nce of the operating force.

[Illustration: Fig. 26. Babcock & Wilcox Boiler and Superheater Equipped
with Babcock & Wilcox Chain Grate Stoker. This Setting has been
Particularly Successful in Minimizing Smoke]

When a condition arises in a boiler room requiring the fires to be
brought up quickly, the operatives in handling certain types of stokers
will use their slice bars freely to break up the green portion of the
fire over the bed of partially burned coal. In fact, when a load is
suddenly thrown on a station the steam pressure can often be maintained
only in this way, and such use of the slice bar will cause smoke with
the very best type of stoker. In a certain plant using a highly volatile
coal and operating boilers equipped with ordinary hand-fired furnaces,
extension hand-fired furnaces and stokers, in which the boilers with the
different types of furnaces were on separate stacks, a difference in
smoke from the different types of furnaces was apparent at light loads,
but when a heavy load was thrown on the plant, all three stacks would
smoke to the same extent, and it was impossible to judge which type of
furnace was on one or the other of the stacks.

In hand-fired furnaces much can be accomplished by proper firing. A
combination of the alternate and spreading methods should be used, the
coal being fired evenly, quickly, lightly and often, and the fires
worked as little as possible. Smoke can be diminished by giving the
gases a long travel under the action of heated brickwork before they
strike the boiler heating surfaces. Air introduced over the fires and
the use of heated arches, etc., for mingling the air with the gases
distilled from the coal will also diminish smoke. Extension furnaces
will undoubtedly lessen smoke where hand firing is used, due to the
increase in length of gas travel and the fact that this travel is
partially under heated brickwork. Where hand-fired grates are
immediately under the boiler tubes, and a high volatile coal is used, if
sufficient combustion space is not provided the volatile gases,
distilled as soon as the coal is thrown on the fire, strike the tube
surfaces and are cooled below the burning point before they are wholly
consumed and pass through as smoke. With an extension furnace, these
volatile gases are acted upon by the radiant heat from the extension
furnace arch and this heat, together with the added length of travel
causes their more complete combustion before striking