Sawdust is next wave in renewable energy

Sawdust is a tiny piece of wood that fall as powder from wood as it is cut by a saw. In other words, sawdust is basically a waste of small particles available in saw-milling industries, pulp plant and paper industries as well as wood processing industries, usually at quite large volume in form of heaps and mostly burnt off resulting in the environmental pollution (Rominiyi et al., 2017; Duanguppama et al., 2016). Sawdust is produced through the cutting, sizing, re-sawing, edging, trimming and smoothing of wood (Figure 1). In general, processing of 100 kg wood in sawmill produces around 12–25 kg sawdust (Varma and Mondal, 2016a). This biomass resource a 2nd generation resource (Ahorsu et al., 2018). Currently, sawdust is mainly used for manufacture of particle board in paper mills, although it has potential for releasing heat energy (Varma et al., 2019).   In many cases due to lack of better ways of handling, this waste is commonly disposed into the environment without any treatment. Common disposal methods include heaping at the mill sides, open air combustion, disposal along roadside and water bodies. Abandonment of sawdust at saw mills causes aesthetic impacts; burning results in the environmental pollution; while abandonment along the road side causes air quality impact as a result of wind, which often blows and suspends the wood dusts into the atmosphere. This practice causes respiratory problem in human and air pollution (Ohimain, 2012; Rominiyi et al., 2017). However, these problems can be overcome by using this waste biomass to transform its internal energy into usable forms of energy through thermal conversion processes. Combustion (burning), gasification and pyrolysis are three fundamental thermal conversion processes. (Varma et al., 2019). Combustion is a simple thermal decomposition process produces heat for power generation. However, as per environmental point of view it is not a reliable process because, it generates high content of carbon dioxide and other harmful gases, and also the thermal efficiency of this process is low. Gasification is very efficient process and produces syngas (CO + H2), but it has the disadvantage of requiring high investment cost (Kumar et al., 2008). However, pyrolysis is an attractive process as it is simple to operate and inexpensive (Bridgwater, 2003). During last few years, pyrolysis process has received much attention as it produces energy in the form solid (bio-char), liquid (bio-oil) and gases from biomass/wastes by heating in inert atmosphere (Bartocci et al., 2018; Yang et al., 2006). Biomass types and their particle size, reactor types, operating parameters such as pyrolysis temperature, heating rate and vapour residence time determine the composition and yield of the products In pyrolysis process (Lu et al., 2009). For the pyrolysis of different biomass/ wastes have been used Several reactors like continuous, semi batch and batch types (Shadangi and Mohanty, 2014; Abnisa et al., 2013; Azargohar et al., 2013; Arami-Niya et al., 2011; Salehi et al., 2009). Continuous reactors are those that give higher liquid yield as compare to batch or semi batch reactor. Although the complexity of the process and control are very high in the continuous reactor, the design of these reactors needs detailed knowledge of the process. Furthermore, for any new biomass, batch or semi batch reactors are employed to explore the characteristics of process as well as generate the kinetic data which are essential for reactor design. A semi batch reactor, however, allows partial filling of reactants with the flexibility of adding more as time progresses (Varma et al., 2019).

Figure 1. Wood sawmills

In pyrolysis, the yield of bio-oil initially increases with increasing temperature, reaches the optimum at the intermediate temperature of 500 C and decreases thereafter, , the gaseous products yield rises and bio-char yield reduces continuously with increase in temperature. Bio-char yield increases and gaseous products yield reduces with rise in Wood sawdust particle size.  Considering that the yield of the bio-oil is not appreciably affected by the particle size, although the maximum yield of the bio-oil is observed for the size of the intermediate particles of the biomass.  Gaseous products yield rises with the rise in N2 flow rate, whereas bio-char yield decreases. However, bio-oil yield initially rises with the rise in N2 flow rate, achieves optimum value and decreases thereafter with increase in N2 flow rate (Varma et al., 2019).

Several properties of bio-oil mean that it can be used as an energy fuel after refining and improvement and, in addition, as a feedstock for important synthetic compounds. Bio-char can also be used as a solid fuel and antecedent for activated carbon. It also helps in rise of crop production through soil acidity neutralization. Wood sawdust is a good potential renewable energy source for pyrolysis, this can be supported if all the pyrolysis products are used proficiently (Varma et al., 2019).

References

Ahorsu, R., Medina, F., Constantí, M. (2018). Significance and Challenges of Biomass as a Suitable Feedstock for Bioenergy and Biochemical Production: A Review. Departament d’Enginyeria Química, Universitat Rovira i Virgili, 43007 Tarragona, Spain; richard.ahorsu@urv.cat (R.A.); magda.constanti@urv.cat (M.C.).

https://www.eurekalert.org/pub_releases/2018-12/uoml-rsi121118.php

Rominiyi, O.L., Adaramola, B.A., Ikumapayi, O.M., Oginni, O.T. and Akinola, S.A. (2017) Potential Utilization of Sawdust in Energy, Manufacturing and Agricultural Industry; Waste to Wealth. World Journal of Engineering and Technology, 5, 526-539.

https://doi.org/10.4236/wjet.2017.53045

Varma, A.K., Thakur, L.S., Shankar, R., Mondal, P. (2019) Pyrolysis of wood sawdust: Effects of process parameters on products yield and characterization of products. Waste Management 89 (2019) 224–235.