An Assessment of the Emissions and Global Warming Potential of Gas Turbines for LNG Applications

Paper i proceeding, 2009

This paper concentrates on the emissions module of what is part of a wider project dealing with various aspects of gas turbine usage as drivers for Liquefied Natural Gas (LNG) production. The framework is known as TERA, a Techno-Economic and Environmental Risk Analysis, developed at Cranfield University with the core of the study being the performance module whilst the risk, economics and environmental modules are built around the performance. Whilst TERA exists for aviation and power production no such system is available for assessment of LNG production. With environmental issues high on the public agenda new legislation on emissions can be expected, especially in Europe. This will mean Oil & Gas companies will have to look for ways to reduce their emissions. One way to reduce turbo machinery losses is to replace out dated and/or obsolete machinery having less overall energy efficiency. The selection of turbomachinery involves assessments of risk, both economic and technical, as well as environmental impacts of the new technology. The core to all of this is the performance assessment, the primary basis on which selection is made. An aviation emissions model, developed at Cranfield University, is adapted for industrial applications. Technical performance calculations are made using the inhouse software called Turbomatch. Performance results for three typical days of the year (summer, winter and spring/autumn) are fed into the emissions model to get the levels of NOx, CO2, H2O, CO and unburnt hydrocarbon emissions. Later, NOx, CO2 and H2O emissions levels are fed into the environmental module to estimate the damage the engine causes to the environment over 100 years with respect to global warming. Two hypothetical engine configurations are investigated based on engine data available in the public domain. The first one, an 85MW single spool industrial machine (SSI-85), is used as the baseline to compare against a 100MW triple spool, intercooled aeroderivative (ITSA-100). The results suggest that the ITSA-100 produces more NOx but has less carbon emissions and consequently less global warming effects. This has varied economic impacts depending on which emission is a priority for reduction. CO2 and H2O emissions are more important than NOx for LNG gas turbine applications. The paper shows how this simple but effective system can be utilised to give a viable comparison between one or more proposed solutions for turbomachinery selection and replacement. The scope of the system is expanded as other modules come together to give a total assessment in terms of technical, economic, environmental and risk perspectives for LNG production.