By both of these processes valuable constituents were burned or driven off by the heat and lost. These were mainly methyl alcohol, acetic acid, and wood tar.
Modern industry so emphatically disapproves of any waste of materials that apparatus has been devised to produce charcoal which allows of recovery of the by-products at the same time. In northern Michigan, which is practically the only district in the United States in which the charcoal industry as an industry still survives, long steel tubes or retorts are built with brick fire-boxes under each end, much as a stationary boiler is set. Into these retorts are run steel cars loaded with the wood. The retorts being closed, the heat drives or distills off the moisture and gaseous compounds through pipes connecting them with condensing apparatus. After about twenty hours the wood has been charred, the doors of the kilns are suddenly opened and the cars are rushed into other and similar retorts for cooling, while fresh loads of wood replace them in the first.
Standard Beehive Coke Oven
Beehive Ovens
As may be surmised vast quantities of wood and of wood-producing land are required for extensive charcoal manufacture, and this is the most serious problem for the manufacturer of charcoal. Several square miles of timber land must be cut over each year and the wood efficiently transported in order to operate a large plant profitably.
Pig iron as a by-product is a rather novel idea, but that is practically what the charcoal pig iron produced in our Lake Superior region is. Several companies operate wood distillation plants for the production of methyl alcohol, acetic acid, acetate of lime, etc., and use their charcoal in the manufacture of charcoal pig iron from the ores so close at hand.
The very low sulphur content and the small amount of ash have been the great advantages possessed by charcoal over other solid fuels. Resulting characteristics made charcoal pig iron a former favorite for manufacture of certain articles such as chilled car wheels, etc., and it, therefore, brought a higher price than coke pig iron. During recent years, however, by careful selection of coal and improvements in the coking process the sulphur and ash of coke have been so reduced that charcoal has not so great an advantage as formerly. Charcoal iron to-day brings only about $1.50 per ton more than coke iron; whereas, the differential a few years ago was as great as $5.00 or $6.00 per ton.
Charcoal is quite fragile and structurally weak, so much so that blast furnaces for its use cannot be built higher than sixty feet; whereas, the great strength of coke allows them to be built to exceed one hundred feet in height with correspondingly increased output. What this means may be realized by every one conversant with the demands of modern industry.