T 1307/05 04-09-2007

Reasons for the Decision

1. The appeal complies with Articles 106 to 108 and Rule 64 EPC and is therefore admissible.

2. Background

The invention relates to long term power augmentation in industrial gas turbines with a multi-stage axial flow compressor by injecting into its intake liquid water in an amount over and above what is necessary for full humidification of the working fluid and for an extended period of time. The double effects of evaporative cooling and added mass flow of such continuous, high level water injection (also termed "wet compression" or "overspray"), result in an increase of power output beyond that of conventional evaporative cooling, where no liquid water enters the compressor.

Wet compression per se is a known measure for boosting power output in gas turbines as is clear from the prior art cited in opposition. This is also acknowledged by the Appellant. The claimed invention therefore now focuses on the specific amounts and duration of this wet compression.

3. Allowability of the Amendments under Article 123(2) EPC

3.1 In deciding the question of allowability of amendments under Article 123(2) EPC the Board, following well-established practice (see e.g. the Case Law of the Boards of Appeal, fifth edition, December 2006 - hereinafter the CLBA - section III.A.2), must consider whether the amendments in question are directly and unambiguously derivable from the application as filed, taking into account matter which is implicit to a person skilled in the art.

3.2 The independent claims 1, 14 and 16 of each of the requests have their origin in as filed claims 1 with 3, claim 33 with 35, and claim 77 respectively. To these claims have been added in combination further features which in particular define - expressed in different terms in the requests - lower limits of the amount and duration of wet compression.

As regards duration, the step of adding water droplets is required to be "for a continuous period of", in the main request, "at least 90 minutes", or, as in the first to third auxiliary requests, "more than 90 minutes", or, as in the fourth auxiliary request, "greater than 90 minutes". In the fourth auxiliary request the claims additionally require that the "process is used for at least six hours within a given twenty four hour period".

In accordance with each of the requests the amount of water added must be sufficient to provide a working fluid to the compressor inlet which comprises "at least three-quarters of one weight percent (3/4 wt %) of liquid water in admixture with fully humidified air".

3.3 Minimum duration and amount are disclosed separately in different passages in the originally filed application documents. The parties are in agreement that the only passage in the originally filed application which mentions 90 minutes in the context of duration is found on description page 10, lines 1 to 13.

As for the required amount of water of at least 3/4 wt % of liquid water in admixture with fully humidified air it is common ground that the relevant passages in the originally filed application are:

- claim 49

- claim 67

- page 19, lines 4 to 11

3.4 The Board firstly notes that in each of the above passages the values appear in a specific context.

3.4.1 The first paragraph of page 10 discusses the duration in the specific context of a conventional compressor water washing system. This follows from the paragraph itself (lines 2 to 4) ("augmentation is simply accomplished by continuously providing .... at least a conventional compressor water wash amount of liquid water" (italics added)) and its explicit mention in the following paragraph, lines 14 to 16 providing further detail of "this particular aspect". Finally, this passage indicates that an "at least conventional compressor water wash amount of liquid water" is involved, which on page 21, lines 5 to 7, is given as "typically between 0.1 to 0.5 per cent by weight of the working fluid"

Claim 49 as dependent on claim 33 includes first and supplemental means for providing liquid droplets positioned adjacent, respectively further away from the compressor inlet and which are appropriately sized to provide the 3/4 wt % of water. Claim 67 is dependent on claims 53 and 52 which include features of a spray rack group with spray rack pipe and a sufficient number of spray rack nozzles as means for providing the 3/4 wt % water. Finally, the passage on page 19 undoubtedly relates to the embodiment of figure 3, as follows from the reference to the immediately preceding paragraph on pages 18 and 19 in its opening lines ("the invention in this regard"). This embodiment is detailed in the final two paragraphs of page 19 continued onto page 20 as including a spray rack group assembly 201 with spray rack water nozzles 305 at one of the compressor inlets. None of these passages provides any specific values for the duration of the extended wet compression.

3.4.2 Not all of the above features in italics are included in claims 1, 14 and 16 according to any of the requests, so that the features of minimum duration, respectively minimum amount, have been extracted in isolation from their original context. Following established jurisprudence, see in particular T 1067/97 cited in CLBA, section III.A.1.1, page 240, third paragraph, this is only justified in the absence of any clearly recognizable functional or structural relationship among the features.

3.4.3 The Board is not convinced that this is so in the case at hand. The discussion on page 21, line 3 onwards, is significant in this regard. It distinguishes between extended wet compression using only conventional compressor water washing, which produces lower levels of power augmentation (up to 10%), and - see final paragraph of page 21 - arrangements with plural water spray means, one of which is in the form of a spray rack group assembly as in figure 3 and specifically linked to the 3/4 wt % figure, which results in higher levels of augmentation, above 10%. It stands to reason that these different levels depend on differences in design and operating conditions such as in particular amount and duration. In the Board's view these are thus inextricably linked with the particular designs. Their abstraction from that particular context thus represents an unallowable generalization of the extracted features in question to apply to a wider range of arrangements than that defined by the specific context.

3.5 For the same reasons, the combination of the above features in claims 1, 14 and 16 of each the requests, in the Board's view extends beyond the content of the application as filed. As is evident from the above, these features consistently appear separately from each other in different, distinct embodiments. Their combination, in the Board's opinion, presents the skilled person with a new set of conditions for wet compression which are not derivable from the original application.

3.5.1 Neither the passage on page 6, lines 30 to 32, nor that on page 10, third complete paragraph, in the Board's view serve to establish an incontrovertible, necessary and exclusive link between the two features. Lines 30 to 32 of page 6 may combine extended periods and high levels in a single context, but it does so only in the most general terms (which may also be read as stressing the fact that the invention provides a way in which wet compression is "pragmatically implemented" to allow extended periods and high levels). Likewise the third paragraph of page 10, relating to a "second aspect of the invention", when read in context is open to different readings, for example focusing on the concept of controllable augmentation or modification as one further separate idea out of many presented in the following paragraphs on pages 10 and 11 describing further aspects of the invention. In any case neither passage can detract from the fact that the features in question are presented in separate, distinct contexts. In as far as these passages might reflect on the motivation of the skilled person to consider these features in combination and abstracted from their respective contexts, this bears upon the question of obviousness, rather than on the issue of what is unequivocally and clearly disclosed to the skilled person in the as filed application.

3.5.2 Nor is it "clear beyond any doubt" that the introduction in combination of the minimum duration and amount after isolation from their respective contexts results in subject-matter that "provides a complete solution to a technical problem unambiguously recognizable from the application" as stipulated in T 284/94 (OJ EPO 1999, 464), see head-note I. The Board notes that the 38 filed description pages and 81 filed claims including 12 independent claims offer a multiplicity of different ideas and definitions of the invention, each addressing different problems or part problems. Of these the passage on page 6 - the sole to mention extended duration and high levels in combination - is only one. The skilled person is hard put to identify among these many different threads of development a clear teaching that the claimed specific minimum duration and amount in combination and of themselves represent a complete solution to any particular problem in wet compression.

3.6 Finally, the Board is also not convinced that the specific minimum duration of 90 minutes as appearing in claims 1, 14 and 16 of each of the requests has a clear and incontestable basis in the first paragraph of page 10 cited by the Respondent. This paragraph states parenthetically that augmentation by wet compression is over a period of time "extended beyond what would be dictated by on-line wash considerations". Further on conventional compressor water washing is stated to be "typically limited in duration to from about thirty to perhaps about ninety minutes".

3.6.1 The Board firstly notes that the upper duration limit for conventional washing is expressed in rather uncertain terms, lying somewhere "from about thirty to perhaps about ninety minutes" (italics added), followed by a qualification regarding practical and economical considerations in determining the correct value ("as determined by what is practically recoverable in performance terms from continued washing versus costs ..."). This passage thus teaches the 90 minutes for conventional compressor washing as an approximate ("about"), tentative ("perhaps") value about which maximum duration may vary depending on cost and practical considerations, rather than as a distinct demarcation. Given such terms and the practical proviso the Board believes that this passage teaches the skilled person that if he is to avoid conventional compressor washing durations at all he will stay well clear of the tentative value of "perhaps about 90 minutes".

3.6.2 In its first line the above passage on page 10 refers to "this first aspect" which is detailed in the immediately preceding paragraph at the bottom of page 9. That paragraph (first two lines) speaks of "a process used for six hours or more within a given 24 hour period". Though this paragraph could refer to a total duration of intermittent periods of operation (it does not mention continuous wet compression), it may also be read as a lower bound on the duration of continuous wet compression, which is entirely consistent with the passage on page 10 of extending beyond conventional durations. The Board notes that this minimum six hour process time itself appears in original independent claims 22 and 26, whereas the value of 90 minutes does not feature in any of the as filed claims.

3.6.3 From the above the Board concludes that an exact value of 90 minutes as the lower bound for the duration of power output augmenting wet compression is not directly and unambiguously derivable from the first paragraph of page 10 read on its own or contextually, together with the preceding paragraph on page 9. This conclusion applies irrespective of whether the value of the lower bound is included, as in the formulation "at least 90 minutes", or not, as in the formulation "more than" or "greater than 90 minutes", or, whether, as in the fourth auxiliary request, it appears additionally together with the indication that the process is used at least six hours in a 24 hour period.

3.7 In summary the Board holds that there is no clear and unambiguous basis in the original application for introducing in combination into claims 1, 14 and 16 of all requests the features of the lower bounds on duration and amount which are moreover extracted in isolation from respective, different contexts. It also holds that such a clear and unambiguous basis is absent for the specific value of 90 minutes as lower bound on the duration. In conclusion therefore the Board finds that the subject-matter of claims 1, 14 and 16 according to each of the main and first to fourth requests extends beyond the content of the application as filed. The ground mentioned under Article 100(c) EPC therefore prejudices the maintenance of the patent as amended according to any of these requests.