How long before I can return to China on another 72 hour Visa?

I will be travelling from Manchester to Beijing and onto Korea. I will be staying in Korea for 10 days before repeating the same route back (Korea -> Beijing -> Manchester). Am I allowed a 72 hour layover in Beijing on both legs of my trip?
I.e. Manchester to Beijing - Stay in Beijing for 72 hours - Fly to Korea.
Followed by: Korea to Beijing - Stay in Beijing for 72 hours - Fly to Manchester.