Solid Deposition in Gas Turbines of a Cogeneration Plant, Sumatra, Indonesia, Mechanism and Remediation

A rapid build up of solid deposits occurred in the fuel system of gas turbines of the Duri Field Cogen plant and forced to shut down the plant frequently, which resulted in a great reduction in both electric power and steam output and hence curtailed tremendously the field production of heavy oil. A comprehensive study of the fuel gas delivery system and fuel gas quality was undertaken to determine the root cause of solid deposition. The results of the study show that the pale yellowish solids recovered from the fuel system are mixtures of elemental sulfur and wax. Both elemental sulfur and wax were derived from the fuel gas delivered to the plant where they were detected in the gas at trace levels (sub ppm). The occurrence of sulfur and wax deposition was somewhat surprising as the routine monitoring of the gas showed their levels were well within operation specifications all the time. Interpretation of composition data of numerous gas samples and solid deposits combined with operation conditions of gas turbines and gas phase chemistry provided insights of the solid deposition process. The problem was caused by the significant pressure drop encountered in the fuel gas delivery system of the turbines, which induced a measurable temperature drop and the associated phase changes of elemental sulfur and wax hydrocarbons from gas phase to condense phase leading to their deposition and turbine plugging. A remediation measure was developed and implemented.