The industrial Trent is starting to gain market share, with contracts in Canada, UK and Denmark. It has become an attractive option for the lightweight, high efficiency gas turbine market.
The most recent order for Rolls Royce’s industrial Trent turbine was in November 1998, from SK Power of Denmark, for two machines to be used at the highly sophisticated Avedøre 2 multi-fire plant, which is due to enter commercial operation in October 2001. This order has followed on from the installation of the Trent at Whitby in Canada, and installations at three locations in the UK. These are Seal Sands on Teesside, a 62 MWe cogeneration plant at Rolls-Royce’s own facility in Derby, and a 100 MWe plant at Heartlands Power next to the Fort Dunlop site in Birmingham. The Trent can be configured to provide embedded ‘mix-and-match’ technology in the rapidly expanding distributed and complex-cycle market.
The industrial Trent turbine is derived from the Trent 800, which is an extension of the RB211 series aero engine. Rolls-Royce claims a number of benefits for the system. These include the following:
High output. Rolls-Royce claims that at 51 MWe, the industrial Trent is the most powerful aero-derivative based packaged power system available.
High simple cycle efficiency. At 42 per cent, the Trent has one of the highest simple cycle gas turbine efficiencies in the world.
Good low ambient temperature characteristics.
The unit maintains good operating performance over a wide ambient temperature range, with a comparatively high efficiency at part load conditions.
To achieve these, Rolls-Royce defined a number of criteria that the design package had to meet. These included the following:
Low first cost;
Ease of Installation;
Low operating costs;
Low first cost includes the cost of both the capital equipment and the installation.
The Trent is a modular aero-derivative engine that uses three coaxially independent running shafts. Each shaft rotates at its own optimum speed when the unit is brought on-line.
The LP shaft comprises a two-stage LP compressor driven by a five-stage LP turbine. The IP shaft comprises an eight-stage IP compressor driven by a single stage IP turbine. The HP shaft comprises a six-stage compressor driven by a single stage HP turbine.
The Trent is modular. This has several advantages; it makes installation, availability and maintenance easier, it is beneficial for transport, simplifies spares, reduces downtime when an outage occurs.
The modules are pre-balanced, and are thus interchangeable. As a result, when major maintenance is required, the engine can be replaced by a lease engine, or a module can be replaced by a new or leased module, to enable the plant to continue operation. The Trent module can be removed and replaced by a small team in less than a day. This ability derives from the fact that the Trent, being an aeroderivative machine, is light and thus easy to move.
Pre-balancing modules also means that major assembly changes can be carried out on site.
One of the advantages offered by the Trent is that it is very compact. The Trent occupies a site area of just 250 m2 for simple cycle operation, and 600 m2 for combined cycle operation.
The small size gives low mechanical inertia. This, combined with low thermal inertia, means that it can reach full output very rapidly, burning less fuel in the process. This is a major benefit for a mid-range or peaking plants which operates intermittently with frequent starts and stops.
Because of this, and because of the fact that it has good part load characteristics, the Trent is a good machine to hold in spinning reserve and for frequency regulation duties.
Low emission combustion
Trent uses a Dry Low Emissions (DLE) combustion system to restrict NOx and CO emissions below 25 ppm. There are 8 combustors in the HP core module. This system is a series-staged premix, lean-burn process with radial swirl inlet to the primary zone to achieve adequate flame length. A pilot diffusion flame is a key requirement to reduce the number of stages. A two-stage burner is used in the Trent, but three-stage versions have been tested, and achieve single figure NOx levels.
The Trent was first installed at Whitby in Canada. Difficulties were encountered in achieving the 25 ppm target, and the machine was given an extension to operate at a higher level. These difficulties took longer than expected to resolve, but it is expected that Whitby will soon be operating at the original design level.
For liquid fuel operation, water injection is used to suppress NOx production.
When the engine is started, rotation of the HP compressor draws air through the LP compressors via the starter motor. The air enters into the IP compressors before entering the radial combustion chambers.
Fuel is injected into each combustor from on-engine fuel manifolds by an Engine Management System (EMS). The fuel is mixed with the air flow and ignited. Ignition is achieved by 16 ignitor plugs, two plugs mounted within each torch chamber of the eight combustors.
Operation and control of the engine, the supply of fuel and oil, and all auxiliary systems is split between the Package Control System (PCS) and the Engine Management System (EMS), such that there is minimum overlap between the systems.
|Modular design of the Trent
| the-trent-consists-of-eight-engine-modules-li-li-lp-compressor-li-li-inter-compressor-duct-and-ip-compressor-li-li-internal-gearbox-li-li-hp-system-li-li-ip-turbine-li-li-external-gearbox-li-li-lp-turbine-li-li-non-modular-parts-b-lp-compressor-b-the-lp-compressor-module-comprises-an-annular-duct-joined-by-six-radial-support-vanes-a-two-stage-rotor-assembly-straddles-a-single-stage-stator-stage-b-inter-compressor-duct-icd-and-ip-compressor-b-the-icd-formsTablesEngine specifications Trent expected performance (50 Hz)