What sort of pellet mill can be used for biofuels?

Question

I'm thinking that it would be useful to have a pellet mill at home to turn biowaste into fuel pellets. It would be nice to turn sawdust and wood shavings into fuel pellets as well but that I think is a different ball game as it requires much greater ability to grind and extrude the wood, and heat it to fuse the lignin so that the pellets stay coherent.

So, are the food pellet machines suitable for making biofuel pellets?

I was thinking you might user wood chips instead of wood pellets. It is explained here why pellets are better. Reasons exposed do not necessarily apply to your case, and one of them suggest that you should add drying the waste to the process you are thinking of. — J. Chomel, Aug 03 '18 at 11:45
Wood pellets are not sustainable the way they are produced in many parts of the world. — Graham Chiu, Aug 03 '18 at 12:15

score 1 · Answer 1 · answered Sep 03 '18 at 19:17

It would seem from this article that a food pellet machine is not suitable, and you need a wood pellet machine though this may be a biased article as the site is a pellet machine supplier.

Food pellet machines don't produce enough heat to fuse the lignin in coffee grounds to allow the pellets to retain their shape.

score 1 · Answer 2 · answered Oct 16 '18 at 22:42

A quick search of AliExpress turns up many small scale wood (or other biomass) pellet machines such as this one. Pellet mills vary internally in their grinding and screening/pressing die sizes, but they all operate in about the same manner: they grind material, then press it through a die to create a pellet. Pressure is what ends up creating the pellet, and nothing more. The primary reason, at least to my understanding, that you don't want to use a food mill for biofuels is that the biofuel raw material (sawdust, dried maure, rice husks, etc.) will gum up the works and make it unusable for food again.

Food pellet machines don't use heat to fuse the pellets. – Graham Chiu Oct 17 '18 at 01:29 — Graham Chiu, Oct 17 '18 at 01:29

score 0 · Answer 3 · answered Sep 03 '18 at 17:30

Given the variability of biowaste available to the home owner, I suspect that such a machine isn't practical.

Workaround 1:

Develop a means to use a conventional pellet feeder in a common wood heater. This would allow you to use pellets when you are going to be away longer than the normal run time of the stove.

This can be of two forms:

Always present. The unit feeds into a corner of the wood heater, so that you can set it up ahead of time, and it starts to feed when the stove temp drops below a certain point. For this it needs some form of ignition system.
Quick conversion. You decide when the stove is cold whether it's going to next run on a load of wood or a load of pellets.

Workaround 2:

Look at your biowaste and see if you can find other ways to burn it.

Burn directly. Wood chips and sawdust both will burn fine with a grate, and forced air. Downdraft stoves tend to do better at this.
Form into shapes other than pellets. Fusing is difficult. May have to use some cheap adhesive. I'd give first look at sodium/potassium silicates for this. (Waterglass) they are cheap and environmentally benign.

Note: Insurance companies take a dim view of wood heat at the best of times. You are going to have troubles with any DIY uncertified unit. Consider generating heat in an external, uninsured building, and moving heat as hot water to your house.

This opens a third possibility of having rapid very hot fires used to heat a large tank of water, which in turn can be circulated to the house as needed. Insulate the tank well, and you have a system where you make a fire once every two weeks for domestic hot water in the summer, and every day during a February cold snap.

The question supposes you already have a pellet fire. – Graham Chiu Sep 03 '18 at 19:07 — Graham Chiu, Sep 03 '18 at 19:07

What sort of pellet mill can be used for biofuels?

3 Answers3