This device, shown in Fig. 93, is designed to utilize the waste
products of combustion as they pass from the furnace to the chimney.
Its use permits a high and consequently efficient temperature under the
boilers and yet saves the excess of heat. It acts also as a mechanical
boiler cleaner, furnishing a settling chamber for the deposit of the
impurities separated by the heat which nearly equals that of the live
steam in the boiler. This device adds largely to the water capacity of
the boiler, frequently containing one-half the weight of the water held
in the boiler itself.
It will be readily understood that the openings between the vertical
tubes are ample for the chimney flue area and that the device is
located between the chimney and the boiler, with the waste furnace heat
passing between the tubes.
[Illustration: Fig. 93.]
The economizer shown in Fig. 93 consists of sections of vertical
4-1/2″ boiler tubes fitted to their top and bottom headers by taper
joints. The top headers are provided with caps over each tube to permit
cleaning out the sediment and remove and replace any tube that may
become damaged. The several top headers are connected together at one
end by lateral openings and the bottom headers are also connected as
shown in cut, having hand holes opposite each bottom header to provide
for cleaning out.
_Mechanical scrapers_ are made to travel up and down each tube to keep
them clear of soot. These are controlled by an automatic mechanism and
driving head, as shown in Fig. 93.
The important features about the economizer are, 1, its adaptability
to any type of boiler, 2, the saving attained by utilizing that heat
which has necessarily been an almost total waste, 3, the purifying of
the water by means of the intense heat and slow circulation of the feed
water.