A1258607680RZGWh

1
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

2
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.

3
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
4
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
5
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
6
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.
Bottom tray
Thermsiphon reboiler
Bottoms product
From Lieberman, N.L., Process Design for
Reliable Operations, Gulf Publishing, Houston,
1983
7
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
8
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
9
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. Lets 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
10
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.)

11
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

12
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.

13
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?
Or, must we shutdown the entire plant when
regenerating an individual unit?
14
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
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
15
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
Ethane
C2H6
C2H4
Propane
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?

16
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
1000
980
960
Temperature (C)
940
920
900
880
860
0
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?

17
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?
18
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.
19
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.
20
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
21
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

22
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.
23
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).
Boilers
High pressure
Medium pressure
Low pressure
Liquid
24
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?

25
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
26
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).
High pressure
What is the correct response when this consumer
requires more steam?
Medium pressure
Low pressure
Liquid
27
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.
28
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?

29
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 dont. We must respond rapidly!
30
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,

31
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
32
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
33
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
34
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.
35
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
Final Blend
N-Butane
FT
FC
FCC Gas

Premium
FC
Alkylate
Final Blend
FC
Many different customers
Manufactured continuously
One blending process
http//www.mcscbahrain.com/projects.htm
36
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

1. Determine the best (optimal) transient behavior

2. Achieve good process control over a wide
range for a non-linear process
37
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