Risk Analysis of Gas Turbines for Natural Gas Liquefaction

Abstract

Procurement of process plant equipment involves decisions based not only on an economic agenda but also on long term plant capability, which in turn depends on equipment reliability. As the greater global community raises environmental concerns and pushes for economic reform, a tool is evermore required for a specific and critical selection of plant equipment. Risk assessments based on NASA’s Technology Readiness Level (TRL) scale have been employed in many previous risk models to map technology in terms of risk and reliability. The authors envisage a scale for quantifying the technical risk. The focus of this paper is the technical risk assessment of gas turbines as mechanical drivers for producing liquefied natural gas (LNG). This risk assessment is a cornerstone of the technoeconomic environmental and risk analysis (TERA) philosophy developed by Cranfield University’s Department of Power and Propulsion in U.K. Monte Carlo simulations are used in order to compare the risks of introducing new plant equipment against existing and established plant equipment. Three scenarios are investigated using an 87MW single spool, typical industrial machine, a baseline engine followed by an engine with increased firing temperature, and finally an engine with a zero staged compressor. The results suggest that if the baseline engine was to be upgraded, then the zero staging option would be a better solution than increasing the firing temperature since zero staging gives the lower rise in total time to repair (TTTR) or downtime. The authors suggest a scaling system based on NASA’s TRL but with modified definition criteria for the separate technology readiness levels in order to better relate the scale to gas turbine technology. The intention is to link the modified TRL to downtime, since downtime has been identified as a quantitative measure of technical risk. Latest developments of the modeling are looking at integrating risk analysis and a maintenance cost and scheduling model to provide a platform for total risk assessment. This, coupled with emissions modeling, is set to provide the overall TERA tool for LNG technology selection.