PETROKEMYA (SABIC) Control Loop Performance Monitoring and Assessment Presentation at KFUPM Monday, 24 th November 2008 Petrokemya Olefins-III by Khalid T. Al-Ruwaili Manager, Control System Department Petrokemya, SABIC v
Contents Introduction The incident Study objectives Study findings Solution & Decision i Project implementation Benefits 2
Introduction When it comes to performance of Control Loops in Process Industries, it is said that the day plants were built, it started to go bad. With continuous operation, wear & tear, material variation, seasonal changes, and changes in process characteristics, plants drift away from their optimal performance. Most industries realize it only after a big process upset or production loss. 3
The incident In Olefins-II, the VHP to HP steam-let-down valve PV-8660 had problems since plant startup. So, Operations kept the valve in MANUAL mode, as its performance in AUTO mode was not satisfactory. When the Process Gas Compressor (BK-0201) tripped on 31st December 2004, VHP Steam demand came down, and because PV- 8660 got stuck at 20%, HP steam header pressure dropped. This reduced turbine speed of BFW pump and caused lack of BFW, and in turn eight (8) millisecond furnaces tripped. Olefins-II plant was down for 16 hours, and total production loss was equivalent to 3680 metric tons of ethylene (SR 5, 851,200). 4
Study objectives Main objectives of the CSD survey were, To study the reasons for performance-deterioration of control loops over a period of time, due to which control loops in various plants of Petrokemya were kept in MANUAL mode, and not in their DESIGN MODE of operation. To develop a system and apply the latest hardware / software tools to study, monitor, and improve the performance of critical control loops, on a continuous basis. 5
Study findings Control Loops working alright, but may deteriorate anyway Change in the process characteristics Operations prerogative Control Valve problems Inadequate control scheme design Other reasons 6
Study findings (cont) Category Description Controllers status VCM Plant PVC Plant PPS Plant lyethylene Po Olefins-I Olefins-II Olefins-III Utilities Overall 1 2 Controllers apparently working alright but may deteriorate anyway Change in process characteristics Auto 279 470 87 0 532 829 989 159 3345 Manual 9 5 9 0 16 21 2 5 67 3 Operations prerogative Manual 25 26 12 0 20 464 101 7 655 4 Control Valve problems Manual 3 4 4 0 8 3 4 2 28 5 Inadequate design Manual 8 4 0 0 0 3 47 3 65 Total per Plant 324 509 112 0 576 1320 1143 176 4160 Loops on Auto: 3345 (of 4160) Loops on Manual: 815 (of 4160) 7 7
Control Loops working alright but Control loops are tuned during plant initial commissioning PID parameters are set based on experience Problematic control loops are tuned through trial and error Plants may run for their lifetime with sub-optimal controls Control valves become mechanically deficient Flow control valve does 1-2 million reversals/year Valve packing frequently over-tightened to prevent emissions Causes valve stiction and control loop cycling Process characteristics change with time Equipment fouling, wear, modifications Even well-tuned control loops develop problems 8
Control Loops working alright but (cont) Limit of Operability Alarm Limit Reduction in benefits Lowering of set point to maintain safety margin Variability increases over time Reduced Profit Running further from Constraints Increased Maintenance Costs Equip & Valves Cycling Increased Operator Loading Alarms, Intervention reqd. After optimization 9 Performance decreases over time 2 3 years later 9
Control Loops - symptoms of poor performance Excessive variance Oscillatory behavior Disclosing events Increased alarm frequency Operator intervention ti Loops placed in manual mode Controller output saturation Excessive Variance Oscillatory Behavior Frequent alarms Operator intervention PID Tuning changes Loop in manual Output runs into limits Poor Control Loop Service 10
Change in the Process Characteristics Compared to the original design, process characteristics change with time. Plant modifications, equipment wear & tear or fouling and varying plant loads, contribute to deterioration in the performance of control loops. For example, Plants are modified, debottlenecked, or added with new equipment In VCM plant, guided wave radar level instruments were identified and successfully used as a replacement for obsolete and problematic displacer type level instruments. In Olefins-I, nearly 56 VORTEX flow meters are installed in place of Orifice plates in furnace dilution steam flow meter applications, to overcome problems like, frequent plugging of impulse tubing with coke particles, and unstable & oscillating flow measurement. 11
Operations prerogative Over a period of time, plant operating personnel develop opinion on some control loops that there will be problems irrespective of the actions they take. Or, the Operators do not keep some control loops in their designed MODE of operation due to other reasons. For example, In PVC plants, 15 Poly Reactor pressure control loops are in MANUAL mode, against their designed AUTO mode, to avoid releasing VCM to atmosphere. 12
Control Valve problems Hysteresis Stiction Nonlinear Installed Characteristic Oversized Control Valve These problems cannot be solved through tuning Hysteresis Stiction Non-linear characteristic Oversized valve 13
Inadequate Control Scheme design Process units or equipment are provided with inadequate control schemes to control them, or inadequate field instrumentation to measure the required process variables. When it comes to performance of control loops, it becomes very difficult to judge, whether adequate control schemes are provided in the first place. For example, When we compare three ETHYLENE plants in Petrokemya, which were built at different times, the number of control loops and field instruments t in each ethylene plant kept increasing i significantly. ifi 14
Solution & Decision In the first phase of the project, we decided to go in for the following, Control Loop Performance Monitoring and Assessment package Control Loop Tuning package Alarm Management System (AMS) package And, in the second phase, we plan to go in for the following, Plant-wide Advanced Process Control Real-Time Optimization 15
Project implementation (Olefins-II) We decided to implement the project in Olefins-II first. We prepared Invitation-To-Bid (ITB) documents and sent them to renowned Automation Companies. After technically and commercially evaluating the proposals, we selected the solution offered by Honeywell for Olefins-II. Deliverables, Loop Scout OperTune Alarm Scout Advanced Alarm Management (AAM) Alarm Configuration Manager (ACM) Alarm and Event Analysis (AEA) User Alert (UA) Loop Scout Server, Advanced Alarm Management (AAM) Server PowerEdge 1800, Xeon 3.0 GHz, Dual CPU, SATA Raid-5 hard disk 16
Project implementation (VCM) Then we moved on to Vinyl Chloride Monomer (VCM) plant. This time, we selected Process Automation Systems (PAS) after technically and commercially evaluating the proposals from renowned automation companies. Deliverables, ControlWizard TuneWizard Alarm Analysis Module Alarm Documentation and Rationalization (D&R) module Automatic Data Update (ADU) module Real Time Alarm Management Application PlantState Suite Server DELL tower, Xeon 3.0 GHZ, Dual CPU, 4GB SDRAM memory, 73 GB Raid-5 hard disk 17
Project implementation (VCM) Internet Clients External Firewall Business LAN Controller Performance, Controller Tuning, Alarm Management Servers Internal Firewall Process Control Network OPC DA Server Clients DCS 18
Project implementation (VCM) ControlWizard Treemap Performance Display provides a visual overview of loop performance, loop importance, and draws attention to problem areas. Assessment Details viewer shows data used for analysis, lists statistics, and provides corrective actions 19
Project implementation (VCM) Assessment Details viewer shows data used for analysis, lists statistics, and provides corrective actions. Advanced Assessment Details viewer provides autocorrelation, impulse response, and power spectrum plots, as well as detailed results of performance analyses. 20
Project implementation (Olefins-III) Too many alarms causing nuisance Many alarms were disabled (process safety) History Module (HM) of Honeywell DCS overflowing Difficult to retrieve alarm history of last few hours 12 % - BADPV alarms Null reading for fraction of a second. Mainly temperature alarms/defective thermocouple 30 % - OFFNORM alarms Change of state Deluge valve Pump seal leak Burner scanner failure 21
Project implementation (Olefins-III) 55 % - PVHI and PVLO alarms Process value exceeding high/low alarm limits Wrong selection of alarm limits Poor controller tuning Varying feedstock Controllers were tuned by Honeywell Alarm limits were corrected based on feedstock Dead bands were created to allow for process swing Time delay was provided for process swing. Bad PV alarms were removed for temperatures 22
Project implementation (Olefins-III) Olefins-III NUM MBER OF ALARMS P ER HOUR 42 Journey from Overloaded Workstation to Robust" Workstation % PLANT UPSET 23
Benefits Continuous monitoring of all loops Automatic assessment Non-invasive Provides an overview of all loops Prioritization of maintenance efforts Problem identification & diagnosis Scheduled reporting Maintain Advanced Process Control benefits Typically, 40-70% of savings from APC projects are achieved by optimizing the performance of control loops Reduce frequency & severity of abnormal situations Poor performance of control loops contribute to 30% of preventable/unplanned plant downtime 24
Benefits (Cont) In Olefins-III, We achieved 93% reduction in total alarms per day (from 52,000 to 4,000 for 4 workstations). We moved from "overloaded" workstation to "robust" workstation. We achieved this within 7-weeks of installing the system. Operators are now able to concentrate ce on process related issues better than before. Nearly 95% of control loops run in their designed MODE. We achieved stable operation of C2-splitter splitter, and overall production increase of 3% (Capacity of the plant is one (1) million-tons-per-year of ethylene). 25
Thank You Any Questions? Khalid T. Al-Ruwaili Manager, Control System Department 26