[Stoves] Saving the WBT

Crispin Pemberton-Pigott crispinpigott at gmail.com
Mon Aug 19 15:44:55 CDT 2013


Dear Frank

 

It is a difficult question to answer. Do you want the actual energy
available from a particular piece of wood or the heat theoretically
available, or what it would be if it was dry?

 

If the fuel is moist, then the gasification or the volatiles energy has to
evaporate that moisture to get it out of the way. Unfortunately the amount
of gas you can make from a bit of wood literally changes with the moisture
level because the moisture is involved in the chemistry of what happens in
the processes.

 

With respect to coal, I was not even about to get a carbon content of the
'volatiles' let alone an energy figure. 

 

I suspect you are not going to get a good answer, and whatever answer you
get is not going to be very useful in a real world problem.

 

Regards

Crispin

 

 

 

Dear Stovers,

 

 

I am trying to determine the best way to calculate the energy in the Natural
Volatiles. The sample we place in the iron pipe of the oven dried biomass we
can test or 'look up' the energy value. In the char remaining after 450c
deg. (char-ash) we can give that a value of 34.78 kJ/g. Then for the total
NV in the fuel we just subtract the total biomass from the char energy
remaining. All done in the pipe. Then use the energy calculated from the
increase temperature of the water to determine efficiency. 

 

I am still wondering what to do with the moisture in the fuel. Any
suggestions?

It is like the NV fraction but with possible varying results. As Alex
reminded me in his writings there is the water-reaction that can increase
the energy output or the LHV stealing energy from the NV. So depending on
the stove and operator working the catalyst to control the internal body
temperature the water can be a plus or minus.  My thinking now is to just
use the dry NV value as the total energy of the biomass. Like playing golf.
You have a par 5 and you can go above or below depending on your day. The
dry NV value is the value we use and we go above or below 100% efficiency
depending on how good the stove and operator controls the catalyst and if
water is included in with the biomass. 

 

>From the replies it's a bit hard to tell but it seems we are mostly all in
agreement. : )

 

Regards

 

Frank

 

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