PTO Pellet Mills, what are the Problems when making Wood Pellets?

If you’re looking to make wood pellets on a small scale, you’ll be trying to keep your equipment spend to a minimum. Therefore, for those people who already own a tractor, PTO pellet mills are obviously appealing. However, before you considering purchasing any equipment I would encourage you to read my how to make wood pellets page. You should really only start to consider purchasing a pellet mill once you’re confident you understand how the process really works. Hint, its a lot more complicated than most people realise.

PTO Pellet Mill
A typical Chinese PTO pellet mill

The image you can see above is a typical example of a PTO pellet press imported from China. For a pellet mill of that size you will be able to produce around 50 kg/s of wood pellets and up to 100 kg/h of animal feed. A PTO pellet mill of that size will require a 30-40 HP tractor. If you already own a tractor the appeal is obvious. It would mean no need to purchase a separate diesel or electric motor to power the pellet mill, reducing the cost of investment. However, there are various problems with a PTO pellet mill which you need to consider.

No Control over Material Feed Rate

Many people are not aware of how important the rate of feed into the pellet mill really is. Wood pellet quality and press productivity are significantly influenced by the material feed rate. If you just load up the hopper on the PTO pellet mill you are probably going to experience a pellet press blockage. To avoid a blockage and produce the best quality wood pellets you need a consistent rate of feed to create a wave infront to the rollers but not covering the rollers. This way steam created from the pellet making process can escape and not create issues.

PTO Pellet Mill Feed Rate
To produce the best quality wood pellets you want to feed just enough material infront of the roller (A) but no more.

With a PTO pellet mill setup, there is only one source of power at one speed. Therefore a variable speed material feed system is not possible. So the user has to stand by the PTO pellet mill slowly metering in material to produce the best results. This is obviously very time-consuming. Therefore you have to consider the value of the pellets compared to your time to produce them.

The second aspect is torque, while diesel engines do have a lot of torque compared to a gas/petrol unit they still cannot compare to an electric motor, particularly at variable speeds. There is also the question of running costs as a PTO setup is the most inefficient way to produce pellets.

The Problems of Power and Efficiency

The fact is that the PTO pellet mill is not a very efficient wood pellet making the process. In most cases, the tractor engine will be far more powerful than really required. Furthermore, there are the energy efficiency losses from transmitting power from the engine to the PTO and through the pellet mill gearbox.

Tractor PTO
Powering a pellet mill via a PTO is the least energy efficient means of generating power due to mechanical energy losses.

So you really have to consider, for the amount of diesel it takes to run a PTO pellet mill is the process efficient enough? Remember, you have to factor in the other energy costs of processing the material. For instance, when you are making wood pellets from logs, that involves going through a chipper and hammer mill.

The Safety Issue

Finally, there are serious safety concerns around operating a PTO pellet mill. Many people die each year from PTO related accidents. With a pellet mill, you are standing directly next to the shaft. Furthermore, many people choose not the fix the recommend protective covers. Even with the covers fitted, there is still a chance of accidents occurring.

PTO Safety Guide
If you are going to purchase a PTO pellet mill, you should always fit a protective guard.

Conclusions on PTO Pellet Mills

There are several advantages to a PTO pellet mill. It means you don’t have to purchase an additional motor and with the pellet mill linked to the three-point hitch its also portable. However, it’s important to remember the pellet mill is only one part of the pellet production process. You may also need a chipper, hammer mill and potential even some form of drying equipment to get the material to the perfect moisture content. Therefore, you shouldn’t consider a PTO pellet mill purely on its own merits. You need to consider how well a PTO pellet mill would fit into your wider pellet production set up.

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