Boundary layer theory approach to the concentration layer adjacent to a ceiling wall of a hydrogen leakage: Far region

The field of the hydrogen leakage in partially open space can be divided into two main regions according to the importance of the hydrogen concentration distribution and the flow behavior. These two regions are the jet region and the boundary layer region which are adjacent to the ceiling wall of the space, resulting from impinging the hydrogen jet to the wall. The boundary layer region in turn can be divided into two regions, according to the modeling of the flow. These regions are the stagnation-point boundary layer region and the far boundary layer region. Previously, we studied the region of stagnation-point flow (Hiemenz flow) [El-Amin MF, Kanayama H. Boundary layer theory approach to the concentration layer adjacent to a ceiling wall at impinging region of a hydrogen leakage. Int J Hydrogen Energy, in press.]. The current paper is devoted to analyze the far region of the boundary layer adjacent to the ceiling wall using the boundary layer theory. Also, an experiment has been conducted on the hydrogen leakage in partially open space to estimate the concentration distribution vertically at the center of the domain under the ceiling wall. In order to verify the boundary layer theory approach, a comparison between the measurements and the boundary layer theory approximations is investigated and the results showed a good agreement. The wall shear stress, the local friction factor, the friction drag and the non-dimensional drag coefficient of the ceiling wall are calculated. Also, both momentum and concentration boundary layer thicknesses are estimated.     

Fractionation and concentration of kraft black liquor lignin with ultrafiltration

Kraft black liquor lignin is a biofuel that is separated from the cellulose during kraft pulping. Improved technology and energy integration in paper mills have led to an energy surplus at many mills. It is therefore of great interest to extract the lignin from the pulp mill and sell it as fuel to replace fossil fuel in other furnaces. The fractionation of kraft black liquor with a total dry matter content of about 15 wt% has been studied using ultrafiltration. The flux for three polymeric membranes with different cut-offs was investigated as well as their retention of lignin and other process specific substances. The retention of lignin for the three membranes with cut-offs of 4,8 and 20 kDa was 80%, 67% and 45%, respectively. The retention of sulphur and sodium was zero for all three membranes. The purity of the final lignin fuel is of importances as the ash content preferably should be as low as possible. The flux and retention during concentration and diafiltration of the black liquor were therefore studied. The dialfiltration operation was conducted in batch and semicontinuous mode. The lignin purity was 36% in the original kraft black liquor and 78% after semi-continuous dialfiltration.     

CONCENTRATION POLARIZATION ANALYSIS AT THE ENTRANCE REGION OF A FLAT SHEET PERVAPORATION MODULE FOR VOC REMOVAL

Concentration polarization is a phenomenon that is inherent in all membrane separation processes, which is difficult if not impossible to measure experimentally. Concentration polarization in a pervaporation module causes flux decline and is therefore an important issue in predicting the performance of the membrane unit for evaluation and optimization. Short-form (small L/D ratio) membrane configurations, commonly used for membrane evaluations or certain material separations, compound the complexity of process modeling that addresses concentration polarization since a substantial portion of the membrane flow channel would be considered as an “entrance region” based on the flow profile that is not fully developed. This article employed the classic boundary layer theory, combined with mass transfer phenomena in a pervaporation process that is used in volatile organic compound (VOC) removal from contaminated water sources, to theoretically analyze the concentration polarization severity in the entrance region of a flat sheet membrane module.     

Application of computational fluid dynamics analysis for improving performance of commercial scale selective catalytic reduction

The performance of commercial scale selective catalytic reduction (SCR) system is strongly dependant upon the degree of mixing between NH₃ and NOx or NH₃ concentration distribution at the catalyst layer according to the reaction kinetics of SCR catalysts. Insufficient mixing of the reduction agent and NOx mass flow necessitates an uneconomically large catalyst volume and high NH₃ slip to meet the required NOx emission values. The effective methodology which can increase the performance of commercial scale SCR through improving NH₃ concentration distribution at the catalyst layer using computational fluid dynamics (CFD) analysis was suggested and applied to the real operations. The operation results have shown that the performance of commercial SCR was improved from 54.4% to 74.8% as NH₃ concentration deviation at the catalyst layer was reduced from 23.6% to 8.6%. It is established that the increase of NH₃ concentration uniformity at the catalyst layer contributes to improvement of performance of commercial scale SCR.     

不同单体浓度下三种聚季铵的合成及其性质

采用不同单体浓度制得了三种系列聚季铵(即季铵盐型阳离子聚合物):丙烯酰胺-二甲基二烯丙基氯化铵共聚物;丙烯酰胺-三甲基单烯丙基氯化铵共聚物和季铵化丙烯酸铵均聚物.研究了单体浓度对产物的阳离子度、分子量的影响.     

氧化法草酸母液的循环利用

在实验基础上,运用数学解析方法,确定了草酸母液浓缩方案的各参数。对按最佳方案浓缩母液与不循环利用母液的两种情况进行了对比。对母液浓缩过程中的一些问题提出了看法。     

海洋生物通过海水途径对铯,钴,锌的浓集与排出研究

本文报道了海洋生物通过海水途径对铯，钴，锌的浓集与排出研究的实验结果。实验生物为珍珠贝，梭子蟹，黑鲷和扇贝，均取自广东大亚湾海域，在分别含一定浓度的Ｃｓ，Ｃｏ或Ｚｎ的海水中培养７ｄ。进行浓集实验，然后以浅海挂养或清洁海水池养的方式进行排出实验，用原子吸收分光光度计测定生物不同组织或器官中元素的含量。     

用分子蒸馏器浓缩不饱和脂肪酸

Pharmaceutical oil is obtained from peanut oil by wiped film short path distiller(SPD).The concentration ofeffective unsaturated fatty acids in the pharmaceutical oil is more than five percentages,the evaporation rate is more than25%.The experiment results indicate that the optimum technology parameters for wiped film SPD are that feed flow rateis 131 mL/h,operation pressure is 0.1 Pa,agitation speed is 140 rmp,temperature of feed is 190℃and the best evapo-ration is 260℃.     

Modeling, simulation and stabilizing H∞-control of an oscillating continuous crystallizer with fines dissolution

In this contribution, a detailed model for a continuous crystallizer with fines dissolution is derived. The main focus of this article is the identification of physical reasons responsible for oscillations occurring in these crystallization plants. In contrast to many other crystallization models used in literature for the investigation of such limit cycles, detailed kinetic expressions for crystal growth and attrition, as well as for the separation of fines in the annular zone, are incorporated. By dynamic simulations of the model and by comparison with measured data, an undesired dissolution of larger crystals can be identified as a possible reason for the appearance of sustained oscillations. Finally, a stabilizing feedback controller is designed using H_∞-theory. It is demonstrated in simulations that this controller enables stable operation of the crystallizer even at a high fines dissolution rate.     

循环水系统优化运行

乙二醇厂循环水系统总能力为13 000m3/h,长周期运行暴露出装置化冰管冬季有积冰,循环水运行、水场旁滤部分等问题。通过改造化冰管、优化和改造循环水工艺流程、不停车清洗预膜和对旁滤系统的改造,既达到了降低能耗和清洁生产的目的,又提高了装置的运行能力。