Feedwater heaters preheat water in steam turbine and locomotive boilers to improve efficiency and prevent thermal shock damage. There are two types: open and enclosed. Open heaters mix steam directly with water, removing corrosion-causing oxygen. Enclosed heaters heat water indirectly through a bundle of pipes in a sealed shell.
A feedwater heater is a component of steam turbine and steam locomotive installations used to preheat water in the primary boiler system. These components help improve the overall thermal efficiency of the boiler and also protect against thermal shock damage. There are two types of feedwater heaters, open and enclosed, both of which use exhaust steam from the locomotive’s turbine or cylinders to heat the water. Open feedwater heaters mix this steam directly with the feedwater which not only serves to heat the water but also removes some of the corrosion causing oxygen from it. Enclosed heaters are constructed much like primary boilers with the water circulating through a series of tubes enclosed in a steam filled shell.
Locomotives and turbines draw the steam that supplies their motive power from large and complex boilers. These boilers heat water in a dense bundle of tubes, causing it to evaporate rapidly and form high-pressure steam. The water used to replenish the spent boiler feed is pumped from holding tanks or a locomotive tender at or near room temperature. Introducing this cooler water into the much hotter boiler can have a number of negative effects. The first is an evident lowering of the boiler water temperature which negatively affects its overall efficiency and the second is a potential damage to the internal structure of the boiler due to thermal shock.
To prevent these problems, a feed water heater is used to bring the water temperature up to an acceptable level before it is introduced into the boiler. The exhaust steam from the locomotive’s turbine or cylinders is typically used to heat the water, further increasing the efficiency of the system. There are two basic types of feed water heaters, namely those with open or closed steam exposure systems.
An open feedwater heater uses a direct exposure system to heat the feedwater. In this system, the water is exposed to direct physical contact with the heating steam. The water is sprayed or cascaded over horizontal trays into a closed vessel. The steam is introduced to the bottom of the vessel and heats the water as it rises. This system has the added benefit of removing a significant amount of the corrosion-causing oxygen from the water before it is pumped into the primary boiler.
Enclosed water heaters are constructed similar to the primary boiler with a tightly packed bundle of pipes placed within a sealed shell. The feed water is pumped through the pipes and the steam is circulated through the shell, thus heating the water indirectly. The water formed from the condensing vapor within the shell is then routed back to the feed water supply tank for reuse.
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