Comparative VS softwood pellets, advice and feedback?

[Did67]

So we are 16.5 / 3.6 = 4.6 kWh / kg

It is the legal minimum (European standard - ex: Din +)

[Christophe]

The big difference in terms of caloric value is that so-called "dry" logs are, in reality, wetter than pellets: in general, around 20% for logs and, here, 10% for your pellets (provided that 'there is no moisture uptake) ...

Yes quite. In addition, it is known that it is easier to dry softwood (1 year may be enough) than hardwood (2 years minimum) ... hence probably the difference in combustion, I think that in general, hardwood logs still contain more average humidity than coniferous trees ... because people burn it too quickly ... (or worse sell it ... I have already had oak. .. fortunately only for 2 cubic meters).

Short:

a) What is interesting in pellet stoves is that the tank is automatically heated by combustion (via losses in the stove): there is therefore a additional and systematic fuel drying (not necessarily valid with a pellet boiler unless it has a fuel buffer volume near the heating body ... Is this the case with ökofen did67?)

I would like to know the humidity of a pellet that arrives in the brazier!

b) Yes for the recovery of humidity, that's why the pellets are sold in a tightly sealed plastic bag and you have to be careful with storage (especially valid for bulk storage ... eh Did67!)

[Christophe]

10% is a limit.

Commercially, many manufacturers "guarantee" humidity levels below (7%), which allows them to "guarantee" a higher PCI. I have often seen (and used) softwoods at 5,0 kWh / kg.

I had 8% in mind ok ... but 2% humidity difference is very little. I mean that following storage it is easy to make a difference of 2% humidity in a few hours ...

Also, see the remark on the "re-drying" that I just made ...

5.0 kWh? Waw ... It seemed to me that the standard was 4.5 kWh / kg?

[Did67]

... Is this the case with ökofen did67?)

I would like to know the humidity of a pellet that arrives in the brazier!

b) Yes for the recovery of humidity, that's why the pellets are sold in a tightly sealed plastic bag and you have to be careful with storage (especially valid for bulk storage ... eh Did67!)

1) Logs and pellets have nothing to do with humidity: the pellets come from artificially dried sawdust ...

2) I do not think that their humidity level still varies much in the buffer tank: the stay is too short, the space confined, the temperatures low and the pellets are "plasticized" (this is the high extrusion. pressure / temperature which causes a kind of film to form which "holds" the pellets together).

The tank is right next to it, hung on the boiler ... But it is roughly at the temperature of the boiler room. At home, it's around 24 ° ... My boiler is in an insulating cocoon. You can put your hand, it's barely warm ...

3) On the other hand, during storage, there can be a return of humidity. If bags are not waterproof. Or if a silo is not ...

However, I never did a test (with the microwave technique, which I had described on one of the wires dedicated to pellet boilers).

[Did67]

I had 8% in mind ok ... but 2% humidity difference is very little. I mean that following storage it is easy to make a difference of 2% humidity in a few hours ...

The standard is "max 10%". Most serious commercial products are at 7 or 8% ...

The mass heat of change of state of water being high, each% figures immediately!

[Gaston]

For liquid water, the specific heat is 4 J · kg⁻¹· K⁻¹.
For vaporization, the enthalpy is 2 Jkg⁻¹

Passing 1kg of liquid water at 20 ° to steam at 100 ° therefore requires 80 * 4185 + 2264000 = 2431400 675 J = XNUMXWh

If you increase the humidity in 1kg of pellet by 1%, add 10g of water, which will consume 6,75Wh to vaporize it.

At the same time, the 10g of water replaced 10g of fuel which could have produced around 45Wh.

In total, 1% more humidity represents about 50Wh / kg less.

Note that in the case of moisture uptake, it is "only" 6,75 Wh because the weight of pellets burned has also increased by the quantity of water absorbed.

[Christophe]

The mass heat of change of state of water being high, each% figures immediately!

Energetically yes of course ... hence my remark on the recovery of humidity!

I mean that following storage it is easy to make a difference of 2% humidity in a few hours ...

I would be curious to see how much humidity is 8% pellets that have been exposed to 50-60% RH (the "average" humidity of any dwelling)

Frankly I do not believe too much in your theory of "plasticization" ????

ps: what is the microwave technique? I missed that at the time ...

[Did67]

I would be curious to see how much humidity is 8% pellets that have been exposed to 50-60% RH (the "average" humidity of any dwelling)

Frankly I do not believe too much in your theory of "plasticization" ????

ps: what is the microwave technique? I missed that at the time ...

1) Attention: a silo is closed; its RH drops, once the present moisture is absorbed; we are moving towards a balance between very dry pellets and dry air (and not ambient air, perpetually renewed!).

[This is the principle of the tin boxes in which our grandmothers kept the dry cookies; alas, to nibble, we opened constantly, so it softened very quickly]

I do not have the measurements, but allow me to think that in the case of a sealed silo, filled once, the end result is ... negligible. The few hundred g of water contained in the incoming air as the silo is emptied is very little ...

2) YOU take a large dish that goes in the microwave. You weigh P1. You put a layer of pellets. You weigh P2.

Then you spend a minute in the microwave. You leave. You weight. P3. You mix. I don't know if it's a minute. Take smaller times and stay close by, so that it does not catch fire !!!

You start again until: a) the weight no longer moves; b) the pellets start to "brown". We can then consider that they are dry.

You calculate the quantity of water evaporated: weight of the pellets P2 - P1. Then you calculate the "losses" ...

[Ahmed]

Of course, the difference in dryness between logs and pellets results from artificial drying for the latter. My comparison was established by starting with dry logs "in the air" and not simply "dried" logs, as one can easily find for sale * (for reasons of cost of capital immobilization). It would be possible to dry the logs to the same degree, with a similar result, but it would be impossible to avoid moisture uptake, except to imagine a sealed packaging ...
The lignin which is visible on the outside forms a rather tight film, on the other hand the temperature during manufacture must probably partially roast the wood; these two factors must limit the return of humidity. However, the first point must be weighted, since many micro cracks break the continuity of the film and constitute as many entries towards exchange surfaces.

* I strongly advise consumers of wood logs who can, to plan their needs so that they have a stock a year in advance. This is so that the logs (split and final length) can spend a summer before use.

[Christophe]

Here I come from the store, I took a bag of softwood from the same manufacturer:

pellets_fireland_resineux.jpg (129.27 KB) Viewed 6046 times

Prices have changed since last week:
a) 4.49 € on sale at 3.89 € for softwood
b) 3.99 € on sale at 3.69 € for hardwood

Well, for the characteristics it is, as expected, in a pocket handkerchief for say kif kif bourricot!

pellets_fireland_resineux_PCI.jpg (61.96 KB) Viewed 6046 times

The differences between a softwood and hardwood pellets "on paper" are therefore minimal:

a) The density of hardwood pellets is not increased by 750 kg / m3 (but it is probably identical)
b) 0.5% better durability for softwoods

On paper, this is therefore limited to durability ...

What are the additives? I thought there was none?