<br><br><div class="gmail_quote">On Sun, Oct 17, 2010 at 10:43 PM, Kevin <span dir="ltr"><<a href="mailto:kchisholm@ca.inter.net">kchisholm@ca.inter.net</a>></span> wrote:<br><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div bgcolor="#ffffff"><div><font face="Arial" size="2">What are your thoughts on the optimum moisture
content of biomass feed to a gasifier? On the one hand, with low fuel moisture
content, there is a low endothermic load on teh reaction. On the other hand, a
high moisture content could yield greater hydrogen content in the output
gas.</font></div>
<div> </div>
<div><font face="Arial" size="2">To take things to the limit, what are your thoughts
on feeding a gasifier with torrified wood?</font></div>
<div> </div></div></blockquote><div><br><br>there isn't really any maximum limit on h2o until you are referencing to a particular reactor, and the degree or lack thereof of external heat sources. in principle if you have unlimited external heat, you do not need any combustion internally, and can just crack tars with heat and reduce the chars with steam. this is otherwise called "perfect indirect gasification".<br>
<br>on a more typical downdraft fixed bed air blown gasifier, the optimum moisture content is still going to relate to the degree of external heat being added through the air and fuel, the insulation of whole system, and other particualrs of the reactor. if just a straight through no preheating design, we usually say 15% is ideal (or top, depending on who is resporting). but this assumes a good pull rate. if you are trying to maximize the range of flow, then much less moisture is ideal.<br>
<br>the ideal in all cases, would be to be able to vary the water content in real time, in relation to real temps measured in the reactor. being stuck with one moisture content of the fuel is always non-optimal except for one thin slice area of operation.<br>
<br>i've been surprised how much higher the moisture content can go with a full heat recycling rig like we and others are doing. these are closed top designs, not open top where higher moisture is much easier. we're regularly seeing good operation in the 20-30% moisture range. <br>
<br>here's some numbers from our recent workshop, with caveats for our still figuring out the testing process. the main point here was to get better numbers on the kg/kwh. this required accurate moisture measurements using the oven method (not a spike meter), so the moisture numbers at least are accurate. all are dry basis.<br>
<br>
Current results (subject to modification as we better refine the process):<br><br>
10/13 (Weds)-<br>
Dry Mass Consumed: 31.4 kg<br>
kWh Produced: 24.75<br>
kg/kWh: 1.3<br>
Average MC: ~24% (mass weighted average)<br><br>
10/14 (Thurs)-<br>
Dry Mass Consumed: 26.6 kg<br>
kWh Produced: 21.75<br>
kg/kWh: 1.2<br>
Average MC: ~35%<br><br><br>we still need to get the gas analyzer inline during these runs. we did reach the point where the gas quality was decreasing as fuel moisture increased. this surprised me. the temps in the reactor were still above tar making temps. there wasn't goo in the cyclone collection glass. but the gas was clearly reducing in quality as the amount of work lights we could support was reduced. the why for this we need to explore a bit more.<br>
<br>jim<br><br><br><br><br><br><br><br><br></div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div bgcolor="#ffffff">
<div><font face="Arial" size="2">Thanks!</font></div>
<div> </div>
<div><font face="Arial" size="2">Kevin</font> </div>
<blockquote style="border-left: 2px solid rgb(0, 0, 0); padding-left: 5px; padding-right: 0px; margin-left: 5px; margin-right: 0px;" dir="ltr"><div><div></div><div class="h5">
<div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal;">----- Original Message ----- </div>
<div style="background: rgb(228, 228, 228) none repeat scroll 0% 0%; font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;">
<b>From:</b>
<a title="jim@allpowerlabs.org" href="mailto:jim@allpowerlabs.org" target="_blank">jim mason</a>
</div>
<div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal;"><b>To:</b> <a title="gasification@bioenergylists.org" href="mailto:gasification@bioenergylists.org" target="_blank">gasification@bioenergylists.org</a>
</div>
<div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal;"><b>Sent:</b> Monday, October 18, 2010 2:08
AM</div>
<div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal;"><b>Subject:</b> [Gasification] the most
important thing (quite possibly) i'velearned to date</div>
<div><br></div><br><br>there are many variables to move around in a gasifier,
and all of them are<br>important. but once the basics are in order, i'm coming
to the conclusion that<br>the most impactful thing one can do/add/fix to the
basic imbert design is to use <br>the ic engine exhaust to heat the incoming
fuel.<br><br>no, i don't have any numbers on this yet (we hope to get these
soon), but the<br>anecdotal experiences keep piling up. the biggest
flexibility gains i'm finding<br>both in poor fuel shape/size and moisture
tolerance, as well as gas turndown ratio, <br>are from the ic exhaust heat
exchanger. on our rig, this is called the pyrocoil. other<br>rigs call this
something else.<br><br>this is not terribly surprising. the ic exhaust is the
biggest waste heat<br>source we have around a gasifier. in principle, the ic
exhaust has about about<br>3x or 4x the heat available as the outgoing syngas.
the incoming fuel similarly<br>has much more heating capacity than the
incoming air (the multiple i forget at<br>the moment, but i do know the
incoming air can only take up about 1/2 of the<br>heat available in the
outgoing syngas).<br><br>also, the ic exhaust is much hotter than the outgoing
syngas after preheating<br>the incoming air. thus you can use the ic exhaust
to do much more than dry the<br>fuel. you can it to drive the fuel through
pyrolysis, and really, get it up to<br>about 4-500c before it falls into the
hearth proper. this is a big difference<br>from the typical situation of still
moist fuel falling into the hearth.<br><br>not only can you use the ic exhaust
to add a very significant amount of heat to<br>the system, you can also use it
to change the character of pyrolysis in the<br>reactor. a typical downdraft
has very high temp short residence time pyrolysis<br>right on top of the
nozzles. this high temp pyrolysis optimizes the creation of<br>teritary tars,
or refractory tars, which are difficult to crack again (given<br>lots of
double carbon bonds). if you externally drive pyrolysis at lower temp<br>over
longer time, you get more primary and secondary tars, which are easier
to<br>crack downstream (fewer double carbon bonds). this seems to allow
hearth<br>conditions to be less perfect and still get good gas
out.<br><br>using ic exhaust to heat incoming fuel is not a complete get out
of jail free<br>card. but to me it seems the most impactful new thing one can
do on these rigs.<br>it seems to have more of an impact than any other single
thing we've done to<br>date on the gek.<br><br>yes, all of it is important,
and all of it should be tended to, but the above is<br>my current vote for the
biggest bang for the effort. hopefully we can get some<br>proper numbers on
this soon (and prove or disprove the above
conjecture).<br><br>jim<br><br><br><br><br><br><br>------------------------------------------------------------------------------<br>Jim
Mason<br>Website: <a href="http://www.whatiamupto.com" target="_blank">http://www.whatiamupto.com</a><br>Current
Projects: <br> - Gasifier Experimenters Kit (the GEK): <a href="http://www.gekgasifier.com" target="_blank">http://www.gekgasifier.com</a><br>
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<br></blockquote></div><br><br clear="all"><br>-- <br>------------------------------------------------------------------------------<br>Jim Mason<br>Website: <a href="http://www.whatiamupto.com">http://www.whatiamupto.com</a><br>
Current Projects: <br> - Gasifier Experimenters Kit (the GEK): <a href="http://www.gekgasifier.com">http://www.gekgasifier.com</a><br> - Escape from Berkeley alt fuels vehicle race: <a href="http://www.escapefromberkeley.com">www.escapefromberkeley.com</a><br>
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