CIESC Journal ›› 2019, Vol. 70 ›› Issue (2): 625-633.doi: 10.11949/j.issn.0438-1157.20181090

• Process system engineering • Previous Articles     Next Articles

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

Xiuhui HUANG(),Jun WANG,Guomin CUI   

  1. School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai 200082, China
  • Received:2018-09-27 Revised:2018-10-21 Online:2019-02-05 Published:2018-10-29
  • Contact: Xiuhui HUANG E-mail:hxh@usst.edu.cn

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

CLC Number: 

  • TQ 028

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)

PX/%(mass) MA/%(mass)
S 1 378.35 0.123 8200 68.3 26.6 4 0.5 0.6
D 1 357.75 0.12 251181 0 14.9 73 0.1 12
B 1 390.35 0.13 136142 93.6 6.4 0 0 0

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"

"

EM ——塔板效率,无量纲
F ——进料质量流量,kg·h?1
h ——摩尔焓,J·mol?1
hF,j ——第j级上的进料摩尔焓,J·mol?1
Ki , j ——相平衡常数
Lj ——第j级上的液相质量流量,kg·h?1
Mj ——第j级上的质量流量,kg·h?1
Qj ——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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