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This study describes a technique for automated and accurate inductance estimation in synchronous DC–DC buck and boost converters. The method of inductor value estimation is based on the dependence of the steady-state output voltage on the inductance value, in the case of a fixed inductor peak current. The measurement algorithm yields effective inductance value, and is aimed to be executed once during the start-up procedure under light load current condition. As the measurement is performed during the start-up sequence with low-load current, a dedicated current sensor with high accuracy can be employed, allowing to target high measurement accuracy in the range of ±5%. The presented technique is developed to enable the automated design of a digital controller for general purpose DC–DC converter but can be used in different applications such as analogue feedback-loop adjustment or improving the digital current estimator accuracy. [ABSTRACT FROM AUTHOR]

The fractional frequency transmission system (FFTS) can multiply increase transmission capacity by using a lower frequency to reduce the reactance of the AC transmission system. The modular multi-level matric converter (M^3C) as the new generation of the AC/AC converter is the critical equipment of FFTS. The self-start control strategy for M^3C-based FFTS is proposed and the whole start-up procedure is divided into the uncontrollable stage and controllable stage. The model of the equivalent circuit in an uncontrollable stage is built and the mathematical relation between the maximum charging current and the current-limit resistor is obtained. Finally, a digital simulation system of M^3C-based FFTS is established, and the effectiveness of the proposed control strategies is verified by simulation results.

The fractional frequency transmission system (FFTS) can multiply increase transmission capacity by using a lower frequency to reduce the reactance of the AC transmission system. The modular multi-level matric converter (M3C) as the new generation of the AC/AC converter is the critical equipment of FFTS. The self-start control strategy for M3C-based FFTS is proposed and the whole start-up procedure is divided into the uncontrollable stage and controllable stage. The model of the equivalent circuit in an uncontrollable stage is built and the mathematical relation between the maximum charging current and the current-limit resistor is obtained. Finally, a digital simulation system of M3C-based FFTS is established, and the effectiveness of the proposed control strategies is verified by simulation results. [ABSTRACT FROM AUTHOR]

In a simulated process control task, we investigated the effects of refresher training and acute social stress on performing a standard operating procedure (SOP) containing a production and monitoring task and knowledge recall after a retention interval of two weeks. In a 2 × 2 between-group design (Factor 1: induced social stress, Factor 2: refresher training), 76 engineering students performed an SOP at t1 in week 1 and at t2 in week 3. A MANOVA in week three (t2) indicated a main effect of the refresher training for the SOP execution containing a production and a monitoring task and an impairing effect of stress on the monitoring task. That means that after a retention interval, stress mainly affects the SOP's monitoring task. An additional correlational analysis showed that knowledge test performance is negatively associated with cortisol level and that retentivity is a strong predictor for knowledge test performance and production task performance, too. Practitioner Summary: We investigated effects of social stress and refresher training on performing a standard operating procedure (SOP) after a retention interval of two weeks. The impact of social stress reduced the monitoring task performance as part of the SOP, but not the production outcome. Without refresher training, performance is significantly worse. Abbreviation: SOP: Standard Operating Procedure; MANOVA: Multivariate Analysis of Variance; CSB: Chemical Safety and Hazard Investigation Board; TSST: Trierer Social Stress Test; P-TSST: Placebo Trierer Social Stress Test; WaTrSim: Water Treatment Simulation; HPA axis: hypothalamic pituitary adrenal axis; WIT-2: Wilde Intelligenztest – 2; SPSS: Statistical Package for the Social Sciences; ANOVA: Analysis of Variance. [ABSTRACT FROM AUTHOR]

The start-up procedure of wind turbines is one of the most complex operating conditions, which includes the dynamic changes of pitch angle decreasing, rotor speed increasing and generator grid-connected, and implies the complex evolution of attack of angle and aerodynamic load. Besides, the velocity and direction of the inflow have strong unsteadiness in the field, which makes the variation of the angle of attack more complex. To reveal the aerodynamic behaviors of the full-scale wind turbine in the start-up procedure, a field measurement campaign was conduct on a 100 kW wind turbine with blade angle of attack, aerodynamic pressure distribution and operating parameters measured in this paper. Aerodynamic power, lift and drag, angle of attack, lift coefficient and pressure distribution were analyzed. As results, the start-up procedure can be divided into free acceleration stage, fast acceleration stage, tip-speed ratio adjustment stage and normal operation stage. The normal forces of airfoils produce the main power to drive the turbine to accelerate in the acceleration stages. The standard deviation of angle of attack decreases continuously with the increase of rotor speed. The flow around the thick airfoil at the blade inner section presents a three-dimensional stall delay effect, and the effect is weakening with the increase of rotor speed. The results reveal the variation of angle of attack and aerodynamic load during the start-up process of a full-scale wind turbine in the field, and provide valuable field measured data for the validation of aerodynamic model. • AOA and aerodynamic load were measured on a 100-kw wind turbine in the field. • The evolutions of AOA and aerodynamic load in the start-up procedure were revealed. • It provides valuable and detailed field measured data for aerodynamic model validation. [ABSTRACT FROM AUTHOR]

The significance of dynamic simulation models for estimating the behaviour of combined cycle power plants is widely acknowledged. In part B of this study, the dynamic behaviour of a sub-critical three-pressure-stage heat recovery steam generator is numerically investigated, employing the process simulation tools Aspen Plus Dynamics and Apros. A wide set of measurement data from an existing power plant is applied to validate the generated dynamic models during warm start-up procedure. The numerical results follow qualitatively the transients during initial start-up phase and show good agreement during the post start-up phase. Furthermore, similar qualitative behaviour between both process simulation codes used is observed. The obtained results suggest that the dynamic simulation models are capable to reliably predict the system response to failure malfunctions and to modifications in design and control structures. The provided measurements are of high relevance for other researchers due to the fact that such detailed experimental data is proprietary and rarely published in scientific literature. [ABSTRACT FROM AUTHOR]

In part A of this study, investigations into the capability of different process simulation codes to predict the real behaviour of a combined cycle power plant during part loads and off-design operation are carried out. The combined cycle power plant with a sub-critical three-pressure-stage heat recovery steam generator is built using the process simulation software tools Aspen Plus Dynamics and Apros. The generated numerical models are validated against the measurements at different steady-state operation points, namely 100%, 80% and 60% loads. The numerical results obtained display a very good agreement towards the given data with a maximal relative error of about 5% for the pressure and less than 1% for the temperature and the mass flow rate. Furthermore, the validated models are also evaluated against the dynamic measurements during a transient operation for a time period of 400 min. Apros and Aspen Plus Dynamics models predict qualitatively the right developments of the plant parameters. However, the simulated results deviate quantitatively from the experimental data with a maximum relative error of about 10%. It can be concluded that the dynamic simulation models can represent accurately the real combined cycle power plant at different steady-state loads, while they can capture the plant behaviour during the off-design operation with less accuracy. [ABSTRACT FROM AUTHOR]

• Two-phase olive-mill waste and cattle manure were anaerobically co-digested. • Start-up and stabilization stages were studied in semicontinuous stirred tank reactor. • Propionic accumulation was the key factor in the methanogenic phase inhibition. • Total period of 140 days was required to start-up and stabilization the process. • During the stable period the methane productivity was 0.34 LCH 4 /L R d at 40-d HRT. In this work, the start-up and stabilization stages of mesophilic anaerobic co-digestion of 2POMW and CM in a semi-continuously fed stirred tank reactor (SSTR) were analyzed. Volatile fatty acids (VFAs) were monitored and used as the main control parameter for the start-up and stabilization stages, as well as to evaluate the potential inhibition episodes. The results showed that accumulation of propionic acid was the key factor in the inhibition of the methanogenic phase, leading to process imbalance. To avoid the problems associated with inhibition by high VFA concentrations, several reinoculations were performed using a suitable inoculum adapted to VFA degradation. The start-up phase was carried out in batch conditions for 97 days, reaching a final concentration of propionic acid of 12.77 mg/L. From that moment, the reactor was fed in a semi-continuous mode with a hydraulic retention time (HRT) of 40 days. A total period of 140 days was required to achieve a stable performance of the reactor with a methane productivity of 0.34 LCH 4 /L R d. [ABSTRACT FROM AUTHOR]

For large-scale SOFC power generation systems, a shorter start-up time of SOFC cell stacks with relatively large heat capacity is one of the most important technological issues to determine the flexibility in SOFC system operation. In this study, start-up procedures have been examined to shorten the start-up time period. The conventional heating procedure using pre-heated hot air and self-heating by SOFC operation at low temperatures had a difficulty to shorten the start-up time period because of the limitation in power generation at lower temperatures. In this study, as an alternative start-up procedure, catalytic combustion at the SOFC cathodes is, for the first time, demonstrated to be useful on the system level. The applicability of the catalytic combustion to shorten the start-up time period has been verified numerically as well as experimentally by using a large-scale cell stack cartridge. This unique start-up procedure enables to operate SOFC-based large-scale power generation systems. [ABSTRACT FROM AUTHOR]

Fuel cell systems based on liquid fuels are particularly suitable for auxiliary power generation due to the high energy density of the fuel and its easy storage. Together with industrial partners, Oel-Waerme-Institut is developing a 3 kW el PEM fuel cell system based on diesel steam reforming to be applied as an APU for caravans and yachts. The start-up time of a fuel cell APU is of crucial importance since a buffer battery has to supply electric power until the system is ready to take over. Therefore, the start-up time directly affects the battery capacity and consequently the system size, weight, and cost. In the presented work a novel start-up strategy for the steam reforming fuel processor is introduced. The new approach includes the reactive heating of WGS reactors by using reformate from oxidative steam reforming (OSR) instead of the sequential heating of the fuel processor. The start-up procedure is demonstrated on a 10 kW steam reformer and a parameter study is carried out. Subsequently, the new procedure is tested on the complete fuel processor. Here, the OSR operation starts after 15:20 min and provides reformate for reactive heating of the WGS reactors. Steam reforming operation can be started after 23:40 min, which is 9 min earlier than applying sequential heating of the fuel processor. Until SR operation, the total energy consumption sums up to up to 5.9 MJ fuel and 13 Ah (12 V) electric energy. [ABSTRACT FROM AUTHOR]

This work describes the development of a compact ethanol fuel processor for small scale high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) systems with 200–500 W electrical power output. Promising markets for reformer fuel cell systems based on ethanol are mobile or portable leisure and security power supply applications as well as small scale stationary off grid power supply and backup power. Main components of the fuel processor to be developed were the reformer reactor, the shift converter, a catalytic burner and heat exchangers. Development focused in particular on the homogeneous evaporation of the liquid reactants ethanol and water for the reformer and burner and on the development of an efficient and autarkic start-up method, respectively. Theoretical as well as experimental work has been carried out for all main components separately including for example catalyst screening and evaporator performance tests in a first project period. Afterwards all components have been assembled to a complete fuel processor which has been qualified with various operation parameter set-ups. A theoretically defined basic operation point could practically be confirmed. The overall start-up time to receive reformate gas with appropriate quality to feed an HT-PEMFC ( x CO < 2%) takes around 30 min. At steady state operation the hydrogen power output is around 900 W with H 2 and CO fractions of 41.2% and 1.5%, respectively. [ABSTRACT FROM AUTHOR]

A new high temperature heat pump using water as refrigerant has been designed and built for testing on a laboratory test bench that reproduces the operating conditions of real-case industrial applications. Experimental investigations of this heat pump were carried out in the condensing temperature range of 130–140 °C. A new dynamic model has also been developed using Modelica to take into account the presence of non-condensable gases and the purging mechanism. In addition, a new combined finite-volume and moving boundary method (FV-MB) approach is applied for the plate heat-exchanger models and a moving boundary (MB) approach between phases is implemented for the models of the purging and the flash evaporation systems. The start-up phase of this high-temperature heat recovery and heat enhancement of the heat pump are simulated experimentally and numerically. A comparison between both results is presented and analyzed. Global energy savings and the environmental benefits have been illustrated. [ABSTRACT FROM AUTHOR]

In process automation, skill decay has not been investigated systematically. In two experimental studies, refresher interventions (RIs) were compared to support skill and knowledge retention of a start-up procedure on a simulated process control task. Based on theories of proceduralisation, the ‘testing-effect' and mental practice, four different RIs were designed. In Study 1 (N = 68), two experimental groups (EGs) received either an RI called ‘Practice' or an RI called ‘Skill Demonstration'. Both RIs support skill retention, but the Skill Demonstration-RI performed with a higher mental workload. In Study 2 (N = 68), two EGs received an RI called ‘Symbolic Rehearsal' or an RI called ‘Procedural Knowledge Test', and aimed at supporting knowledge retention. Both EGs supported knowledge retention but showed moderate skill decay. Results imply that RIs affect skill and knowledge retention differently and should be applied in accordance with the task requirements and their dependence on accurate skill or knowledge maintenance. Practitioner Summary:Although widely acknowledged in process automation, skill and knowledge decay of operators and its consequences have not been investigated intensively. The results of two experiments show that skill and knowledge decay can be attenuated and even avoided by refresher interventions which are not costly and easy to implement. [ABSTRACT FROM PUBLISHER]

Abstract: The share of renewable energies in electricity and heat supply besides the conventional energy resources gains more importance. Accordingly, the efficiency and flexibility of modern thermal power plants should be further improved. To design such a system, it is necessary to generate detailed computer models that can accurately predict the power plant behaviour during fast transients, part loads and start-up procedures. In this work, a dynamic simulation model for a subcritical three-pressure-stage HRSG (heat recovery steam generator) is built, employing the advanced processing simulation software Aspen Plus Dynamics®. The simulation results obtained from the HRSG model are validated towards the dynamic measurements during warm start-up procedure. The capability of processing simulation software used to estimate the dynamic behaviour of real HRSG is demonstrated. The HRSG model shows high accuracy at different part loads with a maximum relative error of about 5%. The good agreement suggests that the HRSG model is very reliable and is capable to predict the operational processes. [Copyright &y& Elsevier]

Abstract: We demonstrate that the performance of a high-temperature polymer electrolyte fuel cell with a phosphoric acid-based electrolyte is almost independent of the way of introducing the acid into the membrane electrode assembly (MEA). The same power densities were obtained with different MEAs in which the poly(2,5-benzimidazole) membrane was either pre-doped or not and in which either one or two catalyst layers were impregnated with H3PO4. Chemical analysis after shut down revealed that in all these MEAs the phosphoric acid distribution between the membrane and the electrodes was nearly the same. An MEA with acid impregnation via the electrodes was started up rapidly from room temperature, delivered a power density of 120mWcm−2 at 600mV (H2/air, 160°C, ambient pressure) after only 11min and was operated for 1000h (degradation rate: 0.06mV/h). Based on the analysis of the H3PO4 content in the MEA components, reflections on the kinetics of the redistribution of phosphoric acid within the MEA are provided. [Copyright &y& Elsevier]

Abstract: This paper presents a static and dynamic simulation model of a supercritical once-through heat recovery steam generator (SC HRSG) and its application to investigate the load changes and start-up processes for next generation high efficiency combined cycles. The scale and complexity of the modern combined cycle power plants based on high pressure and temperature steam requirements are increasing. To design such a system, it is necessary to generate detailed computer models. This study describes the upgrading of a validated sub-critical heat recovery steam generator model to a supercritical once-through heat recovery steam generator up to 250 bars in the high pressure circuit. The SC HRSG model is built using commercial simulation software named Advanced Process Simulation Software (APROS). The model includes advanced control circuits to have a high level of accuracy, especially during start-up. The comparison between the simulation results and the designed data in steady state and different load changes are documented. The obtained results demonstrate that the simulation is very reliable to predict the start-up procedure for the SC HRSG. Through a comparative study, the differences in the thermal efficiency and the steam parameters between super/sub-critical heat recovery steam generators during warm start-up process are assessed. [Copyright &y& Elsevier]

Abstract: For an ATR start-up operation over a Ni based catalyst supported on a cordierite monolithic substrate. Several initial feed temperatures of oxygen and steam were tested to determine the suitable start-up procedure. The supply of oxygen prevents carbon deposition below 700K without decreasing of catalytic activity and catalyst’s mechanical strength. Furthermore, ATR was possible to be carried out by the supply of steam at temperatures higher than 723K. At steam feed temperatures of less than 723K, the catalytic activity was found to decrease. XRD spectra indicated that the oxidation of Ni metal occurred on the deactivated catalyst. We considered that oxidation of Ni metal is preventable by the supply of steam at above the temperature where CPOX occurred. [Copyright &y& Elsevier]

Spontaneous formation of the active layer in biological filters for removal of iron, manganese and ammonium from ground water usually takes a few months. Inoculation of the new filters with well-established filter material is a common start-up procedure. An operational approach for inoculation of new filters using backwash sludge, instead of filter material, is elaborated here. The sludge is obtained from an already well-established biofilter used for removal of iron, manganese and ammonium. This procedure reduces the start-up time of the filters to 2 weeks only. The successful application of the described start-up procedure was demonstrated in two new plants treating ground water of different qualities. In one of these plants, the ground water contained increased concentrations of iron, manganese and ammonium, and in the other, only manganese concentration was increased. [ABSTRACT FROM AUTHOR]

• Dynamic simulation model of sub-critical, three-pressure-stage HRSG is developed using PPSD. • All process, automation and electrical components of the real power plant are modelled. • Model validation during warm start-up procedure is carried out. • A comparison between PPSD, Apros, and Aspen Plus Dynamics is performed. The energy market is one of the largest and most important markets around the world. Where flexibility and efficient operation in the start-up of combined cycle power plants (CCPPs) play an essential role in the competitiveness of CCPPs in the energy market. Moreover, to study the CCPPs, the Dynamic simulation is suitable tool for predicting the behavior of power plant with high accuracy. In this paper, we study the details of warm start-up procedure of CCPP, with subcritical, natural circulation and three-pressure stages heat recovery steam generator. Examining the capability of Power Plant Simulator & Designer (PPSD) by validating the numerical results of PPSD with operational data of real power plant. In addition to compare numerical data of PPSD by another numerical data acquired using another two dynamic simulation tools APROS and ASPEN Plus Dynamics to ensure the capability of PPSD to perform such simulations. The model built based on a real power plant design data with all geometry including heat exchangers, turbines, pipes valves, pumps, and control circuits as well. PPSD shows accurate results with high quality in both qualitatively and quantitatively, compared to the measured data and other simulations well. Moreover, it shows that it is capable to perform a dynamic simulation of CCPP with relatively shorter computation time and user-friendly tools. [ABSTRACT FROM AUTHOR]

THE STORK Island Systems has introduced The Stork development system for creating installation programs. Developers create a user interface, configure the disks, and build media set. Additional features allow the […]