University of Genoa

Solutions for Combined Cycle FlexibilityAlessandro Sorce, Phd

Thermochemical Power Group DIME – University of Genoa (Italy)tpg.unige.it

University of Genoa

Who is speaking?

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• PhD defense on april 2013 on “monitoring and diagnosis of energy Systems” Solide Oxide Fuel Cell Diagnosis (Genius Project) Internship c/o Power diagnostic Center di Siemens (monitoring of European and Asiatic

CCPP)

• Collaboration with Tirreno Power: Diagnostic Control Room (2013-2014) data reconciliation Algorithm: Develop and test Focus on special tasks Global Monitoring and Report system, GMR

• (2015- present) Large Size Power Plant Law for Power Plant management Environmental Impact Flexible Long term monitoring

University of Genoa

About What?

1. Large Size Heavy Duty Gas Turbine

2. HDGT Control Systems:- Control Loops and typical target- Methods for Minimum Environmental Load reduction

3. Combined Cycle Management- Start-up of the Combined Cycle

4. Maintenance cost and the Impact of Flexibilization

5. Monitoring and Diagnosis of CCPP- ST Example

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University of Genoa

Heavy Duty Gas Turbine are exploited in electricity generation tipicallycoupled with a Steam Bottoming Cycle as a Combined Cycle

Increase of Efficiency and power output is due to the higher Turbine InletTemperature reached, combined with higher pressure ratio.

1. Heavy Duty Gas Turbine

9HA

510 MW

41.8

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University of Genoa

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Turbogas General Electric 9FA+eCOMPRESSORE BRUCIATORI TURBINA

Rapporto di compressione

15,4 N° camere di combustione 18 Numero di stadi 3

Numero di stadi 18N° bruciatori per ogni camera

6 Stadi rotorici raffreddati 2

Potenza assorbita 250 MW Tecnologia DLN 2.6+ Stadi statorici raffreddati 3

Temperatura aria all’uscita

390°C

Net Power Output: 261 MW (ISO)

Simple Cycle Efficiency: 37,3 % (ISO)

University of Genoa

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Turbogas General Electric 9HA

University of Genoa

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Turbogas Alstom GT26 - ReHeatCOMPRESSORE BRUCIATORI EV TURBINA HP

Rapporto di compressione

34 N° camere di combustione 24 Numero di stadi 1

Numero di stadi 22BRUCIATORI SEV

TURBINA LP

Numero IGV 3 N° camere di combustione 24 Numero di stadi 4

Temperatura aria all’uscita

550°C Gross Power Output 262 MW

High Turn Down Capability: 20% with respect to Base Load

Is the only ReHeated HDGT TOT 615 °C => High Steam CycleEfficiency

Blade Cooling air Temperature is reduced via Steam Cooled Heat Exchangers => Close Integration between GT and Bottoming Cycle

University of Genoa

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AEN Turbogas GT26 - ReHeat

University of Genoa

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AEN Turbogas GT36

University of Genoa

Potenza netta: 269 MW (ISO)

Rendimento netto in ciclo aperto: 39,6 % (ISO)

Rapporto di compressione: 17,7 (ISO)

T ingresso Turbina (TIT): 1230 °C

Numero stadi compressore: 15

Numero stadi turbina: 4

Portata metano a MAX carico: ca 19 Nm3/s

Portata dei gas di scarico: 690 kg/s

T gas di scarico (TETC): 570 °C

AE 94.3 A2 (2007)

Turbogas Ansaldo Energia AE94.3 A2

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University of Genoa

Turbogas

Turbogas Ansaldo Energia AE94.3 AAE 94.3 A (2015)

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University of Genoa

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Turbogas Siemens 8000H

Gross Power Output 400 MW12

University of Genoa

In the operating range, Load control is managed by actingon both mass flow rates to control Turbine OutletTemperature (TOT). In fact even if the firingtemperature (FT) and the related Turbine InletTemperature (TIT) are more critical with respect toperformance, environmental and high temperature materialissues, the TOT is easier to measure.

2. Gas Turbine ControlGT Load Control acts over two main parameters to regulate combustion:

• m_f, fuel mass flow rate => Fuel Control Valves• m_a, air mass flow rate => HDGT – Inlet Guide Vanes

Two attributes of the Combustion can be regulated:Quantity (i.e. the amount of energy delivered)Quality (i.e. the combustion temperature)

m_a

m_f

TOT

TIT

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University of Genoa

In general for a GT the air mass flow rate is proportional to:

• density (suction temperature and pressure)• Section flow (Inlet Guide Vanes position)• Rotational speed

The rotational speed is imposed by the grid, suctionconditions are usually related to ambient conditions:→ the only way to regulate the mass flow rate is the IGV

Inlet Guide Vanes

There are two extreme position: IGV Max - fully openIGV Min - fully closed (bounded by compressor instability issues)

GT Control: IGV, Inlet Guide Vane

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University of GenoaGT Control: IGV e m_fuel

2. IGV_min (fully closed), increase of the TOT Temperature with the load. Reduction of the air-fuel ratio (AFR), Load Control.3. Regulating IGV, AFR is fairly constant and so TOT, Load Control4. IGV_max (fully open), a load increase (due to increase of fuel) reduces the AFR increasing TOT, until T limitation is reached, Load Control.

1. Start up Phase: GT reaches full speed no load (FSNL). Speed Control

5. Max Load OTC Control

TET = TOT

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University of GenoaREHEAT GT control: IGV + 2 m_fuel

Regulating IGV, temperatures are controlled to follow a specific OPC (OPerationalConcept)

IGV_max Temperature increases with the Load

Maximum allowed temperature is related to the management mode selected for the machine

IGV_min Up to 10% Load, all the fuel is burned just in the EV (as in simple cycle)

IGV_min over 10% Load The temperatures at SEV inlet are enough to allow fuel auto-ignition in SEV

OPC

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University of Genoa

HRSG materials limits the maximum TOT (TOT) ≤ 650 °C

MAX TEMPERAT. HRSGReducing the compressor inlet mass flow rate via IGV,also pressure ratio β is reduced. If the controls isdesigned to mantain a fixed TIT (Performance /Environmental Choice), it results in highertemperature at turbine outlet.

= > = ; TOT=TIT*(1/ )^(k-1)/k

Even if it will be possible to reduce furthercompressor mass flow rate without instabilityissues (stall and surge), the HRSG limit ontemperature will be reached.

GT Control in CCPP: Effects over HRSG

Which are the other limit to the TIT variation ?

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University of Genoa

The pollutant emission if a gas fired Turbine and relevant to the local environment are :

Nitrogen Oxide, NOx, a mix of NO ed NO2which create acid rain and smog int heatmosphere; Are created by high temperaturecombustion, so related to Base Load.

Carbon monoxide (strongly correlated also toUnburned HydroCarbons, UHC), is caused bythe not complete combustion of the NaturalGas. Main cause are low temperature and lowresidence time in the combustion chamber, it ismainly related to Low Load.

TG Controls: effect on emissions

The residence time usually does not change much on part-load because the normalized flow approximately remains constant with a variable load

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University of GenoaFlame Type

Emission Limit at Full Load:Premix Flame (NOx reduction)

Premix Lean Flame Instability (Humming)

Increasing Premix

Frequency of humming close to structuralfrequency (phisical Acceleration)

Reducing NOx

Increase CC instability

Limit to the maximum Energy to the Combustion Chamber

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University of Genoa

Ansaldo Solution - AE94.3A2 : burners VeLoNOxTM (Very Low NOx)

24 Burners, each burner is divided into 2 burners stage:- axial (rich combustion)- diagonal (lean combustion)

• Up to 60% of GT speed the combustion ispartly Premixed and the mix is fed by theaxial burner while trough the diagonal onejust air is fed;

• From FSNL both burners are fed withpremixed air and fuel with different ratio asfunction of the load

• The MEL is limited by CO @40% of load

TG Control: Burner design -1

Load

Ramp

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University of Genoa

PILOTRich, Higher temperatures, stability

PREMIXLean, Lower Temperature, less NoxProduction

Ansaldo Solution - V94.3A2 : bruciatori VeLoNOx (Very Low NOx)

TG Control: Burner design -1

Annular Chamber

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University of Genoa

General Electric solution - 9FA+e: Bruciatori DLN 2.6+

18 burners, each burner is divided into 6 burner stages:• The 5 external burner stages can manage both diffusion and premix combustion• The central burner stage is fed just by premixed fuel (PM1)

• FSNL: central burner in premix while the external burners stage are in diffusion(high NOx).

• 20 % load 3 external burners switch to premix mode,• 30 % load all in premix mode (MEL).

DLN 2.6+ system, with the IBH system allows toreach a very low TG MEL (70 MW - 26% )

NOx < 30 mg/Nm3CO < 30 mg/Nm3

TG Control: Burner design -2

Load Transition Piece

Fuel nozzle

Forward can

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University of Genoa

Alstom solution : EV + SEVThe EV burner, is a two stages lancecombustor (similar to the Siemens/Ansaldo one).The combustion system has morethan 2 free variables

TG Control: Burner design -3

SEV burner is made by alance which introduce fuel inan apt designed Combustionzone where flue gas from HPturbine flows. Thecombustion is initiated bythe autoignition of the fuel

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University of Genoa

Acoustic instabilitiesIn lean premixed combustion systems, flows are designed to be turbulent to enhance the mixing of fuel and air. Theturbulence causes a fluctuating heat release resulting in acoustic waves travelling through the combustion chamber, arereflected at the boundaries, and travel back to the burner. There they tend to influence the flow field and close a thermo-acoustic feedback cycle, allowing combustion instabilities to develop.

In a lean premixed combustion chamber, there are always someacoustic instabilities present.These instabilities are not dangerous during normal operation.They become dangerous when the amplitude rises too much orwhen a dangerous frequency arises in the spectrum (structuralresonance)

Combustion Hummig and Acceleration Monitoring / Analysis => TG Derating or Trip

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University of Genoa

Acoustic instabilities

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Passive Solutions: - Humming Frequencyes <> Combustion

Chamber Frequencyes- Design for low frequency Vortex reduction- break the symmetry (e.g. CBO)

Active Solutions: to damp combustion oscillationsevery burner was fitted with a direct drive valve feed-back controlled by a pressure measurements J. Hermann, A. Orthmann, Combustion Dynamics: Application

of Active Instability Control to Heavy Duty Gas Turbines

University of GenoaPollutant Control - NOxPrimary measures: For new gas turbines, dry low NOX premix burners (DLN) are BAT. For existing gas turbines, water andsteam injection (1.7 Meuro @140MWth) or conversion to the DLN technique is BAT (2 Meuro @140MWth).

DLN burner

Secondary measures: For most gas turbines and gas engines,Selective Catalitic Reactor, SCR is also considered to be BAT.Retrofitting of an SCR system to a CCGT is technically feasiblebut is not economically justified for existing plants. This isbecause the required space in the HRSG was not foreseen inthe project and is, therefore, not available. The capital costsof an SCR for gas turbines or internal combustion engines arein the range of EUR 10 to 50/kW (based on electrical output)

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University of Genoa

CO is a pollutant which is created only a part load. The CO limits the turndown capability of a gas based Power Plant =>Minimum Environmental Load. This aspect become crucial nowadays as a flexibility quality.

Primary measures: reduction in CO formation are achieved by Combustion Optimization (good design of the combustionequipment, optimisation of the temperature (e.g. efficient mixing of the fuel and combustion air) and residence time in thecombustion zone, and/or use of an advanced control system. just a cold spot can quench the reaction!

Calculated reaction time to achieve a CO concentration of 10ppm in a commercial gas turbine exhaust.

Secondary measures: To reduce the CO emissions, the application ofoxidation catalysts is BAT with the associated emission levels for naturalgas firing mentioned

Pollutant Control - CO

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University of Genoa

POWER HR

TambACTCC

ISOCC CfPPP /

TambACTCC

ISOCC CfCSCSCS

TambCfCSTambCfP

Boundary Conditions: Ambient

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The main seasonal effect over GT maximum power production isrelated to the ambient temperature.

During summer, the Capacity of a Combined Cycle can drop of more than 10%

University of Genoa

Boundary Conditions: Gas quality

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For the gas turbine operator, the most likely issues associated with fuel composition variation areassociated with the combustion system in the gas turbine and include: high levels of pollutant emissions, especially oxides of nitrogen and carbon monoxide component life and integrity issues due to factors such as flame flashback and unstable combustion operability issues such as ignition problems and flame failure

[4] Brown M., Bryant N., Haynes D., Study on LNG Quality Issues, a study for the European Commission –JRC Institute for Energy prepared by Advantica Ltd., Loughborough, The UK, April 2008

Fundamental properties of the fueland air/fuel mixture are: Heat content Flame speed Autoignition temperature Autoignition delay time Flammability limits Stoichiometric flame temperature

D J Abbott , J P Bowers*, and S R James, THE IMPACT OF NATURAL GAS COMPOSITION VARIATIONS ON THE OPERATION OF GAS TURBINES FOR POWER GENERATION

Typically units are tuned to a specific heating value and there is a 5% tolerance on this design value. However, the rate of change is not allowed to exceed 0.1%/s.

University of Genoa

Boundary Conditions: Gas quality

30Riccius, Smith, Guthe, Flohr, THE GT24/26 COMBUSTION TECHNOLOGY AND HIGH HYDROCARBON (“C2+”) FUELS, GT2005-68799

higher hydrocarbons are summarized as “C2+”, which is the sum of all molefractions of hydrocarbons with more than one C-atom. At the same timetodays gas supplies may carry a large and varying content of inert gases,mainly CO2 and some N2

The higher hydrocarbons typically increase the reactivity of the fuel-air mixture which lead to increased flammability limits (often advantageous) and higher flame propagation speed cases lead to flame flashback and combustor hardware damage.

University of GenoaCCPP – Performance evolution (design)

Why 50 Hz Machine produces approx. 40% more power than the 60 Hz ones equipped with the same technology?

Rotational force depend on squared rotational speed => 3600^2/3000^2=1.4460 Hz machine size must be ca 40% smaller than the 50 Hz

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University of GenoaCCPP – Performance evolution

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2003 2005 2007 2009 2011 2013 2015

LHV

Effic

ienc

y [%

]

I - CCPP [18] UK - CCPP [19] UK+IE - NGPP [20]

D - NGPP [20] FR - NGPP [20] DK+FI+SE -NGPP [20]

[18]AEEGSI, Relazione 24 Giugno 2016, 339/2016/l/efr; http://www.autorita.energia.it/it/docs/16/339-16.htm

[19]Departement of Energy & Climate Change, DIGEST OF UNITED KINGDOM ENERGY STATISTICS 2015

[20]Ecofys, International comparison of fossil power efficiency and CO2 intensity - Update 2014 Final Report

These operating efficiencies are yearly averages and cover the full range of different situations that may affect efficiency, e.g. different load modes and factors, different cooling systems, different ages or climatic conditions

LCP BREF, DRAFT 06 2016

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University of GenoaBoundary Conditions:Electrical Market

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Power market evolution is heavily impacting thermal generation: load factor reduction, number of start up increase, with a direct effect on the profitability of these Assets, often leading to mothballing or closure of these plants. Some Gas Assets will be able to survive via more flexibility : in terms of minimum load, ramp rates, start up time… which can lead to ancillary services revenues. Gas units needed for the security of the system will require the introduction of a sustainable capacity remuneration mechanism.

Wim BroosSVP Thermal Fleet Management

University of Genoa380 MW CCPP: Operating Data

121115

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152

168

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3 65

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Flexibility operation data 2009 - 2013Start up [n°] Operating hours [h] Poly. (Operating hours [h])

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University of Genoa

UCTE Handbook: “Ancillary services” are all services which support elementary functions of electric power system and they are supplied by subjects dealing of production, control and transmission of electric power.

Ancillary Services are: • frequency control;

• reactive power and voltage control;

Part of those services are mandatory, other are offered on a special market (Mercato dei Servizi di Dispacciamento, MSD), where Active power is «payd as bid», on the base of the TSO (Transmission System Operator) indications.

Ancillary Services – MSD

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University of Genoa

Flexibility: Solution for CCPP

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University of GenoaReduce Minimum Environmental Load: To compete on the electricity market an high turn down capability is mandatory (T.D. < 40% B.L.),

the limit is related to Gas Turbine to maintain a minimum fuel/air ratio avoiding CO production.The Minimum Environmental Load, for the gas turbine is tipically located close to the IGV full closed position,minimum air mass flow rate.

GT solutions to reduce the air taking part to combustion:• IGV extra closure• Compressor recirculation (Inlet bleed heating – anti icing)• Reduction of compressor inlet density (inlet heating)• Optimized burner design (staged combustion)• Combustion chamber by-pass (through Blow-off / cooling air valves)

other solutions:• CO Catalyst

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University of Genoa

IGV Extra Closure

Through the IGV extra closure it’s possible to reduce the minimum air mass flow rate to the combustionchamber resulting in higher combustion temperatures at lower load, avoiding CO formation.

Minimizing the MEL: IGV position

Power reduction Impact on Efficiency

-11% - 2.5%

TETC = TOTCO CO

before

after

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University of GenoaMinimizing the MEL: By-passing Burner

An optimization of the minimum load performance can be obtained by reducing the mass flow rate entering the combustion chamber through:- Regulating Blow-off valves: discharging mass flow directly to the HRSG diffusor (MEL -12%)- Regulating Cooling valves: increasing the air mass flow rate fed to cool the 2° and 3° vanes (MEL -4%)

Blow-off Valves

Cooling Valves

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University of Genoa

GE solution: IBH Valves, Inlet Bleed Heating

A mass flow rate up to 5% of the air is recirculated to thecompressor inlet to:

• Avoid Ice formation when the inlet temperature is very low• Control the surge margin• Extend premix combustion to lower load

Low MEL: Recirculating compressor

Power reduction Impact on Efficiency

-22% -10%

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University of Genoa

The Inlet Bleed Heating (IBH) reduce the mass flow rate of the air entering the combustionchamber thanks to:

- direct effect, the spilled mass flow rate (-5%)- indirect effect, the decrease of the air density at compressor inlet (-7%) .

Hp: Turbine Inlet Temperature constant (air/fuel ratio constant)

Compressor discharge mass flow recirculationLow MEL: Recirculating compressor

IBH CLOSED IBH OPEN (5% recirculated mass flow)

Air to the compressor % 100% 93% (+20°C CIT)

Compression Power MW 120 117

Flows to the burners % 100% 88%

Espansion Power MW 240 211

GT Net Power MW 120 94 (-22%)

GT Fuel Power % 100% 85% (+20°C CDT)

GT efficiency % 28 % 25 % (-10%)

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University of Genoa

Inlet Heating:MEL reduction and part load efficiency

An optimization of the part load performance can be obtained increasing the inlet temperature by the means ofan heat exchanger. The effect is the reduction of the off-design condition (higher efficiency) during part load,while maintaining the same power production. Moreover this solution help to decrease the MEL.

This upgrade requires the installation of and air water Heat exchanger in the filter house resulting in anaddictional pressure drops at GT inlet

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Load / Base Load ISO20°C (+5°C) 25°C (+10°C) 30°C(+15°C) 35°C (+20°C)

GT inlet temperature

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University of Genoa

Shutting Down SEV Alstom Based –Combined Cycle can reach a VeryLow Load (20% ca), no reheat Cycle

TG Control: Burner design

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Combustors are gradually shut-down, which can lead to not uniform discharge temperature distribution

University of GenoaMinimizing the MEL: CO catalyst Flue gas post processing:A grid composed by platinum to be introduced in HRSG, oxidizes CO to CO2 with an efficiency higher than 95%

The CO catalyst allows the reduction of the MEL of 25% withoutadditional impact over the GT off-design

there are still knowledge gaps in how to apply CO catalyst in practice,how to assess and follow up their performances and what are theCAPEX and OPEX versus the flexibility gains.

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University of Genoa

Case Study: flexibility in the electrical market: start up cost Vs production revenues

Typical Price Profile of the Day Ahead Italian market

Daily Cycling is mandatory

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University of Genoa

Case Study: flexibility in the electrical market: start up cost vs production revenues (Base Load)

CCPP #1 CCPP #2 CCPP #3Gas cost during Start up euro 12000 8000 6500

Energy produced during start-up MWh 50 40 30Power Base Load MW 385 385 385

eta base load % 56 56 56Specific cost Base Load euro/MWh 59.1 59.1 59.1

CCPP#3: 2 start-up / day

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University of Genoa

Case Study: flexibility in the electrical market: start up cost vs production revenues (Base Load)

CCPP #3 CCPP #3 MEL CCPP #3 PmaxGas cost during Start up euro 6500 6500 6500

Energy produced during start-up MWh 30 30 30Power Base Load MW 385 385 420

MEL MW 175 140 175

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University of Genoa

4. Combined Cycle Management

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Combined Cycle Power Plant management have to take intoaccount: the market price of the electricity the variability of the fuel cost, the cost of start-up maneuver the cost of maintenance

In particular nowadays, in Europe: More Renewables drives the need for CCPP flexibility CCPP’s have to change load faster Daily start-up and even double daily start-ups Faster Start -up times Required

Main interest on:- Reduction of time and costs

of the plant start-up- Evaluation of the cycling

impact (maintenance costs)- Extended long term

monitoring condition

University of Genoa

CCPP start-up

Start up maneuvers affects thick components which operates at high temperature, due to thermo-mechanic fatigue, mainly:- Steam Turbine Rotor - High Pressure Drum

The are systems which cap the run up velocity to avoid exceeding the “permissible” thermal stress:- Rotor Stress Evaluator - Boiler Stress Evaluator

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University of Genoa

Start-up Efficiency Impact

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Taking into account the start-up, the efficiency drops from 54.7 to 53.6

• The primary energy burnt during anaverage start-up is ca 1900000 MJ(48300 Sm3 di gas) with an electricalproduction of 185 MWh

• This electrical production has quite noimpact with respect to economical gain

• During a typical daily 15 h Loadprofile, 4775 MWh are produced withan average gas consumption of31.500.000 MJ. CSN = 6583 kJ/KWh(eta=54.7)

• Taking into account the start-up theCSN rise up to 6714 kJ/kWh (eta=53.6)

University of GenoaCombined Cycle Start-up Potential Saving

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Potential to save time by: 1.Decrease/cancel HRSG purging time 2.Increase HRSG pressurization ramp rate 3.Anticipating steam turbine start-up 4.Increasing steam turbine ramp up rate5.GT load strategy: increase load as quick as possible to reach quicker Pmin (context of tertiary reserve) Potential to save fuel by: 1.Keeping installation as hot as possible during shutdown 2.Decreasing/cancelling HRSG purging time 3.Increasing HRSG pressurization ramp rate 4.Anticipating steam turbine start-up 5.Increasing steam turbine start-up ramp up rate 6.GT load st-up strategy: wait for steam turbine start-up before to increase the GT load

1) HRSG Purge (Blow off open –Electrical Drive)2) Ligth on3) GT speed Ramp (Blow off open – Mixed Gas/Electrical Drive)4) Syncronization (Blow-off Closed – Gas Drive)5) GT Load Ramp

1 2

FSNL

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4

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University of Genoa

Purge Time Reduction

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Two Standards Apply:- API 616 Gas Turbines for the Petroleum, Chemical, and Gas Industry Services

Purge 3 - 5 the volume of the exhaust system (generic)- NFPA 85 (National Fire Protection Association) Boiler and Combustion Systems Hazards Code

(Specific for the HRSG) Purge prior to the lightoff of the combustion turbine shall be accomplished by atleast five volume changes and for a duration of not less than 5 minutes.This volume shall be calculated based on the following:(1) The combustion turbine operating at full load with no supplementary HRSG firing(2) The volume from the combustion turbine inlet to the portion of the HRSG or other combustion turbine exhaust systems where the combustion turbine exhaust gas temperature is reduced to at least 56°C (100°F) below the lowest autoignition temperature of the fuel(s) for which the system has been designed

In no case shall the volume in 8.8.4.2.1.2(2) be less than the volume of the HRSG enclosure between the combustion turbine outlet and the outlet of the first evaporator section in the HRSG.

API 616 NFPA85HRSG + Camino HRSG + Camino Fino a EVA AP

Purge Volume m3 8400 8400 3280portata d'aria m3/s 41.5 41.5 41.5n. ricambio volumi # 3 5 5tempo PURGE min 10.1 16.9 6.6

Purge Credit isanother HW SW option to skippurge time

University of GenoaSt-Up: FSNL Behaviour

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Gruppo TG1 (MW) TG2 (MW) TV (MW) CCGT (MW)GE in 1+1 70 - 72 142GE in 2+1 70 70 140 280AEN in 1+1 146 - 70 216AEN in 2+1 146 146 150 442

Minimo TecnicoGradiente di

Carico TG (MW/min)

Tempo per il massimo

carico (min)

AEN 6.5 -13 40 - 20

GE 20 13

University of GenoaSt-Up: 2+1 AEN/Siemens (Hot Pressurized)HRSG PURGING

FLAME ON TG1

FLAME ON TG2

Minimo tecnico

Full load

Total Time= 65 minutes

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University of GenoaSt-Up: 2+1 GE (Warm)HRSG PURGING FLAME ON

Minimo tecnico

Tempo complessivo= 85 minuti

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University of GenoaGT behaviour impact over Start-up Costs

exhaust temperature @ partial load Higher exhaust temperature at FSNL/lower load HRSG pressurization with lower gas consumptionspeed up and load up gradients reduce start up time and cost

Start up cost of 2 differentUnits:

• Unit 1 gas turbine TETC480°C @FSNL

• Unit 2 gas turbine TETC480°C@80MW 0

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University of GenoaGT Control: IGV e m_fuel – OPFLex VLP

Allows independent control of load and exhaust temperature withinthe gas turbine boundaries … true GT flexibility product• Simple interfaces for integrating into existing plant operation• Requires OpFlex AutoTune to manage combustor operability

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Temperature matching with the bottoming Cycle Stand Still Temperature

Dr. Artur Ulbrich, Andy Jones, Christian Schäferkordt, Stuart Simpson, Increasingcompetitiveness of CCGT plants in a dynamic market: An owner´s approach

University of Genoa

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GT Control: IGV e m_fuel – OPFLex VLP

Dr. Artur Ulbrich, Andy Jones, Christian Schäferkordt, Stuart Simpson, Increasingcompetitiveness of CCGT plants in a dynamic market: An owner´s approach

University of Genoa

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GT Control: IGV e m_fuel – OPFLex VLP

Dr. Artur Ulbrich, Andy Jones, Christian Schäferkordt, Stuart Simpson, Increasingcompetitiveness of CCGT plants in a dynamic market: An owner´s approach

University of Genoa

Pressurization gradient for Drum-type HRSG 6/8 °C of Tsat/min, to be monitored with BSE (Boiler

Stress Evaluator)

Length of main steam piping Important design impact – length between bypass

and ST

Drains design Drains review to reduce the main steam piping

warming time

St-Up: Bottoming Cycle Limitations

Once trough Benson Boiler, is an option for start up not constrained by the Drum thickness

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P Drum HP ini 0 bar P Drum HP ini 6 barP Drum HP ini 12 bar P Drum HP ini 20 bar

Minimum HP ST pressure

University of GenoaReduce cost of Start-up: ST characteristicSpeed up available @ lower pressure Steam Turbine with direct connection from the HP/IP body to condenser during start up

allow a wide range of speed up pressure (anti-Ventilation Valve).Lower weight of the rotor Impulse design steam turbine allows faster load up due to lower rotor weight and

dimension.

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University of Genoa

Start up are classified on the base of the initial conditions of the bottoming Cycle when the start up maneuver is initiated:• Steam Turbine Metal Temperature ( Rotor centre or first vane);• High Pressure Drum Pressure

Start –Up Type Stand Still (h) HP DrumPressure (bar)

T RotorCentre(°C)

Gradiente giri TV(rpm/min)

Full Speed time (min)

Cold t>64 p<2 < 150 75 40

Warm 16<t<64 p<12 150 < T < 370 150 20

Hot t<16 p<12 T > 370 300 10

Hot pressurized t<16 p>12 T > 370 300 10

Some times to avoid cold start up conditions (below theductile to brittle transition temperature) auxiliary steam isused to mantain the rotor in warm conditions

62

To mantain HRSG temperature, the flue gas stack damper isclose after shut down.

GT flue Gs Temperature

Main Steam Steam Temperature

ST Metal Temperature

Temperature Mismatch < 50 K (stress reduction)

St-Up: Bottoming Cycle Initial Conditions

University of Genoa

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St-Up: Bottoming Cycle Initial Conditions

University of GenoaRotor Stress Evaluator (RSE)

The Rotor Stress Evaluator (RSE) is the system which limits the gradient of ST and GT load in order to reduce the fatigue on the components

1. Basing on temperature measurement representative of the rotor surface (Starting Probe), Temperature distribution is calculated

2. If Relative Comparative stress exceed a threshold, a load reduction is triggered for the GT.

-RSE give no information about start up impact on the residual steam turbine life (Damage Calculation),

-the definition of “Permissible” is not clear

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University of GenoaStress Evaluation and Low Cycle Fatigue

The stresses in the rotor are produced by:- temperature gradients in the material (Thermal

Stress),- the centrifugal force, - the pressure.

Thermal Stress

the main contributor: about the 95% of the overall stress during start up transient

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University of GenoaWarm Start-up (T_initial =345°C )

0

100

200

300

400

500

600

0 100 200 300 400 500 600 7000

100

200

300

400

500

600

POW

ER [M

W]

TIME [min]

TEM

PERA

TURE

[°C]

Surface Temperature Mean Temperature Center TemperatureTurbogas Power Steam Turbine Power

0 100 200 300 400 500 600 700

-400

-300

-200

-100

0

100

TIME [min]

STR

ESS

[M

Pa]

Radial StressCircumferential StressAxial Stress

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University of Genoa

Start Up Downtime

[ h ]

Initial Rotor

Temperature

[°C ]

Mean Gradient

[°C/h ]

Temperature

Variation

[°C ]

Maximum

Number of

Cycles

Specific Life

Consumption

[%]

Warm 40 345 255 170 3300 0.03

0 100 200 300 400 500 600 7000

100

200

300

400

TIME [min]

ST

RE

SS

[M

Pa]

SurfaceCenter

Warm Start-up (T_initial =345°C )

- During the shut down thermal stress not exceed 40 Mpa- Considering as fatiguing cycle the stresses caused by start up and shut down, a fully-reversed loading condition is not

got. Therefore it is possible to consider a zero-max-zero profile loading condition and neglect shut down impact over LCF

67

University of GenoaCLE Curves – HP Rotor

such curves allows to:

knowing in advance the reduction ofturbine's life connected to a givenmaneuver or gradient of temperaturechangemaking choices on the reduction of

warm up and load times, and then onthe increase of temperature gradientsthat the rotor will have to endurechoosing whether to sacrifice some of

the useful life of the rotor to gaingreater operating flexibility

CLE= f(total range of Temp [°C]; Temp gradient [°C/h])

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University of GenoaCurve CLE – HP Rotor

HOT6 h SS

Ti = 450 °CN > 100000

HOT18 h SS

Ti = 394 °CN = 14000

WARM40 h SS

Ti = 345 °CN = 3300

COLD144 h SS

Ti = 150 °CN = 600

COLD240 h SSTi = 90 °CN = 600

69

University of GenoaST Yearly Life Consumption EstimationBasing on operating conditione the average yearly start-up related life consumptionwas evaluated

Miner-Robinson rule was use to combine LCF Life Expenditure and creep effect due to high temperature normal operation (creep-rupture life 300,000 h ).

low cycle fatigue a yearly consumption 5.05% (as in table 4)Creep yearly Life Consumption 1% (3000 Operating Hours /Year)Total Yearly Life Consumption 6.05%

17 years until defects nucleation

70

University of Genoa

6h/d 10h/d

14h/d

24h 2/7

24h 5/7 Weekly

MontlhyQuarterly

TGATGB

TGC

0

100

200

300

400

500

600

700

0 5000 10000 15000 20000 25000 30000

STAR

TS

EQUIVALENT OPERATIVE HOURSProfili di carico Cycling Limit Limiti per la manutenzione

Maintenance Cost in CCPP

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The LTSA, Long Term Service Agreement, offers to the power plant owner a series of planned maintenance outages. Interval between outages is defined on the base of the operating duty of the machine (load profile)

FH/avv_lim=31.7

Usually Equivalent Operative Hours,EOH , are use to taking intoaccount the impact of start-up (1 start- up = 10 Fired Hours) and this was used to evaluate maintenance costs over the MaintenceInterval (e.g. 25000 EOH) (hourly cost approach) (ca 180eur/h).

Fired Hours

Star

ts

Nowadays the maintence limit is reached on the maximum number of starts, so if the machine is operatedfor less than 31.7 hours per start-up the maintence costrelated increases (tipically up to 6000 eur )

University of GenoaMajor Factors Influencing GT Maintenance

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Gas Turbine Hot Part, and in particular Blades andVanes, as function of operative conditions, areaffected by several wear mechanisms.

Operational ProfileAverage Fired

Hours (h)Critical Damaga

Mechanism Fired Hours to end life

Cicle to end life

Fatica CreepOss.

CiclicaQuarterly 2160 Oss Ciclica 23500 129 62 11Monthly 720 Oss Ciclica 23500 163 183 30Weekly 92 Fatica e Oss Ciclica 23500 255 1462 261Daily 10 Fatica 4100 414 13500 2400

Daily operational profile reduce the number of fired hours for maintenance interval (from 23500 to 4100) and so the time for Power Production => Maintenance Cost per hours increase of a factor 5.7

C. Rinaldi, V. Bicego, P.P Colombo, Rapporto CESI, Aprile 2004

Heavy-Duty Gas Turbine Operating and Maintenance Considerations GER-3620M (02/15)

University of GenoaMaintenance Interval

73

Different methodology to take into account the impact of Operational lifeto evaluate the Maintenance Interval :• Opzione A: Numbers of start-up and fired hours (FH) are not correlated,each one has its own threshold which triggers the Maintenance, (GeneralElectric approach);• Opzione B: Each start up cycle –or fast transient event- is counted witha number of Equivalent Operative Hours (EOH), the sum of the total EOHdepends liearly from both FH and start up numbers; (Ansaldo, Siemens,Alstom approach)• Opzione C: A more complex correlation is used (No O&M adopted it)

What are Operative Equivalent Hours (EOH)?Cyclic thermal stress due to start up and fast transient are taken into account by and equivalent amount ofEquivalent Operative Hours (=> EOH)Under normal condition 1 Fired Hours is equivalent to 1 EOH.This value is modified if aggresive fuel, higher flame temperature than standard is used.

B method will be used for following consoderationsconsiderting each start up maneuverequal to 10 EOH and each FH queal to 1 EOH. A limit to a maximum 600 start ups is added

University of GenoaEx: Maintenance Costs

74

Outages Interval [EOH]

Minor 4000

HGPI 25000

Major 50000

Running Inspection Standby Inspection Scheduled Maintenance

Maintenance Costs €

HGPI Costs 4500000

HGPI Interval 250000 EOH

EOH / Start Up 10 EOH

Hourly Maintenance Cost (eur/EOH) 180

Expected cost/St-up 1800

Numbers of start up maintenance Thrshld 6000

100

200

300

400

500

600

700

0 5000 10000 15000 20000 25000 30000N

um. O

f Sta

rt-u

pFH

Maintenance Thresholds

University of Genoa

6h/d 10h/d

14h/d

24h 2/7 24h 5/7 Weekly

MonthlyQuarterly

TGATGB

TGC

0

100

200

300

400

500

600

700

0 5000 10000 15000 20000 25000 30000

Yearly Operational Profile

Profili di carico Cycling Limit Limiti per la manutenzione

Comparison of Operational Profiles

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Operational Profiles Yearly operation Hours Yearly start-up6h/d 2106 35010h/d 3538 35314h/d 4981 355

24h 2/7 2309 4824h 5/7 6051 50

Weekly 8551 50Monthly 8541 11Quarterly 8539 3

OperationalProfiles

Maintenance IntervalFH/avv EOH / MI FH / MI

6 h/d 6 9600 360010 h/d 10 12000 600014 h/d 14 14400 8400

24 h 2/7 48 25000 2069024 h 5/7 120 25000 23077

Weekly 168 25000 23596Monthly 730 25000 24662Quarterly 2182 25000 24886

• 11,44 h for TGA;• 10.29 h for TGB;• 9.4 h for TGC.

average FH / avv:

FH/avv_lim=31.7

University of Genoa

TG: compressor efficiency

Nowadays Full load operation covers just a fraction of a CCPP life (Load Factor around 60%)To increase the range of the monitoring resultsbase lines are now created taking into account not just the full load conditions

Test

Train

η =ℎ _ − ℎ

ℎ − ℎℎ = ,

5. Flexible Monitoring of CCPP

An Hybrid, knowledge based and Data Driven model are the used to create

reference base line

The first rule of monitoring is: «make them comparable»

Several filter strategies are usuallyadopted: Steady state, full load, active auxiliaries

Such approach is applied to allthose components which

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University of GenoaFLEXIBILITY – Process Control

77

University of GenoaOn line Performance Monitoring

78

University of Genoa

Final Summary

1. Large Size Heavy Duty Gas Turbine

2. HDGT Control Systems:- Control Loops and typical target- Methods for Minimum Environmental Load reduction

3. Combined Cycle Management- Start-up of the Combined Cycle

4. Maintenance cost and the Impact of Flexibilization

5. Monitoring and Diagnosis of CCPP- ST Example

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