What are the Challenges when Making Wood Pellets from Logs?

Over the years I’ve processed many different sources of woody biomass into pellets. However, I must admit processing logs into wood pellets presents one of the biggest challenges, especially on a small scale. You are dealing with wood in its rawest form, therefore it requires the most processing before you finally get a good quality end product. Logs have to go through various size reduction processes before the material can enter the pellet mill. Furthermore, with logs, the issue of moisture content is front and centre. So let’s get into it!

Making Wood Pellets from Logs
Making wood pellets from logs presents many challenges

What will the Wood Pellets be Used for?

Before you even start to think about processing logs into wood pellets and purchasing equipment you really need to understand your end user/customer. You need to appreciate how you prepare the logs for making wood pellets affects the quality of the end product. Material preparation is one of the most important aspects of how to make wood pellets.

Are you Making Wood Pellets for Pellet Stoves and Boilers?

Wood ash
Leaving the bark on the logs will mean a higher ash content for the wood pellets produced.

If so you need to understand the combustion devices your wood pellets will be used in. You see, processing whole logs (bark and all) will produce something called a standard grade wood pellet. These types of wood pellets will produce ash content between 1-2%. They can be used in some pellet boilers, but very few pellet stoves. Therefore producing standard grade wood pellets limits your potential customer base. Furthermore, your customers will expect to pay less for standard grade wood pellets over premium grade wood pellets.

What are Premium Grade Wood Pellets?

Premium grade wood pellets are designed to work with all pellet stove and boilers. They also demand the highest price point. Premium grade wood pellets are evaluated on their density, durability, fines (dust) content and their ash content. With a premium grade wood pellet the ash content must be below 1%. Now, this is very significant if you intend to use logs to make wood pellets. As the bark on the surface of the logs produces a lot of ash during combustion. Therefore if you are aiming to produce premium grade wood pellets it will involve more material processing to remove the bark.

Are you Making Wood Pellets for BBQ’s?

BBQ Wood Pellets
The flavour produced from BBQ wood pellets can actually be improved by leaving the bark on the logs

While still obviously a fuel pellet, making wood pellets for BBQ’s and smokers has different requirements. The quantities of wood pellets being burnt are significantly less than that used in a pellet stove or boiler. Therefore, the issue of ash content and ash build up in the burn pot is not of concern. With wood pellet BBQ’s the main emphasis is obviously on producing food with the best flavour possible. Therefore when it comes to making BBQ wood pellets from logs you may actually want to leave the bark on the logs. The bark can actually produce some of the best-flavoured wood smoke.

Are you Making Wood Pellets for Animal/Horse Bedding?

Another growing market for wood pellets is that of horse bedding products. Consumers like the benefits that wood pellet bedding provides over using sawdust or straw. The absorbency of the wood pellets means the bedding doesn’t have to be changed as frequently. Furthermore, the lower dust content of wood pellets over other products means a healthier environment for the horses. When it comes to making wood pellets to be sold as a horse bedding product, obviously ash content is not of concern. Therefore you would not have to remove bark from the logs before processing.

How do you Remove Bark from Logs?

So let’s presume you have assessed your customer’s requirements and you intend to produce premium grade wood pellets. Therefore you are going to need to remove the bark from the logs before any further processing. You can’t chip the logs and then decide you want to make premium grade wood pellets. At that point, its too late, and there are no processing methods available to remove bark from wood chips. If you are producing wood pellets on a small scale for personal use you may look at hand tools such as a bark peeler or bark spade. However, this is extremely labour intensive and not really a practical option to take. The video below shows the effort and skill it takes to peel logs by hand.

The next step up from using a manual hand too to remove the bark from logs is an electric hand-held tool. Essentially its a special blade fitted to an angle grinder. If you are thinking of making wood pellets on a small scale from logs this is a far more practical option than using a manual hand tool.

If you’re looking for even more automation with your pellet making setup you could look into purchasing a proper log debarking machine. These machines have a conveyor on which the logs are loaded and rotated against a toothed debarking wheel and then dispatched out the other side. If you looking to install a small to medium sized pellet plant making premium grade wood pellets, this is probably the way to go.

Using a Suitable Wood Chipper to Process the Logs

So whether you are processing logs with the bark removed or not, the logs will need to be chipped. Chipping is only the first stage of the size reduction process when it comes to making pellets. After chipping we then need to process the chips through a hammer mill. However, the size of chips is also important, as it affects how well the hammer mill performs. For small logs you could consider something like the PTO log chipper as shown in the video below:

Whatever chipper you use its important to get chips to a sufficiently small size. Hammer mills generally perform better when the chips are around 1 inch in diameter. Processing larger chips than this through the hammer mill can often lead to potential issues, even damage to the hammer mill. Also, properly reducing logs to a small enough particle size can even help to avoid issues such as blocked pellet mill die.

The Moisture Content Issue with Logs

Processing logs to a suitably small particle size for making wood pellets is one issue. However, another significant issue is the moisture content of the logs. What is commonly referred to as a ‘dry’ log for stoves probably still has around 20% moisture content. When it comes to making wood pellets, you really want a raw material between 12-15% content. Therefore when it comes to making wood pellets from logs your almost always going to have to have some sort of drying setup available.

Conclusions on Making Wood Pellets from Logs

To process logs into wood pellets obviously involves more time, effort and equipment than many other woody biomass materials. Therefore you need to do your calculations to make sure it makes financial sense to process logs into wood pellets. For BBQ pellets due to the significant profit margins, it does make financial sense. However, when making fuel pellets or animal bedding pellets you really need to make sure you have done the cost per ton figures correctly. Furthermore, if you are having to transport the logs over a significant distance to the pellet mill or pellet plant, those costs can be significant. Anyway, I hope you found this post useful. Please make sure to read my other posts on the pellet making process. šŸ™‚

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