從丙烷中分離丙烯是一種高能耗的蒸餾過程。蒸氣壓縮通常用於分離丙烯和丙烷。蒸氣壓縮的大多數研究都是在給定壓力下進行的。眾所周知，壓力越低，揮發度差就越大，分離所需的能量就越少。在傳統的塔中，蒸餾的能量可以通過在盡可能低的壓力下操作來最小化。該極限通常由冷凝器中的最大冷卻能力決定，而冷凝器的最大冷卻能力又由冷卻水的溫度決定，這種做法被稱為浮動壓力控制。在蒸氣減壓塔中，冷凝器和再沸器由熱交換器代替。輔助冷凝器和再沸器可能存在也可能不存在。運行限制取決於壓縮機的防喘振控制。此外，有必要確保在再沸器中用作蒸汽的壓縮蒸汽基本上不被過冷以避免熱交換器的振動。
在這項研究中，使用ASPEN Plus動力學研究了帶有輔助冷凝器的蒸汽減壓丙烷-丙烯塔的浮壓控制實施方案。提出了一種包括基本庫存控制，質量控制以及壓力控制的控制方案。為了將操作保持在壓縮機喘振曲線的安全範圍內，調節了壓縮蒸汽作為熱媒到達底部並通過輔助冷凝器的分流。結果表明，當塔壓力降低1 kg / cm2時，塔可以在頂部和底部的產品純度要求下運行。
據我們所知，這是首次在文獻中討論瞭如何為蒸氣再壓縮蒸餾實施浮動壓力控制。

The separation of propylene from propane is an energy-intensive distillation process. Vapor recompression is commonly used for the separation of propylene and propane. Most studies of vapor recompression were carried out at a given pressure. It is well known that the lower the pressure, the higher the volatility difference and less energy is required to perform the separation. In a traditional column, energy of the distillation can be minimized by operating at the lowest pressure possible. The limit is usually determined by the maximum cooling capacity in the condenser, which is in turn determined by the temperature of the cooling water. Such a practice is known as floating pressure control. In a vapor-recompression column, the condenser and reboiler were replaced by a heat exchanger. Auxiliary condenser and reboiler may or may not be present. The operating constraint is determined by the anti-surge control of the compressor. Furthermore, it is necessary to ensure that the compressed vapor which acts as steam in the reboiler is not substantially subcooled to avoid the vibration of the heat exchanger.
In this study, the implementation of floating pressure control for a vapor-recompression propane-propylene column with an auxiliary condenser is studied using ASPEN Plus dynamics. A control scheme that includes basic inventory control, quality control as well as pressure control was proposed. To keep the operation within safe region of the compressor surge curve, the split of the compressed vapor going to the bottom as heating medium and passing through the auxiliary condenser is adjusted. It is shown that the column can be operated under product purity requirements of top and bottom when column pressure is reduced by 1 kg/cm2.
To our knowledge, this is the first time how floating pressure control can be implemented for a vapor-recompression distillation is discussed in the literature.

Abstract i
Table of Contents iii
List of Figures iv
List of Tables v

1. Introduction 1
1.1 Research background 1
1.2 Research motivation and scope 4
1.3 Thesis organization 4

2. Review of Related Literatures 5
2.1 Propylene-propane Separation 5
2.2 Vapor recompression 8
2.3 Floating pressure control 10
2.4 Optimal control of propylene-propane separation 14

3. Steady State and Dynamic Simulation 17
3.1 Process flow diagram 17
3.2 Thermodynamic model 19
3.3 Control valve sizing………………...……….............................................................21
3.4 Base control scheme…….....…..……………............................................................23
3.4.1 Simulation flow sheet......................................................................................23
3.4.2 Controller tuning………………………………………….............................25
3.5 Pressure control..........................................................................................................27
3.5.1 Importance of multi-step pressure reduction 30

4. Process Optimization and Control 32
4.1 Optimal operation at fixed pressure 33
4.2 Implementation of optimum HV01 opening pressure reduction……………………38
4.3 Optimal operating pressure 41
4.3.1 Maintaining acceptable product purity 41
4.3.2 Cooling capacity limits pressure reduction 43
4.4 Anti-surge control 44

5. Conclusion 49
6. References 51

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