Dynamic simulation and analysis of control strategies of acetic acid dehydration tower in PTA plant

doi:10.11949/j.issn.0438-1157.20181090

Abstract

Abstract:

The research object of this paper is acetic acid dehydration tower in PTA plant. The dynamic model was based on the dynamic mathematical model of the balance level and supplemented with the set dynamic parameters and the steady state model which was derived by using Aspen Plus. Next, the temperature of the sensitive stage was controlled by the reflux flow, and the column kettle reboiler duty was proportional to the feed flow F ₁. Aspen Dynamics was used to simulate the control strategy CS1, which has the dynamic response analysis of the key index parameters in the acetic acid dehydration tower after disturbance of the feed flow. To ensure the concentration of acetic acid at the bottom of the tower is more stable when the feed flow is disturbed, the heat load of the bottom tank reboiler is used to control the acetic acid concentration in the tower, and the control strategy CS2 is designed. Two kinds of different control strategies were analyzed and compared to their dynamic responses to obtain better control strategies under the same target conditions, which provided direction and guidance for the actual production and control strategy design.

Key words: control, dynamic modeling, dynamic simulation, acetic acid dehydration tower, response analysis

摘要：

以PTA装置醋酸脱水塔为研究对象，在该醋酸脱水塔的稳态模型的基础上，通过建立的平衡级动态数学模型以及补充设置好的动态参数，利用Aspen Plus软件建立好动态模型。以Aspen Dynamics软件为工具，用回流流量控制灵敏板温度，塔釜再沸器热负荷与进料流量F ₁呈比例控制，模拟设计出了控制策略CS1。又为了保证在进料流量扰动时塔底醋酸浓度更加稳定，利用塔釜再沸器热负荷来控制塔釜醋酸浓度，设计出了控制策略CS2。将两种不同的控制策略对其动态响应进行分析比较，得出在相同目标条件下表现更优的控制策略，为实际生产和控制方案的设计提供方向和指导。

关键词: 控制, 动态建模, 动态仿真, 醋酸脱水塔, 响应分析

CLC Number:

TQ 028

Xiuhui HUANG, Jun WANG, Guomin CUI. Dynamic simulation and analysis of control strategies of acetic acid dehydration tower in PTA plant[J]. CIESC Journal, 2019, 70(2): 625-633.

黄秀辉, 王俊, 崔国民. PTA装置醋酸脱水塔的动态模拟及控制策略分析[J]. 化工学报, 2019, 70(2): 625-633.

Figures/Tables 13

Fig.1 Acetate dehydration steady state process flow

Fig.2 Acetic acid dehydration tower (C-1) model

Fig.3 Temperature and composition distribution of steady-state acetic acid dehydration tower

Table 1 C-1 tower discharge results in acetic acid dehydration process under actual overload conditions

Outlet stream

Temperature/K

Pressure/MPa

Flow/

（kg·h^-1）

HAc/

%(mass)

Water/

%(mass)

NPA/

%(mass)

S ₁

D ₁

B ₁

Table 2 Dynamic mathematical model of distillation column

方程	平衡级方程式
质量平衡方程(M)	$d (M j X i, j) d t = L j - 1 x i, j - 1 + V j + 1 y i, j + 1 - (L j + S L j) x i, j - (V j + S V j) y i, j + F j z i, j$
相平衡方程(E)	$y i, j = K i, j x i, j * = K i, j x i, j - (1 - E M i, j) x i, j - 1 E M i, j, E M i, j = x i, j - x i, j - 1 x i, j * - x i, j - 1$ , $x i, j * = x i, j - (1 - E M i, j) x i, j - 1 E M i, j$
归一方程(S)	$∑ i = 1 5 x i, j α = 1, ∑ i = 1 5 x i, j β = 1, ∑ i = 1 5 y i, j = 1$
热平衡方程(H)	$d (M j h j) d t = M j d h j d t + h j d M j d t = L j - 1 h j - 1 + V j + 1 h j + 1 - (L j + S L j) h j - (V j + S V j) H j + F j h F, j + Q j$

Table 2 Dynamic mathematical model of distillation column

方程	平衡级方程式
质量平衡方程(M)	$d (M j X i, j) d t = L j - 1 x i, j - 1 + V j + 1 y i, j + 1 - (L j + S L j) x i, j - (V j + S V j) y i, j + F j z i, j$
相平衡方程(E)	$y i, j = K i, j x i, j * = K i, j x i, j - (1 - E M i, j) x i, j - 1 E M i, j, E M i, j = x i, j - x i, j - 1 x i, j * - x i, j - 1$ , $x i, j * = x i, j - (1 - E M i, j) x i, j - 1 E M i, j$
归一方程(S)	$∑ i = 1 5 x i, j α = 1, ∑ i = 1 5 x i, j β = 1, ∑ i = 1 5 y i, j = 1$
热平衡方程(H)	$d (M j h j) d t = M j d h j d t + h j d M j d t = L j - 1 h j - 1 + V j + 1 h j + 1 - (L j + S L j) h j - (V j + S V j) H j + F j h F, j + Q j$

Fig.4 Three-phase balance model of vapor-liquid-liquid rectification tray structure

Fig.5 Open loop sensitivity analysis of C-1 column in R 1

Fig.6 Two control strategies of acetic acid dehydration tower

Fig.7 CS1-CS2 strategy response plate temperature control response

Fig.8 Control response of CS1-CS2 strategy to bottom acetic acid mass fraction

Fig.9 Control respones of CS1-CS2 strategy to top of acetic acid mass fraction

Fig.10 Control response of CS1-CS2 strategy to heating of tower reboiler

E_M	——塔板效率，无量纲
F	——进料质量流量，kg·h^?1
h	——摩尔焓，J·mol^?1
h_F,j	——第j级上的进料摩尔焓，J·mol^?1
K_i _, _j	——相平衡常数
L_j	——第j级上的液相质量流量，kg·h^?1
M_j	——第j级上的质量流量，kg·h^?1
Q_j	——与外界的热量传递，kJ·h^?1
SL _j	——液相采出，kg·h^?1
SV _j	——气相采出，kg·h^?1
t	——时间

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