Asnaes - New hub, blades and blade bearings

DONG Energy, the largest Danish utility company, generates electricity for distribution throughout Northern Europe. Howden completed a retrofit of VARIAX® ID fans on the 640MW unit 5 at Asnæs Power Station, Denmark in 2003.

To meet the additional system resistance that occurs when adding an SCR system, the fan performance of the existing ID fans had to be increased by approx. 1500Pa.

To date the upgraded fans and their performance have exceeded the client's expectations. The combination of Howden technology know-how and smooth project execution ensured that the overall outage period for the client was reduced to a minimum.

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Axial fan variax

The challenge

To protect the environment and comply with European environmental legislation, the client had to reduce the emission of oxides of nitrogen (NOx) by installing a selective catalytic reduction (SCR) system. To meet the additional system resistance that occurs when adding an SCR system, the fan performance of the existing ID (induced draught) fans had to be increased by approx. 1500Pa.


The existing VARIAX ID fans were supplied back in 1978; the actual supply consisted of two single-stage fans, ASN-3400/2000S, 990rpm, 6628Pa, each with a 4200 kW motor. The original hubs were made of spherical cast iron and equipped with forged aluminium blades with erosion shields.

The result

As the upgrade did not require any changes to the existing ductwork and foundations the final overall expense was considerably lower than that for installing new fans. The solution also provided the client with more efficient fans and an extension of the recommended service intervals.

The solution

Because the existing ID fans were incapable of meeting the increased pressure a solution with new fans or an upgrade of the existing fans had to be found.

Based on the latest technology developed, designed and tested in Howden's centre of excellence for axial flow fans in Naestved, Denmark, an upgrade solution was provided which did not require any changes to the existing ductwork connected to the fans or the existing foundations.

The main feature of the upgrade was the installation of our specially designed high pressure profile blades. The new blades were made of nodular cast iron that increases blade life considerably compared to the original aluminium. These new blades were fitted to a brand new bolted steel hub, which together with our unique oil-lubricated blade bearings extend service intervals significantly. As well as replacing the existing rotor components, new guide vanes in the inlet box and diffuser were installed and minor changes to the stator implemented.

A new main motor (customer supply) was also installed.


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