Journal of Energy Bioscience 2024, Vol.15, No.1, 32-47 http://bioscipublisher.com/index.php/jeb 38 Biochemical conversion methods, by leveraging the natural metabolic processes of microorganisms, effectively transform various types of biomass into high-value biofuels and byproducts, offering broad application prospects and significant environmental benefits. In the future, with continuous technological advancements and widespread application, biochemical conversion methods are expected to play a more important role in the global energy structure. 4.3 Thermochemical conversion methods Thermochemical conversion methods use heat and chemical reactions to convert biomass into biofuels and other energy carriers. The main thermochemical conversion methods include pyrolysis, gasification, and direct combustion. Pyrolysis process involves heating biomass in the absence of oxygen to decompose it into bio-oil, syngas (a mixture of carbon monoxide and hydrogen), and char (Sieradzka et al., 2020). The bio-oil can be further refined into biofuels, while syngas can be used for electricity generation or as a feedstock for chemical production. Pyrolysis operates at temperatures between 300 °C and 600 °C (Mensah et al., 2022). Gasification process converts biomass into syngas through partial oxidation at high temperatures (above 700 °C). The syngas produced can be used directly for electricity generation or further processed into liquid fuels via the Fischer-Tropsch synthesis. Gasification is highly efficient and can handle a variety of biomass feedstocks (Amin et al., 2022). Direct combustion is the simplest thermochemical conversion method, involving the burning of biomass to produce heat, which can be used for power generation or industrial processes (Bajpai et al., 2020). Although direct combustion is widely used, it has lower efficiency compared to other thermochemical methods and, if not managed properly, can lead to higher emissions. The advantages of thermochemical conversion methods lie in their ability to produce a diverse range of energy products and their potential for integration with existing industrial processes. However, compared to biochemical methods, they typically require higher capital investment and more complex technologies. In summary, energy conversion processes are crucial for transforming agricultural biomass into biofuels and other energy carriers. Photosynthesis provides the basic biomass, while biochemical and thermochemical methods offer various pathways to convert this biomass into usable energy forms. Understanding and optimizing these processes are essential for maximizing the energy potential of agricultural products and supporting their dual role as both food and fuel. 5 Utilization of Agricultural Products for Energy 5.1 Direct combustion and co-firing Direct combustion is the simplest and most traditional method of utilizing biomass for energy. In this process, biomass such as wood, crop residues, and other organic materials are burned to produce heat, which can be used for space heating, industrial processes, or electricity generation. This method has been used for centuries, particularly in rural and developing regions where access to other forms of energy is limited. Co-firing is an advanced application of direct combustion, where biomass is burned alongside coal in existing coal-fired power plants. This approach allows for the reduction of greenhouse gas emissions and the efficient use of existing infrastructure. By integrating biomass with coal, co-firing can reduce the carbon footprint of power generation and provide a transitional pathway towards more sustainable energy systems (Li et al., 2018). Biomass sources for direct combustion and co-firing include wood, crop residues, and animal manure. These materials can be processed into fuelwood, charcoal, or briquettes to enhance their energy density and ease of transport (Maina et al., 2019). 5.2 Bioethanol and biodiesel production Bioethanol and biodiesel are two of the most common biofuels derived from agricultural products. Bioethanol is primarily produced through the fermentation of sugars and starches found in crops such as corn, sugarcane, and wheat. The production process involves milling the feedstock to release fermentable sugars, fermenting these sugars with yeast, and then distilling the ethanol (Limayem and Ricke, 2019; Kumar and Verma, 2021). Bioethanol is commonly blended with gasoline to create E10 (10% ethanol) or E85 (85% ethanol) fuel blends,
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