Hydrothermal carbonization (HTC) is a thermochemical process used to convert organic materials into a coal-like substance, typically referred to as hydrochar. This process occurs in the presence of water at elevated temperatures (typically between 180°C and 250°C) and under autogenous pressure (which is the pressure generated by the water at these temperatures). The process can take anywhere from a few hours to several days, depending on the desired outcome.

Key Aspects of Hydrothermal Carbonization:

1. Feedstock:

   • HTC can process a wide variety of organic materials, including agricultural residues, sewage sludge, food waste, and even wet biomass that would be difficult to process using other thermochemical methods like pyrolysis.

2. Process Conditions:

   • Temperature: Typically 180°C to 250°C.
   • Pressure: The process occurs under the pressure generated by water at the given temperature, often between 10 and 40 bar.
   • Residence Time: The reaction time can vary from several hours to a few days, depending on the feedstock and desired properties of the hydrochar.

3. Product:

   • The primary product is hydrochar, a carbon-rich solid that can be used as a soil amendment, for energy production (as a fuel), or as a precursor for activated carbon.
   • The process also produces process water, which contains dissolved organic compounds and nutrients, and gases such as CO2.

4. Advantages:

   • HTC is particularly effective for wet biomass, as it does not require drying of the feedstock.
   • It can potentially reduce the environmental impact of waste by converting it into useful products.
   • The hydrochar produced has a higher energy density compared to the original biomass and can be used as a renewable energy source.

5. Applications:

   • Waste Management: Converting organic waste into hydrochar reduces the volume of waste and can produce a valuable product.
   • Soil Amendment: Hydrochar can improve soil properties by enhancing nutrient retention and soil structure.
   • Energy Production: Hydrochar can be used as a solid fuel or further processed into activated carbon for use in filtration systems.

HTC is seen as a promising technology for sustainable waste management and renewable energy production, particularly in applications where wet biomass is abundant.