In 2006, RWE nPower, approached Power System Services as experts in Air preheater performance optimisation, to investigate ways in which Air Leakage can be significantly reduced. The aim of the exercise was to increase efficiency and establish an improved availability certificate for what is a peak demand operating station.
Power System Services produced a design, which effectively doubled the number of Radial divisions both hot and cold plus also Axial divisions, whilst retaining side loading cold end baskets. The Double Sealing was achieved by introducing radial walls onto which Corten Seals could be bolted. The additional seal clearly reduces direct leakage by creating interference to air flow and pressure pockets when passing the Sector plates.
In addition to Double Sealing, the unreliable moving sector plate mechanism was fixed.
Power System Services provided Air Leakage guarantees of 6.5% and achieved <5%. The scheme was a complete success and contributed significantly towards re-certification of available output to 680MW from 600MW. Unit 2 has now been modified in exactly the same way.