Ideal Heat Integrated Distillation Column Research Articles

A case study of HIDiC design and energy saving

The ideal Heat Integrated Distillation Column (HIDiC) has been studied by computer simulation and examination. Its concrete structure has been designed as for an example with the simulator for its operation and design. The performance of mass and heat transfer presumed on the simulation have been examined by test units. As a result, it is found that the ideal HIDiC appears to be practical applications, and it might save energy 30% more than conventional distillation columns.

Potential energy savings in ideal heat-integrated distillation column

An ideal Heat-Integrated Distillation Column (HIDiC), having no reboiler and no condenser, is constructed in such a manner that its rectifying and stripping sections are separated, while connected through a compressor and a throttling valve. Its manipulation is completed by exchanging heat between the two sections. The ideal HIDiC is expected to be more efficient than conventional columns, at the expense of some energy to raise the pressure of the rectifying section. In this paper, it is shown by thermodynamical consideration that the ideal HIDiC has a high potential of texergy loss reduction in the operation compared with conventional columns. The effects of feed and distillate composition, and relative volatility on energy saving characteristics are simulated in this paper, and the possibility of energy saving is found for feed compositions.

Operating an ideal heat integrated distillation column with different control algorithms

The operation of an ideal heat integrated distillation column is addressed. Five control strategies, namely, single loop composition control system, multi-loop composition control system, multivariable internal model control (IMC) system, modified multivariable IMC control (MIMC) system and nonlinear process model based control (NPMC) system, are design and applied to the process. Simulation results demonstrate that all the control systems are capable of keeping both end products on their specifications. The NPMC is the best one in the operation of the ideal HIDiC. It can very smoothly realize setpoint transition and efficiently counteract external disturbances. The MIMC ranks the second for the regulatory responses to feed composition disturbances have relative longer setting time. The next comes to the multi-loop composition control system. Although it works well for the operation of the ideal HIDiC, it produces relative larger oscillations and longer setting time in the system responses. The IMC can not compete with the multi-loop composition control system because it is extremely sensitive to operating condition changes. The single-loop composition control system is the worst one for the responses of the uncontrolled product is extremely sluggish.

Identification and Internal Model Control of an Ideal Heat Integrated Distillation Column (HIDiC).

An appropriate structure for a reduced-order model of transfer function type is first proposed for an ideal heat integrated distillation column (HIDiC) based on the process dynamics. The reduced-order model could well represent the process not only in steady state but dynamic state as well. A multivariable internal model control (IMC) system is designed and applied to the ideal HIDiC. The simulation results demonstrate that the IMC controller can deal with the interactive nature of the ideal HIDiC more effectively than PI controllers, indicating the IMC controller could be a better means for operation of the ideal HIDiC in the case where high system performance is required. However, the ideal HIDiC is extremely sensitive to changes in operating conditions and this makes it necessary to adopt an on-line model adaptation mechanism to facilitate the performance of the IMC controller.

98/00684 Optimization of specific rate of heat pumping in combined heat pump cycles

Although the ideal heat-integrated distillation column (ideal HIDiC) is much more thermodynamically efficient than its conventional analogues, its applications in the chemical and petrochemical process industries have been restrained due to the great difficulties and complexities in the design and implementation of internal heat integration between the rectifying section and the stripping section. For the avoidance of these difficulties and complexities, a novel simplified configuration for the ideal HIDiC, termed the SIHIDiC, is proposed and studied in this paper. Only three internal heat exchangers are used to approximate the internal heat integration, and their locations and sizes are key decision variables for process synthesis and design and should be considered to enhance thermodynamic efficiency in process development. A simple stepwise procedure is thus derived for process synthesis and design, and the SIHIDiC is then evaluated through intensive comparison with conventional distillation columns and the ideal HIDiC in terms of the separations of ethylene/ethane and benzene/toluene binary mixtures. The results obtained indicate that the SIHIDiC could be an excellent candidate to approximate the ideal HIDiC with reduced capital investment and somewhat similar (if not smaller) operating cost. The SIHIDiC offers essentially a much simpler way than the current available methods to design and implement the concept of the ideal HIDiC into separation processes.

Determining Appropriate Configuration of Ideal Heat Integrated Distillation Columns(HIDiC).

The major concern in developing various kinds of heat integrated distillation columns is the strong interaction and high sensitivity resulting from heat integration (Takamatsu, 1996), which could drastically deteriorate system potential performance. Hence, it is of great importance to design processes so as to make these undesired properties as small as possible, namely to increase system dynamic resilience. As for the ideal heat integrated distillation column (HIDiC), we already know that its symmetrical specifications, such as equal feed split, middle feed location and same structures between rectifying and stripping sections, are the main reasons for strong interaction between top and bottom control loops (Huang et al, 1996). In order to make the ideal HIDiC have higher dynamic resilience, these kinds of symmetrical specifications should be deleted. A previous work (Huang et al, 1996) already explored how to improve the system resilience through appropriately assigning feed thermal condition q and feed location under general configuration of the ideal HIDiC. As to the effects of symmetrical structure between rectifying and stripping sections, its effects are still not clear. In this work we will concentrate on this problem by studying three possible configurations of the ideal HIDiC. Both time and frequency domain techniques have been employed to assess the potential effects of system configuration towards system performances, and the results obtained are further evaluated through rigorous nonlinear closed-loop simulation.

Performance Evaluation of Ideal Heat Integrated Distillation Columns.

In order to understand the operating feasibility of the ideal heat integrated distillation column (HIDiC), its control systems are studied in both time and frequency domains with respect to three operating conditions (i.e., feed thermal condition, q q = 0.5 and q > 0.5). It was found that the ideal HIDiC could be operated quite smoothly under all these operating conditions. However, the strongest interaction between top and bottom control loops is observed at q=0.5, and the system resilience may be degraded when q strays from 0.5 because of the strong gain directionality of the process.The feed location also strongly affects the dynamic performance of the ideal HIDiC. Placing feed in the middle of the process could intensify the interaction between the top and bottom control loops. Therefore, the determination of both feed thermal condition and feed location should be based on a careful compromise between steady state energy saving and dynamic resiliency of the system.

Dynamics of ideal heat integrated distillation columns.

An ideal heat integrated distillation column (HIDiC), which has neither a reboiler nor a condenser, was studied based on its non-linear and linearized dynamic models. It was found that heat integration between rectifying and stripping sections does not lead to an unstable plant. Moreover, the thermal interaction appears to be relatively stronger at low pressure difference than that at high pressure difference.Strong gain directionality has been found in the ideal HIDiC, where the pressure difference and feed thermal condition correspond to low and high gain direction respectively. With proper design of the process, thermal interaction, affects the system time constant only to a limited extent, and intensifies the interaction within a dual point composition control scheme. In fact, the degree of coupling between top and bottom control loops is governed by feed thermal condition since it is in line with high gain direction and can simultaneously introduce changes of both internal and external flows.

Minimum and Total Reflux in Ideal Heat Integrated Distillation Column(HIDiC).

It is shown that the conditions of the minimum amount of heat transfer and total reflux in the ideal heat integrated distillation column (HIDiC) exist corresponding to a conventional column. The importance of temperature distribution through the column is also indicated and its calculation method are shown.

A numerical consideration on dynamic modeling and control of ideal heat integrated distillation columns.

In this paper, an ideal heat integrated distillation column (HIDiC), which has neither a reboiler nor condenser, is considered. A dynamic model, capable of doing both static and dynamic simulations of the ideal HIDiC is derived. Based on this model, the system properties and control feasibility are studied. It is found that the ideal HIDiC could be regulated quite well with manipulation of feed thermal condition and the pressure of either rectifying or stripping section. The efficient way to control its top and bottom product qualities is to use composition inferential systems to realize direct composition control.

Conventional Plate to Plate Calculation with Consideration of Plate to Plate Temperature Difference in Ideal Heat Integrated Distillation Column(HIDiC).

先の報告では, 理想的内部熱交換型蒸留塔 (HIDiC) の概念とその可能性が1理論段当たりの伝熱量一定との仮定での段数計算によって示されてきた.しかしながら実際には, 1理論段当たりの伝熱量は濃縮部と回収部との対応する段間の温度差に依存する.本報告では, 理想的HIDiCの両部間の温度差を考慮した簡易逐次段計算法を提案した.ここでは回収部頂部の蒸気組成は濃縮部と回収部との操作線の交点の状態に等しいとの近似を用いている.