Biomass
Background of Pyrolysis Technology
Pyrolysis is a modern waste treatment technology that has gained significant attention in recent years for its ability to process organic solid waste efficiently and sustainably. Interest in pyrolysis intensified in the early 1990s when foreign researchers identified dioxins—highly toxic and carcinogenic compounds—being released during traditional waste incineration. This discovery prompted a reevaluation of incineration-based waste management in many developed countries due to its potential for secondary pollution.
In response, significant investments were made in developing alternative treatment technologies. Pyrolysis emerged as a promising solution. Environmental experts worldwide now recognize pyrolysis as a viable pathway for the environmentally responsible treatment, reduction, and resource recovery of organic solid waste.
Principle of Pyrolysis
Pyrolysis is a thermal decomposition process that occurs under anaerobic or oxygen-limited conditions. When organic solid waste is exposed to high temperatures without oxygen, it breaks down into smaller molecular compounds. The primary products of pyrolysis include:
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Combustible Gas: e.g., methane, ethane, hydrogen, carbon monoxide
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Liquid Byproducts: e.g., methanol (CH₃OH), acetone (CH₃COCH₃), propionic acid (C₂H₅COOH), acetaldehyde (CH₃CHO), tar, and mineral spirits
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Solid Residues: e.g., coke and carbon black
This process converts waste into valuable energy and material resources, with a significantly lower environmental impact than incineration.
Reaction Equation
Organics + Heat (in adiabatic, anoxic conditions) → Pyrolysis Gas + Liquid Byproducts (Tar/Oil) + Solid Residue (Char/Carbon)
Biomass Pyrolysis Applications
Due to the relatively low yield of fuel oil from agricultural waste—such as almond shells—the process emphasizes the conversion of feedstock into combustible gas rather than liquid fuel. A small fraction of fuel oil may be produced, but most of the output is syngas generated through controlled thermal decomposition. This gas is partially used to meet the system's own energy demands, with the remainder converted into electricity and supplied to the national grid via a gas generator.
During the start-up phase, the pyrolysis reactor requires an external energy source—typically natural gas. Once operational stability is reached, the process becomes self-sustaining through the internal combustion of pyrolysis gas. The primary components of this gas include methane, ethane, hydrogen, and carbon monoxide. After purification, it fuels a combustion furnace. Because this gas is relatively clean-burning, the resulting emissions require only minimal treatment to meet regulatory standards.
Product Distribution from Low-Temperature Pyrolysis of Almond Shells
Based on internal testing, the output is approximately:
Of the combustible gas generated, 40% is used to satisfy the system’s internal energy requirements, while 60% is converted into electricity.
Byproducts and Agricultural Benefits
Wood Vinegar: A versatile liquid byproduct widely used in agriculture. It serves as a plant growth enhancer, soil conditioner, deodorizer, feed additive, and organic fertilizer.
Biomass Char (Biochar): This solid residue is an excellent soil amendment and organic carbon fertilizer. It improves water retention, supports microbial activity, and gradually releases nutrients, making it valuable for sustainable agriculture. It can also be densified and used as a carbon-neutral fuel source.
