Control configurations for an energy integrated distillation column

Koggersbøl, A.; Andersen, Birger; Nielsen, Jimmi; Jørgensen, Sten Bay

doi:10.1016/0098-1354(96)00150-0

Cited by 6 publications

(6 citation statements)

References 3 publications

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“…The temperature profile in a distillation column is closely related to the pressure profile. For the IVaRDiP, this relationship in the almost binary distillation column may illustrated using the elastic mechanical analogue shown in Figure . Here, the column is balanced between temperatures that correpond to the selected heat-pump pressures P L,set = and P H,set = .…”

Section: Methodsmentioning

confidence: 99%

“…For the present example column, this could be performed using the ( D , P H ) configuration to control the two purities while P L is used for column pressure control. Now, if the bottom purity is suddenly decreased due to a disturbance, then the controllers would increase P H and decrease P L to increase the vapor flow rate while keeping the condenser pressure constant . The increased internal flows enhance the separation and, in this way, the disturbance could be rejected.…”

Section: Methodsmentioning

confidence: 99%

“…Now, if the bottom purity is suddenly decreased due to a disturbance, then the controllers would increase P H and decrease P L to increase the vapor flow rate while keeping the condenser pressure constant. 9 The increased internal flows enhance the separation and, in this way, the disturbance could be rejected. However, in addition, the increased internal flow rates result in a larger pressure drop across the trays, such that the pressure on the lower trays is increased, because the pressure is controlled at the column top, thereby effectively controlling the top temperature, as illustrated in Figure 5.…”

Section: Control Implicationsmentioning

confidence: 99%

See 2 more Smart Citations

Operating Pressure Sensitivity of DistillationControl Structure Consequences

Andersen

Gani

et al. 2006

Ind. Eng. Chem. Res.

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The influence of pressure variations upon distillation operation does not seem to be well-understood in the open literature, because contradicting statements concerning the importance of pressure control on binary distillation are found. To minimize energy consumption, it is recommended to operate columns at minimum pressure; however, even if column pressure is controlled, instability may still occur when both product purities are controlled in a decentralized control structure. In this paper, operating pressure sensitivity is classified according to the pressure sensitivity of the vapor-liquid equilibrium (VLE) relationship for the mixture being separated. Operating pressure sensitivity is shown to become significant at high internal flow rates. It is furthermore shown that this sensitivity may lead to a situation where different values of the internal flow rate may produce the same product purity, which commonly is labeled "input multiplicity" of the separation. This input multiplicity is shown to occur through a theoretical analysis combined with simulation of the case study and an extended series of experiments. The input multiplicity can be explained by two opposing effects from varying internal flows: the first comes from the well-understood effect of changing the slope of the operating lines, whereas the second is due to the effect of pressure on the VLE relationship. Understanding the input multiplicity or, rather, the pressure sensitivity is relevant for efficient exploitation of the separation capacity of the column through proper control structure selection, i.e., for determination of where to place sensors in a distillation column for controlling pressure. It is shown that the distillation column is most efficiently utilized by controlling the pressure at the column bottom/top for a negative/positive-pressure-sensitive mixture. It is furthermore concluded that controlling the column pressure at the proper end of the column may be crucial to column stability when both product purities are controlled in a decentralized control structure. In an experimental verification, it is demonstrated that, for separating a mildly negative-pressure-sensitive mixture, the distillation column separation capacity is most efficiently exploited when controlling the column pressure at the bottom of the distillation column. For the investigated mixture, it is shown that a 20% higher capacity may be obtained at a lower energy requirement. Thus, a significantly (20%) lower energy expenditure per produced unit is realized through the improved control structure, when compared to conventional control of the column pressure at the top of the distillation column.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Control Implicationsmentioning

confidence: 99%

See 1 more Smart Citation

Operating Pressure Sensitivity of DistillationControl Structure Consequences

Andersen

Gani

et al. 2006

Ind. Eng. Chem. Res.

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“…There is an overall energy balance in heat pump distillation (Koggersbol et al, 1996;Chandra and Devotta, 1998).…”

Section: Optimization Variable For Shpdmentioning

confidence: 99%

Optimal Design and Optimal Operation of Separate Heat Pump Distillation

Zhu

Feng

2003

Can J Chem Eng

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For a distillation system, in which relative volatility is large in low composition range and small in high composition range, using separate heat pump distillation (SHPD) can markedly save energy. In this paper, vapour flow rate to compressor is proposed as a parameter for system optimization, from the viewpoint of system energy balance. This parameter can be used for both optimal design and optimal operation of SHPD. Mathematical models for optimal design and optimal operation are formulated to minimize total annual cost and annual operating cost respectively. Optimal design of SHPD is performed and evaluated through process simulation, for a typical case study for the distillation of ethanol-water system. The results show that SHPD has notable energy saving and economic benefit when compared with conventional distillation. Optimal operation of SHPD is also evaluated for changes in feed composition which is an operating variable.Pour un système de distillation, dans lequel la volatilité relative est grande dans une faible gamme de composition et petite dans une forte gamme de composition, le recours à la distillation à pompes à chaleur séparées (SHPD) peut permettre d'importantes économies d'énergie. Dans cet article, le débit de vapeur par rapport au compresseur est proposé comme paramètre pour l'optimisation du système, en termes de bilan d'énergie. Ce paramètre peut servir à la conception optimale et au fonctionnement optimal de la SHPD. Des modèles mathématiques pour la conception optimale et le fonctionnement optimal sont formulés pour minimiser le coût annuel total et le coût de fonctionnement annuel, respectivement. La conception optimale de la SHPD est effectuée et évaluée par la simulation de procédé, pour un cas-type de distillation d'un système éthanol-eau. Les résultats montrent que la SHPD permet des économies notables d'énergie et présente un avantage économique par rapport aux procédés de distillation classiques. Le fonctionnement optimal de la SHPD est également évalué quant aux changements dans la composition de l'alimentation qui est une variable de fonctionnement.Keywords: separate heat pump distillation, inlet vapour flow rate, annual cost. D istillation remains by far the most widely used separation technique for separation of liquid mixtures despite its high energy requirement. To reduce energy consumption in distillation, many energy efficient schemes have been developed, such as multi-effect distillation, heat pump distillation, thermally coupled distillation, and so on. Heat pump distillation is a successful and promising energy saving technique among these schemes (Gelegenis and Koumoutsos, 1996). Heat pumping is also a well recognized technique to reduce CO 2 emission and thermal pollution for environmental considerations in process engineering (Fonyo and Benko, 1998).Massive theoretical analysis, experimental studies and industrial practices have shown that heat pump distillation has a higher thermodynamic efficiency compared with conventional distillation (Mostafa, 1981;Barnwell and...

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“…Often it is assumed that the more complex the distillation system, the more complex the control, or the more complex the dynamic behavior 1, 2. In any case, distillation systems are sensitive to changes in process conditions 3, 4. Therefore, once a distillation system has been configured, the subsequent issue is the design of an appropriate control system, mainly in order to evaluate the feasibility of operation.…”

Section: Introductionmentioning

confidence: 99%

Conventional Proportional‐Integral Control of a Dividing‐Wall Distillation Column with Discrete Measurements

et al. 2016

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The problem of controlling an energy-efficient dividing-wall distillation column (DWDC) with a discrete key variable measurement is addressed. Usually, controllers are tuned in a systematic and simultaneous way, based on a certain control system configuration and conventional discrete proportional-integral controllers. The same stable pole-assignment approach to linear dynamics is followed here that approximately describes the convergence of each control loop. Tuning relationships in terms of sampling time and predecessor parameters of physical insight are obtained. The control system performance is simulated for disturbance rejection in an energy-efficient DWDC for separating a ternary mixture of benzene, toluene, and xylene. This tuning technique can be effective with a sampling time as long as that corresponding to current measurement instruments.

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Control configurations for an energy integrated distillation column

Cited by 6 publications

References 3 publications

Operating Pressure Sensitivity of DistillationControl Structure Consequences

Operating Pressure Sensitivity of DistillationControl Structure Consequences

Optimal Design and Optimal Operation of Separate Heat Pump Distillation

Conventional Proportional‐Integral Control of a Dividing‐Wall Distillation Column with Discrete Measurements

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