Blast Furnaces 101

How blast furnaces operated……and charcoal vs. coke 

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Stock Yard – Where raw materials were stored and kept dry.
Charging House – Where the furnace is “charged” (loaded full of materials).
Charge – Charging the furnace meant layering it with iron ore, limestone, and charcoal (or coke), in 0.5 to 1.5 inch
            pieces. If the materials are of good quality they can be added directly to the furnace. Lower quality materials
            are burned first in ore burners. Many of the Sanborn maps show each furnaces ore burners. 
Engine Room – aka Engine House, where the steam engines, pipes, boilers, etc. are housed. Sometimes furnaces                  varied in how their engines were set up. 
Casting House – Once the materials were melted in the furnace stack, the molten iron flows into channels called                  “pigs” hence the name pig iron. The iron was either cooled in those molds or ladled into other molds. 
Slag Wheel – the impurities left behind after the iron was melted was called slag, and, after cooling down were pulled
             out with the slag wheel. Not all furnaces used a wheel, and sometimes they were water wheels instead of                  being used for slag.

If you eliminate virtually all of the impurities from iron you end up with steel!

HOW IT WORKED:

In a blast furnace, fuel [charcoal or coke], ore, and flux (limestone) are continuously supplied through the top of the furnace, while air (sometimes with oxygen enrichment) is blown into the lower section of the furnace, so that the chemical reactions take place throughout the furnace as the material moves downward. 

Huge quantities of air blast in at the bottom of the furnace [hence the name BLAST FURNACE], and the calcium in the limestone combines with the silicates to form slag. Liquid iron collects at the bottom of the blast furnace, underneath a layer of slag. The blacksmith periodically lets the liquid iron flow out and cool.

At this point, the liquid iron typically flows through a channel and into a bed of sand. Once it cools, this metal is known as pig iron

The raw materials require 6 to 8 hours to descend to the bottom of the furnace where they become the final product of liquid slag and liquid iron. These liquid products are drained from the furnace at regular intervals. The hot air that was blown into the bottom of the furnace ascends to the top in 6 to 8 seconds after going through numerous chemical reactions. Once a blast furnace is started it will continuously run for four to ten years with only short stops to perform planned maintenance. [Back in Lawrence Co.’s furnace days, the furnaces ran 9 months out of the year and 6 days out of the week. Robert Hamilton started the practice at Pine Grove Furnace of shutting down in observance of the Sabbath.]

To read more about this process, click HERE

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Charcoal vs. Coke

Coke: The coke is produced from a mixture of coals. The coal is crushed and ground into a powder and then charged into an oven. As the oven is heated the coal is cooked so most of the volatile matter such as oil and tar are removed. The cooked coal, called coke, is removed from the oven after 18 to 24 hours of reaction time. The coke is cooled and screened into pieces ranging from one inch to four inches. The coke contains 90 to 93% carbon, some ash and sulfur but compared to raw coal is very strong. The strong pieces of coke with a high energy value provide permeability, heat and gases which are required to reduce and melt the iron ore, pellets and sinter.

Charcoal: Charcoal is a light black residue consisting of carbon, and any remaining ash, obtained by removing water and substances. It is usually produced in a slow process of burning in the absence of oxygen. The resulting soft, brittle, lightweight, black, porous material resembles coal.

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Charcoal pile, circa 1900

Why The Switch?

According to Eugene Willard: “As the years passed it became evident that one necessity was lacking to make the Hanging Rock Iron Region a great industrial section of the United States that was a superior fuel coal. The earlier manufacturers used charcoal but after they had denuded the adjacent country of the raw material for furnace fuel they found it impossible to compete with the iron masters in Virginia, Pennsylvania and even Kentucky, who had the richest coal in the world at their very doors. Hence the shutting down of so many of the old furnaces within the past quarter of a century.”

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As Mr. Willard described, and as you can see in this picture of Hecla, the furnaces had stripped most trees from Lawrence County to produce charcoal. They were running out of resources and needed a new source of fuel: coal (coke). Here’s what happened:

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Lawrence Furnace was rebuilt into a coke-fueled furnace. 

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Hamilton Furnace was rebuilt into a coke furnace. 

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Slag went from looking like this [Center Furnace]…………………………….to looking like this! [Hamilton Furnace]

The furnaces that did not convert…went out of blast. 

Lawrence county Ohio genealogy and historical website