Single-stage System Research Articles

A multicut generalized benders decomposition approach for the integration of process operations and dynamic optimization for continuous systems

The integration of process operations and dynamic optimization leads to large scale optimization problems whose monolithic solution is challenging. In this paper we propose a new formulation of the integrated planning, scheduling, and dynamic optimization problem for continuous single stage systems. We analyze the structure of the problem using Stochastic Blockmodeling and we show that the estimated structure can be used as the basis for a multicut Generalized Benders decomposition (GBD) algorithm, which can solve the problem in reduced computational time. Furthermore, we propose an accelerated hybrid multicut algorithm which can lead to further reduction in computational time. Through case studies, we analyze the computational performance of the proposed formulation and decomposition based solution algorithms.

Dual inner circulation and multi-partition driving single-stage autotrophic nitrogen removal in a bioreactor

The single-stage autotrophic nitrogen removal (ANR) process is impeded by a long start-up cycle and unstable operation performance. In this study, an airlift inner-circulation partition bioreactor (AIPBR) was operated continuously for 215 days to explore methods of strengthening the performance and stable operation of the single-stage ANR system. AIPBR start-up period took around 38 days, the total nitrogen removal efficiency was > 85% on day 35. With the decrease of hydraulic retention time and the increase of aeration rate, the nitrogen removal rate increased to 0.85 ± 0.02 kg-N/m3/day. The sludge morphology gradually changed into dark-red floc-coupled granular sludge. Nitrosomonas (9.95%) and Candidatus Brocadia (6.41%) were dominant in the sludge. During long-term operation, AIPBR achieved the dual inner circulation of sewage and sludge and then formed effective dissolved oxygen and sludge partitions to provide a suitable growth environment for various functional bacteria, promote synergy between them, and strengthen the ANR performance.

SCHEMING OF CONTROLLER FOR SINGLE STAGE SOLAR PV FED BLDC MOTOR-DRIVEN WATER PUMP

To optimize the solar photovoltaic (PV) generated power using a maximum power point tracking (MPPT) technique, a DC-DC conversion stage is usually required in solar PV-fed water pumping which is driven by a brushless DC (BLDC) motor. This power reformation stage leads to an increased cost, size, difficulty, and decreased efficiency. As a unique solution, this work addresses a single-stage solar PV energy conversion system feeding a BLDC motor pump, which eliminates the DC-DC conversion stage. A simple control technique capable of operating the solar PV array at its peak power using a common voltage source inverter (VSI), is proposed for BLDC motor control. The proposed control eliminates the BLDC motor phase current sensors. No supplementary control is associated with the speed control of the motor pump and its soft start. The speed is controlled through the optimum power of the solar PV array. The suitability of the proposed system is exhibited through its performance evaluation using MATLAB/Simulink-based simulated results. keywords: MPPT, solar PV array, BLDC motor, Water pump, Voltage source inverter (VSI)

A ranking framework based on interval self and cross-efficiencies in a two-stage DEA system

The evaluation of the performance of a decision-making unit (DMU) can be measured by its own optimistic and pessimistic multipliers, leading to an interval self-efficiency score. While this concept has been thoroughly studied with regard to single-stage systems, there is still a gap when it is extended to two-stage tandem structures, which better correspond to a real-world scenario. In this paper, we argue that in this context, a meaningful ranking of the DMUs is obtained; this outcome simultaneously considers the optimistic and pessimistic viewpoints within the self-appraisal context, and the most favourable and unfavourable weight sets of each of the other DMUs in a peer-appraisal setting. We initially extend the optimistic-pessimistic Data Envelopment Analysis (DEA) models to the specifications of such a two-stage structure. The two opposing self-efficiency measures are merged to a combined self-efficiency measureviathe geometric average. Under this framework, the DMUs are further evaluated in a peer settingviathe interval cross-efficiency (CE). This methodological tool is applied to evaluate the target DMU in relation to the most favourable and unfavourable weight profiles of each of the other DMUs, while maintaining the combined self-efficiency measure. We, thus, determine an interval individual CE score for each DMU and flow. By treating the interval CE matrix as a multi-criteria decision making problem and by utilising several well-established approaches from the literature, we delineate its remaining elements; we show how these lead us to a meaningful ultimate ranking of the DMUs. A numerical example about the efficiency evaluation of ten bank branches in China illustrates the applicability of our modelling approaches.

Application of active magnetic bearings in control and estimation of geared-rotor faults in high speed offset spur gear transmission system

This study is focused on the mathematical modelling, analysis, active transverse vibration control and fault analysis of a single-stage spur geared-rotor system. It uses Active Magnetic Bearings (AMBs) as an auxiliary bearing in addition to the conventional mechanical bearing in rotor fault detection considering the dynamic model with gyroscopic effects. The change in dynamic forces primarily due to the mesh deformation, gear runout, and variable transmission error are considered, which causes unwanted vibration and noise. To prevent the damage of gears and other supporting structures, these forced vibrations and control currents are meticulously investigated. From the dynamic responses of geared-rotor, the AMB control the stiffness and damping to minimize the transmission of forced vibrations to the mountings by closed-loop feedback control system. For an accurate modelling the dynamic transmission error is taken in two orthogonal transverse directions, which has asymmetric transmission error characteristics. Full spectrum is used for frequency domain analysis with tilting phenomena of the gears at high spin speed. An identification algorithm is developed for fault detection and estimation of system parameters from vibration and current of the proposed geared-rotor-AMB system. The robustness of the proposed algorithm is verified with different added percentage of noise and modeling errors.

Single-Stage Grid-Connected PV System With Finite Control Set Model Predictive Control and an Improved Maximum Power Point Tracking

The single-stage grid-connected photovoltaic (PV) topology has recently drawn attention as it can reduce overall losses and installation costs. This paper presents a new control approach for single-stage grid-connected PV systems. The proposed controller is a combination of a finite control set model predictive control (FCS-MPC) and a maximum power point tracking (MPPT) algorithm, which ensures the extraction of maximum power from the PV panels and good transient performance for the output voltage and current. The disadvantages of classical MPPT algorithms in tracking the global maximum power point under fluctuating environmental conditions are avoided by including additional constraints in the cost function of the FCS-MPC. Further, the controller is tested for partial shading in PV. The performance of the proposed controller is compared with the two-stage and single-stage PV configuration with different controls and MPPT algorithms. The simulation results show that the single-stage PV system with the proposed control can effectively extract the maximum power from the PV system and maintain a stable output signal for the transient condition. Finally, experimental results according to a control hardware-in-the-loop (C-HIL) approach are presented to validate the effectiveness of the proposed algorithm.

Codesign of Architecture, Control, and Scheduling of Modular Cyber-Physical Production Systems for Design Space Exploration

Design space exploration (DSE) of cyber-physical production systems (CPPS) is a search problem in the space of potential compositional configurations. Current design methodologies follow the separated design paradigm in which the architecture, control, and scheduling are separately designed. Optimization of each part considers only the corresponding goals of interest and overlooks other aspects by adopting gross assumptions, which makes it difficult to determine the global optimal solution for a given system. To address this problem, in this article, we propose a codesign method that considers the design spaces of architecture, control, and scheduling as monolithic, mixed discrete-continuous spaces. We formulate DSE as an optimization problem and propose a generic iterative algorithm schema involving simulation in the loop to solve the abovementioned new problem. To illustrate the effectiveness of the proposed method, a real single-stage reducer assembly production system is considered. The design results demonstrate that our method provides better solutions than does the separated design method.

Numerical investigation on thermal performance of absorption refrigeration system using MWCNT nanoparticle-enhanced 1-hexyl-3-methylimidazolium cation-based ionic liquids

• Specific heat of HMIM cation based four different ionic liquids were investigated experimentally. • Increase concentration in the MWCNT nanoparticle enhanced ionic liquid improves the COP of the ARS. • The largest COP is presented by 1 wt% MWCNT [HMIM][Pf 6 ] NEIL, followed by 1 wt% MWCNT [HMIM][Tf 2 N] NEILs. In this investigation, the thermal performance of single-stage absorption refrigeration systems (ARSs) utilizing different MWCNT nanoparticle-enhanced 1-hexyl-3-methylimidazolium (HMIM) cation-based ionic liquids with R1234yf refrigerant were analyzed. The specific heats of the various MWCNT nanoparticle-enhanced [HMIM] cation-based ionic liquids were obtained experimentally at a temperature and a concentration of 303–383 K and 0–1 wt%, respectively, and were subsequently used for modeling the solubility and absorption refrigeration cycle. As a result, the maximum specific heats of all considered ionic liquids were examined at the highest temperature of 383 K. The solubility order of R1234yf refrigerant from highest to lowest was [HMIM][Bf 4 ], [HMIM][Pf 6 ], [HMIM][TfO], and [HMIM][Tf 2 N] RTILs. In addition, the maximum COPs of the ARSs were achieved at the temperature and concentration of 363 K and 1 wt%, respectively, which were 0.205, 0.242, 0.286, and 0.259 for the [HMIM][Bf 4 ], [HMIM][TfO], [HMIM][Pf 6 ], and [HMIM][Tf 2 N] MWCNT NEILs, respectively. By applying the proposed system could be simplified at high-temperature applications and prevent undesirable side effects of conventional working pairs such as metal incompatibility, toxicity, and chemical instability.

Scale-up and energy estimations of single- and two-stage vinasse anaerobic digestion systems for hydrogen and methane production

This study evaluated the full-scale vinasse anaerobic digestion for industrial application. Twelve scenarios were simulated, considering single (methanogenic reactor) and two-stage systems (acidogenic + methanogenic reactors), raw and concentrated vinasse, thermophilic and mesophilic conditions for methanogenesis and usage of acidogenic or methanogenic reactor effluent to dilute vinasse. A single-stage anaerobic digestion system of 17,433 m³ necessary to treat all the raw vinasse produced by a mill with a grinding capacity of 3.3 million tons of sugarcane per season can generate a power of 11.1 MW with an energy yield of 4.6 MJ/kg CODremoved. Two-stage system scenarios where vinasse was diluted with acidogenic reactor effluent had worse energetic recoveries than the single-stage system. Nonetheless, the usage of the methanogenic reactor effluent to dilute vinasse and its own influent in a two-stage system achieved an energetic recovery at least 34% higher than that of the single-stage system. In the best two-stage scenario, the total working volume was 19,666 m³, combining thermophilic acidogenic reactors and mesophilic methanogenic reactors, with an energy yield of 7.0 MJ/kg CODremoved. The different combinations of temperatures allow for a safer and more economic operation. The proposed novel industrial configuration can be divided into two parallel acidogenic reactors of 1,800 m³ each, and those reactors are in series with eight parallel methanogenic reactors of 2,828 m³ each. The electricity produced by the full-scale system can supply an energy demand of 24 thousand inhabitants per harvest season (9.7 kWh per ton of sugarcane). This study presents a novel discussion for sugarcane industry decision makers, such as plant managers, process and project engineers, providing a trade-off between highest energy production, optimal COD removal and lowest reactor volume (CAPEX investment) that better fits their needs.

A modified FOGI-FLL feature-based control algorithm for single-stage grid-interfaced solar PV system

A modified FOGI-FLL feature-based control algorithm for single-stage grid-interfaced solar PV system

A thermoacoustic refrigerator with multiple-bypass expansion cooling configuration for natural gas liquefaction

A small-scale, energy-efficient and reliable refrigeration system is required for on-site liquefaction of natural gas in distributed stations. The thermoacoustic refrigerator is regarded as one of the most promising options to meet this demand. However, existing work on thermoacoustic refrigerators to date has been limited to a single cooling temperature only at the liquefaction temperature, without consideration of the significant irreversible losses that arise from the large temperature difference between the natural gas being cooled and the working gas being heated in the heat exchanger. To overcome this limitation, this paper proposes a novel multi-stage thermoacoustic refrigerator with multiple-bypass expansion cooling configuration that is capable of cascade liquefaction of natural gas. The irreversible losses can be reduced greatly by organizing the decreasing temperatures of the natural gas to occur across heat exchangers with decreasingly lower temperatures to achieve smaller temperature drops. Theoretical analyses were performed on the working characteristics of both two-stage and three-stage systems and comparisons are made with the conventional single-stage system. The system performances are compared based on whether the system covers only the sensible heat or the combined sensible and the latent heat of natural gas. Results show that the proposed system improves the relative liquefaction efficiency if it is used to cover only sensible heat of natural gas (improved by 57.0%) or to cover the combined sensible and latent heat of natural gas (improved by 12.6%), when compared to conventional single-stage system. These findings demonstrate the system’s promise for use in natural gas liquefaction applications.

Dynamic response and flexibility analyses of a membrane-based CO2 separation module

Renewable energy sources and fossil-fueled power plants integrated with carbon capture technologies are expected to play an important role in sustainable energy supply in the future. In this regard, this study aims to improve the flexibility of membrane-based CO2 capture units as a promising technology for CO2 capturing by analyzing the system's transient behavior. A rigorous dynamic model for a single-stage membrane separation system is developed, which includes differential equations of transport phenomena across the membrane, mass balances, and pressure distributions. The model is utilized to investigate the dynamic performance of a single-stage counter-current membrane module for separating CO2 from the flue gas of a power plant, including up to 13 vol% of carbon dioxide. Step-changes in feed pressure, feed flow rate, feed composition, and retentate recycling are considered for the analysis. The results show that by step increase in feed pressure from 5 to 8 barg, undershoot behavior is detected, and the membrane module requires about 7 s to reach a steady-state condition. In contrast, by step decrease in feed pressure, there is an overshoot, and the module requires 11 s for new steady. Also, the membrane module responds slowly to step-changes in feed composition and retentate recycling (∼20 s) compared to other step-changes in operating conditions. This paper provides new insights into the dynamics analysis of the membrane process as well as the flexible operation of membrane-based carbon capture systems.

Shape-controlled fabrication of cost-effective, scalable and anti-biofouling hydrogel foams for solar-powered clean water production

• Development of closed-cell hydrogel foams via a controlled foaming − gelation technique. • Demonstration of self-contained solar evaporation and desalination. • Realization of a single-stage water purifier for efficient clean water production. Solar-powered interfacial evaporation has emerged as a sustainable technology for clean water production with a minimized carbon footprint. Fabrication of three-dimensional (3D) steam generators via conventional processing techniques (sol–gel and template-assisted methods) remain one of the main roadblocks toward mass production and scalable applications. In this study, 3D hydrogel foams based on biopolymer composites are developed via a controlled foaming − gelation technique and applied to a monolithic interfacial steam generator. The designed closed-cell structures deliver many important form-factors to the hydrogel foams, such as light-weight, low-cost, low thermal insulation and efficient water diffusion. The hydrogel foam with a maximum height of 3.2 cm attains a high water evaporation rate of 2.12 kg m −2 h −1 and a high cost-effectiveness of 2692 g h −1 $ −1 under one sun. A single-stage water purification system is fabricated based on the high-performing hydrogel foam. Because of its self-floating structure and enhanced passive cooling on open water, the system attains a maximum clean water collection rate of 0.71 L m −2 h −1 under real sky and surpasses a majority of single-stage solar stills. This work demonstrates the rational fabrication of hydrogel foams and combines high-performance solar evaporation with other intriguing properties (i.e., cost-efficient, scalable, anti-biofouling, self-floating and anti-overturning). The system-level design enables facile scale-up of clean water production.

Adsorbent Minimization for Removal of Ibuprofen from Water in a Two-Stage Batch Process

Pharmaceutical products in water, also known as personal pharmaceutical products or PCPPs, are developing contaminants that have the potential to impair human health and the environment in a variety of ecosystems. In this work, waste date stones, a waste product obtained from the seedless dates manufacturing industry, were used to make acid-activated carbon. This material has been utilized to extract the medicinal component ibuprofen from water, with a high adsorption capacity of 126 mg ibuprofen per g of waste date stone-generated activated carbon. A design study was conducted to minimize the amount of activated carbon required, utilizing a two-stage batch adsorption system to optimize the usage of the activated carbon. To test the model and compare the quantities of adsorbent required in the two-stage and single-stage systems under various conditions, several variables were entered into the design model.

Heat pump combined with single-stage or two-stage desiccant wheel system? A comparative study on different humidity requirement buildings

Heat pump desiccant wheel hybrid systems can control indoor temperature and humidity for industrial and civil buildings. To clarify the boundary of heat pump combined single-stage desiccant wheel system and two-stage desiccant wheel system for judging the optimal system under different conditions, the performance of the two systems is analyzed with experiment and simulation method. Firstly, the fresh air process is compared for different humidity set points under typical operation conditions. Secondly, the energy moisture ratio (EMR) of desiccant wheels is analyzed. At last, based on system energy consumption and economy, the humidity boundary of the single-stage and the two-stage dehumidification system is proposed, under different conditions. It is found that the energy performance of desiccant wheel increases with the reducing of humidity set point for both systems, and higher EMR can be obtained by the desiccant wheel of the single-stage dehumidification system for all operation modes. The two-stage dehumidification system is more energy efficient when humidity for the controlled space is lower than 49%, 55% and 40% for high temperature mode, typical summer mode and typical dehumidification mode, separately. With the proposed operation boundary, the optimal system can be quickly judged according to the humidity control requirement and outdoor environment.

Numerical modeling of a novel two-stage linear refrigeration compressor

Abstract Linear compressors have started to apply in refrigeration owing to their oil-free operation, capacity modulation by variable stroke and higher seasonal efficiency. Nevertheless, linear compressors are subject to a high seal leakage loss and piston offset (drift), particularly at high pressure ratios. Meanwhile, there is a reduction in the accuracy of resonant frequency prediction due to very nonlinear gas spring at high pressure ratios, leading to a reduction in the compressor efficiency. Two-stage operation is considered as a feasible solution to the aforementioned issues due to the lower pressure ratio for each stage. A numerical model of two-stage compression system using linear compressors is presented in this study to investigate the system performance under various operating conditions. The proposed numerical model consists of a thermodynamic sub-model, a piston dynamic sub-model and a reed valve dynamic sub-model. Experiments are also conducted based on a refrigeration system with two linear compressors connected in parallel to validate the proposed model. The mean absolute percentage errors of the predicted mass flow rate and power input are 2.47% and 8.49%, respectively. The modeling results show that the coefficient of performance is 5.5 for a two-stage compression system and 2.0 for a single-stage compression system while the condenser temperature and evaporator temperature are 50°C and −23°C, respectively. The two-stage compression system offers superior performance to the single-stage system.

Proportional Hysteresis Band Control for DC Voltage Stability of Three-Phase Single-Stage PV Systems

Ensuring the stability of DC-link voltage in grid-connected photovoltaic (PV) systems plays a critical role in their reliable and continuous operation. DC voltage fluctuation and, in the worst case, DC voltage collapse will dramatically hamper real and reactive power delivery to the grid. This is more the case in single-stage inverters with no DC-DC boost stage, and the DC voltage has a varying nature. This paper proposes a new control approach for ensuring DC-link voltage stability in single-stage PV systems. The proposed control strategy is based on an adaptive hysteresis band controller (HBC), supplementing the conventional control blocks. This strategy offers the capability to prevent fast discharge of DC-link capacitor and keeps it within acceptable limits by quickly modifying phase shift applied to inverter PWM through quick calculations. Results show that the approach greatly improves PV system performance, in various operating modes. The proposed control scheme is implemented in the real-time simulator, OPAL-RT, OP5600 to verify its applicability and effectiveness in real time.

Ultrathin Water-Cast Polymer Membranes for Hydrogen Purification.

Among various H2 purification technologies, the use of membrane technology has been considered an ecofriendly approach for addressing the increasing hydrogen demand. Although many H2-selective membrane materials have been reported, processing them into hollow fibers or thin-film composites (TFCs) via traditional methods either affects the performance of the materials or renders their further processing into applicable membrane forms infeasible. Herein, we propose a water-casting method for fabricating TFC membranes for hydrogen purification with high permselectivity. The film integrity and thickness were manipulated by controlling the spreadability of the casting solution, and the resultant water-cast TFC membrane that comprised an ∼30 nm selective layer demonstrated high H2 permeance and H2/CH4 selectivity of approximately 190 GPU and 100, respectively, under optimized conditions. We performed a mixed-gas permeation test using a simulated off-gas of steam-methane reforming from natural gas in a single-stage system and obtained hydrogen gas of >99 mol % purity. This indicates not only the suitability of the water-cast membranes for satisfying the demand for pure hydrogen as a fuel and chemical reagent but also the great potential of the water-casting method for high-performance membranes in various industrial and environmental applications.

Multi-criteria analysis for screening of reversible metal hydrides in hydrogen gas storage and high pressure delivery applications

Metals and alloys forming reversible hydrides with hydrogen gas are potential building blocks for compact, solid state hydrogen storage systems. Based on the materials’ thermodynamic characteristics, their use as temperature-swing gas compression and delivery systems in the hydrogen economy is also possible. Given the wide variety of materials developed and tested at laboratory and pilot scales, a harmonized method of selecting the feasible material(s) for a particular real-life application is required. This study proposes a system selection framework based on a normalized, multi-criteria metric. Using calculated values of multi-criteria metric, multi-criteria screening and ranking of potential materials has been demonstrated for a particular use case. It is found that the alloy TiMn1.52 having value of additive metric between 0.25 and 0.35 represents the best material for a single stage system. The alloy pair CaNi5–Ti1.5CrMn represents the best alternative for a two-stage system with additive metric values between 0.63 and 0.82. Energy and economic characteristics of the metal hydride gas compression and delivery systems are evaluated and compared with an equivalent mechanical compression system producing the same final effect (i.e., delivery of a given quantity of gas at a defined pressure).

Effect of Sodium on Methanogens in a Two-Stage Anaerobic System

This study evaluated the effects of sodium on anaerobic biomass from the second-stage reactor of a two-stage anaerobic digester. The results indicated that methanogens showed a relatively high sodium tolerance of 2.4 g Na+ L−1. Microbial community analysis showed that viable Methanomicrobiales was the most abundant population by a combined propidium monoazide cross-linking quantitative polymerase chain reaction technique. There was a population shift towards higher abundance of Thermotoga (0.02%), Clostridium (2.50%) and Methanoculleus (13.80%). Biomass activity in relation to increased sodium concentrations was investigated with the adenosine triphosphate test coupled with extracellular polymeric substances measurement. The results showed biomass activity decreased from 33 to 16 µg g−1 volatile suspended solids as sodium concentrations increased from 1.3 to 9.1 g Na+ L−1. Higher EPS production, particularly a greater predominance of carbohydrates, was stimulated by higher sodium concentrations. This study provides insights into the superiority of sodium tolerance of two-stage anaerobic digester in compared with a single-stage anaerobic system.