Short answers, pulled from the story.
A blast furnace is a metallurgical furnace used to smelt ore and produce industrial metals, most commonly pig iron, but also lead and copper. Fuel, ore, and flux are continuously charged from the top while a pressurized hot air blast is forced in from below, driving chemical reactions that separate the metal from the ore.
Abraham Darby is widely credited with first successfully fueling a blast furnace with coke instead of charcoal, beginning in 1709 at Coalbrookdale in Shropshire, England. His original furnace has been archaeologically excavated and is preserved at the Ironbridge Gorge Museums.
The earliest blast furnaces in China are attributed to the Han dynasty in the 1st century AD, though cast iron artifacts have been found in Shanxi Province dating to the 9th-8th centuries BC. By the 5th century BC, cast iron farming tools and weapons were widespread across China.
The oldest known blast furnaces in the West were built at Durstel in Switzerland, in the Märkische Sauerland in Germany, and at Lapphyttan in Sweden, where the complex was active between 1205 and 1300. Traces of possibly earlier furnaces have been found at Noraskog in Sweden, potentially dating to around 1100.
For every tonne of steel produced in an integrated steel mill, between 1.6 and 2.2 tonnes of CO2 are emitted, and 70% of those emissions are attributed to the blast furnace. Blast furnaces are estimated to have been responsible for over 4% of global greenhouse gas emissions between 1900 and 2015.
James Beaumont Neilson patented the hot blast process at Wilsontown Ironworks in Britain in 1828. Within a few years, hot blast cut fuel consumption by one-third when using coke and by two-thirds when using coal, while also significantly increasing furnace capacity.