Based on the heating rate, pyrolysis temperature, and reaction residence time, biomass pyrolysis techniques can be categorized as rapid or slow. Compared to rapid pyrolysis, slow pyrolysis in biomass requires less raw material and produces less costly biochar, while offering higher biochar yields.
Slow pyrolysis is carried out at a relatively low heating rate (typically 0.1-1°C/s) and a reaction temperature generally controlled between 300-500°C. Under these conditions, the biomass undergoes a long residence time (ranging from minutes to hours), resulting in a slow decomposition reaction. Slow pyrolysis in biomass results in biochar production with a high carbon content and a rich pore structure, making it an excellent choice for applications such as soil improvement and carbon sequestration.
Fast pyrolysis, on the other hand, rapidly heats the biomass to 400-600°C at an extremely high heating rate (10-200°C/s). It completes the pyrolysis reaction within a very short residence time (less than 2 seconds). Fast pyrolysis focuses on the production of liquid bio-oil, with bio-oil yields reaching up to 75%. Fast pyrolysis in biomass offers unique advantages in the production of biofuels and industrial chemical feedstocks. However, the biochar produced by rapid pyrolysis is often inferior to that produced by slow pyrolysis in terms of pore structure and carbon stability.
Slow Pyrolysis Ensures High Biochar Yield
Slow pyrolysis, with its unique reaction characteristics, provides a solid guarantee for high biochar yields. During slow pyrolysis, the slow heating rate (typically 0.1-1°C/s) allows sufficient time for the biomass molecules to undergo orderly thermal decomposition and recombination reactions.
From a reaction kinetics perspective, the longer reaction time of slow pyrolysis (ranging from minutes to hours) provides ample time for the biomass pyrolysis reaction to fully decompose.
During this biomass pyrolysis carbonization process, volatile substances in the biomass gradually escape, while carbon is fully retained and enriched, thereby increasing biochar yield.
High-quality Biochar Production
Slow pyrolysis not only achieves high biochar yields but is also the key to creating high-quality biochar.
Biochar exhibits a well-developed pore structure and a large specific surface area, enhancing its adsorption properties. During the biomass pyrolysis process, organic matter within the biomass gradually volatilizes, forming a rich microporous and mesoporous structure. These interconnected pores provide numerous adsorption sites for the biochar, increasing its specific surface area.
This enables biochar to more effectively adsorb nutrients, water, and pollutants from the soil, playing a vital role in soil improvement and environmental pollution control.
The stability of biomass to biochar making is also closely related to the pyrolysis method. Biochar produced by slow pyrolysis has a high carbon content, typically between 70% and 90%, and low hydrogen and oxygen contents. This elemental composition contributes to its high chemical stability. It can persist in the soil for long periods of time, resisting microbial decomposition, and continuously exerts its soil-improving and carbon-sequestering properties.
Wide Adaptability of Raw Materials
Biomass pyrolysis exhibits broad adaptability to diverse biomass feedstock types and forms, giving it unique advantages in biochar production.
Whether it’s agricultural and forestry waste rich in cellulose, hemicellulose, and lignin, such as corn stover, rice husks, and sawdust, or animal manure and food waste, which contain a certain amount of protein and fat, they can all be effectively converted into biochar through slow pyrolysis.
Take corn stover and animal manure as examples. Corn stover is rich in cellulose and hemicellulose. During the slow pyrolysis process, these organic substances gradually decompose and reconstitute under optimal temperature and time conditions, forming biochar with excellent properties.
Although animal manure has a complex composition, containing not only organic matter but also nutrients such as nitrogen, phosphorus, and potassium, as well as microorganisms, slow pyrolysis can adapt to its characteristics, converting it into nutrient-rich biochar with excellent adsorption properties. This biochar can not only be used for soil improvement but also realize resource utilization of waste.
This wide adaptability to feedstocks enables Mingjie Biomass Pyrolysis Plant to fully utilize a variety of biomass resources. It can reduce the cost of biochar production while reducing the pressure of waste on the environment, laying a solid foundation for the sustainable development of the biochar industry. 
