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Subsea process systems engineering

Subsea process systems engineering. Integrated and new processes for separation (vapor pressure and dewpoint control) and water handling, with emphasis on producing cleaner water and dryer gas Design of control systems, including multiphase flow systems and compressors

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Subsea process systems engineering

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  1. Subsea process systems engineering Integrated and new processes for separation (vapor pressure and dewpoint control) and water handling, with emphasis on producing cleaner water and dryer gas Design of control systems, including multiphase flow systems and compressors Performance monitoring for fault detection, reliable operation and shorter shutdown periods Fault detection and safety systems for operation of  large subsea systems

  2. Performancemonitoring • Want to closely monitor the process • Flows, pressures, temperatures • Pressure drop in equipment • Efficiency for compressor, separator • UA for heat exchanger • Traditionally in process industry: “Data reconciliation” • Need to wait for steady-state • Common in control: Kalman filter / Observer • Dynamic, so no need to wait • Need extension to apply for process monitoring

  3. Operation and control • How to best implement close-to-optimal operation using a simple an robust control structure • Optimal operation (active constraints) • Self-optimizing CVs • Example: Get optimal split in compact separator

  4. Subsea gas-liquid separation: Åsgard Hodne (2012)

  5. Marlim subsea separation (Brasil) A – Multiphase desander B – Harp C – Tubular separator D – Outlet vessel E – Water desander F – Hydrocyclone G – Pump H – OIW monitor I – Ejector I • Strong interactions between different process components • Stiff system dynamics due to small hold-ups and low GOR • Pressure drops of inlet cyclonic equipment need to be balanced • Constraints on valve opening/closing speed • Instrumentation is limited compared to top-side

  6. Process Control: Marlim SSAOLevel controller Harp Pipeseparator OutletVessel • Quick response is required (3 sec) • To avoid constant speed changes a dead band is used • Filtration of input can be used Pereira et al. (2012)

  7. Process Control: Marlim SSAOTwo pump flow rate controllers (Min/Max flow) • To keepthe operating pointinsidethe pump envelope • Min opens when flow is less than minimum • Max closeswhen flow is more than maximum Pereira et al. (2012)

  8. Process Control: Marlim SSAOMultiphase choke valve-DP controller • To maintain stable backpressure for the rejects from desnader and hydrocyclone • Asymmetrical dead band is applied to reduce choke movements Pereira et al. (2012)

  9. Process Control: Marlim SSAOTwo hydrocyclone controllers • To keep the reject rate between 2-6% Pereira et al. (2012)

  10. SummaryMain challenges in design • Sand removal • Flowassurance e.g. Hydrates (MEG injection, depressurizing) • Secure foundation & Levelingofsubseaseparators • Durability & Low maintenance • Modularization • Powerdistribution • Compactness for deep-waterapplications • Laboratory test (Technology Qualification Program)

  11. SummaryMain challenges in process control • Simpler (compared to topside control systems ) • Stronginteractionsbetweencontrol loops • Redundancy • Safety & EmergencyShutdown (ESD) • Fast dynamicsofcompact separators • Data transfer to topside • Comes-on-power (slow, suitable for oldbulky systems) • Fiber opticcommunication (fast, high rate, long distance) • Modeling and dynamicsimulations • Controller tuning • Wear and tearofcontrolvalves (constrainton speed ofvalves) • Sluggingflow and well-test Stronginteraction + constraint handling + economicoperation  MPC

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