Grass as fuel

[Grelinette]

I'll come back to this topic: grass clippings as fuel
The debate is now focused on hay, straw and other plants ... but it is not comparable to grass clippings.

What seems interesting to me with grass clippings are 2 things:

- the huge quantities that can be recovered for free and that end up in the dump
- The very nature of this material, certainly very wet, but which has the consistency of a very malleable paste and compressible because ground by the blades of the mower.

To quote the testimonials cited and the ideas proposed, it seems to me quite simple to put this grass paste already ground in a mold such as a metal tube, compressed to the maximum with a lever arm or a hydraulic jack of several tons, then make dry the briquette obtained in full sun in order to burn it in a stove or an insert.

I do not have much time but I am tempted to experience it, without going into an industrial production, because it is the right season to recover grass clippings and to dry the briquettes in the sun!

[izentrop]

Will have to super compress it so that the rest of water does not cause putrefaction, for very little energy withdrawn.
The anaerobic digestion of the grass is 1 at 15000 Kwh / Ha https://www.semencemag.fr/methanisation ... tales.html

[Did67]

I have not read from the beginning.

But it is obvious that when one has a very humid substance (grass clippings it is about 95% of water!), The wet way of the methanisation is to be preferred.

Let's not forget that grass clippings are quite low in C and rich in various elements, including nitrogen. Even dried, combustion will be an ecological disaster: emissions of "smoke", combustion temperature too low, materials too compact with poor draft, nitrogen ends up in some form of NOx, etc ...

The biomasses that are burned are made of carbon fibers and are very poor in other elements: cellulose fibers and / or lignin. Whether Miscanthus, or wood in its various forms (pellets, chips, logs ...).

Already the badly managed combustion of wood, in "machines" where the combustion is badly conducted (regulation by suffocation, without post-combustion, not inverted) is quite catastrophic in terms of emission ... So the dried grass, I dare not even not imagined!

The big difference is that in anaerobic digestion, only C (found in CO₂ and in CH₄) and S [in H₂S, very corrosive even for some stainless!] Emerge, the S being then recovered by the treatment. Other elements, including nitrogen, remain in the digestate and return to the fields.

[Remundo]

in my opinion, we must forget the wet grass briquette that dries in the sun ... it will make a crust on the periphery, while the heart will rot and stay wet.

even half-dry bales of hay left in the open can "go wrong" in the middle making some sort of poor quality silage.

no no, for who wants to burn clippings, it is essential to dry them before, well spread out and in the open air. It is then possible to compact them, but only once dry.

[Did67]

They will always have about 15% water ... It's a matter of hygroscopy.

Cold combustion and emissions "which sting the eyes and scratch the throat" (in short, a stove polluting as much as 500 Euro 6 heavy goods vehicles)

[chatelot16]

my opinion is that what the lawn mower picks is too rich in what it takes to make it rot before drying up ... no hope of making it fuel in a profitable way

methanisation would be the best way to use it if there was a constant flow to run the methanizer ... alas the grass is only available for a period too short that does not make a methanizer profitable

my way of mixing crushed wood is a small method of gaining value for grass mowed just a little better than losing it

[urok]

The anaerobic digestion of the grass is 1 at 15000 Kwh / Ha https://www.semencemag.fr/methanisation ... tales.html

Here is a second good reason not to embark on anaerobic digestion !!

my way of mixing crushed wood is a small method of gaining value for grass mowed just a little better than losing it

yes that's the principle: use it to avoid losing it.

in my opinion, we must forget the wet grass briquette that dries in the sun ...

Exactly !! That is why I recommended a preliminary drying then to form the briquettes from the dry turf. But how ? Is a hand press sufficient?

Let's not forget that grass clippings are quite poor in C and rich in different elements, including nitrogen.

Astonishing answer. If we look at this document: http://www.guidescomposteurs.com/UserFi ... ur%20N.pdf, for hay, the C / N ratio is 25 to 30, hence rather rich in C and poor in N. In addition, the C / N ratio is an indicator of the plant's ability to be broken down by soil microorganisms. . But according to this document: https://fr.wikipedia.org/wiki/Rapport_C/N, it is said that for a C / N> 20 (case of hay), there is not enough nitrogen for there to be decomposition of C. So, a priori, drying should not lead to a decomposition of grass.

The biomasses that are burned are made of carbon fibers and are very poor in other elements: cellulose fibers and / or lignin. Whether Miscanthus, or wood in its various forms (pellets, chips, logs ...).

It is true that the C / N for the straw oscillates between 65 and 120, which would explain its heating value higher than the hay and so that it is more easily found boilers with straw whereas one does not find it for the hay.

The debate is now focused on hay, straw and other plants ... but it is not comparable to grass clippings.

This is the conclusion of the above: we can not compare them. But, the hay seems to me still close to the peat which has (and still is) used as fuel. So, does it work?
To read

[Did67]

Let's not forget that grass clippings are quite poor in C and rich in different elements, including nitrogen.

Astonishing answer. If we look at this document: http://www.guidescomposteurs.com/UserFi ... ur%20N.pdf, for hay, the C / N ratio is 25 to 30, hence rather rich in C and poor in N. In addition, the C / N ratio is an indicator of the plant's ability to be broken down by soil microorganisms. . But according to this document: https://fr.wikipedia.org/wiki/Rapport_C/N, it is said that for a C / N> 20 (case of hay), there is not enough nitrogen for there to be decomposition of C. So, a priori, drying should not lead to a decomposition of grass.

All is relative !!! I was of course talking "fuel". You did not take back the wood, which is in C / N of the order of 200 to 300. There, we have a fuel: practically only carbon ...

Grass clippings, the ratio is less than 10!

Even for composting, it's too much nitrogen. The clippings "liquefy" ... A fortiori as fuel.

The nitrogen present ends up, during combustion, inevitably in NOx, as the S of hydrocarbons gives "acid rain" ... Even the combustion of wood, burned without precaution (piloting, filtrations), despite its poverty in nitrogen, is polluting to very polluting ... Neglecting these aspects is "ecological inconsistency" ...

Another thing is of course the wet decomposition, whether anaerobic (methanization) or aerobic (composting, decomposition in the soil). Here, it is the organisms that take care of this that need, to multiply themselves, to feed themselves properly, of a C / N ratio of about 20 (as we need proteins, animal or vegetable, they need nitrogen in mineral forms - ammonium ions or nitrates). It has nothing to do with a combustion!

[urok]

good evening everyone,
Did67's answer seems to conclude the post. It shows that it does not seem possible to use turf as fuel: low carbon content (and therefore poor calorific value), pollutant (in the form of NOx), corrosive (acid emission, clinker) ... In short , that disadvantages. No wonder we can not find anything about it on the net.
I will continue to leave my grass cut without any use ... Too bad ...
Thank you to everyone who participated in this discussion. It was pleasant.
I think about the next one.
Good continuation.

[chatelot16]

if turf has a c / n ratio of 10 instead of 300 for wood, it's still mainly carbon, so it does not reduce much the calorific value ... it's just that nitrogen increases polution if we burn in a single fireplace and only turf

if you burn in a gasifier with a chemical purification of the gas before burning it became very clean ... a good gas generator can even burn clean pvc!

if we burn the grass or grass mixed in good proportion with crushed wood it works very well! the mixture with wood solves both the problem of drying for good conservation and avoids the problem of pollution by a fuel too rich in nitrogen