energy savings with advanced process control - ciigbc din… · copyright © 2009 yokogawa...

Copyright © 2009 Yokogawa

Energy Savings withAdvanced Process Control

Dinesh Jaguste, PhD

Date : 4th Sept 2010


Yokogawa APC Products

SGSI >800 APC installations

Yokogawa + SGSI >200 APC worldwide>40 In India•Refineries•Petrochemical•Fertilizer•Pulp and Paper•Polymers

Copyright © 2009 Yokogawa Page 3

AGENDAIntroductionAPC ConceptsEnergy Savings with APC

-Furnaces

-Distillation Columns

-Reactors

-Heat Recovery maximization

-Pressure drop minimization

-Steam Power network Optimization


NG price in India ~ 5 Rs/NM3 in 2009~ 10 Rs/NM3 in 2010

Urgency for Energy Efficient Operation

Process Industry – High energy intensity industryØEnergy is the largest variable operating cost after feedstock

Modern plants have tighter energy integrationØComplex dynamics with interacting Multivariable loopsØDifficult Process Control

Minimize Energy Consumption with Advanced Process Control


Potential Energy Investments and benefits

**Source: Dogulas White, ‘Olefin Plant Energy Savings through Enhanced Automation,’ AIChE 2009 Spring National Meeting, Tampa, Florida,

Capital Cost (Time to Implement)

PotentialSavings

LOW MEDIUM HIGH

HIGH Integrated Gas turbine: CogenerationFurnace/separation process upgradeReplace low efficiency process equipments

MEDIUM Improved Automation;Operating ProcedureChanges;Energy KPI Monitoring

Advanced Process ControlOptimizationEnergy Management systems

LOW Increased Insulation;Steam Trap/ LeakManagement;Exchanger MaintenanceCondensate Recovery

Energy Saving : 1-3%Investment < 200000 USDPayback < 1 year


104

102

100

98

96

94

92

90

SPECIFICATION OR LIMIT

BEFORE CONTROL ADVANCEDCONTROL ONLINE

AVERAGE (SETPOINT) MOVES CLOSER TO LIMIT

PE

RC

EN

T O

F LI

MIT

Distribution ofInstantaneous values

Base Case Stabilise Exploit

APC benefits

Example: Maximize reactor temperatureHigher temp: better conversion

Less feed for same productLess recycle

Constraint: run-away reaction

APC inControl Mode

APC inOptimization Mode


What is Advanced Process Control (APC)?

APC is a step beyond Process Control– DCS is enabling technology– Built on foundation of basic process control loops– Process Models predict output from key process variables online and real-time– Optimize Process Outputs relative to quality and profitability goals

ProcessModel

Optimizing ControlCalculations

PROCESSDCS

Economic ObjectivesDesired OutputsConstraints Outputs

Process Data

Model Predictionsfuture process behaviour

OptimumSet Points to PID loops

APC synonymousMultivariable Predictive Control (MVPC)+ Quality Estimators


First Order Second Order

RAMP Second Order Inverse

Step Response Models


Model Predictions (Principle of superposition)

Future changes in Outputs are predicted using past input data

k

T

ikik dMVaCVCVN

i

+∆+= ∑=

− ) ( 1

0


Model Predictions (Principle of superposition)

)( )() ,() ,(

2111211

21 1

MVCVMVCVMVMVCVMVMVfCV

∆∆+∆∆=∆∆∆∆∆=∆

Multivariable Case

MV1

MV2

MV1

MV2

MV1

MV2

CV1(MV1)

CV1(MV2)

CV1(MV1,MV2))


Multivariable Optimizing Predictive Control

Page 11

Hot Water (MV2)

Feed (DV)

Steam (MV1)

T

Temperature (CV)

Feed (DV)

Temperature (CV)

Steam (MV1)

MINIMIZE

Hot Water (MV2)

TerminologyControlled variable (CV) : TemperatureManipulated Variables (MV): Steam, Hot waterDisturbance Variable (DV): Feed FlowOptimization Objective: Minimize Steam flow

Set Point

Open loop response

Past FutureSteam minimized

Temperature

Feed

Hot

Wtr

Stea

m


∑ ∑=

−

=+++

∆++

+

P

j

M

j

q

Sjk

q

R

ujk

q

Tj

q

Q

yjk

u jjjjuese

1

1

0min

( )( ) Pjuxgy

Pjuxfx

jkjkjk

jkjkjk

,...,1 ,

,...,1 , 11

=∀=

=∀=

+++

−+−++

Subject to

1,...,0

1,...,0

,...,1 0

,...,1

−=∀∆≤∆≤∆

−=∀≤≤

=∀≥

=∀+≤≤−

+

+

+

MjuuuMjuuu

Pjs

Pjsyysy

jk

jk

j

jjkj

Model constraint

Inequality constraints

2or 1 , , 1 =−≡−≡ +++++ quueyye sku

jkr

jkjky

jk

What is APC? Mathematically …

A repeated optimization problem!


Reasons for poularity

MVPC provides a systematic, consistent, and integrated solution to process control problems with complex features

•Complex dynamics- e.g long delays, inverse response•Strong interaction (large relative gains)•Multiple changing Constraint handling

Model Predictive Control(Dynamic Constraint Control

@ every minute)

PID

PID

SUM

Monitoring and Optimization (Operator)

Monitoring (Operator)

PIDL/L

SUM

PID PID PID

PID Set PointsValve Positions

Economic ObjectivesConstraints

Enhanced RegulatoryControlIn DCS

APCOn SupervisoryComputer

Multivariable ControlConventional Vs APC

PID Set PointsValve Positions


Quality Estimator(Quality predicted using DCS measurements)

FFBP

Lab MeasurementOr Online Analyzer

FBPPredicted with online(no process and measurement delay)

FBP estimator

Q = f(T, P, F)


Mechanism of APC

Page 15

REFLUX ADJUSTMENTS1500

1300

1100

900

700

500

216

214

212

210

208

OPERATOR CONTROLINFREQUENT, LARGE

ADVANCED CONTROLFREQUENT, SMALL

REFLUX ADJUSTMENTS

RE

FLU

X (t

/d)

SETPOINT CHANGE (yield maximization)

FBP

(deg

C)

FFBP

Measured in Lab

FBPPredicted with online(no process and measurement delay)

FBP estimator

Manual Control

Lab measurement

Online control with APC


Energy Savings with APC Furnaces

üTighter Temperature ControlüPass BalancingüMinimize excess Oxygen


F

F

F

F

T

P

F

T

T

T

T

FUEL OIL

CRUDE TO ATM. COLCRUDE OIL FEED

FUEL GAS

CONSTRAINTS :

• Pass flow dev from average

•Skin temperature

Heater pass balancing

Equalise Pass Temperatures

Adjust Pass Flows

Typically 8 passes


Pass flow to flow-deviation step responses


Pass flow to temp-deviation step responses


Typical pass balance APC performance

APC

BenefitsIncreased furnace run-length due to reduced average coking rateFurnace severity can be increased (If constrained by Skin temperature)Throughput can be increased (for same coking rate)


Tighter Coil Outlet temperature control

Page 21

310

311

312

313

314

315

316

317

318

2006/01/20 05:30

2006/01/21 05:30

2006/01/22 05:30

2006/01/23 05:30

2006/01/24 05:30

301-F-01 Coil Outlet (301-R-01 inlet)Temperature 301TC0301

PV

_301

TC03

04

PIDTuning

Furnace can be operated at higher temperature for same coking rate-Better conversion leads to energy savings


APC

Fuel Savings with minimizing excess O2%

Normally O2% is manually controlledO2% varies due to-Throughput (Heater Feed) variation-Fuel composition variation-Air temperature and relative humidity variation


Energy Savings with APC Distillation ColumnsüTighter Temperature ControlüMinimize Column Pressure üMinimize Reflux


Distillation: Tighter quality control

Impurity in product%

Energy Consumption

Energy consumption increases disproportionately (nonlinearly)with product purity

üAPC helps production on specification with minimum quality giveawayüPrevents quality variation and product blending

(which consumes higher energy)

X1 Xm X2

E2EmE1

Xm-X1 = X2-XmE1-Em > Em-E2


Distillation column stabilized with APC

Page 25

100

102

104

106

108

110

112

114

116

118

120

2005/04/23 05:30

2005/04/27 05:30

2005/05/01 05:30

2006/05/27 16:30

DEG Column top temperature (TI7253) Before and After APC

TI72

53.P

V

APC

Column top temperature maximized with reduced refluxüHigher product yieldüWith lower energy consumption


4.04.2

4.4

4.6

4.85.0

2.4

2.6

2.8

3.0

2005/07/02 05:30

2005/07/04 05:30

2005/07/06 05:30

2006/02/22 15:08

2006/03/17 06:46

2006/03/19 06:46

Reduction in Refyning columns pressures with APC

EP

C40

1.P

VE

PC

403.

PV

2025

30

35

4045

16

18

20

22

2005/07/02 05:30

2005/07/04 05:30

2005/07/06 05:30

2006/02/22 15:08

2006/03/17 06:46

2006/03/19 06:46

Reduction in Rectyfying columns reflux flows with APC

EFC

409.

PV

EFC

403.

PV

Distillation column Pressure minimization

APCAPC

Column pressure reduction leads to Reflux (Energy) reduction For same separation and recovery

Constraints:üMaximum Condenser CapacityüColumn Flooding


Energy Savings with APCReactors

üMaximize ConversionüMinimize excess reactantsüTightly control optimum composition


Heavy Glycol Distillation

O2

Ethylene

Cycle Gas

MEG

EO/EG Manufacturing Process at IGL: 3 streams

Ethanol Purification

AlcoholEthanol

Dehydration - I

Ethanol Dehydration - II

Ethanol Dehydration - III

CO2 Removal Common

CO2

EO Recovery

Purified EO

EO RX - I

EO RX – II

EO RX –III

EO Purification

Glycol Train - I

Glycol Train II

Glycol Train III

TEGDEG HG

•Maximize O2% at reactor inlet•Equal load on all 3 reactors


6.5

6.6

6.7

6.8

6.9

2005/04/23 05:30

2005/04/27 05:30

2005/05/01 05:30

2006/07/13 10:30

Reactor inlet O2% (AR2301) Before and After APC(Reactor inlet O2% maximization -for improving selectivity- with APC)

AR

2301

.PV

EO Reactor inlet O2% (AR2301) Before and After

Ethylene Oxide Reactor inlet O2%

APC

Sectivity Change% versus inlet Oxygen%4700 GHSV, 7% O2, 25% C2H4, 1% CO2, 16 barg, 200 kg/m3/hr

00.5

11.5

22.5

3

6 6.5 7 7.5 8Inlet Oxygen%

Sele

ctiv

ity C

hang

e%

Ethylene -à Ethlene OxideSelectivity improved

Ethyleneà CO2 minimized


Ammonia Plant

Mimimize S/C (excess steam)

Tightly Control Converter inlet H/N ratioMinimize compression energy

Minimize CO2 slipIncrease NH3 yield minimize purge losses

APC

APC

APC


Energy Savings with APCHeat Recovery

üPreheat maximization in CDU


0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

2007/11/03 14:21

2007/11/04 14:21

2007/11/05 14:21

2009/01/02 05:20

2009/01/03 05:20

2009/01/04 05:20

CDU Column top Reflux ratioBefore and After APC

03FC

1605

/03F

C19

01

Total stripping steam consumption (% feed)

1.4

1.5

1.6

1.7

1.8

1

854

1707

2560

3413

4266

5119

5972

6825

7678

8531

9384

1023

7

1109

0

Time (minutes)

Stea

m/F

eed

(%)

Minimize ovhd RefluxMaximize CRs

Energy Savings in CDU Column

Minimize stripping steam

Minimize Overflash (COT)


Energy Savings with APCMinimize Pressure drops

üEnergy Saving in FCCU


Fluid Catalytic Cracker (FCCU)

L T

F

AIR

S

S

P

P

SLURRY

LCO

GASGASOLINE

T

HCNLCN

Reactor

Regenerator

Main Fractionator

Flue GasO2%

Minimize Main Air Blower energy consumptionMinimize excess O2%Minimize RCSV/SCSV pressure drop (Retain controllability)(minimize regenerator pressure)


Page 35

Minimization of Regenerator slide valve pressure drop

23 AUG - 12 SEPT

350

340

330

320

310

300

290

280

270

260

250

240

230

RE

GE

N S

LID

E V

ALV

E D

ELT

A-P

(mba

r)

DAYS

NORMAL LOW CONSTRAINTSMOC-2 OFF SMOC-2 ON ......

(for no-APC test)

another constraint active duringthis period

APC


Energy Savings with APCSteam Power Network

üMinimize Excess O2%üMaximize Steam superheatüMinimize steam ventingüMaximize Power generation

(Minimize steam let down through PRDS)


Steam system

4 Coal fired boilers (62 ata)2 Recovery boilers (62 ata)4 TGs (back pressure and extraction cum condenstation)2 Power networks (Max Power generation ~60 MW)HP header 62 ata (total generation ~ 300 T/H)

MP Header 11.5 ata (consumption ~ 50 T/H)LP Header 5.5 ata (consumption ~ 250 T/H)Excess MP/LP demands met by let down through PRDSHP ERV, MP vent, LP dump (condensation) and LP vent


Control Problem

Control problem : ~ 100 TPD steam venting due to sudden load changes– 12 Batch digestors with staggered batch-schedule

: sudden variation in MP demand – Paper breaks on paper machine: sudden change in

LP consumption– Wood chipper machine start/stop : sudden change

in power demand

BenefitsüSteam venting reducedüSteam generation reduced by minimizing steam let down through PRDS


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