chemical engineering 3p04 process control tutorial # 11 learning goals
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Chemical Engineering 3P04 Process Control Tutorial # 11 Learning goals Level Control – Getting stuff through the plant Multiloop control – Controlling several variables at the same time. F 0. Feed. F 1. F 2. F 3. LC. LC. LC. Level Control – Getting stuff through the plant. - PowerPoint PPT PresentationTRANSCRIPT
Chemical Engineering 3P04
Process Control
Tutorial # 11
Learning goals
1. Level Control – Getting stuff through the plant
2. Multiloop control – Controlling several variables at the same time
The textbook introduces “feed push” and “product pull” level control designs. In this example, you will design a system that holds F2 very close to a constant value and controls all levels. You will achieve the design goals with feedback control only.
Level Control – Getting stuff through the plant
F0
LC LC LC
F1 F2 F3
Feed
Level Control – Getting stuff through the plant
F0
LC LC LC
F1 FC2 F3
Feed
The textbook introduces “feed push” and “product pull” level control designs. In this example, you will design a system that holds F2 very close to a constant value and controls all levels. You will achieve the design goals with feedback control only.
18.2 A process with two distillation towers is shown in Figure 18.2.
a. Identify all liquid inventory in the process.
b. Discuss advantages and disadvantages for each of the inventories.
c. Critique the type of level control, i.e., which variable is adjusted to control the level, for each inventory. If not acceptable, sketch changes and explain.
d. For every inventory, provide a recommended liquid volume and explain your recommendation.
Extension to Tutorial Question 18.2
a. Locate all vapor inventories in the process.
b. What type of process variable is measured and controlled to maintain the total vapor inventory constant?
c. For each vapor inventory identified in part (a), critique the type of control, i.e., which variable is manipulated by each controller. If not acceptable, sketch changes and explain.
d. Are these controllers feedback or feedforward?
Level Control – Getting stuff through the plant
Let’s do interactive Learning Module exercises
18.218.618.1318.14
Feed
Vaporproduct
LiquidproductProcess
fluidSteam
F1
F2 F3
T1 T2
T3
T5
T4
T6 P1
L1
A1
L. Key
Multiloop control – Controlling several variables at the same
time
CONTROLLABILITY
A system is controllable if its CVs can be maintained at their set points, in the steady-state, in spite of disturbances
entering the system.
DK
K
MV
MV
KK
KK
CV
CV
d
d
2
1
2
1
2221
1211
2
1
0
0Model for 2x2 system
Multiloop control – Controlling several variables at the same
time
What is required?
CONTROLLABILITY
A system is controllable if its CVs can be maintained at their set points, in the steady-state, in spite of disturbances
entering the system.
A system is controllable when the matrix of process gains can be inverted, i.e., when the determinant of K 0.
DK
K
MV
MV
KK
KK
CV
CV
d
d
2
1
2
1
2221
1211
2
1
0
0Model for 2x2 system
Multiloop control – Controlling several variables at the same
time
Let’s do interactive Learning Module exercises
20.1420.1520.1620.17
Multiloop control – Controlling several variables at the same
time
Multiloop control – Controlling several variables at the same
time
Feed
MethaneEthane (LK)PropaneButanePentane
Vaporproduct
Liquidproduct
Processfluid
Steam
FC-1
F2 F3
T1 T2
T3
T5
TC-6 PC-1
LC-1
AC-1
L. Key (ethane)
PAH
LALLAH
Please critique the design for the flash
drum.
Multiloop control – Controlling several variables at the same
time• Can we control the CVs with the valvesshown, i.e., is the system controllable?
5
4
3
2
1
0265.179.31.136.0113.
36.5039.180.6567.
043.044.11.00917.
19.044.85.0708.
000.200
/
1
16
1
v
v
v
v
v
dtdL
P
AT
F
The effects of v1 and v2 on steady-state gains are identical, within a constant multiplier. Therefore, the five CVs cannot be independently affected by the five valves.
Det [KP] = 10-7 0
Multiloop control – Controlling several variables at the same
time
Let’s select:
F1 production rate
T6 feed vaporization
A1 product quality
P safety
L liquid to pump
T6v2
v1
T2
A1
P1
sL1
Both v1 and v2 affect all CVs of interest through T6. This is a contraction that reduces the controllability.
Boxes are cause-effect relationships (or transfer functions)
Not a CV!
Feed
MethaneEthane (LK)PropaneButanePentane
Vaporproduct
Liquidproduct
Processfluid
Steam
FC-1
F2 F3
T1 T2
T3
T5
TC-6 PC-1
LC-1
AC-1
L. Key
Split rangePAH
LALLAH
cascade
Multiloop control – Controlling several variables at the same
timeThis is a good design for the flash drum.
TC
FC
Product
Coolant
LC
Coolant effluent
FC
TC
Feed
Multiloop control – Controlling several variables at the same
time
Please critique the design for the
chemical reactor.
TC
FC
Product
Coolant
LC
Coolant effluent
FC
TC
Feed
Multiloop control – Controlling several variables at the same
time
Do not control the same variable with two
feedback controllers (at the same set point
values).