A Chicago group that’s won praise for its distinct hotels has formally closed plans on the historic Detroit Fire Department headquarters downtown, vowing to retain its industrial charm as it becomes an upscale boutique hotel. Aparium Hotel Group said Wednesday that it and Detroit developer Walter Cohen plan a $28 million renovation of the 1929 building on West Larned along with an adjacent structure that once housed the famed Pontchartrain Wine Cellars restaurant. More recently the building, now empty, had become a nightclub called Envy.