Production Separator Control System

“Produced wellhead fluids are complex mixtures of different compound of hydrogen and carbon, all with different densities, vapor pressure, and other physical characteristic. The velocity of the gas carries liquid droplets, and the liquid carries gas bubbles. The physical separation of these phases is one of the basic operation in the production, processing, and treatment of oil and gas.” (Ken Arnold & Maurice Stewart – Surface Production Operations).

Production separator is called “three-phase” separator if they separate the gas and liquid and the liquid stream itself shall be separated into crude oil and water component.

separator

Above is simplified three phase production separator. We are not going to discuss about the process itself how it works or the separator itself (material, dimension, etc) but we are going to discuss about what instrumentation should be put in on that production separtor and what control strategy shall be applied to ensure the production separator can work continuously and safely.

I propose the first thing must be considered is to define what physical property was involved in this system. We have gas so we will have pressure, we have liquid so we will have liquid height or level, we have flowing liquid so we will have flow but it seems not too important in the separation process. And then I propose the second thing must be considered is to define the control hierarchy. The highest hierarchy is mechanical protection, then safety control protection, and then process control regulation, and the last one is monitoring purposes. Safety is the most important in every process. It’s no point to run the process if everybody not sure about the safety. Process control is important after safety to increase productivity, eficiency, and quality.

The mechanical safety protection is the instrument which can self acting to respon on the presence of hazard without any signal initiation. Safety valve (PSV-1) shall be put in to respon the gas overpressure. Only pressure is the most critical property that tend to explossion. Level and flow is not so much consider as highest critical hazard.

Safety control protection (formally called Safety Instrumented System) will consider pressure is potential hazard and level is property that will tend to reach abnormal process once uncontrolled. Safety control will manage pressure and level that will affect to the shutdown of separator. Put in pressure transmitter (PT-1) on the top of separator. Put in Level Transmitter (LT-1) on the oil (condensate) result. Put in Level Transmitter (LT-2) interface on the crude (mixture of compound oil & water). Put in shutdown valve on the INLET (SDV-1), WATER line (SDV-2), OIL line (SDV-3), and GAS line (SDV-4). Define the safety control Cause & Effect matrix. If I was the designer I will make PT-1 Hi-Hi will affect to shutdown inlet SDV-1 and shutdown gas outlet SDV-4. PT-1 Lo-Lo will shutdown all the SDV because the operation is in abnormal, it’s no point to run the process. But in the early start up the Lo-Lo shall be inhibit. LT-1 Lo-Lo will shutdown outlet oil SDV-3, it has low oil that’s no point to run the process. LT-1 Hi-Hi will shutdown the inlet SDV-1. LT-2 Lo-Lo will shutdown the water outlet SDV-2. LT-2 Hi-Hi shall shutdown the inlet SDV-1 also (but my last project did not capture this on C&E). The last one is BDV-1 also must be provided to connect the gas line to flare header. I think when PT-1 Hi-Hi the line to flare header shall be blown by open BDV-1 (but again I did not see it on my C&E last project?). The safety control instrument shall be dedicated only for safety.

separacontrol

Process control regulation adalah process control reguler yang biasa dikenal sebagai PCS (Process Control System). Instrument dan control valve yang dipasang adalah untuk mengontrol separator dalam kondisi reguler, aman, dan process berjalan normal. PT-2 dipasang pada puncak separator untuk mengontrol pressure di dalam separator. PT-2 berfungsi untuk meregulate PCV-1 dengan set-point PT-2 dibawah nilai PT-1 Hi-Hi. PCV-1 akan meregulate pressure yang berpotensi naik dengan merelease pressure ke flare header. PCV-1 harus fail open sehingga PIC harus diset reverse control action. Analog input increase maka anlog output decrease. Ketika PT-2 dan PCV-1 dapat menjalankan tugas rutinnya maka system masih berjalan kontinu secara normal.

Oil pada sisi kanan weir akan diregulate dengan melakukan adjustment pada opening LCV-1 dengan proses variabel LT-3. LCV-1 akan diset fail close. Increasing level akan menyebabkan increasing opening atau increase analog input menghasilkan increase analog output sehingga LIC harus diset direct control action. LT-1 Hi-Hi tidak akan terinisiate ketika close loop LT-3-LIC-LCV-1 dapat menjalankan tuga pengendalian secara kontinu. Penjelasan yang sama untuk LT-4 yang akan meregulate LCV-2. LCV-2 adalah fail close dengan LIC direct control action. Interface level harus dijaga pada kondisi set-point dengan memperlebar atau memperkecil opening dari LCV-2. Apabila close loop LT-4-LIC-LCV-2 dapat menjalankan tugasnya secara stabil maka interface level tidak akan bergerak terlalu ke atas atau terlalu ke bawah. Terlalu ke atas akan menyebabkan process pemisahan dengan metode gravitasi ini tidak akan ada gunanya. Demikian juga jika interface level terlalu low akan menyebabkan ada condensate yang lolos ke water line.

Saya ingin mendengarkan kalau ada yang berpendapat bahwa interface oil dan waternya tidak perlu dikontrol karena interface itu sebenarnya tidak ada karena tidak dapat sepenuhnya memisahkan oil dan water. Well, kalau tidak bisa kenapa metode pemisahan berdasarkan gravitasi dengan weir ini masih diterapkan? Tentu dengan harapan oil dengan specific gravity lebih rendah akan berada di atas sedangkan kandungan air yang specific grafitynya lebih tinggi akan berada di bawah sehingga ada batas specific gravity antara keduanya yang harus dimaintain di tengah. Oleh karenanya sistem kontrol interface harus diterapkan.

Yang terakhir adalah instrument yang dipasang untuk melakukan monitoring. Ke-semua LT memberikan feedback monitoring ke HMI. Local display dan juga glass umum juga digunakan untuk monitoring yang terinstall jadi satu dengan LT. Local display pada PT untuk memonitor pressure juga PG-1 untuk memberikan local reading.

Nova Kurniawan

Sarjana Fisika Teknik ITB, 2004, sekarang bekerja di J Ray McDermott Batam-Indonesia

 

 

10 Responses

  1. Can i get the dimention of the separator cuz i need it for my final year project please

  2. The detail dimension of separator is part of mechanical engineer responsibility. I am an instrument engineer.

  3. Mas Nova, bagaimana menentukan berapa nilai setpoint untuk LC baik yg oil level ataupun yg mixture (oil and water). adakah metoda tertentu…?

  4. Mas Nata,

    Saya belum mengerti metoda apa yang dimaksud. Tetapi selain single loop seperti case saya di atas, ada juga LC di oil level yang dicascade dengan flow. Set-point untuk Oil level menurut saya dipertahankan pada level normal process yaitu 50%. Karena satu-satunya tujuan pengontrolan level adalah agar tidak terjadi over level.
    Juga interface mixture (water and oil) demikian halnya taruh saja di 50%.
    Namun demikiansaya pernah mendapat penjelasan dari seorang process engineer bahwa interface level itu bisa dipertahankan dengan konsep gravitasi, karena specific gravity yang berbeda antara oil dan water maka dibuat ada satu mekanisme tertentu, tanpa menggunakan transmitter & control valve.
    Karena dalam artikel saya konsen pengontrolan level adalah agar tidak terjadi over level maka saya tidak melihat dan tidak tau perhitungan khusus secara kimia, berapa level untuk set-point sebuah separator.

  5. You can get more information about three phase separator at http://www.process-facility.com

  6. salam mas makasih atas informasinya….

  7. hi.. thanks for you information, if you don’t mind i’m copying this document for my paper…

    thanks before

  8. Copying is not allowed. Quote with mentioning the source you took is allowed. Write down the same topics with your own words is the best.

  9. Dear Sirs:
    We have visited your web site and we are very interested in establishing business relationships with your esteemed company.
    Please allow us first of all to introduce our company.

    Our company “HE Trading,” is a new branch to (Elias brothers Co.). It is a leading Import and Export private Syrian company specialized in oil and gas equipment of all kinds, in addition to various electric and mechanical equipment dealing with most of the world’s countries for over forty years as a long-experienced commercial company.
    Our work specially concerns on import for local tenders, and we have another branch in DUBAI – UAE (Isam Trading Co).
    Our experience and capabilities enable us to open up the local market and establish us a good standing position in the various domains of industry. Our vision is to have a much dominant role in the regional market and the international one as well.
    We would like to tell you that we are working on an order for (separators) and we are looking for starting cooperation with your respectable side to achieve a business relation with you if you do not mind.
    Hoping to hear from you soon.

  10. Mas Nova, untuk sizing PSV pada separator 3 fase berdasarkan apa?Misal ada gas yang keluar dengan flowrate 1,5 MM pada tekanan tertentu, apakah kita sizing berdasarkan flowrate gas dan tekanan nya saja? tekanan oil dimasukkan dalam perhitungan?
    Yang biasanya digunakan untuk perhitungan yang mana?
    Terimakasih atas penjelasannya

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: