DES MOINES — Des Moines’ main library downtown has been evacuated and closed after a man walked into its atrium and set himself on fire.Police say witnesses reported the 36-year-old man doused himself with a flammable liquid just before 2 p.m. Tuesday and lit himself on fire. Library staff used a fire extinguisher to douse the flames, and the man was rushed to a nearby hospital for treatment of serious burns.The man’s name has not been released.