Luggage at Beijing Capital Terminal 2

I am travelling to Taiwan, then Hong Kong and my first stop in China will be Shanghai, then Beijing, I am then catching the train to Pyongyang, flying back to Beijing on Air Koryo arriving at 11.30, then flying home on AirAsia at 00.30 the next morning. I know I need a single entry visa for my entry at Shanghai. My question is do I need to go through customs/Immigration when I return to Beijing from Pyongyang and if so will I then need a dual entry visa or can I use the 72 hour visa to check in for my flight home.