Abstract
Substantial quantities of energy are required in conventional distillation columns applied in high-purity separation of close-boiling mixtures. To achieve energy saving of distillation, a novel different pressure thermally coupled distillation (DPTCD) was proposed for separating the close-boiling mixture of n-butanol and iso-butanol. Both this intensified energy integration technique and two other processes, namely conventional distillation (CD) and vapor recompression column (VRC), were simulated in process simulator Aspen Plus. The optimization was carried out to determine the optimal values of design and operating variables on the basis of minimizing energy consumption. Subsequently, the energy saving and economic efficiency of the DPTCD scheme were evaluated through the comparison with the other two processes. The results showed that, compared to the CD and VRC processes, the energy consumption of DPTCD process was decreased by 65.21 and 15.79%, respectively, and the total annual cost (TAC) of DPTCD process can be reduced by 33.75 and 10.46%. It demonstrated that DPTCD scheme was the most promising alternative to reduce the total energy consumption and TAC with high purity (99.1 wt%) n-butanol and iso-butanol products among these separation processes.
Highlights
Distillation is the most common and earliest industrialized unit operation for the separation of liquid mixtures
In this paper, separating the close-boiling mixture of nbutanol and iso-butanol is studied in three different sequences including conventional distillation (CD) process, vapor recompression column (VRC) process and different pressure thermally coupled distillation (DPTCD) process
Based on the effect of such parameters on the heat transfer temperature difference and energy consumption, the optimal design and operating variables such as feed location, the number of the theoretical plates, and compression ratio are obtained. Both the VRC and DPTCD schemes have great energy saving for the binary close-boiling mixture; the DPTCD process can achieve 15.79% energy saving than the VRC process
Summary
Distillation is the most common and earliest industrialized unit operation for the separation of liquid mixtures. The boiling points of iso-butanol and n-butanol at atmospheric pressure are 107.3 and 117.3 °C, respectively, and the relative volatility is slightly larger than 1, which leads to much energy to be consumed in the conventional distillation To solve this problem, two energy saving schemes are proposed: different pressure thermally coupled distillation process and vapor recompression distillation. Thermal coupling in this structure is practical by dividing the conventional distillation column into two individual columns with different pressures, a high pressure (HP) one as rectifier and the other low pressure (LP) as stripper. It should be highlighted that overhead vapor latent heat is the unique heat source without extra external heat
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