{{Unreferenced, date=June 2011 A deaerating feed tank (DFT), often found in steam plants that propel ships, is located after the main condensate pump and before the main feed booster pump. It has these three purposes: # Remove dissolved oxygen (“air”) from the condensate # Pre-heat the feedwater # Provide a storage/surge volume Based on the relevant theoretical

Rankine cycle The Rankine cycle is an idealized thermodynamic cycle describing the process by which certain heat engines, such as steam turbines or reciprocating steam engines, allow mechanical work to be extracted from a fluid as it moves between a heat sourc ...

diagram, there are four main processes, or steps: : 1 to 2 Water pressure is raised from low to high (pump work in) (

feedwater pump A boiler feedwater pump is a specific type of pump used to pump feedwater into a steam boiler. The water may be freshly supplied or returning condensate produced as a result of the condensation of the steam produced by the boiler. These pumps ar ...

) : 2 to 3 Water is heated to boiling (heat input) (

steam generator A Steam generator is a device used to boil water to create steam. More specifically, it may refer to: *Boiler (steam generator), a closed vessel in which water is heated under pressure *Monotube steam generator *Supercritical steam generator or Ben ...

) : 3 to 4 Steam is expanded in the turbine (work out) (

turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating ...

) : 4 to 1 Wet

vapor In physics, a vapor (American English) or vapour (British English and Canadian English; see spelling differences) is a substance in the gas phase at a temperature lower than its critical temperature,R. H. Petrucci, W. S. Harwood, and F. G. Her ...

is condensed (condensing) (

surface condenser A surface condenser is a water-cooled shell and tube heat exchanger installed to condense exhaust steam from a steam turbine in thermal power stations. These condensers are heat exchangers which convert steam from its gaseous to its liquid stat ...

) In the practical implementation of a Rankine cycle, it is common to break the single pump (process 1 to 2) into three pumps: (in water flow order:

condensate pump A condensate pump is a specific type of pump used to pump the condensate (water) produced in an HVAC (heating or cooling), refrigeration, condensing boiler furnace, or steam system. Applications Condensate pumps may be used to pump the condensate ...

, feed booster pump and then

Details

# Dissolved oxygen is removed by injecting auxiliary exhaust steam into the upper portion of the tank (above the feed water level) at roughly the same location (elevation) that the condensate enters the tank. The two are put in close physical contact over a large surface area to maximize heat transfer. As the condensate is heated, the steam drives off any dissolved gasses. Since the steam is injected above the feed water level a steam blanket forms above the water to keep the non-condensable gasses from re-entering the feed water. There is a connection to the gland exhaust system on the upper portion of the DFT that withdraws the oxygen and other non-condensable gasses as they are driven from the condensate. Removing oxygen minimizes

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...

and improves the vacuum quality. # The steam heats the water in the tank # The water in the tank serves as a surge volume within the steam plant. A surge volume allows the plant to change bells (power output level) without running the feed pump dry or flooding the turbines. Consider the plant running in a steady state condition. The bell is increased, more power output demanded, the rate of feed is increased. This draws more water from the condenser, perhaps to the point of being dry and starving the boiler resulting in a loss of propulsion. This is until the water, converted to steam, provides its energy to the turbine and then is condensed in the condenser. The bell is decreased, less power output demanded, the rate of feed is decreased. Since less water is drawn from the condenser the condensate level rises, covering more condenser tubes, reducing the ability of the condenser to maintain vacuum and, if the level is allowed to go high enough, vacuum could be lost and/or water could impinge (and damage) the turbine blades as the turbine normally sits directly above the condenser. Marine steam propulsion Steam power