columns as well as other types of energy--saving distilla--
tion columns． such aLs heat pump c
olumns and Petlyruk
c
olumns acc
ording to r
igor thermodynamic analysis[2。
．
Compressor
Throttling valve
Fig．1． Schematic diagram of ITCDIC (Y1 is overhead product
purity，X is bottom product purity。V is vapor flow rate。L is liq-
uid flow rate。F is feed flow rate and Zf is feed composition)．
Although internal heat integration of SRV
method has great potential of energy saving，it also
leads to complex dynamic behavior． which poses a
great challenge for control design，Very few papers
consider the dynamics and control of different purities
and operation conditions of ITCDIC． Pervious re．
search work about ITCDIC focused mainly on mode
ate~purity system．Huang proposed internal model
control(IMC)and Liu_o presented decentralized PID
control for the moderate system ． However， both
schemes are unable to provide satisfactory control per—
formance for high—and very high—purity systems．De—
spite a large economic incent
ive from high—and very
high-purity products[ 一 。。
．
highly complex and dis—
tinct dynamic behavior makes designing effective con—
trol schemes more difficult for high—and very high—
purity 1TCDIC。which considerably 1imits the practi—
cal application of ITCDIC in the chemical process．
This study first investigates the complex open
loop dynamic behavior of ITCDIC with four different
purities including low一， moderate一， high—and very
high，purities．To obtain some insight into the dynam—
ic difficulties associated with designing appropriate
control schemes for different purities， some distinct
dynamic behavior leading to severe mismatch between
linear model and plant is further studied，In addition，
the effects of increased purity on dynamic behavior and
heat integration are descr
ibed and analyzed in detail．
1 Systems studied
Four distillation columns with different product
purities and different operation conditions are stud—
ied．Besides，a binary mixture， benzene—toluene， is
exploited as an illustrative example，The detailed op—
crating conditions are shown in Table 1．The follow—
ing simulations are based on the dynamic model pro—
posed by Liu in 2000 L ， consisting of energy bal—
anees，material balances and vapor—liquid equilibrium．
ID addition，the pressure difference between the recti—
fying and the stripping sections， P 一P ， and feed
thermal condition， q， are selected as manipulated
variables to control the overhead and bottom product
composition
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