Tom, the rice husk gas composition numbers are actually a wide range in Belonio's handbook, as you suggested. The Belonio tabled are pulled from Kaupp (1984), which are tables for gasifiers, not for TLUDs. As far as I know, there isn't any TLUD rice husk gas composition data anywhere.
Tables copy-pasted below. Table 8. Types and Percentage Composition of Gases Produced from the Gasification of Rice Husk Gasifier at 1000 °C Temperature and at 0.3 Equivalence Ratio. Gas % Composition * Carbon Monoxide, CO 26.1 – 15.0 Hydrogen, H2 20.6 – 21.2 Methane, CH4 0 Carbon Dioxide, C02 6.6 – 10.3 Water, H2O 8.6 – 24.0 * Rice Husk Moisture Content = 10 to 40% Table 9. Composition of Gases Produced from Rice husk Gasifier at 1000 oC Temperature and at Rice Husk Moisture Content of 30%. Gas % Composition * Carbon Monoxide, CO 18.6 – 8.6 Hydrogen, H2 21.5 – 8.7 Methane, CH4 0 Carbon Dioxide, C02 9.5 – 12.6 Water, H2O 18.0 – 21.1 * Equivalence Ratio = 0.3 to 0.6 marc notwandering.com On Sat, Aug 17, 2013 at 6:03 PM, Ronal W. Larson <[email protected]>wrote: > Paul and List: > > Three comments/questions: > > 1. The gas analysis from Belonio was apparently at 1000C in the hot > char, but you believe you are closer to 500 C? > > 2. Is there any way to know what the air equivalency ratio is as you > are operating? even if you are above or below the optimum (of 0.3)? I > guess this is determined by the CO measurements, but I haven't seen any > data for either TLUDs or rockets on that. > > 3. Some reading this exchange may not realize that you light the > pyrolysis gases before adding the burner assembly, then you drop the fan > speed to extinguish the interior burning and can then relight the 80 flame > lets. Other than Belonio, I don't know anyone else doing this. In your > final sentence, people may not realize that your flamelets are still > diffusion type, not premixed. I know no-one getting premixed flames, > either rockets or TLUDs. > > > On Aug 17, 2013, at 5:54 PM, Paul Olivier <[email protected]> wrote: > > It is challenging to try to understand what happens in a char-making TLUD. > My exposure to stoves has been entirely limited to the work of Belonio, > both from a practical and theoretical side. On the theoretical side, the > following is what I have gleaned from Belonio with the help of a young > engineer from the University of Delft. I throw this out to the list with > great trepidation, since I have only been working on this reflection for > about a week. > > Temperature is very important, and it is generated as C reacts with O2 > giving rise to CO2 (initial combustion that supplies heat to the process). > The O2 is supplied from the primary air and from the H2O within the > biomass. The temperature has to be high enough to optimize the endothermic > reactions that take place within the process. The endothermic reactions are > the water gas reaction (C combines with H2O to form CO and H2) and the > Boudouard reaction (C combines with CO2 and to form CO). If the > temperature is high enough, C will not combine with H2 to form methane. If > the temperature is high enough, there will be little tar and oil formation. > The goal is to create a high percentage of CO and H2. > > Then there is the moisture content of the biomass. A moisture content of > 10% is ideal. If there is too much water in the biomass, water is > transformed from a liquid to a gas within the process, and the process > temperature is lowered. Also if there is too much water, the water gas > shift reaction is favored giving rise to CO2 and H2. So if the moisture > content increases beyond what is optimal, there is less CO, more CO2 and > more H2O in the gas. > > Then there is the amount of oxygen being supplied to the process. If too > much oxygen is supplied, the amount of CO and H2 decreases, and the amount > of CO2 and H2O increases. Excess oxygen burns up CO and H2 within the > reactor. This translates into a big inefficiency, since the heat generated > here is generally quite far away from the bottom of the pot. Part of the > oxygen comes from the water, and the rest from the primary flow of air. An > air equivalency ratio of 0.3 is ideal. > > But air must be supplied uniformly up through through the biomass. > Channeling (too much air in some places and not enough in other places) > severely disrupts the entire process. In such a case, the concept of an > ideal air equivalency ratio becomes somewhat meaningless. Some people > design TLUD stoves that handle all types of biomass. But I only know of > about 4 or 5 types of biomass that are sufficiently uniform to be run > through a TLUD in their raw state. Everything else has to be prepared > (splitting, cutting, chipping or pelletizing) to be rendered sufficiently > uniform. Of all forms of preparation, pelletizing appears to be the best. > > If rice hulls are processed at 1000 C, at an equivalency ratio of of 0.3 > and at a moisture content of 10%, the gas content consists of 26.1% CO, > 20.6% H2, 0% CH4, 6.6% CO2 and 8.6% H20 (numbers from Belonio). This adds > up to 61.9% of the total gas. The remainder is mostly N2. > > The presence of CO2 and H2O in the gas gives rise to a dirty gas. In a > stove test, it would be interesting to measure the CO2 and H2O content of > the gas prior to combustion at the burner. If CO is intimately mixed with > CO2 and H2O, the combustion of CO at the burner is compromised. > > When the gas is burned at the burner, heat is generated by the combustion > of CO and H2. Air is about 21% oxygen and 79% nitrogen, and it takes > considerably less oxygen to burn CO and H2 than other more complex forms of > gas such as methane, propane or butane. The molar ratio of air to gas to > burn the CO and H2 in the above proportions is roughly 1.11 mol/mol. The > mixing ratio of air to gas by volume is roughly 0.42 m3/m3. Also if the gas > prior to combustion has a temperature in excess of 500 C, this facilitates > the combustion of CO and H2. If anyone would like to see these > calculations, I will supply the spreadsheet off-list. > > This might explain why the Belonio burner with the burner housing I added > to it functions reasonably well in spite of the fact that the premixing of > air and gas does not take place. So little secondary air is required, the > gas is hot, and the mixing takes place all along the periphery of the two > off-set rings of burner holes. As the gas exits the 80 burner holes, it > does so under mild pressure and sucks in air from the burner housing. > http://www.youtube.com/watch?v=84qDsbBO9p8 > > I have seen several rice hull gasifiers where gas exits through one large > burner hole in the middle of the burner. This produces a single flame with > a long diffusion tail, and the transfer of heat to the pot under such > conditions cannot be optimal. > > So in conclusion, the process temperature within the reactor should be > higher than 700 C, the moisture content of the biomass should be less than > 12%, the air equivalency ratio should be about 0.3, the biomass should be > sufficiently uniform, the temperature of the gas prior to combustion should > be in the range of about 500 C, the gas prior to combustion should contain > little CO2 and H2O, and the mixing of secondary air with gas should as > thorough as possible. > > Thanks. > Paul Olivier > > > > > On Sun, Aug 18, 2013 at 12:19 AM, Ronal W. Larson < > [email protected]> wrote: > >> >> http://www.et.byu.edu/~tom/classes/733/ReadingMaterial/Jenkins-Baxter.pdf >> >> *"Stoichiometric air fuel ratios …………..for biomass they are 4 to 7,"* >> >> I have seen "6" a lot, and the inverse (fuel to air weights) would be 17% >> >> >> On Aug 17, 2013, at 5:49 AM, Alex English <[email protected]> wrote: >> >> >> Ron, Paul, >> Below; Paul refers to 'equivalency ratio'. This would be the amount of >> primary (under fuel air) >> >> *[RWL: Alex, thanks _ I wasn't thinking this way. For your >> moving grate design, this term "under fuel air" makes sense. But for >> TLUDs, I believe the term "under" makes less sense, as all the O2 is used >> up at the pyrolysis front, regardless of its magnitude in volume per unit >> time. Since it would seem that CO needs about half the oxygen as CO2 >> (except some O2 is coming from the biomass and we have to account for H2 >> going to H2O), maybe a number near half (meaning the 30% and 60% numbers >> below) makes sense. Or, maybe Paul's definition of equivalency ratio >> includes excess air - not stoichiometric air. Paul - do you have a cite we >> can go to?* >> * >> * >> >> 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? >> >> *[RWL: I am going to stay away from this, due to press of other >> business. The above cite with Tom Miles as co-author might have some of >> this. I think the 500 C term means at the pyrolysis front. Would you go >> higher?* >> * >> * >> >> "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. >> *[RWL: Maybe, but I think Paul is repeating what I heard often at >> the Stove Camp. All the stoves burning char (not done in TLUDs usually) >> suffer from very high CO production. (emphasis added below in Paul's >> comment).* >> >> >> >> Instance #3 seems plausible. >> *[RWL: Agreed. but there should be a paper to see the details >> and definitions.] *Whew - this is a good topic - but I need >> something more to read. Thanks to both Paul and Alex. Ron >> >> >> >> 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. >> >> >> >> _______________________________________________ >> Stoves mailing list >> >> to Send a Message to the list, use the email address >> [email protected] >> >> 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://stoves.bioenergylists.org/ >> >> >> >> _______________________________________________ >> Stoves mailing list >> >> to Send a Message to the list, use the email address >> [email protected] >> >> 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://stoves.bioenergylists.org/ >> >> >> > > > -- > Paul A. Olivier PhD > 26/5 Phu Dong Thien Vuong > Dalat > Vietnam > > Louisiana telephone: 1-337-447-4124 (rings Vietnam) > Mobile: 090-694-1573 (in Vietnam) > Skype address: Xpolivier > http://www.esrla.com/ > _______________________________________________ > Stoves mailing list > > to Send a Message to the list, use the email address > [email protected] > > 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://stoves.bioenergylists.org/ > > > > _______________________________________________ > Stoves mailing list > > to Send a Message to the list, use the email address > [email protected] > > 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://stoves.bioenergylists.org/ > > >
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