09 apc maintenance cts

7/24/2019 09 APC Maintenance CTS

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February 21, 2016 Reliance Technology Group – APC / RTO 1

Process Engineering GroupProcess Engineering Group

APC maintenanceAPC maintenance

Viknesh RajaViknesh Raja



Scope

Responsibilities

Methods to identify performance degradation

Causes of performance degradation

APC maintenance actiities

Flo!chart of APC maintenance




February 21, 2016 Reliance Technology Group – APC / RTO "

Responsibilities



Responsibilities

#op management$ Attention, focus and isibility%

APC engineers$ Monitor and report performance, configure changes, updatecustom calculations and soft sensors, tune APC parameters and &eep the modelin good fidelity !ith plant behaior and desired ob'ecties% Conduct internal ande(ternal audits%

Plant)C#* engineers$ *et proper control ariable +C- limits, rela( C limits

based on the plant and e.uipment &no!ledge of constraints, chec& that the APCis moing the plant to right constraints based on the operational or economicob'ecties and report any discrepancies to APC group%

Plant instrument engineers$ /eep the base leel P loop performance in goodshape, ma&e sure all APC ariables are lie and !or&ing in APC enironment,

report and !or& !ith APC group to incorporate any configuration and tuningchanges into APC%

Panel officers$ /eep the controller 3, rela( all M limits and report to plantengineers or APC group for any difficulty in doing so% Ma&e sure that the Climits are &ept as per the plant engineer)APC engineer guidelines%





Methods to identify performancedegradation



PREDER: ependent ariable prediction error%

This value is the difference between the predicted and the actual controlled variable

values, calculated as "prediction - actual".

AVPRER: ependent ariable filtered aerage prediction error%

This value is the heavily-filtered average of the absolute value of the prediction error.Use it to determine, on average, how big errors are in the model.

ACPRER: ependent ariable accumulated error +integrated alue of PRR-

When this value is trending upward, a disturbance (or model error) that is decreasing the

actual dependent variable value is occurring.

When this value is trending downward, a disturbance that increases the actual

dependent variable value is occurring.

Prediction error plots are custom configured using dummy CVs.


CV Prediction Errors



Prediction error(1

ACPRER (Dependent !ariable accumulated (integrated prediction error

"#is entry is t#e integrated !alue of prediction errors (predicted minusactual since t#e last prediction initiali$ation.

C#anges in t#is !alue indicate eit#er a mismatc# bet%een t#e model

predicted response and t#e actual process response& or t#at an

unmeasured process disturbance #as occurred.

'onitoring ACPRER is recommended o!er PREDER as time correlated

controller disturbances (prediction errors are better detected by obser!ing

t#e integrated !alue.

"#is !alue ultimately represents t#e current bias& since t#e last prediction

reset& t#at must be added to t#e model predicted dependent !alue to matc#

t#e response of t#e process.




Prediction error(

)#en t#is !alue is trending up%ard& a disturbance (or model error t#at is

decreasing t#e actual dependent !ariable !alue is occurring. )#en t#is !alue is

trending do%n%ard& a disturbance t#at increases t#e actual dependent !ariable!alue is occurring.

"#e controller updates ACPRER during eac# cycle. ACPRER gets reset to t#e

current cycle*s PREDER !alue %#ene!er one of t#e follo%ing conditions

occurs:

(a t#e dependent !ariable predictions are initiali$ed (PRD+,D - 1.

(b t#e absolute !alue of ACPRER becomes greater t#an ///./ (to a!oid

e0ceeding any numerical tolerances for t#e system.




Prediction error(



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Prediction error(2



CV Prediction Error Plot (effect of o!erride



'odel cur!es (!isual inspection

Smoot#ness of model cur!es and !erification %it# process insig#t

"#e model cur!es of APC must accurately represent t#e process c#ange

"#e model cur!es s#ould be interpreted as t#e c#ange in t#at particular CV

corresponding to a unit c#ange in t#e 'V 3eeping all ot#er 'V455s

constant

"%o aspects of t#e model cur!es s#ould be loo3ed at6ain

Dynamics

)#en bot# t#ese aspects are accurate t#e cycling of t#e controller %ill

reduce and t#e control action %ill become smoot# and accurate

"#e final steady state !alue of t#e cur!e is denoted as 6A+, "#e part of t#e cur!e leading to Steady state !alue is called t#e D7,A'+CS




'odel cur!es (!isual inspection(

February 21, 2016 Reliance Technology Group – APC / RTO 1"



'odel cur!es (!isual inspection(




Causes of Performanceegradation



Causes of Performance Degradation

Process c#anges:

E8uipment degradation& ,e% Constraints

'a9or c#ange in operating regime (5eed product spec& flo%s etc ,e% operational ob9ecti!es& or increased unmeasured disturbances

+nstrumentation issues:

Deficient P+D loop tuning& Control !al!e or ot#er issues

Control loop configuration c#anges

;perator understanding:

'V Pinc#ing Conflicting CV Constraints

+nconsistent ob9ecti!es Deficiency in "raining

APC +ssues:

'odel design& Controller fidelity and Soft sensor accuracy issues

"uning <ogic problems





Causes of Performance Degradation (process(1

E8uipment degradation& ,e% Constraints

E8uipment degradation can cause c#anges in t#e be#a!ior of t#e plant

(=> fouling& column fouling& catalyst degradation

+n certain cases t#e e8uipment may be ta3en offline for

ser!icing4maintenance acti!ities (furnace deco3ing

,e% process constraints (control !al!e pressure drop& S;R !s E;R

operations limit t#e mo!ement of 'Vs and CVs

"o ensure good performance of APC necessary action must be ta3en

1. C"S engineer s#ould analy$e and record t#e c#anges in

prediction error (ACPRER 4specific error calculations in CC5

and inform t#e APC engineer.

. APC engineer must c#ange t#e model to ma3e it robust enoug#to #andle t#is. +n some cases model may need to be c#anged or

additional logic may need to be added to ensure t#at t#is

be#a!ior is captured




Causes of Performance Degradation (process(

'a9or c#ange in operating regime (5eed product spec& flo%s etc

Due to ne% guidelines from t#e management t#e operating parameters may

need to be c#anged

"#ese can include c#anging t#e t#roug#put& feed& product specs& product

ratios etc.

5or e0ample 5CC at ?'D can be run in t%o modes

Propylene mode

6asoline mode

Due to t#ese c#anges t#e optimi$ation function may not be !alid. =ence t#e

follo%ing action s#ould be ta3en

C"S engineer must be a%are of t#ese c#anges and must inform t#e

APC engineer t#e ne% optimi$ation ob9ecti!es and t#e lostoptimi$ation potential

APC engineer s#ould ma3e t#e re8uired c#anges in t#e calculations4

costing functions to ensure t#at t#e ne% optimi$ation ob9ecti!es are

ac#ie!ed




Causes of Performance Degradation (process(

,e% operational ob9ecti!es& or increased unmeasured disturbances

APC can predict CV mo!ement %#en it is modeled accurately %it# all

t#e related 'Vs or 55s

@nmeasured disturbances (ambient temperature c#ange %ill cause

une0pected c#ange in t#e CV prediction

Smoot# and small disturbances are compensated for by APC

Sudden and large disturbances can degrade t#e performance of t#e

controller

"#e follo%ing action needs to be ta3en

C"S engineer s#ould identify suc# disturbances by obser!ing

t#e prediction error of t#e concerned CVs and inform t#e APC

engineer APC engineer s#ould model t#e ne% disturbance or incorporate

a %ay of measuring t#is disturbance so t#at t#e CV prediction

become more accurate leading to better model fidelity and better

performance




Causes of Performance Degradation (+nstrumentation(1

Deficient P+D loop tuning& Control !al!e or ot#er issues

APC acts as a super!isory control& #ence base control (P+D loop #as to be

maintained to ensure t#at APC performs at its best

'aintaining good base le!el control is !ery important to APC

"#ere can be many issues %it# base le!el control %#ic# can affect APC

performance

Stic3y !al!es

5aulty transmitters

+naccurate P+D loop tuning

Suc# instrumentation issues can deteriorate APC performance drastically

"#e follo%ing action must be ta3en to ensure t#at t#ese issues do not affect APC

performance

"#e C"S engineer must monitor all P+D loops on a regular basis andmust analy$e and record t#e results

"#e instrumentation4APC engineers of t#e plant are responsible for

ensuring t#at all P+D loops are %ell maintained




Causes of Performance Degradation (+nstrumentation(




Causes of Performance Degradation (+nstrumentation(

Control loop configuration c#anges

APC is modeled assuming a certain control loop configuration

Any c#anges made to t#ese configuration needs to be reflected in APC

Control loop configuration includes t#e follo%ing

C#ange in P+D algorit#m due to migration of DCS

C#ange in !al!e or transmitter types4models

rea3ing cascades

Reconfiguring split range controls

C#anging t#e %ay read4%rite are #andled by t#e DCS

"#e C"S engineer must 3eep trac3 of t#e different configuration c#anges

and must bring t#em to t#e attention of t#e APC and instrumentation

engineer

"#e instrumentation and APC engineer are responsible for ma3ing t#e

re8uisite c#anges to APC to ensure good performance



February 21, 2016 Reliance Technology Group – APC / RTO 2"

Causes of Performance Degradation (;perator(1

'V Pinc#ing Conflicting CV Constraints

Pinching is t#e process of ma3ing t#e upper limit e8ual to t#e lo%er limit for 'Vs

in APC

Pinc#ing pre!ents APC from ma3ing any mo!ement to 'Vs t#ereby restricting

t#eir mo!ements

Conflicting CV limits can #inder APC mo!ement

E; conc and C; conc #ad a common 'V (o0ygen. All t#e ot#er #andles for C;

conc %ere #itting limits as defined by t#e operator. E; column Delta P(CV %as

being constrained at t#e upper limit. "o maintain t#e limit on E; column Delta P

APC %as cutting t#e ; to t#e unit t#ereby cutting plant t#roug#put.

;nce t#e DeltaP limit %as increased t#e plant t#roug#put increased

"#e C"S engineer is responsible for indentifying suc# conflicting limits and

informing t#e operator and APC engineer

"#e operator must rela0 suc# limits after consultation %it# APC engineer




Causes of Performance Degradation (;perator(

+nconsistent ob9ecti!es Deficiency in "raining

Conflict of interest bet%een dept can cause conflicting mo!ements in

APC

Comfort le!el of certain operator maybe be #ig#er compared

;perator training is !ery important to t#e performance of APC as t#ey

%ill be t#e ones %#o %ill be operating t#e plant on a minute by minute

basis <ac3 of operator training leads to lo% confidence& conflicting limits and

a lac3 of %illingness to s%itc# on t#e controller

"#ese can deteriorate plant performance and lead to s%itc#ing off of t#e

controller

"#e C"S engineer must ensure t#at all operators are trained %ell and#a!e t#e re8uired 3no%ledge to run APC

Any inconsistent ob9ecti!es must be discussed and resol!ed bet%een

t#e APC4C"S engineer4instrumentation and operator




Causes of Performance Degradation (APC(1

'odel design& Controller fidelity and Soft sensor accuracy issues

APC can perform to best of it ability if t#e model #as a good accuracy

)#en t#ere is e0cess cycling in t#e 'V mo!ements t#is can be due to an

issues %it# controller fidelity

"#e robustness of t#e model and controller fidelity is ensured using

different tools li3e

R6A

SVD

Condition number

Soft sensors are t#e tools using %#ic# t#e APC measures feed4product

specs

"#ese #a!e to be calibrated and updated regularly so t#at t#ey reflect

true product specs

Suc# soft sensors are modeled usually in ASPE, +B as and %#en

re8uired




Causes of Performance Degradation (APC(




Causes of Performance Degradation (APC( "uning <ogic problems

APC #as many tuning parameters t#at need to be tuned to ensure #ig#

performance

Some of t#ese tuning parameters are

Ran3s

'a0 mo!e

'o!e suppression

'a0 SS step

ECEs

SS Cost

Cost Criteria

"#e C"S engineer must notice %rong mo!ement& cycling or e0cessi!e

mo!ement in 'Vs or lac3 of control of CVs to t#e notice of APC engineer

"#e APC engineer %ill perform t#e re8uisite analysis and %ill ma3e t#e

re8uired c#anges to t#e tuning parameters




APC maintenance acti!ities

APC P f C l l ti



APC Performance Calculations

1% :P Performance ; M < C based Performance nde( Calculations

2% Controllability ; C :imit iolation Calculation < APC #uning

"% Model Fidelity ; C Prediction error trending Calculation < Model Mismatch




APC Performance Degradation

Annual Profits

Controller

Switched On

Controller

Switched Off

Time

Degradation

Time

Degradation of Controller Performance

LostProfit

February 21, 2016 Reliance Technology Group – APC / RTO "0



APC 'aintenance (1

Performance +nde0es:

;n "ime days

'VCP+s Reports CV <imit Violations

CV Prediction errors

Reports 5ormats

Controller Performance Reports

Plant Performance Report Site Performance Report

R+< Performance Report

CV <imits :

Safety <imits

E8uipment <imits

Buality <imits




APC maintenance (

CV 'onitoring is more in!ol!ed and re8uires:

no%ledge of Process and "ec#nology

no%ledge of ;perations no%ledge of plant constraints

CV and 'V mo!ements:

Correctness of Economic Direction

Correctness of direction %rt safety& 8uality and !iolation 'odel fidelity to #old on constraints

Correct cost and tuning

Correctness of priority %rt on safety& e8uipment constraints and 8uality


R+< @ ti + d ;,DA7S



R+< @ptime +nde0 ;,DA7S

+1440 Minutes per ay = 60- DA75AC > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

?Controller Run #ime in *econds +C#:3#- @

1 ;,DA7S > 3A* B ;;;;;;;;;;;;;;;;;;;;;;;

+AFAC-

Adantages < isadantages$

1%AFAC > number of runs in a day

2%Counts the total number of days from commissioning

"%Can be reset

f C



R+< Performance +nde0 'VCP+

+3et 3umber of Ms D 0%5=Ms at :imits B 0%5=Ms at ngg :imits-

'VCP+ > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;(

100

+3et 3umber of Ms -

Adantages < isadantages$1%Ms at limits are debited by 50E +M are free to moe in one direction-

2%*uperfluous Ms are subtracted +:i&e Ms on standby e.uipment-

"%Can account for Cost and Min moe Ms

4%More pleasant results$ 50E for all Ms at constraint

5%Measures the effectieness of controller as designed6%ased on the performance of the :P optimiGer in the APC

7%Historical reference and highlighting unusual day;to;day highs or lo!s

8%alues can be reported for a controller or plant or site or een R:

9%Current, daily, monthly aerages can be easily calculated

10%Ieneric and transparent, easy to implement < easy to interpret




PC)S Screen




'A,AC" is used to detect t#e position of 'V:

- ot# limits clamped& -+nacti!e

1-At upper limit& -At lo%er limit




R+< Performance A!erages



R+< Performance A!erages

For controllers that e(ecute eery minute$

+MP=14"9 B MCP- +MP=+AFAC;1- B MCP-

Daily 'VDP+ > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

+1440 Minutes per day- AFAC

+MMP=+1440="0;1- B MCP-

'ont#ly 'V'P+ > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

+1440="0 Minutes per Month-

+MCP1=M1 B MCP2=M2 BJ-

Plant 'VPP+ > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

+M1 B M2 BJ-

+MPP1=M1 B MPP2=M2 BJ- Site 'VSP+ > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

+M1 B M2 BJ-

+M*P1=M1 B M*P2=M2 BJ-

R+< 'VRP+ > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

+M1 B M2 BJ-

R+< CV Violation Performance +nde0 V;+= V+;<



R+< CV Violation Performance +nde0 V;+= V+;<

For a controller running eery minute$

V;+ > ?C Aboe High limit by a defined tolerance +0 or 100-@

+H=14"9 B -

V;+= > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

+1440 Minutes per day-


1%Can be defined separately for lo!er < upper limit iolation

2%Can indicate Model #uning issues for a good fidelity controller "%mportant Cs can be trac&ed for unacceptable iolation

4%Aerages are 1st order lags

5%Plot needs to be lin&ed, default plots are not aailable in MC

CV <imit Violation F per day (/./ "olerance




CV <imit Violation F per day (/./ "olerance

R+< Performance enefit 'VP+



R+< Performance enefit 'VP+

?MMP D +85 ; 50-@ 'VP+ > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ( 100

50


1%"5E MCP > Gero profit, 85E MCP > 100E profit

2%85E performance is base line, higher alues gies better than design

numbers%

"%All Ms are !eighted e.ually

4%Reflects percentage of baseline benefit achieed by the controller

R+< 'V Performance +nde0 G features



R+< 'V Performance +nde0 features

ased on 'anipulated Variables 'Vs 'onitors Acti!e Constraint of 'Vs

Penalty of H/F if an 'V is targeted at lo%er or upper limit Performance of H/F %ill result if all 'Vs are ;, but all targeted at upper4lo%er limit <o%er t#an H/F could result if 'Vs are pinc#ed& or 3ept ;55

Performance +nde0 Ranges:

Ireater than 85 (cellent et!een 75 D 85 ery Iood et!een 65 D 75 Iood et!een 50 ; 65 Fair :ess than 50 Poor

endor soft!are li&e Aspen < Matri&on can also be used

C based similar performance inde( can also be calculated, !ould improe performance of controllers !here

redundant or multiple Ms for same C are present%


Reports 5ormats




Reports 5ormats

Conflicting ;b9ecti!esI P;s comfort !s C"S constraint pus#ing

R+< Performance Report

Site Performance Report

Plant Performance Report

R+< 'V Performance +nde0 J "o be reported by CE; APC (R"6




p y (

R+< 'V Performance +nde0 J "o be reported by site APC




p y

R+< 'V Performance +nde0 G "o be reported by site C"S




p y




APC maintenance flo%c#art

09 apc maintenance cts

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