High Pressure Operation Research Articles

Pressure Vessel Design for High Temperature and Pressure Testing on Supercritical Carbon Dioxide

Abstract Supercritical carbon dioxide CO2 has been proposed as working fluid in various types of power plants, thanks to its potential higher efficiency and cost reduction with respect to well-known technology of steam cycles. However, the high operating temperature and pressure conditions pose significant concerns in terms of compatibility of supercritical CO2 with the high-temperature sections of the power block. Typically, to address this problem, experiments are proposed, where samples of different materials are kept in contact with the supercritical CO2 in a pressure vessel in order to test the material compatibility. This research deals with designing an innovative openable pressure vessel capable of withstanding the high temperatures (700 °C) and the pressures (100 bar) typical of those power plants. The results obtained by analytical calculation and the finite element method are consistent. The results obtained with both methods are generalizable and the methodology is applicable to any removable pressure vessel that must withstand 100 bar of pressure and a temperature of 700 °C, application field that is outside the ASME B&PV Code Section VIII division 1, standard usually used for the design of nonnuclear pressure vessels. It is important to emphasize that the use of a removable container allows to reduction of the costs of compatibility tests since otherwise, after each test, the pressure vessel would be disposed of. In addition, this allows a reduction of the environmental impact due to the fact that the new container will not be disposed of after each use.

Kinetics and mechanism study of dyes degradation in electric field-promoting catalytic wet air oxidation process

Wet air oxidation (WAO) is a clean and eco-friendly technology for dyes removal, but the high operating temperature and pressure limit its practical application. In the present work, an electric field-promoting (EF-promoting) catalytic WAO process is developed to degrade dyes under room condition. The oxidation kinetics of four different types of dyes and their degradation pathways are studied. A kinetic model is constructed by including the exogenous electric field into the Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism framework, and quantitative structure-activity relationship (QSAR) analysis is conducted to correlate the kinetic parameters to the physicochemical properties of the dyes. A negative linear relationship is found between the adsorption equilibrium constants of the dyes and their first ionization energies, and their surface reaction rate constants are positively linearly associated to Esum (ELUMO + EHOMO). The degradation pathways of the different dyes are proposed according to the degradation intermediates and the activities of the atoms within the dye molecules. The heteroatoms N and S, and the atom C connecting the aromatic rings are identified as the susceptible sites upon the electrophilic attack of O2. Bond cleavage at these sites gives rise to aromatic fragments which are eventually mineralized via carboxyl acids. The results of this work is helpful for guiding the design and operation of the EF-promoting catalytic WAO process into the treatment of various dye wastewaters.

The unexpected weirdness of rate-based simulation of some high-pressure column operations

Diffusion is the process by which molecules move. One way to model multicomponent diffusion is with a version of Fick’s law: (J) = - [D] d(c)/dz where [D] is a matrix of multicomponent diffusion coefficients. [D] is the product of two other matrices, one of which involves partial derivatives of the fugacity or activity coefficients. It is usually the case that all of the elements on the main diagonal of [D] have a positive value. Wambui Mutoru and Firoozabadi (2011, 2012) showed that CO2-rich and N2-rich hydrocarbon systems could have main diagonal elements of [D] that are negative. Using rate-based column simulations, we have found that these negative main diffusion coefficients readily occur in some high-pressure distillation operations. We investigate these processes in more detail and explore the consequences for the design and operation of columns in which this phenomenon is predicted to occur.

Combustion behavior study and flame zone analysis of biogas-fueled gas turbine combustor under O2/CO2 and O2/H2O oxidizing modes

Environmental problems resulting from the increment of greenhouse gases have raised the tendency toward using renewable energy sources alongside carbon-capturing technology via oxyfuel combustion. In this regard, numerical simulation on the feasibility of using renewable biogas in the gas turbine combustor under two combustion modes, namely, O2/CO2 and O2/H2O, at high operating pressure is investigated in the current research. Considering that conventional air-based combustion systems are not suitable for oxyfuel combustion regimes, the modification of the gas turbine combustor will be addressed to provide the necessary conditions for proper operation at higher power densities on an industrial scale. In this study, the focus is on investigating the influences of the primary diluent mass flow rate ratio (PDR) and the O2 content in the oxidizer composition on combustion and thermal behaviors of biogas flame such as distribution of reaction zone and temperature, combustion species, pattern factor, combustion efficiency, CO pollutant emission, and as well as flame stability in different combustion modes. The results indicated that the PDR parameter plays an essential role in the combustion stability within the gas turbine combustor due to its direct exposure to the vortices created in the recirculation zone. Moreover, combustion instabilities were observed for biogas flame at PDR = 15% in both combustion modes and in O2/H2O case at PDR < 25%. It was also found that CO emissions decrease significantly with increasing PDR, so in higher PDR values, CO pollutant levels were observed at 39 ppm and 21 ppm in O2/CO2 and O2/H2O cases, respectively.

Dissimilar welding of austenitic and ferritic steels using nickel and stainless-steel filler: Associated issues

The microstructure development and mechanical behaviour of dissimilar metal welds between ferritic and austenitic steel, as well as their application in nuclear power plants, are discussed in this review paper. Nuclear reactor components, such as steam generators and pressure vessels, consist primarily of SA508 due to their low cost and high operating temperatures and pressures. The welding of dissimilar metals is crucial due to variations in physical characteristics such as thermal conductivity, thermal expansion coefficient, mechanical properties and chemical compositions. The principal challenges of dissimilar ferritic and austenitic steel welding are the subject of this review work. Weldability issues include a sharp change in mechanical and metallurgical characterization across the fusion line, carbon migration, cyclic thermal stresses and residual stresses, which necessitate a thorough investigation of the welded joint. Generally, austenitic steel and nickel-based fillers are used to join austenitic and ferritic steel materials; however, owing to many weldability concerns, nickel-based consumables are replacing austenitic consumables. Another critical issue in the weld joint is the selection of appropriate welding consumables, and detailed explanations of the benefits of employing a buttering layer on the ferritic side are provided. The effect of heat treatment on the metallurgical and mechanical characteristics of the weld joint, as well as the formation of residual stress, has also been thoroughly explored.

Performance of Hypersaline Brine Desalination Using Spiral Wound Membrane: A Parametric Study.

Desalination of hypersaline brine is known as one of the methods to cope with the rising global concern on brine disposal in high-salinity water treatment. However, the main problem of hypersaline brine desalination is the high energy usage resulting from the high operating pressure. In this work, we carried out a parametric analysis on a spiral wound membrane (SWM) module to predict the performance of hypersaline brine desalination, in terms of mass transfer and specific energy consumption (SEC). Our analysis shows that at a low inlet pressure of 65 bar, a significantly higher SEC is observed for high feed concentration of brine water compared with seawater (i.e., 0.08 vs. 0.035) due to the very low process recovery ratio (i.e., 1%). Hence, an inlet pressure of at least 75 bar is recommended to minimise energy consumption. A higher feed velocity is also preferred due to its larger productivity when compared with a slightly higher energy requirement. This study found that the SEC reduction is greatly affected by the pressure recovery and the pump efficiencies for brine desalination using SWM, and employing them with high efficiencies (ηR ≥ 95% and ηpump ≥ 50%) can reduce SEC by at least 33% while showing a comparable SEC with SWRO desalination (<5.5 kWh/m3).

Thermohydraulic Characteristics of Printed Circuit Recuperators in a Supercritical CO2 Brayton Cycle with Nonuniform Minichannels

Supercritical carbon dioxide (SCO2) technologies have been under the spotlight of developed countries because they believe that such applied sciences can be ingenious solutions to resolve energy and environmental problems. The SCO2 power cycle is one of the most promising technologies in this field due to its high efficiency and low expenditure. However, optimal designs of heat exchange devices are a vital issue in the SCO2 power cycle because they account for almost 80% of the capital costs. In this study, the comparison of diverse combinations of convergent and divergent minichannels inside the low temperature recuperator (LTR) and high temperature recuperator (HTR) is suggested to recognize the strengths and weaknesses of nonuniform minichannels at high operating pressures and temperatures. Three-dimensional conjugate simulations are carried out, and existing data in the literature are used to validate the obtained results. The comparison reveals a slight deviation (less than 10%) in temperature and pressure profiles. After the evaluation of the studied cases in terms of thermal and hydraulic characteristics, different criteria are employed to explore optimal combinations of the hot side and cold side minichannels. Totally, the minichannel convergence enhances thermal performance of recuperators (up to 26%), and their divergence improves the hydraulic behavior. Nonetheless, diverging the minichannels imposes greater positive effects than converging them. The overall analysis specifies that the most efficient LTR and HTR would be attained by diverging the hot side minichannel, while the cold side minichannel is kept unchanged. This combination of minichannels allows reaching the highest SCO2 temperature at the outlet of LTR and HTR (456 K and 656 K) with the minimum pressure drops (around 0.02% of inlet pressures) and achieving the best performance indexes (approximately 2). Finally, the comparative study discloses that at low Reynolds numbers (less than 14000 for the hot side and 10000 for the cold side), the nonuniform patterns of minichannels perform better than the complicated structures, such as zigzag, wavy, and other optimized geometries. The average performance enhancements for the hot and cold sides are 36.3% and 37.4%, respectively.

Chemical kinetic analysis to study the potential of fuel staging in reducing the emissions from NH3/CH4-air combustion at different pressures

The combustion characteristics of ammonia/methane blends to enhance the reactivity of ammonia are investigated successfully for carbon–neutral energy applications. However, commercializing ammonia blends demands techniques to retrench the superfluous NOX emissions under fuel-lean conditions. The present study is a chemical kinetic analysis investigating a new ammonia-methane combustion strategy of injecting ammonia into hot methane combustion gases (ammonia fuel staging) to reduce the NOX propensity without ammonia slip. The combustion kinetics of NH3/CH4 mixtures are studied in chemical reactor networks (CRNs), depicting typical burner flow conditions with and without fuel staging. A comparison of the emission chemistry in the fuel-staged CRN model with the single-stage CRN model is carried out for the ammonia mole fraction (XNH3) in the fuel mixture ranging from 20 to 60 % and the equivalence ratio ranges (ϕ) of 0.6–0.9 at both low and high-pressures of 1 and 10 atm, respectively. It is observed that in the single-stage reactor, the entire reactor is an active reaction zone due to the reduced chemical kinetics of methane in the presence of ammonia. Recognizing the need of raising the radical concentration and temperature in the flame zone to enhance ammonia chemistry, a fuel-staged reactor model is proposed. In the fuel-staged model, staged combustion is achieved by injecting NH3 into the lean methane combustion products for the constant combustor power output of 25 kW. Results show that fuel staging enhances the ammonia chemistry at low and high-pressure conditions of 1 and 10 atm. In the fuel-staged reactor, the flame zone of the second stage is observed to be the active reaction zone with maximum NH3 consumption. At low-pressure conditions, fuel staging leads to a reduction in both CO and NOX emissions without ammonia slip. The NOX reduction is due to the stable availability of NO-consuming NHi radicals for the entire duration of combustion in the flame zone via the reactions: 2NH2→NH3+NH and NH3+OH→NH2+H2O. The CO-consuming reactions: NH2+CO→HNCO+H and OH+CO→H+CO2 further reduces the CO emissions from the second stage. However, the augment in ammonia chemistry adversely affected NOX reduction at high-pressure operating conditions due to the lack of NHi radicals for NO consumption. The study contributed to the NOX reduction from ammonia combustion by providing an active high-temperature combustion zone with a self-sustaining NHi environment.

Performance evaluation of liquid nitrogen-cooled cryoprobes using a combined numerical and experimental approach

In this study, the effect of the operating pressure and insertion depth is investigated on the cooling performance of cryoprobes. Two cryoprobes having different diameters are used. Experiments are performed with each cryoprobe for operating pressure ranging from 2.2 to 4 atm and insertion depths ranging from 2 to 15 mm. The temperature of the cryoprobe tip is measured by three thermocouples, and the recorded temperature is used as a boundary condition in the numerical simulations. The optics-based experimental setup, comprising digital holographic interferometry (DHI), is implemented to accurately track the freezing interface for all the experimental cases. The tracked interface using DHI-based intensity maps and the thermocouples placed inside the freezing front provided the means to ascertain the accuracy of the results obtained using numerical simulations. For both cryoprobes, the cooldown time is reduced by a factor of 2 to 3 when higher operating pressure is used. The higher operating pressure resulted in accelerated cooling for both cryoprobes. For the smaller-sized cryoprobe, i.e., Cryoprobe-1, the higher operating pressure is necessary if it needs to be operated for an insertion depth of 6 mm or more. However, for the larger-sized cryoprobe, i.e., Cryoprobe-2, the higher operating pressure only resulted in reduced cooldown time. The temperature data predicted by the numerical simulations are used to quantify the cooling performance of the cryoprobes. The average cooling power for Cryoprobe-1 ranges from 8 to 12 W, while for Cryoprobe-2, it ranges from 10 to 30 W depending on the insertion depth.

Design and Selection of Pipelines for Compressed Air Energy Storage Power Plants

The principle of Compressed-air energy storage is that the compressed air energy storage system uses compressed air as the energy storage carrier, which is a physical Energy storage that uses mechanical equipment to realize energy storage, transfer and utilization across time and space. At present, Compressed-air energy storage is the second largest technology that is considered suitable for GW level large-scale electric energy storage after pumped storage. Compressed air energy storage has outstanding advantages such as large scale, low cost, long service life, and short construction period. As a key link connecting compressors, expanders, and gas storage devices, the compressed air main pipeline has characteristics such as high operating pressure, low internal fluid temperature, large temperature difference between indoor and outdoor pipelines, and frequent start and stop. The design, calculation, and installation of the compressed air main pipeline will affect the economy and reliability of the entire system, and even bring serious destructive accidents. This article comprehensively introduces the selection method and process of compressed air energy storage pipeline design, and further verifies the feasibility and accuracy of the design method through case studies of specific projects. It provides convenience and calculation methods for the large-scale development of compressed air energy storage projects in the future[1].

Energy storage and water splitting applications of self-grown Na2O-NiCl2 upright standing nanoplates: a process of 3D nickel surface modification using seawater.

The recent trend in research fosters the use of abundant seawater for modifying metal surfaces as electrode materials for energy generation, storage, transport, and water-splitting technologies. Economic and ecofriendly seawater is used as a solvent for modifying the surface of 3D nickel-foam (NiF) to Na2O-NiCl2@NiF as an electrode material in electrochemical supercapacitors and water-splitting electrocatalysis applications. The phase of the as-obtained Na2O-NiCl2 is confirmed from the proposed reaction mechanism, followed various physical measurement tests such as X-ray photoelectron spectroscopy and Fourier transform infrared analysis. The formation of Na2O-NiCl2 is caused by a high operation temperature and pressure of seawater solvent, the presence of lone pair electrons on oxygen, and more reactivity of Na for combining with dissolved oxygen than the lone-pair free Cl (towards Ni). In addition to exceptional HER and OER electrocatalytic activities, i.e., 146.3 mV cm-2 and 217 mV cm-2 at a scan rate of 5 mV s-1 to attain the 10 mA cm-2 current density, the Na2O-NiCl2 has demonstrated moderate energy storage ability with considerable durability, i.e., 2533 F g-1 specific capacitance at 3 A g-1 current density even after 2000 redox cycles. The as-assembled Na2O-NiCl2//Na2O-NiCl2 symmetric electrochemical supercapacitor device has ignited a "CNED" panel consisting of nearly forty LEDs with full brightness, offering applied importance in home appliances. In nutshell, seawater-modified metal surfaces can be used for energy storage and water-splitting applications.

Performance prediction of a distributed Joule-Thomson effect cooler with pillars

• Heat transfer and throttling coupling is used to replace the traditional constant enthalpy throttling. • The performance of the J-T cooler is predicted by simulation. • A novel J-T cooler with multi-layer, multi-pillar micro-channels was designed. Hampson type Joule-Thomson (J-T) throttle coolers are widely used for cooling infrared detectors and many electronic components. The conventional J-T throttle coolers are not compact, with low heat transfer efficiency and small cooling capacity. In this paper, a stacked column cluster type microchannel distributed J-T throttle cooler is designed through combining a compact microchannel etched and shaped by photolithography and an atomic diffusion fusion welding process with a J-T throttle cooler. The dimensions of the cooler are 10 mm for the inlet section, 145 mm for the throttling and heat exchange section,10 mm for the expansion chamber, with 6 layers staggered high pressure channels and 6 low pressure channels. The cooling performance of the cooler under various low-temperature and high-pressure operating conditions were studied through simulations, and the results showed that the cold-end temperatures were 158.0, 147.9, 146.1, 144.1, and 141.1 K for an inlet pressure of 5.20 MPa and inlet temperatures of 280.0, 270.0, 260.0, 250.0, and 240.0 K, respectively, with argon as the work gas. The cold-end temperatures were 163.6, 159.4, 156.8, 154.6, and 152.7 K for an inlet pressure of 5.60, 6.00, 6.40, 6.80, and 7.20 MPa respectively in 288.0 K inlet temperature. In the process of working medium flow and heat transfer in the microcolumn group channel of the cooler, the temperature and pressure change significantly. When the working medium in the flow reaches the phase change state, that is, the phase change temperature and pressure reach, due to the gas liquefies and the flow rate drops, the working medium loses the gas throttling refrigeration effect, and the temperature no longer decreases significantly, and the refrigeration temperature is limited by this. In addition, compared with different inlet pressures, when the inlet temperature is 280.0 K, the 5.20 MPa nitrogen throttling refrigeration temperature is close to the argon gas at 2.98 MPa, which are 223.4 K and 234.9 K, respectively. Therefore, high pressure nitrogen can be considered to replace low pressure argon in engineering applications. In view of the problems involved in the research process of traditional micro-channel throttling coolers, the innovative solutions are put forward in this paper, which can bring new innovations and thoughts for the future research and application of such problems.

Single Vs Multichannel Silica-Pectin Ultrafiltration Membranes for Treatment of Natural Peat Water

A comparative study was undertaken to investigate the potential of silica-pectin ultrafiltration membrane on varied operation pressure (0.1-0.3 MPa). Cross-flow ultrafiltration works were explored with tubular alumina substrates in single and multichannel configuration. The silica-pectin sol was prepared from TEOS as silica precursor by sol-gel method, afterward pectin was templated into the silica sol to induce carbon on it. Thereafter, both of single and multichannel alumina substrates was coated by the silica-pectin sol via inner coating technique. The study exhibited better performance of multichannel silica-pectin ultrafiltration membrane (with 4 bores) compared to the single channel membrane in terms of the permeate quality of UV254 rejection, as well as the permeate flux. The UV254 rejection of multichannel silica-pectin ultrafiltration membranes conducted over 84% in compliance with highest permeate fluxes of 234.3 L.m-2.h-1.bar-1 at high operation pressure (TMP 0.3 MPa). The multichannel ultrafiltration membrane permeate flux in this work is slightly high 60-75% over single channel. Hence, both single and multichannel silica-pectin membranes exhibited steady neutralized permeate fluxes under TMP 0.3 MPa conditions for natural 100% peat water concentration, which indicates that fouling is not occurred during filtration time up to 60 min. Therefore, multichannel silica-pectin ultrafiltration membrane in this work is success to treatment of natural peat water, that the natural organic matter removal was found to be fit for uses as clean water sources.

Water management in a novel proton exchange membrane fuel cell stack with moisture coil cooling

Water flooding causes severe degradation of the performance and lifetime of proton exchange membrane fuel cell (PEMFC). In this study, a novel PEMFC stack with in-built moisture coil cooling was designed and the effects of moisture coil cooling on water management in the new PEMFC stack under various operating conditions were investigated. The result showed that the performance of the PEMFC stack was significantly improved due to the moisture condensation under high current density, high operating temperature, high relative humidity and high operating pressure. The output power was increases by 21.62% (525.71 W) at 1600·mA cm−2 while the increased parasitic power was no more than 35W. Moreover, degradation of the cathode catalyst layer after 100 h operation was also reduced by using moisture coil cooling. Compared with the situation without moisture condensation, the maximum decay rate of the cathode catalyst layer thickness after 100 h operation was reduced by 13.01%. Accordingly, the novel design is valuable and can be widely used in the future design of PEMFC.

Potential assessment of transcritical CO2 secondary loop heat pump for electric vehicles

The excellent heating performance and environmental advantages of the transcritical CO2 heat pump system make it a great fit for the electric vehicles (EVs). However, the high operating pressure leads to the possibility of excessive CO2 concentration in the cabin. To ensure the safety of passengers, a secondary loop (SL) system is proposed. In this study, we make a comparison between the traditional direct (TD) system and the SL system for an EV. The results show that the optimal coolant flow rate, with a range of 0.56 to 1.36 L/min in heating mode and 5.60 to 8.80 L/min in cooling mode, can increase the COP of the SL system in all working situations. In the heating mode, the COP of the SL system is 13.98% to 21.96% lower than that of the TD system, and the cruising range of the EV is reduced by 1.4 km ∼ 10.0 km. In cooling mode, the COP of the SL system is 16.95% to 22.45% lower than that of the TD system, and the cruising range has a reduction of 7.7 km ∼ 20.9 km. Results demonstrate that running the SL system in cooling mode rather than heating mode is more detrimental to EVs.

Wear modelling and sealing performance prediction of C/C composite finger seal

Due to the high speed and high pressure operating conditions, wear between the finger seal and the rotor is inevitable, and this leads to an increase of leakage clearance and becomes an important factor affecting the seal life. The theory of anisotropic elasticity was employed to describe the mechanical characteristics of the seal material. An improved Archard wear model was proposed to calculate the nodal wear rate, and the local wear direction was also determined. The wear simulation model and procedure were established based on the Arbitrary Lagrangian Eulerian adaptive mesh strategy. The effects of material density, fabric orientation, pressure differential and rotor speed on the wear characteristics of finger seal and the change of leakage clearance caused by wear loss were studied. The results show that the wear first occurs at the heel area of the finger foot bottom and gradually extends to the toe area. C/C (carbon fibre reinforced carbon matrix) composite finger seal with higher material density has smaller leakage clearance and wear depth. With the increase of fabric orientation angle, the wear depth in the heel area of finger foot is smaller, and the circumferential wear area is narrower. The average wear depth of finger seal decreases with the orientation angle. When the orientation angle is 0, the seal leakage clearance is smaller. The increase of pressure differential not only aggravates the seal wear, but also expands the wear area, and also increases the average contact pressure and leakage clearance. Increasing the rotor speed make the wear depth of the heel area of finger foot gradually increase, but the wear area becomes narrower. The average contact pressure decreases and the average leakage clearance increases. This study provides a theoretical method and basis for the prediction and evaluation of the wear life and performance of C/C composite finger seal.

Torsion-induced failure of a reinforced thermoplastic pipe used in a gas lift system

After servicing for 4.5 years, a reinforced thermoplastic pipe utilized in a gas lift system experienced a burst failure. FTIR, visual inspection, TGA, tensile test, VST, pressure test, DSC, and torsion test were performed to investigate the root cause for the failure. The findings demonstrate that the failed pipe had suffered serious torsion. The torsion led to the significant performance deterioration of reinforced fibers and liner pipe. The liner pipe has multiple torsion morphologies. Tensile test results show that torsion led to the deterioration of the mechanical properties of the liner pipe, especially the modulus (14.7%). There was a 60–80% drop in both elongation at the break and tensile strength of the fibers. Results from the torsion-pressure test illustrate that torsion would lead to a decline in the pipe’s pressure capacity. The operating record indicates that this pipeline was a gas lift pipeline with long-term and high-pressure operations and weekly sweeping operations in winter. The pressure fluctuation was relatively frequent. The pipe failed when the instantaneous pressure exceeded the torsional pipe’s capacity.

Bioinspired and Hierarchically Textile‐Structured Soft Actuators for Healthcare Wearables

AbstractSoft pneumatic actuators possess the increasing potential for various healthcare applications, such as smart wearable devices, safe human‐robot interaction, and flexible manipulators. However, it is difficult to translate the existing technologies to commercial applications due to their inefficient volumetric power, sophisticated control with high operation pressure, slow production, and high cost. To overcome these issues, herein, a caterpillar‐inspired actuator using hierarchical textile architectures based on simple fabrication and low‐cost strategy is designed. Unlike the existing textile‐based pneumatic actuators, the designed actuators are constructed by combining boucle fancy yarns with a novel trilayer‐knit architecture. The as‐prepared actuators concurrently possess fast response (1100° s−1), large bending actuation strain (1080° m−1), high‐power density (272 W m−3), mechanical robustness, easy‐programmable motions, and human‐tactile comfort, which outperforms currently reported textile‐based pneumatic actuators. Furthermore, due to the geometrical transition of the engineered hierarchical structure, the developed actuators exhibit superior dual‐stiffness effect with stress evolution, providing a facile approach to addressing the conflict of flexibility and force output in soft fluidic actuators. This concept as a paradigm provides new insights to develop soft actuators with outstanding design flexibility, adaptability, and multifunctionality using engineered textile‐structure, which has great potential for real‐world applications in medical rehabilitation, physiotherapy, and soft robotics.

Selecting nitrogen carriers used for chemical looping ammonia generation of biomass and H2O by thermodynamic method

The demand for NH3 as a new energy carrier will lead to a gradual increase in its production. The Haber-Bosch process, commonly used today, has high energy consumption, high operating pressure and high CO2 emissions due to hydrogen extraction from fossil fuels. For efficient and environmentally friendly preparation of NH3, chemical looping ammonia generation (CLAG) of biomass and H2O is proposed. The selection of suitable nitrogen carriers is the key in CLAG. Since the variety of available substances is large, a systematic method is needed to perform screening efficiently. In this paper, 28 different oxide/nitride pairs were investigated. We mainly investigated the Gibbs free energy change and the equilibrium compositions in the N-absorption and N-desorption reactions. Suitable nitrogen carriers were selected by the minimum N-absorption temperature, nitrogen transport capacity, sintering resistance, price and by-product. When Al2O3/AlN was used as the nitrogen carrier, the minimum N-absorption temperature was 1371 °C, and the nitrogen transfer capacity was high. When TiO2/TiN was used as a nitrogen carrier, the minimum N-absorption temperature was 966 °C, the nitrogen transfer capacity was lower than Al2O3/AlN, and NH3 and H2 were generated simultaneously in the N-desorption step. Compared with SiO2/Si3N4, Cr2O3/Cr2N, Cr2O3/CrN, MnO/Mn5N2, Fe2O3/Fe4N, ZrO2/ZrN, and MoO2/Mo2N, Al2O3/AlN and TiO2/TiN produced less carbide in N-absorption step and had less mass decay in the cycle, making them more suitable as nitrogen carriers. Appropriately increasing the molar ratio of nitrogen carrier to carbon can improve feedstock utilization and the efficiency of CLAG.

Influence of carbon deposits on Fe-carbide for the Fischer-Tropsch reaction

A well-known observation in the Fe-catalyzed Fischer-Tropsch (FT) reaction is that Fe-carbide catalysts deactivate due to carbon deposition. In comparison, the influence of such carbon deposits on the product distribution has been less widely reported. The present work investigates the relationship between the kinetics of the FT reaction for a carburized Raney-Fe model catalyst and the composition of the catalytic surface with a focus on carbon deposits. The deposition of carbon during the ongoing FT reaction at low pressure decreases the FT activity and increases the CH4 selectivity. Steady-state transient isotopic kinetic analysis (SSITKA) at low pressure shows that the buildup of C deposits affects fast CO conversion sites on the Fe-carbide surface, mainly responsible for CC coupling via a Langmuir-Hinshelwood mechanism, more than slow sites that mainly produce CH4via a Mars-Van Krevelen mechanism. Hindrance of migration of chain-growth monomers by C deposits decreases the amount of longer hydrocarbons. Nevertheless, SSITKA shows that C2 products form faster, which is likely since their formation increasingly depends on monomers formed at proximate CO dissociation sites when the amount of carbon deposits increases. Carbon deposition can be suppressed and reversed by increasing the H2/CO ratio at constant pressure or by increasing the total pressure at constant H2/CO ratio. As such, the FT performance can be stabilized by operating at elevated pressure, even if initially the reaction was started at low pressure. Nevertheless, prolonged operation at low pressure leads to a less reactive character of the C deposits that cannot be removed anymore during high-pressure operation.