Fossil-fired Power Plants Research Articles

Microstructural evolution in 12% Cr heat-resistant steel during compression deformation at 650°C

Microstructural evolution in 12% Cr heat-resistant steel during compression deformation at 650°C

Nanoindentation creep mechanism of gradient ultrafine lamellar γ+Ni5Zr eutectic using electromagnetic levitation coupled with fall casting

A quaternary Ni50Fe20Cr20Zr10 eutectic alloy was designed based on the Ni–Fe–Cr alloy, and the gradient ultrafine lamellar γ+Ni5Zr eutectic was achieved by means of electromagnetic levitation coupled with fall casting (EML-FC). The temperature field, the process of interface migration, microstructural characteristics and the nanoindentation creep property of the alloy were systematically analyzed. During the rapid solidification, since the conical surface served as the main heat dissipation channel, the solid-liquid interface moved from the conical surface towards the top of the cone axis. The gradual decrease in cooling rate from 105 to 103 K s−1 along this direction led to the formation of the gradient ultrafine lamellar γ + Ni5Zr eutectic with the size from 59 ± 12 to 140 ± 36 nm. The nanoindentation creep behavior and mechanism were analyzed by estimating the strain rate sensitivity and activation volume. As the interlamellar spacing of the eutectic decreased, the nanohardness and creep resistance of the alloy gradually increased owing to an increase in grain boundary density and the enhancement of coupling effect between dislocation and grain boundary. In addition, the creep behavior of alloy was sensitive to the loading rate. Increasing the loading rate led to an increase in strain rate sensitivity from 7.69 × 10−3 to 18.89 × 10−3 and a decrease in activation volume from 29 to 12 b3. This special eutectic structure and its improved nanohardness and creep resistance properties offered a potential opportunity to explore a new generation of alloys for the hot-end components of 972 K ultra-supercritical fossil-fired power plants.

Overcurrent Limitation in Hydrogen Storage Power Plants (HSPP)

The importance of electrical energy storage (EES) systems has been increasingly recognized for enabling the large-scale integration of intermittent renewable energy sources (RES) into the power grid. Among these systems, the Hydrogen Storage Power Plant (HSPP) stands out as a solution capable of independently managing the supply and storage of electrical energy based on network requirements. Previous investigations have shown that the HSPP operating in grid forming mode (GFM) can provide the required ancillary services in the form of instantaneous, primary and secondary control reserves similar to conventional fossil-fired power plants. However, unlike these traditional synchronous generators, the HSPP consists of power semiconductor devices, resulting in much lower overcurrent tolerance. This paper addresses this challenge by proposing a simple yet robust control technique that regulates the maximum current across the HSPP grid interfacing inverter functioning in GFM. The results demonstrate that the controller can maintain the maximum current magnitude below a threshold of 1.2 pu while ensuring the required reactive current contribution during a three-phase fault.

Retrofit of a coal-fired power plant with a rock bed thermal energy storage

Power production accounts for about one-fifth of the global final energy consumption and over one-third of all energy-related CO2 emissions. Low-cost, large-scale thermal energy storages are considered as solutions for the decarbonization of fossil-fired power plants by their conversion into power-to-heat-to-power systems, so-called thermal storage power plants. This paper investigates the retrofit of a Chilean coal-fired power plant with an innovative solid media storage from a techno-economic perspective. Selecting a storage capacity of 5.27 GWhth, corresponding to 8 h of discharge, and increasing the inlet steam generator temperature from 590 to 650 °C lead to the highest annual round-trip efficiency of 34.9% and to up to 3.4% lower levelized cost of electricity. Minimum levelized cost of electricity as low as 88.1 €/MWh is attained and considered as close to competitiveness with well-established molten salt storage systems. A sensitivity analysis shows that assuming even five times lower storage costs, initially the strongest driver of capital expenditure, only meant 4% lower levelized costs of electricity on average. On the other hand, the design of electricity purchase for charging, for example with green power purchase agreements, turns out to be the key lever to a successful implementation.

Search for the Optimal Design of a Supercritical-CO2 Brayton Power Cycle from a Superstructure-Based Approach Implemented in a Commercial Simulation Software

Improving the efficiency and flexibility of fossil-fired power plants remains a current and challenging issue. In that regard, supercritical CO2 Brayton cycles offer promising potential. This paper aims to apply a process synthesis approach to the design of a closed Brayton cycle using supercritical CO2 as a working fluid with a coal furnace as a heat source. The general methodology presented here for designing closed power cycles includes the construction of a superstructure containing all relevant possible cycle layouts, the formulation of the cycle-synthesis problem as a mathematical optimization problem, and its solution using an appropriate algorithm. This study was conducted with the help of a process simulation commercial software (PROSIM) and using the Mixed-Integer Distributed Ant Colony Optimization (MIDACO) as a commercial optimization algorithm. This work highlights the limits of a purely technical optimization approach that would ignore the economical layer. The optimal structure obtained regarding Levelized Cost Of Electricity (LCOE) minimization is a configuration with one reheat of the supercritical CO2 in the boiler, two recuperators, and one recompression loop around the low-temperature recuperator; it is associated with a cycle efficiency of 49.35 % and a 10% reduction in the LCOE in comparison to the optimal case found through energy optimization under typical design heuristics constraints.

Conceptual design and evaluation of a hybrid energy system based on a tri-level waste heat recovery: an approach to achieve a low-carbon cogeneration system

Abstract The exhaust waste heat of the fossil-fired power plants and some power generation technologies (such as fuel cells) is a rich source of recoverable thermal energy. Meanwhile, the effective use of the fuel cell's exhaust waste heat in the downstream processes and units can improve the thermodynamic superiority, reduce the environmental impacts caused by the release of waste heat in the environment and enhance the attractiveness and sustainability of the energy process. Here, the multi-variable analysis (thermodynamic, economic and environmental assessments)/optimization of a low-carbon cogeneration process (power and cooling capacity production system) are proposed and investigated. The proposed cogeneration process works under waste heat from the exhaust of a fuel cell, an ejector refrigeration cycle and an organic Rankine cycle (ORC)-driven tri-stage waste heat recovery system. A bi-objective optimization is based on identifying the maximum value of exergy efficiency and the minimum value of the total cost of the system. To highlight the advantages, the behavior of the considered cogeneration process is compared with a system that works under a compressor refrigeration cycle and a single-stage waste heat recovery system (as a reference process). According to the results, the considered process can provide approximately 10% higher exergy efficiency compared to the reference process. Moreover, the overall cost of the considered process can be about 20% lower compared to the reference process. The amount of emitted CO2 from the proposed process can be mitigated by nearly 11 thousand tons compared to the reference process.

Perspectives for Expansion of Concentrating Solar Power (CSP) Generation Technologies in Brazil

The world is moving towards a low-carbon economy through renewable energy sources. In this context, concentrating solar power (CSP) technologies can exploit the rich solar resource in Brazil, diversifying the national electricity mix. The aim of this paper is to support the insertion of CSP generation in the Brazilian bottom-up model MATRIZ by analyzing the environmental performance of three CSP technologies: (i) solar tower power (STP) with a thermal storage system (TSS) of 7.5 h; (ii) solar thermal parabolic trough (STPT) with a TSS of 6 h; and (iii) STPT without TSS. From a life cycle perspective, their freshwater consumption and greenhouse gas (GHG) emissions are addressed by employing the software SimaPro, the Ecoinvent database, and the ReCiPe 2016 method, as well as information from the system advisory model (SAM) and the literature. As a result, STP is the most environmentally sound CSP alternative, presenting lower GHG emissions and water consumption than the two STPT technologies. In general, CSP generation proves to be more environmentally attractive than some fossil-fired power plants and renewable energy sources. Moreover, moving the manufacturing of CSP technologies to Brazil has the potential to reduce GHG emissions from the upstream processes of their value chain.

Effect of NaCl presence caused by salting out on the heterogeneous-homogeneous coupling non-equilibrium condensation flow in a steam turbine cascade

Steam turbine is one of the most important components in fossil-fired and nuclear power plants, its efficiency is of great importance for saving energy and decreasing consumption. The steam density rapidly decreases when the steam expanses, and NaCl dissolved in steam starts precipitating. However, the presence of NaCl will not only affect the non-equilibrium condensation decreasing the steam turbine efficiency, but also erode the steam turbine blade reducing the steam turbine safety and shortening maintenance cycle. The main objective of the current work is to investigate the effect of the NaCl presence on the non-equilibrium condensation process and the loss in steam turbine cascade. Firstly, a non-equilibrium condensation model including homogeneous and heterogeneous condensation process is presented and its accuracy is checked in a steam turbine cascade by comparing with available experimental data. And the results show the accuracy and robustness of the model is quite trustworthy. Secondly, the influence of NaCl concentration on the non-equilibrium condensation flow is investigated in a steam turbine cascade. The results show that the NaCl presence has a significant effect on condensation flow. With the NaCl concentration increasing, the droplets nucleation rate decreases, diminishing the tiny droplet emerging, which weakens homogeneous condensation. As a result, the condensation loss caused by the homogeneous condensation decreases, and even the condensation loss caused by the homogeneous condensation becomes zero when the NaCl particle number reaches 7.5×1014 per kilogram in steam flow. However, the condensation loss caused by the heterogeneous condensation shows a reverse tendence, which increases with the NaCl concentration. At last, the condensation loss and entropy generation caused by the non-equilibrium condensation are checked in steam turbine cascade under different NaCl concentration conditions. The results show that the condensation loss reduces by 9.2% and increases by 42% at the 7.5×10141/kg and 10171/kg NaCl concentrations, respectively. Meanwhile, when the NaCl particle number reaches 7.5×1014 per kilogram, the isentropic efficiency is highest, about 0.884, compared with other cases considering condensation effect. This study proves that the NaCl concentration has a nonnegligible effect on the condensation loss and entropy generation, which must be considered in future steam turbine study.

Correlation of deformation with damage progression behavior around a notch tip under creep and fatigue conditions for W-added 9Cr steel including weld joint

Research concerning heat-resistant steels for the application in fossil-fired power plants has progressed remarkably during the past 60 years. This has resulted in improvements in the electrical efficiency of fossil-fired power plants. Currently, there are plans and programs to develop ultra-supercritical plants designed to operate at steam temperature and pressure conditions of 600/650 °C and 32 MPa. The W-added 9%Cr ferritic heat-resistant steel, that is, ASME grade P92, has been developed as a boiler material for this ultra-supercritical plant. Boiler materials, whose performance is critical for ultra-supercritical plant, are required to possess high creep resistant properties. In addition, these materials are exposed to fatigue induced by thermal stresses, that is, they are operated under creep-fatigue interacting conditions. In this study, mechanical tests under the condition of high temperature creep-fatigue interaction were conducted for P92 steel under stress-controlled and various load frequency conditions using the in-situ observational creep-fatigue testing machine to observe the damage formation behavior around a notch tip composed of voids in mesoscale. On the basis of these results, the effects of damage formation behavior on crack growth life were clarified. Furthermore, for the case of creep deformation, the numerical analyses of vacancy diffusion and concentration around a notch tip were conducted using our proposed numerical method of local stress-induced vacancy diffusion behavior, which is a nanoscale phenomenon to relate these behaviors to the damage formation behavior in mesoscale (μm scale).

Creep rupture prediction using constrained neural networks with error estimates

ABSTRACT Creep rupture prediction for materials serving in fossil-fired power plants has been a critical issue for many decades. There are many empirical methods with several fitting or adjustable parameters that have been proposed for creep rupture strength prediction. Fundamental models based on the microstructure mechanism have been developed but are not widely used due to their complicated nature. Neural Network (NN) is a powerful tool for handling complicated mechanical behaviour; However, unexpected results and excessive errors can be generated. To avoid this, constraints on the first and second derivatives of the creep rupture curves have been introduced and combined with the NN. With the constrained NN models, extrapolated results with controlled errors can be obtained, which is verified by methods for error analysis. Furthermore, ECCC Post Assessment Tests (PATs) 1.1 to 2.2 are satisfied. The methods are illustrated for two creep-resistant austenitic steels Sanicro 25 and Super304H.

Comparative Study on the Aerodynamic Characteristics of National Advisory Committee for Aeronautics (NACA) 0008 and 0020 Series

Energy from wind is observed to be among the most viable renewable energy sources due to its minimal cost in comparison with other sources. Hence, wind energy has an advantage over fossil-fired power plants. Airfoil aerodynamic efficiency is highly important for wind turbine aerodynamic efficiency. The study determined the aerodynamic characteristics of two symmetrical NACA 4-digit airfoils; NACA 0008 and 0020. Comparisons were made in the characteristics of the airfoils, in order to further understand and compare forces at different angle of attack. The coordinates for each airfoil were developed and simulation carried out using ANSYS CFX after generating a mesh and selecting boundary conditions. The results showed that symmetrical NACA 0008 experienced high lift at each angle of attack than NACA 0020. NACA 0020 had some fraction of lift over NACA 0008 only at angle of attack. NACA 0008 appears to be the better of the two airfoils, having greater lift at each angle of attack which encourages its application in wind turbine.

Land-use in the Electric Colombian System: Hidden Impacts and Risks of Large-scale Renewable Projects

In the sustainable development era, massive land-use for electricity production represents a crucial challenge for environmental and social systems. Available information about the use of land in this sector is limited, for that reason in this paper we include the power density methodology to evaluate land-use in Colombia to produce electricity. The power density metric depicts the relation between energy produced and area used in this process, considering extraction-conversion-storage. The analysis between power electricity generation and land-use is made for the Colombian electric system, finding that there is no direct relationship between the area occupied by a generation plant and the electricity produced, since the evidence does not show that at larger areas greater power is obtained. Hydropower plants have large spectrum values of power densities, depending on the dam construction purpose (river-flow control). Fossil-fired power plants require less land for its production even including the fuel extraction area. Photovoltaic and wind-power plants in this comparison have the lowest power density values, accordingly, they require far larger areas and represent a risk for sustainability in this perspective.

The Experimental Evaluation of Energy Efficiency and Carbonic Emission Rates for All Stable Loads of Larger-Scale (+600 MW) Coal-Fired Power Generation Units in Vietnam

Performance guarantees and tests of thermal power plants are usually carried out at 100% rate output capacity. However, fossil-fired power plants have decreased full load hours, affecting energy efficiency, and are subjected to frequent load changes caused by variable renewable electricity and potential grid stability. Therefore, this study is conducted to calculate and draw the characteristic curves for all stable loads of coal-fired power units including the 60%, 75%, and 100% rate output. The study focuses on the corrected plant net heat rates—gross unit outputs, net standard coal consumption rates—throttle steam pressures, and corrected plant net efficiencies—carbonic emission rates. In addition, the experimental investigation for energy efficiency and carbonic emission of the latest larger-scale (+600 MW) coal-fired power generation units in Vietnam are also implemented using a performance guarantee calculation software called “PG_Cal” version 0.0, which is based on a mass and energy balance method by MATLAB programing language. From the results of this study, it is suggested that the performance guarantees and tests of new coal-fired units should be carried out at different stable loads, including minimum load. Vietnam should apply the ultra-supercritical technology for new units in order to increase their efficiency and decrease carbon dioxide emissions.

Towards defining reasonable minimum composition thresholds – Impacts of variable CO2 stream compositions on transport, injection and storage

To set up recommendations on how to define “reasonable minimum composition thresholds” for CO2 streams to access CO2 pipeline networks, we investigated potential impacts of CO2 streams with different and temporally variable compositions and mass flow rates along the CCS chain. All investigations were based on a generic “CCS cluster scenario” in which CO2 streams captured from a spatial cluster of eleven emitters (seven fossil-fired power plants, two cement plants, one refinery and one steel mill) are collected in a regional pipeline network. The resulting CO2 stream (19.78 Mio t impure CO2 per year) is transported in a trunk line (onshore and offshore) and injected into five generic replicate storage structures (Buntsandstein saline aquifers) offshore. Experimental investigations and modeling of selected impacts revealed beneficial as well as adverse impacts of different impurities and their combinations. Overall, no fundamental technical obstacles for transporting, injecting and storing CO2 streams of the considered variable compositions and mass flow rates were observed. We recommend to define minimum composition thresholds for each specific CCS project through limiting i) the overall CO2 content, ii) maximum contents of relevant impurities or elements, iii) acceptable variability of concentrations of critical impurities, and defining impurity combinations to be avoided.

How effective is carbon pricing?—A machine learning approach to policy evaluation

While carbon taxes are generally seen as a rational policy response to climate change, knowledge about their performance from an ex-post perspective is still limited. This paper analyzes the emissions and cost impacts of the UK CPS, a carbon tax levied on all fossil-fired power plants. To overcome the problem of a missing control group, we propose a policy evaluation approach which leverages economic theory and machine learning for counterfactual prediction. Our results indicate that in the period 2013–2016 the CPS lowered emissions by 6.2 percent at an average cost of €18 per ton. We find substantial temporal heterogeneity in tax-induced impacts which stems from variation in relative fuel prices. An important implication for climate policy is that whether a higher carbon tax leads to higher emissions reductions and higher costs depends on relative fuel prices.

An interpretation of creep rupture properties of grade 91 steel service- exposed for 100,000 hours at 600 °C

ABSTRACT Creep rupture data of grade 91 steel used as hot reheat pipes have been reported recently. The data are investigated by comparison with the creep rupture database of the steel in normalised and tempered (NT) states. Four regions H, M, L and G with different values of stress exponent appear in creep of grade 91 steel. The pipes were used in long-term region G (around 600 °C for 100,000 hours) in fossil-fired power plants. Medium- and low-stress regions M and L are confirmed to exist in the service-exposed states. Stress exponents in the two regions are kept unchanged in all the pipes, but the service exposure reduces their remaining creep rupture lives. The reduction is significant in the pipes made by cold bending. The service exposure retards the appearance of long-term region G. Causes of these findings are discussed in this paper.

Zero- and negative-emissions fossil-fired power plants using CO2 capture by conventional aqueous amines

This work investigated the technical and economic feasibility of achieving zero and negative CO2 emissions in both pulverized coal (PC) and natural gas combined cycle (NGCC) power plants, using conventional amine scrubbing with 30 wt% aqueous monoethanolamine. In this work, we refer to “zero emissions” when the amount of CO2 in the exhaust flue gas is equal to that in the intake combustion air, and “negative emissions” when the amount of CO2 in the exhaust flue gas is less that in the intake combustion air. Increasing CO2 capture from 90% to that at zero-emissions for fossil-fired power plants can reduce global CO2 emissions by up to ∼1 Gt/y for the current global power generation mix. Even higher CO2 capture leads to negative emissions of the power plant with part of the CO2 from the intake air removed along with the fossil-fuel derived CO2. With an absorber configuration including a simple solvent intercooler, both PC and NGCC power plants can achieve zero-emissions with a ∼5% and ∼13% increase in CO2 avoidance costs, compared with the costs at 90% CO2 capture. The larger cost penalty for NGCC was mainly due to a temperature bulge at the absorber top. Replacing the simple solvent intercooler with a pump-around intercooler was able to reduce this cost penalty to ∼8%. Further decarbonization of flue gases from zero-emissions to direct air capture (DAC)-level of negative emissions (∼100 ppmv of CO2 in exhaust gases) has incremental costs of over $1000/t CO2 avoided for both PC and NGCC.

How Effective is Carbon Pricing? – a Machine Learning Approach to Policy Evaluation

While carbon taxes are generally seen as a rational policy response to climate change, knowledge about their performance from an expost perspective is still limited. This paper analyzes the emissions and cost impacts of the UK CPS, a carbon tax levied on all fossil-fired power plants. To overcome the problem of a missing control group, we propose a policy evaluation approach which leverages economic theory and machine learning for counterfactual prediction. Our results indicate that in the period 2013-2016 the CPS lowered emissions by 6.2 percent at an average cost of €18 per ton. We find substantial temporal heterogeneity in tax-induced impacts which stems from variation in relative fuel prices. An important implication for climate policy is that in the short run a higher carbon tax does not necessarily lead to higher emissions reductions or higher costs.

Energy Performance of CO2 Capture Processes: Interaction Between Process Design and Solvent

Implementation of amine-based post-combustion CO2 capture on power plants would lead to large penalties on the electric production. Researches focus either on the improvement of process flow scheme to maximize exergy integration or on characterization of new promising solvents to reduce this energy consumption. However, both aspects are often taken into account separately whereas they should be studied simultaneously since the energy efficiency of process modifications also depends on the considered solvent. In order to highlight this point, several schemes based on modifications proposed in literature are investigated for several classes of amine-based solvents and the total energy consumption is determined by a rigorous phenomenological model coupled with an optimization algorithm. Simulation results confirms that the efficiency of process modifications depends on the considered solvent since process improvements make use of the solvent specific properties, in particular the differences between thermodynamic and kinetic properties. General understandings are given on the relative efficiency of process modifications according to measurable solvent properties. Carbon dioxide capture and geological storage is foreseen to be one of the solutions to reduce the atmospheric emissions of fossil-fired power plants. Among the different technologies, post-combustion chemical absorption in amine-based solvents is the most mature at this stage of development. However, the energy consumption of such processes implies a large penalty on the power plant efficiency. The reference configuration used for chemical absorption of CO2 is a conventional absorption/desorption loop operating with monoethanolamine (MEA) where the CO2 is separated from the flue gas by chemical absorption in the solvent and the solvent is thermally regenerated in a stripper, sensible heat being exchanged in an economizer between the hot lean solvent and the cold rich solvent. The released CO2 is then compressed up to 110 bars at supercritical state for transportation and storage. For this base case, the energy requirement leads to a loss of around 11 %-pts in terms of power plant efficiency. In order to reduce this penalty, researches focus either on the improvement of process flow scheme to maximize heat integration or on characterization of new promising solvents. This work intends to emphasize the interaction between solvent properties and optimal process design and how both solvent characterization and process design should be carried out simultaneously, since the energy performance of a process modification is deeply dependent of the chosen solvent. In order to highlight this point, several schemes based on modifications proposed in literature are investigated for two classes of amine-based solvents. For each process flow scheme associated with each solvent, the operating parameters are optimized with respect to the total energy consumption with a dedicated algorithm using rigorous thermodynamic and rate-based models, which are mandatory for a proper representation of all limiting phenomena. By this means, the potential of each configuration is determined in terms of total energy penalty on the power plant.

Power Market Formation for Clean Energy Production as the Prerequisite for the Country’s Energy Security

The paper analyzes the main issues of power market development for clean energy production within the broader framework of ensuring the country’s energy security. In addition, special attention is paid to the technologies aimed at reducing emissions of toxic substances and greenhouse gases by the fossil-fired power plants. Even though the future electricity markets would most likely depend on the high shares of renewable energy sources (RES) in the electricity system, energy efficiency such as the one based on the near-zero emission technologies might also play a crucial role in the transition to the carbon-free energy future. In particular, there are the oxy-fuel combustion technologies that might help to reduce the proportion of unburned fuel and increase the efficiency of the power plant while reducing the emissions of flue gases. Our paper focuses on the role and the place of the near-zero emission technologies in the production of clean energy. We applied economic and mathematical models for assessing the prospects for applying oxy-fuel combustion technology in thermal power plants, taking into account the system of emission quotas and changes in the fuel cost. Our results demonstrate that at the current fuel prices, it is advisable to use economical combined cycle gas turbines (CCGT). At the same time, when quotas for greenhouse gas emissions are introduced and fuel costs increase by 1.3 times, it becomes economically feasible to use the oxy-fuel combustion technology which possesses significant economic advantages over CCGT with respect to the capture and storage of greenhouse gases.