[Stoves] [biochar] [biochar-stoves] A review of chronological development in cookstove assessment methods: Challenges and way forward

Crispin Pemberton-Pigott crispinpigott at outlook.com
Wed Nov 25 22:30:52 CST 2015


Dear Frank

 

This is helpful.

 

I really want to know what I can learn from a TLUD that was loaded with fuel and burned out. If it is possible to get a realistic number for the fixed carbon by operation of a TLUD (special purpose?) instead of having a TGA, this would be of great assistance to simple labs.

 

>From the information below, are you agreeing that running a TLUD in a pyrolysis mode, i.e. low flow air such that it is just able to maintain its combustion, can we get a value for the char that is ‘close enough’ to the actual fixed carbon value?

 

The advantage would be this: we have an unknown fuel – some tree or other. We chop it up and put some into a dish for drying to get the moisture value. 

 

Put some more into the TLUD and pyrolyse it to get a before and after mass. Take a small weighed sample and burn it in the presence of O2 to get the ash %. Calculate backwards to get an ash% for the initial fuel.

 

Now we have the following information either by direct measurement or subtraction:

 

Initial mass

Moisture %

Ash content (dry)

Fixed carbon % of dry mass

Volatile fraction of dry mass

Therefore:

Dry ash-free volatile matter %

Dry ash-free fixed carbon %

 

This is the set of inputs for Hirendra’s method of estimating the ultimate analysis:

 

MASHCON

Moisture

Ash

Sulphur

Hydrogen

Carbon

Oxygen

Nitrogen

 

Because…there are certain truths about biomass content that result in ‘fixed’ ratios.

 

It means with a very simply lab one can get a pretty good estimate (within 1%) of the MASHCON analysis.

 

So, will the TLUD (with thermocouples to confirm the temperature achieved) work as a substitute for the TGA? 

 

Thanks
Crispin

 

 

Dear Crispin and Stovers,

 

Above 450c will get the carbon value above 90% DAF basis when the ash content is low. I also believe that to be true when the ash is high but the Leco measuring CHN I believe may pick up some things from the ash. Oxygen is by difference. And if the char sample being tested sits around can take up moisture (hydrogen and oxygen) so the test for CHN needs to be carefully run. 

 

So I suggest going to 550c to be sure every lab is at least above 450c. 

 

What we are writing about is the Test Method, correct? Every lab doing the same thing and getting the same results. And all being done under N2 Gas in a TGA. This test on a representative sample of the fuel from a specific site and this value used for all labs testing to normalize their results to on the fuel they are actually using. 

 

So we are not talking ‘Representative’. We have defined this carbon as being the ‘fixed carbon’. Unlike the results Tom Reed reported in his book and what the coal people are using where the ‘fixed carbon’ also includes any oxygen and hydrogen etc. etc. in the sample. We have isolated the ‘fixed carbon’ as the fixed carbon in the char. 

 

>From my findings I suggest we give the value as 90% carbon and the rest oxygen and 1 percent hydrogen. But it would be nice to repeat a lot of what Tom Reed did with more appropriate samples for what we are doing. 

  

Drying should be done at 200c - not 105c as with most materials. 

 

Your goal is:

% moisture

% volatiles (550c-N2)

% Total Fixed (calculated)

% ash of the Total fixed to get the (% char DAF)

That DAF sample = 90% of that is carbon + 1 percent H and 9% oxygen - all estimated (until something better comes up).

 

The description of the Real World sample people are going to use along with the analysis above will give labs what they need. All they need to do is collect ‘like’ biomass adjust the moisture and char it under N2 at 550c. Then ash the char produced to estimate the Fixed Carbon in the sample and, using the above estimates, determine the amount of carbon to split into solid-C -> CO and CO -> CO2. Depending on the Task the three fractions are normalized to the Real World fuel - is the way I see it.

 

 

Is this ‘another’ calculation method? Do we need another?

 

Regards

 

Frank

 

Frank Shields

 

 

 

 

 

 

 

 

On Nov 25, 2015, at 3:31 PM, Crispin Pemberton-Pigott <crispinpigott at outlook.com <mailto:crispinpigott at outlook.com> > wrote:

 

Dear Frank and Julien





If you know the pyrolysis temperature is above, say, 550 C, is it true that the remaining char is 'representative' of the fixed carbon content of the fuel? How close is it? What temperature would you say is close enough to give a meaningful fixed carbon number?  





Hirendra Chakbarti is punting a calculation method for ultimate analysis that requires the fixed carbon number. From what I see it requires drying it first because the moisture affects the final dry carbon mass. Still, a mathematical fix might deal with that. 





My specific goal is the fixed carbon content of the original fuel which has a known moisture content, but nothing else save the total mass. 





Thanks

Crispin 





 

Dear Ron and Stovers,

 

My interest is controlling the fuel. This done by 1) collecting fuel like that being used in real World and 2) normalizing the energy value going to the secondary by using pyrolyze gases + (CO -> CO2) values. 

 

I cannot determine any energy efficiency values because this is just one side of the equation. And you do not supply me with the values of this one side as I need them. 

 

The value I am proposing is only useful for energy traveling to another location - secondary. Making char does not require energy, in fact it waste energy. And (bio-)char does not have useful energy, in fact the energy is locked up and cannot be used by soil microbes for 1000 years. So what I propose is not applicatable to what you are talking about and not intended to be so. 

 

Your (bio-)char (not charcoal used for cooking) is not ‘energy’ locked up but should be referred to as carbon. Following the total carbon in the feedstock; separating it into available carbon and non-available carbon (TGA) for optimum then determining the amount actually made from your char-maker is more to what you want. And that being your efficiency values. 

 

But in a World that is connecting fuel energy producing non-available carbon (biochar) and that biochar is made >90% carbon (DAF) I guess it would be ok to assign non-available carbon with an energy value and use in calculations. Lets see if we can do that:

1) we need total energy of the biomass fuel (dry weight)

2) using TGA we need energy of the total char (DAF) 

We assume the char (DAF) is 90+% carbon and assign that an energy value.

3) We determine energy of the pyrolysis gases (total - char)

 4) So thats the total maximum amount of energy assigned to biochar that should be produced in your devise. 

5) You run YOUR device and produce biochar. Ash  a subsample to determine the weight of biochar (DAF). Assign an energy value to it based on biochar (DAF) being >90% carbon. 

 

Now you can calculate the efficiency of your device at producing biochar.

 

Note: If you have wood (dry) and you use the pyrolysis gases for something, you use the CO->CO2 gases for something and use the (Bio-)char left over for something then 100% of the energy in the wood is always used. You are left with efficiency determinations found (compared to that determined by TGA) for making biochar. But if making biochar is found less than expected so to be not very efficient then the non-biochar gases (CO -> CO2) went to join the pyrolysis gases and it still always = all adds up to 100%. You can’t go wrong!

 

Where you can go wrong is if after making the biochar you test it to see if it still has hydrogen and lots of oxygen left indicating not a good biochar and it is then wasted. This is bad.

But if still good for char cooking (due to some volatiles) you are now back to 100% efficiency. You can’t go wrong!

 

100% efficiency every time!

 

Love it!

 

Frank 

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