Fan upgrade at Asnaes power station, Denmark
Howden has upgraded the induced draught fans at Asnaes power station in preparation for the installation low NOx emissions control equipment.
Howden supplied two single-stage induced draught Variax® fans to unit 5 at Asnaes Power Station, Denmark, in 1978. The original hubs were made of spherical cast iron and equipped with forged aluminum blades with erosion shields.
In 2003, Energi E2 decided to upgrade the induced draught fans to make sure that the fans were prepared for the implementation of DNOX. To meet the additional system resistance the fan performance of the existing ID fans needed to be increased by approx. 1500 Pa. The existing induced draught fans did not have enough spare capacity for the increased pressure and therefore the fan installation had to be changed in some way.
The solution chosen was to upgrade of the existing fans, using the latest technology developed, designed and tested in Howden’s centre of excellence for axial flow fans in Naestved, Denmark. The main feature of the upgrade was the installation of blades with a specially designed high-pressure profile. In addition to obtaining optimum pressure, the design also resulted in optimum efficiency.
The blades are made of nodular cast iron that increases the blade life considerably compared to the original aluminum blades. The steel hub was equipped with Howden’s unique oil-lubricated blade bearings and this design optimizes the service intervals. In addition to replacement of rotors, the new high-pressure blade profile also required new guide vanes in inlet box and diffuser as well as minor changes of the stator. A new main motor (customer supply) was also installed. The upgrade did not cause any changes of the duct connection on suction and pressure sides and consequently the existing foundation could be re-used. This considerably reduced the customers’ overall expense in comparison to the installation/delivery of new fans. Moreover of the overall outage time for the power station was reduced.