No abstract
In the last third of the last century, important progress was made in developing the scientific basis for oxidized asphalt production technology. The classification of crude oils and mathematical model developed allow quantitatively predicting the basic parameters of asphalt production based on vacuum distillation and oxidation process using the reference properties of the crude oil. Key words: oxidized asphalt, prediction, classification of crude oils, mathematical model.The evolution of technology for production of any product usually passes through the stage of engineering art where decision-making is based on separate facts and is heuristic in character. Gradual accumulation of knowledge leads to generalizations that allow making decisions based on rigorous calculations. This collected knowledge, which allows quantitatively predicting the basic parameters of product production technology, can be called science.The results of development of domestic asphalt production technology, more precisely, its material implementation, over the last third of the 20 th century were generalized previously in [1]. The reasons for selecting this period of time were discussed there. The present article concerns the development of scientific views in asphalt technology in the same time period. We first analyzed the reviews in monographs published in the mainstream press and articles in the journals Khimiya i Tekhnologiya Topliv i Masel [Chemistry and Technology of Fuels and Oils] and Neftepererabotka i Neftekhimiya [Oil Refining and Petrochemistry] , since the most important events and facts would be reflected on the pages of these publications. We focused most attention on the developments that markedly influenced the development of the prognostic basis of the technology and thus confirmed the right to call it scientific. Many publications that do not consider approaches to the quantitative prediction of some parameters of a technology are not discussed based on the same criterion. Perhaps enough time has not yet passed for a reliable evaluation of such publications.The area of application of asphalts is primarily determined by their consistency. Determination of the degree of softness of asphalts is based on methods of testing that determine arbitrary characteristics; ductility, i.e., the capacity to be drawn into a thread; softening point; penetration, i.e., the depth of needle penetration in asphalt [2, 3].Such tests, although conducted by methods generally accepted in world practice, do not essentially differ from the methods of assessing quality used at the dawn of asphalt production -for example, by pressing with a fingernail.
Based on published data on the air bubble rise velocity in water and using methods of similarity theory and mathematical tools for calculating precipitation processes and surfacing of solid particles in a liquid, the structure of the bubble layer in a tower for production of oxidized asphalts was analyzed. A conclusion was drawn concerning the existence of an ascending gas"liquid stream in the central part of the bubble towers and a descending liquid stream near the walls.In using towers for production of oxidized asphalts in domestic practice, it was hypothesized that movement of the reacting phases (feedstock and air) is countercurrent [1]. However, it was soon shown that the composition[2] and temperature [3] of the liquid phase are the same over the height of the bubble layer in the tower and as a consequence, the tower is an ideal mixing apparatus with respect to the liquid phase. Later, in analyzing the response curves in pulsating perturbation of the gas phase stream, it was shown that the stream of this phase corresponds to an ideal displacement model slightly complicated by longitudinal mixing [4].There is no more detailed information on the structure of the bubble layer in oxidation towers, although they are important for the correct construction and arrangement of air dispersers. The shortage of this information is due to the difficulty in conducting observations in the case of nontransparent viscous liquids.Some other systems, for example, air-water, have been investigated to a greater degree. It was found that in towers of large diameter, the air bubbles that come out of the openings in disperser pipes contract to the center of the tower and in rising, carry some of the liquid after them [5]. For this reason, an ascending gas-liquid stream is formed along the axis of the tower, and a descending liquid stream is formed near the walls. The radius of the ascending stream is on average slightly more than half the tower radius [6].In our opinion, this phenomenon can be explained by an analysis of Bernoulli's equation:where z is the height above the reading plane; p is the pressure; ρ is the density of the liquid; g is the free-fall acceleration; w is the velocity. 0009-3092/06/4202-0109
The change in the radius of the rising gas-liquid stream in the bubbling layer of an air -liquid system was investigated as a function of the temperature and properties of the liquid in laboratory conditions. A method is proposed for the comparative estimation of the radius of this stream in industrial units using the Galilei number, Morton number, and the dynamic viscosity of the liquid.For correctly placing air dispersers which can optimize oxidation in oxidation units, detailed data on the structure of the bubbling layer are required. However, obtaining such data is complicated due to the difficulty of modeling this layer. In industrial towers, investigators observe the rising gas-liquid stream along the axis and the descending liquid stream along the walls [1-3]. Almost equilibrium accumulation of bubbles is observed in some cases [3] and a gas-liquid stream rising along the axis is observed in others [4,5] in columns of small diameter used for determining the parameters of a model layer.The air -water system has been studied the most. In laboratory conditions, it was found that the radius of the rising stream constitutes 60-70% of the radius of the column [4]. Based on the results of extrapolating the laboratory data in [2], it was suggested that the radius of the rising stream in industrial bubbling columns should be considered equal to 55% of the radius of the column on average. Such a structure of the bubbling layer, as demonstrated in [6], should also exist in oxidation units for production of asphalts. This conclusion was based on the methods of similarity theory and experimental data [7] on the rates that air bubbles of different diameter float up. The mathematical apparatus used was developed for calculating precipitation and floating of solid particles in the liquid phase. However, in the case of bubbles, the
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.