Abstract: Under the current trend of heavier and more diverse ethylene feedstock, it is of great significance to study the operation and performance of critical equipment such as cracking gas compressors and addressing operational bottlenecks for achieving long-term stable operation of ethylene plants. The compressor and steam turbine form a mechanical coupling relationship through the "driving-driven" mechanism. As the power source, the steam turbine together with the compressor, acting as the load, constitutes a "power-load" system. Their coordinated and stable operational state is a key factor determining the safety and economic efficiency of the process unit. Fluctuations in the steam turbine's rotation speed are directly transmitted to the compressor, leading to issues such as process parameter instability, mechanical damage to equipment and increased energy consumption. This poses significant threats to the operational stability and safety of the unit. This paper addressed the issue of rotation speed fluctuations observed in the steam turbine of a cracking gas compressor at an ethylene plant following a major overhaul. It analyzes the causes of the problem based on the abnormal phenomena, detailed the step-by-step troubleshooting process involving various corrective measures and ultimately identified the governor pilot valve as the root cause of the failure. Through in-depth research on the structure and operational mechanism of the pilot valve, it was discovered that poor lubricant flow conditions within the throttle valve led to oil fouling and sticking of the sliding valve. By adjusting the oil discharge hole regulating valve of the pilot valve and increasing the oil injection volume, the problem was resolved.

Key words: pilot valve, turbine, rotation speed, fluctuation