The extensive human exploitation has led to a sharp reduction in the reserves of traditional activated carbon raw materials such as coal and petroleum coke, resulting in a global energy and environmental crisis. Therefore, it is necessary to seek a new energy source that is environmentally friendly, low-cost, highly efficient, and sustainable to meet the increasing demand for energy. Biochar is a solid carbon material made from biomass (such as wood, straw, waste, etc.) after high-temperature pyrolysis or oxidation treatment. It has become one of the most promising new materials and energy sources due to its characteristics of being pollution-free, high-yield, and renewable.
Although biomass resources are abundant, outdated technologies for preservation and conversion have resulted in severe waste of these resources. Agricultural residues like straw stalks are burned in the fields, forestry byproducts such as wood chips and sawdust are discarded directly, and food processing waste like shells and peels are buried as garbage. This not only pollutes the environment but also leads to significant biomass resource waste. We must find a suitable solution for biochar production.
How to turn biomass into biochar in a green way? The answer is a biomass carbonization plant. Biomass carbonization plant is used for biochar production, except for soil additivity, fuel, and water treatment agent, biochar can be also processed into activated carbon through activated carbon plant. Therefore, converting biomass materials into biochar not only achieves high-value utilization of waste resources but also meets the substantial demand for activated carbon.
Biochar possesses a well-developed porous structure, a high specific surface area, and abundant surface functional groups, which give it a wide range of applications in the fields of energy and environment.
biomass carbonization process
The biochar process involves the thermal conversion of biomass materials into biochar through a controlled pyrolysis or carbonization process. Biomass, which can include agricultural residues, forestry waste, and even certain types of organic waste, is subjected to high temperatures in the absence of oxygen. This process breaks down the complex organic compounds present in biomass and transforms them into biochar, a carbon-rich substance that can have various agricultural and environmental applications.
The biochar process comprises several key steps:
- Feedstock Preparation: Biomass feedstock, such as crop residues, wood chips, or organic waste, is collected and prepared for the carbonization process.
- Drying: The moisture content of the biomass is reduced to enhance the efficiency of the carbonization process. Lower moisture content leads to a more effective conversion of biomass to biochar.
- Carbonization: The prepared biomass is heated in an oxygen-limited environment to initiate the pyrolysis process. This results in the release of volatile compounds and the conversion of the remaining carbon-rich material into biochar.
- Cooling and Collection: Once the carbonization process is complete, the biochar is allowed to cool down before being collected for further processing and application.
The preparation of biochar can be divided into different methods based on the heating process, including thermal decomposition, microwave carbonization, and hydrothermal carbonization.
- Thermal Decomposition Method: Thermal decomposition refers to the high-temperature cracking reaction of biomass under isolated air conditions. The factors influencing thermal decomposition mainly include carbonization and activation temperatures, carbonization and activation times, types of activating agents, and the concentration and quantity of activating agents.
- Microwave Carbonization Method: Microwave heating involves the high-frequency back-and-forth movement of polar molecules within the heated material, generating a large amount of frictional heat through collisions between molecules, thereby rapidly and uniformly heating both the interior and exterior of the material. Microwave heating offers advantages such as simplicity of operation, fast heating rate, high reaction efficiency, and selective uniform heating. Factors affecting the microwave carbonization method include microwave power, type of activating agent, concentration of activating agent, soaking time, and heating time.
- Hydrothermal Carbonization Method: The hydrothermal carbonization method involves heating biomass (carbohydrates, organic molecules, waste biomass, etc.), catalysts, and water inside a hydrothermal reactor at a certain temperature and pressure to achieve biomass carbonization. Hydrothermal carbonization accelerates the physical and chemical interactions between biomass and solvent, promotes reactions between ions and acids/bases, breaks down the carbohydrate structures in biomass, and ultimately forms biochar materials.
Benefits and Applications of Biochar
In addition to the advantages of strong adsorption capacity, stable chemical properties and strong regeneration ability of carbon materials, biochar also has developed pore structure, high specific surface area, stable aromatic structure and rich surface functional groups. These characteristics make biochar have a wide range of application prospects in the field of energy and environment.
The biochar process offers a range of benefits that contribute to its growing popularity:
- Carbon Sequestration: Biochar acts as a carbon sink, locking in carbon that would otherwise be released into the atmosphere as CO2. This helps mitigate climate change by reducing greenhouse gas emissions.
- Soil Enhancement: Biochar can improve soil fertility, water retention, and nutrient availability. When incorporated into agricultural soils, it enhances crop productivity and reduces the need for synthetic fertilizers.
- Waste Management: The process provides a solution for managing various organic wastes that would otherwise contribute to environmental pollution. These waste materials are transformed into a valuable resource.
- Renewable Energy: While the primary focus is on producing biochar, the biochar process can also yield biofuels and other valuable byproducts through careful control of the pyrolysis conditions.
Development Prospects of Biochar
Biochar, derived from abundant biomass resources, possesses characteristics of being both green and sustainable. The future focus of biochar production lies in the development of environmentally friendly and mild conversion methods, as well as the modulation of microporous structures and surface functional groups of biochar through the selection of activating agent types and content, activation methods, and catalyst types and content. The application research of biochar in the field of energy will contribute to achieving energy diversification and reducing reliance on fossil fuels. In the environmental domain, biochar’s applications can effectively address water and soil pollution.
The utilization of biochar will emphasize the development of multifunctional biochar. This includes enhancing its electrical conductivity, imparting photosensitivity or magnetic responsiveness, to meet the demands of the energy sector. Furthermore, the high adsorption capacity, recyclability, and regenerability of biochar, along with its environmental sensitivity, will expand its applications in the environmental sector.