This study optimized the skid-mounted single mixed refrigerant process - basic process (SMR-NGLP) and boosted process (SMR-PBNGLP) to achieve effective liquefaction of marginal gas fields. Thermodynamic modeling assessed impacts of initial pressure (100-1000 kPa), boost pressure, and pre-throttling temperature on specific power consumption (SPC) and exergy losses. For SMR-NGLP, competing effects create an SPC-minimizing optimal pre-throttling temperature (-65°C to -55°C): higher initial pressures/lower temperatures reduce refrigeration needs but raise compressor loads, while lower temperatures reduce Boil-Off Gas recompression. SMR-PBNGLP optimized universally at 2000 kPa boost pressure, achieving SPC reductions of 17.5%, 16.6%, and 4.8% versus optimized SMR-NGLP for 100 kPa, 500 kPa, and 1000 kPa feeds, respectively. Efficacy diminished with higher initial pressure, highlighting its suitability for low-pressure feeds. Mechanistically, pressure boosting reduced liquefaction temperature gradients, enabling efficient heat transfer with less refrigerant work. Exergy analysis identified throttling valves and compressors as primary loss sources, with SMR-PBNGLP achieving 12-19% lower total irreversibility. Pressure boosting is critical for low-pressure feeds in modular systems. Under optimized conditions for low-pressure feed gas, the pressure-boosted configuration achieves minimum SPC approaching 0.35 kWh/kg, providing design guidance for modular small-scale LNG systems.
Ye et al. (Sun,) studied this question.