As i understand, main difference from earlier puddling furnaces was usage of gas instead of coal as source of energy. Therefore, tricks like regenerative heating become much more effective.For those more knowledgeable of the history of metallurgy, at what points in time could the Siemens-Martin process and the Open Hearth Furnace design have been invented before the time it was in OTL?
When and how did people in Sichuan use gas heating?