A Dispatcher reports an ERJ-170 was flown with two of the same MEL's: 57-52-01 FLAP CANOE SEALS. Maintenance Control was unaware that Dispatch was only able to provide one Performance Limitations penalty calculation for one canoe seal on the ERJ-170; whereas the ERJ-190 can have numerous canoe seals damaged or missing and applied under one MEL performance penalty.

Narrative

An ERJ-170 aircraft was flown with two of the same MEL's: 57-52-01 FLAP CANOE SEALs December 2010. Maintenance Control was unaware that due to this MEL; limiting performance by application of 'Drag45'; and Dispatch [being] unable to provide two 'Drag45' limiting performance calculations; this flight should not have been dispatched. There was a memo earlier in the year that only one 'Drag45' limiting MEL may be applied at a time; and due to both MEL's being on the same wing; I was unaware that this needed to be applied twice. Maintenance Control said this flight was legal to dispatch with both of these MEL's; which I think would have been the case if Dispatch was able to calculate more than one 'Drag45' Limiting Factor.Seeing that the performance was affected by roughly 300LBS of fuel; I added an additional 1;000LBS of fuel from the original release that did not have these limiting MEL's (400 extra and 600 hold). If Maintenance Control was aware that we could not calculate two Performance limiting factors of 'Drag45'; we would not have had this issue. Maintenance Control still said it was legal to fly with both of these MEL's under 57-52-01 FLAP CANOE SEALS.