In regeneratively-heated coke oven batteries, the air required for combustion is taken into the sole flue at the base of the regenerator chambers through air chests provided with flaps that can be adjusted to regulate the amount of air entering the regenerator chambers, depending upon whether a rich gas or lean gas is being burned. Coke ovens of this type occasionally have to be changed over to a different operating mode; and the changeover has to be carried out rapidly. The changeover involves increasing or decreasing the combustible gas supply, a step which can be carried out readily and rapidly. At the same time, the quantity of air per unit of time must be altered with the quantity of gas supplied. The air to be preheated is supplied through openings in air intake chests spaced along the oven battery, such openings being closable by air flaps. In the past, alteration in the gas supply required an alteration in the positions of the air flaps controlling the size of the air chest openings.
A special problem arises in the case of coking plants such as, for example, blast furnace coking plants where it is required to operate intermittently with a lean gas requiring preheating (i.e., blast furnace stack gas) followed by an abrupt changeover to coke oven gas, and vice versa. The quantities of air required to support combustion with these two types of gas differ considerably from one another. Similar circumstances are found in coke oven plants where a changeover is made from non-preheated coke oven gas to gases requiring preheating and vice versa.