Process Operability Class Materials Operation during Transitions Basic
Process Operability Class Materials Operation during Transitions Basic flowsheet Design with Operability LC 1 FC 1 Copyright © Thomas Marlin 2013 The copyright holder provides a royalty-free license for use of this material at non-profit educational institutions
Key Operability issues OPERATION DURING TRANSITIONS 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 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
SU & Shutdown 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 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.
SU & Shutdown Key Operability issues OPERATION DURING TRANSITIONS STARTUP AND SHUTDOWN 1. Operating window 2. Flexibility/ controllability Equipment and process structure: Identify extra equipment needed for startup of the reactor. 3. Reliability Cold product 4. Safety & equipment protection 5. Efficiency & profitability Cold feed 6. Operation during transitions 7. Dynamic Performance Hot effluent 8. Monitoring & diagnosis
SU & Shutdown Key Operability issues OPERATION DURING TRANSITIONS STARTUP AND SHUTDOWN 1. Operating window 2. Flexibility/ controllability Equipment and process structure: Identify extra equipment needed for startup of the reactor. 3. Reliability Cold product 4. Safety & equipment protection 5. Efficiency & profitability 6. Operation during transitions 7. Dynamic Performance 8. Monitoring & diagnosis Cold feed Need heating when the reactor effluent is cold. Heating fluid Hot effluent Is the design complete?
SU & Shutdown Key Operability issues 1. Operating window 2. Flexibility/ controllability OPERATION DURING TRANSITIONS STARTUP AND SHUTDOWN Equipment: Identify extra equipment needed for startup of the distillation column reboiler. 3. Reliability 4. Safety & equipment protection Bottom tray Thermsiphon reboiler 5. Efficiency & profitability 6. Operation during transitions 7. Dynamic Performance 8. Monitoring & diagnosis Bottoms product
SU & Shutdown Key Operability issues 1. Operating window 2. Flexibility/ controllability OPERATION DURING TRANSITIONS STARTUP AND SHUTDOWN Identify extra equipment needed for startup of the distillation column reboiler. 3. Reliability 4. Safety & equipment protection Bottom tray Thermsiphon reboiler 5. Efficiency & profitability 6. Operation during transitions 7. Dynamic Performance 8. Monitoring & diagnosis Before reboiler is functioning, no vapor flows, liquid weeps through trays Bottoms product Valve is normally closed, opened only during startup From: Lieberman, N. L. , Process Design for Reliable Operations, Gulf Publishing, Houston, 1983
SU & Shutdown Key Operability issues OPERATION DURING TRANSITIONS STARTUP AND SHUTDOWN 1. Operating window 2. Flexibility/ controllability 3. Reliability Process flow: Occasionally, equipment must be shutdown for preventative maintenance and modifications. What is needed? 4. Safety & equipment protection 5. Efficiency & profitability 6. Operation during transitions 7. Dynamic Performance 8. Monitoring & diagnosis Unit B Unit A
SU & Shutdown Key Operability issues 1. Operating window 2. Flexibility/ controllability OPERATION DURING TRANSITIONS STARTUP AND SHUTDOWN Process flow: Occasionally, equipment must be shutdown for preventative maintenance and modifications. What is Discuss advantages needed? 3. Reliability • Cooling 4. Safety & equipment protection and disadvantages. How big is the tank? • Storage • Pumping 5. Efficiency & profitability • Heating 6. Operation during transitions 7. Dynamic Performance 8. Monitoring & diagnosis Unit B Unit A
SU & Shutdown Key Operability issues 1. Operating window 2. Flexibility/ controllability 3. Reliability 4. Safety & equipment protection OPERATION DURING TRANSITIONS STARTUP AND SHUTDOWN Process flow: Occasionally, equipment must be shutdown for preventative maintenance and modifications. What is needed? 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. 5. Efficiency & profitability 8. Monitoring & diagnosis • Storage • Pumping Let’s by-pass the tank when possible. • Heating 6. Operation during transitions 7. Dynamic Performance • Cooling and subsequent heating and cooling is inefficient. Unit B Unit A
SU & Shutdown 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 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. )
Regeneration Key Operability issues 1. Operating window 2. Flexibility/ controllability 3. Reliability 4. Safety & equipment protection 5. Efficiency & profitability 6. Operation during transitions 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 7. Dynamic Performance • Equipment that has surface coated due to coke (reactor) or polymer (e. g. reboiler) 8. Monitoring & diagnosis • Filtration that must be backflushed
Regeneration Key Operability issues OPERATION DURING TRANSITIONS REGENERATION 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 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.
Regeneration Key Operability issues 1. Operating window 2. Flexibility/ controllability 3. Reliability 4. Safety & equipment protection 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? 5. Efficiency & profitability 6. Operation during transitions Parallel equipment with isolation valves Single equipment with sufficient storage 7. Dynamic Performance 8. Monitoring & diagnosis Or, must we shutdown the entire plant when regenerating an individual unit?
Regeneration Key Operability issues OPERATION DURING TRANSITIONS REGENERATION 1. Operating window Example of Olefins plant 2. Flexibility/ controllability 3. Reliability Ethane C 2 H 6 4. Safety & equipment protection C 2 H 4 Propane C 3 H 6 5. Efficiency & profitability Gas oil 6. Operation during transitions 7. Dynamic Performance 8. Monitoring & diagnosis C 5 + Feed stocks Fired heaters The operation of the heaters (reactor feed type, feed rate, temp, steam) influence the rate of coke and need for regeneration. C 4 H 10 Separation system Coke buildup: Requires periodic shutdown/decoke
Regeneration Key Operability issues OPERATION DURING TRANSITIONS REGENERATION Example of Olefins plant 1. Operating window 2. Flexibility/ controllability Air and steam X Ethane 3. Reliability Exhaust safely C 2 H 6 4. Safety & equipment protection 5. Efficiency & profitability Gas oil 6. Operation during transitions 7. Dynamic Performance 8. Monitoring & diagnosis X Propane C 2 H 4 C 3 H 6 C 5 + Feed stocks Fired heaters C 4 H 10 Separation system • 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?
Regeneration Key Operability issues OPERATION DURING TRANSITIONS REGENERATION 1. Operating window Tube Wall Temperature : Reactor 2 Temperature (C) 2. Flexibility/ controllability 3. Reliability 4. Safety & equipment protection 7. Dynamic Performance 8. Monitoring & diagnosis = decoke 0 5. Efficiency & profitability 6. Operation during transitions 1040 1020 1000 980 960 940 920 900 880 860 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?
Regeneration Key Operability issues OPERATION DURING TRANSITIONS REGENERATION 1. Operating window 2. Flexibility/ controllability Example – heat exchanger is fouled and must be cleaned. 3. Reliability Process fluids 5. Efficiency & profitability 6. Operation during transitions 7. Dynamic Performance 8. Monitoring & diagnosis Process fluid 4. Safety & equipment protection What equipment is required to be able to take this exchanger out of service for cleaning or repair?
Regeneration Key Operability issues OPERATION DURING TRANSITIONS REGENERATION 1. Operating window 2. Flexibility/ controllability Example – heat exchanger is fouled and must be cleaned. 3. Reliability Process fluids 5. Efficiency & profitability 6. Operation during transitions Process fluid 4. Safety & equipment protection 7. Dynamic Performance 8. Monitoring & diagnosis Since both streams are process fluids, by-passes on each are required. If one were a utility (e. g. , water or steam), no bypass on the utility stream would be required.
Blocked operation Key Operability issues 1. Operating window OPERATION DURING TRANSITIONS BLOCKED OPERATION 2. Flexibility/ controllability 3. Reliability 4. Safety & equipment protection 5. Efficiency & profitability 6. Operation during transitions 7. Dynamic Performance 8. Monitoring & diagnosis “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.
Blocked operation Key Operability issues 1. Operating window 2. Flexibility/ controllability OPERATION DURING TRANSITIONS BLOCKED OPERATION- Lube Oil Manufacture Only one “base stock” manufactured at a time 3. Reliability 4. Safety & equipment protection Subsequent processing Solvent 5. Efficiency & profitability 6. Operation during transitions Solvent recovery and byproduct processing 7. Dynamic Performance 8. Monitoring & diagnosis Only one “base stock” processed at a time; switch about every two days
Blocked operation 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 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
Load following 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 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.
Load following Key Operability issues OPERATION DURING TRANSITIONS LOAD FOLLOWING – BOILER & STEAM SYSTEM 1. Operating window 2. Flexibility/ controllability 3. Reliability 4. Safety & equipment protection A utilities example is shown below, with the fired boilers (B 1 -B 4) and heat integration (producers) providing steam for power (turbines T 1 -T 5) and heating (consumers). Fuel gas B 1 Boilers B 2 B 3 Fuel oil B 4 1 5. Efficiency & profitability High pressure HP 6 2 HP consumer T 2 6. Operation during transitions 7. Dynamic Performance 8. Monitoring & diagnosis 3 7 MP producer T 3 10 Medium pressure MP LP producer T 5 LP LP export Liquid Cond 14 11 12 15 Low pressure T 1 4 9 MP consumer 8 13 T 4 5
Load following 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 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.
Load following Key Operability issues OPERATION DURING TRANSITIONS LOAD FOLLOWING 1. Operating window 2. Flexibility/ controllability PC 3. Reliability 4. Safety & equipment protection 5. Efficiency & profitability 6. Operation during transitions PY x 7. Dynamic Performance 8. Monitoring & diagnosis We adjust the ratios to lower fuel cost; fast pressure control is not affected.
Load following Key Operability issues OPERATION DURING TRANSITIONS LOAD FOLLOWING 1. Operating window 2. Flexibility/ controllability 3. Reliability An example is shown below, with the fired boilers (B 1 -B 4) and heat integration (producers) providing steam for power (turbines T 1 -T 5) and heating (consumers). Fuel gas 4. Safety & equipment protection B 1 B 2 B 3 Fuel oil B 4 1 5. Efficiency & profitability High pressure HP 6 2 HP consumer T 2 6. Operation during transitions 7. Dynamic Performance 8. Monitoring & diagnosis 3 7 MP producer T 3 10 Medium pressure MP LP producer T 5 LP LP export Liquid Cond 14 11 12 15 Low pressure T 1 4 9 MP consumer 8 13 T 4 5 What is the correct response when this consumer requires more steam?
Load following 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 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.
Load following Key Operability issues 1. Operating window 2. Flexibility/ controllability 3. Reliability 4. Safety & equipment protection 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? 5. Efficiency & profitability 6. Operation during transitions 7. Dynamic Performance 8. Monitoring & diagnosis For each boiler, we need a model relating efficiency to the steam generated (load).
Load following Key Operability issues 1. Operating window 2. Flexibility/ controllability 3. Reliability 4. Safety & equipment protection OPERATION DURING TRANSITIONS LOAD FOLLOWING Some issues for load following utilities • Transient - May require storage of material for startup How do we store steam? 5. Efficiency & profitability 6. Operation during transitions 7. Dynamic Performance 8. Monitoring & diagnosis We don’t. We must respond rapidly!
Batch Operation 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 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”, …
Batch Operation Key Operability issues OPERATION DURING TRANSITIONS BATCH OPERATION 1. Operating window 2. Flexibility/ controllability 3. Reliability 4. Safety & equipment protection Batch operation: All materials provided at start of the process. feed time 5. Efficiency & profitability 6. Operation during transitions product time Semi-Batch operation: Some materials introduced after the start of the process. feed 7. Dynamic Performance time 8. Monitoring & diagnosis Reaction product initiator time
Batch Operation Key Operability issues OPERATION DURING TRANSITIONS BATCH OPERATION 1. Operating window 2. Flexibility/ controllability 3. Reliability 4. Safety & equipment protection 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 5. Efficiency & profitability 7. Dynamic Performance 8. Monitoring & diagnosis Flow of heat transfer medium 6. Operation during transitions time product time = heating = cooling time
Batch Operation Key Operability issues OPERATION DURING TRANSITIONS BATCH OPERATION 1. Operating window 2. Flexibility/ controllability 3. Reliability Some plants integrate batch and continuous units. The plant must contain storage capacity to allow the continuous parts to operate without frequent shutdowns. 4. Safety & equipment protection Distillation feed 5. Efficiency & profitability time 6. Operation during transitions 7. Dynamic Performance 8. Monitoring & diagnosis Reactor product time
Batch Operation Key Operability issues 1. Operating window 2. Flexibility/ controllability 3. Reliability 4. Safety & equipment protection OPERATION DURING TRANSITIONS ALL SITUATIONS CONSIDERED Industrial Practice The operating conditions change during transients. For what operation do we “size” the equipment? 5. Efficiency & profitability We must size equipment for the most demanding condition of all operations experienced by the process. 6. Operation during transitions Never use the average operation, especially for these extreme transient operations. 7. Dynamic Performance 8. Monitoring & diagnosis It may be required to have parallel equipment with different capacities when the normal and maximum operations are very different.
Batch operation Key Operability issues 1. Operating window 2. Flexibility/ controllability OPERATION DURING TRANSITIONS BATCH OPERATION – GASOLINE BLENDING Intermediate products from process Products to customers 3. Reliability Regular Reformate FC 4. Safety & equipment protection LSR Naphtha FC FC FCC Gas 6. Operation during transitions FC FT Final Blend • • Premium Alkylate FC 8. Monitoring & diagnosis AT N-Butane 5. Efficiency & profitability 7. Dynamic Performance additives Manufactured continuously Final Blend One blending process Many different customers http: //www. mcscbahrain. com/projects. htm
Batch Operation Key Operability issues OPERATION DURING TRANSITIONS ALL SITUATIONS CONSIDERED 1. Operating window 2. Flexibility/ controllability 3. Reliability The operating conditions change during transients. The control system must follow the desired path. Temperature 4. Safety & equipment protection 5. Efficiency & profitability 6. Operation during transitions time Challenges remain 1. 7. Dynamic Performance 8. Monitoring & diagnosis Determine the best (optimal) transient behavior 2. Achieve good process control over a wide range for a nonlinear process
Key Operability issues OPERATION DURING TRANSITIONS 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 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
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