I develop a big Excel workbook having more than 30000 code lines.
When I compile all the code from the VBE and save the worbook, the worbook
file size increases dramaticaly (from 3500Ko to 7000Ko). It seems that
Excel
saves compiled objects.

Is it possible to avoid Excel keeping compiled objects in the saved file?

Can you do a full export/import with Excel? In Access this is a fairly
well-known issue. To fix it in Access, I create a new database, then go to
File = Get External Data and import everything from the original database.
The size of the mdb reduces by more than half, depending on how much coding
I've done.