[Stoves] Alternative to charcoal

Tue Apr 9 04:27:30 CDT 2013

Dear stovers

Wood or charcoal, the eternal discussion at the List; I don’t know if it possible to bring something new to the discussion but I will try.  My experience is from forest in Norway and Africa, not in Canada. About 200 years ago we changed from open fire to cast iron stoves for cooking and heating and 80 years ago, when I was a child some still used open fire connected to chimney for cooking and heating in the rural arias; today there is about 50% more forest in Norway than for 100 years ago caused partly by less use of wood for cooking/ heating and partly from change of grazing animals. When I was in Africa 1984 to 2000 the forest was shrinking due to charcoal production, need of building materials and need of arable land. In Zambia with a population of 13m recently they had about 2m charcoal stoves each using 2.7 kg charcoal average every day. About 15% of adult people were in one or another way involved into the charcoal business. 

To produce 2,7 kg charcoal you need about 10-12 kg firewood, depending on the kiln. 10 kg of wood like pellets or woodchips into a TLUD will give 10 to 15 hours of cooking on the energy generally by charcoal cooking, left in the air around the kiln and in addition giving 2.5 kg biochar. If you change the wood from the forest with pelletized agriculture, forestry and milling waste and combustible waste from household, marked places, and industry, you save quite a lot of forest, and if the charcoal business with their decentralized infrastructure; change from charcoal to pellets and chopped waste wood, they will not lose their jobs. They will also create new jobs, which are extremely needed.

With regards Paal W

From: Crispin Pemberton-Pigott 
Sent: Tuesday, April 09, 2013 7:18 AM
To: 'Discussion of biomass cooking stoves' 
Subject: Re: [Stoves] Alternative to charcoal

Dear Jock

>The numbers I have for wood pellets suggest around 8,000 BTUs per pound. 

There is a pretty comprehensive list of heat values at the back of a WBT spreadsheet. 12,000 would be a a bit about right for charcoal. The heat value of char produced in a TLUD or a fire has not been very well studied. Jim Jetter’s Aug 2012 paper has some values.

The heat value of wood is only what people are going to get from it, not what it would be if it were dried (which also applies to charcoal).

I am in Central Java at the moment and the charcoal in the lab has been sitting around for a while. The average moisture content is 8.8% according the lab lady Julianna. The heat content is 26.7 MJ/kg which is slightly below the 12,000 BTU mark.

The local wood even after months of drying is about 15-16% moisture. With a heat content of about 19.2 MJ/kg dry at 16% it is 15.7 MJ/kg. Lots of woods have a lower heat value than that and many people use damp wood – no doubt about it. It bubbles and dribbles continuously.  So the reality is that what people put into their stoves is often below ½ the heat value of charcoal per kg. Further, the char produced by a TLUD is expected to be 0% moisture if it is used within a day or so it will pay to keep an eye on what exactly is being claimed. Fresh charcoal has a very low moisture level. Most fuelwood does not. That is the comparison I am thinking of. A direct comparison between the average fuelwood as used and locally made charcoal as used is ≈15.5 v.s. 29.5 MJ/kg.

If I put 1 kg of 15% moisture wattle (15.9 MJ/kg) into a TLUD stove and create 20% char (20% of the moist mass) the net heat provided by the fire is 10 MJ/kg. The heat available from the char is still 29.5 so the total is the difference the bit between: 15.9-10 = 5.9 MJ.

If someone wants to switch from wood fuel to a ‘cleaner’ TLUD and that TLUD is not 1.5 times as efficient in transferring heat, their raw fuel consumption will increase.

Regards

Crispin

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