Compressed Sawdust

[Steven P]

As background to my thoughts, over the year processing my own firewood I create sawdust, and typically this goes onto the paths in the woods or onto the compost. Can I use this as heat tidily - I can throw it on the fire but typically sawdust will spill onto the hearth. I can put it into a card box (think food box such as half a cereal box) outside and just throw a box full on, also a bit of spillage.

 

Yesterday I made up an open box (as an experiment), 5 pieces of old decking, a loose inner liner (5 pieces of pallet), and a 'piston'. Filling the inside of this with sawdust, put the piston on top and then compressing it all with a car scissor jack (I have a spare one in the garage - just trying tis out so not spending money yet). I think the scissor jack is about 2 tonnes strength. Hoping that this will produce a sawdust briquet for me. Also assuming here that the paper briquet makers won't have the power to compress sawdust nicely.

 

Tried this out yesterday with dry sawdust, I haven't opened it yet (figuring that the longer it is compressed the more likely to make what I want). I am expecting it to fail on my first attempts. I reckon that 1 log would be an afternoon sawing (in between household chores, family time, and so on, I don't get long cutting wood at the weekend), it can sit in there for 24 hours.

 

Commercial machines are not viable for domestic firewood.

 

So the question, has anyone done anything like this before and are there any top tips to make a decent enough briquet.

 

Seeing the 'coffee logs' if this works with sawdust then will use my own coffee ground and recycle them onto the fire (they are expensive!) (not admitting to a coffee habit by the way, about 13kg a year all going onto the compost)

 

(note also I am not interested in paper ones, the advertising is good "free fuel" but in reality every time I burn papers (old bank statements and so on) it just kills the fire)

 

 

Right so any tips, and I'll update with the results of my first log later

[Doug Tait]

Like the idea but I imagine you'd need to add a binding agent of some type to hold it together. We'll see when you open it up.

[peds]

Personally, I'd say the coffee grounds are doing much more important work on the compost heap. 

[sandspider]

Following with interest, as I've considered doing similar with quite a lot of sawdust. However, I seem to remember you need a lot of pressure to compress sawdust enough for the lignin to bind together and make something log like. Not sure a 2 ton jack will have the oomph?

[openspaceman]

43 minutes ago, sandspider said:

Following with interest, as I've considered doing similar with quite a lot of sawdust. However, I seem to remember you need a lot of pressure to compress sawdust enough for the lignin to bind together and make something log like. Not sure a 2 ton jack will have the oomph?

Yes you normally have the pressure from rollers pushing a thin layer of sawdust through the die plus the heat from friction with the die locally softening  lignin to bind and form a skin on the pellet as it cools. The actual bonding within the pellet is fairly weak hydrogen bonding of the fibres as the pressure forces them together. The fibres in newsprint are  mostly held together this way but that achieves it by pulping the fibres in a wet process, then drying.

 

Medium pressure briquettes can be made in a press using a wet process but would need a binder of smaller fibres or a glue like starch from boiled potato peelings. The Legacy Foundation promote blending various waste products into cooking briquettes for sub Saharan Africa, partly to alleviate pressure on trees.

 

Here I would be tempted to add some dilute PVA and mixing well before compressing.

[Steven P]

So dry sawdust didn't work, in the die it looked and felt nice and solid but coming out it just crumbled and had shown no interest in sticking together.

 

Not giving up yet, it must have taken an hour to put the mould together, I might try the coffee grounds - this idea has been in my head a couple of weeks and have enough damp coffee to have a go with now. Want to make a small change to the mould, adding a double layer to the liner, when I pulled the single layer out it pulled the edge of the sawdust apart, can cure that and  try again with a different mix.

 

The 2 ton jack was just to see if the idea works at all before buying something with a bit more ooomph.

 

 

Though understanding what you are all saying above, sweeping all the sawdust and putting it on the compost and cutting those couple of extra logs to make up for that looks easier... but experiment started now!

[trigger_andy]

So dry sawdust didn't work, in the die it looked and felt nice and solid but coming out it just crumbled and had shown no interest in sticking together.
 
Not giving up yet, it must have taken an hour to put the mould together, I might try the coffee grounds - this idea has been in my head a couple of weeks and have enough damp coffee to have a go with now. Want to make a small change to the mould, adding a double layer to the liner, when I pulled the single layer out it pulled the edge of the sawdust apart, can cure that and  try again with a different mix.
 
The 2 ton jack was just to see if the idea works at all before buying something with a bit more ooomph.
 
 
Though understanding what you are all saying above, sweeping all the sawdust and putting it on the compost and cutting those couple of extra logs to make up for that looks easier... but experiment started now!

If you’re creating sawdust/chip from processing firewood would you not be better spending your time processing more firewood?

That hour messing around with a mould could have had you over a cube of firewood. Even if you managed to get it to work how productive do you think it would be? A carrier bag worth an hour?

[Steven P]

22 minutes ago, trigger_andy said:

If you’re creating sawdust/chip from processing firewood would you not be better spending your time processing more firewood?

That hour messing around with a mould could have had you over a cube of firewood. Even if you managed to get it to work how productive do you think it would be? A carrier bag worth an hour?

 

 

 

You're right of course, far better ways to spend my time, had an hour to kill yesterday though. It is never going to be mass production, sweep up the sawdust and work out where to put it - compost, paths, or see if I can burn it. Yes about a carrier bag an hour - this time next year, I'll be a millionaire? 

 

(confession time, I would have been using the saw but going to sharpen it Friday with my glasses on I saw how knackered that chain is! New chain on order for Monday, didn't fancy the bigger saw for the amount I have to cut this week)

[trigger_andy]

Just now, Steven P said:

 

You're right of course, far better ways to spend my time, had an hour to kill yesterday though. It is never going to be mass production, sweep up the sawdust and work out where to put it - compost, paths, or see if I can burn it. Yes about a carrier bag an hour - this time next year, I'll be a millionaire? 

 

(confession time, I would have been using the saw but going to sharpen it Friday with my glasses on I saw how knackered that chain is! New chain on order for Monday, didn't fancy the bigger saw for the amount I have to cut this week)

Fair enough.  

 

Ive looked into sawdust log machines. They use very high pressures and are at least £5000. They also need the dust to be under 20% MC to bind. 
 

I’ve about 4 IBC tanks filled with sawdust after the last clean up. They will be getting a dose of diesel and set alight soon. 🤣 

[sime42]

As background to my thoughts, over the year processing my own firewood I create sawdust, and typically this goes onto the paths in the woods or onto the compost. Can I use this as heat tidily - I can throw it on the fire but typically sawdust will spill onto the hearth. I can put it into a card box (think food box such as half a cereal box) outside and just throw a box full on, also a bit of spillage.  

Yesterday I made up an open box (as an experiment), 5 pieces of old decking, a loose inner liner (5 pieces of pallet), and a 'piston'. Filling the inside of this with sawdust, put the piston on top and then compressing it all with a car scissor jack (I have a spare one in the garage - just trying tis out so not spending money yet). I think the scissor jack is about 2 tonnes strength. Hoping that this will produce a sawdust briquet for me. Also assuming here that the paper briquet makers won't have the power to compress sawdust nicely.

 

Tried this out yesterday with dry sawdust, I haven't opened it yet (figuring that the longer it is compressed the more likely to make what I want). I am expecting it to fail on my first attempts. I reckon that 1 log would be an afternoon sawing (in between household chores, family time, and so on, I don't get long cutting wood at the weekend), it can sit in there for 24 hours.

 

Commercial machines are not viable for domestic firewood.

 

So the question, has anyone done anything like this before and are there any top tips to make a decent enough briquet.

 

Seeing the 'coffee logs' if this works with sawdust then will use my own coffee ground and recycle them onto the fire (they are expensive!) (not admitting to a coffee habit by the way, about 13kg a year all going onto the compost)

 

(note also I am not interested in paper ones, the advertising is good "free fuel" but in reality every time I burn papers (old bank statements and so on) it just kills the fire)

 

 

Right so any tips, and I'll update with the results of my first log later

 

 

 

I've nothing to add on the subject of cohesion, (@Openspaceman seems to have addressed the technicalities of that comprehensively anyway).

If you do crack it then i reckon it would be worth incorporating a hole through the centre of the brick, into the mould. For ventilation purposes; it should improve airflow and hence combustion rate.

 

My dad used to have an old trick whereby he'd tamp bandsaw sawdust down hard into a metal tin, (coffee I think as it happens), with a dowel through the centre, which was then removed. Once ignited with a splash of meths it would burn/smoulder quite intensely for half an hour or so. I think he said they used to use it for cooking on in Scouts or something.

 

Also the catering type of charcoal always looks to have a hole through the centre of each bit.