[Stoves] Thick wood and MC in micro-gasifiers was Re: Smoke-free biomass pellet fueled stove

[Frank Shields]

Dear Crispin,

 

<snip>

 

>>I was going to make a chart to post here showing the amount of extra
energy involved but have been travelling.

 

Frank: >>So how would you suggest doing this? 

 

Crispin: >>Just to calculate an excess of heat from the missing charcoal and
it s heat value, minus the moisture evaporation needed to dry the fuel. As
Dr Tom has said, it is nearly linear from 0-30% so that is easy.  Just want
to get a handle on the difference. Then look at why it is happening.

 

Frank: Think the combustion of the secondary just confuses and masks much of
the info we want to know about what happens in the primary. Seems we just
need the chemical components of the gases and particles reaching the
secondary. So some questions:

 

Measuring the chemicals, particles, volume of gas produced and moisture
condensed in the collection bag:

 

The chemicals should be CO2, CO, H and amount and ratio to determine the
combustibility of the gases. 

The particles and their makeup determine the carbon and hydrogen that may
not be combusted in the secondary.

The increased volume of gas produced from C, H and O from the wood turning
into gas should indicate something and I think can be accurately measured.

And the moisture in the collected gas that condensed upon cooling is water
vapor and not the hydrogen that separated. This is the LHV calc. we talk
about(?). 

 

All this is for the TLUD stoves Paul and others use. Not for high
temperature Rocket stoves. But what can be learned from the TLUD I would
think can be used for other stoves. 

 

Is this how you look at it?

 

Thanks

 

Frank

 

Frank Shields

Control Laboratories, Inc.

42 Hangar Way

Watsonville, CA  95076

(831) 724-5422 tel

(831) 724-3188 fax

 <http://www.biocharlab> www.biocharlab.com

 

 

 

 

 

 

 

 

 

 

>Not enough heat, hydrogen produced outside the Hot zone, some other
chemical reaction sucking up the available heat (evaporating water), test
equipment with a positive interference.  

 

All possible. I think it may be that wood or coal (which is old biomass) has
H2 driven from it when it is initially heated and this escapes from the fire
zone into a chilled area inside the stove and gets to the chimney (sneakage
as Tom Miles calls it). What a great word.

 

>Question that may seem unrelated: Does the ThermoWorks IR heat detector
work through glass to measure the heat on the other side? 

 

It will if the glass is not selective for IR and is transparent to IR. Maybe
a quartz window would allow it. I did not check if a quartz window absorbs
IR. Anyone know?

 

>But you talk about 'coal' along with biomass. Wonder how all that differs.
Can coal be used in a TLUD? 

 

The clean stoves being rolled out in Ulaan Baatar right now are TLUD's. The
fuel is raw lignite. They burn extremely cleanly right down to ash. There is
a small amount of clinkering in the Silver stove because it tends to run
with too much primary air and a very high temperature. The ash has a high
melting temp so normally it is not a problem (Nalaikh coal). 

 

>>.The problem is at present the calculation methods do not consider that
stove would every produce large amounts of charcoal so the calculated
results are (erroneously) far from the real values.

 

>So it seems the Stove needs be:    ((WBT) + (biochar produced) = (wonderful
rating))

 

Well, the rating given at present is completely at odds with the actual fuel
consumption and that is not tolerable. Simple as that. You can't say a stove
which saves no fuel saves 50% of the fuel because the calculation method has
an error in it. Therefore, buy my stove! Crikey. You think the customer
won't notice?

 

The issue it raises is that of the heat transfer efficiency and the
efficiency as a system. IF the fuel is the consumption of raw fuel per burn
cycle, then the system efficiency is that amount of fuel applied to the work
done. If you want to chuck out char, that is your business, but that char is
not going to be credited to the stove as a fuel saving. I just saw a kitchen
with a separate charcoal stove used to burn the saved char from a wood fire.
That is smart and is an efficiency, but it is not creditable to the stove
that produces the char, only to the whole system of stoves in that kitchen.
It is quite an interesting problem to define categorically.

 

The two efficiencies (heat transfer and system) are not synonymous. In any
case the way the WBT calculates the thermal efficiency is a proxy for the
heat transfer efficiency, not the HTE so be careful how you state
performance. The actual HTE is quite difficult to establish on a stove.
Using an insulated pot gets a closer answer than most methods, but an
insulated pot gives a misleading answer if you are trying to characterise
the performance of the stove has a cooking device. People don't cook with
insulated pots. So one must decide what the desired metric is. Unfortunately
at present the WBT's calculate fuel consumption from the energy used in the
heat transfer calculation instead of the other way round (which would be
normal):

 

Fuel consumed, work done => efficiency

 

Not:

Work done, efficiency => fuel consumed

because it allows unanticipated errors to be introduced.

 

We have much work to do. I wonder how efficiency we can be about it!

 

Regards
Crispin

 

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