GE Oil&Gas has recently launched a new heavy-duty gas turbine, the MS5002E, which underwent an extensive theoretical and experimental study on fuel flexibility. Today, fuel flexibility is one of the most challenging requirements in the Oil&Gas market. The fuel flexible operation demands a wide variety of assessments, ranging from rig tests of the combustor to theoretical consolidation of the results. The present paper describes the used methodology to increase the capabilities of burning diverse gaseous fuels, at fixed geometry. It analyzes all factors affecting the operation of the combustor with the goal to identify and extend the boundaries. Such boundaries are a result of multiple variables, like resistance to flashback and autoignition, emissions, pressure pulsations and capability of igniting. Flashback is when the reaction velocity overtakes the flow velocity and the flame moves back to the fuel injection points, threatening the integrity of the hardware. The resistance of the MS5002E to flashback and flame holding was evaluated by performing extensive experiments on a single fuel nozzle. Flame holding test results were then used to develop a transfer function for the prediction of the flame holding behavior of different mixtures. Another variable of interest is the resistance to autoignition: MS5002E took advantage of previously defined transfer functions from GE Energy that estimate the temperature above which a given mixture is likely to autoignite, at fixed pressure. Since the MS5002E is a DLN machine, it was also necessary to exclude the possibility of lean-blow-out in the whole operating range: dedicated tests on a single-can basis were used for this scope. Emissions and pressure pulsations were extensively measured on a single-can basis, since these parameters are fundamental for a lean premixed combustor. For particular mixtures, like those with high content of inert gases, the capability of igniting repeatably and reliably is an additional requirement that needs experimental validation. The combination of all the aforementioned variables determines the composition limit of the fuel mixture that the machine can tolerate. As a result of all the assessment, it was possible to achieve an increase in the maximum allowable concentrations for the following constituents: propane (up to 20%), nitrogen (up to 20% with no modifications to the control algorithms; up to 25% with minor modifications to the control algorithms) and hydrogen (up to 5%). Future tests will deliver increased capabilities also for ethane and butane.

The growing concern for the role of man-made CO2 emissions with respect to global warming combined with the large increase in energy demand spurred by developing nations and a growing global population that is foreseen over the next 15 years have recently turned attention to potential CO2-neutral energy supply solutions. Waste heat recovery cycles applied to fossil fueled plants offer a local zero-emission solution to producing additional electric energy, thereby increasing the overall plant efficiency with a considerable reduction in the emission of CO2 per unit of energy produced. GE Oil & Gas with GE Global Research Europe has developed a new and attractive solution for recovering waste heat energy from a variety of thermal sources ranging from reciprocating combustion engines to gas turbines. This new recovery cycle is called ORegen™. The ORegen™ recovery cycle is a rankine cycle, with superheating, that recovers waste heat and converts it into electric energy by means of a double closed loop system. The ORegen™ system represents one of the very few viable solutions for recovering heat from sources (such as mechanical drive gas turbines) whose load may vary dramatically over time or where the equipment is located at a site where water is not readily available. For the temperature range of interest, a thorough comparison between many working fluids was performed, leading to the conclusion that the substance that delivers the highest efficiency is Cyclopentane. A high-efficiency Rankine cycle based on such a working fluid places a particularly high demand on the expansion ratio, which influences some of the basic architectural choices of the expander machine. This article introduces the ORegen™ recovery cycle and describes the process used in GE Oil & Gas to design the family of double supersonic stage turboexpanders, covering the power range of 2–17MW. Examples of the application of the ORegen™ cycle to gas turbine are also provided to demonstrate attractive opportunities to increase the overall plant efficiency.

Due to the substantial increase in sources of gas, natural gas interchangeability is a key subject in the industry today. The extensive pipeline network means that natural gas arriving at appliances, boilers, burners and power plant turbines could come from anywhere. Fuel compositions vary from one source to another. Moreover, most recently, Liquefied Natural Gas has emerged as a major source and the composition of gas derived from LNG substantially differs from the natural gas one. In Dry Low NOx (DLN) systems, those changes in fuel composition can cause dangerous increase in combustion dynamics and can also affect the NOx emissions of the machine. Therefore, in order to meet the growing market demand for gas turbine combustors able to tolerate significant alterations in fuel composition, a system capable of burning gases with differing and variable over time Wobbe Indexes was developed. This innovative system does not involve any combustion hardware modifications. It allows the use of a premixed combustion system that complies with emissions, reliability, and safety, even when burning a fuel that is distinctly different from the original design gas. In particular, the system was developed in order to meet the requirements of a customer for burning any continuously and slowly varying mixture of two fuel gases, whose Wobbe Indexes difference is up to 25%. Since the burner is designed for 100% of the gas with lower Wobbe Index, the gas that has a higher WI needs to be heated, in order to achieve a target Modified Wobbe Index; the same happens for any mixture of the two gases. The system is based on a closed loop control on the Modified Wobbe Index of the fuel. Two turbine control gas chromatographs, located upstream the combustor inlet, measure the gas characteristics (LHV, specific gravity and temperature) and calculates the MWI. If it is different from the target one, it is corrected by modifying the temperature set point of a heat exchanger. The hardware is completed with one more plant gas chromatograph, located upstream the heat exchanger, for evaluating the fast and complete switch from one gas to the other one. In addition to the normal operation, that is with the 100% Lower Wobbe Index gas (L) or 100% Higher Wobbe Index gas (H) or any continuously and slowly varying mixture of these two gases, the system allows both the black and the normal start, the complete switch back and forth between 100% L gas and 100% H gas and load sheds and rejection. Moreover the two gases can be burned in diffusion combustion mode, as available, without requiring any increase in temperature, with no limitation from firing to full load. The capability of the system to adjust to all of the previously described events, potentially dangerous and damaging for the Gas Turbine combustion system, makes it suitable for applications that burn different lots of gases coming from different LNG sources, since it allows the turbine to accommodate the differences in Wobbe Index, due to various gas lots on a pipe line.

The NovaLT™16 gas turbine recently developed in Baker Hughes, a GE company (BHGE), is part of a larger class of gas turbines (LT class) aiming at covering a wide space in the small power range segment and at introducing in the market a state of the art technology engine for what concerns performance, emissions, operability, durability and maintainability. The main purpose of this paper is to describe the entire validation campaign that was performed at BHGE facilities. This campaign can be divided into 3 different phases. The first phase focused on measuring engine performance in a new, clean and unaltered configuration. The second phase focused on emissions, vibration, thermal distribution, auxiliary system performances and the like, in order to validate the design assumption and calculation results across the full operational range. In this phase, more than 2000 sensors were installed across the entire engine, covering all modules, and all functional tests were performed (inside and outside of design space) to guarantee reliable engine behavior. At the end of this test phase, a full engine teardown was performed to allow a detailed parts inspection that confirmed the achievement of the design intent. The standard maintenance plan of the engine requires 35Kh continuous running. Therefore, the third part of the test aimed at validating engine durability with a full endurance test that allowed the identification and correction of any possible remaining operation problem. In this phase, the engine was still equipped with more than 1000 sensors, and was operated continuously following a well-defined operating profile in order to simulate both mechanical drive and power generation modes. This campaign successfully allowed to fine tune several engine control logic details, to monitor emissions behavior across a wide range of ambient temperature and load condition (the test spans from hot to cold day), to analyze trends of standard engine parameters and special instrumentation and, through planned borescope inspection, to evaluate individual component status versus selected operating profile. Data reported in this paper represent a summary of all the data acquired and post processing results, and illustrate how an endurance test can help tuning machine performance predictions in a wide operating range.

The development of current industrial gas turbines is strictly constrained by legislative requirements for low polluting emissions. Lean Premixed combustion technology has become through the years the necessary standard to meet such requirements. Premixed technology introduces a new range of problems: combustion instabilities in many operating conditions. Specifically, lean premixed flames pose the threat of pressure oscillations. This phenomenon is the effect of the strong interaction between combustion heat-release and fluid dynamics aspects. The prediction of acoustic oscillations and combustion instabilities is generally difficult because of the complexity of real combustor geometries. As a result, the design phase is usually performed as a trial-and-error task: a specific design is constructed, tested and modified, in a process that continues until acceptable results are found. A specific tool was developed by GE Energy to help predicting the acoustic behaviour of newly designed partially-premixed combustors, avoiding the traditional trial-and-error process: the tool allows the designer to analyze the problem of combustion instabilities since the early design phase, limiting subsequent testing efforts. A mono-dimensional tool based on the 1-D acoustic model was developed by GE Energy and was applied to the single-can combustor of the GE10 machine (a gas turbine in the 10MW class). All the main geometrical features of the GE10 machine, including fuel line geometry, were considered and modeled in a one-dimensional scheme, in order to build an equivalent model for the linear tool analysis. The main frequencies, measured during tests on the GE10 machine, were compared to the numerical results of the tool, showing good agreement between numerical and experimental results and confirming the predictive capability. This good agreement demonstrates that the model can be used for predicting the effects of design changes, with a reduced need of tests.