Process Operability Class Materials
Process Efficiency
Basic flowsheet
LAH
LAL
Design with Operability
L
2
LC
1
LC
1
FC
1
FC
1
TC
2
TC
1
F
4
fuel
T
10
T
12
T
13
Copyright © Thomas Marlin 2013
The copyright holder provides a royalty-free license for use of this material at non-profit
educational institutions
T
11
Key Operability
issues
PROCESS OPERABILITY: EFFICIENCY
1. Operating
window
2. Flexibility/
controllability
3. Reliability
4. Safety &
equipment
protection
In this Lesson, we will learn
• The objective and degrees of freedom
• Improvement through equipment selection
- Pump/fluid flow
• Improvement through equipment utilization
5. Efficiency &
profitability
6. Operation
during
transitions
- Pump/driver, boiler
• Improvement through process structure
- Ethylene plant, packed bed chemical reactor
7. Dynamic
Performance
8. Monitoring &
diagnosis
• Improvement through operating conditions
- Fired heater/reactor, Flash, CSTR
Key Operability
issues
Degrees of
freedom
EFFICIENCY
1. Operating
window
2. Flexibility/
controllability
3. Reliability
4. Safety &
equipment
protection
5. Efficiency &
profitability
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
Efficiency: We will use this term to imply good
economic performance, which can result from
improved product quality, increased product rate,
lower raw material, effluent and energy consumption,
or other improvements.
Others might say “optimization”.
•
Increase: profit = sales – feed – fuel – electricity - …
•
Reduce effluents (e.g., total SO2, particulates, etc.)
•
Reduce greenhouse gases
•
Reduce use of feed (natural resources)
Key Operability
issues
Degrees of
freedom
EFFICIENCY
1. Operating
window
1. Safety
2. Flexibility/
controllability
2. Environmental
Protection
3. Reliability
3. Equipment
protection
4. Safety &
equipment
protection
5. Efficiency &
profitability
4. Smooth operation
production rate
Let’s recall that these objectives have higher
priority. They must be achieved; then, we
seek to increase profit.
5. Product quality
6. High profit
7. Monitoring &
diagnosis
Additional flexibility is required for
increased efficiency & optimization
6. Operation
during
transitions


7. Dynamic
Performance

8. Monitoring &
diagnosis



Objectives
1-5
Profit/
Efficiency
Key Operability
issues
Equipment
capacities
EFFICIENCY
1. Operating
window
2. Flexibility/
controllability
3. Reliability
Approach 1: Design with the appropriate
equipment capacities.
Recall the general tradeoffs in sizing process
equipment.
4. Safety &
equipment
protection
Small
equipment
5. Efficiency &
profitability
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
Advantages
Disadvantages
Large
equipment
I can complete
and check with
answers in
Operating
Window topic.
Key Operability
issues
Equipment
capacities
EFFICIENCY
1. Operating
window
2. Flexibility/
controllability
3. Reliability
4. Safety &
equipment
protection
Efficiency through equipment capacity: Equipment
with excessive capacity can operate at lower
efficiencies.
Constant
speed
centrifugal
pump
5. Efficiency &
profitability
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
Let’s purchase a really large centrifugal pump for
this application. What do you recommend?
Key Operability
issues
Equipment
capacities
EFFICIENCY
1. Operating
window
Efficiency through equipment capacity:
2. Flexibility/
controllability
3. Reliability
4. Safety &
equipment
protection
Constant
speed
centrifugal
pump
Pump head curve
5. Efficiency &
profitability
Steady-state flow rate
at given conditions
head
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
“system” curve,
pressure drop vs flow
rate
Flow rate
Key Operability
issues
Equipment
capacities
EFFICIENCY
1. Operating
window
Efficiency through equipment capacity:
2. Flexibility/
controllability
Constant
speed
centrifugal
pump
3. Reliability
4. Safety &
equipment
protection
5. Efficiency &
profitability
Do not
oversize
pumps!
head
6. Operation
during
transitions
To achieve the desired flow, we
compensate for the larger pump
by causing a large pressure drop
across a valve .
Too large a pump wastes energy.
7. Dynamic
Performance
8. Monitoring &
diagnosis
Flow rate
Key Operability
issues
Equipment
capacities
EFFICIENCY
1. Operating
window
Efficiency through equipment capacity:
2. Flexibility/
controllability
Most likely
flow rate
3. Reliability
•
head
4. Safety &
equipment
protection
•
5. Efficiency &
profitability
6. Operation
during
transitions
7. Dynamic
Performance
Provide sufficient flow for
the maximum demand
Operate near its maximum
efficiency at the most likely
(design) flow rate
Flow rate
The control valve affects the system (blue) curve
•
8. Monitoring &
diagnosis
The constant speed centrifugal
pump (red curve) is
selected to
Usually about 70% open at design (but, must provide
maximum flow rate)
Key Operability
issues
Equipment
capacities
EFFICIENCY
1. Operating
window
2. Flexibility/
controllability
3. Reliability
4. Safety &
equipment
protection
Follow-up Point #1 - Efficiency through equipment
capacity:
Constant
speed
centrifugal
pump
5. Efficiency &
profitability
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
Do we always install a control
valve? If not, why?
Key Operability
issues
Equipment
capacities
EFFICIENCY
1. Operating
window
2. Flexibility/
controllability
Follow-up Point #1 - Efficiency through equipment
capacity:
No control valve
resistance
3. Reliability
head
4. Safety &
equipment
protection
The constant speed centrifugal
pump (red curve)
The flow is the maximum for
the system, pump and piping
design.
5. Efficiency &
profitability
6. Operation
during
transitions
Flow rate
7. Dynamic
Performance
When the optimum flow rate is always the maximum flow, we
do not use a control valve.
8. Monitoring &
diagnosis
Example, cooling water utility in a chemical plant.
Key Operability
issues
Equipment
capacities
EFFICIENCY
1. Operating
window
2. Flexibility/
controllability
3. Reliability
4. Safety &
equipment
protection
Follow-up Point #2 - Efficiency through equipment
capacity:
Constant
speed
centrifugal
pump
5. Efficiency &
profitability
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
Do we always install a constant
speed pump? If not, why?
Key Operability
issues
Equipment
capacities
EFFICIENCY
1. Operating
window
2. Flexibility/
controllability
Follow-up Point #2 - Efficiency through equipment
capacity: More flexible equipment can save energy at
the expense of higher capital costs.
3. Reliability
4. Safety &
equipment
protection
5. Efficiency &
profitability
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
An alternate design uses a variable speed source of power
(motor or turbine). (The control valve is not needed.)
This design is more energy efficient and may be the best
economically (e.g., lowest NPV).
Key Operability
issues
Equipment
capacities
EFFICIENCY
1. Operating
window
2. Flexibility/
controllability
3. Reliability
4. Safety &
equipment
protection
Follow-up Point #3 - Efficiency through equipment
capacity:
Constant
speed
centrifugal
pump
5. Efficiency &
profitability
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
What is the best pipe diameter?
(Best = trade-off of capital and
operating costs)
Key Operability
issues
Equipment
capacities
EFFICIENCY
1. Operating
window
2. Flexibility/
controllability
Follow-up Point #3 - Efficiency through equipment
capacity: A larger pipe diameter reduces pump work
but increases piping costs.
3. Reliability
4. Safety &
equipment
protection
5. Efficiency &
profitability
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
Pipe diameter “rules of thumb” (guidelines, Woods, 1995)
•
Pumped liquid - velocity of 1 m/s
•
Vapor - velocity of
20-30 m/s
See Woods (1995) for correlations for many systems and fluids
Key Operability
issues
Equipment
utilization
EFFICIENCY
1. Operating
window
2. Flexibility/
controllability
3. Reliability
4. Safety &
equipment
protection
5. Efficiency &
profitability
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
Approach 2: Use existing equipment in most
efficient manner.
We provide extra equipment to
•
Increase reliability
•
Expand the operating window
•
Increase flexibility
•
To capitalize on optimization opportunities
Key Operability
issues
Equipment
utilization
EFFICIENCY
1. Operating
window
2. Flexibility/
controllability
3. Reliability
4. Safety &
equipment
protection
Efficiency through equipment utilization: We can use
the lowest cost from parallel equipment.
Decision is usually made and
implemented by a plant
operator
electricity
motor
5. Efficiency &
profitability
steam
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
turbine
Pumps with different
power sources
Depending on the time of day and the steam usage elsewhere in
the plant, the lowest cost source of work can change! We have
the flexibility to respond.
Key Operability
issues
1. Operating
window
2. Flexibility/
controllability
3. Reliability
Equipment
utilization
EFFICIENCY
Efficiency through equipment utilization: The total
demand of steam must be satisfied. The steam can be
produced in boilers with different efficiencies. We can
optimize.
PC
4. Safety &
equipment
protection
5. Efficiency &
profitability
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
PY
x
PY
x
PY
x
PY
x
We adjust the ratios to lower fuel cost; fast pressure control not affected.
Key Operability
issues
1. Operating
window
2. Flexibility/
controllability
3. Reliability
4. Safety &
equipment
protection
Equipment
utilization
EFFICIENCY
Efficiency through equipment utilization: Several
boilers provide increased reliability. Also, they allow
boilers to be operated near their maximum
efficiencies, compared with one large boiler, as the
total steam demand changes.
88.00
5. Efficiency &
profitability
efficiency
87.00
86.00
boiler 1
85.00
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
boiler 2
84.00
83.00
boiler 3
82.00
boiler 4
81.00
80.00
0.00
0.20
0.40
0.60
steam production
0.80
1.00
Key Operability
issues
1. Operating
window
2. Flexibility/
controllability
3. Reliability
4. Safety &
equipment
protection
5. Efficiency &
profitability
6. Operation
during
transitions
Equipment
utilization
EFFICIENCY
Efficiency through equipment utilization
We must satisfy the plant demand. How much steam
from each boiler (i = 1,4)?
Minimize total fuel = (fuel)i
when
(Steam)i = Demand
 (fuel)i = (Steami*Hvap)/(Hcombust * i)
i = f(Steami)
7. Dynamic
Performance
8. Monitoring &
diagnosis
We will learn how to formulate and solve this type of
problem in 4G03.
Key Operability
issues
Equipment
synthesis
EFFICIENCY
1. Operating
window
2. Flexibility/
controllability
Approach 3: We can increase efficiency by
designing the best process structure (synthesis).
3. Reliability
We provide extra equipment to
4. Safety &
equipment
protection
5. Efficiency &
profitability
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
•
Recover & recycle unconverted feed
•
Recover & recycle solvent
•
Recover & reuse effluents (e.g., water)
•
Use heating (cooling) far from ambient
•
Thorough economic analysis is required to find
the best investment of capital and operating
costs
Equipment
synthesis
EFFICIENCY
Propose a process structure change to increase efficiency/profit
RXN
COMP
Hydrogen,
ethylene
Naphtha
feed
DIST
naphtha
0
REFRIG
0
0
ethane
Ethane
feed
FRACT
propylene
butadiene
……..
Products: Hydrogen to gasoline
methane
Equipment
synthesis
EFFICIENCY
Propose a process structure change to increase efficiency/profit
Recycle unconverted ethane to reactors
RXN
COMP
Hydrogen,
ethylene
Naphtha
feed
DIST
naphtha
0
REFRIG
0
0
ethane
Ethane
feed
FRACT
propylene
butadiene
……..
Products: Hydrogen to gasoline
methane
Key Operability
issues
1. Operating
window
Equipment
synthesis
EFFICIENCY
Efficiency through process structure:.
2. Flexibility/
controllability
3. Reliability
FC
1
4. Safety &
equipment
protection
heat
Cold feed
5. Efficiency &
profitability
Discuss this
packed bed
reactor with an
exothermic
reaction.
Steam
6. Operation
during
transitions
cool
7. Dynamic
Performance
Hot effluent
CW
8. Monitoring &
diagnosis
Is this the best
design? What
alternative(s)
would you
evaluate?
Key Operability
issues
1. Operating
window
2. Flexibility/
controllability
3. Reliability
4. Safety &
equipment
protection
5. Efficiency &
profitability
Equipment
synthesis
EFFICIENCY
Efficiency through process structure: We want to use
raw materials and “energy” (material significantly
hotter or colder than ambient). One typical
structure involves recycle.
Cold product
FC
1
Cold
feed
6. Operation
during
transitions
• Advantages
• Disadvantages
7. Dynamic
Performance
8. Monitoring &
diagnosis
Discuss this
packed bed
reactor with an
exothermic
reaction.
The reactor
effluent is hot.
Hot effluent
Key Operability
issues
1. Operating
window
2. Flexibility/
controllability
3. Reliability
Equipment
synthesis
EFFICIENCY
Efficiency through process structure: One typical
structure involves recycle.
FC
1
Advantages
4. Safety &
equipment
protection
5. Efficiency &
profitability
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
Disadvantages?
Key Operability
issues
1. Operating
window
2. Flexibility/
controllability
3. Reliability
4. Safety &
equipment
protection
5. Efficiency &
profitability
6. Operation
during
transitions
Equipment
synthesis
EFFICIENCY
Efficiency through process structure: One typical
structure involves recycle.
FC
1
Advantages
• Good energy efficiency
(exhaust to environment closer to ambient)
Disadvantages?
• Cannot startup the process (need heating)
• No flexibility for changing operation
7. Dynamic
Performance
8. Monitoring &
diagnosis
• Poor dynamics (see section of dynamic
performance)
I suspect that
we are not
through with
this exercise!
Key Operability
issues
Operating
Conditions
EFFICIENCY
1. Operating
window
2. Flexibility/
controllability
3. Reliability
4. Safety &
equipment
protection
5. Efficiency &
profitability
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
Approach 4: We can increase efficiency by selecting
the best values of operating conditions.
Many conditions can be changed in the process that
do not affect safety …. product quality, but they
affect profit, e.g.,
• Recycle compositions
• Conversion in a chemical reactor
• Intermediate separation
• The best values can change from day to day
• Thorough economic analysis is required to find
the best (optimum) conditions
Key Operability
issues
Operating
Conditions
EFFICIENCY
1. Operating
window
2. Flexibility/
controllability
Goal: Maximize conversion of feed ethane but
do not exceed 864C
3. Reliability
4. Safety &
equipment
protection
5. Efficiency &
profitability
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
What is the best value of the reactor
temperature?
Key Operability
issues
1. Operating
window
Operating
Conditions
EFFICIENCY
“Constraint Control” to push against the constraint: Operate
as close to 864 as is possible, given typical variability
2. Flexibility/
controllability
3. Reliability
4. Safety &
equipment
protection
5. Efficiency &
profitability
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
Goal: Maximize
conversion of feed
ethane but do not
exceed 864C
Key Operability
issues
1. Operating
window
2. Flexibility/
controllability
3. Reliability
Operating
Conditions
EFFICIENCY
Efficiency through operating conditions: In many
conditions, product can be made efficiently or
inefficiently by changing process variable values
within the operating window.
T6
4. Safety &
equipment
protection
5. Efficiency &
profitability
T1
T2
F1
T4
Feed
8. Monitoring &
diagnosis
F2
Process
fluid
Vapor
product
How do I
decrease
energy
cost?
T5
T3
6. Operation
during
transitions
7. Dynamic
Performance
P1
L1
F3
Steam
AC
L. Key
Liquid
product
Key Operability
issues
1. Operating
window
2. Flexibility/
controllability
3. Reliability
Operating
Conditions
EFFICIENCY
Efficiency through operating conditions: In many
conditions, product can be made efficiently or
inefficiently by changes process variable values
within the operating window.
T6
4. Safety &
equipment
protection
5. Efficiency &
profitability
T1
T2
F1
T4
8. Monitoring &
diagnosis
Vapor
product
Use the least
costly heating
T5
Feed
T3
6. Operation
during
transitions
7. Dynamic
Performance
P1
F2
Process
fluid
L1
F3
Steam
AC
L. Key
Liquid
product
Key Operability
issues
1. Operating
window
2. Flexibility/
controllability
3. Reliability
Operating
Conditions
EFFICIENCY
Efficiency through operating conditions: In many
conditions, product can be made efficiently or
inefficiently by changing process variable values
within the operating window.
TABLE OF COMPONENT DATA
flow value
4. Safety &
equipment
protection
Reformate
LSR-Naptha
n-Butane
FCC Gasoline
Alkylate
5. Efficiency &
profitability
Octane
(Oct. no.)
5424.5319
792.95813
282.50996
0
0
91.8
64.5
92.5
78
96.5
RVP
(psi)
4
12
138
6
7
Vol
(%)
Flow max Flow min
(Bl/day) (Bl/day)
17
85
115
22
30
6000
850
350
3000
3000
0
0
250
0
0
Cost
($/BL)
33
27
12
32
38.5
Reformate
FC
6. Operation
during
transitions
LSR Naphtha
FC
Blend these
components
AT
N-Butane
To meet product
specifications
Final Blend
FC
FT
FCC Gas
FC
Alkylate
7. Dynamic
Performance
FC
Flow setpoints
TABLE OF PRODUCT DATA
8. Monitoring &
diagnosis
Regular product
flow
(Bl/day)
6500
Oct. min Oct Max
(Oct. no.)
88.5
100
RVP min RVP max
(psi)
4.5
10.8
Vol min
(%)
0
Vol max Flow max Flow min
(Bl/day)
30
6500
6500
value
($/Bl)
33.5
Key Operability
issues
1. Operating
window
2. Flexibility/
controllability
3. Reliability
4. Safety &
equipment
protection
Operating
Conditions
EFFICIENCY
Efficiency through operating conditions: In many
conditions, product can be made efficiently or
inefficiently by changing process variable values
within the operating window.
Best
Feed
flow rate
How
much
H2
recycle?
5. Efficiency &
profitability
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
hydrogen
gas
feed
Best
reactor
T
reformate
Key Operability
issues
1. Operating
window
2. Flexibility/
controllability
Operating
Conditions
EFFICIENCY
Efficiency calculations can be automated when conditions
change frequently.
3. Reliability
Model
Model Updating
Optimizer
4. Safety &
equipment
protection
Model parameters
Results analysis
5. Efficiency &
profitability
6. Operation
during
transitions
7. Dynamic
Performance
Data Evaluation
This is
basically
HYSIS run
many times
to obtain the
optimum
answer*
Advanced control
measurements
Model
predictive
control
plant operations
8. Monitoring &
diagnosis
PLANT, SENSORS, REGULATORY CONTROL
* Solution
approaches
covered in 4G03
Operating
Conditions
SUNOCO OPTIMIZER RELIABLY SOLVES LARGE
SYSTEMS AND EARNS SUBSTANTIAL BENEFITS
Smithsonian Award-winning application in Sarnia by SUNCOR
Key Operability
issues
EFFICIENCY
1. Operating
window
2. Flexibility/
controllability
3. Reliability
INDUSTRIAL PRACTICE
• Since we have an operating window, flexibility
exists to optimize efficiency
4. Safety &
equipment
protection
• Sometimes we use mathematical models for
optimization (see 4G03 next semester)
5. Efficiency &
profitability
• Sometimes we use plant experiments to optimize
(see 4C03 next semester)
6. Operation
during
transitions
7. Dynamic
Performance
8. Monitoring &
diagnosis
• Optimization can interact with other goals, such
as consistent product quality. Therefore, we
optimize slowly to prevent disturbing the
processes.
Key Operability
issues
EFFICIENCY
1. Operating
window
2. Flexibility/
controllability
3. Reliability
4. Safety &
equipment
protection
In this Lesson, we will learn
• The objective and degrees of freedom
• Improvement through equipment selection
- Pump/fluid flow
• Improvement through equipment utilization
5. Efficiency &
profitability
6. Operation
during
transitions
- Pump/driver, boiler
• Improvement through process structure
- Ethylene plant, packed bed chemical reactor
7. Dynamic
Performance
8. Monitoring &
diagnosis
• Improvement through operating conditions
- Fired heater/reactor, Flash, CSTR