Continuous Operation Mode Research Articles

Ammonia Removal by Simultaneous Nitrification and Denitrification in a Single Dual-Chamber Microbial Electrolysis Cell

Ammonia removal from wastewater was successfully achieved by simultaneous nitrification and denitrification (SND) in a double-chamber microbial electrolysis cell (MEC). The MEC operations at different applied voltages (0.7 to 1.5 V) and initial ammonia concentrations (30 to 150 mg/L) were conducted in order to evaluate their effects on MEC performance in batch mode. The maximum nitrification efficiency of 96.8% was obtained in the anode at 1.5 V, followed by 94.11% at 1.0 V and 87.05% at 0.7. At 1.5 V, the initial ammonia concentration considerably affected the nitrification rate, and the highest nitrification rate constant of 0.1601/h was determined from a first-order linear regression at 30 mg/L ammonium nitrogen. The overall total nitrogen removal efficiency was noted to be 85% via the SND in the MEC operated at an initial ammonium concentration of 50 mg/L and an applied cell voltage of 1.5 V. The MEC operation in continuous mode could remove ammonia (50 mg/L) in a series of anode and cathode chambers at the nitrogen removal rate of 170 g-N/m3.d at an HRT of 15. This study suggests that a standalone dual-chamber MEC can efficiently remove ammonia via the SND process without needing additional organic substrate and aeration, which makes this system viable for field applications.

A Sparse Sampling Sensor Front-end IC for Low Power Continuous SpO 2 & HR Monitoring.

Photoplethysmography (PPG) is an attractive method to acquire vital signs such as heart rate and blood oxygenation and is frequently used in clinical and at-home settings. Continuous operation of health monitoring devices demands a low power sensor that does not restrict the device battery life. Silicon photodiodes (PD) and LEDs are commonly used as interface devices in PPG sensors; however, using of flexible organic devices can enhance the sensor conformality and reduce the cost of fabrication. In most PPG sensors, most of system power consumption is concentrated in powering LEDs, traditionally consuming mWs. Using organic devices further increases this power demand since these devices exhibit larger parasitic capacitances and typically need higher drive voltages. This work presents a sensor IC for continuous SpO 2 and HR monitoring that features an on-chip reconstruction-free sparse sampling algorithm to reduce the overall system power consumption by ∼70% while maintaining the accuracy of the output information. The designed frontend is compatible with a wide range of devices from silicon PDs to organic PDs with parasitic capacitances up to 10 nF. Implemented in a 40 nm HV CMOS process, the chip occupies 2.43 mm 2 and consumes 49.7 μW and 15.2 μW of power in continuous and sparse sampling modes respectively. The performance of the sensor IC has been verified in vivo with both types of devices and the results are compared against a clinical grade reference. Less than 1 bpm and 1% mean absolute errors were achieved in both continuous and sparse modes of operation.

Non-Inverting Quadratic Buck–Boost Converter with Common Ground Configuration for Supercapacitor Applications

This article presents a novel buck–boost converter-based topology suitable for supercapacitors and grid-connected solar PV system applications. The proposed converter can handle a wide range of voltage variations at the input side, making it ideal for extracting most of the energy from supercapacitors or a solar PV system connected to the input side of the converter. The output voltage of the converter is non-inverting which makes the control easier. The design of passive components, continuous mode operation, and discontinuous mode operation are all thoroughly discussed. A low-power hardware prototype of three hundred watts is developed and tested in the laboratory to validate the theoretical aspects of the converter.

Improvement of biogas production and quality by addition of struvite precipitates derived from liquid anaerobic digestion effluents of palm oil wastes

When biogas is produced, the liquid anaerobic digestion effluents (LADE) still contain pollutants. Struvite precipitation is a technique for reducing pollutants as well as recovering useful elements such as nitrogen, phosphorus, and magnesium. This study aims to precipitate struvite from LADE and use it as an additive to palm oil mill effluent (POME) feedstocks in subsequent biogas production systems (batch and continuous operational modes). Struvite precipitation was simply performed using NaOH at a pH range of 8–10 without external sources of magnesium and phosphorus. The result showed that the optimum pH for struvite precipitation was 9, giving the highest yield and purity of struvite. The addition of 5% struvite to POME feedstock improved the performance of biogas production in the continuous stirred tank reactor (CSTR) in terms of stability, high COD removal efficiencies, increased methane yields, and decreased H2S concentrations. The greatest methane yield of 509.8 mL/g-VS and the methane concentration of 65.10% were obtained in the CSTR. The significant decrease in H2S concentration in biogas can increase the energy content of biogas, save on the cost of H2S removal, reduce corrosion, and extend the operating time of gas turbines used for electricity production. The results of this study emphasize the role of integrating struvite precipitation with continuous biogas production in improving the process sustainability and economy. Struvite precipitation from LADE diminishes the polluted wastewater, decreases the long-term process problems of fouling and clogging caused by struvite, and improves the performance of the biogas production.

Energy Intake Models for Intermittent Operation of Dead-End Microfiltration Filling Line

In filling lines equipped with membrane separation devices in the form of filters energy, consumption is only one of the important working parameters, the other being sustainable filter performance in terms of separation efficiency. As the filling line is typically equipped with a valve, intermittent operation of the filter is an important form of its use. Whereas the overall energy consumption of the filtration process is governed by the continuous operation mode, the intermittent mode, characterised by opening/closing of the valve, contributes most to problems of filter failure, i.e., the breakthrough of filtered particles through the membrane. A model for determination of the energy intake of a microfiltration membrane during the opening and closing of a valve is presented in this work. The model is based on computational analysis of the pressure wave signals recorded during the opening/closing of the valve using Fourier transform, and expressed in a nondimensional filter area specific energy intake form. The model is applied to a case of constant pressure dead-end microfiltration with three filter types: a single membrane filter, a stacked filter and a pleated filter with filtration surface areas ranging from 17.7 cm2 to 2000 cm2. Both clean filters, as well as partially clogged filter cases are taken into account. Second order polynomial models of the energy intake are developed and evaluated based on extensive analysis of the experimental data. The analysis of energy intake results show that the largest energy intake was observed for the clean filter case. When membrane fouling occurs at the constant flow rate values it leads to larger energy intake, however, due to a decreasing specific flow rate during fouling these values do not exceed the clean filter case.

On modeling and real-time simulation of a robust adaptive controller applied to a multicellular power converter

Introduction. This paper describes the simulation and the robustness assessment of a DC-DC power converter designed to interface a dual-battery conversion system. The adopted converter is a Buck unidirectional and non-isolated converter, composed of three cells interconnected in parallel and operating in continuous conduction mode. Purpose. In order to address the growing challenges of high switching frequencies, a more stable, efficient, and fixed-frequency-operating power system is desired. Originality. Conventional sliding mode controller suffers from high-frequency oscillation caused by practical limitations of system components and switching frequency variation. So, we have explored a soft-switching technology to deal with interface problems and switching losses, and we developed a procedure to choose the high-pass filter parameters in a sliding mode-controlled multicell converter. Methods. We suggest that the sliding mode is controlled by hysteresis bands as the excesses of the band. This delay in state exchanges gives a signal to control the switching frequency of the converter, which, in turn, produces a controlled trajectory. We are seeking an adaptive current control solution to address this issue and adapt a variable-bandwidth of the hysteresis modulation to mitigate nonlinearity in conventional sliding mode control, which struggles to set the switching frequency. Chatter problems are therefore avoided. A boundary layer-based control scheme allows multicell converters to operate with a fixed-switching-frequency. Practical value. Simulation studies in the MATLAB / Simulink environment are performed to analyze system performance and assess its robustness and stability. Thus, our converter is more efficient and able to cope with parametric variation.

Variance-based global sensitivity analysis of a multi-population, single-chamber microbial fuel cell operating in continuous flow mode at steady state

Microbial fuel cells (MFCs) are environmentally friendly devices which are used to convert chemical energy in organic wastes to electrical energy. MFCs have a strong non-linearity that requires a very sophisticated controlling system. Consequently, this makes optimization and performance study of MFCs a difficult process. For better estimation of the constants used for optimization of MFCs, global sensitivity analysis is performed. The global sensitivity method based on Sobol’s indices coupled with Monte Carlo simulations was applied on multi-population, single-chamber MFC operating in a continuous flow at steady state for the first time. In this paper, first-order and total-order sensitivity indices were used to visualize the impacts associated with six main parameters resulted from the maximization of power density using Matlab. Such parameters are maximum anodophilic-specific growth rate, half-rate constant of anodophilics, curve steepness factor, mediator half-rate constant, number of electrons transferred per mole mediator and decay rate constant of anodophilic bacteria. The results showed that the curve steepness factor has almost no impact on the power density of MFC. While all other studied, factors are sensitive parameters that impact the power density of MFC. It is worth mentioning that maximum anodophilic growth rate and the number of electrons transferred per mole of mediator are the most sensitive parameters that affecting the power density production having total indices of 0.74 and 0.624, respectively. While the half-rate constant of anodophilics, mediator half-rate constant and decay rate constant of anodophilics have almost similar impact by having total-order indices of 0.127, 0.144 and 0.192, respectively. The findings herein are critical in understanding and further model improvement of microbial fuel cells as the most impacting parameters on MFC power density can be optimized further to reduce uncertainty associated with the experimental parameters in the model.Graphical abstract

Enhanced power generation, organics removal and water desalination in a microbial desalination cell (MDC) with flow electrodes

This study introduced a flow electrode microbial desalination cell (FE-MDC), which used activated carbon (AC) particles and carbon nanotubes (CNTs) as the electrode to promote electron harvesting. The recovered electricity energy (0.371 KWh/m3) and columbic efficiency (66.7 %) of the FE-MDC were over 2 times higher than those of the conventional MDC without the flow electrode. Consequently, the salt and COD removal efficiencies were enhanced to 77.8 % and 91.2 %, respectively. Electrochemical analysis implied that the charge transfer resistance of the system was reduced by the flow electrode. Electron accumulation and charging-discharging experiments proved that the flow electrode could accumulate electrons and transfer the electrons to the fixed anode. Bacterial community analysis indicated that the bacterial activity was improved by the flow electrode. The content of the exoelectrogen Pseudomonas increased from 5.0 % to 14.7 %, and Hydrogenophaga improved from 1.4 % to 5.9 %. Finally, a continuous operation mode of the FE-MDC was established, and the flow electrode slurry was returned to the anodic chamber for recirculated utilization. The voltage output, COD removal, and salt removal during the operation mode reached 610 mV, 78.8 %, and 76.1 %, respectively. This study proved that the flow electrode is a promising way to promote the practical application of MDC technology.

Экспериментальное исследование эффективности рабочих процессов в камере ракетного двигателя малой тяги на компонентах кислород–метан

A test bench and a model low-thrust rocket engine operating on the environmentally friendly gaseous components, i.e. oxygen and methane, in continuous and pulse modes are presented. A series of fire bench tests of such model engine was carried out in order to obtain the efficiency criterion values of the working process in the chamber (consumption complex coefficient) and to evaluate thermal state of its structural elements in continuous and pulse operating modes for various values of the operating parameters. Temperature of the outer walls of all structural elements was determined using the Optris PI160 thermal imager. It is shown that transition from continuous to the pulse operation mode of the model low-thrust rocket engine leads to a decrease in the working process efficiency by 30...40%. Raising the pressure in the combustion chamber makes it possible to increase the fuel combustion completeness and, consequently, the consumption complex coefficient.

Design and Analysis of Zeta Converter for Power Factor Correction Using Cascade PSO-GSA-Tuned PI and Reduced-Order SMC

This paper presents the design and analysis of a single-phase power factor correction (PFC) scheme using a DC–DC Zeta converter operating in continuous conduction mode. The presented DC–DC converter exhibits non-linearity due to switching elements that degrades the performance of the converter. Therefore, this paper proposes a non-linear cascade control of particle swarm optimization-gravitational search algorithm (PSO-GSA) tuned proportional-integral (PI) and sliding mode controller (SMC) in outer and inner loop, respectively, to improve the performance of the converter. The robustness of the controller is analysed by applying the load and line variations to the converter. The simulation results showed that the steady state performance indices such as integral absolute error and integral square error, and transient performance indices like settling time and peak overshoot are significantly enhanced for the proposed cascade control scheme compared to the PSO and root locus method of tuning the outer PI with the inner SMC controller. The proposed control scheme gives better performance in terms of power factor improvement, percentage reduction in total harmonic distortion, and efficient tracking of output voltage for change in reference voltage compared to other techniques presented. Further, the performance of the proposed scheme is tested for battery charging application of the solar photovoltaic system. The demonstrated simulation results are validated by implementing the DC–DC Zeta converter in real-time hardware set-up.

PT controlled PCCM buck converter with adaptive pulse train generator and NMOS current sensor

A pulse train controlled buck converter operating in pseudo continuous conduction mode (PCCM) is implemented in the 0.18-μm CMOS process in this paper. An adaptive pulse train generator, which adjusts duty cycle based on the output power, is proposed to improve the output voltage range and transient response. To operate in PCCM, an NMOS current sensor using a double common-gate amplifier with a high slew rate is utilized to detect the falling inductor current. Simulation results demonstrate that the converter obtains a well regulated variable output voltage from 1 V to 4 V, providing a maximum load current of 1000 mA at the switching frequency of 1 MHz. The transient spike is smaller than 35 mV and recovery time is less than 6.3μs for a 300 mA load current step. The peak efficiency is 94.4% at 300-mA load current.

USING N-OVEL COATED SAND AS REACTIVE BED IN PERMEABLE BARRIER FOR ELIMINATION OF METHYL ORANGE DYE FROM GROUNDWATER*

This study investigates the efficacy of sand coated with calcium / aluminum (Ca/Al)-layered double hydroxide (LDH) in the elimination of methyl orange dye from simulated groundwater using method of permeable reactive barrier. For green (sustainable) manufacturing of this sand, aluminum prepared from dissolution of alum (cheap coagulant) can be interacted chemically with calcium extracted from cement kiln dust byproduct to create nanoparticles of Ca and Al that precipitate on the filter sand. Sorption measurements for interaction of methyl orange dye and coated sand was well formulated by Langmuir model with highest value of correlation (determination coefficient= 0.999) and lowest errors (sum of squared errors= 0.0122). Also, the maximum capacity of adsorption was valued of 0.9453 mg/g and the sorption curve can classify as “favorable” type. According to desorption measurements, little percentage of dye (0.91%) can desorb from exhausted coated sand through washing with water due to strength of bonding between sorbent and dye molecules. Also, the exhausted sorbent can regenerate with efficiency not less than 85% after eight of regeneration cycles. Finally, measurements of breakthrough curves in the continuous mode operation using column setup proved that the propagation of dye front (and consequently the longevity of barrier) would increase significantly with thicker barrier and lowest values of influent concentration and flow rate. COMSOL (computer solution) package can use effectively in the simulation of these curves.

STRENGTH AND STABILITY ASSESSMENT OF NPP REINFORCED CONCRETE STRUCTURES REGARDING THE RESULTS OF VIBRATION ANALYSIS

Introduction . The article outlines methodological stages when assessing the resource of nuclear power plant (NPP) operation units with regard to degradation in the dynamic characteristics of reinforced concrete structures obtained by means of vibration analysis methods on the example of hot cells of nuclear installations. Aim : to improve the method currently used for assessing the stress-stain behavior and strength of NPP structures regarding the aging process of reinforced concrete elements under various environmental exposures. Materials and methods . A methodology is proposed for assessing the strength (loading capacity) and stability of NPP structures where significant variations in the properties of reinforced concrete elements have taken place under the action of continuous operation and thermal mode disturbances, thus weakening the element stiffness and, as a result, reducing their strength and stability. Therefore, in order to evaluate the stress-stain behavior and strength of hot cells, calculations should be carried out taking into account the history of structure loading and the process of crack development over the entire operation period. However, no analysis of the history of thermal loading has been performed during the operation period of the NPP under study. In addition, there is a lack of suitable software packages for nonlinear dynamic analysis certified by Rostechnadzor capable of considering the loading history and crack development in reinforced concrete structures. In order to eliminate the mentioned shortcomings, a vibration analysis of the walls and floors of hot cells should be performed to determine the following dynamic characteristics: natural vibration frequency and mode, logarithmic decrement of damping, deformation modulus and Poisson ratio for each wall and floor. Further, based on the obtained experimental data, the stress-stain behavior and strength of hot cells should be calculated using experimental data as calculation input information. The calculation methodology is based on a nonclassical method of modal superposition using the ABAQUS, ANSYS, and Nastran software packages. In order to verify the correctness of the results obtained by vibration analysis, an assessment of floor dynamic characteristics at the point +13.450 in the “П”–“Ж” rows was conducted. Results . The values of deformation modulus and natural vibration frequency obtained in the conducted experiment were found to agree with the calculated values. Conclusions . A methodology for assessing the strength of NPP structures regarding the aging of reinforced concrete under various environmental exposures was presented. The validity of dynamic characteristics obtained using vibration analysis was evaluated.

Optimization of a rotating cylinder electrode electrochemical reactor for metal recovery: An innovative approach and method combining CFD and response surface methodology

The optimization of electrochemical reactors for metal recovery using hydrodynamic and mass transfer models with CFD is addressed. The performance of a rotating cylinder electrode (RCE) electrochemical reactor is considered. The optimization procedure has two stages.The first comprises developing a validated 3D model of metal electrodeposition at different hydrodynamic regimes. The hydrodynamics are described by the Reynolds-averaged Navier‒Stokes (RANS) equations using the standard k-ε turbulence models. The diffusion-convection equation with turbulent mixing and concentration wall function was used for the transport of electroactive species. The model was validated with experimental data obtained in a batch reactor with two different diameters of the RCE. Additionally, the model was validated in the continuous mode of operation as a part of the proposed methodology for one case of the hydrodynamic conditions for each reactor geometry.The second stage presents a methodology for optimizing the operation of an RCE reactor using the abovementioned validated models. The optimization process was carried out using response surface methodology (RSM), where three objective functions were analyzed: the fractional conversion of the reactant, the specific energy consumption, and the current efficiency. The effectiveness of the proposed method was proven by the copper ion recovery in a continuous RCE reactor under optimized conditions.

Modified High Gain DC-DC Converter with APICs for Microgrid

This paper proposes a nonisolated high voltage gain DC-DC converter. The active–passive inductor cells (APICs) makes the converter topology expandable, and it also helps in providing a high gain quality at lower duty cycles. The proposed converter is suitable for high gain applications mainly necessitating microgrid as well as integration of renewable energy sources into the existing grid infrastructure. The merits of the converter can be attributed to the ability to achieve high gain and low current stress and switching losses on power electronic switches. The proposed converter is analyzed in both continuous and discontinuous modes of operation, the efficiency is calculated and simulation results substantiate the operation of the converter.

Model-assisted process design for better evaluation and scaling up of continuous downstream bioprocessing

Continuous process is a promising alternative for tradition batch process in biomanufacturing, which has higher productivity and lower material consumption. However, despite the maturation of necessary technologies for continuous process, there are few discussion about optimization of full continuous process. One possible reason is that the continuous process is such a complex and interacted process that the traditional experiment-based optimization approach is not sufficient anymore. To address that problem, the process simulation tool SuperPro Designer and continuous capture chromatography model were integrated into a model-assisted design platform for better development of continuous process. The influences of different continuous capture operation modes and sub-lot number under various upstream conditions were analyzed for pilot-scale production. The best combination of operation mode and sub-lot number were determined for the highest equipment utilization without any conflict. After the process optimization, the equipment utilization of continuous process was significantly improved to 27.3%. Then, a pilot-scale case study was carried out to validate the proposed approach. The results showed that the scaling up and process design of continuous process were successful. No time conflict and process failure happened and the final product met the release specification. Finally, the cost of goods was evaluated with SuperPro Designer, and the results showed a 17.4% cost reduction for optimized continuous downstream process compared to batch process, which is promoting for the future industrial applications.

Analysis of the behavior of asynchronous electric drive with a closed scalar control system when changing the inductance of the magnetizing circuit

The article was devoted to the study of an automated electric drive with a scalar closed-loop speed control system. Severe duty and operating modes of electric drive determine the actual service life. Wear of the induction motor, as a key link of the electric drive, was associated with deviation from nominal parameters. The deviation of parameters of the induction motor equivalent circuit determined the resultant change of characteristics. The parameters of the equivalent circuit determined the accuracy of the adjustment of regulators and optimal algorithms in the control system of the electric drive. In continuous operation modes the possibility of auto-tuning regulators, which requires stopping or no-load mode, was excluded. The paper considered the influence of the magnetization circuit mutual inductance value of the induction motor on the behavior of the electric drive control system. Evaluation of the behavior of the scalar closed-loop speed control system was performed on the basic energy (power factor, efficiency factor) and mechanical (speed, electromagnetic torque) characteristics of the electric drive.

Optimization-based technoeconomic comparison of multi-stage membrane distillation configurations for hypersaline produced water desalination

Unconventional oil and gas production raises concerns regarding sustainable management of high salinity wastewaters generated in this process. Membrane distillation (MD) is a thermal desalination process capable of treating hypersaline brines such as produced water. The low single pass recovery in MD systems operated in a single stage requires a large recycle stream to achieve the desired recovery, resulting in high energy consumption and operating cost. Multistage configurations in continuous recirculation operation mode offer the potential to reduce the energy intensity of MD systems. However, rigorous analysis is needed to assess the performance of MD configurations when operating in multi-stage mode. We present an optimization-based comparison of economic and energetic performance for five configurations of MD (including DCMD, AGMD, PGMD, CGMD, and VMD) operating in multi-stage continuous recirculation mode. Our findings demonstrate that multistage operation reduces the treatment cost and energy intensity of all MD configurations compared to single stage MD, with the greatest benefit for VMD and PGMD. AGMD with five stages outperforms other configurations with 3.58 $/m3feed treatment cost, followed by VMD, CGMD, DCMD, and PGMD with 3.8, 4.2, 5.4, and 9.06 $/m3feed treatment costs corresponding to twelve, eight, eight, and sixteen stages, respectively.

A dual input single output non-isolated DC-DC converter for multiple sources electric vehicle applications

There is a need to design DC-DC converters capable of handling high voltages and that employ single-stage conversion to integrate renewable energy resources, such as solar photovoltaic cells and fuel cells, for electric vehicle applications. This paper elucidates the design and analysis of a dual input single output non-isolated Cuk-derived converter with a high step-up ratio. The proposed converter can effectively handle two different energy resources that have different electrical characteristics. It makes use of one common inductor between the dual input port, which reduces the passive components and the circuit volume required. The maximum efficiency that can be achieved by this converter is 95.72%, with two main switches and one diode in the circuit. This study involved a detailed analysis of the proposed converter in continuous current operation mode. A continuous current with reduced ripple in the output improves a fuel cell’s operating life-span. The efficacy of the proposed converter is verified through simulation and validated by constructing a 200 W, real-time, scaled-down prototype model.

Efficient maximum power point tracker based on neural network and sliding-mode control for buck converters

Abstract This paper presents detailed design steps of an effective control system aiming to increase the solar energy harvested via photovoltaic power-generation systems. The design of an intelligent maximum power point tracker (MPPT) supported by a robust sliding-mode (SM) controller is discussed in this study. The proposed control scheme is designed to track the MPP and provide a smooth system response by removing the overshoot in the load current during any variation in the connected load. Such a system is suitable for DC–DC buck converter applications. The study begins with modelling the buck converter for a continuous current mode operation. The reference voltage of the tracking system is produced by the proposed neural network (NN) algorithm. The proposed intelligent MPPT integrated with an SM controller is simulated in a MATLAB®/Simulink® platform. The simulation results are analysed to investigate and confirm the satisfaction level of the adopted four-serially connected PV-modules system. The system performance is evaluated at a light intensity of 500 W/m2 and an ambient temperature of 25°C. Applying only the proposed NN algorithm guarantees the MPP tracking response by delivering 100 W at a resistive load of 13 Ω, and 200 W at a load of 6.5 Ω, respectively, with 99.77% system efficiency. However, this simultaneously demonstrates a current spike of ~0.5 A when the load is varied from 50% to 100%. The integrated SM controller demonstrates a robust and smooth response, eliminating the existing current spike.