Design of Externally Fired Furnace

I have taken a project to convert a 2 Ton 3-pass (Pressure Rating 10.54 bar) Steam Boiler of oil fired to wood fired.

Here I have decided to place the furnace externally and the flue is connected to the first pass of the boiler through the duct.

Please guide me in designing the furnace for the above aplication. You reply at the earliest will be helpful to me.

with thanks,
K.P.S

 

[Narasimha]

You can keep about 500,000 BTU/ht/Ft2 heat release rate on Grate and try to maintain about 2.5sec residence time. Vol release rates could be less than 18000 Btu/hr/ft3.

 

Please let me know what is residence time and how can it be calulated.

Here I like to make furnace as a cuboid of dimension(1.6*1.6*1.6)m

Also please tell me,
### Is it advisable to have converging flue duct of rectangular cross section from the external furnace to boiler.

### If the furnace and the flue duct are refractory lined inside and has stationary water Jacket on their outer wall(Water jacket is opened to atmosphere to avoid them being pressure vessel) . Will it affect performance of boiler.

### Since wood has more volatile matter, is it recommanded to give secondary air above the stationary grate. If so at what height from grate we shall give secondary air and will it give positive effect.

with Thanks,
K.P.S