VERTICAL RETORTS AND CHAMBER OVENS 153
operation is about ten seconds. This coal valve is of simple design, and practically consists of a cast-iron plug cock with. an opening about 9 inches square.
The speed of travel of the coal into the retort is clearly sliown by a special form of gastight coal indicator which is operated by a weight resting on the coal in the auxiliary hopper.
Each retort is pro vided with a special form of disk valve, the surf aces of which under all conditions are kept clean, and which, wlien closed, cannot leak. This arrangement enables each retort to be skut off for scurfing, when required.
After leaving the retort the gas passes through the offtake pipe and gas valve to the seal pot, where the heavier tars are deposited by fractional condensation before Teaching the foul main.
Each setting is provided with a seal pot serving two or more retorts, through
Fig. 76.—The Woodall-Duckham Coke Extbactoe.
which a stream of tar is passed in order to dissolve the heavier tars : the gas, however, does not pass through, a liquid seal.
This is one of the most important parts of any system of continuous vertical retorts, as the working of the charge through the retort depends to a gieat extent upon the efficiency of the coke extracting gear.
The coke-extracting device (Fig. 76) is situated along the bottom of a curved plate which. forms the back of a cast-iron hopper attached to the bottom of the retort.
The curved plate takes the weight of the charge in the retort and the manhole and inspection holes in it provide free and immediate access to the retort.
As it rotates, the extractor roller does not shear the coke, but merely allows a definite amount to pass over it into the receiving hopper.