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When GE Power Systems launched its Energy Rentals unit in the summer of 1999, a core strategy of the new business was using GE’s diverse line of power generation products to change traditional approaches to temporary power. A major result of that effort was the development of the world’s largest mobile gas turbine-generator unit: the TM2500, a trailer-mounted version of GE’s widely used LM2500 aeroderivative gas turbine.

In mid-March of this year, five TM2500s were shipped out of Ireland after spending more than four months there, helping the Electricity Supply Board (ESB) of Ireland avert power outages during the winter peak demand season. From two different locations, the leased generating units were ready to supply more than 110 MW of additional power as required by ESB.

It was the second application for the travelling power plants. They were shipped to Ireland directly from Chicago, USA, where they helped Commonwealth Edison meet its warm weather peak demand during the summer of 2000.

“We ran the TM2500s for about 90 hours, which was less than expected, because of our mild summer weather,” said a Commonwealth Edison spokesperson. “But they gave us the security of knowing we were ready if additional power was ever required. And reliability was excellent; when we needed the power, the entire facility was up and running within half an hour.”

Each of the five TM2500s is capable of producing up to 22.8 MW (ISO conditions), or enough power to serve more than 8000 homes. Their combined capability represented 2.5 per cent of the ESB grid’s current capacity of 4700 MW, and gave ESB a safe margin against unexpected demand from domestic and commercial customers.

The five TM2500 units arrived in Ireland by sea in late September 2000, and were unloaded at Cork. Three of the packages were transported to ESB’s Aghada power station and the other two units were taken to a site near the town of Tawnaghmore. They were assembled, converted to 50 Hz, connected and were ready to operate less than 60 days after leaving Chicago.

Following their winter service in Ireland, the five units were disassembled and left the port of Cork on March 13, 2001. Their next stop is a power station in Utah, where starting May 1 – less than 50 days after leaving Ireland – they will supply peaking power throughout the summer until the end of October.

A natural choice

The LM2500 aeroderivative gas turbine was selected for the TM2500 project because of its demonstrated reliability, durability and flexibility. Based on GE Aircraft’s well-proven CF6-6 commercial aircraft engine, more than 500 industrial LM2500 gas turbines are in service today around the world and have between them accumulated more than 23 million operating hours.

To package the gas turbine as a portable unit, Energy Rentals turned to GE Aero Energy Products (formerly S&S Energy Products) in Houston, Texas. For a temporary power application, the traditional LM2500 fixed power generation package had to be modified to fit onto no more than four separate trailers, while maintaining the same performance, noise levels, emissions and operating flexibility.

Figure 1. En route from Cork to the ESB site
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The LM2500 was a natural choice for this application due to its relatively light weight, 50 or 60 Hz operating flexibility and dual fuel capability. The compact size and weight of the LM2500 allowed both the turbine and the generator to be mounted on the same customized trailer, which reduced both setup time and the risk of misalignment of the two components at the customer’s site.

To solve some of the design challenges of converting the LM2500 into an easily transportable gas turbine unit, a GE team developed a special mounting system which isolates the engine and its enclosure from main trailer movement during transport. The new system has reduced the on-site process of aligning the turbine to the generator from two days to as little as half a day.

Fuel flexibility

The TM2500 is a four-trailer system consisting of a main (turbine-generator) trailer, an inlet filter trailer, an exhaust trailer and an auxiliary trailer.

The main section of the TM2500 is a six-axle, air ride suspension trailer that measures approximately 108 feet (32.9 m) long (less tractor) during transport and weighs approximately 210 000 pounds (95 254 kg) fully loaded. At the job site, the main trailer transport equipment is removed which shortens the installed main trailer to just 58 feet (17.7 m).

Ten independent landing legs support and level the main trailer, which provides the base plate for the LM2500 gas turbine. The turbine is ISO-rated at 30 563 hp (22 800 kW) for continuous duty, and the corresponding heat rate is 9280 Btu/kWh (9790 kJ/kWh), LHV.

Figure 2. A TM2500 unit arrives in Cork, Ireland. A single TM2500 unit can be assembled and ready for field testing just three days after arrival on site
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The LM2500 is fitted with a dual fuel system and is capable of operating on either natural gas or liquid distillate fuels. “Switch-on-the-fly” fuel transfer capability is also available where gas curtailments are a threat.

NOx levels of 25 ppm on gas fuel and 42 ppm on distillate fuel can be achieved through the injection of demineralized water through the fuel nozzles. Limited operation at levels as low as 15 ppm NOx is permitted. The TM2500 uses a predictive emissions monitoring system (PEMS) for controlling NOx emissions. Each unit is tested during commissioning and water/fuel ratios are adjusted for local site conditions. During operation, the control system maintains a constant water to fuel ratio, adjusting for ambient conditions and power levels.

The inlet trailer includes the gas turbine inlet air filter, turbine enclosure ventilation fans, and a gas turbine noise abatement system. The inlet trailer backs up to the front of the main trailer, and is connected by an airtight flexible boot.

The exhaust trailer incorporates an exhaust transition, a horizontal exhaust silencer, a 90° exhaust elbow, and a vertical stack. It also includes emissions testing ports and an access hatch for ease of inspection.

The auxiliary trailer contains control system components and all auxiliary systems. The control house is a climate controlled cabin which includes the digital control system featuring an integrated electronic fuel management system with a PLC based programmable sequencer, vibration monitor, fire system monitor, digital meter, and a digital generator protective relay module.

Fast-track development

Since most of the components of the fixed applications of the LM2500 generator sets were used including the generator and control systems, GE Aero Energy Products’ design, procurement, and assembly cycles were shortened to just seven months. After Energy Rentals gave the go-ahead in August of 1999, the first unit was designed, built and tested by March of 2000.

Following rigorous testing, the first unit was delivered to ComEd by the end of April 2000. From its Chicago office, GE’s Industrial Systems’ Engineering Services group provided all of the interconnection engineering and led the site civil work for the ComEd installation.

A single TM2500 unit can be assembled and ready for field testing just three days after its arrival on the site, with the necessary infrastructure in place. The main trailer is positioned with the ten landing legs aligned over steel plates to distribute the load over the site foundation, typically a layer of compacted gravel. The base plate is then levelled by adjusting the individual legs.

“Speed and mobility are certainly among the real advantages of the TM2500,” said ComEd. “Normally it would take 18 months to a year to build a gas fired power station. These units can be rolled onto the site and ready to produce power within three days. That’s a revolutionary approach in the power industry.”

Figure 3. The TM2500 units supplied power to Commonwealth Edison during the summer of 2000
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Once the main trailer is level, the auxiliary trailer is pulled alongside, and a small exhaust elbow is rolled over against the main trailer to disperse the turbine compartment exhaust air. With the auxiliary trailer in place, the inlet trailer is then pulled into position, and attached to the front of the main trailer. Generator inlet filtration and exhaust modules are hoisted on top of main trailer, and the turbine/generator coupling shaft is installed and aligned using specialized laser alignment tooling.

With all of the intra-trailer connections completed and auxiliary power connected to the MCC, the electrical checkout begins, and preparations are made to start the turbine while the 13.8 kV cable terminations are completed. Once final fuel connections have been completed, the unit is started and run to full load, and tested for performance and emissions.

A fully assembled TM2500 trailer covers approximately 70 x 100 ft (21 m x 30 m), up to 60 per cent less space than would be occupied by the diesel units required to achieve a comparable power output. “The portability and small footprint of the TM2500 allowed us to maximize the effectiveness of these units by installing them in a location that would not typically lend itself to a permanent generation site,” said ComEd.

Another advantage is reduced dependence on transmission lines. “Building more power lines is an issue in many parts of the [USA] today,” commented ComEd. “With these compact and portable units, you can put the source of the power closer to the consumer and greatly reduce the need for long distance transmission lines.”

Moving on

While the first five TM2500s were hard at work in Chicago and Ireland over the past 12 months, GE engineers were busy creating a second generation design of the portable power package. GE plans to build several new TM2500 units this year, to be delivered to generating sites in the western USA to meet power needs.

Faced with growing concerns about electric power availability and reliability, power producers are searching for immediate and effective solutions. The TM2500 packagess are uniquely suited to meet these requirements.

In addition to being the largest blocks of temporary power available today, these portable units offer flexibility and rapid installation, both critical factors in reducing the threat of power shortages. Another key benefit: burning either natural gas or distillate fuel with water injection, the TM2500s produce emissions levels well below most environmental regulations.

The TM2500 offers utilities a rental solution to meet an interim demand for clean and efficient power, while they are developing and implementing more permanent solutions.

A fuel for economic growth

Ireland is becoming a victim of its own economic success. Over the past ten years, electricity demand has grown at an average of around five per cent, and by up to seven per cent in more recent years. Fuelled by economic growth, reserve margins have fallen. According to ESB, electricity demand peaked at 4003 MW in January 2001.

Ireland’s installed capacity is 4700 MW and although electricity demand has risen rapidly, there have been no interruptions to supply caused by power shortages. In 2002, the margin between peak demand and generating capacity will ease dramatically with the advent of two new power stations: the ESB/Statoil plant at Ringsend and the Viridian plant in Huntstown. Together, these plants will add almost 800 MW of power to the grid. In addition, further investments will include:

  • EirGrid is to invest IR£500 million ($568.2m) over the next five years improving the country’s transmission system
  • ESB is to spend IR£1.5 billion in the same period to improve the distribution system
  • ESB will make arrangements for additional generators if required for the winter 2001/2002
  • The North/South electricity interconnector is being upgraded to allow increased loads
  • A new gas interconnector with Scotland is being constructed and will enter service in autumn 2002. As the country’s gas infrastructure is extended and when the Corrib gas field comes on stream, opportunities will arise for independent power companies to develop new generating plants.
  • A 115 MW peat fired plant in Edenderry was commissioned seven months ahead of schedule.

ESB has also made arrangements to put in place five new substations to reinforce the network and cater for data centres and internet hotels.

Ireland has begun to liberalize its electricity industry. According to Mary O’Rourke, the Minister for Public Enterprise, 40 per cent of the electricity market will be open to competition in 2002, with full liberalization taking place in 2005