The Early Years
Coal had been mined for many years before the idea of making coke in beehive ovens became popular. Coke is the bones of coal. In a general way, coke is as near a pure carbon as may be had; as near an uncrystalized diamond as can be made. The beehive coke oven transforms the soft, crumbling bituminous coal into a hard, porous substance which will “stand up stiff-backed” under a ponderous load of iron ore and limestone in the blast furnace, where coke is chiefly used. As early as 1860, Connellsville Coke was used exclusively in Pittsburgh’s first successful blast furnace, the Clinton Furnace, and became the benchmark against which all other cokes were measured.
The process of coking is simple, but requires expert care. The shovel never touches the coal from the time it is loaded into the wagon down in the bowels of the earth until it is raked out of the oven in the form of coke, hot and smoking. The coal from the mine is taken from the coal tipple in larries [lorries]; a larry-load fills one oven. The larry travels along a track over the top of the long double row of ovens and drops its load into each through the circular hole in the roof known as the trunnel head. Then the opening in the oven front, measuring about two feet square with an arched crown, is bricked up and plastered with clay, leaving a space for sufficient air to get in the oven, a width of approximately 2 inches (usually measured quickly by the width of the coke makers’ three fingers). The heat in the oven from the last burning fires the fresh load of coal, and then there is nothing to do but let it sizzle while regulating the heat so that the coke does not roast too slow or burn too fast, by enlarging or daubing up the space left for draught. The temperature of the brick interior averages 2,500 degrees faherenheit. The object in baking the coal is to consume as much of the volatile matter (tar, gases, light oil) as possible without consuming the fixed carbon. This is where the coke-maker’s trained eye and judgment comes into play, as he notes and governs the progress of the process according to the tints of the delicate, shimmering flame that dances over the glowing mass. When it has the proper color, and is done, the “drawer” turns the hose on it drenching the load with 850 gallons of water to cool the oven, so that the coke can be handled with the drawer’s long, heavy singletoothed iron rake. Then, there is nothing more to do but fork the light steel-gray product into a railroad car and it is ready for shipment via railroad. The usual conversion period was 48 hours, but on weekends, 72- hour coke was made since Sunday was not a workday. Each worker usually was assigned six ovens so that he would draw three ovens a day. Usually it took about 2 hours to empty each oven.
“The coke from this region [Connellsville] has a silvery luster, metallic ring, is cellular, tenacious, comparatively free from impurities, and is capable of bearing a heavy burden in the [blast] furnace. Its hardness, well developed cell structure, purity and uniform quality have given it a great reputation as a blast furnace coke. The average yield in coke is 65%.” (Bituminous Coal Losses and Mining Methods in Pennsylvania, 1924)