| Layout |
- Low height due to the single-vessel design.
- Easy erection, minimum access platforms, insulation and piping required.
- Since Stork's design requires a specific steam compartment within the vessel above the water level, water levels are somewhat lower than in the tray-type design. This causes slightly less storage volume for a comparable application volume.
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- 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.
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| Operation |
- 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.
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- 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.
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| Safety |
- 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.
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- Two-vessel design has drawbacks in robustness and earthquake-resistance.
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| Application |
- Vacuum deaeration and overpressure in one design.
- Deaeration of demineralized water, make-up water or condensate in varying mixtures is possible.
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- Steam velocities are often very high. This is why the dome of a tray-type deaerator has to be of a relatively large size.
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| Maintenance & spares |
- No maintenance required, only gaskets for manholes and gaskets for sprayers are needed as spare parts to enable inspections.
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- Trays need to be replaced after certain periods of operation.
- In the event of unexpected high loads, risk of tray damage exists.
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| Erection |
- The erection procedure is very straightforward. The deaerator can be installed by local personnel, using the accompanying instructions for erection.
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- 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.
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| Performance |
- 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.
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- Similar performance can be attained with a tray-type design, but with a narrower load range.
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| Oxygen scavenger consumption |
- No oxygen scavenger is required in order to comply with guaranteed oxygen levels, thus resulting in a significant operational cost advantage.
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- Oxygen scavenging is often needed to meet performance guarantee levels.
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| Pressure conditions |
- 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).
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- Lower pressure drop of heating steam.
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| Materials |
- More than 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's deaerator vessels can normally be built entirely using carbon steel.
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- Usually the tray-section and the trays have to be entirely made of stainless steel, thereby increasing production costs.
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| Vent condensing |
- Since the water screen created by Stork's sprayer also acts as an internal direct-contact condenser, our deaerator requires no separate vent 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.
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- An additional vent condenser is needed to limit extensive steam loss, and this adds to the cost.
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