ATTRITION IN THE BUBBLING ZONE OF A STEADY-STATE FLUIDIZED BED

This paper describes the kinetics of attrition in the bubbling zone of a fluidized bed and focuses on the development of an equation for attrition in continuous fluidized beds operating at steady state.

Laboratory data describing batch attrition of a limestone sorbent are applied to the integrated equations to describe overall attrition rate in a full-scale continuous system.     

Alternative hydrocarbon solvents for cottonseed extraction

Hexane has been used for decades to extract edible oil from cottonseed. However, due to increased regulations affecting hexane because of the 1990 Clean Air Act and potential health risks, the oil-extraction industry urgently needs alternative hydrocarbon solvents to replace hexane. Five solvents,n-heptane, isohexane, neohexane, cyclohexane, and cylopentane, were compared with commercial hexane using a benchscale extractor. The extractions were done with a solvent to cottonseed flake ratio of 5.5 to 1 (w/w) and a miscella recycle flow rate of 36 mL/min/sq cm (9 gal/min/sq ft) at a temperature of 10 to 45°C below the boiling point of the solvent. After a 10-min single-stage extraction, commercial hexane removed 100% of the oil from the flakes at 55°C; heptane extracted 100% at 75°C and 95.9% at 55°C; isohexane extracted 93.1% at 45°C; while cyclopentane, cyclohexane, and neohexane removed 93.3, 89.4, and 89.6% at 35, 55, and 35°C, respectively. Each solvent removed gossypol from cottonseed flakes at a different rate, with cyclopentane being most and neohexane least effective. Based on the bench-scale extraction results and the availability of these candidate solvents, heptane and isohexane are the alternative hydrocarbon solvents most likely to replace hexane. Presented in part at the AOCS Annual Meeting & Expo, Atlanta, Georgia, May 1994.     

高压大流量地下水隧道开挖超前帷幕注浆参数研究

锦屏水电站锦屏山隧道开挖中面临高压大流量地下水、且富水地段长(约占隧道全长的40%)的难题。为安全、可靠地进行隧道施工,以注浆材料的适应性、超前帷幕注浆的参数及工艺为研究对象,对浆液做了大量配合比试验,分析其流动性、物理力学性能和凝结时间。研究结果表明:用纯水泥进行单液浆帷幕注浆,其可注性好,可大大地提高注浆加固效果;纯水泥+双液浆对局部小的渗漏水具有很好的封堵效果。对于低于2 MPa的压力水,注浆压力取2~3倍的静水压力;对于高于5 MPa的压力水,注浆压力取净水压力加2~3 MPa。对于在2~5 MPa之间的压力水,注浆压力可灵活选取,但不宜超过7 MPa,注浆应采用孔内循环灌注的方式。地下水发生在断层破碎带时,超前帷幕注浆宜采用全断面帷幕;若出水段以溶蚀裂隙、断层、管道为主宜采用有针对性的局部超前帷幕注浆。该技术成功解决了锦屏山隧道高压大流量地下水封堵的难题,对富水地层地下隧洞施工具有重要参考价值。     

敌敌畏乳油中无芳烃溶剂的开发动态

对现有敌敌畏乳油的构成作了介绍，重点阐述了苯类溶剂对人体的危害，简述了无芳烃敌敌畏乳油的开发意义及动态，我国现有敌敌畏乳油所用溶剂全部是苯类溶剂，苯不仅对人体造成神经系统障碍，而且还危及血液及造血器官，因此开发无芳烃敌敌畏乳油符合人类的需要，具有良好的前景。     

THE ISOTHERMAL COMPRESSIBILITY OF GAS-SATURATED HYDROCARBON LIQUIDS

Volumetric measurements were made on compressed solutions of carbon dioxide in n-decane and trans-decalin at 37.78°C at pressures up to 60 bar. The data were numerically analyzed to yield the isothermal compressibility function of the solutions at their saturation pressures.     

Influence of compaction on the interfacial transition zone and the permeability of concrete

The interfacial transition zone (ITZ) is regarded as a key feature for the transport properties and the durability of concrete. In this study one self-compacting concrete (SCC) mixture and two conventionally vibrated concrete (CVC) mixtures are studied in order to determine the influence of compaction on the porosity of the ITZ. Additionally oxygen permeability and water conductivity were measured in vertical and horizontal direction. The quantitative analysis of images made with an optical microscope and an environmental scanning electron microscope shows a significantly increased porosity and width of the ITZ in CVC compared to SCC. At the same time oxygen permeability and water conductivity of CVC are increased in comparison to SCC. Moreover, considerable differences in the porosity of the lower, lateral and upper ITZ are observed in both types of concrete. The anisotropic distribution of pores in the ITZ does not necessarily cause anisotropy in oxygen permeability and water conductivity though.     

Dynamics in input and output coefficients for land use studies: a case study for nitrogen in crop rotations

Increasingly, model-based approaches play a role in the design and development of new land use systems. Simulation modeling may play a role in the generation of land use systems for land units, and optimization modeling (e.g. linear programming – LP) may be used in the upscaling to farm and region. In the quantification of new land use systems for land units, often equilibrium conditions with respect to soil resources are assumed, following a so-called target-oriented approach. This facilitates ex ante computation of inputs and emissions of nutrients and allows their use in static optimization models based on LP. The condition of equilibrium in soil resources is often not met, nor is it the ultimate aim. Hence, the dynamics in new systems are insufficiently dealt with. This paper presents an approach for the design of land use systems (crop rotations) and their quantification in terms of input and output coefficients, using particular yields and dynamics in soil resources as targets. Interactions between N input and output of succeeding crops are explicitly taken into account. A simple N-balance model is used describing major processes affecting soil N-dynamics. For the Koutiala region in Mali five crop rotations are evaluated that differ in target crop yield, crop choice, crop residue management and external N source. Modeled crop rotations aiming at high yields, in combination with incorporation of crop residues and legumes, result in depletion of soil N stock. Only in crop rotations aiming at high yields and with incorporation of crop residues combined with a supply of large quantities of animal manure, soil N depletion can be prevented. Four approaches are presented of how to use the dynamic input–output coefficients of these systems in land use studies using LP: (i) use of average coefficients, (ii) use of discounted coefficients, (iii) use of pessimistic estimates of coefficients in an optimization of the land use allocation followed by a recalculation of the objective values for the optimized land use with optimistic coefficients, and (iv) a combined use of systems characteristics, i.e. cumulative N-inputs of land use systems over the time horizon and the magnitude of the soil N pool at the end of the time horizon, which can be used as filters for land use systems. Though none of the approaches completely captures the dynamics in input–output coefficients, they enable a well-founded consideration of the consequences of dynamics in, for instance, soil N stocks in static optimization approaches for farm and regional studies.     

地层主曲率在研究储层裂缝发育中的应用

曲面曲率的几何意义可以反映曲面一点邻近区域的具体形态和变形特征,因而可以用主曲率法来评价和预测油气储层裂缝分布和发育程度,应用这种方法对泌阳深凹陷中心安棚鼻状构造带进行了评价。研究结果表明,采用主曲率法预测的结果与地质解释、钻井和测井资料吻合较好,具有很好的应用前景。     

C4烃催化裂解动力学装置进料方法的研究

研究了液态进料法、气态进料法等不同进料方法对C4烯烃催化裂解动力学研究装置物料平衡的影响。结果表明，气态间接进料法可满足动力学研究的需要，并建立了稳定可靠的动力学研究装置。     

Mechanisms of hydrocarbon conversion reactions on heterogeneous catalysts: analogies with organometallic chemistry

Catalysis is central to most industrial processes for chemical manufacturing. As catalytic processes have become more complex and more demanding, selectivity has become the central issue in their design. Selectivity is defined by the relative rates of competing reaction pathways available to crucial intermediates, and can be controlled by subtle changes in the nature of the catalyst, the reactants, and/or the reaction conditions. In order to be able to do this in a systematic manner, a good understanding of the catalytic reaction mechanisms is needed. Here a connection is drawn between the key elementary steps comprising hydrocarbon conversion reactions on surfaces and those known to occur on discrete organometallic complexes. This way, the hydrogenation, dehydrogenation, hydrogenolysis, chain growth, and isomerization reactions typical in heterogeneous catalysis are redefined in terms of hydride elimination, oxidative addition, reductive elimination, migratory insertion, and 1, 2-shift elementary steps, among others. It is suggested that the knowledge already available from organometallic chemistry can be used to further advance the understanding of the surface science involved in heterogeneous catalysis. Thanks to the commonality of the chemistry involved, a better synergy could also be established between homogeneous and heterogeneous catalytic development. These ideas are discussed in this article in a critical and personal way.*Invited contribution to the special volume entitled The Interface between Heterogeneous and Homogeneous Catalysis, stemming from contributions at the recent International Symposium on Relations between Heterogeneous and Homogeneous Catalysis, and dedicated to the memory of Robert L. Burwell.