74 MODERN GAS WORKS PRACTICE
(c) Steaming the fuel-bed sliould be reduced to a minimum. In this type of fumace the waste products escape at high temperatures, and the heat required to raise the steam to the temperature of the setting is appropriated from the heat produced by the combustion of the coke—hence the steam occasions a direct loss. (See remarks on the use of steam, page 68.)
Water-cooled firebars should be avoided.
(d) All flues must be accessible for cleaning while the setting is at work.
(e) The possibility of short-circuiting between the flues—a common fault with these settings—must be provided against.
(/) The loss of heat through, the walls of the furnace by radiation is proportional to the size of the furnace ; thus the fumace having the smallest lieat-radiating surface will be the most economical.
Frø. 22.—Regenerator Retort Bench with Varytng Units.
(g) The farther back the actual fire Stretches, the better will be the heating of the back of the retorts ; on the other hånd, very long grates are difficult of access for cleaning, etc.
(A) If a deep fuel-bed is employed CO will be formed, and this, escaping unburnt will account for considerable loss. In the smaller grates 12 inch.es of fuel depth is ampie. It should not in any case exceed 18 indies, unless, of course, a supply of secondary air above the fuel is arranged for. This point is often difficult to impress upon the country stoker, as charging the furnace little and often entails considerably more trouble.
(«) The front of the fire (above the firebars) must either be sealed with a plate or breezed up so that all air enters beneatli the firebars. For direct fires the ordinary horizontal grate is preferable to th.e modern sloping types.