A deaerator is a device that is widely used for the removal of oxygen and other dissolved gases from the feed water to steam-generating boilers. In particular, dissolved oxygen in boiler feed waters will cause serious corrosion damage in steam systems by attaching to the walls of metal piping and other metallic equipment and forming oxides (rust). Water also combines with any dissolved carbon dioxide to form carbonic acid that causes further corrosion. Most deaerators are designed to remove oxygen down to levels of 7 ppb by weight (0.005 cm³/L) or less.
Manufacturer Descon Engineering Limited
Design Temperature 120 C
Design Pressure 150 PsiG
Hydrotest Pressure 187 PsiG
Capacity 39.6 T/H
Diameter 2200 mm
Shell Thickness 10 mm
Head Thickness 10 mm
There are two basic types of deaerators, the tray-type and the spray-type
Tray-type (also called the cascade-type) includes a vertical domed deaeration section mounted on top of a horizontal cylindrical vessel which serves as the deaerated boiler feedwater storage tank.
Spray-type consists only of a horizontal (or vertical) cylindrical vessel which serves as both the deaeration section and the boiler feedwater storage tank.
Tray-type deaerator
The typical horizontal tray-type deaerator in picture has a vertical domed deaeration section mounted above a horizontal boiler feedwater storage vessel. Boiler feedwater enters the vertical deaeration section above the perforated trays and flows downward through the perforations. Low-pressure deaeration steam enters below the perforated trays and flows upward through the perforations. Some designs use various types of packing material, rather than perforated trays, to provide good contact and mixing between the steam and the boiler feed water.
The steam strips the dissolved gas from the boiler feedwater and exits via the vent at the top of the domed section. Some designs may include a vent condenser to trap and recover any water entrained inthe vented gas. The vent line usually includes a valve and just enough steam is allowed to escape with the
As shown in picture, the typical spray-type deaerator is a horizontal vessel which has a preheating section (E) and a deaeration section (F). The two sections are separated by a baffle(C). Low-pressure steam enters the vessel through a sparger in the bottom of the vessel.
The boiler feedwater is sprayed into section (E) where it is preheated by the rising steam from the sparger. The purpose of the feedwater spray nozzle (A) and the preheat section is to heat the boiler feedwater to its saturation temperature to facilitate stripping out the dissolved gases in the following deaeration section.
The preheated feedwater then flows into the dearation section (F), where it is deaerated by the steam rising from the sparger system. The gases stripped out of the water exit via the vent at the top of the vessel. Again, some designs may include a vent condenser to trap and recover any water entrained in the vented gas. Also again, the vent line usually includes a valve and just enough steam is allowed to escape with the vented gases to provide a small and visible telltale plume of steam
Deaerator-dome
At the top and in the mid portion of the feed tank an inverted domed vessel of sufficient size as dictated, is attached which is called the deaerator. This portion has internals something like a perforated tray to breakdown the down flow of condensate water from the top into fine globules to separate dissolved gases. The heating steam, which is fed at the lower level of the dome, passes upwards to give good intermixing. A small vent pipe at the topmost point of this dome is provided for venting out the dissolved gases. Some designs of smaller sizes may have a vent condenser to trap and recover any water particles escaping through this vent.
The deaerator dome therefore has connections for condensate water inlet (at one side of the dome near the top end) from previous LP feed heater and also a connection for the deaerating steam from the bottom of the dome (which also incidentally heats the feed water). This steam is generally from an extraction point of the turbine to improve the cycle efficiency. The deaerator therefore i
Feed tank
This is generally a horizontally mounted cylindrical steel vessel with dished ends and with internal and external fittings. The size of the same depends on the unit capacity it is associated with. The cylindrical vessel portion acts as storage for boiler feed water supplying to the suction of the boiler feed pumps from a pipe connected to the bottom of the tank, generally in the mid portion.
During cold start of the unit, it is possible the water in the feed tank may be cold. At that time the water has to be heated to bring it up to normal operating temperature to expel the dissolved gases. For this, a provision of a heater pipe inside the tank longitudinally and at the bottom level is provided. A few vertical pipes on this line are provided with holes to distribute the heating steam uniformly to avoid water hammer in the initial stages of heating. For this normally a connection from auxiliary steam header is provided, since the auxiliary steam is available first after startup of the boiler.
A small bore connection with a pipe line to the full length of the feed tank at the bottom is also provided for injection of chemical liquids.
Oxygen scavengers
Oxygen scavenging chemicals are very often added to the deaerated boiler feedwater to remove any last traces of oxygen that were not removed by the deaerator. The most commonly used oxygen scavenger is sodium sulfite (Na2SO3). It is very effective and rapidly reacts with traces of oxygen to form sodium sulfate (Na2SO4) which is non-scaling.
Only oxygen scavenger i.e. Na sulphite (19P) is used into the Deaerator. All the rest chemicals (scale inhibitor—Nalco 72210—phosphate based & alkaliner NH3 gas) are injected as per demand into the discharge of Feed Water Pump whose specifications are as follow.
Design Temperature 120 C
Design Pressure 150 PsiG
Hydrotest Pressure 187 PsiG
Capacity 39.6 T/H
Diameter 2200 mm
Shell Thickness 10 mm
Head Thickness 10 mm
There are two basic types of deaerators, the tray-type and the spray-type
Tray-type (also called the cascade-type) includes a vertical domed deaeration section mounted on top of a horizontal cylindrical vessel which serves as the deaerated boiler feedwater storage tank.
Spray-type consists only of a horizontal (or vertical) cylindrical vessel which serves as both the deaeration section and the boiler feedwater storage tank.
Tray-type deaerator
The typical horizontal tray-type deaerator in picture has a vertical domed deaeration section mounted above a horizontal boiler feedwater storage vessel. Boiler feedwater enters the vertical deaeration section above the perforated trays and flows downward through the perforations. Low-pressure deaeration steam enters below the perforated trays and flows upward through the perforations. Some designs use various types of packing material, rather than perforated trays, to provide good contact and mixing between the steam and the boiler feed water.
The steam strips the dissolved gas from the boiler feedwater and exits via the vent at the top of the domed section. Some designs may include a vent condenser to trap and recover any water entrained inthe vented gas. The vent line usually includes a valve and just enough steam is allowed to escape with the
vented gases to provide a small and visible telltale plume of steam.
The deaerated water flows down into the horizontal storage vessel from where it is pumped to the steam generating boiler system. Low-pressure heating steam, which enters the horizontal vessel through a sparger pipe in the bottom of the vessel, is provided to keep the stored boiler feedwater warm. External insulation of the vessel is typically provided to minimize heat loss.Spray-type deaerator
As shown in picture, the typical spray-type deaerator is a horizontal vessel which has a preheating section (E) and a deaeration section (F). The two sections are separated by a baffle(C). Low-pressure steam enters the vessel through a sparger in the bottom of the vessel.
The boiler feedwater is sprayed into section (E) where it is preheated by the rising steam from the sparger. The purpose of the feedwater spray nozzle (A) and the preheat section is to heat the boiler feedwater to its saturation temperature to facilitate stripping out the dissolved gases in the following deaeration section.The preheated feedwater then flows into the dearation section (F), where it is deaerated by the steam rising from the sparger system. The gases stripped out of the water exit via the vent at the top of the vessel. Again, some designs may include a vent condenser to trap and recover any water entrained in the vented gas. Also again, the vent line usually includes a valve and just enough steam is allowed to escape with the vented gases to provide a small and visible telltale plume of steam
Deaerator-dome
At the top and in the mid portion of the feed tank an inverted domed vessel of sufficient size as dictated, is attached which is called the deaerator. This portion has internals something like a perforated tray to breakdown the down flow of condensate water from the top into fine globules to separate dissolved gases. The heating steam, which is fed at the lower level of the dome, passes upwards to give good intermixing. A small vent pipe at the topmost point of this dome is provided for venting out the dissolved gases. Some designs of smaller sizes may have a vent condenser to trap and recover any water particles escaping through this vent.
The deaerator dome therefore has connections for condensate water inlet (at one side of the dome near the top end) from previous LP feed heater and also a connection for the deaerating steam from the bottom of the dome (which also incidentally heats the feed water). This steam is generally from an extraction point of the turbine to improve the cycle efficiency. The deaerator therefore i
Feed tank
This is generally a horizontally mounted cylindrical steel vessel with dished ends and with internal and external fittings. The size of the same depends on the unit capacity it is associated with. The cylindrical vessel portion acts as storage for boiler feed water supplying to the suction of the boiler feed pumps from a pipe connected to the bottom of the tank, generally in the mid portion.
During cold start of the unit, it is possible the water in the feed tank may be cold. At that time the water has to be heated to bring it up to normal operating temperature to expel the dissolved gases. For this, a provision of a heater pipe inside the tank longitudinally and at the bottom level is provided. A few vertical pipes on this line are provided with holes to distribute the heating steam uniformly to avoid water hammer in the initial stages of heating. For this normally a connection from auxiliary steam header is provided, since the auxiliary steam is available first after startup of the boiler.
A small bore connection with a pipe line to the full length of the feed tank at the bottom is also provided for injection of chemical liquids.
Oxygen scavengers
Oxygen scavenging chemicals are very often added to the deaerated boiler feedwater to remove any last traces of oxygen that were not removed by the deaerator. The most commonly used oxygen scavenger is sodium sulfite (Na2SO3). It is very effective and rapidly reacts with traces of oxygen to form sodium sulfate (Na2SO4) which is non-scaling.
Only oxygen scavenger i.e. Na sulphite (19P) is used into the Deaerator. All the rest chemicals (scale inhibitor—Nalco 72210—phosphate based & alkaliner NH3 gas) are injected as per demand into the discharge of Feed Water Pump whose specifications are as follow.
2 comments:
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Deaerator
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