Feed-Water Heater

Apparatus for heating the water which is supplied to a steam-boiler before it enters the latter. The usual kind saves the heat of the exhaust steam from an engine by causing the feed-water to circulate on one side of tubes or a coil, on the other side of which is the exhaust steam. Steam, or water, may be inside the tubes, which are usually of bra on account of corrosion and their conductivity for heat. If water is inside the tubes, the solids deposited from scaling waters at or near 212° will precipitate inside the tubes and stop them up. In one form the exhaust steam is also a steam-jacket to the heater. Temperatures from 150° to 180° F. are usual. The other type of heater is a coil of pipe in the flues which carry hot furnace gases to the chimney. This saves waste heat in boilers which part with their gases at high temperature. Its difficulties are unequal expansion and corrosion of the pipe, and deposit of fluedust from the fuel. Scrapers have to be used for the exteriors of such pipes, which are best of cast iron, to resist sulphur in the gases. In applying heaters of the first type the lo from increased back pre ure on the steam engine to force the steam through the heater must not be allowed to offset the gain from using hotter feed-water. The injector acts as a feed-heater, and there is some pre-heating of feed in the condensing engine. In many cases of the latter, however, a feed heater between the cylinder and condenser would be an economical addition. Feed-Water Heater.