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 Post subject: Sawdust briquettes
PostPosted: Thu Jan 07, 2016 5:44 pm 
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Not sure if this should be in the Eco section but it does involve heating and, according to what I have read, water.

As a by product of sawing my logs for the fire I produce quite a lot of sawdust. I wondered if, using one of those simple hand compressors, I could make briquettes to add to the fuel on the fire.

Most of what I have read though seems to require the use of waste paper in greater proportion to the sawdust. I realise that water must be involved to help the binding process but do not want to use, and probably do not have enough, paper in the process. Other ideas are even less palatable, glue and used engine oil being among them.

Any ideas?

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 Post subject: Re: Sawdust briquettes
PostPosted: Thu Jan 07, 2016 9:37 pm 
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I think in order to get the lignin in wood dust / shavings to hold the briquette together you need more pressure than a hand press can provide.

Some wood burners allow you to burn dust / shavings directly - rather than as briquettes / logs.

J


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 Post subject: Re: Sawdust briquettes
PostPosted: Fri Jan 08, 2016 9:32 am 
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Seconded, and the mainstream briquettes use vegetable oil and high pressure to aid the sticking process.
Tried using the course chippings from the branch chipper in a friends pellet stove but they blew around too much being lighter than the pellets, shame.

I will try them in the wood burner in a sort of crucible as I have been felling and have rather a lot to spread on the garden.

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 Post subject: Re: Sawdust briquettes
PostPosted: Fri Jan 08, 2016 11:57 am 
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Thanks both, rather as I had suspected, but I will give the raw dust a chance in small amounts. Too much and I think they might exclude oxygen and kill the fire.

Perhaps chucking some in on top of the roaring logs to lengthen the burn instead of putting more logs in and shutting the air inlets.

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 Post subject: Re: Sawdust briquettes
PostPosted: Fri Jan 08, 2016 12:19 pm 
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Spardo wrote:
Thanks both, rather as I had suspected, but I will give the raw dust a chance in small amounts. Too much and I think they might exclude oxygen and kill the fire.

Perhaps chucking some in on top of the roaring logs to lengthen the burn instead of putting more logs in and shutting the air inlets.


Some workshop heaters can burn it - the problem is that it can burn fast - especially shavings. Also, another tip is to put the sawdust in a paper bag and put the bag in for easier handling.

Loads more information here - http://www.workshopstoves.co.uk/

Given that for some stoves (e.g. Bruno) at the above link do NOT recommend sawdust I suspect that some care may also be needed with other wood stoves.

J


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 Post subject: Re: Sawdust briquettes
PostPosted: Fri Jan 08, 2016 12:50 pm 
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I listened in on a conversation a while back about burning sawdust.
One possibility mentioned was a variation on Niemeyjt's theme of putting it in a paper bag.
They mentioned using a metal basket (sort of chip frier thing), put a newspaper in the bottom and sawdust on top.
I have to mention that one person thought it too dangerous: a tendency to explode! I suppose that's why some stove makers recommend not to use sawdust.
Having said that, I think some stoves can manage it quite well. I remember a friend's husband using sawdust to heat his greenhouses in the winter (professional rose-grower in Var) and he never had any problems... well, he did, he went out of business cause he couldn't compete with the foreign suppliers, but that's another story.


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 Post subject: Re: Sawdust briquettes
PostPosted: Fri Jan 08, 2016 1:12 pm 
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I also had the danger of dust explosion in the back of my mind, though I don't know the scientific principle that makes this so.

I was trying to avoid the use of a paper or cardboard container, partly because I don't have enough but also because it doesn't alway burn completely but sends flakes floating up the chimney, I think.

Once I've plucked courage to try a gentle 'sprinkle', I'll let you all know.

If I'm still here that is. 8-| :-o

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 Post subject: Re: Sawdust briquettes
PostPosted: Fri Jan 08, 2016 3:43 pm 
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Just a thought, try bonding the sawdust with watered down PVA glue, and moulding the mix in paper lined flower pots, to make briquettes, leave them to dry out thoroughly first, and then try burning a couple outside, to see how they work, before trying them on the fire

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 Post subject: Re: Sawdust briquettes
PostPosted: Fri Jan 08, 2016 6:16 pm 
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Years ago I had a Greenheart workshop Stove in my workshop, designed to burn sawdust.

To be honest it was a dusty, pain in the arse. It took ages to get going, was messy, really difficult to clean out. I ended up ripping it out and buying a portable gas stove

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 Post subject: Re: Sawdust briquettes
PostPosted: Fri Jan 08, 2016 11:38 pm 
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Spardo wrote:
I also had the danger of dust explosion in the back of my mind, though I don't know the scientific principle that makes this so.

I was trying to avoid the use of a paper or cardboard container, partly because I don't have enough but also because it doesn't alway burn completely but sends flakes floating up the chimney, I think.

Once I've plucked courage to try a gentle 'sprinkle', I'll let you all know.

If I'm still here that is. 8-| :-o



You are right to be cautious about a dust explosion David, and a gentle sprinkle is exactly what you must not do.

When things burn, they burn at the surface. If you make a fine dust, you increase the surface area greatly. You therefore increase the rate at which it will burn. Consider trying to light a 6 inch diameter log compared with 1/8th inch twigs from the same tree.

So fine dusts have the ability to burn very fiercely. Some dusts can even spontaneously ignite. What stops that happening normally is that the dusts are usually sat around in heaps and even if they catch fire, air cannot get in fast enough to fuel the fire.

If you then somehow end up with a lot of dust in the air, rather than in a heap, air has no problem getting to the individual dust particles and allowing them to catch alight/burn. In the wrong concentration of dust in the air, and with a suitable source of ignition, the rate of burning is so rapid that you end up with a chain reaction from one burning particle to the next, and the result is an explosion.

Typical things that create dust explosions are coal, flour, cocoa and wood flour (very fine saw dust). There are many industrial examples of such incidents. They rarely end happily.

Sprinkling sawdust onto a fire is likely to cause a flare up and could cause an explosion if there is already unburned/ smouldering sawdust in the fire.

Many years ago (1948) the cocoa mills in Hull were destroyed by three explosions. The first was a mild pop as some cocoa dust in the air caught alight and had a very mild "explosion" a bit like a balloon bursting. The shockwave from this raised dust that was sitting around on the pipes and machines in the area, this then exploded much more forcibly and this then raised all of the cocoa dust in the building for the third explosion, which destroyed the building, ruptured a fuel tank which caught fire and killed 11.

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 Post subject: Re: Sawdust briquettes
PostPosted: Sat Jan 09, 2016 12:43 am 
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I take your warning seriously Andy because it was what I suspected. I wasn't sure though of the explanation of the explosive tendency and had an idea that it was static related.

This is because I follow from time to time the videos on You Tube of a Belgian lorry driver who has a powder tanker. Although he hasn't explained I sometimes see that when discharging he has an earth lead from his chassis clamped to a rod in the ground.

Funny thing is that way back in my career I also drove such a vehicle, transporting everything from flour and cement to silica sand, plastic pellets and much more - but no-one ever mentioned earthing the tank. :-o

I had read of Peake's glue solution before but was reluctant to introduce what seems to me to be a chemical to the process. Might look into it though, rather than making a hole in our hill. :-?

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 Post subject: Re: Sawdust briquettes
PostPosted: Sat Jan 09, 2016 8:07 am 
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Andy - a fantastic explanation!

That gives another reason to follow the advice to bag sawdust and introduce it as a compacted mass rather than as loose powder.

I think Peakle's glue is for lower pressure binding - at high pressures the lignin in the wood is sufficient to bind.

Rojek used to do some briquette machines - nice, but expensive - http://www.rojek.cz/rojek.asp?jazyk=uk& ... ek=1515114.

Note the working pressure - 180 bar - approx 2500 psi.

J


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 Post subject: Re: Sawdust briquettes
PostPosted: Sat Jan 09, 2016 12:10 pm 
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Yes indeed a static spark could be a source of ignition and could theoretically set off a dust explosion, although IIRC things like flour use dense phase conveying which minimises the likelihood of a dust explosion because there is minimal dust.

There is a real risk of injuring the driver or anyone else around if a tanker is not earthed during discharge. The flow of the non conductive material through the metal pipework can build up enormous static charges on the metal parts (= tanker body, valves etc.). So when the driver then comes to disconnect he can get a belt well in excess of 100.000V.

If you are unhappy using PVA to glue your sawdust together, you could try flour and water, which I think will provide enough adhesive force for the purposes of a briquette. Might be worth a try.

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 Post subject: Re: Sawdust briquettes
PostPosted: Sat Jan 09, 2016 12:58 pm 
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Thank you for all this information - I've certainly learnt a thing or two !


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 Post subject: Re: Sawdust briquettes
PostPosted: Sat Jan 09, 2016 1:04 pm 
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Thank you for your perfectly clear explanation about dust explosion, Andy.


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 Post subject: Re: Sawdust briquettes
PostPosted: Sat Jan 09, 2016 1:21 pm 
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Top Art wrote:
Thank you for your perfectly clear explanation about dust explosion, Andy.


Yes, from me too, thank you. Leaves me even more incredulous that this info and appropriate precautions weren't available, or even highlighted, to me in the 70s though. Were we just lucky?

Also, in the case of my Belgian friend, he has a tipper tank (I did use those but was 'promoted' to a silo discharge) which has metal legs at the rear to the ground to avoid the raised tank falling over but would surely provide the earth themselves. Belt and braces I suppose.

As Blaze says, I too have learned much from this thread and each time someone comes up with an idea someone else has another which may top it.

Flour and water eh? Food for thought indeed. :)

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 Post subject: Re: Sawdust briquettes
PostPosted: Sat Jan 09, 2016 3:30 pm 
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Maybe a little bit over the top for some course waste wood sawdust compared to the other examples of very fine dry powder which forms a dust cloud, unlikely to occur in a wood stove when sprinkling.

Factories are a different case, very fine dust suspended in air and often with some form of ducted air system causing a partial pressure or certainly a really good supply of oxygen/air.

When I did my HSE course on dust explosions they demonstrated it with flour, a teaspoon full in what was a large wendy house with an air blower beneath the flour to cause the dust cloud and they used an ignition but it wasn't bad as bangs go.

Years earlier during school summer holidays we found a "Boys Own" book that described how to make dust explosions in an old Maxwell house coffee tin! What fun we boys used to have, imagine putting that down in print nowadays 8-x

For those that want to know more:
http://www.dustexplosion.info/flammabil ... clouds.htm

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 Post subject: Re: Sawdust briquettes
PostPosted: Sat Jan 09, 2016 8:07 pm 
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Teapot
I agree that a dust explosion is unlikely, but I have also to disagree with your conclusions.

Neither of us know how fine is the sawdust that David is handling and in particular the last few per cent of the sawdust.

Most probably the majority is quite coarse and offers no immediate threat. The fine end however is the problem.

A dust explosion is created with the finest portion of the dusty material, and once an explosive wave front is commenced, the particle size of the dust becomes less and less important. This is why dust explosions in coal mines can be so devastating since once the wave front is generated, anything combustible and small enough to be raised into the air will burn and contribute to the front.

You are right that a relatively high concentration of dust is needed for an explosion - just as you might locally generate by sprinkling dust or throwing dust onto a fire (which is why I responded). That is why throwing a handful of sawdust onto a burning bonfire will create a dust flare as the material burns before it hits the flames.

So yes, I do agree, an explosion is unlikely - but let me put it this way, it is a while since I had an accident in the car, and I might consider myself a safe driver. I will still put the seat belt on next time I venture out.

I should add that I may be sensitised to such events having been about 25m from the point of ignition of an industrial dust explosion when it went off. Luckily no injuries to anyone but IIRC around £500.000 repair bill.

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 Post subject: Re: Sawdust briquettes
PostPosted: Sun Jan 10, 2016 2:31 pm 
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I've decided to buy a cheapo hand press from Amazon (fr ou uk) to test out my various theories based on what has been said here. I reckon the delivered cost will be about €15. All of this type have doubtful reviews, the main complaint seems to be lack of strength in the build and therefore short life. This doesn't matter as long as I have enough use out of it to test the principle.

If it works I have my eye on a much more robust machine from England which I have seen on You Tube and have asked for the cost of delivery to France in readiness. The purchase price is £77.

https://www.youtube.com/watch?v=GYYskltCavk

Will report back in due course.

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 Post subject: Re: Sawdust briquettes
PostPosted: Sun Jan 10, 2016 5:38 pm 
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Piece of thick walled steel tube and a suitable loose fitting piston and put it on a log splitter, manual or electric, was something I was going to try but it's quite low down on the list of jobs to be done. Youtube has some, mainly redneck devices but you pick up some tips, sadly if you can't cancel what you are about to waste €15 on and put it towards a steel tube and at least a sash clamp that would be a shame as you will be disappointed and I don't know your physical size but you'll probably end up bending the arms of it quite quickly.

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 Post subject: Re: Sawdust briquettes
PostPosted: Sun Jan 10, 2016 7:40 pm 
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Teapot wrote:
Piece of thick walled steel tube and a suitable loose fitting piston and put it on a log splitter, manual or electric, was something I was going to try but it's quite low down on the list of jobs to be done. Youtube has some, mainly redneck devices but you pick up some tips, sadly if you can't cancel what you are about to waste €15 on and put it towards a steel tube and at least a sash clamp that would be a shame as you will be disappointed and I don't know your physical size but you'll probably end up bending the arms of it quite quickly.


I realise that Teapot, and I am prepared to sacrifice the money to prove the principle before going for something more substantial, and therefore more expensive. I could also utilise a car bottle jack but really don't have the time for the engineering that would have to go with it.

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 Post subject: Re: Sawdust briquettes
PostPosted: Sun Jan 10, 2016 9:55 pm 
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I think the principle has been proven many many times, it's not like you have discovered the wheel :lol: Just how to make an easy cheap tool to do the job and not like some Sunday supplement magazine jobby where a proper briquette was placed in the gadget to photograph for the picture to make out it works.

That's the big problem good engineering takes time and money but cheap items are just that. Good luck with it anyway, be sure to pop back with some photos and info. My friends bought one years back and after valuable time was used, which could have been put to better use the first briquettes not being wonderfully compressed burnt up really quickly. Good for getting the room warm fast but hopeless if you didn't want the exercise getting up and loading the fire every 30-40mins.

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 Post subject: Re: Sawdust briquettes
PostPosted: Mon Jan 11, 2016 4:24 am 
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This tool is to reform wet shredded paper.

I am not sure it is what you are trying to achieve with wood sawdust and shavings.

Good Luck!

J


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