[Stoves] Shields E450c as a way to test char-making stoves (attn: GACC testers)

[Crispin Pemberton-Pigott]

Dear Frank and All

 

Franks you are beginning to really get a clear picture and I hope to narrow
this down to the essentials. There are too many paragraphs of extraneous
factors to comment comprehensively and most of it leads nowhere so here are
the critical elements:

 

The first is that how a stove uses fuel is not of interest to the tested in
the sense that fuel goes in and it burns. There is no special case where the
determination of a performance metric is influence by the way and when the
stove uses any portion or all of the fuel. That is up to the designer.
Various products have various merits.

 

Paul >>With that distinction in mind, I then point out the Rocket stoves do
NOT have a separately distinct reactor location. 

 

Frank > We only need two numbers. The energy IN and a value related to task
for calculating efficiency. 

 

The pot does not care about the way the fire consumes the fuel. It receives
heat. If it receives it at an acceptable rate, the stove cooks acceptably. 

 

There is not yet agreement in this group as to what constitutes 'efficiency'
in terms of fuel consumption. There is still talk about 'energy efficiency'
which might refer to the energy released by burning some (not all) of the
fuel and the work done, v.s. the energy that was potentially available in
the fuel 'consumed' whether it was dropped, burned, charred, turned in to CO
or anything else including heat.

 

 

Frank > We lab people determine the energy we place in the Reactor and the
value related to the finished task. What the reactor does with the energy to
finish a Task determines a good working reactor or a wasteful one as
determined via efficiency value. We lab people don't care what the reactor
does with the unit of energy we place into the reactor. TLUD, Rocket, rice
burning, dung burning, char burning - we don't care. That's only of interest
of you stove designers. If you don't like the efficiency value we give you
then you need to make some design changes.   

 

Well said! The test is technology independent, if it is a good one. If the
metrics are correctly chosen, the results can make valid comparisons of
performance, which as I said earlier are primarily defined by the policy
managers or programme managers. That is usually total PMO, total CO and
total fuel consumed per burn cycle.

 

Paul >>In Rocket stoves, the primary and secondary air are so intermixed (in
such widely different proportions from one Rocket stove to another and even
dependent upon using thick pieces of fuel verses many small pieces) that
quantification is not likely to be trustworthy.

 

Not to mention unnecessary and pointless for rating purposes. 

 

Frank > .The efficiency value is a single number that is only related if
things are done 'this way' and cannot be compared to tests done this 'other
way'. I agree this is not the place for discussing the properties of
combustion.   

 

If a test result cannot be compared with other test results obtained in the
same project, they are not very useful. If the test method specifies, by
trying to 'control' variables that really are variable, it needs better
metrics that can take care of those variables while still reporting
comparative performance. It is not true that nearly all variables have to be
controlled. That is only necessary if you have not made a good choice about
what to report.  If you report the fuel consumption for an arbitrary task
that is not relevant to the community of interest, the test has little value
to anyone. If you choose a task that is relevant but which has metrics which
do not reflect relevant parameters, again that is inviting disaster. Stove
testers should not be afraid 

 

Frank > Whatever happens, happens in the reactor. A given amount of E450c
may do a single task like boil water or multi tasks like boil water, produce
biochar, heat a room and give light. As to the number of tasks it does that
only matters if it results in less trips to the corner pile of wood. 

 

It is for this reason that we have to deal correctly with the re-use of
useable fuel. Because it is common to use leftover fuel, we should adapt to
this reality. 

 

Paul >> As I see it, the INITIAL value and purpose of the Shields E450c
proposal should be developed and (hopefully) accepted FOR GASIFIER SITUATION
BASED ON MINIMAL AMOUNTS OF PRIMARY AIR. Maybe later there can be
applications concerning Rockets and other stoves. But first we need to
understand (and accept if correct) how E450c can help us test batch-fed
gasifier stoves.

 

I do not yet see why gasifiers deserve special treatment in terms of
testing. It is a stove, it burns fuel. It produces heat, it conveys some of
it to the pot(s). It produces emissions, it has leftovers (if it is a
biomass stove). Yes there are people interested in the production of char.
This is fine. If people want to know the mass of that char it is easy to
report it. I people want to know the properties of that char, there is a fee
attached above the regular test price. No problem. What do we need to know?
We need to know the amount of new fuel drawn from the pile in the corner
each time the test is replicated. 

 

Frank >  The measure of fuel is determine from the loss in weight from the
stock pile. We start with 100 kg of wet as-received biomass. We determine
the percent moisture so to calculate the dry equivalent of fuel for each
gram of fuel removed. We determine the E450c in that dry fuel so now we have
the E450c for each gram of fuel used. We wrap the stock pile in plastic so
not to lose any moisture between tests. And plot the loss of weight of the
stockpile over time (tasks, days, weeks, months, years) so to determine the
fuel use for each task and for each home. 

 

Exactly! Now Frank, for which stoves do we have to find out anything about
the leftover fuel? Is it only for those that re-use the fuel? It seems to me
that unless there is an extra question asked, there is nearly no reason to
measure the heat content of what is left. 

 

What might be really helpful is a way to turn your simple approach into a
poor man's bomb calorimeter. It may require something like a correction for
ash (which I think you didn't mention but can easily be appended). 

 

I will try to reply directly to Ron Larsen's question about the heat content
of char remaining. People can have any test they want added to the necessary
ones. It just costs more. 

 

Frank >  *For a task(s) using a fixed amount of biomass we just need to get
the reactor to 450c or above.

 

Exactly why?

 

Frank >  *For a task(s) using biomass feed into the reactor until the
task(s) is completed (fuel left over) we then pick out the left over usable
biomass that can be used in the next run. 

 

Do we need to examine it if after each run the mass is the same?  I think
not. If there is a variation, we only need to know after the trio (or more)
or runs is completed.

 

Frank >  We add that to the next run and that reduces the trips to the stock
pile and that shows up in the plotting of the stock pile. 

 

That is exactly the question being asked by programme managers. They want to
see a reduction in that consumption. It is surprisingly easy to determine.
It does not involve trying to characterise the heat content of remaining
fuel because the fuel is either thrown into the next fire or disposed of in
some manner (tossed, sold, ground up for medicines). Tests relevant to that
subsidiary industry can be performed for anyone who wishes.

 

Regards
Crispin

 

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