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!

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?

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?

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. 🙂

Making wood pellets on a small scale is a challenge, this is just a fact. There are many different variables which you need to be in control of to produce good quality wood pellets. When you start to learn about how to make wood pellets you will notice the issue of raw material moisture content gets mentioned a lot. There are two main challenges. First, trying to figure out what is the perfect moisture content for the raw material to produce the best quality wood pellets. Secondly, how do I get the raw material to that perfect moisture content?

Generally, when it comes to making wood pellets I’ve found a moisture content of 12% works best most of the time. However, for different species of wood increasing the moisture content slightly up to a maximum of 15% moisture sometimes has benefits. You only really know once you start to process the raw material through the pellet mill. You’re looking for a shiny wood pellet with a smooth surface that breaks off cleanly when leaving the pellet mill. This tells us the natural lignin within the wood has been heated sufficiently to bind the wood pellets together. It should be noted that making wood pellets from logs presents a significant challenge when it comes to material moisture content.

The Challenge of Controlling Moisture Content on a Small Scale

With large scale wood pellet production plants, they have a lot of equipment and a lot of automation. For instance, they can have equipment such as infrared moisture meters constantly scanning the raw material to asses its moisture content. They then have large batch mixers which help to prepare the raw material to the ideal moisture content. Using peristaltic pumps if they need to add moisture they can precisely add in just enough moisture to produce good quality wood pellets very consistently.

On a small scale, the wood pellet making process is very different. Infrared moisture meters are not viable due to their cost. There are various handheld moisture meters on the market, however, you have to be careful. Some moisture meters do not produce accurate results for sawdust and wood chips. On a small scale often the best option is the dry weight test.

What is the Dry Weight Moisture Test?

First, you need some accurate weigh scales that can measure grams (g). I appreciate not everyone uses the metric system, using a weigh scale that can accurately measure ounces is also suitable. Measure out 100g (remember to discount the weight of your container). You then need to dry the material on a low to moderate heat source. You can use a microwave if you’re careful. Frequently measure the weight of the raw material until its weight remains constant. Once its weight stops dropping you have then reached 0% moisture. The difference in weight from start to finish is the percentage (%) of moisture the raw material contains.

So for example, if your raw material now weighs 88g the difference from 100g is 12g. Therefore the moisture percentage of the raw material is 12%. For many woody biomass materials 12% moisture content is often the perfect moisture content to make wood pellets. However, we will get onto that later. One word of caution when drying the raw material. Make sure you do not go beyond 0% moisture and start to burn the raw material. This will mess up the calculation and make it appear that the raw material contains more moisture than it really does.

Is 12% Moisture Content Perfect for Making Wood Pellets?

Quite often I’ve found that a consistently prepared woody biomass raw material at 12% moisture produces the best results. Now consistency is another important aspect of the pellet making process. For instance, let’s say the batch is fairly consistent at 12% moisture, but there is a pocket of the material above or below this. Well, when that pocket of material enters the pellet mill a couple of things could happen.

From Wood Pellets to Dust

So the pellet mill maybe happily processing the material into wood pellets at 12% moisture, then a dry pocket of material enters the machine. The lack of moisture will affect the compression within the die. It will also affect the ability of the pellet press to generate sufficient heat and pressure. This could potentially lead to the process stopping, as the rollers cannot gain traction on the material. Or, instead of wood pellets being produced only dust may emerge from the pellet mill.

Lots of Steam and Blocked Pellet Mill Die

If the pocket of raw material is considerably higher than 12% moisture content there is a possibility that this could lead to a pellet mill die blockage. The first you thing you will notice is considerably more steam emerging from the pellet mill. You will then start to hear the pellet mill motor struggling. With an internal combustion engine, you will hear the motor start to labour. If it’s an electrical motor you will see a spike in the amps the motor is using. If this continues then is likely the engine will stall or the electric motor will trip its breaker.

Lower Wood Pellet Durability

The previous two examples above of either dust or a blocked pellet mill die are at the extremes. The other possibility is just reduced wood pellet quality. You may notice that the pellets produced do not have a shiny surface, or they are emerging from the pellet mill with small cracks. These lower quality wood pellets will have lower durability. They will break more easily producing fines (dust). The consequences for the end users could be significant. For instance, with wood fuel pellets fines will produce more ash content during combustion. It will also produce more smoke. For animal bedding products it will be detrimental to the animal’s health. Wood pellets for horse bedding is a premium product. However, customers purchase them for the lower dust content compared to wood shavings. Therefore, if the wood pellets contain a lot of fines then this will lead to frustrated customers.

Drying Woody Biomass on a Small Scale

With large scale pellet plants, rotary dryers are used. However, on a small scale, rotary dryers are just not viable. Another option that is available is pipe dryers, also known as flash dryers. This option is used more frequently for making wood pellets on a small scale, however, there are some downsides. Flash dryers are often made up a solid fuel stove, large fan and a long section of snaking pipework with a cyclone separator at the end. The fan pulls the smoke from the stove through the pipework along with the raw material you are trying to dry. How successfully it does this depends on the moisture content of the raw material to start with.

Drying Retention Time

The raw material is pulled through the pipework and dried in one single pass. However, the retention time is very low, as the raw material is carried in the hot smoke for only a second or so. Now if the raw material is below for example 25% moisture content this may be sufficient time to dry the material to below 15% moisture. However, if the raw material was produced from virgin wood above 50% this would not be sufficient drying time. Therefore it would require multiple passes through the dryer to get to a moisture content below 15%.

However, repeatedly passing material through the dryer is also likely to lead to a raw material below 12% moisture. Therefore the process is not that efficient and can lead to wasting fuel overdrying the raw material. Furthermore, passing a fairly dry material through the flash dryer also carries significant fire risk.

Flash Dryers Lack of Precise Process Control

Large scale rotary dryers have the benefit from a controlled retention time as the operator can either speed up or slow down the rotation of the dryer. There are blades within the rotary dryer which moves the material from one end of the dryer to the other. This lack of precise process control trying to dry woody biomass on a small scale is often why it’s important to only source a dry material to process into wood pellets.

Conclusions on the Perfect Moisture Content to Make Wood Pellets

You will not know what the perfect moisture content is for your raw material until to have tried to process the raw material. It’s best to get the raw material to an average of 12% moisture and see what happens. On a small scale, it’s unlikely that dryer than 12% will produce good quality wood pellets. However, slightly higher than 12% up to 15% may produce better results. It comes down to trial and error. However, it is worth noting when making wood pellets on a small scale, pellet binders can provide a useful helping hand to smooth out the process.

Before you can make wood pellets you obviously have to have a source of raw material to process. A question I’ve been asked repeatedly over the years is ‘what is the best raw material to make wood pellets?‘ Well to answer that question we need to think about what the wood pellets will be used for. For instance, will the wood pellets be used for heating fuel, animal bedding or BBQs?

Your choice of raw material is probably the most impact factor that will dictate how successful your project is. For instance, is your raw material free or will you have to pay for it? Are there sufficient amounts of this raw material close to where you will make the pellets? How reliable is the supply of this raw material? Resolving all these questions should be the first thing you do before you purchase any equipment such as a pellet mill. Furthermore, how you prepare that raw material can also influence potential issues such as a blocked pellet mill die. Below I’ll go through the different potential uses for wood pellets and how that will influence your choice of raw material.

The Best Raw Material For Fuel Wood Pellets?

In terms of making wood pellets to be used as fuel, you need to focus on the end user and their pellet burning appliance. For instance, will end user be using a small pellet stove or large industrial pellet boiler? Pellet stoves are generally less tolerant to higher ash content wood pellets, where large scale boilers have systems to deal with higher percentages of ash content.

What Effects the Ash Content of Wood Pellets?

The ash content of the pellets is primarily impacted by the choice of raw material. For instance, if you want to achieve the highest standard of wood pellets then you want to avoid wood bark. Wood bark increases the ash content of the wood pellets over the ‘premium zone’ of 1-2%. Therefore if you wish to make wood pellets from logs, you first need to remove the bark. However, if your raw material is wood chips, removing bark is not going to be possible. Therefore, your available raw material will dictate which end users can use the wood pellets for fuel. It will obviously also impact the value per ton of the wood pellets.

There are small pellet stoves which can handle ‘standard’ grade wood pellets with an ash content over 2%, however, it is a small percentage of the pellet stove market. Therefore if you are looking for your largest potential customer base you will need a raw material with little to no bark.

Avoid Making Wood Fuel Pellets from Processed Materials

Over the years I’ve often been asked if materials such as MDF and Chipboard can be used to make wood pellets. While these materials can be processed into wood pellets, I would not recommend that you do so for fuel pellets. The emissions generated from burning these wood pellets can be quite dangerous, and potentially illegal. This also includes making wood pellets from painted wood.

The Best Raw Material For Animal Bedding Wood Pellets?

With animal bedding wood pellets, ash content is obviously not a concern. Therefore it is possible to use logs and wood chip which still contains bark. The absorbency of the pellets is not dictated by the source of wood. However, there are other factors to consider. As stated above with fuel pellets, do not use processed wood as the raw material. Using such a raw material could create health complications for the animal. Therefore you only want to use virgin raw materials. This could be logs, wood chips, shavings or sawdust.

The Best Raw Material For BBQ Wood Pellets?

Particularly when it comes to BBQ wood pellets no form of painted of processed wood should be used. The smoke from BBQ wood pellets provides the food with a great flavour, but you don’t want that flavour to be toxic chemicals. In terms of the type of wood you can use for BBQ wood pellet there are many to choose from. It could be Apple, Cherry, Oak, Hickory and Alder to name just a few. In terms of bark with BBQ wood pellets its a bit different, it can actually provide a benefit. The bark of the wood can produce some of the best flavours in the food. Wood pellet BBQ’s don’t actually burn significant amounts of wood pellets, therefore there are less potential issues with ash build up.

IMPORTANT: Avoid Contaminated Wood!

So above we talked about avoiding processed/painted wood. Well, there is another raw material you should also avoid. If the raw material may be contaminated with stones or metal you should not consider processing it. Even small pieces of stone or metal can cause serious damage to a pellet mill. Best case scenario is some minor damage to the rollers and die which will need replacing. The worst-case scenario is it could cause significant and expensive damage to the pellet mill drive system/gearbox and pellet mill motor.

Ideally, You Want To Find a Dry Raw Material

If you have a large pellet plant and dryer, you can process wet (above 15% moisture) wood into pellets. However, it still costs money to do so. On a small scale, however, there are very limited options to dry wood to below 15% moisture content to process into pellets. Therefore really you need to find a dry raw material. Now back 20 years ago there used to be clean/dry sawdust freely available. For some companies, it was even regarded as a waste product. As such, they would actually pay to have it taken away. Well, times have changed, and most companies who produce such material today realise its value. Therefore now they are either processing it themselves into wood pellets or briquettes, or they are charging for it.

A Local Source of Raw Material to Make Wood Pellets

When it comes to a wood pellet businesses the most significant costs are haulage of the raw material and finished wood pellets to customers. Those that have gone out of business it has often been due to increasing transportation costs. Searching further afield to find suitable raw materials and having to transport wood pellets over longer distances kills profit margins. Therefore finding a suitable source of raw material local to where you intend to make the wood pellets is vital.

Conclusions on the Best Raw Materials To Make Wood Pellets From

Really before you even consider purchasing a pellet mill or pellet plant you need to be confident in your raw material. First, you need to find a raw material that will suit your end users. You then want to make sure it’s not processed wood, it’s free from contamination and ideally dry. Finally, the location of the raw material and how you will get it to your pellet mill/plant is important. Keeping transportation costs under control will be vital to the success of your project.

So if you’ve started looking into how to make wood pellets, you may have come across the discussions over the use of binders. So in this post, I’ll discuss what binders are and if you’ll need them to make wood pellets.

Water and Vegetable Oil for Making Pellets

So first and foremost before using a pellet binder, your attention should focus on water and vegetable oil. If the pellets are exiting the pellet mill in a dry crumbly form adding in a small amount of water to the process can improve pellet quality. The additional water will do two things. It will increase the compression within the die and also increase temperature. This in term will help to melt the natural lignin within the wood to help the pellets form. However, adding too much moisture can generate too much pressure, leading to a blocked pellet mill die.

Adding in small amounts of vegetable oil into the pellet making process can help to lubricate the pellet mill die. This can avoid a pellet mill die blockage by keeping the compression generated under control. However, adding too much vegetable oil will significantly reduce the density of the wood pellets produced. Therefore their density will not be sufficient to withstand packaging and transport. So the addition of vegetable oil should be used sparingly and with care.

What Different Types of Pellet Binder Are Available?

In the feed pellet industry, there are many different types and brands of pellet binder available. They not only aid the pellet making process but they can also add nutritional value to the feed pellets. However, with wood pellet production, if a binder is used more than likely it would be a form of modified corn starch.

Matam Inc Pellet Binders

One manufacturer of modified corn starch pellet binders is Matam Inc with its product PelletBond. It is designed to act as both a wood pellet binder and pellet mill lubricant. The further benefits of the pellet binder being reduced pellet mill energy consumption and increase productivity simultaneously. This product can be particularly useful when trying to make wood pellets with a small pellet mill. The reason being with a small pellet mill it’s harder to get up to the optimum operating temperature to make wood pellets.

Borregaard Pellet Binders

Another pellet binder manufacture is Borregaard with its product Lignotech. This product is heavily used in the animal feed pellet industry, however, it could also potentially be used in wood pellet production. The pellet binder comes in 25kg brown paper bags and its in the form of a powder. Therefore to be able to use this pellet binder you need a way to add in very small and precise amounts of powder into the raw material and pellet mill.

Kiotechagil/Anpario Pellet Binders

Kiotechagil developed a pellet binder called Mastercube, however, it now appears to be produced by Anpario. This pellet binder can do some of the work of producing the pellet chemically instead of purely mechanically with the pellet mill. Therefore, again this presents the benefit of reduced pellet mill energy consumption. Mastercube is produced from plant gums and mineral hardeners. It can help to produce a harder more durable pellet while improving pellet consistency. Mastercube is a popular pellet binder for animal feed pellet plants. However, for wood pellet production I would use a modified corn starch product such as PelletBond.

How Much Binder is Required When Making Wood Pellets?

Typically between 1-3% of the raw material to make wood pellets is made up of a binder when making wood pellets. Therefore the actual impact on cost per ton is very minimal.

Small Pellet Mills Benefit Most From Pellet Binders

So as you may have gathered from the information above, pellet binders make the process of making pellets simpler. It can take some of the work away from the pellet mill to aid in the process and make good quality pellets. This is a particular benefit for small pellet mills, particularly those purchased from China. For the following reasons:

Small Pellet Mill Operating Temperatures and Binders

To produce good quality wood pellets the pellet mill die needs to get over 80 degrees Celsius, this can be quite tricky for small pellet mills. Therefore, adding in 1-3% pellet binder into the raw material mix can be the difference between a small pellet mill making wood pellets at all.

Small Pellet Mill Dies for Wood Pellets

When you purchase a small pellet mill from China, for instance, the machine arrives with a single die. Now, really to make wood pellets you want a pellet mill die with a specific compression ratio to suit that raw material. As this is not provided with many small pellet mills from China, you have to work with what you’ve got. Therefore, through using a pellet binder it’s possible (partially) get around the issue of a die not being ideal for making wood pellets.

Furthermore, the dies that come with small pellet mills from China are often drilled to a poor standard. Rough die holes mean a high likelihood of a blocked pellet mill die. Therefore, a pellet binder can also help to lubricate the process and reduce the odds of a blocked die.

Conclusions on Pellet Binders for Making Wood Pellets

Large scale wood pellet manufacturing facilities do often use a small percentage of a pellet binder such as PelletBond, however, it is more of optional extra. With their equipment, they are able to control the pellet making process precisely in terms of particle size and importantly moisture content. On a small scale, however, it is much more difficult to keep the variables under control at all times. For instance, even when using a binder the moisture content of the raw material is very important. When it comes to making wood pellets on a small scale the use of a pellet binder is less of an option. In fact, I would say if you intend to purchase a small pellet mill from China, for instance, a pellet binder is essential to make wood pellets.

When it comes to making wood pellets the biggest problem that you will come across is a blocked pellet mill die. In this post I wish to explain some of the most common reasons a pellet mill can become blocked and how to go about fixing the issue. First I’ll provide some highlights on how to avoid a blocked wood pellet mill die.

So the above is the ‘highlights’ of what leads to a blocked wood pellet mill die, now let’s discuss the above points in more detail.

1. Preparing the Pellet Mill Die to Avoid Blockages

So something worth noting is that it’s just as easy to block a new die as it is to block an older used die, but for slightly different reasons. A new die (particularly if purchased from China) will have imperfections within the die hole from the drilling process. The hole may appear smooth on its inner surface, however commonly the drilling process will also create small scratches. Even these small scratches can create enough resistance during making pellets to lead to a die blockage. Remember, if the pellet mill rollers cannot generate enough force to overcome the resistance of the die holes, that leads to a blockage.

An older die which was previously used to make wood pellets but has been left idle for more than a few days can create a different issue. Moisture within the air or from a previous production run will lead the die forming rust/corrosion on the inside of the die holes. This again makes the inner surface of the hole rough, which means the roller cannot generate enough force to push the material through the die, leading to a blockage.

How do you Polish a Pellet Mill Die?

So to resolve the issues noted above of a rough surface within the pellet mill die holes, we need a polishing material to pass through the machine. This will typically be a fairly loose biomass material (I prefer using wheat bran), about 10-15% vegetable oil and about 1-2% fine sand. You mix this material thoroughly and slowly process it repeatably through the pellet mill several times. This polishing material will help to clean up the surface of the die holes and remove corrosion.

Pro Tip: Use a polishing material sparingly as if used too often reduce the life of the die and rollers by wearing away their surface. Once the inlet tape on a die has warn away the compression ratio on the die will be unsuitable to make good quality pellets.

2. Preparing the Raw Material

So we have addressed the first issue which can lead to a block pellet mill die by polishing the die holes so they are nice and smooth. Now we need to examine the raw material to make wood pellets.

What is the Particle Size of your Wood?

You need to make sure your woody biomass has been properly processed through a hammer mill with a 5mm screen. This is to ensure that the particles you are placing in the pellet mill (with a 6mm die) are smaller than the diameter of the die hole.

Pro Tip: You also need to make sure there is no contamination within your raw material (stones/metal). These cannot only lead to a die blockage they can also cause some serious damage to the pellet mill itsself. This could include a damaged gearbox or motor.

What is the Moisture Content of your Raw Material?

As you may know from reading the main how to make wood pellets page, knowing and controlling the moisture content of your raw material is vital. The general rule to make wood pellets is you want the raw biomass below 15% moisture content. However, the material also needs to have a consistent moisture content throughout the batch. Taking a sample of raw material which is not consistent may produce a reading between 12-15%, which will produce good pellets. However, if there is a section of material above this, say 20%+, this could easily lead to a pellet mill die blockage when it enters the pellet mill. Therefore preparing the raw material to have a consistent moisture content throughout the batch is essential. No only to avoid blocking the pellet mill die, but to produce consistently good quality wood pellets.

Pro Tip: Even if you have a raw material prepared with the ideal particle size and moisture content, a pellet binder should be considered. A pellet binder can aid the process and reduce the chances of a blocked pellet mill die.

3. Feeding the Pellet Mill Slowly to Avoid a Die Blockage

Good quality wood pellets are only produced once the pellet mill and die get up to operating temperature, which is over 80 degrees Celsius. At this point, the natural lignin within the wood will melt and bind the pellets together. However, before the pellet mill reaches this operating temperature it is very easy to block the die if the raw material is fed into the die more quickly than it can process the material. You want to make sure there is sufficient material in front of the pellet mill rollers, but not to completely cover them.

Pro Tip: The pellet making process creates heat, which releases moisture from the raw material. Filling the pellet mill processing chamber with raw material stops this moisture escaping (steam). This steam is then absorbed by the incoming raw material, which means a raw material above 15% moisture, leading to a die blockage. Hence, only feed the pellet mill at a rate which it can process.

As the temperature of the pellet mill rollers and die increase the productivity of the pellet mill will also increase. At this point, you can increase the rate of raw material feed into the pellet mill. However, you still don’t want to over feed the pellet mill to stop steam escaping. Even at operating tempreture this will still likely lead to a die blockage.

What do you do once you have Finished Making Wood Pellets?

Ok, let’s presume you have finished making wood pellets. You obviously want to leave the pellet mill in a condition that means the die is not blocked for the next production run. Therefore for the last few minutes of operation add in quite a bit of vegetable oil into the mix. This will leave a soft oily material in the die, and make it much easier to start making pellets again next time.

Pro Tip: If you are leaving the pellet mill for more than a few days you will need to run the polishing material through the die again. This will clean off any corrosion/rust which has formed in the die holes.

If you own a pellet stove, boiler or BBQ or you’re looking to purchase one there is a very important lesson to learn. You must keep your wood pellets away from moisture and dry. Otherwise, you will end up with a wet mush that can only be used as mulch on your garden.

To emphasise this point woodpellets.com have produced the video below. It shows what happens when wood pellets come into contact with water. Now, granted the video below is an extreme example. I’ll talk about more realistic wood pellet moisture issues below. However, first please watch the video to see what will ultimately happen if your wood pellets are exposed to moisture.

As you can see in the video, after pouring water onto the wood pellets after just two minutes they start to puff up and expand. After three minutes the wood pellets in the base of the bag (which have absorbed the most moisture) are now just sawdust. Four minutes later due to the expansion of the wood pellets, the bag is becoming ‘like a brick’ and taut. After just five minutes the wood pellets are mush. With a cut in the bottom of the plastic bag, the wet expanding wood pellets pour out.

Why do Wood Pellets Expand when in contact with Water?

The reason wood pellets expand when they come into contact with water is due to how wood pellets are made. First, the raw material is dried to a moisture content suitable to make wood pellets, typically between 12-15%, and then compressed in the pellet mill. Typically, with a suitable compression ratio to produce premium grade wood pellets, the sawdust will be reduced in volume roughly 6:1.

Due to the low moisture content of wood pellets (below 10%) and their high density they now have hydrophilic properties. What that essentially means is that wood pellets are highly absorbent and are searching for moisture. This is true for other biomass fuel pellets, such as grass pellets and hemp pellets. The hydrophilic properties of wood pellets mean they can also be used for other purposes besides fuel. However not all wood pellets absorb moisture (more details below).

Liquid Water is not the real Problem, its Humidity

So as I mentioned previously, the example in the video of pouring water on a bag of open wood pellets is an extreme example. The real problem with wood pellets is humidity. Many people store their 40lb bags of wood pellets in their basement or a shed. While these environments are protected from the rain they tend to be quite damp and humid. Therefore if bags of wood pellets are left open or there are tears in the bags the wood pellets will pull the moisture out of the air. Eventually, the wood pellets will expand back into sawdust. While it won’t happen in 5 minutes as with liquid water, the wood pellets will eventually expand and break apart.

What happens if you use Damp Wood Pellets in a Stove, Boiler or BBQ?

There are some pellet burners manufacturers who will tell you to never use open bags of wood pellets in their equipment. For instance, Clarry produces a portable pellet stove, and their advice is to discard open bags of wood pellets. However, if wood pellets are stored in a low humidity enviroment they will maintain their density. For instance, my wood pellets are just stored in my custom silo room loose, however, its a warm environment with low humidity.

There are a couple of reasons manufacturers are concerned about users putting damp wood pellets in their equipment. First, damp wood pellets will struggle to ignite and will also create more smoke, ash and potentially even creosote. Also, while damp wood pellets are not sawdust mush (yet) they do break apart more easily. Damp wood pellets have a reduced density, and they produce more fines (dust). This dust can be an issue for some automated feed augers depending on their design and quality. Cheap augers with underpowered motors can block up with the fines.

Which Wood Pellets Don’t Expand in Wet and Humid Environments?

So both soft and hard standard wood pellets will expand when the humidity of the environment in which they are stored is too high. However, there is a type of wood pellet which won’t expand and turn to mush. Amazingly, you could even leave these wood pellets out in the rain and they would be fine! They are called torrefied wood pellets, and through a process called torrefaction, the wood becomes hydrophobic.

A stated above standard wood pellets are hydrophilic, which means they attract and absorb moisture. Torrefied wood pellets are hydrophobic, so they repel moisture. The process of how torrefied wood pellets are made is very interesting, and I encourage you to read my post on them. Unfortunately, currently, there are very few manufacturers of torrefied wood pellets. So for the moment leaving your wood pellets out in the rain and then putting them in your pellet stove is not an option.

How can you Test if Wood Pellets are Damp?

So how can you test if your wood pellets have started to absorb moisture from humid air? Well, first the appearance of the wood pellets will change. A quality wood pellet will have a smooth and shiny outer surface. If you can see lots of cracks on the surface of the pellets that’s a good indication they have started to absorb moisture.

The second test I like to call the Snap Test. Essentially you put the wood pellets under horizontal force. A good quality wood pellet will break cleanly into two pieces and with an audible ‘snap’ sound. Wood pellets which have started to absorb moisture will break apart into lots of smaller pieces and create lots of fines (dust).

However, not all wood pellets that don’t pass the snap test are damp. During the wood pellet production process if insufficient moisture is present the natural lignin within the wood will fail to bind the pellets together. However, if we presume the wood pellets you have purchased had passed a premium grade test they should also pass the snap test if they are not damp.

The Absorbency of Wood Pellets does have its Benefits

While the moisture absorbency of wood pellets is not a positive feature when it comes to combustion, there is an application where it is a benefit. Using wood pellets for horse bedding is growing in popularity. Typically wood shavings and straw would be used as bedding materials. However, they can contain quite a large amount of dust which is bad for the health of the horses and can cause respiratory issues.

Wood pellets (made to a certain quality) have a very low percentage of fines (dust). And the high absorbency characteristics of wood pellets means the bedding needs to be changed less frequently. However, wood pellets are very hard to start with. Therefore, best practice is to actually add some water to the bedding to start with. However, these damp softer wood pellets can still absorb a lot more moisture.

Conclusions on Keeping Wood Pellets Dry

When it comes to storing bags of wood pellets do make sure to tape up any tears in the bags to avoid moisture getting in. Also, try to avoid keeping bags in a damp basement or shed where possible.

When it comes to combustion performance of wood pellets, just remember water doesn’t burn very well! Moisture will mean its harder to ignite the wood pellets, more smoke will be produced and therefore potential issues with creosote.

I hope you found this post useful. Please check out my other posts on the home page about making, burning and the other uses for wood pellets. 🙂

Obviously, the main raw material that people think about for fuel pellets is wood. However, many different biomass raw materials can be processed into fuel pellets. Hemp pellets and even cardboard pellets are possible. But what about fuel pellets made from horse manure? Horse stables often have significant disposal costs for manure. Therefore wouldn’t it be amazing to turn this costly raw material into a valuable asset? Well, the answer is obviously yes, but how can you turn horse manure from a cost into a profit?

When it comes to processing and burning manure the first thought for most people is, “But what about the smell?”. Well, odours during combustion can mainly be resolved by making sure the burn is efficient. Therefore that partly means making sure the material is dry before combustion. The video below is of an operation where horse manure is collected, dried and then used in a KSM-Stoker biomass boiler.

Turning Horse Manure from a Cost into an Asset

For many horse owners, the disposal costs of bedding waste can be significant. Therefore making use of the material is an opportunity to turn a cost into a profit. Typically the base bedding material will be straw, hay, shavings or in some cases actually wood pellet bedding. Once the horse manure and bedding is ready for disposal before it can be used for pellet production it needs to be dried.

The video below is of an impressive drying system developed by Organilock. They use their Bio Burner to generate hot water which can then be used to dry the waste. Typically the manure will be at a moisture content around 40% and will need to be dried down below 15% ready for the pellet press. The video below discusses drying various biomass materials, horse manure is also mentioned.

The Organilock drying system uses two large augers. At the end of the first auger, the manure enters a hammer mill with a large screen. This is designed to reduce the particles down so that more effective drying can take place. After the final drying stage has been completed the horse manure can then run through a finer hammer mill screen of 5mm to be ready for the pellet mill.

You may be thinking “why not start with a smaller particle size, the horse manure will dry more quickly?”. Well, trying to hammer mill wet material through a 5mm screen is only going to lead to a blockage of the hammer mill. Now that the horse manure is dry and in small particles it can be compressed through a pellet mill.

Is Burning Horse Manure its most Valuable use?

Horse manure pellets are a high BTU, low ash (compared to grass pellets) and low emission fuel. Therefore they do hold some potential as a locally produced fuel. However, many pellet stoves are designed to only burn premium grade wood pellets. Therefore the potential market for horse manure as fuel is limited.

If you are considering going to the expense of setting up a pellet plant to process horse manure, you should consider selling the pellets as fertilizer and not as fuel. Within the gardening community horse manure pellets are seen as an excellent organic fertilizer and soil conditioner. Selling horse manure pellets in 10kg bags as fertilizer will provide much better profit margins compared to fuel pellets. The same is true for chicken manure/bedding waste.

The Economics of Setting up a Small Pellet Plant

So let’s discuss the economics of setting up a pellet plant to process horse manure into pellets for either fuel or fertilizer. You could probably purchase a budget plant from China for less than $100K. For equipment manufactured in either the US or the EU you’re looking at probably double that. For that sort of money, the plant will be able to produce around 500kg/h of horse manure pellets.

Unless you have a very large stable your not going to be producing sufficient waste to make the plant viable. Therefore you should consider contacting other stables within say a 50-mile radius. You could then look into setting up a cooperative and a pellet plant at a central location. This will keep the delivery costs of the waste to the plant for each member to a minimum. It will also spread the liability of setting up and running the plant.

Conclusions on Processing Horse Manure into Pellets

If you own or operate a horse stable the approach you need to take to address your manure waste issues depends on the scale of your operation. If you are looking after over 20 horses you may be producing sufficient waste to consider purchasing your own dryer and pellet processing equipment. However, if the number of horses is less than that a more realistic option is to group together with other stables and form a collective to deal with the issue. You share the costs and the profits of converting the manure into pellets.

As stated above, you could use the pellets as heating fuel for your own personal use with a suitable pellet stove or boiler which can deal with the ash content. However, the most profitable market for the rest of the horse manure pellets is not as fuel, but as fertilizer.

Back in 2008 when I purchased my first Chinese pellet mill and I was exploring how to make pellets I started to play about with making cardboard pellets. Something I quickly learnt was that making cardboard pellets presented several unique challenges that I’d not experienced with other biomass materials. However, I was eventually able to produce pellets after a long process of trial and error.

The Process of Making Cardboard Pellets

So the first part of the process is actually collecting together a sufficient volume of cardboard waste. Some waste is just paper-based and with light brown colouring. However, some waste has a waxy outer layer. Either type of waste can be compressed into pellets. However, you have to consider how the cardboard pellets will be used.

Potential uses for cardboard pellets include either as fuel or an animal bedding. The waxy cardboard produced more ash when burnt, more details on that below. Also, the waxy material can produce some very odd smelling combustion gases. Therefore I would avoid using waxy materials for fuel pellets. Before you can use the cardboard within a pellet mill it’s obviously got to be reduced in size somehow.

Processing Cardboard in a Hammer Mill

At the time I only had access to hammer mill for raw material size reduction. So first I ripped the cardboard into strips and fed it into the hammer mill. After just a couple of minutes of processing material, it became apprently this was not like processing any other biomass material. The cardboard that came from the hammer mill was not in small 5mm particles, it was more like candyfloss!

With other biomass such as wood and straws, the hammers hit the material and smash it into smaller particles that then pass through the 5mm screen. Cardboard is a soft material made of long thin wood fibres. So the hammers are not able to smash the material, it tears into the material and breaks the fibres apart. However, the hammer mill in doing so also generates a static charge, which means the end result is a very fluffy mass!

Separate Staples from the Raw Material

Much of the waste will contain staples. To avoid damage to the pellet mill it’s very important that you are separate out this metal contamination. On a small scale, you can sort through the raw material before it is fed into the hammer mill and rip out the staples. However, in a commercial operation thats not viable. In that case, an electromagnet should be used before the pellet mill. This will take out the staples before the material enters the pellet mill.

Alternatives to using a Hammer Mill when Making Cardboard Pellets?

Ideally, if you’re going to try and make cardboard pellets you want to get hold of a cross-cutting shredder. A shredder which can crosscut the cardboard into 5mmx5mm squares would be perfect for feeding into the pellet mill. However, there are very few crosscutting shredders of a suitable size to process cardboard sheets. Hence why I’m not able to recommend any such products. However, if you are able to find such a cross-cutting shredder, its a much better option than a hammer mill when it comes to making cardboard pellets.

How does Cardboard Perform in the Pellet Mill?

Cardboard in the pellet mill actually performs pretty well. It’s possible to produce high-density cardboard pellets with no additional pellet binders. However, the moisture content of the material is far too low in most cases for pellets to form. Therefore enough water needs to be added to get the cardboard to between 12-15% moisture content to produce the best pellets.

Are Flat Die or Ring Die Pellet Mills best for Cardboard Pellets?

I’ve tried making cardboard in both flat die and ring die pellet mills. Milled or shredded cardboard is quite a light material, it doesn’t flow well through transfer augers. Therefore this is actually a scenario where a simple flat die pellet mill can actually perform better than a ring die pellet mill for making cardboard pellets.

What are the various uses for Cardboard Pellets?

The two main uses are as either fuel or animal bedding. However, it’s important to note that when used as fuel pellets the ash content could be as high as 7-10%. Many pellet burners can only deal with wood pellets up to a 1% ash content. For instance, the pellets would not work in a simple portable pellet stove. So clearly, the market for fuel pellets is limited.

Really, the best market for cardboard pellets is animal bedding or for litter boxes. In this scenario, the high ash content that the pellets produce is not an issue. I hope you found this post interesting, please visit the home page for the various other posts I’ve made on making, burning and using pellets.

Conventional pellet stoves are great, however, they are not exactly suitable when a small portable pellet stove is needed. Conventional pellet stoves require an electrical supply to ignite the fire, power the feed auger and combustion fan. There is a growing demand for small portable pellet stoves, and the Clarry Pellet Stove is such an example. Originally developed for hunters, no matter what your views on hunting, this is great little portable pellet stove with multiple potential uses.

Benefits of the Clarry Portable Pellet Stove

The key benefits of the Clarry pellet stove are that its a gravity-fed and non-electric design. Therefore this small portable pellet stove can be used in a range of off-grid scenarios. This small portable pellet stove is able to take advantage of one of the key benefits of wood pellets, their ability to flow like a liquid.

Wood Pellet Combustion Efficiency

When it comes to burning wood efficiently there are a few requirements. First, you want to use a dry source of wood. With premium grade wood pellets you are guaranteed a moisture content below 10%. This means you can achieve a very high combustion temperature with little to no smoke. Not only does a minimal amount of smoke mean you are burning the wood as efficiently as possible, but it also means you’ll have minimal if any creosote build-up in the stove. I’ve been burning wood pellets in my pellet boiler for over a decade. While I inspect and clean the chimney every year, I’ve never had any issues with creosote build-up in the chimney.

In the video above it is stated to only use premium grade hardwood pellets. You could try standard grade softwood pellets, however, I suspect that the higher ash content will block up the grate. Clarry also states to never use an open bag of wood pellets because they may have drawn moisture. If the wood pellets have been left in a humid enviroment this may be the case. However, there is an easy way to test the quality of wood pellets.

If the wood pellets have drawn moisture, under horizontal forced they will crumble and break into lots of small pieces. However, if you can snap the pellets with a clean break and minimal dust, then it’s still a good quality pellet. Also, if the wood pellets still have a good surface shine, that’s also a sign of a wood pellet which will produce good combustion results.

The Benefits of Gravity

Not only do you only want to use a dry source of wood, but you also want to slowly feed the fire to maintain a constantly high combustion temperature. This is where the gravity hopper on the Clarry pellet stove comes into play. Small amounts of wood pellets are metered into the fire as required.

You can use wood pellets in any standard portable wood burner with a pellet basket, however, you will not achieve the same combustion results. When you use a pellet basket you will get quite a bit of smoke before the fire gets going. With a gravity system, almost no smoke at all is produced, even at the start of combustion. The other obvious advantage with a gravity pellet hopper is that it’s feeding the fire for you. With the Clarry portable pellet stove, you can get around 8 hours of heat from the gravity hopper before it needs filling again.

Combustion Zone

As the wood pellets burn a void is created which is filled with new fuel falling from above. This is the advantage of wood pellets and their high density, they can flow through a hopper and not bridge. This same principle is also used in a DIY rocket mass heater designed to run on wood pellets. To start the stove a small amount of gel fire starter is put in the ash draw next to the wood pellets that fell through. A couple of minutes after lighting the gell the wood pellets will be achieving a high combustion efficiency.

The many uses of a Portable/Off-Grid Pellet Stove

Clarry originally developed their portable pellet stove over a decade ago for camping. However, since then its become apparent there is a growing demand for portable gravity-feed and non-powered pellet stoves, these uses include:

• Off Grid Homes and Businesses
• Tiny Houses
• Large RV’s and Motorhomes
• Greenhouses

Clarry has also noticed these trends and have amended their instruction manual on how to integrate the stove safely into permanent installations avoiding combustible materials:

Conclusions on the Clarry Portable Pellet Stove

There is a growing demand for portable pellet stoves. Many consumers are looking for a pellet stove that doesn’t require electricity to efficiently burn wood pellets. Along with a gravity hopper its possible to get many hours of heat without having to tend to the stove. The Clarry portable pellet stove is just one example of such a product, I hope to be adding more posts in the future on other portable pellet stoves. In the meantime, I encourage you to read my post on how wood pellet are made. 🙂

When I first became aware of BBQ wood pellets I didn’t have the resources to go out and spend significant amounts of money on a new Traeger pellet grill. Only a few years previously I’d purchased a pretty nice gas BBQ. So started to look into how I could dip my toe in the water so to speak of BBQ wood pellets, to see what sort of a difference they really made to the flavour of the food I’ve been cooking on my gas BBQ. I’d already purchased a bag of Traeger BBQ wood pellets, but I needed something to use them in. I then came across the BBQr’s Delight wood pellet smoker box.

How Does a Wood Pellet Smoker Box work on a Gas BBQ?

The video above is of the small wood pellet smoker box made by BBQr’s Delight. It’s a small cast iron box with a lid. It holds the contents of a single-use bag of BBQ wood pellets. You can then simply place the wood pellet smoker box on top of the grill of your gas BBQ.

Once the BBQ gets up to temperature and heats up the cast iron wood pellet smoker box the pellets will start to smoke. However, they will not burn due to the lack of air flow. You then want to turn down the gas, and shut the lid on the BBQ. The smoke will then exit around the lid of the smoker box and flow over and around your food. Therefore the very last stage of the cooking process is slowly letting the smoke penetrate into the food.

How long you want to leave the food under the lid of the BBQ in the smoke is up to you. It obviously depends on if you prefer a lightly smoked flavour over a stronger smoked flavour. It’s probably best to try shorter periods of time and up the exposure time to suit your own tastes. So for instance, leaving the food to smoke for say 15-20 minutes and doing a taste test.

How does a Wood Pellet Smoker Box compare to a Proper Wood Pellet BBQ?

Ok, personally I was impressed by the smoked chicken I was able to make using the little wood pellet smoker box from BBQr’s Delight. Though I must admit, the first one I received had a crack in the cast iron base. I had to send it back for a replacement as I was concerned in the heat of the BBQ it would break apart. It’s important to note, however, a wood pellet smoker box is no competition for a full on wood pellet BBQ such as those offered by Traeger.

With a full on a wood pellet grill, the main source of heat is BBQ wood pellets. Therefore you’re getting that amazing smokey flavour during the whole cooking cycle. With the built-in thermostatic controls to feed in just the right amount of wood pellets, BBQ wood pellet grills are just in a different league. However, that is also the case when it comes to price. You’re going to have to spend considerably more on a BBQ wood pellet grill than a gas grill.

There are lots of Different BBQ Wood Pellets you can try

As you can see from the video above, Jack Daniels produce their own BBQ wood pellets from their used oak barrels from making the whisky. These pellets are jet black that’s why you can barely see them in the video. Oak is the primary wood used for making BBQ wood pellets. However, there are many others which include Apple, Maple, Cherry, Mesquite, Hickory, Black Walnut, Mulberry, Orange and Pecan.

Conclusions on using a Wood Pellet Smoker Box

Personally, I was quite impressed with my first trials of the BBQr’s wood pellet smoker box. I ended up purchasing their testing kit of single-use packets and went through each one.

I really do like the infusion of flavours which the cast iron smoker can produce. However, it also makes you start to wonder how amazing the food could taste if I had the full control of a wood pellet BBQ. I now just need to save up the money to buy one! But as an introduction into the world of BBQ wood pellets, I would definitely encourage you to give a wood pellet smoker box a try.