150
MODERN GASWORKS PRACTICE
The maximum working temperatures in the combustion chambers are usually about 1,290° C. (2,354° F.) at the top and 1,000° C. (1,832° F.) at the bottom.
The walls of the retorts (Fig. 72) are formed of bricks tongued and grooved so that leakage at the joints is prevented, the bricks being panelled out at the back so that the heat can readily pass through the walls to the charge in the retort, a large surface being presented to the heating gases in the flues.
The retort bricks measure inches from front to back, but owing to the panels the average thickness of fireclay material through whicli the heat has to travel from the combustion chamber to the coal charge is a little over 3 indies. In this manner a retort wall is formed practically equal in strengtli to a solid 4|-inch wall but having a heat conductivity to that of an ordinary 3-inch solid retort.
Fig. 72. Section of Woodall-Duckham Vertical Slot Retort, showing Method of Bonding Special Bricks.
The heating flues are vertical and the division walls separating the flues are constructed of tongued and grooved bricks. The division walls are bonded into the walls of the retorts and into the back walls of the flues, thus forming a very strong and simple construction.
The producer gas and secondary air are brought to the top of the setting and are admitted at the top of the vertical flues, combustion proceeding downwards.
Dampers for producer gas, secondary air, and wagte gases are provided for the purpose of maintaining safe and uniform heating of the retorts, the dampers being operated from platforms placed in convenient positions.
The three- and seven-ton sizes of retorts are built in batteries of six and upwards, and are provided with outside producers situated at the end of the retort beuch.
Five-ton retorts are arranged in settings of two or four retorts complete with