AU728390B2

AU728390B2 - Method for treating particulate material in the fluidized bed method and vessel and plant for carrying out the method

Info

Publication number: AU728390B2
Application number: AU27561/97A
Authority: AU
Inventors: Franz Hauzenberger; Werner-Leopold Dr Kepplinger; Johannes-Leopold Schenk; Felix Wallner; Roy Hubert Whipp Jr.
Original assignee: Voest Alpine Industrienlagenbau GmbH
Current assignee: Primetals Technologies Austria GmbH
Priority date: 1996-05-17
Filing date: 1997-05-15
Publication date: 2001-01-11
Anticipated expiration: 2017-05-15
Also published as: ID17840A; CA2257492A1; PE44398A1; WO1997044495A1; KR20000011107A; ATA87696A; BR9709095A; AU2756197A; JP2000511970A; ZA974251B; AR007085A1; EP0902841A1; AT405522B

Description

1 Method for treating particulate material in the fluidized bed method and vessel and plant for carrying out the method The invention relates to a method for treating, preferably reducing, particulate material in the fluidized bed method, in particular for reducing fine ore, wherein said particulate material is maintained in a fluidized bed by a treating gas flowing from bottom to top and thereby is treated, and a vessel for carrying out the method.

A method of this kind has been disclosed, for instance, in US-A 2,909,423, WO 92/02458 and EP-A 0 571 358. In this method, oxide-containing material, for instance fine ore, is reduced in a fluidized bed maintained 15 by a reducing gas inside a fluidized-bed reduction reactor, with the reducing gas, which via a nozzle grate is fed into the fluidized-bed reduction reactor, flowing through the reduction reactor from the bottom toward the top, whereas the oxide-containing material permeates the -reduction reactor roughly cross-current to -the reducing-gas stream.

SIn order to maintain the fluidized bed, a specific velocity "of the reducing gas inside the fluidized bed zone is required which is a function of the particle size of the charged material.

Due to the relatively high velocity of the reducing gas which is necessary with the known methods there is a substantial discharge of superfines of the oxide-containing material as well as at an advanced stage of the reduction process a discharge of already reduced oxide-containing material from the fluidized bed, said superfines being then contained in the reducing gas. To remove said superfines from the reducing gas on the one hand in order to be able to further utilize the partially oxidized reducing gas, for instance for precedingly arranged reduction reactors, or for the recovery of the oxide-containing material or the already reduced material 1t \Priyanka\Reep\speci\27561-9 7 .doc 29/08/00 2 which otherwise would be lost the reducing gas containing the superfines is conducted through dust separators, such as cyclones, and the separated dust is recycled back into the fluidized bed. The dust separators or cyclones respectively are preferably arranged inside the reactors (cf. US-A 2,909,423); but they can also be installed outside of the reactors.

In practice it has emerged that partially reduced or completely reduced fine-grained particles of the oxidecontaining material tend to stick or cake to each other and/or to the walls of the reactors or cyclones and to the Sconnection ducts or conveying ducts. This phenomenon is referred to as "sticking" or "fouling". Sticking or fouling 15 are functions of the temperature and the degree of reduction of the oxide-containing material. Such sticking or attachment of the partly or completely reduced oxidecontaining material to the walls of the reduction reactors or to other parts of the plant may cause failures, so that it is not feasible to operate the plant continuously over a prolonged time period without any shut-down. It has been found that continuous operation for more than a year is hardly possible.

Removal of the attachments or cakings requires a huge amount of work and entrains substantial costs, namely labor costs and costs arising due to the production loss of the plant. Often, these attachments will detach spontaneously, as a result of which they either drop into the fluidized bed and thus lead to a disturbance of the reduction process, or if the attachments detach themselves from the cyclone cause the dust recycling channels that lead from the cyclone to the fluidized bed to become plugged, so that further separation of dust from the reducing gas will be completely impossible.

In practice, one disadvantage with the known H:\Priyanka\Keep\speci\27561-97.doo 29/08/00 3 fluidized bed methods resides in the inflexibility anddifficulties encountered in splitting up and feeding in the treating-gas stream, that is with the above-described prior-art processes this would be the splitting up and feeding in of the reducing-gas stream. A further disadvantage associated with the prior art is that in each process stage, that is in pre-heating, pre-reduction and final reduction, in most cases two or several product streams leaving the apparatuses allocated to the process stages have to be sluiced out, thus causing substantial expenses in terms of conveying and sluice means. Moreover, two gas supply systems have to be adjusted in each process stage, which in practice presents major difficulties in the case of hot dust-containing gases.

In addition to this, due to the relatively high velocity of the reducing gas there is a substantial consumption of reducing gas. Considerably more reducing gas is consumed than would be necessary -for the reduction process as such, with the excess consumption merely serving to keep up the fluidized bed.

A process for reducing metal ores by a fluidized bed method is disclosed in GB-A 1 101 199. Here, the 25 process conditions have been chosen such that the material will cake together in the course of the reduction process, whereby agglomerates are formed which, due to their size, are not fluidized. Thereby it is feasible to separate the completely reduced material, which is discharged from the fluidized bed reactor in the downward direction, from the not completely reduced material, which remains fluidized.

Smaller product particles are withdrawn at the upper end of the fluidized bed. Thus with this process there likewise result two product streams, necessitating considerable expenses in terms of apparatus.

TR The invention aims at avoiding these p, H \PriyMrnka\Keep\sp*i\27561-97.doo 29/08/00 i- 4 disadvantages and difficulties and has as its object to provide a method of the initially described kind and a vessel for carrying out the method, which enable treatment of particulate oxide-containing material at minimum consumption of treating gas over a substantial time period without the danger of failures caused by sticking or fouling. In particular, it is to be feasible to reduce both the amount of the treating gas required for maintaining the fluidized bed and the flow rate of the same, so that there will only be a minimum discharge of fine particles.

In accordance with the invention, this object is achieved in that a particulate material having a wide grain 15 distribution containing a relatively high portion of fines and a portion of larger particles is used for treatment and that the superficial velocity of the treating gas in the fludized bed is kept to be smaller than the velocity required for fluidizing the portion of larger particiles of 20 said particulate material, wherein all of the larger particles together with the fines are moved upward and discharged from the upper region of the fluidized bed.

It has become apparent that in case of a wide 25 even grain distribution the superficial velocity in the fluidized.bed is maintained within a range of 0.25 to 0.75 of the velocity required for fluidizing the largest particles of said particulate material.

Preferably, a particulate material with a grain -having a medium grain diameter of the grain band of 0.02 to 0.15, preferably 0.05 to 0.10, of the largest grain diameter-of said particulate material is used.

Accordingly, the present invention provides A ST method for treating particulate material in a fluidized bed, wherein a treating gas is passed upwardly through the H: \Piyankia\Kep\speci\27561-97.doc 29/08/00 s bed to maintain the particulate material in the fluidized bed and to treat the particulate material, characterized in that the particulate material has a wide grain distribution containing a relatively high portion of fines and a portion of larger particles, wherein a medium grain diameter of the grain band ranges from 0.02 to 0.15 of the largest grain diameter of said particulate material, and that the superficial velocity of the treating gas in the fluidized bed is kept to be less than the velocity required for fluidizing the portion of larger particles of said particulate material.

For clarity, the calculation of the medium grain diamter of the grain band is explained in the following 15 example. If the largest grain diameter is, for instance, 12 mm, the medium grain diameter of the particulate material used is at least 0.24 mm (0.02 x 12 0.24) and 1.8 mm at the most (0.15 x 12 1.8).

S 20 Herein, suitably, for the treating gas above the fluidized bed a superficial velocity relative to the largest diameter of a vessel designated for receiving the fluidized bed is adjusted for a theoretic cut grain size of 50 to 150m, preferably 0 to 100am, wherein advantageously 25 in the fluidized bed a superficial velocity ranging between 0.3. m/s and 2.0 m/s is adjusted for reducing run-of-mine fine ores.

In a method for the direct reduction of particulate iron oxide-containing material by the fluidized bed method in accordance with the process as set forth in the invention, reformed gas is mixed with top gas forming in the direct reduction of the iron oxide-containing material and is fed to a fluidized-bed reduction zone as a reducing gas and both the top gas and the reformed gas are subjected to COi scrubbing and the reducing gas formed by 0 mixing top gas with reformed gas is adjusted to a specific H: \Priyana\Keep\speci\27561-97.doo 29/08/00 6

H

2 content and CO content.

A vessel for carrying out the method in accordance with the invention is characterized by the combination of the following characteristic features: a cylindrical lower fluidized bed section receiving the fluidized bed and including a gas distributing bottom, a feed duct for the treating gas, and a supply means and a discharge means for particulate material provided above the gas distributing bottom, a cone-shaped section arranged above the 15 fluidized bed section so as to follow upon the same and widening conically upwards, the inclination of the wall of the cone-shaped section relative to the central axis of the reactor amounting to 6 'to 150, preferably 8 to 20 *g o an at least partially cylindrical calming section o, following upon the cone-shaped section and closed -on top, from which a treating-gas discharge duct departs, the ratio of the cross sectional area of the calming section in the cylindrical region to the cross sectional area of the fluidized bed section being 2 2.

A vessel for carrying out an ore reduction method in a fluidized bed, said vessel comprising two cylindrical parts of different diameters and a very short and markedly cone-shaped part provided between the cylindrical parts, is for instance disclosed in EP-A 0 022 098. However, with

STF

R

44 this vessel there are provided two gas supply ducts, namely H:\Priyanka\K*p\pDci\27561-97.doo 29/08/00 i: i 7 one below the lower cylindrical part and one in the coneshaped part. The completely reduced ore is discharged from this fluidized bed reactor in the downward direction.

Preferably, in accordance with the invention the cross sectional area of the calming space in the cylindrical region is large enough for a superficial velocity adjusting in this region that would be sufficient for separating from the gas a grain having a grain size of above 50 jm.

A plant for directly reducing particulate ironoxide-containing material by the fluidized bed method, comprising at least one fluidized bed reactor constructed 15 in accordance with the vessel set forth in the invention, for receiving the iron-oxide-containing material, a reducing-gas feed duct leading to this fluidized bed reactor and a top-gas discharge duct discharging from the fluidized bed reactor the top gas forming in the reduction 20 process, a reformer, a reformed-gas duct departing -from the reformer and uniting with the top-gas discharge duct, the reducing gas formed of the reformed gas and of the top gas entering the fluidized-bed reactor through the ,reducing-gas feed duct, and comprising a -CO scrubber, is-characterized 25 in that both the reformed-gas duct and the top-gas discharge duct run into the CO 2 scrubber and the reducinggas feed duct leads from the CO0 scrubber to the fluidized bed reactor.

In the following, the invention is described in greater detail with reference to the drawing, Fig. 1 showing a sectional view of a vessel according to the invention and Fig. 2 a process diagram for the reduction of iron ore wherein vessels according to the invention can be utilized. Fig. 3 illustrates in diagrammatic form some grain size distributions of iron ores to be treated in accordance with the invention.

H:\Priyanka\Ke*p\speci\27561-97.doo 29/08/00 8 Vessel 1 which is represented in Fig. 1 and constitutes a fluidized bed reactor, in particular a reduction reactor, comprises a cylindrical lower fluidized bed section 3 which is destined to receive a fluidized bed 2 and at a specific height level is provided with a gas distributing bottom constructed as a nozzle grate 4, for feeding and evenly distributing the reducing gas. The reducing gas flows through the reduction reactor starting from the nozzle grate 4, from the bottom toward the top.

Above the nozzle grate 4 and still within the cylindrical fluidized bed section 3 there discharge conveying ducts 6, namely feed ducts and discharge ducts for the fine ore.

The fluidized bed 2 exhibits a bed height 7 from the nozzle 15 grate 4 up to the level of the discharge duct 6 for the fine ore, that is its opening 8.

*o To the cylindrical fluidized bed section 3 there is connected an upwardly flared cone-shaped section 9, the 20 inclination of the wall 10 of this cone-shaped portion 9 to the reactor central axis 11 amounting to maximally 6 to 150, preferably 8 to 100. In this area the continuous increase in the cross section 12 of the cone-shaped section 9 causes a steadily and continuously increasing reduction 25 in the superficial velocity of the upward-streaming reducing gas.

Due to the only slight inclination of the wall of the cone-shaped section 9 it is feasible in spite of the enlargement of the cross section 12 to obtain in said coneshaped section 9 a current without turbulence and without separation from the wall 10. Turbulence, which would cause a localized increase in the velocity of the reducing gas, is hereby avoided. Thereby an even and continuous reduction in the superficial velocity of the reducing gas Sacross the cross section 12 is ensured throughout the entire height of the cone-shaped section 9, that is at H:\Priyanka\Keep\peci\27561-97.doc 29/08/00 9 every level of the same.

To the upper end 13 of the cone-shaped section 9 there is connected a calming section 15 which is provided with a cylindrical wall 14 and which at the top is closed by means of a ceiling 16 which is level (or which is constructed in the shape of a partial sphere). 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 coneshaped section 9 is designed such that the ratio of the cross-sectional area 19 of the calming section 15 to the cross-sectional area 20 of the fluidized bed section 3 is 2.

Inside the reduction reactor 1 there are provided cyclones 21 serving for the dust separation of the reducing gas, which are arranged in the cylindrical section of the calming section 15. Dust recycling ducts 22 that depart 20 from the cyclones 21 are directed vertically downward and open into the fluidized bed. The gas discharge ducts 23 of the cyclones 21 open into the space 24 located between the g ceiling 16 and the reactor ceiling 17.

oo S* 25 In accordance with the invention, -fine ore having a wide even grain distribution comprising a relatively high portion of fines is processed in the reduction reactor 1.

An example of a grain distribution of this type -cou-ld"for instance be as follows: mass fraction up to 4 mm 100 up to 1 mm 72 up to 0.5 mm 55 up to 0.125 mm 33 It has been found that a fine ore of roughly the above H:\Priyafka\Ke9\speci\27561-97.doc 29/0B/00 10 grain distribution can be fluidized without incurring a segregation in the fluidized bed 2, wherein, and this is essential for the invention, the superficial velocity vuper is at all times lower than the minimum fluidizing velocity for the largest particles of the fine ore.

The following ratio has been found to be the optimum operating range for vuper: super 0.25 to 0.75 v (dma,) uper superficial velocity in the fluidized bed 2 above the distributing bottom 4 Vin (dmx) minimum fluidizing velocity of the largest particle of the charged fraction As already mentioned above, a wide grain distribution of the fine ore is essential for the invention. Such a -grain distribution is a feature of runof-mine fine ores, that is of fine ores which are not :subjected to screening after size reduction. Some examples of grain distributions of run-of-mine iron ores are given in Fig. 3. With these grain distributions of run-of-mine iron ores there is always a larger portion of a fine fraction present which is so small that it does not stay in -the fluidized bed but is discharged along with the gas and recycled back via the cyclones. The fine fraction is necessary to ensure the fluidization of the very large particles at merely a relatively low superficial velocity of the treating gas.

In accordance with the invention one exploits the effect that with a wide grain distribution a pulse transmission of the pulse of the particles to the larger particles takes place. Hereby it is feasible to fluidize Slarge particles, even if the superficial velocity of the H:\Priyankla\Ktop\ipeci\27S6I-97.doc 29/08/00 11 reducing gas is below the superficial velocity required for the large particles. In accordance with the invention it is feasible to utilize a fine ore of natural grain distribution (run-of-mine) without any previous screening, exhibiting a da of preferably up to 12 mm, maximally up to 16 mm.

By utilizing the reduction reactor designed in accordance with the criteria set forth above, and by utilizing fine ore having a relatively high portion of fines, the following advantages are obtained with respect to the fluidization behaviour: :a flexible system, in view of the changes in 15 solids density and grain size distribution associated with changing raw material -charges

S

insensitivity to disintegration of grains and thus to changes in the portion of fines incurring between 20 the feed-material stream and the product stream.

The vessel 1 can with equal advantages be utilized as a preheating vessel and as a pre-reduction and final reduction vessel.

A plant in which a vessel 1 of the type described above, constructed in accordance with the invention, is employed to advantage, is described below in greater detail with reference -to the schematic Fig. 2: A plant for producing pig iron or steel preproducts comprises four fluidized bed reactors 1, li, 1 i 1i" of roughly similar construction, which are subsequently connected in series and which exhibit the characteristic features of the vessel 1 described above. Iron-oxide- Scontaining material, such as run-of-mine fine ore, via an S ore supply duct 5 is conducted to the first fluidized bed H:\Priyanka&\Kepspoi\27561-97.do 29/08/00 12 reactor 1, in which in a preheating stage preheating of the fine ore and possibly pre-reduction take place, and is subsequently conducted from fluidized bed reactor 1 to fluidized bed reactor I 1 or from Il to lI respectively via conveying ducts 5, 6. -Inside the second fluidized bed reactor 1, a pre-reduction is effected in a pre-reduction stage and in the subsequently connected fluidized bed reactor I" a more extensive reduction takes place, and inside a fluidized bed -reactor li i arranged last a final reduction of the fine ore to sponge iron takes place in a final reduction stage.

The completely reduced material, that is the sponge iron, is hot- or cold-briquetted in a briquetting 15 plant 25. If necessary, the reduced iron is protected against reoxidation during the briquetting operation by an inert gas system not illustrated.

Prior to feeding -the fine ore into the first :o 20 fluidized bed reactor 1, said -fine ore is subjected to ore preparation, such as drying and sieving, which is not illustrated in detail.

Reducing gas is conducted from fluidi-ed bed S 25 reactor 1 l to -fluidized bed -reactor 1 in counterfiow to the ore flow and via a top-gas discharge duct 26 is .discharged as a top gas 'from the fluidi-zed bed reactor 1 arranged last if viewed in the -flowing direction of the gas and is cooled and scrubbed in a wet scrubber 27. Generation of the reducing gas takes place in a reformer 30 by reforming a natural gas which is supplied through the duct 28 and desulphurized in a desulphurization plant 29. The reformed gas formed from natural gas and steam is essentially made up of H 2 CO, CH 4

H

2 0 and CO 2 Via the reformed-gas duct 31 the said reformed gas is fed to several heat exchangers 32 in which it is cooled down -to f ambient temperature, whereby water is condensated out of H: \Piyanka\lKeep\ sp i\27561-97. do 29/08/00 13 the gas.

The reformed-gas duct 31 opens into the top-gas discharge duct 26 after the top gas has been compressed by means of a compressor 33. The resulting gas mixture is passed through a CO 2 scrubber 34 and freed from CO 2 and is afterward available as a reducing gas. This reducing gas via the reducing-gas feed duct 35 is heated to a reducinggas temperature of roughly 800 0 C in a gas heater 36 connected subsequently to the CO 2 scrubber 34 and is supplied to the fluidized bed reactor l. connected first in the flowing direction of the gas, where it reacts with the fine ores to produce directly reduced iron. The fluidized bed reactors to 1 are connected in series; 15 via the connection ducts 37 the reducing gas passes from fluidized bed reactor l1 i to fluidized bed reactor 1, etc.

Part of the top gas is sluiced out of the gas 20 cycle 26, 35, 37 to avoid enrichment of inert gases, such as N 2 The sluiced-out top gas via a branch duct 38 is supplied to the gas heater 36 in order to heat the reducing gas and there is combusted. Possible shortages of energy are supplemented by natural gas, which is supplied through 25 the feed duct 39.

The sensible heat of the reformed gas leaving-the reformer 30 as well as of the reformer fluegases is utilized in a recuperator 40 in order to preheat the natural gas after it has passed through the desulphuri-zation plant 29, to generate the steam required for the reforming operation as well as to preheat the combustion air supplied to the gas heater 36 via the duct 41 as well as optionally the reducing gas as well. The combustion air supplied to the reformer via the duct 42 is also preheated.

\Priyaika\Keep\speci\27561-97 .doc 29/08/00 1 r 14 in this specification except where the context requires otherwise, the words "comprise", "comprises" and "comprising" mean "include", "includes" and "including", respectively. That is, when the inventor is described or defined as comprising specified -features various embodiments of the same invention may include additional features.

0* 0 0.4 a** 'H \Priyanka\Kep\,.ci\27561-97 .doc 29/08/00

Claims

1. A method for treating particulate material in a fluidized bed, wherein a treating gas is passed upwardly through the bed to maintain the particulate material in the fluidized bed and to treat the particulate material, characterized in that the particulate material has a wide grain distribution containing a relatively high portion of fines and a portion of larger particles, wherein a medium grain diameter of the grain band ranges from 0.02 to 0.15 of the largest grain diameter of said particulate material, and that the superficial velocity of the treating gas in 0 the fluidized bed is kept to be less than the velocity required for fluidizing the portion of larger particles of said particulate material.

2. The method according to claim 1, characterized in that the superficial velocity in the fluidized bed is maintained in a range from 0.25 to 0.75 of the velocity 20 required for fluidizing the largest particles of said particulate material. eo.

3. The method according to claim 1 or 2, characterized in that a particulate material with a grain having a medium grain diameter of the grain band ranging from 0.05 to 0.10 of the largest grain diameter of said particulate material is used.

4. The method according to any one of claims 1 to 3, characterized in that for the treating gas above the fluidized bed a superficial velocity relative to the largest diameter of a vessel designated for receiving the fluidized bed is adjusted for a theoretic cut grain size ranging from 50 to 150 unm. The method according to claim 4, characterized in that the theoretic grain size ranges from 60 to 100pm.

H:\Priyanka\K\speci\27561-97 .doc 29/08/00 -16

6. The method according to claim 4 or characterized in that in the fluidized bed a superficial velocity ranging from 0.3 m/s to 2.0 m/s is adjusted for reducing run-of-mine fine ores.

7. The method according to any one of claims 1 to 6 wherein the treatment is a reducing treatment.

8. The method as claimed in claim 7 wherein the particulare material is fine ore. 0

9. The method for the direct reduction of particulate iron oxide-containing material by the fluidized 15 bed method employing the process as claimed in claim 8, S i wherein reformed gas is mixed with top gas forming in the direct reduction of the iron-oxide-containing material and is fed to a fluidized-bed reduction zone as a reducing gas and both the top gas and the reformed gas are subjected to 20 CO 2 scrubbing and the reducing gas formed by mixing top gas with reformed gas is adjusted to a specific H 2 content and CO content. to.o

10. A method for reducing particulate material in a 25 -fluidized bed substantially as hereinbefore described with reference to the accompanying figures.

11. Use of a vessel characterized by the combination of the following characteristic features -for carrying out the method according to any one of claims 1-to a cylindrical lower fluidized bed section receiving the fluidized bed and including a gas distributing bottom, a feed duct for the treating gas, and a supply means and a discharge means for particulate material provided above the gas l _distributing bottom, H:\Priyanka\Keep\speci\27561-97.doc 29/08/00 17 a cone-shaped section arranged above the fluidized bed section so as to follow upon the same and widening conically upwards, the inclination of the wall of the cone-shaped section relative to the central axis of the reactor being from 6 to 150, and an at least partially-cylindrical calming section following upon the cone-shaped section and closed on top, from which a treating-gas discharge duct departs, wherein the ratio of the cross sectional area of the calming section in the cylindrical region to the cross sectional area of the fluidized bed section is 2 2.

12. Use of a vessel according to claim 11, 20 characterized in that the inclination of the wall of the cone-shaped section relative to the central axis of the reactor is between 8 and 100.

13. -Use of a vessel according to claim 11 or 12, 25 characterized in that -the cross -sectional area of the calming space of the vessel in the cylindrical region is large enough for a superficial velocity adjusting in this S-region that would be sufficient -for separating from the gas a grain having a grain size of above

14. Use of a vessel substantially as hereinbefore described with reference to -the accompanying figures. Use of a plant for directly reducing particulate iron oxide-containing material by the method according to claim 9, the plant including at least one vessel intended to receive the iron oxide-containing material and H:\Priyanka\F*.P\sppci\27S61 97.doo 29/08/00 18 constructed as a fluidized bed reactor, a reducing-gas- feed duct leading to the or each fluidized bed reactor and a top-gas discharge duct discharging the top gas forming in the reduction process from the fluidized bed reactor last in the direction of flow of reducing gas, a reformer, a reformed-gas duct departing from-the reformer and uniting with the top gas"discharge duct, the reducing gas formed of the reformed gas and of the top gas entering the or each fluidized-bed reactor through the reducing-gas feed duct, and comprising a CO 2 elimination plant, wherein both the reformed-gas duct and the top-gas discharge duct run into the CO 2 elimination plant and the reducing-gas feed duct leads from the CO 2 elimination plant to the or each fluidized bed reactor. .16. Use of a plant substantially as hereinbefore described with reference to the accompanying figures. Dated this 2 9 t h Day of August 2000 20 VOEST-ALIPNE INDUSTRIENLAGENBAU GmbH By their Patent Attorneys GRIFFITH HACK Fellows Institute of Patent and Trade Mark Attorneys of Australia 0000 H:\Priyankl\Keep\spci\27561-97.do 29/08/00 0 w c y fti%' -eIS{~