I hold a Thai passport but i'm currently an exchange student in Seoul and wish to travel to Germany

I'm Thai but right now I'm in Seoul as an exchange student. I already have a Korean Alien Card (ARC). I'm planning to travel to Germany in mid-may and in the process of asking for a German Visa. My flight is supposed to transit in Bejing for about 16-18 hours. Do I need a transit G type if i plan to stay in the transit areas?

And what if i want to leave to the city and back again, will the transit G type cover that? Or will I need the L type tourist.

Thanks!