Cycle Gas Turbine Power Plant Research Articles

Effects of rising dynamic requirements on the lifetime consumption of a combined cycle gas turbine power plant

The expansion of renewable energy production in Germany leads to a more volatile and intermittent electricity feed-in. For conventional power plants providing the residual load, this results in a much more dynamic operating mode. This paper aims to investigate the changes in the annual lifetime consumption of a selected combined cycle power plant due to the more dynamic operation. The results show that the significantly more dynamic power plant operation only leads to a moderate increase in life consumption caused by load cycle fatigue. The dominant damaging mechanism is creep fatigue, which is not affected by the dynamics of the operation. Overall, no relevant increase in total lifetime consumption was found due to the increasing dynamics of operation.

Modelling the underlying factors for flexible power plant valuation

In this article the value of a gas fired power plant is estimated through the decision of the power plant's operator to produce electricity. Spark spread options are used as a tool for cash flow evaluation, based on simulated electricity and natural gas prices. We choose to model electricity spot prices through the Schwartz-Smith two factor model and natural gas prices through a mean reverting model. Special characteristics of the plant are those of a typical combined cycle gas turbine power plant, which incorporates flexible and efficient technology. Decisions concerning at starting and running the power plant are made daily and for this reason, plant evaluation is crucial for power plant owners and potential investors. Moreover, investments in installing capacity are extremely costly, making the proper evaluation of the investment vital. We calculate annual profits under different cost scenarios and finding a more than 50% profit decrease when incorporating capacity factors.

New operating strategy for a combined cycle gas turbine power plant

The highly dynamic nature of power demand forces a combined cycle gas turbine (CCGT) power plant to often run at less-efficient part-load conditions. A new operating strategy called EGR-IGVC is proposed in this work to improve the part-load performance of a CCGT plant. The strategy partially recycles the flue gas from the heat recovery steam generator and manipulates the inlet guide vanes to regulate part-load operation and boost plant efficiency. It allows the CCGT plant to set its own acceptable gas turbine temperature limits at any time and thus maximize the plant performance. Our previous CCGT flow diagram in Aspen HYSYS [Liu and Karimi (2018)] is modified to accommodate EGR for evaluating EGR-IGVC. Then, using a case study CCGT plant, EGR-IGVC is compared in detail with the conventional inlet guide vane control (IGVC). The results show that EGR-IGVC improves the plant part-load performance significantly. It increases the plant efficiency by up to 1.2% (actual) and reduces the CO2 emissions by up to 13.8 kg MW−1 h−1. By enabling an effective utilization of low-temperature waste heat and reducing the propensity for NOx formation, EGR-IGVC promises to be a better strategy for the part-load operation of CCGT plants.

Simulating combined cycle gas turbine power plants in Aspen HYSYS

Combined cycle gas turbine (CCGT) power plants are becoming increasingly important for electricity generation. Enhancing their thermal performance is essential for mitigating carbon emissions. This paper aims to present a methodology for simulating the off-design operation of a triple-pressure reheat CCGT plant in Aspen HYSYS. The modeling equations that rigorously capture the full off-design characteristics of various plant components (i.e. compressor, combustor, turbine, heat recovery steam generator, and steam turbines) are implemented in Aspen HYSYS, and a specially tailored procedure is proposed for solving them. The modeling strategy and solution procedure can be extended to simulate the off-design operation of any CCGT plants and are generically applicable to other process simulators (e.g. Aspen Plus, Unisim, and Pro II). To evaluate the model’s performance, its predictions are compared with those of an equivalent model from GateCycle. The results show the predictions of the two models (Aspen HYSYS and GateCycle) agree well. The average differences for the power outputs and thermal efficiencies of the gas turbine, steam cycle, and CCGT plant are less than 2.0%, 1.5%, and 0.6%, respectively. Besides, the differences arise primarily from the different gas enthalpy calculations. Since the model enables easy integration with various energy systems and can be made dynamic for predicting real-time behavior in Aspen HYSYS, it is very useful with wide applications.

Techno-Economic Analysis of Common Work of Wind and Combined Cycle Gas Turbine Power Plant by Offering Continuous Level of Power to Electricity Market

Techno-Economic Analysis of Common Work of Wind and Combined Cycle Gas Turbine Power Plant by Offering Continuous Level of Power to Electricity Market

Decentralized stand-alone Multi Effect Desalination (MED) system using fixed focus type Scheffler concentrator for the remote and arid rural regions of Sultanate of Oman

Rising population and industrialization made desalination of prime importance in physically water scarce Sultanate of Oman for fulfilling the gap between the rising demand and supply of fresh water. Almost 80-85% of the installed and planned desalination plants in the Sultanate are based on Combined Cycle Gas Turbine (CCGT) power plants while remaining are standalone which includes about 5-7% of the installed plants for rural arid and dry regions. All the installed and planned desalination plants utilises fossil fuels for their operation and are based on Reverse Osmosis (almost 90-95% of the plants) and Multi Stage Flash technologies. Sultanate of Oman is a tropical country with most of the regions being arid and dry receiving solar energy most abundantly. But the utilisation of solar energy in the country is mostly limited to installations based on photovoltaic systems. Only recently solar thermal Enhanced Oil Recovery plant with 1 GWth power output has been undertaken in the country at Amal oil field. A pilot standalone Multi Effect Desalination (MED) plant using fixed focus type Scheffler concentrator for remote and arid rural regions of country has been discussed in this paper to address this gap. This pilot plant has been designed for producing 100 kg/day output based on three stage cross flow type multi effect desalination technology with two 16 m2 Scheffler concentrators and operates in the temperature limits of 170 – 90°C. Preliminary testing carried out on the system during summer and winter period has shown that with available insolation above 700 W/m2, steam at a pressure of 8 to 8.5 bar could be generated in a batch experiment after 2-3 hours from starting the operation for 42 to 55 kg of water in the header of the system. This steam generated is further utilised for desalination in three stages. The initial lag period for the system is measured to be 35-50 minutes depending on the quantity of water in the header, wind speed and solar insolation. System comes out of the lag period when solar insolation reaches just above 650-700 W/m2. The desalination output for the system is measured between 60-65 litres per day for the summer period. Batch type intermittent operation, tracking errors, optical concentration losses, receiver convection losses, brine heat losses are few of the reasons observed based on the analysis for the lower output from the system. Experimentation has given a direction to make operation of the system from batch to continuous production while reducing optical and convection losses through appropriate rectifications for increasing overall yield of the system.

Feasibility study of Combined Cycle Gas Turbine (CCGT) power plant integration with Adiabatic Compressed Air Energy Storage (ACAES)

The paper presents the research outcome on integration of an Adiabatic Compressed Air Energy Storage system with a Combined Cycle Gas Turbine power plant to increase its operation flexibility. The study demonstrates the novel hybrid CCGT-ACAES plant including an extended operational load level range and increased operation flexibility which supports the power grid to allow more power generation from connected intermittent renewable energy sources. It is also shown that this new hybrid power plant will avoid the Combined Cycle plant gas turbine operating under the low load level. Lowering the minimum hybrid plant operational load level during air and Thermal Energy Storage charging process to the required minimum Heat Recovery Steam Generator load level eliminates the need for Combined Cycle Gas Turbine plant cycling operation increasing the lifetime of the plant components. Adiabatic Compressed Air Energy Storage plant concept is based on proved and well established direct two-tank Thermal Energy Storage technology used in Concentrated Solar Power plants. Improved hybrid plant flexibility is occupied by slight decrease (2%) in the plant efficiency. Further investigation into alternative advanced Thermal Energy Storage systems based on latent heat and chemical reaction heat would offer better hybrid plant round-trip efficiency across operational plant load level range.

Selective exhaust gas recirculation in combined cycle gas turbine power plants with post-combustion CO2 capture

In the context of the process intensification of Post-combustion Carbon Capture (PCC), Selective Exhaust Gas Recirculation (SEGR) in Natural Gas-fired Combined Cycle (NGCC) plants, a concept where CO2 is selectively recycled to increase concentration and reduce flow rates of the flue gas, is analysed. SEGR operated either in parallel or in series with a downstream PCC system increases CO2 concentration beyond 14 vol% and maintains oxygen levels in the combustor to approximately 19 vol%, well above the 16 vol% limit reported for non-selective Exhaust Gas Recirculation (EGR). Process modelling shows that the current class of gas turbine engines can operate without a significant deviation in the compressor and in the turbine performance. Compressor inlet temperature and CO2 concentration in the working fluid are the two critical parameters affecting the gas turbine net power output and efficiency. A higher turbine exhaust temperature allows the generation of additional steam in the HRSG. This results in an increase in net power output of approximately 42 MW (5.2%) and 18 MW (2.3%), and in net thermal efficiency of 0.55%point and 0.83%point, for the investigated configurations with SEGR in parallel and SEGR in series, respectively. With 30 wt% aqueous monoethanolamine scrubbing technology, SEGR leads to operation and cost benefits. SEGR in parallel with 70% recirculation, 97% selective CO2 transfer efficiency and 96% PCC efficiency results in a reduction of 46% in packing volume and 5% in specific reboiler duty, compared to air-based combustion CCGT with PCC, and of 10% in packing volume and 2% in specific reboiler duty, compared to 35% EGR. SEGR in series operating at 95% selective CO2 transfer efficiency and 32% PCC efficiency results in a reduction of 64% in packing volume and 7% in specific reboiler duty, compared to air-based CCGT with PCC, and of 40% in packing volume and 4% in specific reboiler duty, compared to 35% EGR. On selecting a technology for SEGR applications, CO2 selectivity, pressure drop and heat transfer flow rate are the operating parameters with a larger effect on the power plant performance with SEGR. It is important to minimise oxygen leakages from the air into the flue gas, minimise heat transfer that would otherwise increase CO2-enriched air temperature at compressor inlet, and minimise pressure drop, e.g. a 1 kPa pressure drop results in gas turbine derating of 2 MW (0.7%).

Conditions for economic competitiveness of pumped storage hydroelectric power plants in Egypt

Pumped storage hydroelectric power plants are one of the most applicable energy storage technologies on large-scale capacity generation due to many technical considerations such as their maturity, frequency control and higher ramp rates, thus maintaining following loads in case of high penetration of renewables in the electrical grid. Economic viability of PSHPPs is still questionable when compared with other electricity generation technologies. In this manuscript, the key factors that affect the viability of constructing PSHPP in Attaqa Mountain, Egypt, are defined. An economic comparison between PSHPPs and simple cycle gas turbine power plants has been carried out to identify the conditions at which PSHPPs will have competitiveness as an on-peak solution, over traditional SCGT power plants. This assessment is based on calculating levelized cost of electricity taking into account different scenarios for PSHPP pumping cost and capital cost, and different scenarios for SCGT fuel prices. The results showed the key factors of the best case at which PSHPPs have the highest economic competitiveness over SCGT power plants when fuel prices are non-subsidized. This is only valid provided that the PSHPP’s capital cost should not exceed 4180 $/kW at zero pumping cost.

Optimisation of Combined Cycle Gas Turbine Power Plant in Intraday Market: Riga CHP-2 Example

Abstract In the research, the influence of optimised combined cycle gas turbine unit – according to the previously developed EM & OM approach with its use in the intraday market – is evaluated on the generation portfolio. It consists of the two combined cycle gas turbine units. The introduced evaluation algorithm saves the power and heat balance before and after the performance of EM & OM approach by making changes in the generation profile of units. The aim of this algorithm is profit maximisation of the generation portfolio. The evaluation algorithm is implemented in multi-paradigm numerical computing environment MATLab on the example of Riga CHP-2. The results show that the use of EM & OM approach in the intraday market can be profitable or unprofitable. It depends on the initial state of generation units in the intraday market and on the content of the generation portfolio.

Water and Wastewater Management in Combined Cycle Gas Turbine Power Plants

Water and Wastewater Management in Combined Cycle Gas Turbine Power Plants

Simulation and optimization of a combined cycle gas turbine power plant for part-load operation

Combined cycle gas turbine (CCGT) power plants must often run at part-load conditions, as the electricity demand varies constantly. We present a method and necessary correlations for simulating the part-load operation of a typical CCGT plant in a commercial simulator (e.g. GateCycle). We show that assuming constant values for some equipment parameters (e.g. efficiencies) and ignoring the operating maps of key equipment can overestimate plant performance significantly at part-loads. Furthermore, a rise in the ambient temperature lowers the plant capacity, but increases the plant efficiency. Then, we propose a simulation-based optimization approach that yields an optimal operating strategy to maximize the overall plant efficiency for any part-load. Our strategy forms a basis for evaluating the two widely used operating policies (fuel flow control or FFC and inlet guide vane control or IGVC). Our proposed strategy increases the plant efficiency by as much as 2.63% (absolute) over FFC and 0.93% over IGVC. This work highlights the need for integrating the two cycles (gas turbine and steam) to optimize the plant performance. We find that FFC seems to prioritize the gas turbine and IGVC tends to prioritize the steam cycle, while our proposed strategy strikes an optimal balance between the two.

Improving Prediction Accuracy of a Rate-Based Model of an MEA-Based Carbon Capture Process for Large-Scale Commercial Deployment

Carbon capture and storage (CCS) technology will play a critical role in reducing anthropogenic carbon dioxide (CO2) emission from fossil-fired power plants and other energy-intensive processes. However, the increment of energy cost caused by equipping a carbon capture process is the main barrier to its commercial deployment. To reduce the capital and operating costs of carbon capture, great efforts have been made to achieve optimal design and operation through process modeling, simulation, and optimization. Accurate models form an essential foundation for this purpose. This paper presents a study on developing a more accurate rate-based model in Aspen Plus® for the monoethanolamine (MEA)-based carbon capture process by multistage model validations. The modeling framework for this process was established first. The steady-state process model was then developed and validated at three stages, which included a thermodynamic model, physical properties calculations, and a process model at the pilot plant scale, covering a wide range of pressures, temperatures, and CO2 loadings. The calculation correlations of liquid density and interfacial area were updated by coding Fortran subroutines in Aspen Plus®. The validation results show that the correlation combination for the thermodynamic model used in this study has higher accuracy than those of three other key publications and the model prediction of the process model has a good agreement with the pilot plant experimental data. A case study was carried out for carbon capture from a 250 MWe combined cycle gas turbine (CCGT) power plant. Shorter packing height and lower specific duty were achieved using this accurate model.

Analysis of a Gas Turbine Plant for Distributed Power Cogeneration Along with Heating, Refrigeration and Air Conditioning

ABSTRACTGas turbine plants play important role in power production whenever there has been scarcity of power generated from conventional sources like oil or gas. Researchers have been trying to simulate this kind of power plants for higher outputs with improved system efficiency. In this scenario, present work attempts to study and simulate a closed cycle gas turbine power plant for different configurations. All the components are modelled and integrated to form a power generating and heating system. Parameters like compressor inlet pressure, pressure ratio and turbine inlet temperature are varied. Performance curves of the individual components and the integrated system are plotted and studied. Results obtained show the significance of pressure ratio and turbine inlet temperature. Utilization of heat from turbine exhaust shows the possibility of a cogeneration bottoming cycle that can be used for district heating, refrigeration and air conditioning applications. Also, it is found that inlet pressure of 1...

Investigating the Influence of Helium Based Mixtures Composition on the Temperature Recovery Factor and Prandtl Number Values

The paper studies the influence of thermo-physical and transport properties of gaseous working fluids on the efficiency of closed Brayton cycle gas turbine power plants and gas dynamic temperature stratification device (Leontiev’s tube). It is shown that using helium binary gas mixtures with low Prandtl number Pr values as working fluids instead of pure helium in closed Brayton cycle gas turbine power plants leads to significant drop in the turbo-machinery aerodynamic loading with retention of the heat transfer coefficients in heat-exchangers and with sustainable growth in the pressure losses along the power plant loop components. For the Leontiev’s tube, using the helium binary gas mixtures with low Pr values results in significant drop of the temperature recovery factor r value on the wall in supersonic flow and in rise of the available temperature difference with appropriate increase of heat flow densities and decrease of required heat transfer areas value. The paper analyses the influence of different factors on the value r . Shows that using the gas mixtures with low Pr values as working fluids, injecting gas into supersonic flow boundary layer through permeable wall and arranging regular relief on the wall surface are the most promising solutions for decreasing the value r . Examines the methodologies and correlations known from available open sources to calculate the r values depending on Pr , Reynolds number Re x and Mach number M and presents the calculation results obtained through these correlations for Pr 0,1…1, Re x 10 5 …10 9 and M up to 4. Practically, all the methodologies and correlations examined are in good agreement with experimental data obtained for air with Pr ≈ 0,7 over the intervals of Re x and M considered. However, with further reduction of Pr value the calculation results for r diverge for different methodologies and correlations with up to 35 – 40 % difference for Pr ≈ 0,2 for those which are in good agreement with the air experimental data. Thus, there is a recommendation to conduct further experimental investigations to obtain real r values for different Pr , Re x and M on the flat impermeable wall in supersonic flow for the He - Ar , He - Kr , He - Xe , He - N 2 , He - CO 2 binary gas mixtures in order to verify the methodologies and correlations examined.

CCGT unit commitment model with first-principle formulation of cycling costs due to fatigue damage

Combined cycle gas turbine power plants (CCGTs) play a key role in modern electric power systems due to their operational flexibility and the firmness they provide to the networks where they operate. Due in part to this flexibility and firmness, the function of CCGTs has experienced a significant evolution with the advent of intermittent renewable energy sources such as wind: CCGTs are increasingly required to rapidly vary load levels in order to counterbalance the fluctuations of renewable energy sources and satisfy overall system demand. The purpose of this paper is to develop a methodology that can be used for assessing the optimal operational strategy of a CCGT when subjected to cycling requirements. This is achieved by introducing a unit commitment formulation that takes into account useful life expenditure costs due to fatigue damage accumulation associated to cycling. The case studies presented in this paper show that neglecting fatigue cycling costs when making operational decisions generates suboptimal cost and profit outcomes for CCGT operators. Furthermore, it is shown that profitability of CCGTs is compromised in systems with very significant penetration of intermittent renewable energy sources, due to the increase in cycling costs derived from continuous load-following operation.

Sequential supplementary firing in natural gas combined cycle with carbon capture: A technology option for Mexico for low-carbon electricity generation and CO2 enhanced oil recovery

Combined cycle gas turbine power plants with sequential supplementary firing in the heat recovery steam generator could be an attractive alternative for markets with access to competitive natural gas prices, with an emphasis on capital cost reduction, and where supply of carbon dioxide for Enhanced Oil Recovery (EOR) is important. Sequential combustion makes use of the excess oxygen in gas turbine exhaust gas to generate additional CO2, but, unlike in conventional supplementary firing, allows keeping gas temperatures in the heat recovery steam generator below 820°C, avoiding a step change in capital costs. It marginally decreases relative energy requirements for solvent regeneration and amine degradation. Power plant models integrated with capture and compression process models of Sequential Supplementary Firing Combined Cycle (SSFCC) gas-fired units show that the efficiency penalty is 8.2% points LHV compared to a conventional natural gas combined cycle power plant with the same capture technology. The marginal thermal efficiency of natural gas firing in the heat recovery steam generator can increase with supercritical steam generation to reduce the efficiency penalty to 5.7% points LHV. Although the efficiency is lower than the conventional configuration, the increment in the power output of the combined steam cycle leads a reduction of the number of gas turbines, at a similar power output to that of a conventional natural gas combined cycle. This has a positive impact on the number of absorbers and the capital costs of the post combustion capture plant by reducing the total volume of flue gas by half on a normalised basis. The relative reduction of overall capital costs is, respectively, 15.3% and 9.1% for the subcritical and the supercritical combined cycle configurations with capture compared to a conventional configuration. For a gas price of $2/MMBTU, the Total Revenue Requirement (TRR) – a metric combining levelised cost of electricity and revenue from EOR – of subcritical and supercritical sequential supplementary firing is consistently lower than that of a conventional NGCC by, respectively, 2.2 and 5.7 $/MWh at 0 $/t CO2 and by 4.9 and 6.7 $/MWh at $50/t CO2. At a gas price of $4/MMBTU and $6/MMBTU, the TRR of a subcritical configuration is consistently lower for any carbon selling price higher than 2.5 $/t CO2 and 37 $/t CO2 respectively.

A technical evaluation, performance analysis and risk assessment of multiple novel oxy-turbine power cycles with complete CO2 capture

In recent years there has been growing concern about greenhouse gas emissions (particularly CO2 emissions) and global warming. Oxyfuel combustion is one of the key technologies for tackling CO2 emissions in the power industry and reducing their contribution to global warming. The technology involves burning fuel with high-purity oxygen to generate mainly CO2 and steam, enabling easy CO2 separation from the flue gases by steam condensation. In fact, 100% CO2 capture and near-zero NOx emissions can be achieved with this technology.This study examines nineteen different oxy-turbine cycles, identifying the main parameters regarding their operation and development. It also analyses the use of advanced natural gas (NG) combustion cycles from the point of view of the carbon capture and storage (CCS) and considering political, legislative and social aspects of deploying this technology. Six oxy-turbine cycles which are at the most advanced stages of development (NetPower, Clean Energy Systems CES), Modified Graz, E-MATIANT, Advanced Zero Emission Power AZEP 100% and Semi-Closed Oxy-fuel Combustion Combined Cycle (SCOC-CC)), were chosen to conduct a Political, Environmental, Social, Technological, Legislative and Economic (PESTLE) risk analysis. This compares each technology with a conventional combined cycle gas turbine (CCGT) power plant without carbon capture as the base-case scenario. Overall, the net efficiency of the different oxy-turbine cycles ranges between 43.6% and 65%, comparable to a CCGT power plant, while providing the extra benefits of CO2 capture and lower emissions.A multi-criteria analysis carried out using DECERNS (Decision Evaluation in Complex Risk Network Systems) software determined that, depending on the specific criterion considered, one can draw different conclusions. However, in terms of technology, environment and social opinion, the most promising cycles are the NetPower and CES cycles, whereas from an economic point of view, E-MATIANT is more competitive in the energy market. Giving each factor equal importance, the NetPower cycle must be considered to be the best oxy-turbine cycle based on our analysis.Most of the oxy-turbine cycles are still under development and only a few cycles (e.g., CES and NetPower) are progressing to the demonstration phase. In consequence, political measures such as CO2 tax and emission allowances need to be implemented for oxy-turbine technologies to become the preferred option for fossil fuel power plants burning natural gas.

Effects of nitrogen dilution on the NOx and CO emission of H2/CO/CH4 syngases in a partially-premixed gas turbine model combustor

In this study, the nitrogen dilution effect in H2/CO/CH4 syngas flames on the characteristics of NOx and CO emissions were investigated in a partially premixed gas turbine model combustor. Nitrogen was diluted into the fuel side and combustor liner temperature, and the flame structures were observed in order to find information that was critical for analyzing the results of the NOx and CO emissions. The addition of nonflammable N2 was effective in decreasing the combustion temperature, which was attributed to the reduction in the reaction rate of syngas oxidation as well as the increase in the overall heat capacity of the air-fuel mixture at a constant heat input. NOx suppression was successfully achieved up to the one digit ppmv level for all heat input and all fuel composition by the 60%-fuel side dilution of nitrogen. However, increases in nitrogen dilution increased the possibility of CO emission; therefore, extremely high CO was emitted in a 100%-CO flame at a low load with 60%-nitrogen dilution reaching 10,000 ppmv. The dilution of nitrogen in syngas considerably changed the flame structure, such as flame length, thickness, angle, location, and intensity. These flame structures provided valuable clues for the analysis of the NOx and CO emission results in relation to the flame temperature results. Based on the integration of the test results, a cause-and-effect diagram of NOx and CO emissions was plotted, and the root causes of NOx suppression were determined to be the decreases in both temperature and residence time in the hot combustion zone, and the critical path of these root causes was clarified. Although the nitrogen dilution technique has been investigated in detail, and the effects are fully understood, the careful monitoring of CO and flame detachment from the fuel nozzle is recommended when applying the nitrogen dilution technique to reduce NOx emission, especially in cases of low load operation. A practical dataset was collected from the combustion test at gas turbine relevant conditions for a wide range of fuel compositions. These results and the knowledge gained from this study could be usefully applied for the environmentally friendly and safe operation of integrated gasification combined cycle and synthetic natural gas firing gas turbine power plants.

Gas Turbines - Major Greenhouse Gas Inhibitors

This article explains how combined cycle gas turbine (CCGT) power plants can help in reducing greenhouse gas from the atmosphere. In the last 25 years, the development and deployment of CCGT power plants represent a technology breakthrough in efficient energy conversion, and in the reduction of greenhouse gas production. Existing gas turbine CCGT technology can provide a reliable, on-demand electrical power at a reasonable cost along with a minimum of greenhouse gas production. Natural gas, composed mostly of methane, is a hydrocarbon fuel used by CCGT power plants. Methane has the highest heating value per unit mass of any of the hydrocarbon fuels. It is the most environmentally benign of fuels, with impurities such as sulfur removed before it enters the pipeline. If a significant portion of coal-fired Rankine cycle plants are replaced by the latest natural gas-fired CCGT power plants, anthropogenic carbon dioxide released into the earth’s atmosphere would be greatly reduced.