Stork Spray Type vs a Tray Type
Low total height, because of the single-vessel design.
Easy erection, minimum access platforms, insulation, and piping.
Since the Stork design requires a specific steam compartment within the vessel above the water level, water levels are somewhat lower than in the tray-type design, causing slightly less storage volume for a comparable application volume.
This is usually a two-vessel design or dome-design. It requires more piping, and the connections between vessels makes erection more complicated. More insulation and access platforms are needed.
The storage volume in the lower tank can be used more efficiently, because higher water levels can be used.
During heating-up and filling deaerated water is available, and saturation conditions are present in the whole unit.
There are no thermal stresses as there are no temperature differences present.
The range of operation is approximately 1 to 30.
There are no steam pressure differences.
Sub-cooled drains are easier to handle.
The range of operation is approximately 1 to 4.
Pressure differences between the top- and bottom sections can occur.
The control and safeguarding of the Stork deaerator is very simple and effective.
The large thermal capacity of the stored water results in simple pressure control, the heat-up capacity is high, turbine trip situations can be handled within the Stork standard design.
Low susceptibility to earthquakes thanks to the application of internal deaeration instead of a superimposed deaerator dome.
Single vessel with a minimum of components gives maximum safety.
Two-vessel design has drawbacks in robustness and earthquake-resistance.
Vacuum deaeration and overpressure in one design
Deaeration of demineralized water, make-up water or condensate in varying mixtures is possible.
Steam velocities are often very high. This is why the dome of a tray-type deaerator has to be of a relatively large size.
Maintenance & Spares
No maintenance required, only gaskets for manholes and gaskets for sprayers are needed as spare parts to enable inspections.
Trays need to be replaced after certain periods of operation.
In the event of unexpected high loads, risk of tray damage exists.
The erection procedure is very straightforward. The deaerator can be installed by local personnel, using the accompanying instructions for erection.
Erection is more complex.
If deaerators are placed inside a building, they are usually located at elevated positions. Because of the dome section, the building’s roof needs to be higher when using a tray-type design.
The oxygen content of the boiler feed-water at the outlet of the Stork deaerator will be less than 7 ppb at loads varying between 10% and 110% of design.
Similar performance can be attained with a tray-type design, but with a narrower load range.
Oxygen scavenger consumption
No oxygen scavenger is required in order to comply with guaranteed oxygen levels, thus resulting in a significant operational cost advantage.
Oxygen scavenging is often needed to meet performance guarantee levels.
The deaerator works flawlessly also in “sliding pressure” circumstances.
Due to introducing steam heating below the water level, a small pressure drop in the heating steam occurs (roughly equal to the head of water in the tank).
Lower pressure drop of heating steam.
85 years of experience has shown that, even when applying demineralized water with a minimum pH value of 8, no O2-corrosion occurs in areas where the non-condensable gases come into contact with a carbon steel wall. For this reason Stork deaerator vessels can normally be built entirely using carbon steel.
Usually the tray-section and the trays have to be entirely made of stainless steel, thereby increasing production costs.
A special feature of the Stork deaerator is that it has no separate vent condenser since the water screen created by the Stork sprayer also acts as an internal direct-contact condenser. This enables a high efficiency to be attained. Expulsion of the non-condensable gases cause a slight loss of steam, which usually amounts to about 70 kg/h. The exact amount of steam loss is dependent on the mode of operation and the deaerator capacity.
An additional vent condenser is needed to limit extensive steam loss, and this adds to the cost.