(25b) Fuel Gas System Design – Key to Reliable and Efficient LNG Plant Operation

A well designed fuel gas system in an LNG liquefaction plant ensures a continuous, reliable, and good quality fuel gas supply to all users while optimizing the thermal efficiency of the plant. Fuel gas system design development starts with identifying the fuel gas users, their needs, the applicable design standards, and Owner preference. Fuel gas system design is also influenced by various plant operating modes; such as plant start-up, normal operation, turn down, and upset conditions.

This paper will identify the typical high pressure and low pressure fuel gas users in an LNG plant. Generally, the users with the most stringent fuel gas specification are the gas turbines with their complex burner design. The high pressure fuel gas is usually treated to meet the original equipment manufacturer (OEM) requirements. The fuel gas specification for several commercially available gas turbines used in LNG industry and its impact on fuel gas system design will be analyzed in this paper. The sources of fuel gas generally available within an LNG plant and their impact on overall thermal efficiency will be addressed. The process parameters used to tune the performance of the unit including supply pressure, temperature, composition, specific gravity, wobbe index, and fuel gas heating value will be discussed in detail.

A few case studies to demonstrate the robustness of the fuel gas system, controls, and measurement required to facilitate various plant operating modes will also be addressed.