Reducing total annual cost and CO2 emissions in batch distillation for separating ternary wide boiling mixtures using vapor recompression heat pump

This paper presents cost-effective heat pump assisted vapor recompression (VRC) design algorithms for the separation of ternary wide boiling mixture in batch distillation in order to reduce total annual cost (TAC) and carbon dioxide (CO2) emissions. A minimum TAC and CO2 is required by the batch distillation process industry for any investments in heat integrated systems, such as VRC. Consequently, the design conditions for implementing VRC should be chosen such that the energetic performance is maximum at minimum TAC. The model system selected in this paper is an application involving high temperature lift, that is, hexanol–octanol–decanol ternary wide boiling mixture. First, a systematic simulation algorithm was developed for conventional multicomponent batch distillation (CMBD) and single-stage vapor recompressed multicomponent batch distillation (SiVRMBD) to determine the optimal number of stages based on the maximum TAC savings. The SiVRMBD saves more energy and TAC than CMBD. However, SiVRMBD has a high compression ratio (CR) throughout the operation, which is not practically feasible for the batch distillation processing. Second, in order to increase the performance and minimize the SiVRMBD weakness, a novel optimal multi-stage vapor recompression algorithm was proposed to operate at the lowest possible CR (<3.5) throughout the batch operation while also conserving the most TAC. Overall, the findings suggest that the proposed optimal multi-stage VRC reduces TAC and CO2 emissions significantly when compared to CMBD. Finally, the influence of the different feed compositions on VRC performance is also studied.

Rack-Level Thermosyphon Cooling and Vapor-Compression Driven Heat Recovery: Condenser Model

This paper is focused on the modeling of a brazed plate heat exchanger (BPHE) for a novel in-rack cooling loop coupled with heat recovery capability for enhanced thermal management of datacenters. In the proposed technology, the BPHE is acting as a condenser, and the model presented in this study can be applied in either the cooling loop or vapor recompression loop. Thus, the primary fluid enters as either superheated (in the vapor recompression loop) or saturated vapor (in the cooling loop), while the secondary fluid enters as a sub-cooled liquid. The model augments an existing technique from the open literature and is applied to condensation of a low-pressure refrigerant R245fa. The model assumes a two-fluid heat exchanger with R245fa and water as the primary and secondary fluids, respectively, flowing in counterflow configuration; however, the model can also handle parallel flow configuration. The 2-D model divides the heat exchanger geometry into a discrete number of slices to analyze heat transfer and pressure drops (including static, momentum and frictional losses) of both fluids, which are used to predict the exit temperature and pressure of both fluids. The model predicts the exchanger duty based on the local energy balance. The predicted values of fluid output properties (secondary fluid temperature and pressure, and primary fluid vapor quality and pressure) along with heat exchanger duty show good agreement when compared against a commercial software.

Evaluation of mechanical vapor recompression in the reactive distillation of the N-butanol esterification process

The process of producing esters is usually performed through esterification in a reactor followed by a distillation column to separate the products. However, this design limits the reagent conversion. Reactive distillation is an alternative to get around this issue as it allows greater reagent conversions in reactions limited by chemical equilibrium. It is one of the most famous process intensification techniques. On the other hand, mechanical vapor recompression has been used to recycle waste heat to improve efficiency of conventional distillation columns. In this context, this work evaluated the inclusion of a mechanical vapor recompression system in a reactive distillation process to obtain n-butyl acetate via n-butanol esterification with acetic acid. Systems with and without recompression were simulated in an Aspen Plus™ environment. The addition of recompression resulted in a reduction of 33.65% in the annual cost of the process, while not significantly affecting the purity of the desired product and the reagents’ conversion. From an environmental point of view, the mechanical vapor recompression system adoption resulted in a 12.69% reduction in CO2 emissions, contributing positively to meeting the requirements of the environmental regulations.

Optimal modes of side-section flow in heat-pump-assisted extractive distillation systems for separating allyl alcohol–allyl acetate mixtures with butyl propionate

Objectives. To investigate the influence of side-section flow modes on the energy efficiency of a partially thermally coupled distillation sequence (PTCDS) with a vapor recompression heat pump for the extractive distillation of an allyl alcohol–allyl acetate mixture with n-butyl propionate and identify modes under which the combined use of a PTCDS and heat pump are the most efficient.Methods. Mathematical modeling in the Aspen Plus V10 software package was used as the main research method. The local composition equation of the non-random two-liquid model was used as a model for describing the vapor–liquid equilibrium, while the Redlich–Kwong model was used to consider the non-ideal vapor phase. When modeling the conventional extractive distillation scheme and PTCDS, parametric optimization was carried out according to the criterion of the total energy costs in the column reboilers. For the economical evaluation, Aspen Process Economic Analyzer V10.1 tools were used.Results. For extractive distillation of a mixture of allyl alcohol (30 wt %) and allyl acetate (70 wt %) with n-butyl propionate as an entrainer, the minimum energy consumption was achieved at the same side-section flow mode for the variants of a PTCDS with and without a heat pump. The reduction in energy costs relative to the conventional scheme was 20% for the sequence without a heat pump and 38% for that with a heat pump. An economic assessment was made of the best options in comparison with the conventional extractive distillation scheme. The PTCDS with a heat pump had an advantage over the sequence without a heat pump only for long periods of operation.Conclusions. For the extractive distillation of an allyl alcohol–allyl acetate mixture, the optimal modes for the combined use of a PTCDS with a vapor recompression heat pump coincide with the optimal modes for a PTCDS without a heat pump.