[Stoves] Re Alexis Belonio article, Energy required to 'make' steam

[Simon and Zoe]

Time I put in a few thoughts:

>From the data given (5 litres of water turned to steam in 1 hr 30 mins) I
calculate that steam generation requires on average 2.4 kW of power.

Of course water injection is used to reduce NOx emissions (Gas Turbines in
particular), due to reduction of combustion temperatures. This reduction is
partly due to vapourisation, but addition of steam is also effective as the
specific heat capacity of steam is high compared to other combustion gases
(double that of CO2).

Of course in this case the energy emitted from the stove is broadly the same
(as a stove with similar combustion), although since the water will not be
condensing onto the pot the latent energy required for boiling is
effectively lost.

We also have slightly more gas flow passing the pot at a lower temperature
and further calcs are required to assess whether the increase in velocity
compensates for the drop in temperature in terms of heat transfer to the
pot!

So a lot of energy is required to generate the steam, the real question is
does the improved mixing and draft generation compensate for this?

I would be interested to know how the stove performs when the steam runs
out, the only rice husk stove I've ever seen burnt incredibly cleanly
without any draft or mixing assistance.

Another test may be to fill the water container but redirect the steam pipe
outside of the combustion area, however I suspect that getting the same
steam generation rate will be difficult without the steam pipe being in the
hot combustion zone (perhaps it could be left in situ and the steam captured
in another pipe which directs it away from the combustion area).

Not sure that I've clarified anything, but it seemed that at least some
comment on the energy required for steam generation was needed.

rgds.

Simon


----- Original Message -----
From: "Crispin Pemberton-Pigott" <crispinpigott at gmail.com>
To: "Stoves" <stoves at listserv.repp.org>
Sent: Thursday, April 05, 2007 2:01 AM
Subject: [Stoves] Re Alexis Belonio article


> Dear Kevin
>
> >I suspect that water reduction, or water dissociation, could have a
> >positive effect on biomass combustion processes, by permitting the
> >formation of intermediate compounds that would burn better, or more
> >completely.
>
> Exactly.  My suspicion is that the 15% moisture content is important, or
was
> for the device that tested cleanest at that moisture level.
>
> If so, the Alex's steam enhanced stove should burn cleanest when the rice
> husks are VERY dry and the steam introduced is 17.5% of the mass of husk
> burned (to give 15% moisture in the gases).
>
> Alex: this is important.  Can you test emissons?  Can you test the
emissions
> when burning very dry husks and air-dried husks?
>
> Can you tune the steam injection to be 17.5% of the mass of the husk
burned?
> This could lead to a very important discovery about cleaning up combustion
> with hot water and give us all a lead on where to look for a test fuel
> moisture level for standardized testing.
>
> Many thanks
> Crispin in Waterloo
>
>
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