By injecting water between the low pressure and high pressure compressors of an aeroderivative gas turbine, GE-IAD engineers have demonstrated that a 9 per cent increase in output accompanied by reduced life cycle costs can be achieved. Designated the SPRINT system, uprated LM 6000 units with augmented efficiency have been introduced to the market. The first two production units, both supplied to Southern Electric Power Generation in England for mid-merit independent power generation plants at Chickerell in Dorset and Burghfield in Berkshire, have each clocked in excess of 500 operating hours since start-up in early April 1998. MPS visited the Chickerell installation in late July 1998.
GE Industrial AeroDerivative Gas Turbines (GE-IAD) introduced its new spray intercooling concept, which has been designated as the SPRINT (SPRay INTercooling) system, for its LM6000 aeroderivative gas models at Power-Gen Europe ’98 in Milan, Italy (June 9, 1998). The company claimed that the system would increase the machine’s power output substantially.
“Our tests have demonstrated that by injecting water between the low pressure and high pressure compressors of an LM6000, we have been able to increase the output of this gas turbine by at least 9 per cent,” said Doug Westerkamp, manager of market development for GE-IAD, Evendale, Ohio.
The presentation declared that the benefits of the spray intercooling system include the following:
The 9 per cent power boost at ISO conditions
Over 17 per cent increase in power on hot days (greater than 27°C) with some efficiency improvement
Elimination of inlet chillers for most installations.
Below 0°C, there is very little difference between the output of the latest LM6000PC and the LM6000 SPRINT; they both turn out a specified 51.5 MWe. However, as the ambient temperature increases the fall off in output, mass flow and efficiency is much less in the SPRINT system.
GE collaborated with S&S Energy Products of Houston, Texas (formerly the gas turbine division of Stewart & Stevenson) on the testing of the spray intercooling system. Tests began in early June 1997 at GE’s Evendale, Ohio facility. Field tests were conducted on an LM6000 PA retrofitted with the intercooling system at the Fort Lupton cogeneration facility in Colorado. This unit had been operating on this site since 1994 with four additional LM6000s until the tests were completed in February 1998.
Additional testing, completed in May 1998 on the first production SPRINT LM6000s, verified the power increase. These two units recently began commercial operation at two separate power plants owned by Southern Electric Power Generation Ltd (SEPG) in the United Kingdom.
The first US SPRINT contract has just been placed by the West Texas Municipal Power Agency in Lubbock, Texas, for GE’s S&S Energy Products to repower an existing 22 MWe steam turbine set at Lubbock Power & Light’s (LP&L) Massengale Station. The SPRINT turbine, with its associated Deltak HRSG, will increase the output of the plant to approximately 65 MWe, with a 50 per cent reduction in heat rate. The plant will be called upon to meet peak power demands when it starts to operate commercially in the summer of 1999. Since 1990, LP&L has been operating a GE LM2500 aeroderivative gas turbine generator set that had been packaged by S&S.
In GE-IAD terminology, the spray intercooling lowers the high-pressure compressor inlet temperature, which in turn effectively lowers the compressor discharge temperature. A finely atomised interstage mist injection system is used to cool the low pressure booster discharge air. Water is injected into the airflow path through a series of 24 air-assisted spray injection nozzles that are located in the engine front frame.
Air for the system is supplied from the engine’s eighth stage customer bleed extraction port. This cools down the low pressure booster discharge air in order to lower the high pressure compressor inlet temperature, which in turn effectively lowers the compressor discharge temperature. This form of interstage cooling makes it possible to be able to increase the compressor pressure ratio in order that greater mass throughput can be pushed through the turbine, which will directly increase the machine’s power output.
In addition to being offered for production LM6000 PC units, the SPRINT system is also available for those LM6000 PA models that have already been retrofitted using an LM6000 uprate kit.
First two in the UK
On-site tests have been conducted by GE-IAD on the gas turbines at the Burghfield, Berkshire, and Chickerell Dorset, Mini power plants in the UK. The two S&S packaged units used at these sites are virtually identical except for a few minor adaptations to enable them to conform with the local site conditions.
These tests did indeed verify that the SPRINT LM6000 provides 9 per cent more power than produced by GE’s LM6000 PC/PD model.
SEPG has said that it plans to install seven of these units at distributed generation sites close to substations in major load centres in southern England. The units are automatically controlled to start supplying power to the Southern Electric network whenever the control system software calculates that the system can generate power more profitably under the prevailing market conditions.
These two UK units are the first to use the new Woodward NETCON 5000 automation software – which is a version that has been rubber stamped by GE – while LM6000’s used on off-shore rigs tend to use the more comprehensive and bulky GE Mark 5 Speedtronic systems. The NETCON system has a very user-friendly graphical interface, with very good presentation of condition monitoring and trending data. The operators are able to start up, operate, and shut down their own, or the other similar plants on the system if that is required, from terminals in their own homes
When the writer visited the Chickerell site recently, the simple cycle machine was generating some 47.2 MWe while the ambient temperature was 16°C, with NOx emission down to 18 ppm with 15 per cent oxygen in the exhaust. Records indicated that on the previous day, the plant had been running at a power level of 49 MWe at 14°C with an NOx reading of 15 ppm. CO was more or less consistent at 30 ppm.
Dry low NOx combustors are not used with the SPRINT system, but additional water injection for NOx reduction is introduced via the burner nozzles to keep emission down below 25 ppm. Demineralised water for water injection is provided by a leased Ecolochem reverse osmosis unit on site which supplies 48 USg/m of purified water at a fixed charge per gallon. The SPRINT water consumption at the time was some 8 USg/min.
Due to the very compact dimensions of the plant, visual impact is minimal. The turbine plant is quite remarkably noise and vibration free in the S & S package.
The units need gas at between 8 to 45 bar pressure. Since the gas is supplied on an interruptible supply contract, diesel oil is used as a back-up fuel to maintain availability status. The plant seemed to be running for a steady eight or nine hours every week day between 06.30 and 18.30 hrs at somewhere near full output. This is likely to be increased during the higher winter demand periods.
With deregulation of the electricity supply industry and the introduction of commercial competition, there is bound to be something of a trend towards the installation of distributed generation for peaking and mid-merit duty, particularly in association with major distribution substations in the vicinity of major load centres. Major growth of the market for distributed generation of many types is predicted in many countries around the world where deregulation is just beginning to bite.
In regions where there are substantial transmission constraints, it is quite likely to be more economic to generate additional peak load capacity close to load centres than to pay for use-of-system costs and peak period electricity charges from remote bulk generators.
The systems selected for such duty need to be high efficiency, low investment, simple cycle machines with rapid startup times and low maintenance and manning requirements, capable of frequent stop starts and high ramp rates.
Location close to population centres also means that very low environmental impact is vital. It is not surprising that localized distribution companies prefer to have this kind of facility, which may also be used for frequency regulation, under their own control where national regulatory criteria allow.
The most advanced aeroderivative gas turbines are a natural choice for this because of their modest site space, fuel and water consumption demands and minimal waste discharges. The traditional objection raised to small gas turbines of reducing output with higher ambient temperatures and higher altitude sites appears to have been substantially ameliorated with the new SPRINT system.
|GE LM6000 milestone timeline|
| b-june-1990-b-ge-introduces-lm6000-aeroderivative-gas-turbine-engine-has-90-per-cent-parts-commonality-with-its-cf6-80c2-aircraft-engine-predecessor-b-december-1992-b-first-lm6000-begins-commercial-operation-at-ottawa-health-sciences-centre-a-second-lm6000-begins-cogeneration-service-shortly-thereafter-at-mcdonnell-douglas-canada-s-facility-in-mississauga-both-power-plants-are-owned-by-transalta-energy-corporation-calgary-alberta-canada-b-may-1993-b-ge-introduces-a-dry-low-emissions-dleTablesKey milestones Table 1. Comparison of LM6000 SPRINT and LM6000PC performance