低温拜耳法提高循环效能技术研究

本文简要介绍了循环效率是氧化铝生产中一项非常重要的降低成本的手段,提高循环效率在相同的条件下相应提高产量,因而可以提高生产效率、降低固定成本分摊。在相同的温度体系条件下,提高拜耳法循环效率,可以使每一个立方的循环母液处理更多的铝土矿,而几乎消耗相等的能量,从而多产出氧化铝,提高生产效率,增加产量,摊薄固定成本分摊。

提高氧化铝生产循环效能的技改实践

介绍了低温拜耳法氧化铝生产过程中制约氧化铝循环效能和产品质量的主要因素。通过采用高浓度、低α_k溶出、提高晶种分解过程降温效果;优化晶种添加控制流程;有效控制晶种分解母液浮游物等措施,提高了氧化铝循环效能和产品质量,降低了成本和能耗。

Selection of organic Rankine cycle working fluid based on unit-heat-exchange-area net power

To improve energy conversion efficiency, optimization of the working fluids in organic Rankine cycles(ORCs) was explored in the range of low-temperature heat sources. The concept of unit-heat-exchange-area(UHEA) net power, embodying the cost/performance ratio of an ORC system, was proposed as a new indicator to judge the suitability of ORC working fluids on a given condition. The heat exchange area was computed by an improved evaporator model without fixing the minimum temperature difference between working fluid and hot fluid, and the flow pattern transition during heat exchange was also taken into account. The maximum UHEA net powers obtained show that dry organic fluids are more suitable for ORCs than wet organic fluids to recover low-temperature heat. The organic fluid 1-butene is recommended if the inlet temperature of hot fluid is 353.15-363.15 K or443.15-453.15 K, heptane is more suitable at 373.15-423.15 K, and R245 ca is a good option at 483.15-503.15 K.

On The Rational Dimension of Eco-city Construction

Reasonable ＂eco-city＂in the external between urban and rural areas should make a complete ecological cycle of the system, so that the internal energy efficiency and low pollution, resource use environmentally clean, quiet comfortable life of the people, as well as other elements of the organic： unity of urban greening. So, ＂Eco-City＂, ＂urban ecology＂ are two heterogeneous areas should be treated differently. However, in rural and urban dualistic situation, China advocated ＂ecological city＂ ignored the rural ecological balance, resulting in ＂eco-city＂development directly into＂ urban ecology＂ construction within the city along with the waste of resources, water pollution, serious problems of air pollution, noise pollution, the deep ＂eco-city＂ into representation＂ urban ecology＂, in the standard does not cover up the sound, making the generation between rural and urban＂ material Rift ,＂after all ,can not be filled.

Second Law of Thermodynamics Analysis of Transcritical Carbon Dioxide Refrigeration Cycle

In order to identify the locations of irreversible loss within the transcritical carbon dioxide refrigeration cycle with an expansion turbine, a method with respect to the second law of thermodynamics based on exergy analysis model is applied. The effects of heat rejection pressures, outlet temperatures of gas cooler and evaporating temperatures on the exergy loss, exergy efficiency and the coefficient of performance (COP) of the expansion turbine cycle are analyzed. It is found that the great percentages of exergy losses take place in the gas cooler and compressor. Moreover, heat rejection pressures, outlet temperatures of gas cooler and evaporating temperatures have strong influence on the exergy efficiency, COP and the exergy loss of each component. The analysis shows that there exists an optimal heat rejection pressure corresponding to the maximum exergy efficiency and COP, respectively. The results are of significance in providing theoretical basis for optimal design and the control of the transcritical carbon dioxide system with an expansion turbine.

A Viable Megawatt-Class Space Power Plant under Rankine Cycle

The aim of the article concerns to the achieved research results regarding the viability of a megawatt-class space power plant based on the Rankine cycle for which the main objectives are to highlight the key issues responsible for improving the Rankine cycle efficiency. Two working fluids are studied （water and ammonia） on the basis of its well known characteristics. Cycles operating under top and bottom temperatures approaching the state of the art technology associated to cooling fluid reservoirs are key to improve the efficiency. With such strategy, the achieved thermal efficiency increases more than 20% with respect to conventional power plants. Mentioned benefits associated to the strategy based on the reduction of the required payload capacity, the condenser radiation surface and the power plant mass represent the main advantages of the proposed innovation techniques.

Highly efficient lithium utilization in lithium metal full-cell by simulated missile guidance and confinement systems

The efficient utilization of metallic lithium(Li)is the key to enable application of Li metal full-cell with low amount of excess Li,contributing to higher safety and energy density.Herein,we report an extraordinary Li metal full-cell with only 20%excess Li,which demonstrated significantly improved reversibility and high Coulombic efficiency.Ingenious simulated missile guidance and confinement system(SMGCS)was designed to guide and confine Li deposition through constructing compatible silver lithiophilic sites and nitrate layer.Silver sites act as effective Li nuclei to attract Li ions and direct the initial nucleation.The generated nitrate layer affords an interfacial environment favorable for confined and uniform deep Li deposition,which is theoretically verified by molecular dynamics(MD)simulations.The two combined merits offer a robust and dendrite-free Li deposition,enabling the application of Li metal full-cell with slight excess Li.They also result in an outperformed Li cycling efficiency of ca.99%for over 300 cycles along with deep cycling at a high capacity of 10 mA h cm^(-2)in carbonate electrolytes.The unprecedented high degree of Li utilization opens a new avenue for the future development of highly efficient Li metal full-cells.

A high potential biphenol derivative cathode: toward a highly stable air-insensitive aqueous organic flow battery

Aqueous organic flow batteries have attracted dramatic attention for stationary energy storage due to their resource sustainability and low cost. However, the current reported systems can normally be operated stably under a nitrogen or argon atmosphere due to their poor stability. Herein a stable airinsensitive biphenol derivative cathode, 3,30,5,50-tetramethylaminemethylene-4,40-biphenol(TABP), with high solubility(>1.5 mol L^(-1)) and redox potential(0.91 V vs. SHE) is designed and synthesized by a scalable one-step method. Paring with silicotungstic acid(SWO), an SWO/TABP flow battery shows a stable performance of zero capacity decay over 900 cycles under the air atmosphere. Further, an SWO/TABP flow battery manifests a high rate performance with an energy efficiency of 85% at a current density of60 m A cm^(-2) and a very high volumetric capacity of more than 47 Ah L^(-1). This work provides a new and practical option for next-generation practical large-scale energy storage.

Anion exchange membranes based on long side-chain quaternary ammonium-functionalized poly(arylene piperidinium)s for vanadium redox flow batteries

A new series of poly(arylene piperidinium)-based anion exchange membranes(AEMs)are proposed for vanadium redox flow batteries(VRFBs).The AEMs are fabricated via the Menshutkin reaction between poly(arylene piperidine)without ether bonds in the backbone and various quaternizing agents,including iodomethane,1-bromopentane,and(5-bromopentyl)-trimethylammonium bromide.The properties of the AEMs are investigated in terms of sulfuric acid doping content,swelling,vanadium permeability,ion selectivity,area-specific resistance,mechanical properties,VRFB performance,and cyclic testing.Particularly,a method of measuring the H^(+) permeability of the AEM is developed.It demonstrates that the poly(p-terphenyl-N-methylpiperidine)-quaternary ammonium(PTP-QA)membrane with a QA cation-tethered alkyl chain exhibits high H^(+) permeability,resulting in low area resistance.Combined with its low vanadium permeance,the PTP-QA membrane achieves nearly 370 times higher ion selectivity than Nafion 115.The VRFB based on PTP-QA-based AEM displays high Coulombic efficiencies above 99% at current densities of 80-160 mA cm^(-2).The higher energy efficiency of 89.8% is achieved at 100 mA cm^(-2)(vs.73.6% for Nafion 115).Meanwhile,the PTPQA-based AEM shows good cycling stability and capacity retention,proving great potential as the ion exchange membrane for VRFB applications.

Strain Effect on the Absorption Threshold Energy of Silicon Circular Nanowires

In this work,the influence of strain on threshold energy of absorption in Silicon circular nanowires is investigated.For this purpose,we first have used the density functional theory(DFT) to calculate the electron and hole effective masses.Then,we have obtained absorption threshold energy with two different procedures,DFT and effective mass approximation(EMA).We have also obtained the band structures of Si nanowires both DFT and EMA.The results show that:i) the expansive strain increases the hole effective mass while compressive strain increases the electron effective mass,ii) the electron and hole effective masses reduce with decreasing the wire size,iii) the absorption threshold energy decreases by increasing strain for compressive and tensile strain and its behavior as a function of strain is approximately parabolic,iv) the absorption threshold energy(for all sizes) obtained using EMA is greater than the DFT results.

Achieving superior high-temperature sodium storage performance in a layered potassium vanadate

The high-temperature sodium-ion batteries(SIBs)used for large-scale energy storage have attracted extensive attention in recent years.However,the development of SIBs is still hampered mainly by their poor charge/discharge efficiency and stability,necessitating the search for appropriate electrodes.A simple potassium ion intercalation process is used herein to obtain the potassium vanadate(KV_(3)O_(8))nanobelts.When serving as the anode for SIBs at a high temperature(60℃),the KV_(3)O_(8) nanobelts display superior sodium storage performance with a high capacity of 414mA h g^(-1) at 0.1Ag^(-1),remarkable rate capability(220mAh g^(-1) at 20Ag^(-1)),and super-long cycle life(almost no capacity fading at 10Ag^(-1) over 1000 cycles).Moreover,the ex-situ X-ray powder diffraction reveals no structural changes throughout the whole charge/discharge process,which further confirms their outstanding stability,indicating KV_(3)O_(8) nanobelts are a promising candidate for high-temperature SIBs.