1. Process Operability Class Materials
Operation during Transitions
Basic flowsheet
Design with Operability FC 1 LC
Copyright © Thomas Marlin 2013
The copyright holder provides a royalty-free license for use of this material at non-profit educational institutions

2. OPERATION DURING TRANSITIONS
Key Operability issues
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
OPERATION DURING TRANSITIONS
We will learn about operation during transitions
Transitions involve planned transient behavior between different initial and final conditions.
Continuous processes
Startup and shutdown
Regeneration
Blocked operation
Load following
Batch Processes
No steady-state operation

3. OPERATION DURING TRANSITIONS
Key Operability issues
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
SU & Shutdown
OPERATION DURING TRANSITIONS
STARTUP AND SHUTDOWN
Special equipment and procedures are required for starting and stopping process operations.
These are when most accidents and serious hazards occur - be very thorough in planning and training
Need to load material during startup and drain material for shutdown.
Need to heat and/or cool to approach normal process conditions or return to ambient.

4. OPERATION DURING TRANSITIONS
Key Operability issues
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
SU & Shutdown
OPERATION DURING TRANSITIONS
STARTUP AND SHUTDOWN
Equipment and process structure: Identify extra equipment needed for startup of the reactor.
Cold product
Cold feed
Hot effluent

5. OPERATION DURING TRANSITIONS
Key Operability issues
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
SU & Shutdown
OPERATION DURING TRANSITIONS
STARTUP AND SHUTDOWN
Equipment and process structure: Identify extra equipment needed for startup of the reactor.
Cold product
Is the
design
complete?
Cold feed
Heating fluid
Need heating when the reactor effluent is cold.
Hot effluent

6. OPERATION DURING TRANSITIONS
Key Operability issues
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
SU & Shutdown
OPERATION DURING TRANSITIONS
STARTUP AND SHUTDOWN
Equipment: Identify extra equipment needed for startup of the distillation column reboiler.
Bottom tray
Thermsiphon reboiler
Bottoms product

7. OPERATION DURING TRANSITIONS
Key Operability issues
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
SU & Shutdown
OPERATION DURING TRANSITIONS
STARTUP AND SHUTDOWN
Identify extra equipment needed for startup of the distillation column reboiler.
Before reboiler is functioning, no vapor flows, liquid weeps through trays
Bottom tray
Thermsiphon reboiler
Valve is normally closed, opened only during startup
Bottoms product
From: Lieberman, N.L., Process Design for Reliable Operations, Gulf Publishing, Houston, 1983

8. OPERATION DURING TRANSITIONS
Key Operability issues
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
SU & Shutdown
OPERATION DURING TRANSITIONS
STARTUP AND SHUTDOWN
Process flow: Occasionally, equipment must be shutdown for preventative maintenance and modifications. What is needed?
Unit B
Unit A

9. OPERATION DURING TRANSITIONS
Key Operability issues
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
SU & Shutdown
OPERATION DURING TRANSITIONS
STARTUP AND SHUTDOWN
Process flow: Occasionally, equipment must be shutdown for preventative maintenance and modifications. What is needed?
Discuss advantages
and disadvantages.
How big is the tank?
Cooling
Storage
Pumping
Heating
Unit B
Unit A

10. OPERATION DURING TRANSITIONS
Key Operability issues
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
SU & Shutdown
OPERATION DURING TRANSITIONS
STARTUP AND SHUTDOWN
Process flow: Occasionally, equipment must be shutdown for preventative maintenance and modifications. What is needed?
Cooling and subsequent
heating and cooling
is inefficient.
Let’s by-pass the tank
when possible.
The tank must have a holdup time (V/F) equal to at least the unit shutdown time.
The inventory can be adjusted just before the shutdown.
Cooling
Storage
Pumping
Heating
Unit B
Unit A

11. OPERATION DURING TRANSITIONS
Key Operability issues
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
SU & Shutdown
OPERATION DURING TRANSITIONS
STARTUP AND SHUTDOWN
INDUSTRIAL PRACTICE
The first step is to prepare a detailed startup (shutdown) procedure.
Then, we check the availability of the appropriate equipment to perform the procedure
This is very detailed work and requires considerable experience in plant operation and plant equipment
(Talk with operators and shift supervisors.)

12. OPERATION DURING TRANSITIONS
Key Operability issues
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
Regeneration
OPERATION DURING TRANSITIONS
REGENERATION
Catalyst, adsorbents, fouled surfaces and some other equipment require periodic regeneration. This can involve different materials flowing through the process and even in opposite directions. The switching period varies from hours to months.
Example of regeneration include the following.
Catalyst that loses activity
Adsorbent that has active sites filled
Equipment that has surface coated due to coke (reactor) or polymer (e.g. reboiler)
Filtration that must be backflushed

13. OPERATION DURING TRANSITIONS
Key Operability issues
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
Regeneration
OPERATION DURING TRANSITIONS
REGENERATION
Regeneration involves different operating conditions that can challenge equipment or be hazardous
Different feeds
Exothermic reactions
Different operating conditions
Different downstream processing
Hazards, such as introducing oxygen into an environment that normally contains hydrocarbons
Special transition issues can involve corrosion, contamination, hygiene, toxicology, etc.

14. OPERATION DURING TRANSITIONS
Key Operability issues
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
Regeneration
OPERATION DURING TRANSITIONS
REGENERATION
What is an important factor in defining the structure for continuous processes with regeneration?
How can we best maintain the continuous process operation?
Parallel equipment with isolation valves
Single equipment with sufficient storage
Or, must we shutdown the entire plant when regenerating an individual unit?

15. OPERATION DURING TRANSITIONS
Key Operability issues
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
Regeneration
OPERATION DURING TRANSITIONS
REGENERATION
Example of Olefins plant
C5+
C2H6
C2H4
C3H6
C4H10
Ethane
Propane
Gas oil
Feed stocks
Separation system
Fired heaters
The operation of the heaters (reactor feed type, feed rate, temp, steam) influence the rate of coke and need for regeneration.
Coke buildup: Requires periodic shutdown/decoke

16. OPERATION DURING TRANSITIONS
Key Operability issues
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
Regeneration
OPERATION DURING TRANSITIONS
REGENERATION
Example of Olefins plant
Air and steam X
Exhaust safely X
Ethane
C2H6
Propane
C2H4
C3H6
Gas oil
C5+
C4H10
Feed stocks
Separation system
Fired heaters
What happens when one furnace temporarily stops production for decoking (with air and steam)?
Which of previous strategies is employed (parallel or storage)?
Might significant hazards occur during decoking?

17. OPERATION DURING TRANSITIONS
Key Operability issues
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
Regeneration
OPERATION DURING TRANSITIONS
REGENERATION
Tube Wall Temperature : Reactor 2
1040
1020
= decoke
1000
980
960
Temperature (C)
940
920
900
880
860 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
Time slots (3 days each)
Example trend for one furnace
What affects the slope of temperature vs. time?
What happened at days 45 and 97?
How do we select the best operations?

18. OPERATION DURING TRANSITIONS
Key Operability issues
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
Regeneration
OPERATION DURING TRANSITIONS
REGENERATION
Example – heat exchanger is fouled and must be cleaned.
Process fluids
Process fluid
What equipment is required to be able to take this exchanger out of service for cleaning or repair?

19. OPERATION DURING TRANSITIONS
Key Operability issues
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
Regeneration
OPERATION DURING TRANSITIONS
REGENERATION
Example – heat exchanger is fouled and must be cleaned.
Process fluids
Process fluid
Since both streams are process fluids, by-passes on each are required. If one were a utility (e.g., water or steam), no by-pass on the utility stream would be required.

20. OPERATION DURING TRANSITIONS
Key Operability issues
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
Blocked operation
OPERATION DURING TRANSITIONS
BLOCKED OPERATION
“Blocked operation” involves short periods of continuous, steady-state operation with frequent switches. This policy is required when many products are produced using the same equipment.
Usually, the material produced during the transition has lower value, or in some cases, zero value. Thus, transitions should be expedited.
To satisfy customer demands, product must be stored since no one product is produced continuously at all times.

21. OPERATION DURING TRANSITIONS BLOCKED OPERATION- Lube Oil Manufacture
Key Operability issues
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
Blocked operation
OPERATION DURING TRANSITIONS
BLOCKED OPERATION- Lube Oil Manufacture
Only one “base stock” manufactured at a time
Subsequent processing
Solvent
Solvent recovery and by-product processing
Only one “base stock” processed at a time; switch about every two days

22. OPERATION DURING TRANSITIONS
Key Operability issues
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
Blocked operation
OPERATION DURING TRANSITIONS
BLOCKED OPERATION
Process issues related to blocked operation.
Reduce production rate and mixing during transition
Recycle “mixed” material during transition or store for later re-processing
Transitions from/to some operations are not possible (two phase become miscible, hazardous intermediate state, intermediate product has very low or negative value, etc.)
Desire very fast transition – fast process dynamics with “strong” manipulated variables

23. OPERATION DURING TRANSITIONS
Key Operability issues
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
Load following
OPERATION DURING TRANSITIONS
LOAD FOLLOWING
Some parts of a plant produce material that is required for production elsewhere, and the other section(s) of the plant determine their needs independently. The supplier must satisfy the demands.
Typical utilities are steam, nitrogen, oxygen, hydrogen, (processed) water.
Also, some process materials are manufactured for the process and processed without storage, often to reduce hazards.
Often, many consumers are in simultaneous operation and have time-varying demands. The produce must “follow the load” or demand in a timely manner.

24. OPERATION DURING TRANSITIONS LOAD FOLLOWING – BOILER & STEAM SYSTEM
Key Operability issues
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
Load following
OPERATION DURING TRANSITIONS
LOAD FOLLOWING – BOILER & STEAM SYSTEM
A utilities example is shown below, with the fired boilers (B1-B4) and heat integration (producers) providing steam for power (turbines T1-T5) and heating (consumers). B1 B2 B3 B4 HP 1 T2 MP
producer
consumer LP
Cond T3 T1 T4 T5
export 2 3 4 5 8 9 7 10 6 11 12 13 14 15
Fuel
gas
oil
Boilers
High pressure
Medium pressure
Low pressure
Liquid

25. OPERATION DURING TRANSITIONS
Key Operability issues
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
Load following
OPERATION DURING TRANSITIONS
LOAD FOLLOWING
Some issues for load following utilities
Operating Window – Have sufficient capacity to satisfy demand. How do we know the demand?
We could measure every demand, sum them and produce that amount of steam
Bad idea: Never achieve material balance because measurement errors accumulate.
We could measure steam pressure and control it by adjusting steam generation.
Good idea: Simple and effective. No error accumulation.

26. OPERATION DURING TRANSITIONS
Key Operability issues
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
Load following
OPERATION DURING TRANSITIONS
LOAD FOLLOWING PC PY x
We adjust the ratios to lower fuel cost; fast pressure control is not affected.

27. OPERATION DURING TRANSITIONS
Key Operability issues
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
Load following
OPERATION DURING TRANSITIONS
LOAD FOLLOWING
An example is shown below, with the fired boilers (B1-B4) and heat integration (producers) providing steam for power (turbines T1-T5) and heating (consumers). B1 B2 B3 B4 HP 1 T2 MP
producer
consumer LP
Cond T3 T1 T4 T5
export 2 3 4 5 8 9 7 10 6 11 12 13 14 15
Fuel
gas
oil
High pressure
What is the correct response when this consumer requires more steam?
Medium pressure
Low pressure
Liquid

28. OPERATION DURING TRANSITIONS
Key Operability issues
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
Load following
OPERATION DURING TRANSITIONS
LOAD FOLLOWING
Some issues for load following utilities
Reliability – Network to supply any demand from any supplier.
If Boiler 1 fails, are we sure that we can increase the others sufficiently?
Must have spare capacity; all boilers in operation should not be near their maximum steam productions!
We cannot start a “cold” boiler in time to keep plant in operation.
We may have to keep one or more boilers “warm”, even if not producing significant steam.

29. OPERATION DURING TRANSITIONS
Key Operability issues
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
Load following
OPERATION DURING TRANSITIONS
LOAD FOLLOWING
Some issues for load following utilities
Efficiency – Ability to use the most efficient producers as the demand changes
What data do we need to optimize the boiler load?
For each boiler, we need a model relating efficiency to the steam generated (load).

30. OPERATION DURING TRANSITIONS
Key Operability issues
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
Load following
OPERATION DURING TRANSITIONS
LOAD FOLLOWING
Some issues for load following utilities
Transient - May require storage of material for startup
How do we store steam?
We don’t. We must respond rapidly!

31. OPERATION DURING TRANSITIONS
Key Operability issues
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
Batch Operation
OPERATION DURING TRANSITIONS
BATCH OPERATION
Batch operation
Often the most economical method for manufacturing small quantities and very high purities. Is generally too expensive for producing very large quantities of material.
A batch plant usually produces numerous products
Each product is manufactured in a separate “campaign” involving unique feed materials and processing conditions and shared equipment
Food, pharmaceuticals, “fine chemicals”, …

32. OPERATION DURING TRANSITIONS
Key Operability issues
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
Batch Operation
OPERATION DURING TRANSITIONS
BATCH OPERATION
Batch operation: All materials provided at start of the process.
feed
product
time
time
Semi-Batch operation: Some materials introduced after the start of the process.
feed
time
Reaction
initiator
product
time
time

33. OPERATION DURING TRANSITIONS
Key Operability issues
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
Batch Operation
OPERATION DURING TRANSITIONS
BATCH OPERATION
Batch can have very different operating conditions. For example, it can be necessary to heat a reactor in the beginning of the batch and cool it thereafter.
feed
time
product
time
Flow of heat transfer medium
= heating
= cooling
time

34. OPERATION DURING TRANSITIONS
Key Operability issues
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
Batch Operation
OPERATION DURING TRANSITIONS
BATCH OPERATION
Some plants integrate batch and continuous units. The plant must contain storage capacity to allow the continuous parts to operate without frequent shutdowns.
Distillation feed
time
Reactor product
time

35. OPERATION DURING TRANSITIONS ALL SITUATIONS CONSIDERED
Key Operability issues
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
Batch Operation
OPERATION DURING TRANSITIONS
ALL SITUATIONS CONSIDERED
Industrial Practice
The operating conditions change during transients. For what operation do we “size” the equipment?
We must size equipment for the most demanding condition of all operations experienced by the process.
Never use the average operation, especially for these extreme transient operations.
It may be required to have parallel equipment with different capacities when the normal and maximum operations are very different.

36. OPERATION DURING TRANSITIONS BATCH OPERATION – GASOLINE BLENDING
Key Operability issues
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
Batch operation
OPERATION DURING TRANSITIONS
BATCH OPERATION – GASOLINE BLENDING
Intermediate products from process
Products to customers
Reformate
Regular FC
additives
LSR Naphtha FC AT
N-Butane
Final Blend FC FT
FCC Gas •
Premium FC
Alkylate
Final Blend FC
Manufactured continuously
One blending process
Many different customers

37. OPERATION DURING TRANSITIONS ALL SITUATIONS CONSIDERED
Key Operability issues
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
Batch Operation
OPERATION DURING TRANSITIONS
ALL SITUATIONS CONSIDERED
The operating conditions change during transients. The control system must follow the desired path.
Temperature
time
Challenges remain
Determine the best (optimal) transient behavior
2. Achieve good process control over a wide range for a non-linear process

38. OPERATION DURING TRANSITIONS
Key Operability issues
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
OPERATION DURING TRANSITIONS
We will learn about operation during transitions
Transitions involve planned transient behavior between different initial and final conditions.
Continuous processes
Startup and shutdown
Regeneration
Blocked operation
Load following
Batch Processes
No steady-state operation