Is this Fan Suitable for the Duct System?

Posted in: , on 23. Aug. 2014 - 00:36

Dear all

I'm designing an exhaust system for a wood working facility. Please correct me if I'm wrong as I'm new to this industry:

The system needs about 4.8 m^3/s airflow (with main duct velocity of 20m/s and branch velocity of 23 m/s). The total pressure drop due to the ducts and fittings up to fan inlet is about 1500 Pa. For some reasons, the air cleaning device (bag house) has to be installed on the outlet side of the fan . I already have a fan which can handle this flow rate but the total pressure of the fan at this flow rate is about 1800 Pa according to its fan curve. I obtained the fan curve myself based on the AMCA 210-07 standard and pitot traverse method. I believe if I add the pressure loss due to the bag filter, the fan is not suitable. If I assume the bag filter has the pressure drop of about 1500 Pa after the dust cake has been created, I need a fan which can handle total pressure loss of 3000 Pa @ 4.8 m^3/s which means the fan I have is not suitable. (correct me if I'm wrong)

Also please help me with these 2 questions:

1- Given that the flow rate is enough for the job, how can I increase the fan total pressure ? (is it only through increasing rpm?)

2- If I increase the filter area, does it decrease the pressure loss? If yes, how do I calculate the amount of extra filter area?

Thanks in advance

Re: Is This Fan Suitable For The Duct System?

Erstellt am 16. Sep. 2014 - 10:57

what is your dust load?

for wood dust I don't think dust load is too much so increasing filter area will not reduce pressure drop too much.

Are you sure about dust pressure drop calculation? you can decrease duct pressure drop by decreasing air velocity.

If you don't have horizontal duct 16m/s is enough instead of 20 m/s.

Fan Suitable For Dust System

Erstellt am 17. Sep. 2014 - 01:00

This is a totally half-arsed way to design a system.

It would be irresponsible to double the pressure output of an existing fan without knowing the design limits of the various components (shaft diameter, bearing size and type, impeller strength etc.) and without knowing if the impeller is capable of handling dust.

If you know the system pressures and the bagfilter pressure loss, go to a reputable fan manufacturer and ask for a properly engineered selection. If the dust passes through the fan, don’t forget to mention this.

Michael Reid.