T 0177/96 20-04-1999

Reasons for the Decision

1. The appeal is admissible.

2. Novelty

The objection as to lack of novelty which had been raised by the Appellant in his notice of opposition had already been dropped in the oral proceedings before the Opposition Division. Also in the appeal proceedings novelty was no longer disputed by the Appellant so that this issue requires no further argument.

3. Inventive step

3.1. In agreement with the parties to the proceedings, the Board considers the closest prior art with regard to the subject-matter of Claim 1 to be disclosed by (D1).

This citation describes a process for separating air and recovering work from a waste gas comprising the steps of separating air by rectification into oxygen and nitrogen, taking a stream of nitrogen from a rectification column in which the separation is performed, heating the stream of nitrogen by heat exchange with a stream of fluid which enters into said heat exchange and which does not undergo a change of phase during said heat exchange, there being no compression of the nitrogen intermediate said rectification column and said heat exchange, and without any intervening step of further heating the heated nitrogen stream expanding the heated nitrogen stream in a turbine with the performance of external work, wherein the said fluid comprises said waste gas.

The heat source used for heat exchange between the waste gas and the separated fluid component, such as nitrogen, may be a hot gaseous mixture, waste gas of a steam generator, fuel elements in a nuclear power plant or any object from which heat is transferred directly or by means of a medium to one or several fluid components. The heat source may also consist of oxygen or air and/or fuel which is fed into the fluid component and burnt therein (see (D1), page 3, paragraph 4).

The skilled person investigating further the disclosure of (D1) is taught by the embodiments described in connection with Figures 1 to 3 of the drawings that the hot gaseous mixture used for heat exchange with the nitrogen stream is obtained by combustion of fuel (see "burning chamber of steam generator 89", Figure 1; "burner 88", Figures 2 and 3). He will therefore conclude that the hot gaseous mixture indicated on page 3 of (D1) consists of a gas having a temperature which prevails at the outlet of a fuel burning chamber of well above 600 C (high grade heat).

Claim 1 differs from the disclosure of (D1) in that

(a) the stream of nitrogen is at a pressure in the range of 203 to 709 kPa, and

(b1) the stream of fluid comprises said waste gas and enters at a temperature of less than 600 C into said heat exchange, the waste gas embodying low grade heat, or, according to an alternative, that

(b2) the stream of fluid comprises a heat transfer medium that has been heat exchanged without change of phase with a stream of said waste gas and enters at a temperature of less than 600 C into said heat exchange, the waste gas embodying low grade heat.

3.2. As outlined on page 5, lines 28 to 31 of the patent, the process disclosed leads to a net power saving over comparable prior art processes. The technical problem to be solved can therefore be seen in improving the efficiency of a process such as known from (D1).

It has been illustrated by means of examples discussed in the description of the patent in the passage from page 4, line 31, to page 5, line 25, that the net power consumption is notably smaller in a process in which the low grade waste heat is transferred to the nitrogen stream to be expanded than in processes in which such a use of the waste gas stream is not envisaged, that is a net power consumption of 8.7 MW for the embodiment described compared with a net power consumption of at least 10.7 MW in processes of the latter type.

It has not been substantiated by the Appellant that the examples presented in the patent are incorrect and the Board also has no reason to call these results in question. The problem as defined above is therefore credibly solved by Claim 1.

3.3. The Appellant argues with regard to the issue of inventive step that a stream of fluid with a temperature of less than 600 C used for heat exchange yields less advantageous results than a fluid stream under a higher temperature from which a greater work output can be obtained.

As already set out in the decision under appeal, it forms part of the common knowledge of the person skilled in the art that the higher the temperature of the fluid to be expanded at the inlet of a gas turbine is, the greater the amount of mechanical energy produced will be.

The problem to be solved in the present case does not, however, consist in maximizing the amount of external work produced without taking account of the energy input in the process, but in increasing the efficiency of the process, that is to make optimum use of the energy available in the process with regard to the performance of external work.

3.4. In the Telefax of 16 March 1999 the Appellant cited for the first time inter alia "Klepzig Fachberichte" of October 1979, containing an article by Günther Rückborn of Linde AG, referring to Figure 1, page 556, section 3, first paragraph, page 557, last paragraph, Table 3 and the last complete paragraph on page 558.

According to the above-cited paragraph on page 558, the air separation apparatus of the type L indicated in Table 3 can produce a considerable amount of nitrogen under pressure (2.5 atmospheres above atmospheric) which can be heated to 700 C. In this case, by expansion of the nitrogen in a turbine a power of 630 kW per 10 000 Nm3 N2 can be produced.

The citation neither discloses by which means the nitrogen it to be heated nor that waste gas at a temperature of less than 600 C is used in heat exchange with nitrogen. It is clear for the skilled person that the heating of the nitrogen to a temperature of 700 C requires a heat source temperature well above 700 C.

Contrary to the opinion of the Appellant, the combination of the description of (D1) and "Klepzig Fachberichte" cannot lead in an obvious manner to the subject-matter of Claim 1 as neither of those citations suggests the use of low grade heat waste gas in the heat exchange with the nitrogen stream.

(D2) which also was taken up by the Appellant as being relevant to Claim 1, teaches heating of nitrogen to be expanded in a first step against incoming feed air and, in a second step, further heating the nitrogen, prior to expansion, by means of combustion gases to a temperature well above 600 C such as 1290 C. It follows that (D2), similar to (D1), also teaches employing waste gas of high grade heat and cannot therefore suggest utilization of low grade heat waste gas in the above-said heat exchange.

3.5. In assessing the issue of inventive step the proper question to be asked is not whether the person skilled in the art could have made use of a waste gas stream at a temperature below 600 C for heat exchange with the stream of nitrogen but whether he would have done so in expectation of an increased process efficiency.

The Appellant has argued that no evidence of a prejudice in the prior art that low grade heat cannot be used to improve process efficiency has been shown by the Respondent.

It is acknowledged by the Boards of Appeal that an Applicant or Patentee who seeks to rely on the existence of an alleged prejudice in the art has the burden of proving its existence (see e.g. T 119/82, OJ EPO 1984, 217).

In the present case the Respondent did not, however, rely on the existence of such a prejudice so that there is no obligation for him to prove the prejudice. Contrary to the Appellant's opinion the establishment of a prejudice in the art does not constitute a requirement of the EPC for expounding the presence of an inventive step.

3.6. It has not been shown by the Appellant that any of the citations submitted suggests amending the process for separating air and recovering work from a waste gas as known from (D1) such that low grade heat waste gas at an inlet temperature of less than 600 C is used in the heat exchange with the nitrogen stream to be expanded.

The question of whether and in which manner the step of choosing the pressure of the stream of nitrogen in the range of 203 to 709 kPa under which it is heated contributes to the solution of the underlying technical problem, can be left unanswered since the inventive step of the subject-matter of Claim 1 is already supported by the step of using waste gas at a temperature below 600 C for heat exchange with the nitrogen stream.

At the oral proceedings before the Board, only the citations (D1), (D2) and "Klepzig Fachberichte" were discussed. The other documents cited in the opposition proceedings as well as those submitted by the Appellant with the Statement of Grounds of Appeal, the letter dated 18 February 1996 and the Telefax of 16 March 1999 were no longer dealt with. The Board is satisfied that these documents can also not challenge the validity of the patent in the version as granted.

3.7. To summarize, the Board considers that the solution to the technical problem underlying the invention as defined in the independent Claim 1 involves an inventive step and therefore this claim as well as its dependent Claims 2 to 10, relating to particular embodiments of the invention, are to be maintained.