Wood Pellets Production

Pelleting Plant

Pelleting plant can be also described as pellet plant, pellet line, wood pellet line. This term refers to a set of complete pellet equipment work together to produce various biomass wood pellets on a bulk at one time.


You should pay attention that apart from pellet mill, other auxiliary equipment are sometimes still necessary in the pelleting process of wood pellet line, such as hammer mill, crusher, chipper, hot stove, dryer, cooler, separator, packing machine and so on, but which kind of machines are needed depend on the materials you are going to pelletize. You should bear in mind that the working principle of a wood pellet mill is to combine very small pieces or powder materials into a larger solid form, so if the size of raw material is too big, they will need to be reduced in order to make pellet successfully. Take logs for example, during the pelleting plant, you will firstly use a chipper and then use a hammer mill to preprocess log into very small particles. But if the raw material in the wood pellet line is wood chips instead of wood blocks or logs, these chips can be directly loaded into the hammer mill.

From various raw materials to high density solid wood pellets, the whole wood pellet line should include the following pelletizing processes: size reduction, material transportation, drying, mixing, conditioning, pellet production, sieving, cooling, pellet transportation, bagging and storing pellets.


Step 1 in the pelleting plant: Size Reduction

As we have mentioned before, materials you are going to make into wood pellets must be reduced to a small enough size to fit into the dies. If the raw material is over an inch in size it is usually chipped first, but If the raw material like sawdust, chipping can be skipped. Then you can begin with the hammer mill to continue cutting down their sizes until powder material.


Step 2 in the pelleting plant: Drying

Before starting to make wood pellets, the material must be dried first to get an appropriate moisture content between 10-20%. For in order to let the wood pellet line work smoothly there needs to be some moisture in the material but only in the proper amounts. Drying the material to proper moisture content is critical in making quality pellets. Besides, the drier also serves to heat the raw material which makes it more millable. In some cases the dryer will heat the material enough. In some larger pellet mills the material will be heated with dry steam.


Step 3 in the pelleting plant: Conditioning

Raw material must have the right properties before making into pellets. In most cases, materials contain enough natural lignins to bind the pellets together, while sometimes they will need to be added additional binding agents such as vegetable oil to bind pellets.


Step 4 in the pelleting plant: Pellet Production

Pellet mill is the crucial piece of equipment in the wood pellet line. Generally there are two basic pellet mill types. Flat die and ring die. With a flat die pellet mill the material falls onto the top of a flat die surface and a roller rolls across the material pressing material between the roller and die. A ring die pellet mill has a round ring shaped die. The rollers are inside the ring and press the material against the inside of the die. The pellets are then extruded out of the holes on the outside of the ring.


Step 5 in the pelleting plant: Sieving

Not all pellets form properly. Some will fall apart into small pieces during the pelleting process and these pieces will then be sifted through a screen. Depending on the quality and consistency of the pellets you are producing the pellets may be sifted for sized.


Step 6 in the pelleting plant: Cooling

When the finished pellets leave the mill they will be hot and sometimes are till release moisture vapour so they have to be cooled and dried. The most common way is to spread them out and let them cool and dry naturally. Sometimes air is circulated through them with blowers or fans, or sometimes you can use a cooler as your helper. Care must be taken to not dry them too quickly or they could develop stress cracks.


Step 7 in the pelleting plant: Pellet Transportation

Once the pellets are cooled they will be immediately transported to the bagging facility if it is a commercial pellet mill. Bucket elevators are often used at this stage.


Step 8 in the pelleting plant: Bagging and Storing

At this point the pellets are finished and ready to be used. But if for commercial use, even you just for personal residential purpose to say the least, you will have to pack them properly to prevent being affected with damp as if the pellets absorb moisture they will expand and become no value at all. Wood pellets are commonly put into plastic bags and sealed.