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Publication Title | STEAM INJECTION SYSTEM ON AN EARLY FRAME 3 GAS TURBINE IN A COMBINED CYCLE PIPELINE COMPRESSOR STATION

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Search Completed | Title | STEAM INJECTION SYSTEM ON AN EARLY FRAME 3 GAS TURBINE IN A COMBINED CYCLE PIPELINE COMPRESSOR STATION
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Text | STEAM INJECTION SYSTEM ON AN EARLY FRAME 3 GAS TURBINE IN A COMBINED CYCLE PIPELINE COMPRESSOR STATION | 002



138 PROCEEDINGS OF THE TWENTY-FIRST TURBOMACHINERY SYMPOSIUM
A steam injection system was designed, fabricated and tested to evaluate its field performance. Field testing confirmed the expect­ ed horsepower increase, but an unexpected increase in the exhaust thermocouple spreads at higher steam injection rates was also experienced. Correlation of the combustor liner vs the exhaust thermocouple readings showed some interesting characteristics of these turbines. Operating guidelines for steam injection operation are presented.
INTRODUCTION
Transco has been operating its centrifugal compressor stations at two of its mainline locations since the early 1950s. These stations started out as steam plants, i.e., steam turbines were the prime movers for centrifugal boosters with gas fired boilers sup­ plying the steam. The plant thermal efficiency was quite low.In the early 1960s, Frame 3 gas turbines were added as the throughput of the pipeline was increased. To improve the fuel efficiency, these gas turbines were equipped with supplementary fired heat recov­ ery steam generators (HRSG) to recover heat from the exhaust gases [1]. This steam was used to drive the steam turbines and the older boilers were retired. One boiler is still being used to facilitate initial startup and to maintain control during plant upsets. The current equipment at the Billingsley, Alabama, station is described in Table 1. The equipment at the other station in Tylertown, Mississippi, is similar. These configurations are quite unique within the pipeline industry, as most pipeline stations do not have steam turbines at their sites.
Table 1. Description of Units. Transcontinental Gas Pipe Line Corporation Compressor Station 100, Billingsley, Alabama.
horsepower upgrade option [4) that would have required the change out of most of the hot gas path components at an installed cost of about $1100/hp. All of the gas turbine parts except for the air compressor and the exhaust duct work would have been replaced. An alternate proposal was developed to increase the horsepower of the unit via installation of a steam injection system. The project scope included the following:
• Conduct a major overhaul on the unit to upgrade components to "as new" condition.
• Evaluate the plant demineralized water supply and quality and upgrade as necessary.
• Upgrade the control system for the gas turbine and integrate the steam injection controls as necessary.
• Design, install and test a steam injection system to upgrade horsepower.
The overall cost for this project was estimated to be $500/hp. Based on several considerations including cost and delivery, a decision was made to proceed with the installation of the steam injection system.
STEAM INJECTION TECHNOLOGY REVIEW
Steam injection is fast becoming a mature technology that has gained varied and wide application within the utility, cogenera­ tion, and petrochemical industries. Most of the turbine manufac­ turers are utilizing this technology [5] for NOx reduction and power augmentation. However, injecting water or steam into a gas turbine is not a new idea. Water injection for short periods of thrust augmentation was at one time common in jet aircraft engines, although fans serve this purpose today [6].
Various benefits of steam injection have been known for a long time [7]. However, steam injection application got a significant boost due to mandated NOx emission requirements in California and Japan.In the early 1980s, steam injection was a technology of choice for controlling NOx, especially for combined cycle plants [8, 9, 10]. Steam injection was also being used to augment horse­ power and cycle efficiencies of cogeneration applications that would typically use aircraft derivative gas turbines [11, 12].
Steam injection systems have been successfully retrofitted for NOx control [13] in 251B8 gas turbines and for NOx and power augmentation [14] in Frame 5 gas turbines. Although steam injec­ tion has been successfully utilized for many years, the OEMs have shown reluctance to promote these systems for retrofit applications.
With a steam injection system, a typical gas turbine fired on natural gas produces a NOx emission level of 45-55 ppm at base load rating [15). Use of SCR systems (DeNOx systems) for more stringent NOx control is necessary, and a Nox range of about 15 ppm is achievable. These systems are becoming more reliable and cost efficient, due to better than expected catalyst life.
PROJECT OVERVIEW
After project approval, an overall plan of action was developed. For the older "straight-through" gas turbines, retrofit design for power augmentation required a careful review of the unit's me­ chanical and performance characteristics. Prior to shutdown, a performance test of the gas turbines at the station was conducted to evaluate their condition. The results of these tests are discussed later.
In addition, a plant wide study of steam purity was conL :1cted to determine if water treatment needed to be upgraded to minimize the possibility of hot gas corrosion on gas turbine blades. The oxygen scavenger was changed from a corrogen (catalyzed sodi­ um sulfite) to a more volatile one. This is a volatile oxygen scavenger that contributes no inorganic solids to feedwater. The capacity of the plant demineralized water system was to be in-
Driver/Compressor
Westinghouse/Clark Steam Turbine
Westinghouse/Clark Steam Turbine
G.E. MS3002B/Delaval G.E. MS3002F/Delaval G.E. MS3002F/Delaval G.E. MS3002F/Delaval
HP Rating
Unit No.
1-3 4
5
6
7
8
*
The four gas turbines were equipped with prespeedtronic hy­ draulic fuel regulator controls. Over the years, these controls were becoming difficult to maintain due to age, unavailability of quality spare parts and field support [2]. Although more modem controls were oeing offered, it was difficult to justify upgrades due to cost and experience with upgrades by other users. A decision to imple­ ment cost effective control upgrades on a unit by unit basis was made in 1987. One unit at each location was upgraded in 1988 with a new system with overall good results. A less expensive upgrade was also explored [3].It was becoming evident to management that cost effective solutions require additional engineering resources and extensive user involvement. To assure long term reliability of this equipment, it was critical to develop relationships with spe­ cialized vendors.
A pipeline expansion project required an additional 2000 "peaking" horsepower at this station. The OEM recommended a
Unit 5 was upgraded to 8780 HP as a result of the Steam Injection System
Yr. Installed
06/51 5600 04/57
5620
6800*
72 10
72 10
8460 12/72
1 1/62 11/66 09/68

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