[Stoves] SIZE OF PELLETS

Crispin Pemberton-Pigott crispinpigott at outlook.com
Fri Feb 5 15:35:54 CST 2016


Dear Frank

 

My answer to that question is similar to Julien’s. The mass, thermal conductivity, moisture content, friability and level of volatiles all contribute to make a size selection. 

 

So I made a rule of thumb for coal which is that the fuel particle should weigh 1 gram per kW of maximum output of the combustor.

 

As many briquetted coal products come in the 40-50 g size, that means they are suited to 40-50 kW units which is obviously not a cooking or small space heating stove.

 

I don’t have as snappy an answer for wood pellets but it is a smaller number, perhaps ½ to ¾ the mass.

 

This rule applies well in the 3-50 kW range for low volatiles high carbon fuels like charcoal, coal and semi-coke. Medium carbon fuels with more hydrogen need more protection from excess primary air. Cutting the particle size down helps restrict the airflow. 

 

Regards

Crispin

 

Dear Frank;

Primarily, the size of pellets relates to the size of the stove and its fire.  For a small combustion chamber, the pellets are the right size for primary pyrolysis to finish in a flaming zone before there is substantive char gasification.  If the pellets are too large, then it takes too long for the center of the pellets to reach pyrolysis temperatures.  This relates to the size of the stove, because with a bigger stove, we can accommodate larger fuel pieces such as briquettes and pieces of wood ca. 3-5 cm thick.

Beyond that, are considerations of easy fuel handling, and pellet strength.  We can get denser, stronger pellets if they are smaller.

 

Cheers,

Julien.


-- 

Julien Winter
Cobourg, ON, CANADA

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