Sunday, March 18, 2012

Wood Briquettes and Eco Logs Lesson 2


Eco-Logs and Wood Briquettes 
Lesson 2
Courtesy of
Virginia Hermanson

Rock-hard bonded Eco-Logs that do NOT expand and disintegrate

To this point I have given a basic introduction to the main types of wood briquette / Eco-Log. (1) The hammered or pressed type, and (2) The heat treated extruded type with a hole in the middle. My preference is firmly with the latter, and (3) The super-hard fused wood briquette.

In this post, courtesy of Virginia Hermanson of Homefire Prest logs Ferndale, Washington USA, I have received a further bit of education in the matter of Eco-Logs, their types and their production methods.

Virginia contacted me by e-mail and here is her letter:

Hello Tony,

Loved your information . I thought I would offer my experience with extrusion of sawdust/biomass. My husband invented the machines we use- continuous extrusion with a screw . We use softwood only as that is what is prevalent in the Pacific Northwest USA. We have been in business for over 30 years.  

The logs with the hole in the middle have a heating element ( the hole ) which actually bakes or cooks the wood as it is extruded . Like baking a cake until it is like a rock! It burns well but burns quickly because the hole acts like a chimney –increasing the burn. The other type of log  is made with a piston driven machine. A charge of sawdust is dropped into a die that is then driven into a very long cooling tube. The tube is usually 150 ft long. This “glazes” the outside of the log – holding it in shape. When it is burned each charge springs back into its original shape because it is not densified right through – causing the log to grow or expand into an accordion or bloom . Sometimes even putting the fire out!  

Making logs is difficult – we know . it took many years of sweat and tears to figure out how to do what we do. Our logs burn just like coal – they last well over 12 hours in a woodstove/airtight because they are so dense. We do not add heat – through pressure the log exits our machine at over 280 F . After our logs cool you cannot pound a nail into it. With this great product we have an enormous amount of wear and tear on our parts and must rebuild constantly.  We love what we do and our customers burn more every year.  

We are working on finding an agricultural alternative to wood and have been for the past 10 years. Wood is becoming too expensive and harder to find. I am hoping to be able to switch within the next 5 years.  

Here is a link to our You Tube video of our machines. Also – we have a video on our website telling how and what we do. If you wonder why we have the flat side on our log it’s so they don’t roll…. Thanks for your blog!

Virginia Hermanson  

A 3rd Type of EcoLog Machine developed by the Hermansons

The Hermansons have, over many years, been developing and testing methods of wood and biomass compaction.

Their machines turn scrap and waste wood into rock hard fire logs that burn like coal, last for ages in the fire, and do not swell and go flaky like so many of the Eco-Logs around.

They look pretty like the common EcoLog available here in Ireland - with a couple of major differences, (1) They do not have ridging or banding down the length where each dose of material had been hammered on, and (2) The are very much smoother and denser.

Many of the common types of machine in current use employ pistons or big hammers that ram and squeeze the wood waste into solid logs. These types of briquettes or ecologs however do not have the material properly bound together, and when heated etc. they literally come apart.

The other type of machine in common use employs a large screw that compresses and extrudes the material under massive pressure and additionally employs electric heaters to bake and bond the material.

The difference between the piston ram type of machine and the Hermanson extruder machine is that the latter places such pressure on the wood that the pressure alone causes it to heat to nearly 400F or 204C without using extra heaters. These sorts of temperatures along with the pressure virtually melts or bakes the lignin in the wood which acts like a glue and bonds the material. In the Hermanson's machine, this is done also using a screw to achieve continuous one piece compaction..

The Hermanson process looks great as it uses less energy to produce the goods. My only observation is that the logs look a bit big, maybe a bit of a problem in the small stoves we use in that part of the world. However, I am sure that the diameter of the log is only a matter of fitting different size tools to the machine.

Thank you Virginia for that very interesting lesson in compressed Eco Logs.


1 comment:

Killian said...

Hi Tony As your American linked producer Stated the reason the extruded briquettes tend to be harder is that they are heated to a higher working temperature by combination of compression/heater coil's than compression alone in the ram type. This 1/Binds the lignin better. 2/Evaporates more of the Moisture in the wood. ( the moisture in the expanding to steam in the fire is what tends to break the log apart. The draw back is that the Die/Extruder life is a lot worse than the ram type raising maintenance/running cost. In the region of 1000~1500 hrs which is not a lot .Three to for sets a year under normal running conditions.
Briquetting is not as ECO friendly as most people think. To run a 500Kg hr plant shredding waste wood you are looking as using in the order off about 250~300Kw Hrs of power. Which most likely comes from ESB which is 85% coal/Gas powered. This equates to about 25%of the energy in the wood. If you need to dry it from log wood 40% down to ~15% Relative moisture content You need a burner of about 150Kw (Rule of thumb is 1KwHr/Kg water to be evaporated) That about another 15% of your wood energy gone. Then you have collection delivery Etc all diesel powered
Regarding the Hole in the log it gives a more uniform compaction of the sawdust,its not there to help the log burn.
best solution is to Burn whole Air dried logs wood gassifer boiler.
UK manufacturer extrusion presses, But most Inc equipment on BIO GREENTECH is China sourced or Polish see