Repowering Older Plants - The HRSG View
International Conference Power Plants 2012 Society of Thermal Engineers of Serbia Oct 30th
Nov 2nd , 2012
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Zlatibor, Serbia
Heat Recovery Steam Generators offered by CMI
Heat Recovery Steam Generators offered by CMI
Inherent features Horizontal Horizontal & Vertical HRSGs
Horizontal
Vertical
Accessibility Accessibili ty / Maintainability Maintai nability
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Cleanability
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Duct firing
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Arrangement
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Catalysts
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Erection cranes
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Cycling
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Lets review the specific application of repowering power plants and fuel oil in the following foll owing presentation slides
Introduction to power plants repowering In
the Balkan and Central Europe, there is a large fleet of old coal fired power plants with a potential for repowering into modern combined cycle power plants. Compared
to green field projects, repowering a steam turbine with a new train of gas turbine and HRSG includes some special challenges. Most
of the time, the HRSGs have to be tailored made to suit limited foot print, and existing repowered steam turbine. CMI has completed such a large repowering project, like Senoko in Asia or Dunamenti in Hungary. These experience will be the support throughout this presentation to explain these specific repowering challenges.
Besides
this main topic, CMI will present the HRSG for heavy oil application, and the most recent references in Central Europe.
Concept of Plant Repowering 12
OPTION
REMAIN
11
Condenseur 9
10 8
7
Turbine à vapeur
6 13 5
1
HRSG
NEW
4
3
2 1
: condensats - 2 : eau alimentaire -
5: vapeur
Pompes alimentaires
9:
eau alimentaire. IP - 4: eau alimentaire HP
HP - 6: retour turbine (Cold reheat) -
eau désurchauffe by-pass IP -
12:
3:
10:
7: resurchauffe
- 8 : vapeur LP -
by-pass IP - 11- by-pass LP
eau désurchauffe by-pass LP - 13 : by-pass HP
Repowering Senoko - Project background • Repowering of old 3*120MW steam turbine into efficient CCPP • Main contractor was Alstom using its gas turbine engine GT26B • CMI Vertical HRSG 3P+R in natural circulation • HRSG ‘ tailor designed ’ to suit numerous constraints • Project challenges: - limited foot print of old boiler - existing site very congested - only 18 months outage
ALSTOM GT26 arrival at site
Site limitations 3D model new boiler
Original fired boiler had to contain new GT+ HRSG.
Available area for HRSG was limited to 30.6*28.1m
HRSG indoor includes main auxiliaries (cargo lift, FWP, feedwater tank, etc)
CMI exchanged with Alstom 3D model to make detailed plant modelling
Vertical HRSG flexible layout A Vertical HRSG behind GT class ‘ F ’ for ‘ greenfield ’ is around 35 meters long. In case of Vertical HRSG, tubes length impact directly the overall boiler length. This is not the case for Horizontal HRSGs. This is a special flexibility feature offered by the Vertical HRSG only. Typical tubes length 20.4 m
Typical heigth 9m
GT
Overall boiler length 35 meters
Vertical HRSG flexibility layout To match this repowering limited space (length 30,6 meters), CMI has taken advantage of this flexible arrangement offered by the Vertical HRSG: CMI used shorter tubes length. For unchanged casing cross section, boiler casing was enlarged in proportion
Reduced tube/boiler length
Longest tube 20.4 m Flexible Gas cross section
Gas cross section unchanged
Slightly enlarged boiler width
Vertical HRSG flexibility layout Considering the installed boiler heating surface, this HRSG was arranged in 3 modules in width by 4 levels in height, instead of 2 modules wide by 5 levels height which would have applied otherwise for a ‘ greenfield ’ site. Heating surface modules flexible arrangement
Standard 'greenfield' arrangement
Senoko enlarged casing width
Modular construction HRSG was made of 12 heat exchanger modules prefabricated and hydrotested to reduce erection time. The largest module dimensions was 23.6 meters long * 3.9 wide *2.9 heigth.
Heat exchanger modules unloading and transportation
Congested existing site Boiler modules were transported by hydraulic trailer ‘self propelled ’ which reduced convoy length and help to perform precise movements with large angle orientation wheels in congested site
Heat exchanger modules arriving at the gate of the existing power plant (Site very congested)
Modules erection using hydraulic jacks
28 hydraulic jacks to lift modules on top of structure
Vertical HRSG: No large crane was required.
Vertical HRSG Steel structure with jacks on top for module lifting
Modules erection using hydraulic jacks Considering a congested site, the CMI Vertical HRSG erection features: - no module tilting performed - no large cranes required
Horizontal HRSG typical lifting system
Modules erection sequence The first row of 3 modules was hanged to cables and lifted up just enough to introduce the next row of 3 modules. This operation was repeated until all 4 levels of modules were suspended to one another.
Modules erection sequence Erection cables Temporary plates (peinted in yellow) Final suspensions
First row of modules suspended
Modules erection sequence Hydraulic trailer ‘ self propelled ’ had to manoeuvre in limited space.
Introduction of the second row of modules.
Modules erection sequence The module was positioned exactly and it was attached to the module just above it on each support plates. Then, the hydraulic trailer was lowered and released.
Modules erection sequence
Erection of last row: All modules remained flat during the complete erection sequence
Modules erection sequence Completion of 12 modules suspended
Only adjacent header ends were to be welde
Modules erection sequence The complete assembly (1450 tonnes) was then jacked up on top of the steel structure.
Hydraulic jacks were released, dismantled and installed on the next unit. All modules suspended in final position inside the steel structure
Modules erection sequence Boiler modules erection completed in 6 days only!
Indoor HRSG HRSGs steel structure has been extended to an enclosure wrapped all around for weather protection, noise abatement and aesthetic.
View of completed repowered Senoko Power Plant
Repowering de Dunamenti G3 in Hungary
Unit 9
Unit 8
Repowering Dunamenti - Project background The GDF SUEZ Group, majority owner of the Dunamenti power station, Hungary’s second largest power plant, decided to upgrade its G3 unit, a combined-cycle gas turbine (CCGT) block, from 215 MW to 400 MW, commissioning in 2011. In this repowering process, Dunamenti, the existing gas-fired steam turbine and installed a heat recovery steam generator (HRSG) and a gas turbine. This raised the unit’s efficiency from 36% to 57%. The Dunamenti plant accounted for 7% of all electricity generated in Hungary in 2010, producing 2.6 terawatt-hours. View of the Repowered
Repowering Older Plants - The HRSG View • Repowering of old conventional plants into new efficient CCPP (new GT-HRSG sets with old ST sets) is a cost effective solution, because existing equipments remains such as steam turbine, electrical distribution, cooling system, etc. • Permitting is also more easy as this is an existing power plant. • Compared to ‘greenfield’ plants, repowering of old units always requires ‘ tailor made ’ design to match specific constraints: - remaining equipment's (steam turbine, condenser, etc) - limited available space of the old fired boiler - minimum outage of the existing plant - congested existing site - indoor HRSGs • The Vertical HRSG has proofed to be very flexible and accommodating for those specific repowering constraints.
Design Criteria for HRSG Heavy Fuel Oil Operation •
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Gas turbines are operated typically on natural gas, with no risk of fouling and typical dew point at 60°C. Both Horizontal or Vertical HRSG are suitable for the purpose. Heavy fuel oil has high sulfur content with Acid Dew Point (ADP) up to 145°C Such high sulfur content requires a special HRSG design because all metallic surfaces must remain above ADP to prevent internal corrosion on tubes and ducting. Temperature of condensate water entering finned tubes must be controlled to remain above ADP to avoid acid formation on tubes It limits the heat recovery in the back end of the HRSG Ducting metal must remain above ADP which is not feasible with internal insulation. HRSG must be externally insulated with ducting remaining at inside flue gas temperature.
Design Criteria for HRSG Heavy Fuel Oil Operation Combination of Heat Exchangers arrangement and Sootblowers must maintain permanent industrial cleanliness of finned tubes: Finned tubes Maximum height of solid fins Maximum fins density (160 fpm on heavy oil) Staggered or inline arrangement with constant minimum tubes pitches Limitation of tube rows per bank
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Sootblowers Between tubes banks for on-load cleaning Rotary or Rake type parallel to tubes
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Boiler design for Fuel Oil is different than Natural Gas. This requires specific boiler expertise with references.
Proven HRSG design for Distillate Oil
HRSG designed for continuous operation on distillate oil
Proven HRSG design for Crude Oil
HRSG designed especially for continuous operation with crude oil and equipped with sootblowers
Conclusions
There is real potential for repowering of old steam turbines in the Balkans. In a lot of old conventional plants, fired boilers have exhausted their useful life before its steam turbine. Repowering of those old steam sets into efficient combined cycle with new GTs and HRSG is a cost effective solution. Today, available gas turbines can provide the exhaust energy for steam turbines of 120 -150 MW of which there are many examples in Europe dating back from the 1970’s. These units could be repowered so as to increase power supply with a significant improvement in operating efficiency, flexibility and emissions. CMI has completed the Senoko and Dunamenti plants, which are a very successful example of such repowering. Vertical HRSG has been proofed to be very accommodating for those the specific repowering constraints, which always require a tailor made design to suit limited space. In addition CMI Vertical HRSGs are uniquely fit behind Gas Turbine firing fuel oils.
