• What are the minimum requirements or the prerequisites for implementation of the Advanced Process Control system in downstream complex refinery, consisting of units such as Hydrocracking unit, Vacuum Distillation Unit and Reforming Unit?



  • Syed Mumtaz, Freelance Individual, ab12d@yahoo.com

    In my opinion, APC is outdated given the flexibility in the the newer basic DCS systems. Previously, what APC did mainly was to add feed forward, analyzer based real time or offline feedback and/or multi-variable controls. Many of these functions in a conventional conversion refinery can be configured within the basic controller module. Moreover, If I assume that your refinery is Hydrocracker based, all loops in the unit don't need APC or complex control scheme to improve profitability. There are generally only a few critical loops that need more refined control. For example in the TC for the reactor. Once this done, together with a feed forward for the feed,  it can lead to better quench gas flow, more control on profile and less hot spots. Similar logic applies to other process units.

    In the VDU keeping the vacuum system steady and controlling the TC close at the vacuum heater out lest helps. The other critical areas are the amine system and environmental related emissions control. The latter are better handled by process modifications upstream than just using control systems only. In the amine, the control scheme is fairly straight forward and keeping it simple has more worth, Same goes for the SWS system. Control the top and draw-off temperature to meet bottoms specs. Simplicity pays a lot of dividends but the key is to attend the control responses and controller mal-functions and hunting.



  • Sirajchandra Talukdar, SEPAM, talukdar_siraj@yahoo.com

    I have the experience of APC implementation in NHT,CCR and other PX technology related units.There are benefits in APC implementation subject to capacity/size of the unit as well as feasibility of implementation.



  • Jake Gotham, InSite Technical Services, jake.gotham@insitetechnical.com

    Firstly, there is no point implementing advanced process control if the basic control isn’t well set up. Controllers need to be well tuned, in auto/cascade, control valves in a reasonable operating range (30-70% open) and transmitters within range.

    Implementing advanced control will require specialised skills. Most refineries bring in external consultants to help with this, but it is essential to have refinery staff embedded in this team so that knowledge is retained on-site when the consultant has demobilised.

    APC systems need continuous attention and support. If they are commissioned and then left to the operations team while the APC team focuses its attention on building an application for another process unit, the system will soon fall into disuse. The system will need continuous updating to account for changes in economics, operating modes, new constraints, fouling, flooding, catalyst deactivation/replacement, minor projects etc, etc. This ongoing support should come primarily from the refinery control team, which should be made up of process engineers, control engineers and former panel operators. They should be intimately involved in building and commissioning the APC system alongside the consultant, and then intimately involved in its ongoing performance alongside the panel operators and process engineer.



  • Radu Iscovici, Iscovici Radu PFA, radu@iscovici-radu-pfa.com

    1: Good understanding of the processes.

    2: Good regulatory controls system.

    3: Review of loop tuning.

    4: A verified MPVC technology licensor with an excellent support record.