[Stoves] Heat from combustion of TLUD gases with char remaining
Paul Anderson
psanders at ilstu.edu
Mon Nov 5 06:25:02 CST 2012
To the List Serv readers, I am forwarding the comments from Dr. Hugh
McLaughlin, Professional Engineer (Chemical), who is not subscribed to
the lists for posting messages.
Paul S. Anderson, PhD aka "Dr TLUD"
Email: psanders at ilstu.edu Skype: paultlud Phone: +1-309-452-7072
Website: www.drtlud.com
On 11/4/2012 8:17 PM, Hugh McLaughlin wrote:
> Gentlemen,
>
> Calculations such as these are called "First Law" calculations because
> they assume all heat is recoverable and a joule is a joule.
> Unfortunately, the second law says "You can't win, you can only break
> even and you have to play" and this is where the battle is won or lost.
>
> At issue is the fact that air is used for the combustion in a TLUD -
> and that air merges with the combustion gases, and they both leave at
> an elevated temperature - and that heat loss dictates the overall
> efficiency of the device. Heat moves out of a TLUD via the heated
> vapors, and the unrecoverable heat in those flue gases dominate the
> thermal balance, in addition to the direct gross losses to the
> atmosphere of heating adjacent air and the specific heat of the stove.
>
> A reasonable rule of thumb is 1 standard cubic foot of air has enough
> oxygen to release 100 Btu of heat )don't know what that is in SI, but
> it is a lot harder to remember ...). The on assumes a mean temperature
> for the exiting flue gases, some unknown amount of excess air for
> combustion, and a relative humidity for the combustion air - and one
> can start to aspire to get that one significant figure that Ron
> referenced.
>
> Good luck,
>
> - Hugh
>
> PS: Remember, the hard part of perpetual motion machines is not
> getting them to run - it is getting them to subsequently stop ......
>
> --- On *Sun, 11/4/12, rongretlarson at comcast.net
> /<rongretlarson at comcast.net>/* wrote:
>
>
> From: rongretlarson at comcast.net <rongretlarson at comcast.net>
> Subject: Re: [biochar] Heat from combustion of TLUD gases with
> char remaining
> To: biochar at yahoogroups.com, "Discussion of biomass cooking
> stoves" <stoves at lists.bioenergylists.org>
> Cc: "Crispin Pemberton-Pigott" <crispinpigott at gmail.com>, "Hugh
> McLaughlin" <wastemin1 at verizon.net>, "Doc Anderson"
> <psanders at ilstu.edu>
> Date: Sunday, November 4, 2012, 5:10 PM
>
> Two lists, Paul, Crispin, Hugh
>
> Below is one way to answer Paul's question more fully on the
> energy content of the pyrolysis gas stream.
>
> To Crispin's example, I add two more important (measurable)
> variables: X, the char yield (%w/w), and MC, the moisture
> content (%)
>
> Paul is being generous in urging use of no more than two
> significant figures. We may be lucky to get one with confidence.
> As Tom Miles has just pointed out, the energy content of the char
> can vary a lot - especially if there is a lot of ash content
> (which depends on the species as well as the max pyrolysis
> temperature. But you see 30 MJ/kg a lot for low ash material -
> and that is assumed here.
>
> Rather than using moisture content MC as a useful variable, in
> order to see the trends most easily, I assume unit increments in
> the initial (now moist) biomass fuel input energy content (Y in
> MJ/kg), starting with 18 MJ/kg for bone dry material. It would
> have been just as easy to vary moisture content by 5% or so for
> each row - but then it would be harder to see the smooth
> variations that exist when you start with the "nice" numbers 30
> and 18 MJ/kg..
>
> The basic equation for the upper matrix entries is Z1= Y - 30 *
> X(%); That for the lower char energy entries is Z2 = 30 * X(%).
> This last is (perhaps surprising until you think about it)
> independent of the input moisture content.
>
> Obviously, the energy difference from the initial 18 MJ/kg for
> various moisture contents comes from the moisture in wet fuel not
> providing any energy.
>
> I have not shown entries in the upper left and lower right - as
> they are not realistic. Since we mostly/often don't know either
> the moisture content or the yield very accurately, this below is
> only to help one get in the right ballpark.
>
> For sure, we should not use any single constant number for
> all fuels and pyrolysis processes for the energy content in the
> pyrolysis gases coming from one kg of fuel. I show in bold below,
> in the middle of the upper matrix, gas energy densities that are
> probably often seen. Repeating, for emphasis: these are values
> for an initial 1 kg of (generally not dry, and not much ash
> content) fuel with two major simplifying (but pretty accurate)
> assumptions of 18 and 30 MJ/kg for the fuel and char - and both
> are assumed bone dry.
>
> Ron
>
>
> *Matrix of Pyrolysis Gas Energy (MJ/kg wet biomass) for six
> possible moisture (%, in rows) and five possible char yields (%,
> in columns)*
>
> *
> * *Char yield (%W); char energy of 30MJ/kg*
> *Moisture %* *Fuel Energy MJ/kg* *15%* *20%* *25%* *30%* *35%*
> *0.0%* *18*
>
> 10.5 9 7.5
> *5.6%* *17*
> 11 9.5 8 6.5
> *11.1%* *16* 11.5 10 *_8.5_* 7 5.5
> *16.7%* *15* 10.5 *_9_* 7.5 6 4.5
> *22.2%* *14* 9.5 8 6.5 5
> *27.8%* *13* 8.5 7 5.5
>
>
>
>
>
>
>
>
> *Matrix of Char Energy (MJ/kg wet biomass) for six possible
> moisture (%, in rows) and five possible char yields (%, in columns)*
>
> *
> * *Char yield (%W); char energy of 30MJ/kg*
> *Moisture %* *Fuel Energy MJ/kg* *15%* *20%* *25%* *30%* *35%*
> *0.0%* *18*
>
> 7.5 9 10.5
> *5.6%* *17*
> 6 7.5 9 10.5
> *11.1%* *16* 4.5 6 *_7.5_* 9 10.5
> *16.7%* *15* 4.5 *_6_* 7.5 9 10.5
> *22.2%* *14* 4.5 6 7.5 9
> *27.8%* *13* 4.5 6 7.5
>
>
>
>
> ------------------------------------------------------------------------
> *From: *"Paul Anderson" <psanders at ilstu.edu>
> *To: *"Discussion of biomass cooking stoves"
> <stoves at lists.bioenergylists.org>
> *Cc: *"Crispin Pemberton-Pigott" <crispinpigott at gmail.com>, "Hugh
> McLaughlin" <wastemin1 at verizon.net>, biochar at yahoogroups.com, "Doc
> Anderson" <psanders at ilstu.edu>
> *Sent: *Sunday, November 4, 2012 7:27:11 AM
> *Subject: *[biochar] Heat from combustion of TLUD gases with char
> remaining
>
> Stovers and Biochar-ites,
>
> Crispin has made a very useful comment that should not be buried
> under a
> Subject/Thread called Re: [Stoves] Smoke-free biomass pellet
> fueled stove
>
> So I have started a new thread and invite comments from those who
> know
> much more about this than I do. Can Aprovecho or CSU or ISU (Iowa) or
> U of Dayton or others confirm, adjust or reject the calculations?
>
> Even if the numbers change a little, I believe this could be
> important. We do want to see how it is useful.
>
> Paul
>
> Paul S. Anderson, PhD aka "Dr TLUD"
> Email: psanders at ilstu.edu </mc/compose?to=psanders%40ilstu.edu>
> Skype: paultlud Phone: +1-309-452-7072
> Website: www.drtlud.com
>
> On 11/4/2012 4:59 AM, Crispin Pemberton-Pigott wrote:
> > Dear Paul
> >
> > Have you decided on a favourite value for the heat of combustion
> from the
> > gases developed from a wood fire in the TLUD's? If you have a
> wood at 18.4
> > MJ/kg dry and you have (say) 20% char left at the end, what
> would you
> > consider the heat value per missing kg? Obviously it is not the
> same as the
> > initial wood.
> >
> > So I wanted to explore this with you. Let's set the moisture at
> 15% to be
> > typical of air-dried hot-country fuel wood.
> >
> > Starting with an LHV for the dry wood, the net heat LHV is 15.25
> MJ/kg. If
> > there is 200 g of char remaining, and we treat it as being the
> same as
> > regular hardwood charcoal, we can assign a heat value of 29.5 *
> 0.2 = 5.9 MJ
> > for the remaining char.
> >
> > What remains as heat available is 9.35 MJ. This is from 800 g of
> missing
> > fuel so the energy average per missing gram is 9.35/0.8 = 11.69
> MK/kg or
> > 11.69 Joules per gram.
> >
> > Do you agree with this approach?
> Paul Anderson inserts: I like the approach. But at best we are
> dealing
> with 2 digit accuracy. And it is easier to remember 11 to 12 MJ/kg =
> the pyrolytic heat from TLUD making biochar.
>
> Crispin continues:
> >
> > What it means is that if you put a char-making stove on a scale
> and run it
> > you have a value of heat per g missing from the scale. The
> missing mass is
> > moisture, wood gas and some of the carbon (about 1/2).
> >
> > Using this approach you can determine the net thermal efficiency
> of the
> > flame-to-pot+water. As the amount of char remaining is variable
> and not
> > known until after the test is completed, it is hard to know what the
> > performance is during the test but that is a detail.
> >
> > You can determine if the thermal efficiency has been improved
> should you
> > make changes to the stove body.
> >
> > For those who like details, the heat value of the char is
> usually unknown.
> > It would have to be homogenised and a sample tested in a bomb
> calorimeter to
> > know what it is exactly. As Penn Taylor pointed out, the value
> can range
> > from about 12 to 33 MJ/kg so the real value is going to vary
> from test to
> > test.
> >
> > Regards
> > Crispin
> >
> >
> >
> > _______________________________________________
> > Stoves mailing list
> >
> > to Send a Message to the list, use the email address
> > stoves at lists.bioenergylists.org
> </mc/compose?to=stoves%40lists.bioenergylists.org>
> >
> > to UNSUBSCRIBE or Change your List Settings use the web page
> >
> http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org
> >
> > for more Biomass Cooking Stoves, News and Information see our
> web site:
> > http://www.bioenergylists.org/
> >
>
> __._,_.___
> Reply via web post
> <http://groups.yahoo.com/group/biochar/post;_ylc=X3oDMTJyM2pmaGF0BF9TAzk3MzU5NzE0BGdycElkAzIyNDM4MDUyBGdycHNwSWQDMTcwNzQxODYxMgRtc2dJZAMxMzkzNwRzZWMDZnRyBHNsawNycGx5BHN0aW1lAzEzNTIwMzkyMzU-?act=reply&messageNum=13937>
> Reply to sender
> </mc/compose?to=psanders at ilstu.edu&subject=Re%3A%20Heat%20from%20combustion%20of%20TLUD%20gases%20with%20char%20remaining>
> Reply to group
> </mc/compose?to=biochar at yahoogroups.com&subject=Re%3A%20Heat%20from%20combustion%20of%20TLUD%20gases%20with%20char%20remaining>
> Start a New Topic
> <http://groups.yahoo.com/group/biochar/post;_ylc=X3oDMTJmcW12aGg1BF9TAzk3MzU5NzE0BGdycElkAzIyNDM4MDUyBGdycHNwSWQDMTcwNzQxODYxMgRzZWMDZnRyBHNsawNudHBjBHN0aW1lAzEzNTIwMzkyMzU->
> Messages in this topic
> <http://groups.yahoo.com/group/biochar/message/13937;_ylc=X3oDMTM3YXRldWkzBF9TAzk3MzU5NzE0BGdycElkAzIyNDM4MDUyBGdycHNwSWQDMTcwNzQxODYxMgRtc2dJZAMxMzkzNwRzZWMDZnRyBHNsawN2dHBjBHN0aW1lAzEzNTIwMzkyMzUEdHBjSWQDMTM5Mzc->
> (1)
>
> Recent Activity:
>
> * New Links
> <http://groups.yahoo.com/group/biochar/links;_ylc=X3oDMTJoZ2hsMThwBF9TAzk3MzU5NzE0BGdycElkAzIyNDM4MDUyBGdycHNwSWQDMTcwNzQxODYxMgRzZWMDdnRsBHNsawN2bGlua3MEc3RpbWUDMTM1MjAzOTIzNQ-->
> 1
>
> Visit Your Group
> <http://groups.yahoo.com/group/biochar;_ylc=X3oDMTJmdnZwcTZnBF9TAzk3MzU5NzE0BGdycElkAzIyNDM4MDUyBGdycHNwSWQDMTcwNzQxODYxMgRzZWMDdnRsBHNsawN2Z2hwBHN0aW1lAzEzNTIwMzkyMzU->
>
> Yahoo! Groups
> <http://groups.yahoo.com/;_ylc=X3oDMTJlM2I5MDFoBF9TAzk3MzU5NzE0BGdycElkAzIyNDM4MDUyBGdycHNwSWQDMTcwNzQxODYxMgRzZWMDZnRyBHNsawNnZnAEc3RpbWUDMTM1MjAzOTIzNQ-->
>
> Switch to: Text-Only
> </mc/compose?to=biochar-traditional at yahoogroups.com&subject=Change%20Delivery%20Format:%20Traditional>,
> Daily Digest
> </mc/compose?to=biochar-digest at yahoogroups.com&subject=Email%20Delivery:%20Digest>
> • Unsubscribe
> </mc/compose?to=biochar-unsubscribe at yahoogroups.com&subject=Unsubscribe>
> • Terms of Use <http://docs.yahoo.com/info/terms/> • Send us
> Feedback
> </mc/compose?to=ygroupsnotifications at yahoogroups.com&subject=Feedback%20on%20the%20redesigned%20individual%20mail%20v1>
> .
>
> __,_._,___
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20121105/0aa91786/attachment.html>
More information about the Stoves
mailing list