High Pressure Operation Research Articles

Coupling thermodynamics and economics of liquid CO2 energy storage system with refrigerant additives

Compressed gas energy storage has been applied as a significant solution to smooth fluctuation of renewable energy power. The utilization of CO2 as working fluid in the energy storage system is restricted by high operation pressure and severe condensation conditions. A CO2 mixtures energy storage system without cold storage in the charge period is designed. A comprehensive model and evaluation index that couple the system thermodynamics and economics are established, which is performed in an in-house code. The screened refrigerant additives of R32, R1270, R290, R161, R600a and R600 are examined to blend with CO2. Multi-parameter coupling analysis is carried out to focus on the concurrent relationship between design parameters. Results show that larger system efficiency can be expected when the refrigerant mass fraction moves toward to zero, but it will cause huge capital investment to calcium chloride. This indicates the existence of valley value in the levelized cost of electricity versus refrigerant mass fraction. The refrigerant R32 is mostly recommended due to the resulting largest efficiency and lowest levelized cost of electricity. The proposed system is demonstrated to be more safe and reliable as the storage pressure in high pressure tank is only 5.64 MPa for CO2/R32 (0.85/0.15) as working fluid. The valve exit temperature should be as low as possible and the charge and discharge pressures are preferably located in the ranges of 14–15 MPa for higher efficiency and lower levelized cost of electricity. More charge time and discharge time, longer operating life time, higher peak-hour electricity price and larger station capacity have positive effect on system economic feasibility.

Coupled Computational Fluid Dynamics-Discrete Element Method Model for Investigation of Powder Effects in Nonconventional Laser Powder Bed Fusion Process.

The present study proposes a comprehensive 3D computational fluid dynamics-discrete element method (CFD-DEM) coupled simulation model to investigate the particle dynamics induced by SS316L metal vapor spouting during single-scan-track laser powder bed fusion (L-PBF) processing. The model provides the ability to examine the effects of nonconventional process variables such as the chamber pressure and gravitational force on the suppression of the spatter and denudation phenomena. The simulation results imply that adjusting the gravitational force provides an effective technique for suppressing both spatter formation and powder bed denudation. In addition, the chamber pressure has only a marginal effect on the denudation phenomenon. In particular, under a higher operating pressure, the metal vapor tends to spout in the upward direction, while under a lower pressure, the spouting is more radially distributed. As a result, the simulation results obtained in this study have suggested that the chamber pressure and gravitational force may both provide feasible approaches for suppressing the spattering and denudation phenomena, particularly in the L-PBF processing of light-weight materials.

Bifunctionality of Re Supported on TiO2 in Driving Methanol Formation in Low-Temperature CO2 Hydrogenation.

Low temperature and high pressure are thermodynamically more favorable conditions to achieve high conversion and high methanol selectivity in CO2 hydrogenation. However, low-temperature activity is generally very poor due to the sluggish kinetics, and thus, designing highly selective catalysts active below 200 °C is a great challenge in CO2-to-methanol conversion. Recently, Re/TiO2 has been reported as a promising catalyst. We show that Re/TiO2 is indeed more active in continuous and high-pressure (56 and 331 bar) operations at 125-200 °C compared to an industrial Cu/ZnO/Al2O3 catalyst, which suffers from the formation of methyl formate and its decomposition to carbon monoxide. At lower temperatures, precise understanding and control over the active surface intermediates are crucial to boosting conversion kinetics. This work aims at elucidating the nature of active sites and active species by means of in situ/operando X-ray absorption spectroscopy, Raman spectroscopy, ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Transient operando DRIFTS studies uncover the activation of CO2 to form active formate intermediates leading to methanol formation and also active rhenium carbonyl intermediates leading to methane over cationic Re single atoms characterized by rhenium tricarbonyl complexes. The transient techniques enable us to differentiate the active species from the spectator one on TiO2 support, such as less reactive formate originating from spillover and methoxy from methanol adsorption. The AP-XPS supports the fact that metallic Re species act as H2 activators, leading to H-spillover and importantly to hydrogenation of the active formate intermediate present over cationic Re species. The origin of the unique reactivity of Re/TiO2 was suggested as the coexistence of cationic highly dispersed Re including single atoms, driving the formation of monodentate formate, and metallic Re clusters in the vicinity, activating the hydrogenation of the formate to methanol.

Numerical investigation on flammability of R32 leakage in heat pump outdoor unit with CFD simulation

R32 is receiving significant attention as an alternative refrigerant owing to its higher operating efficiency and lower environmental impact; however, it is classified as flammable refrigerants. There have been some studies on R32 leakages about indoor unit rooms but extremely limited studies about outdoor unit rooms. The outdoor unit room is more cramped than the indoor one, and leakage easily occurs due to high-temperature and high-pressure operating conditions. In this study, the flammability risk was evaluated through a comprehensive R32 leak study in the outdoor unit room. Critical factors including the leak diameter, unit installation height, refrigerant charge, air infiltration, window opening, and room size were carefully selected, and parameter studies and correlation analysis were conducted. As the leak diameter increased from 2 to 8 mm, the R32 volume fraction increased from 7.7 to 46.3%, indicating that the leak diameter is the most significant factor in increasing the R32 volume fraction. Considering that the leak diameter is less than 1 mm in a typical leak accident and the leak occurs with a diameter of 2 mm or more in a catastrophic case, the risk of R32 leak was found to be low under the conditions. By increasing the window opening and unit installation height, the concentration of R32 can be lowered below the LFL, thereby reducing the flammable volume to close to zero.

Structure optimization and operation characteristics of metal gas storage device based on compressed air energy storage system

Compressed air energy storage (CAES) is a key technology for promoting the replacement of fossil fuels with renewable energy. Currently, CAES systems typically require an underground salt cavern, which is limited by geological and geographical conditions. To promote the rapid popularization of CAES, there is an urgent need to develop new gas storage devices with flexible layouts. Metal pressure vessel as a gas storage device is concerned with the benefits of high storage pressure and reliable operation. Considering both strength and fatigue, this study conducted a structural optimization of Tank-D2000 and Pipe-D400 to achieve the design operating life with the minimal quality. Furthermore, the optimized structure was used to study the operating characteristics of the gas storage device by the multi-domain fluid–solid thermal coupling method and the real gas model. The results indicated that the internal convective heat transfer coefficient of the gas storage device was a linear function of time during operation, whereas the external natural convective heat transfer coefficient almost remained constant. The pressure distribution was uniform; however, the temperature difference was large, particularly for D400. Analysis and prediction based on the theory of the polytropic process showed that the polytropic index of D400 was lower than that of D2000, so the heat transfer of D400 was more adequate and the effective capacity of gas storage device under the designed operating pressure range was larger. With an increase in flow, polytropic index increased and was lower at energy storage than at energy release. The pressure prediction error was basically within the range of ±4 %, and the temperature prediction error was within the range of ±3 %.

Enhanced thermal performance of shell and tube phase change heat accumulator with novel biomimetic spider web fins

Shell and tube phase change heat accumulator (STPCA) has many advantages such as flexible arrangement, simple structure and high operation temperature and pressure. However, there are some limitations such as the low thermal conductivity of phase change material (PCM) and much un-melted PCM at the bottom of STPCA. In this contribution, in order to solve aforementioned problems of STPCA, we firstly designed novel biomimetic spider web fins and applied the enthalpy-porosity method to solve the problem of phase transition and obtain the liquid fraction and location of the solid–liquid interface at different times. Then, we compared the enhance heat storage effect of the novel fins with that of normal radial fins. In addition, we further analyze the effects of three different fin arrangements and four different fin radial angles on the thermal storage performance. The results show that the novel biomimetic spider web fins can accelerate the melting of PCM at the bottom of the accumulator, uniform the temperature distribution and greatly improve the heat storage rate of the accumulator. The complete melting time of PCM of the accumulator with the novel web fins is only 48 s, but the radial fins is 140 s, which is much longer than that of the accumulator with the novel web fins. Moreover, the radial angle mainly affects the later melting period, because the angle can affect the natural convection. In this work, the model with a radial angle of 75° shows the better thermal storage performance. This contribution can provide a guidance for STPCA design to improve the heat storage performance.

A non-uniform pressure distribution model on the end face in screw expander and shaft seal leakage characteristics{fr}Etude des paramètres de la Structure sur les fuites d'arbres dans un expandeur à vis basé sur un nouveau modèle de distribution de pression non uniforme sur la face d'extrémité

Pressure distribution on the end face of screw expanders is the primary premise for calculating shaft seal leakage and axial force. Different from other types of expanders, pressure distribution on the screw expander end face is not only affected by operating conditions but also closely related to rotor geometric parameters. To illustrate the leakage characteristics of shaft seal in screw expanders, a non-uniform pressure distribution model on the end face was proposed, and a thermodynamic leakage model in the shaft seal was established. Labyrinth seal, the most widely used sealing assembly, was taken as an example to study the effects of shaft seal parameters on leakage. The influence of four main parameters, namely tooth tip clearance, cavity depth, cavity width, and clearance on the rotor end face, on the leakage of the shaft seal was studied. The results show that pressure on the screw expander end face is non-uniformly distributed, and the average pressure is far less than the highest operating pressure. Moreover, the leakage through the shaft seal rises rapidly with the increase of end face clearance and tooth tip clearance, and a 0.1 mm increment of them can lead to increased leakage up to 108.6% and 52.5%, respectively. And the leakage drops with the increment of cavity width. There is an optimal depth-to-width ratio of about 0.13 for minimum leakage. Clearance on the rotor end face has the most significant influence on the leakage of the seal, followed by the tooth tip clearance, cavity width, and cavity depth.

Performance enhancement of metal hydride hydrogen compressors using a novel operating procedure

The H2 refueling infrastructure's capital and operating expenses are mostly driven by the cost of hydrogen compression. To effectively address this issue, thermally driven H2 compression using metal hydrides (MH) may be used. For industrial customers who have the required infrastructure, such as H2 pipelines, low-grade heat sources, etc., metal hydride hydrogen compressors (MHHC) are particularly promising. However, the H2 compression cycle time issue is brought on by the poor thermal conductivity of the MH's powder. In the present study, a novel MHHC operating procedure is examined numerically. This procedure offers two possible options: The first is referred to as a “Multiple-Cycle Simultaneous Procedure’ (MCSiP for short), as the MH beds' sensible cooling (or sensible heating) and hydrogen's absorption (or desorption) processes start simultaneously and the final pressure is reached after a number of sub-cycles of compression. The second one, dubbed the ”Multiple-Cycle Sequential Procedure“ (MCSeP for short), is similar to the MCSiP mode except that the MH beds' sensible cooling (or sensible heating) as well as the hydrogen's absorption (or desorption) start out sequentially. To evaluate the impact of this procedure on the compressor’s performance, a theoretical model was established and effectively validated by comparison with experimental results reported in the literature. The simulation findings show that the suggested procedure compresses more hydrogen mass at high pressure and is faster than the other operating methods. For instance, 140 NL H2 at a pressure of 110 bar can be obtained with a 70% reduction in compression time compared to the commonly used operating mode utilizing 1.0 kg of MmNi4.6Al0.4 as low pressure MH and 0.832 kg of Ti0.99Zr0.01V0.43Fe0.099Cr0.05Mn1.5 as high pressure MH and operating conditions of 20 bar supply pressure, 293 K absorption temperature, and 373 K desorption temperature.

Enhancing Construction Enterprise Financial Performance through Digital Inclusive Finance: An Insight into Supply Chain Finance

Digital Inclusive Finance (DIF) is a novel approach that employs digital technology to foster the development of inclusive finance, which can effectively alleviate the financing constraints of enterprises. This paper empirically tests the relationship between DIF and the financial performance of construction enterprises, with a focus of supply chain finance (SCF). The findings indicate that DIF can enhance the financial performance of construction enterprises, and SCF is one of the mechanisms through which DIF affects the financial performance of construction enterprises. Moreover, the cross-sectional analysis reveals that the impact of DIF on financial performance is more pronounced in firms with characteristics of private capital-holding and high operating pressure. This study not only enriches the research perspectives of DIF, but also provides valuable insights for policymakers to formulate effective policies.

Machine learning framework for estimating CO2 adsorption on coalbed for carbon capture, utilization, and storage applications

For the purpose of carbon capture, utilization, and storage, carbon dioxide (CO2) injection in coal formations can enhance methane recovery and mitigate climate change. However, measuring CO2 adsorption isotherms using experimental or mathematical models can be time-consuming, expensive, and inaccurate. Thus, this study presents a machine-learning framework that predicts CO2 adsorption in coal formations based on various coal properties and testing conditions. Machine-learning (ML) framework was applied using a dataset of 1,064 points collected for different coal samples at different operating conditions to predict the CO2 adsorption in coal surface. The ML techniques include decision tree regression (DT), random forests (RF), gradient boost regression (GBR), K-nearest neighbor (KNN), artificial neural network (ANN), function network (FN), and adaptive neuro-fuzzy inference system (ANFIS). The applied framework determines CO2 adsorption as a function of coal's physical and chemical properties (moisture, ash, volatile matter, and fixed carbon content), the vitrinite reflectance of the coal samples, and testing conditions (pressure and temperature). Classical statical tools such as R2, root mean square error (RMSE), and average absolute percentage error (AAPE) were used to evaluate the model's performance analysis.The results demonstrated the ability to determine CO2 adsorption for varying coal types and at different temperature and pressure conditions. The statistical measures suggested that RF, GBR, and KNN are very reliable ML models, with RF being the best. At low operating pressure (P < 4 MPa), CO2 adsorption is impacted by any pressure changes, while it is stabilized at high-pressure values and becomes more dependent on the rock properties at high operating pressure (P > 4 MPa). The introduced ML framework offers a technique to evaluate the capability of different algorithms and accurately estimate CO2 adsorption without the requirement of additional experimental measurements or complicated mathematical techniques.

Hydrogen Embrittlement Characteristics of a Die-Casting Die after a High-Pressure Die-Casting Operation

Hydrogen Embrittlement Characteristics of a Die-Casting Die after a High-Pressure Die-Casting Operation

Numerical analysis of a double interlocking padded finger seal performance based on thermo-fluid-structure coupling method

Non-contacting finger seals represent an advanced non-contacting and compliant seal in gas turbine sealing technology. This paper proposes a new structure of non-contacting finger seals with double interlocking pads. The numerical analysis model based on the thermo-fluid-structure coupling method for the new type finger seal was established. The influence of working conditions on leakage of the seal was studied and compared with the single padded non-contacting finger seal. The results show that the interface between the bottom of the finger pad and rotor surface is the main leakage path that forms the gas film with obvious variations of pressure and flow velocity. Under high temperature and high pressure operating conditions, the hydrodynamic effect of the gas film is enhanced, and lifting force is significantly improved. The deformation of fingers is composed of elastic deformation and thermal deformation. At room temperature, the deformation of fingers is mainly elastic deformation and points to the center of the rotor, which reduces the gas film clearance. The deformation of fingers at high temperature and high pressure creates a circumferentially convergent gap between the bottom of the pad and the rotor, which is beneficial to improve the loading capacity and to reduce leakage of the seal. Compared with the typical single padded non-contacting finger seal, the double interlocking padded finger seal proposed in this paper reduces the leakage factor by about 37%, which provides an advanced seal concept with the potential to improve sealing performance under high temperature and high pressure working conditions.

Design of an elevated pressure electrochemical flow cell for CO2 reduction

The electrochemical CO2 reduction reaction (CO2RR) has been proposed as a sustainable way of closing the carbon cycle while synthesizing useful commodity chemicals. One of the possible routes to scale up the process is the elevated pressure CO2RR, as this increases the concentration of the poorly soluble CO2 in aqueous systems. Yet, there are not many studies that focus on this route owing to the inherent challenges with high pressure systems. In this study, a novel high pressure flow cell setup has been designed and validated. The modular design uses a clamp system, which facilitates simple stacking of multiple cell parts while being capable of handling pressures up to 50 bar. The effects of CO2 pressure on the reaction were investigated on a gold (Au) foil cathode in a 0.1 M KHCO3 electrolyte. We successfully measured gaseous products produced during high pressure operation using an inline gas chromatograph. We find that the selectivity toward CO2 reduction products is enhanced while that of H2 evolution is suppressed as the pressure is increased from 2 to 30 bar. The reported setup provides a robust means to conduct high pressure electrolysis experiments in an easy and safe manner, making this technology more accessible to the electrochemical CO2RR community.Graphical abstract

Morphological and Coordination Modulations in Iridium Electrocatalyst for Robust and Stable Acidic OER Catalysis.

Proton exchange membrane water splitting (PEMWS) technology has high-level current density, high operating pressure, small electrolyzer-size, integrity, flexibility, and has good adaptability to the volatility of wind power and photovoltaics, but the development of both active and high stability of the anode electrocatalyst in acidic environment is still a huge challenge, which seriously hinders the promotion and application of PEMWS. In recent years, researchers have made tremendous attempts in the development of high-quality active anode electrocatalyst, and we summarize some of the research progress made by our group in the design and synthesis of PEMWS anode electrocatalysts with different nanostructures, and makes full use of electrocatalytic activity points to increase the inherent activity of Iridium (Ir) sites, and provides optimization strategies for the long-term non-decay of catalysts under high anode potential in acidic environments. At this stage, these research advances are expected to facilitate the research and technological progress of PEMWS, and providing some research ideas and references for future research on efficient and inexpensive PEMWS anode electrocatalysts.

Biodiesel Fuel Production from Soybean Oil Using a Microreactor

The synthesis of fatty acid methyl ester from soybean oil was examined. A microreactor was used as a reactor, and the results were compared with those by batch reaction. In a batch reaction experiment, the concentration of by-product glycerol was large when methanol/soybean oil ratio was low, which inhibited the mass transfer between methanol and oil, and as a result, reduced fatty acid methyl ester yield. On the other hand, when the reaction was conducted under an emulsion state using a microreactor, the initial reaction rate was significantly increased, achieving a specific interfacial area about 7 times larger than that of the batch reaction. Furthermore, the decrease in reaction rate was suppressed and the space-time fatty acid methyl ester yield was successfully increased. When the reaction was conducted under a segmented flow state, the initial reaction rate decreased because of the smaller specific interfacial area. However, the mass transfer coefficient increased about 30-fold, and furthermore, the phase separation was completed immediately after the reaction. Finally, the high temperature and high-pressure flow operation was conducted using a microreactor, which enabled an efficient fatty acid methyl ester production from soybean oil at 2 – 3 times higher space-time yield with less amount of catalyst and/or methanol use compared to the conventional batch production method.

Pressurised Anaerobic Digestion for Reducing the Costs of Biogas Upgrading

The overall purpose of this study is to investigate the potential for producing higher energy biogas at elevated fermentation pressures. Upgrading of biogas is often carried out to increase its methane (energy) content by removing carbon dioxide. Upgrading is used, for example, to give methane of sufficient purity that it can be injected directly into the gas supply grid. In this research, freshwater algae are used as the feedstock for anaerobic digestion (AD) to produce biogas as a source of renewable energy. Although this has been the subject of extensive research over the past few decades, the main reason why AD has not been more widely commercialised is because it can have poor economic viability. In this paper, we used two similar bioreactors of capacity 1.5 L to generate biogas at different pressures. The methane concentration of the biogas increases to at least 70.0% for a headspace pressure greater than 4 bara compared to 57.5% or less when the pressure is less than 1.6 bara. The higher pressure operation therefore reduces the amount of upgrading required leading to a reduction in the cost of this step. Another interesting finding of this study is that the solubility of biogas in the digestate is estimated to be only 3.7% (best fit value) of its solubility in pure water, which is much lower than the values previously reported in the literature.

Comparative thermo-economic analysis of co-axial closed-loop geothermal systems using CO2 and water as working fluids

Co-axial closed-loop geothermal heating systems coupling abandoned oil/gas wells face more grievous corrosion issues than the shallow ground source heat pumps due to the higher temperature and pressure conditions. Instead of water, using CO2 as a working fluid would extract more power and eliminate the corrosion issue; however, these advantages might be offset by the energy and capital cost of high operating pressure. To better guide the working fluid selection for the co-axial closed-loop geothermal heating systems, the effects of using CO2 as a working fluid on the system thermo-economic performance as well as the effects of geothermal gradients and tube diameters are evaluated. We first established a 2D thermodynamic model to simulate the heat extraction from a vertical co-axial closed loop geothermal well and the heat conduction in host rocks and then applied the key parameters into an economic model for the calculation of thermo-economic indicators. It is found that the wellbore set with smaller tube diameters can profit the thermo-economic performance of the co-axial closed-loop geothermal heating system by substantially lowering the total annual cost, promoting the energy efficiency, and slowing down the growth of cost and the descent of energy efficiency within the lifetime of the system. Besides, CO2 will be a better working fluid for small-scale co-axial closed-loop geothermal heating systems leading to lower cost per net power compared to water, and it also can slow down the descent of energy efficiency year by year.

Modeling of single- and double-sided high-pressure operation of solid oxide electrolysis stacks

This study concerns numerical investigation of a solid oxide electrolysis stack, in which the cells are pressurized on only the fuel side (single-sided mode) or both fuel and air sides (double-sided mode). A 90-cell stack model is used to study the effects of the operating pressure on the polarization curves, area-specific-resistance (ASR), temperature, and pressure. The model predicts higher open-circuit voltage (OCV), lower ASR, and lower pressure drops over the flow fields at higher operating pressures. The latter leads to flexibility in the flow field design. The results show that the single-sided mode hinders the OCV increase and reduces the ASR. Nonetheless, the ASR reduction under the double-sided mode is more significant than the single-sided mode. Therefore, the double-sided mode performs better at high current densities since its higher ASR reduction provides a lower increase in the stack voltage (/input power). Moreover, the results indicate a nonlinear relationship between the temperature distribution and the operating pressure under the double-sided mode due to its counteracting effects on the ohmic heat sources and reaction heat sink. It is illustrated that the temperature difference over the stack decreases under the double-sided mode at higher operating pressures and lower current densities.

Modeling and comprehensive analysis of hydrogen production in a newly designed steam methane reformer with membrane system

The use of a hydrogen perm-selective membrane in the conventional steam methane reformer (SMR) is a promising technology for producing ultra-pure hydrogen under moderate operating conditions. A detailed computational fluid dynamics (CFD) analysis is performed on a membrane SMR unit for an on-site hydrogen refueling station (HRS) to get the optimum operating conditions. The developed model was validated with experimental results. The obtained results predicted that the high temperature of the process gas inlet, the high operating pressure, and the low gas hourly space velocity (GHSV) were advantageous. However, these factors must be carefully adjusted to achieve optimal efficiency. Furthermore, the simulation with a counter-current sweep gas flow configuration gave better results than a co-current operation. The estimated optimal conditions for improved CH4 conversion and H2 recovery were 4500 h−1 GHSV, 500 K inlet temperature, and the 8.5 bar operating pressure, representing CH4 conversion and H2 recovery of approximately 94.7% and 95.8%, respectively.

Two-phase analytical modeling and intelligence parameter estimation of proton exchange membrane electrolyzer for hydrogen production

The proton exchange membrane electrolyzer (PEME) is a promising tool for hydrogen production, and internal two-phase transport significantly influences its performance. In this study, a two-phase analytical PEME model incorporating the liquid saturation jump effect was developed, and intelligent parameter estimation using a genetic algorithm was proposed to achieve high-efficiency model validation. In-house experiments and experimental results from numerous papers in the literature were employed to prove the effectiveness of the proposed intelligent parameter estimation. Moreover, the two-phase simulation results demonstrated that the PEME voltage increased significantly when the current density reached the limiting value, and the liquid saturation in the anode catalyst layer (ACL) dropped to nearly zero. Increasing ACL porosity, decreasing ACL permeability, and decreasing ACL thickness could increase the limiting current density within the investigated range. The simulated limiting current density could be > 5 A cm−2 through proper design of the ACL parameters. For high-pressure cathode operation, increasing the cathode pressure and membrane permeability generally benefits water management inside the PEME and therefore increases the limiting current density. This study provides critical support for the design of cells and operating conditions for future PEME studies.