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

Frank Shields frank at compostlab.com
Mon Oct 21 16:08:37 MDT 2013


Dear Crispin and Stovers, 

 

<snip>

 

 

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 >] A sticking point. We may end up deciding on a definition of
efficiency because that the one we have a suitable method (at this time) and
not the one we exactly want. Lets be flexible and cautious here or we will
end up with a method that doesn't work - again. My suggestion is to use
E450c based on HHV DAF. Exclude moisture. We get the effects from moisture
when we plot the as-received fuel as it is being used and I think that the
best way to show what wet (or real) wood does. We calculate efficiency using
the HHV values - but report the moisture content and weight loss from the
stock pile in the 6 Box system. This so NGO reviewers picking out a stove
for mass production can 'read between the lines' after comparing the
efficiency values of different stoves. Dean, you and others know better than
I but do we really know what the water in wood really does?  Can we plot the
results of a water boiling test against the same fuel but having increasing
amounts of moisture and see changes? And get a straight line? If we can't
than I think all the calculations regarding dealing with water in the fuel
is not a valid exercise. We should leave that to plotting biomass used. 

 

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. 

[Frank >] Correct - and to make that comparison we need to either 'control'
or 'state' the differences. 

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 >] If variables
cannot be controlled than they need to be stated in the most organized and
transparent means possible. I think that is my 6 Box system but that needs
to be better organized and include a summery such that a reviewer can take a
quick look, decide if a parameter is way out of line and then turn back to
the page that describes that parameter in detail. When we can't control the
variables then that is the next best thing. As you say "not very useful" if
the report is not organized for easy comparison. 

 

 

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. 

[Frank >] True but the only way I see this being done now is fuel savings. 

 

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. [Frank >] If we had a test method
for doing it that worked we could - but we don't. So its fuel savings we
monitor. 

 

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). 

 

[Frank >] Agree - I think for most fuels the ash will be small and is taken
care of if using look-up tables. But should be in mind and used on fuels we
suspect a lot of ash is present. And not necessary for stovers to test their
own stoves during development. Its only really needed when official tests
are done to compare stoves. For one fuel the ash is the same percentage of
the weight of fuel used so will it make a difference if we call it 0% when
it is 15% when used during stove development? 

.  

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 >]  Not sure.. But temperatures > 450 have released all
the energy we say is in the fuel and reactors of a lower temperature (is
there such a thing?) will leave behind un-burned biomass causing efficiency
values to calculate poorer. But if that is how the stove works that is what
it is. So it doesn't matter (to us heartless lab people). 

 

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 >]  agree

 

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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