OPERATING INSTRUCTIONS:

9.7.1 General:

• Before making a controller ON check whether the controller is Active or not.

• Check HI / LO Limits of all MVs & CVs. It is recommended to put MV limits relaxed and CV limits as per specifications & requirements.

• It is always recommended to make the controller WARM before making it ON.

• For taking any MV in RMPCT mode, ensure that it is in desired DCS (Shed) mode of operation (Auto / Manual / Cascade). When any of the four controllers is put OFF by an operator, all the MVs in that controller will go back to their normal DCS mode (Shed Mode) of operation.

• At least one MV has to be in RMPC mode to make the controller ON. If not the controller will automatically get switched OFF and all the MVs in that controller will go back to their normal DCS mode (Shed Mode).

• Value of any parameter on the RMPCT graphic page in CYAN color means that parameter is within the low & high limit (Normal).

• Value of any parameter on the RMPCT graphic page in YELLOW color means that parameter is touching the low or high limit including its soft/ hard limits.

• Value of any parameter on the RMPCT graphic page in RED color means that parameter is violating the set low or high limit.

• In the event of failure of any instrument or requirement for checking any instrument:

Check whether that instrument is contributing (directly or indirectly) to any MV / CV / DV in any of the controller (ADU2 / VDU2 / NSU2). This can be checked from the

‘Gain Delay’ graphics page or MV / CV/ DV tags list.

Check whether that instrument is contributing (directly or indirectly) to any calculated or inferential variable. This can be checked from the list of input tags for calculated &

inferential variables (chapter: 6.0).

Accordingly, all the related MV, CV, DV, Inferential & Calculated tag need to be taken out from RMPCT mode. After restoration of normalcy of the instrument, the concerned variables can be placed in RMPCT mode again.

• If any of the CV including calculated tag & inferential tags and DV value goes bad (No value; ---) the controller drops that CV / DV automatically. If any of the source tag becomes bad, the calculated / inferential value also goes bad and gets dropped automatically. However if any of the CV or DV shows erratic / random values, then it

does not get dropped automatically and it is advisable to drop that CV / DV manually immediately.

• When a MV is dropped from RMPC mode, operator has to decide whether he wants to put that MV in Service mode or in Feed forward mode. Feed forward mode is useful for prediction purpose provided the indication is healthy, whereas keeping in Service mode will not give any information of that MV to the controller for any calculation. However for safety reasons the default mode for "When MV In Manual" option has been configured as “DROP” to avoid unnecessary moves (when the MV is checked by Instrumentation without putting in drop mode) based on FFWD.

• During communication failure or to put off all three APC controllers at a time use the Master Switch configured in the DCS. Operator can call the schematic GR0293 to accessthe master switch.

• When any of the three APC controllers is Switched OFF due to any reason, an alarm will come on the DCS panel saying the respective APC controller is switched OFF.

• Never put the APC controllers ON from the DCS Schematic page. This is to avoid possible upset / disturbance in the unit. Instead operator must check the MV / CV limits on the profit viewer before putting controller ON.

• Periodically check for automatic lab updation of inferential. In case of discrepancy, inform Technical-APC group.

• If any of the CV has status as WDUP, it means that the CV cannot be controlled within the set limits as its MV’s set low / high values are limiting.

• If any of the MV shows status as HIGH or LOW, check its output at the DCS level for locks if any & take proper actions to bring its output into the floating range.

• When any MV is taken into APC, it will go to SPC mode in DCS. There will not be any mode change for CVs & DVs.

• If the communication between APC machine and DCS gets broken, all MVs in the RMPCT controllers will go back to their Shed Mode.

9.7.2 Controller Specific:

• ADU2 Controller:

a) For taking feed maximization and pass temp balancing strategies under APC control, ensure that FR1804 is in manual and pass flows are in Auto. Under APC control, furnace pass flows (in SPC mode at DCS) will be manipulated for achieving these objectives. When APC controller is switched off, pass flows will go to AUTO (shed) mode and FR1804 will remain in manual. DCS supervisor to ensure that FR1804 is taken back into Auto with pass flows in Cascade mode (normal regulatory control).

b) Product flows in each rundown line are considered as individual MV. Make sure that Product lines, which are not in operation are kept out of APC (i.e., MVs are made OFF). e.g., when only Kero rundown, FR1203, is in line, then keep the other MV FR1204 (Kero to Diesel) OFF from APC Controller and set proper limits for FR1203.

In general, if there are more than one r/d MV for the same product, ensure that the one that can be manipulated is in APC. Keep the other MV in Auto.

c) In the controller, along with product inferential like 95% points, Draw Temperatures are also considered as CVs. Whenever inferential is predicting better, make limits for draw temperature relaxed, so that these CVs does not have any conflict with the inferential limits.

d) If 95% inferential value is showing bad or wrong value, then make that CV off and make draw temperature limits tight. One can control the product quality with draw temperature in such a situation.

e) Dew point inferential is based on empirical equation and hence it is not always perfect. Keep limits considering 4-5 degree positive offset.

f) If any of the skin (or Arch) temperatures are showing bad or wrong values, the maximum skin (or Arch) temp CV shall be kept dropped and inform APC group. The particular tag will be dropped from the calculation and the CV can be taken back inline. The maximum skin (or Arch) temperature will be calculated based on remaining indications. Make sure, that the tag is taken back inline by APC group when the indication is attended and value returned to normal range.

• VDU2Controller:

a) For taking pass temp balancing strategy under APC control, ensure that LR1401 is in manual and pass flows are in Auto. Under APC control, furnace pass flows (in SPC mode at DCS) will be manipulated for achieving this objective. When APC controller is switched off, pass flows will go to AUTO (shed) mode and LR1401 will remain in manual. DCS supervisor to ensure that LR1401 is taken back into Auto with pass flows in Cascade mode (normal regulatory control) and Atmospheric column bottom level under control.

b) In the controller, along with product inferential like 95% points, Draw Temperatures are also considered as CVs. Whenever inferential is predicting better, make limits for draw temperature relaxed, so that these CVs does not have any conflict with the inferential limits.

c) If 95% inferential value is showing bad or wrong value, then make that CV off and make draw temperature limits tight. One can control the product quality with draw temperature in such a situation.

d) If any of the skin (or Arch) temperatures are showing bad or wrong values, the maximum skin (or Arch) temp CV shall be kept dropped and inform APC group. The particular tag will be dropped from the calculation and the CV can be taken back inline. The maximum skin (or Arch) temperature will be calculated based on remaining indications. Make sure, that the tag is taken back inline by APC group when the indication is attended and value returned to normal range.

e) As vacuum column is normally faced with instrumentation problems because of viscous fluid, get the maintenance and instrument rectification on time for better and reliable APC

• NSU2 Controller:

a) In the column, both Top Temperature and bottom temperature are controlled. For column stability and LPG yield / quality, keep the bottom temperature relaxed and control top parameters tight.