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Publications (9)6.79 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: According to the mechanism of the reaction operation involved, reactive distillation columns are often designed to work in a totally refluxed operation mode. The totally refluxed operation mode makes the reflux drum interact solely with the reaction operation involved and retards considerably the dynamics of the latter. The resultant great difference in process dynamics between the reaction operation and the separation operation involved leads frequently to under-damped responses with the degree of under-dampness closely dependent on the inventory control of the reflux drum. With the tight inventory control of the reflux drum, the degree of under-dampness can be suppressed and this presents a favorable effect to process dynamics and controllability of the totally refluxed reactive distillation columns. Two hypothetical ideal reactive distillation columns with and without a side reaction, respectively, and a high-purity ethylene glycol reactive distillation column are employed to examine the unique dynamics and controllability of the totally refluxed reactive distillation columns. The results obtained are in good accordance with the above interpretation. The current work reveals the general behaviors of the totally refluxed reactive distillation columns and can be particularly useful in control system synthesis and design.
    Journal of Process Control 08/2012; 22(7):1182–1197. · 1.81 Impact Factor
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    ABSTRACT: Although material and thermal coupling between the prefractionator and main distillation column renders the fully thermally coupled distillation column (FTCDC) a frequently favorable design option, it also complicates considerably process synthesis and design. In this contribution, a simple algorithm for the synthesis and design of the FTCDC is derived with the optimization of an economical objective function. In terms of an initial process design chosen arbitrarily to meet the given product specification, the algorithm allows the treatment of the continuous operating variables (e.g., the vapor and liquid split ratios) and discontinuous structural variables (e.g., the number of stages in each column section) in a unified manner and permits searches of their optimum values sequentially in each iteration step. The proposed algorithm is characterized by great simplicity in principle and high robustness to the guess of initial process design and the thermodynamic properties of the mixtures separated. Five example problems dealing with the separation of various ternary mixtures with ideal and nonideal thermodynamic properties are employed to evaluate the proposed procedure, and the obtained results demonstrate its applicability and robustness to the synthesis and design of the FTCDC.
    Chemical Engineering Communications - CHEM ENG COMMUN. 01/2012; 199(5):608-627.
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    ABSTRACT: Inventory control is often regarded as less important than product quality control in the operation of reactive and nonreactive distillation columns (i.e., often detuned considerably in control system design). For the high-purity ethylene glycol reactive distillation column, the inventory control of top condenser is, however, an exception and plays actually a crucial role in the stable and effective process operation, reminding the necessity to thoroughly investigate the intricate dynamic mechanism and its complicated implications on control system synthesis and design. In this article, the dynamics of a high-purity ethylene glycol reactive distillation column is examined, and it is found that the complicated dynamics, for example, the nonminimum phase behavior and process nonlinearity, can be suppressed considerably with the tight inventory control of the top condenser. Moreover, an extremely low controllability is detected, implying the potential difficulties in process operation and thus the need of process design modification. In terms of these insights obtained, two control schemes are devised and studied. It is demonstrated that sharp improvement could be acquired in control system performance when the tight inventory control has been implemented in the top condenser. © 2009 American Institute of Chemical Engineers AIChE J, 2009
    AIChE Journal 06/2009; 55(8):2106 - 2121. · 2.49 Impact Factor
  • Kejin Huang, San-Jang Wang, Wenming Ding
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    ABSTRACT: According to the principle introduced in the first two papers of this series, seeking further internal heat integration between reaction operation and separation operation during the synthesis, design, and operation of a reactive distillation column synthesizing methyl tertiary butyl ether (MTBE) from methanol and isobutylene is investigated. Although the MTBE reactive distillation column is characterized by complicated thermodynamic properties and multiple steady states, a substantial reduction of energy requirement and capital investment can still be achieved with the consideration of further internal heat integration between the reaction operation and the separation operation in the two existing steady states. Dynamics and operation of the resultant process designs are then examined in terms of static and dynamic analysis and sharp improvement in process dynamics and controllability is clearly identified through intensive comparison against the simple process design without the consideration of further internal heat integration between the reaction operation and the separation operation involved. It is demonstrated that the more synergistic relationship evolved during the reinforcement of internal heat integration should account for the dramatic improvement in process dynamics and controllability.
    Chemical Engineering Science - CHEM ENG SCI. 01/2008; 63(8):2119-2134.
  • Kejin Huang, San-Jang Wang
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    ABSTRACT: The synthesis, design, and control of a reactive distillation column for decomposing methyl tertiary butyl ether into isobutylene and methanol are reported in this work. Because the reaction is highly endothermic, it is advantageous to consider cautiously internal heat integration between the reaction and separation operations during process synthesis the and design, thereby necessitating deliberate determination of the feed location and judicious distribution of reactive section along the height of the process (Huang et al. AIChE J. 2006, 52, 2518). Through extensive comparison with a simple process design in which the reactive section is located between the rectifying section and the stripping section, it is demonstrated that a substantial reduction of capital investment and energy consumption can be achieved with this strategy of process development. Process dynamics and operation of the resultant process design were further investigated, and a noticeable improvement was gained in process controllability. The major reason for this improvement can be attributed to the fact that a more synergistic relationship has been evolved between the reaction and separation operations in the pursuit of further internal heat integration during process synthesis and design.
    Industrial & Engineering Chemistry Research - IND ENG CHEM RES. 03/2007; 46(8).
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    ABSTRACT: Process intensification calls for the combination of two or more conventional unit operations within one framework, thus giving rise to a challenging coordination problem in process synthesis and design. Seeking synergistic effect among all the conventional unit operations involved is found to be an important principle for process development. Three cases of process intensification are studied to evaluate the principle, including: (i) a hypothetical reactive distillation system; (ii) a reactive distillation column for the hydration of ethylene oxide; (iii) an ideal heat-integrated distillation column. It is demonstrated that simply combining two or more conventional unit operations together does not necessarily tap out the full potentials of capital investment reduction and energy saving. Only after the synergistic effect has been deliberately considered in process synthesis and design, can process intensification be carried out in the most effective manner. Furthermore, seeking synergistic effect appears frequently to yield improved process dynamics and provide additional redundancy to process operation because the underlying conflicts could be attenuated among all the conventional unit operations involved.
    Separation and Purification Technology - SEP PURIF TECHNOL. 01/2007; 57(1):111-120.
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    ABSTRACT: In this work, a novel temperature control scheme is derived for an ideal heat-integrated distillation column (ideal HIDiC), in which a temperature difference between two stages is designated as the controlled variable to circumvent the side-effect of continuous pressure variations in the rectifying section. For making an appropriate compensation to the changes in operating conditions, an inferential signal extracted from the feed stage, n/2+1, is used to adjust the set-point of the temperature difference controller. Control of two ideal HIDiCs, separating, respectively, a binary mixture of benzene and toluene and an ideal ternary mixture of hypothetical components A–C is studied. It is demonstrated that the proposed temperature control scheme can retain a stable operation around the vicinity of the nominal steady state with improved dynamic performance and tolerable steady state discrepancies in comparison with the direct composition control scheme. Moreover, the proposed temperature control scheme is also found to be quite robust to the selection of temperature measurements.
    Chemical Engineering Science. 01/2007;
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    ABSTRACT: Although reactive distillation columns allow direct utilization of heat of reaction to separation operation, the effectiveness of internal heat integration appears generally to be unsatisfactory and their thermodynamic efficiency could quite often be improved substantially through seeking further internal heat integration between the reaction and separation operations. Prudent arrangement of reactive section, effective determination of feed location, and deliberate distribution of catalyst constitute the three methods that can complement internal heat integration within a reactive distillation column. The reactive section is suggested to superimpose properly onto the stripping section for exothermic reactions and onto the rectifying section for endothermic reactions. Feed location and distribution of catalyst should be determined so that the effect of internal heat integration can be maximized to its fullest extent. A sequential procedure is proposed to determine an appropriate process configuration for internal heat integration within a reactive distillation column. Five reactive distillation systems, involving not only equilibrium-limited but also kinetically controlled reactions, are used to evaluate the design philosophy proposed. It has been found that a substantial improvement in system performance can be achieved even for some reaction systems with side reactions and/or unfavorable thermodynamic properties. Seeking further internal heat integration has been demonstrated to be an effective method for refining process design of a reactive distillation column involving reactions with highly thermal effect. These conclusions are of great significance and can provide process designers with additional latitude to elaborate their process designs. © 2006 American Institute of Chemical Engineers AIChE J, 2006
    AIChE Journal 04/2006; 52(7):2518 - 2534. · 2.49 Impact Factor
  • San-Jang Wang, Kejin Huang
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    ABSTRACT: In the process of manufacturing terephthalic acid, very small amount of reactant p-xylene may enter into the feed stream of an acetic acid dehydration column. Traditionally, acetic esters were used as entrainers to separate acetic acid and water by heterogeneous azeotropic distillation (HAD). However, they can contaminate the process. In the study, the feasibility of using p-xylene as the entrainer is evaluated to eliminate the drawbacks of the HAD column using acetic esters as entrainers. An improved column is proposed for the separation of acetic acid and water in the presence of methyl acetate and tiny amount of p-xylene. Two configurations of the HAD column using p-xylene as the entrainer are designed by using different p-xylene purge strategies. The HAD column with a side stream to purge p-xylene accumulated in the column gives the most economical design.A temperature control strategy is proposed for this HAD column to maintain acetic acid compositions in both the aqueous phase of the decanter and the column bottom. The controlled stage temperatures are chosen by singular value decomposition and closed-loop analysis methods. Dynamic simulation results reveal that the proposed control strategy can maintain product purities in spite of feed flow and feed composition changes.
    Chemical Engineering and Processing: Process Intensification. 60:65–76.