Numerical investigation of hydrodynamic and mixing conditions in a torus photobioreactor

It is well-known that the response of photosynthetic microorganisms in photobioreactor (PBR) is greatly influenced by the geometry of the process, and its cultivation parameters. The design of an adapted PBR requires understanding of the coupling between the biological response and the environmental conditions applied. Cells culture under well-defined conditions are thus of primary interest. A particular lab-scale PBR has been developed for this purpose. It is based on a torus shape, that enables light to be highly controlled while providing a very efficient mixing, especially along the light gradient in the culture, that it is known to be a key-parameter in PBR running. A complete characterization of hydrodynamic conditions is presented, using computational fluids dynamics (CFD). After validation by comparison with experimental measurements, a parametric study is conducted to characterize important hydrodynamics features with respect to PBR application (light access, circulation velocity, global shear-stress), and then to investigate a possible optimization of the process via modification of the impeller used for culture mixing. The final part of the study is devoted to a detailed investigation of mixing performance of the torus PBR, by numerically predicting dispersion of a passive tracer in various configurations. The high degree of mixing observed shows the great potential of such innovative geometry in the field of photosynthetic microorganisms cultivation, especially for the design of a lab-scale process to conduct experiments under well-controlled conditions (light and flow) for modeling purpose.     

Population balance modeling of a microalgal culture in photobioreactors: Comparison between experiments and simulations

The growth of Scenedesmus obliquus in photobioreactors was both experimentally investigated and numerically simulated by solving a population balance equation (PBE), accounting for cell growth and division. The PBE is solved using the Finite size domain Complete set of trial functions Method Of Moments (FCMOM) and a wide range of operative conditions, namely both a batch and a continuous reactor under different light intensities, were considered in the experiments and in the numerical simulations. A thorough validation of the mathematical model was performed by comparing the experimental temporal profiles and steady‐state values of the cell density, wet weight, cell average mass, and mass distributions of the microalgal culture with the corresponding simulation results. The parameters of the distribution of division mass were identified to fit the experimental data; specifically, from the continuous reactor data, the dependence of the mean division mass from the cell average mass was obtained. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2702–2710, 2015     

Temperature effect on continuous gasification of microalgal biomass: theoretical yield of methanol production and its energy balance

A microalga, Spirulina, was partially oxidized at temperatures of 850°C, 950°C, and 1000°C, and the composition of produced gas was determined in order to evaluate the theoretical yield of methanol from the gas. The gas composition depended on the temperature, and the gasification at 1000°C gave the highest theoretical yield of 0.64 g methanol from 1 g of the biomass. Based on this yield, the total energy requirement for the whole process including the microalgal biomass production and conversion into methanol was obtained. Energy balance, which was defined as the ratio of the energy of methanol produced to the total required energy, was 1.1, which indicates that this process was plausible as an energy producing process. The greater part of the total required energy, almost four-fifth, was consumed with the microalgal biomass production, suggesting that more efficient production of microalgal biomass might greatly improve its energy balance.     

紫金铜业820kt/a铜冶炼烟气制酸装置设计及运行实践

介绍了紫金铜业有限公司820 kt/a铜冶炼烟气制酸装置的设计和实际运行情况。该装置采用稀酸洗涤净化、ⅢⅠ-ⅣⅡ"3+1"二转二吸工艺流程、低位高效布置干吸系统和活性焦尾气脱硫工艺。在针对实际生产中遇到的一些问题采取相应改进措施后,该装置现已平稳运行一年多时间,各项主要技术指标基本达到甚至优于设计要求,转化率达99.9%,尾气脱硫出口φ(SO2)<0.002 5%。     

陕西锌业180 kt/a硫酸装置转化工序的设计与运行

介绍陕西锌业180 kt/a锌精矿冶炼烟气制酸装置转化工序的设计与运行。转化工序采用"3+1"ⅢⅠ-ⅣⅡ二转二吸工艺,开车后运行正常,各项指标达到设计值,只是由于热量富裕造成循环酸温度过高,酸冷却器结垢腐蚀。为此进行了技术改造,增大了酸冷却器面积。改造后装置饱和蒸汽产量增加,超温问题消除。     

Influence of stirrer type on mixture homogeneity in continuous powder mixing: A model case and a pharmaceutical case

Continuous powder mixers offer a viable alternative to batch processes, but have received very little attention in scientific literature and in the industrial world. Mixer design is still very empirical and is not based on assessed methodologies. In this paper, we report experiments that aimed to compare two very different types of stirrers for a pilot-scale continuous powder mixer, and for two types of mixtures: a model mixture and a real pharmaceutical mixture. The first stirrer A is of the frame type with inclined paddles and internal transporting screw, the other stirrer B is of the shaft type with paddles mounted on it. Results are first presented from the viewpoint of bulk powder flow by hold-up determination and correlation with operating conditions. General relationships are derived which show that the mobile B leads to higher hold-ups, which may be an important drawback. The study of mixture homogeneity globally confirms these findings, especially in a dense phase flow regime. In the fluidised regime, where the stirrer B can be used, attention is drawn to the negative effect of excessive rotational speeds on the quality of the mixtures.     

节能型10万t/a甲醇装置的设计与运行

介绍了山西丰喜肥业集团临猗分公司于2006年开始运行的节能型10万t/a甲醇装置的工程概况;从国产化程度、工艺路线、能量利用、工艺指标等方面论述了该甲醇装置的技术特点。结果表明,甲醇装置国产化率达到98%,各项综合技术经济指标均满足生产要求。     

Kinetics of nucleation and growth of L-sorbose crystals in a continuous MSMPR crystallizer with draft tube: Size-independent growth model approach

The experimental data concerning kinetics of a continuous mass crystallization in L-sorbose - water system are presented and discussed. Influences of L-sorbose concentration in a feeding solution and mean residence time of suspension in a working volume of laboratory DT MSMPR crystallizer on the resulting crystal size distributions, thus on the nucleation and growth kinetics, were determined. The kinetic parameter values were evaluated on the basis of size-independent growth (SIG) kinetic model (McCabe’s ΔL law). It was observed that within the investigated range of crystallizer productivity (220–2,200 kg of L-sorbose crystals m⁻³ h⁻¹), a crystal product of mean size Lm from 0.22 to 0.28 mm and CV from 68.8 to 44.0% was withdrawn. The values of linear growth rate show increasing trend (from 6.6·10⁻⁸ to 7.6·10⁻⁸ m s⁻¹) with the productivity enlargement (assuming constant residence time τ=900 s). Occurrence of secondary nucleation phenomena within the circulated suspension, resulting from the crystals attrition and breakage was observed. The parameter values in a design equation, matching linear growth rate and suspension density with nucleation rate were determined.     

On the small composite granules formed in a continuous rotating conical vessel containing grinding media: effect of the methods of feeding powder on the size and structure of binary composite granules

To investigate the effect of the methods of feeding SiC and CaCO₃ powders on the size and structure of binary composite granules made of the powders, experiments were performed by a simultaneous operation of granulation, grinding and separation in a continuous rotating conical vessel using two kinds of methods for feeding the binary powder. The structure of a composite granule was characterized by comparing the granule size with the size of the SiC-agglomerates contained in the granule.

It was found that (i) by feeding dry SiC with CaCO₃ powders, it was difficult to obtain composite granules smaller than 0.3 mm in size, and that (ii) by feeding SiC-powder with binder in a slurry state, it was possible to make composite granules of larger than at least 0.13 mm, though the structure of composite granules depended on the concentration of SiC-powder in the slurry.     

Solubility and mass transfer of H2, CH4, and their mixtures in vacuum gas oil: An experimental and modeling study

In this work, the solubility data and liquid-phase mass transfer coefficients of hydrogen (H₂), methane (CH₄) and their mixtures in vacuum gas oil (VGO) at temperatures (353.15-453.15 K) and pressures (1-7 MPa) were measured, which are necessary for catalytic cracking process simulation and design. The solubility of H₂ and CH₄ in VGO increases with the increase of pressure, but decreases with the increase of temperature. Henry's constants of H₂ and CH₄ follow the relation of ln H=-413.05/T + 5.27 and ln H=-990.67/T + 5.87, respectively. The molar fractions of H₂ and system pressures at different equilibrium time were measured to estimate the liquid-phase mass transfer coefficients. The results showed that with the increase of pressure, the liquid-phase mass transfer coefficients increase. Furthermore, the solubility of H₂ and CH₄ in VGO was predicted by the predictive COSMO-RS model, and the predicted values agree well with experimental data. In addition, the gas-liquid equilibrium (GLE) for H₂ + CH₄ + VGO system at different feeding gas ratios in volume fraction (i.e., H₂ 85% + CH₄ 15% and H₂ 90% + CH₄ 10%) was measured. The selectivity of H₂ to CH₄ predicted by the COSMO-RS model agrees well with experimental data. This work provides the basic thermodynamic and dynamic data for fuel oil catalytic cracking processes.