From the start in 1982 the Danish power plant Herningvaerket, owned by DONG Energy, was originally a coal fired power plant. The plant has been retrofitted several times and today it is close to meet the target of being a totally CO2 neutral power plant using only biomass for the combustion. In fact, it is one of the largest wood-chip fired power plants in Denmark.
In connection with the latest retrofit in 2009, Herningvaerket contacted Howden for an upgrade of the FD (forced draught) fan. The requirement was to get a fan with a higher pressure performance to match the future operation and at the same time be able to keep the existing motor of 900 kW.
Howden recommended replacing the old hub – diameter 1120 mm with a new and bigger hub – diameter 1250 mm and still keeping the existing impeller outer diameter.
As the Test Block volume was almost unchanged, it was decided to keep the medium pressure blade solution (of course brand new blades were installed). The new hub size made it possible for the Test Block pressure to reach the demanded 7533 Pa.
In order to extend the lifetime of the fan, the new hub was fitted with oil lubricated blade bearings instead of the former grease lubricated ones. At the same time, the old grease lubricated main bearing assembly was upgraded to be oil sump lubricated in a special design, customised to the existing bearing pedestal.
Furthermore, fan regulation was upgraded from mechanical to hydraulic regulation, re-using both the hydraulic cylinder and the hydraulic oil unit from a VARIAX® ID fan replaced earlier.