Nguyen Van Duc Long

Dividing wall column structure design using response surface methodology

Abstract Designing dividing wall columns (DWC) – energy-efficient separators of ternary mixtures – involves multivariable problem solving. These variables interact with each other and need to be optimized simultaneously to obtain the best design. In this work, a practical method employing response surface methodology (RSM) is proposed for DWC design and optimization. The optimum DWC structure can be found in a practical manner while minimizing simulation runs. The proposed method was tested in the design and optimization of an acetic acid purification process. The RSM based optimization effectively copes with interactions between optimizing variables and its predictions agreed well with the results of rigorous simulation. The DWC system designed by the proposed method decreased total annual costs by 44.57% compared with conventional distillation.

Design and optimization of a dividing wall column by factorial design

A factorial design methodology was applied to the design of a dividing wall column, solving the complex multivariable problems and simultaneously optimizing the interacting variables to achieve the best design with respect to total annual cost. Column structure was practically optimized with a minimum of simulation runs. The proposed design method was tested in the design and optimization of an NGL recovery system; it allowed interactions between variables to be identified and quantified. The column system designed by the proposed method reduced reboiler energy consumption and total annual cost by 28.23% and 25.49%, respectively, in case 1, and those by 25.63% and 18.85%, respectively, over conventional distillation in case 2.

Design and optimization of heat integrated dividing wall columns for improved debutanizing and deisobutanizing fractionation of NGL

Dividing wall columns, capable of reducing the energy required for the separation of ternary mixtures, were explored for the energy-efficient integration of debutanization and deisobutanization. A new practical approach to the design and optimization of dividing wall columns was used to optimize dividing wall columns. A conventional dividing wall column and a multi-effect prefractionator arrangement were shown to reduce total annual cost considerably compared with conventional distillation sequence. Various configurations incorporating a heat pump in a bottom diving wall columns were also proposed to enhance energy efficiency further. The result showed that operating cost could be reduced most significantly through novel combinations of internal and external heat integration: bottom dividing wall columns employing either a top vapor recompression heat pump or a partial bottom flashing heat pump.

Energy efficiency improvement of dimethyl ether purification process by utilizing dividing wall columns

The alternative fuel, dimethyl ether (DME), which can be synthesized from natural gas, coal or biomass syngas, has been traditionally used as a diesel substitute or additive. DME purification processes with a conventional distillation sequence consume a large amount of energy. We used dividing wall columns (DWCs) to improve the energy efficiency and reduce the capital cost of the DME purification process. Various possible DWC arrangements were explored to find the potential benefits derived from thermally coupled distillations. The results show that utilizing DWCs can significantly reduce both the energy consumption and investment cost of the DME purification process. The lower energy consumption also results in the reduction of the CO2 emission.

Techno-economic assessment of hybrid extraction and distillation processes for furfural production from lignocellulosic biomass

BackgroundLignocellulosic biomass is one of the most promising alternatives for replacing mineral resources to overcome global warming, which has become the most important environmental issue in recent years. Furfural was listed by the National Renewable Energy Laboratory as one of the top 30 potential chemicals arising from biomass. However, the current production of furfural is energy intensive and uses inefficient technology. Thus, a hybrid purification process that combines extraction and distillation to produce furfural from lignocellulosic biomass was considered and investigated in detail to improve the process efficiency. This effective hybrid process depends on the extracting solvent, which was selected based on a comprehensive procedure that ranged from solvent screening to complete process design.ResultsVarious solvents were first evaluated in terms of their extraction ability. Then, the most promising solvents were selected to study the separation feasibility. Eventually, processes that used the three best solvents (toluene, benzene, and butyl chloride) were designed and optimized in detail using Aspen Plus. Sustainability analysis was performed to evaluate these processes in terms of their energy requirements, total annual costs (TAC), and carbon dioxide (CO2) emissions. The results showed that butyl chloride was the most suitable solvent for the hybrid furfural process because it could save 44.7% of the TAC while reducing the CO2 emissions by 45.5% compared to the toluene process. In comparison with the traditional purification process using distillation, this suggested hybrid extraction/distillation process can save up to 19.2% of the TAC and reduce 58.3% total annual CO2 emissions. Furthermore, a sensitivity analysis of the feed composition and its effect on the performance of the proposed hybrid system was conducted.ConclusionsButyl chloride was found to be the most suitable solvent for the hybrid extraction/distillation process of furfural production. The proposed hybrid sequence was more favorable than the traditional distillation process when the methanol fraction of the feed stream was <3% and more benefit could be obtained when that fraction decreased.

Studying the effect of feed composition variation on typical natural gas liquid (NGL) recovery processes

In this work, the different process schemes used for known NGL recovery methods have been studied with various feed compositions. The original turbo-expander process scheme (ISS) was considered as a base case. The GSP, CRR, RSV and RSVE process schemes are those which focus on improvement at the top of the demethanizer column, while the IPSI-1 and IPSI-2 at the bottom of the demethanizer column. All the process schemes have initially built using ASPEN HYSYS with a common set of operating criteria. Numerous simulation runs have been made later by taking various typical feed compositions classified as lean and rich. Regardless of the common operating conditions set to each process schemes, there exist different performance results obtained from the simulation. Accordingly, the reboiler duty requirement is high for the GSP, CRR, RSV and RSVE due to the need for external refrigeration. However, the IPSI-1 and IPSI-2 simulation result show relatively lower reboiler duty requirement for the self-refrigeration system applied to the systems.

A cost-effective retrofit of conventional distillation sequence to dividing-wall prefractionator configuration

Abstract A dividing-wall prefractionator configuration was investigated for a safe and economic retrofit of the conventional sequence using simple distillation columns. In the proposed retrofit configuration, the first column was modified to a dividing wall column as a prefractionator to supply prefractionated multi-feeds to the subsequent column. To investigate the effectiveness of the proposed configuration, nine near-ideal feed mixtures were considered for analysis. The proposed configuration was then compared with several other alternative configurations. The proposed dividing-wall prefractionator efficiently generates prefractionated multi-feed streams avoiding feed mismatch and remixing effect with low modification cost. Moreover, because the proposed retrofit configuration allows for flexible switching between the dividing-wall prefractionator and the conventional operating mode, a safe retrofit is also ensured by reducing the operational risks. Several industrial retrofit cases were studied to validate the proposed dividing-wall prefractionator configuration.

Purification of 2,3-butanediol from fermentation broth: process development and techno-economic analysis

Background2,3-Butanediol (2,3-BDO) is a synthetic chemical compound that also can be produced by biomass fermentation, which is gaining share in the global market as an intermediate product for numerous applications, i.e. as liquid fuel or fuel additive. Several metabolic engineering fermentation strategies to enhance the production of 2,3-BDO were developed. However, the recovery of 2,3-BDO from its fermentation broth remains a challenge due to its low concentration and its solubility in water and other components. Thus, a cost-effective recovery process is required to deliver the required purity of 2,3-BDO. This paper presents a new process development and techno-economic analysis for 2,3-BDO purification from a fermentation broth.ResultsConventional distillation and hybrid extraction-distillation (HED) processes are proposed in this study with detailed optimization and economic analysis. Particularly, a systematic solvent selection method was successfully implemented to determine a good solvent for the proposed HED configuration based on numerous experimental data obtained with each solvent candidate. NRTL and UNIQUAC property methods were evaluated to obtain binary interaction parameters of 2,3-BDO through rigorous Aspen Plus regression and validated using experimental data. Total annual cost (TAC)-based optimization was performed for each proposed configuration. Even though the HED configuration required 9.5% higher capital cost than conventional distillation, placing an extraction column before the distillation column was effective in removing water from the fermentation broth and significantly improved the overall process economics.ConclusionsOleyl alcohol was found to be the most suitable solvent for the HED of 2,3-BDO due to its high distribution coefficient and high selectivity. The proposed HED drastically reduced reboiler duty consumption and TAC by up to 54.8 and 25.8%, respectively. The proposed design is expected to be used for the commercial scale of 2,3-BDO production from fermentation process.

Reduce Costs and Energy Consumption of Deethanizing and Depropanizing Fractionation Steps in NGL Recovery Process

Abstract In this work, our aim is how to utilize the dividing wall column (DWC) to improve the performance in deethanizing and depropanizing fractionation steps in NGL processing. Starting from an initial conventional column sequence, the initial designs for the conventional DWC and top dividing wall column (TDWC) were obtained by maintaining the number of trays. In succession, they were optimized to reduce the energy consumption. The results show that the DWC and TDWC offer many benefits by decreasing the operating cost including refrigeration cost, as well as reboiler and condenser duty. Furthermore, by using DWC, the purity and recovery of ethane also increases, particularly, from 95 to around 97% and 95 to more or less 98%, respectively. Based on these results, the comparison of performance between the conventional DWC and TDWC was analyzed. Then the influence of utility prices on the operating cost saving of conventional DWC and TDWC was studied. In addition, heat integrating on the top and interreboiling the bottom section of the DWC were also applied to improve the performance of the DWC.

A Study of Complex Distillation Arrangements for Improved Depropanizing, Debutanizing and Deisobutanizing Fractionation of NGL

Abstract The depropanizing, debutanizing and deisobutanizing fractionation steps of processing natural gas liquids were improved through studying complex distillation arrangements, including the double dividing wall column arrangement (DDWC), the sequence including a dividing wall column (DWC) and a bottom DWC (BDWC) and the sequence including a DWC and a BDWC with top vapor recompression heat pump. These arrangements offer benefits by decreasing reboiler and condenser power consumption. Reducing the number of columns and their diameters can potentially reduce construction costs. The result also showed that operating cost could be reduced most significantly through novel combinations of internal and external heat integration: bottom dividing wall columns employing a top vapor recompression heat pump.