Hydrothermal carbonization (HTC)

Hydrothermal carbonization (HTC) is a thermochemical process that converts organic biomass, such as agricultural waste, sewage sludge, or woody materials, into a carbon-rich material known as hydrochar or biochar. The process involves subjecting the biomass to high temperatures and pressures in the presence of water.

During hydrothermal carbonization, the biomass is typically heated to temperatures ranging from 180 to 250 degrees Celsius (356 to 482 degrees Fahrenheit) under pressure, usually between 10 and 25 bar. The reaction takes place in a closed reactor vessel, where the biomass is mixed with water and heated. The combination of heat, pressure, and water triggers several chemical reactions, including hydrolysis, dehydration, decarboxylation, and polymerization.

These reactions result in the breakdown of complex organic molecules in the biomass, leading to the formation of simpler compounds such as water, carbon dioxide, methane, and other volatile organic compounds. Meanwhile, the carbon-rich fraction of the biomass undergoes solidification and forms hydrochar.

The hydrochar produced through hydrothermal carbonization has several beneficial properties. It is rich in carbon and contains a significant portion of the original carbon content of the biomass. Hydrochar resembles coal in terms of its appearance and energy content but typically has a higher fixed carbon content. It is also more stable, less prone to combustion, and has a lower moisture content compared to the original biomass.

Hydrochar can be used in various applications. It can serve as a solid fuel source for energy production, acting as a substitute for coal or other fossil fuels. Additionally, it can be used as a soil amendment to enhance soil fertility and improve water retention. The carbon sequestration potential of hydrochar also makes it a promising candidate for carbon capture and storage (CCS) technologies.

Hydrothermal carbonization offers several advantages as a biomass conversion process. It can handle a wide range of feedstocks, including wet or high-moisture materials that are typically challenging to process through other means. The process is relatively fast, typically taking a few hours, and it operates at lower temperatures compared to other thermochemical conversion technologies such as pyrolysis or gasification.

Overall, hydrothermal carbonization provides a sustainable and efficient way to convert biomass into a valuable carbon-rich product with various applications, contributing to the utilization of organic waste and the development of a circular economy.