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S.N.Raghuraman

Lead System Engineer / ICEE, Engineering Div, ADGAS

I hold Bachelor’s degree in Instrumentation and Mathematics. 28 years of experience in the field of Automation and Control. Started career in a Public Power Utility Company as Instrument Maintenance Engineer, then worked as Automation and Control engineer in Honeywell. Currently working as Lead System Engineer in Engineering Division of ADGAS, Das Island for the past 14 years.

Advanced Process Control Implementation for 3rd LNG Train at ADGAS

Advanced Process Control & Optimisation

Abstract: Advanced Process Control Implementation for 3rd LNG Train at ADGAS ADGAS implemented Advanced Process Control Solution (APC) for LNG Plant with intent to Increase throughput while respecting all the constraints required for ensuring integrity and reliability of its assets. It will also help in improving efficiency and reducing emissions. We have used model based predictive control in implementation of APC. Overall structure of controller includes 5 controllers which are optimized by overall controller using QP technique. This types of implementation is not so uncommon in industry today, however, at ADGAS we had some peculiar challenges which were eventually overcome using innovative solutions. MR Composition Controller Mixed refrigerant (MR) used as cooling medium to produce LNG, consists of predominantly four components: • Nitrogen • Methane • Ethane • propane It is very important to control the composition to ensure efficient cooling. Non-optimal composition leads to either losing opportunity for producing additional LNG or results increased energy consumption for the same LNG. Each component in MR has a makeup valve that becomes handle to adjust the composition. Increasing any one makeup, will have its impact not only on that concentration but also on other components concentration. Hence it is required to make precise and coordinated moves in the makeup valves often together to maintain the composition accurately. It becomes very difficult for operator to control this interactive system. Operator spent considerable time in maintaining this composition in absence of Advanced Process Control system. Advanced process control system using the developed models make coordinated moves on MVs always to maintain the operator set composition. Though APC has been implemented in many LNG plants across the world, MR composition control is done in only very few places. Now ADGAS is one of the auto-MR composition controlled LNG producer. Drier Changeover Moisture removal from feed gas is done by molecular sieves. There are three molecular sieves beds of which 2 are online and one is under regeneration at any given time. Regenerated drier changeover happens every 8 hours. Drier changeover process start with re-pressurizing the regenerated drier using feed gas. As the gas flow to the upstream equipment, that are acid gas removal unit, increases beyond its stable operating zone, operator reduce the LNG production just before re-pressurization. Similarly he increases the production after drier changeover. In APC project, after studying the history of drier changeover, the best operator approach is automated. Now the load reduction and normalization is automated and synched with APC controllers. Automation of the load changes during drier changeover has substantially reduced operator actions and resulted in consistent load reduction and timely recovery resulting more LNG production. MR Optimization As stated before, mixed refrigerant is used as cooling medium for liquefying natural gas. Optimal composition ensure minimum compressor energy for the given LNG production target and no-pinch in cryogenic heat exchangers. Non-optimal composition result in either energy loss in compressor or LNG production loss if the cryogenic exchanger experiences pinch. Calculating optimal MR composition is tough as scenario changes continuously. The major factor affecting MR optimal value are: • Feed gas composition • LNG production target • Ambient conditions • Target LNG temperature In APC project, considering targets and current operating scenario, optimal composition is calculated and sent to operator as advised composition.

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