HRSG - Basic Understanding

GE Energy

Date

HRSG – 101

TPSE – Dave Rogers, Wulang Chriswindarto

What, Where, Why…?

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GE Internal - For internal distribution only.

Heat Recovery Steam Generator

What is an HRSG?

Wikipedia – energy recovery heat exchanger that recovers heat from a hot gas stream. It produces steam that can be used in a process (cogeneration plant) or used to drive a steam turbine (combined cycle power plant)

It’s A Boiler…!!!

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HRSG – More Than Just A Box of Tubes

Overview

Converts exhaust energy

from gas turbine into steam

Enables plant efficiency

from 38% to 58%

$20-$25MM Parts

$8-$9 MM Ship

$10 MM Field Assembly

Modular assembly

Operational Challenges on Installed Based

BOP trips driven by HRSG accessories

25% of forced outage hrs

Drum level issues cause

trips preventing fast starts

Tube cracks and failures

are costly … critical path

during outages

Upgrades to GT often

require HRSG analysis …

potential showstopper

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Differences: HRSG vs Fossil Boiler

HRSG uses exhaust gas (e.g. gas turbine) as a heat source

and typically does not required a dedicated firing system

HRSG do not use fans (draft is from gas turbine exhaust)

HRSG generates steam at multiple pressure levels to

improve heat recovery efficiency

Heat transfer is typically by convection rather than radiation

HRSG do not use membrane water walls

HRSG uses finned tubes to maximize heat transfer

HRSG typically has lower height profile & smaller footprint

Fossil Boiler

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Basic ComponentsWater/ Steam Side:- Economizer/ Pre-heater (gas to heated water)

- Evaporator & Drum (gas to boiling water to steam)

- Superheater (gas to dry steam)

Gas Side:Inlet Duct, Baffles, Structural Steel, Casing, Insulation & Liner, Stack

Accessories:- Silencers (gas & steam side)

- Stack Damper & Bypass Stack Damper

- Supplemental Fire/ Duct Burner

- Feedwater Pump

- CO Catalyst & SCR System

- Valves & Instruments

Superheater

Evaporator

Economizer

Gas in

Gas out

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HP Drum

Integral Deaerator

IP Drum

HP SuperheaterReheaterDuct Burner

HP Evaporator SCR / CO Catalyst

IP EconomizerIP EvaporatorIP Superheater

LP EconomizerLP EvaporatorLP Economizer

Height ~ 85’

Stack Height ~ 150 – 200’

Gas in - 1100 F

NOx

CO

Feedwater – 100 F

Gas Out –180 F

NOx & CO reduced 80%

HP & RH Steam Out

–1050 F

3 Pressure Level Reheater HRSG

LP Steam Out –540 FIn and Out

Length- ~ 100’

50’

20’

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Why HRSG is important?

1. Gas Turbine (GT): Converts Fuel

to Electricity and Waste Heat

3. Steam Turbine (ST):

Converts Steam to

Electricity

2. HRSG:

Converts Waste

Heat to Steam

*Combined Cycle:

A combination of thermodynamic Gas (GT) Cycle and Steam (HRSG & ST) Cycle in an Electrical Generating Power Plant to gain higher power output and efficiency

HRSG is the critical link between gas turbine and steam turbine in a

combined cycle power plant

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Combined Cycle T-S Diagram

5 /

Combined Brayton and Rankin Cycle

T

S

Heat Source

Heat Sink

COMPRESSION

EXPANSION

HRSG

GAS TURBINETOPPING CYCLE

BOTTOMING CYCLESTACK

TEMPERATURE

ENTROPY

COMBUSTION

CONDENSER

EXPANSION

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Typical Energy Utilization Chart

FUEL

(100%)

to Gas Turbine

GT POWER

(35.8%)

ST POWER

(20.9%)

STACK LOSS

(7.1%)

CONDENSER

(32.9%)

EXHAUST HEAT (62.4%) to HRSG

STEAM TURBINE (54.8%)

GT LOSSES

(1.8% ACCESORIES)

HRSG CASING LOSSES

(0.5%)

ST LOSSES

(1% ACCESORIES)

Combined Cycles Systems (with HRSG & ST) Utilize More Fuel EnergCombined Cycles Systems (with HRSG & ST) Utilize More Fuel Energy to y to Produce Useful Work Than GT AloneProduce Useful Work Than GT Alone

Design Philosophy

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HRSG Design Philosophy

SuperHeater

Evaporator

Economizer

Heat Duty

Temperature

Turbine Exhaust Gas

Pinch

Approach

SH EVAP ECON

Pinch Point

The Difference Between Gas Temperature and Saturation Temperature at the Outlet of the Generating Bank

Approach Temperature

The Difference Between Economizer Discharge Temperature and Saturation Temperature

HRSG design is a precise balance of the utilization of exhaust energy to produce steam energy in an economic way

The smaller the pinch and approach temperatures, the more efficient the HRSG, but also the more expensive the design

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0

400

800

1200

0% 20% 40% 60% 80%

Percent Exhaust Energy Used

Tem

pera

ture

°F

Steam and Water

HP

IP / ReheatLP

Tem

pera

ture

°F

Percent Exhaust Energy Used

HRSG Pinch Point Plot

HRSG Types

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HRSG TypesHorizontal

• Horizontal gas flow direction

• Vertical tubes arrangement

• Majority installed

Vertical

• Vertical gas flow direction

• Horizontal tubes arrangement

• Smaller footprint (historically common in Europe or outside US)

Once Through

• Either horizontal or vertical gas flow direction & tubes arrangement

• Once Through eliminates the need of drum

• Phase change from water to steam is free to move throughout the bundle

• Theoretically more agile

Product Features

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Product FeaturesFinned Tubes

Act as heat transfer/ exchanger medium

Fins increase surface areas

Internal insulation & Liner

Prevent heat losses, Provide outside casing temp of ~80 F

Duct Burner

Supplemental firing to increase heat input for peak load

Gas dP 0.25” w.c expected

Burner Skid & Elements/ Runners

BMS-Burner Management System

Flame Scanner

Ignitor

Gas BafflesTo Prevent Gas bypassing the heat exchanger

SCR Systems

NOx reduction by ~ 86%

Gas dP 2-3” wc expected

Skid, Ammonia Based, Injection Grid, Catalyst

CO catalyst

CO reduction by ~ 80%

Gas dP ~ 1” wc expected

Drum & Internals

Steam & water mixture

Is separated to produce dry steam

Manufacturing

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Manufacturing – Heat Transfer Section

Headers

Finned TubesERWBare Tuin Coil Slit

Bare Tubes

Fin Coil Slit

Finned Tubes to header fit upFinned Tubes to header weldHarps Assembly

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Manufacturing – Casing, Insulation & Liner

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Manufacturing - Drums

Field Assembly

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HRSG – Typical Field Assembly

PLACE POOBTAIN

MATERIALS1 - 2 Months 2 - 3 Months 7 - 9 Months SHIP COMPONENTS

3 - 4 Months ASSEMBLY COMMISSION7 - 9 Months 1 - 2 Months

Total Cycle Duration: 21 - 29 Months

MANUFACTURE

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HRSG- Degree of Shop Modularization

1. Harps

2. Modular 4. Full Assembly

3. C-Frame

HRSG Life Cycle Issues & Opportunities

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Considerations for Cycling Operation

Component fatigue damage

Chemistry control

Attemperation

Drum level control

Sulfur dew point corrosion

Critical Components affected by Cycling

HP Drum

HP Superheaters

RH Superheaters

Factors that impact fatigue damage

GT Ramp Rates

Pressure Management

Heat retention during offline periods

HRSG design & construction

HRSG issues

Flow Accelerated Corrosion

(FAC)

Light and Heavy Ammonium Bisulfate Deposits

GT Exhaust Non Uniform Flow

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GE technologies applicable to HRSG

Metallurgy & coatingsCreep, oxidationThermal barrierAnticorrosion

Aeromechanics/CFDBent fin tubeCFD modeling

Life modelsPhysics based & empirical lifing models

Sensing and inspectionPulse eddy current, bore scope, high temp ultrasound, digital radiography etc.

Performance improvementGatecycle, eMapAcoustic cleaning

Water chemistryMonitoring, chemicals, chemistry models, laboratory failure analysis etc.

M&D TechnologyRemote M&D24/7 monitoring

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Thank you.

HRSG - Basic Understanding

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