It is possible to get TWOV and in which city ?

Yes, your entire itinerary is definitely eligible for 24 hour visa free transit and you do not need any kind of visa.

Upon your landing in Xi'an the first what will you do is to approach 24/144 hour visa free transit counter where you will apply for a temporary entry permit in order to be allowed to exit the airport (or better to say a transit area) because your next flight to Harbin will be a domestic one. At the transit counter you will present your flight tickets and here I encourage you to print out your emails with flight tickets for more expedient procedure at the counter.

When your permit is granted, you will cross the immigration and head toward the gate of your flight to Harbin.

Upon landing in Harbin, you will cross the exit immigration and head to your flight to Russia.

Yulia, I have one doubt because I do not see any direct flights between Harbin and Blagoveshchensk. Please, have in mind that you will not have enough time for a third Chinese airport like Heihe or similar. Maybe your first landing in Russia will be Khabarovsk or Vladivostok and that is fine, but you have to be very precise in your presentation. In any case, if your flight from Harbin goes directly (nonstop) to some Russian airport, then you are definitely fine, but again, precise presentation of your flight itinerary is very important!

Thank you very much for your detailed answer.