How many 144h free-visa can I get in one year ?

Hi,

Here is my itinary:
Montreal to Tokyo transiting in Beijing Sept. 29th to Sept. 30th.
Seoul to North Korea transiting again in Beijing Oct. 8 to Oct 10.
North Korea to Montreal transiting another time in Beijing Oct.14 to Oct 15.

Can I get three 144h free-visa in two weeks?

Thank you,