GT Cycle Research Articles

Dynamic simulation and optimization of a novel energy system with Hydrogen energy storage for hotel buildings

In the current study, an innovative smart energy system based on hybrid solar-GT energies is proposed. Transient performance assessment and techno-economic analyses are conducted to evaluate the dynamic performance of the system. The system has three main parts: solar panels, a Hydrogen production and storage system and gas turbine system, a chiller, and several heat exchangers and auxiliary components. The goal is to set a stand-alone system to generate the need of the building, including heating, power, and cooling. The system is an off-grid system due to its energy storage system. The system is analyzed comprehensively from 3E standpoints. A parametric study of key design variables is performed, and optimization is carried out to find the best solution point. Results indicate that at the optimized point, the system reaches the effectiveness of 39.5%, the emission of 0.85 kg/kWh and the Levelized product cost of 0.051 $/kWh. Furthermore, increasing the pressure of the (absorption chiller) AC in the (gas turbine) GT cycle from 1.5 to 7.5 results in a sharp decline in net output work.

Utilization of waste heat from a commercial GT for freshwater production, cooling and additional power: Exergoeconomic analysis and optimization

In this work, a multigeneration system is proposed for power, cooling and freshwater production. The waste heat from a SIEMENS SGT6-2000E GT is utilized to drive a supercritical CO2 recompression Brayton cycle (SCRBC) and multi-effect desalination (MED) with thermal vapor compressor (TVC), while the waste heat from the pre-cooler of the SCRBC is utilized to drive an absorption cooling cycle. Detailed thermodynamic, exergy and exergoeconomic analyses are performed for the proposed multigeneration system using Engineering Equation Solver (EES). A sensitivity study is also performed to study the effects of the main operational parameters on the proposed system performance. Finally, multi-objective optimization using a genetic algorithm approach in EES is carried out to reach the optimal design. The proposed system can consume 34.2% less energy input and reduce CO2 emission by 39.3% compared to the stand-alone systems for power, cooling and freshwater production. The results show that the energy utilization factor and exergy efficiency of the proposed system are improved by 33.6% and 14.3%, respectively, while the total unit product cost is reduced by 11.3% compared to the stand-alone GT cycle. From exergoeconomic optimization, the proposed system can produce 132.4 MW of power, 7.09 MW of cooling and 650 kg/s of freshwater at energy utilization factor of 57.5%, exergy efficiency of 39.7% and total unit product cost of 16.3 $/GJ.

Premixed ammonia/hydrogen swirl combustion under rich fuel conditions for gas turbines operation

Energy storage is one of the highest priority challenges in transitioning to a low-carbon economy. Fluctuating, intermittent primary renewable sources such as wind and solar require low-carbon storage options to enable effective load matching, ensuring security of supply. Chemical storage is one such option, with low or zero carbon fuels such as hydrogen, alcohols and ammonia having been proposed. Ammonia provides zero-carbon hydrogen storage whilst offering liquefaction at relatively low pressures and atmospheric temperatures, enabling ease of transportation in a pre-existing infrastructure. Ammonia can also be used directly as a fuel in power plants such as gas turbines to avoid complete conversion back to hydrogen. It is a relatively unreactive fuel, and so it is of interest to explore the potential utilisation of ammonia/hydrogen mixtures. Hence, the goal of this paper is to provide a first assessment of the suitability of a chosen 70%NH330%H2 (%vol) blend for utilisation within a gas turbine environment, based on primary combustion diagnostics including combustion stability – via OH chemiluminescence - and emissions (NOx and NH3). An established optical generic swirl-burner enabled studies of the influence of equivalence ratio (φ > 1), ambient temperature (<484 ± 10 K) and bypass air, with a focus on NOx reduction, one of the main challenges for ammonia combustion. A numerical GT cycle model is developed alongside the experimental investigation. The results demonstrate that the blend has considerable potential as a fuel substitute with reasonable combustion stability and significant reduction of emissions for the cases without bypass air, due to increased chemical reactivity of unburned ammonia. However, emissions are still above those recommended for gas turbine cycles, with a theoretical cycle that still produces low efficiencies compared to DLN methane, highlighting the requirement for new injection techniques to reduce NOx/unburned NH3 in the flue gases whilst ensuring increased power outputs.

Performance Improvement of Simple Gas Turbine Cycle with Vapor Compression Inlet Air Cooling

Gas turbine cycle power plants are being broadly utilized for power generation around the world. The change in temperature and humidity of ambient air substantially influences the plant performance due to naturally suctioned compressors in gas turbine installations. There appears the change in temperature from under 5 °C to more than 45 °C and humidity deviation from under 25% to over 85% in countries belonging to the hot and humid environment. Performance of GT cycle is a strong function of the ambient air temperature with its specific work output dropping by 0.5-0.9% for every 1°C increase in the temperature of air. Due to this reason, the power output falls off on hot days due to air density becoming smaller. Vapor compression cooling is one of the possibilities for sustaining the temperature of admitting air in the required limits. Present paper deals with thermodynamic analysis of gas turbine cycle and investigate the impact inlet air cooling on the GT cycle performance using vapor compression inlet air cooling.

Thermoeconomic analysis and optimization of a Re-compression supercritical CO2 cycle using waste heat of Gaziantep Municipal Solid Waste Power Plant

This paper presents thermodynamic and thermoeconomic analyses as well as optimization of a re-compression supercritical CO2 cycle. A gas turbine cycle (GT) is adapted as a model to an existing plant to generate additional power in Gaziantep Municipal Solid Waste Power Plant (GMSWPP). The total capital cost rate and total cost rate of the GT cycle are found to be 20.47 $/h and 77.14 $/h, respectively utilizing SPECO by using the exhaust gas of 16 kg/s with 1.9 bar and 566.7 °c. The net power, the energy and exergy efficiencies, the total cost and the total capital cost rates of the GT cycle are optimized by +1.73%, +3.21%, +2.45%, −1.11% and −1.64%, respectively using NSGA-II in MATLAB in the range of 2.5≤PR≤4, 200≤P6≤216, 16≤T0≤23 and 9.1≤LMTD≤12.9. This paper provides an originality such that optimization as well as thermodynamic and thermoeconomic analyses is performed simultaneously for an existing MSW power plant, which can be stressed that there are scarce amounts of studies related on this field. Moreover, as another novelty, it can be emphasized that net power output of such like plants which have similar capacity can be improved using the developed model and NSGA-II optimization method.

Utilization of exhaust gases heat from gas turbine with air bottoming combined cycle

This study investigates the utilization of heat from the exhaust gas and the exhaust air of gas turbine with air bottoming combined cycle (GT-AB) by using steam and absorption bottoming cycles in different combinations. For the utilization of heat from both sources, the results indicate that the maximal efficiency occurs at a GT pressure ratio of 11, the AB pressure ratio is 6 for utilization of heat of the GT exhaust gas and 3 for the utilization of heat of AB exhaust air. The results indicate that for maximal efficiency, utilization of heat from the GT exhaust gas and the AB exhaust air is best performed by the absorption system in a cogeneration plant. However, when the cooling effect of the absorption cycle is used to lower the compressor inlet temperature of the GT and AB cycles, it was found that utilization of heat from the GT exhaust gas by the absorption cycle and utilization of heat from the AB exhaust air by the steam cycle produces the maximal power output.

Comparative analysis on off-design performance of a gas turbine and ORC combined cycle under different operation approaches

This paper presents a comparative analysis on the off-design performance of a gas turbine and organic Rankine cycle (GT-ORC) combined cycle under different operation approaches. A new solving procedure for off-design performance evaluation of the GT-ORC combined cycle was proposed and optimal design parameters for this GT-ORC combined cycle were given. Then simulations were conducted based on the mathematical model and assumptions. The inlet guide vane (IGV) control was applied to regulate the topping GT cycle. Results showed that the sliding pressure operation had an optimal sliding condition to make the GT-ORC combined cycle have the best off-design performance. This condition was a fixed superheat degree of 0.1K for organic vapor, and the operation approach under such condition was named modified sliding pressure operation (MSPO). Simulation results showed the MSPO performed better than the constant pressure operation and bivariate operation under off-design conditions. Therefore, the MSPO might be more suitable for the off-design operation of the GT-ORC combined cycle. Finally, the sensitivity analysis indicated that the MSPO was more favorable for the GT-ORC combined cycle to reduce the influence of ambient temperature.

Energetic Performance Optimization of a SOFC–GT Hybrid Power Plant

Analytic study based on energy analysis is conducted on a solid oxide fuel cell (SOFC) integrated in a gas turbine power plant GT. The Tunisian natural gas is used as fuel for the SOFC and the GT cycle. An external pre-reforming system is installed before the SOFC. Heat recovery systems are adopted to valorize the waste heat at the SOFC and GT exhausts. The gas from the SOFC exhaust is also used as additional supply of the combustion chamber. The equations governing the electrochemical processes and the energy balances of the power plant components are established. Numerical simulations using EES software are performed. The influences of key operating parameters, such as ambient temperature, air flow, pre-reforming fraction and fuel utilization on the performance of the SOFC–GT hybrid system, are analyzed. The integration of the SOFC enhances the hybrid cycle efficiency of about 50%. The increase of the ambient temperature reduces the system efficiencies. The utilization factor has a negative effect on the SOFC temperature and voltage which leads to a decrease in the system performances, while the pre-reforming fraction has a positive effect on the indicated parameters. The SOFC voltage increases with the air molar flow rate. However, required air compressor power becomes important. That reduces significantly the SOFC efficiency. A small improvement of about 2% is obtained for the hybrid cycle efficiency SOFC–GT.

Integration of an atmospheric solid oxide fuel cell - gas turbine system with reverse osmosis for distributed seawater desalination in a process facility

The integration of a hybrid solid oxide fuel cell – gas turbine (SOFC-GT) system and reverse osmosis (RO) plant is evaluated thermodynamically and economically to enhance power generation and desalinate seawater on-site in a coastal energy-intensive industrial facility in the Persian (Arabian) Gulf. The power and fresh water co-generation scheme is based on the conversion of SOFC-GT exhaust thermal power into electrical work by a bottoming organic Rankine cycle (ORC) to drive the desalination high pressure pump. Seven ORC fluids are evaluated in terms of energetic and exergetic performance, as well as system size indicators. Depending upon the organic fluid selected, the net electrical power output generated from the exhaust of a 25MWe hybrid SOFC-GT plant ranges from 1.2 to 2.4MWe at an overall exhaust gas heat recovery efficiency of approximately 8–16% for R245fa and toluene, respectively. Compared with an existing standard GT cycle, the integrated SOFC-GT-toluene ORC-RO system enhances exergy efficiency by approximately 29%, while producing 494m3/h of fresh water. The avoided purchase of fresh water, natural gas, and environmental emissions could generate net annual operating cost savings of 8–21 million USD based on subsidized and unsubsidized gas and water prices, respectively, and would become profitable within three to five years.

Performance evaluation of steam injected gas turbine based power plant with inlet evaporative cooling

Present paper deals with the study for performance evaluation of steam-injected gas turbine (STIG) based power plant with inlet evaporative cooling. It investigates the combined effect of inlet evaporative cooling (IEC), steam injection (SI) and film cooling (FC) on the power augmentation of simple gas turbine cycle. Thermodynamic modeling has been carried out and presented along with results showing the influence of inlet evaporative cooling on various performance parameters of STIG based power plant. Results show that there occurs increment of 3.2% in cycle thermal efficiency due to lowering of the compressor inlet temperature from 318K to 282K at 5% steam to air ratio (SAR). At 1850K turbine inlet temperature and cycle pressure ratio of 24 there occurs increase in thermal efficiency of the GT cycle with IEC, SI and FC as compared to the simple GT cycle. Injection of steam in the combustion chamber enhances the specific expansion work in the gas turbine, which increases at rate of 2.95% for every increase in SAR by 2%. The study shows that gas turbine cycle configuration with inlet evaporative cooling (IEC), steam injection and film cooling is the best combination for obtaining more efficiency and power.

Energy, exergy and economic analysis of an integrated solid oxide fuel cell – gas turbine – organic Rankine power generation system

To improve on-site power generation capacity and efficiency in energy-intensive process plants, the indirect integration of a standard gas turbine cycle with an internal reforming solid oxide fuel cell (SOFC) system and bottoming organic Rankine cycle (ORC) is investigated thermodynamically and economically. Among six ORC working fluids, namely toluene, benzene, cyclohexane, cyclopentane, R123 and R245fa, toluene is found to offer the best thermodynamic performance at favorable system size indicators. Using this fluid, the SOFC-GT-ORC system would enhance power generation capacity by a factor of three relative to the base gas turbine cycle, at energy and exergy efficiencies of approximately 64% and 62%, respectively. This represents efficiency improvements of approximately 34% compared with the base GT cycle, and of 6% relative to the hybrid SOFC-GT sub-system. The avoided purchase of natural gas and environmental emissions could generate net annual operating cost savings of five to nine million USD based on standard associated and sour gas prices, respectively, and would become profitable within three to six years, respectively.

Thermodynamic modeling of a gas turbine cycle combined with a solid oxide fuel cell

This study examines the performance of a high-temperature solid oxide fuel cell combined with a conventional recuperative gas turbine (GT–SOFC) plant, as well as the irreversibility within the system. Individual models are developed for each component, through applications of the first and second laws of thermodynamics. The overall system performance is then analyzed by employing individual models and further applying thermodynamic laws for the entire cycle, to evaluate the thermal efficiency and entropy production of the plant. The results of an assessment of the cycle for certain operating conditions are compared against those available in the literature. The comparisons provide useful verification of the thermodynamic simulations in the present work. The comparisons provide useful verification of the thermal simulations in the present work. Further outcomes indicate that increasing the turbine inlet temperature results in decreasing the thermal efficiency of the cycle, whereas it improves the net specific power output. Moreover, an increase in either the turbine inlet temperature or compression ratio leads to a higher rate of entropy generation within the plant. It was found that the combustor and SOFC contribute predominantly to the total irreversibility of the system. About 60% of the irreversibility takes place in the following components at typical operating conditions: 31.4% in the combustor and 27.9% in the SOFC. A comparison between the GT–SOFC plant and a traditional GT cycle, based on identical operating conditions, is also made. Although the irreversibility of a modern plant is higher than that of a conventional cycle, the superior performance of a GT–SOFC, in terms of thermal efficiency and environmental impact (lower CO 2 emissions), over a traditional GT cycle is evident. It has about 27.8% higher efficiency than a traditional GT plant. In this case, the thermal efficiency of the integrated cycle becomes as high as 60.6% at the optimum compression ratio.

E107 30kW発電試験によるDME化学再生ガスタービンの性能評価(OS-4 省エネルギー・小型分散電源・コジェネ技術,一般講演,地球温暖化防止と動力エネルギー技術)

Chemically Recuperated Gas Turbine (CRGT) is an advanced GT cycle that can increase power generation efficiency by recovering the exhaust heat with endothermic reaction of steam reforming. The CRGT fueled by Dimethyl Ether (DME) was demonstrated using 30kW Micro GT (MGT) as a project funded by METI from 2003 to 2007 and accomplished both 10% reduction of fuel consumption compared with steam injected GT cycle, which is similar proven technology, and NO_x emission level of less than 10ppm. Alternative fuel nozzle had concentric double pipe, one of which was designed to burn DME directly with diffusive combustion, and the other was premixed combustion of low-BTU reformed gas. The reformer, which was designed to fit into the MGT and consisted of 96 SS316-tubes filled with Pt catalyst and alumina balls, top and bottom headers and rectangular duct, recovered 15.3kW heat from exhaust gas and increase fuel heating value by 7.9%. This report provides not only these results but also a lot of useful information including concise specification, designing process and verification test of each mechanical and electrical component, and relevant issues and solutions as well.

05/00898 Performance comparison of Fick's, dusty-gas and Stefan-Maxwell models to predict the concentration overpotential of a SOFC anode

The paper describes two 2D steady-state models for solid oxide fuel cells (SOFC) with planar and tubular geometries fuelled by methane. Following a description of the basic geometries and general premises the approaches, assumptions and simplifications for the calculation of ohmic resistance, convective, conductive and radiative heat transfer are given. The modeling approach of the chemical reactions and molar and thermal balances are depicted in detail with the intention to allow for reproduction of the models. The required boundary conditions and input parameters of the models are also discussed. Relying on models, a bottoming GT cycle is introduced and specified and a base case for operation defined. The influence of pressure ratio, air inlet temperature, air flow rate and anode gas recycling are investigated in a parameter study. For both designs air flow rate and pressure ratio are the most important parameters considering the system performance, but for the tubular system these parameters have less impact than for the planar design. Based on the parameter study, a near-optimum case is defined specifically for both systems and the conditions in the fuel cells are investigated. The cycle balance is different in both systems, as the tubular fuel cell requires a lower air inlet temperature. Both fuel cell systems achieve above 65% electric efficiency.

Finite-volume modeling and hybrid-cycle performance of planar and tubular solid oxide fuel cells

The paper describes two 2D steady-state models for solid oxide fuel cells (SOFC) with planar and tubular geometries fuelled by methane. Following a description of the basic geometries and general premises the approaches, assumptions and simplifications for the calculation of ohmic resistance, convective, conductive and radiative heat transfer are given. The modeling approach of the chemical reactions and molar and thermal balances are depicted in detail with the intention to allow for reproduction of the models. The required boundary conditions and input parameters of the models are also discussed. Relying on models, a bottoming GT cycle is introduced and specified and a base case for operation defined. The influence of pressure ratio, air inlet temperature, air flow rate and anode gas recycling are investigated in a parameter study. For both designs air flow rate and pressure ratio are the most important parameters considering the system performance, but for the tubular system these parameters have less impact than for the planar design. Based on the parameter study, a near-optimum case is defined specifically for both systems and the conditions in the fuel cells are investigated. The cycle balance is different in both systems, as the tubular fuel cell requires a lower air inlet temperature. Both fuel cell systems achieve above 65% electric efficiency.

Thermoeconomic evaluation of CO 2 alkali absorption system applied to semi-closed gas turbine combined cycle

A new carbon dioxide separation system based on CO 2 absorption in aqueous solutions of alkaline salts (sodium and potassium carbonate) was studied with reference to semi-closed gas turbine/combined cycle (SCGT/CC), and compared to results obtained with existing technologies. Use of calcium hydroxide for the regeneration of the exhaust solution was studied in order to obtain a tail-end product, calcium carbonate in the form of precipitated calcium carbonate (PCC) with a wide spread and continuously growing market. The alkali CO 2 absorption process was compared with a conventional amine absorption process (DEA+MDEA), referring to the same SCGT/CC based on the same CO 2 removal efficiency. The comparison allows foregrounding of the possible goals of the CO 2 alkali absorption process with respect to previous amine cycle analyses. The modeling approach focuses on a thermodynamical and economical first comparison of the proposed cycle to previous studies carried out on CO 2 absorption (Energy Convers. Manage. 40 (1999) 1917; Absorption of CO 2 with amines in a semi closed GT cycle: plant performance and operating costs, ASME Paper 98-GT-395, American Society of Mechanical Engineers ASME Publishing, New York, 1998; Greenhouse Gas Control Technologies Conference, Interlaken, Switzerland, Pergamon, Oxford, 1999).

The design of stationary and mobile solid oxide fuel cell–gas turbine systems

A general thermodynamic model has shown that combined fuel cell cycles may reach an electric-efficiency of more than 80%. This value is one of the targets of the Department of Energy (DOE) solid oxide fuel cell–gas turbine (SOFC–GT) program. The combination of a SOFC and GT connects the air flow of the heat engine and the cell cooling. The principle strategy in order to reach high electrical-efficiencies is to avoid a high excess air for the cell cooling and heat losses. Simple combined SOFC–GT cycles show an efficiency between 60 and 72%. The combination of the SOFC and the GT can be done by using an external cooling or by dividing the stack into multiple sub-stacks with a GT behind each sub-stack as the necessary heat sink. The heat exchangers (HEXs) of a system with an external cooling have the benefit of a pressurization on both sides and therefore, have a high heat exchange coefficient. The pressurization on both sides delivers a low stress to the HEX material. The combination of both principles leads to a reheat (RH)-SOFC–GT cycle that can be improved by a steam turbine (ST) cycle. The first results of a study of such a RH-SOFC–GT–ST cycle indicate that a cycle design with an efficiency of more than 80% is possible and confirm the predictions by the theoretical thermodynamic model mentioned above. The extremely short heat-up time of a thin tubular SOFC and the market entrance of the micro-turbines give the option of using these SOFC–GT designs for mobile applications. The possible use of hydrocarbons such as diesel oil is an important benefit of the SOFC. The micro-turbine and the SOFC stack will be matched depending on the start-up requirements of the mobile system. The minimization of the volume needed is a key issue. The efficiency of small GTs is lower than the efficiency of large GTs due to the influence of the leakage within the stages of GTs increasing with a decreasing size of the GT. Thus, the SOFC module pressure must be lower than in larger stationary SOFC–GT systems. This leads to an electrical-efficiency of 45% of a cycle used as a basis for a design study. The result of the design study is that the space available in a mid-class car allows the placement of such a system, including space reserves. A further improvement of the system might allow an electrical-efficiency of about 55%.

SCGT/CC: An innovative cycle with advanced environmental and peakload shaving features

An innovative gas turbine cycle is studied, which can offer several advantages from the point of view of environmental friendship and peakload shaving capabilities. The basic idea of SCGT/CC is of cooling down the exhaust to temperatures as low as to allow full condensation of the water vapor; a large part of the exhaust gases is then recirculated to the compressor; the condensed water can be reinjected by means of a pump at compressor delivery. For maximum performance it is convenient not to inject this water flow, but rather to use it for other purposes; however, water injection produces a power boosting effect (at the expense of a small decrease in efficiency) which can be useful for peakload shaving applications. The working gas composition in the GT cycle is that corresponding to stoichiometric combustion, which opens the possibility of applying techniques for CO 2 recycling and general exhaust gas treatment. The cycle guarantees a high level of efficiency, and its adoption should imply minor modifications to existing equipment.