Where to begin! Ok, so for me ‘How to Make Wood Pellets‘ is such a broad question I could literally go on for days talking about it. Now some of my website readers are looking for lots of detail, where others are just looking for a quick overview. Well, this page will be a brief overview which will lead off into more detailed posts. I’ve provided quick links below to the various sections of the page. I hope you find the information you’re looking for. 🙂
- Source/Prepare a Clean/Dry Raw Material
- Use a Pellet Mill to Compress the Wood into Pellets
- Cooling Wood Pellets and Protecting them from Moisture
- How can you Test the Quality of Wood Pellets?
1. Source/Prepare a Clean/Dry Raw Material
So to make wood pellets we clearly need some wood to start with, but what raw materials are suitable to make wood pellets? Well, practically any woody biomass material can be compressed into pellets. However, for producing fuel pellets I would urge you to stay away from highly processed (chipboard/MDF) and contaminated (painted) wood. Burning wood pellets made from these materials can create some very dangerous emissions.
Can I Make Wood Pellets From Logs?
Sure, you can make wood pellets from logs. H
Pro Tip – If you wish to produce high-grade wood pellets which have less than 1% ash content you will need to remove most of the bark from the logs. Top grades are often referred to as Premium Grade in the US or EN Plus in Europe.
How Does a Hammer Mill Work?
Once the wood is in chips, you can then process them through a hammer mill. The hammer mill will effectively smash the chips into finer particles which pass through a screen. To produce 6mm fuel pellets generally a 5mm hammer mill screen size is used. With the hammer mill when making pellets you want to use a screen size below the size of the pellets your making. The pelletization process produces a more consistent quality product following this rule.
Pro Tip – If your wood chips were produced from virgin timber you will need to let them dry out before processing them through the hammer mill. Wet wood chips will often turn to mush inside the hammer mill and block up the screen.
Is My Material Dry Enough?
So to make pellets we really need to get the raw material below 15% moisture content. The ‘sweet spot’ to produce wood pellets is normally around 12-13%. If you’re dealing with virgin wood the raw material is going to be very wet, we’re talking over 50% moisture. Now, you can naturally dry most wood down to around 20% moisture content. With protection from the elements, good ventilation and enough time this is possible.
However, getting below 20% moisture content without a dryer is very difficult. Drying on a small scale is often not viable, due to the cost of the dryer. Therefore with pelletization on a small scale its best to source a raw material below 15% moisture.
Can Wood be Too Dry to Make Pellets?
Most definitely, we need some moisture to be able to make wood pellets. So if you have a raw material below 12% moisture content, more than likely only dust is going to come out of the pellet mill. So a good setup will have the means to add in small amounts of moisture, either via a drip feed or peristaltic pump. This is where the advantages of a material conditioner will come into play, to properly prepare the wood ready for the pellet mill.
Research has shown that very small changes in moisture have a very significant impact on the pellet making process. I’ve seen this impact first hand. A small change in moisture can have a dramatic impact on pellet quality and pellet mill productivity.
2. Use a Pellet Mill to C
ompress the Wood into Pellets
So to make wood pellet we are going to need a pellet mill. There are many different pellet mills available, from small flat die pellet mills to large ring die pellet mills. Each has its own pros and cons which we will get into in later posts. When purchasing a pellet mill its important to think about product support. What is the cost of the replacement die and rollers for instance?
How Does A Pellet Mill Make Wood Pellets?
The pelletization process works around heat and pressure. The milled up wood material which has previously passed through a hammer mill is dropped into the pellet mill. The pellet mill features a die and a couple of rollers. To make wood pellets the material is forced through the die by the rollers. The pressure on the material also creates heat. Heat then melts the natural lignin contained in the wood. As the material passes through the die it takes the form of a pelletized wood pellet. The lignin acts as the glue to bind the pellets together. However, pellet binders are also used in some circumstances to aid the process.
The diagram above gives hints to the importance of the pellet press die design. The angle of the inlet on the hole and the depth of the die hole are very important. Therefore its much easier to produce wood pellets with a die specifically designed for that purpose. For instance, the depth of the
Flat Die Pellet Mills – Highlights
Flat die pellet mills are commonly made in China. However, there are also a few other companies in Germany and the US who are still producing pellet mills based on this design. The advantages are a more compact form. Therefore, its easier to produce small scale pellet machines. Depending on the design, either the die is fixed and the rollers rotate or vice versa.
While generally cheaper to purchase, there are a few negatives to the flat die design. For instance, there can be issues with rapid
Ring Die Pellet Mill – Highlights
So as you might have guessed, it’s more complicated to produce a ring die pellet mill. However, it has advantages such as the design being more energy efficient. Another advantage of the ring
Can all Pellet Mills Make Wood Pellets?
Now, the answer to this question is tricky, it’s yes and no. In principle, any pellet mill can be set up to make wood pellets. However, some are much better at it than others. You see, many pellet mills were originally designed to process animal feed into pellets. Animal feed pellets are produced to a much lower density than wood pellets. Therefore it’s an easier material to pelletize.
Now, it’s not impossible to get these small Chinese pellet mills to make wood pellets if that’s all you can afford. However, before you decide to do that you need to know what you’re getting into. Hopefully, with my posts on this website, you can make an educated decision.
Buying a Pellet Mill From China – My Experience
So when I first started making pellets back in 2007, I imported a pellet mill from China. It was a version of the PK/KL series flat die pellet mill. My Chinese pellet mill was driven by a single cylinder diesel engine with a crank handle, it’s a scary thought to this day. When you could get the engine started (cold weather? not a chance) the crank handle would often still be attached. It would spin around still attached to the engine until I knocked it off with a broom handle!
This experience taught me several important lessons. First, crank start diesel engines are pretty dangerous. Second, making wood pellets is not as easy as it first seems. However, I kept working with the pellet mill and hammer mill to learn the process and try to resolve the limitations of this equipment for pelletization.
Is it Possible to Make Wood Pellets from Home?
This is a question I’ve been asked many times over the years. Technically yes, you can make pellets from home with the right equipment and knowledge. Making pellets from home will often involve buying the cheapest pellet mills, and as stated above that can present challenges. Some people even attempt to produce their own homemade pellet mill.
Small pellet mills have small productivities per hour. A general rule is for every 1kW of power a pellet mill can make 10kg/h of product. Therefore, you also need to think carefully about various factors such as:
Do you have sufficient time to make the several tons of wood pellets you will need each year?
As you will learn through this website, making pellets on a small scale is not impossible but it’s also not simple either. Making wood pellets has often been
The Dreaded Blocked Pellet Mill Die
There are various challenges during the pelletization process, from properly preparing the raw material to getting the pellet mill ready. It’s frustrating when you see nothing but dust coming out of a pellet mill, but what’s even more annoying is a blocked pellet mill die.
There are many reasons why a pellet mill die may become blocked. The pellet mill
3. Cooling Wood Pellets and Protecting them from Moisture
When the wood pellets leave the pellet mill they are very hot and need to be handled with care. Until the lignin which binds the pellets has cooled they will easily break apart. The product needs to be cooled before they are packaged.
Pro Tip – Pass the wood pellets over a screen as they leave the pellet mill. This will separate out the fines (material which did not form into a pellet) which can be returned into the pellet mill.
Protecting wood pellets from moisture is important to retain their integrity. Wood pellets are highly absorbent, hence why they make such a good product for animal bedding. However, for fuel pellets that’s not ideal, so storing in a dry environment is a must. The only exception to this rule is torrefied wood pellets.
Methods for Cooling Wood Pellets
On a very low budget, you can just spread the pellets out and leave them for several hours before packaging them up into bags. For a small-scale production process, you can use a belt conveyor from the pellet mill with cooling fans. For large scale wood pellet plants a counter flow cooler is commonly used.
The product enters the top and feed out through the bottom. Cool air is pulled through by a large fan and the warm moist air is exhausted out the side of the counter flow cooler. With this method its possible to cool the wood pellets very quickly and then onto the packaging process.
Packaging and Storing Wood Pellets
For small scale pellet production, the most common choice is to pack into plastic bags. The weight of wood pellets in the bags is typically either 40lbs or 20kg. Plastic will do the best job of protecting the product from moisture. There are various small scale packaging solutions available which will measure out the product and then weld the plastic bag top to protect the pellets from moisture.
However, we are all trying to use less plastic today. Therefore you can keep wood pellets loose as I do as long as the environment you’re storing them in is dry and has very low humidity.
How can you Test the Quality of Wood Pellets?
Making a pellet is one thing, making good quality product is another. So how do you test wood pellets to see if they are good quality? There are various tests, for instance, drop the pellet in a glass of water. If the pellet sinks to the bottom of the glass then it has been produced to a high density. Another simple test is to apply horizontal force on the pellet. If it breaks cleanly with few fines then that is a sign of good quality product.
Conclusions on How To Make Wood Pellets
So as I’m sure you gathered from the information above there are many steps to making wood pellets. You need the right equipment and you need the right knowledge.
I’m hoping to provide as much information as possible on the more detailed aspects of the pellet making process, and I’ll place links to those posts in the relevant sections above. 🙂