Twin Fire-Tube Boilers, Abandoned Cold Storage Plant, Minnesota

Fire-tube boilers like these once generated the steam that powered refrigeration equipment in cold storage warehouses, a common setup through the mid-20th century. Running two units side by side gave plant engineers redundancy, letting one boiler operate while the other underwent maintenance or repair. Many such plants used ammonia-based refrigeration systems driven by boiler-generated steam, technology that was largely phased out as electric compressors became the industry standard by the 1970s and 1980s.