Experimental and Modeling Study of the Combustion of Synthetic Jet Fuels: Naphtenic Cut and Blend With a GtL Jet Fuel

Research on the production and combustion of synthetic jet fuels has recently gained importance because of their potential for addressing security of supply and sustainable air transportation challenges. The combustion of a 100% naphtenic cut that fits with typical chemical composition of products coming from biomass or coal liquefaction (C12.64H23.64; M=175.32 g.mol−1; H/C=1.87; DCN=39; density=863.1 g.L−1) and a 50% vol. mixture with Gas to Liquid from Shell (mixture: C11.54H23.35; M=161.83 g.mol−1; H/C=2.02; DCN=46; density=800.3 g.L−1) were studied in a jetstirred reactor under the same conditions (temperature, 550–1150 K; pressure, 10 bar; equivalence ratio, 0.5, 1, and 2; initial fuel concentration, 1000 ppm). Surrogate model-fuels were designed based on fuel composition and properties for simulating the kinetics of oxidation of these fuels. We used new model-fuels consisting of mixtures of n-decane, decalin, tetralin, 2-methylheptane, 3-methylheptane, n-propyl cyclohexane, and n-propylbenzene. The detailed chemical kinetic reaction mechanism proposed was validated using the entire experimental database obtained in the present work and for the oxidation of pure GtL, we used previous results. Kinetic computations involving reaction paths analyses and sensitivity analyses were used to interpret the results.

Advanced and Transformational Hydrogen Turbines for Integrated Gasification Combined Cycles

The U.S. Department of Energy’s (DOE) provides a worldwide leadership role in the development of advanced fossil fuel-based energy conversion technologies, with a focus on electric power generation with carbon capture and storage (CCS). As part of DOE’s Office of Fossil Energy, the National Energy Technology Laboratory (NETL) implements research, development, and demonstration (RD&D) programs that address the challenges of reducing greenhouse gas emissions. To meet these challenges, NETL evaluates advanced power cycles that will maximize system efficiency and performance, while minimizing CO2 emissions and the costs of CCS. NETL’s Hydrogen Turbine Program has sponsored numerous R&D projects in support of Advanced Hydrogen Turbines (AHT). Turbine systems and components targeted for development include combustor technology, materials research, enhanced cooling technology, coatings development, and more. The R&D builds on existing gas turbine technologies and is intended to develop and test the component technologies and subsystems needed to validate the ability to meet the Turbine Program goals. These technologies are key components of AHTs, which enable overall plant efficiency and cost of electricity (COE) improvements relative to an F-frame turbine-based Integrated Gasification Combined Cycle (IGCC) reference plant equipped with carbon capture (today’s state-of-the-art). This work has also provided the basis for estimating future IGCC plant performance based on a Transformational Hydrogen Turbine (THT) with a higher turbine inlet temperature, enhanced material capabilities, reduced air cooling and leakage, and higher pressure ratios than the AHT. IGCC cases from using system-level AHT and THT gas turbine models were developed for comparisons with an F-frame turbine-based IGCC reference case and for an IGCC pathway study. The IGCC pathway is presented in which the reference case (i.e. includes F-frame turbine) is sequentially-modified through the incorporation of advanced technologies. Advanced technologies are considered to be either 2nd Generation or Transformational, if they are anticipated to be ready for demonstration by 2025 and 2030, respectively. The current results included the THT, additional potential transformational technologies related to IGCC plant sections (e.g. air separation, gasification, gas cleanup, carbon capture, NOx reduction) are being considered by NETL and are topics for inclusion in future reports.

Thermo-Economic Analysis of a Photovoltaic-Fuel Cell Hybrid System With Energy Storage for CHP Production in Household Sector

The penetration of renewable sources, particularly wind and solar, into the grid has been increasing in recent years. As a consequence, there have been serious concerns over reliable and safety operation of power systems. One possible solution, to improve grid integrity, is to integrate energy storage devices into power system network: storing energy produced in periods of low demand to later use, ensuring full exploitation of intermittent available sources. Focusing on photovoltaic energy system, energy storage is needed with the purpose of ensuring continuous power flow to minimize or to neglect electrical grid supply. A comprehensive study on a hybrid micro-CHP system based on photovoltaic panels using hydrogen as energy storage technologies has been performed. This study examines the feasibility of replacing electricity provided by the grid with a hybrid system to meet household demand. This paper is a part of an experimental and a theoretical study which is currently under development at University of Bologna where a test facility is under construction for the experimental characterization of a small scale cogenerative power system. This paper presents the theoretical results of a hybrid system performance simulations made of a photovoltaic array an electrolyzer with a H2 tank and a Proton Exchange Membrane fuel cell stack designed to satisfy typical household electrical demand. The performance of this system have been evaluated by the use of a calculation code, in-house developed by the University of Bologna. Results of the carried out parametric investigations identify photovoltaic and fuel cell systems’ optimal size in order to minimize the purchasing of electrical energy from the grid. Future activities will be the tuning of the software with the experimental results, in order to realize a code able to define the correct size of each sub-system, once the load profile of the utility is known or estimated.

Assessment of Solar Steam Injection in Gas Turbines

The concept of solar steam production for injection in a gas turbine combustion chamber is studied for both nominal and part load engine operation. First, a 5MW single shaft engine is considered which is then retrofitted for solar steam injection using either a tower receiver or a parabolic troughs scheme. Next, solar thermal power is used to augment steam production of an already steam injected single shaft engine without any modification of the existing HRSG by placing the solar receiver/evaporator in parallel with the conventional one. For the case examined in this paper, solar steam injection results to an increase of annual power production (∼15%) and annual fuel efficiency (∼6%) compared to the fuel-only engine. It is also shown that the tower receiver scheme has a more stable behavior throughout the year compared to the troughs scheme that has better performance at summer than at winter. In the case of doubling the steam-to-air ratio of an already steam injected gas turbine through the use of a solar evaporator, annual power production and fuel efficiency increase by 5% and 2% respectively.

A Numerical Study on the Reactivity of Biogas/Reformed-Gas/Air and Methane/Reformed-Gas/Air Mixtures at Gas Turbine Relevant Conditions

This study investigates the increase in methane and biogas flame reactivity enabled by the addition of syngas produced through fuel reforming. To isolate thermodynamic and chemical effects on the reactivity of the mixture, the burner simulations are performed with a constant adiabatic flame temperature of 1800 K. Compositions and temperatures are calculated with the chemical equilibrium solver of CANTERA® and the reactivity of the mixture is quantified using the adiabatic, freely-propagating premixed flame, and perfectly-stirred reactors of the CHEMKIN-Pro® software package. The results show that the produced syngas has a content of up to 30 % H2 with a temperature up to 950 K. When added to the fuel, it increases the laminar flame speed while maintaining a burning temperature of 1800 K. Even when cooled to 300 K, the laminar flame speed increases up to 30 % from the baseline of pure biogas. Hence, a system can be developed that controls and improves biogas flame stability under low reactivity conditions by varying the fraction of added syngas to the mixture. This motivates future experimental work on reforming technologies coupled with gas turbine exhausts to validate this numerical work.

Direct Coupling of a Two-Dimensional Fan Model in a Turbofan Engine Performance Simulation

Coupling of high fidelity component calculations with overall engine performance simulations (zooming) can provide more accurate physics and geometry based estimates of component performance. Such a simulation strategy offers the ability to study complex phenomena and their effects on engine performance and enables component design changes to be studied at engine system level. Additionally, component interaction effects can be better captured. Overall, this approach can reduce the need for testing and the engine development time and cost. Different coupling methods and tools have been proposed and developed over the years ranging from integrating the results of the high fidelity code through conventional performance component maps to fully-integrated three-dimensional CFD models. The present paper deals with the direct integration of an in-house two-dimensional (through flow) streamline curvature code (SOCRATES) in a commercial engine performance simulation environment (PROOSIS) with the aim to establish the necessary coupling methodology that will allow future advanced studies to be performed (e.g. engine condition diagnosis, design optimization, mission analysis, distorted flow). A notional two-shaft turbofan model typical for light business jets and trainer aircraft is initially created using components with conventional map-defined performance. Next, a derivative model is produced where the fan component is replaced with one that integrates the high fidelity code. For both cases, an operating line is simulated at sea-level static take-off conditions and their performances are compared. Finally, the versatility of the approach is further demonstrated through a parametric study of various fan design parameters for a better thermodynamic matching with the driving turbine at design point operation.

Optimization of Cycle and Expander Design of an Organic Rankine Cycle Unit Using Multi-Component Working Fluids

Organic Rankine cycle (ORC) power systems represent attractive solutions for power conversion from low temperature heat sources, and the use of these power systems is gaining increasing attention in the marine industry. This paper proposes the combined optimal design of cycle and expander for an organic Rankine cycle unit utilizing waste heat from low temperature heat sources. The study addresses a case where the minimum temperature of the heat source is constrained and a case where no constraint is imposed. The former case is the waste heat recovery from jacket cooling water of a marine diesel engine onboard a large ship, and the latter is representative of a low-temperature geothermal, solar or waste heat recovery application. Multi-component working fluids are investigated, as they allow improving the match between the temperature profiles in the heat exchangers and, consequently, reducing the irreversibility in the ORC system. This work considers mixtures of R245fa/pentane and propane/isobutane. The use of multi-component working fluids typically results in increased heat transfer areas and different expander designs compared to pure fluids. In order to properly account for turbine performance and design constraints in the cycle calculation, the thermodynamic cycle and the turbine are optimized simultaneously in the molar composition range of each mixture. Such novel optimization approach enables one to identify to which extent the cycle or the turbine behaviour influences the selection of the optimal solution. It also enables one to find the composition for which an optimal compromise between cycle and turbine performance is achieved. The optimal ORC unit employs pure R245fa and provides approximately 200 kW when the minimum hot fluid temperature is constrained. Conversely, the mixture R245fa/pentane (0.5/0.5) is selected and provides approximately 444 kW when the hot fluid temperature is not constrained to a lower value. In both cases, a compact and efficient turbine can be manufactured.

Performance Optimization and Economic Analysis of Geothermal Power Generation by Subcritical and Supercritical Organic Rankine Cycles

In a sustainability context, using renewable energy sources to hedge against increasing consumption of fossil fuels and reduce greenhouse gas emissions becomes increasingly important. The geothermal resource has a great application prospect due to its rich reserves and convenient utilization, and Organic Rankine Cycle (ORC) is a effective method to convert the low-grade geothermal to electricity. To improve the performance of geothermal ORC system, working fluid selection, system parameter optimization and the cycle design are the main approaches. Zeotropic mixtures may show superiority as ORC working fluids due to the temperature glides during the phase transitions, which leads to better temperature matches between the working fluid and the heat source/sink. Moreover, owing to the changing temperature during the transition from liquid to vapor in the vapor generator, supercritical ORC provides a great potential in geothermal utilization and irreversibility reduction. This paper displays an investigation on the performance optimization and economic analysis of various working fluids under subcritical and supercritical conditions. To avoid the silica oversaturation, the geothermal water reinjection temperature should not be less than 70 °C. Turbine inlet temperature, condenser outlet temperature as well as turbine inlet pressure (for supercritical ORC) are optimized to maximize the net power output. Moreover, economic analysis is conducted by taking heat exchanger area per unit power output (APR) and the specific investment cost (SIC) as indicators under the optimal net power output condition. The results shows that working fluid with a medium critical temperature yields greater net power output in supercritical ORC and mixture produces larger net power output compared with its pure components in subcritical ORC. Compared with isobutane (R600a) under subcritical condition, isobutane/isopentane (R600a/R601a) and isobutane/pentane (R600a/R601) under subcritical condition, R134a and R1234ze(E) under supercritical condition yield 3.9%, 3.8%, 8.5% and 8.8% more net power outputs, respectively. In addition, R600a/R601a and R600a/R601 under subcritical condition own higher APR and SIC while R134a and R1234ze(E) under supercritical condition possess lower APR and SIC.

Development of Next Generation Gas Turbine Combined Cycle System

Tohoku Electric Power Company, Inc. (Tohoku-EPCO) has been adopting cutting-edge gas turbines for gas turbine combined cycle (GTCC) power plants to contribute for reduction of energy consumption, and making a continuous effort to study the next generation gas turbines to further improve GTCC power plants efficiency and flexibility. Tohoku-EPCO and Mitsubishi Hitachi Power Systems, Ltd (MHPS) developed “forced air cooling system” as a brand-new combustor cooling system for the next generation GTCC system in a collaborative project. The forced air cooling system can be applied to gas turbines with a turbine inlet temperature (TIT) of 1600deg.C or more by controlling the cooling air temperature and the amount of cooling air. Recently, the forced air cooling system verification test has been completed successfully at a demonstration power plant located within MHPS Takasago Works (T-point). Since the forced air cooling system has been verified, the 1650deg.C class next generation GTCC power plant with the forced air cooling system is now being developed. Final confirmation test of 1650deg.C class next generation GTCC system will be carried out in 2020.

Evaluation of Performance Robustness of a Gas Turbine Cogeneration Plant Based on a Mixed-Integer Linear Model

In designing energy supply systems, designers are requested to rationally determine equipment types, capacities, and numbers in consideration of equipment operational strategies corresponding to seasonal and hourly variations in energy demands. However, energy demands have some uncertainty at the design stage, and the energy demands which become certain at the operation stage may differ from those estimated at the design stage. Therefore, designers should consider that energy demands have some uncertainty, evaluate the performance robustness against the uncertainty, and design the systems to heighten the robustness. Especially, this issue is important for cogeneration plants, because their performances depend significantly on both heat and power demands. Although robust optimal design methods of energy supply systems under uncertain energy demands were developed, all of them are based on linear models for energy supply systems. However, it is still a hard challenge to develop a robust optimal design method even based on a mixed-integer linear model. At the first step for this challenge, in this paper, a method of evaluating the performance robustness of energy supply systems under uncertain energy demands is proposed based on a mixed-integer linear model. This problem is formulated as a bilevel mixed-integer linear programming one, and a sequential solution method is applied to solve it approximately by discretizing uncertain energy demands within their intervals. In addition, a hierarchical optimization method in consideration of the hierarchical relationship between design and operation variables is applied to solve large scale problems efficiently. Through a case study on a gas turbine cogeneration plant for district energy supply, the validity and effectiveness of the proposed method and features of the performance robustness of the plant are clarified.