高炉炼铁Blast furnace

热风（约 1100–1250 °C）在风口区与焦炭燃烧，温度高达 2000 °C 以上，生成的 CO₂ 立即与炽热焦炭反应生成 CO。CO 上升时自上而下逐级还原：Fe₂O₃ → Fe₃O₄ → FeO → Fe。石灰石分解为 CaO，与矿石中的 SiO₂ 等脉石结合成炉渣（CaSiO₃），炉渣浮在铁水上方。生铁含碳约 4%，还含少量 Si、Mn、P、S。

Hot blast at about 1100–1250 °C burns coke at the tuyeres above 2000 °C, and the CO₂ formed immediately reacts with glowing coke to give CO. Rising CO reduces the ore step by step: Fe₂O₃ → Fe₃O₄ → FeO → Fe. Limestone decomposes to CaO, which combines with SiO₂ and other gangue to form slag (CaSiO₃) floating on the iron. Pig iron contains about 4% carbon with some Si, Mn, P and S.

中国在公元前 5 世纪已用竖炉生产生铁，比欧洲早一千多年。欧洲 14 世纪出现高炉。1709 年达比用焦炭代替木炭，1828 年尼尔森发明热风技术，大幅降低燃料消耗。现代大型高炉容积超过 5000 m³，日产铁水上万吨。

China produced pig iron in shaft furnaces by the fifth century BCE, more than a thousand years before Europe, where blast furnaces appeared in the fourteenth century. Darby replaced charcoal with coke in 1709, and Neilson's hot blast of 1828 greatly cut fuel use. Modern furnaces exceed 5000 m³ and make over 10,000 tonnes of hot metal a day.

生铁性脆，需在转炉中吹氧把碳降到 2% 以下并除去杂质，才得到钢。高炉-转炉流程每吨钢排放约 1.8–2 吨 CO₂，钢铁业约占全球 CO₂ 排放的 7%。氢气直接还原铁（H₂ 代替 CO）和电弧炉炼钢是主要的低碳替代路线。

Pig iron is brittle; oxygen blown through it in a converter lowers the carbon below 2% and removes impurities to make steel. The blast furnace–converter route emits about 1.8–2 tonnes of CO₂ per tonne of steel, and the steel industry accounts for roughly 7% of global CO₂ emissions. Hydrogen direct reduction (H₂ in place of CO) and electric arc furnaces are the main low-carbon alternatives.