The slanted buildings areas conveyors that bring coal upto furnaces in this structure at Tsinghua University. The coal is burned during wintertime to turn water into steam, which is then piped throughout the campus into radiators to provide heat. Such systems are used throughout Beijing. (In fact, there was a massive effort over the past year to replace major steam pipe arteries.)
In 2001, soon after learning that they’d been awarded the 2008 Summer Olympics, the government undertook a policy of shutting down factories inside of the Fifth Ring Road (or maybe it was the uncompleted Sixth), and relocating them to other provinces.
I think that the only remaining huge smokestacks remaining (and there aren’t a lot of them) inside of the city limits are associated with such heating facilities.
This picture was taken in 2006 from the old Sun Microsystems offices, which were directly across from the facility. During the time that we were there, the building was renovated, and the height of the smoke stack was increased.