APC Utilized at IGCC Plant (ABB)

8/8/2019 APC Utilized at IGCC Plant (ABB)

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AdvancedProcess Control

ABB Value Paper Series


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IGCC technology o ers a number o importantenvironmental bene ts: rst because gasi cationallows the use o both a combustion turbine and asteam turbine in the power production process, anIGCC power plant can achieve an operating e ciencyo about 45 percent, compared to pulverized coal(PC) plants which operate at e ciencies ranging romabout 33 to 40 percent. Particulate matter, sulphur,nitrogen and mercury are removed rom the gasi ed

coal prior to combustion instead o rom boiler exhaustgases post-combustion as in a PC plant. Up to now,re nery-based IGCC plants (mainly in Europe) havedemonstrated good availability per ormance andare more established rather than utility-based coalIGCC plants, with availability in the range o 90%-95% consistently being achieved. Several actors arecommon to these plants that may be contributing tothis good per ormance. It should also be noted thatnon-utility plants have recognized the need to treat thegasi cation system as the up- ront chemical processingplant that it is, and have generally reorganized their

operating sta accordingly. Because IGCC plants arehighly demanding rom a control perspective, they areideal targets or advanced strategies (see or example[3 and [4]]). However literature about actual advancedprocess control applications or IGCC acilities doesalmost not exist.

2. The ISAB Energy Priolo IGCC Plant2.1 Process Overview The Isab Energy (IE) IGCC plant in Priolo, Italy, convertsabout 120 tons/h o heavy residual oil, provided by the

nearby ErgMEd re nery, into more than 500 MW oelectric power. Isab Energy and Isab Energy Servicesare a joint venture between ERG Power & Gas (51%)and International Power Mitsui & Co. Ltd (49%). IsabEnergy and Isab Energy Services represent, respectively,the Owner and the Operator o the IGCC complex.

The Priolo IGCC plant started commercial operation in April 2000 and can be divided in three main areas:

Solvent Deasphalting Unit (SDA) Gasi cation and Utilities Units

Combined Cycle Units (CCU)

Abstract:IGCC (Integrated Gasi cation and Combined Cycle)plants are among the most advanced and e ectivesystems or electric energy generation rom re neryresiduals and are becoming more and more popular inmany regions worldwide. From a control perspective,IGCC plants represent a signi cant challenge: complexreactions, highly integrated design and variable eedcomposition come together requiring coordinated controlto simultaneously satis y production, controllability,

operability and environmental objectives. While all theserequirements seem clearly to demand a multivariable,model predictive approach, not many applicationscan be easily ound in the literature.

This paper describes an ongoing Advanced ProcessControl project at the Isab Energy IGCC plant inPriolo, Italy, and aims to share design considerations,implementation details and preliminary results ach-ieved on the rst units. The project can be seen as thesecond step o a multi-stage plan or increasing pro-cess per ormance through automation improvements.

A ter an overall DCS control revision per ormed in2005, the project team was asked to introduce unitoptimization on some o the most critical areas. This isgoing to be completed by means o several MultivariableProcess Controllers which are contributing to reducesteam and utility consumption, stabilize H 2S removaland minimize environmental impact.

1. IGCC Process Generalities An Integrated Gasi cation Combined Cycle, or IGCC(Integrated Gasi cation Combined Cycle), is a powergeneration system which produces synthesis gas(syngas), mainly composed o CO and H 2, converted

rom ossil uel, such as vacuum residue, heavy oil,petroleum coke, coal and Orimulsion by a partialoxidation process and then burned to generateelectricity rom syngas by combined cycle. IGCCtechnology has become the center o public attentionas one o the prime applications o technology ormaintaining clean air or the world (see or example[1] and [2]). The reason or this is that it enables theproduction o clean gas, equivalent to natural gaseven i at lower heating value, rom in erior uel withexpected reduction o CO

2emissions by use o high

per ormance gas turbines.

AdvancedProcess ControlUtilized at an Integrated Gasi cation Combined Cycle Plant

by Mario Abela Isab Energy Services Srl, Priolo Gargallo (SR) Italy and Nunzio Bonavita , Riccardo Martini ABB PS&S SpA, Genova Italy

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The SDA receives the heavy residue rom the re neryand deasphalts it; the deasphalted oil is then sentback to the re nery while the asphalt is ed to theGasi cation Units. The gasi cation area trans ormsthe asphalt coming rom SDA into clean syngas to beburned in the CCU. It is a wide complex which includesthe ollowing main units (see Figure 2):

2 Gasi cation Units 2 Carbon Recovery Units 1 Sulphur Recovery Unit 1 Heat Recovery Unit 1 Acid Gas Removal Unit 1 Heavy Metals Recovery Unit 1 Waste Water Pre-treatment Unit

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Fig. 1 - IGCC general scheme

Fig. 2 - Gasi cation Flow Diagram

ERG PETROLIREFINERY

Unit 3000 Solvent

Deasphalting

BTZ

Asphalt

HP Steamrom CCU Oxygen

Unit 3100 Gasi cation Soot Water

Sour Gas

Syngas

Unit 3300 Heat Recovery and

Saturation

Expander

Sour Wate

Sour Water

Soot Oil

Syngas to CCU

USo

S

U AR

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REFINERY

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Gasifcation

VanadiumConcentrate

Sulphur

CCU

ElectricPower

SDA

Asphalt


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3. The Advanced ProcessControl Application

3.1 Background and ImplementationPhilosophy

A ter a ew years o success ul operation a ter plantstartup, personnel at Isab Energy elt that the planthad the potential or additional margins and started toanalyze possible strategies or improvements. In 2005they started a collaboration with the vendor in order toreview and improve the basic control scheme, hostedin the plant DCS. This activity led to the introductiono several improvements in the plant control schemeswith the objective o improving process control in

normal and transient operations.

The main changes implemented in the 2005project were:

Revision the coordination layer between theprocess unit (PPU) and the combined cycleunit (CCU), also know as Master Controller,to allow or:

o Better control in steady state conditionso Faster response in transient conditions

o Possibility to handle some speci c operatingconditions (e.g. in one CCU Unit have twotrains in coordination mode, one trainoperated at maximum limit, etc.) thatwere originally not considered

Implementation o pass balancing inthe plant urnace

Implementation o multiple new control loops(cascades, eed orward, ratio-control, etc.)

As part o this advanced regulatory control enhancementproject, Isab Energy supported by vendors specialistsidenti ed some key process units that had the potentialto greatly bene t rom the implementation o a ullyfedged advanced process control system. Three keyunits were then selected by the customer as the objective

or the rst step o an advanced process control (APC)project which has been awarded to the automationvendor. These units were:

Solvent De-Asphalting Unit Gasi er Units (2 trains) Acid Gas Removal Unit (AGR)


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Fig. 4 - Solvent Deasphalting


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Fig. 6 - Acid Gas Removal

Fig. 5 - Gasi cation


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3.2 Project ExecutionThe APC project team was composed o three engineersworking ull time on the project. This included twoexperienced engineers rom the vendor side and one romIsab Energy. In addition, several Isab Energy engineersprovided support or process analysis and simulation,DCS integration, network integration. The project hadits kick-o meeting in October 2006.

The rst unit taken into consideration was Acid GasRemoval, ollowed by Solvent Deasphalting and nallythe Gasi ers. The rst milestone task or the project team

was the development o the basic design speci cationor all the APC applications. This speci cation providedan overview o the design, or all the applications anddescribed in detail the implementation approach.Continuous dialogue and interactions between theproject team was a critical actor in the developmento a design basis that received a high degree oacceptability rom the plant personnel and ensurede cient project execution.

The execution o this kind o project in phases bringsseveral advantages. For example, each application

can be designed, installed and tested in a completelyindependent way, resulting in a greater fexibility andmore e cient use o resources. The project team wasable to gradually introduce new concepts to the plantpersonnel and train them on the use o the new technologywithout any risk o in ormation overload. By keepingits project team members closely involved with eachphase o the design and con guration o these advanced

applications, Isab Energy was able to reduce projectcosts while ensuring they received customized solutionsthat could quickly be put online and maximize theirreturn on investments.

3.4 Technology OverviewKey technologies selected or the APC applicationsare multivariable model predictive control (MPC) andin erential modeling. In addition to that, advanced regul-atory control was applied in several cases to provide betterprocess control and aster disturbance rejection.

At the core o MPC technology is a mathematical modelo the process that is used to predict uture processbehavior. Using this predictive model the controller is ableto calculate an optimum set o process control moveswhich minimize the error between actual and desiredprocess behavior subject to process constraints. Sincethe late 1970s, MPC technology has per ormed reliablyin the petrochemical and re ning industries becauseo its ability to account or process interactions andconstraints, thereby reducing process variability anddriving the process closer to its limits.

For the power production control, MPC strategies arerequired or driving the gassi er to satis y load demandswhile meeting IGCC plant integration, per ormance, andenvironmental objectives.

Multivariable control applications are based on theOptimize ITPredict & Control (P&C) technology rom ABB.

APC Workstation

& OPC Server

ABB DCS

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7 8 9101112

AB

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Fig. 7 - System Architecture


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P&C is an innovative multivariable controller, basedon state-space modeling technology. While re erringto [6] or a detailed description, it is important tounderline that P&C exclusive eatures allow to reacha superior control per ormances in an easy-to-usepower ul environment.

The rst APC step involved our P&C controllers (oneor each unit, two or ach train o gassi er) and a ew

in erential models. In erential models were implementedthrough an ABB Optimize ITIn erential Modeling Plat orm(IMP), whose so tware details are described in [6].

The controllers are hosted on a devoted workstationthat also hosts an OPC Server. A second PC is used asdevelopment and testing environment and is not directlyconnected to the base automation system (see Figure


7). This second workstation per orms data collectionusing the dedicated so tware Optmize IT Data Manager.The APC LAN is connected to the plant LAN by meanso a dedicated Firewall that allows access to the APCLAN only to the authorized personnel. ABB so twareallows remote monitoring and maintenance or bothP&C and IMP so tware.

While engineering monitoring and tuning o the APCapplications is per ormed using dedicated HMIs, eitherremotely or locally, standard operations are per ormeddirectly by use o DCS graphic displays.

Operators manage the advanced application with thestandard operator console where additional pageshave been added or this purpose. Figure 8 shows atypical page in the Acid Gas Removal section.

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Fig. 8 - Typical APC Operator Display


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4. First Results And Perspectives As described in section 3 the our modules (1 or AGR,1 or SDA, 1 or each train in the Gasi cation section)were commissioned one at the time so not to overloadprocess personnel, starting with Acid Gas Removalcommissioned in November February 2007 andcontinuing with the SDA. Gasi ers will be completedwithin July 2007.

First results have been excellent with impressivereturns o investment. To keep the description short

we will illustrate rst results on the Acid Gas Removalsection, which is the one where the APC strategy hasthe longest running period (having been the rst tobe put on-line).

4.1 Control Improvement onSection 3500The multivariabile controller on the AGR section coverstwo columns: Absorber and Regenerator (see Figure6). The Absorber column uses MDEA to separateH2S rom syngas. The Regenerator column uses highquantity o LP steam to strip H

2S rom MDEA. This

unit is very important both or environmental andenergy usage reasons.

The H 2S le t in the syngas out the Absorber columnis one o the main contributors to emissions withspeci c respect to SO 2, and as such it is very importantto stabilize and, where possible, minimize. From anenergy standpoint, this unit is one o the main userso low pressure steam and, as such, there was greatinterest in reducing the steam usage. While theunit absorbs H 2S, there is certain slippage o CO 2 altogether with H

2S to the Regenerator column and

then to the downstream Claus unit. This slippage hasto be within certain limits due to the limited capacityo the downstream unit which acted in the past asthe bottleneck or the entire section.

The objectives have been translated into the ollowingobjectives/constraints or the APC system:

1. H 2S in syngas in absorber overhead2. CO 2 absorption 3. Overall MDEA circulation4. Regenerator overhead temp5. Regenerator pressure

6. Regenerator key tray temperature7. Regenerator Reboiler bottom level

In addition, the ollowing optimization objectiveshave been introduced:

1. Minimization o circulating MDEA in Absorber2. Minimization o Steam/Rich MDEA

ratio in Regenerator

The controller moves multiple MDEA injection streamsto T101 and key variables like steam, overhead refux,and bottom bleed or the Regenerator column. It isimportant to note that the multiple MDEA injectionstreams are located in di erent positions o thetower. The impact o a variation on each stream onH2S and CO 2 is di erent depending on the injectionposition given the di erent kinetics o the reactiono MDEA with H 2S and CO 2. These di erences inthe dynamic response and steady state gains havebeen incorporated in the controller that can use anyslack available in CO 2 absorption and emissions tominimize steam consumption.

The advanced control strategy has proven to be ableto drastically reduce steam usage while maintainingcontrolled variables to their setpoints or insideconstraints. The main advantage provided by the

APC system was the possibility to avoid any risk ooverloading the downstream unit by continuouslyassessing CO 2 absorption and allowing a shi t oMDEA injection to a higher average position. To avoidunnecessary movements and lter the process andinstrumentation natural noise, all setpoint controlobjectives have been implemented in the orm o asetpoint with deadband orm.

APC control o H 2S in the Absorber column overheadhas proven to be very accurate and reliable. In Figure 9a chart o the APC system response to step changes onthe H 2S setpoint is presented. These setpoint changeswere all achieved by the APC system in a short time,without overshoots and excessive perturbations ounit operation. This is a remarkable result given themagnitude o the variation o the steps equal toabout 10 ppm in a ew hours something that veryrarely occurs during normal operations. As a resulto the step changes, the consumption o steam in theregenerator column decreased very heavily, as shown

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by the curve in blue ( or a single reboiler there aretwo twin reboilers). The overall decrease in steamusage was up to 3.5 t/h.

Although such a drastic change in setpoint or H 2So ten not possible in a ew hours, it is quite commonthat changes in actors like: Feed composition

Feed fow Cooling water temperature Other units contribution to emissions Gasi er e ciency

Impact on H 2S content was o a similar quantity over1-2 days. In that case, the presence o a APC systemcapable o minimizing steam while maintaining H 2S

content at target provides large economic bene ts. Thegure below shows the steam consumption reduction

achieved during a night test, when changes in eedcomposition and cooling water temperature togetherwith a small increase o theH 2S setpoint (2ppm) allowed

or a reduction in steam usage o about 2t/h.

Overall, the APC application allowed running the unitin a di erent operating region. The ollowing gurepresents the steam speci c usage (expressed as aratio between the steam and the MDEA circulationrate) over a long period o time, rom the startup othe APC commissioning to the nalization o the APCsystem or the AGR unit. As can be seen by the chart,the reduction in the steam usage is quite relevant.

The overall bene t in terms o energy saving is quiteconsiderable. Steam consumption went rom 35.1 t/h

to 26.1 t/h equivalent to a reduction o about 9 t/h.

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Fig. 9 - APC Management o H 2S content in T101 Overhead


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21/2/07 17.06 21/2/07 19.30 21/2/07 21.54 22/2/07 0.18 22/2/07 2.42 22/2/07 5.06 22/2/07 7.30 22/2/07 9.54

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small Sp increase for H 2 S, overnight Temp decrease

APC turned on

MDEA reduction

Steam reduction (x2)

Steam Flow

H 2 S SP onT101 Overhead

MDEA Flowrate

Delta steam

~ 2 t/h


This reduction is due to changes in operatingconditions that can be described as ollows:

First, steam speci c usage was reduced byoptimizing the regenerator operating conditions

Then, the overall MDEA circulation rate wasreduced by optimizing the Absorber column

operating conditions in two ways

- 22%

o Operating closer to H 2S speci cationso Moving MDEA steam injection to a more

avorable position (average)

As a result, the unit operating conditions have movedas depicted below in terms o steam usage and MDEA

circulation rate.

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Fig. 10 - Steam Consumption Reduction

Fig. 11 - Steam/MDEA Ratio Reduction


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SteamUsage

Circulating MDEA

Without APC

With APC

SteamRatioReduction

CirculatingMDEAReduction

> 45 %

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Fig. 12 - Unit operating conditions be ore and a ter APC

Fig. 13 - Refux Flowrate Reduction


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As a consequence o the success ul results o the APCs project, Isab Energy is evaluating the possibilityo extending them to other units. In particular, thehighest bene ts could be obtained in the ollowingplant sections:

1. Carbon Recovery2. Tail Gas Treatment and Sulphur recovery3. Combined Cycle4. Waste Water Treatment

A proper plan or APC extension to additional units isunder evaluation and will be nalized in the second

hal o 2007.

Re erences:[1] http://www.eere.energy.gov/hydrogenand uelcells/ [2] http://www.gasi cation.org/ [3] Tanaka, H., The Control System applied to Negishi IGCC,

Proc. o Gasi cation technologies 2004, Washington, DC,October 3-6, 2004

[4] Vacca, G., Grugnetti, E., Sulis, S., Barabino, M., Venturino,M., On line monitoring o per ormance indexes and trigger

unctions at Sarlux IGCC plant, Proc. O ERTC Reliability& Asset Management 2004, Berlin, Germany

[5] Enhanced Alarm Management User Manual, ABB Doc. Nr.BG4.1004.EAM 20 Rev.2.0 Date March 2005

[6] Bonavita, N., Martini, R., Matsko, T., (2003), Improvementin the Per ormance o Online Control Applications viaEnhanced Modeling Techniques, Proc. o ERTCComputing 2003, Milan, Italy

As a urther con rmation, Figure 13 shows the trend othe refux stream over more than six months o data.

Analysis shows that the refux fow has decreased oabout 50%. This is quite remarkable given the actthat the original refux fow was not ar rom the designvalue or the unit.

4.2 Comments on ResultsThe positive results shown above (and the similarones achieved in other sections) have been achievedthrough a proper combination o advanced controltechnology, process expertise and deeper insight.

The APC project has proven to be the opportunity toexplore a number o possible operating conditions,sorting out actual process and control limitations romcontrol myths. The improved control tools allowedthe engineers to move the plant into non amiliarconditions, pushing the envelope and discoveringhidden pro t margins that basic control schemesdont allow to harvest. This is not di erent rom thatveri ed on any other process (no matter i its re neries,petrochemical or upstream plants) where APC is appliedas a technology enabling operators to manage the plantmore aggressively without compromising on sa ety

but with much higher economic per ormance.

4.3 Conclusion and Future PerspectivesThis paper has presented a very success ul applicationo Advanced Process Control technology to an IGCCplant. The application dealt with three sections (AcidGas Removal, Gassi er and Solvent Deasphalting)that have been identi ed as interesting benchmarks

or return-o -investment evaluation. The results a terthe rst running period are extremely positive andclearly show that APC has the potential o providingrelevant savings on IGCC plants, mainly through itscapability to greatly increase energy e ciency andreduce steam consumptions.


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APC Utilized at IGCC Plant (ABB)

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