I need to get to Tianjin from Beijing Airport

To catch the fast inter-city bullet trains to Tianjin, you should get to beijing South Railway Station, first. There is no train at the airport. You can take airport express train to Dongzhimen and then change to Subway Line 2 to Liujiayao. Then take a taxi to the railway station. Trains are many each day.

Thanx a lot, Mr. Qi! And if I wanted to take a straight from the airport to the Railway station, have you got any idea about how much would it cost me?

If a direct transport is wanted, you have to take a cab from the Capital Airport to the South Railway Station. The fare is about 100RMB.

Actually, there is a budget but easy way, too. You could take the airport shuttle bus Line3 to arrive at Beijing Railway Station (16RMB)and then hire a taxi to the South Railway Station (20RMB).