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 hope you find the information you’re looking for. 🙂
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 various 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 a high-grade wood pellet which has less than 1% ash content you will need to remove most of the bark from the logs. Top grade wood pellets are often
How Does a Hammer Mill Work?
Once in chips, you can then process the wood 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 screen size is used. With hammer mill material size reduction when making pellets you want to use a screen size below the size of the pellets your making.
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%, and I’ll be writing a post about that. If you’re dealing with virgin wood the raw material is going to be very wet, we’re talking over 50%. Now, you can naturally dry most wood to around 20% moisture content. With protection from the elements, good ventilation and enough time this is possible.
However, getting below 20% without a dryer is very difficult. Drying on a small scale is often not viable, due to the cost of the dryer. Therefore when making wood pellets 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 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, the heat then melts the natural lignin contained in the wood. As the wood passes through the die its takes the form of the pellet. The lignin acts as the glue to bind the pellet together. However, pellet binders are also used in some circumstances.
The diagram to the right gives hints to the importance of the 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, so 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, with regards to
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 as the design is more energy efficient. Another advantage of the ring
Can all Pellet Mills Make Wood Pellets?
Now, the answer to this 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 process. 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 go ahead and do that I would encourage you to read as many articles on this website as possible before you make your 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. However, mine 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 and spin around 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 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 making wood pellets.
Small Scale Mobile Pellet Machine
I did re-engineer the Chinese pellet mill into a mobile pellet machine. The new machine combined a hammer mill and pellet mill with one powerful Perkins diesel engine and hydraulic drive system. Various other modifications were made with the equipment to improve its ability to reliably produce wood pellets. However, the cost to re-engineer the equipment and the low productivity per hour when making wood pellets meant the equipment had its limitations.
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. 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 wood pellets. 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 pellets has often been
The Dreaded Blocked Pellet Mill Die
There are various challenges when making wood pellets, 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. Cool the Wood Pellets and Protect 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 the pellets will easily break apart. The wood pellets need 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 thats not ideal, so storing the wood pellets in a dry environmen is a must.
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 wood pellets enter the top and feed out through the bottom. Cool air is pulled through the wood pellets 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 package wood pellets into plastic bags. Plastic will do the best job of protecting the wood pellets from moisture. There are various small scale packaging solutions available which will measure out the wood pellets 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 the pellets in is dry and has very low humidity. I simply use a large bucket and shovel to load wood pellets into my pellet boiler every couple of days.
How Can You Test the Quality of Wood Pellets?
Making a pellet is one thing, making good quality wood pellets 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 wood pellets.
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. 🙂