Thermodynamic analyses of hydrogen production from sub-quality natural gas

Part I of this paper analyzed sub-quality natural gas (SQNG) pyrolysis and autothermal pyrolysis. Production of hydrogen via direct thermolysis of SQNGs produces only 2 mol of hydrogen and 1 mol of carbon per mole of methane (CH ₄). Steam reforming of SQNG (SRSQNG) could become a more effective approach because the processes produce two more moles of hydrogen via water splitting. A Gibbs reactor unit operation in the AspenPlus™ chemical process simulator was employed to accomplish equilibrium calculations for the SQNG + H ₂O and SQNG + H ₂O + O ₂ systems. The results indicate that water and oxygen inlet flow rates do not significantly affect the decomposition of hydrogen sulfide (H ₂S) at temperatures lower than 1000 °C. The major co-product of the processes is carbonyl sulfide (COS) while sulfur dimer (S ₂) and carbon disulfide (CS ₂) are minor by-products within this temperature range. At higher temperatures (>1300 °C), CS ₂ and S ₂ become major co-products. No sulfur dioxide (SO ₂) or sulfur trioxide (SO ₃) is formed during either SRSQNG or autothermal SRSQNG processes, indicating that no environmentally harmful acidic gases are generated.