Two-stage System Research Articles

Monte carlo simulations for tuning optical properties in a two-stage liquid crystal retarder system via Mueller matrix method

Monte carlo simulations for tuning optical properties in a two-stage liquid crystal retarder system via Mueller matrix method

The kinetics of a two-stage completely stirred tank reactor for treating tofu wastewater by anaerobic digestion

ABSTRACT Tofu wastewater is an inevitable by-product of the bean curd production process. In this study, we used a two-stage continuous stirred tank reactor (CSTR) to treat tofu wastewater. The kinetic analysis of two CSTR reactors was conducted utilizing the material accounting model, microbial accounting model, and first-order kinetic model. The results demonstrated that the methane production coefficient of reactor 1 was 0.00573 LCH4·mg−1 greater than that of reactor 2, which is 0.00533 L CH4·mg−1. The first-order kinetic constants of reactor 1 were poorer than those of reactor 2, and their values are 0.15700 d−1 and 0.11574 d−1, respectively. The microbial yield coefficients of reactors 1 and 2 were 0.009648 and 0.060704, respectively. Under different organic loading rates, the average microbial concentrations were 25.24000 and 2.706667 mg·L−1 for reactors 1 and 2, respectively. The operational performance of the two-stage CSTR anaerobic digestion system was evaluated in order to design a novel and unique method as well as provide a new perspective for enhancing the performance of anaerobic digestion.

Design of a two-stage photovoltaic grid-connected system with dual closed-loop control

Abstract This paper designs a two-stage photovoltaic grid-connected system with dual closed-loop control, cascading the topological structures of photovoltaic cells, boost chopper circuits, and inverter circuits. The front-stage boost chopper circuit control utilizes the incremental conductance method to achieve maximum power point tracking control. The rear-stage inverter circuit employs a dual closed-loop control system with an outer voltage loop and an inner current loop, incorporating a proportional-integral controller, to ensure stable DC-side voltage and unity power factor for grid connection. A simulation model of the two-stage photovoltaic grid-connected system designed in this paper was constructed and analyzed through simulation runs. The firmness of the DC-side voltage and the achievement of unity power factor during grid connection confirmed the operability and resultiveness of the cascaded topology and the control method.

Synergistic microalgal co-cultivation for treatment of municipal wastewater using a two-stage cultivation system and biomass valorization

Synergistic microalgal co-cultivation for treatment of municipal wastewater using a two-stage cultivation system and biomass valorization

Controllable synthesis of hydrogen-bonded organic framework encapsulated enzyme for continuous production of chiral hydroxybutyric acid in a two-stage cascade microreactor

Constructing a framework carrier to stabilize protein conformation, induce high embedding efficiency, and acquire low mass-transfer resistance is an urgent issue in the development of immobilized enzymes. Hydrogen-bonded organic frameworks (HOFs) have promising application potential for embedding enzymes. In fact, no metal involvement is required, and HOFs exhibit superior biocompatibility, and free access to substrates in mesoporous channels. Herein, a facile in situ growth approach was proposed for the self-assembly of alcohol dehydrogenase encapsulated in HOF. The micron-scale bio-catalytic composite was rapidly synthesized under mild conditions (aqueous phase and ambient temperature) with a controllable embedding rate. The high crystallinity and periodic arrangement channels of HOF were preserved at a high enzyme encapsulation efficiency of 59%. This bio-composite improved the tolerance of the enzyme to the acid-base environment and retained 81% of its initial activity after five cycles of batch hydrogenation involving NADH coenzyme. Based on this controllably synthesized bio-catalytic material and a common lipase, we further developed a two-stage cascade microchemical system and achieved the continuous production of chiral hydroxybutyric acid (R-3-HBA).

Uncovering pathway and mechanism of simultaneous thiocyanate detoxicity and nitrate removal through anammox and denitrification

Thiocyanate (SCN−) exists in various industries and is detrimental to the ecosystem, necessitating cost-effective and environmentally benign treatment. In response to alleviate the bacterial toxicity of SCN−, this study developed a two-stage coupled system by tandem of anammox in reactor 1 (R1) and SCN−-driven autotrophic denitrification in reactor 2 (R2), achieving simultaneous removal of SCN− and nitrogen. The total nitrogen removal efficiency of the coupled system was 92.42 ± 1.98%, with nearly 100% of SCN− elimination. Thiobacillus was responsible for SCN− degradation. The deduced degradation pathway of SCN− was via the cyanate pathway before coupling, followed by the co-action of cyanate pathway and carbonyl sulfide pathway after coupling. Although scaling-up study is needed to validate its applicability in real-world applications, this study contributes to the advancement of sustainable and cost-effective wastewater treatment technologies, being an attractive path for low-carbon nitrogen removal and greenhouse gas emission-free technology.

Enhanced performance and economic feasibility of sewage sludge digestion using a two-stage anaerobic digestion with a dynamic membrane and alkaline-thermal pretreatment

This study suggests a high-rate sewage sludge anaerobic digestion (AD) process. An alkaline-thermal pretreatment and a dynamic membrane (DM) were used to enhance AD efficiency and economic feasibility in a two-stage system. The effect of pretreatment on volatile fatty acid (VFA) production in the acidogenic phase was investigated at various hydraulic retention times (HRT). After optimizing the acidogenic phase condition (HRT of 3 days), single- and two-stage AD processes with DM modules were operated simultaneously to compare performance. The highest methane production rates of 0.69 L/L/d for single-stage AD and 1.10 L/L/d for two-stage AD were observed at a total HRT of 12 days. Phase separation enhanced the growth of acetoclastic methanogens. A techno-economic analysis showed that the two-stage AD system would achieve a positive net present value within 2 years. This study demonstrated the feasibility of high-rate AD systems for sewage sludge using DM, alkaline-thermal pretreatment, and phase separation.

Advanced Two-Stage Nanocomposite Membrane System for Methane and Carbon Dioxide Separation from Atmospheric Air

This paper presents an advanced two-stage nanocomposite membrane system designed to efficiently separate and capture methane (CH4) and carbon dioxide (CO2) from atmospheric air and water sources. The membrane system comprises a CO2-selective primary membrane and a CH4-selective secondary membrane, utilizing a hierarchical nanomaterials and polymers structure. The proposed system demonstrates unprecedented versatility, operating effectively across an extensive range of gas concentrations (>20% to <0.02%) and reducing CH4 levels from 100-500 ppm to 5-10 ppm in both aerobic and anaerobic conditions. Performance metrics specify CO2 permeances of 200-2000 GPU and CO2/N2 selectivities of 30-500 at 57 °C and 1 atm feed pressure, surpassing the Robeson upper bound for traditional polymer membranes. The CH4-selective membrane achieves 500-2000 GPU permeances with CH4/CO2 selectivities >50. Furthermore, experimental validation over 1000 hours of continuous operation demonstrated 92% methane capture efficiency under challenging conditions (55 tons/hour methane content at 30 °C). The system's energy consumption of 0.3 kWh/kg of CH4 captured underscores its efficiency compared to traditional methods. This innovative membrane technology offers a promising solution for addressing critical ecological and industrial challenges associated with greenhouse gas emissions in the 21st century.

Numerical investigation of pre-chamber holes diameter geometry on combustion parameters in a hydrogen-powered Turbulent Jet Ignition engine

The search for substitutes for conventional fuels leads to the use of hydrocarbon-free or synthetic fuels. One of them is hydrogen. The use of hydrogen in combination with a two-stage charge creation system leads to the combustion of lean (λ > 1) or very lean (λ > 3) charges. The simulation tests carried out were aimed at determining the best configuration of the chamber connecting the prechamber with the main combustion chamber. Three variants of the diameter of the holes connecting the chambers were selected (d = 0.5; 1.0 and 1.5 mm) in combination with different fuel doses fed to the prechamber. A passive chamber (qo_PC = 0 mg) and an active chamber (qo_PC = 0.4 and 1.2 mg) were used, while simultaneously sending a dose of fuel to the main chamber (qo_MC = 6 mg). The research was conducted using AVL Fire 2022.1 software using the moving mesh of the LDV engine. As a result of simulation work, the most favorable conditions for carrying out the process were determined, considering the thermodynamic effects of the process and the accepted values of nitrogen oxide concentration. The resulting correlation maps of the sizes of the chamber openings and the fuel doses fed to the prechamber may determine the initial selection of possibilities for controlling hydrogen combustion in the TJI system.

Energy and exergy analysis of a two-stage cascade vapor compression refrigeration system with modified system configuration

This study proposes a modification to the two-stage cascade vapor compression refrigeration system by adding internal heat exchangers that function as subcoolers and desuperheater. The influence of each internal heat exchanger proposed on the exergy destruction rate, exergy efficiency, compressor power consumption, ECOP, and COP of the system was investigated. Additionally, various refrigerant combinations were considered as working fluids to evaluate which combination is the most suitable for the proposed system. Mathematical models based on the principles of thermodynamics were established in Engineering Equation Solver (EES), a software used for energy and exergy analysis. The results reveal that the addition of specific internal heat exchangers causes either an increase or decrease in overall system performance, depending on the type of refrigerant combination used. Consequently, there exists an optimal system configuration for each refrigerant combination. Compared with the conventional two-stage cascade refrigeration system, the optimal system configurations in the present study exhibited higher overall system performance. A maximum increase in exergy efficiency, ECOP, and COP of 7.31 %, 9.8 %, and 7.3 %, respectively, can be observed with the refrigerant combination R450A/R404A. Additionally, the results of the exergy analysis identify that the HTC compressor, condenser, LTC compressor, and cascade condenser are the primary contributors to the exergy destruction rate within the system.

Design and performance evaluation of a stick–slip actuator with Z-shaped beam and two-stage amplification system

Abstract In the domain of piezoelectric driving, actuators that utilize the stick–slip effect at high speeds and low frequency have garnered significant interest. This study presents an innovative linear piezoelectric actuator that integrates a two-stage amplification system with a Z-shaped beam mechanism. The designed actuator has good driving speed at low frequency while overcoming the disadvantage of such actuators requiring two flexible mechanisms to achieve reverse motion and poor reverse performance. The structure and scale of the actuator are explained and designed through theory and simulation. The experimental results demonstrate the prototype’s capability for bidirectional motion. Subjected to a 400 Hz and 140 V excitation, the maximum speed of the actuator is 12.88 mm s−1. The maximum load capacity is tested to be of 0.35 N. This research introduces a new approach for the design of high-speed bidirectional motion stick–slip piezoelectric actuators.

The Influence of Helium Addition on the Combustion Process in a Hydrogen-Fueled Turbulent Jet Ignition Engine

There are considerably fewer requirements for the quality of hydrogen combusted in an engine than its quality for fuel cells. Therefore, the analysis was carried out on the combustion of hydrogen–helium mixtures in an engine with a two-stage combustion system (TJI—Turbulent Jet Ignition). A single-cylinder research engine with a passive and active prechamber was used. A hydrogen–helium mixture was supplied to the main chamber in proportions of 100:0, 90:10, 80:20, 30:70, and 60:40 volume fractions. The prechamber was fueled only with pure hydrogen. Combustion was carried out in the lean charge range (λ = 1.5–3) and at a constant value of the Center of Combustion (CoC = 8–10 deg aTDC). It was found that the helium concentration in the mixture affected the changes in combustion pressure, heat release rate and the amount of heat release. It was observed that increasing the proportion of helium in the mixture by 10% also reduces the IMEP by approximately 10% and reduces the rate of heat release by approximately 20%. In addition, helium influences knock combustion. Limits of MAPO = 1 bar mean assumed that knock combustion occurs in the main chamber at values of λ < 1.9. Increasing the excess air ratio results in a gradual reduction in the temperature of the exhaust gas, which has a very rapid effect on changes in the concentration of nitrogen oxides. Studies carried out on the helium addition in hydrogen fuel indicate that it is possible to use such blends with a partial deterioration of the thermodynamic properties of the two-stage combustion process.

In-situ algal control by two-stage nanobubble technology in Taihu Lake: Efficacy and ecological impact

Hydrodynamic cavitation and ozone nanobubble-coupled hydrodynamic cavitation have demonstrated effective algae control in laboratories, but their in-situ potential, especially impact on nutrient salt degradation and microbial communities remain unclear. This study applied two-stage nanobubble technology, combining hydrodynamic cavitation and ozone nanobubbles, in a 3300 m2 semi-enclosed area of Taihu Lake to address these gaps. Results show that the technology efficiently controls algae, reduces odors, improves anaerobic conditions, and lowers ammonia nitrogen. Over 20 days, chlorophyll-a concentration reduced by 77.46% and cyanobacterial phycocyanin by 89.47%. Additionally, the concentrations of 2-MIB, GSM, and DMTS fell below threshold values. Notably, the relative abundance of Cyanobacteria in sediment dropped from 8.53% in the control area to only 1.59%–3.65% in the experimental area. The technology also achieved a significant reduction in ammonia nitrogen, with removal efficiencies of 78.53% in the water column and 39.17% in sediments, though the removal of total phosphorus was limited. Furthermore, the two-stage nanobubble system enhanced the abundance of nitrogen-cycling microorganisms and genes in the water, while promoting nitrogen- and phosphorus-related microbial communities in sediments and inhibiting the cyanobacteria-associated genus Cyanobium PCC-6307. Thus, Two-stage nanobubble technology can be employed for in-situ algal control in aquatic ecosystems.

Municipal wastewater treatment using an innovative two-stage sequential microalgal co-cultivation system with different hydraulic retention time: A sustainable approach to circular economy

The present study proposes a sustainable circular bioeconomy approach for municipal wastewater (MWW) treatment, employing a sub-pilot two-stage sequential microalgal co-cultivation system (TSSCS), and evaluates the impact of hydraulic retention time (HRT) on MWW treatment efficiency, as well as biomass and biomolecule productivity. In the first stage of TSSCS, 2 ratios of Tetraselmis indica and one ratio of Picochlorum sp. (2TS:1PC) were used for the treatment of 75% raw MWW + 25% ASN-III, while in the second stage, 2PC:1TS was employed for the treatment of 50% 2TS:1PC effluent+ 50% ASN-III. At the end of the first and second stages of TSSCS, nutrient removal efficiencies were as follows: total nitrate (TN) was <80% and 90% on HRT-10 and HRT-12; total phosphate (TP) was <85% and 95% on HRT-16, and chemical oxygen demand (COD) was <75% and <85% on HRT-14 and HRT-10, respectively. In the TSSCS, 2TS:1PC (S1) and 2PC:1TS (S2) showed maximum biomass productivity of 2.65 and 2.78g/L on /L on HRT-14 and HRT-12, respectively. Additionally, biomass of 2TS:1PC (S1) and 2PC:1TS (S2) contains lipid content (38.67 and 40.67%), β-carotene (4.09 and 3.00mg/g), and astaxanthin (0.69 and 0.31mg/g), respectively.

Investigation of a novel combined ab- and ad- sorption based thermal energy storage and upgrade system

This paper presents a novel sorption-based cycle combining energy storage with energy upgrade to store low-grade heat for long periods and transform it on demand to usable energy at elevated temperatures. The system consists of an ammonia-water absorption system coupled to a resorption thermal transformer using manganese chloride and calcium chloride as the working pair with an ammonia absorbate. The absorption and adsorption systems are charged by separating the constituent sorbent-sorbate pairs, and they remain separated during the transition season. The discharge consists of a two-stage sorption process between the two systems. This work presents a transient thermodynamic model and analysis of the two-stage sorption system. For a typical solar thermal energy input of 106 °C during charging, and ambient temperatures of 5 °C and 25 °C in the winter and summer, respectively, the system is capable of discharging at an average elevated temperature of 62 °C with an energy storage efficiency of 27 %. This system is capable of simultaneously producing heat at a lower temperature by varying the mass flow rate through the high-temperature salt. The energy storage density of the combined system under different conditions is between 71 and 185 kJ kg−1. In comparison with other conventional single-stage thermal energy storage systems, this combination of absorption and adsorption-based storage provides a higher coefficient of performance for a comparable temperature output.

Life cycle assessment (LCA) and economic analysis of two-stage anaerobic process of co-digesting palm oil mill effluent (POME) with concentrated latex wastewater (CLW) for biogas production

This study outlines the results of a process-based life cycle assessment (LCA) of the environmental performance of biogas production from co-digestion of palm oil mill effluent (POME) and concentrated latex wastewater (CLW) in the two-stage anaerobic digestion (AD) process. Biogas is utilized global across several sectors, including electricity generation, heating, and transportation. The Open LCA 2.0.2 software was used to evaluate the LCA at the midpoint level by using 18 different impact categories. This study reveals the three main contributions of the AD process, which were global warming (8.65 × 102 kg CO2eq), water consumption (5.32 m3), and land use change (3.39 × 102 m2 a crop eq), this result corresponded with the previous study in Malaysia that examined biogas production from the AD of POME In addition, alternative scenarios, in which a single substrate, have been established to quantify the impacts of potential improvements of biogas production to compare with base scenario of co-digestion. The results show that the environmental impacts of the base scenario released were lower than those of the single POME substrate of alternative scenario 1 in most impact categories. Furthermore, economic analysis is a crucial factor in the practical implementation of the AD process. Linking LCA with economic analysis offers a comprehensive perspective on sustainability, balancing environmental impacts with financial performance to optimize the potential of the AD co-digestion process. This is the first study to apply LCA and economic analysis to this specific co-digestion process in a two-stage AD system. The economic analysis of the two-stage AD of co-digesting POME and CLW was 1200 m3/d production of wastewater (70 % of POME and 30 % of CLW) based on the factories' data. The result indicates net present value, internal rate of return, and payback period of 515,813.94 USD, 9.13 %, and 8.87 years, respectively. This work proposed the potential approach for implementing the two-stage AD co-digestion of POME and CLW while concurrently producing valuable bioenergy carriers.

Effects of hydrothermal pretreatment on sulfadiazine degradation during two-stage anaerobic digestion of pig manure

Antibiotics in animal manure pose significant risks to the environment and health. While anaerobic digestion (AD) is commonly used for pig manure treatment, its efficiency in antibiotic removal has been considerably limited. This study investigated the impact of hydrothermal pretreatment (HTP) on sulfadiazine (SDZ) removal in a two-stage AD system. Results indicated that the HTP process reduced SDZ concentration by 40.61%. Furthermore, the SDZ removal efficiency of the AD system coupling HTP increased from 50.90% to 65.04% compared to the untreated system. Biogas yield was also improved by 26.17% while maintaining system stability. Changes induced by HTP in the microbial communities revealed that Firmicutes, Bacteroidetes, Caldatribacteriota, and Proteobacteria emerged as the primary bacterial phyla. Following HTP, the relative abundance of Prevotella, which exhibited a strong negative correlation with SDZ concentration, increased significantly by 25-fold in the acidogenic stage. Proteiniphilum, Syntrophomonas and Sedimentibacter showed notable increases in the methanogenic stage after HTP. The N-heterocyclic metabolism carried out by Prevotella might have been the predominant SDZ degradation pathway in the acidogenic stage, while the benzene ring metabolism and hydroxylation by the Proteiniphilum emerged as the primary degradation pathways in the methanogenic stages. Furthermore, biodegradation intermediates were proven to be less toxic than SDZ itself, indicating that the HTP-enhanced two-stage AD process could be a viable way to lower the environmental risks associated with SDZ. The findings from this study provide valuable insights for removing SDZ from the environment via two-stage AD.

Natural refrigerant matching optimization and characteristic analysis of two-stage Rankine cycle for LNG cold power generation process

Unlike most waste heat recovery, LNG is a multi-component mixture, low temperature and wide boiling range make it difficult to achieve efficient recovery of cold energy with a conventional single-stage Rankine cycle. On the other hand, with the stricter restrictions on hydrofluorocarbons under the Kigali Amendment, more environmentally friendly natural refrigerants deserve more attention as alternatives. Therefore, to improve the recovery efficiency of cold energy, this paper studied the optimal natural refrigerant combination of two-stage Rankine cycle LNG cold energy power generation system, and analyzed the performance characteristics and influencing factors of the system. In addition, in order to verify the application potential of the system, the levelized cost of electricity and payback period of the system for different refrigerant combinations were also analyzed. The results show that at a delivery pressure of 0.6 MPa, the refrigerant combination of ‘ethylene + propane’ has the best power generation performance, with a net generation and exergy efficiency of 9020.8 kW and 35.54 %, respectively. The refrigerant combination of ‘ethylene + propylene’ has the best economic performance, with a levelized power cost and payback period of 0.0355 USD/kWh and 2.76 years, respectively. In the case of high delivery pressure requirements, ‘ethane + propane’ becomes the optimal refrigerant combination, which can simultaneously achieve optimal power generation performance and economic performance. In addition, as the delivery pressure decreases, the power generation and economic performance of the system will improve. It is also found that among all refrigerants, ethane and ethylene have the highest evaporation pressure, which is conducive to obtaining a greater effective enthalpy drop, but the required superheat is also larger, which reduces the heat transfer efficiency of the evaporator to a certain extent.

Optimization of cooling process under varied pulsed conditions in multi-stage thermoelectric systems

This paper addresses the issue of thermoelectric cooling in a pulsed quasi-steady state (repetitive) condition. This situation occurs, for example, for an electronic integrated circuit performing demanding tasks in a discontinuous manner. Using heat reservoirs of selected capacity that are part of the thermoelectric system and appropriate shaping of the time profile of the supplied electrical current, cooling temperatures not achievable in the steady state for the system can be reached in a pulsed manner for a specified period. This process is subject to optimisation. The analysis was carried out for a two-stage system with an internal (interstage) heat reservoir of a given thermal capacity. The aim of the study was to find the relationship between the level of the supercooling temperature, its repeatability and the ability to maintain this temperature for a given time. To this end, two supply current waveforms were adopted and optimised both without and with contact thermal resistance in the system. The lowest subcooling temperature of about 7 K lower than the steady-state temperature was obtained for a very long period and a very short holding time. Decreasing the period or increasing the holding time results in a non-linear increase in temperature. Similar effects are obtained for the contact thermal resistance present in each layer. A full map of the period-thermal resistance–temperature relationship was determined, as well as the supercooling potential curves.

RoboMan: An Adult-Sized Humanoid Robot with Enhanced Performance, Inherent Stability, and Two-Stage Balance Control to Facilitate Research on Humanoids

Creating an adult-sized humanoid robot with stable walking capabilities is a major challenge in robotics. While many renowned research groups focus on robots for perilous work environments and precision tasks, our approach simplifies balance control, making it accessible to robotics research groups and educational institutes. This facilitates the development of complex functionalities such as vision and object manipulation for adult-sized humanoids. This research article introduces RoboMan II, an advanced version of RoboMan I, which won the most prestigious award in all humanoid robot leagues at RoboCup 2016 due to its exceptional performance in walking and playing soccer. RoboMan II features significant improvements in performance, inherent stability, recovery after falls, and balance control. To facilitate its development, RoboMan II is lighter and incorporates a modified foot and parallel structure for its leg to boost its inherent stability, along with a two-stage balance control system for Immediate Response and Gradual Adaptation, enhancing its adaptability in various environments. Our simulation results demonstrate that RoboMan II’s walking stability on flat surfaces improved significantly in the face of minor perturbations, with the number of steps within the stable region increasing from 24%, with only the immediate controller to 58% when both controllers were used. Similar improvements were observed on inclined surfaces. Additionally, the 3D CAD files for all of the robot parts are released as open source in conjunction with this paper to facilitate reproduction and further innovation. The forthcoming RoboMan III will incorporate custom servo motors for increased speed, torque, and enhanced fall recovery, preventing disengagement of the gear box after a fall. It promises to be an invaluable asset for research and practical applications in humanoid robotics.