B.N.F Metals Technology Centre v the Broken Hill Associated Smelters Proprietary Limited, (Bhas)

[1990] APO 39

PATENTS ACT 1952

DECISION OF A DELEGATE OF THE COMMISSIONER OF PATENTS

Re:Patent Application No. 540860 by B.N.F. METALS TECHNOLOGY CENTRE and S.59 Opposition thereto by THE BROKEN HILL ASSOCIATED SMELTERS PROPRIETARY LIMITED, (BHAS)

Background

BNF lodged application 540860 on 17 June 1981.  The Office advertised acceptance thereof in the Official Journal of 6 December 1984.  BHAS lodged notice of opposition under s.59 and the matter came before me for hearing in the scheduled Melbourne sessions of August 1988.  I issued a decision in this matter on 10 October 1988, finding that the opposition was successful on the grounds of non‑compliance with s.40, and allowing BNF time to correct the defects in the specification by way of amendment.
         The present action arises out of a desire by BHAS to be heard in relation to the amended specification, and the matter came before me during the scheduled Melbourne sessions of August 1990.  Mr P. Pearson, patent attorney of Watermark represented BNF and Mr C.M. Bentley, patent attorney of Griffith Hack (Melbourne) advised by Professor Lawson, represented BHAS.
The Specification
         The specification in its accepted form relates to the use of sulphur to remove dissolved copper from molten lead by formation of a copper sulphide dross which floats to the surface of the lead. 

Conventionally, this "sulphur drossing" has been practised as a batch process with inherent disadvantages such as arduous labour, hygiene hazards, and difficulty in achieving consistent output.  The specification refers to, as prior art, a continuous process described in British Patent No. 1524474 (AU 13564/76) which discloses a series of agitated reaction vessels used to avoid back‑
mixing, the charge being continuously transferred from one stage to the next.  The specification suggests that a disadvantage of this known process is that each agitated reaction stage is homogeneous.  This is explained as follows:

"Now the rate of reaction of copper with sulphur in molten lead is initially rapid but slows down greatly as the concentrations of free sulphur and free copper are reduced.  A homogeneous mixture therefore reacts more slowly than one whose composition is continuously changing as reaction takes place.  Moreover, the selectivity of the reaction, as well as removal rate, is better when the copper concentration is high.  If the output is to be of a low copper content and the reactor is homogeneous, the reaction occurs in low copper content lead; this produces a high lead content dross and is thus less efficient than reacting high copper lead.  In order to avoid these problems, the Patentees use a series of reaction stages.  But this is not very efficient, since the major part of the reaction probably takes place in the first stage, and requires relatively expensive equipment."

The invention, which allows the process to be carried out on a small scale, involves the use of a single stirred vertical reaction vessel in which a stream of lead is caused to follow a spiral path from top to bottom.  Claim 1 reads as follows:

"A continuous method of removing copper from lead, by reaction of copper with sulphur in a single stirred reaction vessel maintained under non‑homogeneous conditions, which method comprises introducing copper as an impurity to the upper end of a vertical stirred reaction vessel, feeding sulphur into the stream of lead at the upper end of the vessel, maintaining a dispersion of sulphur in the stream without substantial back‑mixing for a time sufficient to effect reaction between the sulphur and the copper, recovering the stream of lead from the lower end of the vessel, and allowing the formed copper sulphide to float to the surface of the recovered molten lead."

Following issuance of my first decision BNF amended the specification so that Claim 1 presently reads as follows:

"A continuous method of removing copper from lead, by reaction of copper with sulphur in a single vertical stirred reaction vessel provided with an axially located impeller and maintained under non‑homogeneous conditions, the blades of said impeller having a pitch of no more than about 10o to the vertical, which method comprises continuously introducing a stream of molten lead containing copper as an impurity to the upper end of the vessel, continuously feeding sulphur into the stream of lead at the upper end of the vessel, maintaining a dispersion of sulphur in the stream without substantial back‑mixing for a time sufficient to effect reaction between the sulphur and the copper, and such that the contents follow a generally spiral path down the vessel, continuously recovering the stream of lead from the lower end of the vessel, and allowing the formed copper sulphide to float to the surface of the recovered molten lead."

This restructured claim constitutes the major change : most of the other changes are consequential.
Submissions
         In addition to making submissions orally at the hearing, both parties lodged additional written material.  BHAS supplied a statutory declaration by Professor Lawson to which is exhibited a number of calculations dealing with the disclosed reactor vessel.  BNF supplied a written response to that declaration, informally presented.
         In essence, the BHAS submissions are as follows:

.all features of claim 1 as accepted except the requirement "without substantial back‑mixing" were known in the art before the priority date, and this feature was known to be desirable although there was no practical manner of achieving it in a single reactor vessel;

.this criticism applies also to claim 1 as amended;

.the BNF specification does not disclose the manner of achieving the requirement of "without substantial back‑ mixing".

The calculations made by Professor Lawson are intended to confirm his opinion that in the conditions as set by the applicant's own specification, the requirement "without substantial back‑mixing" cannot be achieved.
         I present the BNF written submissions in full, excepting the diagram which accompanied them.
         Thus:

.The theoretical calculations of Professor Lawson show that the decoppering process will not work if the lead is fed continuously through a traditional lead refining kettle which is essentially a near hemispherical vessel stirred at a modest speed.

.The apparatus proposed is significantly different from a lead kettle.  It is tall in relation to its diameter and is stirred rapidly.  The different geometry and the high circumferential velocity of the lead have a large effect and the system is so different to that implied by Professor Lawson's mathematical analysis that it is not surprising to find that the system does not behave as calculated.

.Using Professor Lawson's method of calculation and the vortex shown, the cross section area of lead is about 0.01m2 at A‑A and 0.03m2 at B‑B.  This gives the downward velocity of lead at A‑A 7.3m/s and at B‑B 3.1m/s.  With no circumferential movement the reaction products would rise in the lower portion of the vessel and the vessel would accumulate so much particulate material that it would soon cease to function.  This does not occur.  Because of the high rotational velocity of the lead the particulate material stays in suspension and passes through the vessel with the lead.

.It is acknowledged in the BNF patent (sic) that some mixing may occur.  However, substantial mixing cannot take place as both the efficiency of utilising the reagents and the rate of reaction decrease markedly as the amount of copper present is reduced.  In practice the process requires approximately the same amount of sulphur as is used in batch refining and the residence time of the lead in the reactor is only 5 ‑ 30 minutes which is similar to the reaction time in the batch refining process.

.Thus we must conclude that the theoretical treatment of Professor Lawson refers to a model which does not represent the behaviour in the reaction vessel of the invention and the technology represents a significant step forward in continuous lead refining technology.

Decision

I have to decide whether the amended specification avoids the grounds of objection found in my first decision.  To do this, the claims have to define the invention in such a way that in terms of the disclosure, the defined process involves substantially no back‑mixing.
         I shall now consider the view put by BHAS, as supported by Professor Lawson's declaration, that the process of the invention cannot be operated without the occurrence of substantial back‑ mixing.  Before looking at the Professor's calculations I draw attention to the first point of BNF's written submissions which asserts that the calculations relate to a traditional lead refining kettle ‑ essentially a near hemispherical vessel ‑ quite distinct from the vertical reactor of the invention.  This assertion is clearly incorrect, as a minimal study of the Professor's calculations shows that they are based on dimensions and quantities exemplified in the BNF specification.  Using those figures, the Professor has developed equations for what he describes as:

"The force balance on a spherical particle in the liquid lead when there is a movement such that the velocity difference between the particle and lead is the particle terminal velocity:

Buoyancy force = Drag force + particle weight."

From the equations, he presents a table of the rise velocity of various particles of 0.1mm diameter, and makes final conclusions:

"If one now considers the rise velocity of 0.1mm (100 um) diameter copper sulphide particles (  = 5800 kg/m3) and sulphur particles (  = 2000 kg/m3) these are:

________________________________________________________

ParticleV                  Rep

m/sec

________________________________________________________

Sulphur1.2 x 10‑2             4.5

________________________________________________________

Cuprous sulphide      7.8 x 10‑3              3

________________________________________________________

Lead sulphide         5.7 x 10‑3              2

________________________________________________________

While these calculations are for spherical particles, single particles or agglomerates will behave in essentially the same fashion.  Thus it is clear that any particles larger than about 0.1mm (100 microns) diameter will rise upwards in the reactor against the overall downwards flow of lead if the lead were indeed flowing in plug flow (no back‑mixing).  Since particles larger than this are produced, and they are separated in the second vessel, there must be locally downwards velocities greater than these, i.e. there must be some substantial back‑mixing in the reaction vessel ..."

(Note:    Rep is the particle Reynolds number).
         BNF countered these calculations by submitting (see reproduction earlier in this decision) that:

"The different geometry and the high circumferential velocity of the lead have a large effect ... Because of the high rotational velocity of the lead the particulate material stays in suspension and passes through the vessel with the lead."

Because of these factors, state BNF, the system is so different to that implied by Professor Lawson's mathematical analysis, it is not surprising to find that the system does not behave as calculated.
         It seems to me that BNF is correct in its comments.  Professor Lawson's calculations are somewhat simplified and treat the operation of the reactor as if it is no more than a (slow) vertical plug, flow of molten lead in which particles of PbS and CuS are suspended.  He then looks to the balance of particle buoyancy and weight against the drag force exerted by the molten lead flow.  However, the real situation is that there is vortex flow of the lead owing to the effect of the impeller.  Thus, whereas it is true to say that there are vertical gravitational and drag forces acting on the particles of PbS/CuS, these forces are only components.  The true weight‑like force acting on the particles is a resultant of g and the "centrifugal" force caused by the rotational flow of the lead ‑ this resultant, at the surface of the vortex, being directed at right angles to that surface, at any particular point.  Similarly, the "drag" forces, due to of the high rotational velocity of the molten lead, and its relatively slow vertical movement, have a very high component in a horizontal direction, but a much lesser component in the vertical direction. Further ‑ but not surprisingly having regard to the lack of experimental data, in the specification as pointed out by the Professor ‑ the calculations do not take account of the nature of the flow in the various parts of the reactor i.e. whether turbulent, or laminar.  Consequently, I conclude that the evidence of the opponent is unsatisfactory insofar as it attempts to prove that there cannot be no substantial back‑mixing in the process as described.  On this point, BHAS has also argued that the specification does not describe a process which would enable the requirement of no substantial back‑mixing to be met.  My view of this is that the specification describes various impeller speeds and relative proportions for the reactor, which it says, if followed, will give that requirement.  This description is supported by reference to actual examples of the process.  As there is no evidence to the contrary, I must accept what the specification says, and I conclude that there is sufficient disclosure for a person skilled in the art to construct and operate the reactor as described.
         I turn now to the argument put forward by BHAS about claim 1 as accepted and as amended i.e. all the features of these claims except the requirement "without substantial back‑mixing" were known in the art : and this requirement was known to be desirable although there was no practical manner of achieving it in a single reactor vessel.  This is another way of saying that claim 1 does not define the invention, or, in fact, an invention.  I have concluded above that BNF has found a way of achieving that requirement, and has described it adequately in the specification.  The question remains as to whether claim 1 defines the process properly as required by s.40.
         The relevant feature of claim 1 is:

"maintaining a dispersion of sulphur in the stream without substantial back‑mixing ..."

On my reading of the evidence I agree that although this feature was known to be desirable, it was not achievable in a single vessel reactor before the priority date of the claim.  In these circumstances the invention resides not in the feature concerned, but in the means of achieving it in a single vessel reactor.  In this respect it appears to me that claim 1 defines only the feature per se and not the means for achieving it.  I am confirmed in this view from the written submissions put to me by BNF (reproduced earlier in this decision), in rebuttal of Professor Lawson's calculations.  BNF states about the reactor vessel of the invention:

"It is tall in relation to its diameter and is stirred rapidly.  The different geometry and the high circumferential velocity of the lead have a large effect ... Because of the high rotational velocity of the lead the particulate material stays in suspension and passes through the vessel with the lead."

I note that claim 1 is not limited to including the features of geometry and high rotational velocity here used by BNF to distinguish its invention from the model developed by Professor Lawson.
         Finally, the specification itself, recites:

"The upstream arm of the reactor is preferably a cylindrical vessel having a length to diameter ratio of from 2:1 to 10:1.  In a vessel having a length to diameter ratio below 2:1, it would be difficult to keep the sulphur in suspension for a sufficient length of time without substantial back‑mixing.  Vessels having length to diameter ratios greater than 10:1 could in principle be used but are likely in practice to be expensive and difficult to maintain.

The axial impeller is preferably positioned towards the lower end of the vessel.  A speed of rotation of at least 60 r.p.m. is probably necessary to keep the sulphur in suspension.  The optimum speed will depend on the diameter of the vessel and other factors but is likely to be in the range 100 r.p.m. to 3000 r.p.m."

Claim 1 is silent on the essentials of the description in these two paragraphs, which, in my view, do disclose means of achieving the disputed feature.  (I do not suggest that the actual figures quoted necessarily constitute those essentials).
         Therefore, claims 1 (et al) are not fairly based on the matter described, and the opposition succeeds on this point.  However, were claim 1 to be amended to accord with the description in this respect, it would, in my opinion, define patentable subject matter, and be entitled to grant under the Act.
Conclusion
         I have found that the opposition is successful, in that claims 1 et al are not fairly based on the matter described.  However, I have also found that claim 1 could be amended to remove this defect, and accordingly, I allow BNF 60 days from the date of this decision to propose suitable amendments.
         I award costs in favour of BHAS.

(J.L. ROVETA)

Attorneys for the Applicant: Watermark, Sydney