Abstract: The gas well pressure in the West Sichuan gas field continues to decline, putting a natural gas desulfurization station under low-load operation, which brings challenges such as equipment instability, product quality exceeding limits, and reduced sulfur recovery rates. A comprehensive steady-state model of the desulfurization and sulfur recovery process was built using HYSYS software to analyze the equipment performance as the load decreased from 70% to 20%. The results show that at load of 50%–70%, the unit operates stably with qualified purified gas, though slight instabilities occur in individual equipment at lower loads. At load of 20%–50%, a clear conflict arises between hydraulic performance of tower equipment and purified gas quality compliance—high lean amine circulation rates cause hydraulic instability in towers, while low rates lead to gas quality exceeding standards. Additionally, at load of 20%, fan airflow drops below the surge limit; increasing airflow to avoid surge introduces excess oxygen, severely disrupting the H₂S/SO₂ ratio and causing sulfur recovery rate to plummet from 96.5% to 72.2%. Therefore, below load of 50% , tower internals and packing should be replaced or retrofitted to optimize operating conditions, and pumps must activate minimum flow protection. Especially at load of 20%, fans require the addition of an anti-surge loop or replacement with smaller-capacity fans to ensure stable operation.

Key words: natural gas desulfurization, low-load condition, sulfur recovery, air-to-acid gas ratio, equipment instability