Feed Pressure Research Articles

Performance assessment of a novel porous catalytic reactor with a hydrogen-selective membrane for enhanced methane dry reforming process – CFD investigation

This manuscript offers a thorough examination of the efficiency of a reactor-assisted membrane system for the production of syngas through a process of methane dry reforming (DRM). The proposed strategy aims to bring attention to the optimization of the DRM and reverse water gas shift (RWGS) reactions, towards achieving increased conversions of methane and carbon dioxide, as well as increased purity in syngas production. This goal will be accomplished by integrating a selectively permeable membrane within the central region of the tubular catalytic porous bed reactor. The primary objective of the current research is to quantitatively assess the impact of operational parameters on both the hydrogen flux and concentration distribution of the various components residing in the reactor. This study highlights the impact of inlet feed pressure on hydrogen flux. It is found that an elevation in the inlet feed pressure from 1 to 4 bar yields an average increase in hydrogen flux from 2.60 to 4.21 kg/(m2.h), particularly when the inlet feed pressure is set at 2 bar. However, a subsequent increase to attain a pressure of 4 bar results in a decline in hydrogen flux to a rate of 2.78 kg/(m2.h). Moreover, increasing the inlet feed temperature from 900 to 1100 K leads to a substantial augmentation in the average hydrogen flux, from 7.08 to 8.56 kg/(m2.h), while maintaining a reactor wall temperature of 1000 K. As another finding, a molar ratio of CH4/CO2 of 1 leads to the greatest mean hydrogen flux of 4.73 kg/(m2.h) across the membrane interface. The current research work could provide useful tips/guidelines for efficient reactor design and optimization; it also enhances comprehension of reactor-assisted membrane systems in the context of syngas production.

Molecular-level manipulation of polyamide membranes for high-performance H2/CO2 separation

The preparation of high-performance H2/CO2 polymer separation membranes is an urgent need to reduce the global greenhouse effect. Here, polyamide (PA) membranes with excellent H2/CO2 separation performance are produced using a facile interfacial polymerization (IP) plus heat treatment approach. The synergistic effect of the substrate-confinement and the control of the d-spacing and crosslinking degree of PA membranes creates sufficient H2 selective channels. The effects of test parameters such as feed temperature and feed pressure on membrane performance were investigated. The ultra-high H2/CO2 selectivity of 110 with excellent H2 permeance of 180 GPU is observed at 150 °C and feed pressure of 2 bar. In addition, PA membranes have high-pressure resistance (16 bar), high-temperature resistance (300 °C), and attractive durability (210 h). The excellent performance and facile preparation process make them expected to be one of the most promising membranes for H2/CO2 separation.

Static state synthesis of STT zeolite membranes for high-pressure H2/CH4 separation

STT zeolite membrane with seven-membered rings (7 MR) and nine-membered rings (9 MR) is an ideal alternative for the separation of hydrogen (H2) and methane (CH4). However, the successful synthesis is only possible in rotation conditions, which is difficult to achieve at an industrial scale. Herein we developed a static synthesis approach to prepare high-quality STT zeolite membranes. The precursor transformed in-situ from a liquid state to a semi-solid state to efficiently suppress the nucleation in the bulk gel. This did not affect the growth of the seed layer to form a continuous membrane. The water content was modulated between y = 44 and y = 124 in the molar composition of 1 SiO2: 0.2 TMAdaOH: y H2O. The precursor could be re-used one more time to reduce the total amount of chemical waste. The optimal H2 permeance and H2/CH4 mixture selectivity was up to 6.1 × 10−8 mol m−2 s−1 Pa−1 and 115 at atm pressure. The H2 permeation flux monotonically increased to 2.0 Nm3 m−2 h−1 under feed pressure up to 2.1 MPa. This paves the way for zeolite membranes to high-pressure H2 separation in practical applications.

Experimental and kinetic modelling studies for the design of fixed bed methanol reactor over CuZA catalyst

Direct conversion of CO2 via hydrogenation to value-added chemicals is a vital approach for utilising CO2 emitted into the atmosphere. In this paper, a critical analysis of reaction kinetic modelling studies is explored in a fixed bed reactor to improve methanol yield for different H2 to CO2 ratios by simulating a lab-scale reactor for adiabatic and isothermal conditions. The feed inlet temperature and pressure variations are applied to study the effect of both configurations on methanol production. The results show that the isothermal configuration yields 2.76% more methanol yield compared to the adiabatic reactor. The effect of H2 to CO2 molar ratios of 3, 6 and 9 on the performance of the catalyst and the influence of CO and CO2 hydrogenation is investigated with model simulations. The overall methanol yield is increased from 19.03% to 36.41% with increase in H2 to CO2 molar ratio from 3 to 9. Experiments are performed using commercial copper-based catalyst for different temperatures of 210, 230 and 250 °C at a pressure of 40 bar for H2/CO2 of 3 and GHSV of 720 h−1 as well as at optimal temperature of 250 °C and 50 bar with varying H2/CO2 of 3, 6, 9 for 3 g and 6 g catalyst. The maximum methanol yield of 2.53% and space time yield of 13.59 mg/gcat.h is obtained at H2/CO2 ratio of 9.

Synergistic improvement in gas separation performance of MMMs by porogenic action and strong molecular forces of ZIF-93

In the present study, ZIF-93 metal–organic frameworks were prepared. N2 adsorption tests revealed that the particle size, specific surface area, and pore size of ZIF-93 were 30 nm–45 nm, 869.40 m2/g, and 0.36 nm, respectively. Pebax-based mixed matrix membranes (MMMs) were prepared using ZIF-93 as the filler. The pore diameters of ZIF-93 lied between the kinetic diameters of CO2 and N2; thus, its pore structure provided a fast transfer channel for CO2 and increased the permeability of the membrane. Further, X-ray diffraction showed that the membrane became denser upon introducing ZIF-93 because of the formation of a bridging structure between the Pebax molecular chains and ZIF-93. A denser stacking by moving the Pebax molecular chains closer to each other effectively bettered the CO2 selectivity of the mixed matrix membrane. The test results showed that when the ZIF-93 loading was 10 wt%, the CO2 permeability was 84.85 barrer and the CO2/N2 selectivity was 65.76 at 0.4 MPa, which are 51.57 % and 65.50 % higher than those of the pure Pebax membrane, respectively. When the feed pressure was increased to 0.8 MPa, the CO2 permeability was 94.5 barrer and the CO2/N2 selectivity is 87.5, which are 51.57 % and 65.50 % higher compared with those of the pure Pebax membrane, in order. The membrane performance significantly exceeded that of the 2008 Robeson curve.

Optimal design strategy, heuristics, and theoretical analysis of multi-stage reverse osmosis for seawater desalination

The RO process cannot be operated in a thermodynamically ideal state, and in general, additional pressure is required. In addition, multi-stage RO involves an increased number of design factors compared to single-stage RO, and the feed pressure and SEC of multi-stage RO have a complex correlation with the design conditions. In this study, a comprehensive assessment was conducted to evaluate the advantages of multi-stage RO over single-stage RO. Specifically, we found ranges where the multi-stage process loses its energy advantage over the single stage depending on the total recovery rate and suggested a break-even point in terms of energy, theoretically and practically. Furthermore, we investigated the impact of design factors such as stage recovery rate, number of elements per vessel, and total number of membranes applied to each stage on energy consumption, and we also presented the optimal conditions for the design factors with theoretical support. Finally, we compared all configurations of single and multi-stage RO processes under optimal conditions and suggested an energy-efficient process. These investigations could offer valuable design heuristics for optimal multi-stage RO setups and provide insights into the advantages of multi-stage RO processes over single-stage RO processes.

Permeance of Condensable Gases in Rubbery Polymer Membranes at High Pressure.

The gas transport properties of thin film composite membranes (TFCMs) with selective layers of PolyActive™, polydimethylsiloxane (PDMS), and polyoctylmethylsiloxane (POMS) were investigated over a range of temperatures (10-34 °C; temperature increments of 2 °C) and pressures (1-65 bar abs; 38 pressure increments). The variation in the feed pressure of condensable gases CO2 and C2H6 enabled the observation of peaks of permeance in dependence on the feed pressure and temperature. For PDMS and POMS, the permeance peak was reproduced at the same feed gas activity as when the feed temperature was changed. PolyActive™ TFCM showed a more complex behaviour, most probably due to a higher CO2 affinity towards the poly(ethylene glycol) domains of this block copolymer. A significant decrease in the permeate temperature associated with the Joule-Thomson effect was observed for all TFCMs. The stepwise permeance drop was observed at a feed gas activity of p/po ≥ 1, clearly indicating that a penetrant transfer through the selective layer occurs only according to the conditions on the feed side of the membrane. The permeate side gas temperature has no influence on the state of the selective layer or penetrant diffusing through it. The most likely cause of the observed TFCM behaviour is capillary condensation of the penetrant in the swollen selective layer material, which can be provoked by the clustering of penetrant molecules.

Renewable energy powered membrane technology: Impact of intermittency on membrane integrity

Directly coupled photovoltaic-powered nanofiltration/reverse osmosis is a sustainable and cost-effective solution to brackish water desalination in remote areas. Intermittent operation of the system may cause physical membrane damage and loss of membrane integrity. The potential causes of integrity loss during intermittency include the sudden spontaneous restart process, frequent shut-down events, and osmotic backwash (OB) cleaning with controlled permeate backpressure. A bench-scale crossflow system powered by a solar array simulator was used to perform periodic fluctuation on filtration experiments that in this case cause intermittency. A wide range of feed pressure increase rates (0.17 to 2 bar/s) during the start-up process, up to 1000 shut-down events, and additional permeate backpressure up to 4 bar to enhance OB were applied. Results show that no significant membrane performance deterioration was observed at the highest feed pressure increase rate (2 bar/s), and when the shut-down event number increased to 1000 implying the robustness of NF/RO membranes and spontaneous OB cleaning. When increasing permeate backpressure to 2–4 bar to enhance the OB process, membrane integrity loss of both membranes was observed. This demonstrates the reliability and robustness towards fluctuations, intermittency, and spontaneous OB cleaning in a directly coupled photovoltaic-powered nanofiltration/reverse osmosis system if permeate backwash is avoided.

Navigating the Dynamics of Squeeze Film Dampers: Unraveling Stiffness and Damping Using a Dual Lens of Reynolds Equation and Neural Network Models for Sensitivity Analysis and Predictive Insights

The squeeze film damper (SFD) is proven to be highly effective in mitigating rotor vibration as it traverses the critical speed, thus making it extensively utilized in the aeroengine domain. In this paper, we investigate the stiffness and damping of SFD using the Reynolds equation and neural network models. Our specific focus includes examining the structural and operating parameters of SFDs, such as clearance, feed pressure of oil, rotor whirl, and rotational speed. Firstly, the pressure distribution analytical model of the oil film inside the SFD based on the hydrodynamic lubrication theory is established, as described by the Reynolds equation. It obtained oil film forces, pressure, stiffness, and damping values under various sets of structural, lubrication, and operating parameters, including length, clearance, boundary pressure at both sides, rotational speed, and whirling motion, by applying difference computations to the Reynolds equation. Secondly, according to the significant analyses of the obtained oil film stiffness and damping, the following three parameters of the most significance are found: clearance, rotational speed, and rotor whirl. Furthermore, neural network models, including GA-BP and decision tree models, are established based on the obtained results of difference computation. The numerical simulation and calculation of these models are then applied to show their validity with all given parameters and the three significant parameters separately as two sets of model input. Regardless of either set of model inputs, these established neural network models are capable of predicting the nonlinear stiffness and damping of the oil film inside an SFD. These sensitive parameters merely require measurement, followed by the utilization of a neural network to predict stiffness and damping instead of the Reynolds equation. This process serves structural enhancement, facilitates parameter optimization in SFDs, and provides crucial support for refining the design parameters of SFDs.

Seasonal Variability of Cultivable Nitrate-Reducing and Denitrifying Bacteria and Functional Gene Copy Number in Fresh Water Lake.

This study describes the seasonal course of denitrifying and nitrate-reducing bacteria in a dimictic mesotrophic lake (Lake Scharmützelsee, Brandenburg, Germany) within a three-year period from 2011 to 2013. The bacterial cell numbers were quantified by the fluorescence microscopy, most probable number (MPN) and PCR-dependent quantification of the chromosomal 16S rDNA and of the nirS and nirK gene copy number. The highest seasonal differences (up to three orders of magnitudes) have been measured using MPN in the epilimnion. This variation was not reflected by PCR-dependent approaches or direct microscopical enumeration. At adverse conditions (low temperature and/or low nitrate concentrations), the differences between MPN and gene copy numbers increased by up to five orders of magnitudes and decreased to one magnitude at favourable environmental conditions. These results can be explained best by an increasing ratio of viable but not cultivable (VBNC) cells or dead cells at impairing conditions. In the hypolimnion, the courses of MPN and nir gene copy numbers were similar. This can be explained by a higher feeding pressure and therefore smaller amounts of dormant cells. In the pelagial in general, the total cell numbers enumerated by either microscopical or molecular approaches were similar. In the sediment, more than 99% of the DNA was obviously not related to viable bacteria but was rather DNA in dead cells or adsorbed to particle surfaces.

Artificial neural network and response surface methodology for modeling reverse osmosis process in wastewater treatment

The reverse osmosis (RO) process is widely utilized to reduce highly hazardous chemicals in wastewater, resulting in decreased electrical conductivity and enhanced usability. Reverse osmosis is regarded as an efficient desalination technique, and a comprehensive understanding of the mathematical modeling correlation in the RO system can contribute to the development of advanced RO systems. This research is concerned with the modeling and optimization of the RO process by leveraging machine learning techniques, such as Artificial Neural Networks (ANN) and Response Surface Methodology (RSM). Specifically, an ANN and RSM employing a central composite design (CCD) were performed to analyze the influence of key parameters, including flow rate (30–70 m3/hr), initial conductivity (2000–4000 µs/cm), feed pressure (13–17 bar), and solution temperature (11–39 °C), on the reduction of total dissolved solids (TDS) represent by conductivity in wastewater treatment. The outcomes derived from the RSM-CCD analysis demonstrated that the optimal conditions for achieving the lowest conductivity of 35 ± 10 µs/cm included a solution temperature of 31.6 °C, feed pressure of 16 bar, flow rate of 40 m3/hr, and an initial conductivity of 3500 µs/cm. Five ANN models have been suggested to evaluate the plant’s performance. Model-5 with two hidden layer, eleven hidden layer nodes (20 and 30 nodes) for first and second layers respectively. Moreover, ANN exhibited excellent performance, with a low (MSE) of < 0.0003 and a high (R2) of more than 0.99. These findings highlight the valuable utilization of RSM and ANN methodologies in the modeling and optimization procedures of the RO process.

Evaluación estadística del circuito de clasificación-molienda de la planta de carbón en pulpa de Antapite de la compañía Sierra Sun Group (Perú) empleando modeol s estadísticos de regresión y ANOVA

El presente trabajo pudo mostrar una evaluación estadística del circuito de molienda – clasificación de una planta aurífera de la planta Antapite de la Compañía Minera Sierra Sun Group (Perú). El circuito de molienda empleaba un molino de bolas, cuyo mineral descargado tenía una la ley de oro de 29.50 g/t, el cual alimentaba a un hidrociclón convencional Krebs (de 10 pulgadas de tamaño, 254 mm), cuyo rebose tenía una distribución de oro de 71.30 % (para tamaños de partículas de menos 74 μm). Sin embargo, el objetivo fue aumentar esta distribución a un valor equivalente a 77.39% (para partículas menores a 74 μm), es decir, al menos 5 puntos por encima de la actual. Este rebose alimentó al circuito metalúrgico formado por concentración gravimétrica y/o cianuración – adsorción dependiendo de la mineralogía con la que se encontraba asociada el oro. Se realizó un análisis estadístico de regresión múltiple para las variables de operación del hidrociclón Krebs de 10 pulgadas (254 mm) que permitió obtener la distribución de oro (objetivo mencionado anteriormente). De esta manera se plantearon tres escenarios diferentes, en los cuales se eliminaron las variables no significativas. El primer escenario evaluó la dependencia del tamaño de corte corregido d50C en función de la presión y caudal de la pulpa de alimentación al hidrociclón, el segundo escenario analizó la variable independiente: distribución de oro en el rebose del hidrociclón con respecto a las variables dependientes: caudal alimentado, presión, d50 y d50C para tamaños de partículas menores a 74 μm. Por último, el tercer escenario permitió evaluar la dependencia de la distribución de oro objetivo frente al d50C. Finalmente, se logró definir el parámetro que influye en la dependencia de la distribución de oro objetivo en el rebose, pudiendo encontrar así el valor de d50 (tamaño de corte sin corregir en micras) en función del caudal y presión de trabajo para llegar a la distribución de oro objetivo de 77.39% en el rebose (para partículas menores a 74 μm).

Optimization of Mixed Fluid Cascade Natural Gas Liquefaction Plant Feed Stream Pressure

This paper presents the results of a study on optimising the feed stream pressure of the Mixed Fluid Cascade natural gas liquefaction cycle. The objective is to optimise the pressure of the feed stream to distribute heat effectively over the cooling stages and reduce the energy cost of the cycle. To achieve the goal, the following tasks have been done: constructing the mathematical model of the cycle, per-forming the calculation experiment for different values of the feed stream pressure to determine energy characteristic values, and determining the optimal values of feed stream pressure. The flow characteristics of the working substances in the cycle are determined based on the Peng–Robinson–Stryjek–Vera equations of state and Benedict–Webb–Rubin. The mass flow of the working substance is calculated for each cycle's stage heat load, at both constant and different values of the working point temperatures. The distribution of heat load for liquefying 1 kg of natural gas by stages is displayed, and achievable working point temperatures of the feed flow are determined. The energy consumed by the compressor units and the amount of compression heat dissipated are calculated. The study's main finding is that the optimal feed pressure in the Mixed Fluid Cascade cycle is higher than the standard pressure. The significance of the obtained results lies in the significant reduction of energy costs of the Mixed Fluid Cascade cycle at a feed stream pressure of 13 MPa.

Development of remote-controlled solar-powered pesticide sprayer vehicle

Pest species pose a significant threat to the agricultural industry as they can negatively impact crop productivity and result in potential financial losses due to damage. This research aims to address agricultural challenges in the local area and improve the efficiency of pesticide application. A solar-powered, remote-controlled, semi-automated knapsack sprayer vehicle has been developed to address this issue. It operates using a 100 AH battery that is charged by four 30W solar panels connected in tandem to produce 120 W, providing power to the motors and pump. The vehicle uses a 12 V hub motor to drive the back and steer the front and is equipped with a 12 V window regulator/wiper motor. The vehicle is controlled by a remote control and an HC-05 transmitter and receiver, programmed with an ATMEGA32A linked to a relay board. The vehicle utilizes a 116 psi ≈ 799.8 kPa pump for the sprayer. Results indicate that as the feed pressure increases, the flow rate steadily rises and reaches 4 L per minute at the 799.8 kPa pump. With a pump spray rate of 5 L per minute when increased and a pesticide tank capacity of 20 L, the vehicle can spray for a total of 4 min and cover 159 m. Employing a remote control reduces the need for manual labour, making pesticide spraying more consistent, efficient, and productive. The sprayer also saves time compared to traditional methods and poses no harm to the operator.

Amidoxime-functionalized tetraphenylethylene ladder polymer for efficient membrane-based gas separations

Recent advances in solution-processible polymers of intrinsic microporosity (PIM) have attracted extensive research efforts in membrane-based gas separations due to their significantly enhanced gas permeability originating from inefficient chain packing. However, PIM-based membrane materials exhibit typically only moderate gas-pair selectivity, which is often insufficient especially for challenging gas separations containing highly sorbing feed components such as CO2. More importantly, they suffer from CO2-induced polymer chain dilation commonly referred as plasticization, which leads to poor separation performance under aggressive CO2/CH4 mixed-gas testing conditions. In this work, we conducted amidoxime (AO)-functionalization on a microporous tetraphenylethylene-based ladder polymer (TPE-PIM) by reacting its nitrile groups with hydroxyl amine under reflux conditions. Because of strong inter-chain hydrogen bonding, AO-functionalized TPE polymer (AO-TPE) exhibited a tightened and rigidified microstructure with 64 % reduction in Brunauer-Emmett-Teller (BET) surface area (175 m2/g) as compared to TPE-PIM (485 m2/g) derived from N2 adsorption isotherms at 77 K. As a result, fresh AO-TPE showed decreased gas permeability concurrent with a two-fold increase in CO2/CH4 selectivity (from 18 to 40) compared to TPE-PIM. Under aggressive 50:50 CO2:CH4 mixed-gas testing conditions, AO-TPE showed a strong plasticization resistance with decreased CH4 permeability over total feed pressure ranging from 4 to 30 bar. At 20 bar total pressure, AO-TPE demonstrated a mixed-gas CO2/CH4 selectivity of 37.7 as compared to 14.5 for TPE-PIM. The simple AO functionalization strategy holds promise to be an effective post-modification method to increase gas selectivity and alleviate the detrimental effects from CO2-induced plasticization.

Large-area and high-performance SSZ-13 membranes for N2/CH4 separation

Separating N2 from CH4 is challenging but critical for the purification of unconventional natural gas. Herein, large-area and high-quality SSZ-13 membranes were reproducibly produced on the 50-cm-long tubular alumina supports for the N2/CH4 separation for the first time. The effects of test parameters such as pressure drop, temperature, feed flow rate, water vapor and hydrocarbon impurities on separation performance of the membrane were investigated. A mathematic model for concentration polarization (CP) index was established to evaluate the extent of CP. The CP can be released by decreasing feed pressure and increasing feed flow rate. Separation performance of semi-industrial-scale SSZ-13 membrane was superior to most small-area zeolite membranes. The membrane showed excellent stability in the presence of 5–10 % ethane and propane and saturated water vapor. Selectivity and permeance of the membrane can be restored to its initial values when the impurities are removed. The up-scaling and high-quality membranes have the great potentials for the industrial application in natural gas purification.

Resources recovery from coal gasification residue by combined hydrocyclone and vibrating screen and characterization of separated products

Coal gasification fine slag (CGFS) is a solid waste rich in residual carbon and various inorganic elements produced in the process of coal gasification, and components separation is a prerequisite for its resourceful utilization and harmless disposal. In this paper, a CGFS sample was separated by a combined process of hydrocyclone and high-frequency vibrating screen (HFVS), and three products were obtained by optimizing separation parameters. The properties of each product were analyzed by XRD, XRF, SEM, BET, and TG-DSC. The results showed that the effective separation of residual carbon and ash in CGFS could be achieved at the hydrocyclone feeding pressure of 0.04 MPa and the HFVS aperture size of 0.074 mm, and LOI of the obtained concentrate, middling, and tailing products were 78.57%, 38.17%, and 20.42%, respectively, with a total recovery of residual carbon in concentrate and middling reaching 88.19%. Concentrate particles are mainly irregular or flocculent carbon with well-developed and comprehensive types of pores, as well as high calorific value and good combustion characteristics, which can be used to prepare porous adsorbent materials or as high-quality fuel. Middling is rich in aluminum and silicon elements, and it contains certain mesoporosity, calorific value and moderate combustibility, which suitable for preparing carbon-silicon composites or firing porous ceramics. Tailings have little residual carbon content but mainly consist of tiny spherical particles rich in inorganic element species and content, and it have fewer internal pores and low calorific value, which are suitable for the preparation of building materials, aluminum/silicon-based materials, or ecological restoration materials. This study provides important guidance for resource recovery and utilization of CGFS.

Evaluating the advantage of turbulent flow to diminish concentration polarization in Roto-dynamic RO system

Concentration polarization (CP) is the major shortcoming of the reverse osmosis (RO) system for brackish/seawater desalination. The present study aims to understand the effect of induced shear stress, enhanced flow dynamics, and eddy diffusivity on CP, when the flow is turbulent. In roto-dynamic RO system turbulence can be easily generated by controlling the angular speed of the rotor without increasing the feed discharge. We have numerically simulated the salt rejection by the RO membrane and concentration polarization at the seawater salinity of 500 mol/m3 for two different configurations of roto-dynamic RO system when the flow is turbulent. We have used Reynolds stress model (RSM) and eddy viscosity-dependent eddy diffusivity models for salt transport. In turbulent flow regime, eddy diffusion enhances the mixing. In laminar flow regime, salt concentration over the membrane increases by 60%–110% for 70 bar feed pressure. In contrast, the increment of salt concentration is only about 3%–4% once the flow becomes turbulent, leading to 3–4 times higher permeate discharge for roto-dynamic RO system. Thus, it can increase the longevity of the membrane and improve overall performance of the RO module by delaying membrane scaling and fouling.

Growth characteristics and population dynamics of Macrophthalmus japonicus with decreasing microphytobenthos biomass in muddy estuarine tidal flat

The present study evaluated the population dynamics, growth, and biomass production of the ocypodid crab Macrophthalmus japonicus in muddy estuarine tidal flat through monthly surveys over a 10-year period. The mean annual biomass was 4.71–11.51 (7.9±2.5) g dry·m−2, and secondary production was 2.1–19.3 g dry·m−2·year−1 (11.3±5.3 g dry·m−2·year−1) and 1.59–6.16 (3.71±1.55) g C·m−2·year−1. Two to three cohorts of M. japonicus were observed in each year, with the population density of 10–61 individuals·m−2. New recruitment was noted around August in the summer of each year, with an estimated lifespan of 2–3 years. The production/biomass ratio was 0.46–2.02 (1.38±0.44). The population density of M. japonicus showed stable seasonal variations, while annual growth, production, and biomass decreased over the years. M. japonicus growth was associated with microphytobenthos biomass. In particular, long-term field investigations revealed the association between M. japonicus and microphytobenthos, suggesting that the feeding pressure of M. japonicus affected microphytobenthos biomass. Our findings will contribute to the better understanding of the growth characteristics and population dynamics of M. japonicus as well as the interactions between prey and predators in benthic tidal flat ecosystems, providing fundamental information for estimating material cycles.

Steady-State simulation of cryogenic distillation used for helium isotope separation

Helium-3 (3He) is an invaluable and scarce resource with applications in various scientific and industrial fields. It is typically found mixed with helium- 4(4He) in natural gas and nuclear off-gas, which is industrial source of helium. Therefore, separation of the helium isotope is necessary. Cryogenic distillation is a preferred method of separation due to its higher separation coefficient and processing capacity. In this study, a numerical steady-state simulation of cryogenic distillation column for helium isotope has been conducted using programming. The mathematical model for the equilibrium-state cryogenic distillation process was established and solutions of the thermodynamic formulation was proposed. The simulation provided the distribution of 3He and 4He along each distillation column as well as the profiles of temperature and flow rates along the column, based on the designed specifications including the composition of the feeding mixture, feed flow rate and pressure. The required heat duty of the condenser and reboiler was also calculated, and the column dimensions were estimated. Besides, we have studied the effects of the reflux ratio and feed concentration of 3He on the final isotopic contents of the top and bottom products. The results demonstrated that the distillation simulation could provide crucial theoretical support for the smooth execution of future laboratory experiments.