Journal of Energy Bioscience 2024, Vol.15, No.3, 197-207 http://bioscipublisher.com/index.php/jeb 198 2 Types of Forestry Waste 2.1 Classification of forestry waste Forestry waste can be broadly classified into several categories based on their origin and composition. The main types include logging residues, sawdust, bark, and wood chips. Logging residues are the residues left after logging, including branches, stumps, and leaves, which are usually left on the forest floor and contribute to the accumulation of biomass. Sawdust is produced during the process of sawing logs into lumber and is a fine wood particle that can be used for a variety of purposes, including energy production. Bark is the outer protective layer of trees, which is usually stripped away during wood processing and can be used as fuel or in the production of mulch and other products. Wood chips are small pieces of wood produced by cutting larger pieces of wood and are usually used in pulp mills, as fuel, or for landscaping. 2.2 Quantitative data on forestry waste availability Forestry waste is generated in substantial quantities globally. For instance, agricultural and forestry wastes (AFWs) are produced in huge amounts and are considered an important resource for reducing dependence on fossil fuels (Lin et al., 2021). The availability of forestry waste varies by region and type of forestry activity. For example, sawdust and wood chips are commonly produced in sawmills, while logging residues are more prevalent in areas with active logging operations. 2.3 Environmental impact of forestry waste accumulation The accumulation of forestry waste can have significant environmental impacts. If not managed properly, it can lead to increased fire hazards, pest infestations, and the release of greenhouse gases as the biomass decomposes. Utilizing forestry waste for energy production through thermochemical conversion methods can mitigate these environmental risks. The smart use of AFWs, including forestry waste, requires a combination of available waste streams and local technical solutions to meet sustainability criteria (Song et al., 2020; Bin et al., 2022). This approach not only reduces the environmental impact but also contributes to the circular economy by transforming waste into valuable resources. 3 Overview of Thermochemical Conversion Methods 3.1 Definition and principles of thermochemical conversion Thermochemical conversion refers to the process of converting biomass into energy and valuable chemicals through the application of heat and chemical reactions. This method leverages high temperatures to break down complex organic materials into simpler molecules, which can then be utilized as fuels or chemical feedstocks. The primary principles involve the decomposition of biomass in the absence or presence of limited oxygen, leading to the production of gases, liquids, and solid residues (Uzoejinwa et al., 2018). 3.2 Main thermochemical processes Pyrolysis is a thermochemical process that involves the thermal decomposition of biomass in the absence of oxygen. It produces a mixture of solid (biochar), liquid (bio-oil), and gaseous (syngas) products (Figure 1). Pyrolysis can be further categorized into slow, fast, and flash pyrolysis, depending on the heating rate and residence time (Uzoejinwa et al., 2018; Foong et al., 2020; Jesus et al., 2020). Recent advancements include microwave pyrolysis, which enhances heat transfer efficiency and product yield. The figure illustrates a process for converting lignocellulosic biomass into sustainable energy using pyrolysis technology. The characteristics of the pyrolysis products significantly vary based on process temperature, heating rate, biomass composition, and residence time. Introducing microwave heating into the pyrolysis process is considered an effective solution. Compared to traditional pyrolysis, microwave-assisted pyrolysis offers several advantages, such as faster heating rates, quicker and more uniform heating of large feed quantities, higher energy efficiency, bio-oil with lower water content, and rapid response in pyrolyzer startup and shutdown. Gasification is a process that converts biomass into syngas (a mixture of carbon monoxide, hydrogen, and methane) by reacting the material at high temperatures with a controlled amount of oxygen and/or steam. This
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