Is it possible to store my luggage at Beijing Capital Airport?

Yes, there are left luggage service counters at the airport. Hereunder are the detailed location information:
T1: Gate of Corridor, East side of 2F, Depature Hall
T2: Gate No.10, 2F, Departure Hall
T3: East & West sides of Public Area, 2F, T3-C
About the fare, for one piece of luggage, the fares range from CNY 30-100 for 24 hours. The fare depends on the sizes of your luggage. For more details, you can consult the airport staff when you arriving at the counter.