A Lesson in Wood Briquettes & Eco Logs

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Wood Briquettes

Good Briquettes
This post has been updated 1st January 2016 

"Know your Briquettes", so let us begin with the basics.  Extruded Wood Briquettes or Eco Logs as they are sometimes called come in THREE distinct types:

1.  Those which are solid but break easily into sections and look a bit like compressed sawdust,
2.  Those which are solid and so hard you could hardly drive a nail into them, and
3.  Those with holes through the middle.

All types are classified as briquettes but are made using fundamentally different techniques. Each type looks and feels quite different. Each type stores and handles differently. Each type displays very different burning characteristics. 

Solid Briquettes and Easily Breakable types:

The solid log types are made using a ram or piston type press which simply hammers or squashes layers of sawdust together under great pressure. These briquettes are much lighter in colour because the temperature is not as great in the process. They also break more easily and have a much looser looking texture. When they burn they expand up to twice or more their length in the fire and become spongy in texture. They are not a very good type of briquette. See previous several blog posts for specifics.

Above is a piston or ram type of briquette press. This type usually has a big flywheel to drive the ram. It uses uses less energy and takes a lot less maintenance. The put through of piston press machines is also much greater than screw presses, in fact about 6 times more output per hour on average.

Personally I do not like the hammer mill solid type of wood briquette because of the way it burned. As I have said and show in previous posts, they expand to over twice their length in a fire. They soften out as they expand and therefore burn more like wood shavings. Solid briquettes give the same heat output but the burn characteristics are what I find unsatisfactory.

Briquettes with a Hole.

The briquettes with a hole through the centre are extruded from a screw press using huge pressure. The enormous pressure generates a great deal of heat and further heat is added by electric heaters to closely fuse the particles together. It also makes the briquette have a dark and partially carbonised burned look to it. This glossy carbonised exterior helps protect the briquette from moisture.

The hole is nothing more than the byproduct of the screw thread passing through the middle. This type is usually compressed to just 10% or less of the original mass. The resultant briquette is very dense.

Above is a screw type press. Note the extrusion tube in which is the compression screw, and around which are the electrical heaters in yellow.

 
Screw presses wear out the compression screws quite often and they use a good deal more electrical energy. They also are slower and produce much less per hour than the piston or ram types. However, the screw type press produced a much superior type of briquette. These briquettes are naturally going to be a bit more expensive to produce.

The screw pressed and heat treated type of briquette is very dense. it has a carbonised outside which makes it easy to ignite and also helps it to resist moisture while in storage. It does not expand at all in the fire. It burns for up to twice as long as the ram pressed type, and can be burned along with other fuels including coal. I find that it is possible to get a much longer burn time overall with these briquettes. It still has negative aspects, the main one is IT BURNS TOO QUICKLY. It is therefore not great for long time burning - such as over night.


SOLID FUSED WOOD BRIQUETTES

There is another type of solid wood briquette which is not easily available in Ireland, although I have seen it advertised in the UK. This type is a fused wood briquette. It looks a bit like the solid hammer mill type BUT try breaking one and you will find just how hard it is. The very high pressure at which this type is manufactured causes it to heat and the wood to FUSE into a solid mass.

Because this type is so solid and hard it burns like limps of coal and can burn right through the night. I have received information from Hermanson's in the USA who manufacture this type. Hermanson's have developed their own process and machinery.

This is a very desirable type of wood briquette and the only one that I would have any real interest in using. I have tried the other types and am not impressed.

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Wood Briquettes Eco Logs

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A 2nd Look
at some characteristics of
Wood Briquettes

I has been suggested to me that my initial assessment of some wood products was not scientific and was inaccurate. I do not aim to be a scientific authority, or indeed any sort of authority on the subjects I write about. The opinions are my honest impressions, backed up in any way I can with some bit of science.

So today I take a closer look at one type of compressed wood briquette log - it has a somewhat square profile and is the pale type of briquette.

I have taken a 14cm piece of the briquette and placed it on a hot fire. After some 15 minutes, I measured it and it had expanded to about 20cm. After a period of some 30 minutes it had expanded in length to 26cm.

In expanding, it had become segmented and very soft and flaky. When the door was opened and the air got to it, it burned really quickly.

 You can see here where the mass breaks up and starts to get spongy

 After approximately 1 hour it has just about gone

I appreciate I am not able to be highly scientific, but you will see from my simple experiment that the paler type of wood briquette log rapidly expands to, in this case almost twice its original length, some other types expand even more.

When the mass expands, it allows more oxygen to mix through the fuel and speed up the combustion. This is not perhaps a good feature in fuel for stoves etc. 

I have no argument with the total heat output or other factors of this type of fuel which may prove highly satisfactory in many situations. However, when the mass expands 2x times or more and becomes porous and spongy, the burn rate is going to change a great deal and it will be difficult or impossible to get extended burn times. Expanding mass will also cause the fuel to push out against the glass of a stove or over the edge of a grate.

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