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CPOTE2020 logo
6th International Conference on
Contemporary Problems of Thermal Engineering
Online | 21-24 September 2020

Abstract CPOTE2020-1178-A

Book of abstracts draft
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Theory and experience of the recycle processes in chemical engineering: thermodynamic estimation of their applicability to the recycling of materials in circular economy

Zornitza KIROVA-YORDANOVA, University "Prof. Asen Zlatarov" Bourgas, Bulgaria

The recycle processes are commonly used in chemical engineering, incl. inorganic and organic chemical industry, oil refining, as in metallurgy, food processing, etc. The industrial recycle processes are used for: recycle of unreacted feedstock back to the reaction; recycle of some auxiliary substances (absorbents, adsorbents, catalysts, etc.); recycle of some useful components from treated waste flows. So, the recycle processes ensure maximum usage of feedstock and minimum waste and emissions. The recycle processes are high energy consuming. In comparison with once-through processes, the recycle processes are impossible without some additional energy, necessary to separate the recycled components and to flow them back to the process. This means that to ensure a complete utilization of the feedstock, an additional quantity of some energy resources must be spent. Depending on the feedstock, two cases should be analyzed: first, if the feedstock is a primary energy resource and second if the feedstock is a non-energy natural resource. In the first case the optimisation task could be the minimum of total primary energy resources consumption (CEnC); in the second case the optimisation task is the minimum of total Cumulative exergy of natural resources consumption (CExC). The theory, methodology and optimization tools of the industrial recycle processes are intensively developed for more than 70 years. As the recycle processes are essentially positive feedback processes, the advances of theory of these processes are closely connected with process control theory and experience. The recycling of wastes (materials, substances and elements) is a more complex and difficult problem. In last years the waste recycling is subject of numerous investigations from different aspects and various methodologies are applied. However, the results about efficiency, reliability and sustainability are rather contradictory. A comparison of industrial recycling processes and material recycling shows as some similarities, as well as many substantial differences. The common problem of both processes is the estimation of natural energy and non-energy resources consumption. In this work two goals are posed: first, to compare from a thermodynamic point of view the recycle processes in chemical engineering with the materials recycling in circular economy and second, to estimate the applicability of the theory and experience of the industrial recycle processes to the materials recycling.

Keywords: Recycle processes in chemical engineering, Recycling of materials, Thermodynamic analysis, Cumulative exergy consumption (CExC), Natural resources consumption