Hot blast
James Beaumont Neilson stood at the Wilsontown Ironworks in Scotland during 1828. He had previously worked as a foreman at Glasgow gas works before turning his attention to iron furnaces. Neilson discovered that raising the temperature of incoming air allowed him to cut fuel consumption from 8.06 tons of coal down to 5.16 tons per ton of produced iron. This discovery formed the basis for a new system of preheating blast. He and partners including Charles Macintosh secured a patent for this method on the 1st of January 1828. Thomas Botfield held a historical claim based on an earlier date, but Neilson won the subsequent legal battles. The spread of technology across Britain moved slowly despite these early successes. By 1840, only 58 ironmasters had taken out licenses for the process. These license holders generated royalty income totaling £30,000 per year. When the patent finally expired, there were 80 active licenses. In south Staffordshire alone, 42 of 80 furnaces adopted hot blast usage by 1843.
Early hot blast stoves relied on firebrick-lined vessels with multiple chambers to store heat. The system alternated between storing heat from furnace flue gas and blowing combustion air through the hot chamber. This cycle is known as regenerative heating. The initial heating vessel was constructed from wrought iron plates that quickly oxidized under high temperatures. Neilson substituted cast iron for the original material to improve durability. Thermal expansion and contraction caused frequent breakage of pipes in these early models. Engineers remedied some issues by supporting the pipes on rollers. New methods became necessary to connect blast pipes to tuyeres since leather could no longer be used. The principle eventually found more efficient application in regenerative heat exchangers like the Cowper stove. Modern blast furnaces still use this specific design to preheat incoming blast air with waste heat from flue gas. The Siemens-Martin open hearth furnace also applied this same principle for making steel.
The technology significantly reduced fuel consumption during the British iron industry boom. Higher furnace temperatures increased the daily output capacity of existing facilities. Calder ironworks saw production rise from 5.6 tons per day in 1828 to 8.2 tons in 1833. These gains made Scotland the lowest cost steel producing region in Britain throughout the 1830s. Raw coal could replace coke in many applications where it had been impossible before. Scottish smelters found they could profitably process relatively poor black band ironstone. The reduction in fuel usage meant less sulfur and ash entered the final product. This allowed for better quality control over large scale operations. The slow adoption across Britain contrasted sharply with the rapid economic benefits available to early adopters. By 1843, south Wales showed even slower uptake than other regions despite clear advantages. The financial returns from licensing created a steady income stream for patent holders.
Hot blast enabled the use of anthracite in iron smelting processes previously reliant on charcoal. Good coking coal was only available in sufficient quantities within Great Britain and western Germany at that time. Iron furnaces in the United States depended heavily on vast tracts of forested land for charcoal production. Any given furnace would go out of blast once nearby woods were felled. Attempts to use anthracite as fuel had ended in failure under cold blast conditions. Dr. Frederick W. Gessenhainer filed for a US patent on the 5th of February 1836 regarding hot blast and anthracite. He produced a small quantity of anthracite iron by this method at Valley Furnace near Pottsville, Pennsylvania in 1836. Breakdowns and his illness prevented him from developing the process into large-scale production before his death in 1838. George Crane and David Thomas independently conceived similar ideas while working at Yniscedwyn Works in Wales. They began producing iron by the new process on the 5th of February 1837. Thomas moved to the US to found the Lehigh Crane Iron Company utilizing the process.
Anthracite was eventually displaced by coke in the US after the Civil War. Coke proved more porous and able to support heavier loads in vastly larger furnaces of the late 19th century. The original principle found even more efficient application in regenerative heat exchangers like the Cowper stove. These units preheat incoming blast air with waste heat from flue gas for modern blast furnaces. The Siemens-Martin open hearth furnace also applied this same principle for making steel. Carbon monoxide in the flue gas was burned to provide additional heat in later iterations. The technology spread across Britain relatively slowly despite its clear advantages. By 1840, only 58 ironmasters had taken out licenses yielding £30,000 per year in royalties. When the patent expired there were 80 licenses total. In south Staffordshire alone, 42 of 80 furnaces used hot blast by 1843. Uptake in south Wales remained slower than other regions throughout the period.
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Common questions
Who invented the hot blast system for iron furnaces in 1828?
James Beaumont Neilson invented the hot blast system at Wilsontown Ironworks in Scotland during 1828. He secured a patent for this method on the 1st of January 1828 with partners including Charles Macintosh.
How much fuel did James Beaumont Neilson save per ton of produced iron?
Neilson cut fuel consumption from 8.06 tons of coal down to 5.16 tons per ton of produced iron by raising the temperature of incoming air. This discovery formed the basis for a new system of preheating blast that significantly reduced costs.
When did Dr Frederick W Gessenhainer produce anthracite iron using hot blast technology?
Dr Frederick W Gessenhainer produced a small quantity of anthracite iron by this method at Valley Furnace near Pottsville Pennsylvania in 1836. He filed for a US patent on the 5th of February 1836 regarding hot blast and anthracite before his death in 1838.
What year did south Staffordshire adopt hot blast usage in 42 out of 80 furnaces?
In south Staffordshire alone 42 of 80 furnaces adopted hot blast usage by 1843. By 1840 only 58 ironmasters had taken out licenses for the process generating royalty income totaling £30,000 per year.
Which stove design applies the regenerative heating principle used in modern blast furnaces?
The Cowper stove is a regenerative heat exchanger that preheats incoming blast air with waste heat from flue gas for modern blast furnaces. The Siemens Martin open hearth furnace also applied this same principle for making steel.