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Gryphon International Engineering Services Inc. IAGT Committee www.gryphoneng.com www.iagtcommittee.com
INDUSTRIAL APPLICATIONS OF GAS TURBINES IAGT 2014 LNG SYMPOSIUM VANCOUVER, BRITISH COLUMBIA
Basics of Gas Turbine Energy Systems
An introduction to aero-derivative and heavy-duty industrial gas turbines and their application into cogeneration and combined-cycle projects
Jim Noordermeer, P.Eng. Vice-President – Power & Thermal Generation
Gas Turbines for Cogeneration & Combined-Cycle
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 1 www.iagtcommitee.com
Introduction to the industrial gas turbine generator engine:
heavy-duty frame and aero-derivative, the gas turbine generator package the auxiliaries,
For the cogeneration or combined-cycle power plant.
GAS TURBINE CONCEPTS The Basic Gas Turbine Cycle Brayton Cycle - continuously operating process using air as working fluid:
Ambient Air (state 1)
Compression (1 to 2)
Continuous combustion with fuel (2 to 3)
Expansion to atmospheric pressure (3 to 4)
IdealActual
1
2
3
2'
3'
4
4'
P1
P2
Combustion
Compression
Expansion
s - Entropy
T-Te
mpe
ratu
re
Firing Temperature
1
2 32'
3'
4
4'P1
P2Combustion
CompressionExpansion
V-Volume
P-Pr
essu
re
IdealActual
Compressor
12
Fuel3
Combustor
Turbine
4
Load
Gas Turbines for Cogeneration & Combined-Cycle
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 2 www.iagtcommitee.com
Turbine Section physically drives (rotates) the Compressor Section.
Excess Turbine Shaft Power drives the load – generator.
Firing Temperatures – T3 – have climbed from 1400 deg F, to 2000~2200 and now 2600 deg F with better turbine section materials and cooling methods.
High T3 = power output & efficiency.
Pressure Ratio – P2/P1 – High ratio = high efficiency & specific output (hp/lb/sec).
Gas turbine design pressure ratios vary:
7.5:1 – smaller & older technology GT’s,
35:1 – recent, most advanced GT’s.
Aircraft gas turbines:
jet engines,
turboprops,
low & high-bypass turbofans
Use high pressure ratio, high firing temperature = minimum weight & frontal area.
Gas Turbines for Cogeneration & Combined-Cycle
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 3 www.iagtcommitee.com
Turbine Cycle Variations – of the basic cycle: Reheat or sequential combustion – in high-pressure ratio GT’s.
Hot HP Turbine Section gases reheated by combustion of additional fuel (3a) .
Reheated gases enter into LP turbine section (3a to 4).
Reheat configuration:
increases LP Turbine output,
raises the turbine’s exhaust temperature,
increases simple-cycle power output,
increases combined-cycle power output.
Example: Alstom GT24/26.
Compressor
12
Fuel3
Comb 1
Turbine 4
Load
Fuel Comb 23a
Gas Turbines for Cogeneration & Combined-Cycle
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 4 www.iagtcommitee.com
Turbine Cycle Variations – of the basic cycle: Recuperated or Regenerated GT’s For low-pressure ratio units with high fir-ing temperatures.
External regenerative heat exchanger - transfers exhaust heat to compressor dis-charge air.
Regenerative Configuration:
Saves fuel Increases efficiency
Example: Solar Mercury 50
Inter-Cooled GT’s
For high-pressure ratio multi-shaft units.
LP compressor air directed to external heat exchanger.
Cooling medium (water or air) decreases air tempera-ture. Cooled air re-enters HP compressor.
Intercooled Configuration:
decreases HP compressor power, improves efficiency & specific output
Example: 100 MW GE LMS100, w/ air or water cooling.
Compressor
1 2a
Fuel3
Combustor
Turbine
4
Load
Intercooler
2
Compressor
12
Turbine
4
Load
Fuel
3
Combustor
2a
Gas Turbines for Cogeneration & Combined-Cycle
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 5 www.iagtcommitee.com
Turbine Cycle Variations – of the basic cycle: Spraywater Cooling – like intercooling.
Clean water injected before the LP compressor, and between LP & HP LM6000 compressor of the multi-shaft aero-derivative GE LM6000 Sprint
Increases HPC mass flow Increased pressure ratio Increased power output & efficiency @ high ambients
Intercooled & Recuperated GT Rolls-Royce WR-21 marine drive unit.
Special high-efficiency configuration.
Exhaust recuperator & sea-water cooled intercooler.
For interest only - there are no land applications.
Gas Turbines for Cogeneration & Combined-Cycle
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 6 www.iagtcommitee.com
Basic Components of the Gas Turbine
Compressor Section: Frequently multi-stage axial; centrifugal in smallest units.
Each stage: row of stationary blades (stators) & rotating blades.
Outlet guide vanes (OGV) & diffuser – straighten & slow air stream prior to en-try into the combustor section.
Compressed air bled out & used for cool-ing purposes in hot sections.
Compressor air bled out for startup & part-load operation.
Pivoted-variable inlet guide vanes (IGV’s) – industrial & aero-derivative units - manage bulk inlet air flow.
IGV’s sometimes manipulated to keep exhaust temperatures high for cogenera-tion or combined-cycle steam generation considerations.
Many aero-derivative units employ varia-ble stator vanes (VSV) to control air flow and rotor speed in the higher-pressure section. LM6000 Compressor with variable bleed valves (VBV), IGV’s and VSV’s
courtesy of GE Energy
Gas Turbines for Cogeneration & Combined-Cycle
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 7 www.iagtcommitee.com
Basic Components of the Gas Turbine Combustor Section: Multi-can (basket) design, or an annular ring design.
For standard diffusion-combustion systems (i.e. non dry low-NOx), gaseous or liquid fuels introduced via nozzles located at the head of each combustor can, or front of combustion annulus chamber.
Portion of compressor air introduced directly into the combustion reaction zone (flame). Remainder introduced afterwards – for flame shaping and quenching to T3.
Water or steam injection – for envi-ronmental or power enhancement.
Transition ducts / liners - care-fully shape the hot gases for the turbine section.
Fuel and steam and/or water in-jection manifolds & hoses around the circumference of the com-bustor section.
Current generation dry low-NOx (DLN or DLE) combustion sys-tems use lean pre-mix principle, frequently multi-nozzle.
LM6000 Combustor Section courtesy of GE Energy
Gas Turbines for Cogeneration & Combined-Cycle
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 8 www.iagtcommitee.com
Basic Components of the Gas Turbine Turbine Section: Usually multi-stage axial design.
Each stage - stationary nozzle row imparts correct angle to hot gases, for succeeding rotating blades.
Most critical section of turbine: 1st few stages.
Nozzle & rotating blade exposed to “red-hot” gases at design firing temperature.
Far in excess of acceptable creep-fatigue limits for en-gineered alloys employed.
Rotating blade – survival under high centrifugal & me-chanical stresses.
Internal cooling passages cast and machined into noz-zles & blade. Cooled compressor bleed air passed through to maintain material temperatures at accepta-ble limits.
LM6000 Turbine Section - courtesy of GE Energy
Gas Turbines for Cogeneration & Combined-Cycle
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 9 www.iagtcommitee.com
Creep-resistant directionally-solidified (DS) & single-crystal (SC) blade produc-
tion technology – introduced from the aircraft GT world.
Thermal barrier coatings (TBC) employed to protect aerodynamic surfaces & materials from corro-sion, oxidization and erosion. Turbine Nozzle w/ TBC & cooling air exit holes
Turbine row assembly, showing blade attach-ments to the rotating disk, and blade cooling air exit holes
Gas Turbines for Cogeneration & Combined-Cycle
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 10 www.iagtcommitee.com
THE GAS TURBINE ASSEMBLY The Basic Gas Turbine Machine Individual compressor, combustor & turbine sec-tions and casings bolted to-gether. Supported via struts & baseplates - to make a complete machine.
Rotating compressor & tur-bine sections mechanically interconnected.
Compression power provided by turbine section’s power. Excess turbine shaft power drives pump, compressor or generator via output shaft:
Cold-end drive Hot-end drive
LM6000PC and 6FA courtesy of GE Energy.
60~70% of turbine’s power output used by compressor.
Remaining 30~40% available as true shaft output power, e.g. typical nominal 50 MW single-shaft industrial gas tur-bine produces ~150 MW in the turbine section, giving ~100 MW to compressor section.
Gas Turbines for Cogeneration & Combined-Cycle
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 11 www.iagtcommitee.com
Gas Turbine Variations – from the single-shaft design. Single-Shaft with PT – industrial & aero-derivative units.
Single-shaft GT operates at the speed and firing temperature – keeps itself self-sustained.
It’s exhaust gases passed to aerodynamic-coupled free power turbine (PT) which drives the load – at fixed (generator) or variable (me-chanical drive) speed.
Frequently called a “jet”, or “gas-generator”, for convenience.
Multi-shaft, with & without PT Industrial units designed for variable-speed mechanical drive or deriv-atives of aircraft engines.
Basic compressor & turbine sections divided into HP and LP units. HP and LP each operates at different speed – depends upon load & ambi-ent conditions. The LP compressor (LPC) is coupled to and is driven by LP turbine (LPT). The HP compressor (HPC) is coupled to and is driven by the turbine (HPT).
In some three-shaft machines, an intermediate compressor (IPC) & turbine (IPT) also used, in between LP & HP sections (configuration not shown).
Fixed or variable-speed loads are driven off LP shaft.
Some units can drive off cold-end or hot-end of LP shaft.
In some cases, these multi-shaft units, act as “gas generator”, and PT is required to drive the load.
Fuel
HPT LPTLPC HPC
Load
Fuel
HPT LPTLPC HPC PT
Load
Compressor
FuelCombustor
HPTLoad
GasGenerator
PowerTurbine
PT
Gas Turbines for Cogeneration & Combined-Cycle
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 12 www.iagtcommitee.com
AERO-DERIVATIVE & HEAVY-DUTY INDUSTRIAL GAS TURBINES The “THERMODYNAMIC COUSINS” – sharing the same basic cycle. Aero-Derivative GTs – based on aircraft engines. Usually low weight & low frontal area (generally inconsequential for industrial service).
The original jet engines have their nozzles removed & power turbines (PT’s) installed for industrial service.
Later turbo-prop & turbo-fan engines – industrialized by redesign of the prop or fan takeoff drives’; or a PT.
Most aero-derivatives (compared to same-size industrial cousins):
very efficient – because of high T3 and P2/P1
less steam generation due to lower flows.
Major Maintenance – by complete removal of gas turbine from package – special lifting frames required.
Modules disassembled into smaller components - LPC, HPC, combustion module, HPT and LPT, etc.
Minor maintenance activities – conducted at site.
Major maintenance & overhaul - unit returned to certified shop.
Lease engines available – replaces original engine while under repair.
Gas Turbines for Cogeneration & Combined-Cycle
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 13 www.iagtcommitee.com
Heavy-Duty Industrial GTs – heavier and more rugged.
Optimized to operate over narrow speed range & base-load duty.
Typically – scheduled maintenance intervals longer than aero units.
Heavy multi-cylinder castings and fabrications.
Large bolted horizontal and vertical split joints.
Heavy built-up rotors & journal bearings.
Large solid couplings
Large baseplates and frames.
Major Maintenance – usually accomplished at site: removal of top half cylinder; removal of diaphragms and blade rings; lifting and removal of the turbine rotor; subsequent blade removal.
Gas Turbines for Cogeneration & Combined-Cycle
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 14 www.iagtcommitee.com
COMPARISON – Aero-Derivative & Heavy-Duty Industrial Gas Turbines
Aero-Derivative Heavy-Duty Industrial Performance Up to 50 MW.
Up to 41~42% efficiency (LHV). Generally, less waste heat oppor-tunity from the exhaust gases.
Up to 240 MW+. Up to 35~40% efficiency (LHV). Good waste heat opportunity. Large units with high exhaust temperatures allow re-heat combined-cycle
Fuel Aspects Natural gas to light distillates and jet fuels. Most require relatively high gas pressures.
Natural gas through to distillates and cheaper heavy or residual fuels. Generally require lower gas pressures. Expensive treatment of heavy / residual fuels is re-quired.
Start-Up Quick startup – 5~20 minutes. Relatively low horsepower starters usually electro-hydraulic
20 to 60 minutes depending on size. High horsepower diesel or motor starters, also some are started by the motoring of the generator itself
Loading Quick loading, sometimes 10~25%/min
Slower loading, 1~10%/min depending on size
Shutdown Many larger units require a short time of motoring to cool internals after a trip, but can then be shut-down
Many units require 1~2 days on turning gear after shutdown, but most can be motored to assist quicker cool down
Gas Turbines for Cogeneration & Combined-Cycle
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THE GAS TURBINE PACKAGE Packaging – completes the machine. Needs to be straightforward to install & commission, and easy to maintain.
Driven Equipment Typically:
synchronous generators – rated per ANSI C50.14. process or pipeline compressors occasional use as large pumping sets for oil.
For cogeneration / combined-cycle – typically a generator.
2-pole (3600 rpm) or 4-pole (1800 rpm) for 60 Hz. Air-cooled, water-cooled (TEWAC) or hydrogen-cooled (the largest units).
Generator output voltages:
600V for the very smallest GT’s, to 2.4 and 4.16 kV for the 3~8 MW class units, 13.8 kV for the 10 MW+ units, 27.6 kV for the 100 MW+ units.
Excitation systems for voltage & power factor/var control – brushless or static
Double-helical or epicyclic gearboxes – when GT output speed doesn’t
match generator speed.
Gas Turbines for Cogeneration & Combined-Cycle
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Air Inlet Systems Critical to GT health and for noise mitigation.
High-volume multi-stage high-efficiency filtration systems – capture atmospheric particles; prevent their deposition on bladepath.
Inlet Air Heating – via coils or bleed air systems - for anti-icing; inlet temperature / performance optimization; DLE con-trol.
Inlet Air Cooling – via coils – for inlet temperature / perfor-mance optimization.
Evaporative Cooling Systems & mist eliminators.
Tuned inlet air silencers – absorb sound & acoustic emissions from
intake.
Many companies providing all the air inlet filtration, cooling, heat-ing, and silencing equipment to
GTG packagers.
Plus supplying exhaust systems – silencers, expansion joints, by-pass systems, stacks & enclo-
sures.
Gas Turbines for Cogeneration & Combined-Cycle
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Lubricating Oil Systems Main, auxiliary and emergency lubricating and control oil (as required) sys-tems – provided for gas turbine and driven equipment.
Aero-derivatives – usually fire-resistant synthetic lube oils.
Power turbines, gearboxes & generators – mineral-based lube oils.
Most heavy-duty industrial GT’s have common lube oil system.
Lube oil – cooled by aerial fin-fan coolers, or oil-to-water heat exchangers.
Fuel Systems Aero-derivative & heavy duty gas turbines – light-liquid or gaseous fuels.
Only frame units – operate on heavy fuel oils & crude oils.
Fuel control systems for gaseous and liquid fuels include:
filters, strainers and separators; block & bleed valves; flow control/throttle and sequencing valves, manifolds and hoses.
For natural gas duty – sometimes reciprocating or centrifugal gas com-pression equipment required, plus pulsation dampening equipment.
Complex dry low-NOx (DLE) units – some units require several throttle valves, staged and sequenced to fire:
pilot / ignition, primary, secondary and/or tertiary
nozzle and basket sections (as applicable) of the DLE combustion system for startup/shutdown, speed ramps, and load changes. Several fuel mani-folds usually required.
Gas Turbines for Cogeneration & Combined-Cycle
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 18 www.iagtcommitee.com
Acoustic and Weatherproof Enclosures Most smaller industrial & almost all aero-derivative GTG packages – pre-packaged - com-plete drivetrain enclosed in acoustic enclosure(s).
The turbine & generator compartments - sepa-rately ventilated
Can be easier and quicker to install. 40~50 MW+ industrial GT machines - too large to pre-package.
Components shipped in major blocks – assembled at site. Enclosures or buildings (if required) built around the complete drivetrain.
Controls and Monitoring Complex combinations of digital PLC and/or processor systems – Woodward; vendor-proprietary systems; occasionally DCS-based.
Systems include, manage, sequence, monitor and control:
GT fuel control and speed/load control generator’s voltage, power factor or var control breaker synchronization auxiliaries vibration, temperature & pressure monitors sequence of events recorders certified metering systems communication to plant DCS.
Gas Turbines for Cogeneration & Combined-Cycle
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 19 www.iagtcommitee.com
Miscellaneous Auxiliaries starting and turning gear sys-
tems;
inlet manifolds;
exhaust diffusers or plenums;
water wash systems;
water and steam injection (if re-quired);
gas detection systems;
fire detection and CO2 suppres-sion systems;
battery and charger systems;
ventilation and heating;
exhaust expansion joint;
silencer & stack systems (sim-ple-cycle).
Complete Package Examples
Rolls-Royce Trent Package
Gas Turbines for Cogeneration & Combined-Cycle
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 20 www.iagtcommitee.com
GE LM6000 NXGN Package
Gas Turbines for Cogeneration & Combined-Cycle
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 21 www.iagtcommitee.com
GE LM2500 / LM2500 Plus Package
Gas Turbines for Cogeneration & Combined-Cycle
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 22 www.iagtcommitee.com
Rolls-Royce RB211 Package / Plant
Steam Turbines and Condensers
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 1 www.iagtcommitee.com
An introduction to the application of steam turbine generators and condensing systems to combined-cycle power plants. Typical applications included.
The Basics of Steam Steam behaviour is complex
Change one property, i.e. pressure, volume, temperature, energy or moisture, then all other properties change
Shows interrelationship of steam properties
Vertical axis: Enthalpy (H) – internal energy – btu/lb
Horizontal axis: Entropy (S) Irrecoverable energy in fluid – btu/lb.F
Lines of:
Constant pressure Constant temperature Constant moisture Steam saturation line Constant superheat
Steam Turbines and Condensers
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 2 www.iagtcommitee.com
h2s at 100%efficiency
h2at 75%
Turbineefficiency 0%
h2=h1 at 0%efficiency
25%
50%
75%
100%
h2at 25%
Entropy, btu/lb.F
Enth
alpy
, btu
/lbIni
tial
Pressur
e
Initial
Exhaust Pressure
Tempera
ture
h2at 50%
STEAM ENERGY PROCESSES and the MOLLIER DIAGRAM Extract energy (btu) by expanding from P1 (at T1, H1) to lower pressure P2 (resulting in new T2, H2)
Energy released – enthalpy drop = H1-H2
1 hp = 2540 btu/hr 1 kW = 3413 btu/hr
Perfect expansion (no losses) = Vertical line = highest heat drop
In practice – always losses: Line curves to right
The longer the line the better:
increase initial pressure increase initial temperature decrease final pressure increase expansion process efficiency
Thus the push for:
higher pressure and temperature boilers and HRSGs
for decreased turbine exhaust backpressure and condensing pressures
higher efficiency units.
Steam Turbines and Condensers
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 3 www.iagtcommitee.com
STEAM TURBINES Steam Turbines consists of:
Casing with steam inlet and outlet connections
Enclosing a shaft which hold disk(s)
Disks hold blades or buckets at the periphery
Stationary nozzles – attached to casing – manage the angle of steam approaching rotating blade
In the steam turbine, steam is expanded in 1 of 2 basic ways:
IMPULSE DESIGN:
Nozzles expand & direct steam onto blades
High speed impulse jet pushes blades
Pressure drop occurs across nozzle
No pressure drop occurs along the axial length of the rotating blade
Steam Turbines and Condensers
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 4 www.iagtcommitee.com
STEAM TURBINES
REACTION DESIGN:
Pressure drop and expansion occurs across both the rotating and stationary blades
Blades behave like high-pressure fire hose, rotating from the reaction that occurs – sudden change from high pressure to high
velocity steam
Reaction = small gain in efficiency
But, maintaining rotating blade tip clearances is critical
Modern steam turbines combine these two basic designs (impulse and reaction) in varying degrees – cost & efficiency reasons.
Steam Turbines and Condensers
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 5 www.iagtcommitee.com
STEAM TURBINE EXHAUST CONFIGURATIONS
Backpressure Steam Turbines generally exhaust to a steam system above atmospheric pressure volume of steam is relatively small blade path consists of relatively small nozzles, blades, and cylinders exhaust piping relatively small
Any inlet-to-exhaust pressure ratio > 2:1 acceptable
Exhaust pressures above 200 psig rare
Turbine capacity only limited by process steam amount needed
However, backpressure STGs > 50 MW relatively rare
Rarely used in combined-cycle configuration.
ProcessSteam
SteamSupply
Steam Turbines and Condensers
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 6 www.iagtcommitee.com
Condensing Steam Turbines generally exhaust to system / location significantly below atmospheric
pressure (inches of mercury absolute, i.e. inch HgA) specific volume of steam very high much larger blading and nozzle areas required cylinders become very large near the exhaust of the unit exhaust hood / diffuser after the last stage blades – slows down steam
in an orderly manner, to minimize exhaust losses Condensing refers to the condensing system attached to unit – which acts to condense or turn back to water (condensate) the exhaust steam
Steam volume decreases by orders of magnitude – steady-state vacuum created / maintained in “closed vessel”
Sized from as small as ~5 MW, up to the 1500 MW+ units employed in utility service. Combined-cycle plants: maximum size 200~250 MW.
Inlet pressure: up to 2400 psig Maximum inlet temperatures 900~1050 F Condensing pressures: 0.75 inch HgA for coldest condensing systems - up to maximum of ~10 inch HgA for air-cooled condensing systems @ high ambients
SteamSupply
Condenser
Steam Turbines and Condensers
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Comparison Each of condensing & backpressure turbine: receives the same 250,000 lb/hr of 900 psig, 900
deg F steam is expanded to 60 psig in backpressure unit or expanded to 1.5 inch HgA in condensing unit. Backpressure Steam Turbine: 16 MW useful 60 psig process steam @ ~ 405 deg F Condensing Steam Turbine: 33 MW no process steam condensate (hotwell) ~92 F (usually to deaerator) Push for increasing efficiencies – developers are seeking to take advantage of this low-grade, high-volume heat for other useful processes
Steam Turbines and Condensers
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 8 www.iagtcommitee.com
Westinghouse Single Auto-Extraction Backpressure Steam Turbine
Westinghouse Double Auto-Extraction Condensing Steam Turbine
Steam Turbines and Condensers
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EXTRACTION, ADMISSION and REHEAT CONSIDERATIONS Extraction Steam Turbines Tapping point somewhere in blade path
Steam at intermediate pressure obtained
Extractions can be either automatic (controlled), or uncontrolled pressure
TWO EXTRACTION TYPES – applicable to either backpressure or condensing: Controlled Extraction: Poppet, spool or grid valves installed at intermediate steam chest
Valve position manipulated by the control system to maintain pressure
Uncontrolled Extraction: No controlling valves at the tap-off point
Delivery pressure function of steam flow downstream of tap-off point
Admission Steam Turbines Admission steam turbines: Similar to extraction units – either controlled or uncontrolled
Requires trip & throttle valve – for turbine trips
Some STG units configured as admission/extraction – i.e. can accept or deliver steam.
SteamSupply
ProcessSteam Process
Steam
ProcessSteam
SteamSupply
ProcessSteam
Steam Turbines and Condensers
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 10 www.iagtcommitee.com
Reheat Steam Turbines Special condensing turbine configuration Common for large non-nuclear (fossil) utility units for decades Becoming common for largest combined-cycle plants - where
inlet pressures & temperatures rising
Steam expanded through HP turbine – taken as cold-reheat to HRSG reheat section – reheated back to original inlet steam temperature – admitted back to intermediate-pressure turbine section as hot reheat
improves back end wetness
increased power & efficiency
multi-cylinder configurations
additional reheat & intercept valves required
Inlet / reheat temperatures 1000~1050 F
Initial pressures: 1250 ~ 2400 psig
Reheat pressures: 400 ~ 600 psig.
+ $$ cost
SteamSupply
ColdReheat
HotReheat
HP IP 2 x LP
Crossover
Exhaust Exhaust
Steam Turbines and Condensers
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 11 www.iagtcommitee.com
Combined Gas & Steam Turbine Drivetrain Reduced plant costs Slight efficiency
improvement Simplified electrical
connections Gas turbine connected to one end of generator Steam turbine to the other end via clutch GE version: STAG Some smaller gas turbine manufacturers offer similar configuration – with either backpressure or condensing STG: e.g. Solar STAC
Steam Turbines and Condensers
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 12 www.iagtcommitee.com
TYPES OF CONDENSING SYSTEMS Water-cooled surface condensers and wet condensing systems Air-cooled condensers Alternative condensing systems
Water-Cooled Surface Condensers
Most efficient - most popular condensing systems – where environmental permits Large amount of cooling water required.
2 MAJOR TYPES Surface Condensers with Once-Through Cooling Water Systems Simplest
Best performance
Requires river, lake or sea and pumphouse
Generally restricted to <=18 deg F rise
Steam Turbines and Condensers
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Surface Condensers with Evaporative Cooling Towers: Eliminates hot water discharge back to original water source
Closed-circuit system for condenser cooling water
Circulating water obtained from the basin of cooling tower, heated in condenser circuit, returned to tower
Makeup water required – from evaporation, drift & blowdown
Blowdown treatment & chemical injection required
May require plume abatement
2 MAJOR TYPES
Natural-draft cooling towers: Distinctive hyperbolic shape.
Cooling air flow induced naturally by the hotter (less dense) air in the tower drawing colder (denser) air from outside, at the bottom.
Mechanical-draft cooling towers: Create airflow through tower by either:
Induced-draft (fan at top)
Forced-draft fans (located at the air inlet to the tower, susceptible to icing).
Steam Turbines and Condensers
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 14 www.iagtcommitee.com
Dry or Direct Air-Cooled Condensers (ACC) Where water is scarce Where powerplant can’t afford
even small amounts of cooling water evaporation (i.e. no cooling tower)
Steam turbine exhaust steam enters central plenum/pipe A-Frame: finned tubes sloped down towards condensate collection system Variable or dual-speed cooling fans Steam condenses as it progresses toward the hotwell. Performance dependent on dry bulb temperature Concerns: Cold weather operation Icing Alternative Condenser Systems Parallel / hybrid condensing – combo of direct air-cooled condenser + surface condenser & cooling tower.
Wet-surface air-cooled condensers (WETSAC).
Cooling Ponds: 1~2 acres of water surface area required – per MW of condensing.
Steam Turbines and Condensers
Gryphon Int’l Eng’g IAGT-Vancouver – LNG Symposium – May-2014 IAGT www.gryphoneng.com Page 15 www.iagtcommitee.com
Condenser Performance Comparison
Cogeneration / CHP Principles
Gryphon Int’l Eng’g IAGT www.gryphoneng.com www.iagtcommitee.org
COGENERATION DEFINITION
“The simultaneous production of two or more forms of useful energy (usually electricity and heat) from a single fuel source”
Cogeneration / CHP Principles
Gryphon Int’l Eng’g IAGT www.gryphoneng.com www.iagtcommitee.org
MAJOR EQUIPMENT usually associated with Cogeneration / CHP cycles Steam generator or boiler Steam turbine generator (STG) Gas turbine generator (GTG) Heat recovery steam generator (HRSG) Reciprocating Gas, Dual-Fuel or Diesel engine generator
Cogeneration / CHP Principles
Gryphon Int’l Eng’g IAGT www.gryphoneng.com www.iagtcommitee.org
Exhibit #5 – Steam-Generator and Back-Pressure Steam Turbine
Cogeneration / CHP Principles
Gryphon Int’l Eng’g IAGT www.gryphoneng.com www.iagtcommitee.org
Exhibit #6 – Steam-Generator and Condensing Steam Turbine
Cogeneration / CHP Principles
Gryphon Int’l Eng’g IAGT www.gryphoneng.com www.iagtcommitee.org
Exhibit #7 – Combined-Cycle Cogeneration
Cogeneration / CHP Principles
Gryphon Int’l Eng’g IAGT www.gryphoneng.com www.iagtcommitee.org
Exhibit #8 – Gas Turbine & HRSG
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