WO1996020381A1

WO1996020381A1 - Reactor for heating and treating materials in a controlled atmosphere

Info

Publication number: WO1996020381A1
Application number: PCT/EP1995/004372
Authority: WO
Inventors: Ugo Brusa
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-12-28
Filing date: 1995-11-07
Publication date: 1996-07-04
Anticipated expiration: 1997-06-28
Also published as: ZA9510621B; PL320959A1; MX9704773A; IT1267362B1; FI972746L; FI972746A7; AU3982395A; BR9510432A; EP0800640A1; FI972746A0; ITTO941078A0; JPH10511450A; CA2208835A1; CN1171840A; ITTO941078A1

Abstract

A reactor comprises a reaction chamber (1) into the upper part of which a first preheated material is introduced. A second material, which may comprise solid, liquid and/or gaseous constituents, is introduced into the lower part of the chamber (1), at different locations and in different amounts. The solid materials on the floor of the chamber are stirred, made to advance towards discharge means (17) and indirectly heated by devices (3) rotating within the chamber (1), which devices (3) are heated while being in the upper part of the chamber (1) and yield heat to the materials while being in the lower part of the chamber (1).

Description

REACTORFORHEATINGANDTREATINGMATERIALSINACONTROLLED ATMOSPHERE

The present invention concerns a reactor for heating and treating materials in a controlled atmosphere, by a continuous process.

More particularly, the invention can be employed for reducing metal oxides, but it can be employed also for different treatments, such as coal degassing, lime roasting, metal melting and so on.

It is known that, especially for reducing metal oxides, it is generally desired to attain high reaction speeds and to utilise reducing materials as cheap as possible. Moreover, reoxidation of the material being treated is to be avoided. It is also known that the cheapest source of reducing materials is coal which, when suitably heated, evolves reducing gases, including hydrogen. However, in conventional reactors, where the coal is introduced with the oxide charge, the reducing properties are ineffectively exploited, resulting in very long processing times and in a greater coal consumption. When a higher reaction speed is desired, reactors are utilized where methane or combustible oils which evolve hydrogen are introduced into the material. For instance, a known reactor of this kind comprises a rotating cylinder in which the material to be reduced is heated by direct irradiation and the reducing fluids are insufflated through ducts solidary with the cylinder.

The known system is not satisfactory for various reasons: direct irradiation of the material does not allow a strong and uniform heating of the mass; the methane and the combustible oils are relatively expensive hydrogen sources; the system is complex due to the need both of connecting the ducts solidary with the rotating cylinder to stationary feeders, and of controlling air supply so as to avoid reoxidation of the material.

According to the invention on the contrary a reactor and a process for treating materials in a controlled atmosphere are provided, which reactor and process allow high reaction speeds without need to employ expensive materials, ensure a uniform heating and require no complex feeding apparatus.

The invention provides a reactor comprising a reaction chamber associated at one end, in its upper part, with means for introducing a charge of a first material to be treated, and at the opposite end, in its lower part, with means for discharging the treated materials, characterized in that the reactor further comprises: means for the introduction of further materials into the lower part of the reaction chamber, in alternative or in addition to the first material and below the latter; means for indirect heating of the materials introduced and for continuously stirring said materials and advancing them towards the discharge means; and means, located in the upper part of the reaction chamber, for introducing oxidizing gas which exothermically reacts with the gases evolved during the treatment, the indirect heating means being arranged so as to continuously move between the upper and the lower parts of the chamber, being heated in the upper part by the heat evolved by said hexothermic reaction and yielding said heat, in the lower part of the chamber, to the materials being treated.

The invention further provides a process where a first material to be treated is introduced into a reaction chamber at a first end thereof, and the treated material is discharged from a second end of the chamber, characterized in that the first material is introduced into the upper part of the chamber so as to fall on the chamber floor; in that further materials, which become covered by the first material, are introduced into the lower part of the chamber, in alternative or in addition to the first material; and in that the materials on the reaction chamber floor are continuously stirred, are made to move towards the discharge end and are indirectly heated by heating means which are movable between the upper and the lower parts of the chamber and which yield the heat absorbed in the upper part of the chamber to materials being treated.

The invention will be better understood with reference to the accompanying drawings, which show a longitudinal sectional view (Fig.l), a plan view (Fig.2) and a transversal sectional view (Fig.3) of the invention, respectively. As shown in Fig.1 , the reactor comprises a treatment chamber 1 where a refractory cylinder 2 rotates. The cylinder is equipped with parallel rows of fins 3, e.g. made of refractory steel, which are arranged concentrically with the cylinder and are mounted thereto. These fins are to make the materials present in the chamber advance, while stirring and homogenizing them, and to indirectly heat same, by yielding them heat absorbed in the upper part of chamber 1, as will be better explained hereinafter.

Cylinder 2 is supported by a shaft 4, driven by a motor-reducer 5 and cooled by a coolant liquid introduced through a rotating seal 6.

The upper part of chamber 1 is in communication with a preheater 7, it too comprising a rotating cylinder 8 equipped on its inner surface with radial fins oriented according to the generatrices of cylinder 8. In the preheater, a charge 9 (e.g. finely subdivided metal oxides) is heated by the fumes evolved during treatment effected in chamber 1. Charge 9 is introduced into preheater 7 by means of a conveyer belt 10, a hopper 11 and a chute 12. Preheater 7 is rotated by means of wheels 13 which rest on suitable supporting structure (not shown), and is associated with chimney 14 for gas exhaust.

At the end opposite to preheater 7, chamber 1 is associated with a device 15 for discharging the treated material from the chamber bottom, for instance a screw driven by a motor- reducer 16. That screw is located within a tube 17 which can be associated with cooling means, if the material is a completely treated product, or which will be thermally insulated from the outer environment, if the material treated in the reactor is to undergo further thermal treatment.

Fig. 2 further shows that the reactor comprises a group of feeders 18 (for instance screws operated by respective motor-reducers 19) for the possible introduction into the lower part of chamber 1 , below the primary charge 9 and at a plurality of locations spaced apart along the chamber, of a secondary solid charge, for instance coal in powder or in grains. A duct 21 , communicating with tubes 20 (Fig.3) housing screws 18, allows mixing liquid substances with the coal, for instance combustible oils which are introduced together with or through the coal. Other ducts 22 can convey gaseous materials, for instance methane, propane, etc., into the lower part of chamber 1. Also those materials can be introduced in alternative or in addition to the coal and/or the combustible oils.

The materials supplied through feeders 18 and ducts 21, 22 will generally be introduced in different amounts at the different locations along chamber 1 , so that just the amount of material actually needed by the reactions at a given location will be provided at that location.

Lastly, Fig.3 shows that ducts 24 with nozzles 25 are provided in the upper part of chamber 1 to introduce oxidizing agents (e.g. air) into the chamber for reaction gas combustion. That combustion is the main heat source for heating fins 3. By suitably adjusting the volume rate of oxidizing gas, a continuous control of the atmosphere in the upper part of the chamber can be achieved. Burners 23, also located in the upper part of the chamber, may supplement the heat provided from the combustion, whenever this is necessary.

The operation of the reactor is as follows. The primary charge 9 fed through the hopper 11 falls into preheater 7 where it is made to advance towards chamber 1 and is heated by the hot fumes leaving chamber 1. Charge 9 passes from preheater 7 into chamber 1 where it falls on the secondary solid charge fed through feeders 18 and/or on the fluid substances introduced through ducts 21, 22.

The mass present in the lower part of chamber 1 is stirred by fins 3 of cylinder 2, which fins make the mass advance towards discharge means 15 and, above all, yield absorbed while in the upper part of the chamber to the mass heat. The continuous stirring ensures a homogeneous heating. While the mass advances, it is combined with new amounts of solid secondary charge and/or of fluids to the extent necessary to maintain the reactions. The gases released by the reactions between the oxides and the reducing substances pass then to the upper part of chamber 1 where they burn due to the action of air or other oxidizing gases introduced through ducts 24, thereby heating fins 3 while they move in the upper part of chamber 1. If it is necessary to supplement the heat provided by such combustion, also burners 23 will be operated. Thanks to the indirect heating of the material, a good separation is maintained between the atmospheres of the upper and lower parts of chamber 1 (oxidizing and oxidized atmosphere in the upper part, reducing atmosphere in the lower part), so that the risk that the material becomes reoxidized is kept limited. At the end of the treatment, the material is discharged through tube 17, where the same atmosphere as in the lower part of the chamber is maintained.

If the reactor is utilized for instance for degassing coal, only one or more lower feeders 18 will be active and preheater 7 will not be employed.

The advantages of the invention clearly result from the above description. Besides achieving separation between different atmospheres, as already said, the reactor optimally exploits the ancillary materials (coal, combustible oils, natural gases) since those materials are introduced along the whole reactor length and in different amounts. Thus coal, which is a cheap material, can be employed as ancillary material, while maintaining high reaction speeds. Moreover, it is possible to use materials of granulometry even considerably smaller than that usually utilised, as the mass is continuously stirred by the fins and agitated also by the gases, if any, introduced from below, so that a high porosity is maintained even with finely divided materials.

It is evident that modifications and variations are possible without departing from the scope of the invention. Moreover, use of the reactor is not limited to the examples described above, but the reactor itself can be used for any other treatment demanding a controlled atmosphere and giving rise to evolution of gases which can be made to exothermically react in the upper part of the chamber.

Claims

1. A reactor for heating and treating materials, the reactor comprising a reaction chamber (1) associated at one end and in its upper part with means for the introduction of a charge (9) of a first material in powder or in grains to be treated, and, at the opposite end and in its lower part, with means (15, 17) for discharging the treated materials, characterized in that the reactor further comprises: means (18, 20, 21, 22) for the introduction of further materials into the lower part of the chamber, in alternative or in addition to the first material and below said first material; means (3) for indirectly heating the materials introduced and for continuously stirring and advancing said materials towards the discharge means (15, 17); and means (24, 25), located in the upper part of the chamber (1), for the introduction of oxidizing as which exothermically reacts with gases evolved during treatment, the means (3) for indirect heating continuously moving between the upper and the lower part of the chamber (1 ), being heated in the upper part by the heat generated by the exothermic reaction and yielding the heat to the material being treated, in the lower part of the chamber.

2. A reactor as claimed in claim 1, characterised in that the means (3) for heating, stirring and continuously advancing the material comprise a first rotating cylinder (2) equipped with groups of coplanar fins (3) arranged concentrically with the cylinder (3) and arranged so as to engage the material present on the chamber floor.

3. A reactor as claimed in claim 1 or 2, characterised in that the means (10, 11, 7) for the introduction of the first material comprise a preheater (7) where the material is heated by the fumes generated by the combustion of said gases, before being passed to the reaction chamber (1).

4. A reactor as claimed in claim 3, characterised in that the preheater comprises a second rotating cylinder (7), provided on its internal surface with radial fins (8), arranged along cylinder generatrices, in order to make the material advance towards the reaction chamber (1) during preheating.

5. A reactor as claimed in any preceding claim, characterised in that it further comprises burners (23) located in the upper part of the chamber to provide supplementary heat to the indirect heating means (3), while the latter are in said upper part.

6. A reactor as claimed in claim 1 , characterised in that the means (18, 20, 21 , 22) for the introduction of the further materials are arranged so as to introduce said further materials at different locations spaced along the chamber length, in different amounts for the different introduction locations.

7. A reactor as claimed in claim 6, characterised in that said further materials comprise solid constituents in powders or in grains, and/or liquid constituents and/or gaseous constituents, and the means (18, 20, 21, 22) for introduction of said further materials comprise:

a plurality of feeders (18) of the solid constituents; a duct (21), in communication with each said feeder (18), for the introduction of the liquid constituents, possibly jointly with the solid constituents; one or more ducts (22) for the direct introduction of the gaseous constituents into the lower part of the chamber (1).

8. A reactor as claimed in claim 1 , characterised in that the discharge means ( 17) are arranged in an environment thermally insulated from the outside.

9. A reactor as claimed in claim 1, characterised in that the discharge means (17) are arranged in an environment provided with means for cooling the discharged material.

10. A reactor as claimed in any preceding claim, characterised in that the first material is a metal oxide to be reduced and the further materials comprise coal, combustible oils, light hydrocarbons.

11. A method of treating and heating materials in a controlled atmosphere, where a first material to be treated is introduced into a reaction chamber (1) at a first end thereof, and the treated material is discharged from a second end of the same chamber, characterized in that the first material is introduced into the upper part of the chamber (1) so as to fall onto the chamber floor; in that further materials are introduced into the lower part of the chamber ( 1 ), in alternative or in addition to the first material, and in that the material on the floor of the reaction chamber is continuously stirred, made to advance towards the discharge end and indirectly heated by heating means (3) that move between the upper and the lower part of the chamber (1) and yield the heat absorbed in the upper part of the chamber (1) to the material.

12. A method as claimed in claim 11 , characterised in that the heating of the means (3) for the indirect heating of the materials is obtained at least in part thanks to the combustion of gases evolved during treatment.

13. A method as claimed in claim 11 or 12, characterised in that the first material is preheated by the fumes generated by said combustion.

14. A method as claimed in claim 11, characterised in that the further materials are introduced at a plurality of locations spaced apart between the first and second ends of the chamber (1), in different amounts for the different locations.

15. A method as claimed in claim 14, characterised in that the further materials comprise solid constituents in grains or in powder and/or liquid constituents and/or solid constituents, the liquid constituents being introduced jointly with or through the solid constituents, and the gaseous constituents being directly introduced into the reaction chamber (1).

16. A method as claimed in claim 11, characterised in that the treated material is maintained at a substantially constant temperature while being discharged.

17. A method as claimed in claim 11 , characterised in that the treated material is cooled while being discharged.

18. A method as claimed in any of claims 11 to 17, characterised in that said treatment is the reduction of metal oxides forming the first material, and the further materials comprise coal and/or combustible fuels and/or gaseous hydrocarbons.

19. A method as claimed in any of claims 11 to 17, characterised in that the treatment is the degasification of coal forming the solid constituents of said further materials.