Process control system

Details Process control system Process control system

2001-03-13

2004-04-20

Khatri, Anil (Department: 2121)

Data processing: generic control systems or specific application

Generic control system, apparatus or process

Optimization or adaptive control

C700S033000, C700S042000, C700S282000, C700S287000, C700S289000, C700S290000

Reexamination Certificate

active

06725103

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process control system, and more particularly to a process control system for realizing the optimal process coordinate control.
2. Description of the Related Art
FIG. 56
shows an example of a conventional process control system which is a multi-input/output control system including a main input provided with an optimal operation decision means.
The conventional example shown in
FIG. 56
will be explained hereunder. A process
5609
to be controlled is composed of a first fuel control valve
5610
, a first boiler
5611
, a control valve
5612
, a turbine
5613
, a generator
5614
, a second fuel control valve
5615
, a second boiler
5616
, and a steam load facility
5617
.
A control system
5600
is composed of an optimization model storage unit
5601
, an optimal operation decision means
5602
, a generator output control means
5605
, a first boiler steam pressure control means
5606
, and a second boiler steam pressure control means
5607
.
The optimal operation decision means
5602
inputs an process data input
5638
inputted from the process
5609
to be controlled and an optimization model
5630
stored in the optimization model storage unit
5601
, and decides an optimal operating point for the process operation. The optimization model
5630
stored in the optimization model storage unit
5601
is expressed by Formula 1. Here, Formula 1 is composed of an objective function formula 1a and constraint function formulas 1b to 1g.
The optimal operation decision means
5602
decides the optimal operating point for the process operation using the optimization model
5630
expressed by Formula 1.
Formula 1
Minimize:
X
1
+X
2
  (1a)
Subject to:
X
1
min≦X
1
≦X
1
max  (1b)
X
2
min≦X
2
≦X
2
max  (1c)
Y
1
+
Y
3
=
L
  (1d)
Y
1
=
a
1
(0)+
a
1
(1)×
X
1
+
a
1
(2)×
X
1
2
  (1e)
Y
2
=
a
2
(0)+
a
2
(1)×
X
1
+
a
2
(2)×
X
1
2
  (1f)
Y
3
=
a
3
(0)+
a
3
(1)×
X
2
+
a
3
(2)×
X
2
2
  (1g)
In Formula 1, X
1
, X
1
min and X
1
max indicate a flow, a minimum flow and a maximum flow of a fuel
5620
of the first boiler
5611
, respectively. X
2
, X
2
min and X
2
max indicate a flow, a minimum flow and a maximum flow of a fuel
5626
of the second boiler
5616
, respectively. Y
3
indicates a steam flow at an outlet
5625
of the second boiler
5616
. Y
1
and Y
2
indicate a steam flow of a turbine exhaust
5623
and a generation output
5635
of the generator
5614
, respectively. L indicates a steam flow
5627
of the steam load facility
5617
. The steam flow
5627
(L) is inputted to the optimal operation decision means
5602
from the process
5609
as a part of the process data input
5638
.
By converting the units of the variables X
1
, X
2
, Y
1
, Y
2
, and Y
3
into the quantity of heat, Efficiencies 1 and 2 are shown below:
Efficiency 1=(
Y
1
+
Y
2
)/
X
1
Efficiency 2
=Y
3
/
X
2
Here, Efficiency 1 indicates an efficiency of the first boiler
5611
, the control valve
5612
, the turbine
5613
, and the generator
5614
, and Efficiency 2 indicates an efficiency of the second boiler
5612
.
Generally, plant devices vary in efficiency with loads, so that Formulas 1e, 1f, and 1g indicate efficiency variations due to such loads. The turbine
5613
is a back-pressure turbine, and a part of the given steam energy is used to drive the generator
5614
for the generation output
5635
, and the remainder (lost energy excluded) is used to supply steam to the steam load facility
5617
.
Among the constraint function Formulas 1b to 1g, Formulas 1e, 1f, and 1g expressing the efficiencies of plant devices are a process operation characteristic function. Here, ai(j); i=1, 2, 3; j=0, 1, 2 indicate process operation characteristic function parameters and are stored in the optimization model storage unit
5601
.
Decision of the optimal operating point means to decide the values of the variables X
1
, X
2
, Y
1
, Y
2
, and Y
3
for minimizing the objective function value expressed by Formula 1a, which meet, for example, the constraint functions expressed by Formulas 1b to 1g.
As a tool for solving an optimization problem expressed by a numerical formula model such as Formula 1, for example, there is “NUOPT-Modeling Language SIMPLE by MATHEMATICAL SYSTEMS, INC.” available.
It is assumed that the values of the variables X
1
, X
2
, Y
1
, Y
2
, and Y
3
decided by the optimal operation decision means
5602
are X
1
*, X
2
*, Y
1
*, Y
2
*, and Y
3
*, respectively. The values X
1
*, X
2
*, Y
1
*, Y
2
*, and Y
3
* indicate the optimal operating point for the process operation. In this example, as shown by Formulas 1d to 1g, when one of the five variables (X
1
, X
2
, Y
1
, Y
2
, and Y
3
) is decided, the residual four variables are decided.
In an example of the prior art, as shown in
FIG. 56
, the optimal operation decision means
5602
decides the optimal value Y
2
* for the variable Y
2
corresponding to the generation output
5635
of the generator
5614
, that is, an optimal generator output
5631
based on Formula 1, and outputs the decided optimal generator output
5631
to the generator output control means
5605
. The generator output control means
5605
outputs a generator output control output
5634
to the control valve
5612
of the turbine
5613
and controls the flow of a steam
5622
at the inlet of the turbine
5613
so that the output
5635
of the generator
5614
becomes equal to the optimal generator output
5631
.
The first boiler steam pressure control means
5606
outputs a first boiler steam pressure control output
5632
to the first fuel control valve
5610
and adjusts a first fuel control valve fuel
5620
, and thereby controls a steam pressure
5633
at an outlet
5621
of the first boiler
5611
so as to be equal to a given pressure set value. The second boiler steam pressure control means
5607
outputs a second boiler steam pressure control output
5636
to the second fuel control valve
5615
and adjusts the second fuel control valve fuel
5626
, and thereby controls a steam pressure
5637
at the outlet
5625
of the second boiler
5616
so as to be equal to a given pressure set value.
In
FIG. 56
, the operations of the control system
5600
and the process
5609
will be explained qualitatively hereunder. The generator output control means
5605
sends up-output (down-output)
5634
to the control valve
5612
in order to increase (decrease) the generator output
5635
so that the generator output
5635
becomes equal to the optimal generator output
5631
.
The up-operation (down-operation) of the control valve
5612
decreases (increases) the steam pressure at the first boiler outlet
5621
. The first boiler steam pressure control means
5606
sends the up-output (down-output)
5632
to the first fuel control valve
5610
so as to increase (decrease) the first fuel control valve fuel
5620
, thereby to increase (decrease) the decreased (increased) steam pressure. Besides, the up-operation (down-operation) of the control valve
5612
increases (decreases) the steam pressure of each of turbine exhaust
5623
, a steam header
5624
, and the second boiler outlet
5625
.
Then, the second boiler steam pressure control means
5607
sends the down-output (up-output)
5636
to the second fuel control valve
5615
so as to decrease (increase) the second fuel control valve fuel
5626
, thereby to decrease (increase) the increased (decreased) steam pressure.
Generally, the steam load facility
5617
requires the steam pressure of the steam header
5624
to be at a predetermined value.
Therefore, as explained above, the control system
5600
controls the steam pressure
5637
at the outlet
5625
of the second boiler
5616
, instead of controlling the steam flow generated by the second boiler
5616
. As a result, the steam load
5627
required by the steam load facility
5617
becomes e

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