[Stoves] Tar characterization

Sat Nov 12 23:21:17 CST 2016

Hi Frank,

Personally, I'd like a little more fidelity than a TGA and 
ultimate/proximate analysis (but without necessarily going too 
detailed). I think some interesting models of a TLUD could be developed 
with a bit better understanding of the incoming flow composition to the 
combustion zone. The gasification process is not my area of expertise: 
I'd need to speak with my colleagues about what they can measure, beyond 
the "normal" stuff. Because a TLUD is more more uncontrolled than an 
industrial gasifier, I just don't know what sort of starting range of 
species we expect to see.

Cheers,
Paul

On 13/11/2016 3:26 PM, Frank Shields wrote:
> Stoves,
>
> All we really need is to characterize the fuel. The moisture is an 
> easy one. Ash is an easy one. Particle size and shape is an easy two. 
> The organic fraction is what we need to work on. I’m thinking we need 
> to develop a Table of the flammable volatiles being released from the 
> Standard Combustion Chamber (SCC) using a specific biomass at 
> different temperatures when operated to simulate for a specific stove 
> type. Flammability measured per the O2 feed into that heated tube 
> (mentioned before) and measuring temperature increase or CO2 exiting.
> So we have a specific biomass (or a representative biomass) and heat 
> in the combustion chamber using controlled heating coils and 
> controlled air flow and measure the flammability of the gasses 
> leaving. Perhaps end up with a table like this:
> Moisture %
> Size distribution range and uniformity coefficient
> Size shape
> Ash %
> Total volatile matter % dw
> Flammability at 450 deg. C
> Flammability at 550 deg. C
> Flammability at 650 deg. C
>
> Once we start testing and with suggestions from others I am sure we 
> will change the above as we learn more as what tests are such they are 
> shown to effect the combustion process.  Any specific biomass will 
> have their own reading from the above tests. When testing stoves the 
> above results of the fuel used is reported along with the results.
>
> Readings of a specific nature like measuring the chemicals released 
> that change all the time means nothing. It is only the flammability of 
> the released gases thats important. And, perhaps, the pattern of this 
> flammability as temperatures in the combustion chamber or air flow 
> change.
>
> Each different design of a stove tested using a single fuel (single 
> mapping of flammability and characteristics) will result in different 
> degrees of success based on cooking. So it is the job of the stove 
> designer to optimize success using a fuel he/she specifics based on 
> the above tests. The fuels stay the same and the stoves modified to 
> work with a fuel. That stove can be marketed in places where that fuel 
> is available.
>
> I don’t see this being that hard. A local fuel that is close to the 
> established mapping that works best for Pauls TLUD (for example) can 
> be modified to fit using equipment sent to them to do the job. Dry, 
> chip, split or clean - whatever is needed. Low temperature may just be 
> interested in temperatures to 550c while Rockets need the mapping up 
> to higher temperatures.
>
> So no expensive or special equipment needed for testing. Only a lot of 
> research using a Standard Chamber and operated to simulate a stove 
> type. Someone needs to design and build the combustion chamber.
>
>
> Regards
>
> Frank
>
>
>
>
>
>
>
>
>
>
>> On Nov 12, 2016, at 7:58 PM, Paul Medwell 
>> <paul.medwell at adelaide.edu.au <mailto:paul.medwell at adelaide.edu.au>> 
>> wrote:
>>
>> Hi Tami,
>>
>> Thanks for the detailed response.
>>
>> The answer to your question is "the more we can have the better". 
>> Realistically, it would be too easy to end up with too much 
>> information and just become overwhelmed. Even if it were possible to 
>> obtain full speciation measurements of the pyrolysis/gasification 
>> products, it probably isn't practicable to use. For example, in the 
>> case of gaseous turbulent combustion there is already too much of a 
>> compromise needed for methane combustion: detailed kinetic mechanisms 
>> are often too large for CFD...obviously the problem becomes much 
>> worse for other fuels. There is a huge amount of work in the area of 
>> kinetic mechanism reductions (mainly for engine fuels), but detailed 
>> kinetics of tars seems out of the question any time soon.
>>
>> In the first instance, it would be interesting to see a plot of the 
>> mass spectrum of the pyrolysis/gasification products in a TLUD 
>> (before the secondary air inlets) for different operating conditions. 
>> It would also be nice to know the global C/H ratio. We are in the 
>> process of getting a new GC/MS, but only to 300 amu. We'll wait and 
>> see how that goes. The long-term plan is to include this in a model 
>> of the system, as well as subsequent experiments of the specific 
>> details of soot production in the combustion zone. However, this is 
>> all work to be done in the future.
>>
>> Cheers,
>> Paul
>>
>>
>> On 13/11/2016 6:52 AM, Bond, Tami C 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> 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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>>
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