Thermodynamic Analysis of

Area of Science:

• * Geochemistry and Chemical Engineering
• * Thermodynamics and Energy Resources

Background:

• * In situ underground pyrolysis of tar-rich coal is vital for China's energy security and sustainable coal utilization.
• * Actual underground conditions (high pressures) differ significantly from laboratory simulations, necessitating specific thermodynamic studies.
• * Understanding these conditions is key to optimizing coal resource management and reducing reliance on oil and gas.

Purpose of the Study:

• * To conduct a thermodynamic investigation of tar-rich coal pyrolysis under simulated in situ underground conditions.
• * To determine key thermodynamic functions (enthalpy, Gibbs free energy, entropy) for tar-rich coal.
• * To analyze the impact of temperature and pressure on the primary pyrolysis reactions.

Main Methods:

• * Determination of standard thermodynamic functions for tar-rich coal.
• * Construction of ten representative primary pyrolysis reactions based on coal oil components.
• * Analysis of Gibbs free energy and equilibrium constant changes across temperatures (200–800 °C) and pressures (atmospheric to 10 MPa).

Main Results:

• * Standard enthalpy of formation: -72.27 kJ·mol⁻¹.
• * Standard entropy: -37.79 J·mol⁻¹·K⁻¹.
• * Standard formation Gibbs free energy: -60.01 kJ·mol⁻¹.
• * Increased pressure (atmospheric to 10 MPa) elevated the initial reaction temperature for all primary pyrolysis reactions.
• * Underground conditions shift the initial reaction temperature to a higher gradient.

Conclusions:

• * Thermodynamic data provides a basis for understanding tar-rich coal pyrolysis.
• * Pressure significantly influences the initial reaction temperature, shifting it higher under in situ conditions.
• * Adjusting temperature and pressure can direct the product distribution of in situ underground coal pyrolysis.