Thermal Power Output Research Articles

Time-Interval-Varying Optimal Power Dispatch Strategy Based on Net Load Time-Series Characteristics

In China, with the increasing permeability of wind power, the power supply capacity is enough overall, but has shortage in partial-time. During peak hours, the capability of wind power consumption is poor and the power balance becomes more difficult. In order to maximize the utilization of wind power, the net loads are chosen as the response objectives, which contain significant uncertainties and have no probabilistic distribution characteristics. Under the traditional day-ahead power dispatch mode with fixed length time intervals and in the regions with insufficient hydroelectricity, the thermal generators take charge of the peak-load shaving. The frequent adjustments of thermal power output affect the system operation safety, economic benefits, and environmental benefits. Thus, a time-interval-varying optimal power dispatch strategy based on net load time-series characteristics is proposed in this paper. The net loads respond differently to intervals. The length of each time interval is determined based on the net load time-series characteristics analyzed by random matrix theory. The dispatch mode in each time interval is determined according to the characteristic quantification index calculated by the empirical modal decomposition and sample entropy. The proposed strategy and method can extend the continuous and stable operation time of the thermal generators, reduce the coal consumption caused by the ramping operation, and improve the safety, stability, and economy of the system. Furthermore, the proposed dispatch mode is environmentally friendly with reduced environmental cost and increased carbon credits. An actual provincial power grid in northeast China is taken as the example to verify the rationality and effectiveness of the proposed method and strategy.

Evaluation of the potential of nanofluids containing different Ag nanoparticle size distributions for enhanced solar energy conversion in hybrid photovoltaic-thermal (PVT) applications

Hybridising photovoltaic and photothermal technologies into a single system that can simultaneously deliver heat and power represents one of the leading strategies for generating clean energy at more affordable prices. In a hybrid photovoltaic-thermal (PVT) system, the capability to modulate the thermal and electrical power output is significantly influenced by the spectral properties of the heat transfer fluid utilised. In this study, we report on one of the first experimental evaluations of the capability of a multimodal silver nanofluid containing various particle shapes and particle sizes to selectively modulate the solar energy for PVT applications. The diverse set of particle properties led up to a 50.4% enhancement in the solar energy absorbed by the nanofluid over the 300 nm—550 nm spectral region, where silicon is known to exhibit poor photovoltaic conversion performances. This improved substantially the absorption of solar energy, with an additional 18–129 W m−2 of thermal power being generated by the PVT system. Along with the advancements made in the thermal power output of the PVT system, a decrease of 4.7–36.6 W m−2 in the electrical power generated by the photovoltaic element was noted. Thus, for every ∼11 W m−2 increase of thermal power achieved through the addition of the nanoparticles, a reduction of ∼3 W m−2 in the ability to generate clean electricity was sustained by the PVT. Despite the energy trade-offs involved under the conditions of the nanofluid, the PVT system cumulatively harvested 405 W m−2 of solar energy, which amounts to a total conversion efficiency of 45%. Furthermore, the economics of the additional energy harvested through merging of the two systems was found to reach an enhancement of 77% under certain European conditions.

Energy and exergy analyses of a combined cycle power plant with inlet fuel heating

By using exhaust gas as heating source, a combined cycle power plant with inlet fuel heating is investigated experimentally. Energy analysis and exergy analysis are carried out under different power load and ambient temperature. The results reveal that the thermal efficiency of the power plant system increases as power load increases. The thermal efficiency and power output at 5? are 54.15% and 412 MW, respectively, while when the ambient temperature is 35?, the thermal efficiency and power output are 52.3% and 330 MW, respectively. Under the same conditions, the combustion chamber has the highest irreversibility rate, while the air compressor has the lowest. The irreversibility rate of the power plant system increases in line with power load. The second-law efficiency increases from 37.0-50.12% when the power load changes from 30-100%.

Hydrogen-air premixed combustion in a novel micro disc-burner with an annular step

A novel micro disc-burner with an annular step using the hydrogen/air premixed mixture is developed in this work, which can act as a heater or heat source with a high stability for the miniature power generators. The combustion and thermal performance of this combustor is studied by the means of numerical simulation. The results show that the excess enthalpy combustion appears at a small equivalence ratio. The thermal output power of the combustor increases with the increased Reynolds number. It is interesting to find that the upper and lower limits of thermal output power and its ratio in the total heat release amount change approximately linearly with the Reynolds number. It is found that the thermal output power and its ratio in the total heat release amount under any conditions are smaller than 102.8 W and 31.41%, respectively. The effects of the thermal conductivity and surface emissivity of solid wall on the combustion characteristics are studied. Both thermal output power and its ratio in the total heat release amount decrease with the increased thermal conductivity. Additionally, the thermal output power remarkably decreases with the decreased surface emissivity. The current work not only provides the guideline for applying this combustor but also helps us to gain insight into the heat transfer characteristic in the radial micro-channel.

Research on the valley-filling pricing for EV charging considering renewable power generation

The real-time dispatch of electricity grids faces two new challenges: the volatility of renewable energy power generation and the impact caused by the large-scale charging demand of electric vehicles (EVs). Under the premise that China's renewable energy power generation is a prior connection to the grid, this article aims to guide the coordinated charging of EVs through the design of the time-of-use charging price mechanism and to help achieve valley-filling. The peak and valley hours were divided according to the load of baseload units that do not include renewable energy power generation. A nationwide discrete choice experiment has been conducted to investigate the willingness to pay of 2637 Chinese consumers for charging at different times and to analyse the influence of heterogeneous factors. Finally, the power economic dispatch model has been used to simulate the effect of the charging time-of-use pricing on the cost and load of the regional power system. Policy recommendations are provided based on consumers' willingness to pay for charging at public charging stations and home chargers at different times on weekdays and weekends. The simulation shows that under the EV charging time-of-use price mechanism with a 50% price increase during peak hours and a 50% price reduction during valley hours, the total power cost of Beijing-West Inner Mongolia power systems is reduced by 302.3 million CNY compared with the current scenario. The average peak-valley difference of thermal power output can also be reduced by 11.7% on weekdays.

Performance of Multi-Well Exploitation and Reinjection in a Small-Scale Shallow Geothermal Reservoir in Huailai County

The sustainable development of a shallow aquifer geothermal reservoir is strongly affected by the reinjection–production strategy. However, the reinjection–production strategy optimization of a small-scale exploitation unit with tens of meters of well spacing is site specific and has not yet been fulfilled. This study numerically investigates sustainable heat extraction based on various reinjection–production strategies which were conducted in a single-phase aquitard–aquifer geothermal system in Huailai County, Hebei Province, China. The response of the water level and production temperature is mainly discussed. The numerical results show that production without reinjection induces the highest production temperature and also the water level drawdown. Although reinjection in a single doublet well system is conducive to the control of water level drawdown, the introduction of the thermal breakthrough problem causes a decrease in the production temperature. The thermal breakthrough and sustainability of geothermal reservoirs highly depend on the well spacing between the production and reinjection wells, especially for the small-scale field. Therefore, a large well spacing is suggested. A multi-well system facilitates the control of water level drawdown while bringing intensive well interference and thermal breakthrough. Large spacing between the production and reinjection wells is also the basic principle for the design of the multi-well system. A decrease in openhole length leads to an increase in the production temperature and output thermal power. An increase in the production rate affects the thermal breakthrough highly and shortens the lifetime of the geothermal system. Furthermore, the extracted thermal energy is highly affected by the reduction in the reinjection temperature. The results in this study can provide references to achieve sustainable geothermal exploitation in small-scale geothermal reservoirs.

Phase change materials for thermal energy storage: A perspective on linking phonon physics to performance

Thermal energy storage is being actively investigated for grid, industrial, and building applications for realizing an all-renewable energy world. Phase change materials (PCMs), which are commonly used in thermal energy storage applications, are difficult to design because they require excellent energy density and thermal transport, both of which are difficult to predict from simple physics-based models. In this Perspective, we describe recent advances in the understanding of the equilibrium and transport properties of PCM materials that can help accelerate technology development. We then emphasize how the microscopic phonon picture of both liquids and solids enables a better understanding of novel PCM systems and their predictive power. We then show how this microscopic picture can be used to understand kinetic processes, such as supercooling, and how it can impact the thermal power output in thermal energy storage systems.

Real-time heliostat field aiming strategy optimization based on reinforcement learning

The heliostat field aiming strategy optimization is a crucial topic in solar power tower (SPT) plants. The optimal aiming strategy attempts to maximize the thermal power output while preserving certain operational limits. While existing methods could produce high-optimality results, they cannot be applied to real-time optimization for ultra large scale problems due to high computational complexity. In this work, an effective and scalable optimization method is proposed to achieve real-time optimization for ultra large scale problems, enabling efficient and robust SPT plant operations under varying solar conditions (i.e., cloud shadowing variations). The real-time optimization problem is reformulated as a reinforcement learning problem, capturing the learning from the intrinsic sequential decision-making process, to minimize unnecessary repetitions of computations. A Crescent Dunes-like SPT plant is studied, with the allowable flux density as the optimization constraint, and the results show that the proposed method provides better or comparable performance compared to heuristic optimization methods with an order of magnitude less computation time.

CFD Simulation of Syngas Combustion in a Two-Pass Oxygen Transport Membrane Reactor for Fire Tube Boiler Application

The oxygen transport membrane reactor technology enables the stable combustion of syngas and reduction in NOx emission. Applying the syngas combustion membrane reactor to fire tube boiler can integrate oxygen separation, syngas combustion, and steam generation in a single apparatus. In this study, a CFD model for oxygen permeation and syngas combustion in a two-pass LSCoF-6428 tubular membrane reactor for fire tube boiler application was developed to study the effects of the inlet temperature, the sweep gas flow rate, and the syngas composition on the reactor performance. It is shown that the inlet temperature has a strong effect on the reactor performance. Increasing the inlet temperature can efficiently and significantly improve the oxygen permeability and the heat production capacity. A 34-times increase of oxygen permeation rate and a doubled thermal power output can be obtained when increasing the inlet temperature from 1073 to 1273 K. The membrane temperature, the oxygen permeation rate, and the thermal power output of the reactor all increase with the increase of sweep gas flow rate or H2/CO mass ratio in syngas. The feasibility of the syngas combustion membrane reactor for fire tube boiler application was elucidated.

Effect of blowing ratio on film-cooling effectiveness of ginkgo shaped holes: a numerical approach

Modern gas turbine engines operate at high temperatures to improve thermal efficiency and power output. Increased rotor inlet temperatures increase the rate of heat transfer to the turbine blades, which requires sophisticated cooling schemes to keep the blade temperature at acceptable levels. This work is a numerical investigation of film cooling techniques as applied to gas turbines. The cooling performance of two differently shaped holes, namely, Ginkgo Forward and Ginkgo Reverse, were investigated in terms of centerline and local lateral cooling effectiveness, and a comprehensive comparison was made with the cooling performance of a cylindrical hole. The investigations were performed at a constant density ratio (DR = 2.0) and three different blowing ratios (BR = 1.0, 1.5, and 2.0). Under all of the operating conditions, the results demonstrated significant augmentation in centerline and lateral cooling effectiveness when the Ginkgo Reverse shaped hole was used, followed by the Ginkgo Forward and cylindrical cooling holes. For the shaped cooling holes, the low velocity gradient through the film alleviated the jet lift-off and turbulence, resulting in decreased entrainment of hot gas to the bottom surface. To conclude, the prominent lateral dispersal of the coolant due to the shaped cooling holes significantly enhanced thermal protection and the overall cooling performance.

Field-scale experimental and numerical analysis of a downhole coaxial heat exchanger for geothermal energy production

The experimental and computational analyses of a 500 m deep coaxial borehole heat exchanger system for geothermal power generation are studied in this paper. The experiments are carried out on a high temperature resourced well with an average thermal gradient of 0.38 °C/m. The experiment lasts 456 h, and the findings are described in terms of fluid inlet and outlet temperatures, subsurface temperature distribution profiles over time, and flowrate. The in-situ ground temperature distribution profile is measured using Distributed Temperature Sensing System for different hours of the experiment. A detailed, three-dimensional, unsteady-state, finite volume-based computational model has been developed, which solves conjugate fluid-flow and heat transfer phenomena. The simulation outcomes are compared to the results of the experiments. With validated numerical model, to determine the circle of influence, temperature profile of the ground is observed at various radial distances from the borehole. A parametric study is performed by varying inlet temperature of the fluid, mass flow rate, and the thermal conductivity of the ground. The numerical model developed also predicts the temperature recovery behavior of the ground. The results indicate that the average output thermal power for 456 h from the geothermal system ranges from 172 kW to 262 kW based on operating condition chosen and the total thermal energy generated changes between 82 MWh and 194 MWh from a single borehole. After the extraction is terminated, around 86% of the initial ground temperature is restored after 456 h.

Coupled thermal–hydraulic–mechanical model for an enhanced geothermal system and numerical analysis of its heat mining performance

The operation of an enhanced geothermal system (EGS) involves a complex thermal–hydraulic–mechanical (THM) coupling process, which is important for exploiting the geothermal energy contained in hot dry rocks. In this study, the THM coupling mechanism in an EGS reservoir is explained, and a fully coupled THM mathematical model with local thermal nonequilibrium of a dual media is established, considering the dynamic changes in the properties of the rock matrix, fractures, and fluid during EGS operation. The model is verified through an example of the thermoelastic consolidation of a saturated soil. The heat transfer, fluid flow, and mechanical characteristics of a geothermal reservoir over 40 years are studied via a numerical simulation of a 2D geometric model. The effects of fracture occurrence, coupling conditions, and model parameters on the mining performance are analyzed. The results show that the dual-media model can reflect the anisotropy in the temperature, pressure, and stress due to the presence of fractures. An area with a more complex fracture network and smaller spacing is found to be more conducive for heat transfer. The inlet–outlet pressure differences, thermal expansion coefficient of the rock matrix, and initial fracture permeability have significant effects. When the inlet–outlet pressure difference is increased from 4 to 10 MPa, the heat extraction ratio increases from 56% to 89% at 40 years, and the initial output thermal power is increased from 9.2 to 24.9 MW. When the coefficient of thermal expansion is increased from 1 × 10−6 to 7 × 10−6 K−1, the heat extraction ratio is increased from 54% to 84%, and the initial output thermal power is increased from 8.5 to 19.7 MW. When the initial permeability is increased from 1 × 10−11 to 2.5 × 10−11 m2, the heat extraction ratio increases from 74% to 92%. These results provide a reference for optimizing the mining effect of the EGS.

Experimental research of metal hydride heat storage reactor processes

The results of the experimental research of thermal, mass exchange and dynamical characteristics of processes inside the low temperature metal hydride (MH) thermal energy storage system are presented. Single stage pressure driven MH heat storage system of closed cycle concept was studied and tested. Intermetallic compound (IMC) LaFe0.1Mn0.3Ni4.8 in the quantity of 5 kg was used as main hydrogen storage/heat emitter element in the reactor. Nominal maximum hydrogen capacity of the reactor is 850 st.l. with though resulting effective volume of cycled hydrogen ended up to be around 240-250 st.l. The reactor type and intermetallic alloy, which were used in the series of experiments, proved to be somewhat suitable for the task, but more advanced heat exchange design along with selection of different type of IMC promise to increase the cycled effective volume along with the system dynamics, resulting in greater thermal energy power output.

Simulation System for PeLUIt 150 MW Nuclear Reactor by using vPower

In developing the PeLUIt 150 MW nuclear power plant based on the High Temperature Gas-cooled Reactor (HTGR) technology, with the helium-coolant and output thermal power of 150 MW, the PeLUIt simulator is also developed for training the operators and educating other technical personnel. Referred to the balance of plant (BOP) design of the PeLUIt, the simulator utilized the vPower simulation platform to simulate the secondary loop for power generation with a water-steam Rankine cycle. The paper focuses on developing the secondary loop’s main components: steam generator, steam turbine, condenser, deaerator, and feedwater pump. The reactor module in the primary loop is simplified as a heat source with 150 MW output. The steam generator that connects the primary and secondary loops is modeled with the heat exchanger module by transferring heat from helium to water/steam. Meanwhile, pressure and flow parameters can also be simulated for both helium and water/steam flows in steady-state and transient operating conditions. The steady-state simulation results are almost the same as the design data. The differences in the main steam temperature, feedwater pressure, and feedwater temperature, are 0.03%, 0.53%, and 0.02%, respectively. Meanwhile, the transient condition carried out in the loss of coolant accident showed a decrease in flowrate of 43.31 kg/s and an increase in temperature of feedwater and main-steam of 52.32 and 15.38 °C, respectively. In addition, there was a pressure drop of around 10.37 (feedwater) and 10.16 MPa (main-steam).

Parametric investigation of combustion process optimization for Gas Turbines at SJ Putrajaya

Gas Turbine (GT) power plants have been represented as essential assets of energy units because of their numerous advantages compared to conventional coal power plants. However, their low thermal efficiency may make the continuous baseload operations a lossmaking alternative and threaten to continue. This fact is raising the importance of performing thermodynamic investigation according to the current operations’ conditions. This paper aims to conduct a thermodynamic investigation for two Siemens V94.2 gas turbine (GT) units based on current operations’ conditions. The reason for selecting these units is because they are operating at a much lower thermal efficiency than the designed thermal efficiency, and due to the age factor, the GTs are not suitable for major retrofitting due to poor return on investments. A numerical model is designed to simulate the overall thermodynamic process in the gas turbine using MATLAB SIMULINK.The obtained numerical results are validated by comparing them with the operational data collected from the stations. The thermal efficiency is increased by 30%, with a maximum output power equal to 140MW. The power output had decreased by 0.2% when the ambient temperature was increased by about 6.0 oC. A graphical optimization, where various conditions are plotted as graphs, is also carried out to achieve the maximum thermal efficiency and power output. Finally, a number of recommendations are made to address decreased thermal efficiency and output power.

Improving the performance of a nanofluid-based photovoltaic thermal module utilizing dual-axis solar tracker system: Experimental examination and thermodynamic analysis

• A PVT module integrated with a novel solar tracker system (STS) was built. • This STS has two intermittent on/off switching motors for azimuth and tilt angles. • Various coolants and tracking modes were compared using thermodynamic equations. • Results were compared from energy, exergy, and entropy generation viewpoints. • PVT module with STS had 268.24/20.8 W energy/exergy rate higher than fixed PV unit. The purpose of this experimental research is to improve the electrical and thermal output power of a photovoltaic thermal (PVT) module equipped with an automatic dual-axis solar tracker system. The focus of this study is on characterizing the performance of a PV unit and a PVT module both with three different modes of fixed, one-axis tracking, and dual-axis tracking. These modules were installed at the rooftop of the engineering faculty building of Ferdowsi University of Mashhad, Iran. The test fluids are deionized water and silicon carbide nanofluid (SiC/water) with 0.5% and 1% mass fractions. The experiments are executed on non-cloudy days with stable weather conditions during September. The thermodynamic analysis is carried out in terms of energy, exergy, and entropy generation to identify and compare the performance of various modules considered in the experiments. It is found that the proposed nanofluid-based PVT module integrated with the solar tracker system has no significant inverse effect on electrical efficiency thanks to using intermittent on/off switching electro-motors. The results showed that considering the power consumption of the pump and tracking electro-motors when nanofluid-based PVT module (SiC/water 1%) with dual-axis, one-axis, and fixed modes are utilized, the increases in the obtained overall energy (exergy) rates compared to that of the fixed PV unit are 268.24 (20.8 W), 245.91 (16.51 W), and 210.32 (9.64 W), respectively.

Experimental investigation on performance of hydrogen additions in natural gas combustion combined with CO2

Natural gas with H2 is widely used for lean-burn combustion, which leads to NOx emission as the main problem for it. For decreasing NOx emission and increasing thermal efficiency, the investigation on seeking the influence of H2 fractions on the mixture of CH4 and CO2 was conducted. Firstly, the ignition timing was decided through thermal efficiency and brake mean effective pressure (BMEP) for CH4 only. Then, combustion characteristics of CH4, CH4+CO2 and CH4+CO2+H2 were compared with volume percentage of H2 changing from 5% to 30%. Finally, the H2 injection strategy was checked between closed and open valve injections. Among these discussions, thermal efficiency, power output, BMEP and fuel consumption were evaluated. Results show that CO2 addition decreases power output and BMEP, leading to much more fuel consumption and lower thermal efficiency. When H2 is added, at the rich mixture conditions (λ＜1.0), power output and thermal efficiency decrease sharply as the mixture is enriched. However, at the lean-burn conditions (λ＞1.0), the decrease in flow rate of lower heating value (LHV) and increase in power output finally result in the higher efficiency with H2 addition. Moreover, when λ＞1.0, both low fuel consumption and high efficiency can be obtained with H2 addition to achieve the high BMEP. Furthermore, the open valve injection could obtain higher thermal efficiency, power output and BMEP with lower fuel consumption, suggesting that the H2 injection strategy should be well controlled with the ignition timing.

Model predictive control based on deep learning for solar parabolic-trough plants

In solar parabolic-trough plants, the use of Model Predictive Control (MPC) increases the output thermal power. However, MPC has the disadvantage of a high computational demand that hinders its application to some processes. This work proposes using artificial neural networks to approximate the optimal flow rate given by an MPC controller to decrease the computational load drastically to a 3% of the MPC computation time. The neural networks have been trained using a 30-day synthetic dataset of a collector field controlled by MPC. The use of a different number of measurements as inputs to the network has been analyzed. The results show that the neural network controllers provide practically the same mean power as the MPC controller with differences under 0.02 kW for most neural networks, less abrupt changes at the output and slight violations of the constraints. Moreover, the proposed neural networks perform well, even using a low number of sensors and predictions, decreasing the number of neural network inputs to 10% of the original size.

Assessment of Electrical and Thermal Performance of Photovoltaic Thermal Air Collector in the Climate of Pantnagar, Uttarakhand

The photovoltaic thermal collector (PVT) produces electricity and extracts heat from a common area exposed to solar radiation. The present work provides a methodology to assess the potential of PVT at any location. The climate of Pantnagar (a town situated in the Terai belt of Uttarakhand) is selected for the study. An unglazed PVT air heating collector is modelled, taking account of both electrical and thermal aspects of design. The performance of the collector is then simulated on four days, representing average weather of four seasons observed in North Indian Plains, in correspondence with the typical meteorological year (TMY) data of 2006-2015 for the location. The diode parameters and characteristic curves of PV module selected for PVT are obtained for reference and operating conditions. The operating temperature of solar cell and heated air are plotted after convergence of numerical solution at available data points. Finally, electrical and thermal power output of the PVT with associated optical and thermal losses are obtained. The highest electrical power output of 223 W (136 W/m2) is observed at 12:20 hours (IST) on equinox of September while highest thermal power output of 411 W (251 W/m2) is obtained at 12:20 hours (IST) on summer solstice.

Impacts of carbon trading and wind power integration on carbon emission in the power dispatching process

Currently, many low-carbon approaches are being applied in the power dispatching process, such as dynamic economic emission dispatch (DEED), wind power integration and carbon trading. Furthermore, these approaches may influence the carbon emission from electricity. To investigate such joint influence, this paper firstly builds a stochastic DEED model in the forms of chance-constrained programming related to wind power uncertainties. After that, the established model is transformed to a deterministic form by discussing relevant statistical characteristics. Next, an auxiliary decision-making method is designed to draw the optimal dispatching solution upon real-time price of carbon trading. Finally, empirical analysis shows that: (1) the minimization of carbon emissions and fuel costs comes at the expense of the reliability of wind power integrated system, for reasons that the decrement rate of thermal power output is about 60.8% from higher reliability level to lower level, (2) the decrement rate of carbon emissions (0.01%–0.012%) is superior to the growth rate of fuel costs (0.0011%–0.0022%) as the carbon trading price increases, which proves that carbon emission reduction can be effectively realized by carbon trading rather than substantial increase in fuel costs, and (3) carbon trading is conducive to the improvement of carbon emission efficiency.