Dynamic modeling and characteristic analysis of natural gas network with hydrogen injections

With the transformation of energy structure, the proportion of renewable energy in the power grid continues to increase. However, the power grid's capacity to absorb renewable is limited. In view of this, converting the excess renewable energy into hydrogen and injecting it into natural gas network for transportation can not only increase the absorption capacity of renewable energy but also reduce the transportation cost of hydrogen. While this can lead to the problem that hydrogen injection will make the dynamic characteristics of the pipeline more complicated, and hydrogen embrittlement of pipeline may occur. It is of great significance to simulate the dynamic characteristics of gas pipeline with hydrogen injection, especially the hydrogen mixture ratio. In this paper, the cell segmentation method is used to solve each natural gas pipeline model, the gas components are recalculated in each cell and the parameters of partial differential equation are updated. Additionally, the dynamic simulation model of natural gas network with hydrogen injections is established. Simulation results show that for a single pipeline, when the inlet hydrogen ratio changes, whether or not hydrogen injection has little influence on the pressure and flow. The propagation speed of hydrogen concentration is far less than that of the pressure and flow rate, and it takes about 1.2 × 10⁵ s for the 100 km pipeline hydrogen ratio to reach the steady state again.     

Dynamic modeling and controllability analysis of an ethanol reformer for fuel cell application

This work presents a controllability analysis of a low temperature ethanol reformer based on a cobalt catalyst for fuel cell application. The study is based on a non-linear dynamic model of a reformer which operates in three separate stages: ethanol dehydrogenation to acetaldehyde and hydrogen, acetaldehyde steam reforming, and water–gas-shift reaction. The controllability analysis is focused on the rapid dynamics due to mass balances and is based on a linearization of the complex non-linear model of the reformer. RGA, CN and MRI analysis tools are applied to the linear model suggesting that a good performance can be obtained with decentralized control for frequencies up to 0.1 rad s⁻¹.     

Dynamic similarity in solar chimney modeling

Dimensionless variables are proposed to guide the experimental study of flow in a small-scale solar chimney: a solar power plant for generating electricity. Water and air are the two working fluids chosen for the modeling study. Computational fluid dynamics (CFD) methodology is employed to obtain results that are used to prove the similarity of the proposed dimensionless variables. The study shows that air is more suitable than water to be the working fluid in a small-scale solar chimney model. Analyses of the results from CFD show that the models are dynamically similar to the prototype as suggested by the proposed dimensionless variables.     

Dynamic modeling of a methanol reformer—PEMFC stack system for analysis and design

Considerable effort has been devoted to the modeling of proton exchange membrane fuel cells (PEMFCs) as well as fuel processing units (FPUs). Many of these models consider only steady state analysis; the available dynamic models typically operate only in simple open loop configurations. However, a liquid fuel processor/PEMFC stack power unit for vehicular application will require tight integration and regulation of multiple units in order to function economically and reliably. Moreover, vehicular operation is inherently dynamic in nature, so traditional steady state process design approaches will be of limited value.This work addresses a minimum set of subcomponents necessary for modeling an overall vehicular power system. Additionally, the integration and control of these sub-units is addressed so that the unit can be operated as needed in a vehicular application by following a reference power trajectory. A number of design and operational parameters can be adjusted and the impact on system performance studied. Based on this preliminary analysis, heuristics are developed for optimal operation and design.     

Dynamic modeling and control of plate heat exchanger

A general model has been developed to suggest the transient responses of a plate heat exchanger. The predicted and experimental step responses of the system have been analyzed using the frequency response analysis. The results indicate that the system is represented by a first order lag and dead time. A closed fit between the simulated and experimental data has been obtained.To verify the presented model, temperature control has been applied on the plate heat exchanger using both conventional and fuzzy logic controllers. Results show that the performance of the fuzzy logic controller produces transient responses with less settling time and less oscillatory behavior compared to that under the conventional controller. Comparisons between simulated and experimental responses indicate that the developed model is capable of predicting the transient responses of the plate heat exchanger, satisfactory.     

Dynamic behavior and modeling of prismatic lithium-ion battery

The inevitable vehicle collision has made the safety of lithium-ion battery (LIB) carried by electric vehicles (EVs) a problem that restricts the further and large-scale promotion of EVs. Therefore, establishing the numerical mechanics model of LIBs and studying their mechanical integrity are imperative. In this study, we design indentation, compression, and drop-weight experiments for prismatic LIBs (PLIBs). Mechanical integrity and internal short circuit are analyzed in consideration of state of charge (SOC) and dynamic effects. A homogeneous PLIB model that considers anisotropic property, SOC, and dynamic effects is developed for the first time for application in different loading conditions. After its effectiveness is validated, the affecting parameters (ie, SOC and impact velocity) of the mechanical behaviors during dynamic loadings are investigated using the established model. The results show that strain rate effect and SOC state have impact on the mechanical properties of PLIB. However, the strain rate effect has much larger influence than the SOC state. Results may shed lights on the safety design of PLIBs in a mechanical aspect.     

Dynamic modeling and analysis of a shell-and-tube type gas-to-gas membrane humidifier for PEM fuel cell applications

A gas-to-gas humidifier using membranes is the preferred technology for external humidification of fuel cell reactant gases in mobile applications because no extra power supply is required and there are no moving parts. In particular, a shell and tube structure is compact, which allows its easier integration in a fuel cell vehicle.

This paper proposes a mathematical model for the humidifier using the principles of thermodynamics, including analysis of heat and mass transfer and of static and dynamic behaviors. Firstly, the heat and mass transfer behavior was simulated and the results compared with the experimental data. Secondly, the model was used to investigate the sensitivity of the geometric parameters and the effects of various operating conditions on performance. Finally, step responses of the humidifier at various flow rates were analyzed.     

Dynamic modeling and analysis of a 20-cell PEM fuel cell stack considering temperature and two-phase effects

Dynamic characteristics and performance of a PEM fuel cell stack are crucial factors to ensure safe, effective and efficient operation. In particular, water and heat at varying loads are important factors that directly influence the stack performance and reliability. Herein, we present a new dynamic model that considers temperature and two-phase effects and analyze these effects on the characteristics of a stack.     

Dynamic modeling and simulation of a palm wastes boiler

A state-space dynamic model for a palm wastes boiler is being developed and simulated. The unique feature of this boiler is that it uses wastes in the form of fiber and shell from the palm oil processing as its fuels. Specific characteristics of oil palm waste boilers are non-uniform fuel feed, compositions, sizes and moisture content of the fuel. These features introduce additional dimensions to the difficulty of boiler control. The superheated steam produced is used to generate electricity, which drives numerous motors and other equipment for palm fruit processing thus causing severe interactions between the power plant and other parts of the mill. The main work of this paper is the development of a dynamic model and simulation of the boiler. The boiler unit can be divided into several sections for analysis viz., the furnace, superheater, drum, risers, and downcomer. A tenth-order, physical, linearized process model was developed. The linearized model consists of ten first-order simultaneous equations and is represented by a (10 x 10) state matrix and (4 x 10) input matrix in the state space form.     

Dynamic modeling and dynamic responses of grid-connected fuel cell

The active distribution network (ADN) is a new effective approach to facilitate connecting distributed generation (DG) to the network, where the DG is controlled to support the system stability during various kinds of disturbances. Fuel cell is one of the most important DGs, however there are still many issues left to be solved in order to meet the requirements of the ADN, such as dynamic modeling, dynamic responses to power systems, especially during voltage dip, system fault, etc. In the existing grid-connected fuel cell researches, most of the dynamic models did not consider air compressor and its parasitic power consumption. Hence, a dynamic model of grid-connected proton exchange membrane fuel cell (PEMFC) is presented by considering dynamic modeling of the air compressor and its parasitic power consumption. Based on the model, the mutual influences between power system and fuel cell are analyzed when the fuel cell is synchronously grid-connected. The dynamic responses of the fuel cell and its low voltage and fault ride-through capability are studied when the power system fault or voltage dip occurs. Finally, based on the dynamic simulation of the typical power systems with a PEMFC, the theoretical basis and guiding suggestions are presented for grid-connection, dynamic operation, and off-grid of fuel cells.     

Dynamic system modeling of thermally-integrated concentrated PV-electrolysis

Understanding the dynamic response of a solar fuel processing system utilizing concentrated solar radiation and made of a thermally-integrated photovoltaic (PV) and water electrolyzer (EC) is important for the design, development and implementation of this technology. A detailed dynamic non-linear process model is introduced for the fundamental system components (i.e. PV, EC, pump etc.) in order to investigate the coupled system behavior and performance synergy notably arising from the thermal integration. The nominal hydrogen production power is ～2 kW at a hydrogen system efficiency of 16–21% considering a high performance triple junction III-V PV module and a proton exchange membrane EC. The device operating point relative to the maximum power point of the PV was shown to have a differing influence on the system performance when subject to temperature changes. The non-linear coupled behavior was characterised in response to step changes in water flowrate and solar irradiance and hysteresis of the current-voltage operating point was demonstrated. Whilst the system responds thermally to changes in operating conditions in the range of 0.5–2 min which leads to advantageously short start-up times, a number of control challenges are identified such as the impact of pump failure, electrical PV-EC disconnection, and the potentially damaging accentuated temperature rise at lower water flowrates. Finally, the simulation of co-generation of heat and hydrogen for various operating conditions demonstrates the significant potential for system efficiency enhancements and the required development of control strategies for demand matching is discussed.     

Dynamic tank in series modeling of direct internal reforming SOFC

A dynamic tank in series reactor model of a direct internally reforming solid oxide fuel cell is presented and validated using experimental data as well as a computational fluid dynamics (CFD) model for the spatial profiles. The effect of the flow distribution pattern at the inlet manifold on the cell performance is studied with this model. The tank in series reactor model provides a reasonable understanding of the spatio‐temporal distribution of the key parameters at a much lesser computational cost when compared to CFD methods. The predicted V–I curves agree well with the experimental data at different inlet flows and temperatures, with a difference of less than ±1.5%. In addition, comparison of the steady‐state results with two‐dimensional contours from a CFD model demonstrates the success of the adopted approach of adjusting the flow distribution pattern at the inlet boundaries of different continuous stirred tank reactor compartments. The spatial variation of the temperature of the PEN structure is captured along with the distributions of the current density and the anode activation over‐potential that strongly related to the temperature as well as the species molar fractions. It is found that, under the influence of the flow distribution pattern and reaction rates, the dynamic responses to step changes in voltage (from 0.819 to 0.84 V), fuel flow (15%) and temperature changes (30 °C), on anode side and on cathode side, highly depend on the spatial locations in the cell. In general, the inlet points attain steady state rapidly compared to other regions. Copyright © 2017 John Wiley & Sons, Ltd.     

Dynamic modeling and simulation of air-breathing proton exchange membrane fuel cell

Small fuel cells have shown excellent potential as alternative energy sources for portable applications. One of the most promising fuel cell technologies for portable applications is air-breathing fuel cells. In this paper, a dynamic model of an air-breathing PEM fuel cell (AB-PEMFC) system is presented. The analytical modeling and simulation of the air-breathing PEM fuel cell system are verified using Matlab, Simulink and SimPowerSystems Blockset. To show the effectiveness of the proposed AB-PEMFC model, two case studies are carried out using the Matlab software package. In the first case study, the dynamic behavior of the proposed AB-PEMFC system is compared with that of a planar air-breathing PEM fuel cell model. In the second case study, the validation of the air-breathing PEM fuel cell-based power source is carried out for the portable application. Test results show that the proposed AB-PEMFC system can be considered as a viable alternative energy sources for portable applications.     

Dynamic analysis and control of a solar power plant—I Dynamic analysis and operation criteria

The paper (splitted in two parts) describes the main results of the study concerning dynamic analysis and control of the EEC solar power plant, coupled to the grind for the first time in April 1981.High temperature solar energy systems require quite sophisticated receivers, able to work with considerable radiation flux, and well designed and controlled steam generators, to meet the severe constraints imposed by the turbine on the produced steam quality.In the case of the EEC solar power plant using a water cooled solar receiver, receiver and steam generator are, actually, the same component, which indeed is subject to a number of stringent somewhat conflicting requirements, concerning, in particular, its transient behavior.This latter aspect plays a fundamental role in view of the environmental conditions, i.e. of the irregularity of the power source due, for instance, to passing of clouds.In this Part I of the work, it is shown how a carefull dynamic analysis of the process is necessary for the verification and the assessment of the receiver design, the precise formulation of the plant operation procedures and safety conditions, the specification of the control system requirements. In particular, it is recognized that such kinds of processes can be adequately simulately by means of accurate partial derivatives models, based on suitable simulation codes.     

Dynamic modeling of the environment in a naturally ventilated, fog-cooled greenhouse

A dynamic simulation model for heat and water vapor transfer in a naturally ventilated, fog-cooled greenhouse was developed to predict the temperatures of air, plant, cover and floor surface and the relative humidity in the greenhouse. Transpiration and evaporation were also predicted. An experiment was conducted on a hot summer day (Aug. 9, 2004) in the Tokyo area to measure the environments inside and outside a glass-covered greenhouse with a floor area of 26 m². The greenhouse was cooled intermittently by spraying water fog at a constant rate of 0.01 kg s⁻¹ for different fogging and interval times (0.5 min on followed by 1.5 min off; 1 min on–3 min off and 1.5 min on–4.5 min off). The system of equations of the model was solved numerically by using the predictor–corrector technique for the differential equations and the iteration procedure for the algebraic equation. The input parameters to the model were the meteorological conditions and the thermo-physical properties of the greenhouse cover, plant, air and soil. The predicted results using the present model were compared with the measured values and showed a good agreement at different fogging and interval times.     

Mathematical dynamic modeling and thermal-hydraulic analysis of HANARO

This paper describes the development of a dynamic model of HANARO (High-Flux Advanced Neutron Application Reactor), an open tank in pool type research reactor. The reliable dynamic model of the reactor and its cooling systems is developed to perform the thermal-hydraulic analysis for transients. The developed dynamic model is properly implemented in the transient simulation code, H-SIM, which is compiled and executed on a personal computer (PC) using the DESIRE simulation language. The H-SIM is intended for simulating efficiently the operational characteristics and the thermal-hydraulic behavior of HANARO for many transients. The simulation for HANARO transients shows a proper thermal-hydraulic behavior trend for the power step change. Results from the H-SIM with reference calculations are found in general to be very encouraging and the dynamic model is judged to be versatile to fulfill its intended purpose.     

Dynamic modeling of a solar hydrogen system under leakage conditions

Dynamic behaviors of an integrated solar hydrogen system have been modeled mathematically, which is based on a combination of fundamental theories of thermodynamics, mass transfer, fluid dynamics, and empirical electrochemical relationships. The model considers solar hydrogen system to be composed of three subsystems, i.e., solar cells, an electrolyzer, and a hydrogen tank. An additional pressure switch model is presented to visualize the hydrogen storage dynamics under a leakage condition. Validation of the solar hydrogen model system is evaluated according to the measured data from the manufacturer's data. Then, the overall was simulated by using solar irradiation as the primary energy input and hydrogen as energy storage for one-day operation. Finally, electrical characteristics and efficiencies of each subsystem as well as the entire system are presented and discussed.