Fan Selection For Wood Fired Fire Tube Boiler

Now I am Converting A Oil Fired Fire Tube Boiler of 2Ton and 10.54 bar to a Wood Fired Boiler. I have decided to provide Fan for Mechanical Draft.

Please asdvise me whether to select ID Fan or FD Fan.

I have been advised by my friends that use of FD fan is economical in power consumption, blades will not be over heated, discharge rate will be low because density of air is higher than flue gas than in ID Fan, Except that on using FD fan pressure inside furnace will be higher than atm. pressure, so while opening door for charging wood logs on grate, there will be back fire.

Your advice in this regard will be helpful to me.

with thanks
K.P. Sachidhanandhan

 

[Narasimha]

What is the configuration of the boiler? Generally single ID fan is more suitable for such small boilers.

 

[butelja]

It would seem that safety considerations will require the ID fan. As an alternative, have you considered using a stack so you have natural draft?

 

[butelja]

I accidentally submitted my earlier post too soon. Without specific experience to the contrary, it would seem that fouling of the ID fan could be a problem in a wood fired application. That was my reason for mentioning a stack.

 

Respected Sirs,

What Mr.Narashimha says is correct. We often go for single ID fan for small boilers. My Question is Why can't we use only FD fan for such applications, instead of going for ID fan which has many demerits.

I feel demerits in using FD fan is,
## Back fire in furnace, while loading wood logs, since pressure inside furnace is greater than Atmospheric Pressure.

Boiler Specifications Are:
2 Tonnes - 3 Pass - External Furnace Wood Fired -Fire Tube - Horizontal Steam Boiler.


Your valuable ideas and suggestions will be very much helpful to me.
with Thanks,
K.P. Sachidhanandhan
pasachi@hotmail.com

 

[Narasimha]

For such small fans, ID/FD cost wise difference is marginal compared to boiler cost. For external fired and small boilers, you can't make air tight furnace and if it is nor air tight all hot gases will leak into boiler room. This itself is enough to prevent FD use. ID draw backs are not so great as you think. If you can make air tight furnace with air tight fuel feeding and ash removal, yes FD can be used. I don't think anybody does that.

 

[12344]

For Mr. K.P. Sachidhanandhan, using a FDF may not be a problem after all. I have experienced converting oil-fired to wood-fired, bagasse-fired, coco shell-fired, and ricehull-fired boilers. In actual operation using FDF, if you have existing FDF, you may adjust your dampers to regulate the flow of air in the furnace. However, if you have problems with the government regulation about particulate emissions, IDF must be used to utilize multi-cyclone dust collectors. Combination of FDF and IDF is quite uneconomical due to power cost to maintain the atmospheric pressure inside the furnace. Eliminating FDF and opening one side of the furnace provides negative or vacuum furnace. Furthermore, you must select IDF to handle flue gas with accordance with your new combustion calculation using wood with enough contingencies to supply air to the furnace, provide enough static pressure for the losses, and velocity for your dust collector. With this you may not need FD Fan.

 

[Cormoran]

In this case I like ID fan.