Gas turbines for liquefied natural gas

21st February 2013

The Department of Power and Propulsion at the UK's Cranfield University is collaborating with Royal Dutch Shell in a project which looks at equipment selection for a liquefied natural gas (LNG) plant. The project uses TERA as a tool to aid the selection process, where the TERA is a Techno-Economic and Environmental Risk Assessment. The tool originates at Cranfield with successful applications in the Civil Aviation, Power Generation and Marine fields. 

Shell is interested in renewing existing LNG liquefaction plants whilst keeping environmental and economic criteria in mind. With mounting pressures in the way of emissions legislations and consequent emissions taxes, there is an ever increasing need to carefully and systematically select the plant equipment. Shell also has many plants where dated equipment needs replacement. A tool is required to aid the decision making process.

The TERA will be used as an optimiser to pin-point the optimum turbomachinery for LNG applications. The TERA philosophy is being used to select gas turbines as prime movers for the plant. Various gas turbines have been analysed as potential mechanical drivers. The analysis is based on four modules with the performance module as the core. The performance is conducted using the Cranfield 'in-house' simulation code called Turbomatch. This is a robust and flexible code used to simulate design point and off design scenarios of gas turbines in a range of operational conditions. Simulations can be run at different loads, altitudes, and varying ambient conditions. The results of the core performance simulation are fed into the other modules for further analysis.

The environmental module first predicts the raw NOx, CO2, CO, unburnt hydrocarbons and water vapour emissions of each respective engine. These can then be used to calculate any emissions taxes given the legislation that applies. The secondary function of the environmental module gives an index for the overall global warming potential, which aids in making comparisons between the engines.  

Shell are interested in high availability and reliability of equipment whereby the longer the plant can run without downtime the better. The risk module uses Monte Carlo simulations to analyse the engine on a component-by-component basis. The NASA Technology Readiness Level (TRL) scale is used for ranking the different engines. The measure of availability and reliability is the overall downtime that the Monte Carlo simulations predict. In this way the technology readiness can be linked to the downtime associated with that particular engine, which acts as a quantitative way of measuring reliability and availability.

In a world where global warming is at the forefront of the agenda and supply of traditional oil and gas at affordable prices is unsteady, the economic value and logistical importance of LNG is evident. The challenge to the industry lies in selection of plant equipment whilst keeping the emissions and economics in perspective. Technical risk assessment helps us decide which equipment will keep the plant running for the longest period without downtime. The research is expected to last till 2012 whilst preliminary results are being delivered.

Cranfield University is based in Cranfield, Bedfordshire, UK.


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