[Stoves] Testing gases from stoves

Sun Apr 5 12:51:03 CDT 2015

Dear Crispin,

See below; 

<snip>

> 
> The helium is detected as a carrier gas as far as I know how it works. More on that in May. 

We can use argon or helium for the bleed gas if one or the other is used as carrier and we can detect the one left as bleed gas. ICP-MS uses argon so lots of labs have argon available. I know I have brought this up before and resulted in no solution - but finding a way to use a bleed gas as surrogate standard is most important for us - as I see it. 

> 
> There is a problem in principle with the method you outline below requiring one rather large change to make it work. 
> 
> The SeTAR's chemical mass balance test method (currently advertised with a heterogeneous test cycle as the standard burn cycle) is not a carbon mass balance method for a very good reason. Carbon in combustion gases, measured and referenced to a known carbon content of the fuel, making the carbon proxy for fuel gas, doesn't work for biomass combustion in cooking stoves. 
> 
> Hood-based or stack-based emissions measurements that rely on a carbon mass balance method will only work if the fuel is fed into the fire continuously and the production of carbonaceous ash ‎is produced continuously in a steady state device. That is definitely not a wood-fired cooking stove's mode of operation. 

Thats because for hood based measurements you have: mg/L X flow rate X dilution = mass of combustion component. LOTS of variables that are poorly controlled and subject to quick changes during the process. To base mg/l per, 0.5 L per minute of surrogate standard cuts all that error because the measure of bleed of a gas can accurately be measured (flow meter and inverted water-filled graduated cylinder filled with the gas for one minute) so emission dilution and velocity is not in the picture. Just two very controlled variables (mg/l and steady surrogate std.). 

> 
> What I mean is that the fire might burn very well at high power but not be burning much carbon at all. That is the issue. Later it might burn at a lower power but mostly combusting charcoal. In effect the fuel composition (composition of what is burning) changes continuously and the calculation of a carbon-based mass balance method assumes that it be constant. ‎It is not obvious at first when looking at the formulas but it is an underlying assumption. The method assigns to the fuel gases an attribute it may not possess (a constant carbon fraction) something known as a 'category error'. 
> 
> Under certain conditions, particularly when igniting wet coal with hot wood, or damp wood, the stove will manufacture oxygen and hydrogen from water from an endothermic water gas shift reaction to such an extent that the oxygen level in the stack exceeds the level in ambient air. In this condition all formulas for combustion performance break down and the answers become ridiculous. In fact they are giving wrong answers long before breakdown is reached but it is not obvious.

If you can accurately measure the combustion gases along with hydrogen, oxygen etc. it is not that they give “wrong answers” but rather there is a wrong interpretation of results. First we need accurate data. Then we re-work the "formulas for combustion performance break down” per the condition and location of that process. First we need accurate data! drawn from different locations during during combustion then develop the formulas for the process. 

> 
> Thus I adopted some years ago a different approach using a total chemical mass balance instead of a carbon mass balance and the calculations not only come right the answers are correct (imagine!)
> 
> A few people have studied this approach in depth, including Yixiang Zhang, Tafedzwe Makonese, David Beritault, Odnoo in Ulaanbaatar and Harold Annegarn. 
> 
> The promise it holds is that the chemical mass balance approach can be applied accurately to the combustion of a fuel that is continuously changing it total chemistry. If you use carbon as a proxy for fuel and the fuel is wood, and the stove is making charcoal, you can calculate a number, no problem, but the number doesn't represent what just happened. 
> 
> Hood-and-velocity systems and mass balance systems both have significant challenges but 'on balance' mass seems to offer some important advantages, mostly to do with the measurement of condensed volat‎ile particles and the issue of wood (well, damp wood) making O2 and H2.  

I think if we can come up with a way to eliminate the “Hoof and velocity” systems entirely  We all need to work towards finding a way to do this IMO because only then will your ‘ on balance’ mass stand a chance of succeding. 

> 
> Paul and Julien and I are considering holding a brief Test Camp at which this would be covered in a minor class on calculating performance outputs. I am in South Africa at the moment discussing changes to the SeTAR method with Harold that will make the approach 'universal', I guess is the right word.  
Wish I could be there!

> 
> Biomass burned in an inhomogeneous manner ‎presents special problems for the tester that haven't been addressed by methods designed for burning solid fuels in a steady state or liquid fuels at a variable rate. 
> 
> The EPA carbon balance methods, for example, give results that are out in excess of 100% of value when applied to some wood stoves, and that is overall with larger errors during the burn. ‎Some overall corrections can be applied after the test but that doesn't address the problem of real time readings which are the basis of gas mass and PM mass totals. 
Surprise! Surprise!
> 
> The chemical mass balance approach seems to offer a way forward.

Regards
Frank in 'hopefully rain today' in dry California. 

> Regards
> Crispin in wonderful windy Muizenberg
> 
> +++++++++
> 
> PDF Granville-Phillips Gas Analysis Products <http://www.hovacinc.com/images/VQM_Comparison_of_Ion_Trap_Quadrupole_Mass_Spectrometers.pdf>
> 
> Try the above. Scroll down to a few pages to see what the mass spec will read 
> 
> Thanks
> 
> 
> 
> 
> Frank Shields
> franke at cruzio.com <mailto:franke at cruzio.com>
> 
> 
>> On Apr 4, 2015, at 7:28 PM, Inversiones Falcon <invfalcones53 at yahoo.com <mailto:invfalcones53 at yahoo.com>> wrote:
>> 
>> Hi Frank I did not get any file, will you pleas send it to me.
>> 
>> Best reagard
>> 
>> Gustavo
>> 
>> From: Frank Shields <franke at cruzio.com <mailto:franke at cruzio.com>>
>> To: Discussion of biomass cooking stoves <stoves at lists.bioenergylists.org <mailto:stoves at lists.bioenergylists.org>>; "franke at cruzio.com <mailto:franke at cruzio.com> com" <franke at cruzio.com <mailto:franke at cruzio.com>> 
>> Sent: Saturday, April 4, 2015 5:12 AM
>> Subject: [Stoves] Testing gases from stoves
>> 
>> 
>> 
>> 
>> 
>> Dear Crispin and Stovers,
>>  
>> I found this to be an interesting report (attached) . I have been looking for a system that would test the combustion gases of interest – and helium.  And I found it!  It think this system (ion trap mass spectrometer or quadrupole mass spectrometer) may be what’s in Crispin’s hand held tester(?).  I think it may teat for helium but, perhaps, is just not set up to do it because  ‘Who would want to test helium along with combustion gases?’ – We Would!
>> This could make testing gases much more accurate and easier.  How I suggest it working is as follows:
>> We pipe in helium at ~ 0.5L/minute into the stove at fuel level in a known and steady rate during the combustion experiment.  So we know the total carbon in the stove from the added fuel and the constant rate helium is leaving the stack.  We monitor the CO, CO2, H, O2 produced during the experiment and determine their concentrations. The volatile carbon not determined will be tars and other unburned carbon.
>> The calculations are: (combustion components) per (helium detected). 
>> This makes it such we do not care about dilution of primary or secondary air. We can make adjustments to them during the experiment and it will not make a difference.  We only need to make sure we have complete mixing where we pull out the gas sample for testing.  The helium is called a Surrogate Standard and knowing that every minute there is 0.5 liters leaving the stack no matter how diluted or how fast it leaves makes that a solid unit of measure we can ratio the components of interest off. We only need to have the makers of combustion measuring device add helium to the other components of interest and we add helium to the front end of the experiment at a steady known rate. 
>>  
>> Regards
>>  
>> Frank
>>  
>> Frank Shields
>> franke at cruzio.com <mailto:franke at cruzio.com>
>> 
>> 
>> 
>> 
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