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Problems Caused By Dynamic Operations

Some research showed that 80% of one company’s problems could be attributed to dynamic effects such as surge pressures and transients. This is a significant finding and shows how the industry can improve by reducing these problems.

Shutdowns

Transients generally cause the highest and lowest flows, temperatures, pressures etc and so are possibly the major cause of unwanted/unplanned shutdowns. Yet most can be avoided and dynamic simulation studies are the best way of identifying the cause of any shutdowns. They are non-intrusive and allow the actual incidents to be studied (or ‘replayed’) to find the underlying causes. In recent years we have had excellent success by combining the investigative capability of simulation with the ability of SCADA Historians to record what actually occurred.

It is useful to be aware that most historians do not store data frequently enough to fully capture many fast events such as surges and fast transients.

Control systems and individual controllers can become unstable in some situations. Standard auto-tuning can be very effective during normal (stable) operation but does not guarantee that the overall control scheme performs well during start, stop or turndown operations.
Dynamic simulation was first developed to study the control of plant and is still one of the best techniques for designing or diagnosing controllers and control strategy.
Done at design stage it allows engineers to plan for potential problems early and so prevent handover and operating problems.

Damage

• Weld damage
• Valve innards being damaged
• Pipe movement
• Exchanger failures
• Air vents and vacuum breakers being damaged after first use
• NRV failure & leakage
• Pump Damage
• Compressor (surge and backward rotation) damage

Undesirable Operations

Excess flaring, noise, PSVs lifting and bursting discs rupturing all occur due to transients and all have an undesirable impact upon smooth successful operations.
We also get asked to investigate low capacity caused by poor hydraulics,  air/gas collection or due to operator’s low confidence or the perceived/real risk of shutdowns.