Straw - Rice Husk - Almond Shell
I had a recent letter asking about straw briquettes and how effective they are. Truth is I know nothing much about straw as a bio fuel - so like any PC geek, I do a bit of digging on the web.
So I learn that straw briquettes are an ecologically clean, nontoxic bio fuel.
(1) They are made in a variety of ways - just like wood briquettes. Some are better than others. The highly compressed types are better than the less dense sort.
(2) They come in various shapes and configurations. shown above is the full body circular section with a diameter of 50mm. The length can be varied by order.
(3) The above type have a typical density: of 1.2g/cm3
(4) Typical calorific values vary between 3800 - 4700 kcal/kg or you could multiply by 4.18 to get Kj/Kg 15,884 to 19,646 This is roughly the same heat output as peat briquettes
(5) Ash content typical is 5.8 %. This is high compared to wood, and even higher than some coals. The ash content of woods varies greatly between different fuels. Typically between 0.43 and 1.82 percent of the mass of burned wood (dry basis) results in ash.
Wood based fuels the ash content varies quite a bit between different types of timber product, stemwood 0,4-0,6%, stem bark 2-5% and 1-2% branches. The ash content is highest in those parts of a tree where growth occurs. In the leaves, needles and branches and leading shoot varied between 2 and 6%. Generally though, wood based fuels can be expected to give a 1 to 2% ash content.
For comparison, Typical Ash Content in Coals are:
Anthracite Coal : 9.7 - 20.2 weight %
Bituminous Coal : 3.3-11.7 weight %
Lignite Coal : 4.2 weight %
Straw briquettes are commercially produced in many places, currently on the web are adverts for supply of large quantities from Ukraine among other countries.
Other types of bio briquettes on offer include almond shell and rice husk. If you would like the figures on these - why not go and look them up?