In Korean pulp and paper industry, a self-sufficiency rate of pulp for making paper is far less than 20%. While market price of kraft pulp has been sharply rising, it is a hard work to produce competitive products without influencing a manufacturing cost. Therefore, domestic wood chips are necessarily required for consistent growth of pulp and paper industry in Korea.
The Forest Management Operation Project (FMOP) managed by the Forest Service in Korea has been generating a large amount of woods every year. This study aimed to use these acquired products economically and effectively by evaluating alternative raw materials for wood pellets instead of using them.
Wood pellets are mostly made from clean sawdust and wood chips from softwood and hardwood. The wood must have been debarked prior to passing through the sawmill. Sawdust of hardwoods can be mixed in with that of softwood, but successful production of hardwood pellets without binders is more difficult. Wood pellets are a condensed uniformly sized form of biomass energy, making them easier to store and use than many other biomass fuels. Pellet heating technology is also quite simple, minimizing operation and maintenance requirements. Wood pellets are a common type of biomass and are green fuel.
Biomass is any biological material that can be used as fuel?including grass, corn, wood, and biogas as well as other forestry and agricultural residues. Unfortunately, the self-sufficiency rate of wood in Korea is only around 16%. Such low self-sufficiency rate of wood prevents wood from being used as raw materials for wood pellets. This implies that new alternative lignocellulosic biomass must be explored to substitute for wood. It must be noted that pellets can be manufactured from lignocellulosic raw materials such as corn stalk, bark, leaves, soy bean stalk, PKS and so on. Then new technology like torrefaction was applied to improve heating efficiency of pellets made of such lignocellulosic biomass. Torrefaction is a thermal pre-treatment technology, which produces a solid biofuel product that has superior handling, milling and co-firing capabilities compared to other biofuels. It is a thermochemical pretreatment method utilizing an operating temperature of 200°C to 300°C under low or little oxygen atmosphere and atmospheric pressure. Furthermore, if torrefaction technology able to improve heating value of pellets is applied, it will be greatly helpful to use lignocellulosic biomass as limited resources in Korea economically and effectively. Through this technology, various types of lignocellulosic biomass could be used to make a high grade pellets.
For pellets as solid fuel, most of lignocellulosic biomasses showed high ash and nitrogen contents except for wood and palm kernel shell (PKS). It is well known that high ash and nitrogen contents negatively influence a boiler performance and durability. With the exception of ash and nitrogen contents, the pellets made of different lignocellulosic biomasses had a premium grade quality regarding heating value, moisture contents, density, fine dust contents and so on. Despite good quality of various lignocellulosic biomass, it was necessary to improve their heating value by the torrefaction. Biomass as fuel source has lower energy density, higher moisture content and is more difficult to mill/grind into small particles than more traditional energy sources such as fossil fuels. The material is highly hydrophilic and thereby absorbs moisture when transported and stored, which may lead to storage and transportation problems, uncontrolled biological degradation processes and in worst case scenario, self ignition. Torrefaction was a pre-treatment technology that improved all of the above mentioned drawbacks of biomass application.
For pellets, most of lignocellulosic biomasses showed high ash and nitrogen contents except for wood and palm kernel shell (PKS). High ash and nitrogen contents negatively influence a boiler performance. With the exception of ash and nitrogen, the pellets made of all lignocellulosic biomasses had a premium grade quality regarding heating value, moisture contents, density, fine dust contents and so on.
Torrefaction greatly contributed to the improvement of heating value. Non-torrefied wood pellets had a heating value of about 4,300 kcal/kg, but torrefied wood pellets had a heating value of about 7,000 kcal/kg. It is important to note that biomasses with low heating value before torrefaction had less increase than those with high heating value.
The conclusion comes from the fact that torrefied lignocellulosic biomass could be valuable raw materials for making solid fuels like pellets.