Chapter Thirty One - Gas Turbines

Variable geometry gas turbines for improving the part-load performance of marine combined cycles – Gas turbine performance

The Externally-Fired Combined Cycle (EFCC) is an attractive emerging technology for powering high efficiency combined gas and steam turbine cycles with coal or other ash bearing fuels. In the EFCC, the heat input to a gas turbine is supplied indirectly through a ceramic air heater. The air heater, along with an atmospheric coal combustor and ancillary equipment, replaces the conventional gas turbine combustor. A steam generator located downstream from the ceramic air heater and steam turbine cycle, along with an exhaust cleanup system, completes the combined cycle. A key element of the EFCC Development Program, the 25 MMBtu/h heat-input Kennebunk Test Facility (KTF), has recently begun operation. The KTF has been operating with natural gas and will begin operating with coal in early 1995. The US Department of Energy selected an EFCC repowering of the Pennsylvania Electric Company`s Warren Station for funding under the Clean Coal Technology Program Round V. The project focuses on repowering an existing 48 MW (gross) steam turbine with an EFCC power island incorporating a 30 MW gas turbine, for a gross power output of 78 MW and a net output of 72 MW. The net plant heat rate will be decreased by approximately 30% tomore » below 9,700 Btu/kWh. Use of a dry scrubber and fabric filter will reduce sulfur dioxide (SO{sub 2}) and particulate emissions to levels under those required by the Clean Air Act Amendments (CAAA) of 1990. Nitrogen oxides (NO{sub x}) emissions are controlled by the use of staged combustion. The demonstration project is currently in the engineering phase, with startup scheduled for 1997. This paper discusses the background of the EFCC, the KTF, the Warren Station EFCC Clean Coal Technology Demonstration Project, the commercial plant concept, and the market potential for the EFCC.« less

Power plants operating in a combined cycle have higher thermal efficiency (up to 80% INEE, 2022) and greater generating power when compared to traditional single cycles, such as gas or steam turbines operating alone. Gas turbines have unique characteristics in the steel making process, being able to operate with gases of low calorific value from steel plants, such as blast furnace gases (BFG), and with conventional fuels, such as natural gas, and even with a mixture of these gases enriched with the steel plant gas (BOF). This study aims to dynamically model and simulate the behavior of gas turbines and propose solutions for the optimization of the distribution of fuel gases in gas turbines operating in a combined gas/steam cycle, finding the ideal solution in terms of cost reduction and maximization of net income. The plant has a combined cycle block formed by two gas turbines of 90 MW each and a steam turbine of 320 MW, totaling 500 MW. The model was simulated with the GT operating in parallel with the power grid and the combined cycle with compressor inlet guide vane (IGV) control. The model was developed in MatLab's Simulink®.

The efficiency and flexibility of combined-cycle gas turbines (CCGT) are gaining importance in view of more decarbonized energy systems. Therefore, an adequate representation of CCGTs in large-scale energy system models is required. When modeling large-scale energy systems, a trade-off between detailed representation of the technical restrictions and reasonable computing times emerges because of limited computing capacities.We present an approach that accounts for the operational dependencies between the gas and steam turbines of a CCGT but remains applicable in large-scale market models. Duct burners and bypasses that enable the solo operation of steam or gas turbines are also modeled. We implement our approach using the well-established Joint Market Model and apply it in a case study of the German electricity system in 2040.Our modeling approach captures more detailed operation modes, while increases in computation time remain limited. Thus, the approach is advantageous when turbine-wise modeling and analysis of CCGTs is required, e.g. for a detailed analysis of start-ups and operations. The results show no substantial differences between the aggregated market results of five cases investigated. The consideration of bypasses and duct burners yet leads to higher contribution margins for individual CCGTs – with stronger effects observed for more efficient groups.

The system-level simulation model for Natural Gas Combined-Cycle (NGCC) plant combines advanced G class turbine with various fuels was performed in the study. The commercial chemical process simulator, Pro/II® V8.1.1, is used in the study to build the analysis model. There are three major sections which are gas turbine (GT), heat recovery steam generator (HRSG) and steam turbine (ST).The study envisages two analyses as the basic and feasibility cases. The former is the benchmark case which is verified with the reference data of exist NGCC power plant located in Dah-Tarn, Taiwan. The Dah-Tarn NGCC power plant introduces the advanced M501G gas turbine from Mitsubishi Heavy Industries, Ltd. (MHI) and the system efficiency of the combined-cycle is 58.75 % (LHV). The latter introduces a feasibility study with advanced gas turbine and actual parameters in Taiwan. The SNG from carbonate fuel feed to M501G based combined-cycle is evaluated in the feasibility study cases first, and the mixture gas of SNG and syngas is also evaluated to compare the different of overall performance with the pure SNG case.The results show that the system efficiency of pure SNG case is around 57 % (LHV). For the mixture gas case, the maximum ratio of syngas to SNG is 1:19, due to keep the same composition of methane is 85.9 % with the Dah-Tarn NGCC power plant. The efficiency of mixture gas case is 55.75 % (LHV).The study shows the possibility way to use coal and reduce the CO2 emission. The another advantage is the using of SNG could increases the usage of combined-cycle in Taiwan, due to the prices of natural gas is higher than coal in Taiwan and results in the higher idle capacity.

Retrofitting existing power generation plants by repowering is becoming an attractive option to improve plant performance with less cost. “Hot Windbox Repowering” involves utilizing the hot exhaust gas from a combustion gas turbine and using it as combustion air for an existing fossil-fuel boiler. “Combined Cycle Repowering” or “Full Repowering” involves completely replacing the existing boiler with a combined cycle consisting of a gas turbine(s) and a heat recovery steam generator (HRSG). The existing steam turbine will be used in both repowering scenarios. This paper discusses an engineering study and summarizes the results obtained from repowering an existing heavy-oil / natural gas fired steam power plant in the north east of the United States. The plant consists of a 600 MW boiler and steam turbine. Several engineering studies were considered and evaluated thermodynamically and economically to retrofit such plant. Several options were considered involving different gas turbines, gas turbine combinations, and different repowering methods. The best option is based on retrofitting the unit by a combination of both, hot windbox repowering and combined cycle repowering. The proposed design consists of one gas turbine repowering the windbox of the existing boiler, and a second gas turbine operating in a separate combined cycle configuration with the generated superheated steam tying into the main steam line and expanding in the existing steam turbine. Several heat balances were developed to assist in obtaining meaningful results for this feasibility study. Actual costs were obtained for the gas turbines and heat recovery steam generators (HRSG), as well as installation costs for a more accurate evaluation. The results indicate that the combined output of the repowered unit will generate an additional 295 MW and reduce the heat rate by more than 11 percent at full load and annual average ambient conditions. The estimated capital cost of the project is expected to range from $235 to $245 millions.

On the possible increasing of efficiency of ship power plant with the system combined of marine diesel engine, gas turbine and steam turbine, at the main engine - steam turbine mode of cooperation This paper presents a concept of a ship combined high-power system consisted of main piston engine and associated with it: gas power turbine and steam turbine subsystems, which make use of energy contained in exhaust gas from main piston engine. The combined system consisted of a piston combustion engine and an associated with it steam turbine subsystem, was considered. An algorithm and results of calculations of the particular subsystems, i.e. of piston combustion engine and steam turbine, are presented. Assumptions and limitations taken for calculations, as well as comparison of values of some parameters of the system and results of experimental investigations available from the literature sources, are also given. The system's energy optimization was performed from the thermodynamic point of view only. Any technical - economical analyses were not carried out. Numerical calculations were performed for a Wärtsilä slow-speed diesel engine of 52 MW output power.

This article provides the energy and exergy based performance analysis of a solid oxide fuel cell (SOFC) – gas turbine (GT) – steam turbine (ST) combined cycle power plant. The system utilizes the GT exhaust heat for fuel and air preheating subsequently in a fuel recuperator (FR) and an air recuperator (AR) before finally producing steam in a heat recovery steam generator (HRSG) coupled with the ST cycle. It considers 30% external reforming in a pre-reformer (PR) by steam extracted from the bottoming ST plant. The study considers the effect of additional fuel burning in the combustion chamber (CC) as a means for increasing the net GT and ST power output. A detailed parametric analysis based on variation of compressor pressure ratio (CPR), fuel flow rate (FFR), air flow rate (AFR), current density, single level boiler pressure and ST inlet temperature (STIT) is also provided. Results indicate improved system performance at higher CPR. The optimum single level boiler pressure is found to be 40bar with 50% additional fuel burning. Burning of additional fuel improves the GT and ST power output, however with reduction in the plant’s overall efficiency. Further comparison of performance with a similar other system where the AR is placed head of the FR indicates slightly better performance of the proposed system with FR ahead of AR (FRAOAR).

This paper investigates the possibility of applying a new technique called Gas/Steam Path Analysis (GSPA), that is based on the principles of Gas Path Analysis (GPA), to gas as well as steam turbine plants (as one unit) that are main parts of a combined cycle power plant by way of simulation. In order to facilitate this investigation two pieces of software were developed at Cranfield University. With this technique, it was possible to monitor the major components of the combined cycle, and hence predict the faults that may occur within the cycle beforehand. Faults looked at were, fouling and erosion of gas and steam turbine units, heat recovery steam generator degradation (scaling and/or ashe deposition), and condenser degradation. The obtained results from GSPA calculations of the cases investigated showed that “GSPA” technique can be equally applied to either gas turbine cycle, steam turbine cycle, or to the combination of the two in a form of combined cycle. The procedure, assumptions made, and the results obtained are presented and discussed herein.

Chapter 7 - Gas Turbine and Heat Recovery Steam Generator

In gas-cooled solar power plants the radiant energy of the sun is transferred to the cycle fluid in a cavity type solar receiver and converted into electric energy by means of a combined gas and steam turbine cycle incorporating a waste heat steam generator. The design and optimization of the energy conversion system in accordance with solar-specific considerations are described with particular regard to the gas turbine. In designing the energy conversion system several variants on the combined cycle with waste heat steam generator are investigated and special measures for the improvement of the cycle efficiency, such as the refinement of the steam process through the addition of pressure stages are introduced. It is demonstrated that the solar power plant meets the requirements both for straight solar and constant load operation with fossil fuel substitution. In order to establish the possibilities of attaining high part-load efficiencies in straight solar operation, two modes, variable and constant speed of the gas turbine, are compared with one another.

This work investigated the engineering and economic implication of converting simple cycle gas turbine power plants to combined cycle power plants using a gas turbine power plant in Rivers state as a case study. A gas turbine model which behaves like the real engine in the field was created and the performance parameters were estimated. Steam turbine plant operating on the superheat Rankine cycle fired by the exhaust gases of the gas turbine through a heat recovery steam generator was simulated and incorporated in the gas turbine cycle to form a combined cycle plant. Engineering and economic performance parameters such thermal efficiency, specific fuel consumption (sfc), heat rate (HR), payback period, net present value (NPV) and levelized cost of electricity (LCOE) of the gas turbine plant and the simulated combined cycle plant were estimated. The economic parameters were estimated for project lifetime of 20 years, discount rate of 10% and electricity price of N75 per kWh. The thermal efficiencies of the gas turbine cycle steam turbine plant and the combined cycle plant are 33.66%, 27.42% and 50.20% respectively. The sfc and the HR of the three systems are 0.0616 kgs-1 /MW, 10,695 kJ/kWh; 0.1254 kgs-1 /MW, 13127 kJ/kWh and 0.0413 kgs-1 /MW, 7171kJ/kWh respectively. The payback, the NPV and the LCOE of the gas turbine plant are 5.32yrs, $25.87 million and N69.94 per kWh respectively. The respective values of the combined cycle plant are 4.36yrs, $63.80 million and N66.64. The study shows that it is possible to obtain additional power of over 49% the installed capacity from the existing simple cycle gas turbine power plants.

The thermal-economic optimization of a combined cycle power plant (CCPP) which can provide 140 MW of electrical power is discussed in this paper. The CCPP is composed of a gas turbine cycle (including, air compressor, combustion chamber, gas turbine), heat recovery steam generator (HRSG), steam turbine, condenser system, and a pump. The design parameters of such a plant are compressor pressure ratio (rAC), compressor isentropic efficiency (ηAC) gas turbine isentropic efficiency (ηGT), and turbine inlet temperature (T3), pinch difference temperature (ΔTpinch), steam turbine inlet temperature (Ta), steam turbine isentropic efficiency (ηST), and pump isentropic efficiency (ηPUMP). The objective function was the total cost of the plant in terms of dollar per second, including sum of the operating cost related to the fuel consumption, and the capital investment for equipment purchase and maintenance costs. The optimal values of decision variables were obtained by minimizing the objective function using sequential quadratic programming (SQP). The effects of change in the demanded power and fuel price on the design parameters werestudied for, 100, 120, and 140MW of net power output.

This study identifies vital gas turbine (GT) parameters and quantifies their influence in meeting the DOE Turbine Program overall Integrated Gasification Combined Cycle (IGCC) plant goals of 50% net HHV efficiency, $1000/kW capital cost, and low emissions. The project analytically evaluates GE advanced F class air cooled technology level gas turbine conceptual cycle designs and determines their influence on IGCC plant level performance including impact of Carbon capture. This report summarizes the work accomplished in each of the following six Tasks. Task 1.0--Overall IGCC Plant Level Requirements Identification: Plant level requirements were identified, and compared with DOE's IGCC Goal of achieving 50% Net HHV Efficiency and $1000/KW by the Year 2008, through use of a Six Sigma Quality Functional Deployment (QFD) Tool. This analysis resulted in 7 GT System Level Parameters as the most significant. Task 2.0--Requirements Prioritization/Flow-Down to GT Subsystem Level: GT requirements were identified, analyzed and prioritized relative to achieving plant level goals, and compared with the flow down of power island goals through use of a Six Sigma QFD Tool. This analysis resulted in 11 GT Cycle Design Parameters being selected as the most significant. Task 3.0--IGCC Conceptual System Analysis: A Baseline IGCC Plant configuration was chosen, and an IGCC simulation analysis model was constructed, validated against published performance data and then optimized by including air extraction heat recovery and GE steam turbine model. Baseline IGCC based on GE 207FA+e gas turbine combined cycle has net HHV efficiency of 40.5% and net output nominally of 526 Megawatts at NOx emission level of 15 ppmvd{at}15% corrected O2. 18 advanced F technology GT cycle design options were developed to provide performance targets with increased output and/or efficiency with low NOx emissions. Task 4.0--Gas Turbine Cycle Options vs. Requirements Evaluation: Influence coefficients on 4 key IGCC plant level parameters (IGCC Net Efficiency, IGCC Net Output, GT Output, NOx Emissions) of 11 GT identified cycle parameters were determined. Results indicate that IGCC net efficiency HHV gains up to 2.8 pts (40.5% to 43.3%) and IGCC net output gains up to 35% are possible due to improvements in GT technology alone with single digit NOx emission levels. Task 5.0--Recommendations for GT Technical Improvements: A trade off analysis was conducted utilizing the performance results of 18 gas turbine (GT) conceptual designs, and three most promising GT candidates are recommended. A roadmap for turbine technology development is proposed for future coal based IGCC power plants. Task 6.0--Determine Carbon Capture Impact on IGCC Plant Level Performance: A gas turbine performance model for high Hydrogen fuel gas turbine was created and integrated to an IGCC system performance model, which also included newly created models for moisturized syngas, gas shift and CO2 removal subsystems. This performance model was analyzed for two gas turbine technology based subsystems each with two Carbon removal design options of 85% and 88% respectively. The results show larger IGCC performance penalty for gas turbine designs with higher firing temperature and higher Carbon removal.

A three stage combined power cycle with a Brayton cycle as the topping cycle, a Rankine cycle as the middling cycle and an Organic Rankine Cycle (ORC) as the bottoming cycle is proposed in the present investigation. A two-stage Gas Turbine Power Plant (GTPP) with inter-cooling, reheating and regeneration based on the Brayton cycle, a single-stage Steam Turbine Power Plant (STPP) based on the Rankine cycle, and a two-stage ORC power plant with reheating based on ORC with atmospheric air as the coolant is considered in the present study. This arrangement enables the proposed plant to utilize the waste heat to the maximum extent possible and convert it into electric power. As the plant can now operate at low sink temperatures depending on atmospheric air, the efficiency of the combined cycle power plant increases dramatically. Further, Steam Turbine Exhaust Pressure (STEP) is positive resulting in smaller size units and a lower installation cost. A simulation code is developed in MATLAB to investigate the performance of a three stage combined power cycle at different source and sink temperatures with varying pressure in heat recovery steam boiler and condenser-boiler. Performance results are plotted with Gas Turbine Inlet Temperature (GTIT) of 1200 to 1500 °C, Coolant Air Temperature (CAT) of −15 to +25 °C, and pressure ratio of GTPP as 6.25, 9.0 and 12.25 for different organic substances and NH3 as working fluids in the bottoming ORC. Simulation results show that the efficiency of the three stage combined power cycle will go up to 64 to 69% depending on the pressure ratio of GTPP, GTIT, and CAT. It is also observed that the variation in the efficiency of the three stage combined power cycle is small with respect to the type of working fluid used in the ORC. Among the organic working fluids R134a, R12, R22, and R123, R134a gives a higher combined cycle efficiency.