Maurizio Ciofini, Italy, and Ian Kay and Tayo Montgomery, USA, GE Oil & Gas, present a gas turbine solution for the LNG industry that was originally developed for commercial airliners.
The oil and gas industry is continuously striving to improve the return on investment (ROI) for new projects by optimising the cost of construction of facilities, as well as by designing for lower OPEX. Another key factor is the assurance of continuous revenue flow, therefore designing for high production certainty by minimising outages and reducing the time to complete maintenance actions.
Over the last 45 years, GE has been one of the leading manufacturers of aeroderivative gas turbines, with more than 5000 units produced for use in a variety of marine and industrial applications. Approximately one-fourth of these have been ordered for oil and gas applications in upstream, midstream and downstream installations. This includes more than 100 gas turbines ordered for the demanding LNG industry, having accumulated 1.6 million operating hours. To address the challenges of a more competitive world, in January 2017, GE Oil & Gas announced the introduction of the LM9000 gas turbine as a derivative of the highly successful GE90-115B turbofan used to propel the Boeing™ 777 commercial aeroplane. The primary application for the LM9000 gas turbine will be as a driver for compressors in the refrigeration process at LNG plants.
Proven in the sky
The Boeing 777-200LR and -300ER have become some of the leading twin-aisle widebody aircraft ordered in the last 12 years. They are all powered by the GE90-115B turbofan. As of December 2016, 52 operators had 2015 engines in service, having accumulated more than 43 million operating hours since the GE90-115B entered commercial service in 2004. These GE 90-115B engines are operated mostly on long-haul flights with a dispatch rate exceeding 99.97%. Considering the excellent dependability and high thrust rating of this engine model, GE decided to develop an aeroderivative gas turbine version in the 90 000 shaft-horsepower range.
The LM9000 development programme is using a well-proven design-for-reliability process based on a series of tollgates, requiring oversight from multiple disciplines and organisations within the GE Oil & Gas and GE Aviation teams to ensure a robustly defined product. When GE launches a new product, the features are very clearly defined to ensure they meet the needs of the customers who operate in challenging industry environments. It was determined that operators in the power generation and combined heat and power industries could also benefit from gas turbines in the size of the LM9000, so members from GE Power joined the product line team and development programme.
Design and construction features
The LM9000 will have a four-stage low pressure compressor (LPC) driven by a single-stage intermediate pressure turbine (IPT), a nine-stage high pressure compressor (HPC) driven by a two-stage high pressure turbine (HPT) and the output will be delivered by a free power turbine (LPT). This free power turbine will have an operating range of 2400 – 3780 RPM. The combustion system is based on the experience of more than 1000 GE aeroderivative gas turbines equipped with dry low emissions systems having accumulated more than 25 million operating hours. The LM9000 will take advantage of this vast experience to deliver less than 15 ppm NOx while operating at compressor pressure ratios higher than 30:1.
The LM9000 will have a gas fuel system with the option of having dual-fuel features to operate on liquid fuels. Dual-fuel capability is of greater importance for units in remote areas, offshore, or where gas fuel curtailments may be necessary. An important feature of fuel flexibility for LNG operators is the ability to inject high volumes of inert gases, particularly nitrogen, into the gas fuel stream. The LM9000 is being designed to be able to operate on pure methane, as well as blends of containing more than 35% nitrogen by volume with the remainder being methane, equivalent to a modified Wobbe Index of 30 Btu/scf/R0.5 (1.5 MJ/m3/K0.5).
The LM9000 gas turbine will deliver more than 65 MW at the shaft over a range of speeds under standard ISO conditions. Combining the speed flexibility of the free power turbine with constant high power will generate increasing torque as the speed is reduced. This delivers huge separation margin above the absorbed torque of driven compressors, giving operators flexibility to start and run the LNG plants under any condition they may face without the need to reduce the pressure in the process (SOP) by venting the refrigerant.
Designed for maintainability
The architecture of the gas turbine has been designed for on-condition maintenance with borescope ports to easily inspect the interior of the engine. As determined by these inspections, at the appropriate time the gas turbine will be easily removed from the package to perform major maintenance actions. The unit can be replaced by a spare or leased engine to maintain the customer’s site operational. GE has selected alloys throughout the engine to allow for longer periods between maintenance actions. In fact, at the targeted temperatures for the combustion and turbine sections, it is expected that the hot section exchanges will be performed after 36 000 hours and the major overhaul at 72 000 hours. Intermediate inspections to conduct borescope inspection, and to evaluate the condition of the exterior components will be performed every 12 000 hours.
Lessons learned from the onshore and offshore packages of the GE LM2500 and LM6000 family of gas turbines are being incorporated into the package design of the LM9000. The LM9000 package has utilised the LM6000 SeaSmart mini-skid concept to aid in maximum ‘safety in design’ to provide a controlled engine removal and installation when the vessel is in motion. The mini-skid feature allows for improved ergonomics for technicians when performing this activity. The removal and installation of either the super-core or entire gas turbine will be able to be completed in 24 hours. Concepts for further improvements were taken from the development of Marine LM6000 package, such as the gas turbine facility connections, especially inlet and exhaust plenums.
The design of the LM9000 aeroderivative gas turbine brings several key advantages over the closest aeroderivative gas turbine by delivering 65 MW shaft output over a wide range of speeds. This means it will generate very high torque from start to full speed, a key feature for mechanical drive applications, especially in the LNG industry where the driven compressors require high power at lower speeds when the process piping has significant residual pressure.
The free power turbine allows the gas turbine to operate at high efficiency over a wide range of ambient, absorbed power and speed conditions. Having a free power turbine simplifies LNG plant design configuration and associated CAPEX by removing the need for a helper motor and allows starting the LNG train in the loaded (pressurised) condition without venting process gas. It is based on the GE90-115B aircraft engine, which has more than 2000 engines in commercial service having accumulated 43 million hours of operation. The condition-based maintenance philosophy, multiple access ports for borescope inspections, and structural design features are all tailored to meet aviation quality metrics for high reliability and maintainability. The package is designed so that the engine can be swapped in less than 24 hours to meet the high availability requirements of LNG plants. The LM9000 meets stringent space requirements of offshore and onshore LNG plant layouts with smaller footprints and simpler balance of plant.
The advantages of the LM9000 translate into significant CAPEX and OPEX savings over the life of the LNG plant in comparison to alternate gas turbines in this class. For instance:
- 20% more power.
- 25% fewer trains needed.
- 50% longer maintenance interval.
- 40% lower NOx emissions.
- 20% lower total cost.
The oil and gas market has faced challenging times in recent years. However, the downturn has provided a shared impetus between customers and the supply chain to innovate both technically and commercially to find new ways of working together to bring resources to the market economically. This has driven operators to strongly focus on productivity, reliability, flexibility and operational excellence. Today’s biggest challenges all come back to providing technology that breaks new ground, enabling operations to reach new levels of performance. GE Oil & Gas has continued to invest in technology development to meet those requirements, and believes that the LM9000 is a great example of that.
This article was originally published in LNG Industry. To receive your free copy, click here.
Read the article online at: https://www.lngindustry.com/special-reports/10072017/shoot-for-the-sky/