo. According to an embodiment of the invention, a desired amount of circulation gas can be added to the gas mixture that is fed into each preheating silo, its amount being adjustable by means of the circulation gas control unit. In this way, the temperature of the material bed in the preheating silo can be influenced. According to an embodiment of the invention, the gas line between the gas heating unit and each preheating silo comprises a means for adjusting the amount of gas mixture.

In the following, the invention is described in more detail with the aid of an example and with reference to the appended drawings, in which

Fig. 1 shows the equipment according to the invention.

Fig. 1 shows the method of and the equipment for pre-treating material according to the invention, comprising a preheating system 1 for pre-treating the material that is fed into the smelting furnace 2. According to the invention, the feed material 5 in a granular form is homogenized and fed into preheating silos 3, of which there are preferably several in the process in a parallel relationship, three according to the example. In the preheating silo 3, the feed material 5 forms an even material bed, within which heating and the evaporation of impurities take place under the effect of a hot gas mixture 4 that is fed into the preheating silo 3. In connection with the silo 3, a means 12 is arranged for an even distribution of the gas mixture in the silo. The feed material 5 is fed into the preheating silos, for example, through feeding silos (not shown in the figure) so that the ma- terial flow that is fed remains even. Each preheating silo 3 is connected, at the lower part thereof, to the smelting furnace 2, such as an electric furnace, wherein the material is smelted. Typically, the preheating silo 3 is connected to the smelting furnace by feeding channels 6, of which there are preferably sev- eral; for example, at least three per one preheating silo 3 so as to allow an even feed of the material into the smelting furnace 2.

According to the invention, the gas pressure in each individual preheating silo 3 of the preheating system 1 is adjustable. According to the invention, there is one common gas cleaning equipment 10, such as a cascade scrubber, per each preheating system 1 , the amount of exhaust gas 16 that is fed into it being adjusted by means of control equipment 18, such as valves that are connected to the gas line of each preheating silo. The washed circulation gas 19 is directly fed into a gas heating unit 8. According to the example of the invention, one common gas heating unit 8 is arranged for the preheating silos in a gas line 7, containing a burner and a combustion chamber, wherein the gas mixture 4 that is fed into the preheating silos 3 is heated. According to the invention, the preheating system 1 may also contain several gas heating units 8. An amount of exhaust gas 16, which is required and which is preferable for the smelting proc- ess, is recycled from each preheating silo 3 to be washed in the gas cleaning equipment 10. The amount of exhaust gas that is fed from each preheating silo into the gas cleaning equipment is adjusted, depending on the pressure in each preheating silo. If the pressure in an individual preheating silo is disadvantageous, as measured for the process, its magnitude can be influenced by adjust- ing the amount of exhaust gases so that the pressure becomes even. Hence, the gas pressure in each individual preheating silo is influenced. Part of the circulation gas can be removed from the process before it is fed into the gas cleaning equipment 10. According to the example, the preheating system also includes control equipment 11 so that the amount of gas that is fed into the in- dividual preheating silo can be adjusted from the common gas heating unit 8. According to the invention, the amount of circulation gas that is fed from the gas cleaning equipment 10 can be adjusted by means of pumps 13. The ex- haust gas 17 that is released from the smelting furnace 2 is washed in at least one gas cleaning equipment 9 before feeding it to be heated in the gas heating unit 8. After the circulation gas pumps 13, the circulation gas, i.e., the exhaust gas 16 that is released from the preheating silo can also be directed to the gas line 7 by means of a separate circulation gas line. By feeding the circulation gas 15 after the control equipment 11 that adjusts the amount of gas mixture 4, the temperature of the gas mixture 4 that is fed into each preheating silo can be influenced as desired. The amount of circulation gas 15 that is fed into the gas mixture 4 can be adjusted by means of a circulation gas control device 14. This can be used, when so desired, in adjusting the temperature of the heating gas mixture to the desired value for the individual preheating silo 3 of the preheating system 1 ; and, hence, the temperature of the preheating gas and, thus, also that of the material in the preheating silo are influenced.

The invention is not merely limited to the application examples describe above, but many variations are feasible within the inventive idea defined by the claims.

Claims

CLAIMS:

1. A method of pre-treating material that is fed into a smelting furnace (2), such as an electric furnace, whereby the feed material is directed to a preheating system (1) comprising several preheating silos (3), each including at least one feed pipe (6) that is connected to the smelting furnace and a means (12) for distributing the preheating gas in the preheating silo, characterized in that the exhaust gas (16) that is released from each preheating silo (3) of the preheating system is directed to common gas cleaning equipment (10), and the gas pressure in each individual preheating silo is controlled by adjusting the amount of exhaust gas that is fed into the equipment.

2. A method according to Claim 1 , characterized in that the exhaust gas (16) is directed from the gas cleaning equipment (10) to at least one gas heating unit (8).

3. A method according to Claim 1 or 2, characterized in that the amount of gas that is fed into the gas heating unit (8) is adjusted by means of circulation gas pumps (13).

4. A method according to Claim 1 , characterized in that the exhaust gas (17) releasing from the smelting furnace (2) is washed and directed to at least one gas heating unit (8) to heat the gas mixture (4) that is fed into the preheating silo.

5. A method according to Claim 1 , 2, 3 or 4, characterized in that the amount of gas mixture (4) that is fed into each preheating silo (3) is adjusted.

6. A method according to Claim 1 , characterized in that the temperature of the gas mixture (4) that is fed into each individual preheating silo is adjusted by directing a required amount of circulation gas (15) to the gas mixture (4) that is heated in the gas heating unit (8) before the gas mixture is fed into each preheating silo (3).

7. Equipment for pre-treating material that is fed into a smelting furnace (2), such as an electric furnace, whereby the equipment includes a preheating system (1) comprising several separate preheating silos (3) for heating the feed material, each containing at least one feed pipe (6) that is connected to the smelting furnace and a means (12) for distributing the preheating gas in the preheating silo, characterized in that common gas cleaning equipment (10) is arranged for the preheating silos (3) for washing the exhaust gases (16) of the preheating silos, whereby a control unit (18) for adjusting the amount of exhaust gas is arranged in the exhaust gas line of each preheating silo.

8. Equipment according to Claim 7, characterized in that the gas cleaning equipment (10) is a cascade scrubber.

9. Equipment according to Claim 7, characterized in that the gas cleaning equipment (10) is a Venture scrubber.

10. Equipment according to Claim 7, characterized in that the control unit (18) for adjusting the amount of exhaust gas consists of at least a valve.

11. Equipment according to Claim 7, characterized in that, in the gas line (7) of the preheating system, there is at least one gas heating unit (8) for heating the gas mixture (4) that is used in the preheating silo (3).

12. Equipment according to any of the preceding claims, characterized in that a desired amount of circulation gas (15) can be added to the gas mixture (4) that is fed into each preheating silo (3), its amount being adjustable by means of a circulation gas control unit (14).

13. Equipment according to any of the preceding claims, characterized in that, in the gas line between the gas heating unit (8) and each preheating silo (3), there is equipment (11) for adjusting the amount of gas mix- ture.