Journal of Energy Engineering

$\mathrm{Low}\text{-}{\mathrm{NO}}_x$ combustion with deep air staging technology is commonly adopted to reduce ${\mathrm{NO}}_x$ emissions in coal-fired power plants. However, introducing deep air staging results in a strong-reducing atmosphere, which may cause high-temperature corrosion on the water-cooled wall. In general, alleviating the reducing atmosphere around the water-cooled wall is undoubtedly the lowest-cost and highest-efficiency technique. This study aims to investigate the influence of burner mass-flow rate bias and injection direction offset on high-temperature corrosion and combustion in a 660 MWe opposed wall-fired boiler. The results show that decreasing the load of burners close to the sidewalls can not only reduce the high-temperature zone and the CO and ${\mathrm{H}}_2\mathrm{S}$ concentrations near the sidewalls but also improve combustion characteristics by controlling ${\mathrm{NO}}_x$ emissions. Taking the high-temperature corrosion, combustion, and ${\mathrm{NO}}_x$ emissions into account, it is recommended to decrease the load of burners close to the sidewalls by 10%. In addition, as the burner injection direction offset increases from 0° to 7°, the high-temperature zone near the sidewalls enlarges slightly, but as the burner injection direction offset further increases from 7° to 10°, the high-temperature zone near the sidewalls increases significantly. Considering the high-temperature corrosion, combustion and ${\mathrm{NO}}_x$ emissions, 7° may be the optimal value of the burner injection direction offset angle and is applied to the actual retrofit. The actual industrial application shows that compared to that before the retrofit, the temperatures near the sidewalls change slightly after the retrofit, but the CO concentrations significantly decrease and the boiler efficiency increases from approximately 93.27% to 93.46%. After a long period of operation, good performance without high-temperature corrosion of the sidewalls is achieved.

Technologies for improving engine performance and fuel economy have proven effective and promising to reduce emissions. However, owing to the increased pressure and temperature of the mixture by the turbocharging system, one negative result is a higher risk of knocking. This is not conducive to the safety of the engine or a reduction in fuel consumption. Low-temperature combustion by a diluted mixture in the cylinder has been validated to effectively reduce the knock occurrence and ${\mathrm{NO}}_x$ emission. Because the ignition timing advances by suppressing the knock caused by the mixture dilution, the fuel economy could be improved in the spark-ignition (SI) turbocharged engines. In this study, the intake valve closing (IVC), exhaust valve closing (EVC), and exhaust gas recirculation (EGR) strategies as different dilution methods were applied to investigate their effects on combustion, emission, and fuel consumption. The experimental results showed that all these dilution methods were beneficial for decreasing the maximum burned gas temperature, thereby reducing emissions of ${\mathrm{NO}}_x$. The external EGR showed more benefits to suppress the knocking, and thus the reduced fuel consumption compared to the inner EGR (valve overlap). The external EGR method had showed larger effects on the combustion phase and fuel economy than IVC and EVC. In addition, the difference between the IVC and EVC was small when external EGR was added.

Thermal runaway is an essential problem to be solved urgently for electric vehicles, and the safety issues have attracted the attention of researchers. Proper thermal management systems can effectively reduce the surface temperature of battery pack and improve the uniformity of the temperature distribution, which can effectively prevent the occurrence of thermal runaway phenomenon. This paper takes the large-capacity square-shell lithium-ion battery as the research object, and conducts in-depth research on its heat production under different working conditions through simulation. A hybrid battery thermal management system based on heat pipes, microchannel liquid-cooled plates, and phase-change materials was established, and the thermal management performance under world light vehicle test cycle conditions was studied. The results indicated the temperature evolution of each battery tended to be consistent in the first 1,500 s. In the subsequent process, the discharge rate of the battery was positively correlated with the speed of the vehicle and therefore brings the corresponding temperature response. During world light vehicle test cycle, the maximum temperature difference of the lithium battery module was 3.5 K. At the end of the test, the average temperature difference of the lithium-ion battery module was 3.2 K.

Abstract

Reversible polymer electrolyte membrane (PEM) fuel cells have attracted significant research attention in the last decade due to the associated benefits. However, flow-field design of the bipolar end plates, among various other parameters, largely affects its performance. Thus, the present paper focuses on determining hydrogen storage capacity of a typical activated carbon (aC) electrode employed in a reversible modified PEM fuel cell with varied designs of flow-field. Three flow-field orientations—pin-type, parallel, and interdigitated—are used and their performance is evaluated. The fabrication method of the electrode, reversible modified PEM fuel cell, and different orientations of micro flow channels is disclosed. The characterization of the employed aC electrode is done using scanning electron microscopy (SEM), x-ray diffraction analysis (XRD), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). The fabricated cells are tested by linear voltage sweep and results are recorded. The result analysis revealed that the interdigitated flow-field design leads to better distribution of the reactants and encourages higher hydrogen adsorption in the carbon electrode compared to the other flow-field designs under consideration. The electrochemical hydrogen storage capacity of the carbon electrode with interdigitated flow-field design is found to be 1.47 weight percentage (wt. %), whereas for parallel and pin-type designs, it stands at 1.40 wt. % and 1.36 wt. %, respectively. The obtained energy storage density is comparable with the commercially available metal hydride based compressed hydrogen canisters. It is surely a step forward toward developing a reversible PEM fuel cell with enhanced performance capable of storing the charge, like a battery, with many potential applications.

Practical Applications

The presented work is a contribution toward the development of a commercially viable hydrogen fuel cell with potential applications in the automotive industry, farm machinery, defense industry, power sector, remote area power systems, etc.

Abstract

Distributed generation (DG) refers to small-scale generation resources that are located at or near end-consumers, such as photovoltaic (PV) solar systems. DG systems have become increasingly popular in recent years owing to their economic efficiency, reliability, and sustainability. However, the increasing adoption of DG is creating new obstacles for system operators due to the uncertainty in forecasting future demand. One concern is the possibility of facing a utility death spiral as a feedback loop between, on the one hand, the increasing adoption of DG and increasing electricity rates to cover generation and transmission overheads with, on the other hand, reduced demand from the grid. The goal of this study was to investigate the effects of the penetration of DG on the power infrastructure and wholesale power markets considering the dynamic pricing of electric power. To achieve that goal, a complex system-of-systems (SoS) simulation for wholesale power markets and infrastructure is developed using agent-based modeling (ABM), Optimal Power Flow (OPF), and reinforcement learning (RL). The simulation framework is enabled by (1) consumer behavior that compares the benefits of installing DG versus the costs of conventional power from the grid; and (2) the dynamic pricing of electric power. Several RL algorithms are compared, including basic RL, multiplicative RL, Roth-Erev RL, a modified Roth-Erev, and a variation of the aforementioned algorithms using a Gibbs-Boltzmann cooling factor by means of a grid of learning parameters relevant to each technique. The results show that (1) low-cost generators, such as nuclear power plants, are the least affected by the penetration of DG, while high-cost generators are the most affected, (2) a utility death spiral is unlikely to occur, and (3) a modified Roth-Erev RL algorithm can be used by generating companies to maximize their gross profits by optimizing their supply curves considering the feedback effect on DG adoption rates. Overall, the proposed simulation framework can assist policymakers and future researchers in studying the interaction between dynamic pricing in wholesale power markets and the adoption of DG. By simulating the long-term effect of DG on the electric power infrastructure and market, policymakers can introduce regulations and incentives to strategically influence the rate of adoption of DG.

Practical Applications

DG using PV systems has been growing in recent years. However, there are concerns that the increasing penetration of DG would start a feedback loop where the lower demand for power from the grid would push utilities and generating companies to increase electricity rates to maintain profits and cover overhead, which can again motivate consumers to install DG systems. To investigate that feedback loop, this study developed a model that simulates the interacting effect of consumer behavior to adopt DG and dynamic pricing by utility companies. The results show that low-cost generators, such as nuclear plants, would be the least affected. The results also show that the best economic decision for generating companies may be to keep electricity rates unchanged to avoid accelerating DG penetration. The framework presented in this research can be used to create simulations of wholesale power markets affected by DG, which can guide decisions related to DG regulations, consumer incentives, and future grid expansion plans.

Tight reservoirs are subsurface formations with extremely low permeability, in which a high resistance to flow can be expected while developing hydrocarbons. Typically, to obtain economic production rates from such reservoirs, multistage fractured horizontal wells (MFHWs) are necessary. During reservoir development, the mutual coupling effect between fluid flow and stress fields cannot be ignored. In this study, a discrete fracture model (DFM) was proposed to simultaneously simulate reservoir deformation and fluid flow behaviors. The finite-element method (FEM) was utilized to obtain the numerical solution for both pore pressure and strain. The numerical simulator was verified using a commercial software, and perfect agreement was obtained. The results indicate that the coupling of flow and geomechanics has important effects on the evolution of the physical parameters of the formation. Some petrophysical properties of tight reservoirs noticeably deteriorate in the early stage of production; for example, the conductivity of hydraulic fracturing can be reduced by up to 90%. The effect of secondary fractures (SFs) on productivity is significant in the early stage. Natural fractures (NFs) mainly increase productivity when the pressure front reaches them at a later stage. Moreover, the tight oil flow capacity can be enhanced by increasing the hydraulic fracture (HF) density, initial conductivity, and the angle between the HFs and SFs. This study shows that fractures impact productivity, considering the full coupling of the flow and geomechanics of MFHWs in tight oil reservoirs. This provides valuable information for the design of hydraulic fracturing and production development programs.