Experimental investigation of pressure fluctuation propagation in two orthogonal directions using a clapboard-type internally circulating fluidized bed

In this work, the pressure wave propagation in the vertical and horizontal directions has been studied using a self-designed clapboard-type internally circulating fluidized bed. The effects of flow regimes and solid mixture on the pressure wave propagation characteristics were analyzed in terms of time-averaged pressure, standard deviation, power spectral density, dominant frequency, propagation time delay, and attenuation. The superficial velocity ratio had a remarkable effect on the pressure wave propagation time delay in the vertical direction but had less influence on the pressure wave propagation in the horizontal direction. The particle circulation provided an extra resistance force to the horizontal pressure wave propagation and resulted in an increase in the pressure wave decay factor in the horizontal direction. The addition of glass beads and salt greatly increased the time delay and decay factor both in vertical and horizontal directions. The addition of 15% corn powder (Geldart-C group) reduced the propagation time delay but increased the decay factor.     

Numerical investigation of binary particle mixing in gas-solid fluidized bed with a bubble-based drag EMMS model

Heterogeneous flow structure of bubbling deeply affects gas–solid momentum transfer in a binary gas–solid fluidized bed. This work presented a binary particle bubble-based Energy Minimum Multi-scale (EMMS) model, and an assumption that bubble-emulation drag force acting on solid 1 and solid 2 depending on each solid volume ratio in the emulation phase was applied to simplify the force balance of the binary particle-phase. The bubble-based EMMS drag was incorporated in the Eulerian multi-fluid model to predict the mixing behaviors of two binary particle systems. The simulation results agree well with the experimental observations in terms of binary solid mixing, bed expansion, and bubble diameter. Compared with the prediction results by the Gidaspow drag model, the jetsam solid fraction and bubble size predicted by the present drag model is in more agreement with the measured results, which indicate the EMMS drag model is an alternative choice for modeling binary gas–solid bubbling system.     

Evaluation of the specific radioactivity of 40 elements created by nuclear transmutation of fission products

A burnup calculation was performed to analyze Après ORIENT process which aims at creating highly-valuable elements by nuclear transmutation of fission products (FPs) separated from LWR spent nuclear fuels. In this paper, numerical evaluation of the specific radioactivity of 40 created elements, from reloaded each FP element, with atomic number from 31 to 70 at the end of the time of 5-year-cooling after the irradiation for 1125 days in each LWR and FBR was carried out. These 40 created elements were classified in 6 categories according to levels of the specific radioactivity and the length of additional cooling period, which was needed for the specific radioactivity to decrease below the exemption level defined by International Atomic Energy Agency. As a result, created ₃₁Ga, ₃₂Ge, ₃₃As, ₃₅Br, ₆₈Er, and ₇₀Yb did not contain any radioisotopes at the end of the 5-year-cooling. It should be noted that created ₃₇Rb, ₅₇La, and ₆₀Nd had much lower specific radioactivities than natural composition of them. Moreover, specific radioactivities of created ₄₀Zr, ₄₂Mo, ₄₄Ru, ₄₆Pd, ₄₉In, and ₅₄Xe were sufficiently lower than their exemption levels at the end of the 5-year-cooling. On the other hand, created ₃₉Y, ₄₅Rh, ₅₀Sn, ₅₂Te, ₅₈Ce, ₅₉Pr, ₆₅Tb, and ₆₆Dy needed additional cooling period less than 10 years until their specific radioactivities decreased below their exemption levels. Then, each additional cooling period required for created ₄₈Cd, ₅₁Sb, ₆₄Gd, and ₆₉Tm was estimated at 10–100 years. Additionally, specific radioactivities of other 13 created elements would not decrease below their exemption levels even if they had been stored for 100 years. There could be significance to create important elements as resources classified in first 4 of the 6 categories defined in this paper, by nuclear transmutation of fission products. In consideration of the efficiency of creation, the radioactivity, and the importance as resources of each product, ₄₄Ru, ₄₆Pd, ₅₂Te, ₆₀Nd, and ₆₆Dy were specially selected as the most important created elements to be more researched in the future Après ORIENT program.     

Analysis of two-phase flow characteristics in a natural circulation loop using the drift-flux model taking flow pattern change and subcooled boiling into consideration

This study investigated the steady-state characteristics of a two-phase natural circulation loop based on the drift flux model, taking flow pattern change and subcooled boiling into consideration. Transcendental equations of non-dimensional loop mass flow rate under various conditions were also derived. The model proposed herein was verified by comparing our results with experimental data found in literature. In addition, various steady-state characteristics of a natural circulation loop were analyzed and discussed; these characteristics include the one-third-power dependence of the single phase mass flow rate on heating power, the incipient power of two-phase flow, the maximum mass flow rate, and the existence of multiple solutions under certain conditions. This study also examined the effects of changing important parameters.     

Radiation shielding mass saving for the magnet coils of the VISTA spacecraft

Radiation shielding structure of a design concept with inertial fusion energy propulsion for manned or heavy cargo deep space missions beyond earth orbit has been investigated. Fusion power deposited in the inertial confined fuel pellet debris delivers the rocket propulsion with the help of a magnetic nozzle. The nuclear heating in the super conducting magnet coils determines the radiation shielding mass of the spacecraft. It was possible to achieve considerable mass saving with respect to a recent design work, coupled with higher design limits for coil heating (up to 5 mW/cm³). The neutron and γ-ray penetration into the coils is calculated using the S_N methods with a high angular resolution in (r–z) geometry in S₁₆P₃ approximation by dividing the solid space angle in 160 sectors. Total peak nuclear heat generation density in the coils is calculated as 3.143 mW/cm³ by a fusion power of 17 500 MW. Peak neutron heating density is 1.469 mW/cm³ and peak γ-ray heating density is 1.674 mW/cm³. However, volume averaged heat generation in the coils is much lower, namely 74, 163 and 337 μW/cm³ for neutron, γ-ray and total nuclear heating, respectively. The net mass of the radiation shielding for the magnet coils is 200 tonne by a total mass of 6000 tonne of the space craft.     

轴流铅铋泵流场分析及优化

铅铋泵作为铅铋冷却快堆一回路的关键输送设备,其安全运行对铅铋冷却快堆的安全至关重要。液态铅铋合金在泵内流动特性对泵的长期安全运行有重要影响,为了研究轴流铅铋泵泵内流场,通过Workbench/BladeGen软件建立了主泵叶轮模型,在ANSYS CFX软件中数值模拟泵内流场,并根据数值模拟结果改进了导叶片厚度,优化了动叶片翼型出口角,从而改善泵内流场。研究结果表明,铅铋泵叶片型线出口附近角度变化过快会导致叶片压力分布不均匀,产生局部高压的现象,进而可能造成更严重的冲蚀。优化导叶片厚度以及动叶片出口液流角后,泵内流场整体迹线较为平稳,导叶片出口处铅铋合金流速可以维持在1.8 m/s左右。      

Thermodynamic analysis and techno-economic assessment of synthetic natural gas production via ash agglomerating fluidized bed gasification using coal as fuel

Implementing coal to synthetic natural gas (SNG) is a key way to deal with the conflict between supply and demand of natural gas in China. For the coal to SNG process, gasification is a crucial unit, which determines the syngas composition and influences cost of coal to SNG system. In this current study, a coal to SNG system using ash agglomerating fluidized bed gasification is designed and modeled. According to the above results, the thermal performance and technoeconomic assessment of the coal to SNG system are performed. The research demonstrates that exergy efficiency and energy efficiency of the whole system are 55.37% and 61.50%, respectively. Additionally, the results of the economic evaluation show that the SNG production cost is 1.87 CNY/Nm³ with a coal price of 250 CNY/t and an electricity price of 0.65 CNY/kWh. Sensitivities to variables such as water price, electricity price, total equipment cost and coal price are performed. Coal price represents the most important sensitivity, but the sensitivity to water price is relatively small.     

Numerical analysis on combustion process and sodium transformation behavior in a 660 MW supercritical face-fired boiler purely burning high sodium content Zhundong coal

CHEMKIN software was used to optimize the reaction mechanism of sodium in flue gas to study the influence of targeted design for purely burning Zhundong (ZD) coal on boiler characteristics. Then, the optimized 32-step elemental reaction was combined with CFD software. An eddy-dissipation concept model considering detailed chemical reactions was used to simulate the transformation behavior of sodium-containing substances. The combustion characteristics of the 660 MW face-fired boiler under various loads were also simulated. The field distribution in the furnace and the migration path of sodium along the track of pulverized coal particles were obtained. The results show that the interference between each burner in the furnace is small at the BMCR load, and the phenomenon of “wind wrapping fire” is distinctly clear. The temperature at furnace outlet is approximately 970.98 °C. At a low load, the combustion in the furnace is stable, and the temperature at the furnace outlet reaches the design value. The sodium present in ZD coal is involved in the reaction after it is released in the form of Na and NaCl. Sodium is present in different forms in the main burner zone, mainly NaCl (67%), NaOH (12%), Na (9%), and Na₂SO₄ (7%). The forms of sodium at the furnace outlet are NaCl (50%), Na₂SO₄ (37%), Na₂Cl₂ (9%) and NaHSO₄ (4%). A small amount of Na₂SO₄ is formed by NaHSO₄ reaction in the main burner zone. It then reacts to form NaSO₄, wherein NaHSO₄ is formed by path 2. Na₂SO₄ is mainly generated in the burnout zone through path 1, and paths 2, 3, and 4 are hardly observed. The findings of this research can provide reference for the design of a purely fired ZD coal boiler and further studies on slagging observed on the heating surface.     

Experimental investigation on gasification characteristics of polycarbonate (PC) microplastics in supercritical water

In order to solve the problem of marine microplastics and realize the harmless resource utilization of plastics, the gasification experiments of polycarbonate (PC) microplastics were carried out in supercritical water and a novel seawater gasification of microplastic experiment was investigated. In this paper, the effects of different operating conditions (temperature, time, feedstock concentration, pressure) on gasification performance were discussed. The gasification kinetic of microplastics in supercritical water was calculated. The experimental results showed that the increase in gasification temperature and time enhanced the cracking reaction and free radical reaction of the microplastics to increase the gasification efficiency, while the reduction in feedstock concentration improved the gasification efficiency by increasing the gasification level of unit feedstock. The change in pressure had no significant effect on gasification due to the fact that the properties of the supercritical water were not significantly changed. It was found that the valuable results that all alkali metal salts in seawater promote hydrogen conversion, while in terms of carbon conversion, only KCl, CaCl₂, NaHCO₃ and seawater had a significant catalytic effect on the gasification. Seawater gasification of microplastics was a potential resource utilization method. Finally, it was considered that the PC plastic gasification conformed to the random nucleation and subsequent growth model (n = 3), and the reaction activation energy was 230.45 kJ/mol, which was smaller than that of traditional pyrolysis.     

海水淡化喷嘴分布特性的实验研究

为验证国产喷嘴性能,对低温多效海水淡化用进口M5型工程喷嘴和一种国产研制型蓝色喷嘴做了单喷嘴的喷淋布液分布实验,对比分析了这2种喷嘴的全周向喷淋布液分布特性以及喷淋流量和盐水浓度对其布液分布的影响。实验结果表明：研制型蓝色喷嘴与M5型喷嘴的喷淋布液分布规律基本一致;单喷嘴喷淋布液规律并不随流量的增大而发生大的变化;盐水浓度对喷嘴的喷淋布液分布规律影响不大。实验证明国产喷嘴性能良好,满足工程应用要求。