uring the net return on economizer investment, all
of these factors must be considered.

When the feed water is such that scale will quickly encrust the
economizer and throw it out of service for cleaning during an excessive
portion of the time, it will be necessary to purify water before
introducing it into an economizer to make it earn a profit on the
investment.

From the foregoing, it is clearly indicated that it is impossible to
make a definite statement as to the relative saving by heating feed
water in any of the three types. Each case must be worked out
independently and a decision can be reached only after an exhaustive
study of all the conditions affecting the case, including the time the
plant will be in service and probable growth of the plant. When, as a
result of such study, the possible methods for handling the problem have
been determined, the solution of the best apparatus can be made easily
by the balancing of the saving possible by each method against its first
cost, depreciation, maintenance and cost of operation.

Feeding of Water--The choice of methods to be used in introducing feed
water into a boiler lies between an injector and a pump. In most plants,
an injector would not be economical, as the water fed by such means must
be cold, a fact which makes impossible the use of a heater before the
water enters the injector. Such a heater might be installed between the
injector and the boiler but as heat is added to the water in the
injector, the heater could not properly fulfill its function.

TABLE 18

COMPARISON OF PUMPS AND INJECTORS
_________________________________________________________________________
| | | |
| Method of Supplying | | |
| Feed-water to Boiler | Relative amount of | Saving of fuel over|
| Temperature of feed-water as | coal required per | the amount required|
| delivered to the pump or to | unit of time, the | when the boiler is |
| injector, 60 degrees Fahren- | amount for a direct-| fed by a direct- |
| heit. Rate of evaporation of | acting pump, feeding| acting pump without|
| boiler, to pounds of water | water at 60 degrees | heater |
| per pound of coal from and | without a heater, | Per Cent |
| at 212 degrees Fahrenheit | being taken as unity|