The difference between hardwood pellets vs softwood pellets
There are two common types of wood pellets: hardwood pellets and softwood pellets. They differ in many ways, as described below.
Material characteristics of hardwood pellets vs softwood pellets
Hardwood pellets
- Types and Sources of Wood
Hardwood usually includes oak, birch, hickory, etc. These woods come mainly from mature trees and have a relatively long growth cycle. For example, oak grows slowly, and its wood has a dense structure and fine texture, which gives it high density and strength even before it is processed into pellets. These wood resources are common in some areas with abundant forest resources and are widely used in furniture manufacturing, construction and other industries. Their waste and surplus wood are high-quality raw materials for hardwood pellets.
- Chemical Composition and Structural Properties
Hardwood has a relatively high lignin content. Lignin is a complex organic polymer that gives wood its high hardness and wear resistance. At the same time, the cellulose fibers in hardwood are relatively short but tightly packed, making the physical structure of hardwood particles more compact. This structural characteristic results in hardwoods releasing heat steadily and continuously when burned, leaving relatively little residue and low ash content.
Material characteristics of hardwood pellets vs softwood pellets
Softwood pellets
- Types and sources of wood
Softwoods are mainly pine and fir. They grow relatively quickly and are abundant. Pine, for example, is a common softwood that is widely distributed and cultivated in the forests of the northern hemisphere. In addition to the main trunk of the tree, branches and other parts of softwoods can be used to make pellets. During the wood processing process, such as pulp production in paper mills or the primary processing stage in wood processing plants, a large amount of softwood chips is produced, which is an ideal raw material for the production of softwood pellets.
- Chemical Composition and Structural Properties
Softwoods have a relatively low lignin content and a high cellulose content. The cellulose fibers are long and straight. This makes softwood pellets relatively soft and easy to work with. However, due to their relatively loose structure, the flame can be more active and burn relatively quickly when burning. Softwood also has a relatively high resin content, which to some extent affects its combustion characteristics and odor, and may require more attention to prevent oxidation and deterioration during storage.
Physical properties of hardwood vs softwood pellets
Density of wood pellets
- Density of hardwood pellets
Due to the dense structure of the raw material wood, the density of the finished pellets is generally high, usually around 1.2 – 1.3g/cm³. This high density means that hardwood pellets are more compact during storage and transportation, taking up relatively little space. And during combustion, the high-density pellets can release heat steadily and continuously, with high combustion efficiency. They are suitable for use in situations that require a stable supply of heat over a long period of time, such as industrial boilers.
- Density of softwood pellets
The density of softwood pellets is relatively low, usually between 1.0 and 1.1 g/cm³. The low pellet density has some advantages. For example, in domestic heating systems, the lower density makes the pellets easier to ignite, and they release heat quickly during the initial stage of combustion, causing the room temperature to rise faster. However, due to their low density, softwood pellets require extra care during storage and transportation to avoid crushing, and they have slightly less energy per unit volume than hardwood pellets.
Particle size and shape of wood pellets
- Particle size and shape of hardwood
During the pressing process, hardwood particles often take on a relatively regular shape due to the high hardness of the raw material. They are usually cylindrical in shape, 10–30 mm long and 6–10 mm in diameter. The surface is relatively smooth because when hardwood is pressed, its internal structure is tightly aligned under pressure, and the particles are tightly bound together. This regular shape and size facilitates even feeding and stable combustion in combustion equipment.
- Particle size and shape of softwood pellets
The shape of softwood pellets is also mostly cylindrical, but due to the soft nature of the wood, they may be slightly deformed during the pressing process. The size range is similar to that of hardwood pellets, but the surface of softwood pellets may be relatively rough. This is because the fiber structure of softwood is not as compact as that of hardwood after pressing, and the fibers on the surface of the pellets may be exposed to some extent.
Physical properties of hardwood vs softwood pellets
Combustion properties of hardwood pellets vs softwood pellets
Calorific value of wood pellets
- Calorific Value of Hardwood Pellets
The low calorific value of hardwood pellets is generally high, usually between 19 and 21 MJ/kg. This is because hardwood itself has a high energy density and can release a lot of heat during combustion. The combustion process is relatively stable, with a long-lasting flame that can provide continuous and stable energy support for industry and large heating systems. For example, the use of hardwood pellets in large central heating boilers can maintain a relatively high water temperature for a long period of time, meeting the heating needs of a large number of users.
- Calorific Value of Softwood Pellets
The lower calorific value of softwood pellets is generally around 17-19 MJ/kg. Although the calorific value is slightly lower than that of hardwood pellets, softwood pellets can release heat quickly at the start of combustion, making them more suitable for use in some small heating appliances or in situations where rapid temperature rise is required. For example, in small residential pellet stoves, softwood pellets can raise the indoor temperature in a relatively short period of time, providing the user with a warm environment..
Combustion properties of hardwood pellets vs softwood pellets
Combustion speed and stability
- Burning rate and stability of hardwood pellets
Hardwood pellets burn relatively slowly due to their dense structure, and it takes longer for oxygen to penetrate the interior of the pellets for complete combustion. This slow and stable combustion process makes the flame produced by burning hardwood pellets relatively stable, without violent fluctuations. At the same time, due to the moderate burning rate, hardwood pellets produce less residue after combustion, which is beneficial for the cleaning and maintenance of combustion equipment.
- Combustion speed and stability of softwood pellets
Softwood pellets burn relatively quickly because their structure is loose, making it easier for oxygen to enter the interior of the pellets and causing the combustion reaction to proceed rapidly. During combustion, the flame of softwood pellets is relatively active and prone to flame jumping. However, softwood pellets can also burn completely during combustion. You just need to control the feeding rate to prevent combustion from proceeding too quickly, thereby avoiding the underutilization of heat.
Cost comparison of processing hardwood pellets vs softwood pellets
Processing difficulty of wood pellets
- Hardwood pellets are difficult to process
Hardwood is relatively difficult to process into pellets. Due to its hardness, it requires more powerful crushing equipment during the crushing process, and the equipment also wears out more quickly. For example, if a hammer crusher is used, hardwood can cause greater wear on the hammers, which need to be replaced more frequently. During the pelleting process, hardwood pellets require higher pressure to form well, which places higher demands on the pelleting equipment.
- Processing difficulty of softwood pellets
Softwood pellets are relatively easy to process. Softwood is soft and crushes easily, and can be processed to the right particle size using standard crushing equipment. Softwood also requires relatively low pressure during the pressing process, and has low requirements for the pressing equipment. As a result, the processing cost of softwood pellets is relatively low, and there is less wear on the equipment.
Processing costs for hardwood pellets vs softwood pellets
- Cost of hardwood pellets
The cost of hardwood pellets is relatively high. This is partly because hardwood itself has a long growth cycle and resources are relatively scarce, resulting in higher raw material costs. On the other hand, due to the difficulty of processing, the costs of equipment wear and energy consumption during processing are also higher. The combination of these factors means that the price of hardwood pellets is usually higher than that of softwood pellets.
- Cost of softwood pellets
Softwood pellets are relatively inexpensive. Cork grows quickly, is widely available and relatively inexpensive. Because they are relatively simple to process, and equipment and energy costs are low, softwood pellets are more competitive in the market and are suitable for cost-sensitive users and applications.
Cost comparison of processing hardwood pellets vs softwood pellets
Hardwood pellets vs softwood pellets each have their own characteristics and advantages in different application scenarios. We can choose the right wood pellets for our needs, taking into account factors such as heating method, equipment type and cost considerations.
