Exergy, exergoeconomic and environmental analyses and evolutionary algorithm based multi-objective optimization of combined cycle power plants

A comprehensive exergy, exergoeconomic and environmental impact analysis and optimization is reported of several combined cycle power plants (CCPPs). In the first part, thermodynamic analyses based on energy and exergy of the CCPPs are performed, and the effect of supplementary firing on the natural gas-fired CCPP is investigated. The latter step includes the effect of supplementary firing on the performance of bottoming cycle and CO₂ emissions, and utilizes the first and second laws of thermodynamics. In the second part, a multi-objective optimization is performed to determine the “best” design parameters, accounting for exergetic, economic and environmental factors. The optimization considers three objective functions: CCPP exergy efficiency, total cost rate of the system products and CO₂ emissions of the overall plant. The environmental impact in terms of CO₂ emissions is integrated with the exergoeconomic objective function as a new objective function. The results of both exergy and exergoeconomic analyses show that the largest exergy destructions occur in the CCPP combustion chamber, and that increasing the gas turbine inlet temperature decreases the CCPP cost of exergy destruction. The optimization results demonstrates that CO₂ emissions are reduced by selecting the best components and using a low fuel injection rate into the combustion chamber.     

Exergoeconomic optimization of a 1000 MW light water reactor power generation system

A typical 1000 MW pressurized water reactor nuclear power plant is considered for optimization. The thermodynamic modeling is performed based on the energy and exergy analysis, while an economic model is developed according to the total revenue requirement method. The objective function based on the exergoeconomic analysis is obtained. The exergoeconomic optimization process with 10 decision variables is performed using a hybrid stochastic/deterministic search algorithm namely as genetic algorithm. The results that are obtained using optimization process are compared with the base case system and the discussion is presented. Copyright © 2009 John Wiley & Sons, Ltd.     

Solar aided power generation of a 300 MW lignite fired power plant combined with line-focus parabolic trough collectors field

Nowadays, conventional coal or gas fired power plants are the dominant way to generate electricity in the world. In recent years there is a growth in the field of renewable energy sources in order to avoid the threat of climate change from fossil fuel combustion. Solar energy, as an environmental friendly energy source, may be the answer to the reduction of global CO₂ emissions. This paper presents the concept of Solar Aided Power Generation (SAPG), a combination of renewable and conventional energy sources technologies. The operation of the 300 MW lignite fired power plant of Ptolemais integrated with a solar field of parabolic trough collectors was simulated using TRNSYS software in both power boosting and fuel saving modes. The power plant performance, power output variation, fuel consumption and CO₂ emissions were calculated. Furthermore, an economic analysis was carried out for both power boosting and fuel saving modes of operation and optimum solar contribution was estimated.     

Exergoeconomic estimates for a novel zero-emission process generating hydrogen and electric power

This paper presents the exergoeconomic analysis of a novel process generating electric energy and hydrogen. Coal and high-temperature heat are used as input energy to the process. The process is a true “zero-emission process” because (a) no NO_X is formed during coal combustion with sulfuric acid, and (b) the combustion products CO₂ and SO₂ are removed separately as compressed liquids from the overall process. The process cycle is based on two chemical reactions. The first reaction takes place in an electrolytic cell and delivers the hydrogen product. In the second step, coal reacts with sulfuric acid in a high-pressure combustion reactor. The combustion gas is expanded in a gas turbine to produce electric power. The combustion products are compressed and separated so that almost pure CO₂ can be removed from the cycle. The overall process is characterized by very high energetic and exergetic efficiencies. However, the overall process is very capital intensive. The electrolytic cell dominates the costs associated with the overall process. Detailed results of the thermodynamic simulation, the economic and the exergoeconomic analyses of the process including estimates of the product costs are presented.     

Multi-objective optimization of a joule cycle for re-liquefaction of the Liquefied Natural Gas

A LNG re-liquefaction plant is optimized with a multi-objective approach which simultaneously considers exergetic and exergoeconomic objectives. In this regard, optimization is performed in order to maximize the exergetic efficiency of plant and minimize the unit cost of the system product (refrigeration effect), simultaneously. Thermodynamic modeling is performed based on energy and exergy analyses, while an exergoeconomic model based on the total revenue requirement (TRR) are developed. Optimization programming in MATLAB is performed using one of the most powerful and robust multi-objective optimization algorithms namely NSGA-II. This approach which is based on the Genetic Algorithm is applied to find a set of Pareto optimal solutions. Pareto optimal frontier is obtained and a final optimal solution is selected in a decision-making process. An example of decision-making process for selection of the final solution from the available optimal points of the Pareto frontier is presented here. The feature of selected final optimal system is compared with corresponding features of the base case and exergoeconomic single-objective optimized systems and discussed.     

The performance analysis and evaluation of C‐PV/T aided power generation system

In this paper, a novel solar aided power generation (SAPG) hybrid system based on the structural characteristics of coal‐fired power generation is established. In this system, the extraction steam of No.8 low pressure heater is replaced by the hot water coming from a concentration‐photovoltaic/thermal (C‐PV/T) module. The extraction steam returns into the steam turbine to do work, which increases the output power. And the electricity from the parallel C‐PV/T module goes directly into the power grid, which increases the generated power. The C‐PV/T module coupled with coal‐fired power generation improves the solar energy efficiency and provides hot water. As a case study, the economic calculation is performed with actual operation data extracted from a 600‐MW coal‐fired unit. The results show that the total efficiency increased by 1.3%, the coal fuel consumption is lowered by 11 g/kW·h, and the investment recovery period is approximately 7 years. This study offers a theoretical support to the engineering demonstration.     

Thermo-economic modeling of an indirectly coupled solid oxide fuel cell/gas turbine hybrid power plant

Power generation using gas turbine (GT) power plants operating on the Brayton cycle suffers from low efficiencies, resulting in poor fuel to power conversion. A solid oxide fuel cell (SOFC) is proposed for integration into a 10 MW gas turbine power plant, operating at 30% efficiency, in order to improve system efficiencies and economics. The SOFC system is indirectly coupled to the gas turbine power plant, paying careful attention to minimize the disruption to the GT operation. A thermo-economic model is developed for the hybrid power plant, and predicts an optimized power output of 20.6 MW at 49.9% efficiency. The model also predicts a break-even per-unit energy cost of USD 4.65 ¢ kWh⁻¹ for the hybrid system based on futuristic mass generation SOFC costs. This shows that SOFCs may be indirectly integrated into existing GT power systems to improve their thermodynamic and economic performance.     

Solar gas turbine systems: Design, cost and perspectives

The combination of high solar shares with high conversion efficiencies is one of the major advantages of solar gas turbine systems compared to other solar-fossil hybrid power plants. Pressurized air receivers are used in solar tower plants to heat the compressed air in the gas turbine to temperatures up to 1000 °C. Therefore solar shares in the design case of 40% up to 90% can be realized and annual solar shares up to 30% can be achieved in base load. Using modern gas turbine systems in recuperation or combined cycle mode leads to conversion efficiencies of the solar heat from around 40% up to more than 50%. This is an important step towards cost reduction of solar thermal power. Together with the advantages of hybrid power plants—variable solar share, fully dispatchable power, 24 h operation without storage—solar gas turbine systems are expected to have a high potential for market introduction in the mid term view.In this paper the design and performance assessment of several prototype plants in the power levels of 1 MW, 5 MW and 15 MW are presented. Advanced software tools are used for design optimization and performance prediction of the solar tower gas turbine power plants. Detailed cost assumptions for the solarized gas turbine, the solar tower plant and further equipment as well as for operation and maintenance are presented. Intensive performance and economic analysis of the prototype plants for different locations and capacity factors are shown. The cost reduction potential through automation and remote operation is revealed.     

Thermo-economic modeling of a solid oxide fuel cell/gas turbine power plant with semi-direct coupling and anode recycling

Power generation using gas turbine (GT) power plants operating on the Brayton cycle suffers from low efficiencies, resulting in poor fuel to power conversion. A solid oxide fuel cell (SOFC) is proposed for integration into a 10 MW gas turbine power plant, operating at 30% efficiency in order to improve system efficiencies and economics. The SOFC system is semi-directly coupled to the gas turbine power plant, with careful attention paid to minimize the disruption to the GT operation. A thermo-economic model is developed for the hybrid power plant, and predicts an optimized power output of 21.6 MW at 49.2% efficiency. The model also predicts a breakeven per-unit energy cost of USD 4.70 ¢/kWh for the hybrid system based on futuristic mass generation SOFC costs. Results show that SOFCs can be semi-directly integrated into existing GT power systems to improve their thermodynamic and economic performance.     

Techno-economic analysis of using corn stover to supply heat and power to a corn ethanol plant – Part 2: Cost of heat and power generation systems

This paper presents a techno-economic analysis of corn stover fired process heating (PH) and the combined heat and power (CHP) generation systems for a typical corn ethanol plant (ethanol production capacity of 170 dam³). Discounted cash flow method was used to estimate both the capital and operating costs of each system and compared with the existing natural gas fired heating system. Environmental impact assessment of using corn stover, coal and natural gas in the heat and/or power generation systems was also evaluated. Coal fired process heating (PH) system had the lowest annual operating cost due to the low fuel cost, but had the highest environmental and human toxicity impacts. The proposed combined heat and power (CHP) generation system required about 137 Gg of corn stover to generate 9.5 MW of electricity and 52.3 MW of process heat with an overall CHP efficiency of 83.3%. Stover fired CHP system would generate an annual savings of 3.6 M$ with an payback period of 6 y. Economics of the coal fired CHP system was very attractive compared to the stover fired CHP system due to lower fuel cost. But the greenhouse gas emissions per Mg of fuel for the coal fired CHP system was 32 times higher than that of stover fired CHP system. Corn stover fired heat and power generation system for a corn ethanol plant can improve the net energy balance and add environmental benefits to the corn to ethanol biorefinery.     

Comprehensive evaluation of coal-fired power plants based on grey relational analysis and analytic hierarchy process

In China, coal-fired power plants are the main supplier of electricity, as well as the largest consumer of coal and water resources and the biggest emitter of SO_x, NO_x, and greenhouse gases (GHGs). Therefore, it is important to establish a scientific, reasonable, and feasible comprehensive evaluation system for coal-fired power plants to guide them in achieving multi-optimisation of their thermal, environmental, and economic performance. This paper proposes a novel comprehensive evaluation method, which is based on a combination of the grey relational analysis (GRA) and the analytic hierarchy process (AHP), to assess the multi-objective performance of power plants. Unlike the traditional evaluation method that uses coal consumption as a basic indicator, the proposed evaluation method also takes water consumption and pollutant emissions as indicators. On the basis of the proposed evaluation method, a case study on typical 600 MW coal-fired power plants is carried out to determine the relevancy rules among factors including the coal consumption, water consumption, pollutant, and GHG emissions of power plants. This research offers new ideas and methods for the comprehensive performance evaluation of complex energy utilisation systems, and is beneficial to the synthesised consideration of resources, economy, and environment factors in system optimising and policy making.     

Modified exergoeconomic modeling of geothermal power plants

In this study, a modified exergoeconomic model is proposed for geothermal power plants using exergy and cost accounting analyses, and a case study is in this regard presented for the Tuzla geothermal power plant system (Tuzla GPPS) in Turkey to illustrate an application of the currently modified exergoeconomic model. Tuzla GPPS has a total installed capacity of 7.5 MW and was recently put into operation. Electricity is generated using a binary cycle. In the analysis, the actual system data are used to assess the power plant system performance through both energy and exergy efficiencies, exergy losses and loss cost rates. Exergy efficiency values vary between 35% and 49% with an average exergy efficiency of 45.2%. The relations between the capital costs and the exergetic loss/destruction for the system components are studied. Six new exergetic cost parameters, e.g., the component annualized cost rate, exergy balance cost, overall unavoidable system exergy destruction/loss cost rate, overall unavoidable system exergy destruction/loss cost rate, overall unavoidable system exergy production cost rate and the overall unavoidable system exergy production cost rate are studied to provide a more comprehensive evaluation of the system.     

Trade-off in emissions of acid gas pollutants and of carbon dioxide in fossil fuel power plants with carbon capture

This paper investigates the impact of capture of carbon dioxide (CO₂) from fossil fuel power plants on the emissions of nitrogen oxides (NO_X) and sulphur oxides (SO_X), which are acid gas pollutants. This was done by estimating the emissions of these chemical compounds from natural gas combined cycle and pulverized coal plants, equipped with post-combustion carbon capture technology for the removal of CO₂ from their flue gases, and comparing them with the emissions of similar plants without CO₂ capture. The capture of CO₂ is not likely to increase the emissions of acid gas pollutants from individual power plants; on the contrary, some NO_X and SO_X will also be removed during the capture of CO₂. The large-scale implementation of carbon capture is however likely to increase the emission levels of NO_X from the power sector due to the reduced efficiency of power plants equipped with capture technologies. Furthermore, SO_X emissions from coal plants should be decreased to avoid significant losses of the chemicals that are used to capture CO₂. The increase in the quantity of NO_X emissions will be however low, estimated at 5% for the natural gas power plant park and 24% for the coal plants, while the emissions of SO_X from coal fired plants will be reduced by as much as 99% when at least 80% of the CO₂ generated will be captured.     

Techno‐economic comparison of boiler cold‐end flue gas heat recovery processes for efficient hard‐coal‐fired power generation

An important method to increase the efficiency of thermal power plants is to recover the exhaust gas heat at the boiler cold‐end with the stepwise integration of a steam turbine heat regenerative system. To this end, there are currently three typical heat recovery processes, that is, a low‐temperature economizer (LTE), segmented air heating (SAH) and bypass flue (BPF). To provide useful guidance to thermal power plants for optimal and efficient processes, the thermal economy and techno‐economic performance of the three aforementioned processes were calculated and compared using an in‐service 600‐MW hard‐coal‐fired ultra‐supercritical power unit as a reference. The results demonstrate that with the use of the LTE, SAH and BPF, respectively, to recover the exhaust heat, reducing the exhaust temperature from 122 °C to 90 °C, the net standard coal consumption rate of the 600‐MW unit can be reduced by 1.51, 1.71 and 2.81 g/(kW h). The initial costs of the three heat recovery projects are 1.69, 2.91 and 2.53 million USD. If the 600‐MW unit runs 5500 h per year at the rated load, the three processes can increase the earnings of the unit by 0.49, 0.52 and 0.94 million USD from coal savings annually, meaning that their dynamic payback periods are 4.42, 8.66 and 3.29 years, respectively. The results indicate that for a hard‐coal‐fired power unit, the coal savings achieved by exhaust heat recovery are notable. Among the three processes, SAH shows the worst techno‐economic performance because it induces a significant increase in initial costs while obtaining a limited increase in thermal economy, while BPF exhibits the best techno‐economic performance owing to the significant increase in thermal economy. Copyright © 2016 John Wiley & Sons, Ltd.     

Thermoeconomic analysis of pressurized hybrid SOFC systems with CO2 separation

In this paper, the results of the thermodynamic and economic analyses of distributed power generation plants (1.5 MWe) are described and compared. The results of an exergetic analysis are also reported, as well as the thermodynamic details of the most significant streams of the plants. The integration of different hybrid solid oxide fuel cell (SOFC) system CO₂ separation technologies characterizes the power plants proposed. A hybrid system with a tubular SOFC fed with natural gas with internal reforming has been taken as reference plant. Two different technologies have been considered for the same base system to obtain a low CO₂ emission plant. The first technology involved a fuel decarbonization and CO₂ separation process placed before the system feed, while the second integrated the CO₂ separation and the energy cycle. The first option employed fuel processing, a technology (amine chemical absorption) viable for short-term implementation in real installations while the second option provided the CO₂ separation by condensing the steam from the system exhaust. The results obtained, using a Web-based Thermo Economic Modular Program software, developed by the Thermochemical Power Group of the University of Genoa, showed that the thermodynamic and economic impact of the adoption of zero emission cycle layouts based on hybrid systems was relevant.     

Thermo‐economic‐environmental multiobjective optimization of a gas turbine power plant with preheater using evolutionary algorithm

In this study, the gas turbine power plant with preheater is modeled and the simulation results are compared with one of the gas turbine power plants in Iran namely Yazd Gas Turbine. Moreover, multiobjective optimization has been performed to find the best design variables. The design parameters of the present study are selected as: air compressor pressure ratio (r_AC), compressor isentropic efficiency (η_AC), gas turbine isentropic efficiency (η_GT), combustion chamber inlet temperature (T₃) and gas turbine inlet temperature. In the optimization approach, the exergetic, economic and environmental aspects have been considered. In multiobjective optimization, the three objective functions, including the gas turbine exergy efficiency, total cost rate of the system production including cost rate of environmental impact and CO₂ emission, have been considered. The thermoenvironomic objective function is minimized while power plant exergy efficiency is maximized using a genetic algorithm. To have a good insight into this study, a sensitivity analysis of the results to the interest rate as well as fuel cost has been performed. In addition, the results showed that at the lower exergetic efficiency in which the weight of thermoenvironomic objective is higher, the sensitivity of the optimal solutions to the fuel cost is much higher than the location of Pareto Frontier with the lower weight of thermoenvironomic objective. Copyright © 2010 John Wiley & Sons, Ltd.     

Efficient design of feedwater heaters network in steam power plants using pinch technology and exergy analysis

A design method is presented based on pinch technology and exergy analysis to reduce heat transfer irreversibility of the feedwater heaters network in steam power plants. In order to show the effects of this method, an extensive study was performed on four steam power plants. The results show that applying this method can decrease the fuel consumption and the condenser load. It also increases the boiler, the feedwater heaters network, and the turbine exergetic efficiencies. On the whole, the results show that applying this method, with a target pinch temperature of 3°C, increases the cycle 2nd law efficiency 0.3–1.3% and the fossil fuel consumption decreases about 64 × 10⁶kg annually for 8000 operating hours per year of the studied steam power plants. Copyright © 2007 John Wiley & Sons, Ltd.     

Thermo-economic optimization of an indirectly coupled solid oxide fuel cell/gas turbine hybrid power plant

Power generation using gas turbine (GT) power plants operating on the Brayton cycle suffers from low efficiencies, resulting in poor fuel to power conversion. A solid oxide fuel cell (SOFC) is proposed for integration into a 10-MW GT power plant, operating at 30% efficiency, in order to improve system efficiencies and economics. The SOFC system is indirectly coupled to the GT, in order to minimize the disruption to the GT operation. A thermo-economic model is developed to simulate the hybrid power plant and to optimize its performance using the method of Lagrange Multipliers. It predicts an optimized power output of 18.9 MW at 48.5% efficiency, and a breakeven per-unit energy cost of USD 4.54 ¢ kW h⁻¹ for the hybrid system based on futuristic mass generation SOFC costs.     

Study of MW-scale biogas-fed SOFC-WGS-TSA-PEMFC hybrid power technology as distributed energy system: Thermodynamic,exergetic and thermo-economic evaluation

Advanced biogas power generation technology has been attracting attentions, which contributes to the waste disposal and the mitigation of greenhouse gas emissions. This work proposes and models a novel biogas-fed hybrid power generation system consisting of solid oxide fuel cell, water gas shift reaction, thermal swing adsorption and proton exchange membrane fuel cell (SOFC-WGS-TSA-PEMFC). The thermodynamic, exergetic, and thermo-economic analyses of this hybrid system for power generation were conducted to comprehensively evaluate its performance. It was found that the novel biogas-fed hybrid system has a gross energy conversion efficiency of 68.63% and exergy efficiency of 65.36%, indicating high efficiency for this kind of hybrid power technology. The market sensitivity analysis showed that the hybrid system also has a low sensitivity to market price fluctuation. Under the current subsidy level for the distributed biogas power plant, the levelized cost of energy can be lowered to 0.02942 $/kWh for a 1 MW scale system. Accordingly, the payback period and annual return on investment can reach 1.4 year and about 20%, respectively. These results reveal that the proposed hybrid system is promising and economically feasible as a distributed power plant, especially for the small power scale (no more than 2 MW).     

Analysis of MTH-System (Methylcyclohexane-Toluene-Hydrogen-System) for hydrogen production as fuel for power plants

The utilization of hydrogen (H₂) gas as green energy fuel in power plants is a great challenge due to its storage, deployment and transportation. Herein, we propose a simulation based study of H₂ fueled power plant by using Methylcyclohexane-Toluene-Hydrogen-System (MTH-System). A 266 MW gas turbine was selected and the performance of MTH-System for power plant was investigated. The process for methylcyclohexane (MCH) production was not discussed here. However, the conversion of MCH into gaseous H₂ for power generation was discussed in detail. A sustainable process flow diagram (PFD) was developed. The heat integration b/w power plant and dehydrogenation reactor reveal that, minimum 70% MCH conversion is required to accomplish the heat demand of whole system. The effect of addition of H₂ recycle stream to dehydrogenation reactor and combined cycle power plants was investigated. The sensitivity and economic analysis reveal 2291.4 $/kW capital cost based on dehydrogenation of MCH for power production and 0.186 $/kWh output electricity cost based on complete MTH-System.