[Stoves] Tar characterization

Frank Shields franke at cruzio.com
Sat Nov 12 15:09:57 CST 2016


Hi Tami, Stovers,

This is great for someone interested in working on this.

We don’t need it to be over analyzed. As a stove heats up volatiles come off as a function of heat, particle size, air flow and time based on the makeup of the biomass. I don’t think there is a need to know the make-up (cellulose, lipids, oils, lignin etc) but may be helpful. Therefore we may only need the mapping of these volatiles as they come off. 

Heating without oxygen will give the total volatiles that come off and travel to the secondary to ignite and provide heat at the point of cooking. That is one good measurement to get total. A TGA could do this like what Tom Reed did.  

But we need more. Because the volatiles are what is used for secondary combustion we need to map their release as the fuel heats up. I am thinking a Standard Combustion Chamber (perhaps 15 cm dia X  30 cm long) with rings of separate heating elements along the inside from top to bottom and controlled air flow at top or bottom. This is a combustion chamber fitted with only primary air and the gases determined as they leave the chamber that would normally be used for the secondary. These gases are what we measure. Their rate and concentration. With this type of set up I think we could match fuels to different stoves. Flexible enough to simulate any stove type.

How to measure the gases I am not sure about. The helium surrogate could be used to monitor the rate specific gases come off per gram of fuel. But what we really need is the flammability of the gases. I am thinking of a stainless heating tube fitted with heating coil used to weld plastics. Oxygen introduced and combustion gases bled into the oxygen flow and temperature of the stainless tube monitored. Or better might be simply plot the CO2 released from the SS tube. It could all be very simple. 

Regards

Frank

Frank Shields
Gabilan Laboratory
Keith Day Company Inc.
1091 Madison Lane
Salinas CA  93907
(831) 246-0417 cell
fshields at keithdaycompany.com










> On Nov 12, 2016, at 12:22 PM, Bond, Tami C <yark at illinois.edu> wrote:
> 
> Hi Paul, and all,
> 
> Sorry that I have not been keeping up with Stoves discussions….
> 
> We have fussed a bit with trying to characterize the organic matter emitted from wood combustion. 
> 
> What kind of characterization do you want? Full speciation is well-nigh impossible. But one needs to start with the question of what you want to know and why? 
> The problem is that this stuff is complex chemically and doesn’t take well to matching with standards. 
> 
> Brief summary of what I know:
> - GC/MS is really hard for characterization because it is poor at identifying compounds that are large (molecular weight) and polar. Wood organics are both. You’ll get the light organic material, but that’s a very small fraction of the emissions. You can get into derivatization of the emissions before GC/MS and that may get you a little more. See all Jamie Schauer’s, Wolfgang Rogge’s work. Most of it ends up being classified as “UCM” (unresolved complex mixture). 
> - FTIR— have tried a little. Although it nominally gives you functional groups, and occasionally you can see differences between one kind of wood or burning condition and another, it’s not very quantitative. Plus there are a lot of overlaps between the interesting functional groups, so you can’t distinguish some of them.
> - 1NMR— kind of like FTIR— you can sort of see functional groups and that’s about it. 
> - UV-Vis— used for humic matter (and some “tar” isn’t far off that)— Again not quantitative, rather just gives a sense of how strong an absorber it is. You won’t see any structure as you do in UV-Vis of individual compounds. There are so many compounds that the entire spectrum smooths out. 
>     —> From our UV-Vis work we found that most of the stuff dissolves in methanol, not hexane not water. (Chen & Bond, Atmos Chem Physics 2010, open access)
> - 13CNMR— which can get at the carbon skeleton rather than functional groups… tough. You need HUGE sample sizes and they don’t stay suspended because anything concentrated enough to measure wants to precipitate. We ended up using DCM, I think— I’d have to check. And then, the result was not all that interesting: we again couldn’t distinguish the unsaturated bonds, e.g. aromatic vs conjugated but linear bonds. 
> - LC/MS— expensive and full of artifacts— I’ve never gotten into it. Too expensive and haven’t seen the benefit, although I’d be interested if someone tried.
> 
> The question, again, is what you want to know and why. If it’s some kind of physical property of the emissions, you’d be better off measuring that.
> 
> Tami
> 
> 
> 
>> On Sep 2, 2016, at 12:22 PM, Paul Medwell <paul.medwell at adelaide.edu.au <mailto:paul.medwell at adelaide.edu.au>> wrote:
>> 
>> Dear Philip,
>> 
>> Thanks for another great suggestion.
>> 
>> This is also something that is planned. As part of an unrelated project we have been looking at this: we are still in the process of finding a solvent that has a collection yield, that doesn't interfere with (or gives an interference profile that we can correct for) and that OH&S will let us have. Fortunately, for the cookstove work there are fewer constraints than the other project (which is limited to sampling extremely low flowrates). We'll find a solution and share it.
>> 
>> Cheers,
>> Paul
>> 
> 
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