Ron, Paul,
Below; Paul refers to 'equivalency ratio'. This would be the amount of
primary (under fuel air) divided by the theoretical amount of air
(stoichiometric) for complete combustion of that fuel. Then he speaks of
CO2, CO and H2 production and syngas quality and variable fuel moisture
contents. It would be nice to see data that would correlate to his
instance #2. I have yet to see "Syn" gas composition measurements from a
TLUD. "process temperature might be below 500C" Where does this number
come from?
"A lot of CO is emitted by the stove"
Here he refers to CO that fails to be combusted in the burner portion of
a stove making it sound like it is a consequence of conditions that
occur in the fuel bed. "Syn"gas quality does affect burner performance
but burner parameters also affect stack CO emissions.
Instance #3 seems plausible.
Alex
Paul writes;
Ron,
One should look at a stove according to what it is designed to use as
fuel. Let us look, for example, at stoves that process rice hulls.
In a first instance, the stove might simply burn rice hulls. Here we are
talking about direct combustion where an air equivalency ratio situates
close to 1. Such a stove will produce a lot of CO2 and H2O as well as
relatively high levels of CO. The fuel for such a stove is rice hulls.
In a second instance, the air equivalency ratio might be 0.6, the
process temperature might be below 500 C, the moisture of the biomass
might be 20% or more, and too much secondary air might be applied to the
combustion of a dirty syngas containing a lot of CO2 and H2O. Since the
production of CO and H2 is suboptimal, it might make sense in this
instance to burn the char in order to maximize the production of energy.
But unfortunately burning the char has serious problems: a lot of CO is
emitted by the stove, and heat is generated far below the pot. If the
char is burned within this second stove, the fuel for such a stove is
rice hulls.
In a third instance, the air equivalency ratio situates close to 0.3,
the process temperature rises above 800 C, the moisture content of the
biomass situates at 10%, and the supply of secondary air is kept low,
but still adequate, to achieve total combustion of the syngas. Here the
production of CO and H2 is optimized, the temperature of the syngas
prior to combustion at the burner reaches as high as 500 C, and not too
much secondary air is mixed in with the syngas. In this instance, up to
30% of the weight of the rice hulls would still remain as biochar. But
it would make no sense to burn this biochar, since the production and
combustion of the syngas were optimized.
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