Energy-efficient biochar production for thermal backfill applications.

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Engineered thermal backfills are crucial for preventing heat migration around underground crude oil pipelines over 25-50 years.
• Biochar, with its low thermal conductivity and inert nature, is a promising material for thermal backfills.
• Traditional biochar production via pyrolysis is energy-intensive, necessitating optimization for cost-effectiveness and sustainability.

Purpose of the Study:

• To optimize biochar production for thermal backfill applications by investigating the impact of pyrolysis temperatures on energy efficiency, yield, thermal conductivity, and soil stability.
• To identify the most suitable pyrolysis temperature for producing biochar that meets the long-term performance requirements of thermal backfill materials.

Main Methods:

• Ten biochar samples were produced from water hyacinth and sugarcane bagasse at pyrolysis temperatures ranging from 300 °C to 700 °C.
• The produced biochars were analyzed for thermal conductivity, energy consumption during production, yield, and long-term carbon stability in soil.
• Performance metrics were evaluated against the requirements for thermal backfill applications in the crude oil industry.

Main Results:

• Biochar thermal conductivity remained consistent (0.10-0.13 W m⁻¹ K⁻¹) across different pyrolysis temperatures.
• The lowest pyrolysis temperature (300 °C) yielded the most biochar with the least energy consumption but exhibited poor soil stability.
• A pyrolysis temperature of 400 °C was identified as optimal, offering significant energy savings (at least 60% compared to 700 °C) while ensuring adequate carbon stability for thermal backfill applications.

Conclusions:

• Pyrolysis temperature critically influences biochar properties, impacting its suitability for specific applications like thermal backfill.
• A 400 °C pyrolysis temperature is recommended for producing energy-efficient and stable biochar for underground pipeline thermal management.
• This research provides valuable insights for tailoring biochar production processes to meet industrial material demands.