Vapor Recompression Heat Pump Research Articles

Novel heat pump assisted distillation configurations for energy and economic savings and their application on propylene/propane and I-butane/N-butane separation systems

Various configurations of vapor recompression heat pumps were previously proposed for enhancing its thermodynamic and/or economic performance. The outcomes of prior publications were documented using fundamentally distinct separation systems, making it challenging for process engineers to decisively determine the optimal processing options for a particular separation task. This difficulty arises from the variations in thermophysical properties exhibited by the materials involved. Despite limited research on bottom flashing heat pumps, they offer advantages over vapor recompression such as lower operating pressure and temperature in process sections. This can result in cost savings and safer operation. In this paper, novel configurations of bottom flashing are proposed, based on the ideas and schemes, previously proposed for vapor recompression. The novel processing systems were proposed and applied on propylene/propane and i-butane/n-butane separation processes as samples of close-boiling distillation systems. This study showed that the bottom flashing systems showed greater economic performances compared to vapor recompression for i-butane/n-butane separation. total annual costs savings of 19.0% was obtained, using the novel configuration of heat recuperated bottom flashing configuration on isobutane/n-butane separation. Also, annualized costs of the systems based on bottom flashing were 10.9%, 4.2% and 7.3% lower than their equivalent vapor recompression processes.

Energy-saving extractive distillation process for the separation of close-boiling 2, 6-xylenol and p-cresol mixture

1) Background2,6-xylenol and p-cresol are widely used in medicine synthesis, which are both important raw materials in chemical engineering. It is shown significant economic benefits to separate 2,6-xylenol and p-cresol. Owing to the extremely relative volatility between 2,6-xylenol and p-cresol, it is difficult to separate the two phenolic compounds through conventional distillation. 2) MethodsThe results of vapor–liquid equilibrium analysis, COSMO-SAC and reduced density gradient result are used to investigate molecular interaction in the separation system, indicating diethylene glycol (DEG) as the optimal solvent. Accordingly, we propose an energy-saving extractive distillation process with DEG as an efficient entrainer for the separation of 2,6-xylenol and p-cresol. Total annual cost (TAC) and CO2 emission are investigated for optimization and estimation of the proposed process. In addition, three energy-saving scenarios for further reductions in TAC and CO2 emission are proposed. 3) Significant FindingsCompared with the benchmark process, the TAC and CO2 emission of the energy-saving design vapor recompression heat pump assisted extractive distillation separation sequence B are reduced by 26.18 % and 49.18 %, respectively, which indicates that the considerable industrial potential of the proposed design.

Applicability exploration and sustainable assessment of heat integration and vapor recompression heat pump to side-stream extractive distillation processes for separating ternary azeotropic system

The side-stream extractive distillation (SSED) process is attracting extensive attention due to its high energy efficiency for separating ternary azeotropic mixture. However, the correlation between the bottom temperature level of distillation columns depending on the flowrates and compositions of side streams and the introduction of heat integration (HI) and vapor recompression heat pump (VRHP) technology is ignored. In the work, a range of initialization extractive distillation processes including one conventional extractive distillation (CED) process and five SSED processes considering different flowrates, compositions, and feed locations of side streams are proposed for separating acetonitrile/isopropanol/water ternary azeotropic system. The optimization results with the minimum the total annual costs (TAC) as the optimization objective show that not all SSED schemes are superior to the CED separation process, and the SSED separation schemes can achieve up to a 2.72 % reduction in the TAC. Following that, the HI and VRHP assisted extractive distillation schemes are proposed based on the temperature levels between the top and bottom of different distillation columns and compressor restraints for the initialization extractive distillation schemes mentioned after optimization. Moreover, sustainable evaluations covering economy, energy consumption, environment, and energy utilization are implemented for the extractive distillation schemes proposed. The evaluation results indicate that the CED-HI scheme overcomes all SSED-HI and SSED-VRHP schemes in terms of economic costs, but the optimal SSED-HI processes can reduce 8.77 % of energy consumption and 4.73 % of CO2 emissions, while the energy utilization raised from 1.70 % to 1.78 % compared to the CED-HI process.

Design and 4E analysis of heat pump-assisted extractive distillation processes with preconcentration for recovering ethyl-acetate and ethanol from wastewater

The separation of ternary azeotropes with a high content of one component using extractive distillation is energy intensive, and the introduction of preconcentration can significantly improve process economy. In this paper, the conventional three-column extractive distillation (TCED), four-column extractive distillation (FCED) with preconcentration, and three-column extractive distillation with integrated distillation column (TCED-IDC) are established and economically optimized to minimize the total annual cost (TAC) for recovering ethyl-acetate (EAc) and ethanol (EtOH) from wastewater containing a large amount of water. The preconcentration and solvent recovery functions can be integrated in IDC. Following that, the vapor recompression heat pump (VRHP) is introduced to further reduce energy consumption for the TCED-IDC process. The two VRHP-TCED-IDC processes are correspondingly designed. Simultaneously, the processes proposed are evaluated in terms of economy, energy consumption, environment and exergy destruction (4E analysis). The environmental analysis is performed via calculating Global Warming Potential (GWP) index using Life Cycle Assessment method. The two VRHP-TCED-IDC processes demonstrate superior performances with regard to 4E analysis. The most efficient VRHP-TCED-IDC process reduce over 32.0 %/16.0 %/6.8 % of TAC, 53.4 %/42.4 %/33.7 % of energy consumption, 62.0 %/53.0 %/45.9 % of GWP, and 49.7 %/35.7 %/29.3 % of exergy destruction compared to the TCED/FCED/TCED-IDC processes, respectively.

Simulation and modification of an Ethane-Ethylene separation Unit using vapor recompression heat Pump: Energy, Exergy, and economic analyses

This paper presents a comprehensive analysis involving simulation and thermo-economic evaluation of thermal integration technology, specifically the vapor recompression method, applied to an existing ethane-ethylene distillation process. The study commences with the simulation of the current process, revealing a favorable level of accuracy as evidenced by the strong agreement between simulation outcomes and real plant data. The energy analysis highlights key parameters, with consumption rates of 0.4 kg of refrigerant per kg of vapor in the condenser and 0.743 kg of heating fluid per kg of liquid in the reboiler. Moving to the economic analysis, the total investment cost for the existing process is estimated at 16,925,333 USD. However, a noteworthy concern is the high refrigerant consumption in the condenser, leading to elevated operational costs within ethylene production facilities. Consequently, this study focuses on reducing refrigerant consumption and enhancing the thermodynamic efficiency of the ethane-ethylene distillation column. Simulation results for the proposed process demonstrate an investment cost of 968,837 USD, marking a 5.72 % reduction compared to the current process. The optimization process, driven by sensitivity analysis, determines the optimal outlet fluid pressure for the compressor, setting it at 3730 kPa. Under this optimized condition, refrigerant consumption for condensing the overhead vapors within the distillation column drops by a significant 34.29 % compared to the base case. From an energy perspective, the optimal Mechanical Vapor Recompression method leads to a substantial reduction in utility consumption, decreasing the rate for feed separation from 3.92 kg of utilities per kg of feed to 1.52 kg of utilities per kg of feed. This represents an impressive improvement in process efficiency. The exergy analysis reveals that the Joule-Thomson valve is the primary contributor to total exergy loss. Notably, the reboiler and distillation column's condenser exhibit significantly reduced exergy losses, 33.77 % and 39.05 % lower, respectively, compared to the base case. This emphasizes the positive impact of the proposed optimization on exergy efficiency.

Energy-saving process development for the purification of propylene glycol based on MVR heat pump distillation combined with thermally coupled technology

In the process of recovering organic compounds from wastewater generated by propylene oxide (PO) production plant, the low concentration of propylene glycol (PG) in the wastewater makes it difficult and energy-intensive to achieve the high concentrations purify of PG using conventional distillation technology. Additionally, there is no publicly available commercial technology for this purpose. Therefore, the aim of this work is to develop an energy-efficient PG purification process based on mechanical vapor recompression (MVR) heat pump distillation combined with thermally coupled technology. Several energy-saving methods were implemented as follows. Firstly, MVR distillation technology was used to purify PG from 2.22% to 33.3% in the PG concentration tower, and the gas at the top of the tower was compressed and pressurized to serve as the heating medium for the reboiler, which significantly reduced the consumption of fresh steam. Secondly, in order to achieve heat matching, the dehydration tower was divided into two parts. The surplus steam compressed by the compressor was then served as the heat source for the reboiler of the first dehydration tower to reduce steam consumption, while achieving 98.7% water removal. Thirdly, the condenser of the de-heavy tower and the scraping film evaporator were thermally coupled to reduce the consumption of heating and cooling media. Based on the aforementioned energy-saving measures, the developed optimization process can achieve PG purification of over 90%, while significantly reducing costs. The total annual cost (TAC) is reduced by 34.89% compared to the traditional distillation process.

Sustainable design and multi-objective optimization of heat pump assisted extractive distillation process for separating a ternary mixture of methyl acetate, tetrahydrofuran and methanol

The separation of a ternary mixture of methyl acetate (MeAc), tetrahydrofuran (THF), and methanol (MeOH) produced from chemical or pharmaceutical plants can not only recover the valuable chemicals but also reduce the environmental pollution caused by the emission of waste organics. In this study, a two-step extractive distillation process with four columns (FCED) with dimethyl sulfoxide and p-xylene serving as the entrainers was firstly proposed to separate the ternary mixture by using Aspen Plus simulation. The vapor recompression heat pump (VRHP) technology was introduced to improve the thermodynamic efficiency of the proposed FCED process. Subsequently, a multi-objective optimization using the non-dominated sorting genetic algorithm-II was employed to optimize the designed processes to accomplish a Pareto front trade-off in three crucial indicators, i.e., total annual cost (TAC), CO2 emission, and exergy efficiency. A Pareto ranking method, i.e., the technique for order of preference by similarity to ideal solutions combined with entropy weighting approach, was used to choose the best solution from the Pareto front. The results indicate that, compared to the FCED process, TAC (8-year payback period) and CO2 emissions of the VRHP-assisted FCED are reduced by 8.75% and 33.26%, respectively, while the exergy efficiency is increased by 8.06% from 3.67% to 3.96%, demonstrating that the introduction of VRHP can significantly improve the performance of the FCED process.

Economic and environmental assessment of heat pump integration in thermally coupled hybrid separation

Process intensification of thermally coupled hybrid separation is presented in this paper. Production of ethyl acetate via reactive distillation with a stripper column (RDS) is employed as a basic thermally coupled hybrid separation process. The reactive distillation column has a condenser and a reboiler and the stripper column has a reboiler only. In addition, no auxiliary separation equipment such as a decanter or a regeneration column is required. On the other hand, despite the RDS process being highly integrated, it has several bottlenecks; large equipment (columns and heat exchangers); high external energy requirements for both cooling and heating. Also, it is known for large recycles (liquid and vapor). Therefore, to further intensify the RDS process, including a heat pump is proposed. A mechanical vapor recompression heat pump (MVRHP) is employed to reduce external cooling and heating requirements; to replace conventional energy source (heating steam) by an external source (compressor driven by electricity from renewable sources). Two different alternatives of heat pump-assisted RDS processes are designed. Performance and effectivity of the designed alternatives are compared with original RDS process using several indicators, including energy aspects, process economics, and environmental footprint. Results show that MVRHP can be deployed in the RDS process effectively reducing energy requirements while no equipment size changes (columns) are needed. Heat pump-assisted RDS processes show better economic performance despite higher capital costs. More importantly, when MVRHP is introduced in the RDS process, environmental footprint in form of CO2 emissions is decreased significantly. Finally, heat pump application in thermally coupled hybrid separation is highly recommended despite higher capital costs. Lower amount of emissions and utilization of electricity from renewable sources being the main benefits.

Research and design experience of a 150 kt/a CO2 capture and purification project in the Shaanxi Guohua Jinjie power plant

There was little research and demonstration experience in large flue gas carbon projects in China. 150 kt/a flue gas CO2 capture project in the Guohua Jinjie power plant, which is the largest-scale flue gas carbon capture project in China, effectively solved this technical bottleneck. The performance of the used compound amine absorbent, phase change absorbent, and the ionic liquid was described, and the compatibility of performance was considered in the project; new energy-saving processes integrated mechanical vapor recompression heat pump, interstage cooling, and split flow desorption. The plane layout of the project was put forward, and the utility consumption of the capture system was analyzed. The paper explained the health, safety, and environmental protection instructions, presented test category tables, and developed energy consumption and economic analyses. The results showed that the renewable energy consumption per unit product was 2.32 GJ/t CO2, the loss of absorbent was less than or equal to 1.0 kg/t CO2, and the total investment (excluding tax) of the project was 13.8398 million yuan. When the CO2 sales price (excluding tax) was 203.43 Yuan/t, the yield was 0 %, and when the CO2 sales price (excluding tax) was 260.949 Yuan/t, the yield was 8 %. The feasibility study research conclusions indicated that the project was technically and economically feasible.

An effective procedure for the development of vapor recompressed Kaibel dividing-wall distillation columns

While combining the Kaibel dividing-wall distillation column (KDWDC) with vapor recompression heat pumps (VRHPs) represents a promising way of process intensification, it faces great complexity, computational intensity, and tediousness. In this work, based on its thermodynamic characteristics, an effective procedure is proposed for the development of the VRHP assisted KDWDC (VRHP-KDWDC) processing a wide boiling-point quaternary mixture. The VRHP-KDWDC should be derived following the decreasing order of temperatures of the available heat sources. More specifically, while the first step is to explore the economic feasibility of process intensification by the vapor stream of the second intermediate product, the second step by the vapor stream extracted from the common rectifying section. The procedure allows maximizing the performance of the VRHP-KDWDC with rather low complication, computational intensity, and tediousness. The separations of four wide boiling-point quaternary mixtures, including benzene, toluene, o-xylene, and tri-methyl-benzene and n-pentane, n-hexane, n-heptane, and n-octane with and without component dominance in feed, are studied to evaluate the proposed procedure and the outcomes all demonstrate its simplicity, effectiveness, and efficiency. The proposed procedure is also applicable to the development of the VRHP-DWDC processing a ternary mixture and other complicated VRHP-KDWDCs processing a mixture with more than four components.

Heterogeneous Azeotropic Extractive Coupled Heat Pump Distillation for Triethylamine‐Dichloromethane‐Acetone‐Water

AbstractThere are three kinds of binary azeotropes and one kind of a near‐boiling compound with clamping zone characteristics in the triethylamine‐dichloromethane‐acetone‐water system, which belongs to complex quaternary systems. A four‐column distillation process of heterogeneous azeotropic extraction for the separation of the system was designed, simulated, and optimized to obtain more suitable process parameters and energy consumption distribution of each column. On this basis, taking the total annual cost (TAC) as the comprehensive economic evaluation index and CO2 emission as the environmental evaluation index, the thermal integration technology and mechanical vapor recompression (MVR) heat pump technology were applied to the energy‐saving research of the distillation process for the system. The results indicate that compared with the conventional four‐column heterogeneous azeotropic extractive distillation process, the thermal integration distillation process and single‐column MVR heat pump coupled thermal integration distillation process can save energy consumption and TAC, and it can reduce CO2 emission.

A novel economical reactive distillation with two reaction sections for separating isobutene in C4 to save energy and reduce CO2 emissions

In this study, the conventional reactive distillation (RD) process and the reactive distillation with two reaction sections (RD-TRS) are proposed to separate isobutene from C4. The arrangement of RD-TRS strengthens reaction and distillation processes, and reduces the operation cost and capital investment. Because the temperature between the top and bottom of the RD-TRS column is less than 15 ℃, the vapor recompression heat pump technology can be applied. Hence, the heat pump reactive distillation with two reaction sections (HRD-TRS) is proposed. Finally, the three processes are optimized with the minimum total annual cost (TAC) as the evaluation indicator. The results show that, compared with RD, CO2 emissions of RD-TRS and HRD-TRS processes decreases by 16% and 21%, respectively; TAC of RD-TRS and HRD-TRS decreases by 19.7% and 52.7%, respectively; TEC of RD-TRS and HRD-TRS decreases by 21.6% and 75.5%, respectively. The thermodynamic efficiency increases from 18% for RD, to 19% for RD-TRS, and 22% for HRD-TRS.

Configuring topologically optimum vapor recompressed dividing-wall distillation columns to maximize operating efficiency

For dividing-wall distillation columns (DWDCs) separating a heavy-component dominated and wide boiling-point ternary (HCDWBT) mixture, a significant amount of excessive heat exists inevitably in stripping the heavy-component from the intermediate-component and it can be employed to initiate the development of vapor recompression heat pump (VRHP) assisted DWDC (VRHP-DWDC). Despite dividing wall may locate in the top, middle, and bottom, the optimum VRHP-DWDC is found to involve uniformly-two VRHP circles. While the first one serves to compress and transform the excessive heat resulted from the separation of the heavy-component from the intermediate-component, the second one to compress and transform the overhead vapor stream of the light-component pre-heated sequentially with the condensate from the first one and the bottom product stream of the heavy-component, both releasing the temperature-elevated latent heat to the pre-fractionator’s or common stripping section. The processing of two HCDWBT mixtures of benzene/toluene/o-xylene and n-pentane/n-hexane/n-heptane are selected to assess the derived optimum topological configurations of the VRHP-DWDC and their optimality is confirmed through detailed comparisons with the DWDC and two VRHP-DWDCs involving only one VRHP circle. The proposed strategy helps to tap the full potential of the VRHP-DWDC with considerably alleviated complication in process development.

Energy-saving distillation process for mixed trichlorobenzene based on ORC coupled MVR heat pump technology

Trichlorobenzene is a mixture of three isomers which are 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene and 1,3,5-trichlorobenzene. Due to the boiling points of the three components are close to each other, the adoption of conventional distillation process requires a large amount of energy. To reduce the distillation energy consumption, heat integration technology and mechanical vapor recompression (MVR) heat pump technology are applied to the separation of the system. Since the waste heat in the MVR heat pump distillation process has not been utilized, the Organic Rankine cycle (ORC) coupled MVR heat pump distillation process was proposed to convert waste heat to electricity for the compressor and the parameters of the ORC system are optimized to determine the optimal working fluid and its parameters. The study results showed that compared with the four-column conventional distillation process, the heat integrated distillation process and MVR heat pump distillation process can reduce energy consumption by 32.7% and 83.5%, save the total annual cost (TAC) by 12.4% and 22.9%; the ORC coupled MVR heat pump distillation process with the best working fluid were R113 and R601a can reduce energy consumption by 18.8% and save TAC by 1.42% compared with the MVR heat pump distillation process.

Towards energy saving and carbon reduction of pressure-swing distillation for separating the ternary azeotropic mixtures by thermodynamic insights and process intensification

The recovery and separation of organic solvents such as tetrahydrofuran (THF), ethanol (EtOH), and methanol (MeOH) are important to protect the environment and save resources. Such ternary mixture has two azeotropes and one distillation boundary that makes separation difficult to be carried out using ordinary distillation technique. In this work, we developed a systematic approach for heat-integration (HI) and vapor recompression heat pump (VRHP) assisted triple-column pressure-swing distillation (TCPSD) for the recovery and separation of these valuable compounds. Firstly, the thermodynamics topological analysis is introduced to evaluate the feasibility of TCPSD for separating the ternary azeotropic mixture THF/EtOH/MeOH. Different separation sequence is determined via the combination of residue curve, component balance line, isovolatility curve, and distillation boundary. Subsequently, the potential application of HI and VRHP technologies is additionally explored for further minimizing the energy consumption and it is found that both process intensification technologies provide significant improvement in terms of economic, environmental impact, and energy efficiency. Relative to the traditional TCPSD, the application of VRHP technology to the TCPSD sequence B, in particular, provides 43.5% and 76.4% reduction in TAC and CO2 emission, respectively, while it improves the energy efficiency 100.4%.

Enhanced extractive distillation processes for separating n-hexane and 1,2-dichloroethane via bottom flash heat pump

In the industrial process to synthesize ethylene sulfate, a film-forming electrolyte additive for lithium-ion batteries, a significant amount of liquid mixtures of n-hexane (HE) and 1,2-dichloroethane (DCE) are generated, whose separation is challenging because of the formation of a minimum-boiling azeotrope. Hence, in this study, the conventional ED process for separating the HE/DCE mixtures was firstly investigated. Subsequently, since the temperature difference between the overhead vapor and bottom liquid is large, which is not favorable to the application of the vapor recompression heat pump technology, two bottom flash heat pump (HP) assisted extraction distillation (ED) processes, i.e., the bottom flash HP assisted ED (BFHP-ED) process and the coupled vapor recompression and bottom flash HP assisted ED (VRBFHP-ED) process are proposed and optimized in terms of the minimal total annual cost (TAC). The results show that, the thermodynamic efficiency increases from 7.63% for ED, to 13.76% for BFHP-ED, and 13.16% for VRBFHP-ED processes, while CO2 emissions of the BFHP-ED and VRBFHP-ED processes can be reduced by 41.05% and 39.19%, respectively.

Synergy of electrification and energy efficiency improvement via vapor recompression heat pump and heat exchanger network to achieve decarbonization of extractive distillation

Considering ongoing energy transition and zero-carbon electricity, distillation processes as end-user sector need to rethink energy use, and eventually substitutes fossil fuel sources by renewable energy sources. Hence, in this article, we design several ensemble configurations for extractive dividing wall column (EDWC) as wide-boiling systems to investigate the role of energy efficiency improvement and electrification based on renewable energy sources in the decarbonization of distillation processes. Vapor recompression heat pumps paly a dual role to achieve decarbonization of distillation process via efficiency improvement and electrification. The intermediate heating methods (i.e., intermediate reboiler, IR and feed evaporator, FPH) can reduce payback times of heat pump via reducing temperature quality of heat source. Heat exchanger network can comprehensively and effectively recovery waste energy to achieve energy efficiency improvement. To achieve complete decarbonization of distillation process, a novel multistage heat pump is proposed by combination of heat exchange network and intermediate heating methods (EDWC-MHP-FPH-IR-HEN). The economic assessment shows the payback period of EDWC-MHP-FPH-IR-HEN is 4.53 years and compared with original EDWC, it achieves only 4.83% TAC reduction and can achieve significant (44.97%)TAC reduction with five-year and ten-year payback period,respectively. This result demonstrates long pay period still impede the complete electrification of distillation and only in long runing period, heat pumps can provide huge economic potential. To improves the economic viability of heat pump, technological innovation such as the decrease in the electricity price from renewable energy resources and policy such as CO2 tax are explored using sensitivity analysis. The result show that CO2 tax is mainly driving force for electrification in distillation. This work can provide insights for the decarbonization of distillation processes via electrification.

Insights on sustainable separation of ternary azeotropic mixture tetrahydrofuran/ethyl acetate/water using hybrid vapor recompression assisted side-stream extractive distillation

The energy-efficiency of the traditional distillation-based processes are low, which results in waste of resources and environmental pollution. Therefore, a sustainable extractive distillation (ED) process should be developed to reduce energy consumption and CO2 emissions while improve the energy efficiency. In this work, a systematic approach is developed for the first time, for the separation of ternary azeotropic mixture containing Tetrahydrofuran (THF)/Ethyl acetate (EtAC)/Water via the combination of side-stream distillation and vapor recompression heat pump techniques. Firstly, the conceptual design of the various intensified schemes such as single (or double) side-stream(s) ED configurations are developed. Subsequently, the developed configurations were optimized using mesh adaptive direct search algorithm to obtain the optimal operating conditions of the established processes. Vapor recompression heat pump technique is used to further reduce the energy consumption. The sustainability of the various established configurations is assessed via the comparison of total annual cost (TAC), CO2 emissions, energy consumption, and thermodynamic efficiency. Overall, it was revealed that the TAC, CO2 emissions, and energy-consumption for the integrated vapor recompression assisted side-stream ED process were reduced by 33%, 49%, and 38%, respectively, relative to the conventional triple column ED. Likewise, the thermodynamic efficiency was improved by 52%.

Enhanced energy efficiency and reduced CO2 emissions by hybrid heat integration in dimethyl carbonate production systems

This study presents energy-efficient design alternatives for dimethyl carbonate production by combining various heat integration routes of reactive and pressure-sensitive distillation columns. The design of the hybrid heat-integrated sequences was based on internal and external heat integration with a vapor recompression heat pump (VRHP). The conventional pressure-swing separation design and the proposed hybrid heat integration processes were compared subject to a constraint of high product purity of 99.5%. The combined sequence of internal and external heat integration resulted in a cost reduction of 30.28% by eliminating the low-pressure (LP) column reboiler. The VRHP combined with external heat integration fully eliminated the heat duty of the high-pressure (HP) column condenser and the LP column reboiler, resulting in 38.33% energy savings and a 37.5% reduction in CO2 emissions. The two hybrid sequences with external heat integration showed better energy and economic efficiency and more reduced CO2 emissions than the VRHP combined with internal heat integration, since the reflux flow rate of the HP column and the reboil flow rate of the LP column were dramatically reduced.

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

Abstract 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.