HomeWorld RegionsEuropePeak practice: choosing a brand new engine for variable load generation

Peak practice: choosing a brand new engine for variable load generation

Leading Belgian power provider SPE explains why the utility chose the Rolls-Royce Trent 60 DLE gas turbines to replace the diesel engines at the Ghent Ham peaking power station site.

Frederik Vael, SPE, Belgium

SPE, the second largest player in the Belgian energy market, decided in 2006 to go ahead with a project to replace the diesel engines at the Ghent Ham power station site with two new aeroderivative gas turbines, which would be operated as a peak power plant. After a tendering procedure, the Rolls-Royce Trent 60 DLE gas turbine, packaged by Turbomach Switzerland, was chosen for the project.

The turbine package is designed in such a way that the Trent engine can be removed or exchanged easily and quickly. Source: Philippe Debeerst and SPE, Luminus
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In late 2008 the demolition of two diesel engines and the construction of the gas turbines had been completed, and the Trents started generating electricity for the customers of the SPE-Luminus group.

History of the peaking power project at Ghent Ham

SPE is Belgium’s second largest power producer, generating electricity at 21 power plants in Flanders and Wallonia, mainly located near Ghent and along the Meuse river. One of those plants, the Ghent Ham power plant is located near the city centre of Ghent. It has a history dating back to the 1920s, when a coal fired power plant was built at the site.

In the late 1960s, still under the authority of the city of Ghent, construction of the diesel hall started which soon became a landmark of the Ghent skyline due to its high chimney. Three large diesel engines with a power output of approximately 25 MW each were installed over a period of almost 15 years.

The original brick built power station in Ghent with its historic community landmark tall chimney. The exhausts for the new Trent sets can clearly be seen on the roof.
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After the Ham power plant was integrated into the production park of SPE, and connected to the national grid, these diesel engines were operated increasingly as a peaking power plant or even an emergency power plant, with limited operating hours.

Studies undertaken by international consultants showed Belgium was lacking peak production capacity. Also Belgium was gradually importing more power from its neighbour countries, mainly France. In combination with the growing importance of wind energy in Europe, sustainable but less predictable, this created a need for new peak power capacity and/or a higher utilization ratio of peak power plants in Belgium. SPE could also see several reasons to build a new peaking power plant.

Having more than 1.5 million customer accounts that it supplies with electricity and/or gas under the brand name of Luminus, SPE also needed additional capacity to cover the needs of its customers. Furthermore, it offers more flexibility in SPE’s generation portfolio, it can provide backup for other SPE production assets, it can be used for black-start and VFR (very fast reserve) and it allows for using the combined-cycle power plants more optimally. Having significant power production out of renewable energy sources, SPE also welcomes the new peaking power plant to provide back-up power for the intermittent output of its wind farms and hydro power plants.

As the aforementioned needs mostly required a peaking power plant with a few thousand operating hours per year, rather than an emergency power plant, the decision was made to replace some of SPE’s existing emergency capacity by a new, gas fired, high efficiency peak power plant. Having a good balance between high efficiency, low investment cost, short lead time, compactness and fast start-up, aeroderivative gas turbines in a simple-cycle configuration were chosen as a technology for the new peak power plant.

The Ghent Ham site, and more specifically its diesel hall, was chosen for the project, because a lot of existing infrastructure could be reused, i.e. gas and power connections, cooling water intake, control room, etc. The diesel engines, having been operational for almost 40 years and requiring lots of manpower for operation and maintenance, were sacrificed. Two diesels had to be demolished before the construction of the gas turbines could start, whereas the third one remained operational during the construction phase.

This had a huge effect on the environmental impact of the plant. Effectively, since the commissioning of the project, emissions of CO2, NOX, SOX and dust have been reduced significantly, and the noise level of the power plant has gone down to values even lower than the ambient noise level.

Vibrations, often very annoying for people in the neighbourhood when the diesels were running, have almost completely disappeared. In fact, this important environmental improvement was one of the main drivers for the project, certainly given the location of the Ham power plant in close proximity to the centre of Ghent.

In autumn 2006, the demolition of the two diesel engines started. After six months of work, moving more than 4000 tonnes of steel from the site, only the concrete foundations of the diesels were left. These foundations were reused, but they had to be adapted in order to fulfil their new task. Finally, in summer 2007 the diesel hall was ready for the arrival of the two gas turbine generator packages and their auxiliary equipment (transformers, low voltage switchgear, air intake and ventilation system).

The heart of the new Peak Power Plant

The gas turbines selected for the project were Rolls-Royce Trent 60 DLE machines. Main drivers for the selection of this type of turbine were their high efficiency, resulting in a high number of ‘profitable’ operating hours, the high power output at a limited ground occupation area (certainly compared to the diesels), the very short start-up time (less than ten minutes from start to full load) and the low maintenance costs. The turbine and the package are designed in such a way that the complete turbine can be removed and/or exchanged easily and quickly à‚— which is very convenient for the complete gas turbine change-out at 50 000 operating hours as well as for the hot section (HP and IP core) change-out at 25 000 operating hours.

Although these turbines are not yet very common in the Belgian power industry, Rolls-Royce has a fleet of over 3500 industrial gas turbines operational worldwide. Also the Trent 60 DLE gas turbine, chosen for the project at the Ham power plant, is derived from an aircraft engine, the Rolls-Royce Trent 800. Whereas the industrial Trent 60 was developed only recently, and therefore has few references as yet, the reference list for the Aero Trent 800 is impressive.

The gas turbine packages are mounted on the structural concrete foundations that originally supported the diesel engines.
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Currently over 440 Aero Trent 800 engines are in service powering over 200 aircraft, accumulating over ten million flight hours and over two million flight cycles, having a 99.9 per cent dispatch reliability and showing a very low removal rate. The Aero Trent 800 may therefore certainly be considered as a proven technology, setting industry standards.

The industrial Trent 60 DLE machine is very similar to its parent engine, the Aero Trent 800. The design, with three independent shafts, has been preserved for the industrial Trent, and also the engine core (IP and HP compressor and turbine) is common for both engine types.

The most eye-catching difference is the removal of the front fan, which is replaced by a two-stage LP-compressor with the same pressure ratio as the aero fan. On the compressor side, a LP bleed is included in the industrial engine, for low speed operation. On the turbine side, the last two stages of the power turbine (LP turbine) were lengthened, and the exhaust was redesigned to recover all thrust. Also a rear end drive was added.

In addition, the annular combustor of the Aero Trent 800, designed for liquid fuel, has been replaced by low emission combustors. Dry low emission and water injected options are available, for natural gas only or for dual fuel combustion. The engines at the Ham power plant have a DLE (dry low emissions) combustion system, and operate on natural gas only.

This type of gas turbine has a rated power output of 51 MW and a rated electrical efficiency of 42.1 per cent. Both NOX and CO emissions (at 15 per cent O2 in the exhaust gases) are below 24 ppm (except at very low load of the machine), which is lower than required by government.

Inlet Spray Intercooling System

Due to lower density of air at higher temperatures, power output of a gas turbine decreases significantly if ambient temperature increases. Also for the Trent 60 DLE gas turbines at the Ham power plant, the maximum power output of 58 MW each will only be achieved at low ambient temperatures, being below 2 à‚°C. Above this temperature, the power output of the turbine gradually decreases.

To avoid this, and thus to keep the power output of the gas turbine at its maximum level over a wider range of temperatures, the ISI (Inlet Spray Intercooling) system has been installed on the machines at the Ham power plant. This new development by Rolls-Royce (of which the Ghent Ham project is the first industrial application) allows the turbines to run at their maximal power output, up to a temperature of 25 à‚°C, except for a small power reduction at low ambient temperatures to avoid frozen water droplets in the turbine.

The ISI-system is a two-part power boost system. A fogging system first brings the relative humidity if the intake air up to 100 per cent due to water injection in the air intake ducts, and then a set of wet compression nozzles additionally injects very small droplets of water at the inlet of the LP-compressor of the gas turbine. The injected water causes not only a more efficient compression, but also a higher mass flow through the turbine, and therefore also a higher power output.

How many hours the Trent sets will run will also be determined by market prices, as SPE’s Trading and Optimization department will schedule the operation regime of the turbines based on both internal needs and market opportunities.

Certainly, lots of starts and a limited number of operating hours per start can be expected, which results in an operating regime similar to that of most Aero Trent 800 engines from which they are derived. The high reliability of the Aero Trent 800 engines in this operation regime is therefore very promising for this peak power plant.

Rolls-Royce and SPE have joined forces to build two Trent 60 gas turbines on another existing SPE site. This time however, two Trent 60 WLE engines, capable of dual fuel operation, are to be installed in Angleur, near Liàƒ¨ge. Apart from the water injection for emission reduction and the dual fuel capability, the turbines for the Angleur project will also be distinctive from the ones in Ghent due to their ability to produce an additional 6 MW of electric power over an even wider range of ambient temperatures.

SPE is very proud to be the launching customer for both the ISI-system and this new 64 MW Trent gas turbine, which will indeed be implemented for the first time at the Angleur project. The continuous effort by Rolls-Royce to increase power output of the Trent (ISI at Ham, 64 MW at Angleur) makes the engine a very attractive one, certainly for peak power application.

However, also for cogeneration plants, the engine could be an interesting option, as proved by multiple projects in other countries. With an exhaust flow of more than 150 kg/sec at approximately 440 à‚°C, steam production in a heat recovery boiler is possible, with or without additional firing.

Due to its high electrical efficiency, high primary energy savings could be obtained if heat is recuperated maximally. This opens perspectives for the Belgian cogeneration market, as the certificate system specifically supports high efficient cogeneration plants.