10.2.2 The condenser air cooling section
In order for the air cooling section to perform efficiently, its position within the condenser and the method of venting must be optimised, and the transport of incondensable gases from the condensing zone must be effective.
This ensures that the air cooling process is achieved with minimum pressure loss through the condenser, and without creating stagnation regions within the main condensing zone or introducing excessive steam penetration into the air cooling section.
Two different air cooling section designs have been adopted in the UK. One extracts incondensable gases and steam from the cooling water inlet end of the condenser; the other uses multi-point extraction from various points along the condenser length; these are illustrated for a pannier condenser in Fig 4.38.
Air cooling sections designed on the first principle have the basic features of a redistribution passage for the steam and incondensable gas mixture in the tube axial direction, together with a baffling arrangement towards the cold end of the condenser to force the mixture across the tubenest before final extraction.
In multi-point extraction condensers, the steam and incondensable gas mixture usually make one transverse pass of the air cooling section tubes, and no facilities are provided for reintroduction of the mixture into the air cooling section tubenest.
Condensers with single and multiple water passes, and with single and multiple vacuum arrangements have adopted both types of air cooling section, and have generally operated satisfactorily.
The single-point air extraction concept generally requires a higher pressure drop in the condenser to ensure satisfactory flow through the air cooling section than the multi-point arrangment, but it reduces the probability of excessive steam carryover to the air extraction equipment.
With the introduction of air extraction equipment which incorporates a direct contact pre-condenser, the carryover of steam is not such a critical factor in determining the air extraction capacity.