WO1987007705A1

WO1987007705A1 - Method and equipment for continuous feeding in separate phases in fuel furnaces, such as cupolas

Info

Publication number: WO1987007705A1
Application number: PCT/IT1987/000053
Authority: WO
Inventors: Paolo Bennati
Original assignee: Paolo Bennati
Priority date: 1986-06-05
Filing date: 1987-06-04
Publication date: 1987-12-17

Abstract

Method and equipment for continuous feeding of melt furnaces with the supply in separate phases of metal charge, fuel, air and/or metallurgical metal materials, and the possibility of using different types of fuel, changing the coke bed in order to vary the analysis, and improving the furnace's performance and heat yield.

Description

METHOD AND EQUIPMENT FOR CONTINUOUS FEEDING IN SEPARATE PHASES IN FUEL FURNACES, SUCH AS CUPOLAS.

DESCEIPTIOI

Depending on the heat source fuel furnaces are divided in¬ to those using solid, liquid or gaseous fuel, or electric furnaces. In some types of furnace, such as cupolas, the fuel is burnt after being mixed with the melt material. This means these furnaces have a mixed charge and joint phases,as the metal charge, fuel (which is generally solid) and so on are loaded in the furnace together, usually in alternate layers. In this type of furnace, which is also called blast furnace, the cold or hot air is blasted into the material through tuyeres around the perimeter of the furnace and connected to a distribution wind box fed by a fan.

However, at present, mixed charge and tuyeres require an in-, crease in air velocity and injection force, so that the air can reach the centre of the furnace and melt all the mate¬ rial, including that in the centre. Such a condition can^"in¬ fluence fuel reaction, and the resistance from the material tends to keep combustion towards the walls and prevent it spreading towards the centre. This gives high temperatures near the lining, causing considerable wear and the possibi¬ lity of only short melting campaigns on one hand, and con¬ siderable heat dispersion outwards on the other, due to the cooling fluids used to prevent the furnace itself from mel- ting.

The present trend is to use water-cooled tuyeres protruding' into the furnace. This has somewhat improved the yield, but the structure has become more complex as the tuyeres have to be cooled. In mixed-phase furnaces, the charge fed through the top is usually composed of the metal elements to give the final composition, the fuels (generally coke) and also flux for the slag or gangue, or reaction materials. The hot gases passing through the charge can encourage or cause undesir- ed energy-consuming reactions which reduce yield still fur¬ ther. This usually happens to a lesser extent in blast fur¬ naces using liquid or gas fuel where metal charge feeding is a separate phase. These furnaces present positive as¬ pects as regards dust and gas emission. Furthermore, gas has low values of latent heat and sensible heat. However, they have not found widespread use because normally they can not be the only means of melting.

This invention aims to reduce or even eliminate the draw¬ backs of the traditional feeding system of melt .furnaces, e.g. cupolas, and to put forward a multi-feed system to improve their efficiency, reduce fuel consumption and in¬ crease melt campaings and hence running costs. Another aim is to propose a feed system allowing for com¬ bustion in the centre of the furnace, where it is diffi- cult with present techniques. Hence this method envisages a method of continuous feeding, as in Claim 1. It also con¬ cerns equipment^'-.for feeding furnaces (such as cupolas) in separate phases, as in Claim 7.

This method and equipment enablesthe use of different types of fuel - solid, liquid or gaseous, and. combinations of them - while still keeping combustion right in the centre ^"of the furnace. The fuel, air, melt materials, flux and other metallurgical materials are conveyed to the combus¬ tion ^•zone in separate phases. Centralized combustion also allows long campaigns without the lining having to be re¬ made. So the latent heat is used directly in the furnace and the gases are fully oxidized, which means combustion can be controlled in relation to metallurgy, thus separat¬ ing it from the energy yield. Continuous feeding through a central column that can be ad- ^'justed in height is a real breakthrough in metal melting and remelting, allowing gas combustion inside the furnace and recovery of latent and sensible heat for heating the charge. This design means improved energy yield, simplified equip¬ ment and controlled melting conditions. The invention provides for:

- central combustion with reduced heat loss and less ther- mically stressed refractory material - total combustion of the gases in the furnace, with re¬ covery of latent and sensible heat which is partly trans¬ mitted to the charge and partly to the air flowing . through the central column - introduction of combustion materials, carburizers and any other materials directly into the combustion zone to pre¬ vent element loss in the slag

- reduced dust in the top gas, which requires less cleaning before offtake - adjustable bed height for controlling carburizers analy¬ sis. Further details are set out in the description below and the drawings. Figure 1 is a diagram of the melting furnace and Figure 2 is an enlarged cross-section. In these drawings, (10) is the complete furnace, compris¬ ing a shell (11) lined with refractory material (12) with a charging throat_. (13) and a suction collar manifold (14) at the top, and a hearth (15) with access door, a casting channel (16) and a slag channel (17) . This method provides for separate feeding into the centre of the charge melt materials, at least one fuel, one carbu- rizer, one supporter of combustion and additional metallur¬ gical materials. The separate phases are fed from above down into the centre of combustion, which depends on the height of the coke bed (30) .

There can be different types of alternative fuels, e.g. so¬ lids, gas or liquids separately, or in various combinations while still in different phases. Hot or cold air be.inject¬ ed either downwards from the centre of the furnace and.out- wards, or from outside the furnace.

The melt materials are fed through the throat (13) from a hopper (18) which is replenished using a lifting and batch¬ ing system (19) . The charge is removed from the hopper (18) by a conveyor system (not shown) .

The solid fuel, carburizers, alloys, flux etc. are fed by a batching system (20') into a hopper (20) at the top of a screw feeder (21) operating in a central column (22) . The hopper (20) is under pressure and fitted with a pressure control system to prevent gas entering from the bottom of the column (44) , while the screw feeder (21) is driven by a variable-speed motor (23) .

The central column (22) has a double wall housing at least une duct (22'}. Air is blown in by a fan (24) and driven down into the furnace through the duct (22' ). The air flows along the duct (22') and is heated by the column before be¬ ing injected into the centre of the furnace. The air can be injected through outlets (25, 25') at different heights and also directly into the coke bed (30) via outlet (25''). Combustion occurs mainly in the centre of the furnace, and the hot gas rising melts the material and preheats the charge.

The tuyeres (26) can be used for integrating the combustion air. The central column (22) contains nozzles (27) for in¬ jecting liquid or gaseous fuel. Total combustion occurs with the support of air delivered through the nozzles (25) . Not being in contact with the other combustion materials which are transported in separate phases, the burnt gas can not cause undesired reactions.

The fuel nozzles (27) can be controlled by sensors, depend¬ ing on the presence of residual combustion gas. At least the lower part (28) of the central column (22) is fitted with a cooling system. The cooling pipes, the li- quid and/or gaseous fuel pipes and the control circuits are all housed in the duct (22').

The central column (22) with the hopper (20) , the air feed device (24) , the motor unit (23) and the cooling equipment for the column (22) are all placed on a platform (31) which is supported by a lifting system (32) that can raise the column right out of the furnace for maintenance of the lin¬ ing or of the column itself. In this way the height of the

5 coke bed can be varied, hence also the carburizing pro¬ cess.

The gas. ^' passing through the manifold (14) is sent into a mechanical dust separator (33) and then into an expan¬ sion chamber (34) linked to the hopper (18) so that the me- ic^' Lai (-iiarge is partially heated through the bottom of it^'. Heat exchangers can be placed in the chamber to provide for further heat recovery. After leaving the chamber, the gas reaches the filter (35) at a low temperature.

5 In order to adapt the method and equipment to other condi¬ tions and types of furnace, such as blast furnaces and cu¬ polas, the following variation has been designed to allow feeding of solid phases from outside through the sides of the furnace. 0 The invention illustrated in Figures 3 and 4 represents a system for feeding separate phases, in which the liquid, gaseous or powdery materials are fed from above down to the centre of the furnace, while granular-size solid materials are conveyed into it from outside at reaction level, _.. ^' : 5 through the outer shell.

Further details are set out in the description below and the drawings. Figure 3 is a diagram of the melt furnace and figure 4 is an enlarged cross-section. According to the invention, the melt materials are sent in- 0 to the furnace via the charging throat, and, with the help of feeders, the liquid, gaseous or powdery materials are conveyed through ducts (25,25') passing through the central column (22). The solid or granular-sized fuel, carburizers. alloys, flux etc. pass into the furnace through the side wall on a level with the coke bed (30) via batch feeders (21,21') fitted into the shell and safeguarded from any backfire or gas return. These batchers are placed as re- quired and in a sufficient number to ensure even distri¬ bution of the fuel and granular carburizer. Capacity can also vary depending on the metallurgical requirements, and control can be from a central unit, based on combus¬ tion parameters. The introduction of f el/carburizer through the feeders means that the height of the coke bed can be varied -con¬ tinuously and rapidly.

Claims

1) A method for continuous feeding of fuel furnaces, such as cupolas, with a shell for receiving a metal charge from above, containing a variable height coke bed on the bottom. It is characterized by the fact that at least one fuel, one supporter of combustion, one carburizer and additional metallurgical

fed into the centre of the charge in separate phases, which are con¬ veyed downwards along the furnace axis to the centre of combustion, which depends on the height of the coke bed. 2) Method as in Claim 1) , characterized by the fact that the separate phases are conveyed to the centre' of com¬ bustion down a central column which can be adjusted in height.

3) Method as in Claims 1) and 2) , characterized by the fact that the fuel is fed separately from the air. It is so¬ lid and can be mixed with other solid phases.

4) Method 'as in Claims 1) and 2) , characterized by the fact that the fuel is fed separately from the air and other solid phases, in the form of a liquid or gas or a. mix- ture of both.

5) Method as in Claims 1) and 2) , characterized by the fact that the fuel is fed separately from the air and includ¬ es a solid fuel that can be mixed with other solid pha¬ ses, and at least one liquid or gaseous fuel. 6) Method as in Claims 4) and/or 5) , characterized by the fact that the air is injected into the centre of the fur¬ nace on at least two different levels for precombustion and postcombustion. 7) Equipment for continuous feeding of fuel furnaces, such as cupolas, with charge batching and loading units (18, 19) , a means for supplying compressed air (24) , and ma¬ nifolds (14,33,34,35) for collecting, cooling, cleaning and discharging furnace gas, characterized by the fact that it includes a central feeding column, (22) connect¬ ed above to a hopper (20) receiving at least one solid fuel, one carburizer and/or additional metallurgical

5 materials and including a feeding screw (21) for convey¬ ing the materials from the feeding hopper (20) downwards into the centre of the furnace, and by the fact that the column has at least one lengthwise duct (22') conveying at least the air, with air outlet nozzles (25,25 ' ,25' ' ) i u at least two different levels.

8) Equipment as in Claim 7) , in which the chamber or duct 22') in the central column (22) also houses pipes (27) for conveying downwards into the centre of the .furnace a liquid or gaseous fuel in addition to or in replace- 5 ment of the solid fuel fed via the screw.

9) Equipment as in Claims 7) and 8) , in.which the central column (22) with its associated elements can be adjust¬ ed in height, depending on coke bed requirements.

10) Equipment as in Claims 7) to 9) , in which nozzles (26) 0 are provided for in the outer shell for injecting air from outside as well, on at least two different levels.

11) A method for continuous feeding of fuel furnaces, such as cupolas and blast furnaces, with separate phase de¬ livery of solid, powdery, liquid or gaseous materials, 5 characterized by the fact that all except the solid ma¬ terials are conveyed separately downwards into the cen-r tre of combustion, while the granular-size solid materi¬ als are sent separately into the furnace from outside, through the outer shell, on a level with the combustion 0 zone.

12) Method as in Claim 11) , in which the materials conveyed separately from above into the centre of combustion in¬ clude at least one fuel, one carburizer, one supporter of combustion and additional alloys in the form of a liquid, gas or^' powder, and in which the solid, granu¬ lar-size materials are conveyed in separate phases in¬ to the furnace through the shell, including at least one fuel, one carburizer and alloys. 13) Equipment for continuous feeding of melt furnaces in separate phases, with solid, powdery, liquid or gaseous materials to cause and maintain combustion. The shell receives a metal and/or mineral charge from above, and contains at the bottom a variable height coke bed. The equipment is characterized by.^'the fact that it includes a central column which can be adjusted in height, extend¬ ing vertically into the furnace and including piping for separate delivery of the liquid, gaseous and powdery ma¬ terials down to the coke bed, and side feeders for send- ing granular-size materials through the shell.

14) Method and equipment..for continuous feeding in melt fur¬ naces in separate phases, described and claimed for the above objectives.