Environmental protection: Why not directly burn logs, wood chips or other biomass materials? One reason is the moisture content. Even the moisture content of air-dried wood tends to be about 30%, while the moisture content of wood particles is less than 10%. The difference is that the smoke produced by burning particles is significantly reduced. Second, the pellets produce less ash, which is removed during the pelleting process due to the soil and bark. Third, and most importantly, energy density. The energy density of wood pellets is more than 3 times larger than wood chips. This greatly reduces storage requirements, allowing more fuel to be transported in a given truck space without taking up much storage space. Finally, the pretreatment of the particles is simple. Its uniform shape and size allow the use of smaller and simpler feeding systems, reducing costs. This high-density and uniform shape can be stored in standard silos and delivered by rail car delivery and truck container delivery.

 

The convenience of particles is reflected in the following aspects:

 

1. Density: about 650 kg per cubic meter

 

2. It has the same fluidity as liquid, the best choice for automatic systems

 

3. Can be used in furnaces and boilers

 

4. Can be used for small and large applications

 

5. Easy to handle, store and transport

 

6. Improve the combustion characteristics of raw materials

 

Sawdust is the most common raw material used to make pellets, because it does not require excessive pretreatment before entering the pelletizer. Nevertheless, there are other optional raw materials. The selection range includes wood waste (surplus sawdust, shavings, wood peel, etc.), yard waste (grass, leaves, branches, forsythia, wisteria and shrubs), farm waste (corn cobs, corn stalks, straw stalks) and other biomass wastes . The most common agricultural biomass used to make pellets include: reeds, miscanthus, switchgrass, spiny thistle, olives, rapeseed, sunflower, grapes, and citrus fruits.

 

Characteristics of high-quality pellets：

 

In the high-end wood pellet market, “premium pellets” refer to particles with very low ash content, such as 0.3%. Whether it is a high-quality pellet depends on its mechanical durability and moisture content.

 

1.Mechanical durability

 

Mechanical durability simply refers to the compactness of the particles and the goodness of the mechanism. High-density particles can better withstand the impact of transportation, and the combustion efficiency is higher in the particle burner. When the high-quality particles leave the granulator, its surface should be very smooth, with few or no cracks. If the pellets are cracked and fluffy, it is because there is too much water in the pellets and the internal compression force of the pellet mill is insufficient.

After cooling, the high-quality particles should resemble a colored crayons. The surface of the particles should be smooth and shiny. Compared to others, wood pellets tend to be more shiny. The most important thing is that the particles are smooth and compact. Try to hit the surface of the particles with a hard object to see if it is intact or broken easily. The length of the particles is not really that important. However, if the pellet is too long (more than 1 inch), it may cause damage to the auger of the pellet burner.

 

2.Moisture content

 

The less moisture in the pellet, the more energy the pellet burner can use. However, a certain proportion of water is required in the granulation process. If high-quality granules are to be produced, the water content must be kept as low as possible. The goal is that the water content of the finished particles is below 10%.

Wood is indeed superior to other widely available raw materials, especially agricultural waste. This is due to the low density of agricultural waste, which increases transportation and storage costs. Its ash content is greater because it contains many elements such as silicon, calcium, potassium, chlorine and sulfur. These minerals appear after crops are fertilized. When burning, crops such as straw tend to leave more slag, a black substance inside boilers and heat transfer equipment. Chlorine will corrode metals. Although these factors are not good, they can be mitigated by specific boilers, and can also be controlled by grasping the amount of fertilizer and harvest time.

 

3.Quality particle test

 

As mentioned above, the moisture content of high-quality granules is less than 10%, which has high compactness. The easiest way to test the quality of particles is to place the particles in a glass of water. If the particles sink to the bottom, it means that they have high density and strong pressure resistance. Conversely, if the particles float, it means that their quality is poor, their density is low, their mechanical durability is low, and they are more likely to break and produce fine powder. The second test method is to use a container that can hold at least one liter of water and first determine the weight of the container itself. Fill the pellets and weigh again. Now, fill the container with water and weigh it. Subtract the weight of the measuring container twice, then divide the weight of the pellet by the weight of the water. If it is a high-quality pellet, the result should be 0.6-0.7 kg/liter, which is the specific gravity of the pellet. Specific gravity is a key indicator for judging whether particles are produced under appropriate pressure. Poor quality particles, if the specific gravity is below 0.6, will easily collapse and produce too high powder.