Abstract
Distillation processes are an essential component of any chemical plant for the separation and purification of condensable mixtures. However, distillation columns account for the largest contribution to the total energy consumption of chemical processes due to their high heat demands. Consequently, there is a strong need for energy efficient column designs to reduce drastically the carbon dioxide emissions and thus to reach the settled climate goals of the chemical industry. In this paper the FluxMax approach is used to identify energy optimal column designs. The representation of the distillation process by the elementary processes mixing, heating/cooling and phase separation leads to increased degrees of freedom of optimization compared to classical column modeling approaches. In this way, a non-conventional design with minimal energy consumption is identified. The energy-optimized configuration is a column with improved heat transfer between vapor and liquid streams. MESH equations are used for the validation of the FluxMax design, as they are state-of-the-art in process modeling tools. While the new design reduces the energy demand by up to 64 % compared to the classical design, additional heat exchange area is required to exploit the energy reduction potential. A multi-objective optimization – energy duty vs. heat exchanger area – is carried out to identify the optimal trade-off between energy demand and heat exchanger area related capital cost. The highly energy-efficient designs identified by the FluxMax approach may be realized in practice by horizontal columns or modularized container solutions.
Highlights
In order to achieve the ambitious goal of greenhouse gas emission neutrality within the European Union by 2050, the chemical industry is required to reduce drastically carbon dioxide emissions (European Commission, 2018)
The results show that an improved heat exchange reduces the energy demand up to 64% compared to classic distillation columns, and can contribute to the reduction of carbon dioxide emissions
This paper proposes an approach to design distillation columns with significantly reduced energy requirements
Summary
In order to achieve the ambitious goal of greenhouse gas emission neutrality within the European Union by 2050, the chemical industry is required to reduce drastically carbon dioxide emissions (European Commission, 2018). Energy-Efficient Distillation Processes to identify energy optimal distillation column designs Most of these publications are based either on shortcut methods such as the Fenske-Underwood-Gilliland method (Fenske, 1932; Gilliland, 1940; Underwood, 1949) or on rigorous tray-by-tray model formulations (Biegler et al, 1997). In this way the minimum energy demand of non-ideal multi-component mixtures can be estimated efficiently Another shortcut method was proposed by Adiche and Vogelpohl (2011), which allows the design of distillation columns for the separation of azeotropic mixtures. In addition to the objective functions for identifying the most energy efficient design as well as the stage minimal configuration, an extension of the classical modeling approach based on the MESH equations is derived This serves as a benchmark of the results obtained by the FluxMax formulation. It is shown that the novel FluxMax design has a signifcantly lower energy demand than distillation column designs based on the regular MESH equations
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