Journal of Energy Bioscience 2024, Vol.15, No.3, 197-207 http://bioscipublisher.com/index.php/jeb 200 3.3 Comparative analysis When comparing pyrolysis, gasification, and combustion, several factors such as efficiency, product yield, and applicability to forestry waste must be considered. Gasification generally offers higher efficiency in converting biomass to energy compared to pyrolysis and combustion. This is due to its ability to produce a high-energy syngas that can be used in various applications (Labaki and Jeguirim, 2017; Ong et al., 2020). Pyrolysis, particularly fast and microwave pyrolysis, can also be efficient but is more complex and requires precise control of operating conditions (Foong et al., 2020; Jesus et al., 2020). Combustion, while straightforward, is less efficient in terms of energy conversion but is highly effective for direct heat and power generation. Pyrolysis is notable for its ability to produce a diverse range of products, including biochar, bio-oil, and syngas, making it versatile for different applications (Uzoejinwa et al., 2018; Foong et al., 2020). Gasification primarily produces syngas, which is valuable for its high energy content and versatility in chemical synthesis. Combustion yields heat and ash, with no intermediate products, making it less versatile but highly effective for immediate energy needs (Labaki and Jeguirim, 2017; Vega et al., 2019). All three methods are applicable to forestry waste, but their suitability depends on the desired end products and specific application requirements. Pyrolysis is advantageous for producing biochar and bio-oil, which can be used for soil amendment and as a renewable fuel, respectively. Gasification is suitable for producing syngas from forestry waste, which can be used for power generation or as a feedstock for chemical production. Combustion is ideal for direct energy recovery from forestry waste, providing a straightforward solution for heat and power generation (Labaki and Jeguirim, 2017; Vega et al., 2019). 4 Pyrolysis of Forestry Waste 4.1 Mechanism and process conditions of pyrolysis Pyrolysis is a thermochemical conversion process that involves the thermal decomposition of organic materials in the absence of oxygen. The process conditions, such as temperature, heating rate, and residence time, significantly influence the yield and quality of the pyrolysis products. Typically, pyrolysis occurs at temperatures ranging from 300 ℃ to 700 ℃. The heating rate can vary from slow to fast, affecting the distribution of bio-oil, syngas, and biochar produced. For instance, slow pyrolysis, which operates at lower heating rates and longer residence times, tends to favor biochar production, while fast pyrolysis, with higher heating rates and shorter residence times, is optimized for bio-oil production (Lee et al., 2020; Jha et al., 2022). 4.2 Types of pyrolysis There are three main types of pyrolysis: slow, fast, and flash pyrolysis. Slow Pyrolysis operates at low heating rates (0.1 ℃/s~1 ℃/s) and long residence times (hours to days), producing a higher yield of biochar (Lee et al., 2020). Fast pyrolysis features a rapid heating rate (10 ℃/s~200 ℃/s) and short residence times (seconds), maximizing the production of bio-oil (Jha et al., 2022). Flash Pyrolysis is an extreme form of fast pyrolysis with very high heating rates (>1 000 ℃/s) and very short residence times (milliseconds), primarily producing bio-oil and syngas. 4.3 Products of pyrolysis and their energy potential The primary products of pyrolysis are bio-oil, syngas, and biochar, each with distinct energy potentials. Bio-oil is a liquid fuel that can be directly used for heating or further refined into transportation fuels. It has a high energy density and can be upgraded to improve its performance (Jha et al., 2022). Syngas, a mixture of hydrogen, carbon monoxide, and other gases, can be used for power generation or as raw materials for producing chemicals and fuels. Biochar is a carbon-rich solid product that can be used as a soil amendment to improve soil health and sequester carbon, or as a raw material for combustion and gasification due to its high fixed carbon content and energy density (Lee et al., 2020). 4.4 Optimization strategies for maximizing bio-oil yield and quality To maximize the yield and quality of bio-oil, several optimization strategies can be employed. The type of biomass used can significantly affect the yield and quality of bio-oil. Lignocellulosic feedstocks, for example, are
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