EP0902841A1

EP0902841A1 - Process for the treatment of particulate matter by fluidisation, and vessel with apparatus to carry out the treatment

Info

Publication number: EP0902841A1
Application number: EP97921513A
Authority: EP
Inventors: Werner-Leopold Kepplinger; Felix Wallner; Johannes-Leopold Schenk; Franz Hauzenberger; Roy Hubert Whipp, Jr.
Original assignee: Voest Alpine Industrienlagenbau GmbH
Current assignee: Primetals Technologies Austria GmbH; Brifer International Ltd
Priority date: 1996-05-17
Filing date: 1997-05-15
Publication date: 1999-03-24
Also published as: PE44398A1; AR007085A1; AU728390B2; CA2257492A1; WO1997044495A1; ID17840A; BR9709095A; KR20000011107A; ATA87696A; ZA974251B; AT405522B; AU2756197A; JP2000511970A

Abstract

In a process for the treatment of particulate matter by fluidisation the particulate matter is held and treated in a fluidised bed (2) with the treatment gas flowing from the bottom to the top. To minimise consumption of the treatment gas, and to reduce the entrainment of fines by the treatment gas, particulate matter with a wide ranging grain size distribution and a relative large content of fines is used and the empty pipe flow rate of the treatment gas in the fluidised bed (2) is kept smaller than the flow rate required for the fluidising of the larger particles of the particulate matter.

Description

Process for treating particulate material in a fluidized bed process, and vessel and installation for carrying out the process

The invention relates to a process for treating, preferably reducing, particulate material in a fluidized bed process, in particular for reducing fine ore, the particulate material being held in a fluidized bed by a treatment gas flowing upward and being treated, and a vessel for carrying out the Procedure.

A method of this type is known, for example, from US-A-2,909,423, WO 92/02458 and EP-A-0 571 358. Here, oxide-containing material, e.g. Fine ore, reduced in a fluidized bed maintained by a reducing gas within a fluidized bed reduction reactor, the reducing gas which is introduced into the fluidized bed reduction reactor via a nozzle grate flowing through the reduction reactor from bottom to top, whereas the oxide-containing material cross-flows the reduction reactor approximately penetrated to the reducing gas flow. In order to maintain the fluidized bed, a certain speed of the reducing gas within the fluidized bed zone is required, which depends on the particle size of the material used.

Because of the relatively high speed of the reducing gas required in the known processes, there is a strong discharge of fine particles of the oxide-containing material and, in the case of advanced reduction, a discharge of already reduced oxide-containing material from the fluidized bed, these fine particles then being contained in the reducing gas. In order to remove these very fine particles from the reducing gas - on the one hand, to be able to continue to use the partially oxidized reducing gas, for example for upstream reduction reactors, or to recover the otherwise lost oxide-containing material or material that has already been reduced - the reducing gas containing the fine particles is removed by dust separators, guided like cyclones, and the separated dust is returned to the fluidized bed. The dust separators or cyclones are preferably arranged inside the reactors (cf. US Pat. No. 2,909,423); however, they can also be installed outside the reactors.

In practice it has been shown that partially reduced or reduced fine-grained particles of the oxide-containing material tend to stick or bake to one another and / or to the walls of the reactors or cyclones and connecting lines or delivery lines. This phenomenon is referred to as "sticking" or "fouling". The "sticking" or "fouling" depends on the temperature and the degree of reduction of the oxide Materials. The sticking or application of the partially or completely reduced oxide-containing material to the walls of the reduction reactors or other system parts can lead to faults, so that it is not possible to operate the system continuously for a longer period of time without switching it off. It has been shown that continuous operation beyond a year is difficult.

The removal of the attachments or caking is very labor-intensive and causes high costs, e.g. Labor costs as well as costs that are caused by the loss of production of the system. Often there is an automatic detachment of the attachments, whereby they either fall into the fluidized bed and thus lead to a disruption of the reduction process, or - if the attachments detach from the cyclone - cause the dust return channels leading from the cyclone to the fluidized bed to be laid so that a further dust separation from the reducing gas is completely impossible.

A disadvantage of the known fluidized bed processes in practice lies in the inflexibility and difficulty in dividing and feeding the treatment gas stream, i.e. in the above-described prior art methods for dividing and feeding the reducing gas stream. It is also disadvantageous in the prior art that at each process stage, i.e. preheating, pre-reduction and final reduction, usually two or more product streams have to be removed from the apparatus associated with the process stages, which means a considerable outlay on conveying and lock devices. In addition, two gas supply systems must be regulated at each process stage, which is very difficult in practice for hot dust-containing gases.

In addition, due to the relatively high speed of the reducing gas, there is considerable consumption of reducing gas. Much more reducing gas is consumed than would be necessary for the actual reduction process, the additional consumption merely serving to maintain the fluidized bed.

A process for reducing metal ores by means of a fluidized bed process is also known from GB-A-1 101 199. The process conditions are chosen so that the material cakes during the reduction, which forms agglomerates that are not fluidized due to their size. As a result, the finished, reduced material, which is discharged downward from the fluidized bed reactor, is separated from the not completely reduced material, which remains fluidized. Smaller product particles are drawn off at the upper end of the fluidized bed. With this procedure So there are also two product flows, which means that a corresponding outlay on equipment is required.

The invention aims to avoid these disadvantages and difficulties and has the object to provide a method of the type described above and a vessel for carrying out the method, which a treatment of particulate oxide-containing material with minimal consumption of treatment gas over a very long period without the Enable the risk of business interruptions caused by "sticking" or "fouling". In particular, the amount of treatment gas required for maintaining the fluidized bed and its flow rate should be able to be greatly reduced, so that only a minimal discharge of fine particles takes place.

This object is achieved in that particulate material with a broad grain distribution with a relatively high proportion of fines and a proportion of larger particles is used for the treatment and that the empty tube speed of the treatment gas in the fluidized bed is kept lower than that for fluidizing the proportion of larger ones Particles of the particulate material necessary speed, all larger particles are moved up together with the fine fraction and discharged from the upper region of the fluidized bed.

It has been found that with a wide uniform grain distribution, the speed of the tube in the fluidized bed can be maintained in a range from 0.25 to 0.75 the speed necessary for fluidization of the largest particles of the particulate material.

A particulate material with a grain is preferably used, of which the mean grain diameter of the grain belt is 0.02 to 0.15, preferably 0.05 to 0.10, of the largest grain diameter of the particulate material.

In this case, an empty tube speed is expediently set for the treatment gas above the fluidized bed, based on the largest cross section of a vessel receiving the fluidized bed, for a theoretical limit grain size of 50 to 150 μm, preferably 60 to 100 μm, advantageously for reducing the "run of mine" Fine ore an empty tube speed in the fluidized bed between 0.3 m / s and 2.0 m / s is set. In a process for the direct reduction of particulate iron oxide-containing material in the fluidized bed process according to the process according to the invention, reformed gas is mixed with top gas formed in the direct reduction of the iron oxide-containing material and fed to a fluidized bed reduction zone as reducing gas, and both the top gas and the reformed gas of a CO ₂ - Washed and the reducing gas formed by mixing top gas and reformed gas is adjusted to a certain H ₂ content and a CO content.

A vessel for carrying out the method according to the invention is characterized by the combination of the following features:

A cylindrical lower fluidized bed part which receives the fluidized bed and has a gas distribution base, a feed line for the treatment gas and a feed and discharge for particulate material above the gas distribution base,

A cone part which is arranged above the fluidized bed part and adjoins it and widens conically upwards, the inclination of the wall of the cone part to the center axis of the reactor being 6 to 15 °, preferably 8 to 10 °,

• an at least partially cylindrical calming part adjoining the cone part, which is closed at the top and from which a treatment gas discharge line emerges, wherein

• The ratio of the cross-sectional area of the calming part in the cylindrical region to the cross-sectional area of the fluidized bed part is> 2.

A vessel for carrying out an ore reduction process in a fluidized bed, which has two cylindrical parts of different diameters and a very short and strongly conical part between the cylindrical parts, is known for example from EP-A-0 022 098. In this vessel, however, two gas feeds are provided, one below the lower cylindrical part and one in the conical part. The reduced ore is discharged downwards from this fluidized bed reactor.

According to the invention, the cross-sectional area of the calming space in the cylindrical region is preferably so large that an empty pipe speed is established in this region, which would be sufficient to separate a grain larger than 50 μm from the gas.

A system for the direct reduction of particulate iron oxide-containing material in a fluidized bed process with at least one fluidized bed reactor designed according to the vessel according to the invention for receiving the iron oxide-containing material, a reducing gas feed line to this fluidized bed reactor and a top gas discharge leading to the reduction from the fluidized bed reactor with top gas discharge A reformer, a reforming gas line originating from the reformer and merged with the top gas line, the reducing gas formed from the reformed gas and top gas reaching the fluidized bed reactor via the reducing gas supply line, and with a C0 ₂ scrubber, is characterized in that both the reforming gas line as well as the top gas discharge lead into the C0 ₂ scrubber and the reducing gas feed line leads from the COy scrubber to the fluidized bed reactor.

The invention is explained in more detail below with reference to the drawing, in which FIG. 1 shows a vessel according to the invention in section and FIG. 2 shows a process scheme for reducing iron ore, in which vessels according to the invention can be used. 3 illustrates in the form of a diagram grain size distributions of iron ores to be treated according to the invention.

The vessel 1 shown in FIG. 1, which represents a fluidized bed reactor, in particular a reduction reactor, has a cylindrical lower fluidized bed part 3 receiving a fluidized bed 2, which at a certain height has a gas distributor plate designed as a nozzle grate 4 for supplying and uniformly distributing the reducing gas is provided. The reducing gas flows through the reduction reactor from the nozzle grate 4 from bottom to top. Above the nozzle grate 4 and still inside the cylindrical fluidized bed part 3, delivery lines 5, 6, etc. Inlets and outlets for fine ore. The fluidized bed 2 has a layer height 7 from the nozzle grate 4 to the height of the discharge 6 for the fine ore, i.e. whose opening 8 on.

Connected to the cylindrical fluidized bed part 3 is an upwardly conically widening cone part 9, the inclination of the wall 10 of this cone part 9 to the reactor center axis 11 being a maximum of 6 to 15 °, preferably 8 to 10 °. In this area, the continuous enlargement of the cross section 12 of the cone part 9 leads to a steadily and continuously increasing reduction in the empty pipe speed of the reducing gas flowing upwards

Due to the only slight inclination of the wall 10 of the cone part 9, it is possible to achieve a flow in this cone part 9 despite the widening of the cross section 12 without formation of eddies and tearing from the wall 10. This creates eddies which would cause a local increase in the speed of the reducing gas , Avoided is a uniform and continuous reduction of the empty tube speed of the reducing gas over the cross section 12 over the entire height of the cone part 9, that is. at any height. At the upper end 13 of the conical part 9 there is a calming part 15 provided with a cylindrical wall 14, which is closed at the top with a flat (or a partially spherical) ceiling 16. An opening 18 for discharging the reducing gas is arranged centrally in the reactor ceiling 17 arranged above the ceiling 16. The enlargement of the cross-sectional space of the conical part 9 is carried out in such a way that the ratio of the cross-sectional area 19 of the calming part 15 to the cross-sectional area 20 of the fluidized bed part 3> 2.

In the interior of the reduction reactor 1, the dust separation for the reducing gas serving cyclones 21 are provided, which are arranged in the cylindrical portion of the calming part 15. Dust return lines 22 starting from the cyclones 21 are directed vertically downward and open into the fluidized bed. The gas discharge lines 23 of the cyclones 21 open into the space 24 lying between the ceiling 16 and the reactor ceiling 17.

According to the invention, fine ore with a wide, uniform grain distribution with a relatively high fine fraction is processed in the reduction reactor 1. A distribution of this type of com would be about the following:

Mass fractions up to 4 mm 100% to 1 mm 72% to 0.5 mm 55%

It was found that a fine ore with approximately this grain distribution can be fluidized. without segregation occurring in the fluidized bed 2, whereby, and this is essential to the invention, the empty tube speed V | _{it is} always _lower than the minimum fluidization speed for the largest particles of fine ore.

The following relationship was found as the optimal operating range for v _empty :

v _empty - 0.25 to 0.75. v _min (d _m J

V _{| eer} - empty _{tube velocity} in the fluidized bed 2 above the distributor _plate 4 ^v _mιπ (d _max ) - minimum fluidization velocity of the largest particle of the fraction used As already mentioned above, a broad grain distribution of the fine ore is essential for the invention. Such a grain distribution is given in "Run of Mine" fine ores, that is to say in fine ores that are not subjected to classification after comminution. Some examples of grain distributions of "Run of Mine" iron ores are shown in FIG. 3. With these grain distributions of "Run of Mine" iron ores, there is always a larger proportion of a fine fraction which is so small that it does not remain in the fluidized bed, but is discharged with the gas and is returned via the cyclones. The fine fraction is necessary to ensure the fluidization of the very large particles with only a relatively low empty tube speed of the treatment gas.

According to the invention, the effect is used that there is a pulse transmission of the momentum of the small particles to the larger particles with a wide grain distribution. This enables large particles to be fluidized, even if the empty tube speed of the reducing gas is below the empty tube speed required for the large particles. According to the invention, fine ore with natural grain distribution (run of mine) can be used without prior classification with d ^, ^ preferably up to 12 mm, maximum up to 16 mm.

The use of the reduction reactor, which is designed according to the criteria mentioned above, and the use of fine ore with a relatively high proportion of fine particles result in the following advantages for the fluidization behavior:

• Flexible system with regard to changing the solids density and grain size distribution with changing use of raw materials

• Insensitive to grain breakdown and thus change in the fine fraction between the feed and product stream.

The vessel 1 can also be used with the same advantages as a preheating vessel and as a pre- and final reduction vessel.

A system in which a vessel 1 described above and designed according to the invention is advantageously used is described in more detail below with reference to the schematic FIG. 2:

A plant for the production of pig iron or steel intermediate products has four fluidized bed reactors 1, 1 \ 1 ", I '" which are of approximately the same design and are connected in series, and which have the features of the vessel 1 described above. Containing iron oxide Material, such as "Run of Mine" fine ore, is fed via an ore feed line 5 to the first fluidized bed reactor 1, in which preheating of the fine ore and possibly a pre-reduction takes place in a preheating stage, and then from fluidized bed reactor 1 to fluidized bed reactor 1 'or from 1' to 1 "via delivery lines 5, 6 passed. In the second fluidized bed reactor 1 'there is a pre-reduction in a pre-reduction stage and in the downstream fluidized bed reactor 1 "there is a further reduction and in a last arranged fluidized bed reactor 1""an end reduction of the fine ore to sponge iron in an end reduction stage.

The finished reduced material, that is, the sponge iron, is hot or cold biquetted in a briquetting system 25. If necessary, the reduced iron is protected from reoxidation during the briquetting by an inert gas system (not shown).

Before the fine ore is introduced into the first fluidized bed reactor 1, it is subjected to an ore preparation, such as drying and sieving, which is not shown in detail.

Reducing gas is conducted in countercurrent to the ore flow from fluidized bed reactor 1 to fluidized bed reactor 1 'to 1'"and is discharged as top gas via a top gas discharge line 26 from the last fluidized bed reactor 1 in gas flow direction and cooled and washed in a wet scrubber 27. The reduction gas is produced by Reforming of natural gas supplied via line 28 and desulfurized in a desulfurization plant 29 in a reformer 30. The reformed gas formed from natural gas and steam essentially consists of H ₂ , CO, CH ₄ , H ₂ O and CO ₂ fed via the reformed gas line 31 to a plurality of heat exchangers 32, in which it is cooled to ambient temperature, as a result of which water is condensed out of the gas.

The reformed gas line 31 opens into the top gas discharge line 26 after the top gas has been compressed from a compressor 33. The mixed gas thus formed is sent through a COy scrubber 34 and freed from C0 ₂ , and it is now available as a reducing gas. This reducing gas is supplied via the reducing gas feed line 35 in a gas heater 36 arranged downstream of the COy scrubber 34 to a reducing gas temperature of approximately Heated at 800 ° C. and fed to the first fluidized-bed reactor 1 "'in gas flow-through, where it reacts with the fine ores to produce directly reduced iron. The fluidized-bed reactors 1""to 1 are connected in series, that Reducing gas passes through the connecting lines 37 from the fluidized bed reactor 1 "'to the fluidized bed reactor 1" etc.

Part of the top gas is removed from the gas circuit 26, 35, 37 in order to avoid an enrichment of inert gases such as N ₂ . The discharged top gas is fed via a branch line 38 to the gas heater 36 for heating the reducing gas and burned there. Any missing energy is supplemented by natural gas, which is supplied via the feed line 39.

The sensible heat of the reformed gas emerging from the reformer 30 and of the reformer fumes is used in a recuperator 40 to preheat the natural gas after passing through the desulfurization system 29, to generate the steam required for the reforming and to supply the gas heater 36 via line 41 Preheat the combustion air and possibly also the reducing gas. The combustion air supplied to the reformer via line 42 is also preheated.

Claims

Claims:

1. A process for treating, preferably for reducing, particulate material in a fluidized bed process, in particular for reducing fine ore, the particulate material being held and treated in a fluidized bed (2) by a treatment gas flowing from the bottom up, characterized in that particulate Material with a broad grain distribution with a relatively high proportion of fines and a proportion of larger particles is used for the treatment and that the empty tube speed of the treatment gas in the fluidized bed (2) is kept lower than the speed necessary for fluidizing the proportion of larger particles of the particulate material , whereby all larger particles together with the fine fraction are moved upwards and discharged from the upper region of the fluidized bed.

2. The method according to claim 1, characterized in that the empty tube speed in the fluidized bed (2) is maintained in a range from 0.25 to 0.75 of the speed necessary for fluidizing the largest particles of the particulate material.

3. The method according to claim 1 or 2, characterized in that a particulate material is used with a grain, of which the mean grain diameter of the grain belt 0.02 to 0.15, preferably 0.05 to 0.10, of the largest grain diameter particulate material.

4. The method according to one or more of claims 1 to 3, characterized in that for the treatment gas above the fluidized bed (2) an empty tube speed based on the largest cross section of the fluidized bed (2) receiving vessel for a theoretical grain size of 50 to 150 microns , preferably 60 to 100 microns, is set.

5. The method according to claim 4, characterized in that an empty pipe speed in the fluidized bed (2) between 0.3 m / s and 2.0 m / s is set for reducing "Run of Mine" fine ores.

6. A process for the direct reduction of particulate iron oxide-containing material in a fluidized bed process using the process according to one or more of claims 1 to 5, wherein reformed gas in the direct reduction of the iron oxide-containing The resulting top gas is mixed and fed as a reducing gas to a fluidized bed reduction zone and both the top gas and the reformed gas are subjected to a CO ₂ scrubbing and the reducing gas formed by mixing top gas and reformed gas to a specific H ₂ content and a CO Content is set.

7. Vessel for performing the method according to one or more of claims 1 to 6, characterized by the combination of the following features:

A cylindrical lower fluidized bed part (3) receiving the fluidized bed (2) with a gas distribution base (4), a feed line (35, 37) for the treatment gas and a feed and discharge for particulate material above the gas distribution base (4),

• a cone part (9) arranged above the fluidized bed part (3) and adjoining it, widening conically upwards, the inclination of the wall (10) of the cone part (9) to the center axis of the reactor (11) being 6 to 15 °, preferably 8 to 10 °,

• An at least partially cylindrical calming part (15) adjoining the cone part (9), which is closed at the top and from which a treatment gas discharge line (26, 37) starts

• The ratio of the cross-sectional area (19) of the calming part (15) in the cylindrical region to the cross-sectional area (20) of the fluidized bed part (3) is> 2.

8. A vessel according to claim 7, characterized in that the cross-sectional area (19) of the calming space (15) in the cylindrical area is so large that an empty tube speed is set in this area, which would be sufficient to separate a grain larger than 50 microns from the gas .

9. Plant for direct reduction of particulate iron oxide-containing material in the fluidized bed process according to claim 6, with at least one vessel designed as a fluidized bed reactor (1 to 1 "') according to claim 7 or 8 for receiving the iron oxide-containing material, a reducing gas feed line (35, 37) this fluidized bed reactor (1 to 1 '") and a top gas discharge line (26) which removes the top gas that forms during the reduction from the fluidized bed reactor (1), with a reformer (30), a reformed gas line (31) starting from the reformer (30), which ends with the top gas line (26), the reducing gas formed from reformed gas and top gas passing through the reducing gas feed line (35, 37) into the fluidized bed reactor (1 to 1 "'), and with a CO _: - elimination system (34) , both the reformed gas line (31) and the top gas discharge line (26) opening into the COy elimination system (34) and the reducing gas line Supply line (35, 37) leads from the CO ₂ elimination system (34) to the fluidized bed reactor (1 to 1 "').

[Received at the International Office on October 23, 1997 (October 23, 1997); claims 7-9 originally amended; all other claims unchanged (2 pages)]

The resulting top gas is mixed and fed as a reducing gas to a fluidized bed reduction zone and both the top gas and the reformed gas are subjected to a CO ₂ scrubbing and the reducing gas formed by mixing top gas and reformed gas to a specific H ₂ content and a CO Content is set.

7. Use of a vessel (1) characterized by the combination of the following features for carrying out the method according to one or more of claims 1 to 6:

8. Use according to claim 7, characterized in that the cross-sectional area (19) of the calming space (15) of the vessel (1) in the cylindrical area is so large that an empty tube speed is set in this area, which for separating a grain larger than 50 microns from the gas would suffice.

9.Use of a plant for the direct reduction of particulate iron oxide-containing material in a fluidized bed process, with at least one vessel designed as a fluidized bed reactor (1 to 1 "') for receiving the iron oxide-containing material, a reducing gas feed line (35, 37) to this fluidized bed reactor (1 to 1 '") and a top gas discharge line (26) which discharges the top gas which forms during the reduction from the fluidized bed reactor (1), with a reformer (30), a reform gas line (31) starting from the reformer (30), which is connected to the top gas line (26 ) flows together, the reducing gas formed from reformed gas and top gas passing through the reducing gas supply line (35, 37) into the fluidized bed reactor (1 to 1 '"), and with a CO ₂ elimination system (34), both the reforming gas line (34) 31) as well as the top gas _{t Λ}

14

Derivation (26) lead into the CO ₂ elimination system (34) and the reducing gas supply line (35, 37) leads from the CO ₂ elimination system (34) to the fluidized bed reactor (1 to 1 '") for carrying out the method according to claim 6.

CHANGED SHEET {ARTICLE 19)