The prison in Pforzheim accommodates 36 custody prisoners at the moment. By the end of 2018 the number will be 51 and by the end of 2020 80.
Baden Wuerttemberg has a law regarding custody pending deportation (“Abschiebehaftvollzugsgesetz”).
Support for people who are in custody pending deportation is provided by the evangelical church of Baden Wuerttemberg. (Link)