[Stoves] Biomass testing questions
list at sylva.icuklive.co.uk
Sun Jan 18 17:00:09 CST 2009
On Sunday 18 January 2009 20:35:02 frank wrote:
> >On the basis that most biomass takes the approximate form C6H7O3
> >shouldn't that be 7.5%?
I'll correct that, it should be C5H703 which does give 6%!
> >You've lost me there, isn't water the only volatile component that
> >just consisted of H and O with no carbon involved?
> That was not very clear. The water is gone with the 105 deg drying
> temperature before I start char making.
I know but pyrolysis is the splitting of the (dry) wood by heat, so
the "split" products have to consist of combinations of H, C and O. Water is
the only compound given off that only consists of H and O.
> I am thinking the fixed char is
> the carbon left after the wood oxygen has gone off taking some carbon as
> CO and CO2 along with it.
Yes but is also takes off groups with carbon, oxygen and hydrogen attached.
The higher the temperature the less oxygen is as a proportion in these
compounds but essentially as you remove H you also remove C and O. So the
fixed carbon slowly decreases and O and H recombine with the C to be
liberated as vapours. I don't know how they separate off the fixed carbon to
> I am thinking I can wrap a metal pipe with heating element and
> insulation. Have a slow flow of N passing through. Read CO, CO2 and O2
> at the exit. Fill with known amount of oven dry fuel (105 - 110 deg. C)
> and purge with nitrogen until the Oxygen level is zero. Add heat slowly
> to 400 deg. C and monitor (plot) the CO and CO2 readings and make sure
> there is no leaks by the O2 at zero. (unless free O2 comes off the
> fuel?). As it stays at 400 deg c the CO and CO2 should go down to zero
> meaning all the wood O2 has left, no more pyrolysed gases,
I doubt any free oxygen would leave the char.
Its true that once the char was held constant at 400C it would stop evolving
offgas, so no further compounds containing O would leave but there would
still be about 20% of the mass of char that would be less volatile substances
containing C, H and O.
> and just
> C+H+N is left to make the Char. So its the amount of oxygen in biomass
> that determines the amount of fixed carbon and amount of pyrolyzed gases
> that will be produced after low temperature lipids and resins have left.
> - I think?
Actually I think it's the ratio of lignin:cellulose:hemicellulose that
determines the char yield at any given temperature.
> I can measure the O2 (calculate from CO + CO2), and have the
> equipment to measure carbon and nitrogen and H is left. But if there is
> still Oxygen left in the char I am on to plan B.
Plan B it is then ;-)
> Just still looking for easily obtained measurements that we can use to
> charatorize the combustion of biomass.
I'm still interested in what you come up with.
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