Dear Crispin,
Your statement "The result is xx g of PM and gases per MJ of useful
heat." is interesting.
I suggest it is the same as PM and gases per MJ per hour. We still need
to know the fuel energy and the amount of fuel that burns per hour to
give the amount of pollutant released. And knowing the numbers of hours
run will give the total PM released during that time. "useful energy" is
the same as time because if the Thermal Efficiency (TE) is high less
time is needed for the stove to operate to finish the job. If all the
heat goes up the stack the stove will need to run all night to heat the
room or boil the water.
But I still look at this differently.
It is fun and educational to look at all these parts separatlyy. And
knowing all the parts is important..We can study the parts forever and
never get around to putting them together and improve real world
problems - and that is what we are doing! Someday we need to look at
the whole picture. Going from 1) what fuel (quality and quantity) is
available, 2) what it is used for (heat, cooking, light), 3) a list of
stoves etc. and a rating system using that fuel type (WBT, light, room
heat produced, PM etc), 4) shape of house, climate, village layout. and
5) how to convince the people to use the stoves. Others know better but
it is something like that.
We need to keep these five steps separate because each has its own major
variables. And to get anywhere we need to control these variables
leaving one available to improve upon- like any experiment. You have a
stove that produces very low PM and has high TE. (TE = useful heat =
time) When looking at just PM major variables (without looking at TE)
is fuel quality, operation, and climate. Lets start our list of
stoves with your stove. Determine fuel quality of the fuel you know
works (moisture, energy, ash, particle size and shape, packing,
resident (fixed for coal) carbon). Make adjustments to moisture and
retest to get the range. Do the same with all the other variables to get
the range your stove works best. Do the same with different operation.
Then operate the stove in a cold room, hot room, add fans to blow air
etc. We have enough variables here to keep us real busy. Stoves running
liquid fuel or pellets have much less work. We need to develop a fuel
chart with all the necessary data on them and then we can determine the
fuel range that will run best in your stove at reduced PM.
Then if we want to add TE (making that the new variable) we work within
the range of fuels and conditions above that produced reduced PM and
find the new range for TE for the intended use be it cooking or heating.
Again -something like that. Find out the (step 4 above) best shape of
house and village layout for the prevailing winds to keep PM from one
stack from going into another house, climate, and the best house shape
to provide even heat and light with best location for cooking is
established. We can introduce our stoves (from a list of stoves)
designed for the available fuel, produces low PM and high TE for heat
and cooking. Only then can we make a difference.
Thats the way I look at it. I realize the above may be way too much. But
I think we can approach it that way and if we only get control over some
of the major variables we may be able to make a difference.
Regards
Frank
Crispin Pemberton-Pigott wrote:
Dear Frank
Your initial reply stimulates a number of things so I will respond later on more of them. The thermal eff one is worth commenting on right awat.
++++++++
Now we are starting to mix things up. I agree that different fuels will
give different results in the same stove. We get different results with
tests around the world using that specific stove and charted for each
fuel selected for testing. Several charts for that same stove based on
each of several fuels. But you throw in "thermal efficiency" (TE) as
another variable. We are not ready to do that yet. Only after we test
many different stoves and compare to the charts of the same fuel used in
the tests do we look at TE to determine how long a stove must operate to
get the same job done. And calculate the PM 2.5 released.
++++++++
I think you are mixing the units in a sort of a way that means I did not explain myself clearly.
In the US many of the regulations state ' xx many g/hr of particles can be emitted per hour'. This is classic EPA-speak. It is intended to limit the _concentration_ of a pollutant in the environment. A more direct one is to limit the ppm in the chimney, something the power stations initially had to meet.
After meeting the ppm requirement by pumping in air to dilute it, the EPA said wait, you are not emitting any less, you are just spreading it around.
So they came up with total emissions per power plant, per stove and per anything else. But stoves amd power plants are very different in size so little ones could emit huge amounts of PM and still boil water and pass inspection. This happened with cars too.
So the next obvious step is to specify the emissions per kg burned because for any fuel, the total heat is related to the mass burned.
Then people pointed out that the fuel moisture varies so they made it per _dry_ kg of fuel. Then the coal people said there is far more ash in coal than wood so they said emissions per kg of dry, ash-free fuel (DAF).
As fuels have completely different moisture, heat and ash contents, (witness for furore over Roger Samson's rice hull stove test) the the emissions per MJ gives a much more meaningful answer and avoids several of the implications above. The moisture issue drops away as it is automatically catered for iñ the LHV as is the kg. There is heat and there are emissions for each quantity of heat.
Now I am saying the thermal efficiency of the stove when used for heating is as relevant. There is little point in saying this stove emits xx g of PM per MJ of heat generated if two stoves have very different thermal efficiencies. This is because one will have to burn much more fuel to deliver the quantity of heat needed.
The result is xx g of PM and gases per MJ of useful heat. The moisture, density, carbon content, ash level, emissions per kg or hour matter not at all. To 'do anything' the emitted PM can be calculated, which means the emissions per hour can be calculated, and so on.
Re the building: for years in Ulaanbaatar they tested the performance of the buuilding (insulation) and attributed it to the stove. Silly, really. It can rate the stove's ability to heat a building at all, but tou can calculate that easily from the thermal efficiency and burn rate of a known fuel.
Thanks for thinking and responding.
Crispin
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--
Frank Shields
Soil Control Lab
42 Hangar way
Watsonville, CA 95076
(831) 724-5422 tel
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[email protected]
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