How many double covalent bonds are in an alkane?

None.

Alkanes are hydrocarbons (made up of hydrogen and carbon) that contain no double bonds and so are fully saturated.

Being fully saturated means that every possible space is taken up by hydrogen, and double bonds with other carbons are effectively wasting spaces.

Hydrocarbons with double bonds are called alkenes, and triple bonded hydrocarbons are called alkynes.