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The study shows the results of the emission simulation in a small-sized combustion chamber. The influence of temperature and equivalence ratio on CO and CxHy in the combustion chamber was investigated. Experiments and calculations were carried out for the following modes: temperature at the inlet of the combustion chamber Tinlet = 323 ... 523 K; equivalence ratio φ = 0.2 ... 0.33; normalized flow rate at the inlet of the combustion chamber λ = 0.1 ... 0.3. The simulation of combustion of natural gas was carried out. The studies were conducted using CFD software and experimental methods. Measurements of the combustion products composition were carried out by the method of sampling collection and subsequent chromatographic analysis. The flow and combustion processes were simulated in a three-dimensional steady formulation using the Reynolds-averaged Novier-Stokes equations (RANS) and in a transient formulation using the Large Eddy Simulation (LES) method. The combustion processes were simulated by Flamelet Generated Manifold model in conjunction with the probability density function method (PDF). In addition to the above methods, the method of the reactor network model (RNM) was used to simulate the emission. As a result, a comparison of the calculated and experimental data of concentrations values of combustion products and emissions indices averaged over the combustion chamber outlet was conducted. According to the results of the calculated-experimental study obtained: - the simulated concentrations values of the main combustion products such as CO2 and H2O qualitatively and quantitatively coincide with the experimental data (the discrepancy is less than 5%) for all three approaches — RANS, LES, RNM; - when modeling CO emissions, the discrepancy between the calculated emission indices obtained by the RANS and LES methods is greatly underestimated relative to the experimental data, whereas the values calculated by the RNM method deviate from the experiment by less than 10%; - mass concentration values of unburned hydrocarbons obtained by the RANS method are overestimated relative to the experimental values, while using the LES with RNM methods, the discrepancy does not exceed 10%.

General Electric (GE) DLE gas turbines typically use a Gas Chromatograph (GC) and/or a Wobbe Index Meter (WIM) to monitor changing fuel properties during operation. These conventional fuel sensors experience a significant time lag during operation, so a patented buffer volume device and a software algorithm is used to compensate for this lag and to ensure that the control system including metering valves can react to rapid fuel changes. Computational Fluid Dynamics (CFD) was used to design and analyze the buffer volume device that increases the time and distance taken by the gas to the metering valve. This delay provides the control system time to adjust the metering valves when the fuel transitions at the combustor to maintain gas turbine combustor stability and operation during rapid gas property changes that could otherwise result in a trip or flame-out condition. In GE’s Aeroderivative Gas Turbine Gas Fuel transfer system, the innovative buffer volume was the critical component, and this paper describes its performance in detail.

Supercritical water gasification of dilute ethanol at the industrial scale promises a sustainable route to bio-syngas production for use in combined cycle power plants. Cost-effective bio-syngas production would reduce reliance on fossil fuels for electricity generation and reduce greenhouse gas emissions by utilizing waste biomass resources. Continuous supercritical water gasification offers high reactant conversion at short residence times without an added catalyst. The decomposition of ethanol in supercritical water is studied in a continuous reactor at 560 °C, 25 MPa, residence times between 3 and 8 s, and a constant initial ethanol concentration of 8.1 wt%. High-resolution, in-situ Raman spectroscopy facilitates identification of reaction products. Significant yields of H2, CO, and CH4 indicate the dominance of a dehydrogenation reaction pathway at studied conditions, while minor yields of ethane indicate a secondary dehydration reaction pathway. Ethylene yields are virtually nonexistent, indicating rapid hydrogenation of ethylene to ethane at these conditions. Ethanol dehydrogenation to H2, CO, and CH4 results in an overall fuel value upgrade of 84.5 kJ/mol-EtOH. Dehydration of ethanol to ethane results in an overall fuel degradation of −3.8 kJ/mol-EtOH.

A modified cone calorimeter for controlled atmosphere combustion was used to investigate the gases released from fixed bed rich combustion of solid biomass. The cone calorimeter was used with 50 kW/m2 of radiant heat that simulated a larger gasification system. The test specimen in the cone calorimeter is 100mm square and this sits on a load cell so that the mass burn rate can be determined. Pine wood was burned with fixed air ventilation that created rich combustion at 1.5–4 equivalence ratio, Ø. The raw exhaust gas was sampled using a multi-hole gas sample probe in a discharge chimney above the cone heater, connected via heated sample lines, filters and pumps to the heated Gasmet FTIR. The FTIR was calibrated for 60 species, including 40+ hydrocarbons. The hydrogen in the gas was computed from the measured CO concentration using the water-gas shift reaction. The exhaust gas temperature was also measured so that the sensible heat from the gasification zone was included in the energy balance. The GCV of the pine was 18.8 MJ/kgpine and at the optimum Ø the energy in the rich combustion zone gases was 14.5 MJ/kgpine, which is a 77% energy conversion from solid biomass to a gaseous fuel feed for potential gas turbine applications. This conversion efficiency is comparable with the best conventional gasification of biomass and higher than most published conversion efficiencies for coal gasifiers. Of the energy in the gas from the rich combustion 35% was from the CO, 20% from hydrogen, 35% from hydrocarbons and 10% sensible heat. Ash remained in the rich burning gasification zone. As the biomass is a carbon neutral fuel there is no need to convert the gasified gases to hydrogen, with the associated energy losses.

Hydrogen has often been studied as a possible fuel of the future due to its capabilities to support zero emissions and sustainable energy conversion. Hydrogen can be used in a fuel cell to generate electricity at high efficiencies and with zero emissions. In addition, hydrogen can be renewably produced via electrolysis reactions that are powered from otherwise curtailed renewable energy. One possible means of storing and delivering renewable hydrogen is to inject it into the existing natural gas (NG) system and thus decarbonize gas end-uses. The NG system has potential to serve as a storage, transmission and distribution system for renewably produced hydrogen. Despite the potential of hydrogen to reduce the carbon intensity of the NG system, the unique characteristics of hydrogen (low molecular weight, high diffusivity, lower volumetric heating value, propensity to embrittle pipeline materials) has led to justified concerns over the safety of introducing hydrogen blends into the NG system. While many studies have attempted to quantitatively predict leakage rates of hydrogen using classical fluid mechanics theories, such as Hagen-Poiseuille flow, there have been limited studies which quantitatively assess gaseous fuel leakage to support the predictions made from theoretical analyses and computations. In this paper we present a summary of the literature related to gaseous fuel leakage and results from preliminary experiments which support the idea that entrance effects may significantly affect gaseous fuel leakage from practical leak scenarios such as NG fittings, resulting in similar leakage rates between hydrogen and NG.

This paper presents an application of MRI to measure flow distribution in fuel cell channels. Solid Oxide Fuel Cells (SOFC) are able to efficiently produce electricity directly from the oxidation of the natural gas by electrochemical conversion. The distribution of fuel gas between the high numbers of parallel flow paths within the fuel cell assembly is critically important to ensure high efficiency and uniform conditions within the fuel cell assembly. Practical approaches in conjunction with numerical models are needed to understand and control the physical processes taking place within fuel cells in order to design them to be efficient and reliable. The paper outlines a non-invasive experiment using magnetic resonance imaging (MRI) to measure the distribution of flow within an SOFC subassembly. The method quantifies the flow distribution by modelling the gas using water at Reynolds similar conditions. Water has a magnetic moment that can be imaged using an MRI scanner. Two-dimensional cross-section scans were taken perpendicular to the direction of flow in the fuel cell channel to measure area and velocity. The study evaluated a range of image resolutions and outlined how the data was processed to provide mass flow rates in each channel using the known fluid properties. At the highest image resolution the total mass flow rate was within 1% of the independent measurement from the experimental rig. The distribution of flow between the channels showed a similar trend to the computational model. The initial results demonstrate the feasibility for the method to measure flow in the SOFC channels.

This paper presents the engine performance, combustion process, and exhaust emissions from of a turbocharged spark ignition (SI) WP-10 off-road engine developed to operate on gaseous fuels applicable to a wide range of the higher heating value (HHV) (900 to 1400 BTU). The HHV of the fuels was varied by blending of propane or carbon dioxide (CO2) into natural gas (NG). The developed engine was designed to operate at 1800 rpm and 175 kW. A new method of calculating the specific heat ratio of the bulk gases with the calculated bulk gas temperature and composition was proposed. The specific heat ratio calculated using this method was lower than the value derived from the conventional Log P-Log V method. The application of the specific heat ratio calculated in calculating the heat release process increased the heat release rate (HRR) and the total heat released during combustion. In addition, it also resulted in retarded phasing of CA50 and CA95 defined as the crank angle location when 50% and 95% of total energy was released. The effects of the fuel composition on engine performance, combustion process, and exhaust emissions were experimentally investigated. It achieved a brake thermal efficiency of about 32.8%. The exhaust emissions are in compliance with both EPA and CARB regulations. The addition of propane to NG increased the HRR, accelerated the combustion process, and shortened the combustion duration. This was the result of the quicker flame propagation property of propane. The HRR observed with propane blending was featured with two heat release peaks. The peak HRR observed with 1400 BTU fuel was about 10% higher than that observed with NG only operation. As expected, the blending of CO2 to NG was shown to slow down the combustion process, and retarded the combustion phasing, especially during the completion of combustion.

Identifying fugitive methane leaks can improve predictive maintenance of the extraction process, can extend gas extraction equipment lifetime, and eliminate hazardous work conditions. We demonstrate a wireless sensor network based on cost effective and robust chemi-resistive methane sensors combined with real time analytics to identify leaks from 2 scfh to 1000 scfh. The chemi-resistive sensors were validated to have a sensitivity better than 1 ppm in methane plume detection. The real time chemical sensor and wind data is integrated into an inversion models to identify the location and the magnitude of the methane leak. This integrated sensing and analytics solution can be deployed in outdoor environment for long term monitoring of accidental methane plume emissions, generate recommendations about fixing them, and ensure compliance with local government regulations.

Hydrogen as one of energy sources is attracting attentions because of CO2 free combustion that can deaccelerate global warming. Recently, hydrogen enriched combustion technology for gas turbine combustors is developing, in which hydrogen is added to natural gas. However, hydrogen-rich combustion has different combustion characteristics from conventional natural gas combustion. In particular, such variety of combustion characteristics may lead to combustion oscillation, which may cause fatigue breaking of structural elements due to resonance with components. Combustion oscillation is mainly induced by thermo-acoustics interaction. Therefore, it is necessary to investigate characteristics of hydrogen-enriched combustion sufficiently. To understand combustion characteristics of enriched hydrogen mixture, combustion experiments were performed for various ratios of hydrogen in the fuel mixture. In this study, a mock-up combustor of a micro gas turbine combustor is used, where a radial swirler is installed to mix fuel and air and stabilize the flame. To grasp the characteristics of combustion oscillation, pressure fluctuation was detected by a pressure sensor installed at the bottom of the combustor. It is found that larger hydrogen ratio in the fuel mixture extends the range of large pressure fluctuation region expressed by the root-mean-square value. Succeedingly, more detail oscillation characteristics were examined by FFT analysis. In the case of natural gas 100%, the oscillation of around 350 Hz was detected. On the other hand, in the case of the hydrogen-contained fuel mixture, two kinds of oscillating frequencies around 200 and 400 Hz were detected. To examine the cause of the difference among these three oscillating frequencies, a simplified stepped tube model with closed- and open-end is considered. For further investigation, acoustic boundary conditions were measured by acoustic impedance method. Moreover, to obtain the representative flame positions and temperature in the combustor, CFD calculations were performed, and the measured acoustic impedance was combined with the CFD results. Then, parametric studies with various thermo-pressure interaction index were performed to obtain the effect of thermo-pressure interaction index on natural frequencies and gains using the Nyquist plot. As a result, it was found that the self-excited oscillation limit is sensitive to the value of thermo-pressure interaction index.

As power plant combustion turbines (CTs) are pushed towards higher thermal efficiencies, increased attention is being given to operating requirements for their fuel gas supply such as the maximum allowable rate-of-change in pressure. It is important to perform detailed analyses for multi-unit plants to ascertain whether pressure transient events, such as those caused by initial trip of one or two combustion turbines, will cause additional combustion turbines to trip off. In this paper, single and dual CT trips were postulated in a near-realistic combined cycle power plant. Predictions of the gas flow behavior, along with propagation and superposition of pressure waves, was carried out using the method of characteristics (MOC) for compressible flows. Specifically, the rate of change in fuel gas supply pressure to each CT was monitored and compared against a typical manufacturer limit of 0.8 bar/s. Instances where simulations showed this threshold exceeded were noted, since such events correspond to automatic valve closure that would shut down one more CT and thereby further reduce plant electrical output. The overall goal of fuel gas transient analyses is to improve pipeline designs, iteratively when necessary, such that those additional trips are avoided. To that end, this paper presents several simulation cases to illustrate pressure transient phenomena and to show the impact of various pipeline design alterations, some of which caused 40% reductions in the worst pressure rate-of-change during simulations.

In this work, the detailed model of intermediate temperature solid oxide fuel cell (IT-SOFC) and gas turbine (GT) hybrid system with biomass gas (wood chip gas) as fuel was built, with the consideration of fuel cell potential loss such as polarization loss and heat loss. Detailed performance of key component such as reformer, fuel cell and gas turbine of the hybrid system was studied under different biomass gas fuel compositions and steam/carbon ([S]/[C]) ratios. The results show that the hybrid system can reach the efficiency of 59.24% under the designed working condition. The biomass gas from different sources and processes usually have varied fuel concentrations, especially for methane (CH4), hydrogen (H2), carbon monoxide (CO) and water (H2O), which could significantly affect the performance of hybrid system. Results show that the change of H2 proportion has the most significant influence to system output power, CO and CH4 have similar influence trend. System electrical efficiency increases slightly with the change of H2 proportion while decreasing significantly with the increase of CO and CH4 proportion. The increasing composition of CH4, H2 and CO in biomass gas fuel benefits the output power of hybrid system, but results in the higher risk of overheat as well, which might cause safety problems. The composition of water in biomass gas affects the [S]/[C] ratio of system, and results show that maintaining the [S]/[C] ratio at a certain level can guarantee the temperature of key components in the hybrid system below the limits, which can satisfy the safety standards. The results show this technology has a good application prospect. (CSPE)

For anode-supported planar solid oxide fuel cells (SOFCs), the thick anode support layer (ASL) prevents the supply of fuel gas to the anode functional layer (AFL) where the electrochemical reactions take place. Shortage of the fuel gas at the active region results in concentration polarization. SOFC designs with porosity gradient anode may improve the cell performance. In order to investigate the effect of the porosity distributions on mass transfer characteristics of SOFC, a three dimensional half-cell model is developed based on the computational fluid dynamics (CFD) method. The numerical model solves continuity equation, conservation of momentum, multi-component mass transfer and electrochemical reaction. According to the numerical results, a SOFC design with a higher porosity gradient anode could effectively enhance mass transport of the fuel gas in the AFLs, which would lead to the reduction of polarization loss. It is also found that high porosity gradient among the anode layers could improve the H2 concentration gradient in the porous anode, which is beneficial to facilitate diffusion of the fuel gas in the porous anode. Concentration overpotentials of the SOFC decrease with the increase of the porosity gradient, especially for the low inlet H2 molar fraction. These findings indicate that the comprehensive performance of SOFC can be effectively improved by employing a high porosity gradient anode.Copyright © 2016 by ASME

The focus of this research was to examine the effects of adding exhaust gas recirculation (EGR) on a large bore 2-stroke, lean-burn natural gas (2SLB) engine in its stock configuration, using a previously determined optimal spark plug. EGR has been a common emissions reduction technology used for on-road gasoline, natural gas, and diesel fueled vehicles. EGR — both cooled and uncooled — is found in nearly all on-road and many off-road engines. The optimal spark plug was found in other research and it was tested with various rates of EGR. The test platform was a 1971 Cameron AJAX-E42 single-cylinder engine — common to the natural gas industry. The engine had a bore and stroke of 8.5 × 10 inches, respectively. The engine displacement was 567 cubic inches with a trapped compression ratio of 6:1. The engine was modified to include electronic spark plug timing capabilities along with a mass flow controller to ensure accurate fuel delivery. Each EGR configuration was examined at spark timings of 14, 11, and 8 CAD BTDC. Tests were conducted using an air-cooled, eddy-current power absorber at an engine speed of 525 RPM and load of 400 1b.-ft. of torque. Due to its large thermal inertia, the engine was operated for three hours prior to data collection to ensure representative and operation. In-cylinder pressure data were collected using a piezoelectric pressure transducer at increments of 0.25 CAD. Various levels of EGR and spark timing conditions were evaluated against engine performance including both regulated and unregulated exhaust emissions. Volumetric EGR rates of 2.5% showed reduced NOx emissions and improved fuel efficiency while rates of 5% did not yield NOx reductions.

Siemens SGT-800 gas turbine is the largest industrial gas turbine within Siemens medium gas turbine size range. The power rating is 53MW at 39% electrical efficiency in open cycle (ISO) and, for its power range, world class combined-cycle performance of >56%. The SGT-800 convectively cooled annular combustor with 30 Dry Low Emissions (DLE) burners has proven, for 50–100% load range, NOx emissions below 15/25ppm for gas/liquids fuels and CO emissions below 5ppm for all fuels, as well as extensive gas fuel flexible DLE capability. In this work the focus is on the combustion modelling of one burner sector of the SGT-800 annular combustor, which includes several challenges since various different physical phenomena interacts in the process. One of the most important aspects of the combustion in a gas turbine combustor is the turbulence chemistry interaction, which is dependent on both the turbulence model and the combustion model. Some turbulence-combustion model combinations that have shown reasonable results for academic generic cases and/or industrial applications at low pressure, might fail when applied to complex geometries at industrial gas turbine conditions since the combustion regime may be different. Therefore is here evaluated the performance of Reynolds Averaged Navier-Stokes (RANS) and Scale Adaptive Simulation (SAS) turbulence models combined with different combustion models, which includes the Eddy Dissipation Model (EDM) combined with Finite Rate Chemistry (FRC) using an optimized reduced 4-step scheme and two flamelet based models; Zimont’s Burning Velocity model and Lindstedt & Vaos Fractal model. The results are compared to obtained engine data and field experience, which includes for example flame position in order to evaluate the advantages and drawbacks of each model. All models could predict the flame shape and position in reasonable agreement with available data; however, for the flamelet based methods adjusted calibration constants were required to avoid a flame too far upstream or non-sufficient burn out which is not in agreement with engine data. In addition both the flamelet based models suffer from spurious results when fresh air is mixed into fully reacted gases and BVM also from spurious results inside the fuel system. The combined EDM-FRC with a properly optimized reduced chemical kinetic scheme seems to minimize these issues without the need of any calibration, with only a slight increase in computational cost.

Stable combustion is one of the main requirements for combustion chambers of gas turbine engines. Therefore, the prediction of combustor stable operation limits during the design stage is an important task. The stable operation limits with a sufficient degree of accuracy can be determined by experiments or using computational fluid dynamics. The present paper describes a numerical and experimental investigation of swirled premixed flame stabilization in a modular swirled burner (MSB). The burner has a vane swirler and a diffuser with a cylindrical tube downstream of the swirler. This design has several advantages. First, the cylindrical tube protects the flame from external disturbances and acts as the pre-chamber in which combustion efficiency can reach high values. Secondly, the swirled flow of the fresh mixture passes along the walls of the tube and prevents them from overheating. The influence of the swirler vanes angle on MSB lean blow out (LBO) was experimentally and numerically investigated. The results of the experiments were also used to validate the simulation results. All studies were conducted under atmospheric conditions in an open-space laboratory environment. Three-dimensional modeling was carried out using the large eddy simulation (LES) with a Smagorinsky–Lilly subgrid model. Combustion was described within the Flamelet Generated Manifold model. Initially, the influence of the size and shape of outlet boundary, the mesh resolution and turbulent-chemistry interaction models was investigated. As a result the configuration of the model was received, which allows simulating LBO with sufficient accuracy. Stable operation limits for several types of MSB geometries and different fuels (methane and propane) were subsequently established. It was found that in the case of swirler vane angle equal to 45 degrees the range of stable operation limits is wider than in the case of 60 degrees. The influence of pre-chamber length on LBO was studied only numerically. It was discovered that with increasing pre-chamber length, the LBO limits become wider, but the possibility of the tube walls overheating becomes higher too.

A chemical equilibrium model for fixed-bed gasification is developed, which allows the prediction of the syngas composition, the amount of residual coal or ash, as well as the amount of tars as a function of the gasification temperature and the elemental composition of the biomass and the tars. Moreover, the combustion heat of the gas fuel is calculated, as well as the conversion and process efficiency, in order to perform further analyses which allow the determination of energy potential for different types of biomass under several conditions of moisture and equivalence ratio of gasifying agent. Performance of the proposed model is compared to prediction of some models which were found to be relevant in the literature review. An assessment to the model is also carried out. For this purpose, a case-study is performed for African palm (Elaeis guineensis) shells using a commercial gasifier. Experimental data obtained from the biomass used in the case-study are used to feed the model and perform the assessment. Actual results and model predictions (results) are compared varying the equivalent relation between 0.05 and 0.65, and the moisture content form biomass between 0 and 20%. This case is proposed as a benchmark case for further applications.Copyright © 2015 by ASME

The use of natural gas in spark-ignited internal combustion engines optimized for minimum emissions has repeatedly shown a significant reduction in exhaust emissions over that of gasoline. Pronounced variations in unprocessed natural gas composition can however present an emissions problem for engines used in natural gas recovery where unrefined wellhead gas is used as the fuel. This study is twofold involving both experimental analysis and theoretical development with a computer model that simulates wellhead gas combustion. On the experimental side, Fourier transform infrared spectroscopy (FTIR) was used to analyze emissions of a 2.4L four-cylinder spark-ignited natural gas engine operating on fuels of varying composition. A comparative assessment is made between CO, NO, THC, CH4, and CH2O emissions of the engine operating on refined pipeline natural gas and those of the engine operating on the same gas with added CO2, N2, and C3H8 diluents. Diluents were added to the fuel individually to isolate the effect of each and to approximate wellhead gas. Additionally, a burn rate analysis was conducted which shows changes in the rate of fuel energy liberation with changes in diluent concentration. On the theoretical side, a two zone computer model of engine operation was developed that would simulate operation of the engine under varying fuel composition as found in various natural gas recovery wells throughout the United States. Results show that exhaust concentrations of NO and THC were strongly affected by addition of both inert and reactive diluent due to their strong dependence on in-cylinder temperature. Emissions of CO, CH4, and CH2O were also found to depend on diluent concentration; however, to a much lesser extent with emissions of CO being seemingly unaffected by addition of N2 for the compositions tested. Burn rate analysis shows that the introduction of inert constituents to the fuel decreases the fuel burn rate while addition of propane increases the burn rate. The whole of the analysis indicates a strong dependence of emissions on fuel composition and that significant potential exists for emissions reduction of engines operating on unprocessed natural gas.Copyright © 2015 by ASME

Fuel flexibility is a key feature for Dry Low NOx (DLN) combustors, which shall be capable of accepting a wider range of fuel compositions to meet more and more challenging requests from the Oil and Gas market segment (upstream and downstream applications). Non-methane hydrocarbons (C2+) are one of the main targets of GE Oil & Gas efforts to enlarge the fuel flexibility of DLN combustors, as they are often present in high concentration in fuel gas streams that customers would like their gas turbine to be fed with. The main concerns with such fuel gases in DLN combustor are: the risks of flashback, hardware overheating, increased combustion dynamics and NOx emission, ignition in unexpected locations (with potential damage of the combustor, operability issues and impact on durability). In order to assess the capability of the current Frame 5 DLN1 hardware design with high C2+ fuels, a single can full pressure test campaign was conducted on a full size DLN1 combustor at Sesta Combustion Lab (Italy). The combustion chamber was successfully tested in premix mode up to 50%v. of ethane content, observing safe and reliable operation with regard to the above mentioned risks. Special tests were carried out in both Premix and Lean-Lean operating modes, in order to verify the ability of the combustor to maintain a stable and harmless flame and assess the operability margins in the different operating conditions of the combustor. Tests demonstrated a good margin already with the current design. After optimizing the air flow path, the expected performances also in terms of NOx and CO emissions and combustion dynamics were achieved in the investigated ethane content range. These tests outcomes allowed a paramount enlargement of the Frame 5 DLN1 capability in terms of acceptable C2+ concentration in fuel gas.

Operators of heavy duty gas turbines desire more flexibility of operation in compliance with increasingly stringent emissions regulations. Delivering low NOx at base load operation, while at the same time meeting aggressive startup, shutdown, and part load requirements for NOx, CO, and unburned hydrocarbons is a challenge that requires novel solutions in the framework of lean premixed combustion systems. The DLN2.6+ combustion system, first offered by the General Electric Company (GE) in 2005 on the 9F series gas turbines for the 50 Hz market, has a proven track record of low emissions, flexibility, and reliability. In 2010, GE launched a program to incorporate the DLN2.6+ into the 7F gas turbine model. The primary driver for the introduction of this combustion system into the 60 Hz market was to enable customers to capitalize on opportunities to use shale gas, which may have a greater Wobbe range and higher reactivity than traditional natural gas. The 7F version of the DLN2.6+ features premixed pilot flames on the five outer swirl-stabilized premixing fuel nozzles (“swozzles”). The premixed pilots have their roots in the multitube mixer technology developed by GE in the US Department of Energy Hydrogen Gas Turbine Program. A fraction of air is extracted prior to entering the combustor and sent to small tubes around the tip of the fuel nozzle centerbody. A dedicated pilot fuel circuit delivers the gas fuel to the pilot tubes, where it is injected into the air stream and given sufficient length to mix. Since the pilot flames are premixed, they contribute lower NOx emissions than a diffusion pilot, but can still provide enhanced main circuit flame stability at low-load conditions. The pilot equivalence ratio can be optimized for the specific operating conditions of the gas turbine. This paper presents the development and validation testing of the premixed pilots, which were tested on E-class and F-class gas turbine combustion system rigs at GE Power & Water’s Gas Turbine Technology Lab. A 25% reduction in NOx emissions at nominal firing temperature was demonstrated over a diffusion flame pilot, translating into more than 80% reduction in CO emissions if increased flame temperature is employed to hold constant NOx. On the new 7F DLN2.6+, the premixed pilots have enabled modifications to the system to reduce base load NOx emissions while maintaining similar gas turbine low-load performance and bringing a significant reduction in the combustor exit temperature at which LBO occurs, highlighting the stability the pilot system brings to the combustor without the NOx penalty of a diffusion pilot. The new combustion system is scheduled to enter commercial operation on GE 7F series gas turbines in 2015.

In the development process of gas turbine combustion chambers, finding countermeasures for thermoacoustically induced pressure pulsations is a major focus. This paper presents a novel system consisting of a multi-layered and multi-functional high frequency damping and cooling structure that is implemented on the sequential burner front panel of the GT26/GT24 gas turbines. The device features multiple single Helmholtz dampers and an advanced convective near wall cooling system to improve the cooling capability and to reduce the cooling mass flow and thereby reducing NOx emissions. The acoustic properties of the dampers and their placement have been defined as function of the identified acoustic mode shapes. The latter is very important since the dampers are designed to counteract screech tones that have acoustic wave lengths of the order of one burner front face width. In order to identify the acoustic mode shapes, multiple dynamics pressure measurements are applied in the full scale engine. The near-wall cooled damping front panel design represents a new technology which has been developed and successfully validated at engine level in fuel gas and oil operation. The restrictions of the stable operating range due to pulsations are completely eliminated resulting in an increase of operational flexibility and lifetime. In addition to a thorough treatment of the damper’s acoustic performance, information on the improved near wall cooling scheme is given in the paper, too.

Under all circumstances, an engine and its driven equipment(s) must be prevented from operating at a speed above the maximum allowed speed — to ensure the safety of the equipment, plant and its personnel. However, meeting this requirement is particularly challenging for power generation units where the drive train is composed of electric generators driven by free power turbines (i.e. aerodynamically-coupled power turbines), since during load-shed events or circuit breaker failure, full loss of load happens almost instantly. During these events, usually the Fuel Metering Valve is fully closed by the Engine Control System and the Fuel Isolation Valve is closed by the safety system. But, fuel gas continues to flow to the system during the closing of the valves, and furthermore, the fuel gas trapped in the piping between the valve and the fuel injectors still has enough pressure to flow to the combustion chamber and add energy to the system, which at that point has almost no external load, thus likely to cause an over-speeding of the drive-train. This paper is to report a dynamic model created for drive-train over-speed predictions. In this model, fuel flow rate to the engine is calculated based on the principle of conservation of mass together with the fuel gas equation of state. The calculated fuel flow rate is then used to find the amount of power supply to the drive train, which in the next step is converted to the torque applied on the shaft. Finally, Newton’s second law is used to determine the angular acceleration and the angular speed. This approach is applied to two different variations of the Industrial RB211 Engine — the DLE (Dry Low Emission) RB211 and Non-DLE RB211 — which have different designs of the fuel gas system and the burners. For both cases, the results using the modeling approach presented in this paper demonstrate around 99% agreement with the actual measured over-speed values recorded during trip events. The model allows studying the drive train speed for different operating conditions and failure cases, and also makes it easy to understand and quantify the effect of fuel gas system parameter variation on drive-train over-speed.

It is important that gas turbines used in Oil & Gas applications can burn a wide variety of fuels with the minimum impact on the environment or project economics. This paper is an introduction for those unfamiliar with gas turbine combustion in any detail into how emissions such as NOx are formed, and how the two most common types of gas turbine combustion system — the ‘conventional’ diffusion flame combustor and the Dry Low Emissions (DLE) combustor operate. There are many types of gaseous and liquid fuels that can be used in Gas Turbines, which can come from a wide range of natural and industrial sources. These different potential fuels are discussed, along with the flexibility of the two different combustion systems to accept different types of fuel. Some of the common contaminants found in these fuels are also discussed, along with the impact these have on the operability and maintenance of industrial and aero-derivative gas turbines, and methods to minimize the impact of these contaminants identified. Finally the paper looks at recommendations on liquid fuel storage to minimize operational issues on liquid fuels.

Recently, energy resource depletion and unstable energy prices have become global issues. Worldwide pressure to secure and make more gas and oil available to support global power needs has increased. To meet these needs, alternative fuels composed of various types of fuels have received attention, including biomass, dimethyl ether (DME), and low rank coal. For this reason, the fuel flexibility of the combustion system becomes more important. In this study, H2 and CH4 were selected as the main fuel composition variables and the OH-chemiluminescence measurement technique was also applied. This experimental study was conducted under equivalence ratio and fuel composition variations with a model gas turbine combustor to examine the relation between combustion instability and fuel composition. The combustion instability peak occurs in the H2/CH4 50:50 composed fuel and the combustion instability frequency shifted to higher harmonic of longitudinal mode based on the H2 concentration of the fuel. Based on instability mode and flame length calculation, the effect of the convection time during the instability frequency increasing phenomenon was found in a partially premixed gas turbine combustor. The time-lag analysis showed that the short convection time in a high H2 concentration fuel affects the feedback loop period reduction and, in these conditions, high harmonics of longitudinal mode instability occurs. This fundamental study on combustion instability frequency shifting characteristics was conducted for H2/CH4 composed fuel and the results contribute key information for the conceptual design of a fuel flexible gas turbine and its optimum operation conditions.

The main benefits of operating a combustor under flue gas recirculation conditions are the increase in efficiency of the post combustion carbon capture and storage process and the potential to reduce NOX emissions while keeping the thermal load of the gas turbine constant. The latter is primarily caused by the change in thermodynamic properties of the combustive mixture with increasing vitiation. As a result, the dominant NOX formation pathways change with increasing FGR ratio. In a partially premixed combustor, the formation of NOX emissions can also be influenced by the fuel mixing behavior. Different setups lead to combustive mixtures with different degrees of homogeneity as well as influencing the distribution of the mixture within the combustion chamber. In this paper the combined effects of the variation of mixture homogeneity and the flue gas recirculation ratio on the NOX emissions and the stability range is experimentally investigated for different fuel gases. The experiments are performed on the atmospheric laboratory test rig, which is equipped with a partially premixed combustor. The burner is equipped with modular fuel gas nozzles allowing for the variation of the fuel mixing behavior. Exhaust gas measurements are performed to evaluate the influence of the parameters on the emissions profile of the combustor and to compare the results to a theoretical study. The results of this study show that the level of nitric oxide emissions as well as the potential to decrease said emissions with FGR operation is dependent on the mixing behavior of the combustor. Furthermore, the combined effects of fuel gas nozzle and FGR operation lead to a proposal of an operational strategy for the combustor which combines the advantages of low nitric oxide emissions and a broad range of stability.

Condensation of gaseous fuel is investigated in a low temperature combustion (LTC) engine fueled with double direct-injected diesel and premixed gasoline at two load conditions. Possible condensation is examined by considering real gas effects with the Peng–Robinson (PR) equation of state (EOS) and assuming thermodynamic equilibrium of the two fuels. The simulations show that three representative condensation events are observed. The first two condensations are found in the spray some time after the two direct injections (DI), when the evaporative cooling reduces the local temperature until phase separation occurs. The third condensation event occurs during the late stages of the expansion stroke, during which the continuous expansion sends the local fluid into the two-phase region again. Condensation was not found to greatly affect global parameters, such as the average cylinder pressure and temperature mainly because, before the main combustion event, the condensed phase was converted back to the vapor phase due to compression and/or first stage heat release. However, condensed fuel is shown to affect the emission predictions, including engine-out particulate matter (PM) and unburned hydrocarbons (UHCs). Specifically, it was shown that the condensed fuel comprised more than 95% of the PM in the low load condition, while its contribution was significantly reduced at the high load condition due to higher temperature and pressure conditions.

In this work, the detailed model of a high temperature Solid Oxide Fuel Cell (SOFC) and Gas Turbine (GT) hybrid system was established by using MATLAB/Simulink platform, based on the equations of mass and energy balance and thermodynamic characteristics, with the consideration of various polarization losses and fuel cell heat loss. Influence of different biomass gases on the hybrid system performance was studied. Results show that the electrical efficiency could reach up to over 50% with four types of gasified biomass, higher than other hybrid power system using biomass gases. Biomass gases from different sources have different composition and calorific value, which significantly affect the hybrid system performance. The system output power and efficiency fueled with wood chip gas are higher than the system fueled with other three types of fuel. Restricted by compressor surge safety zone, the adjustable range of biomass gas fuel flow rate is small. The speed of the gas turbine has a significant impact on the hybrid system parameters such as output power and efficiency. When the rotational speed of the gas turbine is lower than the rated value, the hybrid system performance parameters change significantly, on the contrary, the hybrid system performance parameters change slightly.

Nearly all states now have renewable portfolio standards (RPS) requiring electricity suppliers to produce a certain fraction of their electricity using renewable sources. Many renewable energy technologies have been developed to contribute to RPS requirements, but these technologies lack the advantage of being a dispatchable source which would give a grid operator the ability to quickly augment power output on demand. Gas turbines burning biofuels can meet the need of being dispatchable while using renewable fuels. However, traditional combustion of liquid fuels would not meet the pollution levels of modern dry, low emission (DLE) gas turbines burning natural gas without extensive back-end clean-up. A Lean, Premixed, Prevaporized (LPP) combustion technology has been developed to vaporize liquid ethanol and blend it with natural gas creating a mixture which can be burned in practically any combustion device in place of ordinary natural gas. The LPP technology delivers a clean-burning gas which is able to fuel a gas turbine engine with no alterations made to the combustor hardware. Further, the fraction of ethanol blended in the LPP gas can be quickly modulated to maintain the supplier’s overall renewable quotient to balance fluctuations in power output of less reliable renewable power sources such as wind and solar. The LPP technology has successfully demonstrated over 1,000 hours of dispatchable power generation on a 30 kW Capstone C30 microturbine using vaporized liquid fuels. The full range of fuel mixtures ranging from 100% methane with no ethanol addition to 100% ethanol with no methane addition have been burned in the demonstration engine. Emissions from ethanol/natural gas mixtures have been comparable to baseline natural gas emissions of 3 ppm NOx and 30 ppm CO. Waste heat from the combustor exhaust is recovered in an indirect heat exchanger and is used to vaporize the ethanol as it is blended with natural gas. This design allows for startup on natural gas and blending of vaporized ethanol once the heat exchanger has reached its operating temperature.Copyright © 2014 by ASME

Fuel gas for many Combined Cycle Power Plants is supplied directly by the gas provider’s regulator station in locations where the gas pipeline pressure is sufficient without further compression. Other locations require one or more onsite compressors to boost the fuel gas pressure. A rising concern is the fuel gas system transient response immediately after a significant reduction in the plant fuel gas consumption. Transient analysis models have been developed for typical fuel gas systems of combined cycle plants to ensure that the system is configured to respond appropriately to unplanned disturbances in fuel gas flow such as when a gas turbine trip occurs. Pressure control (regulator) and booster compressor control loop tuning parameters based on quantitative transient model results could be applied to set up targets for use in specifying and commissioning the fuel gas system. Case studies are presented for typical large combined cycle plants with two gas turbines taking fuel from a common plant header. This is done for designs without or with fuel gas booster compressors.Copyright © 2014 by ASME

Recent discoveries of vast natural gas reserves in the United States have led to increased domestic natural gas production, resulting in lower prices. Utility and large industrial facilities are performing solid fuel conversions on their boilers to natural gas as a cost-effective and efficient fuel solution. Natural gas is not only economically beneficial but also environmentally efficient with cheaper prices and reduced SO2, NOx, and CO2 emissions. The Environmental Protection Agency (EPA) has recently released mandatory requirements that directly affect the cost effective operation of solid fuel boilers, resulting in natural gas becoming a more economically appealing choice of fuel for facility operators. As more facilities consider boiler fuel conversions, it is important to understand all facets of the conversion, from the thermal evaluation of the boiler, to the complete design, supply and installation of the new firing system. Zeeco will provide specific details and recommended practices from a recent Circulating Fluidized Bed (CFB) Boiler solid fuel conversion to natural gas application designed for 1.3 billion Btu/hr of heat input for the maximum continuous steam rating. The information will detail the boiler conversion from a solid fuel fluid bed to a 100% natural gas fired boiler design. Thermal performance results, design and supply of the complete new gas firing system, and installation conversion assistance for the boiler modifications and firing system installation details are also provided.

The purpose of this paper is to show how compact heat exchanger technology can offer energy savings and hence cycle efficiency improvements on new and existing gas turbine installations by being utilised for fuel gas heating. After a brief introduction to high temperature compact heat exchanger technology and comparison to traditional equipment, thermodynamic cycle analysis for a combined cycle gas turbine plant (CCGT) is used show the advantages of compact technology over conventional technology, analysing the fuel gas heating, to illustrate the overall savings. A case study is used to demonstrate an increase in net LHV electric efficiency in the range of 0.5 to 1.17 % achievable using high effectiveness compact diffusion bonded heat exchangers in fuel gas heating. Intermediate pressure and high pressure feed water heating is considered for increasing the fuel gas inlet temperature to the combustor. The model is built in Excel and is extended to a capital expenditure overview based on new or a retrofitting in existing plants.

It is estimated that 30% of the over 1 billion cubic feet per day of natural gas produced in the Bakken shale field is lost to flaring. This flared gas, were it to be collected and used in DLE power generation gas turbine engines, represents approximately 1.2 GW of collective electric power. The main reason that much of this gas is flared is that the infrastructure in the Bakken lacks sufficient capacity or compression to combine and transport the gas streams. One of the reasons that this gas cannot be utilized on-site for power generation is that it contains significant amounts of natural gas liquids (NGLs) which make the gas unsuitable as a fuel for natural gas-fired gas turbine engines. A Lean, Premixed, Prevaporized (LPP) combustion technology has been developed that converts liquid fuels into a substitute for natural gas. This LPP Gastm can then be used to fuel virtually any combustion device in place of natural gas, yielding emissions comparable to those of ordinary natural gas. The LPP technology has been successfully demonstrated in over 1,000 hours of clean power generation on a 30 kW Capstone C30 microturbine. To date, 15 different liquid fuels have been vaporized and burned in the test gas turbine engine. To simulate the vaporization of NGLs, liquids including propane, pentane, and naphtha, among other liquids, have been vaporized and blended with methane. Emissions from the burning of these vaporized liquid fuels in the test engine have been comparable to baseline emissions from ordinary natural gas of 3 ppm NOx and 30 ppm CO. Autoignition of the vaporized liquid fuels in the gas turbine is controlled by the fraction of inert diluent added in the vaporization process. The LPP technology is able to process an infinitely variable composition of NGL components in the fuel stream by continually adjusting the amount of dilution to maintain a heating value consistent with natural gas. Burning the flare gases containing NGLs from a well locally, in a power generation gas turbine, would provide electricity for drilling operations. A microgrid can distribute power locally to the camps and infrastructure supporting the drilling and processing operations. Using the flare gases on-site has the benefit of reducing or eliminating the need for diesel tankers to supply fuel for power generation systems and equipment associated with the drilling operations.Copyright © 2014 by ASME

Heavy duty gas turbines are very flexible combustion tools that accommodate a wide variety of gaseous and liquid fuels ranging from natural gas to heavy oils, including syngas, LPG, petrochemical streams (propene, butane…), hydrogen-rich refinery by-products; naphtha; ethanol, biodiesel, aromatic gasoline and gasoil, etc. The contemporaneous quest for an increasing panel of primary energies leads manufacturers and operators to explore an ever larger segment of unconventional power generation fuels. In this moving context, there is a need to fully characterize the combustion features of these novel fuels in the specific pressure, temperature and equivalence ratio conditions of gas turbine combustors using e.g. methane as reference molecule and to cover the safety aspects of their utilization. A numerical investigation of the combustion of a representative cluster of alternative fuels has been performed in the gas phase, namely two natural gas fuels of different compositions, including some ethane, a process gas with a high content of butene, oxygenated compounds including methanol, ethanol, and DME (dimethyl ether). Sub-mechanisms have specifically been developed to include the reactions of C4 species. Major combustion parameters, such as auto-ignition temperature (AIT), ignition delay times (AID), laminar burning velocities of premixed flames, adiabatic flame temperatures, and CO and NOx emissions have then been investigated. Finally, the data have been compared with those calculated for methane flames. These simulations show that the behaviors of alternative fuels markedly differ from that of conventional ones. Especially, DME and the process gases appear to be highly reactive with significant impacts on the auto-ignition temperature and flame speed data, which justifies burner design studies within premixed combustion schemes and proper safety considerations. The behaviors of alcohols (especially methanol) display some commonalities with those of conventional fuels. In contrast, DME and process gas fuels develop substantially different flame temperature and NOx generation rates than methane. Resorting to lean premix conditions is likely to achieve lower NOx emission performances. This review of gas turbine fuels shows for instance that the use of methanol as a gas turbine fuel is possible with very limited combustor modifications.

This paper describes the latest results from the development of a liquid fuel solution for the 4th generation DLE system for Siemens medium size gas turbines. Gaseous fuels are the dominating fuels for industrial gas turbines. However, many customers need to be able to run on liquid fuel as backup. The demand for dry low NOx emissions when operating on liquid fuel is increasing. The aim for the 4th generation DLE system incorporated in the recently released SGT-750 [1] is to have emission levels well below market demands on both gas and liquid fuel. This paper will highlight the technical challenges when adding liquid fuel operation to a combustion system optimized for gas operation. The stand-alone spray characteristics for a liquid fuel nozzle is quite easy to predict, but the final combustion performance in a hot air cross flow environment is all but easy to predict by numerical simulations or cold flow tests [2]. Due to the complexity of the challenge, the development program focused on a selection of concepts for which fuel/air mixing calculations were made. The investigation was completed by testing in a full scale, single burner high pressure combustion test rig.Copyright © 2014 by ASME

Flue gas recirculation in combined cycle power plants using hydrocarbon fuels is a promising technology for increasing the efficiency of the post combustion carbon capture and storage process. However, the operation with flue gas recirculation significantly changes the combustion behavior within the gas turbine. In this paper the effects of external flue gas recirculation on the combustion behavior of a generic gas turbine combustor was experimentally investigated. While prior studies have been performed with natural gas, the focus of this paper lies on the investigation of the combustion behavior of alternative fuel gases at atmospheric conditions, namely typical biogas mixtures and syngas. The flue gas recirculation ratio and the fuel mass flow were varied to establish the operating region of stable flammability. In addition to the experimental investigations, a numerical study of the combustive reactivity under flue gas recirculation conditions was performed. Finally, a prediction of blowout limits was performed using a perfectly stirred reactor approach and the experimental natural gas lean extinction data as a reference. The extinction limits under normal (non-vitiated) and flue gas recirculation conditions can be predicted well for all the fuels investigated.

One of the preferred ways to reduce NOX formation in an aero-engine is to operate lean throughout the whole operational range; however the lean combustion suffers from poor stability. To avoid the problem associated with stability, often a rich pilot flame is used along with a main flame to act as a source of heat and radicals to the main flame. The focus of the paper is to discuss the influence of the liquid fuel spray characteristics and effect of flow parameters on the lean blow out (LBO) limits of a piloted burner. In order to understand the observed remarkable LBO limits of the pilot flame with Jet A-1 (LBO = 145 kg-air to kg-fuel at 0.1 MPa of combustor pressure), velocity field measurements by laser Doppler Anemometry (LDA) technique have been performed. Furthermore, the flame structure has been analyzed with OH* chemiluminescence imaging. Experimental results show that the LBO limits of the burner running with liquid fuel further improves with an increase in combustor pressure. Such improvement in LBO limits is attributed to the change in the liquid fuel distribution caused by the change in the combustor pressure. For gaseous fuel measurements, results indicate that the equivalence ratio and the momentum ratio of the pilot jet to the co-annular flow are the dominating parameters that control the mixing process in the combustor and the ensuing effect on the flame structure and location of flame stabilization is substantial. The flame stabilizes either along the centreline or along the shear layer between two jets. Such information is useful in designing a lean partially premixed combustion system where a pilot flame is required to stabilize a main lean flame.Copyright © 2014 by ASME

The performance of a micro gas turbine in terms of global efficiency and exhaust emissions at different loads and methane-hydrogen blends has been experimentally studied. The load was varied from full load down to half load. A critical comparison between experimental data and results of the 3D CFD analysis of the combustor is discussed in order to study the effects of part load operation. Additional objective of the present study is to extend the numerical analysis of the combustor in order to describe the influence of a wider range of hydrogen concentrations in the fuel gas mixture. Numerical simulations were performed through the commercial code ANSYS CFX 14.5. Turbulence model adopted was the RSM RANS model, which ensures a good evaluation of effects of swirled turbulent flows in the combustion chamber. The oxidation of methane is simulated by using multistep kinetics models. They assure a better reproduction of CO emissions with load. Boundary and initial conditions were defined by using experimental data, when available, and results of numerical matching analysis, which assumes importance in case of absence of specific measurements at combustor inlet. Discussion of results is mainly focused on the variation in terms of exhaust gaseous emissions and temperature distributions in the combustor by varying load and fuel. A numerical evaluation of the MGT combustor behavior in critical conditions is also presented.Copyright © 2014 by ASME

Lifting a flame from the flow generating nozzle to some distance apart has a wide variety of effects on the properties of the resulting combustion phenomenon. The reason of this influence is the generation of a non-reacting flow domain where mixing takes place prior to the combustion reaction. It is obvious that the quality of premixing that can be achieved strongly depends on the time that is given to flow and the intensity of the turbulence that is mixing fuel and air. The most important parameter that is characterizing this time is the size of the premixing zone quantified by the so called lift-off height (LOH). Additionally, when employing liquid fuel the lift-off of a flame provides time to achieve better pre-evaporation of the fuel. As a consequence, better mixing of fuel and air helps to avoid high temperature regions that may be a result from an inhomogeneous equivalence ratio distribution. From safety considerations a major advantage of this method compared to the application of a premixing duct is that the risk of hardware destruction by flame flash back can be eliminated. The current work extents the knowledge on lifted flames by the investigation of flames that are generated with an airblast atomizing nozzle that was designed to resemble systems close to application. Lifting of the flame is achieved applying a combination of swirling and non-swirling inflow ducts. A wide range of operating conditions as well as gaseous and liquid fuels are used to investigate their influence on the lift-off height. The lift-off height and location of the reaction zone was determined by means of chemiluminescence of OH* and it is shown, that the impact of pressure drop and preheating temperature on the LOH is different for gaseous and liquid fuels.

Siemens Industrial Turbomachinery AB (SIT) Finspong is increasingly asked by customers to consider if a wider range of gas compositions may be operated in its gas turbines. A large part of these fuel compositions contain high concentrations of highly reactive components like hydrogen and ethane. Such fuel compositions are characterized by higher flame speeds than the standard natural gas which introduce increased risk for flashback and premature combustor and/or fuel nozzle distress. The SIT approach for fuel flexibility testing, Experimental Burner In Test engine (EBIT) uses a separate feed for testing a selected fuel composition in one burner in a standard gas turbine installation where the other burners use fuel from the standard fuel system. The separate feed is operated as a slave to engine governor heat demand, but can also be controlled independently. This paper describes how EBIT was used to test the capability of the SIT 3rd generation DLE burner to satisfactorily operate using highly reactive fuel components such as ethane and hydrogen. Combustion monitoring techniques and measurements to check flame behavior and assess flashback potentials of the tested fuel compositions are described. Results from testing show that the SIT 3rd generation DLE burner allows extending the levels of reactive fuel components accepted for operation on the SGT-700 33MW engine and SGT-800 50MW engine.

Analysis of the Oil & Gas market segment showed that potential MS5002E customers could benefit from firing the gas turbine with distillate oil as a back-up fuel, mainly to provide power when the fuel gas is not available (e.g. when the plant itself is being commissioned). To address this customer need, the design of a dual fuel system for such mission should target simplicity, reliability and minimize the additional cost with respect to the single gas version. To achieve these targets, the development of the dual fuel system for the MS5002E leveraged the efforts made by GE for the design of a liquid fuel system for Frame 9F-1 series with no need of atomization air. Moreover, the emission capability during liquid fuel operation was enhanced allowing the mixing of water and fuel before injection in the combustion chamber and using of improved injection technology, thus improving the efficiency of water injection with a significant reduction in the required water flow rates; the importance of this achievement is related to both the increasingly stringent regulation on this subject and the often poor availability of water in the Oil & Gas market segment. The system is capable of continuous operation without water injection for applications where emissions are not critical; in these cases a small amount of demineralized water is employed occasionally for fuel line cooling and flushing, thus helping to guarantee constant performances of the injectors, and to maintain liquid fuel start-up capability over time. This paper presents the expected performance, in terms of ignition capability, emissions, operability and expected hardware durability on LF/water-fuel emulsion operation, based on a single can rig test campaign. The new liquid fuel cartridges were tested from ignition to base load at ISO and extreme simulated ambient conditions, both with and without water injection, showing promising performance in terms of combustor operability and emissions. All the combustor components were instrumented with thermocouples to assess variations in the hardware thermal levels with respect to the single gas conditions, and identify possible issues related to the transient and steady-state liquid fuel operation. Further development and testing will be carried out in the next phases of the development, and the performance will be confirmed by a dedicated engine test at the first commercial opportunity.

In this study, an electricity and value-added chemicals cogeneration system using methane-fueled single chamber solid oxide fuel cells (SC-SOFCs) was successfully developed and investigated. The SC-SOFCs, which operated on methane/oxygen gas mixture with a ratio of 2:1, achieved an open-circuit voltage of 1.0 V and a maximum peak power density of ∼ 840 mW.cm-2 at 700 °C. By passing the exhaust gas of the fuel cell through a Ru/Al2O3 catalyst at 700 °C, the synthesis gas is obtained with a methane conversion of higher than 95%, while CO and H2 selectivity is higher than 92%. This study provides a novel strategy for energy conversion which is one of the major concerns in energy field and a new frontier for improving the energy efficiency of SOFCs.Copyright © 2013 by ASME

Fuel combustion performance was quantified through measurement of the gravimetric response of the fuel as well as the energetic behavior. A Simultaneous Thermogravimetric Analyzer (STA) was used to measure the gravimetric, sensible energy, and latent heat energy (including heat of pyrolysis) for fuels. The heat release rate and heat of combustion of the fuels as a function of temperature released due to the combustion of the pyrolysis gases was measured using a Micro-Combustion Calorimeter (MCC). Fuels were tested at a heating rate of 20°C/min from room temperature to 800°C in inert (nitrogen) environment. Fuels considered in this study included US eastern coal, biomass (cornstover and switchgrass), polystyrene, glycerol and mixtures of some of these fuels. Biomass feedstocks were also evaluated for the effect of water leaching on fuel performance. A lumped model energy balance on a fuel particle revealed that fuel volatility can be ranked based on the net energy required to produce the volatile gas times the ratio of the heat of combustion to the heat of decomposition. This is different compared with previous research results in that it includes the temperature dependence of the fuel production in the volatility.

A wide range of fuels are used in industrial gas fueled engines. Fuels include well-head gas, pipeline natural gas, producer gas, coal gas, digester gas, landfill gas, and liquefied petroleum gas. Many industrial gas fueled engines operate at high power density and at ultra-lean air-fuel ratios for low NOx emissions. Engines operate in a narrow air-fuel ratio band between misfire and knock limits. To utilize this wide range of fuels effectively it is important to understand knock properties. Methane number determination for natural gas blends is traditionally performed with research engines at stoichiometric conditions where the onset of knock is identified through subjective audible indication. The objective of this paper is to develop a process to determine knock onset through direct indication from pressure transducer data at lean operating conditions characteristic of lean-burn industrial gas engines. Validation of the method is provided with methane number determination and comparison of pipeline natural gas. A Waukesha F2 Cooperative Fuel Research (CFR) engine is modified to incorporate piezoelectric pressure transducers at the cylinder head and conversion from natural aspiration to boosted intake and variable exhaust back pressures (to simulate turbocharger operation). The new pressure sensors enable Fast Fourier Transform calculation of pressure data to calculate amplitude at characteristic knock frequency.

This paper reviews the technical approach and reports on the results of ASPEN Plus® modeling of two patented approaches for integrating a gas turbine with reciprocating internal combustion engine for lower emissions and higher efficiency power generation. In one approach, a partial oxidation gas turbine (POGT) is located in the 1st stage, and the H2-rich fuel gas from POGT exhaust is cooled and fed as main fuel to the second stage, ICE. In this case, the ICE operates in lean combustion mode. In the second approach, an ICE operates in partial oxidation mode (POX) in the 1st stage. The exhaust from the POX-ICE (a low BTU fuel gas) is combusted to drive a conventional GT in the 2nd stage of the integrated system. In both versions, use of staged reheat combustion leads to predictions of higher efficiency and lower emissions compared to independently providing the same amount of fuel to separate GT and ICE where both are configured for lean combustion. The POGT and GT analyzed in the integrated systems are based upon building them from commercially available turbocharger components (turbo-compressor and turbo-expander). Modeling results with assumptions predicting 50–52% LHV fuel to power system efficiency and supporting NOx < 9 ppm for gaseous fuels are presented for these GT-ICE integrated systems.

In this paper, the results of the evaluation of using ethanol in a GE 61B gas turbine are presented. For better understanding, combustion analysis for natural gas was performed as a comparison point, calculating fuel and air requirements at the entrance and exit of the combustion chamber, obtaining the principal emissions for both fuels at different temperatures and relationships air-fuel. Using design data taken from the manufacturer website, the four main processes of a complete Joule-Brayton cycle were calculated. In that way, the results were used as a thermodynamic basis in this work. Focus on the combustion turbine, setting the temperature at the entrance of the combustion chamber and varying the temperature at turbine inlet. Afterward, using the temperatures resulted by the calculations, stoichiometric air-fuel ratio and mole fractions were found. Finally, varying air-fuel ratio at diverse mixtures, there were obtained the emissions for both fuels. As results, there were obtained the fuel requirements for natural gas and ethanol, finding that for ethanol, due to its lower calorific value, the amount of fuel is higher in order to obtain the required temperature. In terms of emissions, there was no convincing evidence that ethanol represents a minor emission source than natural gas; therefore, it could be a good substitute of natural gas in those countries were ethanol is produced.

Coal-fueled fuel cells can be an important part of the future power generation infrastructure. The coal can be gasified through partial oxidation process to produce a carbon monoxide rich gaseous fuel. But this fuel gas cannot be used as fuel in the conventional polymer electrolyte fuel cells (PEFC). The idea that is introduced and investigated in this paper is to develop a single cell PEFC that can be fueled with carbon monoxide. It is shown that this idea is feasible. Also, the preliminary results of the experiments are presented to investigate the effects of various design, fabrication, and operational conditions on the performance of the single cell PEFC fueled with carbon monoxide.Copyright © 2013 by ASME

Modern gas turbine combustors have to fulfill two major requirements. On the one hand they have to provide reliable operation with low emissions; on the other operational flexibility is of utmost importance. Alstom’s new AEV (Advanced EnVironmental) burner — an evolution of the proven EV burner technology — is one key feature to fulfill both on engine level. It can be operated on fuel gas and oil. In order to achieve low NOx emissions, modern combustors are operated in lean-premixed mode which is prone to thermoacoustic instabilities. This is accounted for by the implementation of multi-volume dampers. These dampers feature high damping performance in a broad low-frequency range thus widely enlarging the operating window. During transient operation, especially when switching from gaseous to liquid fuel and vice versa, the specific switching procedure with sophisticated fuel flow control schemes allows for a very smooth transmission. Another very important aspect is the optimization of leakage and cooling air into the combustion chamber. In order to validate the reduction of both, multiple thermal paint applications for fuel gas and oil operation in the full scale engine were performed at different engine loads up to baseload. In this paper, the AEV burner, broadband acoustic dampers, optimized cooling and leakage schemes, as well as innovative fuel switchover and operation concepts are described. It is shown that the combination of all of them makes the GT13E2 outstanding in fuel and operational flexibility featuring low emissions over the whole operating window.Copyright © 2013 by Alstom Technology

Biomass is a clean, renewable energy source with a large potential to contribute significantly to power generation, promising a more environmentally friendly production of electricity in future, with lower greenhouse gas emissions. A large variety of biomass feedstock exists, including agricultural and biomass residues and by-products, with wood, sludge, and waste among them. Biomass can be used directly to generate electricity if converted to more user-friendly sources of energy, e.g. by fermentation producing mainly methane (biogas) and by gasification leading mostly to hydrogen and carbon monoxide (syngas), allowing a more efficient use of the product gases compared to direct combustion, besides further advantages, with less amounts of ash and corrosive species. The resulting product gases can be burned in small to large scale gas turbines, stand alone, process integrated or in combined cycles. In a hybrid power plant, an increase of the electrical efficiency of small gas turbines to more than 50 % can be reached, by coupling a gasifier or biogas reactor with a fuel cell (FC) and a micro gas turbine. To widen the acceptable range in the variation of fuel composition and conditions and to ensure a reliable and more efficient operation, it is of outmost importance to expand our knowledge on biogenic gas mixtures with respect to modeling capabilities e.g. of major combustion properties, thus enabling predictive calculations. The present work is dealing with the use of representative biogenic gas mixtures for decentralized power production. The concept of coupling a gasifier or biogas reactor with a fuel cell and a micro gas turbine (hybrid power plant) is followed. The product gases are stemming from the fermentation of sludge and algae as well as from the gasification of their residues and wood, in addition. Their combustion behavior — lower heating value (LHV), Wobbe index, adiabatic flame temperature, laminar flame speed, and ignition delay time — is calculated for the relevant parameters — fuel-air ratio, pressure — and discussed with respect to the intended use.

The aim of this work is to experimentally and numerically analyze the performance of a combined power plant, composed by a steam oxygen fluidized bed biomass gasifier fed by woods, a Solid Oxide Fuel Cell (SOFC) and an Organic Rankine Cycle (ORC). The gasifier model is developed and validated by means of experimental activities carried out with a bench scale gasifier in our lab. Different compounds (Benzene, Toluene, Naphthalene, Phenols) were chosen to analyze the tar evolution in the gaseous stream during the gasification process. Hot gas cleaning (based on catalytic ceramic filter candles inserted in the freeboard of the gasifier - UNIQUE concept) is adopted to remove tar and particulate at high temperature from the fuel gas stream. The numerical analysis is carried out by means of the software Aspen Plus®. In particular, the SOFC and the gasifier are modelled using proper developed Fortran subroutines interfaced to the basic software. The adopted SOFC model was already validated by the authors in previous works. Finally, a realistic ORC is modelled. Different moisture contents in the range of 10–30 % (i.e. in a deviation of 10% around the usual wood moisture content of 20%) are investigated in the simulations, as also the degree of purity of the oxygen used in the power plant (between 25 and 95%, rest N2). The power requirement for the production of pure oxygen for this kind of gasification technology leads to a reduction of the electrical efficiency of the whole power plant. For this reason a sensitivity analysis was conducted to find the optimal operation conditions in order to maximise the syngas content in the produced gas (H2, CO) maintaining a high overall electrical efficiency.Copyright © 2013 by ASME

Limited fuel resources, increasing energy demand, and stringent emission regulations are drivers to evaluate process off-gases or process waste streams as fuels for power generation. Often these process waste streams have low energy content and their operability in gas turbines leads to issues such as unstable or incomplete combustion and changes in acoustic response. Due to above reasons, these fuels cannot be used directly without modifications or efficiency penalties in gas turbine engines. To enable the use of the wide variety of ultra-low and low Btu fuels in gas turbine engines, a rich catalytic lean burn (RCL®) combustion system was developed and tested in a subscale high pressure (10 atm.) rig. Previous work has shown promise with fuels such as blast furnace gas (BFG) with Lower Heating Value (LHV) of 3.1 MJ/Nm3 (85 Btu/scf). The current testing extends the limits of RCL® operability to other weak fuels by further modifying and improving the injector to achieve enhanced flame stability. Fuels containing low methane content such as weak natural gas with an LHV of 6.5 MJ/Nm3 (180 Btu/scf) to fuels containing higher methane content such as landfill gas with an LHV of 21.1 MJ/Nm3 (580 Btu/scf) were tested. These fuels demonstrated improved combustion stability with an extended turndown (defined as the difference between catalytic and non-catalytic lean blow out) of 140°C–170°C (280°F–340°F) with CO and NOx emissions lower than 5 ppm corrected to 15% O2.

Various alternative fuel technologies have been proposed as a solution to the negative environment impact caused by greenhouse emissions from fossil fuel combustion processes. One of those alternatives technologies is the inclusion of biomass (fuel crops and agricultural and municipal wastes) as feedstock to produce gaseous and liquid fuels via thermal gasification processes. Biomass thermal gasification is a clean technology, which does not increase the atmosphere carbon concentration since biomass is a neutral carbon energetic source. Wild cane is an invasive grass with a remarkable ability to establish and spread quickly. Thus, it has the potential to yield high biomass for the production of energy. Moreover, wild cane is considered as one of the species that most produces energy per hectare crop. Although wild cane occurs as a weed in most of the Colombian geography, it does not have an extensive potential use. However, wild cane can be included as feedstock for the production of bio-fuels via partial oxidation or thermal degradation (pyrolysis). Fuels produced through this technology can be used for heat o power generation in order to decrease the dependence of farms on fossil fuels. The current paper presents results on the wild cane potential to produce gaseous fuels through thermal gasification using air-steam mixtures for partial oxidation. Also, wild cane thermochemical properties are presented. The CEA (chemical equilibrium with applications) program from NASA was used to estimate the production of gaseous fuels as a function of the operating conditions, which include equivalence ratio (Φ) and steam to fuel ratio (S:F). Based on gas composition, the energy density of the gaseous fuels was estimated. Furthermore, the energy conversion was also calculated in order to estimate the efficiency of the gasification process. Wild cane thermochemical properties were obtained using ultimate, proximate, and thermogravimetric analyses (TGA). Thermogravimetric analyses were carried out using N2 as carrier gas and under different heating rates (β: 10, 20, and 35 °C/min). Based on TGA data and using the isoconversional method (i.e., free-model), the activation energy (E) was estimated. In general, the results show that the increase in operating conditions (equivalence ratio (Φ) and steam to fuel ratio (S:F)) results in gaseous mixtures rich in H2 and with a low CO content. On the other hand, the CH4 production is only possible at Φ > 4 and increases with increased Φ. The average activation energy was ∼ 162 KJ/Kmol.Copyright © 2013 by ASME