In Western Pennsylvania, Ohio, and Virginia, were great beds of high grade coking coal. In this region and particularly around Pittsburg, numerous blast furnaces and steel mills grew up. The coke for these was made in the most convenient way—in the wasteful beehive ovens.
Battery of By-Product Coke Ovens, Showing Gas-collecting Main
As the name signifies, these ovens or retorts are brick chambers shaped like beehives. In the larger plants they are built either in single rows against long hills or in double rows back to back. Over the tops of the ovens in each row runs a car called a charging “lorry.” Coal is poured from the bottom of this through a hole in the top of each oven while it is still hot from the preceding charge. No air gets in except that admitted through the hole in the oven top and a small slit left over the one side door, through which the coke is drawn when the coking process is finished. The heat of the oven starts the distillation of the moisture and the volatile compounds which escape through the hole in the oven top. The small amount of air admitted burns a little of the coal and gas and raises the temperature of the oven to that required for coking.
After 48 or 72 hours a spray of water is thrown in over the glowing coal to quench the fire. The partially cooled coke is drawn through the open door, sorted and loaded into cars for shipment.
Though this method of coking is a very wasteful one, it yet produces the larger quantity of the coke made in the United States. However, conditions are rapidly changing and it will not be many years before the much less wasteful “by-product” process gains the ascendency. By 1914 it had already come to produce about twenty-five per cent of the total coke made here, and since that date the percentage has been rapidly increasing.
The By-product Process
Top of Ovens with Charging Bin and Lorry at Far End
By this system of coking a greater yield of coke is obtained and most of the by-products are saved. The value of the latter depends largely, of course, upon local conditions, such as transportation, costs of the material, cost of labor, and available market for the coke oven gas. They are usually figured as having a value of $1.50 per ton of coal coked, equivalent to a total of $71,000,000 per year for the coal coked in the United States.