September 27, 2007

Upgrade or Replace your ID Fan? Answers in Hot Topic Hour

On September 7 there were hundreds of years of fan experience represented in the presenters and participants in a Hot Topic Hour on booster fans. Existing plants face big challenges when they add scrubbers with 20” w.g. pressure drop and SCR systems with 6” w.g. How do they deal with this increased resistance?

Jim Greenzweig of FlaktWoods summarized the options as follows:

• When adding an SCR and/or FGD System to an existing coal-fired unit, many choices are available for the required fan equipment.

• Improving the condition of the existing fans is one of the lowest cost and most overlooked methods of effectively increasing unit output.

• Blade tip extensions to existing centrifugal fans is the next lowest cost approach, but this normally introduces some efficiency decrease.

• Rotor Retrofits to existing centrifugal fans is the next lowest cost and can provide the opportunity for efficiency gains in some cases.

• When completely new fans are required, both Centrifugal and Axial Fans are normally viable options.

• The choice of which type of fan is best to use involves many factors and is normally not straight forward.

• In many cases, either Centrifugal or Axial Fans could be used for a given application. The choice of which type is used will involve factors such as:

§         Expected load model for the Unit (Base Loaded or Variable)

§         Importance of First Cost vs. efficiency

§         Comfort level with various technology (i.e.: VFD, Axial Fans, etc…)

§         Expectations for future spare parts and maintenance expenditures

§         Personal preference of those doing the evaluation

David Marshall of Howden Variax was on a trip to South America but still managed to connect and provide insights on axial fans for this application. More than 70 percent of the Variax installations are either booster or ID fans. Six hundred and twenty-four have been sold to Chinese power plants and 450 to utilities in the U.S. Germany has been the third largest market with 285 fans.

The decision on whether to choose axial or centrifugal depends on pressure and volume. In general, axial is more competitive when you exceed one million cfm. A two stage axial fan can develop 35” w.g. in each stage, but centrifugal fans can be designed for higher pressures.

The power point presentations are in the FGD Decision Tree. You can view them through the following links.

Jim Greenzweig - FlaktWoods

Continuing Decision Process For: Products

Custom Designed Fans

http://www.mcilvainecompany.com/FGD_Decision_Tree/subscriber/Tree/DescriptionTextLinks/FlaktWoods Hot Topic Hour Sept. 27.htm
 

David Marshall - Howden

Continuing Decision Process For: Products

Booster Fan Design and Materials

http://www.mcilvainecompany.com/FGD_Decision_Tree/subscriber/Tree/DescriptionTextLinks/David Marshall, Howden Variax - Booster Fan Design and Materials - September 27, 2007 Hot Topic Hour.htm