There are several Air China lounges in Beijing Capital Airport: first class, business class in various terminals but the one to which we specifically are referring here is the one in Terminal 3E mezzanine floor by gate E19. We spent several long layovers here recently and so got a good idea of what the service and schedule looks like during operating hours.
The lounge follows the first scheduled flight and until the last meaning it is essentially closed for an hour a day between 2:30am and 3:30am. It is accessible by Air China Business class ticket holders, Star Alliance Gold members and Priority Pass holders. The staff at the check in desk are always very helpful even when their English can be a bit limited.
The lounge can get crowded around lunch time, so it is good to get the first seat you can find even when there is plenty of room to stretch out. There are wonderful magazines, comfy chairs, tables to work from and quieter areas where one can either nap in pods or sit in a more noise proofed salon. There is a kiosk by the entryway that gives you an internet access from your boarding pass scan.
As far as the food and beverage offerings go there a very good and eclectic selection of sandwiches, cookies, sushi, Chinese traditional hot food and a variety of alcoholic and non alcoholic drinks.
The facilities have exclusive use showers and we found the toilets were always being cleaned by the staff. There are many employees constantly replenishing food and clearing plates so that there is always a clean and hospitable environment. The high open air ceilings of the airport means it stays pretty quiet and it is a good place to spend a longer layover.