[Stoves] Smoke-free biomass pellet fueled stove

[Crispin Pemberton-Pigott]

Dear Tom and All

Penn was I think looking at the Literature if I remember correctly and I can't definitely say he did his own evaluations. I am referring to the cited numbers. I am pretty sure it is in his Masters thesis. 

I agree completely with what you say about the TLUD char. I have seen stoves that do a good job of self-extinguishing in terms of smoke though the char burn continues so the extinguishing time will change the LHV. An open fire has everything from torrefied wood to black carbonaceous ash. 

I was concerned about the calculation methods (as usual) when I saw a rice hull gasifier being tested and the char heat value was given as 29.5 MJ/kg which is the default value in the WBT 4.1.2. That is clearly in error as the true value is somewhere near 12. 

When the amount of char is small the result is not much affected but we are seeing so many stoves that can't burn the char that the miscalculation is starting to affect policy making. Over-reporting the char heat content (which is almost always a wild-assed guess (WAG) ) reports an inflated net heat transfer efficiency, if the quantity is significant, by a LOT. Let's talk 40 to 80% error. This is intolerable. 

This error is in addition to the fuel consumption miscalculation referred to earlier. One could say it is a concurrent not a concatenated error as it affects the net heat transfer number not the overall efficiency if the latter is calculated correctly. It is still highly misleading for rice hull gasifiers.

I think it can be corrected. Perhaps Jim J has already done so.

Regards
Crispin
-----Original Message-----
From: "Tom Miles" <tmiles at trmiles.com>
Sender: "Stoves" <stoves-bounces at lists.bioenergylists.org>
Date: Sun, 4 Nov 2012 11:54:00 
To: 'Discussion of biomass cooking stoves'<stoves at lists.bioenergylists.org>
Reply-To: Discussion of biomass cooking stoves
	<stoves at lists.bioenergylists.org>
Subject: Re: [Stoves] Smoke-free biomass pellet fueled stove

Crispin stated, "As Penn Taylor pointed out, the value can range from about
12 to 33 MJ/kg so the real value is going to vary from test to test."

Crispin,
Were Penn's analyses done on charcoal from a combustion stove or a TLUD? It
seems to cover a range from high ash char to high carbon char. 

Has any sampling and analysis been done on the variability of char quality
from TLUD's?    

I have often wondered how consistent the char is from a TLUD. While the
maximum heat treat temperature (HTT) is probably consistent, the time that
the char is exposed to these temperatures probably varies. Degree of
carbonization, which will determine the LHV, will depend on when the cook
decides to quench the char.

Tom



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