[Stoves] clean fuel

[andrew]

On Sunday 30 December 2007 16:57, Tom Miles wrote:
>Steve wrote
> > Darn, meant to add, are any of our bio mass techniques
> > suitable/clean enough for feeding solid state fuel cells with
> > their gas products.

> Steve,
>
> You may find a few projects using cleaned methane from landfill
> gas to run fuel cells. I reviewed a proposal for one of these
> early this year. The first step is to make a pipeline quality gas
> from landfill gas. The second is to run the fuel cell. The third
> is find a use for the waste heat from the fuel cell. The forth is
> to figure out how to pay for it. At the moment they are highly
> subsidized and highly capital intensive. Fuel cells are running
> $4,500-$6,000/kW compared with $2,000-$3,500 for competing
> renewable technologies.
>
> Having said that all small scale electrical generation options are
> expensive. Gasifiers can run from $2,000-$10,000/kWh. Organic
> Rankine Cycle (ORC) generators are in the upper end of this range.

In deference to Paul I'll attempt to move this bit of the discussion 
to [biconversion], though it will still reference the [stoves] 
thread. All such attempts have failed in the past because that list 
hasn't achieved critical mass and it spans a broad spectrum that 
people already discuss on other forums.

I think establishing the relative total efficiencies of competing 
technologies is relevant to [stoves], especially following Sharon 
Gordon's recent query. With Philip Lloyd's proposition that an 
electric hob transfers 40% of the thermal power into the pot and 
Steve's 30% grid delivery from a thermal power station (inc 
transmission losses) that gives an overall 12%, doesn't even a 3 
stone fire beat that?

Whilst biomass has many disadvantages compared with fossil fuels 
there may well be niches where it scores on quality. I remember one 
of the advantages quoted for the simcoa charcoal plant (which 
operated from 1989 till at least 1999 but I haven't seen recent 
mention, possibly since Lurgi were taken over by air liquide??) was 
the low ash in the jarrah charcoal.

I've recently mentioned on one of the lists that coal formation ( 
from plant material) results from high temperature and compression 
such that water remains liquid and a very good solvent, when it 
finally flashes off it leaves all sorts of heavy metal salts in the 
coal. I wonder if similar is true of natural gas and oil (from 
marine animals??), we do know that all fossil fuels suffer from 
sulphur content. I've seen ss exhausts on a genset running on land 
fill gas corroded by sulphur acids and many domestic flue grills 
corroded to points with both natural gas and oil burners that 
suggest sulphur content is the problem.

In Tom's case above I think they will find sulphur a problem even 
from domestic landfill because of the nature of which bit of the 
phyto or zoo mass the volatile solids derived.

Moving on a bit; it looks like one of the things holding back fuel 
cells is contamination of the membrane which forms the separator 
between the electrodes through which the H2 migrates to find an 
oxygen molecule. So making pure H2 is a key requirement to fuel 
cells.

I am told by a colleague working on dual cycle solid oxide fuel cells 
that a syn gas from the woody part of a tree may well be a suitably 
clean source of hydrogen, the CO then providing the additional 
thermal oxygen step. 

AJH