Feed Water Heating
Feed water heating has a number of advantagesUsing an open or direct contact feed water heater, where the water is raised to near-steam temperature is the most effective, the cheapest and the most convenient system of de-aeration.
Heating boiler feed water by means of exhaust steam effects a saving of about 1% of fuel for each 6ºC rise in the temperature of the feed water. Consequently, heating the water from 10° to 99ºC saves about 14% fuel.
Besides the fuel saving, heating the feed water increases the actual steaming capacity of the boilers. Using surplus of exhaust steam, above that required for heating the boiler feed water, to heat buildings will realize additional economies. If all of the exhaust steam from engines or turbines can be utilized for heating during the heating season, it will pay to shut down the condenser.
The first and most important use for the exhaust steam is to heat the feed water, since all of the heat of the exhaust steam so utilized is returned undiminished to the boilers.
Some other valuable advantages:
Lower temperature difference at the feed water inlet to the steam boiler reduces thermal stress in the material.
Higher feed water temperature reduces the shrink and swell in the steam drum and simplifies the water level control.