As noted in my previous post Visiting Local History , our region in the early 1900's had built nearly 500 beehive ovens used for refining locally mined coal into high quality coking coal used in local metallurgical applications such as copper smelting and fueling blast furnaces in the production of steel. Why coking coal? It's virtually 100% carbon, with impurities removed, and can be used as fuel to heat ovens to very high temperatures - in the1600 to 2500 F range. But then I read that to produce coking coal, beehive ovens must be heated to over 1,100 degrees F for 2 to 3 days in a low oxygen environment? How can that work?
As usual, relying on pictures to learn and tell the story is most fun for me. Following is a photo taken in 1912 of beehive ovens being constructed by Carbon Hill Coke Co. at their facility in Wingate, Pierce County (Carbonado).
Image courtesy Washington State Historical Society, 2009.108.2, circa 1912
We can see each oven being built with bricks in a circular "beehive" shape with openings at the top and then on the side at surface level. When operating, coal is introduced into the oven from the top. Air is supplied initially to ignite the coal and heat the oven. Once up to temperature and mostly closed off, carbonization of the coal starts and produces volatile matter which burns. Exhaust gasses escape to the atmosphere. Impurities in the coal not already driven off as gasses accumulate as slag bi-product, leaving "melted" hot coke, nearly 100% pure carbon, to be discharged out the door at the side and watered down. Once initially heated, ovens retained sufficient heat to "coke" the next batch introduced from the top. Slag biproduct, once discarded, eventually found marketable uses as ingredients in brick making, cement and even fertilizer. The following table provides a breakdown of coke yields and bi-products at Pierce County coke ovens as reported by the Bureau of Mines.
When nearing completion, the Carbon Hill Coke Co. array of beehive ovens appeared as follows:
Image courtesy Washington State Historical Society, 2009.108.1, circa 1912
Note the large brick structures set at either end of the row of ovens. I would guess that this was to help enclose the entire area with earth for insulation purposes?
The period from 1910 thru 1929 were the days of prosperity for coking coal in Washington, as shown in the following compilation of annual reports from the Federal Bureau of Mines.
Must have been some real parties going on in 1918. Short-lived though.
As we see, 1937 ended the days of coking coal in Washington State. Why? By this time, furnace technology had advanced significantly, reducing the need for coke, and imports of coke from Europe could be brought in at significantly lower cost.
Coke ovens are still fun to go see, like these at Wilkeson.
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