Re: straw briquettes

[AJH <andrew.heggie@dtn.ntl.com>]

On Mon, 7 Oct 2002 08:00:56 +0300, "elk" <elk@wananchi.com> wrote:

>I've had some experience with straw briquette 'logs' here. About 10 years ago I was processing Nile Perch filleting waste to fishmeal & used compressed straw logs as a fuel for clarifying fish oil by-product (to be used as boiler fuel).
>
>Though hard and dense- with an attractive glaze to the surface- these logs could in no way be compared favourably with wood as a fuel. They expanded upon burning and created much smoke, little flame and a lot of ash. 
>
>All biomass is not equal when it comes to it's value as fuel.

I actually agree with this last sentence, despite Tom Reed having said
all biomass having the same energy density on an ash free, dry basis,
there is little doubt wood is amongst the easier to burn cleanly.

The difference is probably all to do with the way you set about
burning "difficult" biomass. With the straw briquette being smoky we
can see that a lot of the mass is leaving the fire as unburnt
material. So a more sophisticated (and hence likely more expensive)
combustion device is required. I still feel there is more scope in
making these difficult fuels burn well. I see ELK made a similar
observation in Message-ID: <000001c26aac$364c89a0$9b47083e@42v2501>
when replying to Stephen Gitonga.

The bit about expanding on heating is something I have commented on
before, I think it means that whilst compressed, the straw has not
undergone the change in cell structure that high densification
achieves. Once the binding force is overcome, by heat, the fibers
regain their original shape. To some extent this is true of wood
pellets, whilst these are squeezed to the extent that the cell walls
collapse and the lignin flows and on cooling binds the contents, it
does not pay to put any more power into the process than to form a
skin around the centre. Drop a wood pellet in water and it reverts to
dust fairly quickly.

Ronal commented on my meaning of binder, I was happy to use the term
for both the twine and the glue as it is the end result we are looking
at, and that is to form the material into an energy dense product
which can fuel a stove. The question is which will be cheapest? I tend
to not consider clay because of the extra mass it introduces, though
for local use it must be ideal.

I too would like to see Das' woodgas mantle lamp if pictures could be
put on the website.

AJH

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