Multi-cycle Operations Research Articles

On kinetic modelling for solar redox thermochemical H2O and CO2 splitting over NiFe2O4 for H2, CO and syngas production.

This study aims at developing a kinetic model that can adequately describe solar thermochemical water and carbon dioxide splitting with nickel ferrite powder as the active redox material. The kinetic parameters of water splitting of a previous study are revised to include transition times and new kinetic parameters for carbon dioxide splitting are developed. The computational results show a satisfactory agreement with experimental data and continuous multicycle operation under varying operating conditions is simulated. Different test cases are explored in order to improve the product yield. At first a parametric analysis is conducted, investigating the appropriate duration of the oxidation and the thermal reduction step that maximizes the hydrogen yield. Subsequently, a non-isothermal oxidation step is simulated and proven as an interesting option for increasing the hydrogen production. The kinetic model is adapted to simulate the production yields in structured solar reactor components, i.e. extruded monolithic structures, as well.

The Optimized Design of a NPC Three-Level Inverter Forced-Air Cooling System Based on Dynamic Power-loss Calculations of the Maximum Power-Loss Range

In some special occasions with strict size requirements, such as mine hoists, improving the design accuracy of the forced-air cooling systems of NPC three-level inverters is a key technology for improving the power density and decreasing the volume. First, a fast power-loss calculation method was brought. Its calculation principle introduced in detail, and the computation formulas were deduced. Secondly, the average and dynamic power losses of a 1MW mine hoist acting as the research target were analyzed, and a forced-air cooling system model based on a series of theoretical analyses was designed with the average power loss as a heat source. The simulation analyses proves the accuracy and effectiveness of this cooling system during the unit lifting period. Finally, according to an analysis of the periodic working condition, the maximum power-loss range of a NPC three-level inverter under multi cycle operation was obtained and its dynamic power loss was taken into the optimized cooling system model as a heat source to solve the power device damage caused by instantaneous heat accumulation. The effectiveness and feasibility of the optimization design based on the dynamic power loss calculation of the maximum power-loss range was proved by simulation and experimental results.

새로운 멀티프로세서 디자인을 위한 상위수준합성 시스템의 회로 복잡도 최적화 ILP 알고리즘

In this paper, we have proposed a circuit complexity optimization ILP algorithm of high-level synthesis system for new multiprocessor design. We have analyzed to the operator characteristics and structure of datapath in the most important high-level synthesis. We also introduced the concept of virtual operator for the scheduling of multi-cycle operations. Thus, we demonstrated the complexity to implement a multi-cycle operation of the operator, regardless of the type of operation that can be applied for commonly use in the ILP algorithm. We have achieved is that standard benchmark model for the scheduling of the 5th digital wave filter, it was exactly the same due to the existing datapath scheduling results.

Cobalt/cobaltous oxide based honeycombs for thermochemical heat storage in future concentrated solar power installations: Multi-cyclic assessment and semi-quantitative heat effects estimations

The present study relates to the preparation and evaluation of small-scale honeycomb structures as compact reactors/heat exchangers via exploitation of the cobalt/cobaltous oxide (Co3O4/CoO) cyclic reduction–oxidation (redox) heat storage scheme. The structures considered included in-house extruded monoliths (pure cobalt oxide and cobalt oxide/alumina composites) and commercial cordierite substrates coated with Co3O4. The samples were subjected to multi-cyclic redox operation under air flow, in the temperature range of 700–1000°C. Reduction occurred during heating up to 1000°C, while oxidation took place during cooling. Redox performance was evaluated on the basis of on-line oxygen release/consumption measurements, while continuous monitoring of imposed air flow reactor inlet/outlet temperatures facilitated the preliminary estimation of heat dissipation in the duration and after completion of the exothermic reaction (oxidation). For all samples, redox performance remained stable in the course of multi-cyclic exposure. In terms of heat transfer, there is strong indication that both composition and the geometry of the honeycomb are important. The pure Co3O4 extruded honeycomb exhibited the highest heat dissipation efficiency but suffered from severe deformation upon multi-cyclic operation. The addition of a small amount of alumina in the aforementioned composition (10% on the basis of total initial mass of oxides), particularly when combined with an increase of the honeycomb wall thickness, substantially improved macro-structural stability upon thermal/redox cycling. The Co3O4-coated cordierite monoliths showed essentially the same normalised redox performance with the pure Co3O4 extruded honeycomb, however the overall heat dissipation achieved was lower. Regarding the effect of redox cycling on the structural stability of studied formulations, pure Co3O4 samples exhibited notable swelling. In the case of the extruded body, this resulted to structural collapse while for the coated cordierite honeycomb, expansion of the coating layer led to partial channels blocking. Based on relevant morphological and structural post-analysis, it was concluded that formation of cobalt aluminate largely reduced swelling intensity.

Highly dispersed copper species supported on SBA-15 mesoporous materials for SOx removal: Influence of the CuO loading and of the support

In the present work, organized mesoporous SBA-15 and amorphous Aerosil 380 silicas were modified by copper incorporation through wet impregnation of copper nitrate to obtain SOx regenerable adsorbents. Impregnation, drying and calcination conditions were carefully controlled in order to obtain highly dispersed Cu2+ species assumed to be Cu–O–Si species. Materials were evaluated as SOx adsorbents through multicycle adsorption/regeneration experiments and were fully characterized before and after sulfation by XRD (X-Ray Diffraction), XRF (X-Ray Fluorescence), SEM (Scanning Electron Microscopy) and TEM (Transmission Electron Microscopy) analyses. The influence of the nature of the support and of the copper loading on the adsorbent behavior was studied. Results show that the adsorbent performances in SOx trapping along multicycle operations depend on both the copper loading and the nature of the silica support. The characterizations of the aged adsorbents suggest that their deactivation along multicycle operations is due to the copper species sintering. Results show that there is an optimal copper loading for a maximal SOx adsorption efficiency.

Reversible and multi-cyclic protein–protein interaction in bacterial cellulosome-mimic system using rod-shaped viral nanostructure

The type II cohesin domain and type II dockerin of bacterial cellulosome were cloned from Clostridium thermocellum and expressed with the fusion of tobacco mosaic virus coat protein (TMVcp) and enhanced green fluorescent protein (EGFP), respectively, in Escherichia coli. The TMVcp-cohesin fusion protein was assembled to the stable and rod-shaped nanostructure (TMVcp-Coh rod) under a particular buffer condition, where many active cohesin proteins are biologically and densely displayed around the 3-dimensional surface of TMVcp-Coh rod. Using EGFP-dockerin as a fluorescent reporter, we confirmed that the Ca2+-dependent binding and dissociation between native cohesin and dockerin were reproduced with the two recombinant fusion proteins, TMVcp-cohesin and EGFP-dockerin. The multi-cyclic binding-dissociation operation of TMVcp-Coh rod and EGFP-dockerin was successfully performed with maintaining the reversible cohesin-dockerin interaction in every cycle. EGFP that was fused to dockerin as a proof-of-concept here can be switched to other functional proteins/peptides that need to be used in multi-cyclic operation.

Membrane fouling control in the integrated process of magnetic anion exchange and ultrafiltration

Magnetic anion exchange (MIEX) has been increasingly concerned owing to its excellent performance for the removal of dissolved organic carbon in the treatment of drinking water. In this study, the ability of ultrafiltration (UF) membrane fouling control was analyzed by different combination processes of MIEX-UF. A single cycle and multi-cycle operations were conducted, and the separated and integrated processes of MIEX-UF were compared. Membrane filtration resistance, removal of organics, and morphologies of the membrane surface were analyzed. The results of the short-term operation did not show any obvious improvement in the membrane fouling control in the separated process (compared to UF alone); however, a marked improvement was obtained in the integrated process. The membrane filtration resistance analysis showed that the cake resistance (Rc) and pore blocking resistance (Rp) in the integrated process were only 52 and 24% of the values in the separated process. The multi-cycle operation demonstrated that the cumulative rate of hydraulically irreversible fouling was 0.0021 in the integrated process and was much lower than that in the separated process (0.0182). The mechanistic analysis shows that in the integrated process, a dynamic layer was formed on the membrane surface by the deposited MIEX beads, which markedly decreased the accumulation of the membrane foulants on the membrane surface and in the membrane pores.

CuO/SBA-15 materials synthesized by solid state grinding: Influence of CuO dispersion and multicycle operation on DeSOX performances

In this study, copper oxide (CuO) has been dispersed into an organized mesoporous silica (SBA-15) using the solid state grinding method. The resulting CuO/SBA-15 materials were evaluated as SOx adsorbents and were fully characterized before and after sulfation. The influence of the calcination conditions on the copper dispersion was studied. Results show that the textural properties of the materials and the formed copper species are closely related to the calcination procedure. The adsorption performances increase with the copper dispersion. It was found that despite the high GHSV value used in this work (25,000h−1), the highly dispersed copper species confer a high efficiency to the adsorbent. Cyclic adsorption/regeneration experiments show a surprising but explainable increase in the adsorption efficiency in the second cycle followed by a slight but monotonic deactivation in the subsequent cycles, as a result of the progressive sintering of the copper species.

Design of a variable valve hydraulic lift system for diesel engine

A continuous variable valve lift (VVL) mechanism for a diesel engine is proposed in this research. The hydraulic mechanism, which consists of a driving plunger, a driven plunger, a hydraulic cylinder, and a hydraulic oil tank, is the key part of the VVL mechanism. Simulation is conducted to study the relationship between maximum valve lift and rotation angle of driving plunger. Calculation results indicate that the maximum valve lift decreases with increasing rotation angle. A prototype was manufactured and successfully tested in a single-cylinder diesel engine. The experiments, which were conducted at different rotation angles of the driving plunger, validate the accuracy of the calculation results. The difference between experimental valve lift curve and cam lift curve is considered the result of oil leakage. Rotating the driving plunger is an effective method to regulate valve lift. Working stability of the VVL mechanism is validated through a multi-cycle operation. Experimental results indicate that the VVL mechanism is effective and reliable for realizing continuous VVL in engines.

Purification of equine chorionic gonadotropin (eCG) using magnetic ion exchange adsorbents in combination with high-gradient magnetic separation.

Current purification of the glycoprotein equine chorionic gonadotropin (eCG) from horse serum includes consecutive precipitation steps beginning with metaphosphoric acid pH fractionation, two ethanol precipitation steps, and dialysis followed by a numerous of fixed-bed chromatography steps up to the specific activity required. A promising procedure for a more economic purification procedure represents a simplified precipitation process requiring only onethird of the solvent, followed by the usage of magnetic ion exchange adsorbents employed together with a newly designed 'rotor-stator' type High Gradient Magnetic Fishing (HGMF) system for large-scale application, currently up to 100 g of magnetic adsorbents. Initially, the separation process design was optimized for binding and elution conditions for the target protein in mL scale. Subsequently, the magnetic filter for particle separation was characterized. Based on these results, a purification process for eCG was designed consisting of (i) pretreatment of the horse serum; (ii) binding of the target protein to magnetic ion exchange adsorbents in a batch reactor; (iii) recovery of loaded functionalized adsorbents from the pretreated solution using HGMF; (iv) washing of loaded adsorbents to remove unbound proteins; (v) elution of the target protein. Finally, the complete HGMF process was automated and conducted with either multiple single-cycles or multicycle operation of four sequential cycles, using batches of pretreated serum of up to 20 L. eCG purification with yields of approximately 53% from single HGMF cycles and up to 80% from multicycle experiments were reached, with purification and concentration factors of around 2,500 and 6.7, respectively.

A Low Energy and High Performance <formula formulatype="inline"> <tex Notation="TeX">${\rm DM}^{2}$</tex></formula> Adder

A novel Dual Mode Square (DM 2 ) adder is proposed. The DM 2 adder achieves low energy, high performance and small area by combining two independent techniques recently proposed by the authors: dual-mode logic (DML) and dual-mode addition (DMADD). DML is a special gate topology that allows on-the-fly adaptation of the gates to real time system requirements, and also shows a wide energy-performance tradeoff. DMADD is probability based circuit architecture with a wide energy-performance tradeoff; however its utilization in a pipelined processor requires multi-cycle operation in some cases. We show how DML circuits avoid this requirement, and thus make it possible to transparently plug-in the DM 2 adder and derive full benefits from the DMADD. Previous work showed that the DMADD can lead to energy savings of up to 50% at the same clock cycle, compared to conventional CMOS solutions. Simulation results in a 40 nm standard process shows that the proposed DM 2 approach achieves additional energy savings of 27% to 36% for 64-bit and 32-bit adders, respectively, compared to DMADD.

A Class-E Direct AC–AC Converter With Multicycle Modulation for Induction Heating Systems

Induction heating systems are the technology of choice in many industrial, domestic, and medical applications due to its high performance. The core component of such systems is the power supply, which is usually composed of a rectifier stage and a resonant inverter. In order to simplify and further optimize the performance of the power supply, a class-E direct ac-ac converter featuring multicycle modulations is proposed in this paper. The proposed converter is composed of two switching devices that enable the direct ac-ac conversion. Single- and multicycle operation modes have been analytically described to prove the benefits, in terms of peak voltage reduction and output power control capabilities. A prototype featuring SiC junction-gate field-effect transistor devices, which perfectly fit these applications, has been designed and built to prove the feasibility of the proposed converter. The experimental results match the analytical results and validate the benefits of this converter.

Development of a novel-synthesized Ca-based CO2 sorbent for multicycle operation: Parametric study of sorption

One of the most promising technologies for CO2 capture is the Calcium Looping Cycle, which is based on the reversible carbonation reaction of CaO. The main challenge for CaL technology is the deterioration of CO2 capture capacity during multicyclic operation. In this work, the triethanolamine (TEA) was used as a complexing agent in a modified sol–gel method for the preparation of sintering resistant CaO–Ca3Al2O6. The sorbent showed high capture capacity (0.45g/g sorb. or 84% carbonation conversion) which was retained after 45 cycles. Parametric study of sorption was realized by varying the carbonation and calcination conditions (temperature and CO2 concentration). Under severe conditions of calcination temperature at 950°C in pure CO2 flow after 100 cycles the sorbent still retained almost 40% of the initial sorption capacity corresponding to 30% carbonation conversion.

Metal oxide-stabilized calcium oxide CO2 sorbent for multicycle operation

This work proposes a number of metal oxide (M: Al, Zr, Mg and Y)-stabilized calcium oxide (CaO) CO2 sorbents directly produced from two-step calcination (argon and air atmospheres) of acidified natural limestone sources. The incorporation of a metal support into the CaO structure during limestone acidification step mainly aims to enhance sorbent stability. This study is focused on (i) the determination of the optimum mixing ratios, (ii) the analysis of the effect of precursor (soluble or insoluble) on sorbent activity, as well as (iii) the investigation of the influence of calcination atmosphere on sorbent durability and activity. A M/Ca molar ratio of 0.1 was found to offer the optimum composition to obtain the best activity for Zr- and Al-stabilized CaO samples under mild operating condition, while a M/Ca ratio of 0.4 was the optimum ratio for Mg-stabilized sorbent. The activity of metal (Zr, Al and Mg)-stabilized CaO sorbents with optimum composition was also investigated during severe operation condition (presence of CO2 in the calcination atmosphere), where an intensification of structural sintering is usually expected. The results indicated a considerable sorbent stability improvement for the metal oxide-stabilized CaO in comparison to pure CaO which showed significant cyclic capacity decay under similar conditions. Among the studied materials, Zr-stabilized CaO showed the most adequate behavior in severe operating condition. However, the cost impact of Zr-stabilized sorbent might be a matter of concern. On the contrary, Al-stabilized CaO sorbent could be an interesting choice due to low cost of Al-precursors used in the material preparation. The choice of Al-precursors, which was found to affect the sorbent activity, is discussed in detail.

Preparation of copper-based oxygen carrier supported by titanium dioxide

Chemical-looping combustion (CLC) is an indirect oxygen combustion strategy, considered to be the most cost-effective power generation technology with the carbon dioxide (CO2) inherently concentrated. The oxygen carriers in the combustion process are subjected to severe environments, such as high temperatures, multi-cycle operations, and thermodynamic limitations. Thus, the preparation of an oxygen carrier with high durability and better kinetics under harsh environments could be an essential part of the development of the CLC process. In this study, copper oxide (CuO) was selected as an active ingredient, and was supported on the titanium-dioxide-based supporting materials, which was either directly from commercial titanium dioxide powder (TiO2) (anatase 99 %) or from tetrabutyl titanate, depending on methods. Three preparation methods were applied, including mechanic mixing (MM), sol–gel (SG), and wet impregnation (WI). Test results indicated all prepared oxygen carriers functioned properly in the multi-cycles of reduction and oxidation (redox) in thermogravimetric under 800 °C. Characterization and activity tests revealed that the CuO, prepared by the SG method was well-dispersed, highly active, and thermally stable in redox reactivity than those by the MM and WI methods. Furthermore, nucleation and diffusion models could better describe kinetics of prepared oxygen carrier based on the SG method.

A Novel High-Power – Long Cycle Life Energy Storage System for Large-Scale Applications

A novel system and method for removing heat from batteries, capacitors and other energy storage devices during high rate or multi-cycle operation has been proposed in this work. By modifying the exposed posts and inter-cell connecting bus-bars, heat transfer will be increased thus reducing the operating temperature of the battery. Because valve-regulated lead-acid (VRLA) batteries generate higher levels of internal heat, and because they have a lower thermal mass and lower heat transfer properties, these modifications are particularly valuable for these types of batteries. This thermal management technology can be used to improve the operating life of large batteries such as VRLA stationary batteries used for UPS and standby power applications. In very high-power energy storage applications such as load-leveling, peak-shaving or spinning reserve, battery life may be increased to as much as two times by reducing the operating temperature ten degrees centigrade using these proposed concepts.

Thrust Estimates of a Partially Filled Multi-Cycle Pulse Detonation Rocket Engine

Partially filled multi-cycle operation usually happens in pulse detonation rocket engines (PDREs). Thrust estimates of PDREs under such operating conditions will provide significant reference for relevant studies. An analytical model for thrust estimates is proposed in the present study. This model is based on Wintenberger' model for impulse calculation and empirical formula for specific impulse prediction of partially filled tubes; moreover, it takes into account performance penalty created by obstacles preliminarily, which are introduced to accelerate deflagration to detonation transition. Four specific analytical models are developed according to three previously proposed empirical formulas and a fitting one proposed for partial filling effect. Comparisons between model predictions and experimental measurements are carried out to validate the reliability of the models. It is found that the models make reasonable estimates and one of the models performs very well over a wide range of conditions. Discussion and analysis on the proposed model and partial filling effect are also performed in this study. Although there are many other factors that should be considered in evaluating thrust of partially filled multi-cycle PDREs, the present study supplies a rapid and effective means for thrust estimation and provides some modeling ideas meanwhile.

Improved hydrophilicity, permeability, antifouling and mechanical performance of PVDF composite ultrafiltration membranes tailored by oxidized low-dimensional carbon nanomaterials

Polyvinylidene fluoride (PVDF)–oxidized carbon nanotubes (OMWCNTs), PVDF–graphene oxide (GO) and PVDF–OMWCNTs–GO composite ultrafiltration membranes were prepared by solution-blending the ternary mixture of PVDF–oxidized low-dimensional carbon nanomaterials–dimethylacetamide in combination with the phase inversion method. The microscope images of the PVDF matrix microstructure showed that the composite membranes exhibited a bigger mean pore size and higher roughness parameters than pristine membranes. The contact angle of the membranes decreased from 78.5° (PVDF) to 66.8° (PVDF–OMWCNTs), 66.4° (PVDF–GO) and 48.5° (PVDF–OMWCNTs–GO). For the PVDF–OMWCNTs, PVDF–GO and PVDF–OMWCNTs–GO composite membranes, there was a 99.33%, 173.03% and 240.03% increase in permeation flux and a 21.71%, 17.23% and 14.29% increase in bovine serum albumin (BSA) rejection, respectively, compared with those of the pristine membranes. The newly developed composite ultrafiltration membranes demonstrate an impressive prospect for the anti-irreversible fouling performance in multi-cycle operations from BSA treatment. Additionally, the addition of OMWCNTs and GO increased the tensile strength of composite membranes from 1.866 MPa to 2.106 MPa and 2.686 MPa, respectively. Conspicuously, the PVDF composite ultrafiltration membranes endowed with oxidized low-dimensional carbon nanomaterials demonstrated fascinating hydrophilicity, permeability, antifouling and mechanical performance and promising application prospects owing to the rich oxygen-containing functional groups, high specific surface and synergistic effect of inorganic additive.

Chemical Looping Combustion (CLC) of two Victorian brown coals – Part 2: Assessment of interaction between CuO and minerals inherent in coals during multi cycle experiments

This paper is part two in a series of two papers on chemical looping combustion using Victorian brown coal. Part one described the assessment of interaction between CuO and minerals inherent in two Victorian brown coals during one cycle CLC experiments with CuO. This second paper describes the assessment of performance of CuO with the same two coals but in multicycle operations. The chemical and physical properties of CuO, such as reactivity and mass loss rate, have been investigated in five consecutive reduction and oxidation cycles with two brown coals. The experimental results are compared with thermodynamic simulation results using FACTSAGE. The percentage of combustion achieved using CuO and CuO conversion during multicycle operation are reported. Also investigated is the carbon deposition on CuO during CLC with both the coals during five cycles operation.The extent of Loy Yang coal combustion and reoxidation of CuO resulted in less than 0.3% weight loss per cycle. However, this value was around 2% per cycle for CuO–Morwell coal mixture reduction and re-oxidation of CuO in air. The high reactivity and conversion rate with high conversion of CuO was observed during cyclic operation. The percentage of combustion at the end of the 5th cycle with CuO was more than 97% with Loy Yang coal, as compared to 91% with Morwell coal. Fresh oxide particles and solid residues were characterized using SEM to illustrate surface morphological changes due to combustion.

Experimental Investigation of a Multi-Cycle Single-Tube Pulse Detonation Rocket Engine with a Coaxial Rotary Valve

We developed a novel coaxial rotary valve for a multi-tube PDE. Since this single valve can supply three different gases (fuel, oxidizer and purge gas) into a combustor, the unification of the valve systems for three different gases is possible by using our newly designed valve. A PDRE system can be simple and lightweight by using this valve, and thus its thrust-weight ratio can be increased. We proposed the design of a multi-tube rotary-valved PDRE system by this rotary valve. Moreover, in preparation for a multi-tube rotary-valved PDRE, we carried out the multi-cycle operation experiment by the single-tube rotary-valved PDRE system. The combustion wave velocity was measured to confirm the operation of the PDRE system. Deflagration-to-detonation transition (DDT) was confirmed and DDT distance decreased under the condition of high operation frequency. In addition, a maximum operation frequency was 159 Hz.