If you have special grounds you can apply for a national visa (D-visa) for longer than 90 days, but for a year at the most. Special grounds are decided by the Embassy. Contact the Embassy on ambassaden.khartoum-migration@gov.se for more details.
If the Embassy decides you have special grounds you will be asked to fill out the form and the required documents stated below.
Only if you have special grounds could you be entitled to national visa (D-visa).
The requirements are the same as for a Schengen visa (Required documents) with the following exceptions:
Back to visitors permit over 90 days.