Heat Integrated Distillation Column Research Articles

Impact of the control properties on the energetic and economic performance of Heat-Integrated Distillation Columns under variable feed composition

Heat Integrated Distillation Columns (HIDiC) are highly energy-efficient technologies whose performance has been validated through robust optimization algorithms and practical tests. Despite these configurations are dynamically controllable technologies, the simultaneous relationship between dynamics and optimal energetic and economic performance under variable feed composition has not been analyzed. Thus, this paper tackles this gap in literature. Five binary mixtures and three feed composition were examined in this study. The optimization of these configurations was firstly achieved using a Boltzmann-based optimizer while the control properties were obtained through the closed-loop process analysis using the IAE criterion and rigorous simulations in Aspen Dynamics in a second stage. Results showed that the HIDiC configurations with the best dynamic behavior do not match with the HIDiC columns with the best energetic and economic performance. However, suboptimal HIDiC configurations experienced only slightly less energetic and economic benefits but better dynamic properties that the best HIDiC configurations. Particularly, the best suboptimal HIDiC columns to separate the mixtures with relative volatility (α) lower than 1.4 were determined for a feed composition of 25 mol% for the light component. Nevertheless, the most adequate HIDiC columns to separate mixtures with α>1.4 were obtained for equimolar feed composition and feed composition of 75% for the light component.

Global Modeling of Heat-Integrated Distillation Column Based on Limited Local Measurements

The heat-integrated distillation column (HIDiC) has more energy-saving potential than conventional distillation columns. However, its nonlinearity and coupling effects pose significant challenges for the online operation of the HIDiC. To overcome these challenges, it becomes necessary to utilize accurate nonlinear models for design optimization or control schemes. Traditional modeling methods require extensive tray information, implying the impractical use of numerous sensors in real-world applications. This paper proposes a modeling approach for the HIDiC based on a limited number of measurements. It only requires the measurement of a finite amount of tray information to construct a global model of the HIDiC. This method serves as an online observer, providing real-time information about the entire column, and also enables the prediction of tray concentration changes. The proposed model forms the basis for developing model-based online monitoring and control schemes. Experimental simulation results demonstrate that the proposed method achieves high accuracy in global observation and prediction for the HIDiC.

Design and parameter tuning of active disturbance rejection control for uncertain multivariable systems via quantitative feedback theory

This paper proposes a new parameter tuning approach for active disturbance rejection control (ADRC) of multi-input multi-output (MIMO) uncertain systems. Firstly, decentralized ADRC (DADRC), dynamic decoupling ADRC (DD-ADRC), and inverted decoupling ADRC (ID-ADRC) are introduced. Three control schemes are uniformly transformed into a two-degree-of-freedom (2DOF) equivalent structure for analysis. Then, a parameter tuning approach based on multivariable quantitative feedback theory (QFT) is proposed to achieve the desired performance. Considering the coupling effects, the QFT performance specifications are reformulated to reduce the conservatism in design, and the closed-loop stability conditions are studied to establish the robust stability performance specification. Finally, the control schemes and the proposed tuning approach are applied to a heat integrated distillation column (HIDiC) process. The effectiveness of the parameter tuning approach is verified, and the respective advantages of the ADRC control schemes are analyzed in parameter tuning and simulations.

Novel approach to design and optimize heat-integrated distillation columns using Aspen Plus and an optimization algorithm

Heat-integrated distillation columns (HIDiC) are sustainable technologies whose optimized designs may reduce up 80% the energy consumption, cooling water and CO2 emissions regard to the traditional columns. This paper shows a novel approach to design and optimize HIDiC columns using Aspen Plus and a stochastic optimization algorithm. This approach was designed to deal with the convergence problems in order to improve the search for the best solutions but also keep a continuous optimization process. The performance of the approach was evidenced through the optimization of the HIDiC columns used to split four close-boiling binary mixtures. Results showed that the design and optimization of these columns was successfully tackled by the approach implemented. As a result, the approach enabled to reduce convergence problems, keep a continuous optimization process and improve the quality of the solutions found. This fact demonstrates that the approach performed an adequate handling of purity specs and temperature driving forces, which were defined as constraints of the optimization problem. Based on the performance determined, this approach may be adapted and used as an approximated short-cut method to design and optimize other binary HIDiC columns. However, through an adequate adaptation, this approach may be extended to design and optimize HIDiC columns for separating ternary mixtures.

Study of dynamic performance of heat-integrated distillation columns considering the effect of relative volatility of the mixtures

In this paper the dynamic performance of Heat-Integrated Distillation Columns (HIDiC) is presented. The dynamic performance was determined for the optimal HIDiC designs optimized previously using a constrained Boltzmann-based estimation of distribution algorithm. Eight close-boiling mixtures, covering a range of relative volatility (α) from 1.12 to 2.4, were used as case studies. The dynamic behavior was obtained under open and closed-loop process analysis. The results obtained showed that the HIDiC columns undergo worse dynamic performance than their equivalent traditional columns for all case studies. Furthermore, it was notorious that the difference in the dynamic behavior of both configurations kept a relatively uniform trend for most systems. However, a marked difference in the dynamic properties was determined for the mixture close to azeotropic behavior, which experienced a considerably larger control effort.Thus, the novel findings disclosed in this paper show that, although the HIDiC sequences experienced worse dynamics than the conventional columns, the HIDiC configurations reached a stable dynamic behavior for all the range of α of the mixtures under study. Nevertheless, high control difficulties were particularly determined for the HIDiC configuration used to separate the mixture with α close to unity (mixture of xylenes), which in fact is the HIDiC sequence with the best energetic and economic benefits.Hence, the energetic and economic potential of the HIDiC columns is not limited by the dynamic behavior for most case studies analyzed, at least in theoretical terms. However, such potential might be particularly reduced or unharnessed in the separation of the mixture with α near the azeotropic behavior due to the dynamics of the HIDiC column for this separation.So, the findings presented in this paper allow to infer that sequential or simultaneous dynamic studies must be achieved along with the optimization of the HIDiC columns to determine the integral performance (energetic, economic and dynamic) of these configurations.

Machine learning based system identification of a realistic heat integrated distillation column using particle swarm optimization

In the petrochemical industry, heat integration is one of the most commonly used methods for saving energy in the distillation column. The component of the liquid mixture can be estimated by correctly modeling or identifying the respective heat integrated distillation column (HIDC). Previously, system identification for HIDC has been performed using steady state data in an open loop configuration. However, the data obtained from steady state does not characterize realistic HIDC. Complex nonlinear modeling is required to account for the nonlinearities present in HIDC. In this study, a unique approach is presented to identify a dynamic closed-loop HIDC system using Support Vector Regression (SVR). Here, HYSYS is used to simulate HIDC in a fairly realistic environment and the resulting data is used in MATLAB for system identification. Particle Swarm Optimization (PSO) is used to optimize the SVR parameters, which gives better results than conventional metaheuristic optimization approaches. The proposed approach is also verified by accurately estimating the mole fraction of benzene-toluene mixtures in a dynamic HIDC. In terms of root mean square error (RMSE) and regression coefficients (R), the proposed strategy outperforms artificial neural networks (ANN) and radial basis function (RBF) models. The proposed technique reduces the RMSE by 80% and 47% compared to ANN for the mole fractions of benzene and toluene, respectively.

A Comparison of the Exergy Efficiencies of Various Heat-Integrated Distillation Columns

Distillation has relatively low thermodynamic efficiency, so it is a prime target for process intensification studies. The current research aims to study exergy losses in various heat-integrated distillation columns. A conventional industrial-scale i-butane/n-butane fractionator has been selected as a case study for the comparison of the performances of various heat-integrated designs. The Aspen Plus® process simulator is used to perform steady-state simulations and exergy analyses of the conventional distillation column (CDC), internally heat-integrated distillation column (iHIDiC), externally heat-integrated double distillation columns (EHIDDiC), and vapor recompression (VRC) systems. The results of these exergy analyses show that a modified VRC system (ηE = 10.69%) is the most efficient design for this separation. The exergy efficiency of the conventional VRC system is the same as that of the CDC (ηE = 9.27%). The EHIDDiC system (ηE = 9.77%) is somewhat better than the CDC, whereas iHIDiC shows poor exergy efficiency (ηE = 8.09%), even lower than the CDC.

Study on a novel reactive internally heat integrated distillation process for the synthesis of ethyl acetate and its column configuration

The production of ethyl acetate (EA) by reactive distillation (RD) has the disadvantage of high energy consumption. In order to solve this problem, the application of reactive internal heat integrated distillation was explored on the basis of RD process, and energy saving was further realized. The influence of different configurations of reactive internally heat integrated distillation column (RHIDiC) on the process were also studied. In this study, the symmetrical reaction internal heat integrated distillation column (S-RHIDiC), the upper aligned reaction internal heat integrated distillation column (UA-RHIDiC) and the lower aligned reaction internal heat integrated distillation column (LA-RHIDiC) were compared with RD in economic benefits, environmental protection, energy saving performance, and thermodynamic efficiency. In addition, all processes were optimized with TAC as the economic indicator. The results showed that S-RHIDiC process has the optimal economic benefits, environmental performance, energy consumption and thermodynamic efficiency. Compared with RD, the total annual cost (TAC) of S-RHIDiC was reduced by 32.56%, CO2 emissions were reduced by 52.79%, the TEC was reduced by 29.37%. The thermodynamic efficiency of RD, S-RHIDiC, UA-RHIDiC and LA-RHIDiC processes were 6.71%, 9.12%, 6.75% and 6.8%, respectively.

The dynamic model of a rectification heat exchanger using the concept of heat-integrated distillation column

A dynamic model of the apparatus used for thermal rectification of mixtures was developed, where in a channel-type exchanger the thermal separation of substances is accompanied by diaphragm heat exchange. In the description of the channel-type exchanger applied in heat-integrated distillation columns, a new approach in mathematical modelling was used combining the model of thermal resistance (in the description of the diaphragm heat exchange) and the theoretical tray model (in the description of the mass transfer). In the literature, it wasn't presented yet the influence of industrial constraints (grow up of deposits on the heat transfer surface or hold up of liquid inside the channel of exchanger) on the heat-integrated distillation column behaviour in the dynamic state. Thus, the authors carried out the numerical simulations for the proposed dynamic model subjected to industrial constraints. The transient characteristics, obtained from the simulations, show that the channel-type exchanger is dynamically stable under industrial constraints. Moreover, the dynamic model confirmed that the distillate purity isn't strongly sensitive on the above constraints (the distillate purity deteriorates approximately by 1%). What's more, the transient characteristics show that the commonly used a proportional–integral–derivative controller can be applied in proposed technology under industrial constraints.

Impact of temperature approach on the behavior of the rectification heat and mass exchanger under fouling constraints

In industrial applications, thermal separation of substances is carried out in rectification and distillation columns and each one of them is equipped with condenser and reboiler. Such technology is energy-consuming, i.e. it requires high heat supply to the reboiler, and significant waste heat discharge through the condenser, to the environment. The new approach assumes thermal separation carried out in a system of channels where heat distribution is sustained through a diaphragm, i.e. channel walls and the number of reboilers and condensers is reduced to minimum. This type of apparatus serves for heat transfer and simultaneous thermal separation of substances, thus mathematical model of rectification heat and mass exchanger (HME) exercises the concept of heat-integrated distillation column (HIDiC) in a channel-type geometry. As it has been shown in previous studies, such technology has a potential of reducing energy consumption by 40%–60% compared to rectification columns currently used in industry. The model of the channel-type exchanger uses a theoretical tray model for describing mass transfer, combined with our in-house mathematical description of diaphragm heat transfer that takes fouling resistance into account.Numerical calculations carried out in this work were focused specifically on the impact of fouling on the operation of channel-type heat and mass exchanger. Key issues covered in this work included the impact of fouling on the purity of collected fractions (which have to meet guidelines given by process designer) and the intensity of internal heat streams (which are decisive for energy-saving). In the parametric study, the minimum temperature difference between mixture streams in the stripping and rectifying sections was also included.The simulation results showed that for considered mixture of fractions, assuming a realistic range of fouling thermal resistances, the sensitivity of channel-based heat and mass exchanger to fouling is negligible, and the purity of distillate is hardly affected.

Energy-saving investigation of pressure-swing distillation strengthening configurations for benzene/isobutanol binary azeotrope

Benzene (PhH)/isobutanol (IBA) is one of untraditional binary azeotropes with opposite non-ideal behaviors under different pressure in the chemical industry. An untraditional pressure-swing distillation configuration (UPSD) can effectively separate this type of mixture, which is characterized by IBA being at the bottom of low-pressure column (LPC) and PhH being at the top of high-pressure column (HPC). According to this feature, two important methods to improve energy efficiency - vapor recompression (VRC) and internally heat-integrated distillation column (HIDiC) are applied to this configuration. Specifically, five variants are designed and optimized to minimize total annual cost (TAC). As compared to the UPSD configuration, the results show that two variants called VRC-UPSD and HIDiC-UPSD can respectively reduce energy costs by 74.26% and 69.74% and CO2 emission by 66.61% and 57.48%. Importantly, despite the use of expensive compressors in both configurations, TAC is reduced by 38.13% and 44.96%, respectively.

Novel integrated energy-efficient dual-effect single mixed refrigerant and NGLs recovery process for small-scale natural gas processing plant

The design of natural gas liquefaction process operated at offshore regards space as a design variable and requests an integrated and compact process due to space limitation. This study proposes an integrated process for natural gas liquefaction and NGLs recovery based on single mixed refrigerant (SMR) cycle. The considered SMR refrigeration cycle functions as dual mixed refrigerant (DMR) to provide two separate refrigeration levels for natural gas precooling and subcooling. NGLs recovery section includes a conventional column and a heat integrated distillation column in indirect sequence to produce lean gas, ethane liquid, LPG and gasoline. Liquefaction operating parameters were optimized using genetic algorithm in search of optimal values for profitable process with optimal energy consumption. NGLs recovery section of the proposed process is flexible, operable in both ethane recovery and ethane rejection modes. Based on base case process, the proposed process lowers energy consumption by 14%. The key features of the proposed process are cold utility recovery through self-refrigeration and ethane liquid recovery.

Energy efficient design through structural variations of complex heat-integrated azeotropic distillation of acetone-chloroform-water system

This study presents enhanced energy savings through structural variations of a heat-integrated distillation column for the separation of ternary azeotropic mixture. The conventional sequence has a decanter followed by pressure-swing distillation (PSD) columns for separating acetone-chloroform-water azeotropic mixture. Based on a significant temperature gradient of the PSD, a double annular column was proposed in order that the heat from hot fluid to cold fluid passed through the shared column wall. The heat transferred to the stages near the reboiler could replace the use of external utility, thereby reducing the total energy consumption of the process. For accurate calculations of heat transfer rate, the trays with the double annular structure were simulated by computational fluid dynamics. However, the energy saving was not effective since the structure could not afford to utilize all the heat transferred and additional energy was required to recover. The newly proposed (partial double annular) structure transferred heat from a high-pressure column to two low-pressure columns. It demonstrated 7,807.78 kW of the theoretical energy saving which was almost double of the heat transfer amount. Consequently, the total utility consumption and total annual cost was reduced by 21.79% and 11.32%, respectively, compared to the conventional sequence.

An internal thermal integration arrangement for multicomponent batch rectifier: Introducing vapor recompression mechanism

In the first paper of this series, an internal heat integrated distillation column (HIDiC) configuration is proposed first time for batch processing that shows a substantial improvement in cutting the energy consumption, CO2 emission and cost. Aiming to further boost the potential of this general batch HIDiC rectifier, the heat pump assisted vapor recompression (VRC) mechanism is introduced in it to enhance the use of internal heat source. Proposing a variable manipulation policy, an operating methodology is figured out to run the hybrid batch HIDiC-VRC configuration at transient states. Finally, the batch processing of a ternary hydrocarbon system is used to demonstrate the thermally integrated hybrid configuration, showing its superiority in reducing the degree of irreversibility over the general HIDiC with reference to a conventional standalone structure.

Concentric Heat Integrated Distillation Column (HIDiC): a new specific packing design, characterization and pre-industrial pilot unit validation

The concept of Heat Integrated Distillation column (HIDiC) was introduced by Mah et al [1] to improve the energy efficiency of distillation processes. Firstly, a brief review of the HIDiC configurations and pilot plants is introduced. The objective of this study is to demonstrate the performance of a new packing specific for HIDiC tested in a concentric HIDiC pilot plant to prove the operability and the overall performance. First, the new specific packing and its characterization are presented. The characterization includes the hydrodynamics, the mass transfer and heat transfer performance. For the experiments on HIDiC pilot plant, several tests are performed at steady state of 90 min. One of these experiments is presented with the operating parameters (boiler heat and pressure ratio). The cyclohexane/n-heptane binary mixture is used for these experiments. The simulation results of a classical distillation column are compared to HIDiC column steady state operation. This comparison demonstrates energy savings about 40 %.

System identification and control of heat integrated distillation column using artificial bee colony based support vector regression

Distillation is a high-energy process widely employed in separating fluid mixtures in the oil and gas industries. Heat integration is one of the practical approaches for energy saving in the distillation columns. Proper identification or modeling of heat-integrated distillation column (HIDC) is employed to predict the composition of fluid mixtures. The nonlinear modeling of HIDC is highly challenging, and methods based on the first principles are not effective in coping with the nonlinearities. Hence, a novel, non-parametric support vector regression (SVR) approach is proposed for system identification and control of HIDC in this work. SVR parameters were optimized using artificial bee colony (ABC) algorithm, which resulted in better performance over other meta-heuristic algorithms. Moreover, the SVR model demonstrated better performance than the artificial neural network models in root mean square error (RMSE) and regression coefficient (R). RMSE and R values for ABC-SVR were found to be 0.0010 and 0.99992, respectively, with the validation dataset. The performance of the SVR and PID controllers are also compared. Integral square error (ISE), integral average error (IAE), integral time square error (ITSE), and integral time average error (ITAE) are the comparison metrics employed, which yielded minimal values of and respectively, for the SVR controller. The proposed model outperforms all other related methods, and it can be used to predict the mole fraction of Benzene in Benzene-Toluene HIDC accurately.

Hybrid two-step optimization of internally heat-integrated distillation columns

Heat integration is one of the most used energy conservation methods in chemical processes, and it typically involves the heat transfer from the vapor stream entering a condenser and the liquid stream entering a reboiler. Nevertheless, this work exploits the idea of heat integration between stages in which heat is supplied at a temperature higher than that at the condenser in a high-pressure column and heat is received at a temperature lower than that at the reboiler in a low-pressure column. Since stages between column are subject to heat integration, a large combinatorial problem arises. Thus, this work proposes a hybrid optimization procedure consisting of two steps: The solution of a deterministic optimization (i.e., MILP problem) and stochastic optimization (e.g., Simulated annealing) to take advantage of the strong points from each optimization technique.

Heat-Integrated Distillation Columns as a Retrofit Cannot Bring Energy Savings to the Ethylene Plant

Separation by distillation is an energy-intensive process. Approximately 40% of energy use in the petrochemical industry is associated with separation by distillation. The heat-integrated distillation column (HIDiC) is a process intensification technology, which aims to reduce the energy required by the distillation process. A study was performed to determine the energy savings that could be achieved by using HIDiC as a retrofit of two critical distillation columns in the ethylene process (ethylene fractionator and deethanizer). The aim was to assess the energy savings of an individual HIDiC and relate it to the energy consumption of the plant as a whole. The outcome of this study is that HIDiC could lower the energy demand, but this itself did not translate into energy savings for the overall plant in either case. The HIDiC ethylene fractionator increased the energy consumption of the overall plant by 16% and the HIDiC deethanizer by 50%. The reasons for this are discussed thoroughly in this article.

Benchmarking of Separation Methods for Bioethanol (<5 wt %) Recovery

Distillation and dehydration account for around 20 to 40% of the total energy consumption for first-generation bioethanol production. Due to the more dilute alcohol concentrations encountered in the second-generation processes, the conventional separation methods are not economically feasible. The main obstacles are the high-energy input demand and low thermodynamic efficiency. In this work, six alternative advanced layouts for alcohol recovery are simulated and benchmarked based on energy consumptions and thermodynamic efficiencies. Among these is the internally heat integrated distillation column, which, despite the research efforts of the last 40 years, is not yet established in the industry. Feed composition has been varied in the range of 0.75–5.0 wt % ethanol. The analysis results show that intensified distillation schemes can improve second law efficiency of about 65 to 80% and reduce energy consumptions by 67% compared to conventional distillation. The most optimal separation technologies investigated requires about 9.8 to 10.4 MJ/kg-EtOH for 0.75 wt % ethanol feed and 1.9–2.0 MJ/kg-EtOH for 5.0 wt % ethanol feed. These are the externally heat-integrated column, the internally heat-integrated column, and a four-effect distillation sequence. The results obtained in this study can allow for more optimal biofuel production, giving rise to potential improved business for sustainable green technology in the future.

Second Law analysis of large-scale sugarcane-ethanol biorefineries with alternative distillation schemes: Bioenergy carbon capture scenario

Distillation is one of the most used separation techniques, despite its high heat demand and low thermodynamic efficiency. Although new distillation schemes have been developed for ethanol-water separation, most of them prescribe expensive sub-atmospheric columns. On the other hand, heat-integrated distillation columns allow significant steam savings since thermally integrated condenser/reboiler of different columns share the same heat duty. In this work, three innovative distillation schemes for large-scale sugarcane-ethanol biorefineries are analyzed aiming at less energy-intense processes, higher thermodynamic efficiencies and steam savings. Ethanol production, power production through bagasse-fired cogeneration, thermodynamic efficiency, heat demand, water usage, steam demand, carbon dioxide intake, and potential of bioenergy with carbon capture and storage are assessed for technical and thermodynamic comparisons of distillations schemes. Results of carbon emissions go beyond the biorefinery boundaries and include sugarcane supply-chain emissions. It is shown that heat-integrated distillation schemes promote huge steam savings compared to conventional ethanol distillation. Distillation Scheme No.2 – with five heat-integrated columns – showed highest steam savings of 63% relative to conventional distillation, while distillation Scheme No.3, prescribing an innovative Petlyuk column for bioethanol distillation, attained the highest thermodynamic efficiency (11.1%) outperforming distillation Schemes No.1 and No.2 (7.65% and 7.03%, respectively). Sankey diagrams express results of carbon dioxide equivalent flows, lost bioenergy with carbon capture and storage potential, water flow and equivalent power flows via the Second Law of Thermodynamics.