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I have seen laboratory documentation from a reputable lab in southeast Asia that a company has achieved a solid fuel product made from landfill material with a high heating calorific value ($CV$) of approximately 10,000 kcal/kg (42 MJ/kg). The technology is referred to as Refuse Derived Fuel (RDF). From what I understand, such calorific values are only even possible with fluid fuels such as liquefied natural gas (etc.) which can get up to 12,000 kcal/kg.

Doing some calculations around the fixed carbon composition of landfill as similar to a question I've asked previously, I found that the fixed carbon ($FC$) content of the feedstock composition must equal approximately 130% to have the CV mentioned above. This number is obviously impossible but I'm very surprised that it was reported by this lab. Similar products usually get a CV of around 2500 - 5000 kcal/kg if they're lucky. There are several formulas to calculate CVs, the one I've used is below and notably only a function of the fixed carbon content to calculate the calorific value [kcal/kg], so perhaps my equation is too simplified?

$$CV = 0.196FC + 14.119$$

The company of course masks the idea saying it's their intellectual property (etc.) but I'm just curious of if this is even possible or should the laboratory's reputation be called into question?

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  • $\begingroup$ It sounds similarly to me like once the cold fusion. $\endgroup$
    – Poutnik
    Commented Dec 8, 2022 at 6:13
  • $\begingroup$ The only chance is for well hydrogenated product and perhaps mistaking gross/net resp. higher/lower CV. See also engineeringtoolbox.com/fuels-higher-calorific-values-d_169.html $\endgroup$
    – Poutnik
    Commented Dec 8, 2022 at 6:17
  • $\begingroup$ Surely a laboratory who have the instruments and expertise to do these tests wouldn't make a calculation mistake like this... $\endgroup$
    – Hendrix13
    Commented Dec 8, 2022 at 6:53
  • $\begingroup$ It may not be a mistake of the lab, but misinterpretation of data at whatever level. Or intention. $\endgroup$
    – Poutnik
    Commented Dec 8, 2022 at 7:00
  • $\begingroup$ Since 2500 kcal/kg is about 10,000 kJ/kg, we could have a mixup of units. $\endgroup$ Commented Dec 8, 2022 at 15:27

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It is clearly possible for fuels to have higher calorific values per kg, even solid ones

Calorific values of fuels are well known and available from many sources. For example, this source list the values of fuel oil as 42.5 MJ/kg (same value if you prefer GJ/tonne) and LPG as 46.3 MJ/kg so there doesn't appear to be a simple obvious limit for fuels. Obviously fuel oil is a liquid and LPG a mildly compressed gas under normal conditions.

But one of the reasons for their higher calorific values is that compounds with larger proportions of hydrogen tend to have higher values than ones with more carbon (which when mostly pure has about 33 MJ/kg).

So solid hydrocarbon compounds should be better. And they are with paraffin wax coming in at about the 42 MJ/kg level.

So there is no good reason to expect even slightly higher values to be impossible. we already have examples fuels with that calorific capacity.

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  • $\begingroup$ LPG LIQUIFIED ... $\endgroup$
    – jimchmst
    Commented Jan 21, 2023 at 23:42
  • $\begingroup$ So it's not just a function of the amount of fixed carbon, like with the equation in my answer? Could you elaborate how these CVs are possible? $\endgroup$
    – Hendrix13
    Commented Jan 22, 2023 at 0:45
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    $\begingroup$ @Hendrix13 In hydrocarbons some of the calorific value comes from the fixed carbon. But quite a lot comes from the hydrogen which burns to water releasing more heat. So you have to take that (and the amount of H) into account to get the total calorific content. $\endgroup$
    – matt_black
    Commented Jan 22, 2023 at 9:55
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    $\begingroup$ @Hendrix13 Worth noting that pure hydrogen has a calorific value of 141.2 MJ/kg. But more complete reaction mechanisms for carbon, hydrogen and oxygen compounds and how to calculate the calorific value are given in this engineering toolbox page. $\endgroup$
    – matt_black
    Commented Jan 22, 2023 at 10:22
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    $\begingroup$ Matt that is what I said. The point is that combustion takes place in the gas phase and LPG has an apparent higher heat because the vaporization energy comes from ambient heat and not from combustion energy. Higher MW fuels require combustion energy to initiate vaporization. $\endgroup$
    – jimchmst
    Commented Jan 30, 2023 at 20:21

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