Multivariable Predictive Control _PTA by rsg18606

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									                                       Multivariable Predictive Control and its
                                     Application on the Solvent Dehydration Tower

                                                          Yo n g Gu , Ho n g ye Su , Jian Ch u


         Na t io n a l K e y L a b o r a to r y o f I n d u s tr ia l Co n tr o l T e c h n o lo g y a n d I n s titu t e o f
         I n d u s tr ia l P r o c e s s Co n t r o l , Z h e j ia n g U n iv e r s i t y , H a n g z h ou , Ch in a , 3 1 0 0 2 7 .
         g u y o n g @ mail . h z . z j. c n


         A b s tr a c t : M u lt iv a r ia b le P r e d ic t iv e Co n tr o l s tr a te g ie s w ith t h e h e l p o f s o f tw a r e p a c k a g e o f
         A P C- H i e c o n a r e a p p li e d to c o n tr o l a S o lv e n t D e h yd r a t io n T o w e r ( S D T ) . A c o n t r o ll e r i s
         d e s ig n e d to h e l p s o lv e t h e p r o b le ms s u c h a s f lu c tu a tio n o f th e f e e d in g , th e c r o s s e f f e c ts a n d
         th e l iq u id f l o o d in g in th e r u n n in g p r o c e s s o f th e to w e r . T h e s ta b i li t y o f S D T is i mp r o v e d
         e v id e n t l y a f te r th e a p p l i c a tio n o f th e c o n tr o l le r . T h e a c tu a l c o n tr o l r e s u lt s h o w s a v is i b le
         r e d u c t io n o f th e c o s t o f H A c a n d a s u b s e q u e n t d is tin c t e c o n o mic a l p r o f it .


                          K e yw o r d s : A d v a n c e d P r o c e s s Co n t r o l, Mu lt iv a r ia b le P r e d i c t iv e Co n tr o l,
         S o lv e n t D e h yd r a tio n T o w e r , A P C- H ie c o n




I N T RO D U CT I O N                                                            P I D c o n tr o l . I n o r d e r t o i mp r o v e t h e c o n tr o l
                                                                                 p e r f o r ma n c e ,   a      mu lt iv a r ia b le      p r e d ic t iv e
Mo d e l- b a s e d p r e d ic t iv e c o n tr o l ( MP C) h a s                 c o n tr o l le r w a s d e s ig n e d b y u s in g th e s o f tw a r e
b e e n d e v e l o p in g f a s t in b o th it s a c a d e mi c                 p a c k a g e o f A P C- H i e c o n to c o n tr o l th e p r o c e s s .
r e s e a r c h a n d in d u s tr i a l a p p li c a t io n . T h e th r e e     A P C- H i e c o n p r o v id e s t h e g e n e r a l f u n c tio n s o f
c h a r a c te r is t ic s o f MP C a r e p r e d ic t iv e mo d e l,            mo d e l- b a s e d p r e d ic t iv e c o n tr o l, i. e . th e c r o s s
r e c e d in g    h o r iz o n       c o n tr o l       and       feedback       e f f e c ts    and       c o n s tr a i n ts   are       in h e r e n t l y
c o r r e c t io n . I n th e p r o c e s s in d u s tr i e s , o n e o f th e   c o n s id e r e d i n th e c o n tr o ll e r a n d th e me a s u r a b le
mo s t a t tr a c t iv e f e a tu r e s o f MP C i s i t s a b il i t y to       d is tu r b a n c e s a r e e f f e c t iv e ly c o mp e n s a te d b y
d e a l w i th c o n s tr a in t s a n d c r o s s e f f e c ts in               f e e d - f o r w a r d a c t io n . A t th e s a me ti me , in o r d e r
mu lt iv a r ia b le          c o n tr o l      p r o b le ms .      Some        to r e s tr a in th e l iq u id f lo o d in g , a f lo o d in g
c o mme r c ia l s o f tw a r e p a c k a g e s b a s e d o n th e               d e te c to r i s in tr o d u c e d in to th e c o n tr o l le r .
p r in c i p le o f th e p r e d ic t iv e c o n tr o l h a v e b e e n          T h u s , th e c o n tr o l s tr u c tu r e s a r e s w i tc h e d
d e v e lo p e d ( A d e r s a I n c . Re p o r t, 1 9 9 1 a , 1 9 9 3 b ,       a u to ma t ic a l ly v ia th e in d ic a t io n o f t h e f lo o d in g
1 9 9 5 c ) . T h e a p p l i c a ti o n o f th e s e s o f tw a r e             d e te c to r . Co n s id e r in g th e s p e c if i c c o n d itio n o f
p a c k a g e s h a s a lr e a d y h a d lo ts o f in s ta n c e s a l l         th e to w e r , t h e in n e r - r e f lu x f lo w r a te c o n tr o l
o v e r th e w o r ld ( R ic h a le t , e t a l. , 1 9 7 8 ; R ic h a l e t,     a n d th e p r e s s u r e c o m p e n s a t e d te mp e r a tu r e
1 9 9 3 ) . I n th is p a p e r , t h e a p p l ic a t i o n o f MP C            c o n tr o l a r e a ls o in tr o d u c e d in to th e c o n tr o l
s tr a te g ie s o n th e S o lv e n t D e h yd r a t io n T o w e r             s ys te m. T h e c o n tr o l p e r f o r ma n c e a f t e r th e
( S D T ) , w ith th e h e l p o f th e s o f tw a r e p a c k e t o f           a p p li c a t io n o f A P C- H ie c o n is v e r y s a t is f y in g .
A P C- H ie c o n ,      is       in tr o d u c e d .    The       process
p a r a me te r s a r e u n s t a b le u n d e r th e c o n v e n tio n a l
2 . T E CH N I CA L F E A T U RE S A N D F O RME R                                      tr a d it io n a l c o n tr o l, w h e n th e r e f lu x f lo w r a t e is
CO N T RO L S T A T U S O F T H E S D T                                                 a b o v e 4 2 t/h , liq u id f lo o d in g e a s il y ta k e s p la c e .
                                                                                        T h e c h ie f c a u s e f o r th e s e p r o b le ms is th a t th e
2 . 1 T e c h n ic a l F e a tu r e s o f th e S D T                                    c a p a c i t y o f th e S D T c o u ld n o t f i t t h e e n l a r g e d
                                                                                        lo a d . T h e s itu a t io n w a s n o t i mp r o v e d mu c h
P r o d u c in g p u r if ie d te r e p h th a l i c a c id ( P T A ) ,                 e v e n a f t e r mo s t p a r t o f th e to w e r h a d b e e n
a c c o r d in g t o th e A mo c o P a te n t, P X , H A c ,                            c h a n g e d f r o m s ie v e p la te to s tu f f in g . T h is
Ca ta l yz e r ( C o - Mn ) , a s s i s t Ca ta l yz e r ( H Br ) a n d                 le a d s to th e r e s u l t th a t th e S D T b e c o me s v e r y
a ir     are       fed         in to        O x yg e n a t in g        Re a c to r      s e n s i t iv e to d is tu r b a n c e s . T h e S D T h a s f o u r
c o n tin u o u s l y.       Under           c e r t a in   pressure          and       p a r ts o f f e d - in ma te r ia ls : tw o o f th e m a r e v a p o r
te mp e r a tu r e , P X is mo s tl y o x yg e n a te d in to                           a n d th e o th e r tw o a r e liq u id . A mo n g th e m, o n l y
CT A f ir s t, th e n a f t e r c r ys ta l li z a tio n , it is                        th e l iq u id ( F I 4 0 8 , s e e F ig . 1 ) d r a w n o u t f r o m
p u r if ie d      to      e l i mi n a te        4 - CBA         by     a d d in g     th e r e a c to r is me a s u r a b le . T h i s p a r t o c c u p ie s
h yd r o g e n ,        f in a l l y       th e     PTA(>99.9%)                   is    n e a r l y 4 0 % o f th e f e e d r a te . T h e o t h e r 6 0 % o f
o b ta in e d . S o th e P T A d e v ic e c a n b e d iv id e d                         th e f e e d r a t e is u n me a s u r a b le a n d f lu c tu a t e s
in to      tw o          p a r ts      ---         O x yg e n a t io n        and       f r e q u e n tl y.
P u r if ic a tio n . D u r in g th e p r o d u c tio n o f P T A ,
th e r e is 2 m o l H 2 O p r od u c e d w h il e 1 mo l T A                            2 . 2 F o r m e r Co n tr o l S ta tu s o f th e S D T
w a s o b ta in e d . T h e H 2 O p r o d u c e d w il l d i lu te
H A c S o lv e n t, w h ic h c a n b e r e u s e d o n ly b y                           I n th e f o r m e r t e c h n i c a l d e s ig n o f t h e S D T , th e
d e h yd r a t io n th r o u g h a s o lv e n t d e h yd r a tio n                      c o n tr o l     s t r a te g ie s     are     to     adjust         th e
to w e r . T h e S o lv e n t D e h yd r a t io n T o w e r is a n                      c o n c e n tr a t i o n o f H 2O th r o u g h s te a m f lo w r a t e
i mp o r ta n t d e v ic e in th e O x yg e n a t io n p a r t . I t                    a n d to a d j u s t th e c o n c e n tr a t io n o f H A c th r o u g h
c a n b e r e g a r d e d a s a b in a r y d i s t i l la t io n c o lu mn              r e f lu x f lo w r a te . T h e tr a d i tio n a l c o n tr o l lo o p s
to s e p a r a t e th e H 2 O a n d H A c . T h e H 2 O                                 a r e a s f o l lo w s :
c o n ta in e d in th e s o lv e n t a t th e b o t to m o f to w e r                   D o u b le c a s c a d e c o n tr o l s y s t e m f o r me d b y
s h o u ld n o t b e o v e r 8 % a s r e q u ir e d . O th e r w is e ,                 c o n d u c tiv it y       CI C4 0 2     at   th e   b o tto m,      th e
th e r e d u n d a n t w a te r w i l l a f f e c t th e t e mp e r a tu r e            te mp e r a tu r e T I C4 2 4 a t th e b o t to m a n d th e
in th e r e a c t o r . H o w e v e r , th e H A c c o n ta in e d in                   s te a m f lo w r a te F I C4 2 4 .
th e w a t e r a t th e to p o f to w e r s h o u ld b e a s l i t tl e                 Ca s c a d e          c o n tr o l     s ys te m     f o r me d       by
a s p o s s i b le , s o a s to r e d u c e th e c o s t o f H A c ,                    c o n d u c tiv it y CI C4 0 1 a t th e to p a n d r e f lu x f lo w
p r o te c t th e e n v ir o n me n t a n d d e c r e a s e th e r u s t                r a te F I C4 2 1 .
o f e q u i p me n t.                                                                   H o w e v e r , f ro m th e v e r y b e g in n in g , th e a b o v e
I n th e Ch e m ic a l F a c to r y o f a c e r t a in Ch e mi c a l                    c o n tr o l s ys te ms h a v e n o t b e e n a d o p te d to
F i b e r Co mp a n y, th e ma in p r o b le ms o f S D T l ie                          a c h i e v e th e q u a li t y c o n t r o l o f b o th th e b o tto m
in th e f o l l o w in g th r e e a s p e c ts . F ir s t, th e                         a n d to p p a r t o f th e to w e r s i mu l ta n e o u s l y. F o r
o p e r a t io n f le x i b i l i ty o f S D T is li mi t e d w h e n                   s o me r e a s o n , o n ly T I C4 2 4 - F I C4 2 4 c a s c a d e
th e lo a d is in c r e a s e d t o 1 3 0 % o f it s o r ig in a l                      c o n tr o l c a n b e a p p l ie d . T h e r e f o r e , o n ly th e
d e s ig n .    Second,             th e     s e p a r a t in g    e f f ic i e n c y   b o tto m q u a li t y o f S D T is c o n tr o ll e d in th e
c a n n o t me e t th e o r ig i n a l ly d e s ig n e d in d e x                       f o r me r c o n t r o l s y s t e m. T h u s , th e c o n d u c tiv i t y
u n d e r th e h ig h lo a d c o n d it io n . T h ir d , u n d e r                     CI C4 0 1 a n d CI C4 0 2 a r e o n ly r e f e r e n c e in d e x .
T h e o p e r a to r s u s u a l ly a d j u s t th e s e t p o in t s o f
b o tto m te m p e r a tu r e T I C4 2 4 a n d r e f lu x f lo w                                           3.       A D V AN CE D               P RO CE S S            CO N T RO L
r a te F I C4 2 1 to ma n i p u la te th e to w e r . D u e to th e                                        S T RA T E G Y O F T H E S D T
lo n g ti me - d e l a y, th e lo n g ti me r e s p o n s e a n d th e                                     T o s o lv e th e p r o b le ms d e s c r i b e d i n th e a b o v e
s tr o n g c r o s s e f f e c ts , th e te mp e r a tu r e a n d                                          s e c t io n ,     we       choose      th e     s o f tw a r e     packet
p r e s s u r e tr e n d s in th e S D T a r e u n e v e n u n d e r                                       A P C- H ie c o n w h ic h is b a s e d o n th e s tr a te g ie s o f
c o n v e n tio n a l P I D c o n tr o l. S o th e p r o d u c tio n                                       MP C. MP C h a s b e c o me th e ma in a p p r o a c h in
q u a li t ie s a r e o f te n u n s ta b le f o r th e h ig h                                             th e a d v a n c e d in d u s tr i a l p r o c e s s c o n t r o l. I t u s e s
d iv e r s i t y.                                                                                          th e f o l lo w in g th r e e k in d s o f v a r ia b l e s :
A t th e s a m e t i me , th e c o r r e la t io n b e tw e e n                                            CV : Co n tr o l le d V a r ia b l e
p r e s s u r e a n d te mp e r a tu r e o f te n c o n f u s e s th e                                     MV : Ma n i p u la te V a r ia b le
r e la t io n b e t w e e n th e b o tto m c o mp o n e n t a n d                                          D V : Me a s u r e d D is tu r b a n c e V a r i a b l e
b o tto m te m p e r a tu r e .                                                                            T h e k e y to a s u c c e s s f u l a p p li c a t i o n o f MP C
I n a d d it io n , th e u n e x p e c te d c h a n g e s o f w e a th e r                                 d e p e n d s o n th e s e le c t io n o f CV , M V a n d D V
lik e r a in s to r m a f f e c ts t h e S D T g r e a t l y, w h e n                                      a n d th e a c c u r a c y o f th e p r o c e s s mo d e l. I n th e
th e r e f lu x t e mp e r a tu r e T I 4 4 6 w ill h a v e a b ig                                         A P C- H i e c o n Co n tr o ll e r d e s ig n e d f o r th e S D T ,
f lu c tu a t io n .                                                                                       th e CV s , M V s a n d D V s a r e li s t e d i n T a b le 1 .
T h e w o r s t th in g to th e S D T is th a t it g e ts e a s i l y
in to th e liq u id f lo o d in g mo d e . T h e s y mp to m o f                                           Table 1 APC-Hiecon Controller Variables List
f lo o d in g is t h a t th e d if f e r e n t ia l p r e s s u r e o f th e                                    CVs                      MVs                     DVs
                                                                                                                CV          CIC401.P     MV      FIC421.S        DV
to w e r         PDI422                 in c r e a s e s        e x p o n e n ti a l l y.             In        1           V            1       P               1        FI408.PV
                                                                                                                CV          CIC402.P     MV      FIC424.S        DV
c o n s e q u e n c e , th e b o t to m t e mp e r a tu r e in c r e a s e s                                    2           V            2       P               2        TI446.PV
                                                                                                                CV          PDI422.P                             DV       PIC904.P
r a p id l y w h i l e th e b o tto m l iq u id l e v e l d e c r e a s e s                                     3           V                                    3        V
                                                                                                                CV          TIC424.P
s p e e d i l y.                                                                                                4           V


T h e s c h e ma ti c f lo w c h a r t is d e p ic te d in F ig . 1 .


       PIC904                                                                                              3 . 1 P r o c e s s M o d e l o f th e S D T
        KPA
                                                                              E404
                3DV


      APC-HIECON
                                                                                                           T h e p r o c e s s c o n tr o l le r d e s ig n r e l ie s o n th e
      CONTROLLER                  2MV
                                                                                              TI446
                                                                                              deg C
                                                                                                           a v a i la b i li t y, o r d e v e lo p me n t, o f a p r o c e s s
                                                    PDI422
                                                     KPA
              4CV                                                                                          mo d e l th a t d e s c r i b e s th e p r o c e s s d yn a mi c s
                                                                                                D404
      FI408
      KG/HR
                       TIC424
                        deg C                                                                              w ith s u f f i c i e n t a c c u r a c y to e n a b le d e s ig n o f a
                                                                                     FIC420
                                                                                                           c o n tr o l le r t o a c h ie v e t h e r e q u ir e d c lo s e d lo o p
     FIC424           FIC424.SP                                                      KG/HR
     KG/HR              KG/HR
                                                                    CIC401
                                                                    ms/cm
                                                                                                           p e r f o r ma n c e . T o id e n t if y th e p r o c e s s mo d e l ,
                                         T403

                 E403                               FIC421.SP        FIC421                                MV s n e e d to b e c h a n g e d s te p b y s t e p d u r in g th e
                                                      KG/HR          KG/HR

    CIC402
    ms/cm
                                                                                                           r e s p o n s e te s t. I n th i s p r o j e c t, s te p c h a n g e s o f
                                                    LIC405
    FIC419
                                         E405
                                                      %                                                    th e s e t p o in ts o f F I C4 2 1 a n d F I C4 24 a r e ma d e
    KG/HR
                                                                                              G405
                                                                                                           o n e b y o n e f o r s e v e r a l t i me s . T h e s p e c i a l
                          G404

                                                                                                           p a t te r n s o f th e s te p c h a n g e s a r e s h o w n in F ig .
                                                                                                           2 . ( T R me a n s th e ti me f o r a CV to r e a c h a
 F ig . 1 F lo w c h a r t o f t h e S D T
                                                                                                           s te a d y s t a t e . )
                                                                                 a n d f lo o d in g c o n tr o l le r a r e s h o w n in T a b le 3
                                                                                 a n d 4 . T h e ba s i c c o n tr o l le r is d e s ig n e d to k e e p
               2 * TR        ∆                                                   th e b o tto m t e mp e r a tu r e T I C4 2 4 a r o u n d th e s e t
  TR                         TR        1 /3 T                                    p o in t     and     min i mi z e        th e      to p     c o n d u c tiv it y
F ig . 2 T e s t S ig n a l P a tt e r n                                         CI C4 0 1 w h il e th e o th e r p a r a me te r s , CI C4 0 2
                                                                                 a n d P D I 4 2 2 , a r e r e s te d i n th e r e a s o n a b le s c o p e .
F o r th e D V s , s in c e th e y c a n n o t b e c h a n g e d a s             T h e r e is a n o th e r s p e c i a l c o n tr o l le r to h a n d le
th e MV s , th e o n ly w a y to id e n t if y t h e p r o c e s s               th e l iq u id f lo o d in g . T h e p r i ma r y a i m in th e
mo d e l is to h a n d le lo n g t e r m n o r ma l o p e r a t io n             f lo o d in g c o n tr o l le r is t o d r a w th e d if f e r e n t i a l
d a ta . T h e D V s a r e l i k e l y to h a v e a lo t o f                     p r e s s u r e P D I 4 2 2 b a c k to th e id e a l s c o p e . A
c h a n g e s d u r in g a lo n g t i me p e r io d .                            f lo o d in g d e t e c to r , w h ic h            is d e t e c tin g       th e
T h e te s t d a t a o f MV s a n d D V s a r e d e a lt w i th b y              P D I 4 2 2 , is e mb e d d e d i n to th e p r o g r a m. T h u s ,
th e id e n tif ic a t io n to o l o f th e A P C- H i e c o n . T h e           th e       c o n tr o l       s tr u c t u r e s      are         s w i tc h e d
p r o c e s s mo d e l w a s o b t a i n e d e a s i l y i n th is w a y.        a u to ma t ic a l ly v ia th e in d ic a t io n o f t h e f lo o d in g
T h e p r o c e s s d yn a mi c s is r e p r e s e n te d b y th e               d e te c to r .
i mp u ls e r e s p o n s e mo d e ls w h i c h d e s c r i b e th e
r e la t io n s h i p b e tw e e n C V s a n d MV s , D V s . H e r e            T a b l e 3 Ba s ic Co n tr o l le r S tr u c tu r e
th e a l mo s t e q u iv a le n t L a p lu s tr a n s f e r f u n c t io n s            CVs                                 MVs

f o r th e mo d e ls a r e l is te d in T a b l e 2 .                                                                                 FIC421.SP
                                                                                                   CIC401.PV                          (Position        and
                                                                                        CV1                                 MV1
                                                                                                   (Minimization)                     Speed
                                                                                                                                      Constraints)
T a b l e 2 T r a n s f e r F u n c t i o n s L is t
                                                                                                                                      FIC424.SP
                 F I C4 2 1                F I C4 2 4                                              CIC402.PV                          (Position        and
                                                                                        CV2                                 MV2
                 -0.012*                   0.01*                                                   (Max Constraint)                   Speed
  CI C4 0 1 - 3 s                                                                                                                     Constraints)
                 e /( 1 + 2 5 s )          e - 3 . 5 s /( 1 + 1 2 s )
                 0 . 0 0 3 6*              -0.004*
  CI C4 0 2 - 4 s                                                                                  PDI422.PV
                 e /( 1 + 2 0 s )          e - 0 . 5 s /( 1 + 7 s )                     CV3
                                                                                                   (Max Constraint)
                 0.002*                    0.003*
  PDI422
                 e - 0 . 5 s /( 1 + 7 s )  e - 0 . 5 s /( 1 + 3 s )                                TIC424.PV
                 - 0 . 0 0 1 4*            0.002*                                       CV4        (Setpoint
  T I C4 2 4                                                                                       Control)
                 e - 0 . 5 s /( 1 + 8 s )  e - 0 . 5 s /( 1 + 4 s )



3 . 2 Co n tr o l le r d e s i g n o f th e S D T                                T a b l e 4 F lo o d in g Co n tr o ll e r S tr u c t u r e
                                                                                        CVs                                 MVs


U s in g th e d e s ig n to o l o f A P C- H ie c o n , a MP C                                     CIC401.PV
                                                                                                                                      FIC421.SP
                                                                                                                                      (Position        and
                                                                                        CV1        (Without                 MV1
c o n tr o l le r   is    n a tu r a ll y d e s ig n e d        f r o m th e                       Control)
                                                                                                                                      Speed
                                                                                                                                      Constraints)
p r e v io u s l y i d e n tif ie d p r o c e s s mo d e l . T h e ma in
                                                                                                                                      FIC424.SP
ta s k s d u r in g th e d e s ig n w o r k a r e to tr a n s l a t e                              CIC402.PV
                                                                                                                                      (Position        and
                                                                                        CV2        (Without                 MV2
                                                                                                                                      Speed
                                                                                                   Control)
th e c o n tr o l o b j e c ts o f t h e S D T to s p e c i a l f o r m s                                                             Constraints)

of     th e    s o f tw a r e     packet         and      to     tu n e   th e                     PDI422.PV
                                                                                        CV3        (Setpoint
c o n tr o l le r e l a b o r a te l y. T h e f e a tu r e s o f th e                              Control)

c o n tr o l le r l i e in th e f o l l o w in g th r e e a s p e c ts .
                                                                                                   TIC424.PV
S wi tc h b e tw e e n b a s ic c o n tr o l le r a n d flo o d in g                    CV4        (Without
                                                                                                   Control)

c o n tr o l le r . T h e s tr u c tu r e s o f b a s i c c o n tr o l le r
I n n e r - r e f lu x    f lo w    rate    c o n tr o l.   It   is   th e    T h e c o mp e n s a t io n e q u a t io n is a s f o l lo w s :
in n e r - r e f lu x f lo w r a t e th a t r e a ll y in f lu e n c e th e      T I C4 2 4 . S P = T O + γ ( P O - P I 4 2 2 A . P V)               (2)
s e p a r a t in g e f f ic ie n c y o f th e S D T r a th e r th a n         T I C4 2 4 . S P :        Set      point         of        th e      b o t to m
th e     o u t e r - r e f lu x    f lo w   rate.     In     order       to   te mp e r a tu r e
o v e r c o me t h e e f f e c t o f th e f lu c tu a tio n o f th e          P I 4 2 2 A . P V : Bo t to m p r e s s u r e
r e f lu x te mp e r a tu r e , th e in n e r - r e f lu x f lo w r a te      T O : N o r m te mp e r a tu r e
c o n v e r s io n is in tr o d u c e d in to th e s ys te m. T h e           PO: Norm pressure
A P C- H ie c o n c o n tr o l le r c a lc u l a te s t h e s e t p o in t    γ : Co e f f i c i e n t
o f th e in n e r - r e f lu x f lo w r a te . T h e n t h e s e t p o in t
o f th e in n e r - r e f lu x f lo w r a te is tr a n s f e r r e d to       4 . P E RF O R MA N CE O F A P C- H I E C O N
th e s e t p o in t o f th e a c tu a l r e f lu x f lo w r a te . T h e      A f te r th e a p p lic a t io n o f A P C- H i e c o n o n th e
c o n v e r s io n e q u a t io n is li s t e d a s th e f o llo w s :        S D T , th e f r e q u e n c y o f liq u id f lo o d in g is
F I C4 2 1 . S P = F I C4 2 1 . M* ( 1 + λ ( T 0 - T I 4 4 6 . P V ) )        g r e a t l y r e d u c e d a n d th e a v e r a g e c o n c e n tr a t io n
(1)                                                                           o f H A c a t th e to p o f th e t o w e r is d e c r e a s e d f r o m
F I C4 2 1 . M: S e t p o in t o f in n e r - r e f lu x f lo w r a te        3 . 0 % to 2 . 6 % .
T 0 : Bo il in g p o in t o f th e r e f lu x f lo w                          T h e t i me tr e n d s o f th e k e y v a r ia b le s b e f o r e th e
λ : Co e f f i c i e n t                                                      a p p li c a t io n a r e s h o w n in F ig . 3 a n d th o s e a f te r
                                                                              th e a p p li c a t io n a r e s h o w n in F ig . 4 . ( T h e s c a l e s
P r e s s u r e c o m p e n s a te d te m p e r a tu r e c o n tr o l.        o f tw o f ig u re s a r e d if f e r e n t. T h e s c a le o f F ig . 4
T h e to p p r e s s u r e P I 4 2 2 B w a s b a d l y c o n tr o l l e d     is s ma ll e r . ) T h e r e a r e f i v e c u r v e s in b o th o f th e
b e c a u s e o f t h e p r o b le m o f a v a lv e i n S D T . T h e         tw o f ig u r e s , w h ic h r e p r e s e n t th e t i m e tr e n d s o f
c o r r e la t io n      b e tw e e n   b o tto m     pressure        and     f iv e d if f e r e n t v a r ia b l e s ( i. e . CI C4 0 1 , CI C4 0 2 ,
b o tto m te m p e r a tu r e o f t e n c o n f u s e s th e r e l a tio n    T I C4 2 4 , P D I 4 2 2 , P I42 2 B) . I t c a n b e d r a w n
b e tw e e n th e b o t to m c o mp o n e n t a n d b o tto m                 f r o m th e f ig u r e s th a t th e s t a n d a r d d e v ia t io n o f
te mp e r a tu r e . Co n s e q u e n tl y, it is n e c e s s a r y to        CV s i s r e d u c e d g r e a t ly a f te r th e a p p li c a tio n .
c o mp e n s a t e th e b o t to m te mp e r a t u r e b y th e               Under        th e     tr a d i tio n a l    PID            c o n tr o l,      th e
pressure.                                                                     o p e r a to r s h a v e to d e a l w ith th e liq u i d f lo o d in g
                                                                              ma n u a l l y. A s s h o w n in th e f r a me d p a r t o f th e
F ig . 3 T i me T r e n d s Be f o r e th e A p p li c a t io n               F ig . 3 , d u r in g th e f lo o d i n g , th e t i me r e c o v e r in g
                                                                              to th e s te a d y s t a t e i s v e r y lo n g a n d th e
                                                                              a mp l itu d e       of     th e    tr e n d s        is     very          h ig h .
                                                                              Me a n w h i le , a s s h o w n in th e f r a me d p a r t o f F ig .
                                                                              4 , th e A P C - H ie c o n c o n tr o l le r c a n h a n d le th e
                                                                              liq u id f lo o d in g a u to ma t ic a l l y.


                                                                              T h e f lo o d in g h a s b e e n r e s tr a in e d q u ic k l y a n d
                                                                              th e a mp l i tu d e o f th e tr e n d s is c o mp a r a t iv e l y
                                                                              mu c h lo w e r .
F ig . 4 T i me T r e n d s A f te r th e A p p l ic a t io n   5 . CO N CL U S I O N


                                                                W ith          th e      successful            a p p l ic a t i o n    of      th e
                                                                A P C- H ie c o n , th e S D T c o u ld s te a d i ly r u n a t a
                                                                p o in t n e a r th e f lo o d in g l i mi t. I t s h o w s th e
                                                                a d v a n ta g e        of     th e      mo d e l- b a s e d       p r e d ic t iv e
                                                                c o n tr o l          s o f tw a r e      p a c k e t,      th e        c o n tr o l
                                                                p e r f o r ma n c e          is       i mp r o v e d      v is i b ly.      The
                                                                r e d u c t io n o f th e c o s t o f H A c is v e r y s a t is f y in g
                                                                a n d a d is t i n c t e c o n o mic a l p r o f i t i s o b ta in e d .
                                                                Me a n w h i le , it b r in g s o th e r g o o d e f f e c t s l ik e
                                                                p r o te c tin g t h e e n v ir o n me n t a n d d e c r e a s in g th e
                                                                r u s t o f e q u i p me n t.

								
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