Analysis and evaluation of a heat integrated horizontal distillation system
Introduction
The production of chemicals from second-generation (2G) feedstock requires gathering adequate feedstock for one central plant (Maity et al. 2015), which can be challenging. This makes small-scale factories based on local flexible production an attractive alternative. Thus, one may explore a small-scale modular separation system tailor-made for mobile refineries, to enable fast and cost-effective manufacturing of customized products at various locations. Therefore, a container format that is easily configured for different products and processes is considered here. The container format allows on-site transportation to provide manufacturing anywhere, enabling the benefits of localized service delivery without duplication of equipment at multiple locations. We focus on the development of separation technology for the separation of mixtures containing light alcohols from small-scale production facilities of alcohols from 2G biomass (such as straw and wood chips). The paper deals with development of a steady-state model using process systems engineering tools. Its purpose is to describe sufficiently the separation system and perform analysis and evaluation in terms of energy requirements. The proposed horizontal separation system aims at reduction of the costs (such as capital cost and operating cost) associated with conventional distillation systems and novel intensified and highly integrated designs such as reactive distillation, diabatic distillation, internally heat integrated distillation column (HIDiC) and the divided wall column (Kiss et al. 2013). The feasibility of other horizontal distillation systems, in separating binary liquid mixtures, has been demonstrated by experimental and numerical simulation studies (Seok et al. 1985, Ramirez-Gonzalez et al. 1992). Recently, Kim et al. (2013) and Jang et al. (2015) have shown experimentally and numerically the potential energy savings using a diabatic rectangular horizontal column in liquid binary mixtures. Here, the separation system is also horizontal. It consists of two sections, i.e. a stripper and a rectifier. The system has no trays. Therefore, the separation is rate-based. It operates in continuous mode, it can handle viscous liquids (or liquids containing solids), high-value temperature sensitive components and offers opportunities for heat integration. The steady state model is based on the two-film theory of mass transfer. It assumes phase equilibrium at the vapor-liquid interface and counter-current flow of the vapor and liquid phases. It is applied to different mixtures and is compared with conventional separation technologies.
Section snippets
Horizontal heat integrated separation system
The system is shown in Figure 1. It consists of two, co-axially arranged tubes. The inner tube operates as a stripper and the outer one as a rectifier. The feed consists of light alcohols, water and temperature sensitive compounds and enters the stripping section at reduced pressure preventing decomposition of the temperature sensitive compounds. The heavy product of the stripper consists of water and valuable compounds and the light product consists of more light alcohols. The stripper light
Modelling objective
The objective is to develop a model to describe the fundamental phenomena taking place in the diabatic horizontal distillation system. The model needs to predict, qualitatively, for both chambers the internal flow rate profiles, the temperature and the composition profiles in the vapor and liquid phases. The model, at steady-state, is applied to simulation studies, sensitivity analysis, evaluation and analysis in terms of economics and energy and for design studies. The model is used as a tool,
Model application and results
Case 1: Ethanol-water. The mixture of ethanol-water has been selected to highlight the application of proposed design using the developed steady-state model. That mixture is common after fermentation of 2G biomass. Table 1, lists the values of the variables specified to solve the model.
Solving the heat integrated distillation system over the tube length, the internal flowrate, temperature and composition profiles have been obtained, as shown in Figure 3a-c, respectively. Figure 3a shows the
Conclusions
In this paper, an adiabatic horizontal distillation system, intended for small-scale separations of chemicals from 2G bio-refineries, has been described. The development of a process model to provide a meaningful description, in absense of experimental data, of the separation system using process systems engineering tools, has been demonstrated. The model predicts the internal flow rate, temperature and composition in stripping and rectifying sections as well as the energy demands. It serves as
Acknowledgement
The authors would like to acknowledge the financial support of the SYNFERON (journal no. 4106-00035B by Innovation Fund Denmark) project and Morten J.G. Larsen for designing Figure 1.
References (7)
Renew. Sust. Energ. Rev.
(2015)- et al.
Hydrocarb. Process.
(1985) - et al.
Korean J. Chem. Eng.
(2015)
Cited by (1)
Economic analysis of a horizontal diabatic separation system
2019, Chemical Engineering Research and DesignCitation Excerpt :In the stripping section, the temperature profiles are nearly constant, close to the boiling point of the mixture and lower than 60 °C (maximum temperature limit in the stripper, to enable recycling of enzymes). In the rectifying section, the temperature is high at the inlet of the rectifying section (length at 6 m) due to the vapor compression and reduces towards the end of the rectifier due to heat transfer to the stripping section (Papadakis et al., 2018a). In the stripping section, the ethanol composition reduces towards the end of the tube meaning that no ethanol is in the heavy product.