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[Display omitted] • Nonlinear dynamic model of a green ammonia synthesis system is developed. • Start-up of H 2 and N 2 subsystems and warm start-up of ammonia reactor are studied. • System dynamic responses under fluctuations of renewable energy are also analyzed. • Bed temperature, H 2 /N 2 ratio and pressure are well maintained by PID controllers. • Buffer tank decreases the reactor variation and is important for pressure control. Green ammonia production system driven by renewable electricity will be under frequent dynamic operation due to the fluctuation of renewable energy. The nonlinear dynamic model of a green ammonia synthesis system is developed and the dynamic responses of PEM (proton exchange membrane) electrolysis subsystem, PSA (Pressure swing adsorption) subsystem and ammonia synthesis subsystem during the start-up process and under the fluctuation of renewable electrical current are analyzed. The start-up dynamic results show that the hydrogen production rate of PEM electrolysis system is positively correlated to the current. The nitrogen output of PSA system is affected by the adsorption time, adsorption pressure, bed length, and air velocity. A start-up period of 300 min from the warmed-up state to the design state can maintain the temperature rise rate of the ammonia synthesis reactor at approximately 40 K/h. The dynamic results under step fluctuations of electrical current show that the PEM electrolysis subsystem and the PSA subsystem response fast compared to the ammonia synthesis reactor and buffer tanks. Using large buffer tanks to smooth the fluctuation allows the system to slide with the variation of renewable current to some extent, resulting in a higher outlet ammonia fraction when the current increases. Different volume ratios of the hydrogen tank to the nitrogen tank volume can lead to different variations of the hydrogen/nitrogen ratio. PID controllers can effectively maintain the bed temperatures, hydrogen/nitrogen ratio, and pressure of the ammonia synthesis reactor at their set points despite fluctuations in renewable electrical current. Buffer tanks are necessary to compensate for the imbalance between the flow rate fluctuation caused by current change and the flow rate regulation caused by PID controllers. [ABSTRACT FROM AUTHOR]

• It is the basis for integrated energy system scheduling based on flow-regulation. • A hydraulic-thermal coupling dynamic model for heating network is proposed. • The modified forward–backward iteration is proposed for model calculation. • The exact hydraulic and thermal dynamic processes of heating network are obtained. • A data-driven hydraulic-thermal dynamic model is proposed for fast calculation. The district heating is expected to play a crucial role in the decarbonization of integrated energy systems within the context of attaining carbon neutrality. The literature review reveals a research gap in the investigation of models that account for the hydraulic-thermal coupling dynamic characteristics of heating networks in integrated energy systems, particularly those based on the flow-regulation mode. This discrepancy may affect the safety of the heating networks and contribute to the inefficient scheduling of integrated energy systems, which motivates this study. In this study, it refutes the harsh hypotheses in previous studies, making it more closely related to the real hydraulic and thermal conditions of heating networks. A mechanism-driven model is proposed, which involves the coupled hydraulic and thermal dynamic characteristics of heating networks. The modified forward–backward iteration as a calculation method is carried out, which is embedded with the method of characteristic and upwind difference. A data-driven hydraulic-thermal dynamic model is proposed for fast calculations. For model validation and case analysis, three heating networks in the integrated energy systems are utilized. The simulation results indicate that 1) The hydraulic and thermal average relative errors between the measured data and the simulation results are 0.396% and 0.091%, respectively, validating the effectiveness of the proposed dynamic mechanism model; 2) Compared to the current quasi-dynamic model, the proposed dynamic mechanism model could reflect the characteristics of heating networks more accurately and simulates the dynamic processes with higher resolution. These results demonstrate that the fluctuations of water head and pipe flow can reach 61.24 ∼ 237.53 m and −4.26 ∼ 32.16 kg/s, respectively. The average temperature difference between the two models is around 0.264 °C; 3) Compared to the forward–backward iteration, the modified forward–backward iteration has a superior convergence performance and calculation accuracy; 4) Compared to the quasi-dynamic model, the proposed data-driven model increases the overall accuracy of hydraulic-thermal calculations and significantly reduces the amount of time required. The average calculation time of the data-driven model is 0.0349 s, while those of the quasi-dynamic model and the proposed mechanism model are 352.92 s and 624.13 s, respectively. In conclusion, the proposed mechanism model of hydraulic-thermal coupling calculation and the related data-driven model are suitable for the dynamic simulations of heating networks in integrated energy systems. [ABSTRACT FROM AUTHOR]

The dynamic model of a poly-generation system based on a biogas-fed solid oxide fuel cell (SOFC) plant is presented in this paper. The poly-generation plant was developed in the framework of the FP7 EU-funded project SOFCOM ( www.sofcom.eu ), which consists of a fuel-cell based polygeneration plant with CO 2 capture and re-use. CO 2 is recovered from the anode exhaust of the SOFC (after oxy-combustion, cooling and water condensation) and the Carbon is fixed in the form of micro-algae in a tubular photobioreactor. This work focuses on the dynamic operation of the SOFC module running on steam-reformed biogas. Both steady state and dynamic operation of the fuel cell stack and the related Balance-of-Plant (BoP) has been modeled in order to simulate the thermal behavior and performance of the system. The model was validated against experimental data gathered during the operation of the SOFCOM proof-of-concept showing good agreement with the experimental data. The validated model has been used to investigate further on the harsh off-design operation of the proof-of-concept. Simulation results provide guidelines for an improved design of the control system of the plant, highlighting the feasible operating region under safe conditions and means to maximize the overall system efficiency. [ABSTRACT FROM AUTHOR]

This paper presents new approach for determining buildings technical system energy performance. This new methodology describes a mathematical model for accurately predicting indoor temperature and heat losses of the space heating and domestic hot water system components. The entire model is described by system of ordinary differential equations which can be solved using standard numerical techniques. The innovative aspect of the method is the integral approach in mathematical modeling of buildings energy needs and technical systems heat loss, taking into account heat accumulation in all considered parts (building envelope + technical system). Such approach allows a detailed insight of the system behavior for chosen working conditions. This model can serve for energy performance calculations in a wide variety of buildings types and their technical systems. The calculation example is given for family house, equipped with conventional space heating and domestic hot water heating system, with the time step of 1 min and for characteristic day of each month within a year. The results are compared against those obtain from EN ISO 13790 and standard series EN 15316. The comparison shows significant differences in determination of the annual delivered energy to the heating system (33%), as a consequence of difference in estimation of the energy need for heating (15%) and calculation of the technical systems recoverable heat losses utilization factor, which seems to be underestimated. The delivered energy to the space heating and domestic hot water heating system differs 25%, while the energy delivered to the generation system differs 4%. [ABSTRACT FROM AUTHOR]

The energy markets deregulation coupled with the rapid spread of unpredictable energy sources power units are stressing the necessity of improving traditional power plants flexibility. Cyclic operation guarantees high profits in the short term but, in the medium-long time, cause a lifetime reduction due to thermo-mechanical fatigue, creep and corrosion. In this context, Combined Cycle Power Plants are the most concerned in flexible operation problems. For this reason, two research groups from two Italian universities have developed a procedure to estimate the devices lifetime reduction with a particular focus on steam drums and superheaters/reheaters. To assess the lifetime reduction, it is essential to predict the thermodynamic variables trend in order to describe the plant behaviour. Therefore, the core of the procedure is the power plant dynamic model. At this purpose, in this paper, three different dynamic models of the same single pressure Combined Cycle Gas Turbine are presented. The models have been built using three different approaches and are used to simulate plant behaviour under real operating conditions. Despite these differences, the thermodynamic parameters time profiles are in good accordance as presented in the paper. At last, an evaluation of the drum lifetime reduction is performed. [ABSTRACT FROM AUTHOR]

The deregulated energy market and the increasing quota of electrical capacity covered by non-predictable renewable sources require strongly irregular and discontinuous operation of thermoelectric plants to satisfy users demand and compensate the variability of renewable sources. As a consequence, due to thermo-mechanical fatigue, creep and corrosion, a lifetime reduction of the most critical components occurs. The availability of a procedure able to predict the residual life of plant devices is necessary to assist the management decisions about power plants’ operation and maintenance scheduling. The first step of this procedure is the capability of simulating the plant behaviour versus time by evaluating the trends of the main thermodynamic parameters that describe the plant operation during different transient periods. In this context, the main contribution of the present paper is to propose a complete procedure able to simulate the plant dynamic behaviour and estimate the residual life reduction of some components. Indeed, two different models, developed by two different research groups, of the same single pressure heat recovery steam generator unit are presented and utilized to characterize the dynamic behaviour of the above mentioned power plant. The main thermodynamic variables during different transient operation conditions are predicted and good correspondence between the two methods is obtained. It can be also noted that, when the geometry and size of the devices are considered, the thermal inertia related to heat exchangers tubes, pipes and other physical masses causes a delay in the system response. Moreover, a residual life estimation of the most stressed component is presented. [ABSTRACT FROM AUTHOR]

Highlights: [•] A novel dynamic model for thermocline thermal energy storage systems is presented. [•] Adaptive grid technique used. [•] Accuracy is improved while using an order of magnitude fewer states and equations. [•] Effects of numerical diffusion are minimized. [•] Model more accurate under temperature (and density) inversion. [ABSTRACT FROM AUTHOR]

• The system analysis program for the 5 MW Small Modular Supercritical CO 2 Brayton-Cycle Reactor System is established and validated. • When the reactor power decreases, the power decrease percentage of the regenerator is the largest and the heat transfer may deteriorate. • At the case of the reactor rod ejection accident, the reactor system is with the good ability of the negative feedback regulation and certain self-stability. • When the temperature of cooling water only increases by 1 °C, the system output power can reduce about 10%. Ensuring the sufficient cooling capacity of the cooler is significant. • The compressor is more sensitive to the input parameter disturbance caused by the reactor and cooler. Small nuclear reactor system (SMR) has good development prospect in energy supply because of its flexible arrangement, wide application, and low cost. Among many small nuclear reactor systems, the Brayton cycle reactor system with supercritical CO 2 (SCO 2) as a working medium stands out. It has the advantages of high conversion efficiency, simple design, compact structure, high inherent safety, and is suitable for almost all nuclear power systems, especially small modular reactors (SMR). However, due to the unique thermophysical properties of SCO 2 , the transient operation characteristics of the system and the coupling effect between the main equipment are not precise. In this study, a dynamic model of the 5 MW modular SCO 2 Brayton cycle reactor system was established, and the system's dynamic operation characteristics and off-design control strategy were evaluated. Firstly, the steady-state simulation of the system is carried out to verify the physical model of the main equipment. Secondly, the typical transient operating conditions such as the reactor power fluctuation, reactor reactivity insertion, cooling water flow rate and temperature fluctuation, and loss of the external load are calculated. The dynamic characteristics of the system and the coupling effect between the main equipment are analyzed. The simulation results show that the control system is with good control effect and regulation ability under the condition of the reactor control rod ejection accident. The system is quite sensitive to the change of the cooling water temperature and flow rate. When the external load is lost, the turbine bypass control method can quickly match the system output power and keep the rotor speed reasonably. The dynamic modeling of the system is beneficial for the analysis of the operation characteristics and control effect of the system under variable conditions. It can provide the basis for the design, evaluation, and control strategy formulation of the system. [ABSTRACT FROM AUTHOR]

• Development of a plug-flow model for dynamic thermal behaviour of district heating. • Comprehensive study of a district heating supplied by combined heat and power plant. • Optimization of the pipes network diameter of the entire district heating. • Parametric analysis for the economic optimization of the entire system power plant. • Energy savings (11.7 GWh/y), and avoided carbon dioxide (16.1 kt CO2 /y) This paper presents a novel dynamic simulation tool able to assess and optimize the energy, environmental and economic performance of standard and innovative district heating/cooling systems. To this aim, several design and operating parameters (e.g.: weather conditions, heat selling price for users, national unitary price of electricity, etc.) are dynamically taken into account. The heating and cooling demands and loads of the buildings to be fed by the network working fluid are dynamically calculated. The system pipeline network is modelled through a suitable plug-flow approach. Fluid temperatures are calculated in each network node. The optimization of several system design and operating parameters is achieved for different objective functions. A suitable analysis is considered for selecting the most convenient urban zones for system application. The whole simulation model is implemented in a suitable computer code written in MatLab. By such tool useful design criteria and feasibility analyses can be obtained. To show the capabilities of the presented simulation tool, a novel case study, referred to a district heating system supplied by an existing thermoelectric power plant, was developed. The conducted analysis is based on system optimizations focused on the number of users, the selling heat/electricity prices and system geometric features. As for example, for minimizing the system payback to about 14.0 year, the optimal number of users and network length are 5 × 103 and 2.7 km, respectively. In this case the primary energy savings and the avoided carbon dioxide emissions are about 11.0 GWh/y and 16.1 kt CO2 /y, respectively. [ABSTRACT FROM AUTHOR]